Agreement Between Tongue-Based Oscillometric and Invasive Blood Pressure in Anesthetized Dogs of Various Weights
ABSTRACT
This study aimed to evaluate the agreement between oscillometric blood pressure (OBP) measured from the tongue and invasive blood pressure (IBP) measured from the dorsal pedal artery in anesthetized dogs of various body weights. Forty-five client-owned dogs undergoing general anesthesia for surgery or imaging scan were included; weights ranged from 2.5 to 42.6 kg. Agreement between paired IBP and OBP during normotension was verified with reference standards used in small animals and humans. The data were stratified by body weight (≤5 kg versus >5 kg). In the >5 kg group (n = 29), the bias ± standard deviation for mean (2.1 ± 7.9 mm Hg) and diastolic pressure (−2.7 ± 7.9 mm Hg) exhibited reliability that met human standards (<5 ± 8 mm Hg). However, in the ≤5 kg group (n = 16), the bias ± standard deviation met only veterinary standards (≤10 ± 15 mm Hg) for mean (3.1 ± 10.2 mm Hg) and diastolic pressure (−2.5 ± 12.6 mm Hg). Agreement for systolic pressure did not meet either standard for both groups. This study demonstrates that tongue-based OBP is a close estimate of mean/diastolic blood pressure in anesthetized dogs (>5 kg) during normotension by small-animal and human criteria.
Introduction
Arterial blood pressure is a vital sign that is routinely monitored via invasive blood pressure (IBP) or noninvasive blood pressure (NIBP) measurements during general anesthesia.1–4 IBP measurements are considered to be more accurate than NIBP measurements, but IBP measurements may not be always obtainable.1,2 NIBP monitoring techniques using Doppler and oscillometric devices commonly used in veterinary medicine, as indirect measurements, require optimization of the accuracy of NIBP measurements.2–5 Whereas the Doppler technique only provides systolic arterial pressure (SAP) estimates,5 the oscillometric blood pressure (OBP) device calculates SAP and diastolic arterial pressure (DAP) electronically using fixed or variable parameter identification points based on the mean arterial pressure (MAP) values and heart rate.3–5 Because the failure to properly recognize abnormalities in arterial blood pressure can lead to diagnostic and therapeutic errors, a thorough understanding of the interpretation of NIBP measurements is essential to ensure appropriate decision-making in the management of blood pressure abnormalities in anesthetized dogs.1–5
The accuracy of OBP is potentially influenced by the site of cuff placement, and it is generally agreed that the oscillometric technique is more appropriate for use in animals weighing >5 kg.6,7 The thoracic limb is a primary cuff-placement site, and cuff positions above or below the carpus, above or below the hock, or on the tail have been compared in previous studies.2,8 Recently, a study investigated the possible agreement between OBP measured from the tongue and IBP in anesthetized beagles weighing 11.1 ± 1.2 kg.9 The study suggested that OBP measured from the tongue provides an accurate assessment of the MAP and DAP.9 However, the experiment was conducted exclusively on beagles, and the fact that dogs of various weights and breeds were not investigated constitutes a limitation.
The congruence between certain commercially available oscillometric monitors and IBP measurement has been investigated in dogs.2–4,8,10–12 NIBP validation for small animals depends on any one of the following two sets of criteria: (1) the American College of Veterinary Internal Medicine (ACVIM) criteria and (2) those of the American Association for Medical Instrumentation (AAMI). ACVIM criteria governing NIBP monitor use stipulate a mean bias and precision of ≤10 and ≤15 mm Hg, respectively, compared with those of IBP.13 Absolute differences between IBP and NIBP are limited to 10 mm Hg of 50% and 20 mm Hg of 80% of all NIBP and IBP measurements, respecitvely.13 AAMI criteria governing NIBP device use stipulate a mean bias and precision of <5 and <8 mm Hg, respectively, in relation to the reference standard.14 The AAMI standards for humans are stricter than are those for small animals.4
The objectives of this clinical investigation were to determine if OBP measured from the tongue is a favorable estimate of SAP, MAP, and DAP in various weights of anesthetized dogs (≤5 kg versus >5 kg) according to the ACVIM and AAMI criteria.
Materials and Methods
Animals
This clinical study was approved by the Institute of Animal Care and Use Committee of Seoul National University (SNU-200712-1) and performed at the Veterinary Medical Teaching Hospital of Seoul National University between October and December 2020. All owners consented to the academic use of patient information. A total of 45 client-owned dogs undergoing general anesthesia for surgery or imaging scan were included in this study. Included dogs were those who already had an arterial catheter as part of their monitoring plan during anesthesia. No exclusion criteria were applied regarding the disease state of the animals or the anesthetic protocol used. All patients described in this study were clinically managed according to modern standards of care.
Procedure
The dogs were classified based on the American Society of Anesthesiologists grading scale according to preanesthetic examination results and underlying diseases. Before anesthesia, food and water were withheld for 12 and 3 hr, respectively. The cephalic vein was catheterized using an over-the-needle polyurethane cathetera. Hartmann’s solutionb or plasma solution Ac was infused at 5–10 mL/kg/hr during the perioperative period. Antibiotic therapy (cefazolind 22–33 mg/kg IV) was administered every 2 hr during surgery. Dogs were sedated with acepromazinee (0.005 mg/kg IV) or midazolamf (0.1–0.2 mg/kg IV). A constant infusion rate of a combination of remifentanilg (6 μg/kg/hr), lidocaineh (3 mg/kg/hr), and ketaminei (0.6 mg/kg/hr) or that of remifentanil (6 μg/kg/hr) and ketamine (0.6 mg/kg/hr) was maintained for analgesia. Induction was performed with alfaxalonej (1–2 mg/kg IV), and the doses were titrated to effect. Following orotracheal intubation, the patients were connected to a rebreathing circuit systemk, and anesthesia was maintained with isofluranel in oxygen 100%. The respiratory rate was individually adjusted to maintain the end-tidal carbon dioxide concentration within a capnometryvalue range of 35–45 mm Hg (4.6–6.0 kPa) under pressure-controlled ventilation. An intra-arterial catheter (22–24 gauge) was inserted in the dorsal pedal artery after intubation. The arterial catheter was connected to a transducer systemm that had previously been calibrated against a mercury column via fluid-filled (heparinized 0.9% sodium chloride; 2 IU mL−1) noncompliant tubing (500 mm length). For this system, a zero-level reference was set at the height of sternum in lateral recumbency. It was intermittently flushed for purposes of eliminating air bubbles and preventing clots. A multiparameter monitorn was connected to the transducer. Arterial pressure waveform accuracy was established by visually inspecting the presence of two wave deflections following the fast-flush test.15 The fast-flush test was conducted by drawing the fast-flush tab and rapidly discharging it numerous times, and all IBP system damping coefficients were appropriate for this study. During anesthesia, lead II electrocardiography was used to continuously monitor heart rate and rhythm. A multiparameter monitor was used to continuously monitor IBP measurements, including SAP, MAP, and DAP, respiratory rate, oxygen saturation, end-tidal carbon dioxide concentration, end-tidal concentration of isoflurane, esophageal temperature, tidal volume, and compliance from spirometry and oxygen saturation, which were recorded every 5 min during anesthesia.
Experimental Protocol
All dogs were positioned in lateral recumbency before surgery. Single-tube disposable cuffso were positioned rostral to the lingual frenulum (Figure 1) and connected to a veterinary OBP monitorp, which had been validated for tongue oscillometric technique in a previous study.9 The tongue circumferences were measured to calculate the tongue circumference ratio (cuff bladder width:circumference). Cuff size was determined based on the manufacturer’s recommendations (a range indicator in the “optimal range,” marked by a bolded line on the cuff). In cases in which the OBP monitor failed to read the blood pressure, the cuff was repositioned, and the instrument was restarted. Measurements were taken when systolic IBP was in normal ranges (90–139 mm Hg). OBP measurement was initiated at the start of data collection. At the end of each measurement cycle, the OBP and IBP were recorded simultaneously.
Citation: Journal of the American Animal Hospital Association 59, 3; 10.5326/JAAHA-MS-7325
Paired comparisons between the IBP and the OBP measured from the tongue (SAPTONGUE, MAPTONGUE, and DAPTONGUE) were performed. After discarding the initial measurement, five consecutive measurements were recorded. Vascular catheters were removed following data collection, and each dog recovered from anesthesia.
Statistical Analyses
MedCalcq was used for all statistical analyses, and the ACVIM guidelines were used for sample size determination; these guidelines stipulate that a minimum of eight animals is required for comparisons involving an intra-arterial method. Bland-Altman analysis with multiple measurements per subject was employed to examine the agreement between IBP and OBP.14 Underestimation and overestimation of the IBP result were indicated by positive and negative biases, respectively, and precision was defined as the standard deviation of the mean bias between the paired results.14 Overall mean bias measurements (bias = IBP − OBP), precision (mean bias standard deviation), and 95% limits of agreement (mean bias ± [1.96 × precision]) were presented.14 The Bland-Altman analysis was performed by dividing the overall data by the number of cases in the >5 kg of body weight (BW>5 kg) and those ≤5 kg (BW≤5 kg).
Results
Sample
There were three males (7%), 16 castrated males (35%), 14 females (31%), and 12 spayed females (27%). The mean age of the dogs was 6.8 ± 3.8 yr (range, 1–15 yr), and the mean weight was 12.3 ± 12.0 kg (range, 2.5–42.6 kg). Sixteen dogs weighed ≤5 kg, and 29 dogs weighed >5 kg. The most represented breed was Maltese (n = 8, 17.8%), followed by miniature poodle (n = 7, 15.6%), Labrador retriever (n = 5, 11.1%), Pomeranian (n = 4, 8.9%), and others (n = 21, 46.6%). Seventeen were admitted for orthopedic surgery (37.8%), 25 for soft-tissue surgery (55.6%), and three for imaging scans (6.6%). The cuff circumference ratio was 0.42 ± 0.06. OBP measurements were performed five times in each dog for a total of 225 measurements. The IBP was recorded 225 times, at each display of the OBP device results at the end of the measurement cycle. All dogs recovered from anesthesia without systemic abnormalities.
Bland-Altman Analysis with Multiple Measurements per Subject
Table 1 and Figure 2 show the agreement between IBP and OBP measured from the tongue, stratified by body weight (≤5 kg, >5 kg). SAPTONGUE in BW>5 kg and BW≤5 kg did not satisfy either the ACVIM or the AAMI criteria and underestimated the invasive SAP. The mean bias and precision of MAPTONGUE and DAPTONGUE in BW>5 kg met the ACVIM and AAMI criteria. However, MAPTONGUE and DAPTONGUE in BW≤5 kg only met the ACVIM criteria.
Citation: Journal of the American Animal Hospital Association 59, 3; 10.5326/JAAHA-MS-7325
Discussion
This study aimed at determining the agreement between IBP and OBP measured from the tongue in clinical settings. According to the ACVIM criteria, MAPTONGUE and DAPTONGUE were clinically interchangeable with IBP in both groups, whereas SAPTONGUE was not. In addition, MAPTONGUE and DAPTONGUE in BW≤5 kg did not satisfy the AAMI criteria, exhibiting less reliable results than BW>5 kg.
In a previous study, the tongue was considered an OBP cuff placement site, demonstrating reliable estimates of MAP and DAP according to ACVIM and AAMI criteria in normotensive, anesthetized beagles, whereas SAP did not satisfy any criteria.6 The present study, as in previous experiments, revealed that MAPTONGUE and DAPTONGUE in BW>5 kg were in acceptable agreement with the IBP in clinical settings, based on ACVIM and AAMI criteria. However, in BW≤5 kg, MAPTONGUE and DAPTONGUE only satisfied the ACVIM guidelines, a result that differs from those of the previous study. The SAPTONGUE exhibited poor agreement, failing to satisfy either set of criteria in either group.
In this study, a positive bias indicated an underestimation of the IBP, and wide limits of agreement indicated poor agreement between the two methods in general. Not only did SAPTONGUE fail to satisfy the ACVIM and AAMI criteria but it also had a positive bias, revealing an underestimation of the invasive SAP. Furthermore, a wide limits of agreement reflected a poor agreement with invasive SAP in both groups. Poor agreement with the SAP is considered a feature of OBP devices and is not dependent on the cuff site.2 Significant underestimation of SAP by OBP devices has been reported at other cuff placement sites (thoracic and pelvic limbs) in dogs.2,16–18
MAPTONGUE and DAPTONGUE in BW>5 kg proved clinically acceptable, satisfying both sets of criteria. However, in BW≤5 kg, MAPTONGUE and DAPTONGUE did not satisfy the AAMI criteria. In general, consensus holds that oscillometric technique is optimal for animals weighing >5 kg.6 Apparently, OBP measurement is less reliable in cats and small dogs owing to their smaller peripheral arteries, potentially resulting in a pulse pressure insufficient to produce detectable cuff pressure oscillations.1,19 In this study, the oscillometric equipment included a veterinary-specific OBP device with a setting for large and small dogs, and the manufacturer’s instructions recommended the small dog setting for any animal weighing <8 kg, which was the procedure followed here. In BW≤5 kg, for MAPTONGUE and DAPTONGUE, the ACVIM criteria were satisfied, whereas those of the AAMI criteria were not. Therefore, when interpreting MAPTONGUE and DAPTONGUE, careful interpretation is considered necessary for animals weighing ≤5 kg.
The current study has certain limitations. First, OBP and IBP were exclusively obtained from the tongue and the dorsal pedal artery, respectively. Blood pressure is not consistent throughout a dog’s body, and that measured invasively potentially varies according to measurement site and body location.20 Second, measurements were taken only in the normotensive range. Because these animals were client owned, the anesthesiologists were obliged to exercise caution and manipulate blood pressure pharmacologically if hypotension developed (SAP <90 mm Hg).21 Third, because there are no results for long-term use in this study, it is necessary to check the possibility of tongue swelling or venous congestion during a long procedure.
Conclusion
MAPTONGUE and DAPTONGUE are fairly accurate estimations of IBP when the patient weighs >5 kg according to ACVIM and AAMI criteria. However, when the patient weighs ≤5 kg, cautious reading is required because in such cases these measures only meet the ACVIM criteria. Furthermore, SAPTONGUE is no replacement for invasive SAP in any size of patient.
An anesthetized dog to measure oscillometric blood pressure from tongue (tongue circumference ratio: 0.47). (A) Measurement of the tongue circumference using a metric tape. (B) A cuff placed around the tongue. Cd., cranial; Cr., caudal.
Bland-Altman plots of the agreement between invasive arterial blood pressure and oscillometric blood pressure measured from tongue. Bland-Altman plots are plotted between (A) invasive systolic (SAPinvasive), (B) mean (MAPinvasive), and (C) diastolic (DAPinvasive) arterial pressure versus oscillometric systolic (SAP≤5 kg), mean (MAP≤5 kg), and diastolic (DAP≤5 kg) arterial pressure, respectively, in dogs weighing ≤5 kg, and versus oscillometric (D) systolic (SAP>5 kg), (E) mean (MAP>5 kg), and (F) diastolic (DAP>5 kg) arterial pressure, respectively, in dogs weighing >5 kg. The continuous line represents mean bias, dotted wide lines represent the limits of agreement (mean bias ± 1.96 standard deviations), and dotted closed line represents the zero level.
Contributor Notes
