Length of stay in a hospital emergency room due to asthma and chronic obstructive pulmonary disease: implications for air pollution studies.

The aim of this paper is to model the length of stay following hospital emergency due to asthma and chronic obstructive pulmonary disease (COPD) as well as those factors relating to its duration. Clinical records of all those hospital emergencies for asthma and COPD in people aged over 14 at the Hospital Clinico Universitario of Valencia (HCUV) during years 1993-1995 were reviewed. Data were analysed by entry and discharge time, sex, age and destination. Parametric survival models (exponential, Weibull and log-normal) were used for each diagnostic. Percentiles and relative percentiles were calculated; 1369 asthma emergencies and 2734 cases COPD were observed. The mean length of stay was 5.21 hours for asthma and 6.32 for COPD log-normal model was the best parametric model. Lengths of stay are greater for those hospital admitted. Stays, in cases of asthma, were shorter during months of August and November, with no differences for other variables. Also a shorter duration of stay for the month of August was found. Women are seen to stay for longer periods than men. Time modelling of emergency admission for asthma and COPD permits its use in the determining of the dates of incidence for episodes of asthma and COPD based on hospital admissions data, as seeing a median of delay in emergency rooms greater than 6 hours. For studies on air pollution impact these results imply that all those admissions during the early hours of the morning should be categorised as events of the previous day.