A comparative study of upper limb and lower limb blood pressure measured by auscultatory and oscillometric method with intra-arterial blood pressure in hemodynamically unstable patients

Abstract

Introduction: Blood pressure (BP) measurement frequently guides management in critical care. Direct readings from a major artery is considered the gold standard. However, intra-arterial cannulation is associated with many risks. Hence, alternative noninvasive BP (NIBP) measurements are used for prolonged monitoring of BP among critically ill patients. Discrepancies between intra-arterial BP (IABP) and NIBP measurement can adversely affect therapeutic decisions and may have a negative impact of outcomes. Objectives: To compare upper limb and lower limb BP measured by auscultatory and oscillometric methods with IABP (by arterial cannulation) in hemodynamically unstable patients. Materials and Methods: Patients in the medical intensive care unit of Pushpagiri Institute of Medical Science and Research Centre were included over 24 months (50 patients admitted) in the clinical cross-sectional study. All patients who had a systolic BP (SBP) below 100 mmHg with an intra-arterial line were included under the study after obtaining an informed consent from the patient/patient's bystander. The study design was approved by the Ethics Committee at Pushpagiri Institute of Medical Science and Research Centre. Choice of cuff size was made based on the limb circumference (midarm and midcalf) and manufacturer guidelines. BP was measured in arm using a welch allyn aneroid manometer. Oscillometric NIBP was relied on an MP20 model (Philips Medical Systems) connected to the nondisposable, reusable cuff. The intra-arterial catheter was connected through a pressure transducer to the monitor (Philips). With the patient supine, the pressure transducer was zeroed at the level of the mid-axillary line and the correct shape of the arterial pressure waveform was ascertained. Measurements: BP was measured at 0 h, 3 h and once the patient becomes hemodynamically stable using auscultatory, oscillometric, and IABP at arm and calf, respectively. Quantitative variables were expressed as mean standard deviation, whereas categorical variables were expressed as frequency (%). Karl Pearson's Correlation Coefficient was used to find our relationship of BP measured by two different methods with BP measured using arterial cannulation. P < 0.05 was considered the threshold for statistical significance. Statistical analyses was performed using a Statistical Software Package SPSS version 20. Results: Out of 50 patients admitted in a hemodynamically unstable state, 68% were male and 32% were female. Male-to-female ratio was 2.125. The mean age of patients was 65.9 ± 12.2. Majority of the patients belonged to the age group 61–70 years (30%) and the least number of patients in age group <50 years (8%). Arm SBP and diastolic BP (DBP) measured by auscultatory and oscillometric method at the arm showed a positive correlation to intra-arterial SBP (IASBP) and intra-arterial DBP (IADBP) at 0 h, 3 h and once stable, which were statistically significant. Similarly, Arm SBP and DBP measured by auscultatory and oscillometric method at calf showed positive correlation to IASBP and IADBP at 0 h, 3 h, and once stable, which were statistically significant. The method used for measuring BP was irrelevant at 0 h and once stable, but at 3 h, SBP was better measured by the oscillometric method than by the auscultatory method. Conclusion: Noninvasive methods (auscultatory and oscillometric) can be used reliably for measuring BP in hemodynamically unstable patients instead of intra-arterial methods. Correlation tends to improve as BP becomes more stable.