Background

Mechanical ventilation is a limited and labor-intensive resource, requiring a team of physicians, nurses, and respiratory therapists working together to effectively manage the patients requiring these resources. Bed management and staffing models are complicated for several reasons. One, mechanical ventilation is generally restricted to intensive care units with small, fixed numbers of beds relative to the hospital. Second, each type of provider (MD, RN, RT) has a different provider-to-patient ratio to be safe and effective. Third, there are likely seasonal variations in the incidence of acute respiratory failure and a resultant fluctuation in the utilization of mechanical ventilation. The magnitude of this variation throughout a year likely varies based on hospital geography, hospital urban/rural designation, hospital teaching status, hospital size, and the given years severity of influenza. Understanding hospital-level seasonal variation in case volume of acute respiratory failure may help in healthcare systems planning and resource allocation and anticipate needs for surge capacity for influenza pandemics.

In a previous analysis we examined the national, quarterly case volume and case-fatality for each ICD9 code for respiratory failure and then stratified the national respiratory failure population by hospital characteristics of bed size, urban/rural, teaching status, hospital control, census region (2002-2011), and census division (2012-2014). This was a large, nation-level overview.

In this analysis, we take advantage of the fact that from 2002-2011 in the NIS, hospital identifiers were used that could follow hospitals throughout the years. In this scenario, we are then able to calculate the respiratory failure case volume of each hospital for each quarter for each year. Therefore, this analysis is from the perspecitve of the individual hospital or health system to help each system understand and hopefully predict the range of respiratory case volume change they can anticipate from one quarter to the next.

General question:

What is the range of seasonal variation of acute respiratory failure case volume that a hospital can anticipate based its characteristics?

Study Aims:

Describe the range of change in quarterly hospital case volume of acute respiratory failure within a calendar year.

Describe the hospital characteristics that are associated with the magnitude of change from minimum to maximum quarter within a year.

Create and test a model to predict magnitude of change.

Data Overview

“NIS is the largest publicly available all-payer inpatient health care database in the United States, yielding national estimates of hospital inpatient stays. Unweighted, it contains data from more than 7 million hospital stays each year from ~1,000 hospitals. Weighted, it estimates more than 35 million hospitalizations nationally”

  1. 20% stratified sample of US community hospitals drawn from states participating in HCUP. For 2011, these states comprise ~97% of US population

Unit of Analysis Hospital-Quarter For each year, the sum of respiratory failure cases is calculated for each hospital for each quarter. Then summary statistics are calculated for each year:

  • Mean:
  • Standard deviation:
  • Maximum:
  • Minimum:
  • Absolute difference:
  • Relative difference:
  • Sum:

Definitions Key

While in the prior analyses we explored each ICD9 code for respiratory failure with/without inclusion of procedure codes for mechanical ventilation, in this analyses we have pared down the case definition to one that includes any of the diagnostic codes among any of the discharge diagnoses with any of the mechanical ventilation codes among the procedure codes. From teh resource utilization perspective, we opined that this was both most comprehensive of all respiratory failure but also narrowed down to the population that is utilizing the limiting resource of mechanical ventilation. The following ICD-9-CM diagnostic codes were used to construct a respiratory failure case definitions:

  • 518.5 Pulmonary insufficiency following trauma and surgery
  • In 2012 the 518.5 was replaced/expanded by 3 more specific subcodes:
    • 518.51 Acute respiratory failure following trauma and surgery
    • 518.52 Other pulmonary insufficiency, not elsewhere classified, following trauma and surgery
    • 518.53 Acute and chronic respiratory failure following trauma and surgery
  • 518.81 Acute respiratory failure
  • 518.82 Other pulmonary insufficiency not elsewhere classified
  • 518.83 Chronic respiratory failure
  • 518.84 Acute and chronic respiratory failure

Furthermore, each definition includes one version with only the diagnostic code(s) and one version with any of the ICD-9- CM procedure codes:

  • 96.70 Continuous mechanical ventilation of unspecified duration
  • 96.71 Continuous mechanical ventilation of < 96 h consecutively
  • 96.72 Continuous mechanical ventilation for > 96 h consecutively

Datasets Construction

Initial data management was performed using SAS 9.4 SURVEY family of procedures accounting for the complex survey design. Statistics were output to CSV files for use within R. Further data management for graphical presentation and within year statistics were performed in R

To view SAS code use the following link (can be added later).

To view R code select the button to the right.

nis_summary <- read.csv('summary_2002_2011_arf.csv', stringsAsFactors = F)

Hospital Summary Measures by Year

Hospitals’ Relative Change in Case Volume by Hospital Characteristics