Continuous Flow Apneic Ventilation

Abstract

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 1/min (0.4—1.4 1 + kg^‐1 min‐^‐1). Airway pressure (P_aw) 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 · min_‐1. Group II (n = 7) was managed similarly to the first group, insufflating endobronchial air using the optimal flow of 1.0 1 · kg ¹ · 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 Paoj values during CFAV and IPPV; however, all animals were adequately oxygenated. During 5 h of CFAV, adequate CO₂ elimination was achieved in all animals. There was no difference in PaO₂, Paco₂ and shunt fraction (Qs/C}t) with CFAV at 30 min and 5 h. Differences in HR, Qt, and systemic vascular resistance at 30 min and 5 h were related to the hypothermia during the developing course of experimentation. With the catheters above the carina, gas distribution studies demonstrated gas limited to the large airways with no peripheral distribution, resulting in low Pao₂ levels and elevated Paco₂ levels. Endobronchial catheters permitted gas distribution to the peripheral airways, and oxygenation and ventilation were normal.