Validation of a nomogram used to predict lithium concentration in overdose

Extracorporeal Treatment (ECTR) is an essential component in management of severe lithium toxicity. The Extracorporeal Treatments in Poisoning (EXTRIP) group’s suggested indications for ECTR include “if the expected time to obtain a [Li+] < 1.0mEq/L with optimal management is >36h”. Buckley et al. developed a lithium nomogram which could help predict the fall in lithium concentrations for chronic poisoning. Our aim is to externally validate the lithium nomogram in a cohort of cases with chronic accumulation and acute on chronic lithium poisoning. A retrospective analysis of suspected cases of chronic accumulation and acute on chronic lithium poisoning referred to our Toxicology Unit from May 2013 to 2020 was performed. Out of 51 cases, 29 cases of chronic accumulation and eight cases of acute on chronic poisoning were analysed after excluding 14 cases who required haemodialysis. In chronic accumulation cases, the nomogram correctly identified 10 out of 14 patients whose [Li+] failed to drop below 1.0 mmol/L by 36 h (sensitivity 71.4% [95% CI 42 − 92%]), and 8 out of 15 patients whose [Li+] dropped below 1.0 mmol/L by 36 h (specificity 53.3% [95% CI 27 − 78%]), resulting in the positive predictive value (PPV) of 58.8%, negative predictive value (NPV) of 66.7% and accuracy of 62.1%. Our study shows that the lithium nomogram is moderately sensitive at identifying patients with chronic lithium accumulation who will have a serum lithium concentration >1 mmol/L at 36 h without ECTR.

体外治疗（Extracorporeal Treatment, ECTR）是重度锂中毒临床管理的核心组成部分。中毒体外治疗工作组（Extracorporeal Treatments in Poisoning, EXTRIP）提出的ECTR推荐适应证包括：若经最优治疗后，血清锂浓度[Li+]降至＜1.0mEq/L的预计时长＞36小时。Buckley等人开发了一款锂浓度列线图（Lithium Nomogram），可用于预测慢性锂中毒患者的血清锂浓度下降趋势。本研究旨在在慢性锂蓄积（Chronic Lithium Accumulation）及慢性基础上急性加重的锂中毒（Acute on Chronic Lithium Poisoning）病例队列中，对该锂浓度列线图开展外部验证。本研究对2013年5月至2020年期间转诊至本院中毒科（Toxicology Unit）的疑似慢性锂蓄积及慢性基础上急性加重锂中毒病例进行了回顾性分析（Retrospective Analysis）。最终纳入的51例病例中，排除14例需接受血液透析（Haemodialysis）的病例后，共对29例慢性锂蓄积病例及8例慢性基础上急性加重锂中毒病例进行分析。在慢性锂蓄积病例中，该列线图正确识别了14例36小时内血清锂浓度未降至1.0mmol/L以下的患者中的10例（灵敏度(Sensitivity) 71.4%，95%置信区间(Confidence Interval, CI) 42%−92%），以及15例36小时内血清锂浓度降至1.0mmol/L以下的患者中的8例（特异度(Specificity) 53.3%，95%CI 27%−78%）；据此计算得到阳性预测值（Positive Predictive Value, PPV）为58.8%、阴性预测值（Negative Predictive Value, NPV）为66.7%，整体准确率为62.1%。本研究结果显示，在未接受ECTR的慢性锂蓄积患者中，该锂浓度列线图对36小时时血清锂浓度＞1mmol/L的病例具有中等程度的识别灵敏度。