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.

Open Approach to the Transversus Abdominis Plane in Horses: A Cadaver Feasibility Study

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.

Large animal ventilator-integrated volumetric capnography generates clinically acceptable values of physiologic dead space in anesthetized healthy adult horses

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.

Optimization of lung ventilation and perfusion in anesthetized horses using a ventilation mode with flow-limited expiration

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.

The dilutional volume of morphine and xylazine administered via caudal epidural catheter affects cranial spread of analgesia in healthy standing 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.

Evaluation of Three Methods of Sensory Function Testing for the Assessment of Successful Maxillary Nerve Blockade in Horses

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.

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.

Caudal epidural catheterization for pain management in 48 hospitalized horses: A descriptive study of demographics, complications, and outcomes

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.

Effects of 7.2% hypertonic saline solution on cardiovascular parameters and endogenous arginine vasopressin secretion in euvolemic isoflurane-anesthetized horses

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.

Intratracheal oxygen administration increases FIO2 and PaO2 compared with intranasal administration in healthy, standing horses

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.

Flow-controlled expiration improves respiratory mechanics, ventilation, and gas exchange in anesthetized horses

OBJECTIVE

Mechanical ventilation is usually achieved by active lung inflation during inspiration and passive lung emptying during expiration. By contrast, flow-controlled expiration (FLEX) ventilation actively reduces the rate of lung emptying by causing linear gas flow throughout the expiratory phase. Our aim was to evaluate the effects of FLEX on lung compliance and gas exchange in anesthetized horses in dorsal recumbency.

ANIMALS

8 healthy horses.

PROCEDURES

All animals were anesthetized twice and either ventilated beginning with FLEX or conventional volume-controlled ventilation in a randomized, crossover design. Total anesthesia time was 3 hours, with the ventilatory mode being changed after 1.5 hours. During anesthesia, cardiac output (thermodilution), mean arterial blood pressures, central venous pressure, and pulmonary arterial pressure were recorded. Further, peak, plateau, and mean airway pressures and dynamic lung compliance (Cdyn) were measured. Arterial blood gases were analyzed every 15 minutes. Data were analyzed using ANOVA (P < 0.05).

RESULTS

FLEX ventilation resulted in significantly higher arterial oxygen partial pressures (521 vs 227 mm Hg) and Cdyn (564 vs 431 mL/cm H2O) values compared to volume-controlled ventilation. The peak and plateau airway pressure were lower, but mean airway pressure was significantly higher (4.8 vs 9.2 cm H2O) in FLEX ventilated horses. No difference for cardiovascular parameters were detected.

CLINICAL RELEVANCE

The results of this study showed a significant improvement of the Pao2 and Cdyn without compromising the cardiovascular system when horses were ventilated by use of FLEX compared to conventional ventilation.

Comparison of the zip skin closure system with conventional suture for skin closure of ventral midline incisions in horses

OBJECTIVE

To compare the application and healing of the zip skin closure system (ZSCS) with sutured closure by use of a split-scar model of ventral midline incisions in horses in a prospective, randomized experimental study.

ANIMALS

8 adult horses.

PROCEDURES

All horses underwent an exploratory ventral midline celiotomy with a standardized 30-cm skin incision. Each horse was randomized to have either the cranial 15 cm closed with suture and caudal 15 cm with the ZSCS or vice versa (split-scar model). Skin closure time was recorded and compared. Photography and skin biopsies were taken preoperatively and 14 days postoperatively. Cosmetic appearance was assessed by use of a proposed equine celiotomy incision score. Healing at 14 days was assessed by histopathology.

RESULTS

Skin closure times were faster with the ZSCS compared to sutured incisions. At 14 days postoperatively, the cosmetic appearance (equine celiotomy incision scores) for ZSCS incisions were better than sutured closure and histologic healing scores were not different between methods of closure. Subcuticular sutures were associated with deep dermal inflammation and necrosis independent of epidermal closure methods.

CLINICAL RELEVANCE

While limitations to the utility of the ZSCS are recognized, the potential benefits of expedient closure, good cosmetic outcome, and satisfactory healing make this method viable for closure of linear wounds or incisions in horses.

Clinical effect of buprenorphine or butorphanol, in combination with detomidine and diazepam, on sedation and postoperative pain after cheek tooth extraction in horses

The objective of this study was to compare effects of butorphanol (BUT) or buprenorphine (BUP), in combination with detomidine and diazepam, on the sedation quality, surgical conditions, and postoperative pain control after cheek tooth extraction in horses, randomly allocated to 2 treatment groups (BUT: n = 20; BUP: n = 20). A bolus of detomidine (15 μg/kg, IV) was followed by either BUP (7.5 μg/kg, IV) or BUT (0.05 mg/kg, IV). After 20 min, diazepam (0.01 mg/kg, IV) was administered and sedation was maintained with a detomidine IV infusion (20 μg/kg/h), with rate adjusted based on scores to 5 variables. All horses received a nerve block (maxillary or mandibular), and gingival infiltration with mepivacaine. Sedation quality was assessed by the surgeon from 1 (excellent) to 10 (surgery not feasible). A pain scoring system (EQUUS-FAP) was used to assess postoperative pain. Serum cortisol concentrations and locomotor activity (pedometers) were measured. Horses in BUP and BUT required a median detomidine infusion rate of 30.2 μg/kg/h (20 to 74.4 μg/kg/h) and 32.2 μg/kg/h (20 to 48.1 μg/kg/h), respectively (P = 0.22). Horses in the BUP group had better sedation quality (P < 0.05) during surgery and higher step counts (P < 0.001) postoperatively. Buprenorphine combined with detomidine provided a more reliable sedation than butorphanol. However, the EQUUS-FAP pain scale became unreliable because of BUP-induced excitement behavior.

Cervical Epidural Spinal Analgesia for Acute Management of Severe Unilateral Forelimb Lameness: Case Report

A 20-year-old Quarter Horse gelding was presented with severe right forelimb lameness (5/5 AAEP Lameness Scale) due to a tear of the superficial digital flexor muscle which was diagnosed via palpation of swelling and ultrasonography revealing major muscle fiber disruption and hematoma formation. When traditional systemic therapy (non-Steroidal anti-inflammatories) did not restore clinically acceptable comfort and the risk of supporting limb laminitis became a reasonable concern, a cervical epidural catheter was placed between the first and second cervical vertebrae in the standing, sedated patient using ultrasound guidance. The gelding was treated with epidural morphine (0.1 mg/kg every 24 h then decreased to 0.05 mg/kg every 12 h) and was pain-scored serially following treatment. Spinal analgesia was provided for 3 days. Pain scores significantly decreased following each treatment with morphine, and the gelding was successfully managed through the acutely painful period without any adverse effects associated with the C1-C2 epidural catheter placement technique, the epidural morphine, or contralateral limb laminitis. At the 2-month follow-up, the gelding was walking sound with no complications seen at the catheter insertion site. In this case, spinal analgesia using epidural morphine administered via a cervical epidural catheter was an effective and technically achievable option for pain management associated with severe forelimb muscle injury in a horse.

Pharmacology of the Equine Foot: Medical Pain Management for Laminitis

One of the biggest challenges in managing laminitis in horses remains the control of pain. The best analgesic approach is a multimodal approach, including nonsteroidal anti-inflammatory drugs, opioids, and/or constant rate infusions of α-2 agonists, ketamine, and lidocaine. Recent literature indicates that amitriptyline and soluble epoxide hydrolase inhibitor might be beneficial. Clinically oriented studies will be needed if they have a place in laminitis pain management. The systemic pain control can be combined with local techniques such as long-acting local anesthetics or epidural catheterization that allows for administration of potent analgesic therapy with a lower risk of negative side effects.

Effect of thermodilution injectate volume and temperature on the accuracy and precision of cardiac output measurements for healthy anesthetized horses

OBJECTIVE

To compare the accuracy and precision of cardiac output (CO) measurements derived from 4 thermodilution protocols that used different injectate temperatures and volumes in healthy adult horses.

ANIMALS

8 healthy adult horses.

PROCEDURES

Horses were anesthetized and instrumented with Swan-Ganz catheters. The CO was derived from each of 4 thermodilution protocols (IV injection of physiologic saline [0.9% NaCl] solution chilled to < 5 °C at volumes of 1 mL/15 kg of body weight [protocol A; control], 1 mL/25 kg [protocol B], and 1 mL/35 kg [protocol C] or maintained at 17 °C at a volume of 1 mL/15 kg [protocol D]) 3 times during each of 5 measurement cycles, with a 30-minute interval between cycles. During each measurement cycle, protocol A was performed first, and protocols B, C, and D were performed in a randomized order. Mean CO and within-subject variance in CO were compared among the 4 protocols.

RESULTS

Mean CO did not differ significantly among the 4 protocols. The within-subject variance for CO measurements derived from protocols C and D, but not protocol B, was significantly greater than that for protocol A (control).

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that, in healthy adult horses, decreasing the thermodilution injectate volume to 1 mL/25 kg from the recommended volume of 1 mL/15 kg did not adversely affect the accuracy or precision of CO measurements. However, use of smaller injectate volumes or use of injectate at approximately room temperature is not recommended owing to a clinically unacceptable increase in CO measurement variability.

Use of Polyamide (Nylon) Cable Ties for Vascular Ligation of Healthy Equine Jejunal Mesentery

Jejunal vascular ligation is an essential step in performing jejunojejunostomy. Hand sewn ligation is typically used and can increase operative time with long sections of bowel to be removed. Nylon cable ties (NCT) have been used for vascular ligation in horses but are yet to be investigated for application on the mesenteric vasculature of the gastrointestinal tract. Our objective was to evaluate the efficacy and short-term safety of NCT jejunal mesenteric vessel ligation in healthy horses. Eight healthy adult horses underwent midline celiotomy. A segment of jejunal mesentery was identified (≥4 arcades). Briefly, three fenestrations (proximal, middle, distal) were made 5–10 mm apart adjacent to the first and last vascular arcade to be ligated. Two sterilized NCT were passed to encircle the mesentery through the proximal and middle fenestrations, separated by intact mesentery. NCT were closed tightly and the vascular pedicle transected with Mayo scissors through the distal fenestration. Jejunojejunostomy was then performed and the mesentery sutured closed. The number of vascular arcades and time to ligate using NCT were recorded. At 2 weeks, horses underwent repeat celiotomy to assess the healing of the NCT ligation site and an equal number of vascular arcades were hand sewn double ligated using 2-0 Polyglactin 910 as a timed comparison. NCT mesenteric ligation was significantly faster than hand sewn methods (P < 0.01). Effective hemostasis was achieved in all cases. There was no evidence of local infection or adhesions at 14 days post-operatively. Further investigation in the long-term effects in horses as well as horses with strangulating jejunal lesions are needed for clinical application.

V-Gel® Guided Endotracheal Intubation in Rabbits

Background: General anesthesia in rabbits is associated with higher morbidity and mortality relative to other mammalian species commonly anesthetized. Unique challenges related to endotracheal intubation (ETI) in rabbits contribute to this risk. Objective: To improve the safety of ETI in rabbits, we developed two new ETI methods using a supraglottic airway device (v-gel^®) to facilitate ETI and compared them to traditional "blind" technique. We hypothesized that relative to blind ETI, v-gel^® guided ETI provides more successful placement of the endotracheal tube (ETT) in a shorter time. Outcomes included number of intubation attempts, time for achievement of ETI, endoscopic findings, and serial arterial blood gas (ABG) analysis. Study Design: Prospective, randomized, and crossover study. Methods: Ten female, New Zealand White rabbits aged 1-2 years old, weighing 4.3 ± 0.4 kg, were anesthetized four times. Each time, ETI was performed with one of the following techniques: Method 1: v-gel^® guided, polypropylene catheter facilitated, intubation using a cuffed ETT; Method 2: v-gel^® guided intubation using an uncuffed ETT directly inserted through the device airway channel; Method 3 and 4: Blind intubation with uncuffed or cuffed ETT. Upper airway endoscopy was performed before intubation attempts and after extubation. Serial ABG analysis was performed during the peri-intubation process. Results: V-gel^® guided techniques allowed successful ETI on the initial attempt for 9/10 subjects using Method 1 and 10/10 using Method 2. Relative to the v-gel^® guided techniques, the blind techniques required more intubation attempts. A median of 2 attempts (range 1-4, p < 0.007) were required for the uncuffed ETT, and a median of 4 (range 1-4, p < 0.001) attempts were performed for the cuffed ETT. The time to perform successful ETI was positively correlated with the number of attempts (ρ = 0.82), while successful ETI was negatively correlated with number of attempts (ρ = -0.82). Endoscopic findings showed mild to moderate laryngeal trauma. In the absence of oxygen supplementation, ABG analysis demonstrated low PaO₂, while PaCO₂ remained consistent. Conclusions: Facilitated ETI using the v-gel^® guided techniques allows for the rapid establishment of a secure airway to provide ventilatory support for rabbits undergoing general anesthesia.

Agreement of Bioreactance Cardiac Output Monitoring With Thermodilution in Healthy Standing Horses

Bioreactance is the continuous analysis of transthoracic voltage variation in response to an applied high frequency transthoracic current and was recently introduced for non-invasive cardiac output measurement (NICOM). We evaluated NICOM compared to thermodilution (TD) in adult horses. Six healthy horses were used for this prospective, blinded, experimental study. Cardiac output (CO) measurements were performed simultaneously using TD and the bioreactance method. Different cardiac output scenarios were established using xylazine (0.5 mg/kg IV) and dobutamine (1.5–3 mcg/kg/min). Statistical analysis was performed by calculating the concordance rate, performing a regression analysis, Pearson correlation, and Bland Altman. The TD-based CO and NICOM values were highly correlated for low, normal and high CO values with an overall correlation coefficient. A 4-quadrant plot showed an 89% rate of concordance. The linear regression calculated a relationship between NICOM and TDCO of Y = 0.4874 · X + 0.5936. For the corrected Bland Altman agreement, the mean bias and lower/upper limits of agreement were −0.26 and −3.88 to 3.41 L/min, respectively. Compared to TD, bioreactance- based NICOM showed good accuracy at induced low, normal, and high CO states in normal horses. Future studies performed under more clinical conditions will show if this monitor can help to assess hemodynamic status and guide therapy in horses in ICU settings and under general anesthesia.

Neuromuscular blockade with atracurium for ophthalmic surgery in horses-Effects on surgical and anesthetic characteristics and recovery quality

OBJECTIVE

To study the surgical, anesthetic and recovery qualities of horses receiving either a neuromuscular blocking agent (atracurium) or intravenous lidocaine (treatment groups A and L, respectively).

ANIMALS STUDIED

A total of thirty horses presented for ocular surgery were used in this study.

PROCEDURE

Horses were randomly assigned to receive either atracurium (group A) or a lidocaine constant rate infusion (group L). Surgical quality was graded on a scale from 1 (excellent)-5 (poor). While anesthetized, the heart rate, oxygen saturation and mean arterial blood pressure, and end-expiratory carbon dioxide and desflurane concentration were monitored and recorded every 5 minutes. Recovery was scored on a scale from 10 (best)-115 (worst).

RESULTS

Horses in treatment group A needed significantly less desflurane then horses in treatment group L (p = 0.04). Horses in treatment group A had a significantly better surgery score of 1 (1-2) (median and range) then horses in treatment group L (2.5; 1-5) (p = 0.02). The quality of recovery was significantly better in horses in treatment group A compared with treatment group L, and horses needed significantly less time to reach the standing position.

CONCLUSIONS

Atracurium and lidocaine CRI are safe methods of anesthesia for equine patients undergoing ocular surgery. Horses receiving atracurium needed less desflurane and had better surgery and recovery scores than horses receiving a lidocaine constant rate infusion.

A critical evaluation for validation of composite and unidimensional postoperative pain scales in horses

Proper pain therapy requires adequate pain assessment. This study evaluated the reliability and validity of the Unesp-Botucatu horse acute pain scale (UHAPS), the Orthopedic Composite Pain Scale (CPS) and unidimensional scales in horses admitted for orthopedic and soft tissue surgery. Forty-two horses were assessed and videotaped before surgery, up to 4 hours postoperatively, up to 3 hours after analgesic treatment, and 24 hours postoperatively (168 video clips). After six evaluators viewing each edited video clip twice in random order at a 20-day interval, they chose whether analgesia would be indicated and applied the Simple Descriptive, Numeric and Visual Analog scales, CPS, and UHAPS. For all evaluators, intra-observer reliability of UHAPS and CPS ranged from 0.70 to 0.97. Reproducibility was variable among the evaluators and ranged from poor to very good for all scales. Principal component analysis showed a weak association among 50% and 62% of the UHAPS and CPS items, respectively. Criterion validity based on Spearman correlation among all scales was above 0.67. Internal consistency was minimally acceptable (0.51–0.64). Item-total correlation was acceptable (0.3–0.7) for 50% and 38% of UHAPS and CPS items, respectively. UHAPS and CPS were specific (90% and 79% respectively), but both were not sensitive (43 and 38%, respectively). Construct validity (responsiveness) was confirmed for all scales because pain scores increased after surgery. The cut-off point for rescue analgesia was ≥ 5 and ≥ 7 for the UHAPS and CPS, respectively. All scales presented adequate repeatability, criterion validity, and partial responsiveness. Both composite scales showed poor association among items, minimally acceptable internal consistency, and weak sensitivity, indicating that they are suboptimal instruments for assessing postoperative pain. Both composite scales require further refinement with the exclusion of redundant or needless items and reduction of their maximum score applied to each item or should be replaced by other tools.

Comparison of one-layer Utrecht pattern with two-layer (simple continuous/Cushing) pattern for jejunojejunostomy in healthy horses in vivo

OBJECTIVE

To compare end-to-end jejunal anastomoses with a one-layer (Utrecht) and two-layer (simple continuous/Cushing) patterns.

STUDY DESIGN

Experimental study.

ANIMALS

Eight healthy adult horses.

METHODS

Jejunal end-to-end anastomoses were performed in randomly assigned one-layer or two-layer patterns. Horses were recovered from surgery and monitored for complications. At 14 days, the opposite pattern was performed (cross-over design) prior to euthanasia. Duration of closures was compared between patterns. Serosal width was measured before harvesting anastomotic sites from the first procedure. Luminal diameter was measured, and sections were collected for histological evaluation of heating after routine and immunohistochemical staining.

RESULTS

One-layer closure was faster (716 ± 86 s) than two-layer closures (1136 ± 111 s). Postoperative complications were minimal. No difference was detected in lumen size between groups. The lumen was reduced by 18% after one-layer and 15% after two-layer closures (p = .34). Serosal adhesions to the mesentery without clinical evidence of obstruction were observed in two horses with two-layer closure. Histopathological scores for inflammation, infection, and healing did not differ between groups.

CONCLUSION

Jejunal anastomosis with one-layer Utrecht technique was about 7 min faster and led to similar luminal reduction and histological healing scores as two-layer jejunojejunostomies.

CLINICAL SIGNIFICANCE

The outcomes of one-layer Utrecht jejunojejunostomies in healthy horses justify clinical evaluation of this technique.

Use of polyamide cable ties during experimental omentectomy in adult horses with histopathological assessment

OBJECTIVE

To report the use of nylon cable ties (NCT) for omentectomy in the horse.

STUDY DESIGN

Experimental study.

ANIMALS

Eight healthy adult horses.

METHODS

Horses underwent nylon cable tie (NCT) ligation of the greater omentum after ventral midline celiotomy. The time required to complete the omentectomy was recorded. Horses were recovered for 14 days before repeat celiotomy, adhesions assessment, and histological examination of the omentectomy site using a proposed histologic grading scheme. The total time for omentectomy procedure and histologic score was assessed for normality. Data are expressed as mean ± standard deviation.

RESULTS

NCT ligation provided sufficient hemostasis to complete the omentectomy (28 ± 15 s), without rescue ligation. No gross evidence of intra-abdominal adhesion or morbidity was associated with the omentectomy site 14 days after surgery. NCT were intact at the site of application, covered with smooth fibrous connective tissue. Adiponecrosis with minimal inflammation and fibrovascular occlusion of omental vessels was present at the surgical site. Mild inflammation was present at the NCT-tissue interface.

CONCLUSION

The use of NCT resulted in fast and effective omentectomy in healthy horses without short-term evidence of inflammatory reaction or intra-abdominal adhesion.

CLINICAL SIGNIFICANCE

The described technique provides an alternative for omentectomy in healthy adult horses.

Changes in Arterial Blood Pressure and Oxygen Tension as a Result of Hoisting in Isoflurane Anesthetized Healthy Adult Horses

Background: In anesthetized adult horses, changes in recumbency can influence the cardiovascular system but how arterial blood pressures and oxygen tension change in isoflurane anesthetized animals as a direct result of hoisting has not been investigated. Objective: To evaluate effects of hoisting on hemodynamic function and pulmonary gas exchange in isoflurane-anesthetized horses. Study Design: Prospective, experimental study. Methods: Six adult horses were anesthetized three times using isoflurane in pure oxygen (inspired fraction 0.9-1.0), and allowed breathing spontaneously in lateral recumbency. After 45 min horses were hoisted using a single hoist-hobble system for 5 min and returned into left lateral recumbency. Heart rate (HR), respiratory rate (RR), and systolic (SAP), diastolic (DAP), and mean arterial blood pressures (MAP) were measured every minute starting from 5 min before to 5 min after hoisting. Arterial blood gas samples were collected before, during, and after hoisting. Results: Significant changes in hemodynamic parameters and PaO₂ but not PaCO₂ were found between baseline recordings and measurements obtained during and early after hoisting. The MAP decreased within the 1st min of hoisting from a mean of 74 ± 17 mmHg at baseline to 57 ± 20 mmHg (p < 0.05). Thereafter, it rapidly recovered to baseline before continuing to rise to higher than baseline values and then remaining elevated for 5 min after horses were returned into lateral recumbency. Simultaneously, the HR increased by 6-9 beats per min during the initial 3 min of hoisting before returning close to baseline values (p < 0.05). The PaO₂ decreased significantly from a mean of 324.9 ±137.0 mmHg at baseline to a mean of 141.3 ± 104.2 mmHg during hoisting (p < 0.001) without recovering any more to baseline values. Clinical significance: Hoisting an adult horse during or at the end of isoflurane anesthesia carries the risk of a precipitous, though short-lived (1-2 min), drop in arterial blood pressures and a persistent decrease in arterial oxygenation. While in systemically healthy animals the observed functional impairments were not life-threatening, they may be more severe in systemically compromised horses.Therefore, arterial blood pressures and oxygenation must be carefully monitored when hoisting sick equine patients during or at the end of inhalant anesthesia.

The effects of flumazenil on ventilatory and recovery characteristics in horses following midazolam-ketamine induction and isoflurane anaesthesia

BACKGROUND

Flumazenil antagonises the actions of benzodiazepines. There has been no prior research specifically investigating this anaesthetic reversal agent for horses.

OBJECTIVES

To determine the effects of flumazenil administration in horses on (a) ventilatory parameters after midazolam-ketamine induction and maintenance with isoflurane in oxygen and on (b) the characteristics of recovery from general anaesthesia.

STUDY DESIGN

Blinded, randomised, crossover experiment.

METHODS

Six horses were randomly assigned to receive high-dose flumazenil (F_high , 20 µg/kg), low-dose flumazenil (F_low , 10 µg/kg) and saline (control). Cardioventilatory parameters were monitored. After 90 minutes of isoflurane anaesthesia, a bolus of F_high , F_low or saline was administered i.v. The horses were recovered using head and tail rope assistance. The times to first movement, to achievement of sternal recumbency, to the first attempt to stand and the total recovery time were determined. The recovery quality was evaluated using a 115-point recovery scoring system. The cardioventilatory parameters and recovery times were analysed using mixed-effects regression analyses. Intraclass correlation (ICC) analysis was used to evaluate the recovery scores. A Mann-Whitney U test assessed the relationship between recovery score and flumazenil administration.

RESULTS

A significant difference with flumazenil administration was found for SpO₂ , mean arterial pressure, I:E ratio, minute volume of ventilation (MV) and peak inspiratory pressure. There was a significant difference with flumazenil administration for the time to sternal recumbency, the time to the first attempt to rise and the total recovery time. There was no significant difference in total recovery score with flumazenil administration.

MAIN LIMITATIONS

Plasma levels of midazolam and flumazenil were not obtained.

CONCLUSIONS

Flumazenil has a dose-dependent effect on MV and recovery time, which may make it useful in cases for which a prolonged anaesthetic recovery is undesirable.

Accuracy of tidal volume delivery by five different models of large-animal ventilators

OBJECTIVE

To determine the accuracy of tidal volume (V_T) delivery among 5 different models of large-animal ventilators when tested at various settings for V_T delivery, peak inspiratory flow (PIF) rate, and fresh gas flow (FGF) rate.

SAMPLE

4 different models of pneumatically powered ventilators and 1 electrically powered piston-driven ventilator.

PROCEDURES

After a leak flow check, each ventilator was tested 10 times for each experimental setting combination of 5 levels of preset V_T, 3 PIF rates, and 4 FGF rates. A thermal mass flow and volume meter was used as the gold-standard method to measure delivered V_T. In addition, circuit systems of rubber versus polyvinyl chloride breathing hoses were evaluated with the piston-driven ventilator. Differences between preset and delivered V_T (volume error [ΔV_T]) were calculated as a percentage of preset V_T, and ANOVA was used to compare results across devices. Pearson correlation coefficient analyses and the coefficient of determination (r²) were used to assess potential associations between the ΔV_T and the preset V_T, PIF rate, and FGF rate.

RESULTS

For each combination of experimental settings, ventilators had ΔV_T values that ranged from 1.2% to 22.2%. Mean ± SD ΔV_T was 4.8 ± 2.5% for the piston-driven ventilator, compared with 6.6 ± 3.2%, 10.6 ± 2.9%, 13.8 ± 2.97%, and 15.2 ± 2.6% for the 4 pneumatic ventilators. The ΔV_T increased with higher PIF rates (r² = 0.69), decreased with higher FGF rates (r² = 0.62), and decreased with higher preset V_T (r² = 0.58).

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that the tested ventilators all had ΔV_T but that the extent of each of ΔV_T varied among ventilators. Close monitoring of delivered V_T with external flow and volume meters is warranted, particularly when pneumatic ventilators are used or when very precise V_T delivery is required.

Protective effects of dexmedetomidine on small intestinal ischaemia-reperfusion injury in 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.

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.

Electrolyte measurement in goats: Comparison of 2 blood gas analyzers and evaluation of the preanalytical blood sample preparation on measurement results

OBJECTIVE

1) To evaluate agreement for electrolyte measurements in goats between a handheld point-of-care analyzer (Abaxis VetScan i-STAT 1) (POC) and a benchtop blood gas analyzer (Opti CCA-TS2) (VBG) and 2) to evaluate effect of sample type on electrolytes values reported by both analyzers.

MATERIAL AND METHODS

In 21 hospitalized caprine patients and 9 healthy research goats, blood samples were collected into heparin-containing tubes (Sodium Heparin 33 IU/2 ml) (TUBE) and a heparinized syringe (Sodium Heparin 430 IU/ml) (SYRINGE). Samples were analyzed using a POC analyzer as well as VBG. Analyzer results were compared using Bland-Altman analysis and Pearson correlation. Comparison between samples was performed using repeated measures ANOVA.

RESULTS

Between analyzers, TUBE yielded a bias (95 % limits of agreement) of 0.07 mmol/l (-4.37 to 4.52) for sodium, while SYRINGE yielded a bias of -6.13 mmol/l (-11.04 to -1.22). Comparison of potassium yielded a bias of 0.09 mmol/l (-0.5 to 0.67) and 0.08 mmol/l (-0.4 to 0.56) for TUBE and SYRINGE, respectively. Comparison of ionized calcium showed a bias of 0.05 mmol/l (0.01-0.1) and -0.02 mmol/l (-0.18 to 0.14) for TUBE and SYRINGE, respectively. Between sample types, the POC yielded a bias of 5.13 mmol/l (0.18-10.09) for sodium, 0.04 mmol/l (-0.12 to 0.2) for potassium, and 0.40 mmol/l (0.12-0.68) for ionized calcium.

CONCLUSION AND CLINICAL RELEVANCE

The POC exhibited clinically negligible bias for electrolyte analysis as compared to VBG. Ionized calcium concentrations were lower in self-prepared heparinized syringes than in heparin-containing tubes, suggesting an effect of heparin concentration on ionized calcium.

Cervical Epidural and Subarachnoid Catheter Placement in Standing Adult Horses

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.

Pharmacokinetics of xylazine after 2-, 4-, and 6-hr durations of continuous rate infusions in horses

Intravenous (i.v.) bolus administration of xylazine (XYL) (0.5 mg/kg) immediately followed by a continuous rate infusion (CRI) of 1 mg kg^-1  hr^-1 for 2, 4, and 6 hr produced immediate sedation, which lasted throughout the duration of the CRI. Heart rate decreased and blood pressure increased significantly (p > .05) in all horses during the first 15 min of infusion, both returned to and then remained at baseline during the duration of the infusion. Compartmental models were used to investigate the pharmacokinetics of XYL administration. Plasma concentration-time curves following bolus and CRI were best described by a one-compartment model. No differences were found between pharmacokinetic estimates of the CRIs for the fractional elimination rate constant (K_e ), half-life (t_1/2e ), volume of distribution (V_d ), and clearance (Cl). Median and range were 0.42 (0.15-0.97)/hr, 1.68 (0.87-4.52) hr, 5.85 (2.10-19.34) L/kg, and 28.7 (19.6-39.5) ml min^-1  kg^-1 , respectively. Significant differences were seen for area under the curve ( AUC 0 ∞ ) (p < .0002) and maximum concentration (C_max ) (p < .04). This indicates that with increasing duration of infusion, XYL may not accumulate in a clinically relevant way and hence no adjustments are required in a longer XYL CRI to maintain a constant level of sedation and a rapid recovery.

Ischaemic preconditioning and pharmacological preconditioning with dexmedetomidine in an equine model of small intestinal ischaemia-reperfusion

Small intestinal strangulation associated with ischaemia-reperfusion injury (IRI) is common in horses. In laboratory animals IRI can be ameliorated by ischaemic preconditioning (IPC) and pharmacological preconditioning (PPC) with dexmedetomidine. The aim of this study was to determine the effect of PPC with dexmedetomidine or IPC in an equine model of small intestinal ischaemia-reperfusion (IR). In a randomized controlled experimental trial, 15 horses were assigned to three groups: control (C), IPC, and PPC with dexmedetomidine (DEX). All horses were placed under general anaesthesia and 90% jejunal ischaemia was induced for 90 minutes, followed 30 minutes of reperfusion. In group IPC, three short bouts of ischaemia and reperfusion were implemented, and group DEX received a continuous rate infusion of dexmedetomidine prior to the main ischaemia. Jejunal biopsies were collected before ischaemia (P), and at the end of ischaemia (I) and reperfusion (R). Mucosal injury was assessed by the Chiu-Score, inflammatory cells were stained by cytosolic calprotectin. The degree of apoptosis and cell necrosis was assessed by cleaved-caspase-3 and TUNEL. Parametric data were analyzed by two-way ANOVA for repeated measurements followed by Dunnetts t-test. Non parametric data were compared between groups at the different time points by a Kruskal-Wallis-Test and a Wilcoxon-2-Sample-test. The mucosal injury score increased during I in all groups. After reperfusion, IRI further progressed in group C, but not in IPC and DEX. In all groups the number of cleaved caspase-3 and TUNEL positive cells increased from P to I. The number of TUNEL positive cells were lower in group DEX compared to group C after I and R. Infiltration with calprotectin positive cells was less pronounced in group DEX compared to group C, whereas in group IPC more calprotectin positive cells were seen. In conclusion, IPC and DEX exert protective effects in experimental small intestinal ischaemia in horses.

Intratesticular mepivacaine versus lidocaine in anaesthetised horses undergoing Henderson castration

BACKGROUND

In horses undergoing castration, direct comparison of intratesticular lidocaine vs mepivacaine as analgesic adjuncts has not yet been analysed.

OBJECTIVE

To compare the effects of intratesticular lidocaine and mepivacaine during equine castration using the Henderson drill under total intravenous anesthesia.

STUDY DESIGN

Randomised, double-blinded clinical study.

METHODS

Thirty-four stallions were anaesthetised using xylazine-ketamine and randomly selected to receive 10 mL either lidocaine or mepivacaine injected into each testicle. Both surgeon and anaesthetist were blinded to the selected treatment. A total of 5 minutes were required to pass between injection and first incision. Routine castration using a Henderson drill was performed. Heart rate, respiratory rate and SpO₂ were serially recorded. Total surgical time, time prior to clamping of each testicle and time to second incision were recorded. Cremaster muscle relaxation, surgical quality scores, number of additional ketamine boluses, recovery time and recovery quality were assessed between groups.

RESULTS

Cremaster relaxation scores were significantly better for the mepivacaine group over the lidocaine group on a 1-3 scoring system (1 being most relaxed, 3 being least). The average cremaster relaxation score on both testicles treated with mepivacaine was 1 compared to the lidocaine treatment averaging 2 [P = .03 first testicle; P = .04 second testicle]. The lidocaine group had an increased number of horses requiring additional ketamine (25% of horses) compared to the mepivacaine group (16% of horses). No other significant differences were observed between the groups.

MAIN LIMITATIONS

The use of only one injection method and lack of post-operative pain scoring limit the conclusions that can be drawn from these results.

CONCLUSION

Intratesticular mepivacaine when compared with intratesticular lidocaine results in improved cremaster muscle relaxation when only waiting five min prior to the start of the procedure.

Comparison between head-tail-rope assisted and unassisted recoveries in healthy horses undergoing general anesthesia for elective surgeries

OBJECTIVE

To compare attempts to stand, duration, quality, and occurrence of injuries between head-tail rope assistance and unassisted recoveries in healthy horses undergoing general anesthesia for elective surgeries.

STUDY DESIGN

Randomized, prospective, clinical trial.

METHODS

Three hundred one healthy horses undergoing elective surgeries were randomly assigned to recover with head-tail rope assistance (group A) or unassisted (group U); 305 recoveries (group A, n = 154; group U, n = 151) were analyzed. Anesthesia was maintained with isoflurane and triple drip. For each recovery, attempts to stand, duration, quality, and recovery-associated injuries were recorded. Data were analyzed by linear regression and analysis of covariance.

RESULTS

Anesthesia duration was similar between groups (mean ± SD, 70 ± 29 minutes). Compared with group U, group A had fewer attempts to stand (median [range], group A = 1 [1-7] vs group U = 3 [1-34]) and shorter duration of recovery (mean ± SD, A = 36 ± 12 minutes vs U = 41 ± 15 minutes). Recovery quality in group A (28 points [15-70]) was better than that in group U (38 points [11-87]). More horses had recovery-associated injuries in group U (9 horses) compared with group A (2 horses). One horse per group was euthanized.

CONCLUSION

Head-tail rope assistance reduced standing attempts, shortened recovery duration, improved recovery quality, and reduced recovery-associated minor injuries after general anesthesia for elective surgery in healthy horses. Fatalities could not be prevented.

CLINICAL SIGNIFICANCE

Head-tail rope assistance may improve recovery in healthy horses after short-duration elective surgeries with isoflurane and triple drip.

Comparison of various types of inert gas components on efficacy of an alveolar recruitment maneuver in dorsally recumbent anesthetized horses

OBJECTIVE

To assess effects of nitrogen and helium on efficacy of an alveolar recruitment maneuver (ARM) for improving pulmonary mechanics and oxygen exchange in anesthetized horses.

ANIMALS

6 healthy adult horses.

PROCEDURES

Horses were anesthetized twice in a randomized crossover study. Isoflurane-anesthetized horses in dorsal recumbency were ventilated with 30% oxygen and 70% nitrogen (treatment N) or heliox (30% oxygen and 70% helium; treatment H) as carrier gas. After 60 minutes, an ARM was performed. Optimal positive end-expiratory pressure was identified and maintained for 120 minutes. Throughout the experiment, arterial blood pressures, heart rate, peak inspiratory pressure, dynamic compliance (C_dyn), and Pao₂ were measured. Variables were compared with baseline values and between treatments by use of an ANOVA.

RESULTS

The ARM resulted in significant increases in Pao₂ and C_dyn and decreases in the alveolar-arterial gradient in the partial pressure of oxygen in all horses. After the ARM and during the subsequent 120-minute phase, mean values were significantly lower for treatment N than treatment H for Pao₂ and C_dyn. Optimal positive end-expiratory pressure was consistently 15 cm H₂O for treatment N, but it was 10 cm H₂O (4 horses) and 15 cm H₂O (2 horses) for treatment H.

CONCLUSIONS AND CLINICAL RELEVANCE

An ARM in anesthetized horses might be more efficacious in improving Pao₂ and C_dyn when animals breathe helium instead of nitrogen as the inert gas.

Evaluation of the effects of gas volume and composition on accuracy of volume measurement by two flow sensors and delivery by a piston-driven large-animal ventilator

OBJECTIVE To evaluate the effects of 4 gas compositions at various volumes (simulated tidal volumes [V_Ts]) on accuracy of measurements obtained with 2 types of flow sensors and accuracy of gas volume delivery by a piston-driven ventilator. SAMPLE 4 gas mixtures (medical air [21% O₂:79% N₂], > 95% O₂, O₂-enriched air [30% O₂:70% N₂], and heliox [30% O₂:70% He]). PROCEDURES For each gas mixture, reference V_Ts of 1 to 8 L were delivered into an anesthetic breathing circuit via calibration syringe; measurements recorded by a Pitot tube-based flow sensor (PTFS) connected to a multiparameter host anesthesia monitor and by a thermal mass flow and volume meter (TMFVM) were compared with the reference values. Following leak and compliance testing, the ventilator was preset to deliver each gas at V_Ts of 1 to 8 L into the calibration syringe. Effects of gas volume and composition on accuracy of V_T measurement and delivery were assessed by ANOVA. Agreements between delivered and flow sensor-measured V_T and preset versus ventilator-delivered V_T were determined by Bland-Altman analysis. RESULTS Flow sensor measurements were accurate and not influenced by gas composition. Mean measurement error ranges for the PTFS and TMFVM were -4.99% to 4.21% and -4.50% to 0.17%, respectively. There were no significant differences between ventilator-delivered and reference V_Ts regardless of gas volume or composition. Bland-Altman analysis yielded biases of -0.046 L, -0.007 L, -0.002 L, and 0.031 L for medical air, > 95% O₂, O₂-enriched air, and heliox, respectively. CONCLUSIONS AND CLINICAL RELEVANCE The PTFS and the TMFVM measured V_Ts and the piston-driven ventilator delivered V_Ts with error rates of < 5% for all gas compositions and volumes tested.

The relationship between intestinal and oral mucosa microcirculation in anaesthetized horses

OBJECTIVE

To compare alteration in intestinal blood flow in anaesthetized horses with changes in oral mucosa blood flow.

STUDY DESIGN

Prospective, randomized clinical study.

ANIMALS

Eight warmblood horses.

METHODS

After induction with guaifenesin and ketamine, anaesthesia was maintained with isoflurane at 1.5 vol% in oxygen. The tissue blood flow was measured using laser Doppler flowmetry at the jejunum, colon, rectal mucosa, oesophageal mucosa and the oral mucosa. After three baseline measurements, blood flow was first increased by dobutamine infusion and thereafter decreased by increasing isoflurane concentration and all measurements repeated twice. anova was used for comparing the measured parameters to baseline and correlation between the different measurement localizations was examined using Pearson correlation (p < 0.05).

RESULTS

Microperfusion at all measurement sites increased significantly during dobutamine infusion and decreased significantly during high isoflurane concentration. There was a significant correlation between flow at the oral mucosa and flow at the jejunum (r² = 0.77, p = 0.002), colon (r² = 0.76, p < 0.001), rectal mucosa (r² = 0.88, p < 0.001) and oesophageal mucosa (r² = 0.83, p <0.001).

CONCLUSIONS AND CLINICAL RELEVANCE

Oral mucosa blood flow can be used in isoflurane anaesthetized horses to reflect changes of intestinal microcirculation.

Effect of butorphanol, midazolam or ketamine on romifidine based sedation in horses during standing cheek tooth removal

BACKGROUND

Standing surgery, especially dental procedures, are commonly performed in horses. This leads to an increasing demand for reliable sedation protocols. Therefore, it was the purpose of this study to investigate the influence of butorphanol, midazolam or ketamine on romifidine based sedation in horses during cheek tooth removal.

METHODS

Forty horses presented for tooth extraction were divided in four groups using matched pair randomization. Group R was sedated with romifidine (bolus 0.03 mg/kg, followed by a constant rate infusion (CRI) 0.05 mg/kg/h) and group RB with romifidine (same dose) and butorphanol (0.02 mg/kg; CRI 0.04 mg/kg/h). Group RM received romifidine (same dose) and midazolam (0.02 mg/kg; CRI 0.06 mg/kg/h) whereas group RK was administered romifidine (same dose) and ketamine (0.5 mg/kg; CRI 1.2 mg/kg/h). If sedation was not adequate a top up bolus of romifidine (0.01 mg/kg) was administered. The quality of sedation and the conditions for tooth extraction, the level of ataxia, chewing, head and tongue movement were evaluated by using a scoring system. The investigator was blinded to the applied sedation protocol. Furthermore, serum cortisol concentrations before, during and after the procedure were analyzed to gain more information about the stress level of the horses.

RESULTS

Horses in group RM showed significantly less chewing and tongue activity compared to horses sedated with romifidine alone or with butorphanol additionally, but also significantly higher levels of ataxia. The quality of sedation was significantly better if romifidine was administered in combination with ketamine compared to romifidine alone. Furthermore, horses of group RK needed less additional romifidine boli compared to all other groups. Blood cortisol concentrations during surgery in groups RB and RM remained unchanged. Horses of group R showed higher cortisol concentrations during sedation compared to horses of groups RB and RM.

CONCLUSION

Romifidine alone at an initial bolus dose of 0.03 mg/kg followed by a constant rate infusion of 0.05 mg/kg/h was insufficient to obtain an adequate level of sedation and led to increased stress levels, whereas the addition of butorphanol inhibited the stress response. The combination of romifidine with either midazolam or ketamine improved sedation quality and surgical conditions.

Effects of controlled hypoxemia or hypovolemia on global and intestinal oxygenation and perfusion in isoflurane anesthetized horses receiving an alpha-2-agonist infusion

BACKGROUND

Aim of this prospective experimental study was to assess effects of systemic hypoxemia and hypovolemia on global and gastrointestinal oxygenation and perfusion in anesthetized horses. Therefore, we anesthetized twelve systemically healthy warmblood horses using either xylazine or dexmedetomidine for premedication and midazolam and ketamine for induction. Anesthesia was maintained using isoflurane in oxygen with either xylazine or dexmedetomidine and horses were ventilated to normocapnia. During part A arterial oxygen saturation (SaO2) was reduced by reducing inspiratory oxygen fraction in steps of 5%. In part B hypovolemia was induced by controlled arterial exsanguination via roller pump (rate: 38 ml/kg/h). Mean arterial blood pressure (MAP), heart rate, pulmonary artery pressure, arterial and central venous blood gases and cardiac output were measured, cardiac index (CI) was calculated. Intestinal microperfusion and oxygenation were measured using laser Doppler flowmetry and white-light spectrophotometry. Surface probes were placed via median laparotomy on the stomach, jejunum and colon.

RESULTS

Part A: Reduction in arterial oxygenation resulted in a sigmoid decrease in central venous oxygen partial pressure. At SaO2 < 80% no further decrease in central venous oxygen partial pressure occurred. Intestinal oxygenation remained unchanged until SaO2 of 80% and then decreased. Heart rate and pulmonary artery pressure increased significantly during hypoxemia. Part B: Progressive reduction in circulating blood volume resulted in a linear decrease in MAP and CI. Intestinal perfusion was preserved until blood loss resulted in MAP and CI lower 51 ± 5 mmHg and 40 ± 3 mL/kg/min, respectively, and then decreased rapidly.

CONCLUSIONS

Under isoflurane, intestinal tissue oxygenation remained at baseline when arterial oxygenation exceeded 80% and intestinal perfusion remained at baseline when MAP exceeded 51 mmHg and CI exceeded 40 mL/kg/min in this group of horses.

TRIAL REGISTRY NUMBER

33.14-42,502-04-14/1547.

Evaluation of intravenous regional anaesthesia and four-point nerve block efficacy in the distal hind limb of dairy cows

Background

Intravenous regional anaesthesia (IVRA) and hindfoot four-point nerve block anaesthesia (NBA) are recommended for local anaesthesia (LA) in the distal limb of dairy cows. Two studies were conducted to compare the efficacy, time until onset and stress responses to IVRA and NBA in dairy cows. In the first cross-over designed study, eight healthy unsedated German Holstein cows, restrained in lateral recumbency (LR) on a surgical tipping table, were treated with IVRA and NBA using procaine 2% as a local anaesthetic. Distal limb desensitization was tested by electrical (e-), mechanical (m-) and thermal (t-) nociceptive stimulation 10 min before and 15 and 30 min after LA. Hormonal-metabolic (blood concentrations of cortisol, lactate, non-esterified fatty acids, and glucose) and cardio-respiratory (heart and respiratory rate, mean arterial blood pressure) stress responses to treatment were assessed at predetermined intervals. In the second study, six healthy, unsedated German Holstein cows in LR were treated (crossover design) with IVRA and NBA. Short-interval e-stimulation was measured by the time until complete distal limb desensitization.

Results

In the first study, four of eight cows responded to e-stimulation 15 min after IVRA, while none of the cows treated with NBA responded until the safety cut-off level was reached. E-stimulation revealed complete desensitization of the distal limb 30 min after LA in all cows. Half of the cows did not respond to m- and t-stimulation before LA, so no further evaluation was performed. Stress reactions to IVRA and NBA treatment were similar, but differences may have been masked by stress response to LR restraint. In the second study, complete desensitization was achieved 12.5 min after NBA, while one of the six cows still responded to e-stimulation 20 min after IVRA.

Conclusion

Hindfoot nerve block anaesthesia and intravenous regional anaesthesia induced complete desensitization of the distal hind limb in dairy cows. However, the anaesthesia onset after NBA was significantly faster than that of IVRA, which may be clinically relevant in the field, particularly when distal limb anaesthesia is required for major claw surgeries under time constraints.

Influence of catecholamines at different dosages on the function of the LiDCO sensor in isoflurane anesthetized horses

OBJECTIVE

To compare the lithium dilution method for cardiac output (LiDCO) and bolus-thermo-dilution (BTD) measurements before and during infusion of dobutamine, dopamine, phenylephrine, or noradrenaline at 2 different doses in anesthetized horses and to examine the correlation between sensor voltages (saline-blood exposed) and possible measurement errors.

DESIGN

Prospective experimental study.

SETTING

University teaching hospital.

ANIMALS

Nine Warmblood horses.

INTERVENTIONS

Following 90 minutes of equilibration, 3 different doses of dobutamine (0.5-3 μg/kg/min), dopamine (1-5 μg/kg/min), phenylephrine (0.5-3 μg/kg/min), or noradrenaline (0.1-0.5 μg/kg/min) were administered for 15 minutes in anesthetized horses, and measurements using the LiDCO were performed at the lowest and highest doses. Pairs of LiDCO and BTD measurements were collected and sensor voltages exposed to blood and saline were measured before and at the end of each infusion period. Agreement between LiDCO and BTD was assessed with the Bland-Altman method.

MEASUREMENT AND MAIN RESULTS

The biases (2 standard deviations) before infusion of dobutamine, dopamine, phenylephrine, and noradrenaline were 1.1 (5.7), 1.6 (7.3), 0.2 (6.6), and 1.5 (4.1) L/min, respectively, and minimally and nonsignificantly changed following low-dose catecholamine infusions. Following infusion of higher doses, biases were significantly higher compared to baseline with 10.7 (7.8), 11.2 (11.9), 6.9 (11.7), and 3.5 (3.8) L/min, respectively. The difference between saline- and blood-exposed sensor voltage decreased during infusion of high doses of catecholamines with correlations (r_s = 0.62) between cardiac output differences and sensor voltage differences (saline-blood).

CONCLUSIONS

This study demonstrated that catecholamines could lead to overestimation in a dose-dependent fashion in LiDCO measurements. Monitoring changes in sensor voltage differences (saline-blood) is a valuable and clinically applicable tool to predict errors in LiDCO measurements.