Acute hypercapnic respiratory failure in patients with chronic obstructive lung disease: risk factors and use of...

On the basis of a retrospective survey by this unit it was suggested that patients with acute ventilatory failure should be given sufficient controlled oxygen treatment to raise the arterial oxygen tension (PaO2) to above 6.6 kPa, with the addition of a respiratory stimulant if the hydrogen ion concentration ([H+]) rose above 55 nmol/l and assisted ventilation if the patient remained acidotic despite these measures. This study was designed to verify the prognostic factors that determine survival in acute ventilatory failure and determine the outcome when our guidelines were implemented.

One hundred and thirty nine episodes of acute hypercapnic (type II) respiratory failure were studied prospectively in 95 patients admitted with acute exacerbations of chronic obstructive lung disease. Patients had to have a PaO2 below 6.6 kPa and an arterial carbon dioxide tension (PaCO2) above 6.6 kPa while breathing air.

The mortality associated with episodes of acute ventilatory failure was 12%. Patients who died tended to be older and were significantly more acidotic, hypotensive, and uraemic on admission than those who survived, but they had similar degrees of hypoxaemia and hypercapnia. Death occurred in 10 of the 39 episodes in which arterial [H+] rose to 55 nmol/l or above, compared with seven of the 100 episodes in which it remained below 55 nmol/l. The respiratory stimulant doxapram was used in 37 episodes and was associated with a reduction in [H+] below 55 nmol/l within 24 hours in 23 episodes. Assisted ventilation was used in only four episodes.

Arterial [H+] is an important prognostic factor for survival. Most patients treated according to the guidelines outlined above can be managed successfully without assisted ventilation.