Continuous positive airway pressure ventilation in dogs with acute cardiogenic pulmonary edema is associated with improved clinical parameters and reduced diuretic and oxygen requirements.

OBJECTIVE: To retrospectively compare efficacy of a continuous positive airway pressure (CPAP) helmet against standard oxygen supplementation (STD) administered by nasal cannulae in dogs with acute cardiogenic pulmonary edema (ACPE). ANIMALS: 83 dogs (STD group, n = 41; CPAP group, 42) hospitalized for ACPE (January 2019 to April 2021). METHODS: Mean respiratory rate, heart rate, systolic arterial pressure, and rectal body temperature were compared between and within groups before and at 1 (T1), 2 (T2), 3 (T3), 6 (T6), and 12 (T12) hours from the beginning of STD/CPAP therapy. Duration of oxygen supplementation, hospitalization time, total diuretic dose, additional pharmacological interventions and mortality rates were compared between groups. The veterinary bedside lung ultrasound in emergency score, thoracic radiographs, and arterial blood parameters were compared between and within groups before and at the end of CPAP/STD therapy. RESULTS: Within both groups, clinical parameters decreased during the observation period. Mean respiratory rate and heart rate were significantly lower in the CPAP group than the STD group at T1, T2, T3, T6, and T12. Mean systolic arterial pressure was significantly lower in the CPAP group than the STD group at T2, T3, T6, and T12. Mean oxygen supplementation duration, cumulative loop diuretic dose, and both veterinary bedside lung ultrasound in emergency score and arterial PaCO2 at the end of CPAP/STD therapy were significantly lower in the CPAP group than the STD group. No significant differences were observed in hospitalization time and mortality rates. CLINICAL RELEVANCE: The addition of helmet CPAP compared with standard oxygen administration showed a faster clinical improvement with lower cumulative loop diuretic and shorter oxygen supplementation in dogs hospitalized for ACPE.

Inclusion of airway pressure release ventilation in the management of respiratory failure and refractory hypercapnia in a dog.

OBJECTIVE: To describe the use of airway pressure release ventilation (APRV) to relieve hypercapnia in a dog undergoing mechanical ventilation. CASE SUMMARY: A 3-month-old male Shar-Pei mix presented to the emergency department with suspected noncardiogenic pulmonary edema. Due to severe hypercapnia, mechanical ventilation was initiated. The hypercapnia failed to improve with conventional pressure control mechanical ventilation, bronchodilator administration, suctioning, or endotracheal tube replacement. The dog was transitioned to APRV and maintained in this mode for 36 hours. A modified APRV protocol in which inverse inspiratory to expiratory ratios ranged from 4.3:1 to 6.0:1 was utilized, resulting in a drastic improvement in the patient's hypercapnia. The patient eventually was transitioned off the ventilator, and no respiratory abnormalities have been noted at subsequent recheck examinations. NEW OR UNIQUE INFORMATION PROVIDED: This case documents the first use of APRV to relieve refractory hypercapnia in a dog undergoing mechanical ventilation and is one of the only recorded cases of using APRV for this purpose in the medical literature at large. APRV may be considered in cases of hypercapnia when traditional therapies fail, although caution is warranted as this mode of ventilation can also worsen hypercapnia.

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

OBJECTIVE: To 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 DESIGN: Prospective randomized crossover study. ANIMALS: A group of 15 adult male dogs undergoing elective orchidectomy. METHODS: Dogs 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). RESULTS: Median 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 RELEVANCE: CPAP 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.

Comparison of single-breath continuous positive airway pressure manoeuvre with inhaled salbutamol to improve oxygenation in horses anaesthetized for laparotomy.

OBJECTIVE: To compare the efficacy of single-breath continuous positive airway pressure manoeuvre (CPAP-M) with inhaled salbutamol, and a combination of both. STUDY DESIGN: Randomized, clinical study. ANIMALS: A total of 62 client-owned horses (American Society of Anesthesiologists status III-V) anaesthetized for laparotomy. METHODS: Horses were premedicated with intravenous (IV) xylazine (0.4-0.6 mg kg-1), anaesthesia was induced with midazolam (0.06 mg kg-1 IV) and ketamine (2.2 mg kg-1 IV) and maintained with isoflurane in oxygen using volume-controlled ventilation without positive end-expiratory pressure. If PaO2 was < 100 mmHg (13.3 kPa), either a CPAP-M (50 cmH2O for 45 seconds) or salbutamol (0.002 mg kg-1) was administered. The intervention was considered successful if PaO2 reached 100 mmHg (13.3 kPa). If PaO2 remained < 100 mmHg (13.3 kPa), treatments were switched. PaO2/FiO2 ratio and estimated shunt fraction (F-shunt) were derived from data obtained from arterial blood gas measurements. Dynamic compliance (Cdyn) was calculated from variables recorded at the moment of arterial blood analysis. Fisher's exact tests compared success rates between treatments, and linear models were performed to test whether the treatment modified the values of the measurements; p < 0.05. RESULTS: Salbutamol was the first intervention in 28 horses and was effective in 22 horses. CPAP-M was the first intervention in 34 horses and was effective in 26 horses. CPAP-M after salbutamol was performed in six horses, with four responders, and salbutamol after CPAP-M was administered to eight horses, with one responder. Salbutamol, but not CPAP-M, significantly decreased F-shunt. Both salbutamol and CPAP-M significantly increased Cdyn. CONCLUSIONS AND CLINICAL RELEVANCE: Salbutamol and CPAP-M were comparably effective in improving oxygenation and Cdyn in anaesthetized horses with PaO2 < 100 mmHg (13.3 kPa). Whether combining both treatments might be beneficial needs to be confirmed on a larger number of horses.

Comparison of CPAP and oxygen therapy for treatment of postoperative hypoxaemia in dogs.

OBJECTIVE: To compare 5 cmH2 O of continuous positive airway pressure with oxygen therapy in dogs recovering from general anaesthesia with low SpO2 values. continuous positive airway pressure is more effective than oxygen therapy in restoring normoxaemia (SpO2 ≥95%). MATERIALS AND METHODS: Prospectively, dogs recovering from anaesthesia, with SpO2 <95% after extubation (T0), were randomised and treated with continuous positive airway pressure (FiO2 0.21) or oxygen (O2 ; FiO2 0.35-0.40) therapy. Dogs were monitored with SpO2 every 15 minutes for 1 hour (T15, T30, T45, T60). Data from normoxaemic dogs (SpO2 >95%) were used as control (CTR). RESULTS: Of the 42 dogs enrolled, 34 completed the study. Eleven dogs were treated with O2 , 10 with continuous positive airway pressure and 13 were CTR. The SpO2 values at T0 were similar in the continuous positive airway pressure and O2 groups and were lower than in the CTR group. At T15, T30, T45 and T60, the SpO2 values in the continuous positive airway pressure group were higher than at T0; these were similar to those of the CTR group at the same time-points. In the O2 group, SpO2 values were significantly higher at T45 and T60 than at T0; 45.5% of dogs became normoxaemic at T45 and the remaining dogs became normoxaemic at T60. The average time to reach normoxaemia in the O2 group (53.1±7.3 minutes) was longer than in the continuous positive airway pressure group (15.0±0.0 minutes). CLINICAL SIGNIFICANCE: In dogs recovering from general anaesthesia with pulmonary gas exchange impairment, normoxaemia is restored more effectively and rapidly by using continuous positive airway pressure than by oxygen therapy.

Effects of continuous positive airway pressure administered by a helmet in cats under general anaesthesia.

OBJECTIVES: The aim of this study was to evaluate the respiratory effects of non-invasive continuous positive airway pressure (CPAP) administered by a helmet in healthy cats under anaesthesia. METHODS: Fifteen healthy male cats scheduled for castration were anaesthetised with medetomidine (20 µg/kg), ketamine (10 mg/kg) and buprenorphine (20 µg/kg) intramuscularly. When an adequate level of anaesthesia was achieved, a paediatric helmet was placed on all subjects. The helmet was connected to a Venturi valve supplied with medical air and cats received the following phases of treatments: 0 cmH2O (pre-CPAP), 5 cmH2O (CPAP) and 0 cmH2O (post-CPAP). Each treatment lasted 10 mins. At the end of each phase an arterial blood sample was drawn. The following data were also collected: mean arterial pressure, respiratory rate, heart rate and the anaesthesia level score (0 = awake, 10 = deep anaesthesia). The alveolar to arterial oxygen gradient (P[A-a]O2) and the venous admixture (Fshunt) were also estimated. Data were analysed with two-way ANOVA (P <0.05). RESULTS: The arterial partial pressure of oxygen was higher (P <0.001) at CPAP (103.2 ± 5.1 mmHg) vs pre-CPAP (77.5 ± 7.4 mmHg) and post-CPAP (84.6 ± 8.1 mmHg). The P(A-a)O2 and the Fshunt were lower (P <0.001) at CPAP (4.4 ± 2.3 mmHg; 7.4 ± 3.1%) vs pre-CPAP (18.9 ± 6.4 mmHg; 22.8 ± 4.6%) and post-CPAP (15.6 ± 7.3 mmHg; 20.9 ± 4.6 %). No other parameters differed between groups. CONCLUSIONS AND RELEVANCE: Non-invasive CPAP applied by a helmet improves oxygenation in cats under injectable general anaesthesia.

Evaluation of the effects of helmet continuous positive airway pressure on laryngeal size in dogs anesthetized with propofol and fentanyl using computed tomography.

OBJECTIVE: To evaluate the effect of 5 cm H2 O of continuous positive airway pressure (CPAP) on laryngeal size in spontaneously breathing anesthetized dogs via computed tomography (CT). DESIGN: Prospective, randomized, cross-over clinical study. SETTING: University teaching hospital and referral private practice. ANIMALS: Eight healthy client-owned dogs undergoing CT. INTERVENTIONS: Dogs were sedated with acepromazine 20 µg/kg IM and induced with fentanyl 2 µg/kg and propofol 3-5 mg/kg IV before being maintained on fentanyl (5 µg/kg/h) and propofol (0.3 mg/kg/min) constant rate infusion. Dogs received an air/oxygen mixture with (CPAP) and without (NO-CPAP) 5 cm H2 O of CPAP in a random order. Each study step lasted 15 minutes. MEASUREMENTS AND MAIN RESULTS: Ten minutes after the beginning of each study period, a CT scan of the laryngeal region was obtained at end-expiration. CT images were analyzed to determine the laryngeal cross-sectional area (CSA; cm2 ), total volume (VTOT ; cm3 ), and laterolateral and dorsoventral diameters (DLL and DDV , respectively; cm). Differences between the 2 treatments were analyzed with t-test for paired data (P < 0.05). Compared to the NO-CPAP, during CPAP the CSA increased by 53.3 ± 23.1% (ie, from 3.3 ± 0.8 to 5.1 ± 1.3 cm2 , P = 0.0004), VTOT increased by 52.4 ± 13.6% (from 6.2 ± 1.7 to 9.4 ± 2.4 cm3 , P < 0.0001), and DLL and DDV were 55.5 ± 13.3% (3.6 ± 0.8 vs 2.4 ± 0.5 cm, P = 0.006) and 20.3 ± 8.8% larger (3.2 ± 0.7 vs 2.7 ± 0.6 cm, P = 0.0002), respectively. CONCLUSIONS: Laryngeal volume and cross sectional area increased during the application of 5 cm H2 O of helmet CPAP in spontaneously breathing anesthetized dogs.

Preliminary evaluation of the use of high-flow nasal cannula oxygen therapy during recovery from general anesthesia in dogs with obstructive upper airway breathing.

BACKGROUND: Brachycephalic airway syndrome can pose a risk of complicated recovery from anesthesia as a result of irritation to the excess pharyngeal andlaryngeal tissue present in affected dogs. High-flow nasal cannula (HFNC) oxygen therapy is a respiratory support modality that offers provision of continuous positive airway pressure via high gas flow rates. The HFNC system actively warms and humidifies inspired gases, which improves comfort and facilitates tolerance of the high flow rates in people and dogs. HFNC oxygen therapy was applied to brachycephalic dogs that developed increased work of breathing or hypoxemia in the recovery phase of anesthesia to determine if this device would be tolerable and effective for relief of upper respiratory difficulty. KEY FINDINGS: The HFNC nasal prong interface is well suited to the brachycephalic facial structure. The application of HFNC was found to reduce dyspnea scores in patients with signs of upper airway obstruction after general anesthesia. Aerophagia and changes in PCO2 were noted. SIGNIFICANCE: Application of HFNC in the recovery period may result in improved airflow during times of somnolent obstructive breathing, not unlike the use of continuous positive airway pressure therapy in sleep-disordered breathing in people.

Accuracy of oxygen delivery through bubble humidifiers and nasal catheters.

OBJECTIVE: To evaluate the equipment used for nasal insufflation of oxygen and determine its accuracy. STUDY DESIGN: Original study. METHODS: Oxygen delivery assemblies consisting of a flowmeter, bubble humidifier, oxygen delivery tubing and nasal insufflation catheters were assembled. Single and double catheter assemblies were made for four sizes of nasogastric feeding tubes (3.5 Fr, 5.0 Fr, 8.0 Fr and 10.0 Fr) resulting in 64 individual assemblies. A gas flow analyzer measured oxygen flow at the tip of the nasal catheter assemblies and from the pressure relief valve (PRV) of the bubble humidifiers. Statistical analyses were conducted to assess the functionality of assemblies. For functional assemblies, the accuracy of oxygen flow relative to the prescribed flow settings was determined. RESULTS: Catheter size was significantly associated with the functionality of assemblies. Probability (95% confidence interval) of 3.5 Fr, 5.0 Fr and 8.0 Fr assemblies being functional was estimated at 0.53 (0.14, 0.89), 0.83 (0.36, 0.98) and 0.98 (0.76, 0.99), respectively. All 10.0 Fr assemblies were functional. Functional assemblies, in general, consistently under-delivered the prescribed flow because a large portion of set flow was diverted through the bubble humidifier PRV. CONCLUSIONS: Leaks through the PRV cause significant diversion of oxygen prior to it reaching the catheter tips. Smaller patients are particularly susceptible, as small catheters limit oxygen delivery creating proportionally greater leaks through the PRV. CLINICAL RELEVANCE: It was not possible to accurately deliver oxygen because of leaks through the PRV. Targeting a specific outcome (e.g., oxyhemoglobin saturation > 94%, PaO2 80-120 mmHg; 11-16 kPa) and avoiding unnecessarily high fractions of inspired oxygen cannot be done if flow delivery cannot be accurately assured. One possible solution would be to use a bubble humidifier with a 6 psi PRV that does not leak prior to reaching the opening pressure.

Continuous positive airway pressure (CPAP) provision with a pediatric helmet for treatment of hypoxemic acute respiratory failure in dogs.

OBJECTIVE: To evaluate arterial blood gas parameters and pulmonary radiography, before and after provision of continuous positive airway pressure (CPAP) via a pediatric helmet in dogs with acute hypoxemic respiratory failure. DESIGN: Single-center, observational study conducted from 2016 to 2017. SETTING: University teaching hospital. ANIMALS: Seventeen dogs presenting with clinical signs compatible with respiratory failure, confirmed by arterial blood gas analyses. INTERVENTIONS: For each animal arterial blood samples and thoracic radiographs were performed at arrival (T0 ). Hypoxemic dogs (PaO2  <80 mm Hg), without evidence of pneumothorax or pleural effusion, received CPAP ventilation via a pediatric Helmet for at least 1 hour. At the end of CPAP ventilation, a second arterial blood gas analysis was performed at room air (T1 ). The F-shunt was also calculated. MEASUREMENT AND MAIN RESULTS: Respiratory rate, heart rate and rhythm, mean blood pressure, mucosal membrane color, and rectal temperature were recorded. Tolerance to the helmet was evaluated using a predetermined scoring system. Two dogs were excluded from the study for low tolerance to the helmet. In 15 of 17 dogs, a significant difference between T0 and T1 was noted for PaO2 (60.84 ± 3 mm Hg vs 80.2 ± 5.5 mm Hg), P(A-a)O2 (52.4 ± 4.4 mm Hg vs 35.2 ± 6 mm Hg), PaO2 /FiO2 (289.7 ± 14.3 vs 371 ± 21), and %SO2 (91.3 vs 98.8). In 15 of 17 dogs, the helmet was well tolerated. F-shunt significantly decreased following provision of CPAP (37%; range, 8.4-68% vs 6%; range, -5.6-64.3%). CONCLUSION: The use of a pediatric helmet appears to be a suitable device for delivery of CPAP in dogs with hypoxemic acute respiratory failure. The device appears to be reasonably tolerated and improved oxygenation in most dogs.

Effects of continuous positive airway pressure on respiratory function in sedated foals.

OBJECTIVE: To characterize the effects of continuous positive airway pressure (CPAP) delivered by a commercial human CPAP device on respiratory function in foals with pharmacologically induced respiratory suppression. DESIGN: Prospective randomized, cross-over study comparing CPAP with spontaneous respiration and oxygen insufflation. SETTING: University veterinary teaching hospital. ANIMALS: Twelve foals born in consecutive seasons from a university teaching herd. INTERVENTIONS: Foals were randomized to receive 10 minutes of respiratory support by mask oxygen supplementation or CPAP as a first treatment after induction of respiratory depression by intravenous administration of xylazine and fentanyl. Each foal received the alternate treatment after 10 minutes of breathing ambient air, and the procedure was repeated after 48 hours with treatment order reversed. MEASUREMENTS AND MAIN RESULTS: The administration of xylazine and fentanyl by bolus or continuous infusion reliably induced reversible respiratory suppression and recumbency. CPAP was associated with comparable increase in PaO2 relative to mask oxygen supplementation, but with lower respiratory rate, increased oxygen extraction and increased carbon dioxide elimination. Mild increase in PaCO2 was observed during CPAP and O2 supplementation. Expiratory time increased and peak expiratory flow decreased during CPAP. CONCLUSIONS: Findings of the study suggest that CPAP might represent a method for improved respiratory support compared to O2 insufflation due to increased respiratory efficiency. Care must be taken in extrapolation of these findings from foals with pharmacologically induced respiratory compromise to foals with clinical respiratory disease, and further investigation is required to better characterize the cause and impact of marginal hypercapnia observed in these studies.

Comparison of high flow nasal cannula oxygen administration to traditional nasal cannula oxygen therapy in healthy dogs.

OBJECTIVE: To determine the feasibility, degree of respiratory support, and safety of high flow nasal cannula (HFNC) oxygen therapy in sedated and awake healthy dogs, when compared to traditional nasal cannula (TNC) oxygen administration. DESIGN: Randomized experimental crossover study. SETTING: University research facility. ANIMALS: Eight healthy dogs. INTERVENTIONS: Variable flow rates (L/kg/min) were assessed, TNC: 0.1, 0.2, and 0.4 and HFNC: 0.4, 1.0, 2.0, and 2.5. HFNC was assessed in sedated and awake dogs. MEASUREMENTS: Variables measured included: inspiratory/expiratory airway pressures, fraction of inspired oxygen (FiO2 ), end-tidal oxygen (ETO2 ), end-tidal carbon dioxide (ETCO2 ), partial pressure of oxygen (PaO2 ), partial pressure of carbon dioxide (PaCO2 ), temperature, heart/respiratory rate, arterial blood pressure, and pulse oximetry. Sedation status, complications, and predefined tolerance and respiratory scores were recorded. MAIN RESULTS: Using HFNC, continuous positive airway pressure (CPAP) was achieved at 1 and 2 L/kg/min. CPAP was not higher at 2.5 than 2 L/kg/min, with worse tolerance scores. Expiratory airway pressures were increased when sedated (P = 0.006). FiO2 at 0.4 L/kg/min for both methods was 72%. FiO2 with TNC 0.1 L/kg/min was 27% and not different from room air. The FiO2 at all HFNC flow rates ≥1 L/kg/min was 95%. PaO2 for HFNC 0.4 L/kg/min was lower than at other flow rates (P = 0.005). The only noted complication was aerophagia. PaCO2 was increased with sedation and use of HFNC when compared to baseline (P = 0.006; P < 0.01). CONCLUSIONS: Use of HFNC in dogs is feasible and safe, provides predictable oxygen support and provides CPAP, but may cause a mild increase in PaCO2 . Flow rates of 1-2 L/kg/min are recommended. If using TNC, flow rates above 0.1 L/kg/min may attain higher FiO2 .

Efficacy of an alveolar recruitment maneuver for improving gas exchange and pulmonary mechanics in anesthetized horses ventilated with oxygen or a helium-oxygen mixture.

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 [Fio2] > 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 Pao2 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 Pao2-to-Fio2 ratio (439 ± 36) were significantly higher and alveolar-arterial difference in Pao2 (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.

Comparison of three continuous positive airway pressure (CPAP) interfaces in healthy Beagle dogs during medetomidine-propofol constant rate infusions.

OBJECTIVE: To compare the efficacy of three continuous positive airway pressure (CPAP) interfaces in dogs on gas exchange, lung volumes, amount of leak during CPAP and rebreathing in case of equipment failure or disconnection. STUDY DESIGN: Randomized, prospective, crossover, experimental trial. ANIMALS: Ten purpose-bred Beagle dogs. METHODS: Dogs were in dorsal recumbency during medetomidine-propofol constant rate infusions, breathing room air. Three interfaces were tested in each dog in a consecutive random order: custom-made mask (M), conical face mask (FM) and helmet (H). End-expiratory lung impedance (EELI) measured by electrical impedance tomography was assessed with no interface (baseline), with the interface only (No-CPAP for 3 minutes) and at 15 minutes of 7 cmH2O CPAP (CPAP-delivery). PaO2 was assessed at No-CPAP and CPAP-delivery, partial pressure of inspired carbon dioxide (PICO2; rebreathing assessment) at No-CPAP and the interface leak (ΔPleak) at CPAP-delivery. Mixed-effects linear regression models were used for statistical analysis (p<0.05). RESULTS: During CPAP-delivery, all interfaces increased EELI by 7% (p<0.001). Higher ΔPleak was observed with M and H (9 cmH2O) in comparison with FM (1 cmH2O) (p<0.001). At No-CPAP, less rebreathing occurred with M (0.5 kPa, 4 mmHg) than with FM (1.8 kPa, 14 mmHg) and with H (1.4 kPa, 11 mmHg), but also lower PaO2 was measured with M (9.3 kPa, 70 mmHg) than with H (11.9 kPa, 90 mmHg) and FM (10.8 kPa, 81 mmHg). CONCLUSIONS AND CLINICAL RELEVANCE: All three interfaces can be used to provide adequate CPAP in dogs. The leak during CPAP-delivery and the risk of rebreathing and hypoxaemia, when CPAP is not maintained, can be significant. Therefore, animals should always be supervised during administration of CPAP with any of the three interfaces. The performance of the custom-made M was not superior to the other interfaces.

Regional ventilation distribution and dead space in anaesthetized horses treated with and without continuous positive airway pressure: novel insights by electrical impedance tomography and volumetric capnography.

OBJECTIVE: The aim of this study was to evaluate the effect of continuous positive airway pressure (CPAP) on regional distribution of ventilation and dead space in anaesthetized horses. STUDY DESIGN: Randomized, experimental, crossover study. ANIMALS: A total of eight healthy adult horses. METHODS: Horses were anaesthetized twice with isoflurane in 50% oxygen and medetomidine as continuous infusion in dorsal recumbency, and administered in random order either CPAP (8 cmH2O) or NO CPAP for 3 hours. Electrical impedance tomography (and volumetric capnography (VCap) measurements were performed every 30 minutes. Lung regions with little ventilation [dependent silent spaces (DSSs) and nondependent silent spaces (NSSs)], centre of ventilation (CoV) and dead space variables, as well as venous admixture were calculated. Statistical analysis was performed using multivariate analysis of variance and Pearson correlation. RESULTS: Data from six horses were statistically analysed. In CPAP, the CoV shifted to dependent parts of the lungs (p < 0.001) and DSSs were significantly smaller (p < 0.001), while no difference was seen in NSSs. Venous admixture was significantly correlated with DSS with the treatment time taken as covariate (p < 0.0001; r = 0.65). No differences were found for any VCap parameters. CONCLUSIONS AND CLINICAL RELEVANCE: In dorsally recumbent anaesthetized horses, CPAP of 8 cmH2O results in redistribution of ventilation towards the dependent lung regions, thereby improving ventilation-perfusion matching. This improvement was not associated with an increase in dead space indicative for a lack in distension of the airways or impairment of alveolar perfusion.

Controlled mechanical ventilation with constant positive end-expiratory pressure and alveolar recruitment manoeuvres during anaesthesia in laterally or dorsally recumbent horses.

OBJECTIVE: To compare the effects of controlled mechanical ventilation (CMV) and constant positive end-expiratory pressure (PEEP) and interposed recruitment manoeuvres (RMs) with those of CMV without PEEP on gas exchange during general anaesthesia and the early recovery period. STUDY DESIGN: Prospective, randomized clinical trial. ANIMALS: A total of 48 Warmblood horses undergoing elective surgery in lateral (Lat) (n = 24) or dorsal (Dors) (n = 24) recumbency. METHODS: Premedication (romifidine), induction (diazepam and ketamine) and maintenance (isoflurane in oxygen) were identical in all horses. Groups Lat- CMV and Dors-CMV (each n = 12) were ventilated using CMV. Groups Lat-RM and Dors-RM (each n = 12) were ventilated using CMV with constant PEEP (10 cmH2O) and intermittent RMs (three consecutive breaths with peak inspiratory pressure of 60 cmH2O, 80 cmH2O and 60 cmH2O, respectively). RMs were applied as required to maintain PaO2 at > 400 mmHg (> 53.3 kPa). Dobutamine was given to maintain mean arterial blood pressure at > 60 mmHg. Physiological parameters were recorded every 10 minutes. Arterial blood gases were measured intra- and postoperatively. Statistical analyses were conducted using analyses of variance (anova),t tests and the Mann-Whitney U-test. RESULTS: Horses in Dors-RM had higher PaO2 values [478 ± 35 mmHg (63.7 ± 4.6 kPa)] than horses in Dors-CMV [324 ± 45 mmHg (43.2 ± 6 kPa)] during anaesthesia and the early recovery period. There were no differences between horses in groups Lat-CMV and Lat-RM. Other measured parameters did not differ between groups. CONCLUSIONS AND CLINICAL RELEVANCE: Ventilation with CMV, constant PEEP and interposed RM provided improved arterial oxygenation in horses in dorsal recumbency that lasted into the early recovery period, but had no benefit in horses in lateral recumbency. This mode of ventilation may provide a clinically practicable method of improving oxygenation in anaesthetized horses, especially in dorsal recumbency.

Continuous positive airway pressure (CPAP) decreases pulmonary shunt in anaesthetized horses.

OBJECTIVE: To evaluate the effects of continuous positive airway pressure (CPAP) on intrapulmonary shunt, cardiac output and oxygen delivery in horses subjected to a 6 hour period of general anaesthesia. STUDY DESIGN: Randomized, experimental, crossover study. ANIMALS: Ten healthy adult horses. METHODS: Following medetomidine, diazepam and ketamine administration, orotracheal intubation was performed and horses positioned in dorsal recumbency. Anaesthesia was maintained with isoflurane carried in an oxygen and air mix (FiO2 0.5) combined with a medetomidine infusion. Horses were anaesthetized twice and either CPAP (8 cmH2 O) or physiologic airway pressure (NO CPAP) was applied to the lungs for 6 hours; the order of treatments was randomly assigned. Following induction of anaesthesia, cardiovascular and respiratory variables (including arterial blood gas analysis) were recorded every 30 minutes, cardiac output was measured every 60 minutes using the lithium dilution technique and oxygen delivery calculated. If PaCO2 exceeded 100 mmHg (13.3 kPa), controlled ventilation was initiated and horses excluded from further data collection. Groups were compared using a general linear model. RESULTS: Data from eight horses were analysed. PaO2 was 15-56 mmHg (2.00-7.45 kPa) higher (p < 0.001) and shunt fraction 6-14% lower (p < 0.001) in the CPAP group. No differences were seen for cardiac output and oxygen delivery. The lack of difference in oxygen delivery was attributed to lower haemoglobin levels in the CPAP group than in the NO CPAP group. CONCLUSIONS AND CLINICAL RELEVANCE: CPAP of 8 cmH2 O can be used in dorsally recumbent horses to decrease pulmonary shunt fraction without causing a decrease in cardiac output during longterm anaesthesia.

Morfologia e morfometria da traqueia da preguiça (bradypus variegatus): conhecimentos para procedimentos de emergência / Morphological and morphometric trachea sloth (bradypus variegatus): knowledge for emergency procedures

Por ser uma espécie pouco estudada, principalmente do ponto de vista morfológico, objetivou-se conhecer a anatomia da traqueia da preguiça (Bradypus variegatus) a fim de fornecer informações para facilitar a eleição de tubo endotraqueal adequado, máscara laríngea ou cânula de traqueostomia para anestesia e procedimentos de emergência, uma vez que a mesma revelou-se possuidora de uma morfologia especial. Foram investigados 11animais jovens de idades diferentes, sendo quatro machos e sete fêmeas, provenientes do Museu Emilio Goeldi e doados a UFRA. Os exemplares foram perfundidos via intramuscular com solução aquosa de formol a 10% para fins de conservação e posteriormente foram dissecados em nível cervico-torácico, por meio de mesoscopia, expondo-se desde a laringe até os brônquios principais direito e esquerdo ao nível do hilo pulmonar. As traqueias foram divididas em cinco regiões (região cervical, região da primeira flexura, região da segunda flexura, região da terceira flexura e região da carina) as quais foram mensuradas altura e largura, assim como o comprimento traqueal total e parte do material foi submetido à técnicas de rotina histológica. Macroscopicamente, destacou-se a presença de sinuosidades acentuadas em porção médio caudal, contemplando a carina. O comprimento médio traqueal foi de 14,6cm. Microscopicamente, a traqueia era constituída por placas separadas de cartilagem hialina constituindo cada anel, sendo revestido por epitélio estratificado ciliado. Apesar da traqueia da preguiça comum apresentar revestimento padrão encontrado na traqueia de outros animais, na literatura não há registros de outras espécies que tenham morfologia macroscópica nas condições descritas, o que nos leva a sugerir, quando necessário acesso para ventilação de emergência, a prática da IOT e não a de traqueostomia.

As the sloth (Bradypus variegatus) is a little studied species, especially from a morphological point of view, this research aimed to define the anatomy of its trachea. The information would facilitate the selection of a proper endotracheal tube, laryngeal mask or tracheostomy tube for anesthesia and emergency procedures, since it appeared to have a special morphology. Eleven young animals of different ages were investigated, four males and seven females, obtained from the Emilio Goeldi Museum and donated to UFRA. The specimens were infused intramuscularly with 10% aqueous formaldehyde for preservation and were later dissected at the cervico-thoracic level, by mesoscopia, exposing the area from the larynx to the right and left primary bronchi at the hilum. The tracheae were divided into five regions (cervical, first flexure, second flexure, third flexure, and carina) for which length and width were measured, as well as the total tracheal length. Sharp windings were seen in the middle caudal portion, including the carina. The average tracheal length was 14.6 cm. Microscopically, the trachea was made up of separate plates of hyaline cartilage forming each ring, lined with ciliated epithelium. Despite the trachea of the common sloth displaying the same lining pattern found in other animals, there are no reports in the literature of other species having a macroscopic morphology as described here, which leads us to suggest, where appropriate access to emergency ventilation, the practice of IOT and not tracheostomy.

Noninvasive continuous positive airway pressure delivered using a pediatric helmet in dogs recovering from general anesthesia.

OBJECTIVE: To evaluate the feasibility and efficacy of noninvasive continuous positive airway pressure (CPAP) administered with a pediatric helmet in healthy dogs recovering from general anesthesia. DESIGN: Randomized, cross-over, clinical study. SETTING: University teaching hospital. ANIMALS: Fifteen healthy female, client-owned dogs recovering from general anesthesia following elective ovariohysterectomy. INTERVENTIONS: All dogs received the same standardized anesthetic protocol (acepromazine, morphine, propofol, and isoflurane in oxygen). After extubation, a pediatric helmet was placed on all dogs and connected to a venturi valve supplied with medical air. In all patients, the gas flow was set to 50 L/minute and the FiO2 to 0.21. Dogs received the following sequence of treatments, each lasting 20 minutes: 0 CPAP (pre-CPAP), CPAP of 5 cm H2 O (CPAP), and again 0 CPAP (post-CPAP). MEASUREMENTS AND MAIN RESULTS: During the entire study, the following data were collected: pressure and FiO2 inside the helmet, mean arterial pressure, respiratory rate, heart rate, sedation score (0 = awake, 10 = deep sedation), and tolerance to the helmet (0 = excellent, 4 = poor). At the end of each phase, an arterial blood sample was sampled. As compared with the pre-CPAP and the post-CPAP periods, during the CPAP period, the PaCO2 , alveolar-arterial oxygen gradient (P[A-a]O2 ), and respiratory rate significantly decreased. The PaO2 was higher at CPAP (105.6 ± 4.0 mm Hg) compared with pre-CPAP (80.6 ± 6.9 mm Hg) and post-CPAP (86.7 ± 5.8 mm Hg). Tolerance and sedation scores during the CPAP period were not different from those in the pre-CPAP and post-CPAP periods. CONCLUSIONS: Noninvasive CPAP applied through a helmet is a feasible and effective supportive technique in dogs recovering from general anesthesia.