Propofol and hypothermic cardiopulmonary bypass. Vasodilation and enhanced metabolic protection?

Volatile anaesthesia during cardiopulmonary bypass

Since its inception, administering and ensuring anaesthesia during cardiopulmonary bypass has been challenging. Partly because of the difficulty of administering volatile agents during cardiopulmonary bypass, total intravenous anaesthesia has been a popular technique used by cardiac anaesthetists in the last two decades. However, the possibility that volatile agents reduce mortality and the incidence of myocardial infarction by preconditioning the myocardium has stimulated a resurgence of interest in their use for cardiac anaesthesia. The aim of this review is to provide an overview of the administration of volatile anaesthetic agents during cardiopulmonary bypass for the maintenance of anaesthesia and to address some of the practical issues that are involved in doing so.

[Anaesthesia and vasomotor tone during CPB: intravenous anaesthetics]

Anaesthesia during CBP is frequently provided using intravenous anaesthetic drugs, particularly propofol. The effects of the different drugs have been studied during CPB. These drugs have an arterial and venous vasodilator effect during CPB which is dose dependent and is more pronounced for propofol. High doses of propofol or thiopental reduce cerebral blood flow but provide no additional neurological protection.

The oxygen debt during routine cardiac surgery: illusion or reality?

BACKGROUND

Patients undergoing cardiac surgery with the use of cardiopulmonary bypass (CPB) are often thought to have tissue hypoxia and intraoperative oxygen debt accumulation despite the lack of sufficient data to support this assumption.

METHODS AND RESULTS

Oxygen uptake and related parameters, including the plasma lactate and pyruvate concentrations, were studied during the perioperative period in a group of 15 consecutive patients who underwent coronary artery bypass graft surgery. The actual oxygen uptake (VO2) and delivery (DO2) were compared with the individual expected (computed) oxygen transport values. The mean values of DO2 and VO2 were in the range of the expected values. Our results demonstrate a leading role for body temperature in perioperative changes of oxygen consumption rate (r2=0.65, p<0.001). Plasma lactate and pyruvate did not exceed the physiological range in any patient. However, with initiation of CPB, the lactate to pyruvate (LA/PVA) ratio increased (from 9.87 +/- 2.43 at T1 to 12.08 +/- 1.51 at T2, p<0.05). The mean value of the LA/ PVA ratio was elevated during surgery. Later, upon lowering of the plasma lactate concentration in the postoperative period, the LA/PVA ratio decreased to normal values. Without any other evidence of hypoxia, this increase in the LA/PVA ratio could be explained by washout of lactate from previously hypoperfused tissues and intraoperative decrease of lactate clearance.

CONCLUSION

Systemic oxygenation was not impaired during CPB, or during 18 h after surgery in the studied group of patients.

Oxygen consumption after hypothermic cardiopulmonary bypass: the effect of continuing a propofol infusion postoperatively

OBJECTIVE

To evaluate the effect of a fixed rate of infusion of propofol on total body oxygen consumption during the postoperative rewarming phase after cardiopulmonary bypass.

DESIGN

Prospective, randomized, controlled study.

SETTING

Cardiac intensive care unit, university hospital.

PARTICIPANTS

Twenty-four male and female patients undergoing elective first-time coronary artery bypass graft surgery.

INTERVENTIONS

Total body oxygen consumption was measured using a pulmonary artery catheter and thermodilution during postoperative rewarming. Twelve patients had propofol infused at 2 mg/kg/h for 4 hours or until rewarmed.

MEASUREMENTS AND MAIN RESULTS

Total body oxygen consumption was reduced in the propofol group compared with the control group. Oxygen consumption was a median of 30.0 mL/min/m(2) less in the patients receiving propofol (p = 0.01). One patient receiving propofol shivered compared with 4 in the control group (p = 0.14).

CONCLUSION

Administration of propofol during postoperative rewarming reduces total body oxygen consumption and may reduce shivering.

Propofol does not ameliorate cerebral venous oxyhemoglobin desaturation during hypothermic cardiopulmonary bypass

Reductions in cerebral venous oxyhemoglobin saturation (SjO2) occur during the rewarming phase of hypothermic cardiopulmonary bypass (CPB). We prospectively investigated the effects of propofol on these reductions in SjO2 (SjO2 <50%). Fiberoptic jugular bulb catheters were inserted in 30 patients undergoing coronary artery bypass grafting. Patients were randomly allocated to a test or control group. Test group patients (n = 15) received a propofol IV infusion titrated to electroencephalographic burst suppression during CPB. No significant differences in SjO2 <50% were found between the groups either by blood sampling and bench oximetry or fiberoptic oximetry. The arteriovenous difference in lactate concentration became negative in 59 of 120 samples. Propofol was associated with an increased incidence of hypotension (mean arterial pressure <50 mm Hg) (P = 0.023), an increased requirement for vasoconstrictor therapy (P = 0.025), and increases in the lactate oxygen index (P < 0.01). Propofol, when administered in doses that produce electroencephalographic burst suppression, does not attenuate the frequency or extent of reductions of SjO2 below 50% during rewarming from hypothermic CPB. However, it is associated with arterial hypotension and an increase in cerebral anaerobic metabolism.

IMPLICATIONS

Reductions in cerebral venous oxyhemoglobin saturation during the rewarming phase of cardiopulmonary bypass may be related to brain injury. When administered in doses sufficient to produce electroencephalographic burst suppression, propofol did not attenuate the frequency or extent of such reductions in cerebral venous oxyhemoglobin saturation.

A nomogram to evaluate the arterial mixed venous oxygen saturation difference during cardiopulmonary bypass

A nomogram providing the arterial mixed venous haemoglobin saturation difference (S(a-v)O2) corresponding to normal oxygen consumption (VO2) during cardiopulmonary bypass (CPB) was produced. Normal VO2 during CPB (95.8 +/- 20.1 ml/min/m2 at 37 degrees C) was obtained from the literature. The nomogram computes the S(a-v)O2 from the body surface, pump flow, blood haemoglobin and patient temperature; a table is also presented which supplies the S(a-v)O2 ranges corresponding to VO2 mean +/-1 and +/-2SD. The nomogram was tested on 10 subjects undergoing CPB for myocardial revascularization. S(a-v)O2 was determined by arterial and mixed venous blood oximetry 5, 20, and 35 min after the start of CPB. The measured S(a-v)O2 was 27.1 +/- 7.2% while S(a-v)O2 obtained from the nomogram was 24.9 +/- 4.0%, the difference was not statistically significant. Eighteen values (60%) were within the range corresponding to VO2 mean +/-1SD. One value was lower than the S(a-v)O2 value corresponding to VO2 mean - 2SD and was associated with the lowest value of blood haemoglobin. Two values were higher than the S(a-v)O2 value corresponding to VO2 mean + 2SD and were associated with inadequate muscle relaxation. By comparing measured S(a-v)O2 values with those obtained by the nomogram and the table, anaesthesiologists and perfusionists can easily detect patients presenting abnormally low or high VO2 values.

Hemodynamic effects, myocardial ischemia, and timing of tracheal extubation with propofol-based anesthesia for cardiac surgery

Recent interest in earlier tracheal extubation after coronary artery bypass graft (CABG) surgery has focused attention on the potential benefits of a propofol-based technique. We randomized 124 patients (34 with poor ventricular function) undergoing CABG surgery to receive either a propofol-based (5 mg.kg-1.h-1 prior to sternotomy, 3 mg.kg-1. h-1 thereafter; n = 58) or enflurane-based (0.2%-1.0%, n = 66) anesthetic. Induction of anesthesia consisted of fentanyl 15 micrograms/kg and midazolam 0.05 mg/kg intravenously in both groups. The enflurane group received an additional bolus of fentanyl 5 micrograms/kg prior to sternotomy and fentanyl 10 micrograms/kg with midazolam 0.1 mg/kg at commencement of cardiopulmonary bypass (CPB). Patients receiving propofol were extubated earlier (median 9.1 h versus 12.3 h, P = 0.006), although there was no difference in time to intensive care unit (ICU) discharge (both 22 h, P = 0.54). Both groups had similar hemodynamic changes throughout (all P > 0.10), as well as metaraminol (P = 0.49) and inotrope requirements (P > 0.10), intraoperative myocardial ischemia (P = 0.12) and perioperative myocardial infarction (P = 0.50). The results of this trial suggest that a propofol-based anesthetic, when compared to an enflurane-based anesthetic requiring additional dosing of fentanyl and midazolam for CPB, can lead to a significant reduction in time to extubation after CABG surgery, without adverse hemodynamic effects, increased risk of myocardial ischemia or infarction.

Effect of propofol infusion on the endocrine response to cardiac surgery

The effect of propofol infusion on the stress response was studied in patients undergoing coronary artery bypass graft (CABG). Ten patients received propofol infusion during cardiopulmonary bypass (CPB) and ten controls received diazepam. Blood levels of cortisol, adrenaline and noradrenaline were sampled. There was a significant reduction in all three hormones (P < 0.05) in the study group. In addition, the amount of sodium nitroprusside used during CPB was significantly reduced (P < 0.05).

Serum lipid and glucose concentrations with a propofol infusion for cardiac surgery

OBJECTIVE

To document changes in serum lipids and glucose with a propofol infusion technique for cardiac surgery.

DESIGN

Prospective cohort.

SETTING

University teaching hospital.

PARTICIPANTS

22 elective cardiac surgical patients.

INTERVENTIONS

Frequent venous blood sampling.

MEASUREMENTS AND MAIN RESULTS

Serum lipids and glucose were measured at 10 time periods perioperatively, from preinduction until 4 hours post-cardiopulmonary bypass. Plasma propofol concentrations were also measured in 10 of these patients. There was a significant increase in glucose (P < 0.0005) and decreases in cholesterol (P < 0.0005), high-density lipoprotein (P = 0.004), and low-density lipoprotein (P < 0.0005); there was no significant change in triglycerides (P = 0.39). The propofol infusion resulted in acceptable plasma levels throughout the procedure and allowed early extubation in the intensive care unit, after a mean (SD) of 7.14 (5.9) hours. There was a strong correlation between triglyceride and propofol levels at most time periods (r = 0.38 to 0.98).

CONCLUSIONS

This study demonstrates that a propofol infusion technique does not result in elevation of serum lipids and supports its increased popularity in maintenance of anesthesia for cardiac surgery.