From the surgical aspect, the sitting position gives good surgical access to the operative site, improves venous drainage, gives a better view of facial area for monitoring evoked responses from cranial nerve stimulation and allows for better ventilation. Conversely, the sitting position can present complications such as air emboli, postural hypotension and serious cardiac arrhythmias due to surgical stimulation of cranial nerves and brainstem.This paper presents our clinical experience in 180 neurosurgical procedures on the posterior fossa in the sitting position. The standardized anesthetic technique consisted of narcotic, muscle relaxant, nitrous oxide and controlled ventilation. All patients were monitored with EGG, direct arterial and venous pressure, discontinuous blood gases, and expiratory CO, and urinary output. Air embolism was detected via Doppler ultrasonic detector and evacuated through a right atrial catheter.Air was detected, visualized and aspirated in 45 cases for an incidence of 25%, with most episodes occurring early in the procedure. In 11 cases (6%) air was detected on closure. There were no deaths in this series.Fifty-eight patients (32%) had a 10-20 mmHg drop in blood pressure on reaching the sitting position, 19 became temporarily hypertensive (10.5%), and the remainder were normotensive. In 46 patients (25%), bradycardia developed during retraction-manipulation-stimulation of structures on or adjacent to brainstem as well as to cranial nerves. Surgical stress also accounted for the 13 patients (7%) having frequent premature ventricular extrasystoles. One case of profound hypotension and another case of virtual cardiac standstill were noted during the use of the bipolar electrocautery at or near the fifth nerve exit from brainstem. Additional hemodynamic data, the physiopathology, diagnosis and treatment of air embolism is discussed.

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A study was designed to evaluate the adequacy of gas exchange during continuous flow apneic ventilation (CFAV) in dogs. Seventeen dogs (average weight 22.9 kg) were divided into three experimental groups. Group I (n = 7) was anesthetized, paralyzed and ventilated with air using intermittent positive pressure ventilation (IPPV) through a tracheal tube. The tube was removed and each main stem bronchus was cannulated with a 2.5 mm i.d., 4 mm o.d. polyethylene catheter using a fiberoptic bronchoscope. The tracheal tube was replaced to hold the catheters in place. Heated, humidified air was continuously delivered equally to each catheter. Total flows ranged from 8 to 28 l/min (0.4-1.4 l X kg-1 X min-1). Airway pressure (Paw) in the trachea did not exceed 2 mmHg (0.27 kPa). Adequate gas exchange in terms of arterial oxygen and arterial carbon dioxide tension (Pao2 and Paco2) was found after 30 min at flows greater than 16 l X min-1. Group II (n = 7) was managed similarly to the first group, insufflating endobronchial air using the optimal flow of 1.0 l X kg-1 X min-1 obtained from Group I. CFAV continued for 5 h in all animals. Blood gas samples and measurements of systemic blood pressure, heart rate (HR), pulmonary artery blood pressure, pulmonary artery wedge pressure, cardiac output (Qt), and temperature were taken every 30 min. Group III (n = 3) was anesthetized similarly to the other groups. Pulmonary gas distribution was evaluated in relation to catheter placement using Xe133. Results showed significant differences between Pao2 values during CFAV and IPPV; however, all animals were adequately oxygenated.(ABSTRACT TRUNCATED AT 250 WORDS)

Continuous flow apneic ventilation (CFAV) was studied in five adult female patients. After induction of anesthesia with thiopental sodium (5 mg/kg) and fentanyl (5 micrograms/kg), and paralysis with pancuronium bromide (0.12 mg/kg), the patients were ventilated with oxygen at an FIO2 of 1.0 by face mask. Two polyethylene catheters (outside diameter [OD] 2.5 mm) were each inserted into the right and left mainstem bronchi. Each catheter had a curved tip measuring 2 cm in length. The angulation of the catheter tip from the axis was 20 degrees for the right side and 30 degrees for the left side. The endobronchial position was checked by fiberoptic bronchoscopy. Subsequently, tracheal intubation was performed using a 7.5 mm OD tracheal tube. CFAV was started when both catheters were connected to the gas delivery system. Humidified oxygen was delivered at total flows between 0.6 and 0.7 1/min. Arterial blood gases were analyzed every 5 min for 30 min. Monitoring included electrocardiogram, indirect blood pressure, heart rate, temperature, and peripheral nerve stimulation. Adequate oxygenation was maintained in all patients, 39.76 +/- 4.32 kPa (299 +/- 37 mmHg) at 30 min. There was a significant rise in Paco2 (P less than 0.05) at 30 min compared to the control, 4.92 +/- 0.25 kPa compared to 7.30 +/- 0.53 kPa (37.0 +/- 1.9 mmHg compared to 54.9 +/- 4.0 mmHg). There was a mean rise in Paco2 of 0.03 kPa/min (0.6 mmHg/min) compared to 0.5 kPa/min (3.8 mmHg/min) with apneic diffusion ventilation. In one patient there was no increase in Paco2 during the 30 min of CFAV.(ABSTRACT TRUNCATED AT 250 WORDS)