Public Safety Training Facility
Monroe Community College
Rochester, New York
Post Graduate Paramedic CME
Pharmacological Agents in Airway Management
by Bob Breese, EMT-P
Pharmacologic agents are important adjuncts to airway management.
However, their use in the face of poor mechanical skills or judgment
may negate any pharmacologic benefit derived from these agents.
Proper airway management consists of adequate assessment,
identification of non-patent and difficult airway situations, proper
positioning, adequate suction and mastery of ventilatory skills.
Endotracheal intubation should be performed by the most experienced
responder present. Use of pharmacologic agents should only be
undertaken when other means of airway patency have failed.
Certain situations are contraindications for the use of intravenous
induction agents, while others are clearly indicated. Muscle
relaxants must only be administered when there is a certainty of
securing the airway.
Specific pharmacological agents are divided into: Sedative-Hypnotics,
Anxiolytics, Paralytics (muscle relaxants), Anticholinergic drying
agents and local anesthetics.
Review of basics regarding neuronal arousal mechanisms and physiologic
action(s) of pharmacologic agents is essential for safe and
efficacious application of airway adjuncts. The basic elements of
anesthesia include unconsciousness, analgesia, inhibition of noxious
reflexes and skeletal muscle relaxation.
Consciousness - Consciousness is a relative term which denotes a
state of being aware, or perceiving physical facts or mental concepts;
a state of general wakefulness and responsiveness to the environment.
The body maintains arousal and neuronal homeostasis through selective
activation of the hypothalamus, the limbic system and the cerebral
cortex. This level of arousal varies from a state of excitement to
sleep and coma. Arousal is controlled by chemical-mediated excitation
and inhibition of neurons.
While acetylcholine and biogenic amines (dopa, dopamine, seratonin,
etc...) are present in the central nervous system, they are found only
in certain neurons. In contrast, there is a group of amino acids that
are released as neurotransmitters and that also are universal cellular
constituents. Glycine, glutamate and aspartate are three of the 20
common amino acids that are found in the proteins of all cells. g -
aminobutyric acid (GABA) is an inhibitory neurotransmitter,
synthesized from glutamate, while glutamate is an excitatory amino
acid (EAA). Application of these neurotransmitters to the axons and
glial cells of the central nervous system will cause either an
increase or decrease of ion flux, which in turn will effect a
stimulatory or inhibitory response. Stimulatory responses are
generally caused by an increase in Na+ conductance or an increased
level of Ca++ conductance. Conversely, inhibitory responses are
generally caused by increases in K+ efflux or Cl- influx both
resulting in hyperpolarization.
Sedative-Hypnotics - Sedative-hypnotics are medications that inhibit
the CNS, promoting drowsiness or unconsciousness. Rapid onset,
short-acting sedative hypnotics are used in combination with other
medications for rapid sequence induction of anesthesia (RSI).
Barbiturates - Barbiturates are a group of drugs which are derived from
barbituric acid or the salts of barbituric acid, a substance which
seems to inhibit the influx and efflux of Na+ and K+ from CNS neurons.
This is accomplished by slowing the rate of GABA dissociation from
its receptor. GABA receptors are linked to chloride ion channels.
GABA stimulation causes the Cl- channels to remain open, increasing
the intracellular influx of Cl-, which results in neuronal
hyperpolarization and general inhibition of CNS neurons.
Barbiturates, as with many sedative-hypnotics do not produce muscle
relaxation or analgesia.
Generic Name -Thiopental Sodium
Trade Name -Pentathol
Duration -ultra-short acting
Remarks -Thiobarbiturate 30 second onset 5 - 10 minute duration, increased venous capacitance, decreased preload, decreased CO, decreased BP. Reflex tachycardia No analgesia Hypovolemic patients and those with poor cardiac function are prone to hypotension at induction Respiratory significant Metabolism significantly slowed in hypothermia
Generic Name -Methohexitol
Trade Name -Brevital
Dose -1-2 mg/kg
Duration -ultra-short acting
Remarks -Oxybarbiturate 30 second onset, 5-10 minute duration. Similar effects as thiopental but shorter duration. No analgesia. May activate epileptic foci. May induce myoclonus. May be administered rectally with dosing of 30 mg/kg and extended duration of drowsiness 1-2 hours.
Imidazole derivatives - Imidazoles are a class of anti-fungal agents
such as ketaconazole. However etomidate acts as an enhancer of GABA,
which promotes cellular hypperpolarization.
Generic Name -Etomidate
Trade Name -Amidate
Dose -0.3 mg/kg
Onset -<1 min. onset
Duration -10 min. duration
Remarks -Cerebral effects very similar to those of thiopental. No analgesia. Cardiovascular effects minimal. Myoclonus noted. Pain on injection and thrombophlebitis - mixed in propylene glycol, Inhibits key enzymes in steroid production. Long-term use shows
increased morbidity and mortality in ICU patients. Good choice in patients with ventricular dysfunction or ischemic heart disease. For short-term use.
Dissociative anesthetics - Dissociative anesthesia resembles a
cataleptic state in which the eyes remain open and although
non-responsive, the patient may appear wakeful. Varying degrees of
muscle tone and spontaneous limb movements are present. Emergence
delirium may be a problem. Ketamine, a phencyclidine derivative, is
the primary dissociative agent used today, causing a dissociation
between the thalamoneocortical and limbic systems . Ketamine effects
in the CNS that appear to be responsible for anesthetic effects
include interference with the EAA neurotransmitter glumtamate by
blocking the NMDA (N--methyl-D-aspartate) receptor Ketamine may also
bind to peripheral opioid receptors. and may explain its analgesic effects.
Generic Name -Ketamine
Trade Name -Ketalar
Dose -1-3 mg/kg IV, 4-6 mg/kg IM
Onset -1 minute IV, 5 minutes IM
Duration -15 minutes
Remarks -Potent analgesic. Adrenergic activation. Minimal respiratory effect with some bronchodilation. Salivation and increased secretions. Emergence reactions and hallucinations. Rarely used alone.
Other induction agents:
Propofol is an isopropyl alkylphenol formulated as a 1% solution in a
lipid base (hence it's nickname - milk of anesthesia or milk of
analgesia). Propofol acts on the GABA receptor. Propofol is
unrelated to barbiturates, eugenols, or steroid anesthetics. It
produces rapid induction and rapid recovery with little cumulative effect.
Generic Name -Propofol
Trade Name -Diprivan
Dose -10 mg (1ml) every 10 seconds until induction
Onset -rapid (< 60 seconds)
Remarks -More rapid and complete awakening than barbiturates. Reduces
blood pressure more than thiopental. Exaggerated hemodynamic effects in
hypovolemia. Pain with injection into non-antecubital, small
vein. Prolonged exposure to heat may promote bacterial contamination.
Antianxiety agents- Amnestic, anticonvulsant, hypnotic, and sedative
effects. Useful sedation for procedures and tolerance of mechanical
ventilation. These include benzodiazepines and antihistamines.
Because antihistamines have longer duration, only benzodiazepines will
be discussed here.
Benzodiazepines - Benzodiazepines are a large family of medication of
which diazepam is the model. Benzodiazepines are stimulators of the
GABA receptor, increasing the intracellular influx of Cl- ions. This
causes neuronal hypperpolarization. Additionally, benzodiazepines may
increase the availability of the inhibitory amino acid (IAA) glycine,
which may explain the skeletal muscle relaxant and antianxiety effects.
Generic Name -Diazepam
Trade Name -Valium
Dose -2 - 20 mg
Onset -1 - 2 min
Duration -2 - 4 hour
Remarks -Mild sedation. Anticonvulsant action. Seldom used since introduction of
midazolam for sedation.
Generic Name -Midazolam
Trade Name -Versed
Dose -0.15- 0.35 mg/kg until induction or sedation level achieved
Onset -1 - 2 min.
Duration -45 minutes.
Remarks -More retrograde amnesia. Increased incidence respiratory depression in elderly when given with narcotics.
Generic Name -Lorazepam
Trade Name -Ativan
Dose -0.5 - 2 mg
Onset -1 - 2 min.
Duration -45 min.
Remarks -Mild sedation. Anticonvulsant.
Opiates - Derivatives of Morphine act at opiate receptors present in
multiple forms at multiple sites. Opiates are potent analgesics.
Alfentanyl is 5 times more potent than Fentanyl. Sufentanyl is 10
times more potent than Fentanyl. Fentanyl is 3 times more potent than
Generic Name -Morphine
Trade Name -same
Dose -2 - 15 mg
Onset -10 minutes
Remarks -Respiratory depression, Nausea and vomiting. Dysphoria, Muscle rigidity. Hypotension from histamine release.
Muscle relaxants (paralytics) -- In the context of RSI muscle
relaxation is synonymous with paralysis. Muscle relaxants block the
nicotinic acetylcholine receptor motor end-plate, thereby inhibiting
neuromuscular transmission and leading to muscle flaccidity.
Inactivation of the receptor can be attained in two ways: by
depolarizing the receptor continuously, which leads to complex form of
desensitization (depolarizing muscle relaxants); or by competitively
antagonizing the receptor (non-depolarizing agents).
Depolarizing agents are non-reversible. Non-depolarizing agents may be
reversed. Neostigmine, pyridostigmine, and edrophonium are used
clinically to reverse the competitive antagonism of non-depolarizing agents.
Generic Name -Succinylcholine
Trade Name -Annectine
Type -depolarizing agent
Dose -(1 mg/kg adult) (2mg/kg peds)
Onset -60 seconds
Duration -3 - 10 minutes.
Remarks -Cardiac dysrhythmias, Histamine release, Hyperkalemia in trauma/burn patients, increased intraocular and
intracranial pressure, Fasciculation common, Malignant hyperthermia possible.
Generic Name -Rocuronium
Trade Name -Zemuron
Type -non depolarizing
Dose -0.6 - 1 mg/kg
Onset -60 - 90 seconds
Duration - < 20 minute duration
Remarks -increased heart rate, Useful in patients with contraindication to sux.
Generic Name -Vecuronium
Trade Name -Norcuron
Type -non depolarizing
Dose -0.08 - 1mg/kg
Onset -3 minutes
Duration -20 - 35 minutes
Remarks -Hemodynamically benign
Generic Name -Pancuronium
Trade Name -Pavulon
Type -non depolarizing
Dose -0.1 mg/kg
Onset -3 - 5 minutes
Duration -60 - 90 minutes
Remarks -Sympathomimetic activity, increased HR, increased BP
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Updated: February 26, 1998