In this proof of principle study, AGIS was able to discriminate between horses given xylazine from those given 0.9% NaCl with comparable accuracy as auscultation and ultrasonography. The Summary is available in Spanish - see Supporting Information.
Horses underwent either cervical epidural space (CES) catheterization or subarachnoid space (SAS) catheterization while restrained in stocks, under deep sedation (detomidine and morphine) and local anesthesia (mepivacaine 2%) block. Catheters were placed under ultrasound guidance with visualization of the dura, SAS, and spinal cord between the first (C1) and second (C2) cervical vertebrae. Following sedation and sterile skin preparation, operator 1 placed under ultrasound guidance, a 6-or 8-inch Tuohy needle with the bevel oriented caudally. For CES, a 6-inch Touhy needle was used with the hanging drop technique to detect negative pressure, and operator 2 then passed the epidural catheter into the CES. For SAS, following puncture of the dura, cerebrospinal fluid (CSF) was aspirated prior to placement of the epidural catheter. Placement into either CES or SAS was confirmed with plain and contrast radiography. Catheters were wrapped for the duration of the study. CSF cytology was assessed up to every 24 h for the study period. Horses were assessed daily for signs of discomfort, neck pain, catheter insertion site swelling, or changes in behavior. A complete postmortem assessment of the spinal tissues was performed at the end of the study period (72 h). Two horses had CES catheters and five horses had SAS catheters placed successfully. All horses tolerated the catheter well for the duration of the study with no signs of discomfort. Ultrasound was essential to assist placement, and radiography confirmed the anatomical location of the catheters. CSF parameters did not change over the study period (P > 0.9). There was evidence of mild meningeal acute inflammation in one horse and hemorrhage in another consistent with mechanical trauma. Placement of an indwelling CES or SAS catheter appears to be safe, technically simple, and well tolerated in standing sedated normal horses.
Background
Strangulating small intestinal lesions in the horse have increased morbidity and mortality compared to nonstrangulating obstructions due to mucosal barrier disruption and subsequent endotoxaemia.
Objectives
To investigate protective effects of dexmedetomidine on small intestinal ischaemia‐reperfusion injury in the horse.
Study design
Randomised, controlled, experimental study.
Methods
Eighteen systemically healthy horses were randomly assigned to three groups: control, preconditioning, and post‐conditioning. During isoflurane anaesthesia, complete ischaemia was induced in a 1‐m segment of jejunum for 90 minutes. Horses in the preconditioning and post‐conditioning groups received dexmedetomidine (3.5 µg/kg followed by 7 µg/kg/h) before (preconditioning) or after beginning ischaemia (post‐conditioning), and during reperfusion. Jejunal biopsies were collected before ischaemia (baseline‐1), at the end of the ischaemic period (ischaemia), and 30 minutes after reperfusion (reperfusion‐1). Additional biopsies were taken 24 hours after reperfusion from ischaemia‐reperfusion‐injured jejunum (reperfusion‐2). Epithelial injury was scored histologically, and morphometric analyses were used to calculate villus surface area (VSA) denuded of epithelium. Data were analysed using analysis of variance, Kruskal‐Wallis and Wilcoxon two‐sample tests.
Results
In the control group, epithelial injury scores and percentage of VSA denudation for ischaemia‐reperfusion‐injured jejunum were higher compared to baseline‐1 at all time points. The ischaemia and both reperfusion samples from the pre‐ and post‐conditioning groups had lower epithelial injury scores and percentage of VSA epithelial denudation compared to the control group, with no difference from baseline‐1 at any time point for the preconditioning group.
Main limitations
Preconditioning has limited application in the clinical setting with naturally occurring strangulating small intestinal lesions.
Conclusions
Dexmedetomidine was protective for small intestinal ischaemia‐reperfusion injury in the horse when administered before or during ischaemia.
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