Continuous Noninvasive Measurement of Pulsus Paradoxus Complements Medical Decision Making in Assessment of Acute Asthma Severity

Continuous Noninvasive Measurement of Pulsus Paradoxus Complements Medical Decision Making in Assessment of Acute Asthma SeverityPulsus paradoxus (PP) is a pathophysiologic vital sign that historically has been a cornerstone in the evaluation of patients with acute asthma.2, However, the measurement of PP is rarely performed, and the accuracy of its measurement via sphygmo-manometry is questionable. Despite this, PP has been used in a number of asthma studies and continues to be a recommended metric by the National Asthma Education and Prevention Program (NAEPP) expert panel report 2. The value of PP as a pathophysiologic measure is well established. Acute asthma is attributable to airway inflammation and reversible airflow limitation leading to dynamic lung hyperinflation.” PP is a measure of inspiratory impedance as it affects pleural pressure, left ventricular output, and right ventricular output. Therefore, the measurement of PP is pertinent to respiratory distress, inspiratory muscle elastic loading and fatigue, air leakage, and other mechanical consequences of dynamic hyperinflation during acute asthma.
Expert guidelines also support the utility of peak expiratory flow rate (PEFR) measurement in both patient self-monitoring and emergency department (ED) disposition of patients with acute asthma, However, because PEFR is highly dependent on patient technique and effort, values can change considerably from measure to measure. Further, PEFR diaries can be unreliable, which may lead to a misunderstanding of a patient’s personal best PEFR on which the emergent evaluation is based. PEFR also underestimates airway obstruction and the overall severity of an asthmatic exacerbation as air trapping results in dynamic hyperinflation.
A need exists for an objective criterion in evaluating acute asthma that is independent of effort, is well-validated, and is familiar to clinicians. The NAEPP expert panel report 1 guidelines in 199116 specified 12 mm Hg as the PP level that supported hospital admission. This threshold was not tested prospectively in a clinical study. An investigation conducted by our group showed that a PP of 11 mm Hg accurately identified acutely asthmatic pediatric patients who were in need of hospital admission. The PP values in that investigation were calculated post hoc by hand from digitized continuous noninvasive BP data and a respiratory strain gauge. The present study was undertaken to develop and test a signal-processing algorithm that would determine and display automated (AT) PP without the aid of a respiratory phase measure. This study was conducted in adult patients with acute asthma. Signal detection theory was used to identify the AT-PP threshold for hospital admission. Patient dispositions, as determined by the treating physicians, were compared to the AT-PP. A second part of this investigation, which was conducted in the laboratory, identified the reproducible alterations in oximetric plethysmography as a result of induced PP in a healthy adult volunteer. We hypothesize that inspiratory variation in plethysmography is the most logical and clinically appropriate way to measure PP in routine clinical practice.

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