weekly_question 27/11/2022

[Admin]

A 5-week old infant presents with a six-day history of projectile nonbilious emesis. He is awake and responsive. His mother has noticed only one wet diaper in the last 24 hours. On exam the anterior fontanel is sunken. Electrolytes are sodium 136, potassium of 3.5, chloride 92, CO₂ 32. Following a normal saline bolus of 20 mL/kg, the most appropriate maintenance fluid for this patient with possible hypertrophic pyloric stenosis is:

A D10 W with 20 mEq/L potassium chloride

B D10 0.2% saline

C D5 0.9% (normal) saline

D D5 0.45% sodium chloride with 20 mEq/L of potassium chloride

[Admin]

correct answer
C D5 0.9% (normal) saline

Gastric outlet obstruction from pyloric stenosis may result in volume depletion, acid base imbalance and electrolyte abnormalities. The classic finding is hypokalemia, hypochloremia and metabolic alkalosis. Hydrogen and chloride are lost in the emesis and volume depletion occurs from poor intake. Renal chloride conservation initially results in excess bicarbonate and alkaline urine. Eventually, the extracellular volume depletion leads to an increase in aldosterone. With subsequent reabsorption of sodium in exchange for hydrogen and potassium, a low urine sodium and paradoxical aciduria may occur. The bicarbonate normally secreted by the pancreas into the duodenum in response to gastric acid is not neutralized and results in increased serum bicarbonate (alkalosis). This drives potassium into the cells but represents a relatively small fraction of total potassium losses.

Definitive management is pyloromyotomy but the metabolic abnormalities may not allow safe delivery of a general anesthetic until volume, acid base and electrolyte imbalances are corrected. Isotonic saline is the initial bolus fluid replacement of choice restoring volume as well as sodium and chloride deficiency. Half of the sodium deficit is usually replaced in the first 24 hours. This can be calculated as: Total body water (TBW) = 0.7 L/kg Sodium deficit = TBW x (140 - Serum Sodium). As such, in the subsequent maintenance fluids, additional sodium, potassium and dextrose will be required.

In 2018, AAP has issued guidelines recommending the use of isotonic fluids such as NS or LR for children greater than 28 days for maintenance fluids. In this patient who is not having adequate urine output, it is prudent to hold potassium at this time

[Mahmoud ABDELBARY]

D

[iantsai]

D

[Admin]

correct answer
C D5 0.9% (normal) saline

Gastric outlet obstruction from pyloric stenosis may result in volume depletion, acid base imbalance and electrolyte abnormalities. The classic finding is hypokalemia, hypochloremia and metabolic alkalosis. Hydrogen and chloride are lost in the emesis and volume depletion occurs from poor intake. Renal chloride conservation initially results in excess bicarbonate and alkaline urine. Eventually, the extracellular volume depletion leads to an increase in aldosterone. With subsequent reabsorption of sodium in exchange for hydrogen and potassium, a low urine sodium and paradoxical aciduria may occur. The bicarbonate normally secreted by the pancreas into the duodenum in response to gastric acid is not neutralized and results in increased serum bicarbonate (alkalosis). This drives potassium into the cells but represents a relatively small fraction of total potassium losses.

Definitive management is pyloromyotomy but the metabolic abnormalities may not allow safe delivery of a general anesthetic until volume, acid base and electrolyte imbalances are corrected. Isotonic saline is the initial bolus fluid replacement of choice restoring volume as well as sodium and chloride deficiency. Half of the sodium deficit is usually replaced in the first 24 hours. This can be calculated as: Total body water (TBW) = 0.7 L/kg Sodium deficit = TBW x (140 - Serum Sodium). As such, in the subsequent maintenance fluids, additional sodium, potassium and dextrose will be required.

In 2018, AAP has issued guidelines recommending the use of isotonic fluids such as NS or LR for children greater than 28 days for maintenance fluids. In this patient who is not having adequate urine output, it is prudent to hold potassium at this time