Comparison of anesthetic techniques in patients undergoing heart valve replacement

A comparison of isoflurane versus fentanyl as primary anesthetics for mitral valve surgery

We conducted a randomize study of fentanyl compared to isoflurane anesthesia in patients with pulmonary hypertension undergoing mitral valve surgery. Patients were premedicated and randomly assigned to one of two groups: 21 patients had anesthesia induced with thiopental and maintained with isoflurane; 23 patients had anesthesia induced with a fentanyl bolus and maintained with a fentanyl infusion. Adjustments of fentanyl infusion and isoflurane concentration, as well as fentanyl boluses and vasoactive/positive inotropic medication, were administered to maintain preoperative arterial blood pressure. Both groups exhibited similar demographics, similar duration of cardiopulmonary bypass (CPB) surgery, anesthesia, and time from entrance into the surgical intensive care unit (SICU) to endotracheal extubation. However, the time from entrance into the SICU to awake was significantly (P < 0.05) shorter in patients given isoflurane anesthesia. Hemodynamic variables were recorded at baseline and 12 surgical events and compared between and within groups. Significant changes from baseline were demonstrated in both groups upon institution and discontinuation of CPB. Patients receiving isoflurane anesthesia exhibited cardiovascular depression as compared to their baseline. There were no deaths in either patient group. Adequate hemodynamic profiles were achieved in both groups with comparable use of inotropic and vasoactive medication, with the exception of norepinephrine that was administered intraoperatively to significantly (P < 0.05) more patients in the isoflurane-based anesthesia group. Neither technique was associated with acute improvement of right heart performance or pulmonary hypertension, in large part because of morphologic changes of the pulmonary arterial bed, occurring with long-standing mitral valve disease. We conclude that isoflurane-based anesthesia is adequate for this type of surgery, although there is a higher anesthetic algorithm failure rate than with fentanyl-based anesthetic technique.

Adverse neurologic events: risks of intracardiac versus extracardiac surgery

Intracardiac operations such as valve replacements have typically carried a higher risk (4.2% to 13%) of overt central nervous system outcome, compared with coronary artery bypass grafting (CABG) procedures (0.6% to 5.2%). This is likely owing to the increased risk of macroembolization of air or particulate matter from the surgical field during intracardiac surgery. The periods of highest risk for emboli are during aortic cannulation and especially during release of aortic clamps and weaning from bypass. The number of embolic events measured with transcranial Doppler is significantly higher in patients undergoing valve surgery compared with coronary surgery, particularly during cardiac ejection and immediately after bypass. However, there is current evidence that neurologic risk is increasing in patients undergoing CABG owing to the tendency to operate on older patients with more severe aortic atherosclerosis and cerebrovascular disease. Patients having an intracardiac procedure combined with a CABG procedure may be at particularly high risk for adverse neurologic outcome. For all cardiac surgical patients, there is some cause for optimism in that risk may be minimized by improved assessment (e.g., intraoperative transesophageal or epiaortic echocardiographic scanning of the ascending aorta to identify patients at risk) and monitoring (e.g., detection of embolic phenomena, using transesophageal echocardiography or transcranial Doppler technology). Furthermore, in the future, development and testing of more ideal cerebroprotective drugs may allow amelioration of neurologic injury, either by pretreating all patients at risk, or possibly even by delaying treatment until after the suspected occurrence of an insult.

Neuropsychiatric complications of cardiac surgery

Historically, intracardiac operations have carried a higher risk of neurologic complications than coronary artery bypass grafting (CABG) procedures, although the incidence of such complications has been increasing after CABG in recent years. In both intracardiac and extracardiac surgery, macroemboli from the surgical field cause most neurologic complications. The periods of highest risk for emboli are during aortic cannulation, onset of bypass, and weaning from bypass. Risk factors include atherosclerosis of the ascending aorta, advanced age, presence of concomitant cerebral vascular disease, previous neurologic abnormality, duration of surgery, diabetes, and history of failure of the native circulation. Although hypothermia is beneficial in elective circulatory arrest, its usefulness in reducing postoperative central nervous system deficits during routine cardiac operations may be limited. Studies suggest a role for barbiturate protection in intracardiac but not in extracardiac surgery. Studies have not shown better neurologic or neuropsychological outcome with the use of membrane oxygenation and arterial filtration. Recent studies suggest no correlation of neurologic injury with serum glucose levels during CABG, with either duration or severity of hypotension during hypothermic CABG, or with blood gas management during hypothermic CABG.

[Vascular effects of ketamine during anesthesia with diazepam and fentanyl]

Twenty-six adults undergoing elective cardiac surgery were anaesthetized with diazepam and fentanyl (induction with 200 micrograms.kg-1 and 30 micrograms.kg-1 respectively, maintenance with incremental doses). Normothermic constant perfusion output cardiopulmonary bypass was carried out with a membrane oxygenator, haemodilution with Ringer's lactate solution, and cardioplegia with St. Thomas's Hospital solution. The patients were randomly assigned to two groups. They were given either 2 mg.kg-1 of ketamine (group 1) or placebo (5 ml of normal saline) (group 2) via the venous line of the oxygenator. The non pulsatile flow was then kept at a steady rate of 2.41 x min-1.m-2, and no other infusion or treatment was started during the study period (ten minutes). The mean arterial pressure and blood reservoir level were measured every min during this period. The systemic vascular resistances did not change significantly in either group, but remained 27% lower in the ketamine group than in the placebo group (p less than 0.01). The blood reservoir level was 37% higher in the ketamine group (p less than 0.01), suggesting a decreased venous capacitance. It is therefore concluded that ketamine leads to venous constriction, and probably arterial dilation, during fentanyl-diazepam anaesthesia and normothermic cardiopulmonary bypass. The venous effects of ketamine could explain why it is usually well tolerated in hypovolaemic states.