Determining the need for mechanical ventilation is critical for the effective application of a mechanical ventilation device. Mechanical ventilation has risks, especially in a prehospital environment without diagnostic tools such as CXR or ABG. Clinical acumen is vital to adequately predict a patient who will progress to respiratory compromise. Respiratory compromise requiring ventilator support can be identified early in M-massive hemorrhage, A-airway, R-respiratory, C-circulation, and H-hypothermia (MARCH) assessment.

Inability to adequately oxygenate, ventilate, or guard the airway are indications for mechanical ventilatory support – but the cause must be determined. Indications for intubation must be thoroughly considered as intubation and Positive Pressure Ventilation (PPV) have risks. For example, a patient with increased work of breathing due to hypoxia from pneumothorax will be severely harmed by intubation with the introduction of positive pressure that can expand the pneumothorax and result in lethal tension physiology. Additionally, the bleeding patient who has a very high respiratory rate due to global tissue hypoxemia from hemorrhagic shock may have a full cardiovascular collapse with administration of induction intubation medications and positive pressure ventilation. Thus, it is of utmost importance to ensure that intubation and Mechanical Ventilation (MV) are necessary and critical, with a plan for treating the most likely underlying etiology in place.

NOTE: Apneic patients with adequate circulation and an open airway require immediate assisted ventilation (i.e. bag valve mask [BVM]).

Though ABGs are the standard for managing patients with respiratory compromise, they are not often readily available in the operational environment. Utilization of pulse oximetry (SpO2) and capnography/capnometry (EtCO2) can provide a rapid assessment of a patient’s respiratory status (devices to achieve both are readily available in medical logistics systems).

SpO2 values < 90% are indicative of potential oxygenation issues; however, values can be unreliable due to poor perfusion and altitude.

EtCO2 values >45mmHg are indicative of hypoventilation, especially in the absence of tachypnea. Values <35mmHg indicate hyperventilation. It should be determined why the patient is tachypneic and the underlying cause treated. Mental preparation for mechanical respiratory support should be considered, but hypovolemia/hemorrhage must be treated first. Of note, EtCO2 may not perfectly reflect the arterial CO2 value in patients with significant lung injury and impaired gas exchange.2

A high index of suspicion for sepsis or another cause of metabolic acidosis should be considered in patients with low EtCO2 and hyperventilation.

The inability for a casualty to maintain appropriate SpO2 or EtCO2 values through less invasive measures (airway adjuncts, supplemental O2, etc.) indicates the need for escalating support. For locations with point of care blood analyzers, inadequate blood gas values also indicate the need for respiratory support. Hemorrhagic shock will result in tachypnea and a low EtCO2 . Intubation and mechanical ventilation prior to adequate blood resuscitation will result in circulatory collapse. It is critical to determine why the patient is tachypneic prior to intubation. Ruling out and treating both hemorrhage and tension pneumothorax (PTX) must occur before intubation. Additionally, a simple PTX which could result in moderate tachypnea, positive pressure ventilation can rapidly convert a simple PTX into a tension PTX which is immediately life threatening.

WARNING: Prior to the application of mechanical ventilation and/or initiation of invasive airway devices (e.g., Endotracheal Tube (ETT), extraglottic airways), patients must receive adequate sedation (and paralysis as appropriate/required). Never paralyze a patient who has not received sedation (in the prehospital environment, Ketamine should be first line for sedation) Detailed guidelines for the initiation and maintenance of this sedation can be found in the JTS Analgesia and Sedation Management during Prolonged Field Care CPG.

If respiratory insufficiency amenable to respiratory support is identified during the assessment, the initiation of timely mechanical ventilation can improve casualty outcomes. This can be as simple as BVM support or as complex as a critical care transport ventilator (e.g. Hamilton-T1 or Zoll EMV+), See Appendix D: Impact 754, Appendix E: Zoll EMV+ (731 Series), Appendix F: Hamilton-T1, Appendix G: Save II, Appendix H: Ventway Sparrow. 3,4

All casualties requiring advanced airway management should have a Heat and Moisture Exchanger (HME) attached to the BVM or the circuit tubing. This aids in humidification, heat conservation, reduced infection risk, and comfort/compliance. If used with an EtCO2 cap or device, the HME should be placed above the EtCO2 cap/device to enable more accurate EtCO2 measurements.

CAUTION: BVM respiratory support should be utilized as a temporary measure until mechanical ventilators can be applied. BVMs deliver irregular tidal volume (VT) and respiratory rates.

Although PEEP is helpful in maximizing alveoli recruitment it can also contribute to worsening hypotension in hypovolemic patients and concomitant aggressive resuscitation.

NOTE: Many patients may require increased sedation (and paralysis) for effective ventilation. Patients who are not properly sedated may cause issues with high pressure alarms as they breathe over the ventilator increasing their minute volume and intrathoracic pressures.

Gastric decompression is also a necessary step after securing the definitive airway and initiation of mechanical ventilation.