Introduction: The state of anaesthesia may be altered by CPB . We sought to investigate this further.
Method: We studied 20 adult patients undergoing cardiac surgery with CPB. Premedication of oral diazepam 10mg plus intramuscular morphine 10mg and prochlorperazine 12.5mg, was given 90 min before induction of anaesthesia. Anaesthesia was induced with 0.5-1.0mgkg−1 of propofol, then maintained with isoflurane throughout the procedure. Fentanyl was infused using a Graseby 3400 syringe driver controlled by STANPUMP , to maintain an effect site concentration of 3 ng ml−1 using Shafer's pharmacokinetic model. The PaCO2 was maintained between 4.5 and 5.5kPa and alpha-stat blood gas management was used on CPB.
The isoflurane concentration was titrated to maintain the Bispectral Index (Aspect, A-2000) at 45 throughout surgery. BIS, nasopharyngeal temperature and end-tidal isoflurane concentrations were recorded on four occasions (1 before sternotomy, 2 after sternotomy, 3 at normothermia before the end of CPB, 4 after weaning from CPB) at one-minute intervals and the mean value calculated. The same pair of isoflurane vaporizers were used throughout the study and the end-tidal isoflurane concentration was measured using the same anaesthetic gas module (SMART, Marquette-Hellige).
Blood pressure was maintained within acceptable values using phentolamine 0.5-1.0 mg and phenylnephrine 50-100 μg. Heart rate was controlled where necessary using esmolol 0.5-1.0mgkg−1 or glycopyrrolate 0.6-1.2 mg.
Results: Data were obtained from 14 men and 6 women with a mean age of 67yr (range 49-78) and are presented as mean values with 95% confidence intervals.
Discussion: The mean isoflurane concentration was significantly lower post-CPB than pre-CPB. This may be due to changes in blood solubility of isoflurane or the pharmacokinetics of fentanyl during CPB, or factors related to CPB itself.
1 Lundell JC, Scuderi PE, Butterworth JF. Less isoflurane is required after than before cardiopulmonary bypass to maintain a constant Bispectral Index value. J Cardiothorac Vasc Anesth
2 Online at http://pkpd.icon.palo-alto.med.va.gov
(accessed October 2002).