Synopsis
Connect physiological failure to an appropriate support strategy, interpret its benefits and harms, and plan reassessment, recovery and treatment goals.
- Organ support buys time for diagnosis and treatment of the cause; a normal displayed number can depend on substantial ongoing support.
- Assess oxygenation and ventilation separately, using blood gases and the actual respiratory support settings.
- In ARDS, use lung-protective tidal volumes based on predicted body weight and monitor plateau pressure.
Reasoning priorities
Interpret gas exchange in relation to the support producing it.
Record inspired oxygen, mode, tidal volume and relevant pressures with the sample. A PaO2 value is difficult to interpret without FiO2, while rising PaCO2 may reflect inadequate minute ventilation or increased physiological dead space.
Worked reasoning
An intubated adult has ARDS. Predicted body weight from height and sex is 70 kg, although actual weight is 105 kg. The team selects an initial tidal volume of 6 mL/kg predicted weight.
- Calculate 6 × 70 = 420 mL, using predicted rather than actual weight. Confirm the measured delivered tidal volume and synchrony after setting the ventilator.
- Measure plateau pressure with an appropriate inspiratory hold when the measurement is valid. It is 34 cmH2O, above the usual protective target of below 30 cmH2O, so the setting requires reassessment.
- The critical-care team reduces tidal volume to 5 mL/kg predicted weight, or 350 mL, while reviewing respiratory rate, PEEP, acid-base status and potential causes of reduced compliance.
- Repeat assessment shows plateau pressure 28 cmH2O and acceptable gas exchange for the agreed patient-specific targets. Verify blood pressure and perfusion as well, because ventilator changes can affect circulation.
- Continue treating pneumonia and review positioning and other ARDS measures if hypoxaemia remains severe. The lower pressure demonstrates one benefit, but ongoing oxygen need and the overall trajectory determine the next decision.
Key medicines
Noradrenaline infusion: concentration and titration exampleFor the cited 1 mg/mL concentrate, dilute 2 mL with 48 mL of 5% glucose to a total 50 mL: 40 micrograms/mL noradrenaline base. Its SmPC initial rate is 10–20 mL/hour, equivalent to 0.4–0.8 mg/hour, then titrate to the prescribed physiological target.This product specifies central venous administration by controlled infusion. Never give the concentrate undiluted. Check base versus salt units, correct volume deficit where present, monitor rhythm and perfusion, and reduce gradually when support is no longer needed.