Haemodilution
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Definition
This is increased plasma volume, leading to low haematocrit and hyponatraemia.
Pathogenesis
Water intoxication can arise from:
- Administration of too much intravenous fluid.
- Ingestion of too much water, especially if electrolyte levels are depleted.
Aetiology
Haemodilution occurs physiologically in pregnancy. This may result in lower haemoglobin concentrations than in the non-pregnant state. However, many women function well and do not require iron supplementation. It is common in chronic heart failure, where it may contribute to poor outcome.[1] At-risk groups for water intoxication include:
- Infants under 1 year old.
- Athletes - eg, marathon runners/extreme athletes and hikers who drink excessively during prolonged exertion.[2, 3]
- Also associated with the use of methylenedioxymethamfetamine (MDMA, or 'ecstasy') with prolonged dancing and high water intake at raves/events.[4]
- The mentally ill, in association with polydipsia.
Presentation
Symptoms
- Confusion
- Nausea/vomiting
- Seizures
- Coma
It may be fatal.
Signs
Brain oedema.
Management
Treat the underlying cause. Correct electrolyte balance in severe cases of water intoxication. Fkuid restriction may be considered in chronic heart failure.
Pharmacological
Diuretics.
Therapeutic role for haemodilution
- Acute normovolaemic haemodilution (ANH) may be used in operations where there is a large anticipated blood loss. It involves removing some of a patient's own blood and replacing it with fluids, to maintain normal volume. This process ensures that the blood that is lost during the operation is diluted, ie fewer red blood cells are in it. This reduces the load on the heart and allows the blood to flow more easily through the capillaries. The patient's own blood is returned after the operation.
- Haemodilution improves the flow properties of the blood so that, theoretically, oxygen and nutrient supply to the brain is improved (eg, after a cerebrovascular event) and damaged brain cells may survive. This treatment had been shown to reduce brain infarct size in animals with experimental stroke and it was first tried in the 1970s. However, a recent Cochrane review of the (considerable amount of) research showed that there were no benefits from this treatment.[5, 6]
Further reading and references
Androne AS, Katz SD, Lund L, et al; Hemodilution is common in patients with advanced heart failure. Circulation. 2003 Jan 21107(2):226-9.
Noakes T; Hyponatremia in distance runners: fluid and sodium balance during exercise. Curr Sports Med Rep. 2002 Aug1(4):197-207.
Noakes TD, Sharwood K, Collins M, et al; The dipsomania of great distance: water intoxication in an Ironman triathlete. Br J Sports Med. 2004 Aug38(4):E16.
Cherney DZ, Davids MR, Halperin ML; Acute hyponatraemia and 'ecstasy': insights from a quantitative and integrative analysis. QJM. 2002 Jul95(7):475-83.
Asplund K; Haemodilution for acute ischaemic stroke, Cochrane Review, October 2002
Chang TS, Jensen MB; Haemodilution for acute ischaemic stroke. Cochrane Database Syst Rev. 2014 Aug 278:CD000103. doi: 10.1002/14651858.CD000103.pub2.