The Management of Pain in the Neurosurgical Patient

The patient undergoing neurologic surgery should be evaluated closely before surgery for past pain history and previous responses to pain interventions with special attention to pain medications.

A pain treatment plan should be developed collaboratively among the patient, anesthesiologist, and neurosurgeon before surgery. Multimodal and regional/neuraxial techniques, when appropriate, can lessen systemic side effects, improve postoperative pulmonary function, and shorten hospital stays.

In many cases, the knowledge base for pain treatment exists, but clinical implementation is often limited. Because of these challenges, many patients have less than optimal treatment in the perioperative period.

INTRODUCTION

The successful treatment of pain in the postoperative patient is important with all surgical specialties, but in many instances, it is more critical in the patient undergoing neurosurgical or spinal surgery. As illustrated above, pain can very commonly increase sympathetic tone, leading to hypertension, tachycardia, increased intracranial pressure (ICP), and changes in the vasomotor response, while misguided non-vigilant medication administration can also have deleterious effects.

Previously, Dunbar performed a comprehensive look at the issue of postoperative pain in the patient undergoing intracranial surgery, leading to some clarification of the issue. He compared those undergoing intracranial surgery to those who had select extracranial procedures. In this 200-patient retrospective study, the intracranial group did have significantly less pain than the comparison group (p < 0.05). A subset of intracranial patients did, however, have significantly more pain than others in the group: those requiring frontal craniotomies required more opioids and had elevated heart rates, blood pressure, and ICP. This analysis was inconclusive regarding those undergoing intracranial procedures. It is well substantiated that recovery from spinal surgery is more painful than from a craniotomy. In a recent presentation at the European Society of Regional Anesthesia in 2010, data suggested that a high-volume local anesthetic block in the cranium before incision may lower the overall opioid requirements in the postoperative period. This has not been substantiated in a prospective fashion.

In addition, there are inherent difficulties with managing postoperative pain in neurosurgical patients. The other factor that makes this issue more complex is the desire to limit postoperative sedation, as it is clinically imperative to obtain an accurate neurologic exam to guide treatment, as surrogate objective monitors are secondary and have inherent flaws. This gold-standard monitor can be affected adversely if the patient is sedated or obtunded. This conflict of treatment goals can lead to withholding pain medication and techniques, which is also deleterious to patient outcome. This has led to the increased use of mixed agonist/antagonist or partial agonist opioids and decreased use of traditional opioids, like morphine, in some neurosurgical ICUs. Opioids used inappropriately can, because of their known side-effect profiles of cough, nausea, vomiting, constipation, and respiratory depression, increase patient morbidity and mortality. However, recent studies have demonstrated that, when morphine and other potent opioids are titrated appropriately in the presence of postsurgical monitoring, the outcome is not altered.

It is not uncommon to awaken the patient in the operating room to demonstrate intact (or improved) motor and cognitive function, even with the use of intraoperative sensory and motor-system evoked potential monitors (SSEPS, MEPS). The use of short-acting inhalation or intravenous anesthetics has commonly produced an awake patient with poor analgesia. With the recent focus on pain as the fifth vital sign, it is imperative to treat the pain promptly and mindfully when the visual analog scale (VAS) exceeds 5/10. The anesthesia plan should include both intraoperative and postoperative planning to ensure adequate analgesia and a reliable neurologic assessment. One does not preclude the other.

It is critical to realize that the treatment of pain in the neurosurgical patient may influence outcome in a variety of ways. The treatment focus needs to rest on alleviation of pain as the primary goal. Although the hemodynamic consequences of pain, including tachycardia and hypertension, can be treated with sympatholytics (e.g., beta-blocking drugs), this obviously does not provide analgesia. Studies have shown that pain in the postoperative period can adversely influence outcome independent of hemodynamic or intracranial endpoints. Proper pain control may stabilize hemodynamics, reduce blood pressure, and lower cerebral metabolic rate for oxygen consumption (CMRO₂), as well as lower the ICP.

In addition to pain issues, the perioperative period for the craniotomy patient is complex, and needs to be considered systemically, as the question becomes: how much is the intracranial compliance compromised? The surgical stress response causes elevations in total body oxygen consumption and serum catecholamine concentrations. Systemic hypertension is often present after neurosurgical procedures and has been linked to intracranial hemorrhage. Bleeding in the postoperative period can increase mortality, morbidity, and hospitalization. The cerebral consequences of hypertension in the recovery period include cerebral hyperemia and increased ICP. Prevention or control of pain is one of the major factors in limiting these adverse systemic effects.

Over the past decade, developments in intravenous opioids, new regional techniques, and local anesthetics have greatly enhanced our ability to treat this patient group. Pre-emptive analgesia improves the stability of the patient throughout the surgical experience. To minimize pain and decrease the stress response and hemodynamic changes, the surgeon and the anesthesiologist must work as a team. The importance of the anesthesiologist in decreasing anxiety, creating a treatment plan, and executing the plan is crucial to a successful surgical experience.

The surgeon can help reduce the immediate postoperative pain by infiltrating local anesthetic when appropriate, limiting surgical tissue trauma, and participating in the preoperative planning for postsurgical treatment.

Modern pain treatment methods have enabled neuroanesthesiologists to offer their patients numerous modalities for treating the mechanisms that cause pain. The options for interrupting the pain pathway can be divided into four components: transduction, transmission, modulation, and perception. Transduction occurs when one type of energy (temperature, mechanical) is converted to electrical energy via ionic charge separation (i.e., action potentials). Transmission is the transfer of a pain impulse through the nervous system by the first-order, second-order, and third-order neurons via the C and A delta fibers in the spinothalamic tracts to the thalamus and the cortex. Pain modulation describes the alteration of the pain signal by either augmentation or diminution as it travels. Perception is the subjective and emotional interpretation of pain, occurring in the somatosensory cortex and the limbic system. The patient’s genetic, social, and cultural background influences this interpretation. By understanding this complex neural network and its interconnections, the opportunity to affect the pain response is great. The method chosen depends on the surgical procedure and the patient’s comorbidities. The remaining sections of this chapter focus on the key points necessary to enhance outcome, patient satisfaction, and patient safety.

I. PREOPERATIVE ASSESSMENT

A. Preadmission and preoperative considerations

1. Reducing anxiety. Recent studies have shown that reducing anxiety preoperatively or in the immediate postoperative period enhances the ease of controlling pain, blood pressure, and subsequent anxiety, reducing the need for pharmacologic intervention. It is important for the anesthesiologist to have an open dialogue with the patient, using part of the preoperative interview to discuss the plan for intraoperative pain treatment (if an awake test is used), along with postoperative pain management. Studies have demonstrated that a discussion of the patient’s previous experiences, expectations, and fears can be as useful as some anxiolytic medications.

2. Pain treatment history. The prolonged use of oral opioids for chronic pain makes determining the baseline dose of opioids in chronic-pain patients somewhat difficult. The analgesic tolerance to opioid medication can influence dosing in both the intraoperative anesthetic and the postoperative periods. It is important to realize that the use of chronic medications is for a stable pain condition, and it will be necessary to supplement this baseline dose with additional medication. It is helpful to obtain a history of previous experiences with postoperative pain treatment, complications, and adverse reactions. The anesthesiologist should explain in detail the pain treatment plan; patient reassurance should be a high priority. It is well established that patients who have a history of chronic opioid use become tolerant to the opioid effects of nausea, vomiting, sedation, euphoria, and respiratory depression, whereas there is minimal tolerance to pupillary constriction and constipation.

3. Understanding the procedure. The physician providing the postoperative pain relief should understand the procedure being performed. An understanding of the patient’s postsurgical mental status is helpful when the physician chooses a pain treatment plan. Techniques that require an alert patient, such as PCA, should be offered only to those who are able to comply with instructions. Regional anesthesia is possible if the procedure involves only limited portions of the spine.

4. Role of coexisting disease. The patient’s non-surgical disease processes must be considered when tailoring a pain treatment plan. The review of systems is critical in determining what recommendations should be made. The following factors should be considered as part of the preoperative assessment.

a. Neurologic system. The site of surgery and the perioperative morbidity should be considered. The patient’s baseline cognitive and neurologic function also determines whether PCA can be used, and may provide insight regarding intracranial compliance. PCA can be used in children as young as 5 years of age but should be instituted with caution and requires the education of both patients and their parents.

b. Renal system. A patient who has renal disease is prone to complications from drugs that are metabolized by the kidneys. Meperidine, for example, breaks down to normeperidine, which can cause seizures in these patients. Meperidine should be used in a limited fashion in any postsurgical patient, but the risk is high in those who have renal impairment. Morphine and hydromorphone are metabolized to M3G/M6G and H3G/M6G, respectively, and are renally excreted. The 6-glucuronide metabolite is pharmacologically active at the mu receptor, while the 3G metabolite has been implicated in lowering the seizure threshold.

c. Infectious disease. Neuraxial procedures may be contraindicated in the patient who has either a systemic infection or a local infection at the site of the proposed procedure. If a patient is bacteremic or has an infection at the surgical site, regional anesthesia is contraindicated.

d. Hematologic system. An epidural hematoma is a rare but disastrous complication of regional anesthesia. Factors that may contribute to this adverse outcome include abnormalities of the clotting cascade, a history of bleeding during previous surgery, and the use of low molecular weight heparin and other anticoagulants during the postoperative period. This condition may be evaluated both by history and by laboratory examination. If anticoagulation is continued perioperatively, care and timing of neuraxial regional anesthesia procedures, including catheter removal, require vigilance and an appreciation of the regional anesthesia complication rate and the anticoagulant’s kinetics and pharmacodynamics. The reader is referred to the American Society of Regional Anesthesia (ASRA) 2010 Third Edition Guidelines.

e. Cardiovascular system. As noted in a previous section, the physiologic response to intracranial surgery includes hypertension, tachycardia, and catecholamine surges. An increase in blood pressure, heart rate, and catecholamines results in an increase in cardiac workload and may lead to ischemia in those who have perioperative risk factors. When in doubt, a cardiology consultation may be useful in planning the postoperative pain treatment plan. The other risk of the anesthetic and pain treatment is the issue of patients who are cardiovascularly unstable and require support. Furthermore, care must be taken regarding reduction of blood pressure in the presence of intracranial hypertension, as this could result in ischemic insults.

f. Gastrointestinal system. A history of ileus may be a cause for concern in regard to the use of narcotics and an epidural infusion of local anesthetic. Opioids can cause constipation, sympathectomy can cause increased peristalsis, and surgical neuraxial anesthesia can exacerbate ileus. In these cases, it is important to implement a bowel support regimen as a standard part of the program when using intravenous or oral opioids or epidural infusions.

g. Genitourinary system. A history of urinary retention may cause concern for regional neuraxial analgesia as neuraxially administered opioids and local anesthetics can cause urinary retention. In these cases, it is important to implement a urinary support regimen as a standard part of the program when using intravenous or oral opioids or epidural infusions.

B. Summary of the preoperative period. Appropriate preparation in the preoperative period is crucial to the overall success of the neurosurgical pain treatment program. The clinician should develop a mental checklist of assessment points before bringing the patient to the operating theater.

II. THE IMPORTANCE OF PAIN TREATMENT

A. The patient undergoing neurosurgical intervention may develop many perioperative changes that can affect the overall outcome in the absence of pain management. The stress response, which is somewhat dependent on the complexity and the site of surgery, can affect the immunologic response, coagulation, cardiac function, hormonal response, oxygen consumption, and other systems crucial to the neurosurgical patient’s recovery. The anesthesiologist has several options to blunt the stress response, but these methods are successful only when the appropriate procedure is matched with the right patient.

B. The technique of postoperative pain control has been shown to have a major impact on outcome and pain reduction, as demonstrated in thoracic surgery. At the current time, no studies exist in the neurosurgical patient, and the significance of postoperative pain is unclear. Recent studies have suggested that total intravenous anesthesia (TIVA) may be associated with a lower incidence of nausea, vomiting, and pain, as compared to maintenance with volatile anesthetics alone.

III. THE STRESS RESPONSE: AN OVERVIEW

A. Changes in other organ systems. The patient undergoing neurologic surgery is often very sensitive to subtle changes in other organ systems. The pathophysiologic changes associated with the stress response from surgical trauma can greatly affect the outcome from procedures with high risk of morbidity and mortality.

B. Physiologic effects of the stress response. The stress response includes an initial depressed phase and a subsequent hyperdynamic phase.

1. The depressed phase. In the initial portion of the stress response, the body responds by depressing most physiologic functions. This phase is brief in the surgical patient and might even be unidentifiable in some patients.

2. The hyperdynamic phase. The portion of the stress response of most concern to the anesthesiologist and most implicated in morbidity and mortality in the neurosurgical patient is the period of recovery after surgery. The duration of this phase is directly related to the amount of tissue trauma and the patient’s pre-existing disease state. A characterization of this response is given below.

a. Endocrinologic changes. Both catabolic and anabolic responses occur during this phase of the response.

1. Catabolic changes include increases in several hormones: catecholamines, renin, angiotensin II, aldosterone, glucagon, cortisol, tumor necrosis factor, adrenocorticotropic hormone (ACTH), growth hormone, and interleukin (primarily IL-1 and IL-6). These changes lead to hemodynamic instability in some patients and perhaps to changes in cerebral blood flow (CBF) and ICP.

2. Anabolic changes include decreases in insulin and testosterone. The changes can lead to hyperglycemia and imbalances in the hormonal axis, which impact wound healing and response to tissue trauma.

b. Metabolic changes. The stress response’s overall impact on patient outcome may be understood by considering the metabolic balance during this tumultuous time.

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