Blood gas analysis in Mangalarga Marchador horses with colic

Objective. This study aims to distinguish blood gas changes in horses with colic syndrome in which small or large intestine is affected. Materials and methods. Thirty Mangalarga Marchador horses were assessed, divided into groups according to the affected intestinal segment in episodes of colic syndrome (ECS): a group (N=10) of horses suffering from ECS with lesions only in the small intestine, a group (N=10) of horses suffering from ECS with lesions only in the large intestine and a group (N=10) of healthy horses (control). All the animals with ECS were submitted to exploratory laparotomy in order to establish the intestinal segment affected. Blood samples were collected by venipuncture, before surgical procedure to determine sodium, potassium, chloride, urea, glucose, hematocrit, hemoglobin, pH, carbon dioxide partial pressure, total carbon dioxide concentration, bicarbonate, base excess and anion gap. Results. No significant changes were found in plasma levels of Na+, K+, Cl-, pCO2 and anion gap in any type of ECS. Horses with small intestine injuries presented higher levels of tCO2, urea and bicarbonate compared to those with large intestine injuries and to the control group, as well as higher levels of glucose and base excess than the control group. Conclusions. Horses with colic syndrome bearing small intestine injuries show wider variations in the blood gas parameters than horses with large bowel lesions. Key word: Acid-base imbalance, electrolytes, large intestine, small intestine (Source:CAB).


INTRODUCTION
Equine colic syndrome (ECS) or acute abdomen is a multifactorial syndrome that results in deep abdominal pain in horses, with a diversified etiology varying from excessive gas yielded from feed fermentation to obstruction and bowel torsion, commonly requiring surgical intervention (1).The diagnosis of ECS is relatively easy considering the features of the abdominal pain, which cause changes in animal behavior, but its etiology is yet a challenge for veterinarians, especially in the definition of the affected intestinal segment.
The use of supporting diagnosis tools, like hemogram, blood gas analysis and biochemical profile can give information concerning i n f l a m m a t o r y f o c u s e s , d e h y d ra t i o n o r hipovolemia, toxemia, and electrolytic, acidbase or metabolic imbalances, providing a more precise diagnosis, an adequate treatment and a more accurate prognosis (2).P ra c t i c a l l y a l l d i s o r d e r s a f f e c t i n g t h e gastrointestinal tract lead to imbalances in blood pH, bicarbonate, sodium, potassium and chloride that may be immediately corrected to avoid the risk of death.The acid-base and hydro-electrolytic evaluation, as well as the blood gas condition allow choosing the more appropriated treatment for the animal with colic syndrome.Blood gas analyzes the partial O 2 and CO 2 pressure as well as bicarbonate and pH (3), becoming the most appropriate method for evaluating the acid-base balance of organic fluids and their probable disturbances (4).Blood gas evaluation is a very useful parameter for determining the severity of the colic syndrome and also may helps in the identification of bowel lesions (1).
The present work had the aim of evaluating changes in blood gas parameters in Mangalarga Marchador horses suffering from colic syndrome, discriminating the intestinal bowel affected, in order to obtain additional tools for clinical and surgical assessment.

MATERIAL AND METHODS
Animals.All the horses in this work were selected following criteria of clinical signs of colic syndrome at a referred veterinary hospital.The animals were Mangalarga Marchador horses from 3 to 15 years old, from both sexes (18 males and 12 females).The location of the intestinal section affected was established through laparotomy procedure.
The animals were organized in three groups as follows: animals with lesions only in the small intestine (N=10); animals with lesions only in the large intestine (N=10); and healthy animals (control group) (N=10).
Sampling and analysis.Blood samples (2 mL), from the jugular vein, were collected anaerobically through heparinized tubes (Becton Dickinson, São Paulo, Brazil) for blood gas analysis before the surgical procedure.The analysis was done using a portable analyzer (I-Stat 1, Abbott, Princeton, USA), with specific cartridges following the manufacturer´s instructions.The equipment was automatically calibrated before the samples analysis.The cartridge used was EC8+, which is able to determine sodium (Na + ), potassium (K + ), chloride (Cl -), urea, glucose, hematocrit, hemoglobin, pH, partial carbon dioxide pressure (pCO 2 ), total carbon dioxide concentration (tCO 2 ), bicarbonate (HCO 3 ), base excess (EB) and anion gap (AG).

Statistical analysis.
Statistical analysis was performed through Anova test, relating the intestinal bowel affected with the studied parameters.Quantitative variables (mean and standard deviation) were analyzed using the Tukey test, considering a significance level of 5%, using the Instat program.

RESULTS
The values obtained for hemogasometric analysis according to the affected intestinal section are showed in table 1.
Plasma levels of Na + , K + , Cl -, pCO 2 and anion gap did not show any significant alteration (p> 0.05) no matter which was the affected bowel segment.Glucose concentration was higher in 65% of the animals suffering from ECS, compared to the reference values (maximum reference value: 115 mg/dL).Glucose and urea concentrations were higher (p<0.05) in the group of horses with small intestine lesions compared to animals with large intestine lesions and to control animals.The values of hematocrit and hemoglobin did adicionales para realizar una evaluación clínica y quirúrgica.
Venous blood pH was higher in 40% of the ECS cases than in the control animals.However, no differences in blood pH were found between the two groups of horses with colic syndrome (p>0.05).The tCO 2 was higher in horses with small intestine ECS compared to the other two groups of animals (p<0.05).The bicarbonate levels were increased in 70% of the horses with colic syndrome (maximum reference value: 26 mmol/L).It was observed that the highest the bicarbonate value, the more severe the clinical condition of the horses.The group of horses with small bowel lesions had the highest values of bicarbonate compared to the other groups of horses (p<0.05).In 60% of the animals with ECS the value of base excess was above +4 (reference value: -4 to +4), with higher values in the group with small bowel lesions (p<0.05).

DISCUSSION
This work shows evidences of blood gas alterations in horses with colic syndrome.The blood concentration of sodium was at the reference values in all the animals of this study, ECS and control, without any difference between the two groups of horses with colic syndrome.This was also the observation of Navarro et SCE, en comparación con los valores de referencia (valor de referencia máximo: 115 mg/dL).Las concentraciones de glucosa y urea fueron más altas (p<0.05)en el grupo de los equinos con lesiones en el intestino delgado en contraste con los animales con lesiones del intestino grueso y a los animales de control.Los valores de hemoglobina y hematocrito no evidenciaron diferencias entre todos los grupos de caballos (p>0.05).
Como en el presente estudio, Ferreira (8) no encontró variaciones significativas en los niveles al (6) who studied electrolytic alterations in horses with gastrointestinal disorders and did not find changes in sodium concentrations in several types of intestinal lesions.Ihler et al (7) also did not found differences in blood sodium comparing horses that survived or deceased in cases of ECS.During a clinical situation of ECS, anorexia and adipsia due to the severe pain might cause a depletion of extracellular fluid with loss of body water, although with small loss of electrolytes (8).This might lead to hypernatremia by hemoconcentration, but such a situation did not occur.
As in the present study, Ferreira (8) did not find significant variations in potassium levels in horses submitted to temporary fistulization at the cecum.Di Filippo et al ( 9) found lesser serum potassium values in horses that survived to colic syndrome compared to those that died and to the control group.That work was done with animals observed at the moment of the clinical examination, same as our study.The reduction of potassium values in colic cases may be attributed to less feed intake or to gastrointestinal losses (10).
Chloride blood levels also were not affected by the clinical condition of ECS, as in the work of Navarro et al (6).Costa et al (11) observed significant decrease in serum chloride in horses with jejunum isquemia.
Glycemia was higher in horses with lesions in the small bowel.This result was also observed by Di Filippo et al (9) who found hyperglycemia in horses that survived to a colic syndrome.In another study (12) hyperglycemia was evident in animals with induced intestinal obstruction.Hyperglycemia is a frequent finding observed in cases of ECS and is generally associated with an unfavorable prognostic (13).This is related to the high secretion of catecholamines as a consequence of excitation, pain and stress, typical episodes of ECS (14).
Urea blood concentration is regulated by two events: synthesis rate in the liver and clearance rate by kidney.Synthesis rate depends on protein intake and catabolism.Clearance rate depends on glomerular filtration rate and reabsorption activity at the renal tubules (15).In dehydration conditions, as occur in colic syndrome, glomerular filtration rate is diminished resulting in pre-renal azotemia.In the present study, urea values were higher in horses with small bowel lesions, which suggest a greater compromise in that kind of lesions.Di Filippo et al (16) did not find variations in hepatic and renal blood markers in horses submitted to experimental intestinal obstruction.In agreement with those results, de potasio en caballos sometidos a fistulización temporal en el intestino ciego.Di Filippo et al ( 9) encontraron valores menores de potasio en suero en los caballos que sobrevivieron al síndrome cólico en comparación con aquellos que murieron y con el grupo de control.Dicho estudio se realizó observando a los animales en el momento del examen clínico, al igual que en nuestro estudio.La reducción en los valores de potasio en casos de cólico puede atribuirse a un menor consumo de alimentos o pérdidas gastrointestinales (10).
Granot et al (17) found that horses with colic impaction did not have different values of urea compare to animals that died or that survived.
From our results it would be probable that horses with colic syndrome caused by lesions situated at the small intestine may be suffering from a more severe condition of water imbalance than horses with compromised large intestine.
In the present study, the hematocrit values were not different between individuals with colic syndrome and control animals.An increase in the hematocrit may occur in cases of equine colic syndrome as a result of hemoconcentration, dehydration and shock (14).Datt and Usenik (18) found significant hematocrit increase in horses after 12 hours of duodenum obstruction.It seems that hematocrit elevation in gastrointestinal disorders in horses may be more frequent in most severe cases.Concomitant with the result of the hematocrit, hemoglobin values were not significantly different among the groups of animals.However, horses with colic syndrome together had hemoglobin values greater than control horses.This result is in agreement with Silva (12), who found higher hemoglobin values in horses with colic syndrome than in healthy animals.It is plausible that hemoglobin could be a more sensitive indicator than hematocrit of gastrointestinal disorders of horses (18,19).
In our study, 40% of the horses with colic syndrome had increased blood pH in relation to the control group.Other authors also found elevated blood pH in horses with colon and jejunum obstructions (11,19), which was associated with increased bicarbonate concentration.In the present study, the rise in blood pH was linked not only with higher values of bicarbonate but also with more positive values of base excess in both groups of horses with colic syndrome, especially in animals with small intestine lesions.All together 60% of the colic affected horses had base excess values above +4, more severely when lesions occurred in the small intestine.Similar finding was observed in cases of horses with experimental intestinal obstruction (11).The tCO 2 values had significant rise in horses with small bowel lesions.The tCO 2 parameter expresses the alkaline reserve, with bicarbonate as its main component.A high tCO 2 indicates the presence of metabolic alkalosis, and a low tCO 2 indicates a metabolic acidosis (14).These increments in tCO 2 and alkaline reserve in horses with small bowel lesions, were not expected in the situation of pain and stress in horses with colic, which should promote breath rate increment and decrease in pCO 2 (respiratory alkalosis).In contrast with our findings, other authors found metabolic En este estudio, los valores de hematocrito no fueron diferentes entre individuos con síndrome cólico y los animales del grupo de control.Se podría presentar un aumento en el hematocrito en casos de síndrome cólico equino como consecuencia de la hemoconcentración, deshidratación y shock (14).Datt y Usenik (18) encontraron un aumento significativo en hematocrito en los equinos 12 horas después de la obstrucción del duodeno.Parece ser que la elevación del hematocrito en trastornos gastrointestinales en caballos puede ser más frecuente en los casos más severos.De manera concomitante con el resultado del hematocrito, los valores de hemoglobina no fueron significativamente diferentes entre los grupos de animales.Sin embargo, los equinos con síndrome cólico presentaron valores de hemoglobina mayores que los caballos del grupo de control.Este resultado coincide con Silva (12), quien encontró valores más altos de hemoglobina en caballos con síndrome cólico que en animales sanos.Es plausible que la hemoglobina sea un indicador más sensible que el hematocrito para trastornos gastrointestinales en caballos (18,19).
The anion gap was within the reference values in 90% of the horses with colic syndrome.According to the anion gap equation [AG=(Na + +K + ) -(HCO 3 -+ Cl -)] the AG values should be diminished, because the term HCO 3 -is augmented and sodium, potassium and chloride did not have alterations, as it was showed in our work.More research should be done to evaluate if there are other anion alterations in cases of equine colic syndrome.
In conclusion, horses with colic syndrome do not show significant alterations in plasma electrolytic parameters (Na + , K + , Cl -) or in the levels of pCO 2 and anion gap, independently of the intestinal location of the lesion.Horses with small bowel lesions have higher values of tCO 2 , HCO 3 -, base excess, urea and glucose than horses with large bowel lesions, suggesting a condition of metabolic alkalosis and more severe stress.y exceso de base atribuido a hipovolemia y a la generación de ácido láctico.

Table 1 .
Blood gas analysis, hematocrit, hemoglobin, urea and glucose values of horses with colic syndrome classified according to the affected intestinal segment.The values are presented as mean ± standard deviation.