Spinal Morphine for Patients With Obstructive Sleep Apnea

Patients with Obstructive Sleep Apnea (OSA) appear to be especially vulnerable to medications that suppress pharyngeal muscle activity such as general anesthetics and opioids. Opioids can depress the ventilator response to airway obstruction and inhibit the awakening response to hypoxia and hypercarbia, resulting in central respiratory depression. OSA is therefore an important risk factor for serious postoperative complications, including perioperative death. While OSA is increasingly recognized as a serious perioperative concern, current clinical practices are highly inconsistent with regard to the management of surgical patients with OSA. Additionally, the relative safety of intrathecal opioids in this patient population remains unknown.

Total hip and knee arthroplasty (THA and TKA) are among the most common orthopedic procedures performed worldwide1. They have been shown to reduce chronic pain, increase the ability to function independently, and improve quality of life2,3. With an aging and increasingly obese North American population, the uses of THA and TKA are increasing 4. One of the main challenges associated with THA as well as TKA continues to be the perioperative management of patients who are elderly or obese, and their associated co-morbidities. Both THA and TKA are commonly performed under neuraxial anesthesia. Neuraxial anesthesia has been reported to provide multiple benefits when compared to general anesthesia and/or systemic analgesia including superior post-operative analgesia5, reduced opioid consumption6, improved rehabilitation7, and reduced morbidity and mortality8-12. The addition of opioids to the neuraxial local anesthetic solution has been common practice since 1979, when morphine was first shown to provide effective and prolonged analgesia after intrathecal administration13. For both THA and TKA surgeries, intrathecal morphine provides effective analgesia14-16 allowing for a reduction of the dose of intrathecal local anesthetic (thus minimizing side effects)17, and has a marked postoperative opioid-sparing effect14-16. However, these benefits of intrathecal morphine must be weighed against its risks of pruritis, nausea/vomiting, urinary retention, and, of most concern, respiratory depression18.

Eligibility Criteria:
Inclusion Criteria:

1. Adults, aged 18-85
2. ASA physical status I-III
3. Suspected of having Obstructive Sleep Apnea(OSA) or previously diagnosed with OSA
4. Scheduled to undergo elective primary Total Hip or Knee Arthroplasty

Exclusion Criteria:

1. Chronic obstructive pulmonary disease
2. Asthma
3. History of congestive heart failure
4. Valvular disease
5. Dilated cardiomyopathy
6. Implanted pacemaker or defibrillator
7. Diagnosed OSA who are undergoing continuous positive airway pressure (CPAP) treatment
8. Contraindications to spinal anesthesia
9. Contraindications to a component of multi-modal analgesia
10. Local anesthetic allergy
11. Anticipated surgical duration \> 2.5hrs
12. Opioid tolerance (\>250mg/24hr oral morphine equivalent pre-operatively)
13. Pregnancy
14. History of significant cognitive or psychiatric condition that may affect patient assessment, or
15. Inability to provide informed consent.
16. Participation in other clinical studies