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SPA Newsletter.
Hyperkalemia and Pyloric Stenosis.Schwartz D, Connelly NR, Manikantan P, and Nichols JH. Anesth Analg 2003; 97:355-7.Reviewed by: Helen V. Lauro, MD
Review: A retrospective analysis of serum potassium levels in infants presenting with pyloric stenosis for pyloromyotomy was conducted. The authors also examined whether the preoperative potassium value affected the choice of muscle relaxant used for anesthetic induction. One hundred forty three charts of infants who were diagnosed with pyloric stenosis and subsequently underwent pyloromyotomy over a 6 year period from 1995-2000 were reviewed. Exclusion criteria were present in three charts where the potassium sample was reported as hemolyzed. The age range of the remaining 140 patients (in weeks) was 7.3 ñ 4.3. The authors defined their upper limit of normal serum potassium based on their hospital laboratory reference range as 5.3 meq/l. Of 140 patients, the percentages of their patients with potassium levels exceeding this upper limit of normal were: 35.3 = 36%, >5.3 = 30%, >5.5 = 19 %, >5.7 = 9%, >6.1 = 7%, with a mean potassium of 5.7 ñ 0.5 meq/l. Interestingly only 8% of patients manifested the classic hypokalemia, here defined as serum potassium less than 3.6 meq/l. Sixty three patients received succinylcholine, 46 received a nondepolarizer, and 31 an awake intubation. There was no correlation found between administration of succinylcholine and potassium value (mean potassium values in the above groups were 5.0 ñ 1.0 meq/l, 5.0 ñ 0.7 meq/l, and 4.8 ñ 0.8 meq/l respectively.). Electrocardiograms performed in children that received succinylcholine did not reveal any dysrhythmias. An excellent review of the literature follows in the discussion. The possible etiologies of the hyperkalemia, included acidemia due to acid-base changes and psuedohyperkalemia. The authors describe that the latter can be due to1 excessive squeezing at the site of skin puncture (up to 0.44 meq/l),2 fist clenching with or without tourniquet use (up to 1.4 meq/l),3 hemolysis from traumatic venipuncture with a small-gauge needle,4 delayed transport of sample (significant increases),5 icing of the samples during transport (increases up to 0.1 meq/l). Methods of blood drawing are important in evaluating hyperkalemia (heel stick versus venipuncture). The discussion concludes with the debatable question of what absolute value constitutes the upper level of normal potassium in a patient in this age group. The variability is partly dependent on the source (for example The Merck Manual > 5.5), and on the age of the patient. In a neonate to young infant the value has been reported as 5.3, 5.6, and 5.8. The authors raise a very important point in their discussion, which deserves emphasis-there is no absolute cutoff of what numerical value constitutes the upper limit of normal serum potassium. Part of the reason is that the laboratories that validate their own reference ranges before clinical use, do not usually do so via infant blood. That is because most hospitals do not have enough samples on healthy children to adequately define the reference range, despite a desire for age-specific limits on laboratory values. Also, different instruments are used at different institutions. Comments: This study is the first to report hyperkalemia in patients with pyloric stenosis. A hypokalemic, hypochloremic, metabolic alkalosis is the prototype. It is a significant question, which is unanswered in the article, as to how the pediatric anesthesiologist should respond when a surgeon or neonatologist asks him to proceed with surgery in a pediatric patient with elevated serum potassium. Blood draws performed by heel-stick are particularly prone to hemolysis. While hemolysis is measured by a visual determination, and many samples are readily identifiable as grossly hemolyzed, occult hemolysis may be present and hence unreported, still resulting in high serum potassium level. However, the pediatric anesthesiologist cannot medicolegally dismiss that hyperkalemia is artifactual in nature and that the patient is exempt from further evaluation. In view of the fact that many intraoperative variables beside the choice of muscle relaxant can affect serum potassium including ventilatory status of the patient during the case, hyperglycemia (in the presence of insulin deficiency), blood transfusions, and iatrogenic potassium excess, the safest practice may be to follow the individual hospital's upper limit of normal potassium, on the reference range, as was done in this article. In elective cases a high preoperative serum potassium level should be repeated by true venipuncture, with avoidance of all of the possible causes of pseudohyperkalemia mentioned in the discussion of this article. If the repeat potassium level is unchanged an EKG should be performed. With the exception of a very small preterm infant, even in an emergency, serum potassium higher than 6.0 meq/l is unacceptable1, and tall and tented T waves may present. Search for correctable etiologies of hyperkalemia may necessitate evaluation by other services such as endocrinology or nephrology, and possibly require hemodialysis. In emergent cases, serum potassium can be lowered rapidly by 0.5 g/kg glucose as a 10% solution with 1 unit of regular insulin added for each 5 g of glucose. Alternatives to succinylcholine such as rocuronium should be sought, and if not offered rapid-sequence intubating conditions can be obtained by doubling the induction dose of any nondepolarizing muscle relaxant. Myocardial contractility can be stabilized with 10% calcium gluconate 0.5 cc/kg IV over 5-10 minutes, and serum potassium monitored one-two times hourly. 1. Steward, D. J. et al. Manual of Pediatric Anesthesia. 5th ed. New York:Churchill Livingstone, 2001. Table of Contents
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