Intra-aortic balloon pumps (IABPs) are widely used as circulatory assist devices, supporting hemodynamics in critically ill patients. Indications for intra-aortic counterpulsation have expanded to include cardiogenic shock, as an adjunct to high-risk coronary interventions, weaning from cardiopulmonary bypass, preoperative use in high-risk coronary bypass patients, and bridge to therapies such as transplant or durable left ventricular support devices.1
The early diastolic pressure attained during inflation is referred to as the augmented diastolic pressure and is typically greater than the systolic pressure.2 This may confound usual oscillometric noninvasive blood pressure (NIBP) measurement. Oscillometric NIBP measures mean arterial pressure (MAP) at the point of maximum amplitude of oscillation generated by arterial pulsation as pressure cuff deflates.3 Systolic blood pressure (SBP) and diastolic blood pressure (DBP) are calculated by a variety of proprietary algorithms determined by the equipment manufacturer. Factors influencing the various algorithms include excessive noise, altered waveforms, cardiac arrhythmias, and varying pulse pressure—each of which can be distorted by the IABP. There continues to be ambiguity regarding optimal method for blood pressure monitoring in these patients, with some experts suggesting the IABP console MAP as the truest measurement of central aortic pressure.4 Despite being routinely recorded,5 there are no published data evaluating the association between noninvasive and IABP blood pressure in this population.
This study was conducted as a single-center (St. Boniface Hospital, Winnipeg, Canada) prospective observational study. Data were gathered from patients presenting to hospital from August 1, 2017, to March 31, 2019. The study design and protocol were approved by the University of Manitoba Bannatyne Campus Health Research Ethics Board (Ethics Number HS20782) and the St. Boniface Hospital Research Review Committee.
Consecutive patients 18 years old or older in whom an IABP was inserted within the last 24 hours were considered for participation. All IABPs were inserted percutaneously in the cardiac catheterization laboratory by an interventional cardiologist via the femoral artery with fluoroscopic guidance. Patients were excluded if the rhythm was nonsinus or if the patient had an additional circulatory support device placed before enrollment. Invasive blood pressure measurements were obtained from the IABP console (Maquet, Rastatt, Germany) set to 1:1 augmented beat ratio with simultaneous NIBP measurements obtained from an automated digital sphygmomanometer (Philips, Amsterdam, The Netherlands) placed on the right arm. Simultaneous IABP and NIBP measurements were obtained for each patient. SBP, DBP, augmented diastolic blood pressure (ADBP), and MAP were noted. Demographics, height, weight, device size, and reason for IABP insertion were obtained from existing clinical records. Pearson correlation coefficients were computed. Bland–Altman diagrams were created to plot NIBP measurements compared with invasive IABP measurements.
Over the 34 month study period, 36 patients were identified as eligible with three declining participation. Thirty-three patients were included in the final analysis, 56% male with a mean age of 67 ± 9 years (Figure 1). Eight patients (24%) had a previously inserted independent radial arterial monitor. Mean body mass index was 29.5 ± 4.7 kg/m2 and median device size was 40 cm (range, 34–40 cm). Indications for IABP insertion included cardiogenic shock secondary to myocardial infarction (left ventricular failure) (22 patients, 67%), cardiogenic shock secondary to mechanical complication of a myocardial infarction (four patients, 12%), support of high-risk percutaneous coronary intervention (six patients, 18%), and preoperative support of patient with severe coronary artery disease (one patient, 3%). There were no immediate complications from IABP insertion.
Mean heart rate was 82 ± 14 min–1. Noninvasive MAP and IABP MAP were correlated (r = 0.88; p < 0.0001), with Bland–Altman bias –3.2 mmHg (95% limits of agreement [LOA], –15.6 to +9.0 mmHg) (Figure 2A). Noninvasive SBP and IABP SBP were correlated (r = 0.71; p < 0.001) with bias of +19.8 mmHg (95% LOA, –10.0 to +49.7 mmHg) (Figure 2B). Noninvasive SBP and IABP augmented DBP strongly correlated (r = 0.90; p < 0.001) with bias of +0.5 mmHg (95% LOA, –15.3 to +16.4 mmHg) (Figure 2C). Noninvasive DBP and IABP DBP weakly correlated (r = 0.44; p = 0.01) with bias of +5.0 mmHg (95% LOA, –19.2 to +29.3 mmHg) (Figure 2D). Among the eight patients with radial arterial monitoring, a comparison of radial artery to IABP blood pressures was performed (see Supplemental Figure 1, Supplemental Digital Content 1, http://links.lww.com/ASAIO/A489).
Given lack of demonstrated mortality benefit with routine use in post myocardial infarction cardiogenic shock, the use of IABP has declined over past decade. However due to availability, familiarity and cost, it remains the most commonly utilized mechanical cardiac support device in use.6–8
Our data suggest that NIBP measurements are an imprecise representation of IABP blood pressure measurements in patients with IABP. This is particularly true of noninvasive SBP, as the bias of +19.8 mmHg represents a systematic overestimation of true SBP that is unacceptable for clinical use. Although the bias for other measures were more modest (especially noninvasive MAP), the wide limits of agreement suggest that the reliability of noninvasive measurements are poor. When IABP monitoring is not possible (for instance, because of failure of the pressure sensor or transducer; or where the console screen is malfunctioning or not visible), it may be sensible to use the noninvasive MAP as a surrogate, recognizing that blood pressures may be underestimated/overestimated by up to 15 mmHg. Interestingly, noninvasive SBP was more proximate to IABP ADBP than SBP. This may be related to the systematic overestimation of SBP and the fact that ADBP is typically higher than SBP.
Although data suggest that IABP is increasingly used simultaneously with ventricular assist devices9 and extracorporeal membrane oxygenation,10 we deliberately excluded these patients from the study. This limits the generalizability of our findings to those with an IABP as the sole mechanical circulatory assist device. Regardless, no patients considered for our study had simultaneous IABP and ventricular assist device.
Our findings support the use of IABP console blood pressure measurements as the reference standard for monitoring and clinical decision-making. The utility of NIBP measurements by oscillometry is especially dubious for SBP monitoring, with poor reliability and wide margins of error. Acknowledging its imprecision, noninvasive MAP may be a tolerable approximation of IABP MAP where invasive monitoring is prohibitive.
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