Indirect Doppler ultrasonic measurement of arterial blood pressure results in a large measurement error in dorsally recumbent anaesthetised horses

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.

The effect of xylazine on intracranial pressure in anesthetized and standing horses

OBJECTIVE

To determine the effect of xylazine on intracranial pressure (ICP) in standing compared to isoflurane-anesthetized horses.

DESIGN

Prospective, crossover study design.

SETTING

University Teaching Hospital.

ANIMALS

Six adult horses donated to the University. Horses were determined to be healthy via physical examination, complete blood count, and neurological evaluation.

INTERVENTIONS

Horses were anesthetized, maintained on isoflurane in oxygen in left lateral recumbency, and ventilated to normocapnia. Horses were instrumented for intraparenchymal measurement of ICP, invasive blood pressure, pulse oximetry, and end tidal gas analyzer. Xylazine 1 mg/kg was administered IV and ICP, systolic arterial pressure, mean arterial pressure (MAP), diastolic arterial pressure, and heart rate were recorded and cerebral perfusion pressure (CPP) was calculated for the following 15 minutes. Twenty-four to 36 hours following anesthetic recovery, xylazine 1 mg/kg was administered IV and ICP, heart rate, and Doppler blood pressure (BPdop) on the tail were monitored for 15 minutes.

MEASUREMENTS AND MAIN RESULTS

There was a decrease in ICP following administration of xylazine in anesthetized horses (P < 0.003) but not standing horses (P = 0.227). There was an increase in systolic arterial pressure, MAP, diastolic arterial pressure (P < 0.001), and BPdop (P = 0.001) following administration of xylazine. As a result, CPP increased in anesthetized horses (P < 0.03). There was a negative association between ICP and MAP in anesthetized horses (P = 0.007) but not ICP and BPdop conscious horses (P = 0.379).

CONCLUSIONS

Administration of xylazine to anesthetized horses resulted in an increased CPP due to decreased ICP with concurrent increased MAP. Administration of xylazine to standing horses did not result in a change in ICP. However, with the increase in BPdop found in awake horses, it is likely that CPP would also increase in awake horses following xylazine administration.

Comparison of oscillometric, Doppler and invasive blood pressure measurement in anesthetized goats

Arterial blood pressure (BP) can be measured directly using an invasive intra-arterial method. This method is considered a gold standard, however it is potentially hazardous and requires expensive equipment and professional skills. Therefore, two non-invasive methods–Doppler ultrasonic sphygmomanometry and oscillometry–have been introduced in veterinary medicine. Their accuracy has so far been reliably evaluated in various animal species, however only one study included a small group of goats. Therefore, we carried out a large-scale study which aimed to evaluate agreement between the two non-invasive methods and invasive intra-arterial BP measurement in anesthetized goats at various age. The study included 122 goats of two Polish local breeds (Polish White Improved and Polish Fawn Improved): 67 adult females, 35 adult males, and 20 two-month-old female kids. Goats were anesthetized with the intravenous mixture of xylazine and ketamine. BP was measured simultaneously with the three methods in each goat with 7 measurements on average taken. The study showed that according to the criteria of the American College of Veterinary Internal Medicine (ACVIM) oscillometric method yielded BP measurements sufficiently consistent with invasive intra-arterial method in anesthetized adult goats– 95% of oscillometric BP measurements were expected to differ from invasive BP measurements by at most ±20–25 mmHg. The agreement was worse in goat kids–oscillometry significantly overestimated invasive BP measurements, which resulted in highly asymmetrical 95% limits of agreement. Doppler systolic BP very poorly conformed to invasive systolic BP both in adult goats and in kids and all the ACVIM criteria were violated. Concluding, oscillometry, but not Doppler ultrasonic sphygmomanometry, may be regarded as an alternative to invasive BP measurement in large-scale scientific studies involving adult goats, however, individual oscillometric BP measurements should be treated with caution as estimated 95% limits of agreement were wide.

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.

A study of measurement of noninvasive blood pressure with the oscillometric device, Sentinel, in isoflurane-anaesthetized horses

OBJECTIVE

To assess accuracy of noninvasive blood pressure (NIBP) measured by oscillometric device Sentinel compared to invasive blood pressure (IBP) in anaesthetized horses undergoing surgery. To assess if differences between the NIBP measured by the Sentinel and IBP are associated with recumbency, cuff placement, weight of the horse or acepromazine premedication and to describe usefulness of the Sentinel.

STUDY DESIGN

Prospective study examining replicates of simultaneous NIBP and IBP measurements.

ANIMALS

Twenty-nine horses.

METHODS

Invasive blood pressure was measured via a catheter in the facial artery, transverse facial artery or metatarsal artery. NIBP was measured using appropriate size cuffs placed on one of two metacarpal or metatarsal bones or the tail in random order. With both techniques systolic (SAP), mean (MAP), and diastolic (DAP) arterial blood pressures and heart rates (HR) were recorded. A mixed effects model compared the IBP to the NIBP values and assessed potential effects of catheter placement, localisation of the cuffs in combination with recumbency, weight of the horse or acepromazine premedication.

RESULTS

Noninvasive blood pressure yielded higher measurements than IBP. Agreement varied with recumbency and cuff position. Estimated mean differences between the two methods decreased from SAP (lateral recumbency: range -5.3 to -56.0 mmHg; dorsal recumbency: range 0.8 to -20.7 mmHg), to MAP (lateral recumbency: range -1.8 to -19.0 mmHg; dorsal recumbency: range 13.9 to -16.4 mmHg) to DAP (lateral recumbency: range 0.5 to -6.6 mmHg; dorsal recumbency: range 21.0 to -15.5 mmHg). NIBP measurement was approximately two times more variable than IBP measurement. No significant difference between IBP and NIBP due to horse's weight or acepromazine premedication was found. In 227 of 1047 (21.7%) measurements the Sentinel did not deliver a result.

CONCLUSION AND CLINICAL RELEVANCE

According to the high variability of NIBP compared to IBP, NIBP measurements as measured by the Sentinel in the manner described here are not considered as an appropriate alternative to IBP to measure blood pressure in anaesthetized horses.

Doppler blood pressure measurement in pigs during anaesthesia

To determine the accuracy of Doppler blood pressure measurement in anaesthetised pigs eight large white pigs (Sus scrofa) were anaesthetised with zolazepam and tiletamine as Zoletil 100 (4 mg/kg) and xylazine (2 mg/kg) by intramuscular injection followed by isoflurane in 100% oxygen. Blood pressure measurements were recorded using a Doppler probe on the radial artery and a catheter in the femoral artery connected to a transducer. The sample mean of the Doppler measurements were compared with the sample mean of the invasive systolic arterial blood pressure while accounting for the heart rate, end-tidal CO2 and temperature. The predicted error of the Doppler was greatest when pigs were hypotensive and normothermic: 11 mmHg (CI: 6-15). Doppler measurements should be interpreted with caution in anaesthetised pigs that are hypotensive and normothermic.

Inotropes and vasopressors in adults and foals

Successful treatment with inotropes and vasopressors depends on an understanding of the interplay of flow, pressure, and resistance in the cardiovascular system and an appreciation of the pathophysiologic mechanisms leading to inadequate tissue perfusion. Any treatment strategy is necessarily a compromise between the requirements of different vascular beds.Furthermore. the underlying hemodynamic derangements can change rapidly. Therefore. inotropes and vasopressors should be titrated to measures of improved hemodynamic status, and the treatments should be frequently reviewed.

Cardiac emergencies and problems of the critical care patient

Cardiac disease and dysfunction can occur as a primary disorder(ie, with pathology situated in one or more of the cardiac structures) or can be classified as a secondary problem when it occurs in patients with another primary problem that has affected the heart either directly or indirectly. Primary cardiac problems are encountered in horses presented to emergency clinics; however,this occurs much less frequently in equine critical patients than cardiac problems arising secondary to other conditions. Nevertheless,if primary or secondary cardiac problems are not identified and addressed, they certainly contribute to the morbidity and mortality of critical care patients.