Baylor University Medical Center Proceedings July 2017 - 256

the chi-square statistical method was used. A 1:3 case-control
The primary outcome of interest was the occurrence of the
propensity score-matched sampling of the EA and the non-EA
composite of major cardiopulmonary complications (MCPCs),
groups was done using a greedy 8 to 1 digit-matching algorithm
including acute myocardial infarction, cardiac arrest, pneumotechnique without replacement (13). The two matched cohorts
nia, ventilatory support for >48 hours, and unplanned intuba(EA and non-EA) were compared utilizing conditional logistic
tion within 7 days after the surgery. These major complications
regression analyses and McNemar's tests (for dichotomous variwere combined in one binary variable (1, 0). The secondary
ables). Additionally, generalized linear mixed models (Glimmix
outcome measures investigated were the hospital LOS and
procedure of the SAS software) were used to assess the association
30-day mortality.
of EA with LOS in the matched sample. All statistical analyses
Patients who received EA were matched in a 1:3 matchwere two-tailed, and a P value of 0.05 was considered statistiing with a similar group of patients who did not receive EA
cally signiﬁcant.
based on calculated propensity scores. Because we excluded
all patients who received other regional analgesic techniques
RESULTS
such as transversus abdominis plane blocks, we assumed
Of the 24,927 patients who met the inclusion criteria, EA
that the nonepidural groups received traditional postoperawas provided for 15.02% (n = 3745). Within 7 days of the
tive analgesia (i.e., primarily pharmacological treatments). A
surgery, at least one MCPC was encountered in 627 patients,
multiple logistic regression model was utilized to calculate
which corresponds to a 2.52% cumulative risk over the 2-year
the propensity scores after controlling for the patient's demostudy period. Some patients had more than one MCPC. The
graphic characteristics (i.e., age, race, and gender), preoperacumulative risk for 30-day mortality was 1.24% (n = 309) over
tive comorbidities (utilizing modiﬁed Charlson comorbidity
the study period. There were no statistically signiﬁcant diﬀerindex) (11, 12), smoking status, and complexity of procedure
ences between the EA and the non-EA groups in the MCPC
(utilizing the work value unit of the procedure as an indicarates and 30-day mortality in the unmatched sample (Table).
tion of the complexity of the surgery). Modiﬁed Charlson
The 1:3 propensity-matched samples had 2107 patients in
comorbidity index scores are calculated as follows: a score of
the EA group and 6321 patients in the non-EA group. Because
1 is assigned for a history of chronic obstructive pulmonary
of missing data during the matching process, 1638 EA cases
disease, chronic heart failure, myocardial infarction, periphwere excluded. Good matching was achieved between the EA
eral vascular disease/rest pain, diabetes, or cerebrovascular
and non-EA groups, as reﬂected by P > 0.39 for the explanadisease (transient ischemic attack or stroke). A score of 2 is
tory variables in the matched sample (Table). After propensity
assigned for patients on dialysis, patients with radiation and
matching, there were no statistically signiﬁcant diﬀerences in the
chemotherapy without disseminated cancer, or patients with
rates of MCPC (relative risk [RR] 0.91, 95% conﬁdence interval
hemiplegia. Patients with ascites or esophageal varices receive
[CI] 0.66-1.27, P = 0.59), LOS, and the 30-day mortality rate
a score of 3, and patients with disseminated cancer, a score of
(RR 0.71, 95% CI 0.42-1.20, P = 0.201).
6. Also, one point is added for each decade beyond 40 years
of age.
Descriptive statistics
Table. Characteristics of patients who did and did not receive epidural analgesia after open colorectal
of the unmatched sample
surgery in the total population and propensity-matched study cohort
were obtained utilizing
univariate analyses of
Unmatched cohort
Propensity-matched study cohort
PROC FREQ of the SAS
Epidural
Nonepidural
P
Epidural
Nonepidural
P
software; SAS 9.4 software
(n = 3745) (n = 21,182) value
(n = 2107) (n = 6321) value
Characteristics
(Cary, NC) was used for all
Age, mean (SE) (years)
60 (0.24)
61 (0.10)
0.47
62 (0.26)
62 (0.18)
0.78
statistical analyses. Discrete
Women
1793 (48%) 10,951 (52%) <0.001 1058 (50%) 3201 (51%) 0.74
variables are presented as
White
2034 (54%) 15,373 (72%) 0.01
1806 (86%) 5429 (86%) 0.96
frequencies and percentBlack
224 (6%)
2021 (10%)
199 (9%)
595 (9%)
ages. Continuous variables
Hispanic
123 (3%)
1129 (5%)
102 (5%)
297 (5%)
are summarized as means
and standard errors or
Other and unknown
1364 (37%) 2659 (13%)
medians and interquartile
Modified CCI score, median (IQR)
3 (2-4)
3 (2-4)
0.003
3 (2-5)
3 (2-4)
0.99
ranges. Student's t test was
Smoker
615 (16%)
3898 (18%)
0.004
352 (17%) 1110 (18%) 0.39
used to compare the con28.31 (0.11) 28.65 (0.05) <0.001 28.79 (0.15) 28.91 (0.09) 0.50
BMI, mean (SE) (kg/m2)
tinuous variables between
Complexity of procedure (WRVU), mean (SE) 26.95 (0.09) 26.02 (0.04) <0.001 27.24 (0.12) 27.23 (0.10) 0.92
the EA and the non-EA
7-day major cardiopulmonary complications 100 (2.67%) 527 (2.49%)
0.50
47 (2.23%) 154 (2.44%) 0.59
groups in the unmatched
sample. To examine the
30-day mortality
34 (0.91%) 275 (1.30%) 0.045 17 (0.81%) 72 (1.14%) 0.20
association with diﬀerent
Length of stay, median (IQR) (days)
6 (5-9)
6 (4-8)
<0.001
6 (5-9)
6 (4-9)
0.36
categorical variables in
BMI indicates body mass index; CCI, Charlson Comorbidity Index; IQR, interquartile range; SE, standard error; WRVU, work relative value unit.
the unmatched sample,
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