In this representative population-base cohort, we showed that the age-standardized population-based ICU admission rate of children in poverty (income of their household < 0.4 ⅹ median household income of Korea) was 1.6 (126.9/80.2) times higher than that of children not in poverty. The age-standardized population-based mortality rate of children in poverty was 2.7 (11.8/4.3) times higher than that of children not in poverty. The adjusted in-hospital mortality of critically ill children admitted to the ICU was not different between the poverty and non-poverty groups.
The high age-standardized mortality in the impoverished population highlights a critical public health issue (Fig. 1). A child in an impoverished family has a high risk of death. Once children were admitted, the crude in-hospital mortality of children in poverty was not statistically different from that of the non-poverty group (6.0% vs. 5.1%, p = 0.223). In addition, the difference in mortality rates between the two groups was not significant when we adjusted for demographics, hospital factors, and management procedures. The result of adjusted analysis was similar in the high mortality subgroup (mechanical ventilation) and low mortality subgroup (non-mechanical ventilation). It may suggest that there is no disparity in healthcare outcomes in ICU according to poverty. However, the admission rate was high in the poverty group across all age groups. Therefore, the age-standardized mortality of the impoverished population is likely due to high admission rate of the group rather than from high in-hospital mortality rate. We could not identify the cause of high admission rate in the poverty group, but poor pre-hospital health status could be an explanation. In previous studies, the severity scores of patients at ICU admission were higher in uninsured patients [5, 11], which implies worse health status of them at ICU admission. Previous studies conducted at select hospitals were not able to identify disparities in admission rate and population-based mortality because of selection bias [8, 11, 19]. Utilization of high-volume or top-ranked (low mortality) hospitals differed according to poverty status [20, 21], and data from these renowned hospitals could bias admission rates of low-income patients. In our study, we included all hospitals where pediatric patients are admitted to the ICU, except for rare possible administrative losses of insurance claims.
Disparity in resource use was suspected as one of the causes of disparity in healthcare outcomes [5]. The low incidence of mechanical ventilation (35.6% vs. 43.1) and vasopressor use (12.3% vs. 15.8%) in the poverty group might raise suspicion of a passive attitude toward treating patients in poverty. However, the rates of mechanical ventilation and vasopressor uses were different by age group in our previous study [13]. The age distribution of the poverty group was different from that of the overall population, possibly due to the different age distribution of parents under MAP from the general population. When we stratified age into 3 groups (infant, children, adolescent), there were no statistically significant differences in the incidence of mechanical ventilation and vasopressors according to poverty status (Additional file 2: Table S1). In addition, the incidence of other resource-heavy procedures such as transplantation, extracorporeal membrane oxygenation, and hemodialysis was similar between the poverty and non-poverty groups in an NHI system (Table 1) (Additional file 2: Table S1). These findings are contrary to the reported socioeconomic disparities in transplantation [22–24]. The difference might originate from the different health insurance systems.
Low socioeconomic status (SES) could affect pre-hospital health status in various ways. Difficulties in access to care and preventive health services may contribute to the high severity of illness and organ failure on hospital presentation [2]. Other factors such as inadequate health behaviors, lack of parental education, unhealthy environmental factors, and low vaccination rates may contribute to the worse health status of the low SES population [2, 25]. In our study, ER visits and readmission rates after ICU discharge were higher in patients in poverty. Previous studies reported that the increased rate of ER visits in low SES patients is associated with differences in health status rather than health behaviors [26]. Low SES is also associated with a high readmission rate [27, 28]. We suspect that the high ER visit and readmission rate among patients in poverty imply poor health status. Policies to improve the health status of patients in poverty might be requiried to decrease population-based mortality associated with ICU admission.
The adjusted in-hospital mortality, in this study, was similar between the two groups, which might imply that healthcare resources and services were easily accessible during ICU admission without disparity. However, one needs to be cautious in saying there were no healthcare disparities in the ICU. The overall in-hospital mortality rate of children might be too low to identify a disparity compared to adult patients [13, 29]. Furthermore, healthcare disparities might exist in some subgroups of ICU patients.
There are some limitations to this study. First, this study was conducted in a single country where a National Healthcare Insurance System covers the impoverished with a MAP, thus virtually no one is uninsured population. Our findings are more likely to apply to countries with a National Health Insurance system and may yield different results according to insurance status. Second, we could not use physiologic parameters or laboratory findings to evaluate the severity of illness. However, we adjusted for illness severity using the different mortality rates for the primary diagnosis, hospital factors, and treatment requirements, according to a previous study [13]. Despite these limitations, we included virtually all pediatric patients admitted to the ICU, which allowed us to calculate the population-based admission rate and mortality rate without selection bias associated with particular hospitals.
Our findings also have implications for reducing disparities in mortality in patients living in poverty. The National Health Insurance System with a single-payer might work well to provide healthcare in the ICU to impoverished patients without disparity, but policies to improve the health status of patients in poverty are required to decrease ICU admission and improve population-based mortality.