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Abstract

OBJECTIVE To evaluate the effects of 4 gas compositions at various volumes (simulated tidal volumes [VTs]) 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 VTs 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 VTs of 1 to 8 L into the calibration syringe. Effects of gas volume and composition on accuracy of VT measurement and delivery were assessed by ANOVA. Agreements between delivered and flow sensor-measured VT and preset versus ventilator-delivered VT 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 VTs 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 VTs and the piston-driven ventilator delivered VTs with error rates of < 5% for all gas compositions and volumes tested.

Full access
in American Journal of Veterinary Research

Abstract

OBJECTIVE To evaluate efficacy of an alveolar recruitment maneuver (ARM) with positive end-expiratory pressures (PEEPs) in anesthetized horses ventilated with oxygen or heliox (70% helium and 30% oxygen).

ANIMALS 6 healthy adult horses.

PROCEDURES In a randomized crossover study, horses were anesthetized and positioned in dorsal recumbency. Volume-controlled ventilation was performed with heliox or oxygen (fraction of inspired oxygen [Fio 2] > 90%). Sixty minutes after mechanical ventilation commenced, an ARM with PEEP (0 to 30 cm H2O in steps of 5 cm H2O every 5 minutes, followed by incremental steps back to 0 cm H2O) was performed. Peak inspiratory pressure, dynamic lung compliance (Cdyn), and Pao 2 were measured during each PEEP. Indices of pulmonary oxygen exchange and alveolar dead space were calculated. Variables were compared with baseline values (PEEP, 0 cm H2O) and between ventilation gases by use of repeated-measures ANOVAs.

RESULTS For both ventilation gases, ARM significantly increased pulmonary oxygen exchange indices and Cdyn. Mean ± SD Cdyn (506 ± 35 mL/cm H2O) and Pao 2-to-Fio 2 ratio (439 ± 36) were significantly higher and alveolar-arterial difference in Pao 2 (38 ± 11 mm Hg) was significantly lower for heliox, compared with values for oxygen (357 ± 50 mL/cm H2O, 380 ± 92, and 266 ± 88 mm Hg, respectively).

CONCLUSIONS AND CLINICAL RELEVANCE An ARM in isoflurane-anesthetized horses ventilated with heliox significantly improved pulmonary oxygen exchange and respiratory mechanics by decreasing resistive properties of the respiratory system and reducing turbulent gas flow in small airways.

Full access
in American Journal of Veterinary Research

Abstract

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.

Full access
in American Journal of Veterinary Research

Abstract

OBJECTIVE

To determine the accuracy of tidal volume (VT) delivery among 5 different models of large-animal ventilators when tested at various settings for VT 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 VT, 3 PIF rates, and 4 FGF rates. A thermal mass flow and volume meter was used as the gold-standard method to measure delivered VT. In addition, circuit systems of rubber versus polyvinyl chloride breathing hoses were evaluated with the piston-driven ventilator. Differences between preset and delivered VT (volume error [δVT]) were calculated as a percentage of preset VT, and ANOVA was used to compare results across devices. Pearson correlation coefficient analyses and the coefficient of determination (r ) were used to assess potential associations between the δVT and the preset VT, PIF rate, and FGF rate.

RESULTS

For each combination of experimental settings, ventilators had δVT values that ranged from 1.2% to 22.2%. Mean ± SD δVT 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 δVT increased with higher PIF rates (r = 0.69), decreased with higher FGF rates (r = 0.62), and decreased with higher preset VT (r = 0.58).

CONCLUSIONS AND CLINICAL RELEVANCE

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

Full access
in American Journal of Veterinary Research

Abstract

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 (Cdyn), 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 Cdyn 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 Cdyn. 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 Cdyn when animals breathe helium instead of nitrogen as the inert gas.

Full access
in American Journal of Veterinary Research

Abstract

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.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine characteristics of the inflammatory reaction in the jejunum of horses in response to various mechanical manipulations.

Animals—12 adult warmblood horses without gastrointestinal tract disorders.

Procedures—The proximal aspect of the jejunum in each horse was divided into 5 segments, and the following manipulations were performed: manual emptying, placement of Doyen forceps, enterotomy alone, enterotomy with mucosal abrasion, and serosal abrasion. Jejunum samples were collected before (control), immediately after, and 30 minutes after the end of manipulations and histologically evaluated to determine distribution of neutrophils and eosinophils.

Results—Macroscopically, all manipulations resulted in jejunal hemorrhage and edema. Compared with control samples, neutrophil numbers were significantly higher after manipulations in the serosa (after all manipulation types), circular muscle layer (after manual emptying), submucosa (after placement of Doyen forceps), and mucosa (after all manipulations except enterotomy alone). Eosinophil numbers were significantly higher in the submucosa after mechanical abrasion of the serosa and manual emptying versus control samples.

Conclusions and Clinical Relevance—Results indicated mechanical manipulation of the jejunum resulted in local inflammatory reactions characterized predominantly by infiltration of neutrophils. This could contribute to the development of postoperative ileus or adhesions in horses without macroscopically detectable injury of the jejunum during surgery.

Full access
in American Journal of Veterinary Research
History

A 1-year-old 18-kg (39.6-lb) sexually intact male Pygmy goat with tetralogy of Fallot (ToF) was presented for castration, scrotal ablation, and penile amputation at New Bolton Center, School of Veterinary Medicine, University of Pennsylvania. Six months earlier, ToF had been diagnosed in this goat during diagnostic evaluations and treatment for fever and ocular discharge attributed to a mild respiratory infection. On presurgical physical examination for castration, the goat was bright, alert, and responsive and had pink and moist mucous membranes with a capillary refill time of approximately 2 seconds (reference range, ≤ 2 seconds). Peripheral pulses were strong, synchronous,

Restricted access
in Journal of the American Veterinary Medical Association

Abstract

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.

Full access
in American Journal of Veterinary Research

Abstract

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.

Full access
in American Journal of Veterinary Research