0071643192.pdf

TOXICOLOGY

■ Seizuresare typically self-limited, but are associated with acidosis, which

in turn worsens the Na++channel blockade.

■ Rapid deterioration can occur.

DIFFERENTIALDIAGNOSIS

■ False-positive serum TCA screen may occur with carbamazepine,

cyclobenzaprine, diphenhydramine, and phenothizines.

■ Antidysrhythmic overdose

■ Cocaine toxicity

DIAGNOSIS

■ Suspect based on history and presentation.

■ ECG findings of Na++channel blockade:

■ Rightward deviation of the terminal 40 msec of the QRS = terminal

R in lead aVR of >3 mm and S wave in lead I (see Figure 6.1).

■ Prolongation of PR interval

■ QRS widening

■ QRS >100 msec is associated with increased risk of seizures.

■ QRS >160 msec is associated with increased risk of wide-complex

dysrhythmias.

■ Plasma TCA level

■ Serious intoxications are generally >1000 ng/mL.

■ Urine tox screen for TCAs.

■ False positives include diphenhydramine, carbamazepine.

TREATMENT

■ Supportive care

■ Early intubation to avoid respiratory acidosis

■ Gastric lavage and charcoal if early and no CNS depression

■ IV fluid boluses for hypotension

■ Sodium bicarbonate,indications:

■ Rightward deviation of the terminal 40 msec of the QRS

■ QRS >100 msec

■ Ventricular dysrhythmias

■ Hypotension unresponsive to fluids

■ Administer boluses of 1–2 mEq/kg until improvement, then start drip

(3 ampules in 1 L of D 5 W at maintenance rate).

FIGURE 6.1. Sodium channel blockade in TCA toxicity.

(Reproduced, with permission, from Tintinalli JE, Kelen GD, Stapczynski JS. Emergency Medicine: A Comprehensive Study

Guide,6th ed. New York: McGraw-Hill, 2004:1031.)

ECG findings consistent with

sodium channel blockade:

Rightward deviation of the

terminal 40 msec of the QRS

Prolonged PR interval

QRS >100 msec

Sodium bicarbonate is the

treatment of choice for TCA-

induced dysrhythmias.