Emergency Medicine

April 4, 2009

Acute Pain Management and Conscious Sedation

Filed under: Analgesia Anesthesia and Sedation — emergencymed @ 10:23 pm
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The underutilization of sedation and analgesia in the emergency department has been well documented. Reasons for this include misunderstanding of a patient’s response to pain, lack of knowledge of the pharmacokinetics of the various agents used, fear of serious side effects, and issues related to convenience. Patients at risk for receiving suboptimal treatment include children, those who cannot communicate with care givers, the elderly, and the cognitively impaired. It is crucial not to confuse sedation and analgesia.

Clinical Features
Physiologic responses to pain and anxiety include increased heart rate, blood pressure, and respiratory rate. Behavioral changes include facial expressions, posturing, crying, and vocalization. Pain is best assessed using objective scales. Subjective impressions are often incorrect. Pain relief is a dynamic process, and reassessment is mandatory.

Emergency Department Care and Disposition
When treating anxious patients or patients in need of uncomfortable procedures, one should begin with nonpharmacologic interventions (e.g., relaxation, distraction, psychoprophylaxis, biofeedback, and guided imagery). Communication should be appropriate for the developmental age of the patient. A gentle and unhurried approach is best. Procedures should be explained in a clear and honest manner, with time given for questions and answers. With children, discussing the procedure just before it is performed should minimize anticipation of painful procedures. Environmental adjustments, such as dimmed lights, a quiet room, and audiovisual input, may be helpful. Parents should be included in interventions, since their help may be crucial in comforting their child. Certain children will require restraints. Parents should be relieved of the responsibility of restraining their child. Once the necessity for pharmacologic interventions has been determined, consideration should be given to the need for sedation or analgesia, the route of delivery, and the desired duration of effects.

Systemic Analgesia and Sedation
Conscious sedation (CS) is a medically controlled state of depressed consciousness that allows protective reflexes to be maintained. Patients undergoing CS should be able to maintain a patent airway and respond to stimulation or commands. Indications for systemic analgesia and/or CS include treatment of severe pain, attenuation of pain and anxiety associated with procedures, rapid tranquilization, and the need to perform a diagnostic procedure.
Preparation Whenever systemic analgesia or sedation is used, the patient should be continuously monitored (cardiac monitor and pulse oximetry) and under constant observation by a dedicated health care provider who is trained in airway management. Oxygen, suction, and appropriately sized airway equipment should be readily accessible. Precalculated doses of reversal agents should be available: naloxone, 0.1 mg/kg per dose given every 2 to 3 min until desired effect to reverse opiates, flumazenil, 0.01 to 0.02 mg/kg, with additional 0.005 mg doses, to a maximum 0.2 mg per dose and 1 mg total. The half-life of naloxone and flumazenil may be shorter than that of the drugs they reverse. Therefore, patients who require reversal should be observed for a prolonged period of time to avoid rebound cardiovascular or respiratory depression. Flumazenil should not be used in patients on chronic benzodiazepine or tricyclic antidepressant therapy due to the risk of seizure. A baseline blood pressure, heart rate, respiratory rate, and level of consciousness should be assessed and documented every 5 to 10 min. Generally, administering medications intravenously (IV) is the best method for obtaining rapid and safe analgesia or sedation. Other routes may be appropriate (especially in children), but provide less reliable and slower clinical effects, limit the ability to titrate, and result in frequent under- or overmedication. The use of these agents should be individualized to the patient and planned procedure. The physician must consider his or her skill and expertise with the intended medications and what resources are available. Informed consent, with a discussion of the risks and benefits of CS, should be obtained. These agents have a narrow therapeutic index. Using the smallest effective total dose, given in small IV increments and allowing adequate time for peak effect, is generally the safest method of administering these agents.
Analgesia for brief procedures Opiates are the drugs of choice for analgesia. Fentanyl is a synthetic narcotic, that is 100 times more potent than morphine. It has almost immediate onset of action and approximately 30 min duration when administered IV. Fentanyl and other narcotics are relatively contraindicated in patients with hemodynamic or respiratory compromise, as well as those with altered mental status. Fentanyl is less likely to cause respiratory depression, histamine release, and cardiovascular compromise than are other opiates. Administering fentanyl slowly over 3 to 5 min can minimize respiratory depression. Fentanyl is associated with chest wall rigidity at higher doses (5 to 15 µg/kg), which may require naloxone reversal or neuromuscular blockage and intubation. The dose of fentanyl is 2 to 3 µg/kg, with additional doses titrated by 0.5 µg/kg until the desired level of analgesia is reached. Fentanyl is also available in a self-administered lozenge, which has been found practical in the pediatric patient.
Nitrous oxide is an effective analgesic that produces a state of conscious sedation with euphoria and dissociation. It can be used alone or in conjunction with local anesthetics. Nitrous oxide is delivered as a 30 to 50% mixture with oxygen. It should be self-administered through a system that is fail-safe against delivery of a hypoxic mixture. Peak effects are reached within 1 to 2 min, and the patient is fully aroused within minutes of cessation of therapy. Nitrous oxide has minimal respiratory or cardiovascular effects. It is contraindicated in patients who have recently been sedated with another agent, and those with altered mental status, balloon tipped catheters, dyspnea, severe chronic obstructive pulmonary disease, pneumothorax, eye injury, or obstructed viscous.
Ketamine is a dissociative analgesic that also has sedative properties. Ketamine is usually given intramuscularly (IM) or IV to adults. Oral (PO), rectal (PR), IM, and IV administration has been described in children. The dose of ketamine is 4 mg/kg when given PO, PR, and IM. A supplemental 2 mg/kg dose may be given. The IV dose is 1 mg/kg, with additional 0.25 mg/kg doses titrated to the desired effect. Atropine (0.01 mg/kg) is often used as an adjunct to control hypersalivation. Although airway reflexes are usually protected and bronchodilation occurs, ketamine can cause laryngospasm. Ketamine has catecholamine-releasing properties. It should be avoided in the setting of head trauma, and in patients with poor sympathetic tone or prolonged stress. Adults and older children may have unpleasant hallucinations when awakening from ketamine-induced sedation. Placing recovering patients in a darkened, quiet room may minimize this emergence reaction. Low-dose midazolam (0.01 mg/kg IM or IV or 0.1 mg/kg PO) attenuates this experience, but it may lead to respiratory depression.
Analgesia for longer procedures Morphine is the gold standard for this use. Meperidine is a synthetic derivative of morphine that is one-tenth as potent and has a shorter duration. Meperidine causes more histamine release than does morphine, and its primary metabolite, normeperidine, is bioactive and toxic (causing central nervous system excitation and seizures). Meperidine can cause a fatal reaction when used in patients taking monoamine oxidase inhibitors and can accumulate in patients with renal insufficiency. The IV dose of morphine is 0.1 mg/kg, with additional doses of 0.05 mg/kg titrated to the desired effect. The dose of meperidine is 1 mg/kg, with additional 0.5 mg/kg doses given, if necessary. Most adults will require a total dose of 1.5 to 3.0 mg/kg of meperidine for a painful procedure. An adult 1 mg dose of hydromorphone is equivalent to a 5 mg dose of morphine. The Demerol, Phenergar, Thorazine (DPT) cocktail is unreliable, can cause respiratory depression, and has a duration of action of more than 7 h. More appropriate regimens should be used in its place.
Hydroxyzine is synergistic with opiates and has intrinsic analgesic properties. Hydroxyzine, 0.5 mg/kg, can be given PO or IM in conjunction with narcotics. Hydroxyzine will reduce the incidence of nausea and vomiting associated with opiate administration.
Phenothiazines do not enhance analgesia and produce nonreversible sedation. Their use in this setting should be limited to the treatment of nausea.
Ketorolac is a nonsteroidal anti-inflammatory drug (NSAID) that can be given PO, IM, or IV. The IM and IV doses are 0.5 to 1 mg/kg (maximum 60 mg, 30 mg in the elderly). Ketorolac does not cause respiratory depression. It can be used in combination with opiate analgesics. The most common side effects are related to gastrointestinal irritation, platelet inhibition, and renal damage. Ketorolac has not been shown to be more effective than less expensive oral NSAIDs. It should not be used for more than 5 days.
Sedation for brief procedures Benzodiazepines are sedative agents that provide skeletal muscle relaxation, anxiolysis, and amnesia. They have no direct analgesic properties. When used in combination with opioids, it is generally safer to administer the benzodiazepine first for sedation or relaxation, followed by carefully titrating the opioid for analgesia. The dose of opioid required is usually lowered in these cases, and patients are more prone to developing respiratory compromise. Hypotension, another side effect of benzodiazepines, can be avoided by administering these agents slowly. Midazolam is a short-acting (30 to 40 min) benzodiazepine that has been successfully used by PO, PR, nasal, subcutaneous, IM, and IV routes. It is a potent sedative with excellent amnestic properties. An effective adult dosage regimen is 0.25 to 1 mg every 3 to 5 min, until sedation or muscular relaxation occurs. Lower dosages may be more appropriate for the elderly or intoxicated patient. Pediatric doses are IV 0.05 to 0.1 mg/kg per dose every 3 to 5 min (maximum single dose 2 mg, maximum total dose 0.2 mg/kg), IM 0.1 to 0.3 mg/kg, PO 0.5 to 0.75 mg/kg (maximum dose 15 mg), nasal 0.3 to 0.5 mg/kg (maximum dose 5 mg), and PR 0.25 to 0.5 mg/kg (maximum dose 15 mg).
The actions and side effects of barbiturates are similar to those of benzodiazepines. Two important differences must be noted: (1) barbiturates can increase airway tone and, therefore, should not be given to patients with moderate to severe airway disease; and (2) these agents must be used cautiously, since patients may rapidly progress from light sedation to deep sedation to general anesthesia.
Methohexital and thiopental are ultra–short-acting barbiturates, with methohexital having a shorter duration of action. Methohexital, 0.5 to 2 mg/kg, or thiopental, 1 to 5 mg/kg, will produce sedation within 1 to 2 min. These drugs are administered slowly by titrated incremental IV doses. Methohexital may be given rectally to children in doses of 20 mg/kg. Thiopental frequently causes hypotension, particularly when given rapidly. This effect is accentuated in the presence of hypovolemia, or preexisting heart disease. These agents may also cause laryngospasm and paradoxical excitation.
Propofol is an ultra–short-acting anesthetic. When given by infusion, its onset and resolution are rapid (5 to 10 min). It has antiemetic but no amnestic properties. Propofol can lead to profound cardiovascular and respiratory depression especially in the elderly. It is a relatively new drug for the emergency department. Its use in children is controversial. Propofol can be given as a bolus of 2.0 to 2.5 µg/kg, but an infusion is preferred, given at a rate of 25 µg/kg/min and titrated to the desired effect; then a maintenance infusion of 3 to 6 mg/kg/h is continued until the conclusion of the procedure.
Sedation for longer procedures Diazepam is a longer-acting benzodiazepine with anxiolytic and amnestic properties. It has been largely superseded by midazolam. Pentobarbital is a barbiturate that induces sleep and can be administered by various routes. Within 1 min, IV administration can lead to sleep that lasts for 15 to 60 min. Recommended dosage varies greatly. An initial 2.5 mg/kg (maximum, 100 mg) IV dose can be given, followed, as needed, every 5 min by an additional 1.25 mg/kg (maximum total 300 mg). Intramuscular dosage is 2 to 5 mg/kg, with a maximum dose of 100 to 200 mg. Pentobarbital can cause respiratory and cardiovascular depression, particularly when administered rapidly or in conjunction with a narcotic.
Chloral hydrate has been used successfully, particularly in children under 4 years old. It is unlikely to cause respiratory depression. Chloral hydrate can be administered PO or PR at a dosage of 75 mg/kg. Its main disadvantage is its 30- to 60-min onset of action and its prolonged duration (up to several hours).
Disposition Patients are eligible for discharge only when fully recovered. When discharged, the patient must be accompanied by an adult and should not drive. Instructions for care must be given to responsible accompanying adults, since many of these systemic agents impair recall.

Local and Regional Anesthesia
Local and regional anesthesia are essential for emergency department pain management. Agents can be administered topically, by infiltration, and IV. This discussion focuses on topical and infiltrative anesthesia, with a discussion of finger and toe blocks. For discussion of other nerve and regional blocks, please refer to Emergency Medicine: A Comprehensive Study Guide, 5th ed., Chap. 32. Newer, less invasive methods are becoming available.
Infiltrative anesthesia There are two classes of local anesthetics (LAs): amides and esters. Lidocaine is an amide anesthetic with excellent efficacy and a low toxicity profile. The onset of action is 2 to 5 min and the duration 1 to 2 h. Injection of lidocaine is painful due to its acidic pH. Pain can be minimized by buffering the lidocaine with bicarbonate (in a proportion of 1 NaHCO3:9 lidocaine), warming the medication before injection, using small gauge needles (27 or 30 gauge) for injection, and injecting the anesthetic slowly. The addition of epinephrine to lidocaine provides for a longer duration of anesthesia, provides wound homeostasis, and slows systemic absorption (thus decreasing toxicity). The addition of epinephrine increases the pain of injection by lowering the pH of the solution. Epinephrine also decreases local perfusion. It therefore cannot be used in an end-arterial field (i.e., digits, penis, nose, or ears). The vasoconstrictive properties of epinephrine may also make wounds more prone to infection. Bupivacaine has a longer duration than lidocaine and is preferred for prolonged procedures. The onset of action is similar to that of lidocaine. Buffering of bupivacaine is accomplished with 1 NaHCO3:29 bupivacaine. Procaine and tetracaine are ester anesthetics that can be used in patients with allergies to amide anesthetics.
The toxicity of LAs can be severe and lead to cardiovascular collapse, seizures, and death. Toxicity is related to total dose and mode of delivery. The absorption of these agents is site dependent. The maximum dose of lidocaine is 4.5 mg/kg without epinephrine, and 7 mg/kg with epinephrine. The maximum toxic doses of bupivacaine are 2 mg/kg without and 3 mg/kg with epinephrine. When used for intercostal nerve blocks, the maximum safe dose is 10 times less than the mentioned doses for lidocaine and bupivacaine. Please refer to Chap. 32 in Emergency Medicine: A Comprehensive Study Guide, 5th ed., for a full discussion on toxic doses and effects. Allergic reactions to LAs are rare and usually due to preservatives. The safest approach in a patient who claims to be allergic to an LA is to skin test with 0.1 mL of preservative-free anesthetic from the other class of LA. An alternative approach is to use diphenhydramine (0.5 to 1%) for anesthesia. This is also associated with significant toxicity, and its effectiveness is questionable.
Local anesthetic infiltration The most common use of LA is infiltration for wound repair or invasive painful procedures. When repairing wounds, LA is infiltrated into the wound margins or as a “field block” surrounding the wound. When infiltrating intact skin, raising a wheal may cause less pain on subsequent infiltration. LA can also be used in orthopedic procedures, such as fracture and joint reduction, by directly injecting the LA into the affected joint or fracture hematoma.
Digital blocks Finger and toe blocks are advantageous in that less anesthetic is needed, better anesthesia is obtained, and tissues are not distorted. The onset of anesthesia is delayed when compared to LA. Neurovascular status must be assessed and documented before the procedure. Lidocaine or bupivacaine are the most commonly used agents, depending on the time needed to perform the procedure. Epinephrine should not be used in these procedures. Complications include nerve injury and intravascular injection leading to systemic toxicity. Always aspirate before injecting to avoid inadvertent intravascular injection of LA.
The procedure for digital blocks involves sterile preparation of the skin, followed by the introduction of a 27 gauge or smaller needle into the skin (a skin wheal may be raised before deeper injection) and into one side of the extensor tendon of the affected finger just proximal to the web. After aspiration, approximately 1 mL of LA is injected into the tissue on the dorsal surface of the extensor tendon. The needle is advanced toward the palm until its tip is seen beneath volar skin at the base of the finger just distal to the web. After aspiration, 1 mL of LA is injected. Before removing the needle, redirect it across the opposite side of the finger and inject approximately 1 mL across the dorsal digital nerve. Five minutes later repeat the procedure on the opposite side of the finger (Fig. 10-1). An alternative method is to inject a 27 gauge needle into the web space between the affected and adjacent finger, directing the needle to the metacarpal joint of the affected finger. After aspiration, inject 1 to 2 mL into the area of the digital nerve. Before removal of the needle, advance the needle first dorsally and then volarly, and inject 1 mL of LA; repeat on the opposite side. Toes can be blocked in a similar fashion. Great toes can also be blocked using a modified collar block. A 27 gauge needle is introduced on the dorsolateral aspect of the base of the toe until it blanches the plantar skin. As the needle is withdrawn, 1.5 mL of LA is injected. Before the needle is removed, it is passed under the skin on the dorsal aspect of the toe, and 1.5 mL of LA is injected as the needle is withdrawn. The needle is reintroduced through the anesthetized skin on the dorsomedial aspect of the toe and advanced until the plantar skin is blanched; as the needle is withdrawn, 1.5 mL of LA is injected.
Topical anesthetics Common preparations of topical anesthetics (TAs) include tetracaine adrenaline cocaine (TAC) lidocaine epinephrine tetracaine (LET), lidocaine prilocaine (EMLA), and various preparations of lidocaine. TAC and LET are commonly used in place of infiltrative anesthesia. The advantages of these TAs are that they eliminate the need for injection, do not distort wound edges, provide good homeostasis, and are applied painlessly. TAC is a controlled substance, is more expensive, is more toxic, and is no more efficacious than LET. Both LET and TAC should be left in place for at least 20 min for maximal effect. Neither agent should be used on mucous membranes or in end-artery fields. TAC and LET are available in liquid preparations that are used to moisten a cotton applicator, which is then held on the wound. LET also is available in a gel form, which has the advantage of greater ease of application. Topical lidocaine is marketed in a solution, jelly, or ointment. Viscous lidocaine can be used for the temporary relief of inflamed mucous membranes. Lidocaine jelly should be used with the insertion of Foley catheters, the insertion of nasogastric tubes, and other painful procedures. As with infiltrative use of lidocaine, care must be taken not to exceed maximal doses. EMLA is a cream that is used on intact skin. It is particularly useful in the pediatric population to relieve pain associated with IV catheters, venipunctures, lumbar punctures, and other painful procedures. The main drawback of EMLA is that adequate analgesia usually requires 45 min to 1 h of application time.

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