The main findings from this study suggest that inpatient resource utilization for children with NI in the US has changed from 1997 to 2006. The changes were largely attributable to children with NI utilizing children's hospitals more over time. Within children's hospitals, they accounted for both increasing trends and a substantial proportion of resources over the study period, including nearly one-third of all hospital charges. Within all hospitals, infants and children with NI experienced a greater increase in neonatal and neurological admissions and a greater decrease in respiratory admissions than children without NI. The majority of admissions for children with NI occurred for non-nervous-system problems, suggesting that co-morbid conditions affecting other organ systems were a major contributor to inpatient utilization.
Our study contributes to existing literature by describing national inpatient utilization for children with NI who had underlying primary neurological diagnoses (e.g., cerebral palsy) or other diagnoses that are characteristically associated with co-morbid nervous system impairment (e.g., Down Syndrome). As expected, studies restricted to a cohort of children with primary neuromuscular diagnoses report less inpatient utilization (e.g., 2% of all pediatric admissions and 7% of all pediatric hospital charges) than the present study 
. Our findings are consistent with adult studies reporting that NI associated with intellectual disabilities and dementia ranks among the top determinants of health care cost 
. Although the underlying diagnoses and reasons for NI may be different across the age spectrum, patients with NI may account for a substantial share of both pediatric and adult health care resources.
There is a rising proportion of children's hospital use by children with NI, as the total number of hospitalizations for children without NI did not increase within children's hospitals over time. Most US child neurologists work within children's hospitals, and there has been an emergence of multi-disciplinary care coordination clinics that provide comprehensive care for children with NI at children's hospitals 
. Children with NI may be utilizing children's hospitals more often to seek care from providers who are more familiar with and comfortable managing their health problems. Further study is necessary to evaluate whether clinician NI knowledge and care delivery differ between children's and non-children's hospitals.
US physicians have demonstrated deficiencies in working knowledge of the most common forms of NI, and negative provider attitudes toward this population are associated with substandard acute care practices 
. Parents of adolescents with NI report this as a contributing factor that complicates the transfer of their child's health care from pediatric to adult providers 
. In the present study, we observed a trend of rising hospitalizations in adolescent children with NI that was greater than that for children without NI. Further investigation is necessary to determine whether hindered care transition is contributing to this trend.
The rise in the number of admissions associated with gastrostomy with and without fundoplication operations in children with and without NI over time may represent a change in approach to more interventions to bypass oromotor dysfunction, mitigate aspiration from oral feeds, and improve gastroesophageal reflux management in these children. The appropriateness and effectiveness of these operations in children with NI are currently under investigation. It is possible that the decrease in the absolute number of respiratory admissions for children with NI could be related to the rise in gastrostomy and/or fundoplication operations: future studies should investigate whether these operations help prevent pneumonia admissions due to reflux and aspiration 
. We were unable to evaluate this directly in the present study, as the KID does not track individual patients before and after operations.
In the present study, the absolute number of respiratory admissions decreased for children both with and without NI. Prior small area studies report that children with intellectual disability are at higher risk for respiratory hospitalizations that may be ambulatory care sensitive than children without intellectual disability 
. Our study suggests that, nationally, children with NI may have received an equivalent or greater benefit from efforts to improve respiratory heath in children, including better respiratory preventive measures and acute and chronic respiratory care treatments 
. It is possible that some children with NI could have gained exposure to these efforts through improved care coordination within medical homes or other structured clinical programs 
The increasing trend of neonatal admissions for infants with NI is supported by prior studies that report a rising incidence of NI associated with increasing preterm infant deliveries and preterm infant survival 
. However, some recent studies show that the neonatal prevalence of certain NI-related diagnoses, such as cerebral palsy, is now decreasing 
. This may be related to perinatal care improvements that minimize the risk of brain injury, as well as to changing practices associated with prenatal congenital malformation screening and elective termination 
. Using inpatient administrative billing codes to detect NI among neonates limits the interpretation of the trends observed in the present study. Some infants may not be diagnosed with NI until well after their neonatal hospitalization.
Our study has several other limitations. We were unable to determine whether the trends could have been a function of the changing population prevalence of children with NI at large in the US. US census data indicate that the population of all children aged 0–18 y increased by 5.6% from 1997 to 2006. However, to our knowledge, true population prevalence trends of all children with NI remain unknown.
The large shift in the inclusion of hospitals from different states in the KID sampling frame could have affected the study findings. In a post hoc analysis, we restricted the cohort to patients admitted to hospitals that were present in both the 1997 and 2006 KID samples. Similar results were observed. The KID contains hospital discharge rather than individual patient data, which prevented us from being able to determine whether the same sized population of children with NI was being hospitalized more frequently over time. This will be important to evaluate in future health resource utilization and epidemiologic studies of children with NI.
Continuous years of data may be preferable for studying hospital utilization trends when compared with four discrete time points in a 10-y period. The hospitals within the KID used ICD-9-CM coding for all the years of the study. It will be important to evaluate the identification of NI diseases using ICD-10 and other coding systems, as many countries are currently using or implementing them. Errors in ICD-9-CM coding exist, and billing reimbursement may influence which codes are entered for a patient during hospitalization. In some cases, NI may be regarded as a subjective medical condition that cannot be correlated with a specific diagnosis code. As such, the hospital resource use described in the present study may underrepresent children with NI who are hospitalized with that situation. The KID contains hospital charge data, but not cost data. Charge data represent the amount that hospitals billed for services but does not reflect how much hospital services actually cost or the specific amounts that hospitals received in payment.
Despite these limitations, this study demonstrates that children with NI account for a substantial proportion of inpatient resources utilized in the US. Their impact is growing within children's hospitals. Use of large administrative databases like the KID, by itself or in conjunction with other databases, may provide unique perspectives to answer the clinical questions raised by the study findings, including the following. (1) Does care quality differ for children with NI depending on the type of hospital they use? (2) Does inpatient resource utilization for children with NI vary depending on their access to medical homes and preventive care? And (3) How does substandard transition of health care services from pediatric to adult health care providers affect hospital use for adolescents and young adults with NI?
As a higher proportion of hospital resources are accounted for by children with NI over time, children's hospitals, in particular, will need to ensure that (1) adequate clinical and coordinated expertise is focused on the needs of these children, (2) NI clinical assessment and care management training is developed for trainees and junior graduates in pediatric postgraduate educational programs, (3) partnerships between families of children with NI and hospitals are developed and implemented, and (4) care treatment strategies of both nervous and non-nervous-system problems are rigorously evaluated for these children. These system-based efforts have the potential to promote continued quality of care for children with NI. We must ensure that the current health care system is staffed, educated, and equipped to serve, with efficiency and quality, this growing segment of vulnerable children.