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 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)

Constant Flow Ventilation in Anesthetized Patients

“…Why, in contrast to humans, does CFV successfully maintain normocarbia in animals (2)(3)(4)9)? First, relative to their body weight (and thus CO, production), dogs have larger main airways than humans, which facilitates normal levels of VA. Light nitrous ox- (2,4), but this is unlikely because we paralyzed our patients (to ensure apnea during the period of CFV) and thus eliminated respiratory and other muscle work (13).…”

“…First, relative to their body weight (and thus CO, production), dogs have larger main airways than humans, which facilitates normal levels of VA. Light nitrous ox- (2,4), but this is unlikely because we paralyzed our patients (to ensure apnea during the period of CFV) and thus eliminated respiratory and other muscle work (13). Second, the multiple inert gas analysis during CFV demonstrates a widened distribution of VIQ ratios in the canine lung (14), and streaming effects at lobar bronchial bifurcations may add to ventilation inhomogeneity among lobes (9).…”

“…During bronchoscopy or during large airway and intrathoracic surgery, CFV should permit better surgical exposure and a motionless operating field (3,4,7). In low compliance pulmonary disease, CFV should prevent the high inflationary airway pressures with consequent cardiovascular depression and pulmonary barotrauma that can occur during IPPV (3,4,8).…”

“…Constant flow ventilation (CFV) uses very high gas flows (total = 1 L.kg -'.minpl) to maintain normal gas exchange in apneic animals (1)(2)(3)(4), two small orotracheal catheters delivering gas flows into each mainstem bronchus with gas exiting through the open airway. Like apneic diffusion oxygenation (ADO, oxygen flow across the proximal opening of a patent airway) (5), CFV results in good oxygenation.…”

Low-Flow Endobronchial Insufflation With Air for 2 Hours of Apnea Provides Ventilation Adequate for Survival

“…Moreover, use of minimum flows for EI is relevant to EI use during nonemergency clinical situations in view of disadvantages of high flows that include mucosal damage (15), pneumothorax (16), elevation of alveolar pressure with a decrease in arterial pressure (17), and cooling (8).…”