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CHAPTER 22: Pain Control, Sedation, and Use of Muscle Relaxants 147

Clearly, intravenous injection remains the preferred route, whether it further compromise hemodynamic stability. Drugs for treating hemo-
is continuous or intermittent boluses. It is important to note that when dynamic instability after central neuraxial blockade include ephedrine
initiating a continuous infusion or increasing the infusion rate that a (α and β agonist, 5-10 mg), epinephrine (10-100 μg), and atropine
bolus intermittent dose should be administered prior to initiation. This (0.4 mg). Genitourinary blockade (parasympathetic S2-S4) with result-
will optimize the medication and the patient will achieve pain control in ing urinary retention is problematic, occasionally in patients without
a faster time period. bladder catheters.
Opiate withdrawal can be seen in patients receiving opiates for Complications Epidural hematoma formation is a rare but potentially
extended periods when the drugs are discontinued suddenly. Patients devastating complication of central neuraxial blockade. Although exact
who abuse opiates are at risk for this when hospitalized during criti- cutoff values precluding this approach in patients with coagulation
cal illness. One study of trauma/surgical ICU patients reported a 32% disturbances are not known, platelet counts less than 50,000/μL or
incidence of withdrawal in patients receiving opiates and/or sedatives international normalized ratios above 2 generally are considered contra-
who were in the ICU for more than 1 week. Those manifesting with- indications. There is controversy regarding lesser degrees of coagulation
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drawal received higher opiate and benzodiazepine drug doses than their abnormalities because of the lack of outcomes data; however, a con-
counterparts who did not experience withdrawal. The signs and symp- servative approach—where a normal coagulation state is required—is
toms seen in withdrawal are mostly nonspecific. They include pupillary typically adhered to by most clinicians. The use of prophylactic heparin
dilation, sweating, lacrimation, rhinorrhea, piloerection, tachycardia, has been linked to epidural or spinal hematoma formation. Such case
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vomiting, diarrhea, hypertension, yawning, fever, tachypnea, restless- reports have led to recommendations that when prophylactic or low-
ness, irritability, increased sensitivity to pain, nausea, cramps, muscle molecular weight heparin (LMWH) is used perioperatively, neuraxial
aches, dysphoria, insomnia, symptoms of opioid craving, and anxiety. block should be delayed for 10 to 12 hours after the last dose. Indeed,
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The lack of specificity for many of these signs and symptoms may make most recommend leaving existing epidural catheters in place in patients
it difficult to establish a diagnosis of opiate withdrawal in critically ill with coagulation abnormalities until these problems are corrected. In
patients. Patients without previous illicit drug use may also experience 1997, the Food and Drug Administration (FDA) issued a public health
opiate withdrawal when pharmacologically administered opiates given advisory regarding reports of epidural or spinal hematomas with the
for extended periods are stopped suddenly. Whether downward titra- concurrent use of LMWH and spinal-epidural anesthesia or lumbar
tion of opiate doses or regular interruption of opiate administration puncture. Fortunately, the incidence of complications from epidural
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can prevent this is not known. Additionally, titration to a longer acting anesthesia is extremely low. A study of over 4000 patients scheduled
opiate in the form of transdermal fentanyl patch or methadone can be for abdominal or abdominothoracic surgery reported a predicted
considered once the patient is out of the acute phase of their illness. maximum risk for permanent neurologic complications from epidural
Once initiated, the longer acting opiates can slowly be weaned off to placement of 0.07%. An epidural hematoma may be difficult to detect
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prevent withdrawal. in a critically ill patient. New motor deficits and back pain are the most
■ REGIONAL TECHNIQUES FOR ANALGESIA common early signs. Ideally, an awake, interactive patient is preferred so
that serial neurologic examinations can be performed.
Epidural Analgesia: Regional analgesic techniques may be effective Epidural catheter infection is another rare complication. Avoiding
strategies, particularly for postoperative analgesia. Epidural adminis- placement of catheters through inflamed or infected skin is mandatory
tration of pharmacologic agents is an alternative approach to systemic and certainly will reduce this complication risk. Careful, frequent assess-
administration. Local anesthetics may be used to block sensory nerve ments of skin entry sites and catheter dressings are an important part of
transmission. Autonomic nerves are more sensitive to local anesthet- the care of these catheters. Some clinicians advise against placement
ics than sensory nerves. Therefore, loss of sympathetic vascular tone of these catheters in patients with bacteremia or sepsis, although there is
is common with epidural local anesthetics. Motor nerves are most some controversy surrounding this recommendation owing to a paucity
resistant to epidural local anesthetics. of outcomes data. Exact guidelines for the use of epidural analgesia in
Ideally, an epidural catheter is placed at the spinal level that is at the critical illness have not been established. Indeed, it is clear that there is
same level as the pain source. For example, thoracic epidural catheters wide practice variation regarding the use of this technique in critically
frequently are used for patients undergoing thoracic surgical proce- ill patients. 32
dures to optimize the ability to cough and deep breathe after surgery. Neuraxial Opiate Analgesia: Opiates are also used frequently for neur-
Although any local anesthetic may be used, bupivacaine is the most axial analgesia. The presence of opiate receptors in the spinal cord
commonly used drug because of its long duration of action and prefer- was noted many years ago, 33,34 and spinal opiate-mediated analgesia
ential blockade of sensory over motor neurons. A relatively dilute, high- is currently a mainstay of regional anesthesia. Opiate receptors found
volume concentration of local anesthetic is preferred (eg, bupivacaine on the dorsal region of the spinal cord (substantia gelatinosa) medi-
0.125%-0.25%) because of spread over a wider dermatomal distribution. ate analgesia. Analgesia is profound and prolonged with water-soluble
However, some studies have reported that high-concentration, low- opiates such as morphine. Lipid-soluble opiates such as fentanyl have
volume dosing regimens may produce similar analgesia and patient a more rapid onset than morphine but a shorter duration. A single
satisfaction but less profound motor block and improved hemodynamic dose of epidural fentanyl may last 2 to 4 hours, whereas a single dose
stability. Continuous infusions of local anesthetic are typically used, of epidural morphine typically lasts 16 to 24 hours. Accordingly,
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which may provide effective analgesia for days. fentanyl usually is given by continuous infusion through epidural
Side Effects Although central neuraxial blockade is an extremely effec- catheters. Neuraxial opiates can also be given by intrathecal routes.
tive analgesic technique, side effects such as hypotension may limit Much smaller doses are needed when opiates are given intrathe-
its use in critically ill patients. Inevitably, there is some sympathetic cally—typically 10% of the epidural dose is adequate. Opiates given
blockade with administration of local anesthetics for central neuraxial by neuraxial routes produce effective analgesia with less alteration in
block. The resulting venodilation and increase in venous capacitance mental status than systemic opiates. The analgesia tends to be distrib-
produces a relative hypovolemia. Accordingly, patients are routinely uted dermatomally in the region of the spinal cord where the drug is
given crystalloid prior to administration of epidural (or spinal) local administered when lipid-soluble drugs such as fentanyl are used. On
anesthetics. Obviously, patients with hemodynamic instability (eg, septic the other hand, water-soluble drugs such as morphine tend to move
or hemorrhagic shock) may not tolerate decreases in sympathetic tone. rostrally regardless of the spinal cord level of injection. Importantly,
Sympathetic blockade at a high level may block outflow from the cardiac when lipid-soluble neuraxial opiates are used, the injection site must
accelerator fibers at the T1-T4 levels. The resulting bradycardia may be at the same level as the pain source (eg, thoracic epidural after

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