Blood-to-saliva glucose time lag in sedated healthy dogs.

The management of diabetes mellitus mandates measurement of blood glucose. Saliva offers an alternative to blood sampling, but measurement of the salivary glucose concentration is difficult, and the blood-to-saliva glucose time lag is uncertain. We aimed to determine the serum-saliva glucose time lag in the saliva of healthy dogs. The combined duct of the mandibular and sublingual salivary glands of 6 dogs was cannulated to collect saliva and prevent glucose degradation by oral bacteria. Following a 0.25 g/kg IV bolus of dextrose, paired serum-saliva samples were collected at baseline and in twelve 5-min blocks over 60 min. Serum and salivary glucose levels were analyzed with a linear mixed model for repeated measures with a compound symmetry error structure. Mean (±SD) saliva production was 10.3 ± 2.9 µL/kg/min, and the area under the curve (AUCglucose)saliva/serum ratio was 0.006, which highlights the magnitude of the large difference in glucose concentration between the 2 compartments. The serum-saliva glucose time lag was 30-40 min.

Repeatability and accuracy of fingertip pulse oximeters for measurement of hemoglobin oxygen saturation in arterial blood and pulse rate in anesthetized dogs breathing 100% oxygen.

OBJECTIVE: To evaluate the repeatability and accuracy of fingertip pulse oximeters (FPO) for measurement of hemoglobin oxygen saturation in arterial blood and pulse rate (PR) in anesthetized dogs breathing 100% O2. ANIMALS: 29 healthy client-owned anesthetized dogs undergoing various surgical procedures. PROCEDURES: In randomized order, each of 7 FPOs or a reference pulse oximeter (PO) was applied to the tongue of each intubated anesthetized dog breathing 100% O2. Duplicate measurements of oxygen saturation (Spo2) and PR were obtained within 60 seconds of applying an FPO or PO. A nonparametric version of Bland-Altman analysis was used. Coefficient of repeatability was the interval between the 5th and 95th percentiles of the differences between duplicate measurements. Bias was the median difference, and the limits of agreement were the 5th and 95th percentiles of the differences between each FPO and the PO. Acceptable values for the coefficient of repeatability of Spo2 were ≤ 6%. Agreements were accepted if the limits of agreement had an absolute difference of ≤ ± 3% in Spo2 and relative difference of ≤ ± 10% in PR. RESULTS: Coefficient of repeatability for Spo2 was acceptable for 5 FPOs, but the limits of agreement for Spo2 were unacceptable for all FPOs. The limits of agreement for PR were acceptable for 2 FPOs. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that some FPOs may be suitable for accurately monitoring PRs of healthy anesthetized dogs breathing 100% O2, but mild underestimation of Spo2 was common.

Quantification of reservoir bags as airway pressure-limiting devices in a nonrebreathing system.

OBJECTIVE: To evaluate the influence of reservoir bag types, volumes and previous use on the peak pressures (Pmax) and the times to develop 30 cmH2O pressure (P30) within a nonrebreathing system with a closed adjustable pressure-limiting (APL) valve. STUDY DESIGN: In vitro study using three-way factorial design with repeated measure on one factor. SUBJECTS: A total of 75 new anesthesia reservoir bags (five types, three volumes, five bags from each type × volume). The bag types were reusable latex (RL), disposable latex (DL) and three disposable neoprene (DN-1, DN-2 and DN-3). METHODS: Each bag was tested three times (treatments): new, after prestretching and 1 week later. The bags were attached to a Bain system and anesthesia machine with closed APL valve and patient port with O2 flow 2 L minute-1 until Pmax was reached. The Pmax and time to reach P30 values were determined from recorded pressure traces. General linear mixed model analysis was used to examine the effects of bag type, volume and treatment. One-sided 95% upper prediction limits of Pmax were calculated to test the null hypothesis that predicted Pmax of new bags would be ≥ 50 cmH2O for each factor combination. RESULTS: RL bags were the least and DN-3 bags were the most compliant. Prestretching increased compliance in all bag types. Smaller bags of RL, DL and DN-1 were less compliant than larger ones. The predicted Pmax values were < 50 cmH2O only for DN-3 bags after prestretching. The time to reach P30 was critically low when using 0.5 L bags (median 17 seconds). CONCLUSIONS AND CLINICAL RELEVANCE: To minimize the risk of barotrauma, highly compliant reservoir bags (e.g. DN-3) are recommended and reusable bags should be avoided. Bags should be prestretched before first use, 0.5 L bags should be avoided and fresh gas flow minimized.

The effect of midazolam or lidocaine administration prior to etomidate induction of anesthesia on heart rate, arterial pressure, intraocular pressure and serum cortisol concentration in healthy dogs.

OBJECTIVE: To evaluate selected effects of midazolam or lidocaine administered prior to etomidate for co-induction of anesthesia in healthy dogs. STUDY DESIGN: Prospective crossover experimental study. ANIMALS: A group of 12 healthy adult female Beagle dogs. METHODS: Dogs were premedicated with intravenous (IV) butorphanol (0.3 mg kg-1), and anesthesia was induced with etomidate following midazolam (0.3 mg kg-1), lidocaine (2 mg kg-1) or physiologic saline (1 mL) IV. Heart rate (HR), arterial blood pressure, respiratory rate (fR) and intraocular pressure (IOP) were recorded following butorphanol, after co-induction administration, after etomidate administration and immediately following intubation. Baseline IOP values were also obtained prior to sedation. Etomidate dose requirements and the presence of myoclonus, as well as coughing or gagging during intubation were recorded. Serum cortisol concentrations were measured prior to premedication and 6 hours following etomidate administration. RESULTS: Blood pressure, fR and IOP were similar among treatments. Blood pressure decreased in all treatments following etomidate administration and generally returned to sedated values following intubation. HR increased following intubation with midazolam and lidocaine but remained stable in the saline treatment. The dose of etomidate (median, interquartile range, range) required for intubation was lower following midazolam (2.2, 2.1-2.6, 1.7-4.1 mg kg-1) compared with lidocaine (2.7, 2.4-3.6, 2.2-5.1 mg kg-1, p = 0.012) or saline (3.0, 2.8-3.8, 1.9-5.1 mg kg-1, p = 0.015). Coughing or gagging was less frequent with midazolam compared with saline. Myoclonus was not observed. Changes in serum cortisol concentrations were not different among treatments. CONCLUSIONS AND CLINICAL RELEVANCE: Midazolam administration reduced etomidate dose requirements and improved intubation conditions compared with lidocaine or saline treatments. Neither co-induction agent caused clinically relevant differences in measured cardiopulmonary function, IOP or cortisol concentrations compared with saline in healthy dogs. Apnea was noted in all treatments following the induction of anesthesia and preoxygenation is recommended.

Influence of catecholamines at different dosages on the function of the LiDCO sensor in isoflurane anesthetized horses.

OBJECTIVE: To compare the lithium dilution method for cardiac output (LiDCO) and bolus-thermo-dilution (BTD) measurements before and during infusion of dobutamine, dopamine, phenylephrine, or noradrenaline at 2 different doses in anesthetized horses and to examine the correlation between sensor voltages (saline-blood exposed) and possible measurement errors. DESIGN: Prospective experimental study. SETTING: University teaching hospital. ANIMALS: Nine Warmblood horses. INTERVENTIONS: Following 90 minutes of equilibration, 3 different doses of dobutamine (0.5-3 µg/kg/min), dopamine (1-5 µg/kg/min), phenylephrine (0.5-3 µg/kg/min), or noradrenaline (0.1-0.5 µg/kg/min) were administered for 15 minutes in anesthetized horses, and measurements using the LiDCO were performed at the lowest and highest doses. Pairs of LiDCO and BTD measurements were collected and sensor voltages exposed to blood and saline were measured before and at the end of each infusion period. Agreement between LiDCO and BTD was assessed with the Bland-Altman method. MEASUREMENT AND MAIN RESULTS: The biases (2 standard deviations) before infusion of dobutamine, dopamine, phenylephrine, and noradrenaline were 1.1 (5.7), 1.6 (7.3), 0.2 (6.6), and 1.5 (4.1) L/min, respectively, and minimally and nonsignificantly changed following low-dose catecholamine infusions. Following infusion of higher doses, biases were significantly higher compared to baseline with 10.7 (7.8), 11.2 (11.9), 6.9 (11.7), and 3.5 (3.8) L/min, respectively. The difference between saline- and blood-exposed sensor voltage decreased during infusion of high doses of catecholamines with correlations (rs = 0.62) between cardiac output differences and sensor voltage differences (saline-blood). CONCLUSIONS: This study demonstrated that catecholamines could lead to overestimation in a dose-dependent fashion in LiDCO measurements. Monitoring changes in sensor voltage differences (saline-blood) is a valuable and clinically applicable tool to predict errors in LiDCO measurements.

Impact of four different recumbencies on the distribution of ventilation in conscious or anaesthetized spontaneously breathing beagle dogs: An electrical impedance tomography study.

The aim was to examine the effects of recumbency and anaesthesia on distribution of ventilation in beagle dogs using Electrical Impedance Tomography (EIT). Nine healthy beagle dogs, aging 3.7±1.7 (mean±SD) years and weighing 16.3±1.6 kg, received a series of treatments in a fixed order on a single occasion. Conscious dogs were positioned in right lateral recumbency (RLR) and equipped with 32 EIT electrodes around the thorax. Following five minutes of equilibration, two minutes of EIT recordings were made in each recumbency in the following order: RLR, dorsal (DR), left (LLR) and sternal (SR). The dogs were then positioned in RLR, premedicated (medetomidine 0.01, midazolam 0.1, butorphanol 0.1 mg kg-1 iv) and pre-oxygenated. Fifteen minutes later anaesthesia was induced with 1 mg kg-1 propofol iv and maintained with propofol infusion (0.1-0.2 mg kg-1 minute-1 iv). After induction, the animals were intubated and allowed to breathe spontaneously (FIO2 = 1). Recordings of EIT were performed again in four recumbencies similarly to conscious state. Centre of ventilation (COV) and global inhomogeneity (GI) index were calculated from the functional EIT images. Repeated-measures ANOVA and Bonferroni tests were used for statistical analysis (p < 0.05). None of the variables changed in the conscious state. During anaesthesia left-to-right COV increased from 46.8±2.8% in DR to 49.8±2.9% in SR indicating a right shift, and ventral-to-dorsal COV increased from 49.8±1.7% in DR to 51.8±1.1% in LLR indicating a dorsal shift in distribution of ventilation. Recumbency affected distribution of ventilation in anaesthetized but not in conscious dogs. This can be related to loss of respiratory muscle tone (e.g. diaphragm) and changes in thoracic shape. Changing position of thoraco-abdominal organs under the EIT belt should be considered as alternative explanation of these findings.

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). STUDY DESIGN: Experimental study in which a series of treatments were administered in a fixed order on one occasion. ANIMALS: Five adult Warmblood horses. METHODS: Animals were anaesthetized (xylazine, midazolam-ketamine, isoflurane), placed in dorsal recumbency and ventilated with 100% oxygen using peak inspiratory pressure (PIP) and positive end-expiratory pressure (PEEP) of 20 cmH2O and 0 cmH2O, respectively. Thoracic electrical impedance tomography (EIT), spirometry and routine anaesthesia monitoring were performed. At 90 minutes after induction of anaesthesia, PIP and PEEP were increased in steps of 5 cmH2O to 50 cmH2O and 30 cmH2O, respectively, and then decreased to baseline values. Each step lasted 10 minutes. Data were recorded and functional EIT images were created using three breaths at the end of each step. Arterial blood samples were analysed. Values for left-to-right and sternal-to-dorsal centre of ventilation (COV), lung compliances and Bohr dead space were calculated. RESULTS: Distribution of ventilation drifted leftward and dorsally during recruitment. Mean±standard deviation (SD) values at baseline and highest airway pressures, respectively, were 49.9±0.7% and 48.0±0.6% for left-to-right COV (p=0.009), and 46.3±2.0% and 54.6±2.0% for sternal-to-dorsal COV (p=0.0001). Compliance of dependent lung regions and PaO2 increased, whereas compliance of non-dependent lung regions decreased during ARM and then returned to baseline (p<0.001). Bohr dead space decreased after ARM (p=0.007). Interestingly, PaO2 correlated to the compliance of the dependent lung (r2=0.71, p<0.001). CONCLUSIONS AND CLINICAL RELEVANCE: The proportion of tidal volume distributed to dependent and left lung regions increased during ARM, presumably as a result of opening atelectasis. Monitoring compliance of the dependent lung with EIT may substitute PaO2 measurements during ARM to identify an optimal PEEP.

Influence of xylazine on the function of the LiDCO sensor in isoflurane anaesthetized horses.

OBJECTIVE: Previous studies showed an influence of xylazine on the LiDCO sensor in vitro and in standing horses, but did not prove that this interaction caused error in LiDCO measurements. Therefore, agreement of cardiac output (CO) measurements by LiDCO and bolus-thermodilution (BTD) was determined in horses receiving xylazine infusions. STUDY DESIGN: Prospective, experimental study. ANIMALS: Eight Warmblood horses. METHODS: All horses were premedicated with xylazine. Anaesthesia was induced with midazolam and ketamine and was maintained with isoflurane in oxygen. During six hours of anaesthesia CO measurements and blood samples were taken before, during and after a 60 minute period of xylazine infusion. Pairs of LiDCO and bolus thermo-dilution (BTD) measurements of CO were performed. Sensor voltages exposed to blood and saline were measured before, during and after xylazine infusion and compared using Bland-Altman method of agreement with corrections for repeated measures. RESULTS: The CO values (mean ± SD) before xylazine were 34.8 ± 7.3 and 36.4 ± 8.1 L minute(-1) for BTD and LiDCO, respectively. After starting the xylazine infusion, the CO values for BTD decreased to 27.5 ± 6.1 L minute(-1) whereas CO values measured by LiDCO increased to 54.7 ± 18.4 L minute(-1) . One hour after discontinuing xylazine infusion, CO values were 33 ± 6.7 and 36.5 ±11.9 L minute(-1) for BTD and LiDCO, respectively. The difference between saline and blood exposed sensor voltages decreased during xylazine infusion and these differences were positive numbers before but negative during the infusion. There were correlations between xylazine plasma concentrations, CO differences and sensor voltage differences (saline - blood). CONCLUSIONS AND CLINICAL RELEVANCE: This study proved that xylazine infusion caused concentration dependent bias in LiDCO measurements leading to an overestimation of readings. Sensor voltage differences (saline - blood) may become valuable clinical tool to predict drug-sensor interactions.

Variety of non-invasive continuous monitoring methodologies including electrical impedance tomography provides novel insights into the physiology of lung collapse and recruitment ­ case report of an anaesthetized horse.

INTRODUCTION: The use of alveolar recruitment maneuvers during general anaesthesia of horses is a potentially useful therapeutic option for the ventilatory management. While the routine application of recruitments would benefit from the availability of dedicated large animal ventilators their impact on ventilation and perfusion in the horse is not yet well documented nor completely understood. CASE HISTORY: A healthy 533 kg experimental horse underwent general anaesthesia in lateral recumbency. During intermittent positive pressure ventilation a stepwise alveolar recruitment maneuver was performed. MANAGEMENT: Anaesthesia was induced with ketamine and midazolam and maintained with isoflurane in oxygen using a large animal circle system. Mechanical ventilation was applied in pressure ventilation mode and an alveolar recruitment maneuver performed employing a sequence of ascending and descending positive end expiratory pressures. Next to the standard monitoring, which included spirometry, additionally three non-invasive monitoring techniques were used: electrical impedance tomography (EIT), volumetric capnography and respiratory ultrasonic plethysmography. The functional images continuously delivered by EIT initially showed markedly reduced ventilation in the dependent lung and allowed on-line monitoring of the dynamic changes in the distribution of ventilation during the recruitment maneuver. Furthermore, continuous monitoring of compliance, dead space fraction, tidal volumes and changes in end expiratory lung volume were possible without technical difficulties. FOLLOW: up The horse made an unremarkable recovery. CONCLUSION: The novel non-invasive monitoring technologies used in this study provided unprecedented insights into the physiology of lung collapse and recruitment. The synergic information of these techniques holds promise to be useful when developing and evaluating new ventilatory strategies in horses.

A novel flow partition device for spirometry during large animal anaesthesia.

OBJECTIVE: We describe and test a novel device for large animal anaesthesia monitoring that uses standard human medicine spirometry sensors. STUDY DESIGN: In-vitro study. METHODS: The device consists of two adapters that enable the flow to be split evenly into four tubes in parallel, each tube containing a D-lite sensor. The performance of this flow partitioning device (FPD) over a range of flows from 100 to 700 L minute⁻¹ was determined and the pressure versus flow relation, resistance and dead space was compared with a Horse-lite (Moens 2010). RESULTS: Equipped with four D-lite sensors, and a flow of 700 L minute⁻¹ the pressure drop of the FPD was 13.5 cm H2O, resistance 1.17 cm H2O second L⁻¹ and volume (potential dead space) 182 mL, compared to 2.8 cm H2O, 0.24 cm H2O second L⁻¹ and 54 mL respectively for the Horse-lite. The predicted value of the flow partition of » could be confirmed. Limits of agreement were found to be 4.2% in inspiratory direction and 7.1% in expiratory direction. CONCLUSIONS AND CLINICAL RELEVANCE: The FPD is an affordable device that extends the specification of any commercially available human spirometry sensors to large animal applications. However, an increase in total resistance and dead space has to be taken into account. Therefore, the new device could be useful during equine anaesthesia.

Vitamin D is a regulator of endothelial nitric oxide synthase and arterial stiffness in mice.

The vitamin D hormone 1α,25-dihydroxyvitamin D3 [1,25(OH)2D3] is essential for the preservation of serum calcium and phosphate levels but may also be important for the regulation of cardiovascular function. Epidemiological data in humans have shown that vitamin D insufficiency is associated with hypertension, left ventricular hypertrophy, increased arterial stiffness, and endothelial dysfunction in normal subjects and in patients with chronic kidney disease and type 2 diabetes. However, the pathophysiological mechanisms underlying these associations remain largely unexplained. In this study, we aimed to decipher the mechanisms by which 1,25(OH)2D3 may regulate systemic vascular tone and cardiac function, using mice carrying a mutant, functionally inactive vitamin D receptor (VDR). To normalize calcium homeostasis in VDR mutant mice, we fed the mice lifelong with the so-called rescue diet enriched with calcium, phosphate, and lactose. Here, we report that VDR mutant mice are characterized by lower bioavailability of the vasodilator nitric oxide (NO) due to reduced expression of the key NO synthesizing enzyme, endothelial NO synthase, leading to endothelial dysfunction, increased arterial stiffness, increased aortic impedance, structural remodeling of the aorta, and impaired systolic and diastolic heart function at later ages, independent of changes in the renin-angiotensin system. We further demonstrate that 1,25(OH)2D3 is a direct transcriptional regulator of endothelial NO synthase. Our data demonstrate the importance of intact VDR signaling in the preservation of vascular function and may provide a mechanistic explanation for epidemiological data in humans showing that vitamin D insufficiency is associated with hypertension and endothelial dysfunction.

Comparison of an infrared anaesthetic agent analyser (Datex-Ohmeda) with refractometry for measurement of isoflurane, sevoflurane and desflurane concentrations.

OBJECTIVE: To assess agreement between infrared (IR) analysers and a refractometer for measurements of isoflurane, sevoflurane and desflurane concentrations and to demonstrate the effect of customized calibration of IR analysers. STUDY DESIGN: In vitro experiment. SUBJECTS: Six IR anaesthetic monitors (Datex-Ohmeda) and a single portable refractometer (Riken). METHODS: Both devices were calibrated following the manufacturer's recommendations. Gas samples were collected at common gas outlets of anaesthesia machines. A range of agent concentrations was produced by stepwise changes in dial settings: isoflurane (0-5% in 0.5% increments), sevoflurane (0-8% in 1% increments), or desflurane (0-18% in 2% increments). Oxygen flow was 2 L minute(-1) . The orders of testing IR analysers, agents and dial settings were randomized. Duplicate measurements were performed at each setting. The entire procedure was repeated 24 hours later. Bland-Altman analysis was performed. Measurements on day-1 were used to yield calibration equations (IR measurements as dependent and refractometry measurements as independent variables), which were used to modify the IR measurements on day-2. RESULTS: Bias ± limits of agreement for isoflurane, sevoflurane and desflurane were 0.2 ± 0.3, 0.1 ± 0.4 and 0.7 ± 0.9 volume%, respectively. There were significant linear relationships between differences and means for all agents. The IR analysers became less accurate at higher gas concentrations. After customized calibration, the bias became almost zero and the limits of agreement became narrower. CONCLUSIONS AND CLINICAL RELEVANCE: If similar IR analysers are used in research studies, they need to be calibrated against a reference method using the agent in question at multiple calibration points overlapping the range of interest.

Effect of dexmedetomidine vs. acepromazine-methadone premedication on limb to lung circulation time in dogs.

The study compared limb-to-lung circulation times (CT) in dogs under general anaesthesia after premedication with dexmedetomidine (DEX) or acepromazine-methadone (ACE-M). Healthy male and female dogs (n=20) were randomly assigned to receive acepromazine 0.04mg/kg and methadone 0.2mg/kg intramuscularly (IM), or DEX 0.01mg/kg IM. Anesthesia was induced with propofol and maintained with isoflurane at similar concentration in both groups. Mechanical ventilation was started immediately (20breaths/min; inspiratory to expiratory ratio 1:2) and tidal volume was adjusted to achieve an end-tidal CO2 concentration (PE'CO2) of between 3.9 and 5.3kPa. Ten minutes later arterial blood gas was analyzed and baseline data recorded for 3 minutes. A single dose of sodium bicarbonate 0,5mEq/kg was administered intravenously over 10 s starting with inspiration. Limb-to-lung CT was defined as the time interval between the start of bicarbonate injection and the recording of the highest PE'CO2. Following bicarbonate administration, PE'CO2 increased, and then rapidly decreased to baseline in both groups. CT was shorter in the ACE-M group (20±2.3 vs. 27±5.1s). Bodyweight was higher in the ACE-M group (30.6±3.9 vs. 23.3±6.8kg). Mean arterial blood pressure was higher in the DEX group (92±9 vs. 73±7mmHg) but premedication with DEX significantly prolonged CT compared to premedication with ACE-M.

Measurement of tidal volume using respiratory ultrasonic plethysmography in anaesthetized, mechanically ventilated horses.

OBJECTIVE: To compare tidal volume estimations obtained from Respiratory Ultrasonic Plethysmography (RUP) with simultaneous spirometric measurements in anaesthetized, mechanically ventilated horses. STUDY DESIGN: Prospective randomized experimental study. ANIMALS: Five experimental horses. METHODS: Five horses were anaesthetized twice (1 week apart) in random order in lateral and in dorsal recumbency. Nine ventilation modes (treatments) were scheduled in random order (each lasting 4 minutes) applying combinations of different tidal volumes (8, 10, 12 mL kg(-1)) and positive end-expiratory pressures (PEEP) (0, 10, 20 cm H(2)O). Baseline ventilation mode (tidal volume=15 mL kg(-1), PEEP=0 cm H(2)O) was applied for 4 minutes between all treatments. Spirometry and RUP data were downloaded to personal computers. Linear regression analyses (RUP versus spirometric tidal volume) were performed using different subsets of data. Additonally RUP was calibrated against spirometry using a regression equation for all RUP signal values (thoracic, abdominal and combined) with all data collectively and also by an individually determined best regression equation (highest R(2)) for each experiment (horse versus recumbency) separately. Agreement between methods was assessed with Bland-Altman analyses. RESULTS: The highest correlation of RUP and spirometric tidal volume (R(2)=0.81) was found with the combined RUP signal in horses in lateral recumbency and ventilated without PEEP. The bias ±2 SD was 0±2.66 L when RUP was calibrated for collective data, but decreased to 0±0.87 L when RUP was calibrated with individual data. CONCLUSIONS AND CLINICAL RELEVANCE: A possible use of RUP for tidal volume measurement during IPPV needs individual calibration to obtain limits of agreement within ±20%.

Influence of fentanyl on intra-abdominal pressure during laparoscopy in dogs.

OBJECTIVE: To evaluate the influence of fentanyl on intra-abdominal pressures in spontaneously breathing dogs during capnoperitoneum. STUDY DESIGN: Prospective clinical study. ANIMALS: Eleven healthy client-owned and five healthy experimental dogs undergoing laparoscopy. METHODS: Dogs were premedicated with acepromazine (0.03 mg kg(-1) IV) and carprofen (4 mg kg(-1) IV). Anaesthesia was induced with propofol and maintained with isoflurane in oxygen. The abdomen was insufflated with CO(2) (11-16 cm H(2) O). Intra-abdominal pressures were measured with a transducer. Respiratory variables were measured with a spirometry sensor and side-stream capnography. Following preparation, fentanyl (1 µg kg(-1) ) was injected over 30 seconds IV. Data were recorded 5 minutes before, during and 5 minutes after treatment. The following time points were selected for statistical analysis (anova, p < 0.05): -160, -140, -120, -100, -80, -60, -40, -20, 0, 30, 50, 70, 90, 110, 130 and 150 seconds after the start of fentanyl injection. RESULTS: Intra-abdominal pressure increased during inspiration in 15 dogs but decreased in one dog. Fentanyl treatment did not alter these patterns. Peak inspiratory and end-expiratory intra-abdominal pressures continuously decreased over time during the whole experiment and fentanyl exaggerated the decrease in inspiratory pressures but did not affect the rate of decrease in expiratory pressures. Differences between intra-abdominal pressures were stable before, but decreased after fentanyl administration from 4.1 ± 1.4 to 3.3 ± 1.2 cm H(2) O (at 0 and 150 seconds time points). End-tidal CO(2) partial pressures increased from 6.0 ± 0.8 to 6.6 ± 0.9 kPa, respiratory rate decreased from 10.8 ± 2.6 to 7.8 ± 2.2 breaths per minute and tidal volume decreased from 13.7 ± 4.4 to 12.4 ± 2.9 mL kg(-1) after fentanyl but these variables did not change before fentanyl treatment. Airway pressures did not change. CONCLUSIONS AND CLINICAL RELEVANCE: Fentanyl did not increase intra-abdominal pressures in dogs.

Effect of alfaxalone infusion on the electroencephalogram of dogs anaesthetized with halothane.

OBJECTIVE: To describe the effects of alfaxalone on the canine electroencephalogram (EEG). STUDY DESIGN: Experimental study. ANIMALS: Eight healthy adult Huntaway dogs. METHODS: Anaesthesia was induced with propofol and maintained with halothane (0.85-0.95 end-tidal volume %) in oxygen. Animals were ventilated to maintain stable end-tidal CO(2) and halothane concentrations. Following a 30 minute stabilisation period, alfaxalone (0.5 mg kg(-1) ) was infused intravenously over a 5 minute period. The electroencephalogram was recorded from the beginning of the stabilisation period until 60 minutes following the start of alfaxalone treatment. Data were subjected to fast Fourier transformation, and median frequency, 95% spectral edge frequency and total EEG power were calculated. Two-factorial repeated measures anova (time and EEG channels were factors) was used for statistical analysis (p < 0.05). RESULTS: A shift in the dominant frequency band from beta to delta after alfaxalone treatment and occasional burst suppression were observed. Median frequency decreased significantly below baseline (9.2 ± 1.4 Hz) (mean ± SD) during alfaxalone infusion. The lowest value (4.8 ± 1.2 Hz) was recorded 5 minutes after the start of infusion. Spectral edge frequency also decreased below baseline (26.2 ± 1.5 Hz) and the lowest value (22.6 ± 1.5 Hz) also was detected at 5 minutes after the start of infusion. Total EEG power did not change significantly. In some frequencies EEG power increased soon after the start of alfaxalone infusion, then decreased below baseline later (biphasic pattern). CONCLUSIONS AND CLINICAL RELEVANCE: Alfaxalone induced biphasic changes on EEG and decreased F(50) and F(95) in halothane anaesthetized dogs.

Comparison of use of an infrared anesthetic gas monitor and refractometry for measurement of anesthetic agent concentrations.

OBJECTIVE: To assess agreement between anesthetic agent concentrations measured by use of an infrared anesthetic gas monitor (IAGM) and refractometry. SAMPLE-4 IAGMs of the same type and 1 refractometer. PROCEDURES: Mixtures of oxygen and isoflurane, sevoflurane, desflurane, or N(2)O were used. Agent volume percent was measured simultaneously with 4 IAGMs and a refractometer at the common gas outlet. Measurements obtained with each of the 4 IAGMs were compared with the corresponding refractometer measurements via the Bland-Altman method. Similarly, Bland-Altman plots were also created with either IAGM or refractometer measurements and desflurane vaporizer dial settings. RESULTS: Bias ± 2 SD for comparisons of IAGM and refractometer measurements was as follows: isoflurane, -0.03 ± 0.18 volume percent; sevoflurane, -0.19 ± 0.23 volume percent; desflurane, 0.43 ± 1.22 volume percent; and N(2)O, -0.21 ± 1.88 volume percent. Bland-Altman plots comparing IAGM and refractometer measurements revealed nonlinear relationships for sevoflurane, desflurane, and N(2)O. Desflurane measurements were notably affected; bias ± limits of agreement (2 SD) were small (0.1 ± 0.22 volume percent) at < 12 volume percent, but both bias and limits of agreement increased at higher concentrations. Because IAGM measurements did not but refractometer measurements did agree with the desflurane vaporizer dial settings, infrared measurement technology was a suspected cause of the nonlinear relationships. CONCLUSIONS AND CLINICAL RELEVANCE: Given that the assumption of linearity is a cornerstone of anesthetic monitor calibration, this assumption should be confirmed before anesthetic monitors are used in experiments.

Continuous versus intermittent thermodilution for cardiac output measurement during alveolar recruitment manoeuvres in sheep.

OBJECTIVE: To evaluate interchangeability of a thermodilution based STAT mode continuous cardiac output (CCO) measurement method with bolus thermodilution (BTD). STUDY DESIGN: Randomized crossover study. ANIMALS: Ten 9 month old healthy male sheep. METHODS: Each sheep was anaesthetized twice for laparoscopy. On one occasion mechanical ventilation was used immediately after anaesthetic induction (IPPV treatment) and on the other occasion the start of IPPV was delayed and two periods of alveolar recruitment manoeuvres were also performed (RM treatment). Cardiac output (CO) was measured simultaneously with both CCO and BTD at 6 time points. Data were analysed using difference versus mean plots. A priori limits of acceptance were set at ±30% of the mean of every paired measurement. If <5% of the data fell outside of these limits (Chi-square test, p<0.05) the interchangeability of methods was accepted. Proportions of data outside of these limits were also compared between treatments (Fisher's test, p <0.05). Cardiac output data from each treatment and measurement method were also analyzed separately with one-factorial anova and Bonferroni test (p<0.05). RESULTS: A total of 119 measurements were obtained. Cardiac output ranged from 1.9 to 10.4 L minute(-1) (CCO) and from 1.1 to 9.8 L minute(-1) (BTD). The bias and limits of agreement were 0.5±1.9 L minute(-1) . More than 5% of all data fell outside of the limits of acceptance (24/119), and a larger proportion fell outside of these limits in the RM (20/59) compared to the IPPV treatment (4/60). The Bonferroni test detected significant decreases of CO over time in both treatments when measured with BTD but not with CCO. CONCLUSIONS AND CLINICAL RELEVANCE: The STAT mode CCO method is not interchangeable with BTD during acute haemodynamic changes caused by recruitment manoeuvres, thus the results of STAT mode CCO should be interpreted with caution because decreases in CO may not be detected.

Accuracy of isoflurane, halothane, and sevoflurane vaporizers during high oxygen flow and at maximum vaporizer dial setting.

OBJECTIVE: To assess the accuracy of isoflurane, halothane, and sevoflurane vaporizers during high oxygen flow and at maximum dial settings at room temperature and to test sevoflurane vaporizers similarly during heating and at low-fill states. SAMPLE: 5 isoflurane, 5 halothane, and 5 sevoflurane vaporizers. PROCEDURES: Vaporizers were tested at an oxygen flow of 10 L/min and maximum dial settings for 15 minutes under various conditions. All 3 vaporizer types were filled and tested at room temperature (21° to 23°C). Filled sevoflurane vaporizers were wrapped with circulating hot water (42°C) blankets for 2 hours and tested similarly, and near-empty sevoflurane vaporizers were tested similarly at room temperature. During each 15-minute test period, anesthetic agent concentration was measured at the common gas outlet with a portable refractometer and temperature of the vaporizer wall was measured with a thermistor. RESULTS: For each vaporizer type, anesthetic agent concentrations and vaporizer wall temperatures decreased during the 15-minute test period. Accuracy of isoflurane and halothane vaporizers remained within the recommended 20% (plus or minus) deviation from dial settings. Heated and room-temperature sevoflurane vaporizers were accurate to within 23% and 11.7% (plus or minus) of dial settings, respectively. Sevoflurane vaporizers at low-fill states performed similarly to vaporizers at full-fill states. CONCLUSIONS AND CLINICAL RELEVANCE: Under these study conditions, the isoflurane and halothane vaporizer models tested were accurate but the sevoflurane vaporizers were not. Sevoflurane vaporizer accuracy was not affected by fill state but may be improved with vaporizer heating; measurements of inspired anesthetic agent concentrations should be obtained during the use of heated vaporizers.