Page 101 - JSOM Summer 2022

Mechanical Ventilation

A Review for Special Operations Medical Personnel

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Jonathan Friedman, RN, BSN, FP-C *; Seth Assar, MD 2

ABSTRACT
Mechanical ventilation is machine-delivered flow of gases (SF-ODA) begin receiving random and sporadic small-arms
to both oxygenate and ventilate a patient who is unable to fire from a village as they pass. Before having adequate time
maintain physiological gas exchange, and positive-pressure to react to contact, an MRZR all-terrain vehicle is hit with a
ventilation (PPV) is the primary means of delivering invasive rocket-propelled grenade, which causes the moving vehicle to
mechanical ventilation. The authors review invasive mechan- veer off the road and into a sharp ditch at approximately 30
ical ventilation to give the Special Operations Force (SOF) mph. The convoy elements return fire and take cover while
medic a comprehensive conceptual understanding of a core you, a Special Forces Medical Sergeant (18D), tend to the
application of critical care medicine. wounded Servicemember (SM).

Keywords: mechanical ventilation; invasive ventilation; ventila- Your patient is a 30-year-old 5'10", 190-lb male Special Forces
tor; portable ventilator Weapons Sergeant (18B) who has mild respiratory distress with
a respiratory rate (RR) of 24 and a pulse oxygen saturation of
94%, with otherwise normal vitals. He was not wearing body
armor beyond his helmet and hit his chest on the steering wheel
Introduction
during the crash. He has extensive bruising on his right anterior
“But that life may be restored to the animal, an opening thorax and appears to have semidisplaced broken ribs. He is mon-
may be attempted in the trunk of the trachea, into which a itored pending repeat movement. Two hours later he complains
tube or reed or can should be put; you will then blow into of progressive dyspnea. You notice his RR is now 38 and he has
this, so that the lung may rise again and take air.” a saturation of 83% despite 15 liters per minute supplemental
Andrea Vesalius, O administration. He appears to be struggling to breathe. The
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De Humani Corporis Fabrica (1543) decision is made to intubate pending his MEDEVAC.
Mechanical ventilation is the means through which machine- 1. What equipment will you need to perform this task?
delivered flow of gases is used to both oxygenate and ven- 2. What mode and settings on the ventilator will you select
tilate a patient who is unable to maintain physiological gas and why?
exchange. PPV is the primary means of delivering invasive 3. How will you monitor the patient’s condition in this aus-
mechanical ventilation in modern systems. A thorough un- tere environment?
derstanding of the anatomy and physiology of breathing, gas
dynamics, and a basic understanding of the pathophysiology
of chest trauma are key to mastering the ventilator. Complicat- Anatomy and Physiology of the
ing this topic are the prehospital and often austere conditions Respiratory Control Circuit
in which military medical personnel may be forced to oper- The respiratory circuit is initiated by positive output from the
ate. As mechanical ventilation becomes more common in the central pattern generator (CPG) as influenced by central che-
prehospital setting, combat medical personnel would benefit moreceptors in the medulla oblongata of the brainstem and
from understanding fundamentals. Whether as part of med- peripheral chemoreceptors in the carotid body (Figure 1). Col-
ical evacuation (MEDEVAC) or during prolonged field care lectively, these receptors are exquisitely sensitive to changes
(PFC), the mechanical ventilator can become a force multiplier in the partial pressure of CO (PaCO ), pH, and to a lesser
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by freeing up personnel and preserving the fighting force. This extent, the partial pressure of O2 (PaO ). The neurological
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review of invasive mechanical ventilation is designed to give signal intensity for the drive to breath is directly proportional
the SOF medic a comprehensive conceptual understanding of to the deviation from normal (baseline) of these values. Neu-
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a core application of critical care medicine. rons from the CNS project action potentials through cranial
nerves, which conjoin to form the phrenic nerve, and through
the spinal cord, to innervate the diaphragm and other respira-
Case Study
tory musculature to maintain subconscious breathing. Higher
During routine convoy travel in eastern Afghanistan, mem- cortical stimulus can add to respiratory drive through skeletal
bers of a Special Forces Operational Detachment – Alpha “accessory” muscle innervation.
*Correspondence to jbfriedman94@gmail.com
1 Jonathan Friedman is affiliated with the Special Operations Medic Coalition, Kinston, NC, and a registered nurse and critical care paramedic.
2 MAJ Seth Assar is the battalion surgeon of 1/19th Special Forces Group (Airborne), Bluffdale, UT.

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