13754
document
Reduction of isoflurane MAC by fentanyl or remifentanil in rats . OBJECTIVE The main objective of the study was to determine the effects of three different infusion rates of fentanyl and remifentanil on the minimum alveolar concentration ( MAC ) of isoflurane in the rat . A secondary objective was to assess the cardiovascular and respiratory effects of the two opioid drugs . ANIMAL POPULATION Thirty-seven male Wistar rats were randomly allocated to one of six treatment groups . MATERIAL AND METHODS For all treatment groups anaesthesia was induced with 5 % isoflurane in oxygen using an induction chamber . A 14-gauge catheter was used for endotracheal intubation , and anaesthesia was maintained with isoflurane delivered in oxygen via a T-piece breathing system . A baseline determination of the minimum alveolar concentration of isoflurane ( MACISO ) was made for each animal . Fentanyl ( 15 , 30 , 60 micro g kg-1 hour-1 ) or remifentanil ( 60 , 120 , 240 micro g kg-1 hour-1 ) were infused intravenously into a previously cannulated tail vein . Thirty minutes after the infusion started , a second MACISO ( MACISO+drug ) was determined . The carotid artery was cannulated to monitor the arterial pressure and to take samples for arterial gas measurements . Cardiovascular ( heart rate and arterial pressure ) and respiratory ( respiratory rate and presence/absence of apnoea ) effects after opioid infusion were also recorded . RESULTS Fentanyl ( 15 , 30 , 60 micro g kg-1 hour-1 ) and remifentanil ( 60 , 120 , 240 micro g kg-1 hour-1 ) similarly reduced isoflurane MAC in a dose-dependent fashion : by 10 % at lower doses , 25 % at medium doses and by 60 % at higher doses of both the drugs . Both opioids reduced the respiratory rate in a similar way for all doses tested . No episodes of apnoea were recorded in the remifentanil groups , while administration of fentanyl resulted in apnoea in three animals ( one at each dose level ) . The effects on the cardiovascular system were similar with both drugs . CONCLUSIONS We conclude that the intraoperative use of remifentanil in the rat reduces the MAC of isoflurane , and that this anaesthetic sparing effect is dose-dependent and similar to that produced by fentanyl at the doses tested . CLINICAL RELEVANCE The use of remifentanil during inhalant anaesthesia in the rat can be considered an intravenous alternative to fentanyl , providing similar reduction in isoflurane requirements . Due to its rapid offset , it is recommended that alternative pain relief be instituted before it is discontinued .
13755
Intervention_Pharmacological
fentanyl
13756
Intervention_Pharmacological
remifentanil
13757
Intervention_Pharmacological
fentanyl
13758
Intervention_Pharmacological
remifentanil
13759
Intervention_Pharmacological
isoflurane in oxygen
13760
Intervention_Pharmacological
Fentanyl
13761
Intervention_Pharmacological
remifentanil
13762
Intervention_Pharmacological
Fentanyl
13763
Intervention_Pharmacological
remifentanil
13764
Intervention_Pharmacological
remifentanil
13765
Intervention_Pharmacological
remifentanil
13766
Intervention_Pharmacological
remifentanil
13767
Intervention_Pharmacological
fentanyl
13768
Outcome_Physical
arterial pressure
13769
Outcome_Physical
Cardiovascular ( heart rate and arterial pressure )
13770
Outcome_Physical
respiratory ( respiratory rate and presence/absence of apnoea ) effects
13771
Participant_Sample-size
Thirty-seven
13772
Participant_Sex
male