Fluid of Choice in Congenital Hypertrophic Pyloric Stenosis (CHPS)
The fluid of choice for infants with congenital hypertrophic pyloric stenosis is isotonic saline (0.9% NaCl) given as 20 mL/kg boluses, with the number of boluses determined by the initial chloride level. 1
Initial Fluid Resuscitation Strategy
Chloride-Guided Bolus Protocol
The presenting serum chloride is the most sensitive and specific indicator for determining fluid resuscitation needs 1:
If initial Cl⁻ ≤97 mmol/L: Administer two 20 mL/kg isotonic saline boluses separated by one hour before rechecking electrolytes (73% sensitivity, 95% CI 64-80%) 1
If initial Cl⁻ <85 mmol/L: Administer three 20 mL/kg isotonic saline boluses separated by one hour before rechecking electrolytes (73% sensitivity, 95% CI 52-88%) 1
If initial Cl⁻ >97 mmol/L: Proceed with maintenance fluids only 1
Maintenance Fluid Composition
After initial bolus resuscitation, continue with isotonic fluids at 1.5 times maintenance rate 1. For infants under 1 year of age, maintenance fluid requirements are 120-150 mL/kg/day 2.
Electrolyte Correction Principles
Chloride Replacement is Critical
The severity of metabolic alkalosis correlates directly with chloride deficit 3. A chloride dose of 10 mmol/kg body weight reduces plasma bicarbonate by an average of 3 mmol/L 3. This relationship underscores why isotonic saline (which contains 154 mEq/L each of sodium and chloride) is the appropriate choice 1.
Avoid Hypotonic Solutions
Do not use hypotonic fluids for initial resuscitation in CHPS. While general pediatric guidelines recommend isotonic fluids for maintenance hydration in hospitalized children to prevent hyponatremia 2, this is even more critical in CHPS where chloride losses are substantial 3, 1.
Potassium Supplementation
Once urine output is established, potassium supplementation should be added to maintenance fluids at 1-3 mmol/kg/day 2. Hypokalaemia occurs in approximately 9% of CHPS patients at presentation 3.
Monitoring Parameters
Laboratory Assessment
Initial labs: Measure sodium, potassium, chloride, and bicarbonate at presentation 3, 1
Repeat labs: Recheck electrolytes after completing the chloride-guided bolus protocol (after 2-3 hours depending on initial chloride) 1
Pre-operative target: Chloride ≥100 mmol/L, bicarbonate <30 mmol/L, and potassium 3.1-5.2 mmol/L before proceeding to surgery 1
Clinical Indicators
Monitor for signs of adequate resuscitation including improved perfusion, urine output, and resolution of metabolic alkalosis 3, 1. Patients with electrolyte abnormalities at presentation have significantly longer hospital stays (2.6 vs 1.9 days) and require more total fluid (106 vs 91 mL/kg/day) 1.
Common Pitfalls to Avoid
Do not delay surgery for excessive laboratory draws. The chloride-guided protocol reduces unnecessary lab draws by predicting fluid needs upfront 1. Patients with abnormal electrolytes require an average of 2.8 electrolyte panels versus 1.3 in those with normal values 1.
Do not use balanced or hypotonic solutions for initial resuscitation. While there is discussion about balanced solutions versus normal saline in general pediatric populations 2, CHPS specifically requires aggressive chloride replacement that only isotonic saline provides 3, 1.
Do not underestimate fluid requirements based on physical examination alone. Assessment of fluid volume by physical examination and history is inaccurate in vomiting infants; the severity of metabolic alkalosis (reflected by low chloride and elevated bicarbonate) is a more reliable indicator of the fluid deficit 3.