Pathogenesis of postoperative hyponatraemia following correction of scoliosis in children

A balancing act: drifting away from the reflexive use of "ab"normal saline

Maintenance intravenous fluids are the most frequently ordered medications for hospitalized children. Since the American Association of Pediatrics published national guidelines, there has been an increased reflexive use of isotonic solutions, especially 0.9% saline, as a prophylaxis against hyponatremia. In this educational review, we discuss the potential deleterious effects of using 0.9% saline, including the development of hyperchloremia, metabolic acidosis, acute kidney injury, hyperkalemia, and a proinflammatory state. Balanced solutions with anion buffers cause relatively minimal harm when used in most children. While the literature supporting one fluid choice over the other is variable, we highlight the benefits of balanced solutions over saline and the importance of prescribing fluid therapy that is individualized for each patient.

Central diabetes insipidus after staged spinal surgery

Diabetes insipidus (DI) is described following penetrating spinal cord trauma but rarely following instrumented spinal fusion. More commonly, hyponatremia is seen following spine surgery, which may be iatrogenic, attributed to the syndrome of inappropriate antidiuretic hormone release. The authors present a case of a 57-year-old woman who underwent a planned two-stage operation for scoliotic deformity correction. On the third postoperative day, the patient developed hypernatremia (sodium levels of 157 mmol/L) and polyuria. In conjunction with endocrinology, the patient was diagnosed with central DI. The patient was treated with desmopressin acetate (DDAVP), which led to resolution of her symptoms. DDAVP was temporary and eventually weaned off. Central DI is a possible cause of hypernatremia following significant spine surgery. Correct diagnosis is paramount for rapid and appropriate treatment.

Intravenous maintenance fluids revisited

Intravenous maintenance fluid therapy aims to replace daily urinary and insensible losses for ill children in whom adequate enteric administration of fluids is contraindicated or infeasible. The traditional determination of fluid volumes and composition dates back to Holliday and Segar's seminal article from 1957, which describes the relationship between weight, energy expenditure, and physiologic losses in healthy children. Combined with estimates of daily electrolyte requirements, this information supports the use of the hypotonic maintenance fluids that were widely used in pediatric medicine. However, using hypotonic intravenous fluids in a contemporary hospitalized patient who may have complex physiologic derangements, less caloric expenditure, decreased urinary output, and elevated antidiuretic hormone levels is often not optimal; evidence over the last 2 decades shows that it may lead to an increased incidence of hyponatremia. In this review, we present the evidence for using isotonic rather than hypotonic fluids as intravenous maintenance fluid.

The relationship between arginine vasopressin levels and hyponatremia following a percutaneous renal biopsy in children receiving hypotonic or isotonic intravenous fluids

Post-operative hyponatremia is a common complication in children which results from hypotonic fluid administration in the presence of arginine vasopressin (AVP) excess. We evaluated the relationship between the change in serum sodium and AVP levels following percutaneous renal biopsy in children receiving either hypotonic or isotonic fluids. This study was prompted after we encountered a patient who developed near-fatal hyponatremic encephalopathy following a renal biopsy while receiving hypotonic fluids. The relationship between the change in serum sodium and AVP levels was evaluated prior to (T0) and at 5 h (T5) following a percutaneous renal biopsy in 60 children receiving either hypotonic (0.6% NaCl, 90 mEq/L) or isotonic fluids (0.9% NaCl, 154 mEq/L). The proportion of patients with elevated AVP levels post-procedure was similar between those receiving 0.6 or 0.9% NaCl (30 vs. 26%). Patients receiving 0.6% NaCl with elevated AVP levels experienced a fall in serum sodium of 1.9 ± 1.5 mEq/L, whereas those receiving 0.9% NaCl had a rise in serum sodium of 0.85 ± 0.34 mEq/L with no patients developing hyponatremia. There were no significant changes in serum sodium levels in patients with normal AVP concentrations post-procedure in either group. In conclusion, elevated AVP levels were common among our patients following a percutaneous renal biopsy. Isotonic fluids prevented a fall in serum sodium and hyponatremia, while hypotonic fluids did not.

Prevention of hyponatremia during maintenance intravenous fluid administration: a prospective randomized study of fluid type versus fluid rate

OBJECTIVES

To determine the importance of sodium content versus administration rate of intravenous fluids in the development of hyponatremia in postoperative children.

STUDY DESIGN

In this prospective, randomized, nonblinded study, 124 children admitted for surgery received 0.9% (NS) or 0.45% (N/2) saline solution at 100% or 50% maintenance rates. Plasma electrolytes, osmolality, and ADH at induction of anesthesia were compared with values 8 hours (T(8)), and 24 hours (T(24); n = 67) after surgery. Blood glucose and ketones were measured every 4 hours. Electrolytes and osmolality were measured in urine samples.

RESULTS

Plasma sodium concentrations fell in both N/2 groups at T(8) (100%: -1.5 +/- 2.3 mmol/L 50%: -1.9 +/- 2.0 mmol/L; P < .01) with hyponatremia more common than in the NS groups at T(8) (30% vs 10%; P = .02) but not T(24). Median plasma antidiuretic hormone concentrations increased 2- to 4-fold during surgery (P < or = .001) and only reattained levels at induction of anesthesia by T(24) in the N/2 100% group. On multiple linear regression analysis, fluid type, not rate determined risk of hyponatremia (P < .04). Two children on 100% developed SIADH (1NS). Fourteen (23%; 7NS) on 50% maintenance were assessed as dehydrated. Dextrose content was increased in 18 for hypoglycemia or ketosis.

CONCLUSIONS

The risk of hyponatremia was decreased by isotonic saline solution but not fluid restriction.

Randomised controlled trial of intravenous maintenance fluids

AIM

Traditional paediatric intravenous maintenance fluids are prescribed using hypotonic fluids and the weight-based 4:2:1 formula for administration rate. However, this may cause hyponatraemia in sick and post-operative children. We studied the effect of two types of intravenous maintenance fluid and two administration rates on plasma sodium concentration in intensive care patients.

METHODS

A Factorial-design, double-blind, randomised controlled trial was used. We randomised 50 children with normal electrolytes without hypoglycaemia who needed intravenous maintenance fluids for >12 h to 0.9% saline (normal saline) or 4% dextrose and 0.18% saline (dextrose saline), at either the traditional maintenance fluid rate or 2/3 of that rate. The main outcome measure was change in plasma sodium from admission to 12-24 h later.

RESULTS

Fifty patients (37 surgical) were enrolled. Plasma sodium fell in all groups: mean fall 2.3 (standard deviation 4.0) mmol/L. Fluid type (P = 0.0063) but not rate (P = 0.12) was significantly associated with fall in plasma sodium. Dextrose saline produced a greater fall in plasma sodium than normal saline: difference 3.0, 95% confidence interval 0.8-5.1 mmol/L. Full maintenance rate produced a greater fall in plasma sodium than restricted rate, but the difference was small and non-significant: 1.6 (-0.7, 3.9) mmol/L. Fluid type, but not rate, remained significant after adjustment for surgical status. One patient, receiving normal saline at restricted rate, developed asymptomatic hypoglycaemia.

CONCLUSION

Sick and post-operative children given dextrose saline at traditional maintenance rates are at risk of hyponatraemia.

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.

Preventing neurological complications from dysnatremias in children

Dysnatremias are among the most common electrolyte abnormalities encountered in hospitalized patients. In most cases, a dysnatremia results from improper fluid management. Dysnatremias can occasionally result in death or permanent neurological damage, a tragic complication that is usually preventable. In this manuscript, we discuss the epidemiology, pathogenesis and prevention and treatment of dysnatremias in children. We report on over 50 patients who have suffered death or neurological injury from hospital-acquired hyponatremia. The main factor contributing to hyponatremic encephalopathy in children is the routine use of hypotonic fluids in patients who have an impaired ability to excrete free-water, due to such causes as the postoperative state, volume depletion and pulmonary and central nervous system diseases. The appropriate use of 0.9% sodium chloride in parenteral fluids would likely prevent most cases of hospital-acquired hyponatremic encephalopathy. We report on 15 prospective studies in over 500 surgical patients that demonstrate that normal saline effectively prevents postoperative hyponatremia, and hypotonic fluids consistently result in a fall in serum sodium. Hyponatremic encephalopathy is a medical emergency that should be treated with hypertonic saline, and should never be managed with fluid restriction alone. Hospital-acquired hypernatremia occurs in patients who have restricted access to fluids in combination with ongoing free-water losses. Hypernatremia could largely be prevented by providing adequate free-water to patients who have ongoing free-water losses or when mild hypernatremia (Na>145 mE/l) develops. A group at high-risk for neurological damage from hypernatremia in the outpatient setting is that of the breastfed infant. Breastfed infants must be monitored closely for insufficient lactation and receive lactation support. Judicious use of infant formula supplementation may be called for until problems with lactation can be corrected.

Hypotonic intravenous solutions in children

The use of hypotonic intravenous solutions, especially 4% dextrose/0.18% saline, remains standard practice in many paediatric units in the UK. The practice of prescribing hypotonic intravenous fluids derives from the work of investigators in the 1950s, who produced arbitrarily-derived formulae for calculating the maintenance requirements for water and electrolytes in hospitalised patients. Combining these values led to the widespread acceptance of hypotonic solutions such as 4% dextrose/0.18% saline as 'standard maintenance' parenteral fluids. Unfortunately, these calculations do not account for the effects of antidiuretic hormone, the secretion of which is stimulated by many factors encountered during acute illness and especially in the perioperative period. In this setting, the administration of hypotonic intravenous fluids results in the retention of free water and the development of hyponatraemia. The routine administration of hypotonic intravenous fluids has been shown to be associated with severe morbidity and the deaths of many previously healthy children. The problem is compounded by the fact that 4% dextrose/0.18% saline is labelled as 'isotonic'. Whilst this solution is isosmolar compared to plasma, lack of osmotically-effective solutes means that it is hypotonic with reference to the cell membrane. There is no justification for the routine administration of hypotonic intravenous fluids.

[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.

Fatal child abuse by forced water intoxication

BACKGROUND

Although water intoxication leading to brain damage is common in children, fatal child abuse by forced water intoxication is virtually unknown.

METHODS

During the prosecution of the homicide of an abused child by forced water intoxication, we reviewed all similar cases in the United States where the perpetrators were found guilty of homicide. In 3 children punished by forced water intoxication who died, we evaluated: the types of child abuse, clinical presentation, electrolytes, blood gases, autopsy findings, and the fate of the perpetrators.

FINDINGS

Three children were forced to drink copious amounts of water (over 6 L). All had seizures, emesis, and coma, presenting to hospitals with hypoxemia (PO2 = 44 +/- 8 mm Hg) and hyponatremia (plasma Na = 112 +/- 2 mmol/L). Although all showed evidence of extensive physical abuse, the history of forced water intoxication was not revealed to medical personnel, thus none of the 3 children were treated for their hyponatremia. All 3 patients died and at autopsy had cerebral edema and aspiration pneumonia. The perpetrators of all three deaths by forced water intoxication were eventually tried and convicted.

INTERPRETATION

Forced water intoxication is a new generally fatal syndrome of child abuse that occurs in children previously subjected to other types of physical abuse. Patients present with coma, hyponatraemia, and hypoxemia of unknown etiology. If health providers were made aware of the association, the hyponatremia is potentially treatable.

Thiazide-induced hyponatremia in the postoperative total joint replacement patient

The thiazide diuretic is a common medication in the elderly population for the treatment of hypertension. These same patients are the largest population for surgical intervention for joint arthroplasty. Postoperative management of these patients has shown to be complicated by hyponatremia associated with the use of thiazide diuretics. This study evaluates a consecutive series of 408 patients undergoing elective joint arthroplasty. An association was found with the use of thiazide diuretics in the preoperative period and the development of postoperative hyponatremia. The study is presented, along with a relevant review of the literature and suggestions for the orthopedic staff to limit the risk of hypoantremia and prolonged hospitalization in an otherwise stable postoperative course.

Epidemiology, pathophysiology, and management of hyponatremic encephalopathy

Hyponatremia is the most common electrolyte abnormality among hospitalized patients. Death or brain damage associated with hyponatremia has been described since 1935, and it is now evident that hyponatremia can lead to death in otherwise healthy individuals. In the past, it had been assumed that the likelihood of brain damage from hyponatremia was directly related to either a rapid decline in plasma sodium or a particularly low level of plasma sodium. Recent studies have demonstrated that other factors may be more important. These factors include the age and gender of the individual, with children and menstruant women the most susceptible. Although many clinical settings are associated with hyponatremia, those most often associated with brain damage are postoperative, polydipsia, pharmacological agents, and heart failure. Morbidity and mortality associated with hyponatremia are primarily a result of brain edema, hypoxemia, and associated hormonal factors. Management of hyponatremia is largely determined by symptomatology. If the patient is asymptomatic, discontinuation of drugs plus water restriction is often sufficient. If the patient is symptomatic, active therapy to increase the plasma sodium with hypertonic NaCl is usually indicated. Although inappropriate therapy of hyponatremia can lead to brain damage, such an occurrence is rare. Thus, the risk of not treating a symptomatic patient for exceeds that of improper therapy.

Inappropriate secretion of antidiuretic hormone in postoperative scoliosis patients: the role of fluid management

STUDY DESIGN

The present study examined the hypothesis that hypotonic saline therapy before surgery was a major factor in the development of the syndrome of inappropriate antidiuretic hormone secretion.

OBJECTIVES

The influence of fluid therapy and its relationship to the syndrome of inappropriate antidiuretic hormone secretion was studied by measuring patient electrolyte and osmolar responses at given times after surgery.

SUMMARY OF BACKGROUND DATA

Mild renal dysfunction and increased plasma antidiuretic hormone occurs after surgery. Occurrence of the syndrome of inappropriate secretion of antidiuretic hormone after spine surgery is rare. The development of the syndrome of inappropriate secretion hormone after surgery may be related to hypotonic fluid replacement during and after surgery.

METHODS

Twelve patients undergoing surgery for correction of idiopathic scoliosis were assigned randomly to two groups. The control group (five patients) was given isotonic saline, and the trial group (seven patients) was given hypotonic saline.

RESULTS

The trial group developed syndrome of inappropriate antidiuretic hormone secretion with a significant decrease in serum sodium and osmolarity. The control group did not develop syndrome of inappropriate antidiuretic hormone secretion.

CONCLUSIONS

Hypotonic saline therapy predisposes to the development of syndrome of inappropriate antidiuretic hormone secretion, whereas isotonic saline protects patients from syndrome of inappropriate antidiuretic hormone secretion when undergoing surgery for scoliosis.

Hyponatraemia and death or permanent brain damage in healthy children

OBJECTIVE

To determine if hyponatraemia causes permanent brain damage in healthy children and, if so, if the disorder is primarily limited to females, as occurs in adults.

DESIGN

Prospective clinical case study of 16 affected children and a review of 24,412 consecutive surgical admissions at one medical centre.

PATIENTS

16 children (nine male, seven female; age 7 (SD 5) years) with generally minor illness were electively hospitalised for primary care. Consultation was obtained for the combination of respiratory arrest with symptomatic hyponatraemia (serum sodium concentration less than or equal to 128 mmol/l).

MAIN OUTCOME MEASURES

Presence, gender distribution, and classification of permanent brain damage in children with symptomatic hyponatraemia in both prospective and retrospective studies.

RESULTS

By retrospective evaluation the incidence of postoperative hyponatraemia among 24,412 patients was 0.34% (83 cases) and mortality of those afflicted was 8.4% (seven deaths). In the prospective population the serum sodium concentration on admission was 138 (SD 2) mmol/l. From three to 120 inpatient hours after hypotonic fluid administration patients developed progressive lethargy, headache, nausea, and emesis with an explosive onset of respiratory arrest. At the time serum sodium concentration was 115 (7) mmol/l and arterial oxygen tension 6 (1.5) kPa. The hyponatraemia was primarily caused by extrarenal loss of electrolytes with replacement by hypotonic fluids. All 16 patients had cerebral oedema detected at either radiological or postmortem examination. All 15 patients not treated for their hyponatraemia in a timely manner either died or were permanently incapacitated by brain damage. The only patient treated in a timely manner was alive but mentally retarded.

CONCLUSIONS

Symptomatic hyponatraemia can result in high morbidity in children of both genders, which is due in large part to inadequate brain adaptation and lack of timely treatment.