Synopsis
Set, interpret and adjust mechanical ventilation for an adult surgical patient by linking the chosen mode, delivered volume, airway pressures, carbon dioxide waveform and oxygenation to respiratory mechanics and clinical change.
- Ventilation settings are a starting hypothesis. Check the delivered breath, pressure waveform, capnogram, chest movement, saturation and circulation after every change rather than assuming the set value reached the patient.
- For an adult surgical patient without a specialist ventilation indication, the expert consensus starting point is tidal volume 6–8 mL/kg predicted body weight and PEEP 5 cmH2O, followed by individualisation.
- Use predicted body weight, derived principally from height and sex, for tidal-volume selection; actual body weight can dangerously overestimate lung size in obesity.
Key red flags
A flat or abruptly absent capnogram with no expired tidal volume indicates absent effective alveolar ventilation until proved otherwise and requires immediate patient, airway and circuit assessment.
A sudden increase in peak airway pressure with difficult manual ventilation may reflect tube kink or obstruction, biting, secretions, bronchospasm, reduced compliance, endobronchial migration, pneumothorax or a circuit problem.
Falling oxygen saturation with unilateral breath sounds, hypotension and increasing pressure after positive-pressure ventilation raises concern for tension pneumothorax and needs immediate clinical treatment.
Low-pressure or low-expired-volume alarms can indicate disconnection, leak, cuff failure or airway displacement; an apparently quiet ventilator is not reassuring when the capnogram disappears.
Progressive hypotension after increasing PEEP or mean airway pressure may represent impaired venous return or overdistension and requires reassessment of ventilation, volume status and cardiovascular physiology.
The adult elective surgical ventilation approach does not replace ARDS, critical-care, paediatric, obstetric, one-lung or severe obesity protocols, which require population-specific targets and expertise.
A new leak, disconnection, cuff failure or airway displacement lowers delivered and expired volume and may abolish the capnogram despite apparently normal settings.
A fall in pressure after recruitment, high PEEP or rising intrathoracic pressure may indicate reduced venous return, overdistension or an evolving pneumothorax.
Reasoning priorities
Separate peak, plateau and end-expiratory pressures and identify changing resistance or compliance.
Rising peak with unchanged plateau increases the resistive component; rising peak and plateau together indicate increased elastic load or reduced compliance. Check tube, circuit and patient before adjusting a pressure limit.
Worked reasoning
A stable adult without ARDS or another specialist indication has undergone tracheal intubation for elective abdominal surgery.
- Confirm tracheal placement with visual passage and a sustained waveform capnogram, check bilateral ventilation and tube depth, then connect the checked breathing system with audible alarms enabled.
- Select a perioperative starting tidal volume of 6–8 mL/kg predicted body weight rather than actual weight and initial PEEP of 5 cmH2O; set rate, inspired oxygen, flow or inspiratory time and pressure limits for the individual physiology.
- Verify the delivered and expired tidal volume, respiratory rate, peak pressure, plateau where measured, total PEEP, capnogram, saturation, chest movement and haemodynamics rather than accepting the settings display alone.
- Adjust alveolar minute ventilation against ETCO2 trend and arterial gas when required; individualise PEEP and inspired oxygen against oxygenation, mechanics and circulation, avoiding routine recruitment when its haemodynamic cost outweighs benefit.
- Reassess after pneumoperitoneum, positioning, surgical traction, fluid or haemodynamic change, and before transfer or emergence; document settings, measured response and unresolved abnormalities.