Alternating one lung ventilation using a double lumen endobronchial tube and providing CPAP to the non-ventilated lung in a dog

Introduction This case report describes the anaesthetic management of exploratory thoracoscopy and alternating one lung ventilation (OLV) in a dog with a pulmonary bulla, and the application of continuous positive airway pressure (CPAP) to the non‐ventilated lung for preventing and treating hypoxia. Case history A 6‐year‐old, male castrated Border collie was scheduled for exploratory thoracoscopy to investigate spontaneous pnemothorax that had not resolved with repeated suction. Specific requirements for the thoracoscopy were alternating OLV to allow the surgical access to the right middle lobe and its removal, and the examination of the left hemithorax to rule out the presence of other lesions. Diagnosis and management Selective lung ventilation was performed with a double lumen endobronchial tube (DLT), inserted under endoscopic guidance. After a short period of two lung ventilation during preparation of the surgical field, alternating OLV was performed, combining CPAP, provided to the non‐ventilated lung via a Mapleson D breathing system, and positive end‐expiratory pressure (PEEP) applied to the ventilated lung. Left OLV occurred first and resection of the right middle pulmonary lobe was successfully performed; right OLV followed to allow the examination of the left hemithorax. Discussion and conclusions The combination of CPAP and PEEP resulted in a satisfactory intra‐operative management of hypoxemia. Alternating OLV can be performed successfully by using a DLT. CPAP, commonly employed in human medicine, should be considered an important tool in the anaesthetic management of OLV in small animals.     

Ventilation-perfusion relationships in the anaesthetised horse

Ventilation-perfusion relationships were studied by the multiple inert gas elimination technique in seven horses while they were conscious and during inhalation anaesthesia with halothane. A generally good match between ventilation and perfusion was found in the conscious, standing horse. During anaesthesia a huge shunt developed, ie perfusion of completely unventilated lung regions, both in dorsal and left lateral recumbency and whether the horse was breathing spontaneously or mechanically ventilated. The shunt was significantly greater and the arterial oxygen tension (PaO2) significantly lower in dorsal than in left lateral recumbency. Little or no perfusion of low VA/Q regions was observed during anaesthesia, whether ventilation was spontaneous or mechanical. Positive end-expiratory pressure (PEEP) did not significantly improve PaO2 or reduce the shunt. Selective mechanical ventilation of dependent lung regions with PEEP reduced the shunt markedly, an effect that was not achieved by conventional mechanical ventilation with general PEEP. The findings seem compatible with alveolar collapse during anaesthesia, causing shunt, whereas the absence of clearly low VA/Q regions questions the role of airway closure as the major disturbance of gas exchange.     

Use of continuous positive airway pressure in the acute management of laryngeal paralysis in a cat

Continuous positive airway pressure (CPAP) has been is used widely in humans to manage obstructive sleep apnoea syndrome, but it has not been widely used in animals. A brachycephalic cat, with previously undiagnosed laryngeal paralysis, that developed acute upper respiratory tract obstruction on recovery from anaesthesia, is presented. The condition was managed by CPAP, delivered via a facial mask.     

Comparative effects of three different ventilatory treatments on arterial blood gas values and oxygen extraction in healthy anaesthetized dogs

ObjectiveTo compare the effect of invasive continuous positive airway pressure (CPAP), pressure-controlled ventilation (PCV) with positive end-expiratory pressure (PEEP) and spontaneous breathing (SB) on PaO₂, PaCO₂ and arterial to central venous oxygen content difference (CaO₂-CcvO₂) in healthy anaesthetized dogs.Study designProspective randomized crossover study.AnimalsA group of 15 adult male dogs undergoing elective orchidectomy.MethodsDogs were anaesthetized [buprenorphine, medetomidine, propofol and isoflurane in an air oxygen (FiO₂= 0.5)]. All ventilatory treatments (CPAP: 4 cmH₂O; PCV: 10 cmH₂O driving pressure; PEEP, 4 cmH₂O; respiratory rate of 10 breaths minute^–1 and inspiratory-to-expiratory ratio of 1:2; SB: no pressure applied) were applied in a randomized order during the same anaesthetic. Arterial and central venous blood samples were collected immediately before the start and at 20 minutes after each treatment. Data were compared using a general linear mixed model (p < 0.05).ResultsMedian PaO₂ was significantly higher after PCV [222 mmHg (29.6 kPa)] than after CPAP [202 mmHg (26.9 kPa)] and SB [208 mmHg (27.7 kPa)] (p < 0.001). Median PaCO₂ was lower after PCV [48 mmHg (6.4 kPa)] than after CPAP [58 mmHg (7.7 kPa)] and SB [56 mmHg (7.5 kPa)] (p < 0.001). Median CaO₂-CcvO₂ was greater after PCV (4.36 mL dL^–1) than after CPAP (3.41 mL dL^–1) and SB (3.23 mL dL^–1) (p < 0.001). PaO₂, PaCO₂ and CaO₂-CcvO₂ were no different between CPAP and SB (p > 0.99, p = 0.697 and p = 0.922, respectively).Conclusions and clinical relevanceCPAP resulted in similar arterial oxygenation, CO₂ elimination and tissue oxygen extraction to SB. PCV resulted in improved arterial oxygenation and CO₂ elimination. Greater oxygen extraction occurred with PCV than with CPAP and SB, offsetting its advantage of improved arterial oxygenation. The benefit of invasive CPAP over SB in the healthy anaesthetized dog remains uncertain.     

Early experience with continuous positive airway pressure (CPAP) in 5 horses �� A case series

This case series is the first report of the use of CPAP (continuous positive airway pressure) ventilation in adult horses. Two horses and 3 ponies anesthetized for orthopedic procedures in lateral recumbency received 10 cm H₂O CPAP. During anesthesia, arterial oxygen partial pressure tended to increase and arterial carbon dioxide pressure tended to increase despite increased minute ventilation index. The measured cardiovascular parameters were within physiologic limits.     

Effects of an alveolar recruitment maneuver on cardiovascular and respiratory parameters during total intravenous anesthesia in ponies

OBJECTIVE: To evaluate pulmonary and cardiovascular effects of a recruitment maneuver (RM) combined with positive end-expiratory pressure (PEEP) during total intravenous anesthesia in ponies. ANIMALS: 6 healthy adult Shetland ponies. PROCEDURE: After premedication with detomidine (10 microg/kg, IV), anesthesia was induced with climazolam (0.06 mg/kg, IV) and ketamine (2.2 mg/kg, IV) and maintained with a constant rate infusion of detomidine (0.024 mg/kg/h), climazolam (0.036 mg/kg/h), and ketamine (2.4 mg/kg/h). The RM was preceded by an incremental PEEP titration and followed by a decremental PEEP titration, both at a constant airway pressure difference (deltaP) of 20 cm H2O. The RM consisted of a stepwise increase in deltaP by 25, 30, and 35 cm H2O obtained by increasing peak inspiratory pressure (PIP) to 45, 50, and 55 cm H2O, while maintaining PEEP at 20 cm H2O. Hemodynamic and pulmonary variables were analyzed at every step of the PEEP titration-RM. RESULTS: During the PEEP titration-RM, there was a significant increase in PaO 2 (+12%), dynamic compliance (+ 62%), and heart rate (+17%) and a decrease in shunt (-19%) and mean arterial blood pressure (-21%) was recorded. Cardiac output remained stable. CONCLUSIONS AND CLINICAL RELEVANCE: Although baseline oxygenation was high, Pa(O2) and dynamic compliance further increased during the RM. Despite the use of high PIP and PEEP and a high tidal volume, limited cardiovascular compromise was detected. A PEEP titration-RM may be used to improve oxygenation in anesthetized ponies. During stable hemodynamic conditions, PEEP titration-RM can be performed with acceptable adverse cardiovascular effects.     

Hemodynamic and respiratory responses in halothane-anesthetized horses exposed to positive end-expiratory pressure alone and with dobutamine

The influence of positive end-expiratory pressure (PEEP) on the alveolar-arterial O2 tension difference [P(A-a)O2], physiologic right-to-left shunt fraction, physiologic dead space-to-tidal volume ratio, and hemodynamic variables was studied in halothane-anesthetized horses maintained in dorsal recumbency during controlled ventilation. Dobutamine was used to minimize the adverse cardiovascular consequences of PEEP. Six adult horses were anesthetized, using xylazine (2.2 mg/kg of body weight, IM), guaifenesin (50 mg/kg, IV), thiamylal Na (4.4 mg/kg, IV), and halothane (1.5 to 2% inspired) in 100% O2. Mechanical ventilation was controlled to maintain arterial eucapnia for at least 45 minutes during base-line measurements. Hemodynamic and respiratory variables were determined every 15 minutes during equilibration. Each horse was subjected to 4 randomized treatments: 5 cm of H2O PEEP, 10 cm of H2O PEEP, 5 cm of H2O PEEP plus dobutamine (1 microgram/kg/min), and 10 cm of H2O PEEP plus dobutamine (1 microgram/kg/min). Each treatment lasted 15 minutes and immediately followed its predecessor. Although the magnitude of PEEP was randomized with and without dobutamine, PEEP without dobutamine always preceded PEEP with dobutamine. Differences in hemodynamic or respiratory variables among base-line measurements, 5 cm of H2O PEEP, or 10 cm of H2O PEEP were not significant (P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of the mode of ventilation on ketamine/xylazine requirements in rabbits

OBJECTIVE: To evaluate the effect of the mode of mechanical ventilation (MV) on the dose of intravenous anesthetic during 3 hours of ketamine/xylazine anesthesia. STUDY DESIGN: Prospective laboratory study. ANIMALS: Sixty-one adult male New Zealand White rabbits. METHODS: Rabbits were anesthetized (ketamine/xylazine 35 + 5 mg kg(-1), IM), the trachea was intubated and randomized to four groups - (1) CMV-1 (n = 14), ventilated with traditional conventional volume-cycled MV [V(T) = 12 mL kg(-1), RR = 20, positive end-expiratory pressure (PEEP) = 0 cmH(2)O]; (2) CMV-2 (n = 13), ventilated with a modern lung-protective regimen of volume-cycled MV (V(T) = 6 mL kg(-1), RR = 40, PEEP = 5 cmH(2)O); (3) HFPV (n = 17) ventilated with high-frequency percussive ventilation [high-frequency oscillations (450 minute(-1)) superimposed on 40 minute(-1) low-frequency respiratory cycles, I:E ratio = 1:1], oscillatory continuous positive airway pressure (CPAP) of 7-10 cmH(2)O, and demand CPAP of 8-10 cmH(2)O. (4) A fourth group, spontaneously ventilating (SV, n = 17), was anesthetized, intubated, but not ventilated mechanically. FiO(2) in all groups was 0.5. Anesthesia was maintained at a surgical plane by IV administration of a ketamine/xylazine mixture (10 + 2 mg kg(-1), as necessary) for 3 hours after intubation. Total dose of xylazine/ketamine administered and the need for yohimbine to facilitate recovery were quantitated. RESULTS: The total dose of xylazine/ketamine was significantly higher in the HFPV and SV groups compared with CMV-1 (p < 0.01). Fewer animals required yohimbine to reverse anesthesia in the HFPV than CMV-1 group (p < 0.05). CONCLUSIONS: The HFPV mode of MV led to higher doses of ketamine/xylazine being used than the other modes of MV. CLINICAL RELEVANCE: In rabbits, anesthetic dose for the maintenance of anesthesia varied with the mode of MV used. Investigators should be aware of the possibility that changing the mode of ventilation may lead to an alteration in the amount of drug required to maintain anesthesia.     

Continuous positive airway pressure administered via face mask in tranquilized dogs

Objective – To evaluate the tolerance of a continuous positive airway pressure (CPAP) mask in tranquilized dogs and compare PaO₂ in arterial blood in dogs receiving oxygen with a regular face mask or CPAP mask set to maintain a pressure of 2.5 or 5 cm H₂O. Design – Prospective, randomized clinical study. Setting – University teaching hospital. Animals – Sixteen client‐owned dogs without evidence of cardiopulmonary disease were studied. Interventions – Eight animals were randomly assigned to each of 2 treatment groups: group A received 2.5 cm H₂O CPAP and group B received 5 cm H₂O CPAP after first receiving oxygen (5 L/min) by a regular face mask. Animals were tranquilized with acepromazine 0.05 mg/kg, IV and morphine 0.2 mg/kg, IM. An arterial catheter was then placed to facilitate blood sampling for pHa, PaO₂, and PaCO₂ determinations before and after treatments. Direct mean arterial pressure, heart rate, respiratory rate, and temperature were also recorded after each treatment. Measurements and Main Results – CPAP administration was well tolerated by all animals. The mean arterial pressure, heart rate, respiratory rate, temperature, PaCO₂, and pHa, did not differ at any time point between groups. Differences were seen in oxygenation; in group A, PaO₂ significantly increased from a mean of 288.3±47.5 mm Hg with a standard mask to a mean of 390.3±65.5 mm Hg with the CPAP mask and in group B, PaO₂ increased similarly from 325.0±70.5 to 425.2±63.4 mm Hg (P<0.05); no differences were detected between the 2 CPAP treatments. Conclusions – In healthy tranquilized dogs noninvasive CPAP is well tolerated and increases PaO₂ above values obtained when using a regular face mask.     

Effect of 5 cm of Water Positive End-Expiratory Pressure on Arterial Oxygen Tension in Dogs During and After Thoracotomy

Thoracotomy in dogs often is associated with lower than expected arterial oxygen tensions (PaO₂). Pulmonary collapse from opening the thoracic cavity is likely to be responsible for decreased PaO₂ during thoracotomy. To examine whether positive end-expiratory pressure (PEEP) is beneficial to dogs undergoing thoracotomy, PaO₂ and hemoglobin saturation (SaO₂) were measured in dogs randomly assigned to receive 5 cm of H₂O PEEP (n = 7) or no PEEP (n = 9). During surgery in both groups of dogs, PaO₂ progressively decreased ( P < .001), but the decrease in PaO₂ was significantly less in the PEEP group ( P = .027). In both groups, PaO₂ did not decrease enough to have a substantial effect on SaO₂. Furthermore, application of PEEP during thoracotomy did not prevent moderate hypoxemia after surgery and discontinuation of PEEP. Application of 5 cm of H₂O PEEP seems to attenuate the decrease in PaO₂ observed in dogs undergoing thoracotomy, but routine application of PEEP does not seem justified. ©     

Effect of positive end-expiratory pressure on oxygen delivery during 1-lung ventilation for thoracoscopy in normal dogs

OBJECTIVE: To evaluate the effect of positive end-expiratory pressure (PEEP) on oxygen delivery (DO(2)) with 1-lung ventilation during thoracoscopy in normal anesthetized dogs. STUDY DESIGN: Prospective, controlled experimental study. ANIMALS: Eight, adult, intact Walker Hound dogs weighing 25.6-29.2 kg. METHODS: Anesthetized dogs had 1-lung ventilation during an open-chest condition. A Swan-Ganz catheter was used to measure pulmonary hemodynamic variables and to obtain mixed venous blood samples for blood gas analysis. A dorsal pedal catheter was used for measurement of systemic arterial pressure and to obtain arterial blood samples for blood gas analysis. Oxygen delivery was calculated and used to assess the effect of 0, 2.5, and 5 cm H(2)O PEEP during 1-lung ventilation on cardiopulmonary function. Each dog was its own control at 0 cm H(2)O PEEP. A randomized block ANOVA for repeated measures was used to evaluate the effect of the treatment on hemodynamic and pulmonary variables. RESULTS: Use of 5 cm H(2)O PEEP induced a significant augmentation in the arterial partial pressure of oxygen (PaO(2)). Shunt fraction (Q(s)/Q(t)), physiologic dead space (V(D)/V(T)), and the alveolar-arterial oxygen difference (P(A-a)O(2)) decreased significantly after 5 cm H(2)O PEEP, compared with 1-lung ventilation without PEEP. Use of 2.5 cm H(2)O PEEP had no significant effect on cardiopulmonary variables. Use of PEEP had no significant effect on arterial oxygen saturation (SaO(2)), DO(2), and hemodynamic variables in normal dogs. CONCLUSIONS: PEEP had no effect on DO(2) in normal dogs undergoing open-chest 1-lung ventilation because it had no adverse effect on hemodynamic variables. CLINICAL RELEVANCE: PEEP in normal dogs during open-chest 1-lung ventilation for thoracoscopy is not detrimental to cardiac output and can be recommended in clinical patients.     

Endoscopic removal of a bronchial carcinoma in a dog using one-lung ventilation

Objective— To describe anesthetic management of endoscopic electrosurgical removal of a bronchial carcinoma, partially blocking the right main stem bronchus in a Cocker Spaniel.
Study Design— Clinical case report.
Animals— Dog with a bronchial carcinoma.
Methods— To allow sufficient space for the endoscope and to avoid an oxygen-rich gas mixture in the trachea, which carries the risk of an airway fire when electrocautery is used, a 1 lumen endobronchial tube (EBT) was inserted into the left main stem bronchus. One-lung ventilation (OLV) started with a volume-controlled ventilator was switched to pressure-controlled ventilation in combination with positive end-expiratory pressure (PEEP).
Results— Resection of the bronchial carcinoma was successful. The dog was hypercapnic throughout the procedure and a high alveolar-arterial oxygen gradient was measured.
Conclusion— An EBT may be a feasible and safe option to provide OLV for bronchoscopic electrocautery with a closed thoracic cavity in dogs.
Clinical Relevance— EBT intubation for OLV should be considered as part of the anesthetic management of airway diseases treated with bronchoscopic electrocautery.     

Upper airway obstruction (partial asphyxia) as the possible cause of exercise-induced pulmonary hemorrhage in the horse: An hypothesis

New evidence confirmed that over 90% of Thoroughbreds have some degree of recurrent laryngeal neuropathy (RLN). This and the recognition that anything less than full extension of the atlanto-occipital joint in a racehorse implied a reduction in patency of the nasopharynx provided the basis of the hypothesis that exercise-induced pulmonary hemorrhage (EIPH) may be caused by an upper airway obstruction and that partial asphyxia could be the primary mechanism. EIPH was associated most frequently with the congenital (hereditary), left-sided, hemiparetic form of RLN. Other obstructive diseases, such as laryngeal chondritis and subepiglottic cysts, may be rare causes. Atlanto-occipital flexion on its own might also cause EIPH but more commonly was thought to be a factor which added to the upper airway obstruction resulting from RLN. Supporting evidence for this hypothesis was derived from retrospective and prospective studies of medical records; from necropsy findings on naturally occurring and experimentally produced cases of EIPH; from surveys on the prevalence of RLN; and from a literature review on asphyxia in man and animals.Clinical evidence which supported the hypothesis indicated that EIPH was a clinical sign of RLN. The epidemiology and prevalence of EIPH and congenital RLN appeared to be the same and both problems had a similar historical antiquity. It was already known that bilateral RLN caused asphyxia and EIPH and it appeared from this study that so also does untilateral RLN also does. Clinical signs of both EIPH and RLN were induced by exercise; both were capable of causing exercise intolerance; both were exacerbated by high ambient temperatures and humidity; both problems were permanent and incurable. EIPH was associated with neither the clinical signs nor the pathology of any other pulmonary disease, but was consistently associated with RLN. For it to be argued that EIPH was predominantly a clinical sign of RLN it was necessary that both problems should belong to the same etiological family. Once again, this condition seemed to be met, as EIPH and RLN both appeared more likely to be hereditary rather than environmental diseases.The pulmonary pathology of EIPH was compatible with asphyxia and similar to asphyxia in man. The bilateral symmetry of pulmonary hemorrhage in EIPH suggested an upper airway location for its causal mechanism. Secondary mechanisms might include such factors as increased upper airway resistance, increased pulmonary negative pressure, pulmonary congestion, hypoxemia, hypercapnia, pulmonary hypertension, increased capillary-alveolar pressure gradient, pulmonary edema, increased capillary permeability and microrupture of alveolar walls.Attempts to disprove the hypothesis failed. A prospective study of 201 Thoroughbreds showing EIPH revealed that all had an upper airway obstruction and 98% had RLN. The authors concluded that the hypothesis appeared to be viable. EIPH would seem to be not only a clinical sign of congenital RLN but possibly the most common sign of this common disease. In relation to RLN, the hypothesis could be restated as follows:

a) A horse with laryngeal paraplegia, a rare form of RLN, may develop pulmonary hemorrhage with minimal exercise.

b) A horse with laryngeal hemiplegia, a more common form of RLN, may develop pulmonary hemorrhage with severe exercise.

c) A horse with laryngeal hemiparesis, the most common form of RLN, may develop pulmonary hemorrhage with maximal exercise.

From this a maxim could be distilled regarding the conditions which may be needed for inducing pulmonary hemorrhage: The greater the airway obstruction, the smaller the exercise stress; the smaller the airway obstruction, the greater the exercise stress. The study drew attention to the importance of including in the routine necropsy protocol an examination of the intrinsic muscles of the larynx. Asphyxia has not in the past been considered as a possible explanation for sudden death in the horse but it became apparent that this represented an omission.     

Positive end-expiratory pressure during colic surgery in horses: 74 cases (1986-1988).

Positive end-expiratory pressure (PEEP) was applied in 74 anesthetized, ventilated horses during colic surgery, to attempt to increase arterial oxygen tensions. In 28 horses with an initial PaO2 less than 70 mm of Hg, PEEP increased PaO2 values to a mean of 173 +/- 24 mm of Hg. Arterial oxygen content increased from 14.1 +/- 0.05 ml/dl to 17.2 +/- 0.05 ml/dl. In the remaining 46 horses, PEEP increased PaO2 from a mean value of 101 +/- 6 mm of Hg to 194 +/- 15 mm of Hg, and arterial oxygen content increased from 14.9 +/- 0.09 ml/dl to 16.9 +/- 0.07 ml/dl. Cardiovascular depression and decrease in arterial blood pressure was observed after the application of PEEP in 54 horses. These 54 horses required use of pressors (n = 8), inotropes (n = 32), or both (n = 14) to keep the mean arterial blood pressure greater than 60 mm of Hg. Combined with pharmacologic support of blood pressure, PEEP could be a useful clinical treatment of arterial hypoxemia in horses.     

Cardiopulmonary effects of positive end-expiratory pressure in anesthetized, mechanically ventilated ponies

To investigate the cardiopulmonary effects of positive end-expiratory pressure (PEEP), values of 10, 20, and 30 cm of H2O, were applied to anesthetized, dorsally recumbent, ventilated ponies. After IV induction of general anesthesia, PEEP was superimposed on controlled ventilation with 100% oxygen, and changes in gas exchange and cardiac function were measured. Increasing values of PEEP in these ponies caused a linear increase in the mean (+/- SEM) functional residual capacity, from a control value (zero end-expiratory pressure) of 1.7 +/- 0.24 L to 2.2 +/- 0.31, 2.9 +/- 0.32 and 3.4 +/- 0.3 L at PEEP of 10, 20, and 30 cm of H2O, respectively (P less than 0.05). Paralleling these changes, intrapulmonary shunt fraction decreased significantly (P less than 0.05) from a control value of 12.9 +/- 0.5%, to 7.5 +/- 1.1 and 2.1 +/- 0.6%, at PEEP of 20 and 30 cm of H2O, respectively. Cardiac output was decreased by increasing values of PEEP, from control value of 11.7 +/- 1.56 L/min to 9.9 +/- 1.51, 8.8 +/- 1.33 and 5.62 +/- 0.56 L/min at PEEP of 10, 20, and 30 cm of H2O, respectively. Related to decreasing cardiac output, tissue oxygen delivery also decreased as PEEP was increased, from control value of 2.0 +/- 0.09 L/min to 1.8 +/- 0.07, 1.6 +/- 0.06, and 1.03 +/- 0.04 L/min at PEEP of 10, 20, and 30 cm of H2O, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Development of equine upper airway fluid mechanics model for Thoroughbred racehorses

REASON FOR PERFORMING STUDY: Computational fluid dynamics (CFD) models provide the means to evaluate airflow in the upper airways without requiring in vivo experiments. HYPOTHESIS: The physiological conditions of a Thoroughbred racehorse's upper airway during exercise could be simulated. Methods: Computed tomography scanned images of a 3-year-old intact male Thoroughbred racehorse cadaver were used to simulate in vivo geometry. Airway pressure traces from a live Thoroughbred horse, during exercise was used to set the boundary condition. Fluid-flow equations were solved for turbulent flow in the airway during inspiratory and expiratory phases. The wall pressure turbulent kinetic energy and velocity distributions were studied at different cross-sections along the airway. This provided insight into the general flow pattern and helped identify regions susceptible to dynamic collapse. RESULTS: The airflow velocity and static tracheal pressure were comparable to data of horses exercising on a high-speed treadmill reported in recent literature. The cross-sectional area of the fully dilated rima glottidis was 7% greater than the trachea. During inspiration, the area of highest turbulence (i.e. kinetic energy) was in the larynx, the rostral aspect of the nasopharynx was subjected to the most negative wall pressure and the highest airflow velocity is more caudal on the ventral aspect of the nasopharynx (i.e. the soft palate). During exhalation, the area of highest turbulence was in the rostral and mid-nasopharynx, the maximum positive pressure was observed at the caudal aspect of the soft palate and the highest airflow velocity at the front of the nasopharynx. CONCLUSIONS AND CLINICAL RELEVANCE: In the equine upper airway collapsible area, the floor of the rostral aspect of the nasopharynx is subjected to the most significant collapsing pressure with high average turbulent kinetic during inhalation, which may lead to palatal instability and explain the high prevalence of dorsal displacement of the soft palate (DDSP) in racehorses. Maximal abduction of the arytenoid cartilage may not be needed for optimal performance, since the trachea cross-sectional area is 7% smaller than the rima glottidis.     

Endotracheal intubation in horses – are complications truly rare?

Endotracheal intubation is an essential component of general anaesthesia in horses to facilitate delivery of inhalation anaesthetic agent and oxygen, artificial ventilation, and prevent pulmonary aspiration of blood or gastric reflux. Experimental studies have identified a high incidence of tracheal mucosal injury after intubation resulting from direct trauma or local ischaemia from the pressure of the inflated cuff. Recommendations to minimise injury include gentle intubation, disconnection from the anaesthesia machine when moving the horse, and monitoring the endotracheal tube cuff pressure. New studies are needed to evaluate trachea and cuff pressure interactions under current practice conditions, including specialised ventilation modalities such as positive end‐expiratory pressure and continuous airway pressure.     

Detection of Salmonella organisms and assessment of a protocol for removal of contamination in horse stalls at a veterinary teaching hospital

OBJECTIVES: To assess methods of detecting environmental contamination with Salmonella organisms and evaluate a cleaning and disinfection protocol for horse stalls in a veterinary teaching hospital. DESIGN: Original study. SAMPLE POPULATION: 37 horses with diarrhea likely to be caused by Salmonella infection and their stall environments. PROCEDURES: Fecal samples were collected from horses daily during hospitalization; samples were obtained from stall sites after cleaning and application of disinfectants. Fecal and environmental samples were cultured for Salmonella spp and tested via polymerase chain reaction (PCR) assay to detect Salmonella DNA. RESULTS: 1 horse died and 2 were discharged prior to sample collection. Fecal samples from 9 of 34 horses yielded growth of Salmonella organisms on bacteriologic culture, and 23 yielded positive results via PCR assay on > or = 1 occasion. Among environmental samples from 21 stalls, salmonellae were detected at > or = 1 stall site on 6 of 78 occasions, and > or = 1 stall site yielded positive results via PCR assay on 69 of 77 occasions. Salmonella DNA was detected more frequently in samples of stall drains, cracks, and corners. Salmonella spp were cultured from samples of 3 stalls after both initial and second cleaning and disinfection cycles, but no organisms were detected in samples obtained after use of a peroxygen disinfectant. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that stalls in which horses with salmonellosis were housed should only be used to accommodate newly hospitalized horses after samples (collected after 2 cycles of cleaning and disinfection) from drains, cracks, and corners yield negative results on bacteriologic culture.     

Pulmonary edema at recovery after colic operation with in-situ nasogastric tube in a horse

After an uneventful general anesthesia, in a horse negative pressure pulmonary edema developed due to acute upper airway obstruction during the anesthetic recovery phase after colic surgery. No pathologic alteration of respiration was observed until the horse stood up and began suffocating. The horse had recovered with the nasogastric tube in situ. This, together with the postmortem diagnosis of laryngeal hemiplegia resulted in impairment of airflow through the larynx and development of pulmonary edema. Our objective is to alert clinicians about the possible hazard of recovery with an in-situ nasogastric tube.     

Atrial Fibrillation Associated with Anesthesia in a Standardbred Gelding

A Standardbred gelding was anesthetized on three occasions over a 3 year period. Anesthesia was induced with xylazine and thiamylal on the first occasion, with xylazine, guaifenesin, and thiamylal on the second, and with acepromazine, guaifenesin, and ketamine on the third. Anesthesia was maintained with halothane during each episode. The horse had atrial fibrillation (AF) after induction of anesthesia on the first two occasions. Because arterial blood pressure remained within normal limits during AF and anesthesia, conversion to normal sinus rhythm with quinidine was not attempted. Reversion to normal sinus rhythm occurred within 12 hours of recovery after each of the first two anesthetic episodes. The gelding remained in normal sinus rhythm throughout the third anesthetic period and recovered uneventfully. Potential causes for AF in anesthetized horses are discussed.