Evaluation of the effects of medial saphenous venous pressures as an indirect method of measurement of intra-abdominal pressures in the horse.

OBJECTIVE: To evaluate the effect of changes in intra-abdominal pressure (IAP) on medial saphenous venous pressure (MSVP) and hemodynamics in normal horses. DESIGN: Experimental, in-vivo study. SETTING: University Teaching Hospital. ANIMALS: Convenience sample of 7 mixed breed horses; 5 geldings, and 2 mares. INTERVENTIONS: Pneumoperitoneum was induced in horses under standing sedation with carbon dioxide gas using a laparoscopic insufflator for a total of 60 minutes to simulate clinical elevation in IAP. Pressure was increased stepwise to 20 mm Hg over 30 minutes, and maintained at that pressure for 30 minutes to evaluate the effect of sustained intra-abdominal hypertension. The MSVP and vital parameters were recorded, along with direct arterial blood pressure from the transverse facial artery. MEASUREMENTS AND MAIN RESULTS: As IAP increased, MSVP increased in a stepwise manner, in concert with changes in IAP. The consistency in measurement between MSVP and IAP was high (intraclass correlation coefficient = 0.92; P < 0.001) and repeated measures correlation was excellent (r = 0.98; P < 0.001). Heart rate was unchanged over the course of the experiment (P = 0.09), however, respiratory rate increased with increasing IAP (P < 0.001). Arterial blood pressure also increased with insufflation (P < 0.001), with a significant difference at an IAP of 15 mm Hg (P = 0.04). CONCLUSIONS: This report provides preliminary data demonstrating a strong correlation between equine MSVP and changes in IAP, similar to that observed in other species. Further investigations are needed to evaluate this relationship, and to confirm these results in clinical patients.

Evaluation of the effects of intraabdominal hypertension on equine central venous pressure.

OBJECTIVE: To evaluate the effect of changes in intraabdominal pressure (IAP) on central venous pressure (CVP) in normal horses. DESIGN: Experimental, in vivo study. SETTING: University Teaching Hospital. ANIMALS: Convenience sample of 7 mixed breed horses-5 geldings and 2 mares. INTERVENTIONS: Pneumoperitoneum was induced in horses under standing sedation with carbon dioxide gas using a laparoscopic insufflator for a total of 60 minutes to simulate clinical elevation in IAP. Pressure was increased stepwise to 20 mm Hg over 30 minutes, and maintained at that pressure for 30 minutes to evaluate the effect of sustained intraabdominal hypertension. CVP was obtained from the cranial vena cava, concurrent with pressure obtained from the peritoneal cavity. MEASUREMENTS AND MAIN RESULTS: CVP increased as IAP increased up to 12 mm Hg, and declined as IAP increased further. The changes in CVP over time were significantly different (P < 0.03). Repeated measures correlation was positive, and highest, for mean CVP as IAP increased from 0 to 12 mm Hg (r = .70; 95% CI, .43-.85; P < 0.0001). Correlation of mean CVP with insufflation pressure became negative as IAP increased further from 15 to 20 mm Hg (r = -.47; 95% CI, -.66 to -.21; P = 0.0006). CONCLUSIONS: This report provides preliminary data demonstrating a biphasic trend in equine CVP caused by changes in IAP, similar to that observed in other species. Further investigations are needed to evaluate this trend and to confirm these results in clinical patients.

Effect of fluid media on the mechanical properties of continuous pattern-ending surgeon's, square, and Aberdeen knots in vitro.

OBJECTIVE: To investigate the knot holding capacity (KHC) of pattern-ending square, surgeon's and Aberdeen knots each tied in 4 throw combinations using large gauge suture after exposure to media commonly found in equine abdominal surgery. STUDY DESIGN: In vitro mechanical study. SAMPLE POPULATION: Knotted suture strands (n = 10/group). METHODS: Strands of 2 polydioxanone or 3 polyglactin 910 were exposed to 1 of 4 media for 15 minutes. Control suture strands remained dry. Media used included balanced electrolyte solution, 1% sodium carboxymethylcellulose, equine serum, or equine fat. Pattern-ending knots for the 3 knot configurations were loaded to failure in a linear fashion on a materials testing machine to determine KHC. RESULTS: Surgeon's knots tied using media-exposed 3 polyglactin 910 had a significantly higher KHC than the same dry knots with 5 and 6 throws. Square knots tied using media-exposed to 3 polyglactin 910 had a significantly higher KHC than the same dry knots at 5 throws. Aberdeen knots tied with either media-exposed 2 polydioxanone or 3 polyglactin 910 had a significantly higher KHC than their equivalent dry knots. Aberdeen knots had a superior KHC, while requiring less suture than both surgeon's and square knots. CONCLUSION: Media exposure either had no effect on KHC or significantly improved the KHC of all knots investigated. Based on KHC and knot volume, Aberdeen knots tied using media-exposed 3 polyglactin 910 with 3 throws and 1 turn are recommended to end a continuous suture pattern.