Year : 2007 | Volume
: 10 | Issue : 1 | Page : 46--50
Comparison of sevoflurane and isoflurane in OPCAB surgery
BG Venkatesh, Yatin Mehta, Anand Kumar, Naresh Trehan
Department of Anaesthesiology & Critical Care Escorts Heart Institute and Research Centre, New Delhi., India
Department of Anaesthesiology & Critical Care, Escorts Heart Institute and Research Centre, Okhla Road, New Delhi 110 025.
Maintenance of anaesthesia with volatile anaesthetic agents affects the perioperative course of patients undergoing off-pump coronary artery bypass (OPCAB) surgery. This facilitates adequate depth of anaesthesia, reduction in need of analgesic dosage, early extubation and transfer from Intensive Care Unit. We compared two volatile anaesthetic agents sevoflurane and isoflurane in terms of haemodynamic effects, amount of analgesic needed during surgery, quantity of agent needed for maintenance of anaesthesia and postoperative recovery in 40 patients undergoing OPCAB surgery. Anaesthesia was induced with fantanyl, midazolam and thiopentone, and vecuronium was used for muscle relaxation. An Octopus stabiliser was used and coronary anastomosis was performed using internal mammary artery and saphenous vein grafts. Routine monitoring was performed. The depth of anaesthesia was monitored using Bispectral index monitor. The inspired/expired concentration of anaesthetic agents to maintain the desired BIS and the amount of volatile anaesthetic agent needed was also noted. The amount of analgesic used intraoperatively was noted in both the groups. The «SQ»time of awakening«SQ» defined as eye opening on verbal commands, and time of extubation were noted. There were no differences in haemodynamic parameters, depth of anaesthesia, and quantity of agent needed, but patients in isoflurane group required more intraoperative analgesics than sevoflurane group. Time of awakening (48 ± 13 vs 114 ± 21 mins; P < 0.001) and subsequent extubation (124 ± 25 vs 177 ± 36 mins, P<0.001) was earlier in sevoflurane group than isoflurane group. There was no evidence of perioperative myocardial infarction in both the groups. We conclude that sevoflurane and isoflurane can both be safely used in OPCAB surgery, but the awakening and extubation times are significantly less with sevoflurane.
|How to cite this article:|
Venkatesh B G, Mehta Y, Kumar A, Trehan N. Comparison of sevoflurane and isoflurane in OPCAB surgery.Ann Card Anaesth 2007;10:46-50
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Venkatesh B G, Mehta Y, Kumar A, Trehan N. Comparison of sevoflurane and isoflurane in OPCAB surgery. Ann Card Anaesth [serial online] 2007 [cited 2020 Feb 25 ];10:46-50
Available from: http://www.annals.in/text.asp?2007/10/1/46/37924
Fast tracking after cardiac surgery is now a common practice, particularly in off-pump coronary artery bypass surgery (OPCAB). The patients are extubated within 1-6 hrs after surgery. This is achieved with the help of anaesthetic agents having shorter duration of action, decreased narcotic usage, improved surgical techniques and myocardial protection.
Fast track anaesthetic techniques for cardiac surgery have helped to decrease intensive care unit (ICU) stay and hospital length of stay (LOS), with lower utilization of resources and reduced costs without adversely affecting mortality and morbidity. Recently, in-vitro studies and in-vivo animal experiments have shown that volatile (halogenated) anaesthetic agents have a cardioprotective effect on the ischaemic myocardium. These agents mimic ischaemic preconditioning that provides a beneficial effect on myocardial reperfusion injury . , Cardioprotective effects of halogenated anaesthetics have been confirmed in patients undergoing coronary artery bypass graft surgery (CABG) on cardiopulmonary bypass (CPB). , Use of volatile anaesthetics facilitates maintaining adequate depth of anaesthesia, reduction in the need for opioid analgesics, early extubation and transfer from ICU. We compared fast tracking with sevoflurane and isoflurane anaesthesia in patients undergoing elective OPCAB and studied their haemodynamic effects and recovery times.
After obtaining approval from Hospital Ethics Committee and informed consent, forty patients belonging to American Society of Anesthesiolgists, physical status II-IV and New York Heart Association class I or II, scheduled to undergo elective OPCAB were included. Exclusion criteria were obesity, severe renal or hepatic disease, redo surgery, severe cardiac dysrrhythmias or, a left ventricular ejection fraction below 40%. An Octopus 3 coronary stabiliser (Medtronic, Minneapolis USA) was used and internal mammary artery and saphnous vein grafts were used in all the patients. Usual cardiac medications including beta blockers, calcium-channel blockers and nitrates were continued till the morning of surgery. All patients were premedicated with tablet lorazepam (0.04 mg/Kg) on the night before surgery and morning of surgery. Injection morphine sulphate (0.1 mg/Kg) intramuscularly was administered 60 minutes before transferring the patient to the operating room.
Monitoring included five-lead ECG, femoral and pulmonary artery pressures with thermodilution cardiac output (CO) measurement, pulse oximetry, capnography and blood temperature. (Phillips Medical System Pvt. Ltd, M1166A, Andover, Netherland) In all the patients, bispectral index (BIS) monitoring (Phillips Medical System Pvt. Ltd., M1175A, Andover, Netherlands) was applied. Airway agent analyser was used to monitor inspired and expired concentrations of anaesthetic agents (Phillips Medical System Pvt. Ltd., M1183A, Andover, Netherlands).
Anaesthesia was induced with sleep dose of thiopentone sodium, midazolam (0.05-0.1 mg/Kg) and fentanyl citrate (4 µg/Kg). Muscle relaxation was achieved with 0.1 mg/Kg of vecuronium. Following induction and tracheal intubation, patients were randomly allocated to receive either sevoflurane (group I) or isoflurane (group II) in oxygen: air mixture for maintenance of anaesthesia from inspired concentration 0.5-2 % till end-tidal concentration of agent of 1.5-2.0 %. Further top-up doses of fentanyl (50 µg) and vecuronium (1 mg) were repeated at regular interval of 1 hour till the conclusion of surgery. Throughout surgery, BIS of 40-50 was maintained with the help of inhalational agent. Additional doses of fentanyl were administered, if heart rate (HR) increased to more than 90 beats/min. Injection metoprolol (1-2 mg bolus) was used during coronary anastomosis, if HR increased to > 90/min. The Trendelenberg position, IV fluids and norepinephrine infusion. (0.05 - 0.1 µg/Kg/min.) were used to maintain mean arterial pressure (MAP) if necessary.
Haemodynamic measurements included HR, central venous (CVP) and pulmonary artery occlusion pressures (PAOP), MAP and cardiac index (CI) at baseline, post-induction after completing coronary anastamosis and before shifting the patient to recovery room.
Depth of anaesthesia was monitored with BIS, and inspired/expired concentration of anaesthetic agent to maintain the required depth was noted. The total quantity of volatile anaesthetic agent used in each patient was calculated using the formula (Dion) = dialed concentration (%) x total fresh gas flow (L/min) x duration at that concentration (min) x molecular weight (gms) divided by 2412 x density (g/L).  Total amount of opioid analgesic used intraoperatively was recorded for each group. Postoperatively, the time of awakening by means of eye opening on verbal commands and extubation in postoperative recovery ward were also recorded.
In both groups, cardiac morbidity in the form of myocardial ischaemia/infarction was monitored by ECG (ST depression > 1 mm) appearance of new 'q' waves, postoperative cardiac enzymes, creatinine phospokinase (CPK) > 200 and CPKMB > 25 IU, troponin I. measured at 6 and 24 hours after transferring from operating room. Postoperative pain relief was provided with injection tramadol 100 mg, which was administered when weaning was initiated.
All results are presented as mean ± SD. Statistical analysis was performed by Students T-test and a P value of decreased after induction but was not significant statistically. CO was not measured during anastamosis, due to the change in position of the heart by Octopus stabiliser. The amount of IV fluids used to maintain the said CVP ranged from 10001500 ml (crystalloid and colloids). Temperature was maintained between 36.5 to 37.2° C by using warm blanket, warm topical solution and warm IV fluids.
Depth of anaesthesia was monitored using BIS which was maintained at 40-50. The maintenance of anaesthesia to BIS value 40-50 required dial conc of 1.5-2% in both groups. The duration of surgery was 240 ± 10 min in group I, 242 ± 12 min in group II. The total amount of volatile anaesthetic agent used was 34.20 ml in group I and 34.50 ml in group II. (P=non significant)
The amount of top-up dose of fentanyl was significantly more in group II (isoflurane) (265 µg ± 36) than group I (sevoflurane) (150 ± 36 µg, P 200, CPKMB>25 IU) measured at 6 and 24 hours were not observed in both the groups.
Time of awakening i.e. time of eye opening to verbal commands was significantly shorter in group I (sevoflurane) (48 ± 13 minutes) as compared with group II (isoflurane) (114 ± 21, P (177 ± 36 minutes, P  In our study, both agents showed similar favourable intraoperative haemodynamics. In another study, both sevoflurane and isoflurane showed similar haemodynamic effects at 0.5 and 1.0 minimum alveolar concentration (MAC), but sevoflurane showed a tendency to have lower HR and CI compared to isoflurane.  This effect, i.e. mild myocardial depression may be desirable during OPCAB, as myocardial oxygen consumption will be decreased in a beating ischaemic heart.
Conzen et al  in their study on 20 patients undergoing OPCAB, concluded that patients receiving sevoflurane had less myocardial injury than patients receiving propofol. In our study also none of the groups showed increase in CPK and CPKMB in postoperative period, although the number of patients was small. Sevoflurane has been shown to have better ischaemic preconditioning effect than other volatile agents.  This is by affecting the activity of cardiac sarcolemmal and mitrochondrial K+-ATP channels. Volatile anaesthetics reduce ischaemia induced cell damage, infarct development and infarct size by stimulating adenosine receptors, activation of protein kinase C and by increased formation of nitric oxide and free oxygen radicals. The opening of K+-ATP channels confers cytoprotection by decreased cytosolic and mitrochondrial Ca +2 overload.
Fast track approach is to help patients recuperate more rapidly and shorten the period of critical care and length of hospital stay with lower utilization of resources and reduced cost without affecting morbidity and mortality. This is achieved by using ultra short acting drugs, decreased use of narcotics, improved surgical techniques, and adhering to early weaning protocols. The major component of fast-tracking is early extubation, which is within 1-6 hours of surgery. This depends on the anaesthetic and surgical techniques used.
In the present study, time to awakening and extubation was significantly shorter in sevoflurane group than in isoflurane group. Mourad et al  in a group of 75 patients undergoing CABG found that sevoflurane along with low dose of fentanyl allowed early extubation. One of the advantages of OPCAB is that it allows early extubation. This was achieved in our study.
The requirement of fentanyl during intraoperative period was lower in sevoflurane group and this may be one reason for early awakening in this group. Schwab et al  studied the depth of anaesthesia using BIS with different halogenated anaesthetics and found that sevoflurane achieved lower BIS scores at equipotent MAC levels.
Haemodynamic stability is an essential requirement for patients undergoing cardiac surgery. Fast tracking and early extubation has become a realistic anaesthetic practice with the availability of newer shorter acting agents. This can now be achieved without compromising patient safety. The objective of early extubation was achieved using a propofol based technique  in 1996 and later a combination of isoflurane and fentanyl was successfully used to achieve the same goal.  However, use of isoflurane may be associated with tachycardia, which can increase the myocardial oxygen demand and can be detrimental to ischaemic patients undergoing cardiac surgery.  This was not observed in the present study. On the other hand sevoflurane does not have these characteristics, it appears to be less potent coronary vasodilator than isoflurane and is not associated with coronary steal  . Conzen et al  have shown that patients receiving sevoflurane for OPCAB had less myocardial injury during the first 24 postoperative hours than patients receiving propofol.
In a recent study  it was shown that choice of primary anaesthetic agent can influence ICU length of stay. Postoperative troponin-I concentrations and need for prolonged inotropic support were lower in the sevoflurane and desflurane groups. Postoperative cardiac functions were also better preserved with volatile anaesthetics and was considered an important factor related to shorter ICU and hospital length of stay. In our study also, both groups did not show any significant increase in cardiac enzymes in postoperative period.
Lastly the controversial aspects of fast tracking are, the patients awakens early i.e. within an hour due to usage of ultra short acting drugs during surgery, the perception of pain is earlier so the need for supplementing postoperative analgesics is earlier. The other aspect is the need for reintubation for respiratory complication, bleeding or arrthymias, which may be detrimental.
In conclusion, sevoflurane and isoflurane can safely be used for fast track anaesthesia protocol in patients undergoing OPCAB surgery without compromising safety. However sevoflurane provides early awakening and extubation as compared with isoflurane.
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