Opioid-Tolerant Patients

Postoperative pain may be difficult to manage in the opioid-tolerant patient because the standard approaches used for assessment and therapy in opioid-naïve patients are inadequate for opioid-tolerant patients (see Chapter 11 ). Although opioid-tolerant patients typically require higher doses of analgesic medications in the immediate postoperative period, many health care providers still do not provide adequate postoperative pain relief, in part because of the fear of addiction or medication-related side effects. In dealing with patients with chronic opioid use, health care providers often mistakenly interchange several pharmacologic terms (i.e., tolerance, physical dependence, and addiction), a practice that may contribute to misunderstanding and inappropriate treatment decisions.

Tolerance refers to the pharmacologic property of an opioid in which an increasing amount is needed to maintain a given level of analgesia. Physical dependence is another pharmacologic property of opioids characterized by the occurrence of a withdrawal syndrome on abrupt discontinuation of the opioid or administration of an antagonist. Tolerance and physical dependence are pharmacologic properties of opioids and not synonymous with the aberrant psychological state or behaviors associated with addiction, a chronic disorder characterized by the compulsive use of a substance resulting in physical, psychological, or social harm to the user and continued use despite that harm. The exaggerated fear of addiction contributes to the undertreatment of postoperative pain by health care providers; however, the data suggest that there is minimal risk of iatrogenic addiction with use of opioids for pain control in patients who do not have a prior history of addiction.^{[412] [413]}

Several principles for pain assessment and treatment can be applied in the postoperative opioid-tolerant patient. The physician should expect high self-reported pain scores^[414] ; base treatment decisions on objective pain assessment (e.g., ability to deep breathe, cough, ambulate) in conjunction with patients' self-reported pain scores^[414] ; recognize the need to identify and treat two major problems, maintenance of a basal opioid requirement and control of incisional pain; and recognize that detoxification is usually not an appropriate goal in the perioperative period. Likewise, several general strategies can be employed for the treatment of postoperative pain in the opioid-tolerant patient. The physician can create a treatment plan early and discuss it with the patient, surgical team, and nursing staff; replace the patient's baseline or basal opioid requirements postoperatively; anticipate an increase in postoperative analgesic requirements^[414] ; maximize the use of adjuvant drugs; consider use of regional analgesic techniques; and plan for the transition to an oral regimen. Although chronic pain patients are not synonymous with opioid-tolerant patients, many of these patients are

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Although there is no specific threshold or timeframe for when a patient becomes opioid tolerant, after an opioid-tolerant patient is identified, a perioperative strategy for postoperative pain control should be created and discussed with the patient. This may include anticipation or arrangement for a longer than normal length of hospital stay, consultation with the anesthesiology or pain service, and confirmation of the patient's daily opioid intake to facilitate calculation of the patient's basal or maintenance opioid requirement in the postoperative period. Administration of a PRN analgesic regimen alone for opioid-tolerant patients is highly discouraged because replacing the basal opioid requirement in the postoperative period can optimize pain relief and possibly prevent opioid withdrawal. Basal opioid requirements can be administered systemically (typically intravenously or transdermally) until the patient can tolerate an oral analgesic regimen.^[66] For example, 50% to 100% of the patient's baseline opioid requirement can be administered as a continuous infusion as part of an intravenous PCA regimen, with a demand dose to cover the additional incisional pain. Conversion tables ( Table 72-8 ) may facilitate equianalgesic conversion of opioids (i.e., different routes of administration of one opioid, or conversion between two different opioids); however, these tables provide only estimations to assist health care providers in initiating opioid titration.^{[415] [416]}

Opioid-tolerant patients generally require increased postoperative analgesic levels, including a larger demand dose.^{[66] [414]} Patients may require frequent adjustment (e.g., two to three times each day) of the intravenous PCA demand dose or continuous infusion, depending on the analgesic requirements. There is individual variability in response to different opioids, and if a decision is made to

TABLE 72-8 -- Guidelines for equianalgesic dosing of opioid agonists

	Equianalgesic Dose (mg)
Drug	Parenteral	Oral
Morphine	10	30
Codeine	130	200
Fentanyl	0.1	—
Hydromorphone	1.5–2	6–7.5
Levorphanol	2	4
Meperidine	75	300
Methadone	10	20
Oxycodone	15	20–30
Oxymorphone	1	—
*Equianalgesic doses are approximate and are intended to serve only as an estimate of opioid requirements. Actual doses may vary, in part because of wide interpatient variability in response to opioids. Doses should be individualized and gradually titrated to effect.

switch opioids, the choice of opioid is probably not as important as using an equianalgesic dose. Patients may experience different side effects with different opioids, and rotating to another opioid may be reasonable if the patient is not tolerating the first opioid.^{[417] [418] [419]} Adjuvant agents such as NSAIDs should be administered on a regularly scheduled basis to optimize analgesic efficacy and possibly provide an opioid-sparing effect. Use of regional analgesic techniques with neuraxial opioids may provide excellent analgesia in opioid-tolerant patients while preventing withdrawal symptoms.^{[213] [420] [421]}

After the patient is tolerating oral intake, the conversion from intravenous opioids to a form (i.e., oral or transdermal, or both) that would be more suitable for discharge to home may be initiated. Opioid-tolerant patients typically can be converted to a combination of a regularly administered, controlled-release formulation of opioid (i.e., sustained-release morphine or transdermal fentanyl) and short-acting, immediate-release opioid on a PRN basis. Although the conversion of intravenous opioid to an oral or transdermal form can be accomplished over a period of 1 to 2 days in opioid-tolerant patients, this process may take several days in extremely difficult cases. Converting from an intravenous to oral or transdermal form of opioid is not an exact science, and available conversion tables can serve only as a rough guide because of significant interpatient and intrapatient variabilities in the sensitivity to opioids, lack of complete cross-tolerance between opioids (which may lead to greater than anticipated potency of a new opioid), and changes in the levels of pain, which may rapidly decrease in the immediate postoperative period. ^{[415] [416] [418]} Because of these factors, conversion of approximately 50% to 75% of the equianalgesic dose into a sustained-release preparation of opioid or transdermal fentanyl patch, with the remainder converted to a short-acting opioid delivered on a PRN basis, may be a reasonable starting point in patients whose pain is reasonably controlled, although additional titration may be necessary.