• View in gallery

    Bland-Altman plots for paired OBP and IBP values for SAP (A), DAP (B), and MAP (C) in 19 awake dogs positioned in sternal recumbency. The IBP was obtained from the median caudal artery, and OBP was obtained with a cuff placed on a forelimb. The solid horizontal line indicates the mean difference (bias), the horizontal dotted lines represent the 95% LOA, and the diagonal dashed-and-dotted line indicates the proportional bias. Each circle represents a single measurement.

  • View in gallery

    Bland-Altman plots for paired OBP and IBP values for SAP (A), DAP (B), and MAP (C) in 19 isoflurane-anesthetized dogs positioned in sternal recumbency. See Figure 1 for remainder of key.

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Assessment of a commercially available veterinary blood pressure device used on awake and anesthetized dogs

Jeannette Cremer DVM, Dr Med Vet1, Anderson F. da Cunha DVM, MS1, Linda J. Paul DVM1, Chin-Chi Liu PhD1, and Marc J. Acierno DVM, MBA2
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  • 1 1Department for Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.
  • | 2 2Department of Medicine, College of Veterinary Medicine, Midwestern University, Glendale, AZ 85308.

Abstract

OBJECTIVE

To compare results of a commercially available device for oscillometrically measured blood pressure (OBP) with invasively measured blood pressure (IBP) in awake and anesthetized dogs.

ANIMALS

19 adult dogs (mean ± SD body weight, 17.8 ± 7.5 kg).

PROCEDURES

Blood pressures were measured in dogs while they were awake and anesthetized with isoflurane. The OBP was recorded on a thoracic limb, and IBP was simultaneously recorded from the median caudal artery. Agreement between OBP and IBP was evaluated with the Bland-Altman method. Guidelines of the American College of Veterinary Internal Medicine (ACVIM) were used for validation of the oscillometric device.

RESULTS

In awake dogs, mean bias of the oscillometric device was −11.12 mm Hg (95% limits of agreement [LOA], −61.14 to 38.90 mm Hg) for systolic arterial blood pressure (SAP), 9.39 mm Hg (LOA, −28.26 to 47.04 mm Hg) for diastolic arterial blood pressure (DAP), and −0.85 mm Hg (LOA, −40.54 to 38.84 mm Hg) for mean arterial blood pressure (MAP). In anesthetized dogs, mean bias was −12.27 mm Hg (LOA, −47.36 to 22.82 mm Hg) for SAP, −3.92 mm Hg (LOA, −25.28 to 17.44 mm Hg) for DAP, and −7.89 mm Hg (LOA, −32.31 to 16.53 mm Hg) for MAP. The oscillometric device did not fulfill ACVIM guidelines for the validation of such devices.

CONCLUSIONS AND CLINICAL RELEVANCE

Agreement between OBP and IBP results for awake and anesthetized dogs was poor. The oscillometric blood pressure device did not fulfill ACVIM guidelines for validation. Therefore, clinical use of this device cannot be recommended.

Abstract

OBJECTIVE

To compare results of a commercially available device for oscillometrically measured blood pressure (OBP) with invasively measured blood pressure (IBP) in awake and anesthetized dogs.

ANIMALS

19 adult dogs (mean ± SD body weight, 17.8 ± 7.5 kg).

PROCEDURES

Blood pressures were measured in dogs while they were awake and anesthetized with isoflurane. The OBP was recorded on a thoracic limb, and IBP was simultaneously recorded from the median caudal artery. Agreement between OBP and IBP was evaluated with the Bland-Altman method. Guidelines of the American College of Veterinary Internal Medicine (ACVIM) were used for validation of the oscillometric device.

RESULTS

In awake dogs, mean bias of the oscillometric device was −11.12 mm Hg (95% limits of agreement [LOA], −61.14 to 38.90 mm Hg) for systolic arterial blood pressure (SAP), 9.39 mm Hg (LOA, −28.26 to 47.04 mm Hg) for diastolic arterial blood pressure (DAP), and −0.85 mm Hg (LOA, −40.54 to 38.84 mm Hg) for mean arterial blood pressure (MAP). In anesthetized dogs, mean bias was −12.27 mm Hg (LOA, −47.36 to 22.82 mm Hg) for SAP, −3.92 mm Hg (LOA, −25.28 to 17.44 mm Hg) for DAP, and −7.89 mm Hg (LOA, −32.31 to 16.53 mm Hg) for MAP. The oscillometric device did not fulfill ACVIM guidelines for the validation of such devices.

CONCLUSIONS AND CLINICAL RELEVANCE

Agreement between OBP and IBP results for awake and anesthetized dogs was poor. The oscillometric blood pressure device did not fulfill ACVIM guidelines for validation. Therefore, clinical use of this device cannot be recommended.

The development of new equipment for veterinary medicine has resulted in challenges for veterinary professionals who must decide which machines to use in their clinical practices. Often, equipment is introduced into the veterinary field with minimal testing or validation, which offers practitioners little guidance on which to base their selection.

General anesthesia is routinely performed by practitioners, who frequently anesthetize patients for routine procedures. Monitoring the cardiovascular system is part of the evaluation of clinical status and response to anesthetic agents. Blood pressure has been referred to as the fourth vital sign as an adjunct to body temperature, respiratory rate, and heart rate because undetected hypertension or hypotension can have major influences on morbidity and mortality rates.1,2

The American Animal Hospital Association recommends that blood pressure be evaluated during general anesthesia.3,4 This is especially important because hypotension is commonly associated with general anesthesia.5,6 A 2000 study7 that involved a survey of veterinarians in private practice revealed that only a small number had the ability to monitor blood pressure during general anesthesia, and a 2008 study8 in the United Kingdom found that blood pressure monitoring was used in only 11% of anesthetized dogs. Another study9 indicated that pulse oximetry was the method most commonly used by practitioners, whereas blood pressure monitoring was not commonly used.

The Association of Shelter Veterinarians advocate in their guidelines10 for spay-and-neuter programs that pulse oximetry is the monitoring metric of choice. Shelter veterinarians face economic challenges that differ from those of veterinarians at university teaching hospitals or specialty referral centers. Historically, obtaining an oscillometric device for measurement of blood pressure was financially challenging because these devices often were integrated into expensive multipurpose monitors, whereas stand-alone pulse oximetry monitors were more affordable. More recently, inexpensive veterinary-specific oscillometric devices for measurement of blood pressure have become commercially available. These devices resemble human oscillometric devices for measurement of blood pressure and are designed for at-home or in-clinic use. However, to the author's knowledge, no studies have been conducted to evaluate the agreement between OBP and IBP results.

The objective of the study reported here was to evaluate the extent of agreement between results of an inexpensive veterinary-specific oscillometric device for measurement of blood pressure and those of the criterion-referenced IBP system and to assess efficacy of the device in accordance with guidelines of the ACVIM.1 Because a device is validated only for the condition under which the validation test is conducted, blood pressure was measured in awake and anesthetized dogs.1 We hypothesized that results for the oscillometric device would have good agreement with IBP results and would fulfill the ACVIM validation criteria.

Materials and Methods

Animals

Nineteen healthy adult mixed-breed dogs (18 females and 1 male) from the research colony at Louisiana State University were used in the study. Dogs were housed in groups. Food was withheld for at least 8 hours before the start of the study, but dogs had ad libitum access to water. The study was approved by the Louisiana State University Institutional Animal Care and Use Committee (17-044).

Procedures

A physical examination was performed and sedation score assigned for each dog before the start of the procedures.11 A random number table was used to determine the forelimb (right or left) of a dog into which a catheter would be inserted. Skin of the assigned forelimb was aseptically prepared, and a 20-gauge cathetera was placed in the cephalic vein. Propofolb (4 mg/kg, IV) was administered until an adequate effect (loose jaw tone and palpebral reflexes that were decreased from before the propofol injection but still present) was achieved to enable arterial catheterization. Oxygen was provided via a face mask, and dogs were instrumented with ECG electrodes and a pulse oximeterc to monitor heart rate, heart rhythm, and arterial hemoglobin saturation. Respiratory rate was determined by visual observation of chest excursions.

Skin over the median caudal artery was aseptically prepared, and a 20-gauge cathetera was placed into the artery and secured. The arterial catheter was connected to a transducerd via noncompliant tubing filled with isotonic saline (0.9% NaCl) solution. This tubing was replaced between successive dogs. After the arterial catheter was placed, dogs were allowed to recover from sedation for at least 1 hour or until a sedation score of 0 was reached.

The forelimb contralateral to the IV catheter was used for placement of the blood pressure cuff of the oscillometric device.e The circumference of the proximal and distal aspects of the antebrachium was measured, and a cuff that had a width that was 40% of the mean of those 2 measurements was selected. Before measurements were obtained, the IBP system was pressurized to 300 mm Hg and the transducer was connected to a data acquisition system.f The lines were flushed to remove air bubbles that could have changed the damping coefficient of the system. The transducer was leveled with the tip of the arterial catheter for calibration (zero) to atmospheric pressure, and accuracy and linearity were assessed against a mercury manometer by use of a 2-point calibration technique (0 and 150 mm Hg). For oscillometric measurements, the antebrachium to which the cuff was applied was at the same level as the arterial catheter transducer.

Blood pressure measurements were initially obtained in conscious dogs, which were positioned in sternal recumbency with minimal restraint. Before each measurement was obtained, the IBP system was visually inspected and periodically flushed to prevent clot formation and to remove air bubbles. Observation of the quality of the pulse wave and a fast flush test were used to determine the natural frequency and damping coefficient of the IBP system; results were considered to be adequate for each dog.12,13 The data acquisition systemf was used to continuously record heart rate and IBP values for SAP, DAP, and MAP. Five paired (IBP and OBP) values for SAP, DAP, and MAP were obtained for each dog; there was a 4-minute interval between each paired measurement. The mean of the continuously recorded IBP values obtained during each corresponding oscillometric measurement was used for the paired values.

After blood pressures were measured in the awake dogs, the dogs received butorphanol tartrateg (0.3 mg/kg, IM). Dogs were allowed a 15-minute period to become sedated, and anesthesia was then induced with propofol (4 mg/kg, IV, titrated to effect). Each dog was intubated with an appropriately sized endotracheal tube. Anesthesia was maintained with isofluraneh in oxygen delivered via a circle system. Intermittent positive-pressure ventilation was applied with the aid of a mechanical ventilator.i Oxygen saturation as measured by pulse oximetry, end-tidal isoflurane concentration, ECG variables, and end-tidal partial pressure of CO2 were monitored with a multifunctional monitor.c End-tidal isoflurane concentration was maintained for each dog (target range, 0.9% to 1.2%) so that there was loose jaw tone and no palpebral reflex. End-tidal partial pressure of CO2 was maintained between 30 and 40 mm Hg by adjusting tidal volume and respiratory rate. After a 15-minute equilibration period to allow for stabilization of anesthetic depth, blood pressure measurements were collected from the anesthetized dogs in the same manner as for the awake dogs. During oscillometric measurements in the anesthetized dogs, the ventilator was turned off to avoid pulse pressure variation; the ventilator was immediately restarted after the measurement was obtained.

All oscillometric measurements were made by the same investigator (JC), who was unaware of the results obtained for invasive measurements. Repositioning of the cuff and error messages from the oscillometric device during the session were recorded. Possible error messages for the oscillometric device included cuff error, excessive movement, and weak signal.

No attempt was made to pharmacologically manipulate blood pressure, except when there was severe hypotension (MAP < 50 mm Hg) or bradycardia (< 60 beats/min). Treatments for these conditions were performed at the discretion of the anesthesiologist. After measurements were completed, the dogs were allowed to recover from anesthesia, and all catheters were then removed.

Statistical analysis

Agreement between SAP, DAP, and MAP values measured by use of invasive and noninvasive methods in awake and anesthetized dogs was evaluated by use of a linear mixed model, with the difference between paired IBP and OBP values as the response variable and dog as a random effect. The intercept of the model was equivalent to the bias determined by use of Bland-Altman analysis.14 The coefficient of reliability was calculated by dividing the variance for the model (with dog as a random effect) by the total variance observed. Values for the 95% LOA were obtained by calculating variance of the bias. Data were plotted as described by Bland and Altman.14 Alternative models were also fitted, with the difference between paired IBP and OBP values as the response variable, the mean of invasive and noninvasive measurements as covariates, and dog as a random effect.15 The slope, which corresponded to a proportional bias, was tested against a slope of 0. Assumptions of the model (linearity, normality of residuals, and homoscedasticity of residuals) and influential data points were assessed by examining standardized residual and quantile plots. Correlation of variables in the study was evaluated by use of the Pearson correlation coefficient. For all analyses, values of P < 0.05 were considered significant.

Distribution of body weight and the residuals from all mixed models were evaluated for normality by use of the Shapiro-Wilk test. Good agreement was defined as bias within ± 10 mm Hg and SD within ± 15 mm Hg. The statistical analysis was performed with commercially available software.j

Results

Dogs

All 19 dogs completed the study. Body weight of the dogs was not normally distributed, with a median of 13.5 kg (range, 10.3 kg to 32 kg). Median age of the dogs was 26 months (range, 23 to 148 months). On the basis of results of the physical examination and assessment of PCV and total solids concentrations, the enrolled dogs were deemed healthy and assigned an American Society of Anesthesiologists physical status score of 1. Ten paired OBP and IBP values were obtained from each dog.

Awake dogs

In awake dogs, IBP of SAP, DAP, and MAP ranged from 102 to 196 mm Hg, 53 to 114 mm Hg, and 70 to 139 mm Hg, respectively. A total of 72 errors, which included cuff error, weak signal, and motion artifact, were reported by the oscillometric device.

Agreement between OBP and IBP results for SAP, DAP, and MAP was poor. Mean bias for SAP was −11.12 mm Hg (95% CI, −21.91 to −0.94 mm Hg), which differed significantly (P = 0.034) from 0 mm Hg, with 95% LOA of −61.14 to 38.90 mm Hg. The coefficient of reliability was 0.58. Estimated proportional bias was 0.89 mm Hg (95% CI, 0.55 to 1.24 mm Hg), which differed significantly (P < 0.001) from 0 mm Hg (Figure 1). Mean bias for DAP was 9.39 mm Hg (95% CI, 3.45 to 15.33 mm Hg), which differed significantly (P = 0.038) from 0 mm Hg, with LOA of −28.26 to 47.04 mm Hg. The coefficient of reliability was 0.21. Estimated proportional bias was 1.49 mm Hg (95% CI, 1.27 to 1.72 mm Hg), which differed significantly (P < 0.001) from 0 mm Hg. Mean bias for MAP was −0.85 mm Hg (95% CI, −7.94 to 6.23 mm Hg), which did not differ significantly (P = 0.803) from 0 mm Hg, with LOA of −40.54 to 38.84 mm Hg. The coefficient of reliability was 0.37. Estimated proportional bias was 1.36 mm Hg (95% CI, 1.10 to 1.63 mm Hg), which differed significantly (P < 0.001) from 0 mm Hg.

Figure 1—
Figure 1—

Bland-Altman plots for paired OBP and IBP values for SAP (A), DAP (B), and MAP (C) in 19 awake dogs positioned in sternal recumbency. The IBP was obtained from the median caudal artery, and OBP was obtained with a cuff placed on a forelimb. The solid horizontal line indicates the mean difference (bias), the horizontal dotted lines represent the 95% LOA, and the diagonal dashed-and-dotted line indicates the proportional bias. Each circle represents a single measurement.

Citation: American Journal of Veterinary Research 80, 12; 10.2460/ajvr.80.12.1067

Anesthetized dogs

In anesthetized dogs, IBP values for SAP, DAP, and MAP ranged from 81 to 152 mm Hg, 32 to 81 mm Hg, and 57 to 102 mm Hg, respectively. A total of 24 errors (which included cuff error and weak signal) were reported by the oscillometric device. Three dogs developed second-degree atrioventricular block and were treated with atropinek (0.02 mg/kg, IV), which resolved the arrhythmia. Data acquisition was discontinued during the period of atropine treatment and resumed after the arrhythmia was resolved.

Agreement between OBP and IBP results for anesthetized dogs was poor. Mean bias for SAP was −12.27 mm Hg (95% CI, −20.50 to −4.03 mm Hg), which differed significantly (P = 0.006) from 0 mm Hg, with LOA of −47.36 to 22.82 mm Hg (Figure 2). The coefficient of reliability was 0.88, and estimated proportional bias did not differ significantly (P = 0.089) from 0 mm Hg. Mean bias for DAP was −3.92 mm Hg (95% CI, −8.59 to 0.75 mm Hg), which did not differ significantly (P = 0.095) from 0 mm Hg, with LOA of −25.28 to 17.44 mm Hg. The coefficient of reliability was 0.72. Estimated proportional bias was 0.19 mm Hg (95% CI, 0.04 to 0.33 mm Hg), which differed significantly (P = 0.012) from 0 mm Hg. Mean bias for MAP was −7.89 mm Hg (95% CI, −13.36 to −2.41 mm Hg), which differed significantly (P = 0.007) from 0 mm Hg, with LOA of −32.31 to 16.53 mm Hg. The coefficient of reliability was 0.77. Estimated proportional bias did not differ significantly (P = 0.381) from 0 mm Hg.

Figure 2—
Figure 2—

Bland-Altman plots for paired OBP and IBP values for SAP (A), DAP (B), and MAP (C) in 19 isoflurane-anesthetized dogs positioned in sternal recumbency. See Figure 1 for remainder of key.

Citation: American Journal of Veterinary Research 80, 12; 10.2460/ajvr.80.12.1067

Validation

The mean difference between OBP and IBP values for MAP and DAP was < 10 mm Hg and the SD was < 15 mm Hg only in anesthetized dogs (Table 1). For DAP, 39 of 76 (51.3%) of the OBP measurements were within 10 mm Hg of the IBP values, and for DAP and MAP, 73 of 76 (96.1%) and 64 of 76 (84.2%) of all OBP values were within 20 mm Hg of the IBP values. The correlation between OBP and IBP methods was < 0.90 for SAP, DAP, and MAP, independent of whether dogs were awake or anesthetized. The correlation between methods was better for DAP and MAP than for SAP. However, SAP and DAP did not fulfill the ACVIM validation criteria in awake or anesthetized dogs.

Table 1—

The ACVIM criteria for validation of oscillometric devices and summary statistics for comparisons of IBP and OBP results for 19 healthy adult dogs when awake and when anesthetized.

VariableBias (mm Hg)SD (mm Hg)Correlation coefficientPercentage within ± 10 mm Hg*Percentage within ± 20 mm Hg*
ACVIMWithin ± 10Within ± 15> 0.90≥ 50≥ 80
Awake
 SAP−11.1225.520.3526.355.3
 DAP9.3919.210.4352.676.3
 MAP−0.8520.250.50739.576.3
Anesthetized
 SAP−12.2717.910.2634.256.6
 DAP−3.9210.900.5251.396.1
 MAP−7.8912.460.6947.484.2

Bias is the mean of all differences between OBP and IBP results.

Represents the percentage of OBP values for SAP, DAP, and MAP within the specified range of the corresponding IBP values (n = 76 measurements obtained from awake and anesthetized dogs).

Recommended criteria for validation listed in the ACVIM guidelines.1

Value is in agreement with the ACVIM recommendation.

Discussion

The study reported here was conducted to investigate agreement of results for a commercially available handheld oscillometric device for measurement of blood pressure in dogs with IBP and to assess validation of the device in accordance with ACVIM guidelines.1 Good agreement was defined as bias within ± 10 mm Hg and SD within ± 15 mm Hg, which was not achieved for SAP, DAP, or MAP measured in awake or anesthetized dogs. Therefore, the oscillometric device for measurement of blood pressure did not fulfill the ACVIM validation criteria.

For awake dogs, bias of MAP did not differ significantly from 0 mm Hg; however, the 95% LOA were wide, which suggested that measurements could be 38.84 mm Hg higher than or 40.54 mm Hg lower than the actual value. The LOA for SAP and DAP were wide as well. The proportional bias for MAP in awake dogs indicated that with a decrease in pressure, underestimation of the actual value by use of the oscillometric device would increase. Some of the measurements in awake dogs were above reference values reported for dogs,1 which was in contrast to results for anesthetized dogs in which none of the measurements indicated an increase in blood pressure. Bias for MAP in anesthetized dogs was negative and differed significantly from 0 mm Hg, with wide LOA.

Oscillometric devices determine MAP by measuring oscillations emanating from the blood vessel wall during cuff deflation. These oscillations typically crescendo to a point of maximal intensity and then decrescendo as the pressure in the cuff decreases; this is commonly referred to as the oscillometric envelope. The MAP is equivalent to the pressure at the maximum oscillation,16–18 whereas SAP and DAP are estimated with the aid of proprietary algorithms, which may differ among devices. In the present study, agreement for MAP was poor between OBP and IBP results, with overestimation and underestimation of values throughout the range of measured blood pressures. A possible explanation for the incorrect estimation of MAP by the oscillometric device would be that instead of obtaining 1 clear maximal oscillation, a range of approximately even oscillations was generated.19 However, SAP and DAP were also underestimated and overestimated throughout the range of blood pressures, which suggested that the device also had problems with correct calculation of SAP and DAP.

Use of the correct cuff size and placement of the cuff may influence the accuracy of blood pressure measurements.20 When a blood pressure cuff is placed on the antebrachium, indirectly measured MAP has the best agreement with directly measured MAP when the cuff width corresponds to approximately 40% of the thoracic limb circumference.21 For all dogs of the present study, the circumference of the antebrachium was measured, and width of the cuff corresponded to 40% of the circumference. For that reason, it was unlikely that an inappropriate cuff size contributed to the poor agreement between OBP and IBP results.

Agreement between devices for noninvasive measurement of blood pressure and criterion-referenced measurements of blood pressure in conscious22–24 or anesthetized animals25–28 has been investigated. To the authors’ knowledge, evaluation of a device in both conscious and anesthetized dogs has been performed in only 1 study.29 In that study,29 accuracy of OBP was less in conscious dogs than in anesthetized dogs. Any movement may influence the oscillometric envelope and therefore contribute to false measurements.23 The dogs in the study reported here were acclimated to handling and lying in sternal recumbency; however, slight movements such as muscle contractions were unavoidable and may have influenced the measurements. General anesthesia may improve the accuracy of an oscillometric device by providing muscle relaxation and eliminating movement as a source of error.23 Lack of motion can allow the oscillometric device to measure blood pressure more rapidly and with fewer artifacts. Arterial blood pressure is not a static value, and anything that prolongs the measurement process could potentially contribute to inaccurate comparisons between measurements obtained with invasive and noninvasive methods.23 Nevertheless, in the present study, there was lack of agreement between IBP and OBP results for anesthetized and awake dogs despite fewer error messages for the anesthetized dogs.

The ACVIM guidelines1 provide criteria for validation of oscillometric devices, including the recommended bias, SD, required percentage of measurements within 10 to 20 mm Hg of the directly measured blood pressure, and a correlation coefficient > 0.90. Currently, no device has fulfilled the validation criteria. However, several tested devices have had reasonable agreement and can provide clinically useful data, even if they are not totally accurate.28,30,31 In the present study, SAP measurements obtained in awake and anesthetized dogs by use of the commercially available oscillometric device did not fulfill the ACVIM criteria for validation. Although DAP measurements met 4 of the 5 criteria in anesthetized dogs, the correlation coefficient was unacceptable at < 0.90.

A limitation of the study reported here was that no measurements were considered hypertensive (SAP > 150 mm Hg)1 in anesthetized dogs, with most of the measurements in the normotensive range and only a few in the hypotensive range (MAP < 60 mm Hg), without any being severely hypotensive (< 50 mm Hg). Overall, a wide range of blood pressures were included, and because the oscillometric device failed to provide accurate measurements for hypotensive and normotensive values, no further evaluation of measurements of hypertensive values was performed.

Another limitation was that all measurements were obtained with the dogs positioned in sternal recumbency, which does not reflect a common situation for anesthetized dogs. Because the purpose of the study was to compare accuracy of the device in awake and anesthetized dogs, changing the position could have biased the results. For this reason, all measurements were obtained with the dogs in the same body position.

Accurate measurement of blood pressure is an important component of the clinical evaluation of conscious and anesthetized animals, and clinical decisions are often made on the basis of the SAP and DAP readings. Prolonged episodes of hypotension during anesthesia may cause a decrease in perfusion and oxygen delivery to the brain and kidneys.32 Therefore, clinical decisions may not be accurate when made on the basis of results obtained with a device that provides unreliable values, such as the oscillometric device evaluated in the present study.

Acknowledgments

Supported by a Louisiana State University VCS Corp Grant (PG008269) awarded to Drs. Cremer and Paul.

The authors declare that there were no conflicts of interest.

ABBREVIATIONS

ACVIM

American College of Veterinary Internal Medicine

CI

Confidence interval

DAP

Diastolic arterial blood pressure

IBP

Invasively measured blood pressure

LOA

Limits of agreement

MAP

Mean arterial blood pressure

OBP

Oscillometrically measured blood pressure

SAP

Systolic arterial blood pressure

Footnotes

a.

Surflo IV catheter, Terumo Medical Corp, Somerset, NJ.

b.

Propoflo, Abbott Laboratories, Abbott Park, Ill.

c.

CARESCAPE monitor B850, GE Healthcare, Helsinki, Finland.

d.

Physiological pressure transducer, Memscap AS, Skoppum, Norway.

e.

CONTEC08A-VET LCD, Contec Medical Systems, Qinhuangdao, People's Republic of China.

f.

Powerlab data acquisition system, ADInstruments, Colorado Springs, Colo.

g.

Torbugesic, Zoetis, Parsippany, NJ.

h.

Isoflo, Abbott Laboratories, Abbott Park, Ill.

i.

Pneupac ParaPac ventilator, Smiths Medical, Dublin, Ohio.

j.

JMP Pro, version 13, SAS Institute Inc, Cary, NC.

k.

Med-Pharmex Inc, Pomona, Calif.

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Contributor Notes

Dr. da Cunha's present address is Department of Medicine, College of Veterinary Medicine, Midwestern University, Glendale, AZ 85308.

Address correspondence to Dr. Cremer (jcremer@lsu.edu).