one of the toxic pollutants , no , is known as a free radical gas . in recent years , however , no is an endothelial - derived vasodilator molecule and has been examined as a supplemental treatment agent for pulmonary hypertension . it has also been reported that the peri - operative portopulmory hypertension which occurs during liver transplantation is controlled by the administration of no and prostacyclin . in patients with ards , ongoing studies are determining whether or not oxygenation can be enhanced by the pulmonary vasodilation as a supplemental treatment agent . because the side effects due to no2 occurring during the persistent use of no can not be overlooked , that the safety of continued use of no during general anesthesia when used pre - operatively needs to be determined . we managed a case of ards due to pulmonary aspiration in which no which was used in the icu to improve oxygenation and was maintained during abdominal surgery . a 67-year - old man weighing 80 kg had no other notable findings than a history of diabetes mellitus , and the patient visited the emergency care center with a chief complaint of hemoperitonium occurring after a fall injury from a 3 m height . at the time of admission , the patient had a clear mentality and spontaneous respirations . due to persistent intra - abdominal bleeding , the patient had the following findings : blood pressure ( bp ) , 85/50 mmhg ; and heart rate ( hr ) , 110 beats / min . during treatment at the emergency care center , the patient aspirated gastric contents , which led to tracheal intubation . despite the infusion of dopamine ( 20 g / kg / min ) sedation was continued post - operatively , and the patient was transferred to the icu intubated . on postoperative day 1 , during treatment with sedation and ventilator care in the icu , hemodialysis was performed due to the occurrence of sepsis and acute renal failure ( arf ) . was initiated with the following settings : tidal volume ( tv ) , 480 ml ; respiratory rate ( rr ) , 20 breaths / min ; fio2 , 1.0 ; and positive end expiratory pressure ( peep ) , 15 mmhg . an arterial blood gas analysis ( abga ) was performed which showed the following : ph , 7.01 ; paco2 , 60 mmhg ; pao2 , 47 mmhg ; hco3 , 15.1 no was administered at a dose of no from 3:00 pm on post - operative day 1 ( table 1 ) . until post - operative day 2 following the use of no , an abga was performed under the following cmv settings : tv , 450 ml ; rr , 22 breaths / min ; fio2 , 1.0 ; and peep , 20 mmhg . the abga showed as the following : ph , 7.27 ; paco2 , 46.1 mmhg ; pao2 , 126.7 mmhg ; hco3 , 20.7 thus , oxygenation was gradually improving ( table 1 ) . due to the persistent presence of abdominal bleeding , while maintaining no inhalation , the patient was transferred to the operating room ( fig . the patient had the following implants : a catheter in the right subclavian vein for central venous pressure ( cvp ) monitoring , a catheter in the right femoral vein for fluid supply , a catheter in the right radial artery for a continuous arterial blood pressure monitoring , and a colostomy . to maintain vital signs , the patient received an infusion of vasopressin ( 1 unit / hr ) , dopamine ( 15 g / kg / min ) , norepinephrine ( 0.8 g / kg / min ) , and bicarbonate ( 20 meq / hr ) . the patient also had a bp of 103/55 mmhg , a hr of 110 beats / min , and a cvp of 21 mmhg . mechanical ventilation was performed using a ventilator ( savina , drager , germany ) which was used in the icu . with continued cmv ( tv , 400 ml ; rr , 22 breaths / min ; fio2 , 1.0 ; and peep , 18 mmhg ) , the measurements were as follows sao2 , 85 - 90% ; and a peak inspiratory pressure ( pip ) , 34 mmhg . no was infused to the area which was 30 cm remote from the y - piece of the inspiratory limb of the ventilator using a no delivery system ( hy-1002 ; metran co. , germany ) . in the connecting part between the y - piece and inspiratory limb , using an expiratory gas analyzer ( printernox ; micro medical ltd . , england ) , the concentrations of no and no2 were measured ( fig . 3 and 4 ) . the patient 's mental status was sedated with midazolam , which was used in the icu ( the bispectral index [ bis ] was 8) . because the ventilator which was used in the icu was also used in the operating room , due to a lack of availability of a vaporizer , the induction and maintenance of anesthesia were performed using total intravenous anesthesia . with reference to bis measurements , a small dose of propofol ( 2.0 g / ml ) and remifentanil ( 2.0 ng / ml ) were administered using a target - controlled infusion ( orchestra ; fresenius vial , france ) . a muscle relaxant , atracurium , was intravenously adminsitered at a dose of 20 mg / hr . intra - operatively , bis was abruptly increased from approximately 10 to 35 . because the bp was not sufficiently higher for the enhancement of the propofol infusion , to maintain the depth of anesthesia intra - operatively , the concentration of no was maintained at 5.0 - 9.5 ppm , and no2 was 0 - 0.8 ppm . with aggravation of the patient 's vital signs , a swan - ganz catheter for pulmonary artery pressure ( pap ) monitoring was not placed . blood was used as fluid therapy and an intravenous infusion of phenylephrine resulted in an elevation of bp to approximately 110/50 mmhg . thereafter , during the surgery , there were no notable changes in the patient 's status . at the time the surgical procedure was completed , with a continuous infusion of vasopressin ( 1 unit / hr ) , dopamine ( 15 g / kg / min ) , norepinephrine ( 0.8 g / kg / min ) and bicarbonate ( 20 meq / hr ) , the bp was 123/56 mmhg , the hr was 78 beats / min , and the cvp was 13 mmhg . mechanical ventilation was finally set at a tv of 500 ml , a rr of 16 breaths / min , a fio2 of 0.8 ( o2 , 3.2 l / min ; and n2o , 0.8 l / min ) , and a peep of 10 mmhg in an effort to not further increase the pip , tv , and minute volume . with the maintenance of the concentration of no at 5.0 - 10 ppm , an abga was performed , and showed the following : ph , 7.18 ; paco2 , 45 mmhg ; pao2 , 430 mmhg ; hco3 , 16.8 mmol / l ; sao2 , 100% ; and pip , 25 mmhg ( table 1 ) . at this time , the bis was 13 - 20 . the intra - operative blood loss was 1,000 ml . with the transfusion of prc ( 4 units ) , ffp ( 6 units ) , and pc ( 10 units ) , the anesthetic and surgical time was 2 hours and 50 minutes and 2 hours and 20 minutes , respectively . the cmv settings were as follows : tv , 550 ml ; rr , 16 breaths / min ; fio2 , 0.8 ; and peep , 10 mmhg . an abga analysis showed as the following : ph , 7.20 ; paco2 , 39 mmhg ; pao2 , 305 mmhg ; hco3 , 15.2 there were no further improvements in ards . on post - operative day 1 , at approximately 5:00 pm , with the following cmv settings : tv , 500 ml ; rr , 20 breaths / min ; fio2 , 1.0 ; and peep , 20 mmhg , an abga was obtained ( ph , 7.29 ; paco2 , 42 mmhg ; pao2 , 71 mmhg ; hco3 , 20.2 mmol / l ; and sao2 , 92% ; table 1 ) . due to a lack of response to an increased dose of epinephrine and norepinephrine , systolic blood pressure was not maintained at > 80 mmhg . at dawn on post - operative day 2 , due to multiple organ failure , including arf , sepsis , aspiration pneumonia , and respiratory failure , the patient expired . in patients who concurrently have hypoxic pulmonary vasoconstriction ( hpv ) and pulmonary hypertension due to alveolar hypoxia , such as ards , no has been used as a supplemental treatment agent when hypoxemia is not resolved with oxygen supply and the appropriate mechanical ventilation . due to persistent intra - abdominal bleeding , the abdominal pressure was elevated , and the patient had decreased pulmonary function . the most severe form of acute lung injury ( ali ) , ards , has been reported to have various causes . it can be defined as cases in which the pao2/fio2 is < 200 mmhg ( ali pao2/fio2 < 300 mmhg ) and a pulmonary - capillary wedge pressure is < 18 mmhg , despite the presence of bilateral pulmonary infiltrates on chest radiography . according to ards net reports , to reduce pulmonary injury due to mechanical ventilation and to assure that the pip and plateau pressure does not exceed 30 cmh2o , a low tv ( 4 - 8 ml / kg ) , and a respiratory rate which is appropriate for each age group , has been recommended . in which sufficient oxygenation can not be achieved by these methods , although peep which is used as a supplemental method should prevent the alveolar atelectasis and reduce an intrapulmonary shunting , the effects of no in reducing the intrapulmonary shunt due to pulmonary reperfusion from the affected sites to normal alveoli has been improved . besides , there are also effects of no in lowering the pulmonary hypertension . but it can not enhance the survival of patients . also , due to side effects occurring following a long - term use of no , it is not generally used for cases of ali or ards . in patients who have severe hypoxia or life - threatening pulmonary hypertension , the patient reported herein had severe ards because of the elevation of abdominal pressure due to the persistent intra - abdominal bleeding , even after surgery , as well as pulmonary aspiration occurring at the emergency care center at the time of admission . with a single use of positive pressure ventilation , , the abga findings were improved from a pao2 of 47 mmhg and an oxygen saturation 58% prior to the use of no at a fio2 of 1.0 to a pao2 of 126.7 mmhg and a sao2 of 98.4% following the use of no . but the long - term use of no may cause several complications , and these include the synthesis of methemoglobin , the synthesis of nitrogen oxide , and an inhibitory effect on platelet aggregation . in the current case , however , the reasons that no was maintained during surgery are that discontinuation of no would aggravate the pulmonary hypertension , increase the pulmonary vascular resistance , decrease the cardiac output , decrease the mixed venous oxygen saturation ( svo2 ) , decrease the systemic arteral blood pressure , and decrease the pao2 . christenson et al .   conducted a study in 31 patients with acute hypoxemic respiratory failure ( ahrf ) who inhaled no . according to this study , following the discontinuation of no treatment , such parameters as pao2 , svo2 , and kim et al .   reported that rebound pulmonary hypertension developed frequently in cases in which the use of no was abruptly discontinued at a lower dose after its concentration was lowered during a short - term period . these authors therefore proposed that a gradual discontinuation be done through repeated attempts during a long - term period with special attention paid to hemodynamic stability . in regard to the optimal no concentration , there are various reports [ 7,10 - 12 ] . continual use of no ( 10 ppm ) caused a left shift of the dose - response curve and this leads to an improvement of arterial oxygenation and mean pap . but a maximal dose of no ( 100 ppm ) may aggravate oxygenation . in association with this , adhikari et al . conducted a systematic review and a meta - analysis and these authors reported that methemoglobinemia and arf would occur in cases in which a high dose of no ( > 80 ppm ) was used for several days . nishimura et al .   maintained that no2 was not generated in cases in which no would be used at a dose < 20 ppm . according to another study , in cases in which no was used at a dose of 20 ppm at fio2 0.9 , no2 was generated at a dose of < approximately 0.4 ppm . based on these reports , in cases in which the concentration of no was maintained as < 20 ppm during anesthesia , the concentration of no2 would not exceed 5 ppm as a safety limit of no2 . accordingly in the current case , a low dose of no ( 5.0 - 9.5 ppm ) was used during anesthesia . in the current case , no was used since one day prior to surgery . therefore , the period of use was not relatively longer and a low dose of no was used . complications due to the use of no did not occur prior to and following the surgery . it is regrettable , however , that changes in the pap pre - operatively and post - operatively could not be measured due to a lack of the preoperative preparation of a swan - ganz catheter for a pap monitoring . if the occurrence of no2 is minimized , the problems occurring following a sudden discontinuation of no use pre - operatively rather than complications occurring because of the use of no would be more problematic . in conclusion , the maintenance of no inhalation during anesthesia , rather than a sudden discontinuation of no use pre - operatively , would be beneficial for the hemodynamic stability of patients .
inhaled nitric oxide ( no ) is occasionally used to treat hypoxemia for patients with acute respiratory distress syndrome ( ards ) in the intensive care unit ( icu ) . 
 however , it is controversial whether or not to maintain inhalation of no during general anesthesia because of complications , such as nitrogen dioxide ( no2 ) production , methemoglobinemia , and inhibition of platelet aggregation . in this case 
 , a 67-year - old male fell from a roof and was brought to an emergency care center . during management , he vomited gastric contents and aspirated . in spite of tracheal intubation and mechanical ventilation with high oxygen therapy , 
 the hypoxia did not improve . 
 no inhalation with mechanical ventilation was performed to treat hypoxemia due to ards in the icu . 
 we maintained the no inhalation during the surgery for a hemoperitonium . 
 the surgery was completed without intra - operative hemodynamic instability or any complications .