[Air embolism in the sitting position. Oxygen/nitrogen versus oxygen/laughing gas]

Venous air embolism (VAE) is a well-known complication of neurosurgical procedures performed in the sitting position. Nitrous oxide (N2O) intensifies the hemodynamic alterations conditioned by VAE. Therefore the administration of N2O must be discontinued immediately if VAE occurs. Nevertheless, it is still not clear whether N2O should be avoided in such operations as a general policy. The aim of the present study was to investigate the incidence and severity of VAE with O2/N2 as opposed to O2/N2O anesthesia. METHODS. In all, 42 patients (19 men, 23 women) aged 23-80 years were investigated in a randomized order. In all cases an intracranial operation was carried out with the patient in the sitting position. The anesthesiologic management was uniform: modified neuroleptanalgesia (fentanyl, flunitrazepam, droperidol), relaxation with pancuronium, endotracheal intubation, moderate hyperventilation (PaCO2 30-35 mmHg) without PEEP. Half (21) of the patients (group 1) were ventilated with O2/N2 (1:1) and the remaining patients (group 2) with O2/N2O (1:1). Heart rate (HR) arterial blood pressure (AP), central venous pressure (CVP), end-tidal CO2 tension (PE'CO2), and body temperature were monitored continuously. Arterial blood gases were checked once per hour at least. VAE was signaled by changes in the ultrasonic Doppler sounds or a rapid decrease in the end-tidal CO2 tension. The diagnosis of VAE was confirmed by aspirating air bubbles through the right atrial catheter. A vacuum-driven device was used to suction off the embolized air and measure the aspirated air volume. Pulmonary gas exchange was defined by the arterial to end-tidal CO2 difference (PaCO2 - PE'CO2) and by the alveolar arterial O2 quotient (PAO2 - PaO2/PAO2). If a VAE was recognized N2O administration was stopped immediately and ventilation was continued with pure oxygen. Postoperatively all patients were ventilated.

The incidence of VAE was similar in both groups: VAE occurred in five patients in group 1 and in six patients in group 2. In isolated cases distinct increases in the CO2 difference (PaCO2 - PE'CO2) or the O2 quotient (PAO2 - PaO2/PAO2) resulted, with no significant difference between the groups. In patients with VAE the aspirated gas volume (median 6.0 ml in group 1, 75.5 ml in group 2; P less than 0.01) and the duration of aspiration (median 5.0 min in group 1, 22.5 min in group 2; P less than 0.05) were significantly different in the two groups. HR was significantly lower in group 2 1 and 4 h after the beginning and at the end of the operation. MAP was significantly lower in group 2 3 and 4 h after the beginning and at the end of the operation. CVP was significantly higher in group 2 3 h after the start of the operation. The total dose of fentanyl, flunitrazepam and droperidol administered was higher in group 1 than in group 2 (P less than 0.05). The duration of postoperative ventilation was similar in both groups.(ABSTRACT TRUNCATED AT 400 WORDS)