A 60-year-old man is hospitalized due to elective pancreaticoduodenectomy. The patient recently had worsening jaundice and was found to have a tumor in the head of the pancreas causing biliary obstruction. Further evaluation revealed early-stage pancreatic adenocarcinoma. A modified Whipple procedure with resection of the head of the pancreas, distal duodenum, common bile duct, and gallbladder, followed by pancreatic-enteric, biliary-enteric, and enteroenteric anastomoses, is performed. After the surgery, the patient begins enteral feeding. His pain is controlled, but a large amount of output is noted from the surgical drain placed at the pancreatic bed. The drainage fluid appears cloudy and has a high amylase level. A postoperative pancreatic leak is suspected, and nonoperative management is planned. This patient is at greatest risk for which of the following metabolic derangements due to this operative complication?

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11ec25c8_d88e_3d20_bc81_cda7b4f3baf4_MD0003_00 A postoperative pancreatic leak often resolves with conservative management. Surgical drains prevent pancreatic excretions from accumulating in the abdomen and causing peritonitis; however, with high drain output of pancreatic fluid the patient is likely to develop primary metabolic acidosis (low pH, low bicarbonate) with a normal anion gap and compensatory respiratory alkalosis (low PaCO₂). metabolic acidosis Nonanion gap metabolic acidosis (NAGMA) results from the loss of bicarbonate (HCO₃⁻). Exocrine pancreatic fluid is high in HCO₃⁻ as it must neutralize the highly acidic chyme coming from the stomach to facilitate enzymatic digestion in the small intestine. The massive loss of HCO₃⁻ via external pancreatic fluid drainage reduces serum HCO₃⁻, decreasing blood pH. Other conditions involving large-volume fluid loss from the small intestine (eg, high ileostomy output, enterocutaneous fistula) also cause NAGMA.⁻ Exocrine pancreatic fluid⁻⁻ Because HCO₃⁻ and chloride (Cl⁻) are the predominant anions in the body, the loss of HCO₃⁻ increases serum Cl⁻ to maintain an electronegative balance. Due to this relationship, NAGMA is also referred to as hyperchloremic acidosis.⁻ ⁻⁻ ⁻ (Choice B) Elevated pH with low PaCO₂ indicates primary respiratory alkalosis. Low HCO₃⁻ represents compensatory metabolic acidosis, as would be expected with chronic hyperventilation (eg, residing at high altitude).⁻ (Choice C) Anion gap metabolic acidosis results from the accumulation of unmeasured acidic compounds (eg, lactic acid, ketones) in the blood. The unmeasured compounds donate H⁺ to bind HCO₃⁻ and acidify the blood, and the remaining anionic component increases the anion gap.⁻ increases (Choice D) Elevated pH with high HCO₃⁻ and high PaCO₂ represents primary metabolic alkalosis with compensatory respiratory acidosis, as would be expected with the loss of H⁺ that occurs with nasogastric suctioning or severe vomiting.⁻ (Choice E) Low pH with high PaCO₂ indicates respiratory acidosis. High HCO₃⁻ represents compensatory metabolic alkalosis, as would be expected with chronic hypoventilation (eg, obesity hypoventilation syndrome).⁻ Educational objective: Nonanion gap metabolic acidosis (NAGMA) results from the loss of bicarbonate (HCO₃⁻). Because exocrine pancreatic secretions are high in HCO₃⁻, NAGMA is expected with large-volume fluid losses from the pancreas (eg, pancreatic duct leak) or small intestine (eg, high ileostomy output, enterocutaneous fistula).⁻⁻ References: Hyperchloremic acidosis. (http://www.ncbi.nlm.nih.gov/pubmed/29493965)

A 60-Year-Old Man Is Hospitalized Due to Elective Pancreaticoduodenectomy