Hyponatremia in horses with septic pneumopathy

Background: Hyponatremia is common in horses with bacterial pleuropneumonia, but no further characterization of this abnormality has been reported. Objectives: Describe admission plasma sodium concentration ([Na]) in horses with septic pneumopathy and evaluate any association of plasma [Na] with markers of systemic inflammation. Animals: Medical records of horses >1 month of age that between 2008 and 2021 had a transtracheal aspirate (TTA) performed, abnormal TTA cytology, positive TTA culture, pulmonary disease on ultrasonography, radiography or both, and plasma [Na] assessed by direct ion-selective-electrode (dISE). Horses with concurrent diarrhea or azotemia were excluded. Methods: Clinical and clinicopathological variables of interest between hypo- and normonatremic horses were compared. Spearman correlation and Fisher exact tests were used to identify significant associations (P <.05). Results: Twenty of 35 horses had hyponatremia (median, 132 mmol/L; 25-75th interquartile range [IQR], 129.7-133.1 mmol/L; reference range, 134.2-138.4 mmol/L). A higher proportion of horses with systemic inflammatory response syndrome (SIRS) had hyponatremia (P =.01). Hyponatremic patients had higher mean plasma fibrinogen concentration (461 ± 160.5 mg/dL; P =.01) and higher rectal temperature (38.8 ± 0.7°C; P =.02) than normonatremic horses. Negative correlations were found between plasma [Na] and fibrinogen (P =.001; ρ = −0.57) concentrations and between plasma [Na] and rectal temperature (P =.001; ρ = −0.51). Presence or absence of pleural effusion did not influence severity of hyponatremia. Mean duration of hospitalization was longer (P =.04) in hyponatremic horses (9.8 ± 6.6 days). Conclusions and Clinical Importance: Hyponatremia at admission is associated with the presence of inflammation, SIRS, and with longer duration of hospitalization.