Extreme hypocapnia in the critically ill patient

Respiratory alkalosis was the most common acid-base disturbance observed in a computer analysis of 8,607 consecutive arterial blood gas studies collected over an 18 month period in a large intensive care unit.Through a retrospective review of the randomly selected hospital records of 114 patients, we defined four groups based upon arterial carbon dioxide tension (PaCO₂) and mode of ventilation. Group 1, with a PaCO₂ of 15 mm Hg or less, consisted of 25 patients with an over-all mortality of 88 per cent. Group II, with a PaCO₂ of 20 to 25 mm Hg, consisted of 35 patients with a mortality of 77 per cent. Group III, with a PaCO₂ of 25 to 30 mm Hg, consisted of 33 patients with a mortality of 73 per cent, and Group IV, with a PaCO₂ of 35 to 45 mm Hg, consisted of 21 patients with a mortality of 29 per cent (p <0.001). Shock and sepsis were most common in group I patients.These findings suggest that extreme hypocapnia in the critically ill patient has serious prognostic implications and is indicative of the severity of the underlying disease.