General supportive care should be provided as outlined earlier. The usual measures used to raise the blood pressure and heart rate, such as intravenous fluids, β-agonist drugs, and atropine, are generally ineffective. Glucagon is a useful antidote that—like β agonists—acts on cardiac cells to raise intracellular cAMP but does so independent of β adrenoceptors. It can improve heart rate and blood pressure when given in high doses (5–20 mg intravenously).
Calcium antagonists can cause serious toxicity or death with relatively small overdoses. These channel blockers depress sinus node automaticity and slow AV node conduction (see Chapter 12). They also reduce cardiac output and blood pressure. Serious hypotension is mainly seen with nifedipine and related dihydropyridines, but in severe overdose all of the listed cardiovascular effects can occur with any of the calcium channel blockers.
Treatment requires general supportive care. Since most ingested calcium antagonists are in sustained-release form, it may be possible to expel them before they are completely absorbed; initiate whole bowel irrigation and oral activated charcoal as soon as possible, before calcium antagonist-induced ileus intervenes. Calcium, given intravenously in doses of 2–10 g, is a useful antidote for depressed cardiac contractility but less effective for nodal block or peripheral vascular collapse. Other treatments reported to be helpful in managing hypotension associated with calcium channel blocker poisoning include high-dose insulin (0.5–1 unit/kg/h) plus glucose supplementation to maintain euglycemia; glucagon; veno-arterial extracorporeal membrane oxygenation (ECMO-VA); and methylene blue. A few case reports have suggested benefit from administration of lipid emulsion (normally used as an intravenous dietary fat supplement) for severe verapamil overdose.
Carbon monoxide (CO) is a colorless, odorless gas that is ubiquitous because it is created whenever carbon-containing materials are burned. Carbon monoxide poisoning is the leading cause of death due to poisoning in the USA. Most cases occur in victims of fires, but accidental and suicidal exposures are also common. The diagnosis and treatment of carbon monoxide poisoning are described in Chapter 56. Many other toxic gases are produced in fires or released in industrial accidents (Table 58–4).
Organophosphate and carbamate cholinesterase inhibitors (see Chapter 7) are widely used to kill insects and other pests. Most cases of serious organophosphate or carbamate poisoning result from intentional ingestion by a suicidal person, but poisoning has also occurred at work (pesticide application or packaging) or, rarely, as a result of food contamination or terrorist attack (eg, release of the chemical warfare nerve agent sarin in the Tokyo subway system in 1995).
Stimulation of muscarinic receptors causes abdominal cramps, diarrhea, excessive salivation, sweating, urinary frequency, and increased bronchial secretions (see Chapters 6 and 7). Stimulation of nicotinic receptors causes generalized ganglionic activation, which can lead to hypertension and either tachycardia or bradycardia. Muscle twitching and fasciculations may progress to weakness and respiratory muscle paralysis. CNS effects include agitation, confusion, and seizures. The mnemonic DUMBELS (diarrhea, urination, miosis and muscle weakness, bronchospasm, excitation, lacrimation, and seizures, sweating, and salivation) helps recall the common findings. Blood testing may be used to document depressed activity of red blood cell (acetylcholinesterase) and
TABLE 58–4 Characteristics of poisoning with some gases.
plasma (butyrylcholinesterase) enzymes, which provide an indirect estimate of synaptic cholinesterase activity.