Hypo Versus Isotonic Solutions in Intravenous Fluid Maintenance of Acutelly Ill Pediatric Patients-Juniper publishers
Juniper Publishers-Journal of Anesthesia
Abstract
This brief review had as objective to remember the
position of some experts in fluid ressuscitation at the question about
which is the better saline solution, i.e., with less risk of potentially
letal complications related to hypo or hypernatremia, that garantee the
maintenance of hydroelectrolict homeostasis in acute ill pediatric
patients. In the last decades, "hypotonic” and "isotonic” saline
solutions has been investigated and its effects compared, but seems that
the remaining issue is beyond its tonicity, and refers to more about
which, in what phase and clinical condition, a specific saline solution
is more physiologic, or in other words, effective and safe.
Keywords: Hypotonic solutions; Isotonic solutions; Hyponatremia; Hypernatremia; Pediatrics Abbreviations: RCT: Randomized Controlled Trials; ADH: Antidiuretic Hormone; SIADH: Syndrome of Inappropriate Antidiuretic Hormone Secretion; ECF: Extra Cellular Fluid
Introduction
Basic principles on the prescription of parenteral
maintenance fluids in children has been investigated for decades. M.A.
Holliday & W.E. Segar, in 1957, published. The Need for Water
Maintenance in Parenteral Fluid Therapy [1],
presenting a simple formula that results in a hypotonic saline solution
equivalent to NaCl 0.2% and dextrose 5% in water, which became widely
accepted and used, but a variable incidence of hyponatremia has been
reported among cases maintained with this fluid. In a review of
literature published in 2003 [2], it was concluded that isotonic saline solution may be used, instead of hypotonic fluid, as an ideal fluid of maintenance.
Hypotonic Versus Isotonic Saline Solutions
In 2004, in an observational study [3]
involving 1586 children in an emergency department, the administration
of hypotonic fluid was the principal risk factor for hyponatremia. Last
than 1 year after, M.A. Holliday [4] published a letter to the editor suggesting that the hyponatremia in that study [3]
could be result of limited water renal excretion due to non- osmotic
ADH stimulation in cases of hypovolemia or fast and great expansion of
the extracellular fluidin childrenacute ill and mild hypovolemia,
similarly (although less intense) in severe dehydratation, burning and
septic shock. The author [4]
argues too that, after the expansion of extracellular compartment, the
hypotonic saline solution is safe to maintenace,and that the term
"maintenance”, as used in that review [2]
doest not correspondto the original meaning according to the pioneering
works of Gamble, Darrow, Butler and other authors of the 1940s, as a
reposition of insensible and urinay loses after rehydratation
(expansionof ECF). The author [4]
remember that the reposition of hypotonic loses with isotonic saline
solutionwould impose an excessive load of sodium, potential risk factor
to cerebral damage and death.
According the last extensive review [5],
including among others more than 15 RCTs involving at least 2000
patients, majority of whom were surgical and critical care pediatric
patients,the prevalent practice is still the administration of
intravenous hypotonic fluids in both children and adults, despite the
high incidences of iatrogenic hyponatremia. Isotonic fluids has been
more effective in preventing hyponatremia, and are not associated with
development of hypernatremia or fluid overload. In contrast, rapid
volume expansion or high volume of fluid in resuscitation or during
surgery using normal saline may be associated with hyperchloremic
metabolic acidosis, renal vasoconstriction, decreased urine output,
hyperkalemia, and increased incidence of acute renal injury requiring
renal replacement therapy. Although balanced solutions are an isotonic
alternative, data are lacking that support their superiority as
maintenance fluids relative to normal saline [5-7].
A proposed alternative explanation for the occurrence
of iatrogenic hyponatremia or hypernatremia, could be a calculation
error of maintenance fluids for a given patient, it being necessary, at
first, to define and reach the desired state of equilibrium to calculate
the volumes and electrolyte content, and then recalculate the supply at
regular intervals considering the urinary sodium and potassium
excretion and the flow rate in the calculation of free, negative or
positive water clearance, and isotonic losses. The best guidance for
avoiding serious complications would be an algorithm for constructing a
therapeutic plan for each patient in particular [8].
Conclusion
The question "which is the better solution for maintenance of hydroelectrolytic balance" is often presented as "hypo versus
isotonic solutions", what can suggest a reductionism of the issue in a
simple problem of tonicity of fluid (sodium concentration in the
intravenous solution) compared to the plasmatic sodium concentration. It
would be remembered that, once in the bloodstream, sodium is the main
determinant of extracellular compartment volume, and the water
determines its tonicity [9,10].
Thus, better it could be asking which fluid can be considered
physiological, isotonic or not, in each clinical condition, in each
phase of the water and electrolytes supply, ever considering a balance
between lost and gain. This still requires further investigations.
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