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From the Department of Anesthesia, University of Ottawa and Ottawa Hospital, Ottawa, Ontario, Canada.
Address correspondence to: Dr. Dennis Reid, Ottawa General Hospital, Department of Anesthesia, 501 Smyth Road, Ottawa, Ontario, Canada K1H 8L6. Phone: 613-737-8187; Fax: 613-737-8189; E-mail: dereid{at}ottawahospital.on.ca
CHRONIC pain is defined as pain that persists beyond either the course of an acute disease or a reasonable time for an injury to heal or is associated with a chronic pathological process that causes continual pain. Patients with chronic pain syndromes often have significant psychological overlay and emotional problems, mainly depression. They are often involved in ongoing confrontational issues with family, employers, government agencies and private insurance companies, and have usually had extensive involvement with health care professionals.
Chronic pain patients may be scheduled for surgery as part of the treatment of the chronic pain syndrome or for an unrelated condition. Whereas the former offers hope for cure or significant pain reduction, the challenges for the surgical team, particularly the anesthesiologist, are the same for both types of intervention.
Preoperative assessment
The following are the major issues which have to be considered:
Communication
The patient and a significant other should be completely appraised of the anesthetic management plan and how pain control will be achieved. Chronic pain patients are often very knowledgeable about "what works for them". However this is often viewed as drug seeking behaviour, although this is not always the case. The anesthetic plan should be clearly conveyed to the surgeon and the nursing staff.1
Review of medications
Chronic pain patients are often on one or more of the following:
NON STEROIDAL ANTI-INFLAMMATORY DRUGS
The consideration for these are well known to anesthesiologists.
NARCOTIC ANALGESICS
Chronic pain patients often take considerable doses of these and it is important not to scale back the dose in case of withdrawal. Oral therapy can be given up to the time of surgery, but may have to be converted to iv therapy particularly if the patient will be NPO postoperatively.
ALTERNATE ANALGESIC DRUGS
These are the tricyclic antidepressants and the anti-convulsants. They can be given up to the time of surgery, but since most of them cannot be given intravenously they have to be discontinued until the patient is able to take po. These agents are often used to treat neuropathic pain and there is a risk that abrupt cessation may cause an escalation of allodynia and hyperpathia, which can be compounded by the planned surgical procedure, so an alternative parenteral therapy will have to be given.
OTHER ANTIDEPRESSANTS
These can usually be stopped for the perioperative period until the patient is taking fluids, since they are long acting.
HYPNOSEDATIVES
These are mainly the benzodiazepines and are commonly used for sleep and anxiety. If the patient is on large doses of benzodiazepines, then these will have to be continued in some form during the perioperative period to prevent withdrawal.
DRUG WITHDRAWAL
It is important to remember that abrupt stoppage of preoperative therapies without appropriate substitution may result in drug withdrawal symptoms and acute exacerbations of pain and depression and anxiety. The key to successful management is a careful plan. Once the patient has developed any of the above, the situation may get out of control.
ADDICTION
When seeking a history of addiction it is important to ask about alcohol and street drugs. These patients are extremely prone to drug seeking activity.
PAIN ASSESSMENT
The usual pain assessment modalities such as the VAS may be misleading in these patients, who may report a nine out of ten score in order to receive more narcotics. More reliable indications of the degree of pain include the vital signs and the ability to cough, breathe and move around.1
Management
In order to better illustrate the management of these patients it will be helpful to consider the following case study.
Case history
A 56-yr-old ex-fireman with complex regional pain syndrome of the right arm, post traumatic stress disorder, severe depression and alcoholism requires a partial gastrectomy. It is expected that he will have a nasogastric tube in situ for 72 hr.
His medications include:
The following problems were identified at a preoperative conference, which included the anesthesiologist, the patient, his spouse and the nursing unit team leader.
Management of chronic pain medications
MORPHINE SULPHATE CONTINUOUS (MS CONTIN)
The MS Contin should be continued up to the time of surgery and then this baseline narcotic therapy pursued via an iv infusion.
The bioavailability of MS Contin is 50%, therefore 120 mg three times a day would correspond to 7.5 mg•hr–1 intravenously. The patient takes an additional 40 mg of regular morphine sulfate which has a bioavailability of 0.3. Therefore another 12 mg should be added to the infusion resulting in a final infusion of 8 mg•hr–1. This should be started after induction and continued until the patient can resume oral intake. The conversion to an iv narcotic can be done with any combination of narcotic analgesics and conversion tables are readily available as follows:1
BENZODIAZEPINES
Benzodiazepine therapy should be continued to prevent withdrawal, in this case both from benzodiazepines and alcohol. The patient receives 30 mg of diazepam daily and replacement therapy can be achieved with iv diazepam, iv midazolam, or iv or sl lorazepam. In order to minimize infusions, the preferred regimen is sl lorazepam 2 mg tid, which can be commenced immediately postoperatively.
GABAPENTIN (NEURONTIN)
Gabapentin alleviates the burning, lancinating pain of some neuropathic pain syndromes particularly post herpetic neuralgia and diabetic neuropathy.2 There is no iv equivalent. Other anti-convulsants such as dilantin and sodium valproate can be given intravenously, but have not proven to be effective in the management of neuropathic pain. IV lidocaine has been shown to be effective in some neuropathic pain syndromes and could be used as an infusion of 0.5–1.5 mg•kg–1•hr–1 following a bolus of 1.5 mg•kg–1.3 The best solution however is the use of ketamine, which is an N-Methyl-D-Aspartate (NMDA) receptor antagonist and has been shown to decrease allodynia and hyperalgesia associated with neuropathic pain.4,5 It is also effective as a postoperative analgesic particularly in combination with morphine and reduces narcotic requirements.6 In the latter situation ketamine is effective in a low dosage, namely a bolus of 0.5–1 mg•kg–1 at induction followed by an infusion of 20 µg•kg–1•min–1 and this should be started after induction.6 Having covered the patient's baseline narcotic, sedative and anti-neuropathic drug requirements, the issue of acute pain control and the anesthetic management can now be addressed.
Anesthesia management
PREEMPTIVE ANALGESIA
Both iv morphine and ketamine are probably pre-emptive. Other techniques which may be of benefit include, iv ketorolac and epidural bupivacaine/fentanyl.7 In the context of an upper abdominal incision, a thoracic epidural is appropriate particularly in this case where iv patient controlled analgesia may be relatively contra-indicated due to the potential for dependence on iv narcotics. A good choice for postoperative analgesic and intra-operative analgesia in this instance is a bupivacaine/fentanyl epidural with the addition of epinephrine to enhance the block.8 A dermatone specific epidural is important when using a lipophilic narcotic analgesic. In this case the T8–9 interspace should be used. For maximum anesthesia a solution of bupivacaine 0.25%, fentanyl 10 µg•ml–1 and epinephrine 5 µg•ml–1 is appropriate with an initial dose of 7 ml. This should be followed by induction of general anesthesia which should include ketamine 0.5 mg•kg–1, as already discussed. Ketorolac 30 mg intravenously should be given soon after induction and maintenance is established. The epidural should be continued into the postoperative period using a regimen such as bupivacaine 0.1%, fentanyl 5 µg•ml–1 and epinephrine 5 µg•ml–1. The morphine and ketamine infusions should be maintained and lorazepam given sublingually as already discussed.
Other additional medication could include ketorolac 15 mg intravenously every six hours or acetaminophen 650 mg by suppository every six hours. Monitoring of vital signs, ease of breathing, coughing and moving is important. In the context of normal observations by nursing staff, VAS scores not in keeping with observed behaviour should be treated with caution. Weaning back to oral medications should be done before the epidural is removed if possible. It may be necessary to increase the dose of morphine sulphate, long and short acting, during this period, particularly after the epidural is weaned.
Summary
The problems encountered when heavily medicated patients with chronic pain syndromes present for surgery are discussed in a case study. A management plan is proposed. The attending anesthesiologist, the acute and chronic pain service, the surgeon, the nursing staff, the patient and their significant others must be involved from the beginning.
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1 Ready LB, Edwards WT. Management of Acute Pain. A Practical Guide. International Association for the Study of Pain Publications, Seattle, 1992.
2 Watson CPN, Watt-Watson JH. Treatment of neuropathic pain: Focus on antidepressants opiods and gabapentin Pain Res. Manage 1999; 4: 168–78.
3 Cousins MJ, Power I, Smith G. 1996 Labat Lecture: Pain a persistent problem. Regional Anesthesia and Pain Medicine 2000; 25: 6–21.[Medline]
4 Persson J. Axelsson G, Hallin RG, et al. Beneficial effects of ketamine in a chronic pain state with allodynia possibly due to central sensitization. Pain 1995; 60: 217–22.[Medline]
5 Park KM, Max MB, Robinovitz E, et al. Effects of intravenous ketamine, alfentanil, or placebo on pain, pinprick hyperalgesia and allodynia produced by intradermal capsaicin in human subjects. Pain 1995; 63: 163–72.[Medline]
6 Schmid Rl, Sandler AN, Katz J. Use and efficacy of low dose ketamine in the management of acute post- operative pain: A review of current techniques and outcomes. Pain 1999; 82: 111–25.[Medline]
7 Kissin I. Preemptive Analgesia. Anesthesiology 2000; 93: 1138–43.[Medline]
8 Niemi and Breivik H. Adrenaline markedly improves thoracic epidural analgesia produced by a low-dose infusion of bupivacaine, fentanyl and adrenaline after major surgery. Acta Anaesthesiol Scand 1998; 42: 897–909.[Medline]
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