No abstract

During thoraco-abdominal aortic aneurysmectomy, the aorta is replaced from the left subclavian artery to the aortic bifurcation. We wished to describe the haemodynamic events occurring during clamping and unclamping of the thoracic aorta and the metabolic changes associated with the interruption of organ perfusion beyond the left subclavian artery. MethodsWe studied I I patients (58-77 years) undergoing thoracoabdominal aortic aneurysm resection without the use of cardiopulmonary bypass. All patients had normal left ventricular systolic function. No patient had angina.Diazepam, fentanyl, pancuronium, air/O2 anaesthesia was used, An arterial line, a Swan-Ganz catheter and a left double lumen endobronchial tube were inserted. The left lung was collapsed to facilitate surgical exposure. Immediately prior to the application of the thoracic aortic cross-clamp, sodium nitroprusside was infused in an attempt to eliminate excessive hypertension at the time of cross-clamp. This was continued for the duration of the cross-clamp (mean 72 minutes) to maintain systolic arterial pressures between 150-200 mmHg. An IV infusion of five per cent sodium bicarbonate was given to achieve a serum b/carbonate of 30-35 nunol.L-~ prior to unclamping of the aorta. ResultsHaemodynamic results (Table I) Cross-clamping of the thoracic aorta produced an immediate increase in mean arterial blood pressure (MAP). This reverted hack to preclamp levels with removal of the clamp, Mean pulmonary artery pressure (MPAP) increased significantly with clamp application and this increase persisted after removal of the clamp. There was no significant change in either systemic vascular resistance (SVR) or pulmonary vascular resistance (PVR). Cardiac indices (CI) were not affected by clamp application but increased significantly after clamp removal. Both the central venous (CVP) and pulmonary capillary wedge pressures (PCWP) increased with clamp application and these changes persisted after clamp removal.Metabolic results (Table 11) An average of 791 mmol of sodium bicarbonate (range 240-1545 mmol) was infused during the time of crossclamp. Unclamping of the aorta with re-establishment of circulation to liver, gut, and kidneys produced an acid wash out, resulting in a highly significant drop in pH (p < 0.001) and plasma bicarbonate. PCO2 rose significantly Catecholamine release may influence the haemodynamic response to anaesthetic induction with narcotics in patients with coronary disease. 1 Previous studies have yielded conflicting results regarding serum catecholamine responses to narcotic anaesthesia.~-4 We have noted unexplained, potentially deleterious, increases in heart rate (HR) and arterial pressure (AP) in occasional patients during induction with high-dose fentanyl. 5 Therefore we tested the hypothesis that catecholamine release accompanies anaesthetic induction with potent narcotics. MethodsInstitutional approval was obtained and all patients gave informed consent. Thirty-three patients with preoperative left ventricular ejection fraction >0.50...