Pressure algometry for assessment of abdominal wall sensitivity in horses after ventral midline coeliotomy.

OBJECTIVE: To assess the clinical course of abdominal wall sensitivity after ventral midline coeliotomy in horses by determining mechanical nociceptive thresholds (MNTs) during hospitalization, and to determine the inter-observer reliability of pressure algometry on the abdominal wall. STUDY DESIGN: Observational, cohort study. SAMPLE POPULATION: A total of 13 horses presenting with signs of abdominal pain/colic undergoing ventral midline coeliotomy and 10 healthy horses without an abdominal incision. METHODS: Measurements were performed on days 1, 3, 5, 7 and 9 postoperatively using a pressure algometer. Measurement sites were marked left and right, abaxial to the abdominal incision. Cranial to the incision, two control points were marked. Measurements were made by one observer, blinded to the recorded MNT values. To determine inter-observer reliability, five horses (surgical group n = 2; nonsurgical group n = 3) were measured by two observers in a randomized order. RESULTS: Mean MNT values on days 5 and 7 were 9.61 Ncm-2 and 10.14 Ncm-2 in the operated group (p = 0.009 ; p = 0.005) respectively versus 13.00 Ncm-2 on day 1. Wound-associated points showed lower values than control points (p = 0.002). The nonsurgical group did not show a difference between control points and wound-associated points (p = 0.06). No significant differences were found between the surgical and the nonsurgical groups at the wound-associated points on any days measured. The inter-observer reliability was low (intraclass correlation coefficient of 0.26; Cronbach's alpha of 0.27). CONCLUSION: Operated animals showed a reduction in MNT values on days 5 and 7 when compared with day 1 and lower values for the wound-associated points when compared with the control points. Inter-observer reliability was low. Pressure algometry could be a useful tool for assessing wound sensitivity after ventral midline coeliotomy in horses, which may improve pain management postoperatively.

Comparison of different methods to calculate venous admixture in anaesthetized horses.

OBJECTIVE: The aim of this study was to compare different methods to determine venous admixture (Q˙s/Q˙t) in anaesthetized horses. The first objective was to estimate Q˙s/Q˙t using jugular venous blood oxygen content (Q˙s/Q˙tjugular), and a fixed value for the oxygen extraction (F-shunt). The second objective was to assess the influence of blood pressure and positioning on oxygen extraction. The third objective was to perform regression analysis between jugular and mixed venous blood oxygen tensions. STUDY DESIGN: Prospective, experimental trial. ANIMALS: The study was performed with seven warmblood horses that were anaesthetized with detomidine, butorphanol, ketamine, diazepam and isoflurane in oxygen. METHODS: Multiple simultaneous arterial, jugular venous and pulmonary arterial blood samples were taken under normotensive and hypotensive conditions in lateral and dorsal recumbency. Arterial, mixed venous, and end-capillary oxygen content were calculated. RESULTS: A significant correlation between Q˙s/Q˙t and Q˙s/Q˙tjugular was found [intraclass correlation coefficient (ICC) = 0.68, p < 0.001], and Bland-Altman analysis showed a bias of -11.5% and wide limits of agreement (-27.7% to 4.6%). F-shunt significantly correlated with Q˙s/Q˙t (ICC = 0.88, p < 0.001), and Bland-Altman analysis showed a lower bias (-1.97) and narrower limits of agreement (-13.8% to 9.9%). Positioning and blood pressure significantly influenced oxygen extraction. The regression formula was Y = 0.80X + 2.61 (where Y is the calculated mixed venous oxygen tension and X is the jugular venous oxygen tension) when outliers were excluded (ICC=0.82, p < 0.001). CONCLUSIONS AND CLINICAL RELEVANCE: This study shows that F-shunt provides reasonable estimates of Q˙s/Q˙t but can possibly be improved by using simple algorithms without the need for pulmonary arterial catheterization. These algorithms use blood pressure- and positioning-dependent oxygen extraction and regression analysis between jugular venous and pulmonary arterial oxygen tension. Although promising, the validity of these algorithms needs to be determined in future studies.