Why is IV sodium bicarbonate used in TCA overdose?

• A. To alkalinize serum and urine, reducing sodium channel blockade and QRS widening.
• B. To acidify blood to dissolve toxins.
• C. To chelate calcium.
• D. To promote diuresis.

Answer: (A)

TCAs cause dangerous sodium channel blockade in the heart, which leads to widened QRS and potentially life‑threatening arrhythmias. IV sodium bicarbonate is used to treat this by two coordinated effects: raising the serum pH (alkalinizing the blood) and increasing the circulating sodium load. Alkalinizing the serum reduces the ability of the TCA to block the fast sodium channels in cardiac tissue, so conduction improves and the QRS narrows. The extra sodium from the bicarbonate further helps overcome the channel blockade, aiding faster depolarization and stabilizing rhythm. Urine alkalinization is part of maintaining an environment that supports drug elimination and pH control. In short, bicarbonate counters the cardiac sodium-channel–blocking effects of the overdose by both alkalinizing the serum and providing sodium, which together reduce QRS widening and improve cardiac conduction.