Compare and contrast acute and chronic lithium toxicity under the following headings:
a) History, examination findings and biochemical abnormalities. (6 marks)
b) Interpretation of lithium levels. (2 marks)
c) Elimination and decontamination techniques. (2 marks)
Syllabus topic/section:
2.1.14 Environmental Injuries and Toxicology in ICU / Poisoning and drug intoxication: L1
Discussion:
Toxicology is a common presentation to the ICU and therefore a detailed knowledge is expected but
was not demonstrated by many candidates in this question. We recommend candidates improve their knowledge of toxicology in future examination attempts. This question discriminated well between candidates. Successful answers were characterised by the following:
a) Sound knowledge base especially the core concepts of GI disturbance of acute lithium ingestion
as opposed to the neurological disturbance of chronic lithium ingestion. More clinical exposure or
greater in-depth reading is required for some candidates.
b) Attention to the Glossary of terms. Some candidates made no distinction between acute and
chronic lithium ingestion in their answers. This made it impossible to award full marks in a
compare and contrast question.
The Angoff mark of 4.1 suggests that the examiners expected the borderline candidate to struggle with this answer. A tabulated answer is often the best way to deal with these questions:
| Domain | Acute lithium toxicity | Chronic lithium toxicity |
| History |
Often deliberate self harm Mostly GI symptoms Neurologically, often intact CNS features are slow to onset |
Drug changes: NSAIDS, ACE-I, thiazides Non-adherence to level testing Recent acute illness Mostly CNS prodrome, confusion/falls |
| Examination |
Tremor; mostly GI features (bloating) Trivial ST and T wave changes |
Confusion, coma, seizures Tremor, hyperreflexia, rigidity, hypertonia, myoclonus. Hypothyroidism, diabetes insipidus |
| Biochemistry |
Normal bloods, perhaps AKI Anion gap may be negative Lithium levels may be very elevated |
TFTs depressed Hypernatremia Anion gap may be entirely normal Lithium levels may be modestly elevated or normal |
|
Interpretation of lithium levels |
A high lithium level helps to make the diagnosis, but it is not repeated. | The level does not predict the degree of CNS toxicity and instead is used to decide about dialysis (cutoff is 2.5-4.0 mmol/L) |
|
Elimination / decontamination |
Activated charcoal is not indicated. Normal saline resuscitation to restore volume and promote diuresis. Experimental therapies to enhance elimination include: - cation exchange resin - theophylline and caffeine |
CRRT is required if renal function is poor or the level is high. A rebound phenomenon may occur between sessions. Serious clinical features may continue to manifest even after the levels have been normalised with treatment |
Murray et al, Toxicology handbook, 3rd ed. Chapters 3.46 and 3.47 (p. 279-284)
Lavonas E.J, Brent J. Lithium. J. Brent et al. (eds.), Critical Care Toxicology, 2017, p. 991
Oruch, Ramadhan, et al. "Lithium: a review of pharmacology, clinical uses, and toxicity." European journal of pharmacology 740 (2014): 464-473.