To describe the prevalence of hypocapnia and hypercapnia during the earliest period of mechanical ventilation, and determine the association between PaCO2 and mortality.Purpose:
Materials and Methods: A cohort study using an emergency department registry of mechanically ventilated patients. PaCO2 was categorized: hypocapnia (< 35 mm Hg), normocapnia (35–45 mm Hg), and hypercapnia (> 45 mm Hg). The primary outcome was survival to hospital discharge.Results:
A total of 1,491 patients were included. Hypocapnia occurred in 375 (25%) patients and hypercapnia in 569 (38%). Hypercapnia (85%) had higher survival rate compared to normocapnia (74%) and hypocapnia (66%), P < 0.001. PaCO2 was an independent predictor of survival to hospital discharge [hypocapnia (aOR 0.65 (95% confidence interval [CI] 0.48–0.89), normocapnia (reference category), hypercapnia (aOR 1.83 (95% CI 1.32–2.54)]. Over ascending ranges of PaCO2, there was a linear trend of increasing survival up to a PaCO2 range of 66–75 mm Hg, which had the strongest survival association, aOR 3.18 (95% CI 1.35–7.50).Conclusions:
Hypocapnia and hypercapnia occurred frequently after initiation of mechanical ventilation. Higher PaCO2 levels were associated with increased survival. These data provide rationale for a trial examining the optimal PaCO2 in the critically ill.