Many critically ill patients require respiratory support ranging from supplemental oxygen by nasal cannula to intubation with mechanical ventilation. The ICU provides a controlled environment with the personnel, monitoring, and advanced equipment available to adjust to the patient’s evolving respiratory status. However, there are situations where airway management must occur outside of an ICU or operating room, where equipment, monitoring, and familiarity of personnel to advance airway management are variable. This chapter focuses on considerations for airway management for critically ill patients in remote locations including the challenges involved in transporting these patients to the hospital. Even within the hospital environment, remote nonoperating room anesthesia (NORA) sites warrant their own discussion of airway management and, finally, we will consider the truly austere environment.

Critical care transport (CCT) encompasses a wide range of patient transports including scene response, interhospital transfer for higher-level or specialty care, and international medical evacuation. Patients are transported by ground ambulance or aeromedical transport through helicopter (rotor-wing) and airplane (fixed-wing).^2,3 There are no current guidelines defining a CCT team and the provider composition varies across states and countries. In the United States, nurse and paramedic teams are the most common combination of care providers.⁴ Respiratory therapists and physicians may complement teams to provide additional skills for complex medical cases such as pediatric patients or patients requiring mechanical circulatory support.⁴ Working in an austere environment, CCT teams must be prepared with the necessary monitoring equipment, medical devices, and medications to support and provide ICU-level care to the patient throughout transport. This includes the potential for unanticipated time delays from traffic, weather, or mechanical failure.^2,4

The overarching goal of CCT is to safely move a patient to definitive care while avoiding unnecessary risk. On arrival, a CCT team evaluates the patient’s medical condition paying close attention to respiratory status. The patient’s level of consciousness, work of breathing, oxygen saturation, current respiratory support settings including supplemental oxygen or noninvasive positive pressure ventilation, capnography, laboratory findings, and imaging are all assessed.^3,5 If there is concern the patient will be unable to maintain respiratory stability throughout transport, has a high aspiration risk, or altered mental status making transport unsafe, the airway should be secured prior to transport.⁵

Despite a goal to avoid intubation while in transport, changes in clinical status including sudden hypoxic or hypercarbic respiratory failure, aspiration, or worsening mental status may require airway intervention.⁶ Basic and advanced airway interventions for CCT are not standardized and providers must be familiar with the protocol of their transport service.⁵ Basic airway management
including patient repositioning, jaw thrust, and nasal and oral airway adjuncts can allow for initial airway rescue, while advanced airway interventions including supraglottic airway device placement and endotracheal intubation may ultimately be required for improved oxygenation and ventilation. Many services prioritize preoxygenation followed by rapid sequence induction with a goal of expediting airway securement. Data between direct laryngoscopy and video laryngoscopy varies in the prehospital setting. In experienced providers, the first-pass success of both direct laryngoscopy and video laryngoscopy is equivalent, however, after failed first attempt, there is improved second-pass success by immediately switching devices to video laryngoscopy.⁷ Unique challenges with intubation for CCT teams include the environmental impact of temperature, humidity, ambient light, constraints in accessing the patient, positioning challenges, and crew safety while performing airway procedures in an emergent situation.^5,6,7 These factors all contribute to an increased risk for adverse events during airway management in the prehospital setting.⁶

CCT crews and patients are exposed to multiple physiologic stressors during aeromedical transport including noise, vibration, acceleration, gravity force, temperature, and humidity. Altitude, and its effects on the partial pressure of oxygen and gas volume, need to be paid particular attention. As altitude increases, the barometric pressure decreases leading to a decrease in the partial pressure of atmospheric gases.^3,4 The Federal Aviation Administration (FAA) regulates all civilian flights maintain standard cabin pressurization at 6,000 to 8,000 ft above sea level while flying above this altitude. The atmospheric partial pressure of oxygen (PO₂) is 159 mm Hg at sea level and drops to 118 mm Hg at 8,000 ft (Fig. 38.1).^2,3 Patients exposed to this decrease in partial pressure of oxygen may experience hypobaric hypoxia requiring increased supplemental oxygen to maintain adequate oxygenation despite regulating cabin pressures.

Gas expansion due to the drop in atmospheric pressure may affect patient conditions and medical devices. During ascent, gas in contained spaces has the potential to rapidly expand according to Boyle’s gas law (P₁V₁ = P₂V₂). Gas contained within a pneumothorax, pneumocephalus, or intraluminal abdominal air can expand requiring urgent intervention for patient stabilization.^2,4 The endotracheal tube cuff, filled with air, can expand on ascent transmitting high pressure across the trachea or vocal cords leading to mechanical and ischemic injury. Obtaining frequent cuff pressure evaluation, or injecting saline into the cuff in place of air, can both mitigate the risk associated with rapid gas expansion.⁸ For the same reasons, careful attention should also be given to eliminating air from intravenous fluid bags. The use of infusion pumps ensures desired infusion dose delivery and detection of inadvertent air in IV tubing prior to patient injection.⁴

The potential impact of barometric pressure on aeromedical transport ventilators has long been recognized. While lung-protective ventilation (tidal volumes ≤8 mL/kg predicted body weight), utilization of positive end-expiratory pressure (PEEP), and monitoring plateau pressure are standards
routinely accepted in the ICU setting, there are unique challenges for the CCT teams attempting to optimize ventilator settings during transport.⁹ The American Society for Testing Material (ASTM) places guidelines of <10% change in tidal volume as acceptable for portable transport ventilators; however, many ventilators have mixed performance at altitude.¹⁰ With decreasing barometric pressure, higher tidal volume delivery is possible. Ideally, the transport ventilator in use should be certified as safe for use in aeromedical environment, able to compensate for a variety of altitude changes, and able to deliver consistent tidal volumes and minute ventilation within the expected range of barometric pressure.⁴ However, there may be conditions where an alternative, untested ventilator is required, or rapid cabin decompression beyond the expected range occurs. Close attention should be placed on and differences between the programmed compared to delivered tidal volumes to avoid exposing patients to lung injury via alveolar volutrauma or barotrauma.²

The physiologic monitoring of critically ill patients is integral for teams providing stabilizing care while enroute to a destination. Noise levels in transport exceed those of auscultated heart tones and breath sounds making physical exams challenging.⁴ Medical devices should have adequate battery life for transport or the ability to charge from a power source on the transport vehicle.⁴ For aeromedical transport, medical devices must not interfere with communication and navigation systems while the aircraft systems, conversely, must not interfere with the monitoring equipment.² Aeromedical equipment should be certified as compatible with the vibrations, acceleration, temperature shifts, and barometric pressure changes encountered during transport.⁴