Lactate in Bitches with Pyometra
Author's address (for correspondence): R Volpato, School of Veterinary Medicine and Animal Science, UNESP Sao Paulo State University, Distrito de Rubião Junior, s/n. CEP: 18618-970. Botucatu-SP, Brazil. E-mail: email@example.com
Lactate is a compound produced by the anaerobic metabolism of glucose, and hyperlactataemia occurs when the rate of production of lactate exceeds the rate of elimination. This occurs in situations of hypoxia and tissue hypoperfusion. Lactate has been considered a useful prognostic indicator in critically ill patients. Pyometra is a disease of adult female dogs characterized by inflammation of the uterus with an accumulation of exudate, which occurs during the luteal phase. It is one of the most common diseases that occur in the genital tract of female dogs. A total of 31 dogs were diagnosed with pyometra. The diagnosis was confirmed at ultrasonography. Of the 31 dogs, 25 females had open cervix pyometra and six had closed cervix pyometra. Plasma lactate concentrations were determined by an enzymatic colorimetric method. The average concentration (±SD) of plasma lactate in all 31 bitches with pyometra was 3.55 ± 0.46 mm. Healthy dogs had plasma lactate concentrations between 0.3 and 2.5 mm (mean ± SD). Concentrations ranged from 0.8 to 2.9 mm when plasma lactate was measured with a portable device and 0.4–2.6 mm with the blood gas analyser. Even though plasma lactate values vary between several studies and equipment used to measure concentrations, our results for dogs with pyometra are higher indicating hyperlactataemia (Thorneloe et al. 2007, Can Vet J 48, 283–288). Plasma lactate in dogs with closed cervix pyometra was mean ± SD and in dogs with open cervix pyometra, it was mean ± SD. The plasma lactate concentration in dogs with pyometra was higher than in healthy bitches, and there was no influence of patency of the cervix on the concentration of plasma lactate concentrations. Plasma lactate concentrations were similar for animals with open and closed pyometra (3.54 ± 0.52 to 3.64 ± 1.03 mm).
Lactate is a compound produced by the anaerobic metabolism of glucose, and hyperlactataemia occurs when the rate of production exceeds the rate of elimination. This occurs in conditions of hypoxia and tissue hypoperfusion. Assessment of plasma lactate concentration has become a common practice in veterinary medicine to assess the severity and prognosis of medical and surgical conditions. The plasma lactate concentration is a minimally invasive technique, can be performed in venous blood and is considered a reliable indicator of tissue perfusion (McMichael et al. 2005). Lactate has been considered a useful prognostic indicator in critically ill patients (Hughes et al. 1999). Using serial monitoring, changes in serum lactate concentrations strongly correlate with mortality and the development of severe complications (Souza and Elias 2006).
Pyometra is a disease of older adult dogs characterized by inflammation of the uterus with an accumulation of exudate that occurs during the luteal phase of the oestrous cycle. Pyometra is one of the most common diseases of the canine female genital tract. In severe cases, the disease is associated with endotoxemia, septicaemia and systemic inflammatory response syndrome (Pretzer 2008).
Clinical signs of pyometra vary depending on the duration and the degree of cervical relaxation and may include lethargy, depression, anorexia, appetite loss, polyuria, polydipsia, vomiting, hyperthermia, hypotension, dehydration and tachycardia. Bitches with open cervix pyometra generally have a less severe clinical signs than bitches presenting with closed cervix pyometra. Bitches with closed cervix pyometra generally have more severe clinical signs and consequently may have septicaemia and death (Van Israel et al. 2002).
Normal or low concentrations of plasma lactate in dogs with pyometra suggests that the prognosis is good, and anaesthetic and surgical risks are lower than in dogs with hyperlactataemia (Hagman et al. 2009). A study of dogs admitted to a veterinary intensive care unit found that plasma lactate concentration was a predictor of survival. Since then, researchers and clinicians have shown a growing interest in evaluating plasma lactate concentrations in healthy dogs and patients, with interest in the outcome (Thorneloe et al. 2007).
The objective of this study was to evaluate the plasma concentration of lactate in the blood of dogs with pyometra and to determine the effect of opening or closing of the cervix on those values.
Material and methods
A total of 31 dogs were diagnosed with pyometra between August and December 2011. The animals were of a variety of breeds, with an average body weight of 8.5 kg. Ages ranged between 3 and 17 years. The diagnosis of pyometra was made based on the clinical history, physical examination and ultrasound evaluation. The diagnosis was confirmed at ultrasonography. Of the 31 dogs, 25 females had open cervix pyometra and six had closed cervix pyometra.
After the dogs were anesthetized, blood was collected by venipuncture from the jugular vein (5 ml) into tubes containing fluoride as anticoagulant. The blood sample was centrifuged within 30 min after collection (LS-Centrifugal 3–CELM) for 10 min at 1700×g to obtain plasma. The plasma was stored under freezing temperature −18°C. Plasma lactate concentrations were determined by enzymatic colorimetric method using the LOP-PAD Kit® (Katal Biotecnológica Ind. Com Ltda, Belo Horizonte- MG, Brazil). Reference values ranged from 0.3 to 2.5 mm (Hughes et al. 1999). For comparisons of mean plasma lactate concentration between groups, an unpaired Student's t-test was performed. Significance was defined as p < 0.05.
Healthy dogs had plasma lactate concentrations that ranged from 0.3 to 2.5 mm. Concentrations ranged from 0.8 to 2.9 mm when lactate was measured with a portable device and from 0.4 to 2.6 mm with the blood gas analyser. Even with lactate values ranging from several studies and equipment, our results for dogs with pyometra were higher than controls, indicative of hyperlactataemia (Thorneloe et al. 2007). Mean ± SD concentration of plasma lactate in all 31 bitches with pyometra was 3.55 ± 0.46 mm. Plasma lactate concentrations did not differ significantly for dogs with open pyometra compared with closed pyometra (3.54 ± 0.52 and 3.64 ± 1.03 mm, respectively).
Increased lactate concentrations may be due to the difficulty in collecting blood from uncooperative patients requiring severe restraint. Muscle activity and shivering may also moderately lactate values. In addition, blood left at room temperature for extended periods can increase lactate concentrations due to the high baseline lactate production in the red cells. Blood collection in our experiment was performed in anesthetized animals previously prepared for ovariohysterectomy. After collection, blood was placed directly into a tube containing fluoride, which is an anti-coagulant that stabilizes blood lactate by inhibiting glycolysis. Furthermore, the blood sample was centrifuged and frozen within 30 min. These blood collection methods have been shown to produce the most reliable results for determining accurate plasma lactate concentrations (Thorneloe et al. 2007).
One of the biggest challenges to managing cases of pyometra is avoiding the high risk of mortality and morbidity (progression of multiple disorders and controlling tissue hypoperfusion). In these cases, evaluation of plasma lactate concentrations is a good indicator of tissue hypoxia and an important prognostic marker (Almeida et al. 2006).
In the case of canine pyometra, the vast majority of cases are caused by an ascending infection of E. coli and toxins produced by Gram-negative bacteria, which have the ability to inhibit pyruvate dehydrogenase. This leads to an increase in lactate in the cytoplasm of cells without oxygenation deficit in the cell.
Even with more severe clinical signs and more rapid progression in cases of closed cervix pyometra, blood lactate concentrations are not greater than with the open cervix pyometra. In both situations, tissue perfusion is altered and the prognosis is guarded, requiring a fast and efficient veterinary management.
Plasma lactate concentration in dogs with pyometra was greater than in healthy dogs but was not different between dogs with closed or open cervix pyometra. Lactate must be interpreted in combination with physical parameters and clinical evaluation of the patient.
Conflicts of interest
None of the authors have any conflicts of interest to declare.