RSI Positioning & FRC

RSI Positioning & FRC

Why Position Is a Physiologic Intervention (Not Just a Better View)

By Holly Gernatt, BSN, RN, CCRN, Flight Nurse

January 2026

Big Idea

Rapid Sequence Intubation (RSI) rapidly decreases lung volume. Positioning the patient head-up and using early PEEP are two of the most powerful ways we can preserve Functional Residual Capacity (FRC), prevent atelectasis, and reduce post‑intubation oxygen desaturation.

What is FRC?

FRC = Functional Residual Capacity

➡️ The amount of air left in the lungs after a normal passive exhalation.

FRC:

• Keeps alveoli open at end‑expiration

• Acts as an oxygen reservoir during apnea

• Prevents small airway closure

• Stabilizes gas exchange between breaths

Think of FRC as the patient’s built‑in physiologic PEEP.

How RSI Decreases FRC (Step‑by‑Step)

RSI stacks multiple FRC‑reducing factors all at once:

• Supine position → diaphragm pushed upward

• Sedation & paralysis → loss of diaphragmatic and chest wall tone

• Apnea → loss of intrinsic physiologic PEEP

• High FiO₂ (nitrogen washout) → promotes absorption atelectasis

📉 Result: Rapid loss of lung volume + alveolar collapse

This explains why patients often desaturate after a technically successful intubation.

Atelectasis (Plain Language)

Atelectasis = collapsed or airless alveoli.

• Not fluid

• Not pneumothorax

• Simply lung units that have lost air

Collapsed alveoli:

• Do not exchange oxygen

• Create shunt physiology

• Lead to falling SpO₂ and decompensation

Why Head‑of‑Bed Elevation Matters

Head‑up or ramped positioning does more than improve cord visualization.

Physiologic benefits:

• Diaphragm rests lower

• Thoracic volume increases

• End‑expiratory lung volume increases

• Small airway closure decreases

📈 FRC increases

Head‑up positioning = non‑mechanical PEEP.

The Prehospital Reality

Many patients arrive already FRC‑depleted:

• Lying flat in the ambulance

• Obesity, trauma, shock, pain, hypoxia

• Immobilization and straps

RSI starts from an already compromised physiologic state.

Bagging Without PEEP: The Hidden Problem

A BVM without PEEP:

• Delivers intermittent pressure

• Returns alveoli to zero pressure each exhale

• Allows repetitive alveolar collapse

This promotes:

• Atelectasis

• Increased shunt

• Post‑intubation hypoxia

Why Early PEEP Works

Adding PEEP 5 cmH₂O during manual ventilation:

• Replaces lost FRC

• Prevents end‑expiratory collapse

• Reduces absorption atelectasis

• Stabilizes oxygenation before the ventilator

PEEP = mechanical replacement for lost muscle tone.

Practical Crew Takeaways

✔️ Elevate the head of the bed or ramp the patient whenever possible

✔️ Think of positioning as a physiologic intervention

✔️ Use PEEP during BVM ventilation after RSI unless contraindicated

✔️ Match BVM PEEP to initial ventilator PEEP to avoid lung decruitment

✔️ If SpO₂ falls post‑intubation, think lung volume, not tube position

Post‑RSI hypoxia is often a lung‑volume problem, not an airway problem.

Position + PEEP preserve FRC — and FRC preserves oxygenation.

Educational Use Only:The information provided is for educational and training purposes only and is designed to support clinical learning. It does not replace medical oversight, provider judgment, or established protocols. Always follow your organization’s policies and consult medical control when indicated.