Once the airway is secured, assessment of breathing encompasses the respiratory rate, SpO2, work of breathing (in the spontaneously breathing patient), and the adequacy of gas exchange as determined by arterial blood gas analysis. In the ventilated patient, the ventilator itself becomes the primary tool for managing breathing, and understanding how to set and adjust it is a core ICU skill.

Ventilator Settings

The initial ventilator settings for a newly intubated patient should be approached systematically. Tidal volume (VT) should be set at 6–8 mL/kg of predicted body weight (PBW), calculated from height and sex, not actual body weight — obese patients have the same lung volume as lean patients of the same height. Driving pressures above 15 cmH2O are associated with ventilator-induced lung injury (VILI) regardless of the underlying diagnosis, and plateau pressures should be kept below 30 cmH2O where possible.

PEEP (positive end-expiratory pressure) is set to prevent alveolar collapse at end-expiration. The appropriate level depends on the underlying lung condition — a starting point of 5 cmH2O is reasonable for most patients, with higher levels (8–15 cmH2O) used in ARDS to maintain alveolar recruitment. FiO2 should be titrated to achieve SpO2 of 94–98% in most patients, or 88–92% in those with hypercapnic respiratory failure and known CO2 retention.

Respiratory rate is typically set at 14–18 breaths per minute initially, adjusted based on PaCO2 targets. In patients with raised intracranial pressure, PaCO2 may be deliberately manipulated — this is discussed in Section 6.