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- Author or Editor: Emma Gorenberg x
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Abstract
OBJECTIVE
To test the influence of increasing injectate volumes on the regional effects of xylazine and morphine epidural analgesia, with the hypothesis that increasing volume produces more cranial spread of analgesia as determined by thermal threshold (TT) testing.
ANIMALS
6 university-owned research/teaching horses (2 mares, 4 geldings) deemed healthy on physical examination and basic lameness evaluation, aged 6–19 years and weighing 420–560 kg, were used in this prospective, randomized, blinded, cross-over experimental study.
METHODS
After routine placement of a caudal epidural catheter, all animals were subsequently instrumented with a TT testing system at the withers (Location A), the cranial (Location B), and caudal (Location C) abdominal area, over the tuber coxae (Location D), and the hind limb dorsal pasterns (Location E). All horses underwent five testing cycles with 0.2 mg/kg morphine and 0.2 mg/kg xylazine diluted to 20, 35, 50, 75, and 100 mL. TT testing was performed at 2, 4, 6, 8, and 10 hours by blinded investigators.
RESULTS
With increased epidural volume, significantly greater cranial spread of analgesic effect was noted. All epidural volumes caused significant changes in TT testing at location E but only the largest volume resulted in a significant TT testing change at location A.
CLINICAL RELEVANCE
Volume influences the regional effects of caudal epidural analgesia in horses but might affect analgesic reliability.
Abstract
OBJECTIVE
To investigate the mechanisms underlying the improved arterial oxygenation described with flow-limited expiration (FLEX) ventilation in anesthetized horses.
ANIMALS
5 healthy adult research horses.
METHODS
Horses underwent volume-controlled ventilation for 60 minutes (VCV1), followed by 60 minutes of FLEX, and 30 minutes of VCV (VCV2). Main outcomes included the arterial partial pressure of oxygen-to-Fio 2 (PF) ratio and electrical impedance tomography (EIT)-derived functional indices at the end of each phase. The EIT data were used to create regional maps of relative lung ventilation and perfusion as well as regional maps of ventilation/perfusion (V/Q) ratios. Ventilation indices derived from EIT included the fraction of expired volume in 1 second (FEV1; %) and the time it took for the EIT signal to drop to 50% of the peak signal at end-inspiration (TClose50; seconds). Data were analyzed with 2-way ANOVA for repeated measures. P < .05 was considered significant.
RESULTS
The PF ratio increased significantly with FLEX compared to both VCV1 and VCV2 (P < .01). There were no differences in the relative distribution of ventilation nor perfusion between ventilation strategies. However, when ventilation and perfusion were superimposed and V/Q ratio maps were constructed, FLEX had a homogenizing effect toward values of 1.0. The FEV1 was shorter (P < .01) and the TClose50 was longer (P < .001) in all regions during FLEX compared to both VCV1 and VCV2.
CLINICAL RELEVANCE
Our findings suggest that FLEX ventilation in anesthetized horses enhances regional V/Q matching, likely by prolonging expiratory aeration and reducing airway closure.