Using peritoneal and blood lactate as predictor of condition type, surgical referral and prognosis in equine colic cases

ABSTRACT It is important to investigate fast and accurate equine colic syndrome diagnostic forms. Lactate results from anaerobic glycolysis; high levels of it may indicate intestinal disorders with tissue hypoperfusion and hypoxia. The current study aims at investigating whether blood and peritoneal lactate values observed when horses with colic syndrome were hospitalized, were associated with condition type, therapeutic referral, and survival rates. Retrospective analysis was applied to 498 medical records of animals with colic syndrome, at EQUIVET Hospital -SP; 89 cases were herein selected. Based on logistic regression, peritoneal lactate played a more significant part than blood in variables like obstruction type and survival rates. Surgical cases comprised 52.8% of analyzed animals; strangulation changes, 26%; and overall survival, 62.9%. Mean blood and peritoneal lactate level in animals showing strangulation changes reached 5.11 and 7.33mmol/L, whereas non-strangulation cases recorded 3.54 and 3.06mmol/L, respectively. On the other hand, mean blood and peritoneal lactate level recorded for survivors reached 3.43 and 2.42mmol/L, whereas non-survivors recorded 4.84 and 7.13mmol/L, respectively. We concluded that peritoneal lactate measured when horses with colic syndrome were hospitalized was a predictor of condition type, and of animal survival and prognosis. However, blood and peritoneal lactate measurements did not contribute to therapeutic referral.

The prognosis of horses treated with colic syndrome is essential to help define the therapeutic approach to be adopted and to provide owners with information about costs with surgery or patient stabilization (Grulke et al., 2001).Prognosis can vary depending on animals' condition type and on affected site, clinical evolution time, patients' overall condition and complications (Dukti and White, 2009).Mair and Smith (2005) reported 79.6% survival rate in simple small bowel obstructions cases and 54.8%, in strangulation-related injuries.With respect to the larger colon, Dukti and White ( 2009) reported 90% survival rate in simple obstruction cases and 52% in strangulation-related cases.
Lactate has been used and validated as systemic marker of poor tissue perfusion and anaerobic metabolism in horses (Southwood and Fehr, 2013); lactate analysis in peritoneal fluid is more sensitive than that of blood for prognostic purposes (Delesalle et al., 2007).Therefore, the aim of the current study was to investigate whether blood and peritoneal lactate levels, measured at the time horses with colic syndrome were hospitalized, were associated with animals' condition type, therapeutic referral, and survival rates, in order contribute to the therapeutic management and prognosis of horses affected by this disease.

MATERIALS AND METHODS
Medical records of adult horses with colic syndrome treated at EQÜIVET Hospital, Indaiatuba County-São Paulo State, from January 2016 to September 2020, were retrospectively reviewed.
Medical records comprising information about peritoneal and blood lactate measurements performed at hospitalization time, animals' condition diagnosis, treatment type, complications during hospital treatment and case evolution were included in the analysis.Records presenting incomplete medical reports and concomitant illnesses were excluded from the analysis.

Collected
data included blood and peritoneal lactate measurements conducted at hospitalization time; condition site; obstruction type (strangulation or non-strangulation); diagnosis; complications before, during, or after surgical or medical treatment; and outcome (hospital discharge, death, or euthanasia).Animals' survival was defined as hospital discharge.Necropsy reports issued for euthanasia or death cases were compiled.
Portable analyzer (Accutrend® Plus) was used to determine lactate concentrations in anticoagulant-free blood samples collected from animals' external jugular vein, as well as in abdominal fluid samples obtained through abdominocentesis and placed in tubes without anticoagulant.
Recommended temperature ranging from 15ºC to 35ºC was used for lactate measurement purposes.Accutrend® Plus analyzer enables measuring lactate levels ranging from 0.8 to 21.7mmol/L blood value and from 0.7 to 26mmol/L plasma value.However, the device's analyzer registers LOW for values lower than the aforementioned, and HIGH for values higher than them.This test must be performed 60 seconds after the sample is placed on the tape (Accutrend…, 2007).Quantitative values observed for blood and peritoneal lactate levels were used for statistical analysis; 0.6 mmol/L of blood lactate was recorded as LOW in the analyzer whereas 0.7mmol of peritoneal lactate was considered LOW and 27mmol/L of it was considered HIGH.
Multiple linear regression, carried out in IBM SPSS Statistics software version 20, was used to compare independent variables (sex, complications, gastrointestinal segment, peritoneal lactate, blood lactate, therapeutic referral, and obstruction type) to the dependent variable (animal's death).Binary logistic regression was carried out in the same software to compare the significance of dependent variables (venous lactate and peritoneal lactate) to that of independent variables (obstruction type, referral, and animal's survival).Both analyses were conducted at 5% significance level.Moreover, descriptive analysis was performed to investigate samples' features.

RESULTS
Medical records of 498 horses presenting abdominal discomfort, which were treated between January 2016 and September 2020mean number of 103 cases on a yearly basiswere analyzed.Of this total, 89 adult horses (21 Quarter Horses, 20 Brazilian Equestrians, 18 mixed breed, 11 Mangalarga Marchador, six Thoroughbred Lusitano, five Thoroughbred Arabian, three Thoroughbred English, two Campolina, one Breton, one Polo and one Paint Horse) -38 females and 51 males (only 1 stallion) -were selected based on the herein adopted inclusion criteria.Animals' conditions were divided into categories based on the affected site, gastrointestinal segment, obstruction type, need of surgical procedure, survival, and number of complications (Table 1).Regarding condition type, 74% of cases presented non-strangulating obstruction and recorded 77.3% survival rate, whereas 26% of cases presented strangulation changes and recorded 21.7% survival rate.As for digestive segments, gastric disorder cases recorded 100% survival rate; small intestine, 60.9%; large intestine, 66%; small and large intestines, 30%; and other cases, 66.7%.The need for surgical procedure was observed in 52.8% of the 89 included cases.Overall survival rate reached 62.9% -56 animals survived and 16 out of 33 non-survivors were euthanized.Among all 89 selected medical records, 7% reported diseases in animals' stomach; 26%, in the small intestine 53%, in the large intestine; 11%, in the small and large intestines; and 3%, in other sites.Animals belonging to the gastric disorder group, which presented gastric distension due to overload or gas, were included in the study.Affections diagnosed in the intestinal segment, listed as small intestine, comprised 14 compactions, five volvulus (three in the mesenteric root, one due to lipoma and one by the omentum), two incarcerations (in the gastrosplenic ligament and in the epiploic foramen), one rupture and one duodenitisproximal jejunitis.The ones listed as large intestine comprised 10 large colon displacements (one associated with impaction; one, with enterolithiasis in the small colon; and one, with large colon torsion), 19 impactions (six cecal, seven in the large colon (one associated with fecaloma in the small colon), five in the small colon; and one, in the large and small colon), five torsions (four in the large colon and one cecal), five tympany (two in the large colon and three cecal), three colitis, one ceco-colic intussusception, two enteroliths (one enterolith in the transverse colon and small colon and one, in the transverse colon and large colon rupture), and two fecalomas.
Health issues classified as disorders in the small and large intestine comprised five impactions (one of ileum and large colon displacement, two of ileum and large colon, one of small and large colon and colitis, one of large colon and duodenitis-proximal jejunitis), one enteritis and peritonitis, one mesenteric root torsion and small and large colon impaction, one large colon displacement and epiploic foramen entrapment, one cecal entrapment in abdominal hernia, and one inguinal hernia and large colon torsion.The ones named as others comprised one rectal rupture, one peritonitis and one adhesion case.

DISCUSSION
Based on the herein adopted inclusion criteria, 89 out of 498 medical records of horses with colic syndrome, which were treated during the investigated period, were analyzed in the current study.The herein analyzed overall equine colic syndrome profile accounted for surgical rate equal to 52.8%, whereas Laranjeira et al. (2009) observed 0.7% surgical rate in three military units in Rio de Janeiro city, which comprised 770 horses, in total.The low need of surgery observed in these military institutions can be explained by the gastric origin of colic causes, which ranged from 78.1 to 86.6%, whereas the one recorded in the present study reached 7%.
Survival rate reached 62.9% in the current study; the main affected sites comprised large intestine (53%), small intestine (26%), small and large intestines (11%), stomach (7%), among others (3%).On the other hand, Northeastern Brazil recorded lower survival rate (36.7% of cases) among 60 horses with colic syndrome.With respect to disease location, the large intestine was the most affected site (70% of cases), the small intestine accounted for 11.7% of cases, nonspecific causes were observed in 11.7% of animals, stomach was affected in 5% of cases, and small and large intestine accounted for 1.6% of cases (Pessoa et al., 2012).
Large intestine impaction was the most prevalent condition; it accounted for 19 veterinary medical consultations, 7 of them were associated with large colon.This finding corroborates the study conducted by Pessoa et al. (2012), who described large colon impaction as the most observed condition (23 out of 60 colic syndrome cases).
Only peritoneal lactate recorded statistically significant results in the joint analysis applied to peritoneal and blood lactate concentrations.This finding can be explained by the association between the two lactate types in gastrointestinal disorders, since peritoneal lactate levels may increase before blood lactate levels increase.The analysis of both lactate types is better explained by the peritoneal lactate concentration, whose increase is associated with intestinal ischemia.
The comparison between blood and peritoneal lactates based on obstruction type (nonstrangulating or strangulating), has shown statistically significant difference in peritoneal lactate levels.Mean peritoneal lactate concentration of 7.33mmol/L was observed in strangulation changes, whereas 3.06 mmol/L of it was observed in the non-strangulation ones.This statistical difference was also reported by Latson et al. (2005), who recorded mean peritoneal lactate concentration of 8.45 mmol/L in horses with strangulating obstruction and 2.09 mmol/L of it in animals with non-strangulating obstruction.
Therapeutic referral did not show statistical significance after lactate measurement at hospitalization time; this finding can be explained by conditions other than strangulation cases, which required surgery after patients did not show satisfactory evolution in the medical clinic.Strangulation injuries caused change to blood supply in the affected gastrointestinal segment and resulted in ischemia.Thus, peritoneal lactate levels rose due to anaerobic glycolysis and, subsequently, there was an increase in blood levels.These lactate levels were lower in non-strangulating injuries and their subsequent increase may indicate the need of surgical intervention; however, it would require serial lactate measurements in order to monitor patients' evolution (Latson et al., 2005) Based on the comparison between blood and peritoneal lactate concentrations to predict equine colic prognosis, peritoneal lactate was more adequate than blood lactate to predict the likelihood of strangulation injury and death.The higher the peritoneal lactate concentration at hospitalization time, the higher the risk of patients' death.According to Delesalle et al. (2007), peritoneal lactate is more adequate and sensitive to diagnose early ischemic intestinal injuries and to predict their outcome.

CONCLUSION
Peritoneal lactate measurements conducted at the time horses with colic syndrome were hospitalized were considered predictors of animals' condition type, survival and prognosis.The higher the peritoneal lactate concentration at hospitalization time, the higher the risk of death for horses with gastrointestinal colic syndrome.Variables, such as peritoneal lactate, strangulation changes and complications, were associated with negative patient's outcome and with increased risk of death.On the other hand, increased blood and peritoneal lactate concentrations did not contribute to the decisionmaking process associated with therapeutic referral.

Table 2 .
Mean blood and peritoneal lactate concentrations and their variation in non-strangulating and strangulating obstructions observed in 89 horses treated with colic syndrome, from 2016 to 2020, at Equivet Hospital, Indaiatuba County -SP, distributed based on affected segment (B=blood lactate;

Table 4 .
Analysis of variables with significance level, odds ratio and 95% confidence interval, based on outcome "death", in 89 adult horses with colic syndrome, who were treated at Equivet hospital, from 2016 to 2020 Reeves et al. (1989)ve investigated horses with colitis; they only failed to associate blood lactate concentration at hospitalization time with survival when the analysis was carried out 24 hours after it.However, these researchers did not analyze peritoneal fluid lactate, which could be associated with survival at hospitalization time, since lactate concentrations first increase in this fluid.Moreover, since lactate increase is also observed under nonsurgical and non-strangulating conditions, it may take place at lower concentrations.Animals' sex did not play a significant part in the survival rate of patients with colic syndrome analyzed in the current study.On the other hand, the retrospective analysis of 320 acute equine colic cases conducted byReeves et al. (1989)reported statistically significant difference in surgical survival rates among non-castrated (55.8%), castrated males (24.5%) and females (30.9%).