Using the Ventrain With a Small-Bore Catheter: Ventilation or Just Oxygenation?
Use of the Ventrain device has been reported in a number of different situations,2,3 including a report where emergency ventilation using the device was achieved in a porcine model of complete upper airway obstruction.3 In that animal study, the Ventrain was operated via a 3-mm internal diameter, 100-cm long Airway Exchange Catheter (Cook Medical Inc) which allowed for adequate ventilation (ie, normal blood gases). In contrast, the narrow 7-F lumen blocker that Evers et al1 used had an internal diameter of only 1 mm, making it likely very difficult to provide adequate actively assisted expiration (a fundamental feature of Ventrain ventilation). As the PaCO2 in anesthetized and apneic patients has previously been reported to rise at a rate of 3.4 mmHg·CO2·minute−1,4 the 20 minutes required to repair the bronchus would have expected to lead to an approximate 60 mmHg increase in PaCO2 from the pre-Ventrain baseline, even if the patient was apneic. Importantly, this increase would have resulted in a PaCO2 close to the final value that they actually reported. As for the partial pressure of oxygen, the adequate oxygenation may simply have been a result of providing some small amount of oxygen insufflation into the distal bronchus to match the metabolic demands and alveolar oxygen uptake (ie, approximately 250 mL·minute−1 oxygen consumption5).
So although using the Ventrain through a 7F blocker may have allowed the oxygenation needed to safely complete a 20-minute surgical procedure, this might similarly have been accomplished if free flow of oxygen had been provided to the bronchus without any ventilation at all.3 Although the authors should rightly be enthusiastic about the potential for this combined Ventrain and Arndt blocker technique, it should perhaps be tempered pending more investigation of the adequacy of its ventilation capability in clinical practice.