The incidence of hypoxemia in dogs recovering from general anesthesia detected with pulse-oximetry and related risk factors

The postoperative period is critical for the development of complications, including hypoxemia. To detect hypoxemia early and provide appropriate care, continuous monitoring of saturation is necessary: pulse oximetry is an easily accessible and simple method for this purpose. However, a SpO2 cut-off value to detect hypoxemia in dogs recovering from general anesthesia is lacking in the veterinary literature. The objectives of this clinical study are to validate the room air SpO2 test (SpAT), to identify a cut-off value to discriminate hypoxemia (Phase 1), and to apply the SpAT to study the incidence of transient postoperative hypoxemia (TPH) (Phase 2) in dogs with healthy lungs recovering from general anesthesia. Phase 1: 87 dogs recovering from general anesthesia with an arterial line were included. After extubation, SpAT was performed simultaneously with arterial blood sampling. A PaO2 < 80 mmHg was considered hypoxemia. Phase 2: 654 dogs were enrolled. They underwent general anesthesia with different ventilation settings for different procedures. After extubation, dogs were classified as hypoxemic if the SpO2 was lower than the cut-off obtained in phase 1. Phase 1 showed that the SpO2 cut-off is < 95% (sensitivity 100%, specificity 97.4%; area under the curve, AUC = 0.996; 95% Confidence Interval = 0.944-1; P<0.0001). In Phase 2, 169 dogs were hypoxemic. Body Condition Score (BCS) > 3/5, dorsal recumbency, FiO2 1, absence of Positive End-Expiratory Pressure (PEEP) had a significant odds ratio to induce TPH (5.8, 1.9, 3.7, 1.7, respectively). These results showed that SpO2 < 95% indicates PaO2 < 80 mmHg in dogs and TPH occurs in up to 28% of cases. Identification of associated risks could be useful to prevent and to increase awareness for monitoring and treatment.

Tidal volume selection in volume-controlled ventilation guided by driving pressure versus actual body weight in healthy anesthetized and mechanically ventilated dogs: A randomized crossover trial

OBJECTIVE

To compare static compliance of the respiratory system (CstRS) and the ratio of partial pressure of end-tidal to arterial carbon dioxide (Pe'CO2/PaCO2), in healthy dogs using two approaches for tidal volume (VT) selection during volume-controlled ventilation: body mass based and driving pressure (ΔPaw) guided.

STUDY DESIGN

Randomized, nonblinded, crossover, clinical trial.

ANIMALS

A total of 19 client-owned dogs anesthetized for castration and ovariohysterectomy.

METHODS

After a stable 10 minute baseline, each dog was mechanically ventilated with a VT selection strategy, randomized to a constant VT of 15 mL kg-1 of actual body mass (VTBW) or ΔPaw-guided VT (VTΔP) of 7-8 cmH2O. Both strategies used an inspiratory time of 1 second, 20% end-inspiratory pause, 4 cmH2O positive end-expiratory pressure and fraction of inspired oxygen of 0.4. Respiratory frequency was adjusted to maintain Pe'CO2 between 35 and 40 mmHg. Respiratory mechanics, arterial blood gases and Pe'CO2/PaCO2 were assessed. Continuous variables are presented as mean ± SD or median (interquartile range; quartiles 1-3), depending on distribution, and compared with Wilcoxon signed-rank tests.

RESULTS

The VT was significantly higher in dogs ventilated with VTΔP than with VTBW strategy (17.20 ± 4.04 versus 15.03 ± 0.60 mL kg-1, p = 0.036). CstRS was significantly higher with VTΔP than with VTBW strategy [2.47 (1.86-2.86) versus 2.25 (1.79-2.58) mL cmH2O-1 kg-1, p = 0.011]. There were no differences in Pe'CO2/PaCO2 between VTΔP and VTBW strategies (0.94 ± 0.06 versus 0.92 ± 0.06, p = 0.094). No discernible difference in ΔPaw was noted between the strategies.

CONCLUSIONS AND CLINICAL RELEVANCE

While no apparent difference was observed in the Pe'CO2/PaCO2 between the VT selection strategies employed, CstRS significantly increased during the VTΔP approach. A future trial should explore if VTΔP improves perioperative gas exchange and prevents lung damage.

Successful management of pulmonary edema secondary to accidental electrocution in a young dog

BACKGROUND

Human records describe pulmonary edema as a life-threatening complication of electric shock. Successful management requires prompt recognition and intensive care. However, in companion animals, electrocutions are rarely reported, even though domestic environments are full of electrical devices and there is always the possibility of accidental injury. Therefore, it is important for veterinarians to know more about this condition in order to achieve successful patient outcomes.

CASE PRESENTATION

A 3-month-old male Labrador Retriever was presented with a history of transient loss of consciousness after chewing on a household electrical cord. On admission, the puppy showed an orthopneic position with moderate respiratory distress. Supplemental oxygen via nasal catheter was provided, but the patient showed marked worsening of respiratory status. Point-of-care ultrasound exams suggested neurogenic pulmonary edema due to electrical shock close to the central nervous system and increased B-lines without evidence of cardiac abnormalities. Mechanical ventilation of the patient was initiated using volume-controlled mode with a tidal volume of 9 to 15 ml/kg until reaching an end-tidal carbon dioxide ≤ 40 mm Hg, followed by a stepwise lung-recruitment maneuver in pressure-controlled mode with increases of the peak inspiratory pressure (15 to 20 cm H2O) and positive end-expiratory pressure (3 to 10 cm H2O) for 30 min, and return to volume-controlled mode with a tidal volume of 15 ml/kg until reaching a peripheral oxygen saturation ≥ 96%. Weaning from the ventilator was achieved in six hours, and the patient was discharged two days after admission without neurological or respiratory deficits.

CONCLUSIONS

We present a rather unusual case of a neurogenic pulmonary edema subsequent to accidental electrocution in a dog. Timely diagnosis by ultrasound and mechanical ventilation settings are described. Our case highlights that pulmonary edema should be considered a potentially life-threatening complication of electrical shock in small animal emergency and critical care medicine.

Effects of a stepwise alveolar recruitment maneuver on lung volume distribution in dogs assessed by computed tomography

Background

Pulmonary atelectasis is a commonly occurs during anesthesia. In these cases, mechanical ventilation (MV) associated with alveolar recruitment maneuvers (ARMs) and positive end-expiratory pressure (PEEP) is indicated to reverse the condition, ensure adequate gas exchange and improve oxygenation. ARMs can trigger volutrauma, barotrauma, and atelectrauma. Therefore, computed tomography (CT) is the gold-standard method for monitoring lung aeration after ARM.

Objective

To evaluate lung volume distribution after stepwise ARMs using computed tomography (CT).

Methods

Twelve dogs weighing 24.0 ± 6.0 kg, aged 3 ± 1 years, of both sexes and different breeds, underwent orchiectomy or ovariohysterectomy. The animals were anesthetized and ventilated in volume-controlled mode. ARMs were then initiated by positive end-expiratory pressure (PEEP) titration (5, 10, 15, and 20 cmH2O). CT scans, cardiovascular parameters, and ventilatory mechanics were evaluated at all time points. Data were assessed for normality using the Shapiro-Wilk test and a two-way analysis of variance, followed by a post-hoc Bonferroni test to identify differences between time points. Statistical significance was attributed to a value of p of <0.05.

Results

CT demonstrated that the ARMs increased ventilation throughout the lung, including the dependent regions, with volumes that increased and decreased proportionally with PEEP titration. When they reached PEEP 10 and 5 cmH2O descending (d), they remained significantly higher than those in PEEP 0 cmH2O (baseline). Static compliance improved about 40% at PEEP 10d and PEEP 5d compared to baseline. There was an increase in heart rate (HR) from PEEP 15 increasing (i) (74.5%) to PEEP 10d (54.8%) compared to baseline. Mean arterial blood pressure (MABP) decreased approximately 9% from PEEP 15i to PEEP 15d compared to baseline.

Conclusion

Lung attenuation and regional and global volumes assessed by CT showed that maximum pulmonary aeration distribution followed by PEEP titration occurred at PEEP 20 cmH2O, maintaining the lungs normoaerated and without hyperaeration.

Protective technologies of modern methods of respiratory support in neonatal practice

The article  presents  an analysis of literature data  on modern  protective regimens  for invasive respiratory support  in premature newborns  with respiratory distress  syndrome. We have considered positive and negative  aspects of the used methods  of invasive ventilation of the lungs, which are currently widely used as a method  of respiratory therapy  in obstetric hospitals  at any level, even in the category  of children  with extremely and very low birth weight. Modern  protective mechanical ventilation provides for 2 main directions for reducing ventilator-induced lung damage: a decrease in tidal volume (Vt) and the principle  of tolerable  (permissive) hypercapnia. The use of the technique of permissive hypercapnia and regimens with a target volume can reduce the likelihood of ventilator-induced lung injury in newborns. Despite the limited indications for mechanical ventilation in modern neonatology and the widespread use of non-invasive ventilation, for patients who really need mechanical ventilation, the use of volume-targeted regimens offers the best chance of reducing  ventilation complications.

Severe Hypercapnia during Anaesthesia under Mechanical Ventilation in Two Paediatric Patients

A 2-month-old male 1.56 kg Yorkshire terrier (Case No. 1) and a 3-month-old male 2.3 kg Jack Russell Terrier (Case No. 2) were scheduled for ophthalmological surgery under general anaesthesia and neuromuscular blockade. For both patients, volume-controlled ventilation (VCV) was used with set tidal volumes (V_T) of 13 mL/kg and 20 mL/kg for cases No. 1 and 2, respectively. The type of ventilator used did not take into account the intrinsic compliance of the breathing system; therefore, a significant part of the delivered V_T was wasted in the expansion of the breathing system, and did not reach the patients, causing alveolar hypoventilation. Both cases developed low dynamic compliance (C_D), and after a recruitment manoeuvre, EtCO₂ of up to 116 mmHg and 197 mmHg were revealed for cases No. 1 and 2, respectively. The two cases had to be ventilated manually, using positive inspiratory pressures (PIP) of 20-25 mmHg, in order to improve alveolar ventilation and reduce the EtCO₂, as adjustments to the VCV were ineffective. Both patients maintained an oxygen haemoglobin saturation between 94% and 100% throughout the procedure and they recovered well. Using a higher V_T from the beginning, to compensate for the compliance of the breathing system, or the use of pressure-controlled ventilation (PCV), could have potentially helped to avoid these two incidences of severe hypercapnia.

Predicting the effect of fresh gas flow on tidal volume in volume-controlled mechanically ventilated dogs

OBJECTIVES

To determine if the tidal volume (V_T) delivered (V_TDEL) to canine patients being mechanically ventilated by a volume-controlled ventilator differed from the volume set on the ventilator (V_TSET) at three fresh gas flow (FGF) rates. To determine if V_TDEL could be accurately predicted by an FGF-based mathematical model.

STUDY DESIGN

Prospective proof-of-concept study.

ANIMALS

A total of 23 adult client-owned dogs undergoing elective orthopedic surgery.

METHODS

Dogs were anesthetized and ventilated with a volume-controlled mechanical ventilator with constant respiratory rate (f_R) of 10 breaths minute^-1, inspiratory-to-expiratory ratio of 1:2 [fraction of inspiratory time (T_I) in one respiratory cycle (T_tot) 1:3], and V_TSET as body weight (kg) × 15 (mL kg^-1). V_TDEL was measured in 20 dogs at three FGF (500, 1000 and 4000 mL minute^-1). A mathematical model was used to calculate predicted volume (V_TPRED) for each animal at each FGF: V_TSET + {FGF × [(T_I/T_tot)/f_R]}. Linear repeated measures models were fit comparing V_TDEL to V_TSET and to V_TPRED by FGF.

RESULTS

V_TDEL was significantly higher than V_TSET at every FGF (p < 0.05), and differences were larger at higher FGF (p < 0.001). There were no statistically significant differences between V_TDEL and V_TPRED at FGF rates of 500 and 4000 mL minute^-1 and, although the mean V_TDEL was statistically significantly higher than V_TPRED at FGF 1000 mL minute^-1 (p = 0.017), the mean difference of 9 mL was not clinically significant.

CONCLUSIONS AND CLINICAL RELEVANCE

Dogs on volume-controlled ventilators may be ventilated at a higher V_TDEL than intended depending on the FGF settings. Ventilation of small animals at high FGF could inadvertently induce pulmonary damage. A mathematical equation can be used to achieve a desired V_TDEL by adjusting V_TSET values based on FGF, f_R and T_I/T_tot.

Pre-hospital emergency cricothyrotomy in dogs part 2: Airway sealing and ventilation using cricothyrotomy tubes

Cricothyrotomy (CTT) has been recommended for use in the pre-hospital setting for military working dogs and Operational K9s during airway emergencies. Although the CTT can establish a patent airway for spontaneous ventilation, the ability to seal the airway and provide positive pressure ventilation (PPV) using tubes designed for humans has not been determined. Using various CTT tubes placed in cadaver dog airways, this study aimed to determine: (1) Whether the tube cuff could create a functional airway seal with safe intra-cuff pressures; (2) The magnitude of delivered tidal volume (TV) loss during a standard breath to assess the possibility of delivering an adequate tidal volume with a bag-valve device (BVM); (3) The best performing tubes for either test; (4) The reasons behind the findings using observations from upper airway endoscopy, dissection, and measurements. Cadaver dogs of similar weights to MWD and Operational K9 breeds had various CTT tubes placed including three from commercial kits, a standard endotracheal tube, and a tracheostomy tube. The minimum occlusive volume technique was used to inflate the tube cuff and a pressure ≤ 48 cm H₂O with an adequate seal was considered successful. Individual TVs were calculated for each dog and added to the volume lost during delivery of a standard breath from an ICU ventilator. Endoscopy and airway dissection were performed to assess the relationship between tubes cuffs and the airway. The tubes from the CTT kits performed poorly with regards to producing an airway seal with the H&H tube failing to seal the airway all tests. Tracheal dimensions were significantly associated with successful airway sealing (P = 0.0004). Tidal volume loss could be compensated using a BVM in 34/35 tests with the H&H tube in cadaver 8 the only to fail. Tracheal airway sealing is influenced by airway anatomy when tube cuffs are inflated to a target pressure and larger tubes do not always provide a better seal. The CTT tubes tested have the potential to facilitate ventilation with a BVM under the conditions set in this study. The 8.0 mm endotracheal tube performed the best and the H&H the worst in both tests.

Cardiovascular and Gas Exchange Effects of Individualized Positive End-Expiratory Pressures in Cats Anesthetized With Isoflurane

Objectives

To compare the effects of four levels of end-expiratory pressure [zero (ZEEP) and three levels of positive end-expiratory pressure (PEEP)] on the cardiovascular system and gas exchange of cats anesthetized with isoflurane and mechanically ventilated for 3 h with a tidal volume of 10 ml/kg.

Study Design

Prospective, randomized, controlled trial.

Animals

Six healthy male neutered purpose-bred cats.

Methods

Anesthesia was induced with isoflurane and maintained at 1.3 minimum alveolar concentration. PEEP of maximal respiratory compliance (PEEP_maxCrs) was identified in a decremental PEEP titration, and cats were randomly ventilated for 3 h with one of the following end-expiratory pressures: ZEEP, PEEP_maxCrs minus 2 cmH₂O (PEEP_maxCrs−2), PEEP_maxCrs, and PEEP_maxCrs plus 2 cmH₂O (PEEP_maxCrs+2). Cardiovascular and gas exchange variables were recorded at 5, 30, 60, 120, and 180 min (T5 to T180, respectively) of ventilation and compared between and within ventilation treatments with mixed-model ANOVA followed by Dunnet's and Tukey's tests (normal distribution) or Friedman test followed by the Dunn's test (non-normal distribution). Significance to reject the null hypothesis was considered p < 0.05.

Results

Mean arterial pressure (MAP—mmHg) was lower in PEEP_maxCrs+2 [63 (49–69); median (range)] when compared to ZEEP [71 (67–113)] at T5 and stroke index (ml/beat/kg) was lower in PEEP_maxCrs+2 (0.70 ± 0.20; mean ± SD) than in ZEEP (0.90 ± 0.20) at T60. Cardiac index, oxygen delivery index (DO₂I), systemic vascular resistance index, and shunt fraction were not significantly different between treatments. The ratio between arterial partial pressure and inspired concentration of oxygen (PaO₂/FIO₂) was lower in ZEEP than in the PEEP treatments at various time points. At T180, DO₂I was higher when compared to T5 in PEEP_maxCrs. Dopamine was required to maintain MAP higher than 60 mmHg in one cat during PEEP_maxCrs and in three cats during PEEP_maxCrs+2.

Conclusion

In cats anesthetized with isoflurane and mechanically ventilated for 3 h, all levels of PEEP mildly improved gas exchange with no significant difference in DO₂I when compared to ZEEP. The PEEP levels higher than PEEP_maxCrs−2 caused more cardiovascular depression, and dopamine was an effective treatment. A temporal increase in DO₂I was observed in the cats ventilated with PEEP_maxCrs. The effects of these levels of PEEP on respiratory mechanics, ventilation-induced lung injury, as well as in obese and critically ill cats deserve future investigation for a better understanding of the clinical use of PEEP in this species.

Intraoperative Protective Mechanical Ventilation in Dogs: A Randomized Clinical Trial

Objective

To evaluate gas exchange, respiratory mechanics, and hemodynamic impact of mechanical ventilation with low tidal volume (V_T) in dogs with the use of positive end-expiratory pressure (PEEP) or preceded by alveolar recruitment maneuver (ARM).

Study Design

Prospective randomized clinical trial.

Animals

Twenty-one healthy client-owned mesocephalic healthy dogs, 1-7 years old, weighing 10-20 kg, and body condition scores 4-6/9 admitted for periodontal treatment.

Methods

Isoflurane-anesthetized dogs in dorsal recumbency were ventilated until 1 h with a volume-controlled ventilation mode using 8 mL kg^-1 of V_T. The dogs were distributed in 2 groups: in the ARM group, PEEP starts in 0 cmH₂O, increasing gradually 5 cmH₂O every 3 min, until reach 15 cmH₂O and decreasing in the same steps until 5 cmH₂O, maintaining this value until the end; and PEEP group, in which the pressure 5 cmH₂O was instituted from the beginning of anesthesia and maintained the same level up to the end of the anesthesia. Cardiopulmonary, metabolic, oxygenation parameters, and respiratory mechanics were recorded after the anesthesia induction (baseline-BL), 15, 45, and 75 min after BL and during the recovery.

Results

The ARM increased the static compliance (C_st) (15 min after baseline) when compared with baseline moment (24.9 ± 5.8 mL cmH₂0^-1 vs. 20.7 ± 5.4 mL cmH₂0^-1-p = 0.0364), oxygenation index (PaO₂/FIO₂) (505.6 ± 59.2 mmHg vs. 461.2 ± 41.0 mmHg-p = 0.0453) and reduced the shunt fraction (3.4 ± 2.4% vs. 5.5 ± 1.6%-p = 0.062). In the PEEP group, no statistical differences were observed concerning the variables evaluated. At the beginning of the evaluation, the driving pressure (DP) before ARM was significantly greater than all other evaluation time points (6.9 ± 1.8 cmH₂0).

Conclusions and Clinical Relevance

The use of 8 mL kg^-1 of V_T and 5 cmH₂0 PEEP without ARM maintain adequate oxygenation and mechanical ventilation in dental surgeries for up to 1 h. The use of ARM slightly improved compliance and oxygenation during the maneuver.

Effects of the Administration of Different Buffered Balanced Crystalloid Solutions on Acid-Base and Electrolyte Status in Dogs with Gastric Dilation-Volvulus Syndrome: a randomized clinical trial

OBJECTIVE

To investigate the effect of three different buffered balanced crystalloid solutions on acid-base status and electrolyte concentrations in dogs with gastric dilation-volvulus (GDV) syndrome.

METHODS

The study design was a prospective, randomized clinical trial of 40 dogs. The dogs were randomly assigned to one of three groups according to the fluid used: Hartmann's solution (H), Plasmalyte (PL), and Ringerfundin (RF). Hemoglobin, albumin, lactate, electrolyte, and acid-base parameters were determined before fluid administration (T0) and at the end of surgery (T1). Results were assessed by one-way ANOVA, Fisher's exact test, the Wilcoxon signed-rank test, the Kruskal-Wallis test, and a linear mixed-effect regression model. A significance level of 0.05 was used in all analyses.

RESULTS

Bicarbonate and base excess (BE) levels increased and chloride concentration decreased in the PL group; in contrast, strong ion difference apparent (SID_app) decreased and chloride concentration increased in the RF group. The mixed-effect model confirmed a significant interaction between the type of solution and time on the changes in bicarbonate, BE, anion gap (AG), SID_app, and chloride levels.

CLINICAL SIGNIFICANCE

Significantly different effects in acid-base parameters were observed in dogs after intravenous administration of H, PL, and RF. However, clinical significance of these changes is lacking, requiring further investigation in a larger randomized controlled clinical trial.

Evaluation of Lung Aeration and Respiratory System Mechanics in Obese Dogs Ventilated With Tidal Volumes Based on Ideal vs. Current Body Weight

We describe the respiratory mechanics and lung aeration in anesthetized obese dogs ventilated with tidal volumes (VT) based on ideal (VTi) vs. current (VTc) body weight. Six dogs with body condition scores ≥ 8/9 were included. End-expiratory respiratory mechanics and end-expiratory CT-scan were obtained at baseline for each dog. Thereafter, dogs were ventilated with VT 15 ml kg⁻¹ based on VTi and VTc, applied randomly. Respiratory mechanics and CT-scan were repeated at end-inspiration during VTi and VTc. Data analyzed with linear mixed models and reported as mean ± SD or median [range]. Statistical significance p < 0.05. The elastance of the lung, chest wall and respiratory system indexed by ideal body weight (IBW) were positively correlated with body fat percentage, whereas the functional residual capacity indexed by IBW was negatively correlated with body fat percentage. At end-expiration, aeration (%) was: hyperaeration 0.03 [0.00–3.35], normoaeration 69.7 [44.6–82.2], hypoaeration 29.3 [13.6–49.4] and nonaeration (1.06% [0.37–6.02]). Next to the diaphragm, normoaeration dropped to 12 ± 11% and hypoaeration increased to 90 ± 8%. No differences in aeration between groups were found at end-inspiration. Airway driving pressure (cm H₂O) was higher (p = 0.002) during VTc (9.8 ± 0.7) compared with VTi (7.6 ± 0.4). Lung strain was higher (p = 0.014) during VTc (55 ± 21%) than VTi (38 ± 10%). The stress index was higher (p = 0.012) during VTc (SI = 1.07 [0.14]) compared with VTi (SI = 0.93 [0.18]). This study indicates that body fat percentage influences the magnitude of lung, chest wall, and total respiratory system elastance and resistance, as well as functional residual capacity. Further, these results indicate that obese dogs have extensive areas of hypoaerated lungs, especially in caudodorsal regions. Finally, lung strain and airway driving pressure, surrogates of lung deformation, are higher during VTc than during VTi, suggesting that in obese anesthetized dogs, ventilation protocols based on IBW may be advantageous.

Lung Ultrasound for Pulmonary Contusions

Lung ultrasound (LUS) has high sensitivity for the rapid and reliable diagnosis of pulmonary contusions (PC) in patients who have sustained trauma. LUS diagnosis of PC exceeds that of thoracic radiographs in multiple animal and human studies. The sonographer should understand potential caveats and confounding variables for proper diagnosis of PC with LUS. LUS does not replace conventional radiography or computed tomography, especially in the polytrauma patient. LUS should be used concurrently with other point-of-care ultrasound trauma protocols to rapidly optimize patient assessment before movement to the radiology suite.

Definition and clinical evaluation of a recruiting airway pressure based on the specific lung elastance in anesthetized dogs

OBJECTIVE

To determine the specific lung elastance (SE_L) in anesthetized dogs and to evaluate the efficacy of a SE_L-based recruiting airway pressure (RP_aw) at improving global and regional lung aeration.

STUDY DESIGN

Retrospective and prospective clinical study.

ANIMALS

A total of 28 adult dogs were included in the retrospective study and six adult dogs in the prospective study.

METHODS

Retrospective study: SE_L and SE_L-based RP_aw were determined using previously published data. In mechanically ventilated dogs undergoing thoracic computed tomography (CT), SE_L was calculated as ΔP_L/(V_T/EELV), where ΔP_L is the driving transpulmonary pressure, V_T is the tidal volume and EELV is the end-expiratory lung volume. The ratio of lung to respiratory system elastance (E_L/E_rs) was determined. SE_L and E_L/E_rs were used to calculate the SE_L-based RP_aw. Prospective study: dogs underwent thoracic CT at end-expiration and at end-inspiration using the SE_L-based RP_aw, and global and regional aeration was determined. For analysis of regional aeration, lungs were divided into cranial, intermediate and caudal regions. Regional compliance was also calculated. A p value <0.05 was considered significant.

RESULTS

The SE_L and E_L/E_rs were 12.7 ± 3.1 cmH₂O and 0.54 ± 0.07, respectively. The SE_L-based RP_aw was 29.1 ± 7.6 cmH₂O. In the prospective study, the RP_aw was 28.2 ± 1.3 cmH₂O. During RP_aw, hyperinflation increased (p = 0.0003) whereas poorly aerated (p < 0.0001) and nonaerated (p = 0.01) tissue decreased. Normally aerated tissue did not change (p = 0.265). Regional compliance was higher in the intermediate (p = 0.0003) and caudal (p = 0.034) regions compared with the cranial region. Aeration did not differ between regions (p > 0.05).

CONCLUSIONS AND CLINICAL RELEVANCE

An SE_L-based RP_aw reduces poorly and nonaerated lung tissue in anesthetized dogs. In nonsurgical anesthetized dogs, an RP_aw near 30 cmH₂O is effective at improving lung aeration.

Cardiovascular function, pulmonary gas exchange and tissue oxygenation in isoflurane-anesthetized, mechanically ventilated Beagle dogs with four levels of positive end-expiratory pressure

OBJECTIVES

To compare pulmonary gas exchange, tissue oxygenation and cardiovascular effects of four levels of end-expiratory pressure: no positive end-expiratory pressure (ZEEP), positive end-expiratory pressure (PEEP) of maximal respiratory system compliance (PEEPmaxC_rs), PEEPmaxC_rs + 2 cmH₂O (PEEPmaxC_rs+2), PEEPmaxC_rs + 4 cmH₂O (PEEPmaxC_rs+4), in isoflurane-anesthetized dogs.

STUDY DESIGN

Prospective randomized crossover study.

ANIMALS

A total of seven healthy male Beagle dogs, aged 1 year and weighing 10.2 ± 0.7 kg (mean ± standard deviation).

METHODS

The dogs were administered acepromazine and anesthesia was induced with propofol and maintained with isoflurane. Ventilation was controlled for 4 hours with ZEEP, PEEPmaxC_rs, PEEPmaxC_rs+2 or PEEPmaxC_rs+4. Cardiovascular, pulmonary gas exchange and tissue oxygenation data were evaluated at 5, 60, 120, 180 and 240 minutes of ventilation and compared using a mixed-model anova followed by Bonferroni test. p < 0.05 was considered significant.

RESULTS

Cardiac index (CI) and mean arterial pressure (MAP) were lower in all PEEP treatments at 5 minutes when compared with ZEEP. CI persisted lower throughout the 4 hours only in PEEPmaxC_rs+4 with the lowest CI at 5 minutes (2.15 ± 0.70 versus 3.45 ± 0.94 L minute^-1 m^-2). At 180 and 240 minutes, MAP was lower in PEEPmaxC_rs+4 than in PEEPmaxC_rs, with the lowest value at 180 minutes (58 ± 7 versus 67 ± 7 mmHg). Oxygen delivery index (DO₂I) was lower in PEEPmaxC_rs+4 than in ZEEP at 5, 60, 120 and 180 minutes. Venous admixture was not different among treatments.

CONCLUSION AND CLINICAL RELEVANCE

The use of PEEP caused a transient decrease in MAP and CI in lung-healthy dogs anesthetized with isoflurane, which improved after 60 minutes of ventilation in all levels of PEEP except PEEPmaxC_rs+4. A clinically significant improvement in arterial oxygenation and DO₂I was not observed with PEEPmaxC_rs and PEEPmaxC_rs+2 in comparison with ZEEP, whereas PEEPmaxC_rs+4 decreased DO₂I.

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.

Intraoperative Assessment of Fluid Responsiveness in Normotensive Dogs under Isoflurane Anaesthesia

The aim of this study was to evaluate the incidence of fluid responsiveness (FR) to a fluid challenge (FC) in normotensive dogs under anaesthesia. The accuracy of pulse pressure variation (PPV), systolic pressure variation (SPV), stroke volume variation (SVV), and plethysmographic variability index (PVI) for predicting FR was also evaluated. Dogs were anaesthetised with methadone, propofol, and inhaled isoflurane in oxygen, under volume-controlled mechanical ventilation. FC was performed by the administration of 5 mL/kg of Ringer's lactate within 5 min. Cardiac index (CI; L/min/m²), PPV, (%), SVV (%), SPV (%), and PVI (%) were registered before and after FC. Data were analysed with ANOVA and ROC tests (p < 0.05). Fluid responsiveness was defined as 15% increase in CI. Eighty dogs completed the study. Fifty (62.5%) were responders and 30 (37.5%) were nonresponders. The PPV, PVI, SPV, and SVV cut-off values (AUC, p) for discriminating responders from nonresponders were PPV >13.8% (0.979, <0.001), PVI >14% (0.956, <0.001), SPV >4.1% (0.793, <0.001), and SVV >14.7% (0.729, <0.001), respectively. Up to 62.5% of normotensive dogs under inhalant anaesthesia may be fluid responders. PPV and PVI have better diagnostic accuracy to predict FR, compared to SPV and SVV.

Diagnosis of pulmonary contusions with point-of-care lung ultrasonography and thoracic radiography compared to thoracic computed tomography in dogs with motor vehicle trauma: 29 cases (2017-2018)

OBJECTIVE

To determine the accuracy of lung ultrasound (LUS) using the Veterinary Bedside Lung Ultrasound Examination (VetBLUE) protocol and 3-view thoracic radiographs (TXR) compared to thoracic computed tomography (TCT) for diagnosing the presence and quantification of pulmonary contusions (PC).

DESIGN

Prospective cohort study conducted from February 2017 to June 2018.

SETTING

Private emergency and referral center.

ANIMALS

Thirty-two dogs having sustained motor vehicle trauma were consecutively enrolled. Three dogs were excluded from statistical analysis. All dogs survived to hospital discharge.

INTERVENTIONS

Within 24 hours of sustaining trauma, dogs had LUS, TXR, and TCT performed. Using the VetBLUE protocol, LUS PC were scored according to the presence and number of B-lines and C-lines, indicating extravascular lung water. Thoracic radiographs and TCT were scored for PC in a similar topographical pattern to the VetBLUE protocol. Lung ultrasound and TXR were compared to "gold standard" TCT for the presence and quantification of PC.

MEASUREMENTS AND MAIN RESULTS

On TCT, 21 of 29 (72.4%) dogs were positive and 8 of 29 (27.6%) dogs were negative for PC. When LUS was compared to TCT, 19 of 21 dogs were positive for PC (90.5% sensitivity) and 7 of 8 dogs were negative (87.5% specificity) for PC. LUS PC score correlated strongly with TCT PC score (R = 0.8, P < 0.001). When TXR was compared to TCT, 14 of 21 dogs were positive for PC (66.7% sensitivity) and 7 of 8 dogs were negative (87.5% specificity) for PC. TXR PC score correlated strongly with TCT PC score (R = 0.74, P < 0.001).

CONCLUSIONS

In this population of dogs with motor vehicle trauma, LUS had high sensitivity for diagnosis of PC when compared to "gold standard" TCT. LUS provides reliable diagnosis of PC after trauma. More patients with PC were identified with LUS than with TXR, and additional studies are warranted to determine whether this increased sensitivity is statistically significant.

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 (V_TOT ; cm³ ), and laterolateral and dorsoventral diameters (D_LL and D_DV , 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), V_TOT increased by 52.4 ± 13.6% (from 6.2 ± 1.7 to 9.4 ± 2.4 cm³ , P < 0.0001), and D_LL and D_DV 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.

COMPUTED TOMOGRAPHY LUNG VOLUME DIFFERS BETWEEN VERTICAL AND INVERTED POSITIONING FOR EGYPTIAN FRUIT BATS (ROUSETTUS AEGYPTIACUS)

This prospective study characterizes the impact of positioning on the pulmonary volume and pulmonary atelectasis in Egyptian fruit bats (Rousettus aegyptiacus). The soft tissue appearance of atelectactic pulmonary parenchyma can obscure or mask pulmonary pathology. Soft tissue within healthy lung parenchyma caused by atelectasis can efface the margins of pathology, such as pulmonary metastasis or pneumonia, due to overlapping attenuation profiles. Pulmonary atelectasis is an unwanted side effect of anesthesia resulting from muscle relaxation and is exacerbated by high (80-100%) inspired oxygen supplementation during general anesthesia. Positioning can help minimize pulmonary atelectasis. Seven R. aegyptiacus received computed tomography imaging in suspended vertical (head-up) and inverted (head-down) positions that generated images in the dorsoventral plane. Vertically positioned bats had a significantly greater lung volume compared to inverted positioning (P = 0.0053). The nondependent portion of the lung apices in the vertically positioned bats had significantly more negative Hounsfield units (i.e. less dense tissue) than the dependent portions of the lung and was also less dense than both portions of the lungs in inverted positioned bats. Although not an intuitive positioning for bats, a vertical orientation generates less pulmonary atelectasis and a greater lung volume compared to bats positioned in a more natural inverted position. Despite physiologic adaptations to hang in an inverted position when not in flight, avoidance of inverted positioning during anesthesia and anesthetic recovery is recommended based on these findings.