Study:
(1) adult asthmatics aged 18-55 with moderate to severe asthma
(2) failed to reach discharge criteria after 3 hours of therapy in Emergency Department
(3) followed prospectively over 8 weeks for relapse, defined as any unscheduled visit for increasing asthma symptoms
(4) variables analyzed by multivariate analysis for independence in prediction of relapse
Patients excluded:
(1) pCO2 >= 45 mm Hg or PO2 <= 55 mm Hg
(2) PEFR <= 80 L/min after first beta-adrenergic treatment
(3) factors suggestive of COPD
(4) best PEFR in Emergency Department less than their discharge criterion
(5) pregnancy
(6) current diagnosis of pneumonia, congestive heart failure or restrictive lung disease
Rate of relapse over time was linear, with 8% at 10 days and 45% by 8 weeks.
|
Risk Factor
|
Hazard Ratio
|
95% CI
|
|
having made 3 or more visits to the emergency room in the prior 6 months
|
2.3
|
1.6-3.4
|
|
difficulty performing work or activities as a result of physical health in the 4 weeks prior
|
2.7
|
1.6-4.3
|
|
discontinuing hospital-based treatment for the exacerbation within 24 hours without having achieved a peak expiratory flow rate of at least 50% of predicted
|
2.6
|
1.6-4.1
|
Interpretation:
• The number of risk factors present correlated with rate of relapse over the next 8 weeks.
• If no risk factors were present, then relapse rate was about 10%.
• If 1 risk factor was present, then the relapse rate was about 33%.
• If 2 risk factors were present, then the relapse rate was about 66%.
• If all 3 risk factors were present, then the relapse rate was 100%.
Equations for Predicting PEF from Nunn (1989)
Peak expiratory flow for men:
LN(PEF in L/min) =
= (0.544 * LN(age in years)) - (0.0151 * (age in years)) - (74.7 / (height in cm)) + 5.48
Peak expiratory flow for women:
LN(PEF in L/min) =
= (0.376 * LN(age in years)) - (0.0120 * (age in years)) - (58.8 / (height in cm)) + 5.63
