Opioid-Tolerant Patient With CKD and Sleep Apnea After Total Knee Arthroplasty
A 64-year-old man is on postoperative day 1 after right total knee arthroplasty. He has chronic low back pain and takes oxycodone extended-release 20 mg twice daily plus oxycodone/acetaminophen 5/325 mg up to three times daily, a baseline of roughly 80 morphine milligram equivalents per day. He has obesity (BMI 38), obstructive sleep apnea with CPAP that he has used only intermittently since admission, type 2 diabetes, and stage 3b chronic kidney disease with an eGFR of 34 mL/min/1.73 m². Standing orders are ketorolac 30 mg IV every 6 hours, morphine PCA with a basal infusion, promethazine 25 mg IV every 6 hours as needed, and zolpidem 10 mg at bedtime. He rates pain 8/10 with movement and 4/10 at rest, has had two episodes of emesis, and is using his CPAP about half the night. His respiratory rate is 14, sedation is normal, and SpO2 is 94 percent on room air.
1. Critique the ordered analgesic and sedative regimen and state what you would substitute, with the pharmacology behind each change.
Read the worked answer
Several orders need to change.
Ketorolac 30 mg IV every 6 hours: stop. With an eGFR of 34, NSAIDs risk acute kidney injury and hyperkalemia; the drug is contraindicated below a creatinine clearance of 30 and should be avoided or dose-reduced and limited to 5 days between 30 and 60. He also has diabetes and is volume-depleted from emesis. Remove it rather than reduce it.
Morphine PCA with a basal infusion: remove the basal rate and switch to hydromorphone or fentanyl. Morphine-6-glucuronide is renally cleared and accumulates in CKD, causing delayed sedation and respiratory depression. A basal infusion in a patient with OSA who is not reliably using CPAP compounds that risk; use demand-only dosing with an around-the-clock non-opioid backbone.
Promethazine: stop. It is sedating and anticholinergic, adds to respiratory depression, and causes dystonia; treat nausea with ondansetron (check QT) or low-dose dexamethasone.
Zolpidem: stop. Sedative-hypnotics plus opioids plus OSA is a classic triple-risk combination for respiratory depression and delirium; use non-drug sleep measures.
Build instead: scheduled acetaminophen (maximum 3 g/day), an adductor canal or periarticular block if available, ice and elevation, and early mobilization. A gabapentinoid only with renal dose adjustment and monitoring.
2. How do you manage his opioid tolerance so that he neither withdraws nor receives unsafe escalation? Include your discharge plan.
Read the worked answer
Tolerance means his baseline requirement is roughly 80 MME per day; abruptly stopping it will produce withdrawal (agitation, tachycardia, diarrhea, piloerection) that will be mistaken for uncontrolled pain.
Plan: continue his home oxycodone extended-release 20 mg twice daily as the baseline and use a short-acting agent, preferably hydromorphone given the CKD, for breakthrough, delivered as demand-only PCA or oral immediate release. Do not attempt to reset his tolerance after surgery; the goal is baseline plus the surgical increment, then a taper back toward baseline as knee pain improves over 2-6 weeks.
Non-opioid adjuncts are essential in a tolerant patient: scheduled acetaminophen, a regional block, and non-pharmacologic measures. A gabapentinoid can reduce opioid consumption but requires renal dose reduction (eGFR 30-59: roughly 200-700 mg/day in divided doses) and adds sedation in OSA, so use it only with monitoring.
At discharge: reconcile total MME, write an explicit taper back to his presurgical regimen, check the prescription drug monitoring program, avoid duplicate acetaminophen products, and prescribe naloxone with education for him and a household member. Refer to pain management or a transitional pain service rather than simply raising the dose.
3. That evening the nurse finds him difficult to rouse, with a respiratory rate of 8 breaths/min and SpO2 of 88 percent on room air. What do you do, in order?
Read the worked answer
This is opioid-induced respiratory depression with hypoxemia. Act immediately.
Call for help and the rapid response team. Open the airway, stimulate him, apply oxygen and his CPAP, and place him on continuous pulse oximetry plus capnography if available. Stop the PCA and all other sedating medications at once.
Give naloxone titrated rather than as a full ampoule: 0.04-0.08 mg IV every 2 minutes, doubling as needed, titrated to a respiratory rate above 8-10 with adequate saturation. The goal is to restore ventilation without fully reversing analgesia, because full reversal in an opioid-tolerant patient can precipitate severe pain, catecholamine surge, and pulmonary edema. If there is no IV access, give 0.4 mg intramuscularly.
Then find the cause: was a basal infusion or a nurse-administered bolus given, is the pump programmed correctly, did he receive promethazine or zolpidem, is his CPAP off, does he have hypovolemia or infection. Observe for 4-6 hours because naloxone has a shorter half-life than the opioid. Restart analgesia at a lower dose with demand-only PCA, involve the acute pain service, and document the event and the response.