The Pain Physician

The consulting anesthesiologist in an inpatient setting may be called on to provide care for one of three reasons. First, the patient may need a regional nerve block, such as an epidural steroid injection for magnetic resonance imaging–confirmed discogenic pain or epidural catheter placement to assist physical therapy. This consultation is fairly straightforward and is an extension of basic regional anesthesia principles. Second, a child who has been prescribed opioids chronically or other medications that have implications for anesthesia or postoperative pain management may present for consultation. The anesthesiologist must investigate possible drug interactions and determine which chronic medications have been prescribed; this approach is an extension of basic perioperative anesthesia skills. Third, a consultation may be requested to assess and diagnose the source of pain. This scenario is the most complex and requires taking a detailed history and performing a thorough physical examination. These children often require multidisciplinary care beginning with the initial evaluation and extending through treatment.

The Psychologist

Pain is more than just a physical phenomenon. It can cause and be worsened by stress, suffering, family dysfunction, social tension, anxiety, and depression.^5,13 Pain can disrupt almost any aspect of the life of the child or family. Family and school problems can worsen a painful condition and dramatically reduce a child’s level of function. The family is always involved in the child’s suffering and should therefore be included in the pain evaluation process.

Families often are wary about seeing a psychologist and are afraid of being stigmatized. It is important to emphasize that pain is what the child says it is, regardless of whether an obvious organic cause is identified. The child is being treated as a person, not just as the painful body part, and this approach should be emphasized for the child’s family.

Psychology-based therapy includes relaxation training, biofeedback, hypnotherapy, coping skills training, and psychotherapy. Biofeedback is a modality that trains the child to become more aware of his or her body, enhancing the sense of control over it. Therapies aimed at parental and familial aspects of the child’s pain include teaching strategies for behavioral interventions (e.g., distraction), activity pacing, consistent discipline, coaching skills training, stress management, and occasionally, family therapy.

The Physical Therapist

Physical therapy is a crucial component of evaluating and treating chronic pain. The painful condition can cause loss of muscle strength and range of motion. Alterations in the use of a limb affect the biomechanics and daily function of the body. Children can become deconditioned and require a conditioning program to regain lost strength and stamina. These changes affect the original pain site and generate secondary pain problems that need to be addressed.

Physical therapy can benefit many painful conditions (e.g., myofascial pain improves with stretching and range-of-motion exercises) and is the cornerstone of treatment for others (e.g., chronic regional pain syndromes [CRPS]).¹⁴ Emphasizing self-reliance and responsibility for their own care is an important aspect of caring for adolescents. However, young children and older ones in pain cannot be expected to work aggressively at home without beginning with a structured program. Parental involvement is especially important for younger children, but the caretakers must be taught to be encouraging and supportive while not making them the child’s taskmasters.

Therapies provided by physical therapy include stretching, strengthening, and reconditioning programs. Range-of-motion exercises and endurance training are also important. Aquatic therapy is very useful for children who cannot bear weight on lower limbs or have limited range of motion or strength. Massage, heat, and cold therapies are helpful adjuncts to increase functioning and enhance other physical therapy modalities.

Transcutaneous electrical nerve stimulation (TENS) is an effective,¹⁵ low-risk, analgesic therapy that is usually provided under the guidance of a physical therapist. TENS is excellent for localized pain. The fact that it is portable, can be used discreetly, and has few side effects makes it attractive for use at school. Because tolerance to TENS can develop with prolonged use, children need to limit use to no longer than 2 hours at a time. They can take a break for an amount of time equal to the TENS use and then restart it.

The Nurse

Pain nurses play a major role in hospital-wide education of floor nurses regarding assessment and treatment of pain, including the use of epidural and patient-controlled analgesia (PCA) pumps. When starting to see chronic pain patients, the first personnel recruitment should be an advanced practice nurse who can be trained to triage, perform the initial evaluation and intake assessment, and assist with all subsequent pain-related issues that do not require the direct input of a physician.

The Consultant

Anesthesiologists should be cognizant of their limitations and judiciously use of consultants to help make or confirm diagnoses and fashion the best treatment plan. Neurologists typically are well versed in headache management and in the use of many of the medications used for neuropathic pain. Physical medicine and rehabilitation specialists can assist in structuring a treatment plan for a variety of musculoskeletal pains and are accomplished in the treatment of spasticity.

History

The basic history focuses on the pain: location, duration, quality, intensity, aggravating and alleviating factors, associated symptoms, therapies that have been tried, and which tests have been performed and by whom. Pain intensity is often assessed by a 0 to 10 numeric rating scale for children older than approximately 8 years of age. The child must be asked about the current pain level and about the best and worst pain levels to obtain an idea of the pattern of pain and when it peaks. Quality descriptors include burning, sharp, aching, throbbing, tingling, numb, weird, and others; each may give a clue about the type of pain the child is experiencing. Odd descriptors, burning, and tingling suggest neuropathic pain; sharp, tight, and aching may indicate bony or muscular causes; throbbing suggests a vascular component; cramping or pain that comes in waves often suggests spasms of a muscle or hollow viscus.

A vital part of the chronic pain evaluation process is to look for red flags, which are signs or symptoms that may indicate a serious illness. Some of the red flag signs and symptoms for major pain types can be found in Tables 44-1, 44-2, and 44-3. For example, a child with back pain who also has weak legs and incontinence may have a tethered spinal cord. Headache that is worse in the morning and associated with vomiting suggests increased intracranial pressure. Back pain with loss of ankle jerk suggests compression of the S1 nerve root.

TABLE 44-1 Red Flag Signs and Symptoms for Abdominal Pain

TABLE 44-2 Red Flag Signs and Symptoms for Secondary Headache

TABLE 44-3 Red Flag Signs and Symptoms for Back Pain

A complete pain evaluation comprises further history regarding medications, allergies, family history, and a thorough review of systems. Certain painful conditions, such as migraine headaches,¹⁶ fibromyalgia,¹⁷ irritable bowel syndrome,¹⁸ and sickle cell disease, have a genetic basis. Knowing the family history can assist in making the diagnosis. The child sometimes may model his or her behavior after a family member. For example, if a parent has a “bad back” and is functionally compromised, the child also may complain of back pain. This does not mean the child is faking the complaints but simply patterning the behavioral response to pain after a model that he or she understands. Treatment can include reassurance, cognitive behavioral therapy, and gentle physical therapy to restore the child’s functional ability and help him or her with any underlying issues. Family and social histories can be useful in fashioning a treatment plan in conjunction with the general history, physical examination, and relevant testing.

Physical Examination

The physical examination should focus on the area of interest, but a brief general examination is also important. A full screening examination, including a neurologic examination, takes only a few minutes and can be combined with the social history. A systemic illness may manifest as a localized complaint; for example, diabetes can manifest as abdominal pain or leukemia as focal bone pain

When examining a child of the opposite sex, the physician should have a nonfamily observer of the same gender as the child present. Some children are very conscious of their bodies and may consider routine examination maneuvers as invasions of their privacy. The occasional child has a history of being abused and can be further traumatized by even a standard examination. Physicians can demonstrate examination techniques that may make the child uneasy. For example, a pinprick examination requires a needle or sharp object; the examiner should touch his or her own skin with a pin first to demonstrate that blood is not being drawn. Children are often fascinated by the deep tendon reflexes and usually have fun with that examination. Children with chronic pain often have had many examinations, and doing something a little different or fun can help them accept the current evaluation and enhance rapport.

Ancillary Data

By the time chronic pain patients have reached a pain clinic, they usually have undergone several investigative tests, and those data should be reviewed. After it becomes clear that there is no life-threatening illness, the focus should shift away from further testing. This is often a hard transition for families and children to accept, especially if no concrete diagnosis has been made to explain the pain. It is a challenge for them to embrace the thought that the pain itself is the disease rather than something that is still undiagnosed. Any study that may help to explain the pain or make a diagnosis that had not been entertained should be recommended. However, pursuing tests and imaging in an unfocused manner wastes resources and causes families to postpone treatment while waiting for a diagnosis. Until the patient wholeheartedly endorses the treatment plan and becomes active in it, the child or adolescent’s pain will continue unabated.

Abdominal Pain

Abdominal pain is a major source of distress in children that causes anxiety and invites a large amount of testing. This painful condition, formerly referred to as recurrent abdominal pain, is now described as functional gastrointestinal disorders (FGIDs).²⁰ Specific criteria exist for the major categories so that FGIDs are no longer considered diagnoses of exclusion. The pain is thought to be caused by abnormal interactions between the enteric nervous system and central nervous system.²¹ Research suggests that peripheral sensitization and abnormal central processing of afferent signals at the level of the central nervous system play roles in the pathophysiology of visceral hyperalgesia—a decreased threshold for pain in response to changes in intraluminal pressure.²² The history and physical examination focus on excluding warning signs and symptoms of underlying disease (see Table 44-1).^20,23 The role for testing, endoscopy, and radiographic evaluation is limited.

Multidisciplinary treatment of FGIDs includes medication, psychological interventions, and education, which often need to be ongoing. The most important aspect of the treatment plan is to establish realistic goals, which frequently means return of function rather than complete elimination of pain. Although the literature for treatment is sparse, tricyclic antidepressants such as amitriptyline, nortriptyline, or doxepin have been used effectively for FGID-related pain. Anticonvulsants also are useful because they modify nerve conductivity and transmission. Antacids, antispasmodic agents, smooth muscle relaxants, laxatives, and antidiarrheal agents can be added to address symptoms. Data support the use of peppermint oil capsules in managing irritable bowel syndrome, although gastroesophageal reflux can be a limiting adverse effect.²⁴ Children with functional bowel disorders can have abnormal bowel reactions to physiologic stimuli, noxious stressful stimuli, or psychological stimuli (e.g., parental separation, anxiety). Children benefit from cognitive- behavioral therapy, coping skill development, biofeedback, hypnosis, and relaxation techniques (Table 44-4).^25,26

TABLE 44-4 Care Pathway for Abdominal Pain

Headache

Headaches can be categorized as primary or secondary. Primary headaches include migraine, tension, cluster, and trigeminal neuralgia headaches. Secondary headaches are those attributable to head and neck traumas; muscle spasms; vascular disorders; nonvascular intracranial disorders; infection; eye, ear, cranium, nose, sinus, and teeth or mouth diseases; homeostatic disturbances; and psychiatric disorders. Headaches represent one of the more poorly tolerated types of chronic pain, with greater medication use than for other types. Of 77 children with long-term headaches who were followed up to 20 years after the initial diagnosis, 27% were headache free, and 66% had improved.²⁷

Migraines (especially migraine without aura) and tension-type headaches are the most common types of pediatric headaches. The prevalence of migraine ranges from 2.7% to 10%. It occurs more frequently in boys than girls between 4 and 7 years of age, and then the prevalence equalizes between 7 and 11 years of age. After 11 years of age, three times more girls than boys have migraines.^28,29 Studies are not routinely recommended in the absence of focal neurologic findings. However, the practitioner must be alert to red flag signs and symptoms that warrant imaging and laboratory studies to rule out an underlying condition as a cause of the headaches (see Table 44-2).

There is a genetic component to migraine and chronic tension headaches; 50% to 77% of children with migraines have a positive family history for migraine headaches, especially on the maternal side. The clearest genetic link has been established for familial hemiplegic migraine.¹⁶

Children with frequent headaches often suffer from medication overuse headaches due to chronic or repeated use of over-the-counter analgesics. If possible, children should be weaned off analgesics gradually.

Treatments for migraine and tension-type headaches overlap greatly. Pharmacologic interventions can be divided in two types. In the first, abortive treatment focuses on stopping the acute headache. In the second, prophylactic therapy is indicated for patients with more than two headaches per month, for children with severe attacks, and for those with frequent headaches unresponsive to medication (Table 44-5).³⁰

TABLE 44-5 Care Pathway for Headaches

Older medications that have been used successfully to prevent headaches in adolescents include amitriptyline and trazodone. These medications tend to make children drowsy and are prescribed 30 to 60 minutes before bedtime each night. Younger children appear to respond well to the antihistamine cyproheptadine. Overall, few evidence-based recommendations can be made; the lack of randomized, controlled pediatric trials precludes an evidence-based recommendation.³¹ However, the anticonvulsant topiramate is a promising medication for the prevention of migraine headaches.^32–34

Complex Regional Pain Syndrome

Type I and type II CRPS are different only in the presence of a documented nerve injury in type II (formerly called causalgia). Pain is an obligatory feature, often occurring alongside allodynia or hyperalgesia. There must be evidence at some time (not necessarily at the time of diagnosis) of edema, changes in skin blood flow, or abnormal sudomotor activity in the region of pain. There are often features of a motor disorder such as tremor, dystonia, and weakness that sometimes lead to a loss of joint mobility. Nail and hair growth can also be affected. In the past, three distinct stages were described. However, it may be that there are phenotypic subtypes instead of stages.³⁵

From a clinical standpoint, the typical pediatric CRPS patient is older than 10 years of age, Caucasian, female, and very active or a high achiever from an active family, and the child or adolescent presents with lower extremity pain.³⁶ A genetic predisposition is suggested by the clinical observation that CRPS is rare in the African American population. The rarity of CRPS in preadolescent children suggests a developmental aspect to its origin.

It is important to obtain a detailed history of the mechanism of trauma and the signs and symptoms. The examiner should specifically look for pain, allodynia, hyperalgesia, and hyperpathia. Edema and color changes do not have to be present at the time of diagnosis, but there should be a history of such changes in the recent past (Fig. 44-1). A complete neurologic examination includes testing muscle strength, reflexes, sensory responses (e.g., cold, touch, pinprick), capillary refill, temperature, and color differences. The physician should also look for deep tissue hyperalgesia. Occasionally, noninvasive or invasive testing may be helpful, but it is not sensitive or specific. These evaluations may include an electromyogram with nerve conduction velocity (EMG/NCV), quantitative sensory testing (QST), and quantitative sudomotor axon reflex testing (QSART) to detect small fiber dysfunction; thermography; and bone scans. Sympathetic ganglion blocks are not considered necessary for diagnosis, but they can be part of the therapeutic approach.

FIGURE 44-1 Complex regional pain syndrome involves the patient’s left foot and ankle. Notice the cyanosis and mottling. The affected foot was cool, and allodynia was prominent. Left foot toenails had not been trimmed in 3 months.

The therapeutic goal for CRPS is restoration of function. It may seem simple, but in daily practice, this may represent the biggest challenge for the physician and the child. The therapeutic approach to the child with CRPS is multidisciplinary, with a focus on the psychosocial and physical aspects of the disease (Table 44-6). Education is important, and the information available on the Internet is ubiquitous, although it is often discouraging and not applicable to children with CRPS. No isolated treatment technique has been helpful for this condition. Children and physicians should follow an algorithm and adjust the therapeutic strategy every 4 weeks if the child does not respond satisfactorily to chosen measures.

TABLE 44-6 Care Pathway for Complex Regional Pain Syndromes

The mainstay of CRPS treatment is physical therapy. However, the pain can be severe and disabling enough to prevent active participation by the child in the physical therapy program. Pharmacologic therapy is often initiated to facilitate physical therapy. Medications for neuropathic pain (described later) take time to titrate to effect. It is reasonable to use nonsteroidal antiinflammatory drugs (NSAIDs) and opioids for a short time until the primary medications take effect. The psychology team must play an active role in the overall treatment program. Psychosocial issues must be aggressively addressed. With physical therapy, psychology, and medications, most children achieve good results and disease resolution. In unusual refractory cases, for which interdisciplinary outpatient programs are insufficient, inpatient pain rehabilitation programs are recommended.

The role of interventional therapy in the treatment of CRPS is to alleviate the pain and provide the child with the opportunity to tolerate and advance in physical therapy. Sympathetic nerve blocks are widely used in adults although a systematic review revealed a lack of randomized, controlled trials to confirm the effectiveness of this approach in short-term and long-term pain relief.³⁷ Interventional therapies can be a double-edged sword, representing an easy solution that can demotivate the child from taking an active role in his or her physical therapy. However, pain may be too severe to allow physical therapy and thereby accelerate loss of function.

Several techniques enjoy popularity among pediatric pain specialists. For isolated limb CRPS, intravenous regional blockade with local anesthetic and adjuncts such as clonidine, ketamine, or ketorolac is performed. General anesthesia or deep sedation is frequently required because placement of intravenous catheters in the affected limb and inflation of the tourniquet are poorly tolerated. More invasive alternatives include placement of a lumbar sympathetic plexus catheter (Fig. 44-2) and a tunneled epidural catheter in the upper thoracic or lumbar area. The duration of infusion ranges from 3 to 5 days to as long as 4 to 6 weeks, and the procedure requires extensive logistical support. An alternative approach is to place a peripheral nerve catheter for a continuous block.³⁸ Spinal cord stimulation and intrathecal drug delivery are rarely used for pediatric CRPS due to the overall good prognosis with more conservative treatment and the continued growth of the skeleton, which can change the area of paresthesias in the case of spinal cord stimulators.

FIGURE 44-2 Lumbar sympathetic block. A, In the lateral view, the Tuohy needle is in the proper position. Notice the prepsoas spread of contrast agent. B, The dye spreads and clears due to injection of local anesthetic through the catheter. The catheter is tunneled and can be left in place for a week.

Musculoskeletal and Rheumatologic Pain

Musculoskeletal pain is a recognized problem in children and adolescents, and back pain commonly affects adolescents.^39,40–42 Although many factors are blamed for musculoskeletal pain (e.g., heavy backpacks, participation in sports, sedentary lifestyle, scoliosis, increased body mass index), only a few have been proved to contribute to musculoskeletal pain. According to one study, in more than half of cases the cause could not be identified, and only a minority of children had an underlying disease process (e.g., spondylolysis, infection, tumor, disk problem). Radiologic findings correlated poorly with the pain and failed to distinguish between individuals with pain and those without pain.⁴² Selected red flags for back pain are provided in Table 44-3. A care pathway for the evaluation and treatment of back pain in children and adolescents is presented in Table 44-7.

TABLE 44-7 Care Pathway for Back Pain

A special group of children with musculoskeletal pain are those with rheumatologic diseases. Most children referred to the rheumatologist’s office complain of musculoskeletal pain. Only some of them are diagnosed with a true rheumatologic disease; juvenile idiopathic arthritis is the most common form. Besides pain, the diseases often manifest as morning stiffness, fatigue, and sleep problems. The process may progress and cause joint deformities and destruction due to osteoporosis, with resulting growth abnormalities and functional disability. Management combines pharmacologic and nonpharmacologic interventions. The mainstay of therapy is the use of NSAIDs, acetaminophen, and rarely, opioids for severe breakthrough pain. The rheumatologist may prescribe agents such as methotrexate, cyclophosphamide, or systemic corticosteroids for severe flare-ups. Splints, physical therapy, and psychological interventions such as cognitive-behavioral therapy are often used.⁴³ Children with Ehlers-Danlos syndrome or other connective tissue disorders suffer from unstable joints that become very painful from repeated dislocations and mechanical stress.

Some young women present with fatigue, poor sleep, and pain or unusual tenderness in multiple sites. Fibromyalgia is more common in adolescents than expected, and it can be a significant problem. Therapy includes education, medications, and general restorative therapy, with a focus on aerobic reconditioning. Traditionally, tricyclic antidepressants and cyclobenzaprine have been used, and duloxetine and milnacipran are helpful in adults.^44,45 As with many chronic pain conditions, cognitive-behavioral approaches are valuable components of treatment.⁴⁶

Musculoskeletal pain is a particularly difficult problem in children with cerebral palsy.⁴⁷ Spasticity itself can be painful, and the daily stretching exercises are reported to be painful by many children. Some children with cerebral palsy are nonverbal, making assessment even more difficult. The parents or guardians can provide information about how the child expresses pain and how the pain manifests during daily life. If diaper changes seem to hurt, the practitioner should suspect hip or perineal pain. Pain after eating or a history of hard stools may point to constipation-based abdominal pain. A careful and sometimes staged examination is required. A thoughtful, empirical approach to therapy and judicious use of radiologic and laboratory evaluations can often lead to the diagnosis (Table 44-8).

TABLE 44-8 Care Pathway for Nonverbal Patients

Pain in Sickle Cell Disease, Trait, and Variants

Sickle cell disease is a hereditary disorder characterized by abnormal hemoglobin S (see Chapter 9). About 8% of African Americans carry the sickle gene. The homozygous form (sickle cell disease [HbSS]) manifests as a hemolytic anemia with unique vaso-occlusive features. The heterozygous form (sickle cell trait [HbAS]) is milder and manifests as a borderline anemia and rarely with vaso-occlusive features. Sickle cell/hemoglobin C disease (HbSC) has a clinical presentation similar to that of HbSS, but its vaso-occlusive episodes are fewer and usually less intense.

From a pain management perspective, the homozygous HbSS genotype manifests as acute pain attacks (e.g., pain crisis, vaso-occlusive episodes, acute chest syndrome) or as underlying chronic pain with acute exacerbations (e.g., avascular necrosis, vertebral collapse, joint involvement). Treatment frequently requires a multidisciplinary approach with close cooperation between the hematologist, psychologist, and pain physician.⁴⁸ Most of the episodes can be managed at home with NSAIDs or acetaminophen, supplemented with opioids such as codeine or oxycodone or with tramadol. In severe cases, children often are hospitalized and treated with intravenous opioids, although they should be gradually weaned off the opioids as the primary process improves. For episodes of localized, hard-to-control pain or if acute chest syndrome develops, epidural analgesia can provide excellent relief.⁴⁹ Rarely, children require opioid maintenance with long-acting preparations of morphine or oxycodone (Table 44-9). Hyperalgesia over the affected area suggests peripheral or central sensitization, although the role for neuropathic medications is undefined.

TABLE 44-9 Care Pathway for Sickle Cell Disease

Nonsteroidal Antiinflammatory Drugs and Cyclooxygenase-2 Inhibitors

NSAIDs come from various chemical groups (e.g., salicylates, propionic acid, oxicams, naphthylalkalones, fenamates). The mechanism of action is inhibition of cyclooxygenases (COXs) at the prostaglandin H₂ synthetase enzyme. COX-1 is constitutive and always present, and COX-2 is inducible and produced in the body under proper conditions. NSAIDs have different selectivities for COX-1 or COX-2; selective COX-2 inhibitors have predominant action on inducible COX-2. The benefit of selective blockade is decreased risk of gastrointestinal bleeding. Celecoxib is the only selective COX-2 inhibitor available in the United States.

The analgesic and antiinflammatory actions of NSAIDs exhibit a dose-dependent response until they reach maximum effect; beyond which there is no further benefit of dose increase (i.e., ceiling effect). Unlike opioids, there is no development of physical dependence or tolerance with NSAIDs.

The choice of NSAID is empirical and based on clinical judgment. If the child provides a history of good response to a particular NSAID, we tend to continue the same medication or adjust the dose. If the response is inadequate, we select a different medication until we find an effective one. In children with a history of gastrointestinal adverse effects, we prescribe combination preparations with protective agents (e.g., misoprostol) or a histamine₂ (H₂) receptor or proton pump inhibitor, or we switch to a selective COX-2 inhibitor. Preexisting renal disease and disorders that reduce actual or effective intravascular volume vastly increase the risk for renal toxicity, and NSAIDs must be used cautiously in these situations.

Opioids

The use of opioids for treating chronic nonmalignant pain has been associated with many myths and controversies. Their use in the past was reserved for children with acute and cancer-related pain. In selected cases, with appropriate monitoring, opioids can improve quality of life and functional capacity without significant risk of addiction, tolerance, and toxicity. However, a history of substance abuse (mainly in adolescent and young adult populations) and a family member with substance abuse and a dysfunctional social situation are red flags for opioid prescribing.

Opioid agonists are used almost exclusively; agonist-antagonists have less popularity because of their ceiling effect and the potential to precipitate withdrawal when administered alongside a pure agonist. We typically use opioids in two scenarios. The first features opioids as a bridge while titrating other classes of medications to effect or while awaiting physical therapy or an intervention to exert its effect. In the second scenario, we use opioids as maintenance analgesics in carefully selected children (e.g., chronic musculoskeletal pain in a child with cerebral palsy, children with juvenile rheumatoid arthritis or Ehlers-Danlos syndrome). Medication is titrated in increments toward the main goals of optimal (although rarely complete) pain relief, improved function, and minimal adverse effects. Escalations are seen usually with exacerbations of the primary disease process. Common opioid adverse effects that occur with long-term use can be found in Table 44-10.

TABLE 44-10 Opioid Side Effects Associated with Chronic Use

A special medication in this group is methadone. Besides being an opioid agonist, methadone is also reasonably effective in controlling neuropathic components of pain. There are a few exceedingly important caveats for its use. It has a long half-life and presents a risk of accumulation leading to sedation and respiratory depression. The usual 1 : 1 methadone to morphine equianalgesia ratio does not work for dose conversion. The greater the dose of opioid being converted, the more skewed the conversion ratio; the methadone to morphine ratio ranged from 1 : 2.5 to 1 : 14.3 in one study.⁵⁰ Because of the long half-life, dose adjustments should be made no more frequently than every 5 days. A unique adverse effect of methadone among opioids is its potential to prolong the QT interval and modestly increase the dispersion of repolarization on the electrocardiogram.⁵¹ Because the dispersion of repolarization is less than 100 msec, it remains unlikely that methadone can trigger torsades de pointes.

When a child who is taking long-term opioids presents in the operating room, a thorough medication history is essential for developing a perioperative plan. If the child has not taken a morning dose of opioid, that dose should be replaced by the intravenous route to avoid withdrawal. It is essential to convert the home medication into morphine equivalents, and the daily dose of home opioids should be provided as a baseline, with all further dosing being in addition to the baseline, to avoid pain at the time of emergence. Because of tolerance to long-term opioids, larger doses than usual may be required, and it is advisable (as in all children) to titrate to comfort in the immediate postoperative period and use the amount required to achieve optimal analgesia. Opioid consumption during the perioperative period may be more than three times that observed in patients not taking chronic opioids. Sparing use of opioids in the perioperative period results in poor pain management and withdrawal phenomena.^52,53

Adjuvant Drugs