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Patients with respiratory failure or requiring airway protection may need artificial ventilation. A bag-valve-mask device is unreliable and utilizes clinician resources. Although mechanical ventilation is less commonly used in the prehospital setting, it offers superior ventilatory control, especially during prolonged transports. Recognition of basic respiratory physiology and ventilator settings is essential to initiate mechanical ventilation safely and correct the underlying respiratory derangements. Improper ventilator management can worsen the acute disease process and create an inflammatory cascade, thereby worsening lung injury. Participating clinicians within emergency medicine, critical care, and pulmonology benefit from interprofessional collaboration in cases of complex airway management. This activity reviews the physiology of positive pressure ventilation, various ventilator modes, and troubleshooting techniques, providing healthcare professionals with the knowledge and skills to manage patients requiring mechanical ventilation in the prehospital setting. Objectives: Identify the appropriate indications for portable ventilators in emergency medical services based on patient assessment and clinical presentation. Screen patients effectively to determine the need for portable ventilation, considering factors such as respiratory rate, oxygen saturation, and clinical signs of respiratory distress. Apply evidence-based protocols and guidelines to select and use specific portable ventilation modalities for diverse patient populations. Implement effective strategies to improve care coordination among interprofessional team members to facilitate safe mechanical ventilation and handoffs. Access free multiple choice questions on this topic.

Although emergency medical services are known to adopt many innovative procedures and treatments, manual ventilation with a bag-valve-mask device remains the standard of care throughout the US.[1] This method requires the dedication of a team member and provides inconsistent respiratory rates and tidal volumes.[2] The benefits of mechanical ventilation are well-known in the hospital setting, and portable devices are available at a relatively low cost. A 2022 National Association of Emergency Medical Services Physicians (NAEMSP) position statement urges greater prehospital mechanical ventilation adoption.[3] While many reasons may prevent ventilator adoption, unfamiliarity with respiratory physiology likely prevents many clinicians from advocating for ventilator use. According to the US National Emergency Medical Services Information System (NEMSIS) public research dataset, the use of ventilators by emergency medical services during intubations is only 1%.[4]

Hemodynamic Considerations Under normal conditions, the chest cavity is under negative pressure. The negative inspiratory pressure generated by the expansion of the chest cavity not only pulls air into the lungs but also augments venous return to the heart. When the patient transitions to positive pressure ventilation, venous return to the heart (and thus preload) is reduced, which may lower blood pressure. This is often associated with the concurrent drop in blood pressure caused by many sedative agents. The clinician's response to this drop in blood pressure ultimately depends on the patient and is beyond the scope of the chapter; however, a common error is setting the tidal volume too high, and reducing the tidal volume may lead to lower pressures and help mitigate some of this effect. Diagnostics Whenever a ventilator requires troubleshooting or there is a concern for oxygen desaturation or instability, clinicians should consider removing the patient from the ventilator. This action removes a highly complex device and can help determine the source of potential issues. During this time, the patient should be carefully ventilated with a bag-valve-mask device. A loss of consistent EtCO2 waveform can be due to obstruction of the device, tube dislodgement, poor ventilation, or device failure. Among these possibilities, device failure is improbable. Clinicians should assess the tube placement and ensure adequate chest rise and fall. The replacement of the airway device should be considered, and attention should be given to ensure nothing is blocking the EtCO2 tubing if the waveform still does not correct. The sensor should be checked, as secretions may impair its function. Finally, if EtCO2 cannot be corrected, the EtCO2 monitor should be replaced, followed by an alternative monitor.

Whenever a ventilator requires troubleshooting or there is a concern for oxygen desaturation or instability, clinicians should consider removing the patient from the ventilator. This action removes a highly complex device and can help determine the source of potential issues. During this time, the patient should be carefully ventilated with a bag-valve-mask device. A loss of consistent EtCO2 waveform can be due to obstruction of the device, tube dislodgement, poor ventilation, or device failure. Among these possibilities, device failure is improbable. Clinicians should assess the tube placement and ensure adequate chest rise and fall. The replacement of the airway device should be considered, and attention should be given to ensure nothing is blocking the EtCO2 tubing if the waveform still does not correct. The sensor should be checked, as secretions may impair its function. Finally, if EtCO2 cannot be corrected, the EtCO2 monitor should be replaced, followed by an alternative monitor. An increase in minute ventilation or tidal volume may decrease CO2 levels, while decreased or shallow breathing may elevate CO2 levels. However, ventilated patients rely on changes to ventilator settings to manage their systemic pH balance. Patients with increasing CO2 levels should first be removed from the ventilator and assessed for tube displacement, pulmonary edema, and pneumothorax. The patients should receive bag-valve-mask respirations and ensure CO2 improvement with increased respiratory rate. This should be addressed if an underlying issue, such as septic shock, may cause the patient's hypercapnia. When interrogating the ventilator settings, elevated CO2 levels will likely be improved by increased respiratory rate or tidal volume. In cases of sudden worsening of hypoxia, it is essential to confirm tube placement, assess breath sounds, and check for any signs of tracheal deviation or subcutaneous emphysema suggestive of pneumothorax development. If hypoxia is confirmed, increasing PEEP and FiO2 is prudent. In addition, it is crucial to disconnect the patient from the ventilator and manually ventilate them with a bag-valve-mask device and 100% oxygen.

In cases of sudden worsening of hypoxia, it is essential to confirm tube placement, assess breath sounds, and check for any signs of tracheal deviation or subcutaneous emphysema suggestive of pneumothorax development. If hypoxia is confirmed, increasing PEEP and FiO2 is prudent. In addition, it is crucial to disconnect the patient from the ventilator and manually ventilate them with a bag-valve-mask device and 100% oxygen. When an alarm for high inspiratory pressures is detected, it is advisable to check the circuit for any obstructions and ensure adequate sedation and ventilator synchrony. Moreover, if the high peak pressure alarms are triggered with normal plateau pressure, underlying obstructive ventilatory defects should be suspected and treated using bronchodilators. Special Considerations Breath stacking occurs when the patient does not fully exhale. As a result, with each successive breath, the volume of air in the lungs, and consequently airway pressure, increases.[18] This can be dangerous and put the patient at risk of barotrauma. The stacking can occur when patients have severe obstructive disease, particularly asthma. Some ventilators display the volume waveform or the inspired and exhaled volumes. The volume of exhaled air should match the inspired volume, or the waveform should return to zero. If breath stacking is detected, the ventilator circuit should be briefly disconnected, the patient's chest should be gently pushed to exhale all the excess volume, and the ventilator should be reconnected. The respiratory rate should be reduced to allow more time between breaths for exhalation, and if the machine has the capability, the inspiratory time of the breath should be decreased. Permissive hypercapnia is often required to obtain appropriate oxygenation and prevent breath stacking.[19]

Breath stacking occurs when the patient does not fully exhale. As a result, with each successive breath, the volume of air in the lungs, and consequently airway pressure, increases.[18] This can be dangerous and put the patient at risk of barotrauma. The stacking can occur when patients have severe obstructive disease, particularly asthma. Some ventilators display the volume waveform or the inspired and exhaled volumes. The volume of exhaled air should match the inspired volume, or the waveform should return to zero. If breath stacking is detected, the ventilator circuit should be briefly disconnected, the patient's chest should be gently pushed to exhale all the excess volume, and the ventilator should be reconnected. The respiratory rate should be reduced to allow more time between breaths for exhalation, and if the machine has the capability, the inspiratory time of the breath should be decreased. Permissive hypercapnia is often required to obtain appropriate oxygenation and prevent breath stacking.[19] Patients with severe metabolic acidosis, such as diabetic ketoacidosis, rely on respiratory compensation to mitigate the acidemia and thus require significant minute ventilation above normal levels. Intubation should be avoided in these patients whenever possible, and if it is unavoidable, the respiratory rate should be set to match the patient's breathing rate before intubation. The initial end-tidal CO2levels should be noted immediately after intubation, and efforts should be made to maintain or lower that number. Failure to do so results in worsening acidemia and further deterioration of the patient's condition. Acute Respiratory Distress Syndrome

Patients with severe metabolic acidosis, such as diabetic ketoacidosis, rely on respiratory compensation to mitigate the acidemia and thus require significant minute ventilation above normal levels. Intubation should be avoided in these patients whenever possible, and if it is unavoidable, the respiratory rate should be set to match the patient's breathing rate before intubation. The initial end-tidal CO2levels should be noted immediately after intubation, and efforts should be made to maintain or lower that number. Failure to do so results in worsening acidemia and further deterioration of the patient's condition. Acute Respiratory Distress Syndrome Acute respiratory distress syndrome is a complicated condition characterized by severe lung injury and inflammation. Ventilation strategies for these patients should be aimed at minimizing lung injury. Tidal volumes in these patients should be reduced to 6 mL/kg of IBW or lower with higher PEEP and FiO2. Typically, PEEP should be increased to higher than 10 cm H2O. PEEP should be titrated and monitored to ensure patient compliance and improvement. In these patients, lower SpO2 values of 88% to 90% can be tolerated with permissive hypercapnia due to low tidal volumes.[20] Acute respiratory distress syndrome is not readily identifiable in prehospital settings due to specific diagnostic criteria; however, it can be suspected when patients require markedly high levels of oxygen.[21]

Before initiating intubation and mechanical ventilation, the caregivers should try to obtain the patient's preferences. Medical Orders for Life-Sustaining Treatment (MOLST) and do-not-resuscitate (DNR) orders should be considered, and efforts should be made to engage with major healthcare stakeholders in the community to ensure appropriate communication of patient preferences. Mechanical ventilation is a complex process that requires teamwork and interprofessional coordination. Effective communication among team members is crucial. When possible, it is essential to inform the receiving facility in advance to ensure a smooth transition of care and continued ventilation. Prehospital clinicians should coordinate their activities with the rest of the interprofessional healthcare team and seek consultations with clinicians if necessary. Interprofessional care coordination and open communication are essential for achieving the best possible outcomes for ventilated patients. Finally, patients undergoing mechanical ventilation should be reviewed patient-centered to identify potential barriers to care and ensure the delivery of high-quality care.