Comparison between mainstream (Capnostat 5) and a low-flow sidestream capnometer (Capnostream) in mechanically ventilated, sevoflurane-anesthetized rabbits using a Bain coaxial delivery system.

OBJECTIVE: To evaluate agreement between end-tidal carbon dioxide (Pe'CO2) and PaCO2 with sidestream and mainstream capnometers in mechanically ventilated anesthetized rabbits, with two ventilatory strategies. STUDY DESIGN: Prospective experimental study. ANIMALS: A total of 10 New Zealand White rabbits weighing 3.6 ± 0.3 kg (mean ± standard deviation). METHODS: Rabbits anesthetized with sevoflurane were intubated with an uncuffed endotracheal tube (3.0 mm internal diameter) and adequate seal. For Pe'CO2, the sidestream capnometer sampling adapter or the mainstream capnometer was placed between the endotracheal tube and Bain breathing system (1.5 L minute-1 oxygen). PaCO2 was obtained from arterial blood collected every 5 minutes. A time-cycled ventilator delivered an inspiratory time of 1 second and 12 or 20 breaths minute-1. Peak inspiratory pressure was initially set to achieve Pe'CO2 normocapnia of 35-45 mmHg (4.6-6.0 kPa). A total of five paired Pe'CO2 and PaCO2 measurements were obtained with each ventilation mode for each capnometer. Anesthetic episodes were separated by 7 days. Agreement was assessed using Bland-Altman analysis and linear mixed models; p < 0.05. RESULTS: There were 90 and 83 pairs for the mainstream and sidestream capnometers, respectively. The mainstream capnometer underestimated PaCO2 by 12.6 ± 2.9 mmHg (proportional bias 0.44 ± 0.06 mmHg per 1 mmHg PaCO2 increase). With the sidestream capnometer, ventilation mode had a significant effect on Pe'CO2. At 12 breaths minute-1, Pe'CO2 underestimated PaCO2 by 23.9 ± 8.2 mmHg (proportional bias: 0.81 ± 0.18 mmHg per 1 mmHg PaCO2 increase). At 20 breaths minute-1, Pe'CO2 underestimated PaCO2 by 38.8 ± 5.0 mmHg (proportional bias 1.13 ± 0.10 mmHg per 1 mmHg PaCO2 increase). CONCLUSIONS AND CLINICAL RELEVANCE: Both capnometers underestimated PaCO2. The sidestream capnometer underestimated PaCO2 more than the mainstream capnometer, and was affected by ventilation mode.

Agreement of caudal aortic arterial blood pressure with oscillometry using two cuff widths placed on the thoracic or pelvic limbs of sevoflurane-anesthetized rabbits.

OBJECTIVE: To evaluate agreement with central systemic arterial pressure of an oscillometer and two cuff widths placed on the thoracic or pelvic limbs. STUDY DESIGN: Prospective experimental study. ANIMALS: A group of nine New Zealand White rabbits weighing 3.5 ± 0.3 kg. METHODS: Rabbits were sedated with dexmedetomidine and midazolam, then anesthetized with ketamine and sevoflurane. The femoral artery was surgically exposed and a 20 gauge, 5 cm catheter inserted to measure systolic (SAP), mean (MAP) and diastolic (DAP) blood pressure at the iliac artery and caudal aorta junction. Adjustments of vaporizer dial and dobutamine infusion provided a range of invasive blood pressure (IBP). Two measurements of IBP were recorded during the oscillometer cycling phase, and the mean value was used in analyses. Oscillometer cuffs of bladder width 2.0 cm (S1) and 2.5 cm (S2) were placed proximal to the carpus and tarsus. Cuff width to circumference ratio was calculated. Oscillometer SAP, MAP and DAP were paired with corresponding IBP values. Agreement was assessed using linear mixed models (p < 0.05). RESULTS: Cuff ratios for both limbs were 41% (S1 cuff) and 50% (S2 cuff) and 122-139 paired observations were obtained. There was significant limb × cuff interaction with SAP and MAP. The oscillometer overestimated SAP and MAP on the pelvic limb and underestimated SAP and MAP on the thoracic limb. For SAP, the oscillometer overestimated by constant bias (-19 ± 2 mmHg) and proportional bias (0.28 ± 0.02 mmHg per 1 mmHg increase). For MAP, the oscillometer underestimated by constant bias (4 ± 2 mmHg) and was worse with S2 on the thoracic limb. Overestimation was similar between cuffs on the pelvic limb. For DAP, the oscillometer underestimated by constant bias (15 ± 2 mmHg). CONCLUSIONS AND CLINICAL RELEVANCE: Cuff S1 on the thoracic limb provided best estimation of MAP.

Evaluation of lung ventilation distribution using electrical impedance tomography in standing sedated horses with capnoperitoneum.

OBJECTIVE: To determine changes in distribution of lung ventilation with increasing intra-abdominal pressure (IAP) from carbon dioxide (CO2) insufflation in standing sedated horses. STUDY DESIGN: Prospective experimental study. ANIMALS: A group of six healthy adult horses. METHODS: Each horse was sedated with acepromazine, detomidine and butorphanol and sedation maintained with a detomidine infusion. The horse was restrained in a stocks system and a 32 electrode electrical impedance tomography (EIT) belt was wrapped around the thorax at the fifth-sixth intercostal space. EIT images and arterial blood samples for PaO2 and PaCO2, pH and lactate concentration were obtained during capnoperitoneum at 0 (baseline A), 5, 8 and 12 mmHg as IAP increased and at 8, 5, 0 (baseline B) mmHg as IAP decreased. At each IAP, after a 2 minute stabilization period, EIT images were recorded for ≥ 2 minutes to obtain five consecutive breaths. Statistical analysis was performed using anova for repeated measures with Geisser-Greenhouse correction and a Tukey's multiple comparison test for parametric data. The relationship between PaO2 and the center of ventilation in the ventral-dorsal (CoV-VD) and right-left (CoV-RL) directions or total impedance change as a surrogate for tidal volume (ΔZVT) were tested using linear regression analysis. Significance was assumed when p ≤ 0.05. RESULTS: There were no significant changes in CoV-VD, CoV-RL, PaO2, PaCO2, lactate concentration, pH, heart rate and respiratory rate with targeted IAP. There was a significant decrease in ΔZVT compared with baseline A at 5 mmHg IAP as IAP was increased. CONCLUSIONS AND CLINICAL RELEVANCE: Capnoperitoneum causes a significant decrease in ΔZVT in standing sedated horses with increasing IAP.

Plasma histamine concentrations in horses administered sodium penicillin, guaifenesin-xylazine-ketamine and isoflurane with morphine or butorphanol.

OBJECTIVE: Various drugs administered to horses undergoing surgical procedures can release histamine. Histamine concentrations were evaluated in horses prepared for surgery and administered butorphanol or morphine intraoperative infusions. STUDY DESIGN: Prospective studies with one randomized. ANIMALS: A total of 44 client-owned horses. METHODS: In one study, anesthesia was induced with xylazine followed by ketamine-diazepam. Anesthesia was maintained with guaifenesin-xylazine-ketamine (GXK) during surgical preparation. For surgery, isoflurane was administered with intravenous (IV) morphine (group M: 0.15 mg kg-1 and 0.1 mg kg-1 hour-1; 15 horses) or butorphanol (group B: 0.05 mg kg-1 and 0.01 mg kg-1 hour-1; 15 horses). Histamine and morphine concentrations were measured using enzyme-linked immunoassay before opioid injection (time 0), and after 1, 2, 5, 30, 60 and 90 minutes. In a subsequent study, plasma histamine concentrations were measured in 14 horses before drug administration (baseline), 15 minutes after IV sodium penicillin and 15 minutes after starting GXK IV infusion. Statistical comparison was performed using anova for repeated measures. Pearson correlation compared morphine and histamine concentrations. Data are presented as mean ± standard deviation. Significance was assumed when p ≤ 0.05. RESULTS: With histamine, differences occurred between baseline (3.2 ± 2.4 ng mL-1) and GXK (5.2 ± 7.1 ng mL-1) and between baseline and time 0 in group B (11.9 ± 13.4 ng mL-1) and group M (11.1 ± 12.4 ng mL-1). No differences occurred between baseline and after penicillin or between groups M and B. Morphine concentrations were higher at 1 minute following injection (8.1 ± 5.1 ng mL-1) than at 30 minutes (4.9 ± 3.1 ng mL-1) and 60 minutes (4.0 ± 2.5 ng mL-1). Histamine correlated with morphine at 2, 30 and 60 minutes. CONCLUSIONS AND CLINICAL RELEVANCE: GXK increased histamine concentration, but concentrations were similar with morphine and butorphanol.

Comparison of mainstream (Capnostat 5) and two low-flow sidestream capnometers (VM-2500-S and Capnostream) in spontaneously breathing rabbits anesthetized with a Bain coaxial breathing system.

OBJECTIVE: To evaluate agreement with PaCO2 of two low sampling rate sidestream capnometers and a mainstream capnometer in rabbits and the effect of using high fresh gas flow from a Bain coaxial breathing system. STUDY DESIGN: Prospective, crossover study. ANIMALS: A total of 10 New Zealand White rabbits weighing 3.4 ± 0.3 kg [mean ± standard deviation (SD)]. METHODS: Two sidestream analyzers (Viamed VM-2500-S and Capnostream 35) with a sampling rate of 50 mL minute-1 and a mainstream capnometer (Capnostat 5) were tested. All capnometers used infrared spectroscopy and advanced microprocessor technology. Rabbits were anesthetized and intubated with noncuffed endotracheal tubes of 3 mm internal diameter and adequate seal. A sidestream sampling adapter or the mainstream capnometer was attached to the endotracheal tube and connected to a Bain coaxial breathing system. Oxygen (1.5 L minute-1) delivered sevoflurane to maintain anesthesia. An auricular artery catheter allowed blood sampling for PaCO2 analysis corrected to rectal temperature. Inspired and end-tidal carbon dioxide (Pe'CO2) measurements were recorded during blood sample withdrawal. From each rabbit, 10 paired PaCO2/Pe'CO2 measurements were obtained. Each rabbit was recovered from anesthesia and was anesthetized again with an alternate capnometer after 1 week. Data were analyzed using Bland-Altman and two-way anova for repeated measures. RESULTS: Analysis included 100 paired samples. Negative bias reflects underestimation of PaCO2. Bland-Altman mean (±1.95 SD) was -16.7 (-35.2 to 1.8) mmHg for Capnostat 5, -27.9 (-48.6 to -7.2) mmHg for Viamed, and -18.1 (-34.3 to -1.9) mmHg for Capnostream. Viamed PaCO2-Pe'CO2 gradient was greater than other two capnometers. CONCLUSIONS: All three capnometers underestimated PaCO2. Capnostat 5 and Capnostream performed similarly. CLINICAL RELEVANCE: These capnometers underestimated PaCO2 in spontaneously breathing rabbits anesthetized using a Bain coaxial breathing system with high fresh gas flows.

Effect of Instructional Format on Veterinary Students' Task Performance and Emotional State during a Simulation-Based Canine Endotracheal Intubation Laboratory: Handout versus Video.

Video- versus handout-based instructions may influence student outcomes during simulation training and competency-based assessments. Forty-five third-year veterinary students voluntarily participated in a simulation module on canine endotracheal intubation. A prospective, randomized, double-blinded study investigated the impact of video (n = 23) versus handout (n = 22) instructions on student confidence, anxiety, and task performance. Students self-scored their confidence and anxiety before and after the simulation. During the simulation laboratory, three raters independently evaluated student performance using a 20-item formal assessment tool with a 5-point global rating scale. No significant between- or within-group differences (p > .05) were found for both confidence and anxiety scores. Video-based instructions were associated with significantly higher (p < .05) total formal assessment scores compared with handout-based instructions. The video group had significantly higher scores than the handout group on 3 of the 20 individual skills (items) assessed: placement of tie to the adaptor-endotracheal tube complex (p < .05), using the anesthetic machine (p < .01), and pop-off valve management (p < .001). Inter-rater reliability as assessed by Cronbach's α (.92), and Kendall's W (.89) was excellent and almost perfect, respectively. A two-faceted crossed-design generalizability analysis yielded G coefficients for both the handout (Ep2 = .68) and the video (Ep2 = .72) groups. Video instructions may be associated with higher performance scores than handout instructions during endotracheal intubation simulation training. Further research into skill retention and learning styles is warranted.

Cardiopulmonary effects of an infusion of remifentanil or morphine in horses anesthetized with isoflurane and dexmedetomidine.

OBJECTIVE: To examine the cardiopulmonary effects of infusions of remifentanil or morphine, and their influence on recovery of horses anesthetized with isoflurane and dexmedetomidine. STUDY DESIGN: Randomized crossover study with 7-day rest periods. ANIMALS: Six adult horses (507 ± 61 kg). METHODS: After the horses were sedated with xylazine, anaesthesia was induced with ketamine and diazepam, and maintained with isoflurane. After approximately 60 minutes, a dexmedetomidine infusion was started (0.25 µg kg(-1) then 1.0 µg(-1) kg(-1) hour(-1) ) in combination with either saline (group S), morphine (0.15 mg kg(-1) then 0.1 mg kg(-1) hour(-1) ; group M), or remifentanil (6.0 µg kg(-1) hour(-1) ; group R) for 60 minutes. Mean arterial pressure, heart rate, end-tidal carbon dioxide tension, and end-tidal isoflurane concentration were recorded every 5 minutes. Core body temperature, cardiac output, right ventricular and arterial blood-gas values were measured every 15 minutes. Cardiac index, systemic vascular resistance (SVR), intrapulmonary shunt fraction, alveolar dead space, oxygen delivery and extraction ratio were calculated. Recoveries were videotaped and scored by two observers blinded to the treatment. Data were analyzed using repeated measures anova followed by Dunnett's or Bonferroni's significant difference test. Recovery scores were analyzed using a Kruskal-Wallis test. RESULTS: No significant differences were found among groups. Compared to baseline, heart rate decreased and SVR increased significantly in all groups, and cardiac index significantly decreased in groups S and M. Hemoglobin concentration, oxygen content and oxygen delivery significantly decreased in all groups. The oxygen extraction ratio significantly increased in groups M and R. Lactate concentration significantly increased in group S. Recovery scores were similar among groups. CONCLUSIONS AND CLINICAL RELEVANCE: Dexmedetomidine alone or in combination with remifentanil or morphine infusions was infused for 60 minutes without adverse effects in the 6 healthy isoflurane-anesthetized horses in this study.

Thoracic Electrical Impedance Tomography-The 2022 Veterinary Consensus Statement.

Electrical impedance tomography (EIT) is a non-invasive real-time non-ionising imaging modality that has many applications. Since the first recorded use in 1978, the technology has become more widely used especially in human adult and neonatal critical care monitoring. Recently, there has been an increase in research on thoracic EIT in veterinary medicine. Real-time imaging of the thorax allows evaluation of ventilation distribution in anesthetised and conscious animals. As the technology becomes recognised in the veterinary community there is a need to standardize approaches to data collection, analysis, interpretation and nomenclature, ensuring comparison and repeatability between researchers and studies. A group of nineteen veterinarians and two biomedical engineers experienced in veterinary EIT were consulted and contributed to the preparation of this statement. The aim of this consensus is to provide an introduction to this imaging modality, to highlight clinical relevance and to include recommendations on how to effectively use thoracic EIT in veterinary species. Based on this, the consensus statement aims to address the need for a streamlined approach to veterinary thoracic EIT and includes: an introduction to the use of EIT in veterinary species, the technical background to creation of the functional images, a consensus from all contributing authors on the practical application and use of the technology, descriptions and interpretation of current available variables including appropriate statistical analysis, nomenclature recommended for consistency and future developments in thoracic EIT. The information provided in this consensus statement may benefit researchers and clinicians working within the field of veterinary thoracic EIT. We endeavor to inform future users of the benefits of this imaging modality and provide opportunities to further explore applications of this technology with regards to perfusion imaging and pathology diagnosis.

Cardiopulmonary effects of using carbon dioxide for laparoscopic surgery in cats.

The cardiopulmonary effects of capnoperitoneum were investigated in 8 spontaneously breathing, young adult female cats undergoing laparoscopic pancreatic biopsy (intra-abdominal pressure 12 mmHg). Cats were premedicated with acepromazine and hydromorphone, induced with ketamine and diazepam, and maintained using an end-tidal isoflurane concentration of 1.13% in 100% oxygen. Direct systemic arterial blood pressure, heart and respiratory rates, end-tidal carbon dioxide (CO(2)), and isoflurane were recorded every 5 min before insufflation (baseline), during insufflation of the abdomen with CO(2), and following desufflation. Arterial blood samples were drawn at baseline, at 10 and 30 min of insufflation, and 5 min after desufflation for blood gases. The significant findings (P < 0.05) were as follows: insufflation produced an increase in heart rate (5 to 15 min and at 30 min), mean arterial blood pressure (25 to 30 min), and diastolic arterial blood pressure (10 to 30 min). After desufflation, respiratory rate increased for 15 min. The changes were within physiologically acceptable limits in these healthy, anesthetized cats despite no artificial maintenance of minute ventilation.

cAMP triggers Na+ absorption by distal airway surface epithelium in cystic fibrosis swine.

A controversial hypothesis pertaining to cystic fibrosis (CF) lung disease is that the CF transmembrane conductance regulator (CFTR) channel fails to inhibit the epithelial Na+ channel (ENaC), yielding increased Na+ reabsorption and airway dehydration. We use a non-invasive self-referencing Na+-selective microelectrode technique to measure Na+ transport across individual folds of distal airway surface epithelium preparations from CFTR-/- (CF) and wild-type (WT) swine. We show that, under unstimulated control conditions, WT and CF epithelia exhibit similar, low rates of Na+ transport that are unaffected by the ENaC blocker amiloride. However, in the presence of the cyclic AMP (cAMP)-elevating agents forskolin+IBMX (isobutylmethylxanthine), folds of WT tissues secrete large amounts of Na+, while CFTR-/- tissues absorb small, but potentially important, amounts of Na+. In cAMP-stimulated conditions, amiloride inhibits Na+ absorption in CFTR-/- tissues but does not affect secretion in WT tissues. Our results are consistent with the hypothesis that ENaC-mediated Na+ absorption may contribute to dehydration of CF distal airways.