Search

Summary: The most widely used method of assessing the physical status of humans presented for anaesthesia is the American Society of Anaesthesiologists Physical Status Classification System (ASA‐PS). The ASA‐PS has been applied to animals including horses, but its use is problematic. The authors virtually convened a group of internationally recognised equine veterinary anaesthesiologists with the goal of developing a risk assessment tool for the evaluation of healthy and diseased horses presented for anaesthesia. With this survey and analysis, the authors aim to develop a simple rubric system to assess equine anaesthetic risk that augments the ASA‐PS system. The goal is to identify both diseased and healthy horses at increased anaesthetic risk prior to induction of anaesthesia so that measures might be implemented to potentially reduce morbidity and mortality. [ABSTRACT FROM AUTHOR]

Summary: The inability to control pain is the most common reason for cessation of treatment and euthanasia in cases of laminitis, yet pain also serves a unique protective function in these cases, particularly in the acute phase when lamellar integrity is weakened. Successful analgesia requires an understanding of the disease pathophysiology, the sources of pain in laminitis, methods of serial pain evaluation, and methods of analgesia including systemic and regional techniques. This review discusses the approach to analgesia including detail of traditional and novel analgesic medications and techniques with specific reference to the laminitis case. [ABSTRACT FROM AUTHOR]

Summary: Background: The use of pulse oximetry in horses is limited due to inadequate readings with conventional transmission sensor probes. Objectives: The objectives of this study were to 1) develop an improved sensor design for horses to be used at an appropriate anatomical site, and 2) evaluate this design in an experimental study. Study design: In vivo experiment. Methods: A new sensor design for reflectance pulse oximetry at the buccal mucosa was developed. A conventional Nonin 2000SL sensor for transmission pulse oximetry was included into this design. Three different prototypes (N1, N2a, N2b) were constructed and used with the Nonin 2500A Vet pulse oximetry monitor. Thirteen anaesthetised warmblood horses were included into a desaturation protocol (100–70% SaO2). SpO2 and pulse frequency values were recorded, using SaO2 calculated from blood gas analysis and invasive pulse frequency measurements as reference methods. Bias and precision were evaluated by calculations of the root mean square deviation (Arms). The agreement of the methods was tested with Bland‐Altman analysis. Results: The quality of the pulse frequency readings determined the quality of the SpO2‐readings. Good pulse signal strength resulted in a SpO2‐accuracy comparable to that of the original sensor (Nonin 2000SL: Arms = 3%; N1: Arms = 3.60%; N2b: Arms = 3.46%). Especially at heart rates ≤30 bpm, pulse rate readings that were about twice as high as the reference value occurred. Their exclusion from the dataset resulted in a pulse rate accuracy similar to that of the original sensor. Bland‐Altman plots showed limits of agreement typical of pulse oximeters. Main limitations: The pulse frequency accuracy requires further improvement. The usability in clinical cases needs to be tested. Conclusions: The new sensor design has been shown to be suitable for buccal pulse oximetry in horses. [ABSTRACT FROM AUTHOR]

Background In the horse, effects of cardiovascular-active drugs on local perfusion of the gastrointestinal tract are poorly understood. Objectives To determine the effect of drugs commonly used to support blood pressure, on local intestinal blood flow and tissue oxygenation under isoflurane anaesthesia. Study design In vivo randomised crossover experiment. Methods Ten horses were anaesthetised with isoflurane. After 90 min of equilibration three doses (μg/kg bwt/min) of dobutamine ( DOB 0.5/1/3), dopamine ( DA 1/2/5), noradrenaline ( NA 0.1/0.2/0.5) and phenylephrine ( PHE 0.5/1/3) were infused for 15 min, in a randomised order, with a 45 min washout-period. Blood flow and tissue oxygenation ( sO2) of jejunum, colon and stomach were measured using white light remission spectrophotometry and laser doppler flowmetry; heart rate ( HR), mean arterial blood pressure ( MAP), cardiac output ( CO) were measured and systemic vascular resistance ( SVR) calculated. Results Compared to baseline high dose dobutamine significantly increased CO, HR, MAP (P<0.001) and blood flow to the jejunum (+47 ± 26%, P = 0.001) and colon (+29 ± 15%, P<0.001) (mean ± s.d.). Dopamine ( DA5) increased CO but decreased colonic blood flow (−39 ± 21% from baseline, P<0.001), as well as SVR and MAP compared to baseline (P<0.001). Noradrenaline had no significant influence on intestinal perfusion, but increased MAP and SVR from baseline (P<0.001). Phenylephrine ( PHE3) caused a significant decrease in blood flow and sO2, most profoundly at the colon compared to baseline (flow −44 ± 21%; sO2 −16 ± 3%, P<0.001), while MAP and SVR increased and CO and HR decreased (P<0.001). Main limitations The measurement technique only allows for flow measurements in arbitrary units, which can limit comparability to other techniques. Conclusion At the investigated doses dobutamine improved systemic and peripheral haemodynamics, while dopamine decreased MAP and peripheral perfusion. Noradrenaline increased MAP and SVR while peripheral blood flow was maintained, phenylephrine increased MAP, but reduced both local and systemic perfusion. [ABSTRACT FROM AUTHOR]

Reasons for performing study High airway pressures, necessary to keep equine lungs open, can have a detrimental impact on central and peripheral perfusion. Objective The aim of this study was to assess the effects of stepwise increasing airway pressure recruitment on central and intestinal perfusion and oxygenation during isoflurane anaesthesia in horses. Study design In vivo experimental study. Methods Ten anaesthetised horses were ventilated using intermittent positive pressure ventilation immediately after induction. After 90 min, end-expiratory pressure ( PEEP) was increased by steps of 5 cmH2O every 10 min up to a PEEP of 30 cmH2O and decreased back to zero maintaining a constant airway pressure difference of 20 cmH2O. Mean arterial blood pressure ( MAP), heart rate, central venous pressure, pulmonary artery pressure, expiratory isoflurane concentration and cardiac output (thermodilution method) were measured. Cardiac index ( CI) was calculated. Arterial blood gases were taken to measure arterial partial oxygen pressure (PaO2) and calculate arterial oxygen saturation (SaO2). Intestinal microperfusion and oxygenation were measured by laser Doppler flowmetry and white-light spectrophotometry. After ventral median laparotomy, a probe was placed on the stomach, jejunum and pelvic flexion of the colon. An ANOVA for repeated measurements and Tukey's post hoc test were used for statistical analysis (α = 5%). Results Recruitment of the lungs resulted in a significant increase in PaO2 from 201 ± 58 mmHg (baseline) to a maximum of 495 ± 75 mmHg. The CI and MAP decreased continuously with increasing airway pressures. When CI and MAP were 37 ± 9 ml/kg/min and 52 ± 8 mmHg (at PEEP of 25 cmH2O), respectively, a sudden decrease in intestinal perfusion followed by a delayed decrease in oxygenation occurred. Conclusions There was linear correlation between airway pressures and CI and MAP but not between central and gastrointestinal perfusion. Despite improvement of arterial oxygenation the decrease in CI and, therefore, in oxygen delivery PEEP resulted in a decrease in gastrointestinal oxygenation. [ABSTRACT FROM AUTHOR]

Background: Orotracheal intubation is commonly performed for inhalation anaesthesia in horses to ensure safe and reliable administration of volatile anaesthetics and to secure the airways. In human and equine medicine, the occurrence of intubation-associated complications has been described, which can range from mild mucosal irritation to severe necrosis. However, there are only sparse descriptions of mucosal alterations and the course of healing after elective surgery in horses., Objective: To investigate the prevalence and severity of tracheal lesions following endotracheal intubation associated with general anaesthesia in equine patients., Study Design: Prospective, clinical study., Methods: Forty adult Warmblood horses, weighing 400-600 kg, presented for elective surgery under general anaesthesia were included. For orotracheal intubation, a silicone tube was used and inflated until a cuff pressure of 40 cmH 2 O was confirmed. In all horses, endoscopic examination of the trachea with video documentation was performed prior to intubation and immediately after extubation, as well as 1, 3, 5 and 7 days after general anaesthesia. The type (redness, secretion, bleeding, erosions) and degree (0 = non-existent to 4 = severe) of corresponding lesions were assessed and scored. The occurrences of clinical signs were recorded. Statistical evaluation was performed using Friedman's test and Pearson correlation., Results: The median score immediately after recovery from anaesthesia was 6 (2-12) and increased significantly to 11 (4-15) after 1 day (p = 0.021). At day 7, the median score was 0 (0-2) with only four horses showing signs of mild tracheitis, and clinical signs were not observed throughout this time period. The duration of intubation correlated with the degree of tracheal damage (r 2  = 0.67, p < 0.001)., Main Limitations: Clinical, non-randomised study without a control group., Conclusion: Although orotracheal intubation was accompanied by focal inflammation of the trachea, in the present study no horses showed clinical signs and lesions healed within a week., (© 2025 The Author(s). Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.)

Maxillary nerve blocks (MNBs) commonly facilitate dental surgeries in standing horses. The goal of this prospective, blinded, cross-over design trial including 15 client-owned horses was to evaluate 3 methods of sensory function testing for confirming a successful MNB. Testing was performed bilaterally before sedation, 5 min after sedation, and 15 and 30 min after MNB with 0.5% bupivacaine and involved a needle prick dorsal to each naris, hemostat clamping of each nostril, and gingival algometry (measuring sensitivity to pain). Responses to stimulation were numerically scored and scores were summed up to a total score. Total score increases on the blocked side by ≥ 2 between baseline and 30 min Post MNB recordings signified a successful MNB. Sedation in the preceding 6 h, presence of sino-nasal disease, side of dental pathology, age, butorphanol administration, and detomidine dosing (µg/kg/min) throughout the tooth extraction procedure were recorded. In 73% of horses, MNB was successful. Sedation in the preceding 6 h ( P  = .732), age ( P  = .936), side of pathology ( P  = .516), and sino-nasal disease ( P  = .769) were not associated with total scores. Detomidine dosage and butorphanol use did not differ between horses in which the MNB was considered successful and for those in which it was not ( P  = .967 and P  = .538, respectively). Scores obtained with gingival algometry were less closely associated with total scores (rho = .649) than those obtained with needle prick and nostril clamping (rho = .819 and .892, respectively). Therefore, needle prick and nostril clamping are considered the more reliable methods for use in clinical practice to determine the success of an MNB., Competing Interests: Declaration of Conflicting InterestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Objective: Data were extracted from preexisting published studies and evaluated retrospectively to compare lactate and base deficit values at baseline and posthemorrhage with changes in corresponding hemoglobin (Hb) and Hct measurements to assess any association of such changes with severity of hemorrhage over time. To understand the goal, the objective of this study was to demonstrate statistical changes in laboratory values as described above., Methods: Previous prospectively designed experiments on 120 mixed-breed dogs were conducted. Various parameters, including Hb and Hct, lactate concentration, and base deficit, were extracted from the previously mentioned experiments. To validate this retrospective study, subset data on heart rate and arterial pressure were compared. In a subset analysis, 60 experiments were extracted to compare baseline mean arterial pressure to posthemorrhagic values to prove the validity of this model. Published studies were evaluated retrospectively to compare lactate and base deficit values at baseline and posthemorrhage., Results: Arterial pressure is lowest posthemorrhage, increases, then stabilizes. Baseline Hb averaged 15.1 g/dL and Hct 43.4%, and posthemorrhage values averaged 12.1 g/dL (Hb) and 35.3% (Hct). Significant differences were observed for both Hb (3.0 g/dL difference; P < .001) and Hct (8.3% difference; P < .001) posthemorrhage. Lactate significantly increased (2.1; P < .001), and base deficit significantly decreased (5.2; P < .001)., Conclusions: The data collected retrospectively validated the model for significant hypotension. It was then possible to evaluate whether Hb and Hct may accurately predict the degree of hemorrhage. In this model, both Hb and Hct decreased posthemorrhage significantly, although the actual change in Hb and Hct posthemorrhage was modest. Lactate concentration increased, and base deficit decreased., Clinical Relevance: The data suggest that Hb, Hct, lactate, and base deficit should be studied to see if they may have a potential role in guiding resuscitation decisions.

Background: Large colon volvulus is a cause of colic in horses with high morbidity and mortality when not promptly treated. More treatment options are needed to improve the outcome of these cases by protecting against the damage caused by ischaemia and reperfusion injury., Objectives: To determine the effect of preconditioning with dexmedetomidine prior to induction of ischaemia-reperfusion (IR) injury in a large colon volvulus model in the horse., Study Design: Randomised blinded in vivo experiments., Methods: Horses received either a dexmedetomidine (DEX) or saline (CON) constant rate infusion (CRI) immediately following induction of anaesthesia. Venous, arterial, and transmural occlusion of a section of the large colon was performed for 3 h, after which the ligatures and clamps were removed to allow for reperfusion for 3 h. Biopsies of the large colon were taken at baseline, 1 and 3 h of ischaemia, and at 1 and 3 h of reperfusion., Results: The severity of crypt epithelial loss (DEX = 2.1 [0.8-2.8], CON = 3.1 [2.5-4], p = 0.03) and mucosal haemorrhage was decreased (DEX = 2.1 [1.3-3], CON = 3.5 [2.5-4], p = 0.03) in group DEX compared to group CON when graded on a scale of 0-4. Crypt length remained longer (DEX = 369.5 ± 91.7 μm, CON = 238.5 ± 72.6 μm, p = 0.02) and interstitium to crypt (I:C) ratio remained lower (DEX = 1.4 (1-1.7), CON = 2.6 [1.8-5.9], p = 0.03) in group DEX compared to group CON during reperfusion., Main Limitations: Clinical applicability of pharmacologic preconditioning is limited., Conclusion: Preconditioning with a dexmedetomidine CRI prior to IR injury demonstrated a protective effect histologically on the large colon in the horse. Further investigation into postconditioning with dexmedetomidine is warranted as a possible intervention in colic cases suspected of being large colon volvulus., (© 2024 The Author(s). Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.)

Objective: Complications from general anesthesia, including pneumonia and decreased wound healing, are influenced by changes in immune cell function secondary to sedatives and anesthetics. It was hypothesized that immune cell function would be depressed in the early postanesthetic period. The objective was to investigate airway immune cell function before and after a general anesthetic episode in an equine in vivo model using ex vivo cell stimulations with lipopolysaccharide (LPS) for assessment of immune function., Study Design: Prospective experimental study., Animals: Six healthy, adult, institution-owned horses., Methods: Each horse underwent a bronchoalveolar lavage (BAL) 3 days before and immediately after a 2 hour general anesthetic. The BAL fluid was examined for cytology, total nucleated cell count and isolation of immune cells. Airway immune cells were treated with LPS or media (control) for 6 hours and supernatant was analyzed via a commercially available immunoassay for cytokines [tumor necrosis factor alpha (TNFα), interleukin (IL)-1β, IL-6, interferon gamma (IFNγ) and CXC motif chemokine ligand 8 (CXCL8)]. Data were compared using t-tests and Mann-Whitney tests., Results: Before anesthesia (baseline), LPS stimulation induced a significant increase in all cytokines of interest, except CXCL8, versus control samples. Unstimulated cells, after an anesthetic episode, had a significant 1.8-fold increase in IL-1β (p = 0.029), and a significant decrease in IL-6 and TNFα (p = 0.028 and 0.033, respectively) versus baseline. Following anesthesia, stimulated cells had a significant decrease in IL-6 and TNFα (p = 0.037 and 0.042, respectively) versus baseline., Conclusions and Clinical Relevance: This study supports the use of an equine in vivo model to assess airway immune cell function in relation to general anesthetic use., (Copyright © 2024 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Objective: To compare the ability of bioreactance noninvasive cardiac output (BR-NICO) with thermodilution cardiac output (TDCO) for the measurement of cardiac output (CO) in healthy adult horses receiving 2 different IV volume replacement solutions., Design: Prospective randomized crossover study from September to November 2021., Setting: University teaching hospital., Animals: Six university-owned adult horses., Interventions: Horses were randomly assigned to receive 7.2% hypertonic saline solution (HSS) or 6% hydroxyethyl starch (130/0.4) solution (HETA). BR-NICO and TDCO were measured simultaneously at baseline, 10, 20, 30, 40, 50, 60, 90, and 120 minutes before fluid administration and again at the same times after starting a bolus infusion of IV volume replacers. All solutions were administered within 10 minutes., Measurements and Main Results: BR-NICO and TDCO were strongly correlated (Pearson r 2  = 0.93; P < 0.01). Regression analysis showed the relationship between TDCO and BR-NICO was BR-NICO = 0.48 × TDCO + 0.6. For the corrected BR-NICO values, the Bland-Altman agreement mean bias and lower/upper limits of agreement were -0.62 and -5.3 to 3.9 L/min, respectively. Lin's concordance (95% confidence interval) between methods was 0.894 (0.825-1.097). Compared with baseline, HSS increased the CO at 10 and 20 minutes (TDCO and BR-NICO). Compared with baseline, HETA decreased the CO at 10 and 20 minutes (TDCO and BR-NICO) and increased the CO at 90 (TDCO only) and 120 minutes (TDCO and BR-NICO)., Conclusions: BR-NICO strongly agreed with TDCO in the measurement of CO in healthy unsedated adult horses. HSS administration significantly increased CO in the first 30 minutes, while HETA initially decreased CO at 10 minutes but increased CO to above baseline values by 90 minutes., (© Veterinary Emergency and Critical Care Society 2024.)

Background: Bronchoalveolar lavage (BAL) is a common procedure for evaluation of the equine lower airways. Time to resolution of post-BAL inflammation has not been clearly defined., Hypothesis: Residual inflammation, evident by changes in immune cell populations and inflammatory cytokines, will resolve by 72 hours after BAL., Animals: Six adult, healthy, institution-owned horses., Methods: Randomized, complete cross-over design. Each horse underwent 3 paired BALs, including a baseline and then 48, 72, and 96 hours later, with a 7-day washout between paired BALs. Each sample underwent cytological evaluation and cytokine concentrations were determined by a commercially available multiplex bead immunoassay. Statistical analysis was performed by multilevel mixed-effects Poisson regression analysis. Data are reported as marginal means and 95% confidence interval (CI)., Results: Neutrophil, eosinophil and mast cell percentages were not significantly different at any time points. Macrophage percentages were higher at 72 hours (45.0 [95% CI, 41.6-48.4]%) and 96 hours (45.3 [95% CI, 42.9-47.7]%) vs baseline (37.4 [95% CI, 33.5-41.4]%; P < .001 and P = .01, respectively), and at 72 hours and 96 hours vs 48 hours (31.9 [95% CI, 28.1-35.6]%; P < .001). Neutrophil percentage was not significantly increased at 48 hours (P = .11). Interleukin (IL)-6 concentration was increased at 72 hours (5.22 [95% CI, 3.44-6.99] pg/mL) vs 48 hours (4.38 [95% CI, 2.99-5.78] pg/mL; P < .001)., Conclusions and Clinical Importance: Significant lung inflammation was not detected at 72 and 96 hours, suggesting that repeating BAL at 72 hours or more can be done without concern of residual inflammation., (© 2024 The Author(s). Journal of Veterinary Internal Medicine published by Wiley Periodicals LLC on behalf of American College of Veterinary Internal Medicine.)

Horses are the most challenging of the common companion animals to anesthetize. Induction of anesthesia in the horse is complicated by the fact that it is accompanied by a transition from a conscious standing position to uncconconscious recumbency. The purpose of this article is to review the literature on induction of anesthesia with a focus on the behavioral and physiologic/pharmacodynamic responses and the actions and interactions of the drugs administered to induce anesthesia in the healthy adult horse with the goal of increasing consistency and predictability., Competing Interests: Declaration of competing interest None of the authors has any financial or personal relationships that could inappropriately influence or bias the content of the paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

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., Competing Interests: Conflict of interest: None declared., (Copyright © 2024 American College of Occupational and Environmental Medicine.)

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.

The study's objective was to evaluate the feasibility and dispersion of an open approach to the transversus abdominis plane (TAP) block in eight adult equine cadavers. A ventral midline incision was made, starting 2 cm cranial to the umbilicus and extending 25 cm cranially. In total, 0.5 mL/kg of new methylene blue (NMB) was injected per horse, divided into six injections. Using an 18 g, 8 cm Tuohy needle, three injections were made per side. The needle was guided blindly into the TAP using palpation. A 60 mL syringe was attached directly to the needle, depositing ~0.08 mL/kg at each site. The time to complete the injections was recorded for each cadaver. Following injection, the ventral body wall was dissected to determine if the dye was present within the TAP space as well as to measure the extent of the dispersion of the dye, the cranial to caudal extent, and the width of the dye's spread. Complete deposition of NMB into the TAP (six of six sites) was achieved in 5/8 horses. The median time needed to perform all the injections was 263 s. Increased adiposity (retroperitoneal fat) was associated with unsuccessful injections. This approach to the TAP was easily and quickly performed, though less successful in horses with increased retroperitoneal fat and increased BCS.

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-Fio2 (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.

Introduction: Never has the anatomy, the procedure of the transversus abdominis plane (TAP) block, or the perioperative analgesic effects of a bupivacaine TAP block been described in goats., Methods: This report details the relevant anatomy in a cadaveric study combined with the description/use of a TAP block in a controlled, randomized, prospective, blinded clinical study in which 20 goats with urolithiasis presenting for either ventral midline or paramedian celiotomy were enrolled. Anesthesia was induced with ketamine and midazolam and maintained with desflurane in oxygen. An ultrasound-guided TAP block was performed using 0.25% bupivacaine (4 sites, 0.4 mL/kg each site) (bupivacaine-TAP, n = 10) or equal volume of saline (control-TAP, n = 10). When indicated, urethral amputation was performed followed by celiotomy with cystotomy or tube cystostomy. Urethrotomy was performed if warranted. Intraoperatively, a 20% increase in mean arterial pressure (MAP), heart rate (HR) and/or respiratory frequency was treated with an increase in desflurane concentration of 0.5 Vol.%. Goats received ketamine boluses (0.2 mg/kg IV) when moving spontaneously. At 2, 12, and 24 h post-extubation, pain was scored with a descriptive scale. Data were analyzed with an analysis of variance (ANOVA) or the Wilcoxon signed-rank test, and P < 0.05 was considered statistically significant., Results: Bupivacaine-TAP goats exhibited lower end-tidal desflurane concentration requirements ( P = 0.03), lower pain scores at 2-h post-extubation ( P = 0.02), shorter anesthetic recovery times ( P = 0.03) and decreased HR and MAP during surgical stimulation. Goats receiving a bupivacaine TAP block experienced less intraoperative nociceptive input requiring less inhalant anesthetic leading to faster anesthetic recoveries and decreased postoperative pain., Discussion: Ultrasound-guided TAP block is a simple technique to decrease anesthetic requirement while providing additional postoperative comfort in goats undergoing celiotomy., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Morris, Hopster and Fecteau.)

Objective: To evaluate the agreement between the Tafonius large animal ventilator-integrated volumetric capnography (vCap) software and the Respironics NICO noninvasive cardiac output monitor reference system., Animals: Data were collected from 56 healthy adult horses undergoing general anesthesia., Methods: Animals were placed under general anesthesia and connected to the Tafonius large animal ventilator circle system. A flow partitioning device with CO2 and flow sensors was utilized to couple the endotracheal tube to the NICO monitor. Tafonius CO2 and flow sensors are incorporated into the Y-piece of the breathing circuit. Arterial blood samples were collected to determine the partial pressure of arterial carbon dioxide (PaCO2) immediately before data collection. The PaCO2 was input into the Tafonius and NICO monitor, and dead space ventilation (%Vd), end-tidal CO2 partial pressure (ETco2), mixed-expired CO2 partial pressure (Peco2), and expired tidal volume (Vt) were calculated over a single breath. Multiple measurements were completed for each patient, with a total of 200 paired data points collected for analysis. Data were assessed for normality, and Bland-Altman analysis was performed. Bias and 95% limits of agreement were calculated., Results: The limits of agreement for %Vd of the ventilator-derived measurements fell within ± 10% of the NICO monitor reference method., Clinical Relevance: Our results indicate that, when compared to the NICO monitor method, the Tafonius-integrated vCap software provides clinically acceptable values of Peco2, Vt, and %Vd in healthy adult horses.

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.

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 cmH 2 O 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 cmH 2 O) and significantly less PEEP was required to prevent alveolar closure (9.5 ± 1.2 vs 14.0 ± 1.5 cmH 2 O) 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., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Brandly, Midon, Douglas and Hopster.)

The placement of caudal epidural catheters in horses has become more frequent as a multi-modal analgesic strategy. Despite its integration into clinical practice, there are limited reports describing the use of caudal epidural catheterization for prolonged use in horses. The purpose of this study was to characterize the hospitalized caseload undergoing epidural catheterization for long-term epidural analgesic administration, to report the response to epidural therapy and observed complications, and to describe patient outcomes. Medical records of hospitalized equine patients that underwent placement of a caudal epidural catheter for analgesic management between 2017 and 2021 were analyzed retrospectively. For the 62 catheters placed in the 48 cases, the most frequent diagnosis category prompting epidural analgesia was orthopedic (43/48, 89.6%). Synovial sepsis was the most frequent specific diagnosis prompting epidural catheter placement (11/48, 22.9%). The initial response to epidural therapy was characterized as positive for 37/62 (59.7%) catheters. Complications were documented for 46/62 (74.2%) catheters. However, most of these complications were classified as mild (51.6%) or moderate (14.5%), and exaggerated physiologic responses were observed most frequently. Of the horses studied, 52.1% survived to be discharged from the hospital. With awareness of potential complications and vigilant monitoring, caudal epidural catheters should be considered for equine patients as an analgesic strategy., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Douglas, Midon, Shroff, Floriano, Driessen and Hopster.)

Objective: To compare the effects of 7.2% hypertonic and 0.9% isotonic saline (sodium chloride) solutions on cardiovascular parameters and plasma arginine vasopressin (AVP) concentrations in healthy, isoflurane-anesthetized horses., Animals: 8 healthy horses., Procedures: In a prospective, randomized, crossover study, horses were anesthetized with isoflurane twice with a 14-day washout period between anesthetic episodes. While anesthetized, horses received a bolus (4 mL/kg) of 7.2% hypertonic saline solution (HS) or 0.9% isotonic saline solution (IS). Heart rate; systolic, mean, and diastolic arterial blood pressures; and central venous and pulmonary artery pressures were measured every 5 minutes; cardiac output was measured by means of thermodilution every 15 minutes. Systemic vascular resistance (SVR) was calculated. Blood samples were collected before and during anesthesia, and plasma AVP concentrations were determined with a validated ELISA. Data were analyzed with repeated-measures ANOVA and Pearson correlations., Results: HS caused an increase in systolic (P = .003) and mean (P = .023) arterial blood pressures that lasted for 30 minutes. The SVR was increased (P < .001) for 45 minutes with HS compared with the SVR after IS administration. Mean plasma AVP concentration increased (P = .03) 15 minutes after HS administration, with the increase lasting 90 minutes., Clinical Relevance: A bolus of HS resulted in a clinically relevant increase in blood pressure in healthy, isoflurane-anesthetized horses. This effect was attributed to volume recruitment and an increase in SVR. Administration of HS offers an option for improving arterial blood pressure in anesthetized horses.

Objective: To compare the antinociceptive effects of morphine administered via cervical epidural catheter to intravenously administered morphine using a thermal threshold (TT) testing model in healthy adult horses., Study Design: Prospective, randomized, blinded experimental study., Animals: A total of six university-owned adult horses., Methods: Horses were instrumented with a cervical (C1-C2) epidural catheter and TT testing device with probes at withers and thoracic limb coronary bands. All horses underwent three TT testing cycles including cervical epidural morphine administration (treatment EpiM; 0.1 mg kg -1 ), systemic morphine administration (treatment SystM; 0.1 mg kg -1 ) and no morphine administration (treatment Control). Baseline TT was established prior to treatments, and TT was tested at 15, 30, 60, 90, 120, 150, 180, 240, 300, 360, 420, 480, 600 and 720 minutes following treatment. Horses underwent a 5 day washout period between treatments and the order of treatment was randomized. Differences between treatments were analyzed with repeated measures anova., Results: Systemic and epidural morphine administration resulted in significantly higher TT values compared with baseline and control treatment. The duration of effect was significantly longer in treatment EpiM (10-12 hours) than in treatment SystM (1.5-2.0 hours). Horses in treatment EpiM had significantly higher TT values at time points 180-600 minutes (withers) and 300-600 minutes (coronary band) than horses in treatment SystM., Conclusions and Clinical Relevance: Cervical epidural administration of morphine provided antinociceptive effects as measured by increased TT for 10-12 hours compared with 1.5-2.0 hours for intravenously administered morphine. No complications or adverse effects were noticed following epidural placement of a C1-C2 catheter and administration of morphine. The use of a cervical epidural catheter can be considered for analgesia administration in treatment of thoracic limb and cervical pain in the horse., (Copyright © 2022 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Objective: To evaluate the efficacy of 2 different oxygen delivery strategies-intranasal and tracheal insufflation-on the inspired fraction of oxygen (FIO2) in standing horses and to determine the time needed for arterial oxygen partial pressure (PaO2) equilibration., Animals: 6 healthy adult horses., Procedures: In this blinded, randomized crossover design study, horses were randomly assigned to receive oxygen via nasal cannula (group N) or transcutaneous tracheal catheter (group T). After placement of venous and arterial catheters, FIO2 was measured through a catheter placed into the distal portion of the trachea. After baseline measurements were obtained, horses received oxygen at up to 25 mL/kg/min for 1 hour via either intranasal or intratracheal catheter. The FIO2 and PaO2 were recorded at 5, 10, 15, 20, 25, 30, 45, and 60 minutes during and 5, 10, 15, 20, and 30 minutes after oxygen insufflation. Data were analyzed by use of a 2-way repeated measures ANOVA with Tukey-Kramer post hoc testing for pairwise comparisons (P < 0.05)., Results: During oxygen administration, FIO2 and PaO2 increased significantly when compared with baseline, resulting in significantly higher values for group T (37.7 ± 2.4%; 214.6 ± 18 mm Hg) than for group N (34.3 ± 3.9%; 184.1 ± 11 mm Hg). The equilibration time was less than 10 minutes., Clinical Relevance: Intratracheal oxygen administration resulted in better oxygenation than nasal insufflation and should therefore be considered in standing horses that are experiencing severe respiratory compromise. The equilibration between FIO2 and PaO2 is rapid in adult horses.