Supplemental Digital Content
The relationship between hospital and intensive care unit length of stay
Andrew A. Kramer, PhD
Jack E. Zimmerman, MD, FCCM
Supplemental Table 1. Diagnostic groups used in the linear regression equations for both
hospital and ICU stay, respectively. Each diagnostic group was modeled as a binary variable
(yes/no) and received a regression coefficient, except for “AMI Other” which was the
reference group.
Non-operative diagnostic groups
CARDIOVASCULAR DIAGNOSES
Acute myocardial infarction (AMI) :
Anterior
Inferior / Lateral
Non-Q
Other
Cardiac Arrest
Cardiogenic Shock
Cardiomyopathy
Congestive Heart Failure
Chest Pain, rule out AMI
Hypertension
Hypovolemia/dehdration (not shock)
Hemorrhage (not related to GI bleeding)
Aortic Aneurysm
Peripheral Vascular Disease
Rhythm Disturbance
Sepsis (by infection site):
Cutaneous
Gastrointestinal
Pulmonary
Urinary Tract
Other Location
Unknown Location
Cardiac Drug Toxicity
Unstable Angina
Cardiovascular, Other
RESPIRATORY DIAGNOSES
Airway Obstruction
Asthma
Aspiration Pneumonia
Bacterial Pneumonia
Viral Pneumonia
Parasitic/Fungal Pneumonia
COPD (Emphysema/Bronchitis)
Pleural Effusion
Pulmonary Edema (non-cardiac, ARDS)
Pulmonary Embolism
Respiratory Arrest
Respiratory Cancer (oral, larynx, lung, trachea)
Restrictive lung disease (fibrosis, sarciodosis)
Respiratory Disease, Other
GASTROINTESTINAL (GI) DIAGNOSES
GI Bleeding, Upper
GI Bleeding Lower/Diverticultits
GI Bleeding, Varices
GI Inflammatory Disease
Neoplasm
Obstruction
Perforation
Vascular Insufficiency
Hepatic Failure
Intra/retroperitoneal Hemorrhage
Pancreatitis
Gastrointestinal, Other
NEUROLOGIC DIAGNOSES
Intracerebral Hemorrhage
Neurologic neoplasm
Neurologic Infection
Neuromuscular disease
Drug Overdose
Subdural/epidural Hematoma
Subarachnoid Hemorrhage, Intracranial Aneurysm
Seizures (no structural disease)
Stroke
Neurologic, Other
TRAUMA DIAGNOSES
Trauma Involving the Head
Head Trauma with either Chest, Abdomen, Pelvis, or Spine Injury
Head Trauma with Extremity or Facial Trauma
Head Trauma Only
Head Trauma with Multiple Other Injuries
Trauma, Chest and Spine Trauma
Trauma, Spine Only
Multiple Trauma (excluding Head Trauma)
METABOLIC/ENDOCRINE DIAGNOSES
Acid-Base, Electrolyte Disorder
Diabetic Ketoacidosis
Hyperglycemic Hyperosmolar Nonketotic Coma
Metabolic / Endocrine, Other
HEMATOLOGIC DIAGNOSES
Coagulopathy, Neutropenia, Thrombocytopenia, Pancytopenia
Hematologic, Other
GENITOURINARY DIAGNOSES
Renal, Other
MISCELLANEOUS DIAGNOSES
General, Other
Post-Operative Diagnostic Groups
CARDIOVASCULAR SURGERY
Valvular Heart Surgery
Coronary artery bypass graft (CABG) with double or redo valve surgery
CABG with single valve surgery
Aortic Aneurysm, Elective Repair
Aortic Aneurysm, Rupture
Aortic Aneurysm, Dissection
Femoral-Popliteal Bypass Graft
Aorto-Iliac, Aorto-Femoral Bypass Graft
Peripheral Ischemia (embolectomy, thrombectomy, dilitation)
Carotid Endarterectomy
Cardiovascular Surgery, other
RESPIRATORY SURGERY
Thoracotomy, Malignancy
Neoplasm, Mouth, Larynx
Thoracotomy, lung biopsy, pleural disease
Thoracotomy, respiratory infection
Respiratory surgery, other
GASTROINTESTINAL(GI) SURGERY
GI malignancy
GI Bleeding
Fistula, Abcess
Cholecystitis, Cholangitis
GI Inflamation
GI Obstruction
GI Perforation
GI, Vascular Ischemia
Liver Transplant
GI Surgery, Other
NEUROLOGIC SURGERY
Craniotomy or Transphenoidal Procedure for Neoplasm
Intracranial Hemorrhage
Subarachnoid Hemorrhage (aneurysm, arteriovenous malformation)
Subdural/Epidural Hematoma
Laminectomy, Fusion, Spinal Cord Surgery
Neurologic Surgery, Other
TRAUMA SURGERY
Head Trauma Only
Multiple Trauma Sites Including the Head
Surgery for Extremity Trauma
Multiple Trauma (excluding the head)
GENITOURINARY SURGERY
Renal/Bladder/Prostate Neoplasm
Renal Transplant
Hysterectomy
Genitourinary Surgery, other
MISCELLANEOUS SURGERY
Amputation (non-traumatic)
Supplemental Table 2. Parameter estimates for the equation predicting hospital length of
stay.
Variable
Intercept
Acute Physiology Score (per
5 points)
Unable to assess GCS due to
patient being sedated
Mechanical ventilation on day 1
Reformatted Glasgow Coma
Scale (15 - GCS)
Patient admitted after elective
surgery
Received active therapy on day 1
Admitted to ICU from floor
Admitted to ICU from other hospital
Previous length of stay, square
root (days)
Hospital is member of the
Council of Teaching Hospitals
Teaching hospital but not affiliated
with a medical school
# Hospital beds 300 - 399
# Hospital beds 400 - 524
# Hospital beds 525 - 799
# Hospital beds ≥ 800
Medical ICU
Surgical ICU
Mixed Med-Surg ICU
Age (per 5 years)
Female
Race = black
Race = other
Race = latino
Hepatic Failure
Immunosupression
Metastatic cancer
Standard
Error
p-value
0.461
0.057
<0.001
2.110
1.856
0.143
0.094
<0.001
<0.001
-0.067
0.014
<0.001
-1.780
0.616
0.311
1.677
0.157
0.076
0.104
0.119
<0.001
<0.001
0.003
<0.001
0.207
0.259
0.425
-0.521
0.139
<0.001
-0.611
-0.219
0.954
0.306
1.143
0.374
0.716
0.162
0.287
-0.162
0.604
-0.526
0.501
-0.630
0.351
-1.451
0.112
0.119
0.106
0.146
0.103
0.105
0.100
0.074
0.035
0.057
0.099
0.082
0.164
0.248
0.115
0.149
<0.001
0.064
<0.001
0.035
<0.001
<0.001
<0.001
0.027
<0.001
0.004
<0.001
<0.001
0.002
0.011
0.002
<0.001
Estimate
-0.468
Referent categories: Prior location (admission from ER, SDU, or direct admission from home);
Teaching status (Non-Teaching hospital); # Hospital beds (< 300); ICU type (trauma, neurologic, or
coronary care); Race (white); Chronic health items (AIDS, cirrhosis, leukemia/multiple myeloma,
lymphoma, or no chronic health items).
Supplemental Table 3. Parameter estimates for the regression model predicting
ICU length of stay: All variables except for diagnostic groups and spline variables
Variable
Intercept
Acute Physiology Score (per
5 points)
Unable to assess GCS due to
patient being sedated
Mechanical ventilation on day 1
Patient admitted after elective
surgery
Received active therapy on day 1
Admitted to ICU from floor
Admitted to ICU from other hospital
Previous length of stay, square
root (days)
Hospital is member of the
Council of Teaching Hospitals
# Hospital beds 300 - 399
# Hospital beds 400 - 524
# Hospital beds 525 - 799
# Hospital beds ≥ 800
Surgical ICU
Trauma ICU
Neuro ICU
Age (per 5 years)
Race = black
Race = white
Race = latino
Cirrhosis
Immunosupression
Metastatic cancer
Leukemia/multiple myeloma
Standard
Error
p-value
0.188
0.030
<0.001
1.903
1.856
0.072
0.047
<0.001
<0.001
-1.170
0.499
0.114
0.753
0.082
0.040
0.054
0.063
<0.001
<0.001
0.035
<0.001
0.201
0.134
0.135
-0.403
-0.146
0.516
0.335
0.468
0.503
0.285
0.161
0.122
0.240
0.228
0.277
0.264
0.097
-0.337
-0.660
0.049
0.052
0.053
0.071
0.046
0.048
0.143
0.061
0.018
0.062
0.043
0.091
0.113
0.060
0.077
0.153
<0.001
0.005
<0.001
<0.001
<0.001
<0.001
0.046
0.009
<0.001
<0.001
<0.001
0.002
0.020
0.105
<0.001
<0.001
Estimate
-0.755
Referent categories: Prior location (admission from ER, SDU, or direct admission from home);
Teaching status (not a COTH institution); # Hospital beds (< 300); ICU type (medical, mixed medsurg, or coronary care); Race (white); Chronic health items (AIDS, hepatic failure, lymphoma, or no
chronic health items).
Supplemental Table 4. Comparison of multivariable models to predict hospital length of stay:
Linear Regression (Normal distribution) vs. Generalized Linear Model (Gamma distribution with a
log link)
Development
MODEL Normal
Internal
Validation
External
Validation
Gamma
Normal
Gamma
Normal
Gamma
Observed Hospital Length of Stay (days)
9.05
9.05
9.11
9.11
9.93
9.93
Predicted Hospital Length of Stay (days)
9.05
9.10
9.04
9.09
9.52
9.60
Observed - Predicted (hrs.)
0.0
-1.1
1.5
0.4
9.7
7.8
R2 across individuals
17.7%
17.3%
17.7%
17.3%
16.5%
15.9%
R2 across units
80.3%
80.7%
75.4%
74.2%
71.7%
72.8%