Postoperative hyponatraemic encephalopathy following elective surgery in children

Incidence of postoperative hyponatremia and complications in critically-ill children treated with hypotonic and normotonic solutions

OBJECTIVE

To determine the incidence and clinical consequences of postoperative hyponatremia in children.

STUDY DESIGN

We performed a retrospective analysis of postoperative admissions to the pediatric intensive care unit (excluding cardiac, neurosurgical, and renal). The incidence of severe (serum sodium < 125 mmol/L or symptoms) and moderate (serum sodium < 130 mmol/L) hyponatremia in children receiving hypotonic (HT) and normotonic (NT) fluids was calculated.

RESULTS

Out of a total of 145 children (568 sodium measurements; 116 HT and 29 NT), we identified 16 with hyponatremia (11%). The incidences of moderate (10.3% vs 3.4%, P = .258) and severe (2.6% vs 0%; P = .881) hyponatremia were not significantly different in the HT and NT groups. There were no neurologic sequelae or deaths related to hyponatremia.

CONCLUSIONS

In our study group, hyponatremia was common, but morbidity and death were not observed. Careful monitoring of serum sodium level may be responsible for this lack of adverse outcomes. Larger, prospective studies are needed to determine whether the incidence of hyponatremia differs between the HT and NT groups.

Hypotonic versus isotonic saline in hospitalised children: a systematic review

BACKGROUND

The traditional recommendations which suggest that hypotonic intravenous (i.v.) maintenance fluids are the solutions of choice in paediatric patients have not been rigorously tested in clinical trials, and may not be appropriate for all children.

AIMS

To systematically review the evidence from studies evaluating the safety of administering hypotonic versus isotonic i.v. maintenance fluids in hospitalised children.

DATA SOURCES

Medline (1966-2006), Embase (1980-2006), the Cochrane Library, abstract proceedings, personal files, and reference lists. Studies that compared hypotonic to isotonic maintenance solutions in children were selected. Case reports and studies in neonates or patients with a pre-existing history of hyponatraemia were excluded.

RESULTS

Six studies met the selection criteria. A meta-analysis combining these studies showed that hypotonic solutions significantly increased the risk of developing acute hyponatraemia (OR 17.22; 95% CI 8.67 to 34.2), and resulted in greater patient morbidity.

CONCLUSIONS

The current practice of prescribing i.v. maintenance fluids in children is based on limited clinical experimental evidence from poorly and differently designed studies, where bias could possibly raise doubt about the results. They do not provide evidence for optimal fluid and electrolyte homoeostasis in hospitalised children. This systematic review indicates potential harm with hypotonic solutions in children, which can be anticipated and avoided with isotonic solutions. No single fluid rate or composition is ideal for all children. However, isotonic or near-isotonic solutions may be more physiological, and therefore a safer choice in the acute phase of illness and perioperative period.

[Postoperative hyponatremia in children: pathophysiology, diagnosis and treatment]

OBJECTIVES

To review the current data on pathophysiology, causes and management of postoperative hyponatremia in children.

DATA SOURCES AND EXTRACTION

The Pubmed database was searched for articles, combined with references analysis of major articles on the field.

DATA SYNTHESIS

The incidence of postoperative hyponatremia has been evaluated at 0.34% and its mortality significant. Postoperative hyponatremia is triggered by the diminished renal ability to excrete free water, due to antidiuretic hormone release. Inappropriate secretion of antidiuretic hormone is frequently seen after spine, cardiac and neurosurgery but can occur even after minor surgery. In this context, the infusion of hypotonic fluids represents a strong risk factor for developing hyponatremia. Other causes of hyponatremia are represented by extrarenal fluid losses, cerebral salt wasting syndrome, desalination phenomenon, adrenal insufficiency or some medications. Preventive treatment is essential and based on prohibition of hypotonic fluids infusion and the use of isotonic fluids infusions, maintenance of a normal total blood volume, the observance of the good practice recommendations for fluid infusion in children, and frequent blood and urine sodium concentration determinations in patients at risk for developing hyponatremia. Hyponatremic encephalopathy requires an emergent management, consisting in respiratory care and hypertonic sodium chloride infusion. Chronic hyponatremia is most often asymptomatic and the main neurological risk factor is represented by a too rapid correction of plasma sodium, which may lead to centropontine myelinolysis.

The maintenance need for water in parenteral fluid therapy

PURPOSE OF REVIEW

Maintenance fluid therapy represents the volume of fluids and amount of electrolytes and glucose needed to replace anticipated physiological losses from breath, sweat and urine and to prevent hypoglycaemia. For 50 years, this therapy was based on Holliday and Segar's formula, which proposed to match children's water and electrolyte requirements on a weight-based calculation using hypotonic solutions. Recent publications highlight the risk of hyponatraemia in the postoperative period and the facilitating role of a hypotonic infusion, leading some people to recommend replacing hypotonic with isotonic solutions.

RECENT FINDINGS

The postoperative period is at risk for nonosmotic secretion of antidiuretic hormone, which reduces the ability of the kidneys to excrete free water. In the context of antidiuretic hormone release, the associated low urine output makes maintenance volume requirement decrease to 50% of the calculated hourly rate. While isotonic fluids are recommended during anaesthesia, controversies still exist on the nature of fluid for maintenance therapy in the postoperative period. The proof for a benefit of isotonic fluids in this context is weak; further investigations are needed to make a decision. Whatever the choice, an individualized maintenance infusion protocol for each patient is necessary.

SUMMARY

As free water excretion is altered for all children in the postoperative period, it is necessary to reduce the volume of maintenance fluid therapy to half the previously recommended volume. The choice of an isotonic solution should be more pertinent to that of a hypotonic solution, but evidence is lacking for a definitive answer.