Background and aims Intrathecal morphine is commonly used to prolong analgesia after hip arthroplasty performed under spinal anaesthesia. Even if morphine has been incriminated in postoperative respiratory depression, no prospective trial has ever investigated that paradigm with a respiratory polygraph. the objective of this randomised controlled triple-blinded trial was to investigate the effect of intrathecal morphine on number of apneic episodes.

Methods Sixty ASA I-III patients undergoing hip arthroplasty under spinal anaesthesia received either 15mg isobaric bupivacaine 0.5% with normal saline 0.9%, 0.5ml (control group) or 15mg isobaric bupivacaine 0.5% with morphine 100µg, 0.5ml (intrathecal morphine group). a respiratory polygraphy was performed before the surgery and on the first and third postoperative nights. the primary outcome was apnea hypopnea index while lying supine (Supine AHI) during the first postoperative night. Secondary outcomes were AHI during the third postoperative night, and oxygen desaturation index (ODI) in the first and third postoperative nights, among others. Additional outcomes included intravenous morphine consumption and pain scores, along with rates of PONV.

Results Demographic data were similar between groups. Sleep-related outcomes are shown in table 1. Postoperative first night results: Supine AHI was 21 (95%CI:14–27) and 21 (95%CI:12–30) in the control and intrathecal morphine groups, respectively, without significant difference (p=0.91). Secondary polygraphic outcomes were equivalent between groups (table 1). table 2 presents the acute pain-related outcomes.

Conclusions Intrathecal morphine dose does not increase the number of apneic episodes on the first postoperative night. of note, all patients had an increased number of apneic episodes on the third postoperative night.