Peritoneal lactate concentration in Shetland ponies with non‐strangulating intestinal lesions

Background: Increased peritoneal fluid lactate concentrations (PFL) in colic cases have been described as negative prognostic indicators for survival and are typically associated with surgical lesions.Aim of report: To report increased peritoneal lactate concentrations occurring in colic cases receiving medical treatment only that survived to discharge.Case population and setting: Horses admitted for colic from two referral hospitals (United Kingdom 2020-2023, South Africa 2014-2021).Data collection: Retrospective evaluation of records.Horses with PFL >4 mmol/L that were discharged following only medical therapy were included.PFL was classified as mildly (4-5 mmol/L), moderately (5.1-10 mmol/L), and severely increased (>10 mmol/L).Descriptive data was generated, results reported as case numbers and percentage of cases with median and interquartile range (IQR) where appropriate.Clinical observations: Records from colic cases presented to the South African clinic (n = 799) and the UK clinic (n = 250) during the time periods were evaluated.33 cases satisfied the inclusion criteria, all horses were treated medically as deemed appropriate by the attending clinician and discharged.23/33 (70%) were geldings, 3/33 (9%) stallions and 7/33 (21%) mares.Horses were between 1 and 26 years old (median 10 years, IQR 9).The most common breeds were Thoroughbreds (9/33, 27%) and UK native breeds (9/33, 27%), followed by heavy and light draught breeds (4/33, 12%), Warmbloods (4/33, 12%), mixed breeds (4/33, 12%), Arabians (2/33, 6%) and Boerperds (1/33, 3%).Mildly increased PFL was seen in 11/33 (29%) horses.5/11 (46%) were diagnosed with large colon (LC) displacements (3 right dorsal (RDD), 1 left dorsal and 1 unspecified), 3/11 (27%) with LC impactions, one with concurrent RDD, 1/11 (9%) with caecal impaction and 2/11 (18%) with gastric impaction, one had concurrent peritonitis.Systemic lactate concentration (SL) (10/11) in this group ranged from 1.2 mmol/L to 5.7 mmol/L (median 2.5, IQR 1.9).Moderately increased PFL was observed in 13/33 (39%) cases, the most common diagnosis was intestinal impaction (6/13, 46%) (LC (3/6), small intestine (2/6), or both (1/6)).Other diagnoses with moderately increased PFL included enteritis (1/13, 8%), colitis (2/13, 15%), septic peritonitis (1/13, 8%) RDD (1/13, 8%), and cyathostominosis (2/13, 15%).SL within the moderately increased PFL group (13/13) ranged from 0.8 mmol/L to 6.4 mmol/L (median 3, IQR 2.45).Severely increased PFL was present in 9/33 (27%) horses which were diagnosed with colitis (3/9, 33%), septic peritonitis (2/9, 22%), LC displacement (2/9, 22%), enteritis (1/9, 11%), and small intestinal impaction (1/9, 11%).SL (9/9) in horses with severely increased PFL ranged from 1.5 mmol/L to 11.4 mmol/L (median 5.6, IQR 5.9).Main limitations: This is a retrospective case series with only a small number of horses, that varied in breed, age, and sex.Lactate concentration was determined with different benchtop and handheld analysers.Records may have been incomplete.Patients were evaluated and treatment recommendations were made by different clinicians.Conclusions: Horses with severely increased PFL survived to discharge with medical therapy only.This demonstrates that the importance of severely increased PFL should not be overemphasised in the recommendation for surgery in colic patients.