Summary Reasons for performing study: Blood lactate concentration has been shown to be a useful clinical indicator in human patients, but has not been formally investigated in critically ill foals. Objective: To investigate the association of blood lactate with hospital survival, markers of cardiovascular status, metabolic acid base status, sepsis and systemic inflammatory response syndrome (SIRS). Methods: A database containing clinical, haematological, plasma biochemical and hospital outcome data on neonatal foals referred to an intensive care unit in 2000‐2001 was analysed. Seventy‐two foals for which arterial lactate was measured at admission were included in the study. Results: Sixty‐one foals had an admission lactate concentration >2.5 mmol/1. Admission lactate was statistically associated with hospital survival, mean arterial pressure, blood creatinine concentration, bacteraemia, anion gap, lactate concentration at 18‐36 h after admission and evidence of SIRS, but not with packed cell volume or heart rate. Lactate at 18‐36 h was also associated with survival and evidence of SIRS. Anion gap, base excess, base excess due to unidentified anions (BEua), simplified strong ion gap or bicarbonate correctly classified foals for presence of hyperlactaemia (>5 mmol/1) in 80% of animals. Conclusions: Admission blood lactate gives important prognostic information. Lactate should be measured rather than assumed from the anion gap, base excess, BEua, simplified strong ion gap or bicarbonate. Potential relevance: Blood lactate concentrations at admission are clinically relevant in neonatal foals and warrant further investigation. This should include the clinical value of measuring changes in lactate in response to treatment.

Objective: To evaluate the accuracy of a published score designed to predict sepsis in foals in a clinical setting and to evaluate the association of clinical and clinicopathological variables with sepsis. Design: Observational study. Retrospective for data from 1998. Prospective in 1999–2001. Setting: Foal intensive care unit of a university hospital. Animals: Client‐owned foals of less than 10 days of age, presenting from 1998 to 2001. Interventions: None. Measurements and main results: Data from the history and physical examination, together with admission hematology, biochemistry and arterial blood gas analysis were used to generate the published sepsis scores. The same data were investigated for their statistical relationship with sepsis. The presence or absence of sepsis was determined from blood culture, culture of sites of suspected local infection, clinical course and/or post‐mortem examination. The modified sepsis score was calculated for 168 foals, which were classified as septic (86), non‐septic (45) or not possible to classify (37). The modified sepsis score correctly predicted sepsis in 58 out of 86 foals and non‐sepsis in 34 out of 45 foals, resulting in a sensitivity of 67%, a specificity of 76%, a positive predictive value of 84% and a negative predictive value of 55%. Abnormal neutrophil cytology, an immunoglobulin concentration of less than 400 mg/dl, and low blood glucose concentration had the strongest association with sepsis. Conclusions: The low negative predictive value of the sepsis score limited its clinical utility. The sepsis score should not be used to define sepsis in clinical studies, unless previously validated in the study center.

Critical illness, anesthesia, primary cardiovascular disease, and exercise may result in marked hemodynamic alterations. Measuring cardiac output (CO) is central to defining these alterations for both clinician and researcher. In the past 10 years, several new methods of measuring CO have been developed for the human medical market. Some of these methods are now validated in the horse and are in clinical use. The Fick method has been used in equine research for more than a century. It depends on simultaneous measurement of mixed venous (pulmonary arterial) and peripheral arterial oxygen content and oxygen uptake by the lungs. The technique is technically demanding, which restricts its clinical use. Indicator dilution techniques, with indocyanine green, cold (thermodilution), or lithium as the marker, have also been widely used in the horse. The indocyanine technique is cumbersome, and thermodilution requires right heart catheterization, which is not a benign procedure, making both of these methods less than ideal for clinical use. Lithium dilution requires catheterization of a peripheral artery and a jugular vein. It has recently been validated in anesthetized adult horses and neonatal foals. Doppler echocardiography is a noninvasive ultrasound-based technique. More accurate measurements are obtained with transesophageal than with transthoracic measurements; however, both methods require considerable technical expertise. Bioimpedance and pulse contour analysis are 2 new methods that have yet to be validated in the horse. With the currently available technology, lithium dilution appears to be the method of measuring CO best suited to the equine clinic.Key words: Doppler echocardiography; Fick; Hemodynamics; Indicator dilution techniques; Lithium dilution; Thermodilution. The cardiovascular system has a great capacity to adapt to the requirements for oxygen delivery created by different physiological circumstances. In athletic animals, such as the horse, this ability is very well developed, and cardiac output (CO) may be increased to more than 8 times its resting value during intense exercise.1 This ability to adapt may well be a component of the response to disease, when tissue oxygen demand may be increased. However, many disease states result in hemodynamic derangements that can interfere with this adaptive response and often result in inadequate tissue perfusion. Currently, clinical evaluation of the hemodynamic status in patients consists of repeated physical examinations, emphasizing assessment of heart rate, peripheral pulse quality, temperature of extremities, and mucous membrane color and refill time. Ancillary diagnostics, such as indirect blood pressure, hemoglobin saturation by pulse oximetry or blood gas analysis, and blood lactate measurement, are also performed. Measurement of CO would contribute to a more complete understanding of the state of the cardiovascular system but, in the past, has been difficult to perform.There are 4 main situations in which knowledge of CO would be valuable in the horse...