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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.

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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 (r2) 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 (r2 = 0.69), decreased with higher FGF rates (r2 = 0.62), and decreased with higher preset VT (r2 = 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.

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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.

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CASE REPORT: A case of lowland copperhead snake (Austrelaps superbus) envenomation in a dog is described. The dog developed severe and prolonged neuromuscular paralysis, including ventilatory failure. The dog was treated successfully with antivenom, intravenous fluids and mechanical ventilation. CLINICAL SIGNIFICANCE: The toxic components of lowland copperhead snake venom are reviewed.

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This study evaluated the ability of a portable oxygen concentrator (POC) to provide fresh gas to an anesthetic machine via an Ayre's T-piece or a Bain circuit. Fraction of inspired oxygen (FiO2) was compared at flows of 0.5 to 3.0 L/min. Measured FiO2 was 96% at flow rates ≥ 1 L/min. Mean battery life at 1.0, 2.0, and 3.0 L/min was 4.21 ± 0.45, 2.62 ± 0.37 and 1.5 ± 0.07 hours, respectively. The POC proved to be useful and effective during 2 power outages. The POC was sufficient to prevent rebreathing in 70% of dogs using a T-piece circuit and 20% of dogs with a Bain circuit. A significant negative correlation between inspired CO2 and O2 flow rates was noted. A significant positive correlation between inspired CO2 and ETCO2 was documented. The occurrence of hypercarbia was associated with low O2 flow. Battery back-up was essential during power outages. The POC can be effectively used for delivery of anesthesia.

Évaluation d'un concentrateur d'oxygène portable pour fournir une circulation de gaz frais aux chiens subissant une anesthésie. Cette étude a évalué la capacité d'un concentrateur d'oxygène portable (COP) à fournir du gaz frais à l'aide d'une pièce en T d'Ayre ou d'un circuit de Bain. La fraction d'oxygène inspiré (FiO2) a été comparée à des débits de 0,5 à 3,0 L/min. La FiO2 mesurée était de 96 % à des taux de débit de ≥ 1 L/min. La durée de vie moyenne de la batterie à 1,0, à 2,0 et à 3,0 L/min était de 4,21 ± 0,45, de 2,62 ± 0,37 et 1,5 ± 0,07 heures, respectivement. Le COP s'est avéré utile et efficace durant deux pannes d'électricité. Le COP a été suffisant pour prévenir la réinspiration chez 70 % des chiens en utilisant un circuit de pièce en T et un circuit de Bain chez 20 % des chiens. Une corrélation négative importante entre le CO2 inspiré et les taux de débit d'O2 a été observée. Une corrélation positive importante entre le CO2 inspiré et l' ETCO2 a été documentée. L'occurrence de l'hypercarbie était associée à un faible débit d'O2. Une batterie de secours était essentielle durant les pannes d'électricité. Le COP peut être efficacement utilisé pour fournir de l'anesthésie.(Traduit par Isabelle Vallières).

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Research suggests that simulation technology has potential to enhance student achievement, particularly for students having a preference for hands-on learning. The aim of this study was to compare ventilation learning outcomes in students attending traditional lecture versus students using an active learning ventilation simulation. A computer simulation was developed to advance students' learning of mechanical ventilation. Forty-one students were divided into upper and lower strata based on performance rankings and were then randomly assigned to first complete a simulation scenario or view a lecture. Two distinct ventilation topics, controls and clinical, were developed for each instructional method. Students completed examinations three weeks following each respective instructional intervention (lecture or simulation scenarios) as well as one long-term examination and survey six weeks following the second examination. Upper-ranking students who learned the clinical topic through the simulation scenarios outperformed students who learned by traditional lecture. In addition, upper-ranking students scored higher than lower-ranking students in both the clinical and long-term composite examinations. No differences in student scores attributed to instructional method or class rank were identified for the controls topic. Survey results indicated that students were more engaged as learners when using the simulation and wished to have the simulation available during their clinical intensive care unit (ICU) rotations. Use of the simulation was associated with improved performance of upper-ranking students on the clinical-topic exam and was equivalent to lecture as an instructional intervention on the controls-topic exam. The simulation was perceived as an engaging, desirable tool providing immediate feedback.

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Hyperpolarized noble gas (HNG) magnetic resonance imaging (MRI) has been shown to be useful for studying rodent models of lung disease. Image quality can be substantially degraded by signal loss from molecular oxygen entering the airway, requiring invasive surgery to ensure a good seal between the endotracheal (ET) tube and trachea. A modified Foley catheter having an inflatable cuff near the tip provides a novel approach for ensuring image quality for HNG MRI, thereby enabling longitudinal studies and reducing animal numbers. A Foley catheter was modified for rodent intubation and to minimize dead space. Three pairs of age-matched male Sprague Dawley rats 400 (30) g were used. Two pairs were intubated using the Foley and the third with an intravenous catheter. Leak rates were measured from pressure versus time curves within each animal. The pairs were euthanized immediately or six days postrecovery to assess the effects of the procedure on animal health, as reflected by histological examination. The Foley catheter resulted in minimal leak rates (-0.20 (0.03) versus -0.16 (0.05) cmH(2)O/s), and were shown to be well below upper-limit leak rates of -0.5 and -0.7 cmH(2)O/s. Tracheal samples from rats in a separate Foley group (not mechanically ventilated) showed superficial damage six days postextubation (grade = 0). (3)He imaging performed using the Foley showed good image quality. Though some technical issues remain to be solved, a modified Foley catheter used as an ET tube offers the potential to enable longitudinal studies in rodents and reduce animal numbers.

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The increased use in noninvasive imaging of laboratory rodents has prompted innovative techniques in animal handling. Lung imaging of rodents can be a difficult task because of tissue motion caused by breathing, which affects image quality. The use of a prototype flat-panel computed tomography unit allows the acquisition of images in as little as 2, 4, or 8 s. This short acquisition time has allowed us to improve the image quality of this instrument by performing a breath-hold during image acquisition. We designed an inexpensive and safe method for performing a constant-pressure breath-hold in intubated rodents. Initially a prototypic manual 3-way valve system, consisting of a 3-way valve, an air pressure regulator, and a manometer, was used to manually toggle between the ventilator and the constant-pressure breath-hold equipment. The success of the manual 3-way valve system prompted the design of an electronically actuated valve system. In the electronic system, the manual 3-way valve was replaced with a custom designed 3-way valve operated by an electrical solenoid. The electrical solenoid is triggered by using a hand-held push button or a foot pedal that is several feet away from the gantry of the scanner. This system has provided improved image quality and is safe for the animals, easy to use, and reliable.

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OBJECTIVE: To set up a method of applying inhalation anesthesia in rodent using rodent ventilator and to study the dynamic procedure of the in vitro model. METHODS: The output port of the anesthesia machine was connected to the input port of the rodent ventilator, which was connected to a syringe simulating the lung. After supply of anesthetic gas, the gas samples from the input port of the ventilator and the syringe in the end-expiratory phase were collected at 10, 20, 30, 40, 50, 60, 90, 120, 180, 300, 600 and 900 seconds respectively and were determined using the gas chromatography(GC). The ratios of the anesthetic concentrations of the syringe to that of the input port were calculated (CE/CI). In elimination phase, the gas samples from the syringe were collected at 0,10, 20, 30, 40, 50, 60, 90, 120, 180, 300, 600 and 900 seconds respectively and were determined by GC. The ratios of the anesthetic concentrations of the gas at 10, 20, 30, 40, 50, 60, 90, 120, 180, 300, 600 and 900 seconds to that at 0 second were calculated(C'E/C0). RESULTS: CE/CI increased in the inhalation phase, there was an inverse relationship between CE/CI and time, the correlation coefficients were 0.90, 0.95 and 0.93 respectively (P < 0.01). The mathematical fitting equations were y = -0.19 + 0.19x(-1), y = -7.75 + 0.99x(-1), and y = -7.21 + 0.97x(-1) respectively. C'E/C0 decreased in the elimination phase,the correlation coefficients were 0.90, 0.94 and 0.95 respectively (P < 0.01). The mathematic fitting eqations were y = 5.65-0.02x(-1), y = 7.82-0.01x(-1),and y = 8.20-0.01x(-1), respectively. CONCLUSION: The in vitro model of rodent inhalation anesthesia using the rodent ventilator was set up. The establishment of this model has provided a basis for studies on inhalation anesthesia in rodents.

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To perform mechanical ventilation of mice in the absence of highly expensive commercially available devices, we developed a membrane-pump-driven respirator and studied its practicability. The continuous airflow generated by the membrane pump was changed into an intermittent flow by using a multifunction timer. Tidal volume was adjusted by a rotary dimmer regulating the electric power onto the pump. The expiration air left the circuit through openings at the tube connection. Mice were ventilated with room air for 5 h with a tidal volume of approximately 200 muL. In group 1 (n = 6), ventilation was performed with a frequency of 110 min-1, in group 2 (n = 6) with a frequency of 150 min-1. Spontaneously breathing anesthetized mice (n = 6) served as controls. In addition we performed single-lung open-chest ventilation for 1 h in two animals. The parameters of arterial blood gas analyses were within the normal range except for moderate hyperventilation in group 2. Single-lung ventilation led to a significant decline (P < 0.05) of pO2 and SO2, whereas the pCO2 remained within the normal range. Respiratory rate, tidal volume and pressure limitation can be adjusted for optimal ventilation. In addition, the device provides a minimalized dead space and impedes potential alveolar damage caused by negative pressure generated by spontaneous inspiration during positive-pressure ventilation.

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Severe acute hypercarbia occurred in a cat and 2 dogs as a result of anesthesia machine malfunction. In each case, the anesthesia machine had been checked by the anesthesia technician and clinician, and no problems were found. After it was noticed that the same machine had been used on each animal, further investigation revealed an expiration valve that was functional with large breaths or positive pressure ventilation but was not functional with small breaths with low peak inspiratory flow. Rebreathing of expired carbon dioxide occurred, and the patients subsequently became severely hypercarbic. Recovery from anesthesia was prolonged in 2 animals, and cardiac and respiratory arrest occurred in the third. Hypercarbia from rebreathing can be detected through the use of blood gas analysis or end-tidal carbon monoxide monitoring.

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When used properly, anesthesia machines, breathing systems, anesthesia ventilators, and ancillary equipment allow the safe and efficient use of the inhalant anesthetics. Several veterinary anesthesia machines and ventilators have been introduced over the last few years. This article includes a discussion of some of these new pieces of anesthesia equipment, with particular emphasis on changes and innovations in the design of the equipment. In addition, principles of use and care of various anesthetic equipment is included where appropriate.

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Rodent models have been described to investigate lung preservation and reperfusion injury but have significant disadvantages. In large animals single lung transplant studies are probably optimal but problems remain over the ability to rigorously separate the lungs for assessment while promoting medium to long-term animal survival for meaningful investigation. Our aim was to develop a novel and refined large animal model to assess reperfusion injury in the transplanted lung, overcoming the difficulties associated with existing models. Specifically, small animal models of lung transplantation usually have short perfusion times (often one hour) and include extracorporeal circuits while larger animal models often require the contralateral lung to be excluded after transplantation-an unphysiological situation under which to evaluate the graft. A porcine model of left lung allotransplantation was developed in which native and donor lungs are individually ventilated. Sampling catheters placed within the graft lung allowed specimen withdrawal without mixing of blood from the contralateral lung after reimplantation. The model permits a variety of clinical scenarios to be simulated with the native lung supporting the animal irrespective of function in the graft. This model has been used in over 60 transplant procedures with a postoperative survival time of 12 h being readily achieved. The mean operating time was 2.6 h. The mortality rate is 4% in our series. We have found the model to be reliable, reproducible and flexible. We propose this model as an adaptable investigation for evaluating lung reperfusion injury and preservation.

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Hypoxaemia commonly develops during general anaesthesia and in the recovery period in horses. The Hudson demand valve has been used to increase arterial PO2, but it has been found to increase airway resistance considerably when used during spontaneous ventilation. This paper evaluates a modification of the valve designed to reduce this resistance. The effects of the valve and its modification on arterial oxygen (PaO2), and carbon dioxide (PaCO2) tensions were evaluated in four ponies anaesthetised by a total intravenous technique. The valve increased PaO2 from 8.3 +/- 1.1 to 32.7 +/- 7.6 kPa during spontaneous ventilation and to 44.2 +/- 7.4 kPa during intermittent positive pressure ventilation. With the modification, the PaCO2 was increased to 9.0 +/- 2.5 kPa during spontaneous ventilation PaO2 was unchanged by the valve (7.2 +/- 0.4 kPa to 7.1 +/- 0.7 kPa) but it was reduced to 6.4 +/- 0.9 kPa with the modification. The valve was also evaluated in 20 clinical cases during their recovery from halothane anaesthesia. It increased PaO2 from 7.4 +/- 2.1 kPa to 17 +/- 18.3 kPa during spontaneous ventilation and from 8.0 +/- 1.8 kPa to 23.4 +/- 22.2 kPa during positive pressure ventilation. With the modification, PaO2 was increased from 7.8 +/- 1.4 kPa to 10.4 +/- 3.8 kPa during spontaneous ventilation and from 7.6 +/- 1.5 kPa to 14.8 +/- 8.4 kPa during positive pressure ventilation. During spontaneous ventilation PaCO2 was increased from 5.9 +/- 0.4 kPa to 6.2 +/- 0.6 kPa with the unmodified valve and from 6.3 +/- 0.5 kPa to 6.6 +/- 0.5 kPa with the modification.(ABSTRACT TRUNCATED AT 250 WORDS)

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