Ventilation in the Brain-injured Patient

• As we have discussed in previous pearls, the ARDSnet trial forms the basis for ventilatory management in the ICU.  A primary component to current ventilatory management is the focus on maintaining lower and safer distending pressures through the use of lower tidal volumes.
• Similar to last week's pearl on the obstetric patient, these ventilatory settings may not be applicable to all patients.
• Recall that the use lower tidal volumes results in lower minute ventilation.  This leads to the accumulation of CO₂, termed permissive hypercapnia.  In general, we tolerate higher levels of CO₂ in favor of lower plateau pressures.
• For the brain-injured patient, however, increases in CO₂ may increase intracranial pressure (ICP) causing adverse effects.
• Current recommendations for mechanical ventilation in the brain-injured patient include maintaining a P_aCO₂ between 35 - 40 mm Hg.  Thus, you need to be more vigilant at following P_aCO₂ in this patient population.

References

Lapinsky SE, Posadas-Calleja JG, Mcullagh I. Clinical review: Ventilatory strategies for obstetric, brain-injured, and obese patients. Crit Care 2009;13:206-13.