Open-label, parallel group study. Twenty adults each with untreated OSA, CPAP-treated OSA, and no OSA will undergo a stepped-dose target-controlled opioid (remifentanil) infusion, measurement of opioid effects (miosis, respiratory rate, end-expired CO2, thermal analgesia) and plasma drug concentrations. Remifentanil clinical effects, pharmacodynamics (concentration-effect relationships), and pharmacokinetics will be compared between the three groups, as will relationships between effects and nighttime hypoxemia (assessed by home PSG).
The ultimate long-term goal for this research is to improve the perioperative care and pain management of patients with obstructive sleep apnea (OSA). While patients with OSA are believed to be more sensitive to the analgesic and adverse effects of opioids, there are no studies that assess the effects of the OSA gold-standard treatment, namely CPAP, on this purported sensitivity. Furthermore, OSA is a heterogeneous disease and not all patients who carry an OSA diagnosis are likely to have the same opioid sensitivity. At present no easily administered test is able to determine the degree of opioid sensitivity of an individual patient.
The specific goal of this research is to validate or refute, the untested yet "conventional wisdom" that adults with untreated OSA have increased sensitivity to the clinical effects of opioids, especially ventilatory depression. We will test the presumptive hypotheses that a) untreated OSA increases ventilatory, miotic, and analgesic effects of opioids, b) the magnitude of increase is proportional to the degree of nighttime hypoxia, and c) CPAP treatment of OSA normalizes altered opioid responses.
These hypotheses will be tested by evaluating the pharmacodynamics (concentration-effect relationship) of the prototype opioid remifentanil in patients with and without OSA using objective opioid sensitivity markers to determine if patients with OSA have increased sensitivity to opioids and to determine if treatment with CPAP alters this purported sensitivity. Our study drug, remifentanil, is an ultra-short acting μ-selective opioid agonist, which is the same receptor at which longer acting opioids such as morphine act. Since the site of action of remifentanil is the same as other opioids, the results of this study will be able to be generalized to other opioids, improving our clinical understanding and practice in this patient population. Opioid effects will be determined by the decrease in pupil diameter, which is the most sensitive measure of opioid effects at the drug concentrations and subanesthetic doses to be used. The degree to which changes in pupil diameter correlate with changes in respiratory rate will be compared.
