Trends in ER Diagnosis of Pulmonary Embolism, 2001-2010
Trends in ER Diagnosis of Pulmonary Embolism, 2001-2010
The NHAMCS is a sample survey of hospital-based outpatient and ED settings conducted by the Ambulatory and Hospital Care Statistics Branch of the National Center for Health Statistics (NCHS), Centers for Disease Control and Prevention (CDC). The survey is designed to be nationally representative of the utilization of hospital ambulatory medical care services. It uses a 4-stage sampling design that narrows from geographic sampling units to hospitals within these areas to emergency service areas within these hospitals to specific patient visits. Each individual patient visit is weighted using the product of the corresponding sampling fractions at each stage in the sample design to produce national estimates. The NCHS then adjusts sampling weights for survey nonresponse. A detailed description of the survey sample design and data acquisition methods can be found on the CDC website. The NHAMCS is approved annually by the Ethics Review Board of NCHS with a waiver of the requirement to obtain informed consent.
The study period January 1, 2001 to December 31, 2010 was selected to represent the burden of PE after the introduction of CTPA in 1998. NHAMCS data from 1998–2000 does not contain hemodynamic data. Moreover, it may represent a period when many EDs did not yet have CTPA and therefore these data were not included. NHAMCS data from after 2010 is not yet publicly available for review.
The NHAMCS records up to three diagnoses for each visit, which are later converted to International Classification of Disease, Ninth Revision (ICD-9) codes. The ICD-9 codes used to extract all visits with a diagnosis of PE were 415.11 and 415.19. These codes have previously been validated in administrative data. Sensitivity analysis was performed excluding visits where PE was listed as the non-first diagnosis. ED visits were stratified by patient demographics and expected primary source of payment (private/commercial insurance, Medicare/Medicaid, and other). We subcategorized age into those patients under 65 years-old and those 65 years and older, the age cutoff used in the revised Geneva score. We examined clinical characteristics including vital signs at presentation (heart rate [HR] and systolic blood pressure [SBP]), and use of diagnostic testing (computed tomography [CT] and/or magnetic resonance imaging [MRI]). We defined hemodynamically stable patients as those having HR < 110 beats per minute and SBP > 100 mmHg, based on cutoffs from the pulmonary embolism severity index for prognostication in patients with acute symptomatic PE. We categorized disposition into admission (NHAMCS value of admitted to the hospital, admitted to ICU/CCU, admitted to observation, transferred to other medical facility), death (NHAMCS value of death on arrival or death in ED), and all other dispositions (e.g. discharged or left against medical advice). Finally, we collected limited information about the hospitals including geographic region (Northeast, Midwest, South, and West) and whether the hospital was part of a Metropolitan Statistical Area (MSA). US population data were obtained using US Census Bureau intercensal resident population estimates. A small proportion (<10%) of variables had missing data and these visits were excluded from the relevant analyses.
NHAMCS collected a combined CT and MRI variable between 2001 and 2004. We combined MRI and CT variables from the subsequent years to generate a dichotomous variable throughout the study period that indicates if a CT and/or MRI were performed during the patient visit. We then determined the percentage of patients who underwent MRI alone from 2005–2010 to assess the impact of combining the MRI and CT variables.
Descriptive statistics were determined for patient visit characteristics and multivariable logistic regression controlling for patient demographics (age, race, sex) and hospital information (region, Metropolitan Statistical Area status) was used to assess any trends in PE diagnoses among patients who had ED visits over time. We performed an additional multivariable logistic regression controlling for CT and/or MRI use in addition to patient demographics and hospital information. The NCHS guidelines state that estimates based upon fewer than 30 raw observations or with a relative standard error greater than 30% are unreliable. To ensure greater than 30 raw observations, we stratified visits into 2 year blocks for national estimates and figures. We also combined the first 5 years of the study period (2001–5) and compared these data from the subsequent 5 years (2006–10) to assess any for any changes. This ensured most variables contained sufficient raw data to generate robust national estimates. All statistical analyses were performed in Stata/SE 11.0 and 13.0 (StataCorp, College Station, Texas) using the svy command to account for the NHAMCS sampling methodology.
Methods
Data Source
The NHAMCS is a sample survey of hospital-based outpatient and ED settings conducted by the Ambulatory and Hospital Care Statistics Branch of the National Center for Health Statistics (NCHS), Centers for Disease Control and Prevention (CDC). The survey is designed to be nationally representative of the utilization of hospital ambulatory medical care services. It uses a 4-stage sampling design that narrows from geographic sampling units to hospitals within these areas to emergency service areas within these hospitals to specific patient visits. Each individual patient visit is weighted using the product of the corresponding sampling fractions at each stage in the sample design to produce national estimates. The NCHS then adjusts sampling weights for survey nonresponse. A detailed description of the survey sample design and data acquisition methods can be found on the CDC website. The NHAMCS is approved annually by the Ethics Review Board of NCHS with a waiver of the requirement to obtain informed consent.
Study Sample
The study period January 1, 2001 to December 31, 2010 was selected to represent the burden of PE after the introduction of CTPA in 1998. NHAMCS data from 1998–2000 does not contain hemodynamic data. Moreover, it may represent a period when many EDs did not yet have CTPA and therefore these data were not included. NHAMCS data from after 2010 is not yet publicly available for review.
The NHAMCS records up to three diagnoses for each visit, which are later converted to International Classification of Disease, Ninth Revision (ICD-9) codes. The ICD-9 codes used to extract all visits with a diagnosis of PE were 415.11 and 415.19. These codes have previously been validated in administrative data. Sensitivity analysis was performed excluding visits where PE was listed as the non-first diagnosis. ED visits were stratified by patient demographics and expected primary source of payment (private/commercial insurance, Medicare/Medicaid, and other). We subcategorized age into those patients under 65 years-old and those 65 years and older, the age cutoff used in the revised Geneva score. We examined clinical characteristics including vital signs at presentation (heart rate [HR] and systolic blood pressure [SBP]), and use of diagnostic testing (computed tomography [CT] and/or magnetic resonance imaging [MRI]). We defined hemodynamically stable patients as those having HR < 110 beats per minute and SBP > 100 mmHg, based on cutoffs from the pulmonary embolism severity index for prognostication in patients with acute symptomatic PE. We categorized disposition into admission (NHAMCS value of admitted to the hospital, admitted to ICU/CCU, admitted to observation, transferred to other medical facility), death (NHAMCS value of death on arrival or death in ED), and all other dispositions (e.g. discharged or left against medical advice). Finally, we collected limited information about the hospitals including geographic region (Northeast, Midwest, South, and West) and whether the hospital was part of a Metropolitan Statistical Area (MSA). US population data were obtained using US Census Bureau intercensal resident population estimates. A small proportion (<10%) of variables had missing data and these visits were excluded from the relevant analyses.
NHAMCS collected a combined CT and MRI variable between 2001 and 2004. We combined MRI and CT variables from the subsequent years to generate a dichotomous variable throughout the study period that indicates if a CT and/or MRI were performed during the patient visit. We then determined the percentage of patients who underwent MRI alone from 2005–2010 to assess the impact of combining the MRI and CT variables.
Statistical Analysis
Descriptive statistics were determined for patient visit characteristics and multivariable logistic regression controlling for patient demographics (age, race, sex) and hospital information (region, Metropolitan Statistical Area status) was used to assess any trends in PE diagnoses among patients who had ED visits over time. We performed an additional multivariable logistic regression controlling for CT and/or MRI use in addition to patient demographics and hospital information. The NCHS guidelines state that estimates based upon fewer than 30 raw observations or with a relative standard error greater than 30% are unreliable. To ensure greater than 30 raw observations, we stratified visits into 2 year blocks for national estimates and figures. We also combined the first 5 years of the study period (2001–5) and compared these data from the subsequent 5 years (2006–10) to assess any for any changes. This ensured most variables contained sufficient raw data to generate robust national estimates. All statistical analyses were performed in Stata/SE 11.0 and 13.0 (StataCorp, College Station, Texas) using the svy command to account for the NHAMCS sampling methodology.