Comparative biochemical analyses of venous blood and peritoneal fluid from horses with colic using a portable analyser and an in-house analyser

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.

Accuracy of differences in blood and peritoneal glucose to differentiate between septic and non-septic peritonitis in horses

Difference in blood and peritoneal glucose (DBPG) is used in clinical practice to support a diagnosis of septic peritonitis in horses. It is inexpensive, easy and rapid to perform. The aim of this study was to evaluate the accuracy of the DBPG to differentiate between septic and non-septic peritonitis in horses. Blood and peritoneal fluids were harvested from suspected animals. Plasma and peritoneal glucose levels, total nucleated cell count, direct microscopic and microbiological examinations of the peritoneal fluid were evaluated. Using DBPG levels, the animals were classified into two groups: difference ≥ 50 mg/dL (positive test) and difference < 50 mg/dL (negative test). Positive microbiological examination and/or presence of bacteria in direct microscopic examination was used as a gold standard to detect septic peritonitis. The accuracy parameters analysed were: sensitivity, specificity, and positive/negative predictive values, for which the results were respectively: 0.23, 0.91, 0.60 and 0.67. Due to poor accuracy, other cut-off margins and peritoneal glucose concentrations were evaluated. The test was considered most accurate when the DBPG was zero with sensitivity, specificity, and positive/negative predictive values of 0.85, 0.82, 0.73, 0.90 respectively. Peritoneal glucose concentrations alone were not a reliable feature to detect peritonitis. DBPG ≥50 mg/dL, widely used for the diagnosis of septic peritonitis, does not have a good accuracy and the DBPG = 0 has a better accuracy for detecting the disease.

Evaluation of a new handheld point-of-care blood gas analyser using 100 equine blood samples

OBJECTIVES

To determine whether the Enterprise point-of-care blood analysis system (EPOC) produces results in agreement with two other blood gas analysers in regular clinical use (i-STAT and Radiometer ABL77) and to investigate the precision of the new machine when used with equine whole blood.

STUDY DESIGN

Prospective, randomized, non-blinded, comparative laboratory analyser study.

ANIMALS

Horses admitted to a university teaching hospital requiring arterial or venous blood gas analysis as part of their routine clinical management.

METHODS

One hundred equine blood samples were run immediately, consecutively and in randomized order on three blood gas analysers. Results of variables common to all three analysers were tested for agreement and compared with guidelines used in human medicine. These require 80% of results from the test analyser to fall within a defined range or percentage of results from the comparator devices to achieve acceptability. Additionally, 21 samples were run twice in quick succession on the EPOC analyser to investigate precision.

RESULTS

Agreement targets were not met for haematocrit, haemoglobin and base excess for either i-STAT or ABL77 analysers. EPOC precision targets were not met for partial pressure of carbon dioxide, ionized calcium, haematocrit and haemoglobin. Overall comparative performance of the EPOC was good to excellent for pH, oxygen tension, potassium, bicarbonate and oxygen saturation of haemoglobin, but marginal to poor for other parameters.

CONCLUSIONS AND CLINICAL RELEVANCE

The EPOC may be useful in performing analysis of equine whole blood, but trend analysis of carbon dioxide tension, ionized calcium, haematocrit and haemoglobin should be interpreted with caution. The EPOC should not be used interchangeably with other blood gas analysers.

Evaluation of 3 handheld portable analyzers for measurement of L-lactate concentrations in blood and peritoneal fluid of horses with colic

OBJECTIVE

To compare 3 portable handheld analyzers with a bench top blood gas analyzer for measurement of blood and peritoneal fluid L-lactate concentrations in horses admitted with signs of colic.

STUDY DESIGN

Prospective clinical study.

SAMPLE POPULATION

Blood and peritoneal fluid from horses with colic.

METHODS

L-lactate concentrations in heparinized blood and peritoneal fluid were measured serially on 10 occasions to evaluate repeatability of the portable analyzers. Blood and peritoneal fluid L-lactate concentrations were simultaneously evaluated by a bench top and 3 portable analyzers and the results compared by intraclass correlation coefficients and Bland Altman plots. L-Lactate concentrations in a subgroup of peritoneal fluid samples were evaluated by a chromogenic laboratory assay and compared with the bench top and the handheld analyzers.

RESULTS

Portable lactate analyzers had good intra-analyzer reliability for peritoneal fluid. Two portable analyzers had poor intra-analyzer reliability for mid concentrations of L-lactate in blood. L-lactate measurements from portable analyzers were closer to the bench top analyzer at low concentrations of L-lactate than at higher concentrations. Compared with the bench top analyzer, the Lactate Pro and Lactate Plus have the highest intraclass correlation coefficient and the smallest bias for peritoneal fluid and blood L-lactate, respectively. The bench top analyzer and the Lactate Pro had the highest level of agreement for peritoneal fluid compared with the chromogenic assay.

CONCLUSIONS

Although portable analyzers are alternatives for the measurement of L-lactate concentration in field situations, clinicians need to be aware of the variable results between analyzers, especially when extrapolating means or cutoff values from studies using different lactate analyzers.

Blood lactate measurement and interpretation in critically ill equine adults and neonates

Admission blood lactate concentration is widely used as a prognostic indicator in equine medicine and can be a useful indicator of disease severity but typically fails to completely discriminate survivors from nonsurvivors. Increased admission lactate concentrations in adult horses typically return to normal within 12 to 24 hours. Lactate concentrations in neonatal foals are higher than adult concentrations for the first 24 to 72 hours of life. Serial measures reflecting both the magnitude and duration of hyperlactatemia might enable more accurate prognostication and provide insight into disease pathogenesis and could be a valuable therapeutic guide.

Exogenous L-lactate clearance in adult horses

OBJECTIVE

To determine endogenous production of L-lactate and the clearance of exogenous sodium L-lactate (ExLC) in healthy adult horses.

DESIGN

A sodium L-lactate solution (1 mmol/kg body weight qs to 500 mL final volume in 0.9% NaCl) was adminstered IV over 15 minutes. Blood samples for L-lactate concentration [LAC] measurement were collected immediately prior to infusion, at 5, 10, and 15 minutes during infusion and at 1 minute intervals for 15 minutes, at 30, 45, 60, 120, and 180 minutes postinfusion. Disposition modeling and pharmacokinetic analysis was performed using proprietary software.

SETTING

University Teaching Hospital.

ANIMALS

Six clinically healthy adult horses.

MEASUREMENTS AND MAIN RESULTS

Median (range) baseline [LAC] was 0.43 (0.20-0.72) mmol/L for samples obtained every 3 hours over the 24 hours prior to ExLC and demonstrated variability primarily associated with horse. Median [LAC] immediately prior to ExLC was 0.43 (0.35-0.52) mmol/L. A 2-compartment model was used to specify the pharmacokinetic parameters. Median (range) ExLC was 1.05 (0.073-1.75) L·h(-1) ·kg(-1) and t(1/2) β was 29.54 (20.8-38.6) min. Median lactate production based on basal [LAC] immediately prior to ExLC was was 0.49 (0.31-0.93) mmol·h(-1) ·kg(-1) .

CONCLUSIONS

ExLC in healthy adult horses is greater than that of hyperlactemic human patients but similar to normolactemic-sick human patients examined using the same model, supporting development of species, and disease specific ExLC parameters.

Comparison of pH, lactate, and glucose analysis of equine synovial fluid using a portable clinical analyzer with a bench-top blood gas analyzer

OBJECTIVE

To compare agreement between a portable clinical analyzer and laboratory-based bench-top analyzer for analysis of pH, lactate, and glucose concentrations in synovial fluid.

STUDY DESIGN

Prospective experimental study.

ANIMALS

Clinically normal horses (n=8); 6 horses euthanatized for reasons unrelated to the study; 11 horses that had synoviocentesis for reasons other than sepsis; 7 horses that had synoviocentesis for evaluation of sepsis; and 2 horses without recorded clinical data. Median age of horses was 8 years (range, 1 day to 24 years).

METHODS

Supernatant from each synovial fluid sample was analyzed for pH, lactate, and glucose concentrations using an ABL 705 laboratory-based bench-top analyzer and i-STAT portable clinical analyzer. Bland-Altman plots were constructed and concordance analysis performed to determine bias and agreement between the 2 analyzers.

RESULTS

There was acceptable agreement between analyzers for lactate and glucose concentrations, with biases of 0.198 mmol/L and 9 mg/dL and concordance correlation coefficients of 0.97 and 0.96 for lactate and glucose, respectively. The agreement between analyzers for pH was not acceptable, with a bias of -0.057 and concordance correlation coefficient of 0.89.

CONCLUSIONS

This study found that the portable clinical analyzer performed similarly to the bench-top blood gas analyzer for evaluation of lactate and glucose concentrations, but not pH, in synovial fluid.

Effects of aerobic and anaerobic fluid collection on biochemical analysis of peritoneal fluid in healthy horses and horses with colic

OBJECTIVE

To determine whether in healthy horses and those with colic, exposure of peritoneal fluid to room air affects values obtained on biochemical analysis.

STUDY DESIGN

Prospective study.

ANIMALS

Adult horses with a primary complaint of acute abdominal pain (n=29) and 12 healthy horses.

METHODS

Peritoneal fluid was aseptically collected under aerobic and anaerobic conditions. After collection, pH, PCO(2) , PO(2) , HCO(3) (-) , Na(+) , ionized Ca(2+) , K(+) , lactate, and glucose were immediately measured using a commercial blood gas analyzer. Biochemical variables were compared between aerobically and anaerobically obtained samples using a paired t-test.

RESULTS

In healthy horses, peritoneal fluid samples collected under anaerobic conditions had higher PCO(2) and ionized Ca(2+) and lower PO(2) , HCO(3) (-) , and pH compared with samples exposed to air. No differences were observed for K(+) , Na(+) , glucose, and lactate. In horses with colic, samples collected anaerobically had higher PCO(2) , ionized Ca(2+) , Na(+) , and glucose and lower PO(2) , HCO(3) (-) , and pH value compared with samples exposed to air. No differences were observed for K(+) and lactate.

CONCLUSION

Exposure of peritoneal fluid to room air had a significant effect on pH, PCO(2) , PO(2) , and variables associated or dependent on changes in pH such as HCO(3) (-) and ionized Ca(2+) . Interpretation of biochemical analysis of peritoneal fluid may be influenced by sample collection method.

Plasma lactate as a predictor of colonic viability and survival after 360 degrees volvulus of the ascending colon in horses

OBJECTIVES

To determine the relationship between plasma lactate concentration and colonic viability and survival in horses with >or=360 degrees volvulus of the ascending colon.

STUDY DESIGN

Retrospective study.

ANIMALS

Horses (n=73) with >or=360 degrees volvulus of the ascending colon.

METHODS

Medical records (January 2000-November 2005) of all horses examined for colic at Michigan State University Veterinary Teaching Hospital were reviewed. Horses were included only if plasma lactate concentration was measured preoperatively and a diagnosis of >or=360 degrees volvulus of the ascending colon was confirmed by surgery or necropsy. Non-survivors were only included if the ascending colon was evaluated histopathologically. Logistic regression analysis was used to model the relationship between lactate, colonic viability, and survival.

RESULTS

Of 73 horses, 61 were discharged. Mean (+/-SD) plasma lactate concentration was significantly lower in survivors (2.98+/-2.53 mmol/L) compared with non-survivors (9.48+/-5.22 mmol/L; odds ratio [OR]=1.628, 95% confidence limit [CI]=1.259-2.105). Plasma lactate concentration was significantly lower in horses with a viable colon (3.30+/-2.85 mmol/L) compared with horses with a non-viable colon (9.1+/-6.09 mmol/L; OR=1.472, 95% CI=1.173-1.846). Plasma lactate concentration <6.0 mmol/L had a sensitivity of 84% and a specificity 83% for predicting horse survival.

CONCLUSIONS

Our results demonstrate a strong association between plasma lactate concentration at the time of hospital admission and outcome in horses with >or=360 degrees volvulus of the ascending colon.

CLINICAL RELEVANCE

Plasma lactate concentration may help predict colonic viability and horse survival after ascending colon volvulus in horses.