We have studied prospectively the effect of 10 cm H2O of PEEP on the incidence of venous air embolism and on the cardiovascular response to change from the supine to the seated position in a large neurosurgical population. Patients were allocated randomly to receive either PEEP (10 cm H2O, n = 45) or conventional (control, n = 44) ventilation. Cardiovascular and respiratory variables were measured in the supine and sitting positions, and monitoring included precordial Doppler probe, pulmonary artery pressure and expiratory carbon dioxide concentration. Venous air embolism was assumed if changes in precordial Doppler sounds occurred, end-tidal carbon dioxide concentration decreased or air could be retrieved from a central venous multi-orifice catheter. The incidence of venous air embolism (26%) did not differ between patients undergoing conventional ventilation and those undergoing ventilation with 10 cm H2O of PEEP. Venous air embolism was always detected first by alterations in Doppler sounds. Cardiac output was significantly higher in patients undergoing conventional ventilation than in those undergoing ventilation with PEEP in the supine but not in the sitting position. Furthermore, pulmonary vascular resistance increased significantly only in the upright position in those undergoing ventilation with PEEP. The pulmonary artery wedge pressure to central venous pressure gradient did not attain negative values with PEEP or with upright positioning. We conclude that the use of PEEP during neurosurgical procedures performed in the sitting position should be abandoned as it does not decrease the incidence of venous air embolism but is associated with significant adverse cardiovascular effects.

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The effects of the non-depolarizing muscle relaxants pancuronium (Pancuronium) and vecuronium (Norcuron) (0.1 mg/kg) on myocardial blood flow, myocardial oxygen consumption, myocardial lactate balance, cardiovascular dynamics and electrocardiogram were studied in two groups of eight patients undergoing coronary artery bypass surgery. After induction of anaesthesia with 0.015-0.02 mg/kg flunitrazepam, isoflurane (0.5 vol%) and N2O/O2 (l/l), neuromuscular blockade was induced with pancuronium or vecuronium (0.1 mg/kg) combined with a single dose of 0.005 mg/kg fentanyl. Haemodynamic measurements were performed and the electrocardiogram was recorded before anaesthesia, in steady-state anaesthesia, after relaxation with pancuronium or vecuronium combined with fentanyl, and after intubation. The haemodynamic data consisted of heart rate, cardiac index, stroke volume index, mean arterial pressure, total peripheral resistance, pulmonary arterial pressure, pulmonary capillary wedge pressure, right atrial pressure, myocardial blood flow, coronary vascular resistance, myocardial oxygen consumption, coronary aterio-mixed venous content difference, myocardial lactate extraction and rate pressure product. In the vecuronium group, heart rate decreased significantly more (21%) than in the pancuronium group (9%). Therefore myocardial oxygen consumption (48% resp. 35%) and coronary blood flow (31% resp. 18%) decreased more in the vecuronium than in the pancuronium group. The higher metabolic demand in the pancuronium group induced a significantly lower coronary vascular resistance, because the decrease in coronary perfusion pressure was similar in both groups. None of the other haemodynamic parameters differed significantly in either patient group. We did not observe ST-segment depressions or elevations in the ECG, increases in PCWP or myocardial lactate production. Therefore extended myocardial ischaemia can be excluded in our patients who received pancuronium or vecuronium for neuromuscular blockade.

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