Literature Review

Pleth Variability Index shows promise for asthma assessments


Clinical question: Does pulse variability on plethysmography, or the Pleth Variability Index (PVI), correlate with disease severity in obstructive airway disease in children?

Background: Asthma is the most common reason for hospitalization in the United S. for children 3-12 years old. Asthma accounts for a quarter of ED visits for children aged 1-9 years old.1 Although systems have been developed to assess asthma exacerbation severity and the need for hospitalization, many of these depend on reassessments over time or have been proven to be invalid in larger studies.2,3,4 Pulsus paradoxus (PP), which is defined as a drop in systolic blood pressure greater than 10 mm Hg, correlates with the severity of obstruction in asthma exacerbations, but it is not practical in the children being evaluated in the ED or hospital.5,6 PP measurement using plethysmography has been found to correlate with measurement by sphygmomanometry.7 Furthermore, PVI, which is derived from amplitude variability in the pulse oximeter waveform, has been found to correlate with fluid responsiveness in mechanically ventilated patients. To this date, no study has assessed the correlation between PVI and exacerbation severity in asthma.

Dr. Weijen Chang

Dr. Weijen Chang

Study design: Prospective observational study.

Setting: A 137-bed, tertiary-care children’s hospital.

Synopsis: Over a 6-month period on weekdays, researchers enrolled patients aged 1-18 years evaluated in the ED for asthma exacerbations or reactive airway disease. ED staff diagnosed patients clinically, and other patients with conditions known to affect PP – such as dehydration, croup, and cardiac disease – were excluded. PVI was calculated by measuring the minimum perfusion index (PImin) and the maximum perfusion index (PImax) using the following formula:

A printout of the first ED pulse oximetry reading was used to obtain the PImax and PImin as below:

Researchers followed patients after the initial evaluation to determine disposition from the ED, which included either discharge to home, admission to a general pediatrics floor, or admission to the PICU. The hospital utilized specific criteria for disposition from the ED (see Table 1).

Of the 117 patients who were analyzed after application of exclusion criteria, 48 were discharged to home, 61 were admitted to a general pediatrics floor, and eight were admitted to the PICU. The three groups were found to be demographically similar. Researchers found a significant difference between the PVI of the three groups, but pairwise analysis showed no significant difference between the PVI of patients admitted to the general pediatrics floor versus discharged to home (see Table 2).

Bottom line: PVI shows promise as a tool to rapidly assess disease severity in pediatric patients being evaluated and treated for asthma, but further studies are needed to validate this in the ED and hospital setting.

Citation: Brandwein A, Patel K, Kline M, Silver P, Gangadharan S. Using pleth variability as a triage tool for children with obstructive airway disease in a pediatric emergency department [published online ahead of print Oct. 6, 2016]. Pediatr Emerg Care. doi: 10.1097/PEC.0000000000000887.


1. Care of children and adolescents in U.S. hospitals. Agency for Healthcare Research and Quality website. Available at: Accessed Nov. 18, 2016.

2. Kelly AM, Kerr D, Powell C. Is severity assessment after one hour of treatment better for predicting the need for admission in acute asthma? Respir Med. 2004;98(8):777-781.

3. Keogh KA, Macarthur C, Parkin PC, et al. Predictors of hospitalization in children with acute asthma. J Pediatr. 2001;139(2):273-277.

4. Keahey L, Bulloch B, Becker AB, et al. Initial oxygen saturation as a predictor of admission in children presenting to the emergency department with acute asthma. Ann Emerg Med. 2002;40(3):300-307.

5. Guntheroth WG, Morgan BC, Mullins GL. Effect of respiration on venous return and stroke volume in cardiac tamponade. Mechanism of pulsus paradoxus. Circ Res. 1967;20(4):381-390.

6. Frey B, Freezer N. Diagnostic value and pathophysiologic basis of pulsus paradoxus in infants and children with respiratory disease. Pediatr Pulmonol. 2001;31(2):138-143.

7. Clark JA, Lieh-Lai M, Thomas R, Raghavan K, Sarnaik AP. Comparison of traditional and plethysmographic methods for measuring pulsus paradoxus. Arch Pediatr Adolesc Med. 2004;158(1):48-51.

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