Page 1726 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

CHAPTER 124: Toxicology in Adults 1195

TABLE 124-2 Selected Causes of Hypoxemia in Drug Overdose and Toxic Ingestion TABLE 124-3 Selected Drugs/Toxins Causing Tachycardia and Bradycardia
Cause Drugs/Toxins Tachycardia Bradycardia
Hypoventilation Alcohols Amphetamines Antiarrhythmics (types 1a and 1c)
Barbiturates Anticholinergics β-Blockers
Benzodiazepines Antihistamines Calcium-channel blockers
Botulinum toxin Caffeine Carbamates
Cyclic antidepressants Carbon monoxide Clonidine
Neuromuscular blockade Clonidine Cyclic antidepressants
Opioids Cocaine Digoxin
Snake bite Cyanide Lithium
Strychnine Cyclic antidepressants Metoclopramide
Tetanus Drug withdrawal Opioids
Aspiration Drugs/toxins depressing mental status Ephedrine Organophosphates
Pneumonia Drugs resulting in aspiration Hydralazine Phenylpropanolamine
IV drug abuse with pulmonary vascular seeding of infectious agents Hydrogen sulfide Physostigmine
Inhalation injury interfering with lung protective mechanisms Methemoglobinemia Propoxyphene
Cardiogenic pulmonary Antiarrhythmics Phencyclidine (PCP) Quinidine
edema β-Blockers Phenothiazines
Cyclic antidepressants Pseudoephedrine
Verapamil Theophylline
Inert gases Methane Thyroid hormone overdose
Nitrogen
Propane
Noncardiogenic Cocaine also occur from a reflex response to α-adrenergic–induced hypertension
pulmonary edema Ethylene glycol (eg, phenylpropanolamine).
The differential diagnosis of bradycardia includes hypoxemia, myo-
Hydrocarbons cardial infarction, hyperkalemia, hypothermia, hypothyroidism, and
Inhalation injury intracranial hypertension. If bradycardia persists despite correction of
hypoxemia or hypothermia and is hemodynamically significant, atropine
Opioids
0.5 to 1.0 mg IV should be given and repeated every 5 to 10 minutes until
Phosgene a therapeutic response has been achieved or adverse drug effects appear.
Paraquat Three milligrams of atropine is fully vagolytic, so further administration
of atropine beyond this dose is unlikely to be beneficial. An exception to
Salicylates
this tenet is cholinergic poisoning, in which extremely high doses of atro-
Bronchospasm β-Blockers pine may be required to increase heart rate and dry secretions. In selected
Cocaine overdoses, antidotes are available for treatment of bradycardia: calcium
chloride for calcium-channel blocker toxicity; glucagon in β-blocker
Heroin
overdose; sodium bicarbonate in cyclic antidepressant overdose; nalox-
Organophosphates one in opioid and clonidine overdose; and digoxin-specific antibodies in
Drugs resulting in aspiration digoxin toxicity. Refractory and symptomatic bradycardia or heart block
Drugs associated with myocardial depression (cardiac asthma) is an indication for transcutaneous or transvenous pacing or infusion
with dopamine or epinephrine. If transcutaneous pacing is used suc-
5
Alveolar hemorrhage Cocaine cessfully, a prophylactic transvenous pacemaker is not routinely recom-
Pneumothorax Cocaine mended because of theoretical risk of triggering ventricular arrhythmias
6
IV drug abuse with aberrant venipuncture or bullous lung disease by irritating the susceptible myocardium. However, if transcutaneous
pacing is poorly tolerated or ineffective, transvenous pacing has been
Cellular hypoxia Carbon monoxide
shown to be safe in certain overdose settings. 7
Cyanide Table 124-3 includes selected drugs and toxins causing tachycardia.
Hydrogen sulfide Sinus tachycardia and supraventricular arrhythmias commonly result
from sympathetic overstimulation (eg, with cocaine, theophylline,
Methemoglobinemia
amphetamines, or phencyclidine) or inhibition of parasympathetic tone
Sulfhemoglobinemia (eg, with cyclic antidepressants, phenothiazines, or antihistamines).
Anxiety, hypovolemia, hypoxemia, myocardial infarction, hyperthermia,
infection, and pregnancy are in the differential diagnosis. Treatment of
cholinergic excess (eg, with organophosphate, carbamate, physostig- sinus tachycardia should be aimed at correcting the underlying cause. In
mine, and digoxin toxicity), sympatholytic drugs (eg, β-blockers, cloni- the setting of stimulant intoxication, sedation with benzodiazepines is
dine, and opioids), membrane-depressant agents (eg, type 1a and 1c usually sufficient. β-Blockade can be helpful in the setting of excessive
antiarrhythmic drugs, quinidine, and cyclic antidepressants), calcium- sympathetic stimulation and myocardial ischemia; however, nonselec-
channel blockers, and lithium overdose (Table 124-3). Bradycardia can tive β-blockers should not be used alone to treat cocaine toxicity because

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