Table 1. Candidate predictor and outcome variables for asthma prediction rule modeling.
| Candidate Predictor Variable | df1 | Ascertainment & Definition |
|---|---|---|
| Age | 2 | Years (calculated to 0.01 yr) |
| Gender | 1 | Male/female |
| Race2 | 2 | White; Black; Asian; American indian/Alaskan; Native Hawaiian/Pacific islander |
| Asthma control (3-Month) | 1 | GINA guidelines (Yes/No) |
| Prior adverse event | 1 | Prior PICU admission (Yes/No) |
| Respiratory rate | 1 | Breaths/minute (>97.5% ile for age) |
| Degree of breathlessness | 3 | Complete sentences; short sentences; partial sentences; words; no speech |
| Accessory muscle use | 1 | Present/Absent |
| Oxygen saturation by pulse oximetry | 2 | % value |
| Oximeter plethysmograph variability index | 2 | % value |
| Airway resistance | 2 | % predicted or kPa/L/s |
| Forced expiratory volume in 1 second | 2 | % predicted |
| End-tidal carbon dioxide | 2 | mm Hg |
| Exhaled nitric oxide | 2 | Parts per billion |
| Total df | 24 | |
| Primary Outcome Variable | ||
| Need for hospitalization | Length of stay > 24 hours (for admitted subjects) or unscheduled return for asthma care to a physician or hospital within 48 hours (for discharged subjects) | |
| Secondary Outcome Variables3 | ||
| Length of stay > 24 hours | Yes/No | |
| Length of stay | Hours | |
| Value-added elements of in-hospital care | ||
| Total daily dose of albuterol | Milligrams | |
| Total daily duration of continuous albuterol | Hour units | |
| Time to q 4 hr albuterol (hours) | Hour units | |
| For participants discharged to home | ||
| 48 hour relapse3 | Yes/No | |
| Parental perception of improvement | Yes/No |
1
Degrees of freedom. For continuous variables, 2 df are designated to account for possible non-linearity using restricted cubic splines
2
Categorized in accordance with NIH guidelines
3
Secondary outcomes for prediction rule modeling if insufficient occurrence of primary outcome variable and for internal validation of derived prediction rule