Comparison of two different methods for physiologic dead space measurements in ventilated dogs in a clinical setting.

OBJECTIVE: To compare physiologic dead space (V(D)) and physiologic dead space to tidal volume (V(T)) ratio (V(D)/V(T)) obtained by an automated single breath test for carbon dioxide (CO(2)) (method SBT) and a manual calculation (method MC) in ventilated healthy dogs. STUDY DESIGN: Prospective clinical study. ANIMALS: Twenty client-owned dogs, ASA I and II undergoing anaesthesia for clinical purposes. METHODS: Following pre-medication, induction of anaesthesia, and intubation of the trachea, intermittent positive pressure ventilation was commenced. Mixed expired CO(2) partial pressure (PeCO(2)) was measured by two methods: method MC by analysis, using an infrared capnograph, of the expired gas collected in a mixing box and method SBT which calculated it automatically by a device consisting of a mainstream capnograph and a pneumotachograph. At four time points arterial partial pressure of CO(2) (PaCO(2)) was measured. Physiologic dead space variables (V(D) and V(D)/V(T)) were calculated manually (method MC) or automatically (method SBT) using the Bohr-Enghoff equation. Method MC and SBT were compared using Bland-Altman plots and linear regression. Intra-class correlation coefficient (ICC) was used to measure consistency of each method. RESULTS: Four measurement pairs were obtained in all 20 dogs for method SBT and MC. The bias was -1.15 mmHg, 7.97 mL and 0.02 for PeCO(2), V(D) and V(D)/V(T), respectively. Linear regression analysis revealed a correlation coefficient (r(2)) of 0.79, 0.94, and 0.83 for PeCO(2), V(D) and V(D)/V(T), respectively. The ICC revealed an excellent consistency for both methods. CONCLUSIONS: The single breath test (SBT) can be used for clinical evaluation of V(D) and V(D)/V(T) in anaesthetized ventilated dogs. CLINICAL RELEVANCE: Through measuring V(D) and V(D)/V(T) important information about lung ventilation can be obtained and the SBT is an easy method to use for this purpose.

Cardiovascular effects following epidural injection of romifidine in isoflurane-anaesthetized dogs.

OBJECTIVE: To investigate the cardiovascular effects of epidural romifidine in isoflurane-anaesthetized dogs. STUDY DESIGN: Prospective, randomized, blinded experiment. ANIMALS: A total of six healthy adult female Beagles aged 1.25 +/- 0.08 years and weighing 12.46 +/- 1.48 (10.25-14.50) kg. METHODS: Anaesthesia was induced with propofol (6-9 mg kg(-1)) and maintained with 1.8-1.9% end-tidal isoflurane in oxygen. End-tidal CO(2) was kept between 35 and 45 mmHg (4.7-6.0 kPa) using intermittent positive pressure ventilation. Heart rate (HR), arterial blood pressure and cardiac output (CO) were monitored. Cardiac output was determined using a LiDCO monitor and the derived parameters were calculated. After baseline measurements, either 10 microg kg(-1) romifidine or saline (total volume 1 mL 4.5 kg(-1)) was injected into the lumbosacral epidural space. Data were recorded for 1 hour after epidural injection. A minimum of 1 week elapsed between treatments. RESULTS: After epidural injection, the overall means (+/- standard deviation, SD) of HR (95 +/- 20 bpm), mean arterial blood pressure (MAP) (81 +/- 19 mmHg), CO (1.63 +/- 0.66 L minute(-1)), cardiac index (CI) (2.97 +/- 1.1 L minute(-1) m(-2)) and stroke volume index (SI) (1.38 +/- 0.21 mL beat(-1) kg(-1)) were significantly lower in the romifidine treatment compared with the overall means in the saline treatment [HR (129 +/- 24 bpm), MAP (89 +/- 17 mmHg), CO (3.35 +/- 0.86 L minute(-1)), CI (6.17 +/- 1.4 L minute(-1) m(-2)) and SI (2.21 +/- 0.21 mL beat(-1) kg(-1))]. The overall mean of systemic vascular resistance index (SVRI) (7202 +/- 2656 dynes seconds cm(-5) m(-2)) after epidural romifidine injection was significantly higher than the overall mean of SVRI (3315 +/- 1167 dynes seconds cm(-5) m(-2)) after epidural saline injection. CONCLUSION: Epidural romifidine in isoflurane-anaesthetized dogs caused significant cardiovascular effects similar to those reportedly produced by systemic romifidine administration. CLINICAL RELEVANCE: Similar cardiovascular monitoring is required after epidural and systemically administered romifidine. Further studies are required to evaluate the analgesic effects of epidural romifidine.

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

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

Technical validation of a face mask adapted for dry powder inhalation in the equine species.

Development of dry powder inhalation (DPI) for horses requires the use of an adapted face mask. In experiment I, 4 masks (A, B, C and D) were tested and factors influencing the delivery of the dry powder were determined. Mask A was one which is commercially available for metered-dose inhalation. Mask B had the same shape as Mask A but an airtight rubber seal was added for the connection between the mask and horse's head. Mask C was a prototype adapted for DPI with connection for the DPI device between the nostrils, airtight expiratory valves in front of each nostril and airtight rubber seal to attach the mask on the horse's head. Mask D was the same as Mask C but the airtight expiratory valve was situated in front of one nostril and the connection for the DPI device was placed in front of the other nostril. Inhalet emptying and peak inspiratory pressure were measured on 5 healthy horses with each face mask. Both Masks A and B gave a low rate of inhalet emptying. Inspiratory pressures created in Masks C and D were negative enough to ensure inhalet emptying rates of mean +/- s.d. 98.28 +/- 1.79% and 100% respectively. In experiment 2, the face masks giving the greatest inhalet emptying were used to test the therapeutic efficacy of ipratropium bromide DPI. This was tested on 6 horses suffering from acute exacerbation of chronic obstructive pulmonary disease (COPD). At a dose of 200 micrograms/100 kg bwt, ipratropium administered with Mask D improved significantly pulmonary function measurements compared to baseline values and placebo inhalation. With Mask C, a double dose of ipratropium (400 micrograms/100 kg bwt) was necessary to improve these parameters compared to baseline values. This indicated the importance of locating the DPI device in front of one nostril. It was concluded that inhalet emptying is correlated to inspiratory pressures measured in the face masks. Secondly, these pressures are in turn dependent on the air-tightness of the mask, i.e. air-tightness of the expiratory valve and close connection between the horse's head and the mask. Thirdly, position of the DPI device in front of a nostril allows bronchodilation at a dose half that required when the device is placed between the nostrils. Finally DPI using Mask D (EquiPoudre) is a rapid, effective and well tolerated inhalation treatment for COPD horses.

Cardiovascular and respiratory effects of inspired oxygen fraction in halothane-anesthetized horses.

Anesthesia of equids is associated with pulmonary dysfunction. Cardiovascular and respiratory effects of inhalation anesthetic agents and duration of anesthesia have been studied, using oxygen as the carrier gas. To our knowledge, the effects of inspired oxygen have not been determined. We studied the cardiovascular and respiratory effects of 2 inspired oxygen fractions (0.30 and greater than 0.85) in 5 laterally recumbent, halothane-anesthetized horses. Mean systemic arterial blood pressure, cardiac output, central venous pressure, pulmonary arterial pressure, arterial pH, and arterial base excess were similar in horses of the 2 groups during 4 hours of anesthesia at constant end-tidal halothane concentration. End-tidal partial pressure of CO2, arterial partial pressure of CO2 and O2, and alveolar-to-arterial O2 tension difference were greater in horses exposed to the higher oxygen concentration. On the basis of the data obtained, we suggest that greater hypoventilation and ventilation/perfusion mismatch occur when horses are breathing high-oxygen fraction. Arterial partial pressure of O2 was not different between the 2 groups of horses after they were disconnected from the anesthesia circuit and allowed to breathe room air. Horses recovered from anesthesia without complications.

The effect of common bovine respiratory diseases on tidal breathing flow-volume loops.

In order to better understand the bovine breathing pattern, tidal breathing flow-volume loops (TBFVL) were analyzed in 24 healthy cattle of different body weights (range: 37-660 kg) (Group A) and in 28 cattle suffering from the common respiratory diseases: verminous bronchitis (Group B); shipping fever (Group C); acute respiratory distress syndrome (Group D); respiratory syncytial virus pneumonia (Group E); organophosphate poisoning (Group F); and necrotic laryngitis (Group G). Respiratory airflow and tidal volume were measured with a breathing mask-Fleisch pneumotachograph assembly. TBFVL were traced from these values using a computerized method. All the loop indices proposed by Amis and Kurpershoek (1986a) were calculated from 5 representative breathing cycles for each of the 52 animals. The TBFVL shapes and indices were relatively constant in most healthy cattle and were not correlated with the body size. When compared to normal values, animals with moderate respiratory syndromes (Groups B and C) had a more flattened shape to their TBFVL. On the other hand, in most cattle with severe respiratory pathologies (Groups D, F and G expiration tended to be biphasic with the peak expiratory flow (PEF) occurring significantly later than in healthy animals. Both PEF and peak inspiratory flow were increased in all the pathological conditions. The TBFVL indices were more frequently and more severely changed during expiration than during inspiration.

Temperature and humidity of expired air of sheep.

The temperature and humidity of expired air from three adult Merino sheep were measured at air temperatures of 20, 30 and 40 degrees C before and after the animals were shorn. Expired air was apparently always saturated with water vapour. At the higher air temperatures the temperature of expired air was close to deep body temperature; at lower air temperatures, expired air had been significantly cooled, e.g. to 32.3 degrees C in shorn sheep at 20 degrees C air temperature. Expired air was cooler from shorn than from unshorn animals at 20 and 30 degrees C air temperature, possibly due to thermally induced vasomotor changes in the upper respiratory tract. Cooling of expired air would be expected to lead to recovery of some of the water evaporated during inspiration; at 20 degrees C air temperature, this fraction was estimated to be 25% in unshorn sheep and 36% in shorn sheep.

Radiographic characterization of diaphragmatic excursion in halothane-anesthetized ponies: spontaneous and controlled ventilation systems.

A radiograph technique for identification of diaphragmatic segments and quantitation of their contribution to total diaphragmatic function was developed. five anesthetized ponies were studied on 3 separate occasions. Studies were made of the ponies in left lateral recumbency at 2 anesthetic levels (1 and 2 minimal alveolar anesthetic concentrations; halothane) and under spontaneous and controlled ventilation systems. General pattern of diaphragmatic displacement was unchanged by increased depth of anesthesia. Controlled ventilation altered the pattern of diaphragmatic displacement. Diaphragmatic displacement and regional volume changes were a function of active contraction or passive movement.

Flow rates from an intermittent positive pressure breathing-anesthetic delivery apparatus for horses.

Inspiratory flow rates were measured and compared in an equine intermittent positive pressure breathing-anesthesia delivery apparatus powered by a positive phase ventilator, a positive-negative phase ventilator, and a modified positive phase ventilator with automatic flow acceleration at driving pressures of 2,600, 4,400, and 5,200 mm of Hg (50, 85, and 100 psi). The last-named apparatus consistently produced the highest flows for a given ventilator setting and driving pressure. Regardless of the unit used, the greater driving pressures and high ventilator range settings produced the greatest flows.

Ventilation and cardiovascular studies during mechanical control of ventilation in horses.

Eleven out of 12 horses were underventilating while breathing spontaneously during halothane anaesthesia with high arterial carbon dioxide tensions. In addition, large alveolar to arterial oxygen tension gradients were found to be present. Mechanically, controlled ventilation with an intermittent positive pressure of 20-30 cm H2O reduced arterial carbon dioxide levels to normal. The alveolar to arterial oxygen gradients did not increase and in some cases decreased. These (A - a) Po2 gradients were due mainly to true shunt of the order of 30 per cent and not to ventilation perfusion inequality.