Respiratory Disease and Analgesia
59. C.T., a 65-year-old man admitted to the hospital with a hip fracture, has a history of chronic obstructive pulmonary disease (COPD). On admission, C.T. has a nonpurulent productive cough and wheezing. His medical history includes several episodes of pneumonia. Morphine sulfate 6 to 10 mg IM every 3 hours is ordered for his severe hip pain. What risks are associated with using morphine in C.T.? Are there better alternative potent analgesics?
Systemic opioids remain the first-line agents in managing pain in patients with COPD. Careful monitoring orders also should be written along with the opioid orders. Morphine and all other opioid analgesics can depress respiration when given in therapeutic doses and should be used cautiously in patients with advanced respiratory disease and decreased respiratory function. Respiratory rate, tidal volume, and sensitivity to hypercapnia or hypoxemia are all decreased by opioid analgesics.200 Although all opioids and agonists produce respiratory depression at therapeutic doses, there appears to be a ceiling effect to the respiratory depression caused by butorphanol (Stadol), nalbuphine (Nubain), and buprenorphine (Buprenex) at higher doses.201,202 Increased doses of these compounds do not further depress respiration and still provide increased analgesia. The antagonist naloxone reverses the respiratory difficulty (and analgesia) produced by nalbuphine and butorphanol. Although respiratory depression caused by buprenorphine is uncommon, naloxone does not reverse buprenorphine's effects predictably.203 Ventilatory support is the only treatment.
Because C.T. is in severe pain, a lower dosage of morphine should be used initially. Opioids do not always depress respiration when dosed correctly and, in some instances, they actually can improve respiratory function in patients who have recently had a thoracotomy. These patients often are afraid to breathe deeply because of the pain elicited by such activity. The analgesic phenothiazine, methotrimeprazine, nerve block, or epidural anesthetics also can be used with fewer respiratory effects than systemic morphine.204,205 Alternatively, morphine PCA should be considered for C.T., because PCA will allow him to self-administer small, frequent doses, thereby reducing the possibility of opioid-induced respiratory depression.
60. During his admission, C.T. mentions that he was recently diagnosed with sleep apnea. Would your approach to C.T.'s pain management change?
Patients with sleep apnea must be carefully monitored when receiving pain medications and sedation, especially via the parenteral route.
Sleep apnea generally can be described as prolonged apneic episodes during sleep that can be attributed to relative hypotonia of upper pharyngeal muscles. These muscles play an important role in patency of the airway.
During an apneic episode, arterial oxygen saturation falls and carbon dioxide concentration rises, which stimulates arousal by the autonomic nervous system alerting the patient to breathe. This can occur multiple times during sleep and often is unnoticed by a patient with sleep apnea. In severe disease, patients may experience cardiac dysrhythmias owing to repeated falls in oxygen saturation. Chronic and untreated sleep apnea can lead to pulmonary and systemic hypertension, cor pulmonale, and cardiopulmonary arrest.206 Clinicians must exercise caution when providing pain management to patients with sleep apnea. Opioid administration causes relaxation of upper respiratory tract muscles as well as a decrease in the sensitivity to rising CO2. The ability to maintain an open airway is already compromised in a patient with sleep apnea. As a result, patients with sleep apnea may experience respiratory failure, cardiac arrhythmias, and even death.206
Currently, there are no published guidelines on pain management of patients with sleep apnea. It is prudent that C.T. receive continuous cardiac and oxygen saturation monitoring while being treated with opioids. Continuous positive airway pressure (CPAP) may be used to prevent hypoxic episodes caused by opioids.207 Short acting opioids would be preferred if C.T.'s pain can be adequately controlled with these agents.
Use of buprenorphine, a partial opioid agonist, for severe pain in patients with sleep apnea has been postulated, but published clinical trials are lacking. Concomitant use of an NSAID and acetaminophen is recommended to reduce opioid requirements.206
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