Pleth Variability and Asthma Severity in Children

Patients with asthma have obstruction to exhalation resulting in hyperinflation of their lungs. This hyperinflation results in a phenomenon known as pulsus paradoxus in which the physiologic drop in blood pressure normally seen with inhalation is exaggerated. Studies have shown that patients with more severe asthma exacerbations (i.e. more hyperinflation) have a greater degree of pulsus paradoxus. Typically, pulsus paradoxus is measured using a sphygmomanometer, however, researchers have demonstrated that it can also accurately be measured using plethysmography, a term known as pleth variability index (PVI). Using this concept, Arnold et al (2008, 2010) showed that a greater degree of pulsus paradoxus correlates with asthma severity.

The investigators' study aims to simplify the association between PVI and asthma severity. The investigators hypothesize the following:

• Patients with a higher admission PVI will have a higher likelihood of being admitted to the hospital.
• Patients admitted to the Intensive Care Unit (PICU) will have a higher PVI than patients admitted to a floor.
• PVI can be accurately used to gauge response to bronchodilator/anti-inflammatory therapy.
• PVI is as effective as respiratory severity score in predicting asthma severity and in gauging response to bronchodilator therapy.

To do this the investigators will recruit children who present to the pediatric ED in status asthmaticus. They will be connected to a Masimo Radical 7 monitor upon admission to the ED and then again 4 hours later. In addition the investigators will calculate respiratory severity scores at those same time intervals. The investigators will then look at the disposition of the patient upon leaving the ED: discharge to home, admission to an inpatient floor or admission to the ICU.

Inclusion criteria

• Diagnosis of asthma or reactive airway disease upon leaving the ED
• Greater than 10 kg

Exclusion criteria

• Patients in whom effective pulse oximetry tracings cannot be obtained
• Patients who are diagnosed with conditions other than asthma/reactive airway disease that are known to cause pulsus paradoxus