Heat and moisture exchanger vs heated humidifier during long-term mechanical ventilation. A prospective randomized study. Comparison of the effects of heat and moisture exchangers and heated humidifiers on ventilation and gas exchange during weaning trials from mechanical ventilation. Comparison of hydrophobic heat and moisture exchangers with heated humidifier during prolonged mechanical ventilation. Ventilator-associated pneumonia using a heated humidifier or a heat and moisture exchanger: a randomized controlled trial [ISRCTN88724583]. A randomized clinical trial to compare the effects of a heat and moisture exchanger with a heated humidifying system on the occurrence rate of ventilator-associated pneumonia. Hyaline membrane disease. A controlled study of inspiratory to expiratory ratio in its management by ventilator. Clinical utility of hygroscopic heat and moisture exchangers in intensive care patients. Safety of combined heat and moisture exchanger filters in long-term mechanical ventilation. Comparing two methods of delivering high-flow gas therapy by nasal cannula following endotracheal extubation: a prospective, randomized, masked, crossover trial. Prospective, randomized comparison of high-frequency oscillation and conventional ventilation in candidates for extracorporeal membrane oxygenation. Is continuous transpulmonary pressure better than conventional respiratory management of hyaline membrane disease? A controlled study. The effects of passive humidifier dead space on respiratory variables in paralyzed and spontaneously breathing patients. Comparison of three different humidification systems during prolonged mechanical ventilation. Inhaled nitric oxide reduces the need for extracorporeal membrane oxygenation in infants with persistent pulmonary hypertension of the newborn. Prospective, randomized, controlled clinical trial comparing traditional versus reduced tidal volume ventilation in acute respiratory distress syndrome patients. Gradual reduction of endotracheal tube diameter during mechanical ventilation via different humidification devices. Evaluation of a ventilation strategy to prevent barotrauma in patients at high risk for acute respiratory distress syndrome. Pressure- and Volume-Limited Ventilation Strategy Group. Decreased incidence of extra-alveolar air leakage or death prior to air leakage in high versus low rate positive pressure ventilation: results of a randomised seven-centre trial in preterm infants. Randomised trial of volume controlled versus time cycled, pressure limited ventilation in preterm infants with respiratory distress syndrome. Inhaled nitric oxide in term infants with hypoxemic respiratory failure. Double-heater-wire circuits and heat-and-moisture exchangers and the risk of ventilator-associated pneumonia. A prospective, randomized comparison of an in-line heat moisture exchange filter and heated wire humidifiers: rates of ventilator-associated early-onset (community-acquired) or late-onset (hospital-acquired) pneumonia and incidence of endotracheal tube occlusion. The Provo multicenter early high-frequency oscillatory ventilation trial: improved pulmonary and clinical outcome in respiratory distress syndrome. A prospective randomized comparison of conventional mechanical ventilation and very early high frequency oscillatory ventilation in extremely premature newborns with respiratory distress syndrome. [Comparison of postoperative volume therapy in heart surgery patients]. Use of surfactant for prophylaxis versus rescue treatment of respiratory distress syndrome: experience from an Italian-Bulgarian trial. Early versus delayed initiation of continuous negative pressure in infants with hyaline membrane disease. Volume guarantee: stability of tidal volume and incidence of hypocarbia. Comparison of prone positioning and high-frequency oscillatory ventilation in patients with acute respiratory distress syndrome.
Adequate humidification of inspired gases with HMEs during long-term MV remains controversial. In this study, a comparison is made between tracheal secretions during long-term MV either with HME or conventional HH. Both the HME and HH groups were similar with respect to age, sex, diagnosis, duration of MV, SAPS and mortality. Temperature of gases in the tracheal tube was lower and the amount of tracheal instillations was greater in the HME group than in the HH group. Tracheal secretions became thicker between day 1 (control) and day 5, in the HME group than in the HH group. Four and two tube occlusions occurred in HME and HH groups, respectively. Tracheal bacterial colonization was similar in the two groups. Given the advantages of HME (reduced nurses' work and financial cost), HME could be routinely used under cautious surveillance and replaced by HH if difficulty in suctioning occurs. Heat and moisture exchangers (HME) are increasingly used to warm and humidify inspired gases in intubated ventilated patients. But these devices add dead space that may alter the alveolar ventilation. This could impair the efficiency of spontaneous ventilation (SV) during weaning trials from mechanical ventilation. Fifteen patients were tested with an HME (Hygrobac-DAR) and a heated humidifier (HH) (Fischer-Paykel MR 450) in a random order during weaning trials in SV with inspiratory pressure support. Minute ventilation VE, tidal volume), and respiratory rate were recorded and arterial blood was sampled for blood gas analysis with each device. The HME gave a significantly greater VE than the HH (9.3 +/- 0.8 L/min vs 8.1 +/- 0.8 L/min; p < 0.005), because of increased respiratory rate (21 +/- 2/min vs 19 +/- 2/min; p < 0.05). Tidal volume was unchanged for HME and HH (470 +/- 32 mL vs 458 +/- 39 mL). The higher PaCO2 with HME than with HH (44 +/- 2 mm Hg vs 42 +/- 2 mm Hg; p < 0.005) revealed an insufficient alveolar ventilation response to the increase in dead space. Arterial Po2 rose with the HME, but not significantly above the HH values (103 +/- 6 mm Hg vs 97 +/- 6 mm Hg; p = 0.055), possibly because of a positive end-expiratory pressure effect of the HME. The need to increase VE in SV when an HME is used should be taken into account during difficult weaning from mechanical ventilation. Inspired gases must be warmed and humidified during mechanical ventilation. In a prospective randomized study we compared the performance of a heated humidifier (HH) (Draegger Aquaport) and a heat and moisture exchanger (HME) (Pall Filter BB 2215). A total of 116 patients requiring mechanical ventilation (Servo 900 C Siemens) were enrolled into the study and were randomly assigned to 2 groups. Patients in group I were ventilated with a traditional breathing circuit with HH and patients in group II using a simplified circuit with HME. Pre-existing and hospital acquired atelectasis and pneumonia, occurrence of endotracheal tube (ET) occlusion and ventilatory parameters (respiratory rate, tidal volume) were studied. No statistical difference was found between groups for each parameter except the greater frequency of ET occlusions in the II group (0/61 vs 9/55) (p = 0.0008). Pall Filter (PF), a hydrophobic filter, humidifies the dry gases from the condensed water which is put down on the HME surfaces during cooling of saturated expired gases. This purely physical property is linked to the magnitude of the thermic gradient between the expired gases and the ambiant temperature. Performance impairment of PF in our study might be due to high ambiant temperature in the intensive care unit (usually around 28 degrees C) which reduces thermic gradient and water exchanges. We conclude that efficiency of PF may be weak in some conditions of ambiant temperature. Some guidelines to prevent ventilator-associated pneumonia (VAP) do not establish a recommendation for the preferential use of either heat and moisture exchangers (HMEs) or heated humidifiers (HHs), while other guidelines clearly advocate the use of HMEs. The aim of this study was to determine the incidence of VAP associated with HHs or HMEs.
                A randomized study was conducted in the intensive care unit of a university hospital involving patients expected to require mechanical ventilation for >5 days. Patients were assigned to two groups; one group received HH and the other group received HME. Tracheal aspirate samples were obtained on endotracheal intubation, then twice a week, and finally on extubation, in order to diagnose VAP. Throat swabs were taken on admission to the intensive care unit, then twice a week, and finally at discharge from the intensive care unit in order to classify VAP as primary endogenous, secondary endogenous, or exogenous.
                A total of 120 patients were assigned to HMEs (60 patients) and HHs (60 patients); 16 patients received mechanical ventilation for less than five days and were excluded from the analysis. Data analysis of the remaining 104 patients (53 HMEs and 51 HHs) showed no significant differences between groups regarding sex, age, Acute Physiology and Chronic Health Evaluation II score, pre-VAP use of antibiotics, days on mechanical ventilation, and diagnosis group. VAP was found in eight of 51 (15.69%) patients in the HH group and in 21 of 53 (39.62%) patients in the HME group (P = 0.006). The median time free of VAP was 20 days (95% confidence interval, 13.34-26.66) for the HH group and was 42 days (95% confidence interval, 35.62-48.37) for the HME group (P <0.001). Cox regression analysis showed the HME as a risk factor for VAP (hazard rate, 16.2; 95% confidence interval, 4.54-58.04; P < 0.001).
                The patients mechanically ventilated during more than 5 days developed a lower incidence of VAP with a heated humidifier than heat and moisture exchanger. The purpose of this study was to compare the performance of heat and moisture exchanger filters with heated humidifying systems in the mechanical ventilator circuit on the incidence of ventilator-associated pneumonia (VAP) and bacterial colonization.
                Two hundred and forty-three consecutive patients who required mechanical ventilation for 48 hours or more in the adult intensive care unit were randomized to either a heat and moisture exchanger (HME) or a heated humidifying breathing circuit.
                The VAP rate among the group with HME was 11.4%; the rate among the group with heated humidifying system (HHS) was 15.8%. The difference was not statistically significant. Approximately 68% of the patients in the HME group had no pathogen isolated compared with 50% of the patients in the HHS group. This difference was statistically significant (P =.006). However, the distribution of the pathogens among those patients who had the isolated pathogens was mostly identical in the 2 groups.
                Even though the study did not find HME to be significantly advantageous over the HHS, in as much as VAP rate is concerned, other advantages such as reduced nurses workload, reduced financial cost, and better safety made HME a more favorable device for use in our adult intensive care unit. Sixty-nine neonates with severe hyaline membrane disease (HMD) were mechanically ventilated using either a 1:2 or a 2:1 inspiratory to expiratory (I/E) ratio. Survivors in the 2:1 group required a lower fraction of oxygen in the inspired air (FiO2) and lower end-expiratory pressure to achieve satisfactory oxygenation. During the first week of life, time of exposure to FiO2 greater than 0.60 while being mechanically ventilated was 29.7 +/- 7.5 hours for the 1:2 group and 6.6 +/- 2,7 hours for the 2:1 group, while time of exposure to end-expiratory pressure greater than 3 cm H2O was 49.4 +/- 7.9 hours for the 1:2 group and 13.4 +/- 7.4 hours for the 2:1 group. Mortality and the incidence of air leak, patent ductus arteriosus, intraventricular hemorrhage, necrotizing enterocolitis, bronchopulmonary dysplasia, and pulmonary hemorrhage were not different for the two groups. Using an increased I/E ratio during the acute phase of HMD improved oxygenation but did not alter morbidity or mortality. To compare the degree of bacterial circuit colonization, frequency of ventilator-associated pneumonia (VAP), character of respiratory secretions, rewarming of hypothermic patients, disposable costs, and air flow resistance in intensive care patients ventilated using either a heat and moisture exchanger (HME) or hot water (HW) humidifier circuit.
                A prospective, randomized blinded trial of patients in the intensive care unit undergoing mechanical ventilation.
                A metropolitan teaching hospital.
                One hundred sixteen patients undergoing mechanical ventilation for a minimum period of 48 hrs were enrolled.
                Patients were randomized to three ventilation groups using a) an HW circuit with a 2-day circuit change (n = 41); or b) a bacterial-viral filtering HME in the circuit, with either a 2-day (n = 42); or c) a 4-day circuit change (n = 33).
                Circuit colonization was assessed using quantitative culture of washings taken from the circuit tubing and semiquantitative culture of swabs from the Y connectors. Sixty-seven percent of HW circuits became contaminated compared with 12% in the two HME groups (p < .0001). Median colony counts were lower in the HME groups (p < .0001). If circuits at first circuit change were contaminated in the HW group, 89% of subsequent circuit changes became contaminated compared with 0% and 25% for the 2- and 4-day HME groups, respectively. The frequency of VAP, the time to resolution of admission hypothermia, and the volume and fluidity of secretions were similar for all groups. The resistance of the HME after 24 hrs of use was < 0.025 cm H2O/L at gas flows of 40 L/min. HME use resulted in a cost reduction of $1.48 (Australian)/day.
                Circuits with a bacterial-viral filtering HME are less readily colonized by bacteria. Contamination is a random event. Humidification technique has no influence on the frequency rate of VAP, the effectiveness of rewarming, nor the character of the respiratory secretions. Breathing resistance is generally low and disposable costs are reduced when an HME is used. To evaluate the safety of a combined heat and moisture exchanger filter (HMEF) for the conditioning of inspired gas in long-term mechanical ventilation (MV).
                Randomized controlled trial.
                Medical ICU in a large teaching hospital.
                One hundred fifteen consecutive patients who required > or = 48 h of MV.
                Patients were randomized at intubation time (day 1) to receive inspired gas conditioned either by a water-bath humidifier heated at 32 degrees C (HWBH) or by an HMEF (Hygroster; DAR; Mirandola, Italy).
                The two study groups were comparable in terms of primary pathologic condition at the time of hospital admission, disease severity as measured by the Simplified Acute Physiology Score, and ICU mortality. They did not differ with respect to ventilator days per patient (mean +/- SD: HMEF, 7.6 +/- 6.5; HWBH, 7.8 +/- 5.8), incidence of endotracheal tube obstruction (HMEF, 0/59; HWBH, 1/56), and incidence of hypothermic episodes (HMEF, five; HWBH, two). In 41 patients receiving MV for > or = 5 days, the morphologic integrity of respiratory epithelium was evaluated on day 1 and day 5, using a cytologic examination of tracheal aspirate smears. The state of ciliated epithelium was scored on a scale from 0 (poorest integrity) to 1,200 (maximum integrity), according to a well-described method. In both patient groups, the scores slightly but significantly decreased from day 1 to day 5 (mean +/- SD: HWBH, from 787 +/- 104 to 745 +/- 88; HMEF, from 813 +/- 79 to 739 +/- 62; p < 0.01 for both groups); there were no statistically significant differences between groups.
                These data indicate acceptable safety of HMEFs of the type used in the present study for long-term mechanical ventilation. We compared two methods of delivering high-flow gas therapy by nasal cannula, applied immediately after planned endotracheal extubations of NICU patients.
                Thirty NICU patients who were about to be extubated from mechanical ventilation were randomized into two groups; Group 1 received Vapotherm for the first 24 h after extubation, then standard high-flow nasal cannula for the next 24 h, and Group 2 received standard high-flow therapy for the first 24 h, then Vapotherm for the next 24 h. At 24 h after extubation and again 48 h after extubation, a neonatologist who was not aware which modality the patient had been receiving examined the nasal mucosa and applied a scoring system. A research nurse who was unaware of the modality abstracted respiratory rates and respiratory effort scores from a specific study-bedside record. The experimental design was such that a patient could 'fail' extubation either by reintubation for mechanical ventilation, or by rescue to the opposite modality before completing the 24-h test period.
                Fifteen patients were randomized to Group 1 and 15 to Group 2. No differences were apparent between the groups in birth weight, gestational age, age at study entry, gender or underlying pulmonary disorder. Respiratory rates were similar while on Vapotherm (52+/-13 breaths/min, mean+/-s.d.) and high-flow (54+/-14/min). At 24 h after starting the modality, those on Vapotherm had more normal examinations of the nasal mucosa (2.7+/-1.2 vs 7.8+/-1.7, P < 0.0005) and lower respiratory effort scores (1.2+/-0.6 vs 2.0+/-0.9, P < 0.05) than did those on high-flow. No patients failed while on Vapotherm, but seven failed while on high-flow (two reintubations and five rescue switches to Vapotherm, P < 0.005).
                Among NICU patients immediately following extubation, Vapotherm performed better than a standard high-flow nasal cannula in maintaining a normal appearing nasal mucosa, a lower respiratory effort score, and averting reintubation. To compare the safety and efficacy of high-frequency oscillation (HFO) with conventional ventilation in the treatment of neonates with respiratory failure.
                We conducted a multicenter, prospective, randomized trial. Patients were stratified according to pulmonary diagnosis and then were randomly selected for conventional ventilation or HFO. A balanced crossover design offered patients who met criteria of treatment failure a trial of the alternative mode of ventilation.
                Four tertiary, level 3 neonatal intensive care units accepting regional referrals for extracorporeal membrane oxygenation.
                Neonates were eligible for enrollment if their gestational age was > 34 weeks, their birth weight was > or = 2 kg, they were < 14 days of age, they required fractional inspired oxygen > 0.50 and a mean airway pressure > 0.98 kPa (10 cm H2O) to support adequate oxygenation, and they required a peak inspiratory pressure > 2.9 kPa (30 cm H2O) and a rate > 40 breaths per minute to support adequate ventilation. Exclusion criteria were lethal congenital anomalies, profound shock, need for cardiopulmonary resuscitation, and failure to obtain consent.
                Of 79 patients studied, 40 were assigned to conventional ventilation and 39 to HFO. Neonates randomly assigned to HFO required higher peak pressure (3.8 +/- 0.5 vs 3.3 +/- 0.8 kPa, 39 +/- 5 vs 34 +/- 8 cm H2O; p = 0.004) and more often met extracorporeal membrane oxygenation criteria (67% vs 40%; p = 0.03) at study entry than did those given conventional ventilation. Twenty-four patients (60%) assigned to conventional ventilation met treatment failure criteria compared with 17 (44%) of those assigned to HFO (not significant). Of the 24 patients in whom conventional ventilation failed, 15 (63%) responded to HFO; 4 (23%) of the 17 in whom HFO failed responded to conventional ventilation (p = 0.03). There were no differences between the two groups with respect to outcome, need for extracorporeal membrane oxygenation, or complications.
                We conclude that HFO is a safe and effective rescue technique in the treatment of neonates with respiratory failure in whom conventional ventilation fails. The influence of continuous positive airway pressure (CPAP) and positive end-expiratory pressure (PEEP) on mortality and complication rates in severe hyaline membrane disease (HMD) was evaluated in a randomized, prospective study. Patients were admitted to the study if the Po2 was less than 50 mm Hg with FiO2 greater than 0.6. Twenty-four patients in each of three weight groups were equally divided between treatment and control groups. The treatment regimen included CPAP (6 to 14 cm H2O) for spontaneously breathing patients and PEEP for patients requiring mechanical ventilation for apnea or hypercapnia (Pco2 greater than 65 mm Hg). Control patients received oxygen and were mechanically ventilated if they had apnea, hypercapnia, or Po2 less than 50 mm Hg with FiO2 greater than 0.8. Oxygenation improved after the start of CPAP or PEEP; however, Pco2 rose after CPAP was initiated. There was no significant difference between treatment and control groups in mortality, requirement for mechanical ventilation, or incidence of pulmonary sequelae. The incidence of pulmonary air-leak was increased with Peep. the findings suggest that CPAP and PEEP have not significantly altered the outcome of HMD. Passive humidifiers have gained acceptance in the intensive care unit because of their low cost, simple operation, and elimination of condensate from the breathing circuit. However, the additional dead space of these devices may adversely affect respiratory function in certain patients. This study evaluates the effects of passive humidifier dead space on respiratory function.
                Two groups of patients were studied. The first group consisted of patients recovering from acute lung injury and breathing spontaneously on pressure support ventilation. The second group consisted of patients who were receiving controlled mechanical ventilation and were chemically paralyzed following operative procedures. All patients used 3 humidification devices in random order for one hour each. The devices were a heated humidifier (HH), a hygroscopic heat and moisture exchanger (HHME) with a dead space of 28 mL, and a heat and moisture exchanger (HME) with a dead space of 90 mL. During each measurement period the following were recorded: tidal volume, minute volume, respiratory frequency, oxygen consumption, carbon dioxide production, ratio of dead space volume to tidal volume (VD/VT), and blood gases. In the second group, intrinsic positive end-expiratory pressure was also measured.
                Addition of either of the passive humidifiers was associated with increased VD/VT. In spontaneously breathing patients, VD/VT increased from 59 +/- 13 (HH) to 62 +/- 13 (HHME) to 68 +/- 11% (HME) (p < 0.05). In these patients, constant alveolar ventilation was maintained as a result of increased respiratory frequency, from 22.1 +/- 6.6 breaths/min (HH) to 24.5 +/- 6.9 breaths/min (HHME) to 27.7 +/- 7.4 breaths/min (HME) (p < 0.05), and increased minute volume, from 9.1 +/- 3.5 L/min (HH) to 9.9 +/- 3.6 L/min (HHME) to 11.7 +/- 4.2 L/min (HME) (p < 0.05). There were no changes in blood gases or carbon dioxide production. In the paralyzed patient group, VD/VT increased from 54 +/- 12% (HH) to 56 +/- 10% (HHME) to 59 +/- 11% (HME) (p < 0.05) and arterial partial pressure of carbon dioxide (PaCO2) increased from 43.2 +/- 8.5 mm Hg (HH) to 43.9 +/- 8.7 mm Hg (HHME) to 46.8 +/- 11 mm Hg (HME) (p < 0.05). There were no changes in respiratory frequency, tidal volume, minute volume, carbon dioxide production, or intrinsic positive end-expiratory pressure.
                These findings suggest that use of passive humidifiers with increased dead space is associated with increased VD/VT. In spontaneously breathing patients this is associated with an increase in respiratory rate and minute volume to maintain constant alveolar ventilation. In paralyzed patients this is associated with a small but statistically significant increase in PaCO2.
                Clinicians should be aware that each type of passive humidifier has inherent dead space characteristics. Passive humidifiers with high dead space may negatively impact the respiratory function of spontaneously breathing patients or carbon dioxide retention in paralyzed patients. When choosing a passive humidifier, the device with the smallest dead space, but which meets the desired moisture output requirements, should be selected. An efficient humidification system is expected to maintain fluid and easily drainable airway secretions. This study aims to compare the efficiency and safety of three humidification systems during prolonged mechanical ventilation.
                Two-center, prospective, randomized study.
                45 critically ill patients undergoing mechanical ventilation were included in the study and allocated to receive one of three humidification techniques: 1) Bennett Cascade water-bath humidifier (Bennett group); 2) Fisher & Paykel servocontrolled humidifier (F & P group); 3) HME Hygrobac DAR (HME group). Clinical and experimental observations were conducted for 3 to 7 consecutive days and included: body T degree, room T degree, inspired gas T degree, tracheal T degree, relative and absolute humidity, heat and water loss, airway secretion score, need for endotracheal saline instillation and incidence of ETT occlusion.
                The HME group showed a lower temperature of inspired gases compared to the F & P group (p < 0.05); it also showed a lower absolute humidity compared to both Bennett and F & P groups (p < 0.05). A better airway secretion score was obtained in Bennett and F & P groups compared to the HME group (p < 0.01).
                Passive humidification systems provided low degrees of humidity and temperature and could not maintain good secretions. Active systems appeared to satisfy the recommended standards and to allow fluid and easily drainable secretions. We previously reported improved oxygenation, but no change, in rates of extracorporeal membrane oxygenation (ECMO) use or death among infants with persistent pulmonary hypertension of the newborn who received inhaled nitric oxide (NO) with conventional ventilation, irrespective of lung disease. The goal of our study was to determine whether treatment with inhaled NO improves oxygenation and clinical outcomes in infants with persistent pulmonary hypertension of the newborn and associated lung disease who are ventilated with high-frequency oscillatory ventilation (HFOV).
                Single-center, prospective, randomized, controlled trial.
                Newborn intensive care unit of a tertiary care teaching hospital.
                We studied infants with a gestational age of > or =34 wks who were receiving mechanical ventilatory support and had echocardiographic and clinical evidence of pulmonary hypertension and hypoxemia (PaO2 < or =100 mm Hg on FIO2 = 1.0), despite optimal medical management Infants with congenital heart disease, diaphragmatic hernia, or other major anomalies were excluded.
                The treatment group received inhaled NO, whereas the control group did not. Adjunct therapies and ECMO criteria were the same in the two groups of patients. Investigators and clinicians were not masked as to treatment assignment, and no crossover of patients was permitted.
                Primary outcome variables were mortality and use of ECMO. Secondary outcomes included change in oxygenation and duration of mechanical ventilatory support and supplemental oxygen therapy. Forty-two patients were enrolled. Baseline oxygenation and clinical characteristics were similar in the two groups of patients. Infants in the inhaled NO group (n = 21) had improved measures of oxygenation at 15 mins and 1 hr after enrollment compared with infants in the control group (n = 20). Fewer infants in the inhaled NO group compared with the control group were treated with ECMO (14% vs. 55%, respectively; p = .007). Mortality did not differ with treatment assignment.
                Among infants ventilated by HFOV, those receiving inhaled NO had a reduced need for ECMO. We speculate that HFOV enhances the effectiveness of inhaled NO treatment in infants with persistent pulmonary hypertension of the newborn and associated lung disease. To assess the safety and potential efficacy of a mechanical ventilation strategy designed to reduce stretch-induced lung injury in acute respiratory distress syndrome.
                Prospective, randomized, controlled clinical trial.
                Eight intensive care units in four teaching hospitals.
                Fifty-two patients with acute respiratory distress syndrome.
                Traditional tidal volume patients: tidal volume 10-12 mL/kg ideal body weight, reduced if inspiratory plateau pressure was > 55 cm H2O (7.3 kPa). Small tidal volume patients: tidal volume 5-8 mL/kg ideal body weight, to keep plateau pressure < 30 cm H2O (4.0 kPa).
                Mean tidal volumes during the first 5 days in traditional and small tidal volume patients were 10.2 and 7.3 mL/kg, respectively (p < .001), with mean plateau pressure = 30.6 and 24.9 cm H2O (3.3 kPa), respectively (p < .001). There were no significant differences in requirements for positive end-expiratory pressure or FIO2, fluid intakes/outputs, requirements for vasopressors, sedatives, or neuromuscular blocking agents, percentage of patients that achieved unassisted breathing, ventilator days, or mortality.
                The reduced tidal volume strategy used in this study was safe. Failure to observe beneficial effects of small tidal volume ventilation treatment in important clinical outcome variables may have occurred because a) the sample size was too small to discern small treatment effects; b) the differences in tidal volumes and plateau pressures were modest; or c) reduced tidal volume ventilation is not beneficial. Limited data suggest that increased resistance to flow within endotracheal tubes (ETT) may occur in patients whose lungs are mechanically ventilated for more than 48 h, especially when airway humidification is inadequate. This could lead to sudden ETT obstruction or induce excessive loading during spontaneous breathing.
                Twenty-three such patients were randomly assigned to three types of airway humidifier based on three different working principles: a Fisher Paykell hot water system (n = 7), a Pall BB2215 heat and moisture exchanger (HME) hydrophobic filter (n = 8), and a Dar Hygrobac 35254111 HME hygroscopic filter (n = 8). The decrease in internal pressure along the ETT and the flow rate were measured in each patient every 2 days. An "effective inner diameter" was derived from these measurements and allowed the inner ETT configuration to be monitored.
                On the first day of intubation, the mean diameter was similar in the three groups, and was slightly smaller than the in vitro diameter (mean +/- SD: 7.6 +/- 0.6 mm for Fisher-Paykell, 7.7 +/- 0.4 for Pall, and 7.5 +/- 0.4 for Dar). The mean diameter tended to decrease from day to day. At the end of the study, the overall reduction in mean diameter was significantly greater with the hydrophobic HME (Pall) than with the two other systems (Pall: -6.5 +/- 4% vs. 2.5 +/- 2.5% for Dar and 1.5 +/- 3% for Fisher-Paykell; P < 0.01 with analysis of variance). The same was true of the mean reduction in effective inner ETT diameter expressed per day of ventilation (-1.6 +/- 1.5% per day for Pall vs. -0.5 +/- 0.4% for Dar and -0.2 +/- 0.4% for Fisher-Paykell; P < 0.01). In four patients, the ETT became obstructed and emergency repeated tracheal intubation was required. The Pall HME and the Fisher-Paykell system were being used in three and one patient, respectively. Before obstruction, the reduction in ETT diameter was significantly greater for these four patients than for the remaining 23 patients (7.8 +/- 1.4% vs. 3.1 +/- 4.1%; P < 0.01).
                During prolonged mechanical ventilation, significant alterations in inner ETT configuration occur frequently and are influenced by the type of humidification device used. In vivo monitoring of ETT mechanical properties might be clinically useful. A strategy of mechanical ventilation that limits airway pressure and tidal volume while permitting hypercapnia has been recommended for patients with the acute respiratory distress syndrome. The goal is to reduce lung injury due to overdistention. However, the efficacy of this approach has not been established.
                Within 24 hours of intubation, patients at high risk for the acute respiratory distress syndrome were randomly assigned to either pressure- and volume-limited ventilation (limited-ventilation group), with the peak inspiratory pressure maintained at 30 cm of water or less and the tidal volume at 8 ml per kilogram of body weight or less, or to conventional ventilation (control group), with the peak inspiratory pressure allowed to rise as high as 50 cm of water and the tidal volume at 10 to 15 ml per kilogram. All other ventilatory variables were similar in the two groups.
                A total of 120 patients with similar clinical features underwent randomization (60 in each group). The patients in the limited-ventilation and control groups were exposed to different mean (+/-SD) tidal volumes (7.2+/-0.8 vs. 10.8+/-1.0 ml per kilogram, respectively; P<0.001) and peak inspiratory pressures (23.6+/-5.8 vs. 34.0+/-11.0 cm of water, P<0.001). Mortality was 50 percent in the limited-ventilation group and 47 percent in the control group (relative risk, 1.07; 95 percent confidence interval, 0.72 to 1.57; P=0.72). In the limited-ventilation group, permissive hypercapnia (arterial carbon dioxide tension, >50 mm Hg) was more common (52 percent vs. 28 percent, P=0.009), more marked (54.4+/-18.8 vs. 45.7+/-9.8 mm Hg, P=0.002), and more prolonged (146+/-265 vs. 25+/-22 hours, P=0.017) than in the control group. The incidence of barotrauma, the highest multiple-organ-dysfunction score, and the number of episodes of organ failure were similar in the two groups; however, the numbers of patients who required paralytic agents (23 vs. 13, P=0.05) and dialysis for renal failure (13 vs. 5, P= 0.04) were greater in the limited-ventilation group than in the control group.
                In patients at high risk for the acute respiratory distress syndrome, a strategy of mechanical ventilation that limits peak inspiratory pressure and tidal volume does not appear to reduce mortality and may increase morbidity. Two different ventilation techniques were compared in a seven-centre, randomised trial with 181 preterm infants up to and including 32 completed weeks gestational age, who needed mechanical ventilation because of lung disease of any type. Technique A used a constant rate (60 cycles/min), inspiratory time (IT) (0.33s) and inspiratory: expiratory ratio (I:E) (1:2). The tidal and minute volume was only changed by varying peak inspiratory pressure until weaning via continuous positive airway pressure. Technique B used a lower rate (30 cycles/min) with longer IT (1.0 s). The I:E ratio could be changed from 1:1 to 2:1 in case of hypoxaemia. Chest X-rays taken at fixed intervals were evaluated by a paediatric radiologist and a neonatologist unaware of the type of ventilation used in the patients. A reduction of at least 20% in extra-alveolar air leakage (EAL) or death prior to EAL was supposed in infants ventilated by method A. A sequential design was used to test this hypothesis. The null hypothesis was rejected (P = 0.05) when the 22nd untied pair was completed. The largest reduction in EAL (-55%) was observed in the subgroup 31-32 weeks of gestation and none in the most immature group (< 28 weeks). We conclude that in preterm infants requiring mechanical ventilation for any reason of lung insufficiency, ventilation at 60 cycles/min and short IT (0.33 s) significantly reduces EAL or prior death compared with 30 cycles/min and a longer IT of 1 s. We speculate that a further increase in rate and reduction of IT would also lower the risk of barotrauma in the most immature and susceptible infants. Fifty preterm infants weighing 1200 g or more with clinical and radiographic evidence of respiratory distress syndrome, requiring both mechanical ventilation and exogenous surfactant replacement, were randomly allocated to receive either volume controlled ventilation or time cycled, pressure limited ventilation. Tidal volume delivery in each group was deliberately controlled at 5-8 ml/kg so that the only difference between the two groups was the ventilatory modality, the manner in which tidal volume was delivered. The rest of the ventilatory management and clinical care was done according to protocol. The two modes of ventilation were compared by determining the time required to achieve pre-determined success criteria, based on either the alveolar-arterial oxygen gradient or the mean airway pressure as a standard against which the speed of weaning could be objectively assessed. Infants randomised to volume controlled ventilation met success criteria sooner and had a shorter duration of mechanical ventilation. These babies also had a significantly lower incidence of intraventricular haemorrhages and abnormal periventricular echodensities on ultrasound scans. Volume controlled ventilation seems to be both safe and effective in this group of patients. To determine whether inhaled nitric oxide (NO) administered during conventional mechanical ventilation could produce improvements in oxygenation and reduce the incidence of meeting extracorporeal membrane oxygenation (ECMO) criteria in infants with hypoxemia.
                Prospective, randomized, controlled trial. Enrolled infants were assigned to conventional treatment with or without adjunctive inhaled NO. Control infants meeting failure criteria (partial pressure of arterial oxygen (PaO2)<80 mm Hg (10.7 kPa)) were allowed to cross over. Caregivers were not masked to group assignment.
                Neonatal intensive care units at the University of Alabama Hospital and the Children's Hospital of Alabama, October 1993 to May 1994.
                Newborn infants, both term and near-term, with PaO2 less than 100 mm Hg (13.3 kPa) who were receiving mechanical ventilation with 100% oxygen. Exclusion criteria included major congenital anomalies, diaphragmatic hernia, profound asphyxia, and significant bleeding.
                Inhaled NO was initiated in the NO group at a dose of 20 to 40 ppm and advanced stepwise to 80 ppm if PaO2 remained less than 100 mm Hg (13.3 kPa).
                Primary outcome variables were treatment failure and meeting of ECMO criteria before crossover. Improvement in oxygenation and ultimate use of ECMO or high-frequency oscillatory ventilation were secondary outcome variables.
                Seventeen neonates with hypoxemia were enrolled; 16 had echocardiographic evidence of pulmonary hypertension, and eight had extrapulmonary shunting. At 1 hour of treatment, two infants in the NO group responded with increases in PaO2 of more than 100 mm Hg (13.3 kPa); after crossover, two had increases in PaO2 of more than 10 mm Hg (1.3 kPa) and one control infant had an increase in PaO2 of more than 10 mm Hg (1.3 kPa). All control infants met failure criteria and crossed over to receive NO; two had increases in PaO2 of more than 10 mm Hg (1.3 kPa) with NO treatment. Despite initial responses, all subjects in both groups eventually met failure criteria. There were no differences between groups in primary outcome variables.
                Although inhaled NO produced a transient improvement in oxygenation in some infants, it did not reduce the incidence of meeting ECMO criteria in this population. To compare the incidence of ventilator-associated pneumonia (VAP) in patients ventilated in intensive care by means of circuits humidified with a hygroscopic heat-and-moisture exchanger with a bacterial viral filter (HME) or hot-water humidification with a heater wire in both inspiratory and expiratory circuit limbs (DHW) or the inspiratory limb only (SHW).
                A prospective, randomized trial.
                A metropolitan teaching hospital's general intensive care unit.
                Three hundred eighty-one patients requiring a minimum period of mechanical ventilation of 48 hrs.
                Patients were randomized to humidification with use of an HME (n=190), SHW (n=94), or DHW (n=97).
                Study end points were VAP diagnosed on the basis of Clinical Pulmonary Infection Score (CPIS) (), HME resistance after 24 hrs of use, endotracheal tube resistance, and HME use per patient. VAP occurred with similar frequency in all groups (13%, HME; 14%, DHW; 10%, SHW; p=0.61) and was predicted only by current smoking (adjusted odds ratio [AOR], 2.1; 95% confidence interval [CI], 1.1-3.9; p=.03) and ventilation days (AOR, 1.05; 95% CI, 1.0-1.2; p=.001); VAP was less likely for patients with an admission diagnosis of pneumonia (AOR, 0.40; 95% CI, 0.4-0.2; p=.04). HME resistance after 24 hrs of use measured at a gas flow of 50 L/min was 0.9 cm H2O (0.4-2.9). Endotracheal tube resistance was similar for all three groups (16-19 cm H2O min/L; p=.2), as were suction frequency, secretion thickness, and blood on suctioning (p=.32, p=.06, and p=.34, respectively). The HME use per patient per day was 1.13.
                Humidification technique does not influence either VAP incidence or secretion characteristics, but HMEs may have air-flow resistance higher than manufacturer specifications after 24 hrs of use. To compare the performance of an in-line heat moisture exchanging filter (HMEF) (Pall BB-100; Pall Corporation; East Hills, NY) to a conventional heated wire humidifier (H-wH) (Marquest Medical Products Inc., Englewood, Colo) in the mechanical ventilator circuit on the incidence of ventilator-associated pneumonia (VAP) and the rate of endotracheal tube occlusion.
                This report describes a prospective, randomized trial of 280 consecutive trauma patients in a 20-bed trauma ICU (TICU). All intubated patients not ventilated elsewhere in the medical center prior to their TICU admission were randomized to either an in-line HMEF or a H-wH in the breathing circuit. Ventilator circuits were changed routinely every 7 days, and closed system suction catheters were changed every 3 days. HMEFs were changed every 24 h, or more frequently if necessary. A specific endotracheal tube suction and lavage protocol was not employed. Patients were dropped from the HMEF group if the filter was changed more than three times a day or the patient was placed on a regimen of ultra high-frequency ventilation. The Centers for Disease Control and Prevention (CDC) criteria for diagnosis of pneumonia were used; early-onset, community-acquired pneumonia was defined if CDC criteria were met in < or =3 days, and late-onset, hospital-acquired pneumonia was defined if criteria were met in >3 days. Laboratory and chest radiograph interpretation were blinded.
                The patient ages ranged from 15 to 95 years in the HMEF group and 16 to 87 years in the H-wH group (p=not significant), with a mean age of 46 years and 48 years, respectively. The male to female ratio ranged between 78 to 82%/22 to 18%, respectively, and 55% of all admissions were related to blunt trauma, 40% secondary to penetrating trauma, and 5% to major burns. There was no difference in Injury Severity Score (ISS) between the two groups. Moreover, there was no significant difference in mean ISS among those who did not develop pneumonia and those patients who developed either early-onset, community-acquired or late-onset, hospital-acquired pneumonia. The HMEF nosocomial VAP rate was 6% compared to 16% for the H-wH group (p<0.05), and total ventilator circuit costs (per group) were reduced. There were no differences in duration of ventilation (mean+/-SD) if the patient did not develop pneumonia or if the patient developed an early-onset, community-acquired or a late-onset, hospital-acquired pneumonia. Moreover, total TICU days were reduced in the HMEF group. In addition, the incidence of partial endotracheal tube occlusion was not significantly different between the H-wH and the HMEF groups.
                The HMEF used in this study reduced the incidence of late-onset, hospital-acquired VAP, but not early-onset, community-acquired VAP, compared to the conventional H-wH circuit. This was associated with a significant reduction in total ICU stay. Disposable ventilator circuit costs in the HMEF group were reduced compared to the H-wH group in whom circuit changes occurred at 7-day intervals.
                The use of the HMEF is a cost-effective clinical practice associated with fewer late-onset, hospital-acquired VAPs, and should result in improved resource allocation and utilization. To compare the hospital course and clinical outcome of preterm infants with respiratory distress syndrome treated with surfactant and managed with high-frequency oscillatory ventilation (HFOV) or conventional mechanical ventilation (CV) as their primary mode of ventilator support.
                A prospective randomized clinical trial.
                Three community-based level III neonatal intensive care units.
                A total of 125 neonates who were 35 weeks or less estimated gestation requiring intubation and assisted ventilation for respiratory distress syndrome with arterial to alveolar oxygen ratio less than .50.
                Patients were randomized to continue CV (61 patients) or be changed to HFOV (64 patients) after exogenous surfactant administration (100 mg/kg). HFOV was used in a strategy to promote lung recruitment and maintain lung volume. Protocol respiratory care guidelines were followed; otherwise routine care was provided by each neonatal intensive care unit.
                No differences were noted in demographic features between the two study groups. The study population birth weight was 1.51 +/- .47 kg (mean +/- SD), gestational age was 30.9 +/- 2.5 weeks, and study entry age was 2 to 3 hours. Patients randomized to HFOV demonstrated the following significant findings compared with CV-treated patients: vasopressor support was less intensive; surfactant redosing was not as frequent; oxygenation improved more rapidly and remained higher during the first 7 days; fewer infants required prolonged supplemental oxygen or ventilator support; treatment failure was reduced; more patients survived without chronic lung disease at 30 days; need for continuous supplemental oxygen at discharge was less; frequency of necrotizing enterocolitis illness was lower; there were fewer abnormal hearing tests; and hospital costs were decreased. No differences were seen between the two study groups in the frequency or severity of patent ductus arteriosus, air leak, retinopathy of prematurity, or intraventricular hemorrhage. Length of hospital stay and survival to discharge were similar for HFOV- and CV-treated infants.
                When used early with a lung recruitment strategy, HFOV after surfactant replacement resulted in clinical outcomes consistent with a reduction in both acute and chronic lung injury. Benefit was evident for preterm infants both less than or equal to 1 kg and more than 1 kg. In addition, early HFOV treatment may have had a more global effect on patient health throughout the hospitalization, resulting in reduced morbidity and decreased health care cost. To compare the effectiveness and safety of very early high-frequency oscillatory ventilation (HFOV) with conventional mechanical ventilation (CMV) in treatment of the respiratory distress syndrome (RDS) and to evaluate their impact on the incidence of chronic pulmonary disease and early and late morbidity of very low-birthweight neonates.
                A prospective randomized clinical trial.
                Tertiary neonatal intensive care unit in the Perinatology Center in Prague.
                43 premature newborns, delivered in the Department of Obstetrics in the Perinatology Center, were randomly divided into two groups (HFOV and CMV) immediately after delivery; 2 patients in each group died, 2 fulfilled crossover criteria from CMV to HFOV, and 2 were excluded because of congenital malformations. Nineteen patients treated with HFOV were therefore compared with 18 infants in the CMV group.
                The two contrasting modes of ventilation were introduced immediately after intubation. Maintenance of optimal lung volume in HFOV to optimize oxygenation and the therapeutic administration of surfactant after fulfilling defined criteria are important points of the strategy and design of the study.
                Except for a higher proportion of males in the HFOV group (p<0.02), the basic clinical characteristics (gestational age, birthweight, Apgar score at 5 min, umbilical arterial pH), the two groups were similar. In the acute stage of RDS, infants treated with HFOV had higher proximal airway distending pressure with HFOV for 6 h after delivery (p<0.05). For a period of 12 h after delivery lower values for the alveolar-arterial oxygen difference (p<0.03) were noted. The number of patients who did not require surfactant treatment was higher in the HFOV group (11 vs. 1, p<0.001). In the HFOV group the authors found a lower roentgenographic score at 30 days of age (p<0.03) and a lower clinical score in the 36th postconceptional week (p<0.05), using these two scoring systems for assessing chronic lung disease according to Toce scale. The incidence of pneumothorax, pulmonary interstitial emphysema, intraventricular hemorrhage and retinopathy of prematurity in both groups was the same.
                HFOV, when applied early and when the clinical strategy of maintenance of optimal lung volume is used, improves oxygenation in the acute stage of RDS, reduces the need of surfactant administration, and can decrease the injury to lung tissue even in extremely immature newborns to whom surfactant is administered therapeutically. Patients who have undergone cardiac surgery with use of extracorporeal circulation frequently reveal marked hypovolaemia in spite of a highly positive fluid balance. This is thought to be due to transient microvascular damage and extravascular fluid shift. Further volume replacement to achieve haemodynamic stability in the postoperative period may cause fluid overload and congestive heart failure. The present study was designed to investigate whether this fluid overload could be avoided by using a hypertonic-hyperoncotic solution (group I: HHL, 10% hydroxyethylstarch 200/0.5 in 7.2% saline) instead of two different standard colloid solutions (group II: HA, 5% albumin; group III: HES, 6% hydroxyethylstarch in 0.9% saline).
                Twenty-one patients meeting our criteria for hypovolaemia immediately after cardiac surgery were randomly assigned to three groups. Patients in group I received HHL in increments of 150 ml, while patients in group II and group III were given HA and HES respectively in increments of 500 ml until hypovolemia was corrected. Haemodynamic assessment was done using a pulmonary artery thermodilution catheter. Intra- and extravascular volumes, including extravascular lung water (EVLW), intrathoracic blood volume (ITBV), and total blood volume (TBV) were measured by the double indicator technique using lung water software (COLD-System, Pulsion, Munich, Germany).
                Correction of hypovolaemia-related haemodynamic parameters and restoration of normal TBV were achieved by 236 +/- 80 ml of HHL (group I), 857 +/- 244 ml of HA (group II) and 1000 +/- 0 ml of HES (group III) respectively. TBV increased significantly in each group, compared to baseline values. EVLW did not change significantly in any group. We found that the volume-augmenting effect of HHL per millilitre infused solution was more than four times that of HA and HES, primarily as a result of increasing plasma osmolality due to an increase of plasma sodium levels. This pronounced effect on intravascular volume of HHL lasted for only 2 h following infusion, however, and did not lead to any unwanted side effects. In the period between 2 and 20 h after primary volume replacement, further fluid therapy with colloids and crystalloids, guided by clinical signs of hypovolaemia, was necessary in each group of patients. The overall fluid requirements for the first 20 h after operation did not differ among the three resuscitation regimens.
                We found that HHL is a safe and effective solution for acute correction of hypovolaemia after cardiac surgery. The advantages of a smaller initial volume load by HHL cannot be maintained for longer than 2 h. To show if surfactant applied in different social-sanitary realities as prophylaxis of respiratory distress syndrome (RDS) is equally useful and able to reduce mortality and incidence of 3-4 radiological grade RDS.
                Two neonatal intensive care units (NICU) in Italy, one NICU in Bulgaria and one NICU in Romania were involved in a randomized controlled clinical trial of prophylaxis vs rescue treatment of RDS. Babies with gestational age 26-30 wks were randomized before birth to prophylaxis in the delivery-room with 200 mg/kg of porcine surfactant (prophylaxis) or to routine assistance (control). Subsequently the babies developing RDS requiring mechanical ventilation and fraction of inspired oxygen (FiO2) > or = 0.4 to maintain PaO2 about 50 mmHg were allowed to be treated rescue with 200 mg/kg of the same surfactant. To reach end-points of reducing mortality by 40% and incidence of radiological grade 3-4 RDS a total number of 174 patients were required.
                Due to logistic, practical and social-political problems the study was interrupted after enrollment of 93 babies (61 in Italy and 32 in Bulgaria). The Romanian centre did not start the study because it was impossible in the scheduled times to equip it for mechanical ventilation of the newborn infants. Analysis done on an intention to treat basis did not show significant reductions of mortality and 3-4 radiological grade RDS, even if there was a trend towards a reduction in the babies given prophylaxis. A significantly lower number of babies given prophylaxis required a subsequent rescue treatment compared to controls (p < 0.001). There was no difference in other complications such as intraventricular haemorrhage, air-leak syndromes and infections between prophylaxis and control infants. As regards pulmonary gas exchange, the PaO2/FiO2 ratio was significantly improved in the babies given prophylaxis for the first 12 hours of life vs the controls.
                Even if the study was terminated before term, the analysis of the data shows that prophylaxis with surfactant is equally effective in different social-clinical conditions to improve pulmonary gas-exchange, especially in the first critical hours of life of premature babies. Twenty-three infants with HMD of similar severity, who were less than 24 hours of age and who were breathing spontaneously, were divided by random numbers into early and delayed CNP groups. The infants who were treated with CNP before their PaO2 was less than 50 mm Hg while breathing 70% oxygen experienced a significantly greater increase in PaO2 in response to the initiation of CNP, required less time with O2 therapy, required no mechanical ventilation, and had fewer complications. Based on these results, it is suggested that CNP be initiated in infants with HMD, who are less than 24 hours of age and are breathing spontaneously, before the PaO2 becomes less than 50 mm Hg on 70% O2. Excessive tidal volume (V(T)) can lead to lung injury, hypocarbia, and neurologic damage. Volume guarantee (VG) uses exhaled V(T) as the control variable to reduce the risk of volutrauma and more closely control PaCO(2). Our objective was to test the hypothesis that VG combined with assist/control (A/C) will maintain PaCO(2) and V(T) within target range more consistently than assist/control alone during the first 72 hr of life in ventilated preterm infants. Eligible infants were randomly assigned to A/C + VG or A/C alone. Data were recorded directly from the pressure and volume module of the Draeger Babylog 8000+ ventilator. Arterial blood gases were obtained every 2-6 hr, as clinically indicated. In A/C, inspiratory pressure was adjusted to achieve a V(T) of 4-6 ml/kg. In VG, the target V(T) was 5 ml/kg. Subsequent adjustments were made by the clinical team in response to arterial blood gas measurements (ABG). Proportion of breaths and PaCO(2) values outside the target range were compared by chi(2), and continuous variables by t-test. There were no differences in demographic or baseline ventilator variables between the 18 infants in the two groups. For 1,805/11,950 breaths (15.1%), V(T) was > target with A/C + VG, vs. 2,503/9,853 (25.4%) with A/C (P < 0.001). V(T) was < target for 21.7% of breaths with A/C + VG, vs. 35.7% with A/C (P < 0.001). Twenty percent of PaCO(2) values were < target, with A/C + VG vs. 36.3% with A/C, P < 0.05. The proportion of PaCO(2) values > target was similar in the two groups. Oxygenation and mean pH were not different. No complications related to mechanical ventilation were observed. In conclusion, VG significantly reduced hypocarbia and excessively large V(T). This suggests the potential to reduce pulmonary and neurologic complications of mechanical ventilation. Larger studies are needed to establish safety and demonstrate such benefits.
                Copyright 2004 Wiley-Liss, Inc. Both prone position and high-frequency oscillatory ventilation (HFOV) have the potential to facilitate lung recruitment, and their combined use could thus be synergetic on gas exchange. Keeping the lung open could also potentially be lung protective. The aim of this study was to compare physiologic and proinflammatory effects of HFOV, prone positioning, or their combination in severe acute respiratory distress syndrome (ARDS).
                : Prospective, comparative randomized study.
                A medical intensive care unit.
                Thirty-nine ARDS patients with a Pao2/Fio2 ratio <150 mm Hg at positive end-expiratory pressure > or =5 cm H2O.
                After 12 hrs on conventional lung-protective mechanical ventilation (tidal volume 6 mL/kg of ideal body weight, plateau pressure not exceeding the upper inflection point, and a maximum of 35 cm H2O; supine-CV), 39 patients were randomized to receive one of the following 12-hr periods: conventional lung-protective mechanical ventilation in prone position (prone-CV), HFOV in supine position (supine-HFOV), or HFOV in prone position (prone-HFOV).
                Prone-CV (from 138 +/- 58 mm Hg to 217 +/- 110 mm Hg, p < .0001) and prone-HFOV (from 126 +/- 40 mm Hg to 227 +/- 64 mm Hg, p < 0.0001) improved the Pao2/Fio2 ratio whereas supine-HFOV did not alter the Pao2/Fio2 ratio (from 134 +/- 57 mm Hg to 138 +/- 48 mm Hg). The oxygenation index ({mean airway pressure x Fio2 x 100}/Pao2) decreased in the prone-CV and prone-HFOV groups and was lower than in the supine-HFOV group. Interleukin-8 increased significantly in the bronchoalveolar lavage fluid (BALF) in supine-HFOV and prone-HFOV groups compared with prone-CV and supine-CV. Neutrophil counts were higher in the supine-HFOV group than in the prone-CV group.
                Although HFOV in the supine position does not improve oxygenation or lung inflammation, the prone position increases oxygenation and reduces lung inflammation in ARDS patients. Prone-HFOV produced similar improvement in oxygenation like prone-CV but was associated with higher BALF indexes of inflammation. In contrast, supine-HFOV did not improve gas exchange and was associated with enhanced lung inflammation.
There is little evidence of an overall difference between HMEs and HHs. However, hydrophobic HMEs may reduce the risk of pneumonia and the use of an HME may increase artificial airway occlusion in certain subgroups of patients. Therefore, HMEs may not be suitable for patients with limited respiratory reserve or prone to airway blockage. Further research is needed relating to hydrophobic versus hygroscopic HMEs and the use of HMEs in the paediatric and neonatal populations. As the design of HMEs evolves, evaluation of new generation HMEs will also need to be undertaken.