Michael S. Mitchell
EPIDEMIOLOGY
Acute pain is present in 50% to 60% of patients presenting to the emergency department.
Factors contributing to inadequate pain control, or oligoanalgesia, include a limited understanding of the related pharmacology, misunderstanding of the patient’s perception of pain, and fear of serious side effects.
Procedural sedation, formerly called conscious sedation, may be indicated for fracture manipulation or joint reduction, abscess drainage, laceration repair, tube thoracostomy, cardioversion, or a diagnostic study.
PATHOPHYSIOLOGY
Noxious stimuli are first registered peripherally by nociceptors, C fibers, A-ć fibers, and free nerve endings, resulting in the release of glutamate, substance P, neurokinin A, and calcitonin gene-related peptide within the spinal cord.
Pain is modulated at the level of the dorsal root ganglion, inhibitory interneurons, and ascending pain tracts.
Cognitive interpretation, localization, and identification of pain occur at the level of the hypothalamus, thalamus, limbus, and reticular activating system.
CLINICAL FEATURES
The subjective interpretation of pain is variable. Therefore, pain is best assessed using a validated, age-appropriate, objective pain scale.
Competent patients who are awake and cooperative can often reliably localize pain and determine its quality and severity.
Patients who have difficulty communicating with their caregivers due to cultural differences, extremes of age, language barriers, or mental illness may not be able to describe and localize pain.
Physiologic responses to pain and anxiety are nonspecific, but include tachycardia, blood pressure elevation, tachypnea, diaphoresis, flushing or pallor, nausea, and muscle tension.
Behavioral responses to pain and anxiety include facial expressions, posturing, crying, and vocalization.
EMERGENCY DEPARTMENT CARE AND DISPOSITION
Nonpharmacologic treatment of pain may be used alone or adjunctively. Examples include application of heat or cold, immobilization or elevation of injured extremities, explanation and reassurance, relaxation, distraction, guided imagery, and biofeedback.
When pharmacologic intervention is necessary, the desired effect, the route of delivery, and the desired duration of effect should be considered in determining the ideal agent.
ANALGESIA IN ADULTS
NONOPIOIDS
Nonopioid agents may be used alone for mild pain, or adjunctively with opiates for moderate to severe pain. Nonopioid analgesics cause no respiratory depression or sedation.
Acetaminophen is an analgesic and anti-inflammatory agent with no antiplatelet effects that is safe in all age groups. Hepatotoxicity may occur in doses above 140 milligrams/kg/d.
Nonsteroidal anti-inflammatory drugs (NSAIDs) include aspirin, naproxen, indomethacin, ibuprofen, and ketorolac. NSAIDs are analgesics and anti-inflammatory agents with opiate dose-sparing effects, but may cause platelet dysfunction, impaired coagulation, gastrointestinal irritation, and bleeding.
Aspirin also may induce bronchospasm and should be avoided in some asthmatic patients.
OPIOIDS
Opioids have analgesic and sedative effects, but may cause respiratory depression, nausea and vomiting, constipation, urinary retention, pruritus, confusion, and muscle rigidity.
Morphine is a naturally occurring opiate with a 5- to 20-minute onset of effect, a 10- to 30-minute peak effect, and a 2- to 6-hour duration. The dose of morphine is 0.1–1.0 milligram/kg and is commonly administered IV or IM. Morphine may cause hypotension due to histamine release.
Meperidine is a semisynthetic opiate whose use is discouraged in the ED due to the CNS toxicity of its metabolite normeperidine, significant histamine release, and a higher risk of addiction than other opiates.
Hydromorphone is a semisynthetic opiate with a 5- to 20-minute onset of effect, a 3- to 4-hour duration of effect, and less sedation and nausea than morphine. The dose of hydromorphone is 1–2 milligrams IV (0.015 milligram/kg IV pediatric).
PEDIATRIC PAIN MANAGEMENT
Pain experienced by pediatric patients is often unrecognized and undertreated.
The pain these patients feel may be exacerbated by their anxiety, which is oftentimes tied to their developmental stage.
Infants experience pain.
Toddlers experience anxiety, greatly exacerbated by their normal developmental phenomenon of “stranger anxiety.” It is necessary to involve the parents in all aspects of pain control and procedures.
School-aged children usually respond well to distraction techniques.
Adolescents can experience great anxiety with pain and painful procedures, which should be both anticipated and managed.
Pain is managed similarly as adults, with two important considerations: (1) children require more opioid proportionate to their weight and (2) children may not openly indicate pain; thus their pain should be anticipated and treated.
NSAIDs are given for mild pain. Ibuprofen is reserved for those children older than 6 months.
Opioids are given for moderate to severe pain. NSAIDs should be given in conjunction with opioids.
Meperidine is not recommended for children.
PEDIATRIC ANXIOLYSIS MANAGEMENT
Anxiety potentiates pain and can be managed with soothing techniques, distraction, and parental assistance during times of pain and during painful procedures.
Midazolam is a choice agent for use in the ED given its short duration of action and can be used in a variety of routes.
Midazolam can be given PO (0.5 milligram/kg), IV (0.05–05.0 milligram/kg), or intranasally (IN) (0.2 milligram/kg). The oral route takes approximately 20 minutes and can be variable in efficacy. IV and IN routes are generally more predictable. The IN preparation may produce a burning sensation in the nares.
Be prepared for potential paradoxical reactions to benzodiazepines as well as respiratory depression that can be seen with this medication class.
LOCAL AND REGIONAL ANESTHESIA
Local anesthesia can be obtained by infiltrating directly into the area, infiltrating into the area of the peripheral nerves supplying the area, or infusing into the venous system supplying the area to be anesthetized.
Local anesthetics are divided into two classes: amides and esters. Lidocaine is the prototype amide, and procaine the prototype ester. Bupivacaine is an amide anesthetic with duration of action of 2–6 hours, and is preferred for prolonged procedures.
Local anesthetics work by blocking sodium channels and prohibiting the nerve impulse propagation.
The injection pain of local anesthetics can be minimized by slow injection of warm, bicarbonate-buffered solution through a 27- or 30-gauge needle. Also, it is recommended to inject through the margins of the wound rather than into the surrounding, intact skin.
The addition of epinephrine to lidocaine extends the duration of anesthesia and slows systemic absorption. Epinephrine is tolerated for use in end-arterial fields in selected healthy patients, but should be avoided in those with digital vascular injuries, Raynaud disease, or other vascular supply problems.
Local anesthetic toxicity from excessive total dose or inadvertent IV injection can lead to cardiovascular depression, arrhythmias, seizures, and death. The maximum dose of lidocaine is 4.5 milligrams/kg without epinephrine, and 7 milligrams/kg with epinephrine.
Aspiration prior to injection of the anesthetic is necessary to prevent inadvertent IV injection.
In patients who cannot tolerate amides and esters (ie, allergy), both diphenhydramine and benzyl alcohol with epinephrine are alternatives.
TOPICAL ANESTHESIA
Topical anesthetics reduce the discomfort of painful procedures, decrease the need for local infiltration of anesthetics, and maintain wound edges.
The most common topical anesthetics for ED use are lidocaine, epinephrine, tetracaine (LET), liposome-encapsulated lidocaine (LMX), and lidocaine prilocaine (EMLA).
EMLA and LMX are reserved for use on intact skin. LET is for nonintact skin.
Onset of action: EMLA: 30–60 minutes, LMX and LET: 30 minutes.
REGIONAL ANESTHESIA
The following is a brief discussion of regional blocks. Refer to the Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 7th ed. Chapter 40 as well as view videos of each block on the AccessEmergencyMedicine Web site at http://www.accessemergencymedicine.com/multimedia.aspx.
Regional anesthesia is a technique of infiltrating local anesthetic agents adjacent to peripheral nerves and is ideal for complicated lacerations, fractures, and dislocations. Prior to administering regional anesthesia, neurovascular status must be assessed.
Topical anesthetic application may reduce the pain of injection of the regional anesthesia. The onset of action is longer than for typical dermal infiltration. Optimal analgesia is obtained in 10–20 minutes with lidocaine and 15–30 minutes with bupivacaine.
Anatomic variations can distort the usual “landmarks.” Ultrasound guidance to locate the nerve may improve the performance.
DIGITAL BLOCKS
Digital nerve block: Provides anesthesia to the entire finger. See Fig. 9-1.
FIG. 9-1. Digital nerve block. Anesthetic placed as shown blocks both the dorsal (a) and palmar (b) digital nerves, ensuring circumferential anesthesia of the finger. By using the sequence shown, the prior injection provides relief from the injection to follow. See Digital Nerve Block for further details. (Courtesy of Timothy Sweeney, MD.)
Application is to the nerves that lie on the lateral aspects of the finger.
Technique: Inject the finger at the proximal aspect along the lateral edge from the dorsal aspect. Deposit anesthetic and inject additional anesthetic as the needle is withdrawn. Next, insert the needle on the dorsal surface and direct it across the skin to the medial aspect of the finger. Deposit anesthetic and inject while withdrawing needle. Finally, inject over the medial aspect dorsal surface with the same technique as the other side.
Flexor tendon sheath digital nerve block: Identify the distal palmar crease on the palmar aspect of the hand. Have the patient flex the finger against resistance to improve visualization of the flexor tendon (see Fig. 9-2).
Technique: Prepare a sterile block site at the distal palmar crease of the digit to be blocked and insert the needle at a 45-degree angle to the palmar plane with the tip pointed distally. Advance the needle until a “pop” is felt, indicating penetration of the flexor tendon sheath. Inject 2–3 mL of anesthetic solution. If bone is struck before the “pop” is felt, withdraw the needle 2–3 mm and inject the solution.
FIG. 9-2. Transthecal (flexor tendon sheath) digital nerve block. The point of injection is in the middle of the flexor tendon sheath at the level of the distal palmar crease. A 25-gauge needle is advanced at 45 degrees, tip directed distally until it enters the flexor tendon sheath (shown in blue) or until bone is encountered. When the needle is properly placed within the flexor tendon sheath, the anesthetic solution is injected. Diffusion out of the tendon sheath blocks adjacent palmar digital nerves. See Transthecal or Flexor Tendon Sheath Digital Nerve Block for further details. (Courtesy of Timothy Sweeney, MD.)
RADIAL NERVE BLOCK
Provides anesthesia to the dorsal lateral half of the hand and the dorsal aspect of the thumb.
Technique: Inject a large volume of anesthetic (5 mL) just proximal to the anatomic snuffbox.
ULNAR NERVE BLOCK
Provides anesthesia to the entire fifth digit, half of the fourth digit, and the medial aspect of the hand and wrist.
Technique: Deposit anesthetic under the flexor carpi ulnaris tendon just proximal to the distal wrist crease.
DEEP PERONEAL NERVE BLOCK
Provides anesthesia to the web space of the first and second toes, and a small area proximal to the first and second toes on the plantar aspect.
Technique: Deposit anesthetic at the medial malleolus between the extensor hallucis longus and the tibialis anterior tendon.
POSTERIOR TIBIAL NERVE BLOCK
Provides anesthesia to the plantar aspect of the foot.
Technique: Deposit anesthetic posterior to the posterior tibial artery found at the posterior edge of the medial malleolus.
SUPERFICIAL PERONEAL NERVE BLOCK
Provides anesthesia to the dorsal lateral aspect of the foot.
Technique: Deposit anesthetic between the lateral malleolus and the tibialis anterior tendon.
SURAL NERVE BLOCK
Provides anesthesia to the lateral aspect of the ankle.
Technique: Deposit anesthetic between the superior portion of the lateral malleolus and the Achilles tendon.
SAPHENOUS NERVE BLOCK
Provides anesthesia to the medial aspect of the ankle.
Technique: Deposit anesthetic between the tibialis anterior tendon and the superior border of the medial malleolus.
SUPRAORBITAL AND SUPRATROCHLEAR NERVE BLOCKS
Provides anesthesia to the forehead from the vertex of the scalp to the bridge of the nose.
Technique: Deposit anesthetic superior to the eyebrow in line with the pupil. Further, direct needle medially after initial deposit and a wheal is formed to reach the edge of the eyebrow.
INFRAORBITAL NERVE BLOCK
Provides anesthesia to the lower lid, medial cheek, and both the ipsilateral side of nose and upper lip.
Technique: Insert needle inside the mouth at the gingival reflection above the maxillary canine and direct needle superiorly.
MENTAL NERVE BLOCK
Provides anesthesia to the labial mucosa, gingival, and the lower lip adjacent to the incisors and canines.
Technique: Direct needle and deposit anesthetic from the mouth inferior to the canine at the gingival reflection inferiorly to the mental foramen.
AURICULAR BLOCK
Provides anesthesia to the entire ear.
Technique: Deposit anesthetic into several places. From the inferior and superior aspect of the ear, inject anterior and posterior to the ear and deposit anesthetic while withdrawing the needle.
FEMORAL NERVE BLOCK
Provides anesthesia to the anterior thigh and medial leg.
Technique: Deposit anesthetic at the level of the femoral nerve. The needle is inserted 1 cm lateral to the femoral artery at the level of the inguinal crease. The needle is directed in the cephalad direction to the femoral nerve, which lies about 2 cm deep. The needle is inserted until the patient experiences par-esthesias. The needle is retracted slightly and 20 mL of anesthetic is delivered.
PROCEDURAL SEDATION AND ANALGESIA
Sedation is a pharmacologically induced decrease in environmental awareness. Analgesia is relief from the perception of pain.
Sedation level is on a continuum from minimal sedation (patient can respond to verbal stimuli) to deep sedation (patient has purposeful responses with repeated painful stimuli). Only the lightest level of sedation that is necessary for the planned procedure should be used.
The risk of adverse respiratory events increase as the patient advances along the continuum from minimal to deep sedation.
It is imperative to score each patient prior to sedation on the American Society of Anesthesiologists’ (ASA) physical classification system in order to predict their risk of adverse events. Class I and II patients have at most a mild systemic illness and have a low risk of adverse events. Class III and higher (Class III is severe systemic disease) patients have a much higher risk of adverse events.
Assess the Mallampati grading system scale for airways (I–IV) for each patient to assess ease of intubation should it be required.
Physical examination should focus on potential airway or cardiorespiratory problems, including abnormal airway anatomy such as shortened or enlarged neck, micrognathia, trismus, or a large tongue.
Aspiration risk must be managed in accordance with the level of desired sedation. Those patients who have been without oral intake for greater than 3 hours are at a low risk of aspiration. Patients who have ingested clear liquids less than 3 hours prior to desired sedation with urgent indications for the procedure may have a greater risk of aspiration, but clinicians may proceed with sedation for procedures that are truly urgent.
In the case of patient ingestion of a light snack or meal less than 3 hours prior to the desired sedation for a procedure, the clinicians should weigh the urgency of the procedure against the risk for adverse effects as these patients are at the highest risk for aspiration.
The risk for adverse events increases with sedation grade.
The sedation area should include all necessary, size-appropriate equipment for airway management including oxygen, materials needed for endotracheal intubation, suctioning, and alternate airways. Reversal agents, if appropriate, should be readily available.
Minimal sedation requires only direct observation; however, moderate and deep sedation require mechanical monitoring including ongoing cardiorespiratory monitoring, pulse oximetry, and end-tidal CO2capnography. Capnography can detect ventilator changes before clinical observation and prior to the ensuing hypoxemia.
Analgesics are recommended prior to procedural sedation, but may increase the risk of respiratory adverse events. Ketamine possesses both analgesic and anxiolytic properties.
Procedural sedation agents often have a narrow therapeutic index. Administer these agents in small incremental doses, allowing adequate time for the development and assessment of peak effect. Continuous reassessment is required.
Precalculated doses of “rescue” or reversal agents should be at the bedside: naloxone, 0.1 milligram/kg every 2–3 minutes to reverse opiate-induced respiratory depression, and flumazenil, 0.01–01.0 milligram/kg every 1–2 minutes to reverse benzodiazepine-induced respiratory depression during procedural sedation.
Flumazenil should not be used on patients with a history of chronic benzodiazepine or tricyclic antide-pressant use due to the risk of seizures.
PROCEDURAL SEDATION AGENTS
For dosing and administration parameters of each agent, see Table 9-1.
TABLE 9-1 Sedation Agents for Procedural Sedation and Analgesia
NITROUS OXIDE
Used for minimal sedation in a 50:50 mixture with oxygen.
Relative contraindications to its use include pulmonary hypertension (pulmonary vasoconstricting properties and cardiac depressant), pregnancy (inhibits folate metabolism), and concern for pneumothorax.
N2O has opiate agonist properties, and therefore should be used with extreme caution if combined with a sedative or opiate to avoid deep sedation or general anesthesia.
MIDAZOLAM
Midazolam and other benzodiazepines potentiate the effects of CNS gamma-aminobutyric acid (GABA), resulting in chloride influx, which produces sedation, amnesia, anxiolysis, anticonvulsant effects, and respiratory depression.
This agent can be used solely or in conjunction with opioids.
It has a variety of routes, but the IV route is most predictable. Notably, the PO/PR/IM routes can have variable onset and duration secondary to differences in absorption and metabolism.
Intranasal midazolam is safe, but will irritate the nasal mucosa.
Midazolam can cause mild cardiovascular depression.
FENTANYL
This agent is a potent, short-acting opioid.
Rigid chest syndrome can occur with rapid infusion of fentanyl, but can be prevented by using a slow infusion rate and carefully flushing the IV line. Rigid chest is characterized by spasm of the respiratory muscles and is not overcome with opioid antagonists. Rigid chest is treated by neuromuscular paralysis and intubation.
METHOHEXITAL
Very short-acting barbiturate that is useful for quick procedures.
Respiratory depression is noted, especially with subsequent doses after the initial bolus dose.
PENTOBARBITAL
Short-acting barbiturate that has no analgesic properties.
Useful for procedures that are not painful (ie, radio-logic study).
CHLORAL HYDRATE
No longer recommended for use in the ED.
KETAMINE
Ketamine produces analgesia, amnesia, and dissociation with minimal respiratory depression.
It is a dissociative anesthetic and the dissociative phase is met once a dosing threshold is exceeded (typically above 1 milligram/kg infused).
Ketamine is a good agent to use for prolonged procedures (ie, hip spica cast placement on a toddler).
Ketamine has a favorable cardiorespiratory profile, but can cause laryngospasm. This occurs primarily in pediatric patients and usually is overcome with positive pressure ventilation with a bag-valve mask. Those at risk for laryngospasm include infants <3 months of age, those with upper respiratory tract infections, and those undergoing intraoral procedures.
Vomiting is frequently seen during recovery. Consider giving a pre-sedation dose of ondansetron.
Another common complication is bronchorrhea, which may be improved with the use of atropine, 0.01 milligram/kg IV, or glycopyrrolate, 0.004 milligram/kg IV The use of anticholinergic agents is controversial and may not be necessary.
Emergence reactions can occur in adolescents and adults. Midazolam can be given as an adjunct or in those patients who develop emergence reactions.
Ketamine increases intraocular pressure and should be avoided with eye injuries or glaucoma.
Ketamine may increase intracranial pressure; avoid using in the head-injured patient.
ETOMIDATE
Etomidate is an ultra-short-acting sedative agent increasingly used for procedural sedation.
Etomidate has minimal hemodynamic effects and a low risk of apnea.
Adverse effects may include vomiting, myoclonus, short-term adrenal suppression, and CNS depression.
PROPOFOL
Propofol is frequently used in the ED for sedation because it is easy to titrate.
Propofol does not have analgesic properties, thus pre-procedure analgesics are recommended.
Pain associated with administration of propofol can be attenuated by the coadministration of lidocaine, 0.05 milligram/kg.
Propofol is contraindicated in those with egg allergies, since it contains an egg lecithin emulsion.
Respiratory depression and apnea can occur, so rescue equipment should be readily available.
Propofol can induce hypotension. It is essential to attempt to correct hypotension prior to propofol administration.
PROPOFOL AND KETAMINE (“KETOFOL”)
The combination of propofol and ketamine is safe in both adult and pediatric patients.
The combination may provide benefit in attenuating certain side effects of each other; however, these effects remain controversial. Less propofol is required which may reduce hypotension. Less nausea and vomiting is seen than with ketamine alone. Respiratory depression associated with propofol is not diminished when using this combination.
Ketofol recovery time falls between propofol (short) and ketamine (long).
POST PROCEDURAL SEDATION CARE
Patients should be monitored until they return to baseline mental status.
Patients who vomit are at risk for aspiration until they return to baseline mental status.
SPECIAL CIRCUMSTANCES
CRITICALLY ILL PATIENTS
Etomidate is the agent of choice for those ASA III and higher.
Etomidate causes less hypotension than other agents.
Patients requiring sedation may require general anesthesia in the OR.
ELDERLY
Procedural sedation in the elderly is associated with more adverse events. The risk of respiratory depression and aspiration events is increased.
Remove dentures or bridges to prevent aspiration.
Etomidate may be a good choice for the reasons noted above. An analgesic must be used in addition to etomidate.
Reduce propofol dose by 50% doses from those recommended for younger adults because of a greater risk of respiratory depression.
EMERGENCY ENDOSCOPY
Vasovagal reactions can occur with passage of the endoscope causing bradycardia and hypotension.
There is increased risk of apnea, hypoxia, and aspiration due to the passage of the endoscope.
Topical anesthesia may be required to suppress the gag reflex, but may not be necessary if adequate IV sedation is achieved.
Droperidol reduces gagging during upper endoscopy. However, its use is associated with additional side effects including hypotension, dystonic reactions, and rarely, torsades de pointes cardiac dysrhythmia. Avoid using droperidol in patients with prolonged QT interval.
Promethazine combats nausea. Its strong alpha-adrenergic blocking effect can cause transient hypotension.
PROCEDURAL SEDATION IN CHILDREN
Involve the parents by allowing them be present for the beginning of the sedation, thereby reducing the child’s anxiety.
Attempt to create a nonstimulating environment for the young child experiencing procedural sedation. Suggestions for this include maintaining a quiet environment in the room prior to the procedural sedation, allowing the family to hold the child during the beginning of procedural sedation, and postponing placing monitoring equipment on the child until under sedation.
Ketamine and propofol are the most commonly used agents.
Ketamine can cause unpleasant dreams. This is an important consideration when choosing this agent for young children.
Reducing pre-sedation anxiety is essential and may reduce unpleasant dreams. Further, suggestions of “good” dreams may allow for the child to avoid the unpleasant dreams.
Administration of midazolam prior to ketamine is not proven to prevent emergence reactions in children and adolescents.
For further reading in Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 7th ed., see Chapter 38, “Acute Pain Management in Adults,” by James Ducharme; Chapter 39, “Pain Management in Infants and Children,” by William M. Lennarz; Chapter 40, “Local and Regional Anesthesia,” by Douglas C. Dillon and Michael A. Gibbs; and Chapter 41, “Procedural Sedation and Analgesia,” by James R. Miner.