Respiratory, Neurological, and Analgesic/Sedation Pharmacology

Respiratory Pharmacology in Prehospital Care

Respiratory emergencies are among the most common calls EMS providers answer. Several drug classes are used to restore or protect the airway and improve ventilation.

Bronchodilators open constricted airways by relaxing bronchial smooth muscle. The most frequently used prehospital bronchodilators are short-acting beta-2 agonists such as albuterol (salbutamol). Albuterol acts on beta-2 adrenergic receptors in bronchial smooth muscle, causing relaxation and widening of the airway lumen. It is indicated for bronchospasm from acute asthma, COPD exacerbation, and anaphylaxis with bronchospasm. It is given by nebulization or metered-dose inhaler. Side effects include tachycardia, tremor, and hypokalemia with repeated doses. Ipratropium bromide is an anticholinergic bronchodilator often combined with albuterol; it blocks muscarinic receptors to reduce bronchoconstriction and secretions. Contraindications to ipratropium include hypersensitivity to atropine or peanuts (some formulations). Monitoring: continuous SpO2, respiratory rate, lung sounds before and after, and heart rate because beta-agonists can cause or worsen tachycardia.

For severe asthma unresponsive to inhaled therapy, magnesium sulfate (IV) acts as a smooth muscle relaxant and may be carried by ALS units. It must be given slowly; rapid infusion causes hypotension and flushing. Monitor blood pressure and deep tendon reflexes.

Epinephrine (IM or IV) is the cornerstone drug for anaphylaxis with bronchospasm and severe asthma as a secondary option; it stimulates both alpha and beta receptors to reverse bronchospasm and vasoconstriction.

Neuromuscular Blocking Agents and Rapid Sequence Intubation

Neuromuscular blocking agents (NMBAs) paralyze skeletal muscle by blocking acetylcholine at the neuromuscular junction. They do not provide sedation or analgesia; the patient remains conscious unless a sedative is given concurrently. This is the most critical safety point for NMBAs: never administer an NMBA without an appropriate sedative/analgesic agent.

NMBAs are divided into two classes:

• Depolarizing agents (e.g., succinylcholine) bind acetylcholine receptors and cause initial muscle fasciculations, then paralysis. Onset is very rapid (about 45–60 seconds). Duration is short (roughly 10–15 minutes) because it is hydrolyzed by plasma cholinesterase. Contraindications include known or suspected hyperkalemia, personal or family history of malignant hyperthermia, crush injuries older than 24–48 hours, burns, denervation injuries, and prolonged immobilization (risk of fatal hyperkalemia from receptor upregulation).
• Non-depolarizing agents (e.g., rocuronium, vecuronium) compete with acetylcholine without depolarizing the membrane. Onset is somewhat slower than succinylcholine (rocuronium at high doses approaches succinylcholine onset). Duration is longer. Sugammadex can reverse rocuronium rapidly where available.

Rapid sequence intubation (RSI) is the simultaneous administration of a sedative/induction agent and an NMBA to facilitate intubation while minimizing aspiration risk. RSI is a high-stakes intervention requiring advanced training and system medical-director authorization. Monitoring requirements: SpO2 before, during, and continuously after; ETCO2 waveform capnography after intubation to confirm and monitor tube placement; cardiac monitor; blood pressure.

Analgesics in EMS

Pain management is an essential and often undertreated part of prehospital care. The main categories are:

Opioid analgesics (e.g., morphine, fentanyl) bind mu-opioid receptors in the CNS to reduce pain perception. Fentanyl is lipid-soluble, fast-acting, and relatively hemodynamically stable, making it popular in EMS. Major risks: respiratory depression, hypotension, nausea. Naloxone reverses opioid effects and must be available any time an opioid is administered. Monitor respiratory rate, SpO2, blood pressure, and level of consciousness.

Ketamine is a dissociative anesthetic and analgesic that blocks NMDA receptors. At sub-dissociative (low) doses it provides analgesia without full dissociation. At higher doses it produces dissociative anesthesia for procedures or RSI induction. Benefits: generally maintains airway reflexes and hemodynamic stability, making it valuable for hypotensive trauma patients. Risks: laryngospasm (rare), emergence reactions, increased secretions. Monitoring: SpO2, level of consciousness using a sedation scale, and airway assessment.

Sedatives

Benzodiazepines (e.g., diazepam, midazolam, lorazepam) enhance GABA activity, producing sedation, anxiolysis, and anticonvulsant effects. Midazolam is short-acting and water-soluble, making it practical in the field. Risk: respiratory depression, especially combined with opioids. Monitor respiratory status and SpO2 closely.

Sedation scales (e.g., the Richmond Agitation-Sedation Scale, RAMSAY) provide objective reassessment of sedation depth after drug administration. A specific target score should be documented.

Anticonvulsants

Seizure management in prehospital care focuses on benzodiazepines as first-line agents. Midazolam, diazepam, and lorazepam all terminate active seizures by enhancing inhibitory GABA signaling. Intranasal or IM midazolam is effective when IV access is unavailable. Contraindications: benzodiazepines should be used cautiously with known respiratory compromise; have airway management equipment ready.

For refractory status epilepticus, some ALS systems carry levetiracetam or valproate for second-line treatment under medical direction.

Universal Monitoring and Safety Principles

• Always reassess vital signs, SpO2, and ETCO2 (where applicable) before and after every drug administration.
• Document drug name, dose, route, time, and patient response.
• Confirm allergies before administration.
• Know your system's approved drug list and scope of practice; do not administer any agent outside your medical-director protocol.
• Maintain reversal agents (naloxone, sugammadex if available) and airway equipment ready whenever administering sedatives or NMBAs.