Infantile hypertrophic pyloric stenosis (IHPS) results in electrolyte disturbances due to persistent vomiting. Though the significance of hyperventilation in metabolic acidosis is established, debate continues regarding hypoventilation in metabolic alkalosis. We present six cases of respiratory depression requiring ICU admission in infants with hypochloremic, hypokalemic metabolic alkalosis due to IHPS. Keywords:Infantile hypertrophic pyloric stenosis; Hypochloremic; Bronchiolitis; Hypoventilation; Alkalosis; Chemoreceptor; Hypochloremic debate continues regarding hypoventilation (i.e. compensatory respiratory acidosis) in metabolic alkalosis.A few case reports exist in the literature regarding hypoventilation in patients with pyloric stenosis [2][3][4][5][6][7]. We report our experiences of patients with IHPS who had respiratory depression and required pediatric intensive care unit (PICU) admission. We assessed the indications for PICU admissions for patients with IHPS over a 15 year period (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014) at the state's only tertiary pediatric hospital. In particular, we were interested in the detrimental respiratory effects of severe metabolic alkalosis associated with prolonged vomiting in IHPS. Materials and MethodsA retrospective chart review was performed on patients with IHPS admitted into PICU at Princess Margaret Hospital for Children, between 2000 and 2014 inclusive. Charts were reviewed with special attention to presentation, oxygen requirements, apneas and bradypneas, blood results, operative reports, past medical history, investigation of alternative diagnoses, and management. Data entry was completed using Microsoft Excel. The hospital ethics committee approved this study. FindingsThe process for identification of cases for this series is detailed in Figure 1. This discussion will focus on the six cases admitted preoperatively with severe metabolic alkalosis and apneas and/or desaturations. Regarding the two other cases, one was admitted to PICU on day 2 for an acute pre-operative deterioration with massive hematemesis, and the second was admitted to PICU post-operatively for respiratory distress due to concurrent RSV bronchiolitis. This patient had a mixed picture of blood gases, with predominant respiratory acidosis. These cases will not be discussed further.Patient demographics are detailed in Table 1. All infants presented with persistent non-bilious vomiting after feeds, 5 of which had become projectile by presentation. At presentation, median chronological age 7.9 weeks (range: 4-12 weeks), corrected age 4.5 weeks (range: -0.5-12 weeks), and median weight 3.9kg (range: 2.7-4.2). Median duration of symptoms was 2.2 weeks (range: 0.5-6 weeks). Other symptoms included weight loss, reduced urine output (estimated by number of wet nappies), diarrhea, and constipation. On clinical assessment by emergency department physicians, all cases were documented as 'severely dehydrated' on admission.Two of the patients had po...