essentials of neurosurgical anesthesia & critical care || post-operative pain management in...

697A.M. Brambrink and J.R. Kirsch (eds.), Essentials of Neurosurgical Anesthesia & Critical Care, DOI 10.1007/978-0-387-09562-2_72, © Springer Science+Business Media, LLC 2012

Overview

The management of post-operative pain in neurosurgical patients can be challenging.

Many neurosurgical patients may be denied adequate analgesia because of the mistaken belief that opioids may mask neurological deterioration. Despite the diver-sity of neurosurgical procedures and the multiplicity of pain presentations in this population, effective and safe pain relief is possible for the vast majority of patients.

A sound knowledge of the pathophysiology underlying the neurosurgical condi-tion and an understanding of the complications associated with it are essential for optimizing safe post-operative analgesia. Many neurosurgical conditions are highly dynamic. A decrease in the Glasgow Coma Scale (GCS) must be carefully investi-gated as many neurosurgical complications may require urgent surgical and/or ther-apeutic intervention (Table 72.1 ). A deterioration in GCS must not be attributed solely to a relative opioid ‘overdose’ until other causes have been excluded.

Analgesia for major spinal surgery may be especially challenging. Many of these patients suffer from chronic pain and may present with a combination of nocicep-tive and neuropathic pain. A signifi cant number of these patients may be taking opioids pre-operatively. Acute on chronic pain is typically more diffi cult to manage than isolated acute pain.

M. Newton , MBBS, FRCA (*) The National Hospital for Neurology and Neurosurgery , London , UKe-mail: mary.newton@uclh.nhs.uk

T. Fernandez , MBBS, FCARCSI, FIPP, DPM Department of Anaesthetics and Pain Medicine , Imperial College Hospitals Healthcare NHS Trust , London , UK

Chapter 72 Post-operative Pain Management in Patients After Neurosurgical Operations

Mary Newton and Tacson Fernandez

698 M. Newton and T. Fernandez

Neuraxial opioids, alone or in combination with local anaesthetics, can be very effective following spinal surgery. However, the approach requires careful consider-ations; Neuroaxial local anaesthetic/opioids may be contraindicated if there is sig-nifi cant risk of an intraoperative dural tear which could result in unpredictable amounts of local anaesthetic/opioids reaching the cerebrospinal fl uid (CSF). In some centres, administration of opioids (particularly those that are long-acting and water soluble) into the CSF would commit the patient to care high dependency (HDU) care post-operatively. Additionally, local anaesthetic-induced motor block may mask neurological deterioration secondary to spinal cord compression by, for example, haematoma or tissue swelling. If this analgesic technique is used, it is imperative that the patient is monitored by nursing staff familiar with its use in this specialized population of patients. There must be a strict local protocol for the action to be taken in the event of onset of reduced limb power.

Increasing or uncontrolled pain post-operatively requires reassessment and con-sideration of alternative causes (Table 72.2 ), for example, a surgical complication or neuropathic pain.

Prevention

Pain is the fi fth vital sign and requires regular evaluation in combination with appro-priate intervention to maximize pain relief. Effective management of acute post-operative pain reduces the incidence of chronic pain; additionally, it aids early mobilization and may decrease factors associated with immobility (e.g. venous thrombosis and pulmonary atelectasis). Education of patients and clinical staff is vital to optimize acute post-operative pain management.

Table 72.1 Common causes of post-operative/post-procedure decrease in GCS

Common neurosurgical conditions Potential causes of decreasing Glasgow Coma Scale (GCS)

Sub-arachnoid haemorrhage (SAH) (post-clipping/post-coiling)

Re-bleed Acute hydrocephalus Cerebral vasospasm Seizure

Traumatic brain injury (TBI) Re-accumulation of haematoma Haemorrhage into contusion Oedema Seizure

Craniotomy Haematoma (sub-dural/intracerebral etc.) Oedema Seizure Air encephalocoele Infection – e.g. meningitis etc.

69972 Post-operative Pain Management in Patients After Neurosurgical Operations

Pain Scores

Pain is a subjective experience and most measures of pain are based on self-report. Numerous pain scales exist. Descriptive scales, where pain is described as ‘none, mild, moderate or severe’ are easy to use. Numerical scores are less easy to use but are more accurate at assessing the response to an intervention. The most popular numerical scale is the visual analogue score (VAS); it consists of a 100 mm line where 0 mm correlates with no pain and 100 mm correlates with ‘worst pain pos-sible’. The patient is asked to mark the line to ‘score’ their pain. VAS ratings of > 70 mm are indicative of ‘severe pain’.

Education

Education of patients pre-operatively can help to reduce anxiety, post-operative pain, and other associated symptoms. Ideally, it should begin pre-operatively with information about the planned surgical procedure, expected pain relating to it, the hospital’s pain-scoring system (see below) and the importance of effective analge-sia to aid early mobilization to reduce the clinical risks associated with immobility. Patients should be aware of the analgesic modalities available to them; this informa-tion will need to be reinforced repeatedly in the early post-operative phase.

All clinicians involved in the post-operative care of neurosurgical patients need on-going education in acute pain management and the additional considerations for this specialist group of patients. Familiarity with the operative procedure and

Table 72.2 Post-operative complications which may increase pain Complication Cause of pain

Sub-arachnoid haemorrhage (SAH) (post-clipping/post-coiling)

Re-bleed Hydrocephalus Infection

Traumatic brain injury (TBI) Wound infection Re-accumulation of haematoma

Craniotomy Haematoma (e.g. sub-dural/intracerebral) Air encephalocoele Low ICP headache/CSF leak Infection – e.g. meningitis

Spinal decompression/fusion Nerve root compression by disc remnant/haematoma/oedema

Neuropraxia (C2 root especially common) Infection Malpositioned instrumentation Muscle spasm

Intradural/intramedullary spinal cord surgery

Wound infection Haematoma formation Meningitis Low ICP headache/CSF leak

associated complications are particularly important. Clinical staff must be familiar with the hospital’s pain-scoring system and the application of this to optimize anal-gesia. Standardized prescriptions for analgesia used in conjunction with frequent assessment of pain scores can improve post-operative pain management.

Recommended Analgesic Regimes

The World Health Organization (WHO) pain ladder (Fig. 72.1 ) describes a simplis-tic guide to the optimization of analgesia. Urgent action is required for patients in severe pain which frequently requires all three steps of the pain ladder to be initiated simultaneously, in combination with pharmacological adjuncts (Tables 72.4 and 72.5 ) and non-pharmacological adjuncts (e.g. reassurance, explanation of the cause of the pain and the intended management of it, careful positioning, cool/warm packs and eye shades). Prompt action in the provision of good pain relief reduces anxiety. Anxiety is known to exacerbate pain.

Table 72.3 is a guide to appropriate post-operative prescribing of multimodal analgesia in our unit where commonly performed neurosurgical procedures are categorized according to the predicted pain (VAS) in the post-operative period. Details of the timed introduction of multimodal analgesia for intra-cranial surgery are shown in Table 72.4 and for non-intracranial surgery in Table 72.5 .

Freedom fromcancer pain

Strong opiodwith or without

nonopiod, adjuvent

Weak opiodwith or without

nonopiod, adjuvent

Nonopiodwith or without

adjuvent

Pain persistingor increasing

Pain medications: by the mouth by the clock by the ladder

Source: www.who.int/cancer/palliative/painladder/en

Fig. 72.1 WHO pain ladder

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Preventive Analgesia

This describes a reduction in post-operative pain following the administration of a drug that has an effect longer than the expected duration of that agent. There is no evidence to support the best timing of this therapy in the perioperative period. The use of NMDA receptor antagonists has been advocated as preventive analgesic regime in the context of abdominal, gynaecological, orthopaedic and dental surgery. However, general concerns remain regarding the use of ketamine in neurosurgical patients because of its effect on intracranial pressure. Recent work has suggested a similar benefi t following the use of gabapentin which would be more suitable in the context of neurosurgical interventions. Scalp blocks may provide effective and long-standing analgesia post-craniotomy; they are safe and simple to perform. As mentioned above, great care needs to be taken with the use of neuraxial opioids and local anaesthetic in spinal surgery. Potential preventive analgesic therapies that could be considered in expected ‘Major’ and ‘Complex Major Pain’ patient groups are shown in Table 72.6 .

Table 72.6 Preventive analgesic therapies that could be considered in expected ‘Major’ and ‘Complex Major Pain’ patient groups Timing of adjunct Dosage guidelines Precautions

Pre-operative Gabapentin 2 h pre-op (200–600 mg single dose, titrate dose according to age)

High-dose gabapentin may cause drowsiness. Dose reduction in renal failure

Ketamine – not for intracranial surgery Ketamine – not for intracranial surgery 5 min before skin incision –

(0.1–0.5 mg/kg) Psychosis not usually a problem

with low-dose ketamine Local anaesthetic block (LA) LA – see notes in ‘Overview’

Intraoperative ketamine – not for intracranial surgery ketamine – not for intracranial surgery (0.1–0.25 mg/kg repeated at 1 h

intervals) Psychosis not usually a problem with

low-dose ketamine Local anaesthetic block (LA) LA – see notes in ‘Overview’

Post - operative Gabapentin (divided doses 200–1,800 mg/day titrate dose according to age. Caution in renal failure)

Gabapentin – dose reduction in renal failure. Continue for 1 month post-op. Wean off over 2 weeks

Ketamine – not for intracranial surgery Ketamine – not for intracranial surgery Avoid if possible in all patients post-op Psychosis not usually a problem with

low doses (10–50 mg orally three times daily)

Relative Contraindications for Commonly Used Analgesics in the Neurosurgical Population

NSAIDs

The use of NSAIDs in neurosurgical patients is controversial. There are no pub-lished studies about their use in this population. Theoretically, they increase the risk of post-operative bleeding due to their inhibitory effect on platelet function, thus neurosurgeons have great concerns regarding their use, particular in the context of craniotomies and spinal surgery. Following elective supra-tentorial surgery it is highly unusual for patients to present with an intra-cranial haematoma if they have regained their pre-operative status by 6 h post-surgery. In our institution, we have applied this fi nding to our entire neurosurgical population and introduce NSAIDs after 6 h, if the post-operative course of any type of elective surgery has been uncomplicated and there is nothing to suggest a clotting disorder. Introduction of NSAIDs may be delayed in high-risk cases (e.g. spinal cord tumours, large menin-gioma resections, and ‘deep brain’ surgery).

Another concern with the use of NSAIDs is possible impairment of bone fusion (through interference with the complex regulatory system of bone formation that includes prostaglandins) which could be signifi cant following spinal fusion. There is no evidence in humans to support this.

Opioids

If used in doses just suffi cient to relieve pain, they will not signifi cantly affect respi-ratory drive, thus avoiding an increase in PaCO

2 with consequent effects on increas-

ing ICP. Careful titration is the key to the safe use of opioids. Following craniotomy very

small doses may be highly effective (e.g., 1–2 mg morphine repeated if necessary at 5 min intervals in the immediate post-operative phase followed by 5–10 mg orally at later stages). This is in contradistinction to patients in the ‘Major’ and ‘Complex Major Pain’ categories who invariably require much higher doses.

Patient-controlled analgesic (PCA) devices have been used successfully without complication following craniotomy and subarachnoid haemorrhage. For the use of morphine-PCA, some practitioners suggest low 4 h limits (e.g. 15 mg) and re-eval-uate the patient before further dose increase. Patients after major spinal surgery frequently benefi t from additional p.o. slow-release morphine preparations as sup-plementation of the PCA treatment due to more extensive pain levels; however, this requires a high level of patient supervision, such as an HDU environment. Endtidal CO

2 -feedback-control PCA devices have been introduced in an attempt to improve

patient safety when opioid self-administration is desired.

Crisis Management

Nociceptive Pain

Severe nociceptive pain is easier to treat than severe neuropathic pain. Whenever severe pain is present the cause of the pain should be actively sought. There should be a low threshold for further investigation, if it persists or is diffi cult to control. In the late post-operative phase, this may require admission to an HDU for rapid con-trol of pain by intravenous boluses of opioids and other adjuncts.

Neuropathic Pain

Neuropathic pain is classically described as aching, burning, shooting, or stabbing. It may be paroxysmal or spontaneous with no precipitating cause and may be asso-ciated with hyperalgesia or allodynia. It may be a new phenomenon post-operatively or an exacerbation of pre-existing neuropathic pain. It can be very diffi cult to relieve. Although classically resistant to opioids these should be tried to assess whether they are of any benefi t. Dexamethasone (4 mg four times daily for 48 h) can be very effective in the early post-operative phase, if oedema of nerve roots is thought a probable cause. There should be a low threshold to the introduction of gabapentin or amitriptyline if signifi cant neuropathic pain persists. Carbamazepine is the most effective treatment for trigeminal neuralgia (sometimes exacerbated following microvascular decompression) but has a poor side-effect profi le. There are success-ful reports of the use of intra-nasal sumatriptan in refractory cases of trigeminal neuralgia (caution should be exercised in patients with ischaemic heart disease).

Neuropathic pain following spinal cord injury and brachial plexus avulsion is common and can be severe. There is evidence to support benefi t from opioids, ket-amine infusion, and intravenous lidocaine. The latter two have to be administered in an HDU environment. Benzodiazepines may contribute to the management of refractory pain. Their use should be strictly short term and over-sedation and its attendant risks avoided.

Side Effects of Treatment

Constipation, nausea and so on are common post-operatively. They should be antic-ipated and active measures taken to prevent them. Several analgesic have sedative effects on the patients, particularly opioids. Awareness of the possible confounding effects of the analgesic treatment on mental status and neurologic presentation is of paramount importance in the perioperative management of neurosurgical patients. Overmedication with analgesics may result in differential diagnostic problems, which should trigger an immediate neurologic evaluation and frequently require emergency CT imaging of the cranium.

essentials of neurosurgical anesthesia & critical care || post-operative pain management in...

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