Basic ventilator settings

What the ventilator is trying to achieve

• Oxygenation: get enough oxygen into the blood (main controls: FiO2 and PEEP; also mean airway pressure).
• Ventilation: remove CO2 (main controls: minute ventilation = tidal volume × respiratory rate).
• Protect the lungs: avoid over-stretch (high volumes/pressures) and repeated collapse (too little PEEP).
• Synchrony and comfort: match support to the patient’s effort (especially during emergence or in ICU-style modes).

Key terms (plain English)

• FiO2: fraction of inspired oxygen (e.g. 0.3 = 30% oxygen).
• Tidal volume (VT): volume delivered each breath (usually based on ideal body weight).
• Respiratory rate (RR): breaths per minute; with VT determines minute ventilation and CO2 clearance.
• PEEP: positive pressure at end-expiration; helps keep alveoli open and improves oxygenation.
• Peak pressure (Ppeak): highest pressure during inspiration; rises with airway resistance (e.g. bronchospasm, kinked tube).
• Plateau pressure (Pplat): pressure after an inspiratory pause; reflects lung/chest wall stiffness (compliance).
• I:E ratio: time in inspiration vs expiration; too short expiratory time can cause air-trapping.
• Trigger sensitivity: how easily a patient breath triggers the ventilator (too sensitive = auto-trigger; not sensitive enough = missed efforts).

Common modes you’ll meet (intro level)

• Volume-controlled ventilation (VCV): you set VT and RR; pressure varies. Good for predictable minute ventilation.
• Pressure-controlled ventilation (PCV): you set inspiratory pressure and RR; VT varies with compliance/resistance. Often gives lower peak pressures.
• Pressure support (PS): patient triggers breaths; you set support pressure and PEEP. Common during weaning/spontaneous breathing.
• SIMV (if used): mix of mandatory breaths plus patient breaths; settings vary by machine—ask if unsure.

Safe starting settings (adult, intubated, routine GA)

• FiO2: start 0.3–0.5 (higher initially if unwell); reduce to the lowest that keeps SpO2 in target range.
• VT: 6–8 mL/kg ideal body weight (IBW). Consider 6 mL/kg if lung injury, obesity, laparoscopic surgery, or high pressures.
• RR: 10–14/min then adjust to keep end-tidal CO2 (EtCO2) reasonable (often 4.5–6.0 kPa depending on case).
• PEEP: 5 cmH2O as a default; consider 8–10 cmH2O in obesity, laparoscopy, or atelectasis if haemodynamics allow.
• I:E: usually 1:2 (longer expiration if obstructive disease).
• Pressure limits/alarms: set a sensible high-pressure alarm (often ~30–35 cmH2O initially; individualise).
• Fresh gas flow and circuit: ensure appropriate for the anaesthetic technique and that CO2 absorber is functioning.

How to choose VT: ideal body weight (IBW) not actual weight

• Use IBW because lung size relates more to height than weight; using actual weight in obesity risks over-ventilation and high pressures.
• Quick IBW estimate: base VT on height; if unsure, err toward 6 mL/kg and adjust using pressures and CO2.
• Check pressures: if Pplat is high, reduce VT and consider increasing RR instead to maintain minute ventilation.

Adjusting settings: simple rules

• If EtCO2 high (hypoventilation): increase minute ventilation (increase RR first; consider small VT increase if pressures safe).
• If EtCO2 low (hyperventilation): reduce RR (or VT) gradually.
• If SpO2 low: first check the patient and equipment; then increase FiO2, recruit/optimise PEEP, and treat underlying cause (e.g. bronchospasm, atelectasis, pneumothorax).
• If peak pressure rises: think resistance (kinked tube, secretions, bronchospasm) vs compliance (pneumoperitoneum, position, pulmonary oedema). Check Pplat if available.

First-time scenarios: what to do

• Post-intubation: confirm tube position (capnography), bilateral chest movement, auscultation, and secure tube before fine-tuning settings.
• Laparoscopy: expect higher pressures and reduced compliance; consider PCV, slightly higher PEEP, and adjust RR to maintain CO2.
• Obesity: use 6 mL/kg IBW, consider higher PEEP, head-up positioning if possible, and be proactive with recruitment manoeuvres if trained and appropriate.
• COPD/asthma: allow longer expiration (lower RR, I:E 1:3–1:4), avoid breath stacking, accept permissive hypercapnia if needed and safe.
• Emergence on ventilator: if patient is breathing, consider PS with appropriate trigger; avoid over-sedation and ensure adequate analgesia.

Alarms and monitoring: what matters most

• Always monitor: SpO2, EtCO2 waveform, airway pressures, delivered VT (especially in PCV), and haemodynamics.
• High pressure alarm: treat as urgent—check patient, circuit, tube, and lungs.
• Low pressure / low VT / disconnect alarm: think disconnection, cuff leak, circuit leak, or extubation.
• Apnoea alarm (during spontaneous modes): ensure backup ventilation settings are appropriate.

Safety checks before you walk away

• Ventilator mode matches the clinical situation (controlled vs spontaneous support).
• FiO2 appropriate and not left unnecessarily high for prolonged periods.
• PEEP and pressures are reasonable; no persistent high-pressure alarms.
• Capnography present with a stable waveform; EtCO2 consistent with clinical picture.
• Humidification/heat-moisture exchanger (HME) in place if needed; suction available.
• Document key settings and any changes; communicate plan (e.g. target EtCO2, oxygen strategy).