Children with CCC are recognized as having on-going, substantial healthcare needs (3
). While they are a relatively small proportion of children in the U.S., they are highly represented among hospitalized children (5
). Using a multi-institutional database, we demonstrated that children with chronic conditions comprised more than 70% of PICU admissions, and those with CCC comprised just over one-half. We demonstrated that patients with CCC have significant risk for PICU mortality and prolonged LOS beyond that predicted by commonly-used severity-of-illness models. Finally, we showed that the accuracy of predicting PICU mortality was significantly improved with the inclusion of CCC and other covariates, compared to adjusting for severity-of-illness alone, as indicated by a higher C-statistic and significant test of equality.
Earlier studies had not estimated the prevalence of children with CCC admitted to U.S. PICUs. Using 2004–2005 VPS data, Typpo and colleagues found that 52% of children admitted to 28 PICUs had a chronic condition, but the distinction between CCC and NCCC was not examined (20
). Using the 2006 Kids' Inpatient Database, Odetola et al. showed that 41% of children with respiratory failure or need for mechanical ventilation possessed a CCC, but they were not able to identify which children were in a PICU or assess critical illnesses other than respiratory failure (15
). Our prevalence estimates are the first to be based on an U.S. multi-institutional cohort, to stratify chronic conditions into two levels of complexity, and to show that the prevalence of these conditions and their subcategories varied across PICUs.
Previous studies have addressed the association between chronic conditions and mortality. Feudtner et al. examined all pediatric hospitalizations in Pennsylvania over multiple years and estimated the association between hospital mortality and different CCC subcategories (21
). However, they could not distinguish between PICU and non-PICU patients, and they used a proprietary, infrequently-used severity-of-illness risk-adjustment. Odetola et al. did not risk-adjust but only compared mortality of children with CCC to those without chronic conditions (15
). Typpo et al. found an association between PICU mortality and having >3 chronic conditions. While they examined organ subcategories and controlled for acute organ dysfunction, they did not examine CCC nor incorporate a commonly-used mortality risk-adjustment (20
). In order to address these limitations we: a) focused exclusively on PICU patients in a large database; b) used common and valid severity-of-illness risk-adjustment systems; and c) distinguished between chronic conditions by level of complexity and by organ system. We found that children with any CCC, except respiratory, had greater odds of PICU mortality compared to children with no chronic condition, after controlling for severity-of-illness. Importantly, the magnitude of risk varied across organ system subcategories (ranging from an OR of 1.2 for gastrointestinal [P=NS] to 2.9 [P<0.001] for hematologic/immunologic). All patients with CCC had significantly greater odds of prolonged LOS. Finally, no NCCC subcategories were associated with greater risk of PICU mortality, but some were with prolonged LOS, compared to children with no chronic conditions. Cardiovascular NCCC were associated with statistically lower odds of PICU mortality, compared to no chronic conditions.
The independent association of CCC with PICU mortality demonstrates that many CCC confer a significant risk to patients above that predicted by PIM and PRISM. Developed in 2003 and 1996, respectively, PIM2 and PRISM III incorporate few chronic conditions. PIM2 adjusts for seven high-risk diagnoses, including neuro-degenerative disorders, certain immunodeficiencies, certain cardiovascular conditions, leukemia, and lymphoma (12
). PRISM III adjusts for chromosomal abnormalities and oncologic conditions (13
). However, when we estimated SMRs using PIM2 with and without statistically significant CCC subcategories, there was no substantive difference. The lack of difference may reflect our sample containing mostly tertiary PICUs, which care for similarly ill and complex patients. Therefore, institutions were similarly affected by the increased risk of mortality. Further research should address whether CCC rates are lower at community PICUs and whether inclusion of CCCs into risk-adjustment models has more impact when a more diverse sample of PICUs is evaluated.
Our study has a number of limitations. First, chronic conditions often have a range of severity, sequelae, and chronicity that is often not captured in diagnosis coding. Admittedly, this results in some subjectivity inherent in labeling CCC. Nonetheless, identifying children with CCC through diagnoses codes has become an accepted approach. Originally, Feudtner and colleagues constructed their list of CCC using clinical knowledge and a review of Washington State death certificates (1
), and this list has become widely used (5
). However, we felt there were some weaknesses in this list that warranted modification. More specifically, Feudtner's list contains diagnoses that our expert panel assessed to be not complex (eg, benign tumors and tics) or not chronic (eg, ventricular fibrillation), assuming patients receive the standard of care. In addition, there were several CCC that were missing, including several hematologic and rheumatologic conditions, such as hemophilia and systemic lupus erythematosus. Thus, using their original definition of a CCC, we developed a modified list from the available VPS diagnoses (Appendix
) and used it in our analyses. Overall, there is considerable agreement between the two lists, with a few notable exceptions and important additions in our list.
Some of the differences in the measures of association in the PICU mortality model when Feudtner's CCC list and our modified list were used are readily explainable. Using the modified list, cardiovascular and neuromuscular CCCs were associated with increased PICU mortality. These differences are likely attributed to a more discriminatory cardiac diagnosis list that excluded several non-chronic and non-complex conditions and a more expansive list of neuromuscular diagnoses that met Feudtner's CCC definition. Also, using the modified list, gastrointestinal CCCs were not associated with PICU mortality. The only difference from Feudtner's in the modified list was the inclusion of status codes for ostomies and liver transplant, suggesting these conditions may not increase risk for PICU mortality beyond current severity-of-illness adjustments.
Other limitations include a lack of institutional characteristics in our models. Besides annual PICU volume, we were not provided with institutional characteristics. However, hierarchical regression models take into account that subjects receiving care at the same hospitals should not be treated as independent observations, rather they are “clustered within” institutions. In addition, our study is limited to PICU outcomes only, as VPS does not contain information on pre- or post-PICU care. Thus, we could not analyze other important outcomes, such as hospital mortality or LOS. Finally, besides the primary diagnosis, which by VPS definition is present at time of PICU admission, there was no designation of the timing of onset of chronic conditions in relation to admission. VPS diagnoses did not have a “present on admission” flag. So while all diagnoses pertinent to the patient's ICU course were required to be documented, it is conceivable that a small number of conditions first manifested during the admission. However, we were examining chronic conditions, which manifest over time and are unlikely to first appear during a PICU admission.