The severity of sleep hypoventilation in stable chronic obstructive pulmonary disease

An increase in PaCO₂ is the element that defines sleep hypoventilation (SH). We queried if patients with SH, and those with PaCO₂ increases during sleep for shorter time periods than SH (shamSH) differed from the patients without SH (noSH) in other ways.

This was a retrospective re-analysis of data from 100 stable inpatients with COPD with and without chronic hypercapnic respiratory failure. COPD was defined by criteria of the Global initiative for Chronic Obstructive Lung Disease (GOLD). For this study, SH was defined by an increase in PaCO₂ ≥ 1.33 kPa to a value exceeding 6.7 kPa for ≥ 10 min (≥ 20 epochs of 30 s). Patients fulfilling the increase in PaCO₂ for less than 10 min (1-19 epochs) were designated shamSH. All patients had daytime arterial blood gases, lung function tests, and polysomnography (PSG) with transcutaneous CO₂ (PtcCO₂).

Of 100 patients, 25 had PtcCO₂ increase ≥ 1.33 kPa. One never exceeded 6.7 kPa, 15 had SH, and 9 shamSH. SH and shamSH patients had extra CO₂ load (= PtcCO₂*time) both during and between the SH periods compared to the noSH group, the SH group more than the shamSH group.

Using CO₂ load as a measure of severity of sleep hypoventilation, SH patients have worse hypoventilation than the shamSH. Both shamSH and SH groups have extra CO₂ load during and between SH periods, indicating that the SH/shamSH patients may represent a separate group of true hypoventilators during sleep.