Low dose dopamine in lithium poisoning

Management of Lithium Toxicity

Lithium salts have been used in the prophylaxis and treatment of depression and bipolar disorder for >50 years. Lithium has a narrow therapeutic range, and several well characterised adverse effects limit the potential usefulness of higher doses. Acute ingestion in lithium-naive patients is generally associated with only short-lived exposure to high concentrations, due to extensive distribution of lithium throughout the total body water compartment. Conversely, chronic toxicity and acute-on-therapeutic ingestion are associated with prolonged exposure to higher tissue concentrations and, therefore, greater toxicity. Lithium toxicity may be life threatening, or result in persistent cognitive and neurological impairment. Therefore, enhanced lithium clearance has been explored as a means of minimising exposure to high tissue concentrations. Although haemodialysis is highly effective in removing circulating lithium, serum concentrations often rebound so repeated or prolonged treatment may be required. Continuous arteriovenous haemodiafiltration and continuous venovenous haemodiafiltration increase lithium clearance, albeit to a lesser extent than haemodialysis, and are more widely accessible. Haemodiafiltration sustained for >16 hours allows effective removal of total body lithium, thereby avoiding rebound effects. Enhanced elimination should be considered in patients at greatest risk of severe poisoning: namely those with chronic or acute-on-therapeutic toxicity, those with clinically significant features, and those with chronic toxicity whose serum lithium concentration is >2.5 mmol/L. The choice between haemodialysis and continuous haemodiafiltration techniques will depend on local accessibility and urgency of enhancing lithium elimination. Further research is required to establish the potential benefits of assisted elimination on clinical outcome in patients with lithium poisoning.

Methods used to decrease lithium absorption or enhance elimination

OBJECTIVE

To review current methods, well documented and investigational, being used to decrease lithium absorption or enhance lithium elimination.

METHODS

The basic science and clinical literature on lithium were reviewed by a comprehensive Medline search from 1984 to 1996. Additional references were identified by reviewing the reference citations from the results of the Medline search.

RESULTS

Prevention of Absorption: Whole bowel irrigation has been demonstrated to be an effective means of enhancing lithium removal from the gastrointestinal tract. Sodium polystyrene sulfonate resin administration has been shown to be effective in binding lithium elimination in animal and human models. However, the lower limits of effective sodium polystyrene sulfonate dosing and the extent of potassium lowering in humans are questions that need to be answered before sodium polystyrene sulfonate resin can be recommended for routine, use. Enhancement of Elimination: Saline or forced diuresis is not effective in enhancing lithium elimination unless the patient is volume or sodium depleted. The use of continuous arteriovenous hemodiafiltration or low dose dopamine to enhance lithium elimination has only been documented in case reports. Intravenous aminophylline (theophylline) is not consistently effective and its risks outweigh possible benefits. The literature supports hemodialysis as a well documented and effective means of enhancing lithium elimination. Controversy exists over the appropriate indications for its initiation.

DISCUSSION

Given the wide interpatient variability in lithium pharmacokinetics, single case reports do not provide sufficient evidence of the effectiveness of a given method to enhance

Falsely elevated lithium levels in plasma samples obtained in lithium containing tubes

CASE REPORT

We present a case of lithium poisoning in a 15-month-old child. Delayed elevation of the plasma lithium concentration at 13 hours after admission to a hospital was noted. This appeared to be factitiously related to the collection of samples in a speckled green top tube which contains lithium heparin as an anticoagulant.

CONCLUSION

This type of false elevation has not been reported in the medical literature. A follow-up study in five healthy volunteers showed that the lithium concentrations of plasma samples obtained in speckled green top tubes are increased by approximately 1.5 mEq/L (1.5 mmol/L).

The effects of dopamine and a low protein diet on glomerular filtration rate and renal plasma flow in the aged kidney

The aims of this study were to determine the effects of dopamine and a low protein diet on glomerular filtration rate and effective renal plasma flow in the aged kidney. Effective renal plasma flow was measured using 125I-labelled hippuran and glomerular filtration rate using 51Cr-labelled EDTA. Low-dose continuous intravenous dopamine 3 micrograms.kg-1.min-1 in 10 healthy elderly volunteers caused a significant increase in effective renal plasma flow but not in the mean glomerular filtration rate when compared with baseline. However, glomerular filtration rate did increase substantially in 5 subjects (mean 14.4, SD 1.3). This implied that the elderly kidney was working maximally without reserve capacity in half the elderly. Since renal function is likely to be even more reduced in elderly patients with congestive cardiac failure, dopamine infusions may have little place in this condition in some older patients. A low protein diet (0.69 g.kg-1) in the same volunteers reduced glomerular filtration rate, suggesting that protein restriction may help to reduce the increased filtration rate in the remaining nephrons, thereby leading to structural and functional preservation in the aged kidney.