Comparison of high definition oscillometric and Doppler ultrasound devices with invasive blood pressure in anaesthetized dogs

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1 Veterinary Anaesthesia and Analgesia, 13,, doi:1.1111/j x RESEARCH PAPER Comparison of high definition oscillometric and Doppler ultrasound devices with invasive blood pressure in anaesthetized dogs Alenka Seliškar*, Petra Zrimšek, Jerneja Sredenšekà & Aleksandra D Petrič* *Clinic for Small Animal Medicine and Surgery, Veterinary Faculty, University of Ljubljana, Ljubljana, Slovenia Clinic for Reproduction and Horses, Veterinary Faculty, University of Ljubljana, Ljubljana, Slovenia àveterinary Faculty, University of Ljubljana, Ljubljana, Slovenia Correspondence: Alenka Seliškar, University of Ljubljana, Veterinary Faculty, Clinic for Small Animal Medicine and Surgery, Gerbičeva 6, SI-1 Ljubljana, Slovenia. alenka.seliskar@vf.uni-lj.si Abstract Objective To use the American College of Veterinary Internal Medicine (ACVIM) validation criteria to evaluate the performance of high definition oscillometric (HDO) and Doppler blood pressure measurement techniques against invasive blood pressure measurements in anaesthetized dogs. Study design Prospective clinical study. Animals Twenty client-owned dogs. Materials and Methods Invasive blood pressure was measured using a catheter inserted into a pedal artery and an electronic transducer. The sites of cuff placement for the HDO measurements were the mid antebrachium or the proximal tail and, for the Doppler technique, the distal tibia. Agreement between invasive and non-invasive blood pressure measurements was estimated by the Bland Altman method. Results Only 1% and 34% of Doppler measurements were within 1 and mmhg of invasive blood pressure values, respectively. The Doppler device failed to meet the ACVIM validation criteria for blood pressure measurement devices. The best agreement between HDO and invasive blood pressure measurement technique was observed for mean arterial blood pressure (MAP); 67% and 95% of readings were within 1 and mmhg of invasive blood pressure values respectively. In addition, 52% and 87% of diastolic arterial blood pressure (DAP) measurements were within 1 and mmhg of invasive readings. High definition oscillometric readings did not meet ACVIM recommended limits for SAP. Conclusion and clinical relevance The Doppler technique overestimated and the HDO device showed limited agreement with invasive blood pressure measurement in anaesthetized dogs. High definition oscillometry met most of the ACVIM requirements for MAP and DAP while the Doppler technique did not. Keywords anaesthesia, blood pressure, dogs, Doppler, high-definition oscillometry. Introduction Invasive arterial blood pressure is the accepted gold standard for blood pressure measurement (Gains et al. 1995; Bodey et al. 1996; Brown & Henik 1998; Stepien & Rapoport 1999). Since the technique for invasive blood pressure measurement can be technically difficult and uncomfortable for the animal, oscillometric devices for non-invasive measurement of blood pressure have been in widespread 21

2 clinical use for many years in small animals. It is important to know the precision and accuracy of oscillometric devices compared to the gold standard and therefore validation studies are recommended by the 7 ACVIM Consensus Statement (Brown et al. 7). According to this statement, the criteria and recommendations of the Association of the Advancement of Medical Instrumentation (AAMI) must be followed with some adjustments in veterinary patients. The system is considered adequate if the stated conditions are met (Brown et al. 7). Doppler and various oscillometric devices have been compared with invasive blood pressure measurements in conscious or anaesthetized dogs (Bodey et al. 1994, 1996; Stepien & Rapoport 1999; Haberman et al. 6; Deflandre & Hellebrekers 8) and the results indicate poor accuracy and/or precision, especially in hypertensive or hypotensive states, although satisfactory results have been reported in normal and hypotensive pressure ranges (Meurs et al. 1996; Sawyer et al. 4). Some devices have been reported to be more reliable (Bodey et al. 1994, 1996; Gains et al. 1995; Meurs et al. 1996; Sawyer et al. 4; McMurphy et al. 6) than others (Shih et al. 1; Wernick et al. 1). The Doppler blood pressure measurement technique is used widely in anaesthetized patients and, although a widely accepted vital monitor, it is not a highly precise blood pressure measurement device, and does not measure diastolic and mean blood pressures (Stepien & Rapoport 1999; Stepien et al. 3; Haberman et al. 6; Bosiack et al. 1). Conventional oscillometry measures pulse waverelated oscillations in the wall of an artery. The signals are detected by a pressure transducer and converted to blood pressure values. The strongest oscillation is defined as the MAP. An algorithm is used to convert these values to systolic and diastolic pressure readings (Egner 6). A new, highdefinition oscillometric device (Memo diagnostic Pro, S+B MedVet GmBH, Germany) for blood pressure measurement in dogs and cats has been marketed. High-definition oscillometry uses ultraprecise recognition of arterial wall oscillations (vibrations) produced by the incident pulse waves and thus makes it possible to recognize artifacts. A special algorithm is used for detection of presystolic amplitudes, as well as systolic (SAP), mean (MAP) and diastolic (DAP) arterial pressures (Egner 6). The developer claims that some of the characteristics of oscillometric devices have been improved with HDO, such as sensitivity at low amplitudes, better recognition and fewer artefacts at higher heart rates, the possibility of measuring very low pressures, better precision due to an electronic valve and the capability for real time analysis (Egner 6). The aim of this study was to determine the reliability of arterial blood pressure measurements in anaesthetized dogs obtained by the HDO device and the Doppler technique by comparing them to the measurements obtained with the standard invasive blood pressure measurement technique. Materials and methods Twenty client-owned dogs presented for various surgical procedures, were anaesthetized with two commonly used anaesthetic protocols, chosen according to the physical status of the dog. Healthy dogs, classified as ASA 1 according to the guidelines of the American Society of Anesthesiologists, were not included in the study because no cases required invasive blood pressure measurement and dogs classified as ASA 5 were also excluded. After hours cases were not recruited since the single investigator responsible for performing all of the non-invasive measurements was not present at that time. All procedures complied with the relevant Slovenian governmental regulations (Animal Protection Act UL RS, 43/7) and formal consent of the owner was obtained before the dogs entered the study. The study protocol was evaluated and approved by the Institutional Ethics Committee. The anaesthetic protocol for dogs classified as ASA 2 comprised pre-anaesthetic medication with acepromazine (PromAce, Fort Dodge, IA, USA).2 mg kg )1 intramuscularly and methadone (Heptanon; Pliva, Croatia).2.5 mg kg )1 subcutaneously (SC) or intramuscularly (IM). Anaesthesia was induced with propofol (Propofol 1%, Fresenius Kabi, Austria) 3 4 mg kg )1 intravenously (IV) and maintained with isoflurane (Forane, Abbott, UK) delivered in oxygen and air (FiO 2 =.6). Dogs, classified as ASA 3 or 4 received methadone.2.5 mg kg )1 SC or IM. Anaesthesia was induced with midazolam (Dormicum, Roche, Switzerland).1.5 mg kg )1, followed by up to 3 mg kg )1 of propofol IV, and maintained with isoflurane delivered in oxygen and air (FiO 2 =.6). Lactated Ringer s solution (B Braun, Germany) was infused at 1 ml kg )1 hour )1 IV, unless cardiac disease was confirmed before 22 Ó 12 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists,, 21 27

3 anaesthesia, in which case the dogs received fluids at 3 5 ml kg )1 hour )1. Dogs were positioned in right lateral, left lateral or dorsal recumbency, depending on the requirements of the surgical procedure. Blood pressure was measured non-invasively with the use of the HDO device and an ultrasonic Doppler flow monitor (Model 811, Parks Medical Electronics, OR, USA). The cuff width for the Doppler technique was approximately % of the limb circumference (Brown et al. 7). For the HDO method, the cuff was selected according to the manufacturer s instructions (size c1 for small dogs if the cuff was placed on the tail, size d1 for small dogs if the cuff was placed on the leg and size d2 for larger dogs). The site of cuff placement for the Doppler technique was the distal tibia and for the HDO device was the middle of the antebrachium. Both cuffs were placed on the same side of the body. When one of the front legs was in the surgical field the HDO cuff was placed on the proximal tail. Care was taken to ensure that the both cuffs were level with the heart base. Hair was not clipped over the measurement site. Invasive arterial blood pressure was measured using a disposable pressure transducer connected to a monitor (HP Model 78354A, Hewlett Packard GmBH, Germany). A new transducer was used for each dog. It was positioned at the level of the point of the shoulder with dogs in dorsal recumbency, or the mid-sternal level in dogs in lateral recumbency, and the transducer was zeroed to atmospheric pressure before measurements were taken. Arterial catheter placement was performed after induction of anaesthesia. Hair over the left or right dorsal pedal artery was clipped, the skin was prepared aseptically and a - or 22 gauge catheter was inserted percutaneously into the artery. The catheter was connected to a transducer via non-compliant salinefilled tubing and was flushed continuously with.9% NaCl (B Braun, Germany) containing heparin (5 IU ml )1 ). A single investigator with more than 1 year of experience in the use of both the Doppler and the HDO devices performed all of the non-invasive measurements. Blood pressure was measured with the HDO device every 5 minutes. During each HDO measurement three Doppler measurements and three readings of invasive blood pressure were taken to quantify the intra-operator variability (repeatability). Coefficients of variance (CV ± SD) were calculated for each triplet of measurements using the formula: CV (%) = (mean difference between measurements/mean of measurements) 1 (Margiocco et al. 9). The means of the three measurements (Doppler and invasive blood pressure) were used for comparison with the single HDO measurement since blood pressure could change during the time taken to perform a single HDO measurement. Differences between the paired readings for SAP were calculated for the Doppler and invasive measurement as well as the SAP, MAP and DAP for the HDO and invasive measurements. The agreement of the SAP, MAP and DAP, obtained by invasive and HDO methods, as well as the agreement between Doppler and invasive SAP were analysed according to the Bland Altman method (Bland & Altman 1986a, 1995). In our evaluation the bias was calculated as difference between measurements (e.g. HDO minus invasive blood pressure). In order to assess the agreement of paired measurements the 95% limits of agreement were determined to estimate the range of agreement between the two techniques. The upper and lower limits of agreement were calculated as bias ±2SD. The percentage of measurements, where the difference between invasive and non-invasive measurement was <1 or mmhg, was calculated. These values (1 and mmhg) have been named discrepancy levels (Deflandre & Hellebrekers 8). The criteria, we used to evaluate the performance of both non-invasive devices, were selected according to following ACVIM recommendations (Brown et al. 7): the bias of the paired measurements for SAP and DAP treated separately is ±1 mmhg or less; fifty percent of all measurements for SAP and DAP treated separately lie within 1 mmhg of the reference method; eighty percent of all measurements for SAP and DAP treated separately lie within mmhg of the reference method. The ACVIM recommendations (Brown et al. 7) also recommend calculating the correlation coefficient between measurements of two methods. The correlation was omitted from our evaluation since correlation analysis is not appropriate for method comparison (Bland & Altman 1986b). Statistical analysis was performed using Analyse-it for Microsoft Excel (version 1.71) (Analyse-it Software, Ltd. 9) and Sigma Stat 3.5 (SYSTAT Software Inc., USA). Ó 12 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists,,

4 Results Figure 1 Bland Altman plot of agreement between the systolic arterial blood pressure (SAP) obtained by Doppler device and invasive method with trend line. The mean value of Doppler and invasive measurement is presented on the X axis ((Doppler + invasive)/2) and the difference between the Doppler and invasive measurement on the Y axis (Doppler invasive). The solid line indicates bias and the dashed lines the upper and lower limits of agreement. The thick solid diagonal line (trend line) indicates simple linear regression relationship between the differences and the averages of the Doppler device and invasive method for SAP. The regression equation for the trend line is: difference (Doppler invasive) = mean (Doppler invasive). Twenty dogs, 13 females and 7 males, aged between 7 months and 12 years, weighing 3.4 ± 12.5 kg (mean ± SD, range kg) were included in the study. After clinical examination 13 of the dogs were assigned to the ASA 2 category and seven of the dogs to ASA 3 or 4. The number of sequential measurements made on each dog depended on the duration of anaesthesia. The duration of anaesthesia varied from 6 to 21 minutes and 7 to 53 measurements (median 18.5) were obtained from each dog. HDO measurements were successful in 93.6% of attempts. The HDO sometimes failed to measure blood pressure during extended use electrocautery or when the surgeon moved body parts in the vicinity of the cuff. For example, if the cuff was positioned on the tail, errors occurred during surgical exploration of the abdominal cavity in smaller dogs. A total of 423 pressure measurements, successfully obtained by HDO, were evaluated. All 423 Doppler measurements were completed but not all were successful. A series of erroneously high measurements were obtained from one dog, therefore Doppler measurements from that dog were excluded from analysis. A total of 381 Doppler measurements were included in the final evaluation. The coefficient of variance (CV) showing intraoperator variability (repeatability) for the Doppler technique was calculated as 1.5 ± 1.% and CVs for invasive measurements of SAP, DAP and MAP were 3.3 ± 3.4%, 4.1 ± 4.6% and 3.7 ± 4.%, respectively. The Doppler technique did not meet any of the ACVIM recommendations; only 1% and 34% of measurements were within 1 and mmhg of invasive BP values, respectively. A large bias of 27 mmhg was observed (Table 1). More than 8% of HDO DAP and MAP measurements were within mmhg of invasive readings. MAPandDAPmeasurementsalsomettherequirements of more than 5% of them to be within 1 mmhg of invasive values, whereas SAP HDO values did not fulfill the mentioned thresholds (Table 1). Bland Altman plots of the difference between the HDO and invasive measurements against the mean of the measurements are shown in Fig. 2. The biases for all BPs (MAP, DAP and SAP) correspond to the ACVIM recommendation of <1 mmhg. Although the bias for DAP measurements is less than the threshold for validation, its negative value ()7 mmhg) confirms the underestimation of DAP HDO readings in comparison to invasive DAP values. The bias of 7 mmhg for SAP measured by HDO with limits of agreement set at )25 and mmhg indicates an overestimation of SAP by the HDO device compared to invasive values. The differences between the MAP measured by HDO and invasively are equally distributed around zero. Discussion In this study arterial blood pressure measurements were obtained by the invasive method, the HDO device and the Doppler technique in anaesthetized dogs and evaluated against criteria based on the ACVIM recommendations (Brown et al. 7). The Doppler measurement technique failed to meet the criteria. This is in agreement with other studies comparing blood pressure measurements made by Doppler and invasive methods in dogs (Stepien & Rapoport 1999; Haberman et al. 6). From the Bland Altman plot; the Doppler device overestimates systolic BP compared to the invasive measurement. The HDO device is relatively new and there are a limited number of reports evaluating its use in dogs (Chetboul et al. 1; Meyer et al. 1; Mitchell 24 Ó 12 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists,, 21 27

5 Table 1 Agreement of blood pressures in anaesthetized dogs measured by the Doppler technique, the HDO device and invasively Parameter Bias (mmhg)* Limits of agreement (mmhg) ±1 mmhg (%) ± mmhg (%) ACVIM recommendationsà Doppler vs invasive (SAP) HDO vs invasive (SAP) HDO vs invasive (DAP) HDO vs invasive (MAP) < ±1 None )4.1 to )25 to 36 7 )7 )28 to ).5 )21 to *Bias: average of all differences: (non-invasive invasive BP); percentages of invasive measurements (systolic arterial blood pressure (SAP), diastolic arterial blood pressure (DAP) and mean arterial blood pressure (MAP) lying within ±1 or mmhg of the corresponding invasive values; àacvim (American College of Veterinary Internal Medicine) recommended limits for systolic and diastolic values (Brown et al. 7); bold numbers are in agreement with ACVIM recommendations. et al. 1; Wernick et al. 1), cynomolgus monkeys (Schmelting et al. 9; Mitchell et al. 1) and cats (Domanjko Petrič et al. 1). The repeatability of measurements, showing consistency in readings as reported by Wernick et al. (1), was confirmed in the present study. The HDO failed to perform readings in 6.4% of cases which contrasts with the results presented by Wernick et al. (1) where readings were obtained at all measurements. Doppler measurements could be obtained at all times but not all were successful. In one dog a series of very high measurements, in comparison to the measurements obtained with the invasive blood pressure measurement technique, were obtained with the Doppler device. A loose cuff is a possible explanation for these results and therefore these abnormal measurements were excluded from analysis. Mitchell et al. (1) compared HDO and oscillometry (Cardell Blood Pressure Monitor Model 91) in conscious dogs and monkeys with simultaneously recorded invasive blood pressure data captured via radiotelemetry. The HDO device detected hexamethonium bromide-induced decreases in blood pressure in dogs and monkeys but oscillometry only detected the decrease in blood pressure in dogs, not in monkeys. In a study by Meyer et al. (1), torcetrapib-induced increases in blood pressure, assessed by HDO and telemetry, were positively correlated in conscious dogs. Of the various HDO pressure measurements, MAP exhibited the least methoddependent bias and most closely paralleled telemetric blood pressure assessment. In the present study, the best agreement between HDO and invasive blood pressure measurement techniques was observed for MAP which is in agreement with the results of Wernick et al. (1). The ACVIM requirements were met for MAP and DAP measured by HDO. The correlation coefficient was excluded from the evaluation, although the ACVIM guidelines recommend its calculation. The rationale behind this is that the correlation coefficients are a measure of linear association, not agreement: one cannot infer good agreement from a high correlation. It is not how close the points lie to the best-fitting straight line that is important, but how close they lie to line of equality (Bland & Altman 1986b). The greatest difference from the results of Wernick et al. (1) is for SAP readings, with only 36% and 7% of HDO measurements within 1 and mmhg of invasive readings observed in our study, as compared with 52.4% and 82.5%, obtained by Wernick et al. (1). It s evident from trend lines that the largest systematic error is obtained for SAP, but it was present for all the measurements. The HDO device therefore may not be a reliable monitor of SAP in hypotensive dogs. Moreover, the trend lines indicate that the results are not consistent over the range tested for SAP, DAP and MAP, which is a clear weakness in the technique tested. A limitation of the study is that very sick dogs were not included so the performance of the HDO device was not tested in animals with severe hypotension. Dogs in this study were of different breeds and sex and ranged from 8 to Ó 12 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists,,

6 Figure 2 Bland Altman plot of agreement between systolic arterial blood pressure (SAP), diastolic arterial blood pressure (DAP) and mean arterial blood pressure (MAP) obtained by the HDO device and invasive method with trend lines. Mean value of HDO and invasive MAP measurement is presented on the X axis ((HDO + invasive)/2) and the difference between HDO and invasive measurement on the Y axis (HDO invasive). The solid line indicates bias and the dashed lines the upper and lower limits of agreement. The thick solid diagonal line (trend line) shows the simple linear regression relationship between the differences and the averages of the HDO and invasive method for SAP, DAP and MAP. The regression equations for trend lines are: 1) difference (HDO invasive; SAP) = 52.4 ).41 mean (HDO invasive; SAP); 2) difference (HDO invasive; DAP) = 1. ).11 mean (HDO invasive; DAP); 3) difference (HDO invasive; MAP) = 13.9 ).18 mean (HDO invasive; MAP) kg, representing a very heterogenous group. No data on the dogs entering Wernick s study (1) were presented and thus it is difficult to suggest possible reasons for the difference between the results of the two studies. However, the dogs in Wernick s study were in a standardised position of dorsal recumbency during measurements while, in our study, they were positioned in dorsal or lateral recumbency, depending on the requirements of the surgery. In the study by Shih et al. (1) another type of oscillometric blood pressure monitor (petmap; Ramsey, Medical Inc, FL, USA) greatly overestimated blood pressure measurements when hypotension was present, an indication that this device is not a good substitute for invasive blood pressure measurement technique in hypotensive dogs. In contrast, Sawyer et al. (4) found the Cardell Veterinary blood pressure monitor Model 931V gave accurate measurements of SAP and MAP during hypotension. Another type of oscillometric blood pressure monitor (Surgivet V646; SurgiVet, Inc, Waukesha, WI, USA) consistently underestimated blood pressure in anaesthetized dogs at all levels, with low accuracy at high pressures (Deflandre & Hellebrekers 8). Underestimation of non-invasive blood pressure measurements in conscious dogs has also been reported for the oscillometric device, Dinamap model 83 (Haberman et al. 6). Arterial blood pressure measurement assists clinical decision making during anaesthesia, therefore it is important that the results are reliable. No noninvasive device has so far met AAMI standards for the performance of human automated non-invasive blood pressure devices for use in conscious dogs and cats (Brown et al. 7). The oscillometric monitor Surgivet V646 reached the AAMI standard in anaesthetized dogs for MAP at low and normal pressures and was very close to this standard for the overall MAP (Deflandre & Hellebrekers 8). Other oscillometric monitors (Cardell model 91 and Datascope Passport) evaluated by Bosiack et al. (1), were also close to these standards, especially for MAP measurements in the normotensive and hypertensive groups (Cardell) and for DAP measurements in all groups (Datascope Passport). The HDO device in the present study did not meet the AAMI standard, which is also in agreement with the results of Wernick s study (1). The limitations of this study include the effect of differences in measurement sites (cuff placement) on accuracy, not including emergency cases and very 26 Ó 12 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists,, 21 27

7 sick dogs and not testing the devices under low blood pressure conditions. In summary, the Doppler technique overestimated and the HDO device showed limited agreement with invasive blood pressure measurements in anaesthetized dogs. High definition oscillometry met most of the ACVIM requirements for MAP and DAP while the Doppler technique did not meet them. Acknowledgement This work was supported by the Slovenian Ministry of Higher Education, Science and Technology, Programme group P4-53 Endocrine, immune, nervous and enzyme responses in healthy and sick animals. References Bland JM, Altman DG (1986a) Statistical methods for assessing agreement between two methods of clinical measurement. The Lancet 1, Bland JM, Altman DG (1986b) Comparison of methods of measuring blood pressure. J Epidemiol Community Health, Bland JM, Altman DG (1995) Comparing methods of measurement: why plotting difference against standard method of measurements is misleading. The Lancet 346, Bodey AR, Young LE, Bartram DH et al. (1994) A comparison of direct and indirect (oscillometric) measurements of arterial blood pressure in anaesthetised dogs, using tail and limb cuffs. Res Vet Sci 57, Bodey AR, Michell AR, Bovee KC et al. (1996) Comparison of direct and indirect (oscillometric) measurements of arterial blood pressure in conscious dogs. Res Vet Sci 61, Bosiack AP, Mann FA, Dodam JR et al. (1) Comparison of ultrasonic Doppler flow monitor, oscillometric, and direct arterial blood pressure measurements in ill dogs. J Vet Emerg Crit Care, Brown SA, Henik RA (1998) Diagnosis and treatment of systemic hypertension. Vet Clin North Am Small Anim Pract 28, Brown S, Atkins C, Bagley R et al. (7) Guidelines for identification, evaluation and management of systemic hypertension in dogs and cats. J Vet Intern Med 21, Chetboul V, Tissier R, Gouni V et al. (1) Comparison of Doppler ultrasonography and high-definition oscillometry for blood pressure measurements in healthy awake dogs. Am J Vet Res 71, Deflandre CJA, Hellebrekers LJ (8) Clinical evaluation of the Surgivet V646, a non invasive blood pressure monitor in anaesthetized dogs. Vet Anaesth Analg 35, Domanjko Petrič A, Zrimšek P, Sredenšek J et al. (1) Comparison of high definition oscillometric and Doppler ultrasonic devices for measuring blood pressure in anaesthetized cats. J Fel Med Surg 12, Egner B (6) Blood pressure measurement: technology and avoidance of measurement error. Kleintier Konkret J Small Anim Practitioner 4, Gains MJ, Grodecki KM, Jacobs RM et al. (1995) Comparison of direct and indirect blood pressure measurements in anesthetized dogs. Can J Vet Res 59, Haberman CE, Kang CW, Morgan JD et al. (6) Evaluation of oscillometric and Doppler ultrasonic methods of indirect blood pressure estimation in conscious dogs. Can J Vet Res 7, Margiocco ML, Bulmer BJ, Sisson DD (9) Doppler-derived deformation imaging in unsedated healthy adult dogs. J Vet Cardiol 11, McMurphy RM, Stoll MR, McCubrey R (6) Accuracy of an oscillometric blood pressure monitor during phenylephrine-induced hypertension in dogs. Am J Vet Res 67, Meurs KM, Miller MW, Slater MR (1996) Comparison of the indirect oscillometric and direct arterial methods for blood pressure measurements in anesthetized dogs. J Am Anim Hosp Assoc 32, Meyer O, Jenni R, Greiter-Wilke A et al. (1) Comparison of telemetry and high-definition oscillometry for blood pressure measurements in conscious dogs: effects of torcetrapib. J Am Assoc Lab Anim Sci 49, Mitchell AZ, McMahon C, Beck TW et al. (1) Sensitivity of two noninvasive blood pressure measurement techniques compared to telemetry in cynomolgus monkeys and beagle dogs. J Pharmacol Toxicol Methods 62, Sawyer DC, Guikema AH, Siegel EM (4) Evaluation of a new oscillometric blood pressure monitor in isofluraneanesthetized dogs. Vet Anaesth Analg 31, Schmelting B, Niehoff M, Egner B et al. (9) High definition oscillometry: a novel technique for non-invasive blood pressure monitoring in cynomolgus monkey (Macaca fascicularis). J Med Primatol 38, Shih A, Robertson S, Vigani A et al. (1) Evaluation of an indirect oscillometric blood pressure monitor in normotensive and hypotensive anesthetized dogs. J Vet Emerg Crit Care, Stepien RL, Rapoport GS (1999) Clinical comparison of three methods to measure blood pressure in nonsedated dogs. J Am Vet Med Assoc 215, Stepien RL, Rapoport GS, Henik RA et al. (3) Comparative diagnostic test characteristics of oscillometric and Doppler ultrasonographic methods in the detection of systolic hypertension in dogs. J Vet Intern Med 17, Wernick M, Doherr M, Howard J et al. (1) Evaluation of high-definition and conventional oscillometric blood pressure measurement in anesthetised dogs using AC- VIM guidelines. J Small Anim Pract 51, Received 6 April 11; accepted 16 August 11. Ó 12 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists,,