Optimising alkalinisation and its effect on QRS narrowing in tricyclic antidepressant poisoning
Kieran G. Pai, Nicholas A. Buckley, Katherine Isoardi, Geoffrey K. Isbister, Therese Becker, Angela L. Chiew, Rose Cairns, Jared A Brown, Betty S. Chan
Abstract
Aims The objectives were to determine the effect of NaHCO 3 and/or mechanical ventilation on the biochemical profile and serum alkalinisation in tricyclic antidepressant (TCA) poisoning and investigate the impact of effective alkalinisation therapy on the QRS interval in TCA poisoning. Methods This was a retrospective review of TCA poisonings from three Australian toxicology units and a poisons information centre (Jan 2013 to Jan 2019). We included patients with TCA toxicity who ingested>10 mg/kg or had clinically significant toxicities consistent with TCA poisoning, and analysed patients' clinical, electrocardiogram and biochemical data. Results Of 210 patients, 84 received NaHCO 3 and ventilation (dual therapy), 12 NaHCO 3 , 46 ventilation and 68 supportive care treatment. When compared with single/supportive groups, patients who received dual therapy had taken a significantly higher median dose of TCA (1.5 g vs 1.3 g, P < .001), a longer median maximum QRS interval (124 ms, interquartile ranges [IQR] 108‐138 vs 106 ms, IQR 98‐115, P < .001) and were more likely to have seizures (14% vs 3%, P = .006) and arrhythmias (17% vs 1%, P < .001). The dual therapy group demonstrated greater increases in serum pH (median 0.11, IQR 0.04‐0.17) compared to the single/supportive therapy group (median 0.03, IQR −0.01‐0.09, p < .001). A greater proportion of patients reached the target pH 7.45‐7.55 in the dual therapy group (59%) compared to the single/supportive therapy group (10%) ( P < .001). For each 100 mmol bolus of NaHCO 3 given, the median increase in serum sodium was 2.5 mmol/L (IQR 1.5‐4.0). QRS narrowing occurred twice as quickly in the dual therapy vs single/supportive therapy group. Conclusions A combination of NaHCO 3 and mechanical ventilation was most effective in achieving serum alkalinisation and was associated with a more rapid narrowing of the QRS interval. We advise that the maximal dose of NaHCO 3 should be <400 mmol (6 mmol/kg).