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Closed loop control of oxygenation and ventilation during mechanical ventilatory support is essential for remote medical care in an austere environment. Closed loop control allows for expert systems to provide the current standard of care in the absence of on-site expertise. Ventilation may be controlled by simple systems incorporating patient height or by advanced systems incorporating measurements of end-tidal carbon dioxide (ETCO2) and pulmonary impedance. Oxygenation may be controlled by adjustments of inspired oxygen concentrations (FIO2) and positive end-expiratory pressure (PEEP) using pulse oximetry (SpO2) as the input. Control of oxygenation can prevent hypoxemia and has the potential to reduce oxygen requirements. A double closed loop system of oxygenation control including control of FIO2 via SpO2 and control of oxygen generation by a portable oxygen generator (POG) based on FIO2 and minute ventilation (VE) promises safety and efficiency. Remote control of ventilation and oxygenation is possible using existing technology.

Acute lung injury (ALI) is a common condition that leads to respiratory impairment with patients, specifically regarding oxygenation. We have previously demonstrated in a mechanical model that using a portable oxygen concentrator (POC) with pulsed dose delivery of oxygen is an alternative to continuous flow to conserve oxygen and prolong battery life, while still maintaining adequate oxygen delivery. We hypothesize that using a modified POC and pulsed dose oxygen delivery can provide similar oxygenation in an animal model compared to continuous flow oxygen delivered to a reservoir bag. In a crossover study, we induced ALI in 15 locally bred pigs using an oleic acid model. We ventilated the pigs with equipment that is used by Critical Care Air Transport Teams of the United States Air Force. Each animal served as its own control as we compared oxygen delivery using a POC in both continuous flow with a reservoir bag and pulsed dose. We performed this in both volume control and pressure control mechanical ventilation. There was no statistical difference regarding any of the ventilator variables including respiratory rate and tidal volume in the ventilator modes or in oxygen delivery methods, with the exception of mean airway pressures (4.1 +/- 0.9 cm H2O vs. 6.5 +/- 2.7 cm H2O, p=0.03). There was no between groups for the pulsed dose delivery and continuous flow. In volume control, pulsed dose oxygen delivery demonstrated a significant increase in the P:F ratio (168.8 +/- 96.1 vs. 91.7 +/- 65.4, p=0.002) compared with continuous flow. However, this was not seen in pressure control ventilation (89.0 +/- 74.5 vs. 79.1 +/- 65.4, p=0.67). We were able to demonstrate that oxygen delivery using a POC in mechanically ventilated pigs with ALI is feasible.

Mechanical ventilation in an austere environment is difficult owing to logistics, training, and environmental conditions. We evaluated the ability of professional caregivers to provide ventilatory support to a simulated patient using the Simplified Automated Ventilator (SAVe) with a mask hand attended ventilation, mask with single strap unattended ventilation, and supraglottic airway (King LT) ventilation. All three methods were performed using a SAVe with a set tidal volume of 600ml and respiratory rate of 10 breaths per minute. The simulator consisted of a head and upper torso with anatomically correct upper airway structures, trachea, esophagus, and lung which, also measured the delivered tidal volume, respiratory rate, inspiratory flow, and airway pressures. Volunteers used each airway control method to provide ventilation for 10 minutes in random order. Success of each technique was judged as a mean delivered tidal volume of500ml. The major finding of this study was that medical professionals using SAVe resuscitator and the manufacturer supplied face mask with single head strap failed to ventilate the airway model in every case.SAVe, Ventilation, Airway management, Prehospital, Mask Ventilation.