Early effect of carotid endarterectomy on arterial blood pressure measured with an ambulatory monitor.

BACKGROUND: Carotid artery disease and hypertension are associated, and carotid endarterectomy is often followed by acute changes in blood pressure. As the carotid sinus is responsible for short-term blood pressure control, occlusive carotid disease may contribute to the mechanism of preoperative hypertension. METHODS: Ten patients undergoing carotid endarterectomy and eight having a peripheral bypass procedure were studied 2 weeks before and 2 weeks after operation, using home ambulatory blood pressure measurement. RESULTS: A significant fall in both mean systolic (-14.4 mmHg) and mean diastolic (-12.7 mmHg) pressure was observed after carotid endarterectomy (P < 0.006), whereas no change was seen in controls. CONCLUSION: These results suggest that there is an increase in carotid sinus activity in patients following carotid endarterectomy and supports the hypothesis that carotid sinus dysfunction contributes to hypertension in patients with carotid artery disease.

Prospective randomized placebo-controlled trial of aprotinin for elective aortic reconstruction.

BACKGROUND: The serine protease antagonist, aprotinin, reduces perioperative blood loss in cardiac surgery and orthotopic liver transplantation. A pilot study suggested that the drug may also reduce bleeding during infrarenal aortic replacement; the aim was to confirm or refute this observation with a prospective, randomized, double-blind, placebo-controlled trial. METHODS: Some 136 patients were randomized to receive either aprotinin, given as a loading dose of 2 x 10(6) kallikrein inactivator (KI) units followed by 0.5 x 10(6) KI units/h or equal volumes of 0.9 per cent saline. After 80 patients had been randomized the infusion dose was doubled to ensure that plasma levels were similar to those seen in successful cardiac studies. Blood loss, coagulation and haematological parameters were recorded throughout surgery and for 7 days afterwards. Blood was transfused to maintain the haemoglobin level at 100 g/l. RESULTS: Four patients were withdrawn after randomization when found at laparotomy to be unsuitable for the planned reconstruction. The 30-day mortality rate was 4.5 per cent, with no excess complications in either group. Blood loss collected on swabs was reduced from 480 ml in placebo-treated patients to 379 ml with aprotinin (P = 0.014). Blood loss into suction drains in the first 24 h after operation was reduced from 295 to 205 ml in aprotinin-treated patients (P = 0.002). However, no significant reduction was found in intraoperative or total blood loss, or transfusion requirement. CONCLUSION: The small reduction in blood loss in patients treated with aprotinin demonstrated in this study does not support its use in routine elective aortic surgery.

Effect of flow on the resistance of modelled femoral artery stenoses.

An accurate model of the pressure-flow relationship of a stenosis is necessary for the correct interpretation of haemodynamic measurements. Modelled femoral artery stenoses were tested in vitro and the pressure drop: flow ratio (resistance) was most accurately represented by a fixed component (Rf) combined with a variable component (Rv) that increased linearly with flow (Q) such that Rv = SvQ. For stenoses of 68-94 per cent area, Rf increased from 3.2 to 77.7 milliperipheral resistance units (mPRU), while Sv increased from 0.009 to 0.578 mPRU ml-1 min and Rv was dominant for physiological flow rates. It was concluded that the approximation of a significant stenosis to a fixed resistance is incorrect.

Intraoperative heparinisation, blood loss and myocardial infarction during aortic aneurysm surgery: a Joint Vascular Research Group study.

OBJECTIVES: The primary aim of this prospective multi-centre study involving patients undergoing elective abdominal aortic aneurysm (AAA) surgery was to investigate the relationship between intraoperative intravenous heparinisation, blood loss during surgery and thrombotic complications. METHODS: Two hundred and eighty-four patients were randomised to receive intravenous heparin (n = 145) or no heparin (n = 139). Groups were evenly matched for age, sex, weight, aneurysm size, haemoglobin concentration, platelet counts and distal occlusive disease measured by ankle/brachial systolic pressure. RESULTS: There were no statistically significant differences in blood loss (median 1400 ml vs. 1500 ml; z = 0.02, p = 0.98, 95% C.I. = -200 to 200), blood transfused (4.0 units vs. 4.0 units; z = 1.09, p = 0.28, 95% C.I. = -1 to 0) or distal thrombosis between the two groups. However, analysis of the clinical outcome revealed that 5.7% of the non-heparin group but only 1.4% of the heparinised patients suffered a fatal perioperative myocardial infarction (MI); p < 0.05. All MI, including non fatal events, affected 8.5% and 2% respectively (p = 0.02). CONCLUSIONS: Heparin does not increase blood loss or the need for blood transfusion during surgery. Heparin is not necessary to prevent distal thrombosis when the aorta is cross clamped. The results of the study are consistent with the known mechanisms leading to intraoperative MI and strategies for its prevention. Intravenous heparin, given before aortic cross clamping, is an important prophylaxic against perioperative MI in relation to AAA surgery.

Randomized controlled trial of patch angioplasty for carotid endarterectomy. The Joint Vascular Research Group.

A randomized controlled trial was performed to evaluate patch angioplasty for patients undergoing carotid endarterectomy. There were 213 patient episodes affecting 148 men and 65 women, with 109 allocated to patch angioplasty. Following surgery six patients suffered transient ischaemic attacks but these did not delay discharge from hospital. Six individuals (four patched operations, two not patched) required re-exploration for postoperative haemorrhage and eight (two patched procedures, six not) had potentially serious neurological problems after operation. Of these eight patients, four (none receiving patch angioplasty) underwent re-exploration and in each case a clot was removed and a patch inserted; three of the four made a good long-term recovery. The other four patients suffered completed strokes from which one died. Two further patients (one patched procedure, one not) died after operation from myocardial events, giving an overall 30-day stroke or mortality rate of 2.8 per cent. Objective follow-up assessment with duplex scanning at 1 year was completed by 94.8 per cent of patients; significantly more vessel restenoses and occlusions were observed in those not receiving patches (P < 0.01). Patch angioplasty reduces the number of immediate postoperative complications, and significantly lowers vessel restenosis and occlusion rates at 1 year after operation.

Non-invasive monitoring of cardiac output changes during aortic cross-clamping for infrarenal reconstruction--a new technique using suprasternal Doppler-derived cardiac output.

There is a significant morbidity and mortality associated with elective infrarenal aortic reconstruction. To examine the value of continuous cardiac output monitoring for predicting those at risk, 40 consecutive patients were monitored using Doppler-derived cardiac output. The anaesthetist was blind to all information from the monitor and managed the patients using standard techniques. In 28 patients there were no observed changes, while in seven, cardiac output rose after aortic cross-clamping. In five patients a fall in cardiac output occurred after cross-clamping. No cardiac events or cardiac deaths occurred in the 35 patients who showed a rise or no change in cardiac output. However, there were three cardiac events, including one cardiac death in the group of five patients in whom a fall in cardiac output was observed. It would appear that intraoperative non-invasive Doppler-derived cardiac output monitoring successfully predicts high-risk patients who would perhaps benefit from more intensive pre-, peri- and postoperative care.

Effect of aprotinin on neutrophil function after major vascular surgery.

High-dose aprotinin reduces blood loss and blood transfusion requirements during liver transplantation and cardiac and vascular surgery. The mechanism of the haemostatic effect of aprotinin is unclear. A general effect on the anti-inflammatory response may be involved. Because leucocyte activation is part of this process, white cell function was measured in patients undergoing aortic surgery who received high-dose aprotinin therapy (n = 10) and was compared with the results from controls who did not (n = 10). The test group received an intravenous bolus (2 x 10(6) kallikrein inhibitor units) of aprotinin after induction of anaesthesia followed by continuous infusion (0.5 x 10(6) kallikrein inhibitor units/h) until the end of the operation. Blood samples were obtained before operation, immediately after surgery, and 1 and 7 days after operation. Aprotinin maintained significantly better postoperative white cell function as measured by bipolar shape formation (P less than 0.001), unstimulated nitroblue tetrazolium (NBT) reduction (P less than 0.001) and chemotaxis (P less than 0.001). Endotoxin-stimulated NBT reduction was similar in both groups, indicating that neutrophils from treated individuals retained the capacity to respond to oxidative stimuli. Aortic surgery activates neutrophils in vivo, as reflected by impaired chemotaxis and increased superoxide production. Aprotinin protects the cells against this potentially deleterious effect without affecting their ability to respond when provoked. Whether this affects leucocyte interaction with coagulation pathways and contributes to the reduction in blood loss remains to be determined.