Metabolic acidosis is a disorder of the acid–base balance which may be due to bicarbonate losses, deficient acid elimination by the kidney, exogenous intake of acids or an endogenous increased acid production. Within this last group, lactic acidosis should be noted, because of its frequency, morbidity and potential mortality. Lactic acidosis, which is generally caused by accumulation of the l-lactic isomer, can be congenital or secondary, the latter is in relation to tissue hypoxia (type A) or to hepatic, renal or oncologic diseases, intense exercise, seizures or toxics (type B). Less common are the situations where the cumulative isomer is the d-lactic,1–3 which have occasionally been reported in patients suffering from short bowel syndrome (SBS), presenting with a metabolic acidosis, increased anion GAP and neurological symptoms.4,5

We present a case of a ten month old infant with SBS secondary to gastroschisis and intestinal necrosis. He had undergone surgery three times during the neonatal period with a remaining small bowel of 30cm preserving the ileocecal valve. The patient's diet was composed of extensively hydrolysed lactose-free formula, gluten-free cereal, vegetables and chicken. Feeding was done mostly through nasogastric tube, with some participation of oral feeding. Metronidazole 20mg/kg/day and cefixime 8mg/kg/day were administered alternatively the first week of each month as intestinal decontamination protocol. The month before admission, abundant stool production with decreased consistency associated to weight loss was present. Coincidentally, the decontamination protocol was not followed and 48h prior to admission, he developed a respiratory syncytial virus respiratory tract infection. On admission, the anthropometric data showed severe malnutrition: weight 4.41kg (cm (mmol/L) and the anion GAP was increased (27mEq/L) with normal lactic levels (0.7mmol/L). Ketonuria was absent. Correction therapy was started with intravenous fluids containing bicarbonate and oral metronidazole. Prior to this, a venous blood sample in a lithium heparin tube was immediately centrifuged. Plasma was frozen and sent for d-lactic acid analysis to a reference laboratory (Birmingham Children's Hospital, Birmingham, through Reference Laboratory, Barcelona), confirming the suspected diagnosis (d-lactic acid>6mmol/L). The outcome was satisfactory with normalization of neurological symptoms and gradual improvement of the acid–base balance.

d-Lactic acidosis usually originates from an accumulation of d-lactic secondary to an elevated synthesis by gastrointestinal tract bacteria.5 Production of d-lactic is minimal under normal conditions and is easily metabolized by the mitochondrial d-lactate dehydrogenase.2,3 However, in the SBS, a high carbohydrate intake may generate an increased production and subsequent accumulation of d-lactate because of the bacterial overgrowth.1–3 This entity should be suspected in patients associating neurological symptoms and metabolic acidosis with elevated anion GAP without increasing l-lactic acid, as in our case.4,5 We could not find in the literature any report involving such a young infant. We highlight that in our routine blood analysis, only l-lactic acid is detected. When this condition is suspected, it should be confirmed by a special measurement of serum or plasma d-lactic concentration. Normal values of d-lactic acid in blood are undetectable, being those above 3mmol/L pathological.2

The treatment is based on pathogenic flora elimination (administration of oral nonabsorbable antibiotics as metronidazole, neomycin or vancomycin), correction of the acidosis and carbohydrate restriction diet.2,3 Administration of probiotics is controversial. Bifidobacterium breve and Lactobacillus casei are theoretically non d-lactate producing flora and have been occasionally used as adjuvant therapy with antibiotics, in order to replace the pathogenic flora.6 However, two cases of d-lactic acidosis in patients with SBS attributed to the administration of probiotics containing d-lactate producing strains (Lactobacillus acidophilus, Lactobacillus bulgaricus and Bifidobacterium infantis) have been reported.6 Probiotics must be carefully selected in children with SBS.6 There are few data available related to the ideal maintenance therapy due to the lack of controlled studies. Avoiding fast-acting carbohydrate diets, periodical decontamination or the use of non d-lactate producing probiotics are different options which should be individualized in patients at risk of developing d-lactic acidosis.2,3,6

This case is a reminder of the importance of suspecting this rare entity in SBS affected children presenting with neurological symptoms and metabolic acidosis where routine blood tests do not detect the increased anion. In these situations an early treatment should be mandatory.