Introduction Infantile hypertrophic pyloric stenosis (IHPS) is a common gastrointestinal condition that can lead to metabolic alkalosis and, if uncorrected, to respiratory complications. A standardized approach to correct metabolic derangements and dehydration may reduce time until pyloromyotomy while preventing potential respiratory complications. Such an evidence-based policy regarding preoperative care is absent. We aim to formulate a recommendation about preoperative care for infants with IHPS using the Delphi technique. Materials and Methods The RAND/UCLA appropriateness method was used to reach international consensus in a panel of pediatric surgeons, pediatric anesthetists, and pediatricians. Statements on type and frequency of blood sampling, required serum concentrations before pyloromyotomy and intravenous fluid therapy, were rated online using a 9-point Likert scale. Consensus was present if the panel rated the statement appropriate/obligatory (panel median: 7-9) or inappropriate/unnecessary (panel median: 1-3) without disagreement according to the interpercentile range adjusted for symmetry formula. Results Thirty-three and twenty-nine panel members completed the first and second round, respectively. Consensus was reached in 54/74 statements (73%). The panel recommended the following laboratory tests and corresponding cutoff values prior to pyloromyotomy: pH ≤7.45, base excess ≤3.5, bicarbonate <26 mmol/L, sodium ≥132 mmol/L, potassium ≥3.5 mmol/L, chloride ≥100 mmol/L, and glucose ≥4.0 mmol/L. Isotonic crystalloid with 5% dextrose and 10 to 20 mEq/L potassium should be used for fluid resuscitation. Conclusion Consensus is reached in an expert panel about assessment of metabolic derangements at admission, cutoff serum concentrations to be achieved prior to pyloromyotomy, and appropriate intravenous fluid regime for the correction of dehydration and metabolic derangements in infants with IHPS.