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Optimizing Flow-Controlled Ventilation: Impact of I:E Ratios and Oxygen Concentration in a Porcine Model of Total
Tomas Karlsson1,2, Jenny Gustavsson3, Katrin Wellfelt3
1From the Department of Clinical Science and Education, Section of Anesthesiology and Intensive Care, Karolinksa Institutet, Stockholm, Sweden.
Background:
Prehospital airway obstruction is a medical emergency requiring immediate intervention. When the insertion of a larger bore tube over an airway catheter is hindered by obstruction, flow-controlled ventilation (FCV) with expiratory ventilation assistance (EVA) may offer a solution by allowing for ventilation through the airway catheter. This method uses a continuous bidirectional flow, necessitating a high-pressure gas source, typically 100% oxygen. However, in prehospital or military settings, oxygen supplies and exact manual control may be limited. Therefore, evaluating FCV/EVA without 100% oxygen, and with variable inspiratory-to-expiratory (I:E) control is essential to ensure its feasibility in such environments. We hypothesized that arterial oxygenation with 21% oxygen would be feasible and would vary between different I:E ratios.
Methods:
In this randomized crossover trial, FCV/EVA with different I:E ratios and fraction of inspired oxygen were compared in total airway obstruction. 15 crossbred male specific pathogen-free swine, mean (standard deviation [SD]) weight 56.6 (2.1) kg were divided into groups; method A (n = 9) and method B (n = 6), anesthetized, muscle relaxed and desaturated <80%. FCV/EVA was performed for 15 minutes through an airway catheter in the obstructed airway.
Results:
In I:E 1:1 vs 1:2 with 21% oxygen, the mean difference of Sa o2 was 33.8% (95% confidence interval [CI], 16.3-51.4, P =.0020) and Pa o2 was 4.7 kPa (95% CI, 1.3-8.1, P =.0127). Pa co2 decreased more in 1:1 than 1:1 with a pause and 1:2. Pa co2 remained <5 kPa with small variability in 1:1 with 21% oxygen.
Conclusions:
FCV/EVA with 21% oxygen was feasible and maintained oxygenation and ventilation for 15 minutes. An I:E ratio of 1:1 was superior to 1:2. This approach may offer a viable alternative in a totally obstructed airway in resource-limited settings where higher oxygen concentrations are unavailable.
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