Therapeutic hypercapnia in sepsis

Mechanical ventilation is necessary for survival of patients with acute respiratory distress syndrome (ARDS). It was once supposed that ventilation should be adjusted to maintain pCO₂(a) within the normal range but this degree of mechanical ventilation can result in further damage to the lungs.

Less aggressive (low tidal volume) ventilation reduces the risk of further lung injury at the expense of ongoing hypercapnia (pCO₂(a) above the upper limit of the normal range). A landmark study published a decade ago confirmed that despite the hypercapnia, use of low tidal volume ventilation was associated with significantly lower mortality among patients with ARDS, than the use of the then conventional (higher tidal volume) ventilation.

Since that study "permissive" hypercapnia has become a standard of ventilation therapy for critically ill patients. The notion that hypercapnia is not just tolerated but has beneficial effect, independent of the low tidal volume that induced it, has been demonstrated in animal models of lung injury. This work suggests that deliberate induction of hypercapnia (by addition of carbon dioxide) might have therapeutic value for the critically ill. 

However, there is concern that hypercapnia and associated acute acidosis might not be safe in patients with sepsis. This concern is based on the observation that hypercapnia seems to protect against lung injury by anti-inflammatory mechanisms that may render hosts more vulnerable to infection. 

In a recent review paper the authors discuss an accumulating body of experimental research directed at establishing whether or not therapeutic hypercapnia and resulting acute acidosis is safe in the context of sepsis.