Initial Modified Pulmonary Index Score Predicts Hospital Length of Stay for Asthma Subjects Admitted to the Pediatric Intensive Care Unit

Discussion

In our cohort, the initial MPIS was predictive of illness severity and trajectory in pediatric subjects with status asthmaticus. As expected, there were significant differences in respiratory frequency, , and between groups because these data are objective components of the MPIS. Thus, it is important confirmation of the validity of the MPIS that hospital LOS, PICU LOS, and time on continuous albuterol were significantly different between groups. There was only 1 PICU readmission during the study period, suggesting that subjects weaned per MPIS protocol were truly ready for de-escalation of care. In addition, subjects with a higher MPIS were more likely to receive heliox or HFNC support, decisions that were independent of the asthma pathway. Total MPIS was the only factor noted in multivariable analysis to be associated with LOS.

In contrast to the original study published by Carroll et al,⁴ which was designed primarily to assess the reproducibility of the scale and evaluate differences in MPIS for those requiring PICU admission, we examined the association of MPIS with subject outcomes. Our study also had a larger sample size and standardized asthma management.⁴ Importantly, the introduction of our asthma protocol that uses the MPIS was associated with decreased hospital LOS for all pediatric subjects with asthma³ as well as those in the PICU with status asthmaticus.⁷

Several other studies have used the MPIS to evaluate illness severity in pediatric asthma. Maekawa et al⁶ evaluated the MPIS in a cohort of 25 children and found a high interobserver agreement; the investigators concluded that the MPIS was a reliable tool to assess asthma severity in children. Their study was designed to evaluate the reproducibly of the MPIS in children, particularly preschool age children in whom evaluating asthma severity is a major challenge.⁶ Maekawa et al⁶ also evaluated the ability of the MPIS to predict hospital admission in a large cohort of pediatric subjects with asthma. They found that the MPIS showed excellent overlap with Japanese Asthma Guidelines classifications, with the mild group having an MPIS 0–5, the moderate group 6–10, the severe group 11–15, and those with respiratory failure an MPIS ≥16.¹⁰ They did not examine the relationship with admission MPIS and LOS. Buyuktiryaki et al⁹ used the MPIS to evaluate asthma severity in children presenting to the emergency department in Turkey and found that those hospitalized had a higher MPIS at presentation, at 1 h after treatment, and at 4 h after treatment. Multivariable analysis revealed that the MPIS at presentation and at 1 h were associated with hospital admission. The median MPIS noted in their study in the hospitalized group was 6; thus, it is difficult to compare our results as our illness severity was much higher. Admission criteria likely varied between our centers.

Koga et al⁵ evaluated the MPIS in a cohort of 87 children with asthma and found the MPIS was highly correlated among different raters. They found an MPIS of 10 was the optimum cutoff for the initiation of continuous bronchodilator therapy, identical to the cutoff for escalation in our protocol.⁷ There was some disagreement in their study between the subjective and objective exacerbation severity. In addition, their study found a moderate correlation between the MPIS and LOS; however, their mean LOS was 6.3 ± 0.4 d, which was longer than the 3.4 d reported in our study, probably due to differences in in-patient asthma management between centers. Importantly, they did not evaluate the lower cutoff to identify eligibility for decreasing bronchodilator frequency, their asthma management was not standardized, and they did not evaluate differences in LOS between different groups. We did not specifically evaluate the statistical correlation coefficients between hospital LOS and MPIS at admission; however multivariate analysis revealed MPIS was the only factor that was statistically significantly associated with LOS.

The MPIS differentiates illness severity in pediatric patients with asthma well. Importantly, our study found that an increasing MPIS was associated with an increase in hospital LOS. Although decisions about weaning bronchodilators and discharge readiness in our pathway are based on the MPIS, providers always have the option of deviating from the pathway if a patient is not progressing. Decisions to admit the patient to the PICU from the in-patient wards is driven by the MPIS; at the time of the study, however, the emergency department was not using the MPIS to determine patient disposition. Its ease of use, high interobserver reliability, and robustness in a variety of settings indicate that the MPIS is an excellent tool to evaluate pediatric asthma severity.