Sleep disordered breathing and chronic respiratory failure in patients with chronic pain on long term opioid therapy

The use of opioid medication for chronic pain has been increasing. The main aim of this study was to assess how many patients on opioids for chronic pain had sleep disordered breathing (SDB) and the type of SDB. The impact of these medications on daytime arterial blood gas (ABG) measurements and psychomotor vigilance was also studied.

Twenty-four patients (aged 18-75 years) on long-term opioids were prospectively recruited. Patients underwent home polysomnogram (PSG), psychomotor vigilance testing (PVT), and awake daytime ABG. Overnight PSG findings were compared to those of patients matched for age, sex, and BMI referred to our sleep service for evaluation of SDB. PVT results in the patient cohort were compared to PVT in healthy controls.

Forty-six percent of opioid patients had severe SDB as defined by an apnea hypopnea index (AHI) > 30/h. The severity of SDB was similar in opioid-treated pain clinic patients and sleep clinic patients (mean ± SD AHI: Opioid-treated patients 32.7 ± 25.6; Sleep Study comparator group 28.9 ± 24.6, p = 0.6). Opioid patients had a higher frequency of central apneas and a lower arousal index (CAI: 3.9 ± 8.3 vs. 0.3 ± 0.5 events/h; p = 0.004, AI 8.0 ± 4.1 vs. 20.1 ± 13.8, p < 0.001). Pain clinic patients had impaired gas exchange during sleep and wakefulness. Nine of 20 (45%) had daytime hypercapnia, indicating a surprising number were in chronic respiratory failure. Morphine equivalent doses correlated with the severity of SDB. PVT was impaired when compared to a healthy PVT comparator group (RT: Opioid-treated patients 0.43 ± 0.27: Healthy PVT comparator group 0.28 ± 0.03 sec; p < 0.001).

Patients on long-term opioids frequently have severe SDB, which in part is central in origin. PVT was markedly impaired. Half of the patients studied have evidence of chronic ventilatory failure.

A commentary on this article appears in this issue on page 853