Constant flow ventilation in anesthetized patients: Efficacy and safety

Constant flow ventilation (CFV) maintains normal gas exchange in apneic dogs and has potential clinical application during thoracic surgery or pulmonary edema. We compared CFV and intermittent positive pressure ventilation (IPPV) in 5 healthy, anesthetized, (fentanyl, diazepam, and nitrous oxide) and paralyzed patients undergoing nonthoracic operations. Constant flow ventilation was delivered at a total flow of 0.9-1.6 L.kg^-1.min^-1 (nitrous oxide-oxygen at 1:1) into two tubes of 2.5-3.5 mm inner diameter attached to each side of an 8-9 mm inner diameter orotracheal tube (OTT). Under bronchoscopic guidance, the CFV-OTT was advanced to position each ventilating tube at a mainstem bronchial orifice. Gas exhausted through the OTT lumen. If intrathoracic pressure exceeded a preset limit, a solenoid valve automatically interrupted gas flow to the patient to prevent barotrauma. Compared to IPPV, during CFV for up to 30 min average PaCO₂ increased to 69.2 ± 14.5 from 35.9 ± 2.9 mm Hg, reflecting a calculated alveolar ventilation (V̇(A)) of 46 ± 22% of the eucapnic level. We suggest that a technique combining CFV at lower flow rates with IPPV may prove clinically useful by allowing decreased total volume and inspiratory pressure while maintaining normal V̇(A).