Hemodynamic effects of 6% hydroxyethyl starch infusion in sevoflurane-anesthetized thoroughbred horses

Bioreactance noninvasive cardiac output monitoring in euvolemic adult horses subjected with 7.2% saline and 6% hydroxyethyl starch (130/0.4) solution infusions

OBJECTIVE

To compare the ability of bioreactance noninvasive cardiac output (BR-NICO) with thermodilution cardiac output (TDCO) for the measurement of cardiac output (CO) in healthy adult horses receiving 2 different IV volume replacement solutions.

DESIGN

Prospective randomized crossover study from September to November 2021.

SETTING

University teaching hospital.

ANIMALS

Six university-owned adult horses.

INTERVENTIONS

Horses were randomly assigned to receive 7.2% hypertonic saline solution (HSS) or 6% hydroxyethyl starch (130/0.4) solution (HETA). BR-NICO and TDCO were measured simultaneously at baseline, 10, 20, 30, 40, 50, 60, 90, and 120 minutes before fluid administration and again at the same times after starting a bolus infusion of IV volume replacers. All solutions were administered within 10 minutes.

MEASUREMENTS AND MAIN RESULTS

BR-NICO and TDCO were strongly correlated (Pearson r2 = 0.93; P < 0.01). Regression analysis showed the relationship between TDCO and BR-NICO was BR-NICO = 0.48 × TDCO + 0.6. For the corrected BR-NICO values, the Bland-Altman agreement mean bias and lower/upper limits of agreement were -0.62 and -5.3 to 3.9 L/min, respectively. Lin's concordance (95% confidence interval) between methods was 0.894 (0.825-1.097). Compared with baseline, HSS increased the CO at 10 and 20 minutes (TDCO and BR-NICO). Compared with baseline, HETA decreased the CO at 10 and 20 minutes (TDCO and BR-NICO) and increased the CO at 90 (TDCO only) and 120 minutes (TDCO and BR-NICO).

CONCLUSIONS

BR-NICO strongly agreed with TDCO in the measurement of CO in healthy unsedated adult horses. HSS administration significantly increased CO in the first 30 minutes, while HETA initially decreased CO at 10 minutes but increased CO to above baseline values by 90 minutes.

Current Concepts in Fluid Therapy in Horses

Despite the frequent inclusion of fluid therapy in the treatment of many conditions in horses, there are limited studies available to provide evidenced-based, species-specific recommendations. Thus, equine fluid therapy is based on the application of physiology and extrapolation from evidence in other veterinary species and human medicine. The physiologic principles that underly the use of fluids in medicine are, at first glance, straightforward and simple to understand. However, in the past 20 years, multiple studies in human medicine have shown that creating recommendations based on theory in combination with experimental and/or small clinical studies does not consistently result in best practice. As a result, there are ongoing controversies in human medicine over fluid types, volumes, and routes of administration. For example, the use of 0.9% NaCl as the replacement fluid of choice is being questioned, and the theoretical benefits of colloids have not translated to clinical cases and negative effects are greater than predicted. In this review, the current body of equine research in fluid therapy will be reviewed, connections to the controversies in human medicine and other veterinary species will be explored and, where appropriate, recommendations for fluid therapy in the adult horse will be made based on the available evidence. This review is focused on the decisions surrounding developing a fluid plan involving crystalloids, synthetic colloids, and plasma.

Hydroxyethyl starches in equine medicine

OBJECTIVE

To review and discuss the use of hydroxyethyl starches (HES) in equine veterinary medicine, and to provide recommendations for its use.

DATA SOURCES

Veterinary and human peer-reviewed medical literature including scientific reviews, meta-analyses, and original research articles.

HUMAN DATA SYNTHESIS

Increasing evidences on adverse effects after HES use and decreasing support for beneficial effects with regards to volume expansion and colloid osmotic pressure (COP) support in critically ill subjects have led to a recent guideline to limit the use of HES in critically ill people.

EQUINE VETERINARY DATA SYNTHESIS

The rationale for HES use in horses is mainly extrapolated from human medicine, and very limited studies in horses are available. There is limited evidence suggesting a superiority of volume expansion effects of HES over crystalloids. The potential for HES to increase and maintain COP is well supported, but there is no evidence that maintaining or increasing plasma COP influences outcome, tissue edema formation, or rates of complications that potentially relate to edema formation. HES induce dose-dependent changes in coagulopathic parameters, but there is no evidence that HES causes clinical coagulopathies. Insufficient data are available on other adverse effects such as acute kidney injury, or mortality in horses. The use of HES should be restricted in septic patients, but may still have some use in cases of hemorrhagic shock resuscitation, hypoalbuminemia, or perioperative fluid replacement.

CONCLUSION

The evidence supporting the use of HES in horses is weak due to lack of species-specific investigations. Acknowledging species differences, the use of HES should be judicious, yet with some recognition of its benefits in particular cases. More research is necessary to improve knowledge on use of HES in horses and to establish better future recommendations.

Effects of hetastarch 130/0.4 on plasma osmolality, colloid osmotic pressure and total protein in horses anaesthetised for elective surgical procedures

Effects of lactated Ringer's solution (LRS) and hetastarch 130/0.4 (HES) on colloid osmotic pressure (COP), plasma osmolality (OSM) and total protein (TP) were investigated in 18 inhalational-anaesthetised healthy horses. Horses received 4-6 ml/kg LRS (LRS; n=9) or HES (HES; n=9) from anaesthesia induction through 60 min, after which all were administered LRS. COP, TP and OSM were measured before premedication (baseline), postinduction and 30 (n=18), 60 (n=18), 90 (n=18) and 120 (n=12) minutes. Baseline COP, OSM and TP were not different between groups. TP decreased in both groups at all time points after induction. OSM increased from baseline in HES at 30, 60, 90 and 120 minutes. COP decreased at 30-120 minutes in LRS, and at 90 and 120 minutes in HES. Mean COP was higher in HES than LRS at 30 (18.8±0.5 vs 16.3±0.4 mmHg (P=0.001)), 60 (19.1±0.5 vs 15.9±0.4 mmHg (P<0.0001)) and 90 (17.4±0.5 vs 15.4±0.5 mmHg (P=0.005)) minutes. Sixty minutes of HES infusion increases OSM and transiently maintains COP compared with an equal volume of LRS in anaesthetised horses.