Gastroenterology & Hepatology
A 5 week old baby boy is brought to the Emergency Department by his mother. She is worried as he seems constantly hungry and is losing weight. She describes frequent non-bilious vomiting occurring about half an hour after formula feeding. On examination you are able to palpate a small mass in the epigastrium. Which of the following laboratory findings would you expect to find?
Answer:
This patient likely has pyloric stenosis. As vomiting continues, the infant loses hydrogen and chloride ions through emesis of gastric juices. As this metabolic derangement worsens, the kidney attempts to retain hydrogen ions by substituting potassium, resulting in a hypochloremic-hypokalemic metabolic alkalosis.Pyloric Stenosis
Gastroenterology & Hepatology
Last Updated: 15th September 2022
In infantile hypertrophic pyloric stenosis (HPS), hypertrophy of the pyloric sphincter results in narrowing of the pyloric canal. Pyloric stenosis leads to progressive and projectile nonbilious vomiting, typically in a 3- to-6-week-old infant. The incidence is four times greater in male infants than in female infants.
Pathophysiology
With prolonged vomiting, electrolyte and water loss leads to hypochloraemic, hypokalaemic metabolic alkalosis. Hypovolaemia results in an increase in aldosterone and subsequent renal reabsorption of sodium and water. This phenomenon results in a paradoxical loss of hydrogen ions. This alkalosis is worsened by renal reabsorption of bicarbonate. The severity of hypovolaemia and electrolyte abnormalities is directly proportional to the length of the symptoms prior to presentation.
Clinical features
Parents typically report a history of progressive non-bilious vomiting after feeding. There may be a history of formula changes without resolution of symptoms. GORD may have been tentatively diagnosed. The infant may also have poor weight gain, constipation, or symptoms of volume depletion (e.g. decreased wet nappies).
If the presenting history is suggestive, palpation of an olive-shaped upper abdominal mass (often known as an 'olive') confirms the diagnosis. The mass, which is the hypertrophied pyloric muscle, can be palpated in the epigastrium and right upper quadrant. The infant may also show peristaltic waves travelling from left to right across the abdomen on examination. This is due to the stomach attempting to force its contents past the narrowed pyloric outlet. Signs of volume depletion may be present, such as dry mucous membranes, flat or depressed fontanelles, or tachycardia.
Differential diagnosis
- Overfeeding
- Gastro-oesophageal reflux
- Malrotation
- Gastroenteritis
- Food allergy
- Duodenal, jejunoileal or pyloric atresia
Investigations
- An electrolyte panel should be ordered in all suspected cases; common findings include hypokalaemia, hypochloraemia, and metabolic alkalosis.
- Ultrasonography is the most commonly employed study for diagnosis. The sensitivity of ultrasound in diagnosing pyloric stenosis is reported to be 97% to 99%. Pyloric muscle thickness >4 mm and pyloric canal length >17 mm meet the diagnostic criteria for full-term infants.
Management
- Fluid and electrolyte replacement is paramount to the successful management of the infant with pyloric stenosis. Surgery must be delayed until hypovolaemia and electrolyte disturbances are corrected. If alkalosis is not corrected, it will prolong the risk for postoperative depression of respiratory drive.
- Pyloromyotomy is the definitive treatment. Pyloromyotomy involves the extramucosal longitudinal splitting of the pyloric muscle.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
