Evaluation of peritoneal l-lactate concentration in horses in the early post-partum period

BACKGROUND

Peritoneal fluid lactate concentration is an important diagnostic tool in horses with abdominal pain. Information on peritoneal lactate concentrations is lacking following parturition in the mare.

OBJECTIVES

To compare blood and peritoneal lactate concentrations in a population of mares within 36 h post-partum, report a normal reference range and identify any impact of retained foetal membranes (RFMs).

METHODS

This is a retrospective study evaluating healthy mares from which blood and peritoneal samples had been obtained within 36 h of parturition. Exclusion criteria included signs of abdominal pain within this period. Data was interrogated for normality using a Shapiro-Wilk test. Wilcoxon signed-rank test and Bland-Altman analysis were used to compare blood and peritoneal lactate concentrations. Linear regression was used to compare age and breed data with peritoneal lactate concentrations. Significance was defined as p < 0.05.

RESULTS

Forty mares met the inclusion criteria. Mean age was 12.6 ± 4.1 years, and most mares were multiparous (65%). Peritoneal lactate ((1.2 (IQR = 0.9-1.6) mmol/L) was increased compared to blood lactate concentration (0.7 (IQR = 0-1.1)mmol/L; p < 0.001). Plasma total protein (TP) concentrations were 68 (IQR = 64-74) g/L and peritoneal protein concentrations 8 (IQR = 4-9.7) g/L. Six mares developed RFM. The median fold-increase in peritoneal lactate concentration compared to blood lactate concentration was 0.9 (IQR: 0.01-1.7; range: 0-2.5). The reference range for peritoneal fluid lactate concentration was 0-2.5 mmol/L.

CONCLUSION

Peritoneal lactate concentrations in healthy post-partum mares remained within the normal reference range and were not influenced by RFM or parturition. Increased peritoneal lactate in this group warrants further investigation.

Interpreting abdominal fluid in colic horses: Understanding and applying peritoneal fluid evidence

BACKGROUND

Interpreting changes in peritoneal fluid helps clinicians manage colic and other diseases in horses. During abdominal problems in the horse, abdominal fluid characteristics such as color, turbidity, total nucleated and red blood cell counts, cytology, total protein, and l-lactate change in predictable ways, helping the clinician characterize the disease.

DESCRIPTION

Normal abdominal fluid in horses is odorless, clear to light yellow in color, and transparent. Peritoneal fluid becomes more turbid with increasing levels of protein, number of WBCs or RBCs, or with gross contamination following intestinal rupture. The color of abdominal fluid will also change with the type and quantity of cells or other elements present. The transformation of peritoneal fluid color from golden to orange to red represents increasing levels of RBCs, common with strangulating intestinal lesions. Serosanguinous defines fluid that is both turbid and orange to bloody because of increased total protein, WBCs, and RBCs, and is considered classic for diseases characterized by intestinal ischemia. Peritoneal fluid may also be red or blood-colored because of a hemoperitoneum, or secondary to blood contamination during sample collection. l-Lactate measurement in the abdominal fluid has proven invaluable for the identification of strangulating intestinal injury. Cytology acts as an important supplement to cell counts in peritoneal fluid, and the normal ratio of non-degenerate neutrophils:mononuclear cells of 2:1 changes during various gastrointestinal diseases. Culture of peritoneal fluid samples should be performed when septic peritonitis is suspected.

SUMMARY

Abdominal fluid is a sensitive indicator of intestinal injury and a useful tool to direct treatment. Peritoneal fluid evaluation includes gross visual and olfactory examination, nucleated cell count, total protein, RBC count, lactate levels, cytology, and culture. The changes noted in such variables are related to the type and duration of the abdominal problem.

KEY POINTS

 Abdominal fluid interpretation has become central to the triage and management of challenging equine colic patients.  The transformation of peritoneal fluid color from golden to orange to red represents increasing levels of RBCs, common with strangulating intestinal lesions.  Contamination with RBCs at various concentrations may be secondary to vascular (eg, abdominal wall or mesenteric vessels) or splenic trauma during abdominal fluid collection; however, this must be distinguished from orange to red fluid associated with intestinal strangulating obstruction or hemoabdomen  Peritoneal fluid analysis reveals abdominal pathology by recognizing specific changes that occur with disease processes affecting the tissues and organs within this cavity.  Abdominal fluid examination should be used as a tool to direct treatment rather than the definitive test for diagnosis of the acute abdomen  Septic peritonitis in horses most commonly originates secondary to intestinal compromise or accidents (vascular damage, perforation, or surgical manipulation), leading to bacterial translocation into the abdomen.