Mixed Metabolic and Respiratory Alkalosis: An Uncommon Presentation of Superior Mesenteric Artery Syndrome in an Adolescent Male Patient.

Superior mesenteric artery (SMA) syndrome is an uncommon cause of proximal intestinal obstruction resulting from compression of the third portion of the duodenum between the abdominal aorta and the SMA. Patients typically present with postprandial epigastric pain, bilious vomiting, and weight loss, and most exhibit metabolic alkalosis due to persistent loss of gastric acid. We report the case of a 16-year-old male child with progressive postprandial vomiting and significant nutritional decline who was diagnosed with SMA syndrome on the basis of reduced aortomesenteric angle and marked duodenal dilatation on imaging. Uniquely, the patient demonstrated a mixed acid-base disorder, combining metabolic alkalosis from chronic vomiting with respiratory alkalosis likely secondary to hypoxia-induced hyperventilation. The patient underwent Strong's procedure with good postoperative recovery and resolution of symptoms. This case emphasizes the importance of recognizing atypical metabolic profiles in SMA syndrome, maintaining clinical suspicion in adolescents with chronic vomiting and weight loss, and intervening early to prevent complications.