In the United States, asthma accounts for nearly two million ED visits each year [1
]. Management decisions are largely subjective and based on exam findings, vital signs, and pulse oximetry [2
]. Symptoms are often underestimated by the child and parent. Children with longstanding symptoms are less likely to report symptoms and are more likely to present with hypoxia and a severe, life-threatening asthma exacerbation [3
In the present pilot study, we demonstrated the feasibility and compliance of noninvasive PFT results in the ED, as well as the predictive value associated with disposition (admission versus discharge) to aid in resource utilization. Since these measurements have not been utilized in this setting, we set out to determine the feasibility of performing these measurements in this setting with the assistance of respiratory therapy, the compliance of patients with the evaluation techniques, and the post-hoc predictive value of the results (clinicians were initially blinded to the PFT results at the time of admission). Finally, we were interested in a convenient, noninvasive, assessment tool employing tidal breathing analysis that indicates the severity of the wheezing exacerbation. Thus, we are speculating that this objective diagnostic approach may be used in the future to determine from the moment of triage the likelihood that a given patient would require a prolonged ED visit. A decision regarding disposition could then be made early, decreasing the patient's ED length of stay (LOS). Our results supported our hypothesis in that we had a 93% patient acceptance of the study and high compliance rate, which supports the feasibility of performing such a test in the ED. Patients as young as 3 years were able to perform the task with minimal coaching, and age was not a confounding factor in compliance. Once consent data were obtained, the initial assessment was performed in 15 minutes or less.
Pulmonary function tests, including RIP and PT via a mask using a pediatric respiratory profile monitor, have been developed to evaluate patients who are minimally cooperative due to age (neonatal/pediatric population) or clinical condition as presented in the ED [5
]. In earlier studies, these same PFT methods have been utilized in preterm and term infants, infants and children with skeletal dysplasias, and in children with asthma [9
]. In addition, the American Thoracic Society states that TAA and tidal expiratory flow analyses are promising techniques for assessing lung function in children [5
]. Measurements are performed rapidly and repeatedly with minimum disturbance to the child, and there is potential for clinical use to assess patients in acute respiratory distress when other techniques cannot be applied [3
The presence of TAA is reflective of increased work of breathing [5
]. Normal reference values are available in healthy children [12
]. In infants with airflow obstruction secondary to chronic lung disease or acute infection, the change in phase angle correlated with changes in lung resistance. In studies involving adolescents with cystic fibrosis and infants with bronchopulmonary dysplasia or bronchiolitis, the phase angle shift calculated from the motion indices of the rib cage versus the abdominal wall was significantly higher when compared to healthy controls [5
]. Previous studies have also determined that changes measured by the RIP in infants with airflow obstruction after bronchodilators correlate well with changes in lung resistance and compliance [15
]. These data validate the use of RIP in the evaluation and re-evaluation of asthmatics as an objective measure of the severity of asthma/wheezing exacerbation.
As shown in the RIP data, we found that LBI, phase angle, and asthma scores were all significantly higher in those patients admitted versus discharged from the ED. It can be inferred that they had a more severe exacerbation that led to their required admission. Thus, prospective utilization of these parameters in the ED may provide an additional predictive value associated with disposition (admission versus discharge) to aid in resource utilization and to guide therapy. With a larger sample size, it may be possible to predetermine RIP values that further assist in predicting which patients require admission and the type of therapy required. Thus, increased predictability on the decision to admit greatly decreases LOS in the ED. Furthermore, patient satisfaction would likely increase if LOS in the ED were lessened.
In addition to RIP data, the PT analysis provided pulmonary breathing patterns of tidal flow by simultaneous measurement of flow and volume and by CO2 analysis of expired gas. As noted in , our patients typically demonstrated an uneven rise in end-tidal CO2 during expiration (compared to normal children). This rise in CO2 correlates with unequal emptying of CO2 from lung compartments, indicating lower-airway obstruction. Finally, the PFT equipment allows calculation of the above mentioned indices from flow and CO2 determinations, thus enabling real-time data collection and breath analysis for leaks and consistent tidal volume history.
Figure 3 Pneumotachography measurements. (a) End-tidal CO2 pattern in an admitted 12-year-old patient enrolled in our study. Note the rise in end-tidal CO2 during the last portion of expiration (no clear plateau was observed). (b) End-tidal CO2 pattern of a control (more ...)
There are currently no satisfactory normative data for tidal flow measurements in preschool children. Adults, children, and infants with wheezing disorders have been shown in most studies to have lower mean tVEF
when compared to controls [5
]. In older children, tVEF
has correlated well with FEV1
. Treatment with bronchodilators in wheezing infants and young children has been shown to increase tVEF
. It has been reported that tidal breathing analysis is an objective measurement in asthmatics [3
]. In this regard, tidal breathing analysis demonstrated that the patients enrolled in this study had a lower tidal volume compared to the predictive values. Furthermore, a larger sample size may have demonstrated that tVEF
values correlate better with the current subjective measures for deciding patient admission versus discharge.
Our study had a few inherent limitations. Since the study was a pilot study, the initial results are based on a limited sample size. It is anticipated, however, that these positive outcomes, with regard to feasibility, test compliance, and potential predictability of admission, will enable us to perform a much larger prospective study in which PFT will be utilized in patient disposition and therapy guidance. Post-hoc analysis of the enrolled patients, again due to sample size, did not allow a uniform distribution of patients with regard to gender, age, race, or severity of disease. Furthermore, based on the observational study design, the PFT results could not be utilized to guide therapy or triage patients. With regard to PFT methodology, the RIP techniques have the advantage of being noninvasive, require no calibration or cooperation for phase and synchrony evaluations; however, accurate calibration of the RIP technology is difficult and requires detailed regression analysis using RIP and tidal breathing correlations [15
]. In the present study, we used a noncalibrated RIP method for phase and synchrony evaluations and used an abbreviated two point RIP-tidal breathing calibration for evaluation of labored breathing index. Finally, it should be noted that the RIP Lissajous approach was developed for sinusoidal breathing patterns, and not complex patterns associated with some distressed breathing patterns. However, it has been shown that even in distorted loops, the calculated phase angle is still a good estimate of synchrony, and the error has been estimated at <10% [15