Ventilation distribution assessed with electrical impedance tomography and the influence of tidal volume,recruitment and positive end-expiratory pressure in isoflurane-anesthetized dogs

Objective

To examine the intrapulmonary gas distribution of low and high tidal volumes (V_T) and to investigate whether this is altered by an alveolar recruitment maneuver (ARM) and 5 cmH₂O positive end-expiratory pressure (PEEP) during anesthesia.

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

ObjectivesTo 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 designProspective randomized crossover study.AnimalsA total of seven healthy male Beagle dogs, aged 1 year and weighing 10.2 ± 0.7 kg (mean ± standard deviation).MethodsThe 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.ResultsCardiac 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 relevanceThe 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.     

Effects of acepromazine on pulmonary gas exchange and circulation during sedation and dissociative anaesthesia in horses

OBJECTIVE: To study pulmonary gas exchange and cardiovascular responses to sedation achieved with romifidine and butorphanol (RB) alone, or combined with acepromazine, and during subsequent tiletamine-zolazepam anaesthesia in horses. ANIMALS: Six (four males and two females) healthy Standardbred trotters aged 3-12 years; mass 423-520 kg. STUDY DESIGN: Randomized, cross-over, experimental study. MATERIALS AND METHODS: Horses were anaesthetized on two occasions (with a minimum interval of 1 week) with intravenous (IV) tiletamine-zolazepam (Z; 1.4 mg kg(-1)) after pre-anaesthetic medication with IV romifidine (R; 0.1 mg kg(-1)) and butorphanol (B; 25 microg kg(-1) IV). At the first trial, horses were randomly allocated to receive (protocol ARBZ) or not to receive (protocol RBZ) acepromazine (A; 35 microg kg(-1)) intramuscularly (IM) 35 minutes before induction of anaesthesia. Each horse was placed in left lateral recumbency and, after tracheal intubation, allowed to breathe room air spontaneously. Respiratory and haemodynamic variables and ventilation-perfusion (; multiple inert gas elimination technique) ratios were determined in the conscious horse, after sedation and during anaesthesia. One- and two-way repeated-measures anova were used to identify within- and between-technique differences, respectively. RESULTS: During sedation with RB, arterial oxygen tension (PaO(2)) decreased compared to baseline and increased mismatch was evident; there was no O(2) diffusion limitation or increase in intrapulmonary shunt fraction identified. With ARB, PaO(2) and remained unaffected. During anaesthesia, intrapulmonary shunt occurred to the same extent in both protocols, and mismatching increased. This was less in the ARBZ group. Arterial O(2) tension decreased in both protocols, but was lower at 25 and 35 minutes of anaesthesia in RBZ than in ARBZ. During sedation, heart rate (HR) and cardiac output (Qt) were lower while arterial-mixed venous oxygen content differences and haemoglobin concentrations were higher in RBZ compared with ARBZ. Total systemic vascular resistance, mean systemic, and mean pulmonary arterial pressures were higher during anaesthesia with RBZ compared to ARBZ. CONCLUSIONS AND CLINICAL RELEVANCE: Acepromazine added to RB generally improved haemodynamic variables and arterial oxygenation during sedation and anaesthesia. Arterial oxygenation was impaired as a result of increased shunt and mismatch during anaesthesia, although acepromazine treatment reduced disturbances and falls in PaO(2) to some extent. Haemodynamic variables were closer to baseline during sedation and anaesthesia when horses received acepromazine. Acepromazine may confer advantages in healthy normovolaemic horses.     

Effects of two fractions of inspired oxygen on lung aeration and gas exchange in cats under inhalant anaesthesia

ObjectiveTo compare the effects of two fractions of inspired oxygen (FiO₂) (0.4 and 1) on lung aeration and gas exchange during general anaesthesia in cats.Study designRandomized, blinded, controlled study.AnimalsThirty healthy, mixed breed, client owned female cats.Materials and methodsCats were premedicated intramuscularly with acepromazine (0.03 mg kg^?1) and medetomidine (0.015 mg kg^?1). Anaesthesia was induced with propofol (5 mg kg^?1) and, after orotracheal intubation, maintained with isoflurane carried by either 100% oxygen (G100, n = 15) or an oxygen-air mixture with 40% oxygen (G40, n = 15). All cats were placed in dorsal recumbency and breathed spontaneously throughout the entire procedure. Following surgery (ovariectomy), a spiral computed tomography (CT) of the thorax was performed, arterial oxygen (PaO₂) and carbon dioxide (PaCO₂) tensions were measured and alveolar-arterial gradient of oxygen [P(A-a)O₂] calculated. The CT images were analysed for lung aeration by the analysis of radiograph attenuations (Hounsfield units, HU), according to the following classification: hyperinflated area (-1000 to -900 HU), normally aerated area (-900 to -500 HU), poorly aerated area (-500 to -100 HU) and non-aerated area (-100 to +100 HU). The groups were compared using one-way anova.ResultsCompared to G100, the normally-aerated lung area was significantly greater and the poorly-aerated and non-aerated areas were significantly smaller in G40. PaCO₂ was similar in both groups. PaO₂ and P(A-a)O₂ were significantly higher in G100. In both groups, pulmonary atelectasis developed preferentially in the caudal lung fields.ConclusionIn cats anaesthetised with isoflurane, the administration of an FiO₂ of >0.9 significantly impaired lung aeration and gas exchange as compared to an FiO₂ of 0.4.Clinical relevanceAn FiO₂ of 0.4 may better preserve lung aeration and gas exchange in anaesthetised spontaneously breathing cats but monitoring is essential to ensure oxygenation is adequate.     

Assessment of distribution of ventilation and regional lung compliance by electrical impedance tomography in anaesthetized horses undergoing alveolar recruitment manoeuvres

Objective

To examine changes in the distribution of ventilation and regional lung compliances in anaesthetized horses during the alveolar recruitment manoeuvre (ARM).

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.

Intermittent positive pressure ventilation with constant positive end-expiratory pressure and alveolar recruitment manoeuvre during inhalation anaesthesia in horses undergoing surgery for colic, and its influence on the early recovery period

Objective To compare, ventilation using intermittent positive pressure ventilation (IPPV) with constant positive end‐expiratory pressure (PEEP) and alveolar recruitment manoeuvres (RM) to classical IPPV without PEEP on gas exchange during anaesthesia and early recovery. Study design Prospective randomized study. Animals Twenty‐four warm‐blood horses, weight mean 548 ± SD 49 kg undergoing surgery for colic. Methods Premedication, induction and maintenance (isoflurane in oxygen) were identical in all horses. Group C (n = 12) was ventilated using conventional IPPV, inspiratory pressure (PIP) 35–45 cmH₂O; group RM (n = 12) using similar IPPV with constant PEEP (10 cmH₂O) and intermittent RMs (three consecutive breaths PIP 60, 80 then 60 cmH₂O, held for 10–12 seconds). RMs were applied as required to maintain arterial oxygen tension (PaO₂) at >400 mmHg (53.3 kPa). Physiological parameters were recorded intraoperatively. Arterial blood gases were measured intra‐ and postoperatively. Recovery times and quality of recovery were measured or scored. Results Statistically significant findings were that horses in group RM had an overall higher PaO₂ (432 ± 101 mmHg) than those in group C (187 ± 112 mmHg) at all time points including during the early recovery period. Recovery time to standing position was significantly shorter in group RM (49.6 ± 20.7 minutes) than group C (70.7 ± 24.9). Other measured parameters did not differ significantly. The median (range) of number of RMs required to maintain PaO₂ above 400 mmHg per anaesthetic was 3 (1–8). Conclusion Ventilation using IPPV with constant PEEP and RM improved arterial oxygenation lasting into the early recovery period in conjunction with faster recovery of similar quality. However this ventilation mode was not able to open up the lung completely and to keep it open without repeated recruitment. Clinical relevance This mode of ventilation may provide a clinically practicable method of improving oxygenation in anaesthetized horses.     

Effects of intraoperative positive end-expiratory pressure and fraction of inspired oxygen on postoperative oxygenation in dogs undergoing stifle surgery

ObjectiveTo compare the effects of fraction of inspired oxygen (FiO₂) with the addition of positive end-expiratory pressure (PEEP) during anesthesia on arterial oxygenation in the first 4 postoperative hours in dogs. We hypothesized that compared with dogs breathing FiO₂ ≥ 0.95 and no PEEP (ZEEP), the use of intraoperative PEEP would improve postoperative oxygenation, and that the use of PEEP combined with an FiO₂ of 0.4 would further improve it.Study designProspective, randomized study.AnimalsA total of 30 dogs undergoing unilateral stifle surgery.MethodsUsing a standardized anesthetic protocol, dogs were assigned to either FiO₂ ≥ 0.95 and ZEEP, FiO₂ ≥ 0.95 and 5 cmH₂O PEEP or FiO₂ 0.4 and 5 cmH₂O PEEP. All dogs were mechanically ventilated with a tidal volume of 12 mL kg^–1. Dogs breathed room air after recovery from anesthesia. Arterial blood gases were measured during surgical closure and 10, 120 and 240 minutes after extubation. Demographic characteristics were compared with Kruskal–Wallis tests. The effects of treatment and time on the PaO₂, PaCO₂, PaO₂:FiO₂ and shunt fraction (F-shunt) were assessed with mixed-effect models.ResultsThe PaO₂ and F-shunt were lower during anesthesia for dogs breathing FiO₂ 0.4. No differences among groups were measured after extubation for any variable.Conclusions and clinical relevanceCompared with dogs ventilated with FiO₂ ≥ 0.95 and ZEEP, application of 5 cmH₂O PEEP did not improve intraoperative gas exchange. The combination of 5 cmH₂O PEEP and FiO₂ 0.4 resulted in lower intraoperative F-shunt values. However, no benefits from those maneuvers on postoperative PaO₂ and F-shunt were recorded after extubation, suggesting that alterations in pulmonary function imposed by anesthesia were reversed soon after extubation.     

高温对金荞麦光合气体交换和叶绿素荧光特性的影响

以8个野生金荞麦(Fagopyrum dibotrys)种质为试材,在室内模拟35和45℃高温胁迫,测定了各种质气体交换和叶绿素荧光参数,探讨金荞麦对高温胁迫的光合适应机制,并在利用主成分分析和隶属函数法综合考虑各综合指标权重的基础上,评价种质间耐热性强弱。随着高温胁迫强度的增加,各金荞麦种质的净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)、水分利用效率(WUE)、PSⅡ的潜在活性(Fv/Fo)、最大光化学效率(Fv/Fm)、实际光量子产量(Yield)和光化学猝灭系数(qP)等参数均逐渐降低;叶片非光化学荧光猝灭系数(NPQ)则先增加后降低(JQ4、JQ5和JQ7)或一直增加(JQ1、JQ2、JQ3、JQ6和JQ8)。利用主成分分析将9个单项指标转换为相互独立的两个综合指标(第一、二主成分),其权重分别为0.816和0.184。隶属函数法综合评价出8个金荞麦种质耐热性顺序分别为JQ6JQ2JQ3JQ1JQ8JQ4JQ5JQ7。为抵御高温,耐热性强的金荞麦种质通过调节气孔导度,减小蒸腾速率,提高水分利用率,并将过剩的激发能以热的形式耗散掉,以保护光合机构。     

Effects of inhaled ipratropium bromide on breathing mechanics and gas exchange in exercising horses with chronic obstructive pulmonary disease

Six Warmblood horses suffering an acute exacerbation of COPD were tested to investigate whether inhalation of ipratropium bromide (IB) dry powder (2,400 microg) 30 min preexercise would improve their exercise capacity. A cross-over protocol with an inert powder placebo (P) was used. Mechanics of breathing and arterial blood gases were determined before treatment, after treatment but pre-exercise, and during an incremental exercise test. Oxygen consumption (VO2) was also measured before and during exercise, and the time to fatigue recorded. Inhalation of IB reduced total pulmonary resistance (RL) and maximum intrapleural pressure changes (deltaPpl(max)) and increased dynamic compliance before exercise. The onset of exercise was associated with a marked decrease in RL in P-treated horses but not those receiving IB, so that RL during exercise was not affected by treatment. Although deltaPpl(max) was lower at 8,9 and 10 m/s with IB, there were no treatment-related changes in VO2, blood gases, time to fatigue or any other measurement of breathing mechanics. Therefore, although inhalation of IB prior to exercise may have improved deltaPpl(max), it had no apparent impact on the horses' capacity for exercise.     

Effect of passive pneumoperitoneum on oesophageal pressure, cardiovascular parameters and blood gas analysis in horses

Reasons for performing study: Standing surgical procedures are being employed to an ever‐greater extent in horses. Pneumoperitoneum during abdominal surgery might adversely affect the work of breathing. Objectives: To determine whether development of pneumoperitoneum during abdominal surgery adversely influences the work of breathing. Methods: Eight healthy mature horses were equipped with carotid artery and thoracic vena cava catheters and an intraluminal manometry system. The following measurements were obtained before and at +5, +10, +15 and +30 min following establishment of pneumoperitoneum by paralumbar puncture using an 8 gauge needle: vital signs, oesophageal pressure, gastric pressure, arterial and central venous blood pressures, and arterial and mixed venous blood gas analyses. Results: Significant changes in oesophageal pressure, central venous pressure and results of arterial and mixed venous blood gas analysis were not detected. Arterial diastolic and mean pressures and rectal temperature increased slightly (P≤0.05). Conclusions: Passive pneumoperitoneum did not adversely affect breathing mechanics or haemodynamic variables under experimental conditions. Changes in arterial pressure could have occurred as a response to the passive pneumoperitoneum or be related to handling stress. Subtle variations in rectal temperature were not clinically relevant and likely resulted from stress associated with restraint. Potential relevance: It is unlikely that mature horses will develop signs of respiratory difficulty as a result of the development of passive pneumoperitoneum during standing laparoscopy.     

PRRSV和PCV2共感染对猪肺泡巨噬细胞CD80-CD86mRNA转录的影响

用猪生殖与呼吸综合征病毒（PRRSV）与猪圆环病毒2型（PCV2）共感染40日龄健康大白仔猪，利用实时荧光定量PCR技术对共感染仔猪肺泡巨噬细胞（PAM）共刺激分子CD80一CD86的mRNA转录水平进行了定量分析。结果表明，在感染后第3d和第7dCD80与CD86mRNA转录显著下调（P〈0．05），感染后第14dCD86mRNA转录水平仍低于未感染对照组。尽管CD80mRNA转录水平在第14d和第28d高于对照组，CD86mRNA转录水平在第28d高于对照组，两者在第42d均高于对照组，但无显著差异。证实，PRRSV和PCV2共感染可导致猪肺泡巨噬细胞的共刺激分子CD80-CD86基因转录在感染早期明显受到抑制，PAM的抗原呈递能力受到影响。     

Effects of dobutamine on cardiovascular function and respiratory gas exchange after enoximone in isoflurane-anaesthetized ponies

ObjectiveTo evaluate the combined effects of enoximone and dobutamine on the cardiovascular system and respiratory gas exchange in isoflurane-anaesthetized ponies.Study designProspective, randomized, experimental study.AnimalsSix ponies (286 ± 52 kg), aged 5.0 ± 1.6 years.MethodsAfter sedation (romifidine 80 μg kg⁻¹), anaesthesia was induced with midazolam (0.06 mg kg⁻¹) and ketamine (2.2 mg kg⁻¹) and maintained with isoflurane in oxygen. The ponies were ventilated to maintain eucapnia. After 90 minutes (=T0), enoximone alone (0.5 mg kg⁻¹) (E) or enoximone, followed by a constant rate infusion of dobutamine (0.5 μg kg⁻¹ minute⁻¹) (ED) for 120 minutes, was administered. Each pony received both treatments in a crossover trial, with at least 2 weeks between treatments. Heart rate (HR), cardiac output (CO), stroke volume (SV), right atrial (RAP), systolic (SAP), diastolic (DAP) and mean arterial pressure (MAP), blood gases, systemic vascular resistance (SVR), oxygen delivery (D⌽O₂) and several respiratory gas exchange variables were measured before treatment and until T120. Statistical analysis was based on a mixed model with treatment, time and their interaction as fixed categorical effects, pony as random effect, comparing treatments globally (α = 0.05) and at specific timepoints (Bonferroni-adjusted α = 0.00625).ResultsCompared to enoximone alone, ED treatment produced an increase in HR, CO, SV, RAP, SAP, DAP, MAP, packed cell volume (PCV) and D⌽O₂. The difference was significant from T60 to T120 (except at T80) for HR, throughout the observational period for CO, SAP, MAP, PCV and D⌽O₂, from T40 to T120 for DAP, at T10,T60,T80 and T120 for SV and at T10 and T20 for RAP. Overall decreases occurred in SVR and dead space ventilation (V_D/V_T). V_D/V_T was lower at T20 and from T80 to T120. Venous oxygen saturation was increased from T60 onwards.Conclusions and clinical relevanceThe results suggest that enoximone and dobutamine have additive cardiovascular effects and reduce V_D/V_T in isoflurane-anaesthetized ponies.     

Effects of in vitro exposure to hay dust on expression of interleukin-17, -23, -8, and -1beta and chemokine (C-X-C motif) ligand 2 by pulmonary mononuclear cells isolated from horses chronically affected with recurrent airway disease

OBJECTIVE: To examine effects of in vitro exposure to solutions of hay dust, lipopolysaccharide (LPS), or beta-glucan on cytokine expression in pulmonary mononuclear cells isolated from healthy horses and horses with recurrent airway obstruction (RAO). ANIMALS: 8 RAO-affected and 7 control horses (experiment 1) and 6 of the RAO-affected and 5 of the control horses (experiment 2). PROCEDURES: Bronchoalveolar lavage cells were isolated from horses that had been stabled and fed dusty hay for 14 days. Pulmonary mononuclear cells were incubated for 24 (experiment 1) or 6 (experiment 2) hours with PBS solution or solutions of hay dust, beta-glucan, or LPS. Gene expression of interleukin (IL)-17, IL-23(p19 and p40 subunits), IL-8, IL-1beta, and chemokine (C-X-C motif) ligand 2 (CXCL2) was measured with a kinetic PCR assay. RESULTS: Treatment with the highest concentration of hay dust solution for 6 or 24 hours increased expression of IL-23(p19 and p40), IL-8, and IL-1beta in cells from both groups of horses and increased early expression of IL-17 and CXCL2 in RAO-affected horses. Lipopolysaccharide upregulated early expression of IL-23(p40) and IL-8 in cells from both groups of horses but only late expression of these cytokines in cells from RAO-affected horses. Treatment with beta-glucan failed to increase cytokine expression at 6 or 24 hours. CONCLUSIONS AND CLINICAL RELEVANCE: Cells from RAO-affected horses were not more responsive to the ligands tested than were cells from control horses, which suggests a minimal role of mononuclear cells in propagation of airway neutrophilia in horses with chronic RAO.