For emergency physicians who want to ventilate well from the first breath onward
1. Core Philosophy: Vent with Purpose, Not Blind Force
- Mechanical ventilation is a double-edged sword. To maximize benefit and minimize harm, every setting must serve physiology.
- Lung-protective ventilation isn’t just for ARDS—it’s safer for almost every ventilated patient.
- Focus on strain, stress, energy, and hemodynamics rather than fixed numbers alone.
Four injury pathways to avoid:
- Volutrauma / Overstretch — too much tidal volume for available lung units
- Barotrauma — excessive alveolar pressure
- Atelectrauma — repeated alveolar collapse & re-expansion
- Biotrauma / energy injury — cumulative energy (mechanical power) damaging tissue
New evidence emphasizes:
- Driving pressure (ΔP = Pplat – PEEP) is a stronger predictor of mortality than tidal volume or plateau pressure alone — aim ≤ 15 cm H₂O.
- Mechanical power (energy delivered per minute) gives a unifying framework: high RR, Vt, and pressures multiply harm.
Hence our mantra: Vent small, vent gentle, vent smart.
2. Recommended Default Settings (“Safe Base”) + Advanced Tweaks
| Setting | Default | Advanced / Special Adjustments | Physiologic Rationale |
|---|---|---|---|
| Mode | Volume Assist‑Control (A/C‑V) | — | Guarantees set Vt, simplifies pressure monitoring |
| Tidal Volume (Vt) | 6 mL/kg PBW (range 4–8) | Drop to 4–5 if ΔP high or compliance low | Keeps alveolar strain moderate |
| Respiratory Rate (RR) | 16–20 /min | In obstructive: 8–10; in acidosis: cautiously increase | Sets minute ventilation; too fast → auto‑PEEP |
| Inspiratory Flow & I:E | 60 L/min | 80 L/min for obstructive | Faster flow shortens inspiratory time, prolongs exhalation |
| PEEP / FiO₂ | PEEP = 5 cm H₂O; FiO₂ 1.0 → 0.40 fast | ARDS: higher PEEP ladder; in shock, be conservative with PEEP; in obstructive, 0–5 cm | PEEP prevents alveolar collapse; FiO₂ supports oxygenation |
| Plateau Pressure (Pplat) | < 30 cm H₂O | In obese / stiff chest wall, allow modest overshoot if ΔP safe | Indicates alveolar stress |
| Driving Pressure (ΔP) | ≤ 15 cm H₂O | If >15, reduce Vt or adjust PEEP if recruitable | Normalizes Vt to compliance, better predictor of harm |
| Mechanical Power (MP) | Keep < ~17 J/min (approximation) | Use as warning: don’t let RR + Vt + pressure climb simultaneously | Reflects energy load on lung tissue |
3. Step-by-Step Setup & Safety Checks
Step A: Choose mode and set Vt
- Select A/C‑V.
- Measure height → compute PBW.
- Set Vt = 6 mL/kg PBW.
Step B: Choose RR & flow
- Start RR 16–20, flow 60 L/min.
- In COPD/asthma, use RR 8–10, flow ~80 L/min, to maximize exhalation.
Step C: PEEP & FiO₂
- After intubation: FiO₂ 100%.
- Immediately reduce to 40% (or the lowest that achieves SpO₂ ≥ 88–95%).
- PEEP = 5 cm H₂O initially. Use ARDSNet PEEP/FiO₂ ladder to escalate when needed.
- Beware: in hemodynamically unstable patients, high PEEP may worsen BP.
Step D: Safety check (within 2–5 min)
- Inspiratory hold → measure Pplat.
- Compute ΔP = Pplat – PEEP.
- If ΔP > 15 or Pplat > 30 → reduce Vt or re-evaluate PEEP.
- Perform expiratory hold → check for auto-PEEP (flow should return to baseline).
- Watch waveforms — expiratory flow must go to zero before next breath.
- Confirm tube + ventilation via EtCO₂ waveform.
- Monitor blood pressure — be ready for post-intubation hypotension.
4. Bedside Math Cheatsheet
| Metric | Formula | Sample (68 kg PBW) |
|---|---|---|
| Vt | 6 × PBW | 6 × 68 = 408 mL |
| ΔP | Pplat – PEEP | e.g. 26 – 8 = 18 (too high) |
| Minute Ventilation | Vt × RR | 0.408 × 18 = 7.34 L/min |
| Mechanical Power (approx) | 0.098 × RR × Vt (L) × (Peak – ½ ΔP) | If Peak = 32, ΔP = 18: 0.098 × 18 × 0.408 × (32 – 9) ≈ ~16 J/min |
| I:E ratio | Insp time = Vt / Flow; Exp = (60/RR) – Insp | Vt 0.408 L / 60 L/min = 0.408 sec; RR 18 → cycle 3.3 s → Exp = 2.9 s → I:E ~1:7 |
Rule of thumb: If ΔP > 15 → lower Vt 50–100 mL first, then reconsider PEEP if recruitable.
5. Troubleshooting: Problems & Fixes
| Problem | Clue(s) | Intervention |
|---|---|---|
| Hypoxemia | SpO₂ dropping | Check tube, secretions, pneumothorax → climb PEEP/FiO₂ ladder → consider proning if P/F very low |
| High Pplat & ΔP | Alarms / high pressures | Lower Vt; if obese/stiff, focus ΔP ≤ 15 more than strict Pplat |
| High Peak, normal Pplat | Peak alarm, Pplat normal | Airway resistance — suction, bronchodilator, unkink tube |
| Auto-PEEP / stacking | Expiratory flow never reaches zero, hypotension | Lower RR, increase flow, extend exhalation, transiently drop PEEP |
| Post-intubation hypotension | Sudden drop in BP after vent start | Suspect decreased preload, auto-PEEP — drop PEEP, give vasopressors, reassess volume status |
6. Adjusting for Special Conditions
Obstructive Lung Disease (COPD / Asthma):
- Use higher flow to shorten inspiratory time.
- Use low RR to allow exhalation.
- Accept permissive hypercapnia (PaCO₂ up to 60–70 mm Hg, pH ≥ 7.20) unless contraindicated (e.g. elevated ICP, severe pulmonary hypertension, arrhythmias).
Severe ARDS (e.g. P/F < 150):
- Use lower Vt (4–6 mL/kg).
- Use higher PEEP per “high PEEP” ladder, while preserving ΔP ≤ 15.
- Prone early (≥ 16 h sessions) when available.
- Avoid aggressive recruitment maneuvers routinely — brief, gentle only if expert.
7. Sedation, Synchrony & Paralysis
- Start analgesia first (e.g. fentanyl).
- Use light-moderate sedation (propofol / dexmedetomidine).
- If patient fights vent: check trigger sensitivity, flow, Vt first.
- Neuromuscular blockade is not routine—use only if severe, refractory dyssynchrony or during proning initiation.
8. Hemodynamic Support & Post-Intubation Hypotension
- Intubation + positive pressure can cause preload drop and hypotension.
- Be ready: vasopressor push-doses or infusions at hand.
- If BP crashes after intubation: temporarily reduce PEEP, check for auto-PEEP, support circulation aggressively.
9. Mnemonic Summary: “SAFE LUNG”
S = SpO₂ 88–95 %
A = Avoid long high FiO₂
F = Flow adequate (expiratory time)
E = Expiratory flow returns to zero
L = Low Vt (6 mL/kg, adjust)
U = Use PEEP (≥ 5 or per ladder)
N = Numbers: Pplat < 30; ΔP ≤ 15
G = Give hemodynamic support as needed
A/C‑V | Assist‑Control, Volume mode
ARDS | Acute Respiratory Distress Syndrome
ΔP | Driving Pressure (Pplat – PEEP)
EtCO₂ | End‑tidal CO₂
FiO₂ | Fraction of Inspired Oxygen
I:E | Inspiratory : Expiratory ratio
MP | Mechanical Power
PBW | Predicted Body Weight
PEEP | Positive End-Expiratory Pressure
P/F | PaO₂ / FiO₂ ratio
Pplat | Plateau Pressure
RR | Respiratory Rate
SpO₂ | Oxygen Saturation
VILI | Ventilator-Induced Lung Injury
Vt | Tidal Volume
