7.3 Invasive Mechanical Ventilation
Key Takeaways
- After rapid sequence intubation run assist-control volume or pressure control; pressure-regulated volume control is a conceptual hybrid, not a Board-required mode, and pressure support is for a spontaneous patient.
- Dose tidal volume on ideal body weight at 6–8 mL/kg (about 6 in acute respiratory distress syndrome) and set rate, PEEP, FiO2, and I:E to the physiology.
- High peak with a reassuring plateau is resistance; high peak and high plateau is compliance, a mainstem, or a pneumothorax.
- Auto-PEEP needs a disconnect and a long expiratory time; permissive hypercapnia protects lungs unless intracranial pressure or right-ventricular failure forbids it.
- Altitude changes delivered tidal volume and FiO2 on turbine versus compressor vents; treat a disconnect alarm as apnea and trend end-tidal carbon dioxide rather than treating it as an arterial blood gas.
Once the tube is in, the transport ventilator is the patient's minute ventilation for the entire flight. Domain 2 of the August 2026 Board of Certification for Emergency Nursing (BCEN) Certified Flight Registered Nurse (CFRN) outline tests invasive ventilation as the modes a flight nurse must actually run, the numbers that protect lungs and the right ventricle, and the way altitude changes what the machine delivers. BCEN does not publish a required mode list. Do not invent one.
Modes a flight nurse must run
Assist-control volume and pressure
Assist-control volume control (AC-VC) delivers a set tidal volume (Vt) at a set rate. Every patient-triggered breath gets that same volume. Pressure rises as compliance falls, so you watch peak inspiratory pressure and plateau pressure. Assist-control pressure control (AC-PC) delivers a set inspiratory pressure for a set inspiratory time. Volume varies with resistance and compliance. A sudden volume drop means the tube kinked, the patient bit, the chest stiffened, or you disconnected.
Pressure-regulated volume control (PRVC) is a conceptual hybrid: the ventilator targets a volume by adjusting pressure breath to breath. Know the idea. Do not treat PRVC as a BCEN-mandated mode, and do not assume every transport ventilator offers it. Once the patient is spontaneous and ready, pressure support (PS) adds a set pressure to each triggered breath over positive end-expiratory pressure (PEEP). PS is not a safe first mode for a just-paralyzed rapid-sequence patient.
Settings you actually choose
Use ideal body weight (IBW), not the stretcher scale. The exam idea is predicted body weight, not the wet trauma weight.
- Vt 6–8 mL/kg IBW for most adults; about 6 mL/kg for acute respiratory distress syndrome (ARDS) and many trauma chests.
- Rate commonly 12–20 breaths per minute; faster for metabolic acidosis, slower for obstruction.
- PEEP often starts near 5 cm H2O; higher for hypoxemic recruitable lung; lower for obstructive disease and a failing right ventricle.
- Fraction of inspired oxygen (FiO2) starts at 1.0 after the tube, then wean toward a saturation target (often 92–96 percent, or 88–95 percent in some ARDS protocols).
- Inspiratory-to-expiratory (I:E) ratio about 1:2 in most patients and 1:4 or longer in asthma or chronic obstructive pulmonary disease (COPD).
| Physiology | Volume and rate idea | PEEP / I:E idea |
|---|---|---|
| Uncomplicated coma / overdose | 6–8 mL/kg IBW, rate about 12–16 | PEEP about 5, I:E about 1:2 |
| ARDS / wet trauma lung | 6 mL/kg IBW, higher rate if needed | Moderate PEEP, watch plateau |
| Asthma / COPD | 6–8 mL/kg, slow rate | Low PEEP, long expiratory time |
| Pulmonary embolism (PE) / pulmonary hypertension (PH) | Modest volumes, avoid hypercarbia | Low PEEP; do not crush the right ventricle |
Those numbers are clinical teaching starting points, not BCEN-published prescriptions.
Peak versus plateau, auto-PEEP, and permissive hypercapnia
Peak pressure is the sum of airway resistance and alveolar stretch. Plateau pressure, measured with an inspiratory hold when the ventilator allows it, reflects alveolar pressure. High peak with a reassuring plateau is tube obstruction, biting, or bronchospasm. High peak and high plateau is ARDS, obesity, mainstem intubation, or pneumothorax.
Auto-PEEP is gas trapped because exhalation did not finish. Blood pressure falls, peak pressure rises, and end-tidal carbon dioxide can paradoxically fall because output fell. Disconnect, let the chest fall, then resume a slow rate and a long expiratory time.
Permissive hypercapnia means you accept a higher arterial carbon dioxide (PaCO2) to keep Vt and plateau in a lung-protective range. It is appropriate in many ARDS and asthma patients. It is a bad idea when intracranial pressure is high or when a failing right ventricle needs you to avoid hypercarbia and acidosis.
Lung-protective ventilation for trauma and ARDS is low Vt, limited plateau, adequate PEEP, and a rate that keeps pH livable. Right-ventricular (RV)–protective ventilation for PE and PH is the opposite instinct on PEEP: keep PEEP low, avoid hypoxia, avoid hypercarbia, avoid acidosis, and do not crush venous return with huge tidal volumes.
Altitude, turbine versus compressor, and alarms
Cabin altitude lowers partial pressure of oxygen. The same FiO2 delivers less oxygen to blood. Compensate first by raising FiO2. Raise PEEP only if the lung is recruitable and the right ventricle can tolerate it. Boyle's law expands gas in the cuff and in a pneumothorax; recheck both after climb.
Turbine transport ventilators generate flow with a blower and often compensate better as density falls. Compressor or gas-driven ventilators use source oxygen or air and may deliver a different tidal volume and a different FiO2 as altitude and tank pressure change. Know which machine is on your aircraft. Watch the displayed delivered Vt, not the number you typed at sea level.
ETCO2 is a trend, not an arterial blood gas (ABG). Dead space from PE or shock widens the gradient; ETCO2 under-reads PaCO2. Use the waveform for tube confirmation and sudden changes, not as proof of a perfect pH.
Treat every disconnect and low-pressure alarm as apnea. High-pressure alarms mean obstruction, stacking, biting, or a stiff chest. Apnea and low-minute-ventilation alarms mean the patient stopped triggering or the circuit leaked. Power and oxygen-source alarms are mission-enders.
- Run AC-VC or AC-PC first after RSI; save PS for a spontaneous patient.
- Dose Vt on IBW: 6–8 mL/kg, about 6 in ARDS.
- Dump auto-PEEP before you add drugs or PEEP.
- Protect the RV with low PEEP and no hypoxia, hypercarbia, or acidosis.
- Recheck delivered Vt, FiO2, cuff, and connections after climb.
A 70 kg ideal-body-weight trauma patient is developing acute respiratory distress syndrome after a scene tube. Which initial invasive plan matches lung-protective flight teaching?
An intubated asthmatic becomes hypotensive with a rising peak pressure and a falling end-tidal carbon dioxide. What is the best next action?
After climb, which statement about a transport ventilator is most accurate?