a b s t r a c t

Objective: Suicide by organophosphate insecticide (OPI) poisoning is a major clinical concern (predominantly in Developing countries), and 200000 deaths occur annually worldwide. red cell distribution width (RDW) has been used to predict outcome in several clinical conditions. Here, we aimed to investigate the relationship between the RDW and 30-day mortality during OPI poisoning.

Methods: This retrospective analysis was performed between January 2008 and July 2013 in patients admitted to the emergency department after OPI poisoning. A Kaplan-Meier 30-day survival curve was analyzed in patients stratified according to the optimal cut-off point of RDW defined using a receiver operating characteristic (ROC) curve. Multivariate Cox proportional hazards analyses were conducted to determine the independent prognostic factors for 30-day mortality.

Results: Among 102 patients, 21 died, yielding a mortality of 20.6%. Elevated RDW was significantly associated with early mortality in patients with OPI poisoning. Levels of RDW that exceeded 13.5% (hazard ratio, 2.64; 95% confidence interval [CI], 1.05-6.60) were associated with increased mortality in the multivariate analysis. The area under the ROC curve of RDW was 0.675 (95% CI, 0.522-0.829).

Conclusions: This study showed that RDW is an independent predictor of 30-day mortality in patients with OPI poisoning.

(C) 2014

1. Introduction

Organophosphate insecticides (OPIs) have been widely used predominantly in developing countries. suicidal poisoning by OPI, however, is a major clinical and Public health concern, and the annual number of mortalities are approximately 200000 worldwide [1]. Organophosphate insecticide irreversibly inhibits acetylcholinester- ase (AChE) and causes an accumulation of acetylcholine at cholinergic synapses of the central and Peripheral nervous systems. This reaction leads to overstimulation of muscarinic and nicotinic receptors, and the Classic symptoms of OPI poisoning arise from muscarinic, nicotinic, and central nervous systemic effects, including increased secretion, bradycardia, muscle weakness, paralysis, confusion, and respiratory failure [2].

? Financial support/Conflict of interest: None to declare.

* Corresponding author. Department of neurosurgery, Gyeongsang Institute of Health Sciences, Gyeongsang National University School of Medicine, Jinju, Gyeong- nam-Do 660-702, Republic of Korea. Tel.: +82 55 750 8112; fax: +82 55 758 1782.

E-mail address: [email protected] (I.S. Park).

Several prognostic factors for organophosphorus (OP) poisoning are associated with the severity and prognosis, such as the poisoning severity score, Glasgow Coma Scale, Acute Physiology and Chronic Health Evaluation II score, Simplified Acute Physiology Score II, S-100B protein, C-reactive protein, and heart rate-Corrected QT interval [3-8].

The Red Cell Distribution Width is a quantitative measure of the size variability in circulating red blood cells that is used during the differential diagnosis of anemia and is routinely measured as part of the complete blood count. It has been reported that higher RDW values have been found to be an independent predictor of the prognosis among patients with heart diseases, such as acute myocardial infarction, congestive heart failure, and coronary artery diseases [9-11]. Furthermore, elevated RDW is also associated with increased mortality in out-of-hospital cardiac arrest [12]. In addition to cardiovascular diseases, RDW has also been associated with a poor prognosis for other diseases and conditions, including stroke, community-acquired pneumonia , pulmonary embolism, chron- ic obstructive pulmonary disease (COPD), septic shock, and acute pancreatitis [13-18].

http://dx.doi.org/10.1016/j.ajem.2014.02.048

0735-6757/(C) 2014

744 C. Kang et al. / American Journal of Emergency Medicine 32 (2014) 743-746

Red cell distribution width has not yet been investigated as a predictive biomarker of mortality in patients with pesticide poisoning. The aim of this study was to evaluate the association of RDW with the prognosis for OPI poisoning. Our hypothesis was that an elevated RDW is a novel marker of poor prognosis for OPI poisoning.

1. Methods
   1. Study setting

This study was a retrospective, observational, cohort study and was conducted at a single emergency department (ED) for OPI poisoning between January 1, 2008, and July 31, 2013. We analyzed 102 patients in the study. A diagnosis of OPI poisoning is based on a clinical history of the Intentional ingestion of OPIs and a symptomatic presentation (salivation, lacrimation, urination, defe- cation, gastric emesis, bronchorrhea, bronchospasm, and bradycar- dia). Cases involving patients younger than the age of 16 years, unintentional poisoning, coingestion with other agents, prehospital cardiac arrest, transfer to another hospital, or discharge against medical advice were excluded from the current study. The initial management of acute OPI poisoning was performed by decontam- ination with gastric lavage followed by the administration of activated charcoal. A standardized protocol for the treatment of OPI poisoning with atropine and pralidoxime was conducted in each case [2]. Furthermore, if the patients presented respiratory or Hemodynamic compromise, supportive care (including the applica- tion of mechanical ventilation and an inotropic/vasopressor agent) was carried out.

Ethical statement

This study was performed in accordance with the statements of the Declaration of Helsinki. It was also approved by the institutional review board of our hospital and exempted from informed consent.

Data collection

All data were collected from a retrospective chart review. Demographic data, initial vital signs, levels of consciousness (Alert, Voice, Pain, Unresponsive [AVPU] scale), and initial laboratory measures were obtained upon ED admission, including white blood cell count, hematocrit, platelet count, levels of Blood urea nitrogen , creatinine, albumin, Creatinine kinase (CK), and butyrylcholinesterase. The primary end point was the 30-day hospital mortality after ED admission. However, if the patients left the hospital within 30 days, we identified whether they had visited outpatient department or conducted a phone interview.

Statistical analysis

All continuous variables were given as the mean with SD and were tested for normality of the distribution using the Kolmogorov- Smirnov test. All variables were compared using the Student t test or Mann-Whitney U test. Categorical data were described according to the frequency of occurrence (percentage) and compared using the ?² test. The RDW values were divided into 2 groups according to a statistical significant optimal cut-off point for the prediction of 30-day mortality using a receiver operating characteristic (ROC) curve. We applied Cox proportional hazards analysis to determine predictors of 30-day mortality using the backward stepwise method presented as Hazard ratios (HRs) with a 95% confidence interval (CI). Prognostic variables for mortality that were P b .1 in univariate analysis were included in multivariate analysis. Kaplan-Meier survival curves were analyzed, and the survival rates of each group were compared using the log-rank test. A P b .05 was considered statistically significant. All

statistical analyses were performed using SPSS 21.0 software (SPSS Inc, Chicago, IL).

1. Results

A total of 149 cases were screened, and 102 were included in the present study (Fig. 1). Baseline demographic, clinical, and laboratory characteristics of the patients were described and divided according to the cut-off point for RDW more than 13.5% in Table 1. Patients with an RDW more than 13.5% was significantly older than other group. In addition, BUN, creatinine, albumin, and butyrylcholinesterase were also significantly different between 2 groups. The mortality rate within 30 days after ED admission due to OPI poisoning was 20.6% (21 of 102).

Patients who did not survive had significantly higher levels of RDW (13.9 +- 1.8 vs 12.9 +- 0.8, P = .013; Fig. 2) and older (72.2 +- 9.1

vs 53.7 +- 14.7, P b .001). They also had significantly lower levels of hematocrit (39.3 +- 4.4 vs 42.7 +- 4.5, P = .003), increased BUN (20.4 +- 6.9 vs 14.8 +- 5.6, P b .001), increased creatinine (1.1 +- 0.4 vs 0.8 +- 0.3, P b .001), and lower albumin concentration (3.6 +- 0.6 vs

4.2 +- 0.5, P b .001).

The optimal cut-off value of RDW for predicting 30-day mortality was identified from the ROC curve analysis (Fig. 3). The cut-off point for RDW was more than 13.5%, and the area under the ROC curve was 0.675 (95% CI, 0.522-0.829, P = .013). When the RDW was more than 13.5%, the sensitivity was 57.1%, and the specificity was 84.0% (positive predictive value, 48.0%; negative predictive value, 88.3%).

Univariate and multivariate Cox proportional hazards analyses for 30-day mortality are shown in Table 2. In multivariate analysis, age, unresponsive in AVPU scale, and RDW more than 13.5% were independent prognostic factors for 30-day mortality. Patients with an RDW more than 13.5% had a 2.64-fold increased risk of 30-day mortality than did patients with an RDW less than or equal to 13.5% during the follow-up period. A Kaplan-Meier survival curve was plotted of the statistical comparison using the log-rank test; it

Fig. 1. Flow chart describing the process of study patients.

C. Kang et al. / American Journal of Emergency Medicine 32 (2014) 743-746 745

Table 1

Baseline characteristics and laboratory findings for patients with OPI poisoning on ED admission

Variables	All patients (N = 102)	RDW <=13.5% (n = 77)	RDW N 13.5% (n = 25)	P
Age (y)	57.5 +- 15.7	55.5 +- 15.0	63.6 +- 16.4		.037
Male, sex, n	68 (66.7)	48 (62.3)	20 (80.0)		.104
Unresponsivea, n	24 (23.5)	17 (22.1)	7 (28.0)		.544
Initial vital signs
SBP (mm Hg)	136.3 +- 37.7	139.2 +- 36.5	127.5 +- 40.9		.180
Heart rate	92.3 +- 24.3	91.5 +- 22.4	94.5 +- 29.9		.592
(beats per minute)
Respiratory rate 21.8 +- 11.6		21.0 +- 6.0	24.2 +- 21.0	.449
(breaths per minute)
Laboratory findings WBC (x 103/mm3)	15.8 +- 7.7	15.1 +- 7.2	17.7 +- 9.0	.145
Hematocrit (%)	42.0 +- 4.6	42.1 +- 4.7	41.5 +- 4.4	.569
Platelet (x 103/mm3)	276.4 +- 84.4	274.5 +- 63.4	282.5 +- 131.0	.771
BUN (mg/dL)	16.0 +- 6.3	15.1 +- 5.7	18.7 +- 7.3	.033
Creatinine (mg/dL)	0.9 +- 0.3	0.8 +- 0.3	1.1 +- 0.4	.008
Albumin (g/dL)	4.1 +- 0.6	4.2 +- 0.5	3.9 +- 0.7	.026
CK (U/L)	184.5 +- 185.4	189.9 +- 202.8	167.9 +- 118.0	.608
Butyrylcholinesterase	596.2 +- 1424.2	733.5 +- 1611.4	189.8 +- 393.5	.009
(U/L)
30-day mortality	21 (20.6)	9 (11.7)	12 (48.0)	b.001

Abbreviation: SBP, systolic blood pressure.

Data were presented as means with SDs or number with percentage.

^a Unresponsive in AVPU scale.

Fig. 3. Area under the ROC curve to determine the cut-off point for RDW for predicting 30-day mortality during OPI poisoning.

revealed that the survival rate was significantly different between 2 groups (P b .001) (Fig. 4).

1. Discussion

In this analysis of patients with OPI poisoning, we found that elevated RDW was an independent predictor of 30-day mortality. To the best our knowledge, this is the first study to analyze the relationship between RDW and pesticide poisoning, particularly OPI. When the patients were divided into 2 groups according to an optimal cut-off value for RDW (13.5%) for the prediction of 30-day mortality, the higher RDW group showed a significantly lower survival rate.

Red cell distribution width is a measured index of the variation in size of circulating RBCs that is reported using automated hematology analyzers as part of a standard complete blood count analysis and is used to differentiate between multiple causes of anemia. Various studies have been evaluated that have associated RDW with poor prognosis in patients with cardiovascular disease, cardiac arrest, stroke, CAP, pulmonary embolism, COPD, septic shock, and acute pancreatitis [9-18]. In addition, RDW was also a strong and independent predictor of all-cause mortality in community-based samples of middle-aged/older adults or the general population [19,20].

Fig. 2. Red cell distribution width measures as a function of 30-day mortality. Data presented as mean of RDW with SD.

The mechanism underlying the association of RDW with adverse outcome is not well understood. However, it has been suggested that elevated RDW is associated with systemic inflammation and oxidative stress [21-24]. Inflammatory cytokines were found to suppress the maturation of RBCs in bone marrow, allowing immature RBCs to spill into circulation, ultimately increasing the RDW [21,22]. Oxidative stress has also been associated with elevated RDW. Oxidative stress increases anisocytosis by disrupting erythropoiesis as well as by destroying and shortening the survival time of RBCs, thereby increasing the RDW [23,24]. Inflammation and oxidative stress have also been found to be involved in the pathophysiology of OPI poisoning [25-27]. Schafer et al [25] reported the influence of OP poisoning on human dendritic cells that release increased levels of inflammatory cytokines, such as interleukin (IL)-1? and IL-8. It has also been found that oxidative stress could be one of the most important toxic mechanisms in OPI poisoning [26,27]. In light of these findings, although the mechanism is still unclear, we can assume that the elevated RDW can be attributed to the inflammation and oxidative stress that result from OPI poisoning.

1. Limitations

There are some limitations in the current study. First, this is a retrospective, single-institution study that was conducted with a relatively small sample size. Therefore, a larger, prospective, and

Table 2

Cox regression analysis of risk factors for mortality within 30 days in patients with OPI poisoning

	Univariate			Multivariate
	HR (95% CI)	P		HR (95% CI)	P
Age (y)	1.10 (1.05-1.14)	b.001		1.09 (1.04-1.14)	b.001
Unresponsivea	2.57 (0.94-5.51)	.067		3.18 (1.25-8.07)	.015
SBP (mm Hg)	0.98 (0.97-0.99)	.007
Hematocrit (%)	0.86 (0.78-0.95)	.004
RDW N 13.5 (%)	4.76 (2.00-11.33)	b.001		2.64 (1.05-6.60)	.038
Creatinine (mg/dL)	7.08 (2.59-19.34)	b.001
Albumin (g/dL)	0.21 (0.11-0.43)	b.001

^a Unresponsive in AVPU scale.

746 C. Kang et al. / American Journal of Emergency Medicine 32 (2014) 743-746

Fig. 4. Kaplan-Meier survival curve of patients with OPI poisoning. P b .001, according to a log-rank test.

multicenter study should be considered in the future. Second, we did not measure the levels of folic acid, vitamin B12, and iron that might influence the RDW value. Third, we could not know whether 3 patients did not survive for 30 days among the patients who were discharged within 30 days. Fourth, the area under the curve (AUC) of RDW for predicting the 30-day mortality was relatively low (AUC = 0.675), and the optimal cut-off point for RDW (13.5%) was in the reference range of our laboratory (11.5% to 14.5%). However, when we performed Kaplan-Meier survival analysis using the log-rank test for the 2 groups divided according to the optimal cut-off value, the outcomes were significantly different. Accordingly, we consider these results to be Clinically meaningful.

1. Conclusions

In the present study, we can conclude that RDW, which is a simple, inexpensive, and widely used test, is an independent predictor of 30-day mortality in OPI poisoning.

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