Agreement of high definition oscillometry with direct arterial blood pressure measurement at different blood pressure ranges in horses under general anaesthesia

Comparison of Four Arteries for Invasive Blood Pressure Measurements and Dixtal 2010 Oscillometric Values in Horses Anesthetized With Isoflurane: Does the Artery Matter?

This study evaluated the agreement between invasive blood pressure (IBP) values measured in three different arteries and by an oscillometric device (NIBP) with the ones from the transverse facial artery (FA). Six horses (424.2 ± 40.7 kg) were sedated with xylazine (0.6 mg/kg IV), induced with ketamine (2 mg/kg IV) and midazolam (0.1 mg/kg IV), and maintained with isoflurane (1.2 MAC) for 90 minutes in lateral recumbency. FA, auricular artery (AA), lateral digital artery (LDA), and metatarsal artery (MA) were catheterized, and a standard adult cuff was placed on the tail. IBP and NIBP values were recorded at 30, 45, 60, 75, and 90 minutes of anesthesia. Data were analyzed with Shapiro-Wilk and Repeated-Measures Bland-Altman. Values for FA (mm Hg) were 85.4 ± 10.3 for SAP, 70.6 ± 9.3 for MAP, and 58.5 ± 9.5 for DAP. Mean bias and 95% Limit of agreement (LOA) for AA were -1.7 (-29.0 to 25.6), 2.2 (-18.4 to 22.9), 1.9 (-18.2 to 22.0), for LDA: 1.4 (-25.1 to 27.8), 2.9 (-19.3 to 25.0), 2.3 (-18.4 to 22.9), for MA: -3.2 (-28.3 to 22.0), 2.7 (-16.6 to 22.1), 4.9 (-13.8 to 22.2), and for NIBP: -5.7 (-28.3 to 16.9), 7.9 (-9.5 to 25.3), 17.2 (-2.4 to 36.8), for SAP, MAP and DAP respectively. There is a reasonable bias for IBP values among the arteries evaluated, however a wide LOA, demonstrating the arteries are not interchangeable. NIBP method from Dixtal 2010 results in inaccurate blood pressure values in horses.

Agreement of High-Definition Oscillometry (HDO) and Invasive Blood Pressure Measurements at a Metatarsal Artery in Isoflurane-Anaesthetised Horses

Simple Summary

In equine anaesthesia, valid and reliable blood pressure monitoring is crucial for adequate blood pressure management. Various non-invasive blood pressure monitors have been studied with varying results. High-definition oscillometry (HDO) promises greater accuracy than conventional oscillometric devices. With the cuff placed at the tail, the monitor gives satisfactory readings in normotensive anaesthetised horses, while for measuring low and high blood pressure, reliability was inadequate. To date, high-definition oscillometry has not been evaluated at the easily accessible equine metatarsal area. Therefore, the objective of this study was to assess agreement between HDO and invasive blood pressure, both obtained at a metatarsal artery at different blood pressure ranges in anaesthetised horses. Additionally, compliance with the American College of Veterinary Internal Medicine consensus guidelines was assessed. Agreement of HDO and invasive blood pressure was acceptable for mean arterial blood pressure during normotension only. During hypotension and hypertension, measurements were not valid. The monitor failed to meet most of the consensus validation criteria. Consequently, invasive blood pressure measurement remains preferable in haemodynamically unstable patients.

Abstract

High-definition oscillometry (HDO) over the metatarsal artery (MA) in anaesthetised horses has not yet been evaluated. This study aimed to assess agreement between HDO and invasive blood pressure (IBP) at the metatarsal artery, and to evaluate compliance with the American College of Veterinary Internal Medicine (ACVIM) consensus guidelines. In this experimental study, 11 horses underwent general anaesthesia for an unrelated, terminal surgical trial. Instrumentation included an IBP catheter in one and an HDO cuff placed over the contralateral MA, as well as thermodilution catheters. Systolic arterial pressure (SAP), mean arterial pressure (MAP), diastolic arterial pressure (DAP), and cardiac output were measured simultaneously. Normotension (MAP 61–119 mmHg) was maintained during the surgical study. Subsequently, hypotension (MAP ≤ 60 mmHg) and hypertension (MAP ≥ 120 mmHg) were induced pharmacologically. For MAP, the agreement between HDO and IBP was acceptable during normotension, while during hypotension and hypertension, IBP was overestimated and underestimated by HDO, respectively. The monitor failed to meet most ACVIM validation criteria. Consequently, if haemodynamic compromise or rapid blood pressure changes are anticipated, IBP remains preferable.

Bias Associated with Peripheral Non-Invasive Compared to Invasive Arterial Blood Pressure Monitoring in Healthy Anaesthetised and Standing Horses Using the Bionet BM7Vet

To compare arterial blood pressure (ABP) measured invasively (IBP) to ABP measured non-invasively (NIBP) via oscillometry in healthy anaesthetised and standing horses using the Bionet BM7Vet. Fourteen horses were anaesthetised for elective procedures (anaesthetised group) and 10 horses were enrolled for standing blood pressure manipulation (standing group). In both groups, IBP and NIBP-corrected to heart level were measured every 3 min using the Bionet BM7Vet. The overall mean difference (bias), standard deviation and limits of agreement (LOA) were calculated for paired IBP and NIBP systolic (SAP), mean (MAP) and diastolic (DAP) blood pressure measurements. In anaesthetised horses, the NIBP cuff was placed at either the proximal tail base or the metacarpus. Invasive MAP was used to retrospectively characterise measurements into hypotensive (≤70 mm Hg), normotensive (71–110 mm Hg) or hypertensive (≥111 mm Hg) subgroups. In standing horses, the NIBP cuff was placed at the tail base only and invasive MAP was manipulated to achieve hypertension (≥126 mm Hg) and hypotension (≤90 mm Hg) using phenylephrine and acepromazine, respectively. When measuring NIBP at the tail in anaesthetised horses, the Bionet BM7Vet failed on 8/185 occasions and overestimated SAP, MAP and DAP during hypotension and normotension. The biases (lower, upper LOA) for MAP were −11.4 (−33.3, 10.5) and −6.0 (−25.8, 13.8) mm Hg, respectively. Hypertension could not be evaluated. When measuring NIBP at the metacarpus in anaesthetised horses, the Bionet BM7Vet failed on 24/65 occasions and underestimated SAP, MAP and DAP when all ABP subgroups were combined. The bias (lower, upper LOA) for pooled MAP was 3.6 (−44.3, 51.6) mm Hg. When measuring NIBP at the tail in standing horses, the Bionet BM7Vet failed on 64/268 occasions and underestimated SAP, MAP and DAP during hypotension, normotension and hypertension. The biases (lower, upper LOA) for MAP were 16.3 (−10.5, 43.1), 16.6 (−19.5, 52.7) and 30.0 (−8.1, 68.0) mm Hg, respectively. Monitoring NIBP on the Bionet BM7Vet in anaesthetised horses overestimated ABP at the tail and underestimated ABP at the metacarpus. The device inaccurately detected hypotension and should be used cautiously. In standing horses, the Bionet BM7Vet underestimated ABP at the tail, especially during pharmacologically induced hypertension.

Pharmacokinetics of xylazine after 2-, 4-, and 6-hr durations of continuous rate infusions in horses

Intravenous (i.v.) bolus administration of xylazine (XYL) (0.5 mg/kg) immediately followed by a continuous rate infusion (CRI) of 1 mg kg^-1  hr^-1 for 2, 4, and 6 hr produced immediate sedation, which lasted throughout the duration of the CRI. Heart rate decreased and blood pressure increased significantly (p > .05) in all horses during the first 15 min of infusion, both returned to and then remained at baseline during the duration of the infusion. Compartmental models were used to investigate the pharmacokinetics of XYL administration. Plasma concentration-time curves following bolus and CRI were best described by a one-compartment model. No differences were found between pharmacokinetic estimates of the CRIs for the fractional elimination rate constant (K_e ), half-life (t_1/2e ), volume of distribution (V_d ), and clearance (Cl). Median and range were 0.42 (0.15-0.97)/hr, 1.68 (0.87-4.52) hr, 5.85 (2.10-19.34) L/kg, and 28.7 (19.6-39.5) ml min^-1  kg^-1 , respectively. Significant differences were seen for area under the curve ( AUC 0 ∞ ) (p < .0002) and maximum concentration (C_max ) (p < .04). This indicates that with increasing duration of infusion, XYL may not accumulate in a clinically relevant way and hence no adjustments are required in a longer XYL CRI to maintain a constant level of sedation and a rapid recovery.

Agreement between invasive and oscillometric arterial blood pressure measurements using the LifeWindow multiparameter monitor and two cuff sizes in anesthetized adult horses

OBJECTIVE

To assess agreement between oscillometric noninvasive blood pressure (NIBP) measurements using LifeWindow monitors (LW9xVet and LW6000V) and invasive blood pressure (IBP). To assess the agreement of NIBP readings using a ratio of cuff width to mid-cannon circumference of 25% and 40%.

STUDY DESIGN

Prospective, randomized clinical study.

ANIMALS

A total of 43 adult horses undergoing general anesthesia in dorsal recumbency for different procedures.

METHODS

Anesthetic protocols varied according to clinician preference. IBP measurement was achieved after cannulation of the facial artery and connection to an appropriately positioned transducer connected to one of two LifeWindow multiparameter monitors (models: LW6000V and LW9xVet). Accuracy of monitors was checked daily using a mercury manometer. For each horse, NIBP was measured with two cuff widths (corresponding to 25% or 40% of mid-cannon bone circumference), both connected to the same monitor, and six paired IBP/NIBP readings were recorded (at least 3 minutes between readings). NIBP values were corrected to the relative level of the xiphoid process. A Bland-Altman analysis for repeated measures was used to assess bias (NIBP-IBP) and limits of agreement (LOAs).

RESULTS

The 40% cuff width systolic arterial pressure [SAP; bias 7.9 mmHg, LOA -26.6 to 42.3; mean arterial pressure (MAP): bias 4.9 mmHg, LOA -28.2 to 38.0; diastolic arterial pressure (DAP): bias 4.2 mmHg, LOA -31.4 to 39.7)] performed better than the 25% cuff width (SAP: bias 26.4 mmHg, LOA -21.0 to 73.9; MAP: bias 15.7 mmHg, LOA -23.8 to 55.2; DAP: bias 10.9 mmHg, LOA -33.2 to 54.9).

CONCLUSIONS AND CLINICAL RELEVANCE

Using the LifeWindow multiparameter monitor in anesthetized horses, the 40% cuff width provided better agreement with IBP; however, both cuff sizes and both monitor models failed to meet American College of Veterinary Internal Medicine Consensus Statement Guidelines.

Blood Pressure Reference Intervals for Ketamine-sedated Rhesus Macaques (Macaca mulatta)

Appropriate calculation and use of reference intervals have widespread clinical and research implications. Unfortunately, reference intervals for blood pressure in one of the most commonly used NHP species, rhesus macaques (Macaca mulatta), have never been calculated. Although anesthetic drugs and noninvasive methods of blood pressure measurement both have known effects on blood pressure values, their use provides the safest, fastest, and most widely used approach to clinical evaluation and blood pressure collection in this species. We analyzed noninvasive blood pressure measurements from 103 healthy, ketamine-sedated, adult (age, 8 to 16 y) rhesus macaques, representing both sexes, with various body condition scores by using 2 types of sphygmomanometers at 3 different anatomic locations. Reference intervals were calculated for each device, in each location, thus establishing normative data beneficial to clinical veterinarians assessing animal health and encouraging researchers to use noninvasive methods. Age, body condition score, sex, type of sphygmomanometer, and location of cuff placement were all found to influence blood pressure measurements significantly, providing important information necessary for the appropriate interpretation of noninvasive blood pressure values in rhesus macaques.

The effect of insulin infusion on heart rate and systemic blood pressure in horses with equine metabolic syndrome

BACKGROUND

There is little evidence that horses with equine metabolic syndrome (EMS) have higher resting blood pressures than horses with normal insulin sensitivity. However, there are indications that EMS horses have an altered dynamic response to the cardiovascular effects of insulin.

OBJECTIVES

To examine heart rate and the systemic blood pressure response in EMS and control horses during insulin infusion.

STUDY DESIGN

Cross-sectional study.

METHODS

Horses were examined with an oral sugar test (OST) and a euglycaemic hyperinsulinaemic clamp (EHC). Based on the results from the OST, the horses were classified as either EMS or control. Blood pressure was measured before the start of the EHC and at 60, 120 and 180 min of the EHC.

RESULTS

There were 16 EMS and 12 control horses. Mean resting heart rate was higher for EMS horses compared with control (35.6 ± 5.1 vs. 30.3 ± 3.5 beats/min). Systolic, diastolic and mean arterial blood pressure did not differ between groups at the start of the EHC. Blood pressure decreased gradually during the EHC in the control group, whereas the EMS group showed no decline in systolic, diastolic or mean arterial pressure.

MAIN LIMITATIONS

Limited number of horses.

CONCLUSIONS

Horses with EMS have cardiovascular changes that affect resting heart rate and systemic blood pressure during insulin infusion.

Cardiac Monitoring in Horses

Monitoring variables of cardiac performance in horses is challenging owing to patient size, temperament, and anatomic peculiarities. Blood pressure is a major determinant of afterload, but it is not a reliable surrogate of cardiac performance and tissue perfusion. Cardiac output, together with arterial and venous oxygen content, provides insight as to the adequacy of delivery of blood and oxygen to the body as a whole and can be used to gauge the fluid responsiveness and cardiovascular status of the patient. Measurement of intracardiac pressures serves to assess cardiac filling pressures, myocardial performance, and vascular resistance.

Evaluation of oscillometric blood pressure monitor BLT M9000 VET in anaesthetised healthy adult dogs

To examine agreement in anaesthetised dogs between invasive blood pressure measurements and measurements obtained with an oscillometric blood pressure monitor.

MATERIALS AND METHODS

Paired invasive and oscillometric measurements were taken in 24 dogs every 5 minutes during anaesthesia (9 to 37 measurements per dog). Agreement between measurement methods was explored using Bland-Altman plots. To determine the accuracy of the oscillometric measurements, the results were compared with the guidelines recommended by the American College of Veterinary Internal Medicine and the Association for the Advancement of Medical Instrumentation.

RESULTS

In total, 493 paired readings were obtained: 98·6% of oscillometric readings were successful. Biases (±standard deviation) for oscillometric readings of systolic arterial blood pressure and mean arterial blood pressure were 2·1 (±11·5) and -9·8 (±7·6) mm Hg, indicating slight over- and under-estimation, respectively, versus invasive measurements. More than 50% and 80% of systolic arterial and mean arterial pressure measurements were within 10 and 20 mmHg of invasively measured values, respectively. A large negative bias (-14·1 ±9·2 mmHg) against invasive measurements revealed that the oscillometric measures of diastolic arterial blood pressure measurements were under-estimated.

CLINICAL SIGNIFICANCE

In healthy adult anaesthetised dogs, this oscillometric monitor met the American College of Veterinary Internal Medicine requirements for systolic arterial and mean arterial pressure measurement but failed to meet the requirements for the measurement of diastolic arterial pressure.

The effect of anesthetic drug choice on accuracy of high-definition oscillometry in laterally recumbent horses

OBJECTIVE

To determine the accuracy of high-definition oscillometry (HDO) for arterial pressure measurement during injectable or inhalation anesthesia in horses.

STUDY DESIGN

Prospective, clinical study.

ANIMALS

Twenty-four horses anesthetized for procedures requiring lateral recumbency.

METHODS

Horses were premedicated with xylazine, and anesthesia induced with diazepam-ketamine. Anesthesia was maintained with xylazine-ketamine-guaifenesin combination [TripleDrip (TD; n = 12) or isoflurane (ISO; n = 12)]. HDO was used to obtain systolic (SAP), mean (MAP) and diastolic (DAP) arterial pressures, and heart rate (HR) using an 8-cm-wide cuff around the proximal tail. Invasive blood pressure (IBP), SAP, MAP, DAP and HR were recorded during HDO cycling. Bland-Altman analysis for repeated measures was used to compare HDO and IBP for all measurements. The generalized additive model was used to determine if means in the differences between HDO and IBP were similar between anesthetic protocols for all measurements.

RESULTS

There were >110 paired samples for each variable. There was no effect of anesthetic choice on HDO performance, but more variability was present in TD compared with ISO. Skewed data required log-transformation for statistical comparison. Using raw data and standard Bland-Altman analysis, HDO overestimated SAP (TD, 3.8 ± 28.3 mmHg; ISO, 3.5 ± 13.6 mmHg), MAP (TD, 4.0 ± 23.3 mmHg; ISO, 6.3 ± 10.0 mmHg) and DAP (TD, 4.0 ± 21.2 mmHg; ISO, 7.8 ± 13.6 mmHg). In TD, 26-40% HDO measurements were within 10 mmHg of IBP, compared with 60-74% in ISO. Differences between HDO and IBP for all measurements were similar between anesthetic protocols. The numerical difference between IBP and HDO measurements for SAP, MAP and DAP significantly decreased as cuff width:tail girth ratio increased toward 40%.

CONCLUSION AND CLINICAL RELEVANCE

More variability in HDO occurred during TD. The cuff width:tail girth ratio is important for accuracy of HDO.

Blood pressure in Warmblood horses before and during a euglycemic-hyperinsulinemic clamp

Background

Insulin resistance (IR) in humans is related to hypertension and impaired vasodilation. Insulin administration has been shown to lower blood pressure both in insulin resistant as well as in insulin sensitive individuals. The aim of the study was to investigate the association between insulin sensitivity and alterations in blood pressure in healthy horses before and after a euglycemic-hyperinsulinemic clamp (EHC). A 3-h EHC was performed in 13 healthy horses (11 mares, 2 geldings). Blood samples for measurement of plasma glucose and insulin were collected before the start of the EHC, every 10 min during the EHC and immediately after the EHC. Mean, systolic- and diastolic blood pressure was measured before and during the final 10 min of the EHC using an indirect high-definition oscillometric monitor (HDO, horse model) applied to the middle of the coccygeal artery. Five consecutive measurements were made in each horse and on each occasion. Insulin and glucose data from the EHC were used to calculate the mean rate of glucose disposal per unit of insulin during steady state (M/I ratio). Insulin resistance was defined as a M/I ratio <5 mg/kg/min/mUL (Lindåse et al. in Am J Vet Res 77:300–309, 2016).

Results

Insulin administration decreased systolic, diastolic and mean arterial pressure in all horses. The M/I ratio for all horses was negatively correlated with the decrease in systolic blood pressure (r² = 0.55, P = 0.004) and mean arterial pressure (r² = 0.31, P = 0.048) but not diastolic blood pressure (r² = 0.12, P = 0.26). Eight horses were defined as insulin resistant (IR) and five horses had normal insulin sensitivity. The five horses with normal insulin sensitivity showed a greater decrease in systolic blood pressure (−17.0 ± 7.4 vs. −3.4 ± 4.6 mmHg, P = 0.001) and MAP (19.2 ± 14.7 vs. 6.9 ± 8.7 mmHg, P = 0.04) than IR horses. There was no difference in the decrease in diastolic blood pressure between groups (16 ± 12.8 vs. 8.9 ± 12.1 mmHg, P = 0.17).

Conclusions

This study indicates that there is a relationship between insulin sensitivity and systolic and MAP in horses. However, studies on a larger number of horses are needed to confirm this association.

Accuracy and Precision of Noninvasive Blood Pressure in Normo-, Hyper-, and Hypotensive Standing and Anesthetized Adult Horses

Background

Blood pressure is relevant to the diagnosis and management of many medical, cardiovascular and critical diseases. The accuracy of many commonly used noninvasive blood pressure (NIBP) monitors and the accuracy of NIBP measurements in hypo‐ and hypertensive standing horses has not been determined.

Hypothesis/Objectives

The objective of this study was to investigate the accuracy of an oscillometric BP monitor in standing horses before and during pharmacologically induced hyper‐ and hypotension and to compare results in standing and anesthetized horses.

Animals

Eight standing mares from a research herd (SG) and eight anesthetized horses from a hospital population (AG).

Methods

Prospective experimental and observational studies. Invasive blood pressure (IBP) and NIBP, corrected to heart level, were measured simultaneously. In the SG hyper‐ and hypotension were induced by administration of phenylephrine (3 μg/kg/min IV for 15 minutes) and acepromazine (0.05 mg/kg IV), respectively. In the AG NIBP and IBP were recorded during regular hospital procedures.

Results

There was a significant correlation between mean NIBP and IBP in standing (R = 0.88, P < .001) and anesthetized horses (R = 0.81, P < .001). The mean bias (lower, upper limit of agreement) was 16.4(−16.1, 48.9) mmHg for mean BP in the SG and 0.5(−22.3, 23.2) mmHg in the AG. The NIBP device was capable of identifying the increase and decrease in BP in all horses, but in the SG significant correlation between NIBP and IBP was only detected for the normotensive phase.

Conclusion and Clinical Importance

While the evaluated oscillometric BP device allowed estimation of BP and adequately differentiated marked trends, the accuracy and precision were low in standing horses.

Equivalence between invasive and oscillometric blood pressures at different anatomic locations in healthy normotensive anaesthetised horses

REASONS FOR PERFORMING STUDY

Accurate blood pressure measurement is essential for effective clinical assessment and appropriate interventions in anaesthetised horses. Information on the accuracy of oscillometry for blood pressure measurement on the appendages of mature horses is limited.

OBJECTIVES

To assess equivalence between invasive and oscillometric blood pressures at different anatomic locations in horses.

STUDY DESIGN

Prospective experimental study using 6 healthy mature horses.

METHODS

Blood pressure was measured invasively in the right transverse facial artery and noninvasively by oscillometry in nondependent limbs and tail of laterally recumbent sevoflurane- or desflurane-anaesthetised horses. Cuff widths of 5-12 cm were tested on the tail, metatarsus, metacarpus and distal radius/ulna. Equivalence between mean arterial pressure (MAP) oscillometric and MAP invasive was assessed using a linear mixed effects model with a significance level of P≤0.05.

RESULTS

Twenty paired measurements were obtained for each cuff size in each of the locations, totalling 340 measurements. There was only one location (tail) and one cuff width (6 cm; cuff width-to-tail circumference ratio of 0.25) that resulted in equivalence between MAP measured with the oscillometric and the invasive methods (P = 0.8). All other locations (metacarpus, radius/ulna, metatarsus) and cuff widths were not equivalent (P≤0.01).

CONCLUSIONS

A cuff width-to-tail circumference ratio of 0.25 is recommended for accurate oscillometric blood pressure measurement in mature, laterally recumbent anaesthetised normotensive horses. Studies with variable haemodynamics are warranted. Oscillometric measurements at other extremities and/or with other cuff sizes cannot be recommended for clinical use.