Dynamic Relationship Between Time and Serum Cholinesterase in Organophosphate-Poisoned Patients with Linear Mixed Model
Date Issued
2011
Date
2011
Author(s)
Chaou, Chung-Hsien
Abstract
Introduction—Organophosphate poisoning (OPP) occurs worldwide, accounting for 200,000 deaths annually in developing countries. Organophosphorus compounds inhibit the activity of cholinesterase and result in the over-activation of acetylcholine on autonomic ganglia and end organs. Serum cholinesterase (SChE) is of diagnostic value in OPP patients and often checked repeatedly during the treatment course. Most of the previous studies on OPP patients focused on mortality and disease severity, while the recovery pattern of SChE has been rarely addressed. To deal with the repeated measured SChE, correlation within the same patient must be taken into account. The linear mixed model is one of the most commonly used methods in repeated measures of normal data. It adds random effects in order to capture variance resulting from between-cluster level as well as intra-cluster correlation. This study aimed to investigate the dynamic relationship between SChE and time in OPP patients using linear mixed models.
Material and Methods—This study is a retrospective cohort study, utilizing medical records from a medical center in Taoyuan, Taiwan. A total of 212 adult patients who visited the emergency room between 2000 and 2010 due to acute OPP were included, and 131 patients were analyzed after exclusion of 81 patients by criteria. Information regarding basic personal characteristics, first vital signs and severity scores, lab data, type and ingestion amount of organophosphate, treatment, and serial SChE value were collected. Random coefficient model with random intercept and random slope of time were added to address the dynamic relationships of SChE with time and associated factors.
Results—Organophosphate-poisoned patients differ significantly in baseline characteristics, but most patients had lowered initial SChE levels. The histogram of SChE revealed a positively skewed distribution and thus log-transformed SChE (LSChE) was used as the dependent variable. Serial LSChE showed a positive correlation with decreasing magnitude as the time gap increased. The goodness of fit significantly improved after random intercepts and random slopes of time were added to a linear mixed model. Time, type of organophosphate, and first LSChE level were independently related with LSChE level, while type of organophosphate, first LSChE level, and disease severity score were significantly related with the slope of time. Profenophos has lowest LSChE levels among all types of organophosphate. Chlorpyrifos and methamidophos had significant slower and faster rates of LSChE recovery compared with other organophosphates, respectively. Sex, dose of 2-PAM during the initial 24 hours, delay of medical assistance, and quadratic form of time did not significantly affect the recovery of LSChE.
Conclusion—This study constructed a model for recovery of SChE in OPP patients. Several major determinants responsible for the recovery of SChE were also identified. It can be used as a prototype model in further studies on OPP. Clinicians may also make use of such information to guide clinical decisions during initial period of treatment.
Subjects
Organophosphate Poisoning
Serum Cholinesterase
Mixed Models
Random Effects
Type
thesis
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