Flow-controlled expiration ventilation using a piston ventilator: effects of expiration time and speed on respiratory and pulmonary mechanics with focus on hysteresis and compliance in healthy horses.

OBJECTIVE: To investigate the effects of FLow-controlled EXpiration (FLEX) ventilation expiration time and speed on respiratory and pulmonary mechanics in anesthetized horses in dorsal recumbency. ANIMALS: 6 healthy adult research horses. METHODS: In this randomized crossover experimental study, horses were anesthetized 3 times and were ventilated each time for 60 minutes using conventional volume-controlled ventilation (VCV), linear emptying of the lung over 50% of the expiratory time (FLEX50), or linear emptying of the lung over 100% of the expiratory time (FLEX100) in a randomized order. The primary outcome variables were dynamic compliance (Cdyn), hysteresis, and alveolar dead space. The data was analyzed using two-factor ANOVA. Significance was set to P < .05. RESULTS: Horses ventilated using FLEX50 and FLEX100 showed significantly higher Cdyn and significantly lower hysteresis values compared to horses ventilated using VCV. Horses ventilated using FLEX50 had significantly lower alveolar dead space compared to horses ventilated using FLEX100 or VCV. Horses ventilated using FLEX100 had significantly lower alveolar dead space compared to VCV horses. CLINICAL RELEVANCE: Our results demonstrate improved Cdyn, hysteresis, and alveolar dead space in horses ventilated with either FLEX50 or FLEX100 relative to traditional VCV. The use of FLEX with a faster exhalation speed (FLEX50) offers additional respiratory advantages.

Peri-anesthetic environmental and occupational exposure to desflurane waste anesthetic gas in a large animal veterinary hospital.

OBJECTIVES: The goals were to determine the environmental levels of desflurane waste anesthetic gas and the desflurane occupational exposure of operating room staff during the anesthesia of large animal veterinary patients. METHODS: Active environmental sampling was performed using single-beam infrared spectrophotometry. Passive sampling with dosimeter badges was used to measure the occupational exposure of anesthesia and operating room staff. RESULTS: Higher concentrations of desflurane (n = 16) were measured at all recovery timepoints relative to the concentrations measured at all locations and timepoints at the start of anesthesia and surgery (p < 0.05). Time-weighted average desflurane concentrations from dosimeter badges (n = 310) were higher for anesthesia staff than for other operating room personnel (p < 0.0001). CONCLUSIONS: The anesthetic recovery of large animal patients is a period of increased exposure to desflurane waste anesthetic gas for veterinary staff.

Flow-controlled expiration reduces positive end-expiratory pressure requirement in dorsally recumbent, anesthetized horses.

Introduction: Equine peri-anesthetic mortality is higher than that for other commonly anesthetized veterinary species. Unique equine pulmonary pathophysiologic aspects are believed to contribute to this mortality due to impairment of gas exchange and subsequent hypoxemia. No consistently reliable solution for the treatment of peri-anesthetic gas exchange impairment is available. Flow-controlled expiration (FLEX) is a ventilatory mode that linearizes gas flow throughout the expiratory phase, reducing the rate of lung emptying and alveolar collapse. FLEX has been shown to improve gas exchange and pulmonary mechanics in anesthetized horses. This study further evaluated FLEX ventilation in anesthetized horses positioned in dorsal recumbency, hypothesizing that after alveolar recruitment, horses ventilated using FLEX would require a lower positive end-expiratory pressure (PEEP) to prevent alveolar closure than horses conventionally ventilated. Methods: Twelve adult horses were used in this prospective, randomized study. Horses were assigned either to conventional volume-controlled ventilation (VCV) or to FLEX. Following induction of general anesthesia, horses were placed in dorsal recumbency mechanically ventilated for a total of approximately 6.5 hours. Thirty-minutes after starting ventilation with VCV or FLEX, a PEEP-titration alveolar recruitment maneuver was performed at the end of which the PEEP was reduced in decrements of 3 cmH2O until the alveolar closure pressure was determined. The PEEP was then increased to the previous level and maintained for additional three hours. During this time, the mean arterial blood pressure, pulmonary arterial pressure, central venous blood pressure, cardiac output (CO), dynamic respiratory system compliance and arterial blood gas values were measured. Results: The alveolar closure pressure was significantly lower (6.5 ± 1.2 vs 11.0 ± 1.5 cmH2O) and significantly less PEEP was required to prevent alveolar closure (9.5 ± 1.2 vs 14.0 ± 1.5 cmH2O) for horses ventilated using FLEX compared with VCV. The CO was significantly higher in the horses ventilated with FLEX (37.5 ± 4 vs 30 ± 6 l/min). Discussion: We concluded that FLEX ventilation was associated with a lower PEEP requirement due to a more homogenous distribution of ventilation in the lungs during expiration. This lower PEEP requirement led to more stable and improved cardiovascular conditions in horses ventilated with FLEX.

Outcomes of pregnant broodmares treated for colic at a tertiary care facility.

OBJECTIVE: To evaluate, following colic admission during pregnancy, (1) broodmare survival; (2) the frequency of recurrent colic in broodmares and its associated variables, and (3) pregnancy outcome and the variables associated with a negative pregnancy outcome. STUDY DESIGN: Ambidirectional observational cohort study. ANIMALS: One hundred and four client-owned broodmare admissions. METHODS: Admissions of pregnant mares from June 2010 until October 2016 were included. Data were collected until November 2017. Cox proportional hazards regression analysis was performed to evaluate variables associated with broodmare survival. Logistic regression analysis was used to examine the variables associated with recurrent colic and pregnancy outcome. RESULTS: Broodmares from 73/104 (70.2%) admissions were discharged alive. Lesion category, admission hyperlactatemia (hazard ratio (HR) 3.24, 95%, CI 1.28-8.22, P = .013), and admission high packed cell volume (HR 2.89, 95% CI 1.29-6.47, P = .010) were associated with reduced survival. Recurrent colic was observed in broodmares from 33/70 admissions (47.1%). The final multivariable model for recurrent colic included Thoroughbred breed (OR 5.09, 95% CI 1.58-16.4, P = .006) and age (OR .876, 95% CI .747-1.03, P = .105). Overall, negative pregnancy outcome was 14/65 (21.5%). Lesion category, evidence of systemic inflammatory response syndrome (SIRS) in hospital (OR 31.2, 95% CI 2.09-466.5, P = .013), and diarrhea in hospital (OR 379.3, 95% CI 97.1-1482.0, P < .001) were associated with increased negative pregnancy outcome. Altrenogest administration was inversely associated with negative pregnancy outcome (OR 0.029, 95% CI .004-.222, P = .001). CONCLUSION: Pregnant broodmares admitted for colic had lower survival than anticipated and were at risk of recurrent colic. Markers of broodmare disease severity were associated with pregnancy outcome. CLINICAL SIGNIFICANCE: Lesion category, hematologic variables (packed cell volume and l-lactate concentration), evidence of SIRS, and diarrhea were useful for predicting broodmare and pregnancy outcomes.

The effect of intra-articular mepivacaine administration prior to carpal arthroscopy on anesthesia management and recovery characteristics in horses.

OBJECTIVE: To evaluate the effects of intra-articular (IA) mepivacaine administration prior to carpal arthroscopy on anesthetic drug requirements, blood pressure support, hemodynamic variables, and quality of recovery in horses. STUDY DESIGN: Experimental, analytical, cohort study. SAMPLE POPULATION: Twenty-two horses (n = 11 horses/group). METHODS: Horses were anesthetized by using the same protocol, but an IA injection of mepivacaine or saline was performed before carpal arthroscopy. End-tidal isoflurane concentration, heart rate, and mean arterial pressure were recorded at specific time points. Quality of recovery was scored by the anesthetist, who was unaware of group assignment. Data were analyzed by using two-way repeated-measures analysis of variance. RESULTS: Mean arterial pressure was higher during joint distension in the control group compared with baseline (7% higher, P = .02) and with the treatment group (10% higher, P = .04). Heart rate was higher in the control group compared with the treatment group during joint distension (8% higher, P = .04) and chip removal (11% higher, P = .03). Heart rate was higher in the control group compared with baseline during chip removal (5.5% higher, P = .04). Two horses in the control group required additional ketamine vs none in the treatment group. Quality of recovery was not different between groups. CONCLUSION: Intra-articular mepivacaine resulted in fewer detectable reactions to surgical stimulation, with similar recovery scores and blood pressure support requirements. CLINICAL SIGNIFICANCE: Intra-articular anesthesia prior to arthroscopy can be used safely in the horse and should be considered as a part of balanced anesthetic protocols.

The activity and inhibition of poly(ADP-ribose) polymerase-1 in equine peripheral blood mononuclear cells in vitro.

OBJECTIVES: To evaluate the poly (ADP-ribose) polymerase-1 (PARP1) enzyme and its inhibition in horses and explore its potential as a novel therapeutic target for equine intestinal ischemia-reperfusion injury by (1) identifying poly (ADP-ribose) (PAR) as an indication of PARP1 activation in equine cells using available immunoblot analytical techniques, (2) inducing PARP1 activation in an in vitro oxidative DNA damage model, (3) and demonstrating the inhibition of PARP1 in equine cells using commercially available PARP1 inhibitors. DESIGN: Experimental study. ANIMALS: Blood samples were collected from systemically healthy ponies (n = 3) and horses (n = 3). INTERVENTIONS: (1) Equine peripheral blood mononuclear cells were exposed to 3 different concentrations of hydrogen peroxide (H2 O2 ) and were lysed at specific time points. PARP1 activity was then assessed by using immunoblot analyses to determine PAR levels. (2) Equine peripheral blood mononuclear cells were preincubated with defined concentrations of PARP1 inhibitors prior to H2 O2 -mediated PARP1 stimulation. PAR levels reflecting PARP1 activity were determined using immunoblot analyses. MEASUREMENTS AND MAIN RESULTS: Commercially available anti-PAR antibodies were used successfully to identify equine PAR. There was a significant increase in PAR accumulation following treatment with H2 O2 . All of the tested PARP inhibitors significantly reduced PAR accumulation to or below basal levels following treatment with H2 O2 . CONCLUSIONS: This proof of principle study demonstrated that PAR, an indicator of PARP1 activity, can be identified in the equine species using immunoblot techniques, that equine PARP1 can be activated by H2 O2 -induced DNA damage, and that this activation can be inhibited by PARP1 enzyme inhibitors. The data suggest that the PARP1 pathway plays a role in the equine cellular response to oxidative DNA damage and supports its potential as a novel therapeutic target. Further research documenting an increase in PAR levels in vivo and the efficacy of PARP1 inhibitors in an equine intestinal ischemia-reperfusion model is needed.