Comparison of the utility of the classic model (the Henderson-Hasselbach equation) and the Stewart model (Strong Ion Approach) for the diagnostics of acid-base balance disorders in dogs with right sided heart failure

Evaluation of the association between strong ion acid-base disturbances and mortality in dogs: a retrospective study

Acid-base abnormalities are frequently encountered in veterinary emergency and critical care, but information regarding the prognostic value of these findings is limited. Several systems for analysing acid-base disturbances have been reported, but the prognostic abilities of these systems have not been compared in dogs. The objectives of this retrospective study were to determine if the commonly used acid-base interpretation methods (Henderson-Hasselbalch, Stewart and semi-quantitative) have prognostic value, and to compare the performance of the three methods. Electronic medical records were searched to create a database containing point-of-care blood-gas, electrolyte and serum chemistry values for 1024 dogs assessed at a university teaching hospital. Dogs with contemporaneous blood-gas analysis, blood lactate and serum biochemistry samples were eligible for study, and only the first recorded analyses for each patient visit were included. Components of the Henderson-Hasselbalch, Stewart and semi-quantitative methods were calculated. To assess prognostic ability and to compare analysis system performance, receiver-operating characteristic (ROC) curves for survival to hospital discharge were created. Of the 1024 dogs identified, case fatality rate was 23.8%. Area under the ROC curve did not exceed 0.63 for any calculated variable. Performance of all three analysis systems was similar. While some acid-base abnormalities identified were associated with mortality, no individual abnormality or system output yielded sensitive and specific cut-off values for mortality prediction, and no interpretation method outperformed the others. This study suggests that initial acid-base abnormalities have limited prognostic utility and that various analysis systems can be used to assess acid-base disturbances in critically ill dogs.

Chloride:Sodium Ratio May Accurately Predict Corrected Chloride Disorders and the Presence of Unmeasured Anions in Dogs and Cats

Disorders of chloride and mixed acid-base disturbances are common in veterinary emergency medicine. Rapid identification of these alterations and the presence of unmeasured anions aid prompt patient assessment and management. This study aimed to determine in dogs and cats if site-specific reference values for [Cl-]:[Na+] ratio and [Na+] - [Cl-] difference accurately identify corrected chloride abnormalities and to evaluate the predictive ability of the [Cl-]:[Na+] ratio for the identification of unmeasured anions. A database containing 33,117 canine, and 7,604 feline blood gas and electrolyte profiles was generated. Institution reference intervals were used to calculate site-specific reference values for the [Cl-]:[Na+] ratio and the [Na+] - [Cl-] difference. Contingency tables were used to assess the ability of these values to correctly identify corrected chloride disorders. Unmeasured anions were estimated by calculating strong ion gap (SIG). Continuous variables were compared using the Mann-Whitney U test. Correlations between continuous variables were assessed using Spearman's rho (rs). In dogs, site-specific reference values for the [Cl-]:[Na+] ratio correctly identified 94.6% of profiles as hyper-, normo-, or hypochloremic. For dogs with normal sodium concentrations, site-specific reference values for the [Na+] - [Cl-] difference correctly identified 97.0% of profiles. In dogs with metabolic acidosis (base deficit > 4.0), [Cl-]:[Na+] ratio and SIG were moderately but significantly negatively correlated (rs -0.592, P < 0.0001). SIG was significantly greater in dogs with metabolic acidosis and hypochloremia compared to those without hypochloremia (P < 0.0001). In cats, site-specific reference values for the [Cl-]:[Na+] ratio correctly identified 93.3% of profiles as hyper-, normo-, or hypochloremic, while site-specific reference values for [Na+] - [Cl-] difference correctly identified 95.1% of profiles. In cats with metabolic acidosis [Cl-]:[Na+] ratio and SIG were moderately significantly negatively correlated (rs -0.730, P < 0.0001). SIG was significantly greater in cats with metabolic acidosis and hypochloremia compared to those without hypochloremia (P < 0.0001). Site-specific values for [Cl-]:[Na+] ratio and [Na+] - [Cl-] difference accurately identify corrected chloride disorders in both dogs and cats and may aid identification of the presence of unmeasured anions.

The use of elements of the Stewart model (Strong Ion Approach) for the diagnostics of respiratory acidosis on the basis of the calculation of a value of a modified anion gap (AGm) in brachycephalic dogs

Apart from the HH equation, the acid-base balance of an organism is also described by the Stewart model, which assumes that the proper insight into the ABB of the organism is given by an analysis of: pCO2, the difference of concentrations of strong cations and anions in the blood serum – SID, and the total concentration of nonvolatile weak acids – Acid total. The notion of an anion gap (AG), or the apparent lack of ions, is closely related to the acid-base balance described according to the HH equation. Its value mainly consists of negatively charged proteins, phosphates, and sulphates in blood. In the human medicine, a modified anion gap is used, which, including the concentration of the protein buffer of blood, is, in fact, the combination of the apparent lack of ions derived from the classic model and the Stewart model. In brachycephalic dogs, respiratory acidosis often occurs, which is caused by an overgrowth of the soft palate, making it impossible for a free air flow and causing an increase in pCO2– carbonic acid anhydride The aim of the present paper was an attempt to answer the question whether, in the case of systemic respiratory acidosis, changes in the concentration of buffering ions can also be seen. The study was carried out on 60 adult dogs of boxer breed in which, on the basis of the results of endoscopic examination, a strong overgrowth of the soft palate requiring a surgical correction was found. For each dog, the value of the anion gap before and after the palate correction procedure was calculated according to the following equation: AG = ([Na+mmol/l] + [K+mmol/l]) – ([Cl−mmol/l]+[HCO3−mmol/l]) as well as the value of the modified AG – according to the following equation: AGm= calculated AG + 2.5 × (albuminsr– albuminsd). The values of AG calculated for the dogs before and after the procedure fell within the limits of the reference values and did not differ significantly whereas the values of AGmcalculated for the dogs before and after the procedure differed from each other significantly. Conclusions: 1) On the basis of the values of AGmobtained it should be stated that in spite of finding respiratory acidosis in the examined dogs, changes in ion concentration can also be seen, which, according to the Stewart theory, compensate metabolic ABB disorders 2) In spite of the fact that all the values used for calculation of AGmwere within the limits of reference values, the values of AGmin dogs before and after the soft palate correction procedure differed from each other significantly, which proves high sensitivity and usefulness of the AGmcalculation as a diagnostic method.

An attempt to use the peritoneal cavity fluid in the diagnostics of acid-base balance disorders in dogs

The acid-base balance parameters (ABB) of blood are used in the diagnostics and therapy of acidosis or alkalosis type disorders. Nowadays, some reports on the attempts to use the body cavity fluid for the diagnostics of the ABB disorders have appeared in the human medicine. The study has aimed at comparing the acid-base balance parameters (ABB): pH, pCO2, and HCO3 - determined in the arterial blood and the fluid from the peritoneal cavity in dogs. The study was carried out on 20 dogs suffering from ascites developed as a result of the chronic renal failure. 1 ml of full blood was drawn from each dog from its femoral artery to a heparinized syringe equipped with a needle with an internal diameter of 0.7 mm and the puncture of the abdominal cavity was carried out in the white line. In the sample of arterial blood and the sample of the abdominal cavity fluid drawn the ABB parameters were determined. In the group examined, the ABB parameters determined for the arterial blood and the fluid had comparable numeric values and the same nature of the ABB disorder diagnosed on the basis of them. The conclusions are as follows: the results of the effusion fluid gasometry depend on the mechanism of the fluid formation and, in the case when it comes from the developed capillary network, a pressure of gases and remaining ABB parameters are similar to those determined for the arterial blood.