Total venous serum carbon dioxide (tCO2) is known to be elevated in some patients with OSA. To determine how reliable it is as a method of diagnosing OSA and predicting its severity, we reviewed retrospectively the charts of all 44 children, mean age 5.9 years, who had a laboratory diagnosis of obstructive sleep apnea in 1994-1995. All of these children underwent a nap sleep study which was positive, with a respiratory disturbance index (RDI)(number of apneas and hypopneas divided by the duration of study in hours)>5 and a mean of 28, and all had random measurements of tCO2 The majority of the children (59%) had elevated tCO2 (>25mg/dl) with a maximum of 31 mg/dl, 18 (41%) children had normal or low tCO2, but there was poor correlation between the RDI and the tCO2 (r 0.05).

We conclude that tCO2 is useful in diagnosing OSA, but does not reflect its severity in this group of patients.