Download Hospital costs associated with surgical site infections in general and

Hospital costs associated with surgical
site infections in general and vascular
surgery patients
Melissa M. Boltz, DO,a,b Christopher S. Hollenbeak, PhD,a,b,c Kathleen G. Julian, MD,d
Gail Ortenzi, RN, BSN,a and Peter W. Dillon, MD,b Hershey, PA
Background. Although much has been written about excess cost and duration of stay (DOS) associated
with surgical site infections (SSIs) after cardiothoracic surgery, less has been reported after vascular and
general surgery. We used data from the National Surgical Quality Improvement Program (NSQIP) to
estimate the total cost and DOS associated with SSIs in patients undergoing general and vascular
surgery.
Methods. Using standard NSQIP practices, data were collected on patients undergoing general and
vascular surgery at a single academic center between 2007 and 2009 and were merged with fully loaded
operating costs obtained from the hospital accounting database. Logistic regression was used to determine
which patient and preoperative variables influenced the occurrence of SSIs. After adjusting for patient
characteristics, costs and DOS were fit to linear regression models to determine the effect of SSIs.
Results. Of the 2,250 general and vascular surgery patients sampled, SSIs were observed in 186
inpatients. Predisposing factors of SSIs were male sex, insulin-dependent diabetes, steroid use, wound
classification, and operative time (P < .05). After adjusting for those characteristics, the total excess cost
and DOS attributable to SSIs were $10,497 (P < .0001) and 4.3 days (P < .0001), respectively.
Conclusion. SSIs complicating general and vascular surgical procedures share many risk factors with
SSIs after cardiothoracic surgery. Although the excess costs and DOS associated with SSIs after general
and vascular surgery are somewhat less, they still represent substantial financial and opportunity costs
to hospitals and suggest, along with the implications for patient care, a continuing need for cost-effective
quality improvement and programs of infection prevention. (Surgery 2011;150:934-42.)
From the Division of Outcomes Research and Quality, Department of Surgery,a,b Penn State Milton S. Hershey
Medical Center, Department of Public Health Sciences,c and Department of Infectious Disease,d Penn State
College of Medicine, Hershey, PA
THE UNITED STATES has an estimated 2.1 million nosocomial infections per year with postoperative surgical site infections (SSIs) being the third most
common.1 Despite increased implementation of
quality improvement initiatives, SSIs continue to
be an ongoing problem. In 1970, the Centers
for Disease Control and Prevention’s National
Nosocomial Infection Surveillance (NNIS) System
was the first to established criteria to classify SSIs
as incisional (skin or subcutaneous tissue involvement) or organ-space (any body part other than incised layers involved in the operation). The NNIS
also developed a specific risk index using the
American Society of Anesthesiologists (ASA)
Accepted for publication April 22, 2011.
Reprint requests: Christopher S. Hollenbeak, PhD, Department
of Surgery, Penn State College of Medicine, 600 Centerview
Drive, A210. Hershey, PA 17033-0850. E-mail: chollenbeak@
psu.edu.
0039-6060/$ - see front matter
Ó 2011 Mosby, Inc. All rights reserved.
doi:10.1016/j.surg.2011.04.006
934 SURGERY
physical status classification system, wound classification, and operative duration.2
The NNIS reported that, from January 1992
through June 2004, patients undergoing general
surgical procedures including appendectomy, cholecystectomy, colon, gastric, and small-bowel procedures, as well as laparotomy, had a risk of developing
an SSI of 2.5% if they had 1 risk factor or 6.2% if they
had greater than 2 risk factors.2 Several recent studies report rates of postoperative wound infections
between 1.8% and 6.9%, depending on the surgical
procedure.3,4 with extensive research conducted on
patient and intraoperative risk factors.
In addition to increasing morbidity and mortality, SSI is well recognized as one contributing
factor to prolonged hospital duration of stay
(DOS) and causes substantial financial burden to
healthcare systems.5 Policy changes implemented
in 2007 by the Center for Medicare and Medicaid
Services eliminated reimbursement to hospitals
for extra costs associated with injuries or conditions that could have been reasonably prevented,
Surgery
Volume 150, Number 5
such as SSIs.6 As a result, hospitals now have a
greater financial incentive to decrease postoperative surgical complications.7
Although much has been written about estimated excess cost and DOS associated with SSIs
after cardiothoracic surgery, less has been reported
on noncardiac procedures. The objective of this
study was to use institutional data from the
National Surgical Quality Improvement Program
(NSQIP) combined with a single-center accounting database to identify risk factors associated with
postoperative SSIs and to study the excess total cost
and DOS associated with SSIs in patients undergoing general and vascular surgery.
METHODS
Operations. Of 11,250 adult general and vascular inpatient operations performed between 2007
and 2009 at a single academic medical center,
2,250 were selected for analysis using previously
reported NSQIP methodology.8-10 In brief, these
cases were selected because they were the first 40
eligible vascular and general surgery operations
in an 8-day cycle. Because each cycle began on a
different day of the week, these cases captured
approximately 20% of the general and vascular
surgery volume of the hospital.
In all cases, preoperative antibiotics were routinely given within 60 minutes before incision
(>90% compliance with the Centers for Medicare
and Medicaid Services Surgical Infection Prevention parameters). Shaving was not avoided. The
most commonly used preoperative skin antiseptic
agent was a commercially available solution composed of Iodine Povacrylex (0.7% available iodine)
and Isopropyl Alcohol (74% w/w) (DuraPrep
Surgical Solution; 3M Health Care, St. Paul, MN).
Patient data. Patient data were collected by a
clinical nurse reviewer on 60 preoperative patient
characteristics, 18 intraoperative factors, and 22
postoperative occurrences up to 30 days after the
procedure. To maintain data reliability, the clinical
nurse reviewer completed in-depth training on
study definitions, and participated in conference
calls, annual meetings, and site visits. Chart review,
information from morbidity and mortality conferences, and communication with patients by telephone or letter completed the 30th postoperative
day data collection, as described previously.3,8,10,11
SSIs sunder the NSQIP program are defined as
superficial, deep, or organ-space, with criteria based on
the following definitions established by the Centers
for Disease Control and Prevention’s NNIS system.
Superficial SSIs involve the skin or subcutaneous tissue of the incision, whereas deep SSIs involve fascia
Boltz et al 935
and muscle layers. Operations involving areas in
and around the body organs that become infected
are identified as organ-space SSIs.
By definition, the infection must have occurred
within 30 days postoperatively and only involve
tissue that was manipulated or opened during the
procedure to be classified as an SSI.12,13 The clinical nurse reviewer assigned the SSI variable based
on medical documentation of any of the following:
purulent drainage, positive wound culture, or diagnosis of SSI by the surgeon or attending physician.
In addition, the superficial SSI variable was
assigned if medical documentation indicated redness, swelling, or tenderness of the incision, and
the surgeon deliberately opened the wound. Likewise, a deep or organ-space SSI variable was
assigned if radiologic studies or re-operation identified an abscess or other evidence of infection at
the fascia, muscle, or organ level. Stitch abscesses
and infected burn wounds were not classified as
SSIs under the NSQIP criteria.12,13
Cost data for the surgical admissions were
obtained from the clinical cost accounting database used in our institution (McKesson, San
Francisco, CA). These data represented fully
loaded operating costs estimated in the database
from a ratio of costs-to-charges (CCR) methodology. The CCR approach is a standard, costaccounting technique, whereby costs are estimated
as a percentage of hospital charges. Each hospital
department estimates a CCR on a yearly basis; the
following year, department-level charges are multiplied by the CCR and used as an estimate of costs.
The cost for the admission is the sum of all
department-level costs.
Although the CCR approach is imperfect for
estimating hospital costs, it is by far the most
prevalent technique. Previous research14 has demonstrated that department-level CCRs are a reasonable approach for estimating costs within a hospital
and for estimating costs across hospitals for patients within a common diagnosis related group.
Statistical analysis. The statistical analysis was
designed to identify risk factors for developing SSIs
in this surgical population and to estimate the
excess cost and DOS associated with SSIs after
controlling for other potentially confounding patient and surgical variables. Patient characteristics
were compared using the Student t test for continuous variables and the chi-square test for binary
and categorical variables. Logistic regression was
used to determine which patient and preoperative
NSQIP variables influenced development of SSIs.
Total cost and DOS were fit to linear regression
models to determine the effect of SSIs after
936 Boltz et al
Surgery
November 2011
Table I. Characteristics of infected vs uninfected patients
Variable
Category
General surgery
Vascular surgery
Sex
Female
Male
Race/Ethnicity
White
Nonwhite
Preoperative DOS, d
BMI, kg/mm2
BMI < 18.5
BMI 30+
Nondiabetic
Diabetic: insulin-dependent
Diabetic: noninsulin-dependent
Smoker
Radiotherapy
Open wound
Steroid use
ASA class 1
ASA class 2
ASA class 3
ASA class 4 or 5
Wound class
Clean
Clean-contaminated
Contaminated
Dirty
Operative time, h
<4
4–7:59
8–11:59
12+
Emergent operation
No infection, mean/%
(N = 2,064)
SSI, mean/%
(N = 186)
P value*
0.84
0.16
0.95
0.05
<.0001y
<.0001y
0.56
0.44
0.46
0.54
.0140z
.0140z
0.95
0.05
0.90
41.03
0.02
0.55
0.82
0.07
0.12
0.21
0.02
0.09
0.05
0.02
0.33
0.58
0.08
0.95
0.05
1.30
41.49
0.04
0.53
0.77
0.12
0.11
0.25
0.06
0.13
0.06
0.01
0.26
0.64
0.09
.6550
.6550
.0530x
.8654
.1370
.5630
.1380
.0070z
.7350
.1380
<.0001y
.1000
.5170
.6110
.0800
.1100
.7340
0.32
0.46
0.12
0.11
3.99
0.67
0.26
0.05
0.03
0.12
0.16
0.54
0.19
0.11
5.29
0.50
0.30
0.16
0.04
0.10
<.0001y
.0320x
.0060z
.9030
<.0001y
<.0001y
.1820
<.0001y
.4570
.3930
*Variables analyzed with a P value > .2 that are not shown in this Table include the following: age > 18 y; BMI, 18.5–30 kg/m2; history of chronic
obstructive pulmonary disease; hypertension; acute renal failure; chemotherapy; and previous operation within 30 d.
yDenotes statistical significance of P < .0001.
zDenotes statistical significance of P < .01.
xDenotes statistical significance of P < .05.
SSI, Surgical site infection; DOS, duration of stay; BMI, body mass index; ASA, American Society of Anesthesiologists.
adjusting for patient characteristics that may have
independently affected costs and DOS. All statistical analyses were performed using commercially
available software (Stata Statistical Software:
Release 11; StataCorp LP, College Station, TX).
Statistical significance was defined as P < .05.
RESULTS
Demographics. According to the diagnosis related group for admission, the majority of patients
underwent operations on the colon and rectum
(26.2%) or the foregut (15.9%) and bariatric
surgery (11.5%). Vascular procedures comprised
the next largest group of procedures (9.0%). Of
the 2,250 surgical inpatients selected for this study,
186(8.2%) developed an SSI. Patient characteristics stratified by occurrence of SSI are depicted in
Table I; the groups were similar in demographic
characteristics, such as age (P = .57) and race
(P = .66). The groups were also alike with regard
to preoperative characteristics including body
mass index (P = .86), tobacco abuse (P = .14),
steroid use (P = .52), and serum albumin concentration (P = .67).
Boltz et al 937
Surgery
Volume 150, Number 5
Table II. Logistic regression of factors affecting likelihood of surgical site infection
95% Confidence interval
Variable (N = 2,250)
Category
General surgery
Vascular surgery
Sex
Female
Male
Ethnicity
White
Nonwhite
Nondiabetic
Diabetic: insulin-dependent
Diabetic: noninsulin-dependent
Nonsmoker
Smoker
No previous history of steroid use
Steroid use
ASA class 1 and 2
ASA class 3 and 4
Wound class
Clean
Clean-contaminated
Contaminated or dirty
Operative time, h
<4
4–8
>8
Nonemergent operation
Emergent operation
Odds ratio
Lower
Upper
P value*
Reference
0.20
0.09
0.44
<.0001y
Reference
1.51
1.10
2.07
.0100z
0.57
2.28
.7180
1.18
0.53
3.32
1.45
.0090z
.6040
0.97
2.05
.0680
0.69
2.44
.4260
0.90
1.93
.1510
0.88
1.10
2.25
3.02
.1490
.0200x
1.25
2.06
2.58
5.04
.0020z
<.0001y
0.38
1.13
.1310
Reference
1.14
Reference
1.98
0.87
Reference
1.41
Reference
1.29
Reference
1.32
Reference
1.41
1.82
Reference
1.79
3.23
Reference
0.66
*Variables analyzed with a P value > .2 that are not shown in this Table include the following: age and whether the patient was admitted from their
residence or from another institution.
yDenotes statistical significance of P < .0001.
zDenotes statistical significance of P < .01.
xDenotes statistical significance of P < .05.
ASA, American Society of Anesthesiologists.
Yet, some significant differences between the
groups were evident, suggesting risk factors for SSI.
Of the group with SSIs, 54% were male versus 44%
of the control group (P = .014), and 12% of the
SSI group had insulin-dependent diabetes versus
6.6% of the control group (P = .007). Several intraoperative variables including clean (P < .001),
clean-contaminated (P = .032), and contaminated
(P = .006) wound classes, as well as operative times
between 8 and 12 hours (P < .001) were also significant between the 2 groups.
Risk of infection. The logistic regression results
presented in Table II indicate several factors were
important in predicting risk of SSI. Male patients
were at greater risk of developing SSIs (odds ratio
[OR], 1.5; P = .01), as were insulin-dependent diabetics (OR, 1.98; P = .009). Patients with wound
classification of contaminated or dirty (OR, 1.82;
P = .02) and operative times between 4 and 8 hours
(OR, 1.79; P = .002) or greater than 8 hours (OR,
3.23; P < .0001) were also more likely to develop
SSIs.
None of the other variables were statistically
significant, including factors such as smoking
(OR, 1.41; P = .068) and steroid use (OR, 1.29;
P = .426).
Mortality. Of the 186 patients who developed an
SSI, 4 died, which was not statistically significant
(P = .847). Interestingly, all 4 patients who died
had developed organ-space infections, which was
different (P = .019) compared to the 14 patients
with deep incisional infections (P = .560) and the
other 123 patients with superficial incisional SSIs
(P = .076).
938 Boltz et al
Surgery
November 2011
Table III. Logistic regression of factors affecting likelihood of mortality
95% Confidence interval
Variable (N = 2,250)
Category
General surgery
Vascular surgery
Surgical site infection
Age, y
Sex
Female
Male
Ethnicity
White
Nonwhite
ASA class 1 and 2
ASA class 3 and 4
Nonemergent operation
Emergent operation
Odds ratio
Lower
Upper
P value*
Reference
1.52
1.06
1.03
0.64
0.34
1.01
3.61
3.24
1.05
.3420
.9230
.0100y
Reference
1.85
1.00
3.45
.0520z
0.19
3.94
.8490
1.61
31.35
.0100y
4.44
16.85
<.0001x
Reference
0.86
Reference
7.10
Reference
8.65
*Variables analyzed with a P value > .2 that are not shown this Table include the following: whether patients were admitted from their residence or another
institution, diabetes, smoking status, steroid use, any wound class, and operative time.
yDenotes statistical significance of P < .01.
zDenotes statistical significance of P < .05.
xDenotes statistical significance of P < .0001.
ASA, American Society of Anesthesiologists.
After controlling for patient and intraoperative
characteristics, developing an SSI was not a statistically significant factor in affecting a patient’s
mortality (OR, 1.06; P = .923) (Table III).
Hospital costs. Results of a linear regression
analysis shown in Table IV suggest that the excess
cost of an SSI was $10,497 (P = .003). In patients
who had an SSI, male sex added $4,328 (P = .04)
in costs, a nonwhite patient added $10,314
(P = .026), admission from residence added an additional $13,511 (P < .0001), steroid use added
$9,064 (P = .019), and an ASA class 3 and 4 added
$20,647 (P = .053). Also, an operative time between
4 and 8 hours added $10,798 (P < .0001), whereas
an operative time greater than 8 hours added
$10,180 (P = .004), and an emergent case added
$17,498 (P < .0001). Other factors in the regression analysis did not affect the cost of SSIs.
Effect on DOS. As seen in Table V, developing
an SSI added 4.26 days (P < .0001) to the patient’s
DOS. Many of the same factors that were significantly associated with costs also affected DOS.
Male sex added 1.34 days (P = .03), admission
from residence 7.02 days (P < .0001), steroid use
2.99 days (P = .006), ASA class 3 and 4 added
6.48 days (P = .032), contaminated and dirty
wound classes 2.2 days (P = .009), operative time
between 4 and 8 hours added 2.82 days (P <
.0001), and emergent case 3.13 days (P < .0001).
DISCUSSION
Given the continued occurrence of SSIs after
general and vascular surgical procedures, it is
important to understand their associated risk factors and costs to develop quality improvement
programs tailored to prevention strategies and to
make informed decisions regarding the costeffectiveness of these strategies.
In this study of 2,250 surgical inpatients at a
large academic medical center, independent risk
factors for developing an SSI after general or
vascular surgical procedures were male sex,
insulin-dependent diabetes, wound classification,
and operative time greater than 4 hours. Multiple
studies in the literature have previously reported
these clinical variables as risk factors, and this study
adds support to the growing body of literature
regarding SSIs.
At our institution, patients with a cleancontaminated or dirty surgical procedure were 2
to 3 times more likely to develop a wound infection
than clean procedures and 3 times more likely to
have an SSI if the operation lasted greater than 8
hours. As in other studies, smoking and steroid use
were not important risk factors in developing an
SSI.
In terms of mortality, although ASA class was
not a factor in the development of an SSI, patients
with an ASA class of 3 or 4 were greater than 7
Boltz et al 939
Surgery
Volume 150, Number 5
Table IV. Linear regression of factors affecting cost of surgical site infection
Variable (N = 2,250)
Intercepty
Surgical site infection
Category
General surgery
Vascular surgery
Sex
Female
Male
Ethnicity
White
Nonwhite
Patient transferred from another institution
Patient admitted from residence
No previous history of steroid use
Steroid use
ASA class 1
ASA class 2
ASA class 3 and 4
Operative time, h
<4
4–8
>8
Nonemergent operation
Emergent operation
Parameter
estimate ($)
95% Confidence interval
Lower
Upper
P value*
17,703
10,497
16,453
3,574
18,953
17,421
<.0001z
.0030x
Reference
3,547
10,429
3,335
.3120
Reference
4,328
198
8,459
.0400{
1,232
19,396
.0260{
6,545
20,477
<.0001z
1,506
16,622
.0190{
8,862
272
32,895
41,567
.2590
.0530{
5,863
3,189
15,732
17,171
<.0001z
.0040x
11,764
23,231
<.0001z
Reference
10,314
Reference
13,511
Reference
9,064
Reference
12,017
20,647
Reference
10,798
10,180
Reference
17,498
*Variables analyzed with a P value > .2 that are not shown in this Table include the following: age, diabetes, smoking status, and wound class.
yIntercept represents hospital cost for patients without surgical site infections.
zDenotes statistical significance of P < .0001.
xDenotes statistical significance of P < .01.
{Denotes statistical significance of P < .05.
R2 = .26. This indicates that the model explains approximately 26% of overall variation in cost.
ASA, American Society of Anesthesiologists.
times more likely to die after operation --- an
outcome that reflects the serious nature of the
associated comorbidities present at the time of
operation in these patients. The presence of an SSI
did not impact mortality unless it was an organspace infection.
In addition, this study yielded a rate of SSI of
8.2%, which exceeds the current overall reported
rate of approximately 4%.15 Most other studies rely
on administrative databases, electronic markers of
infection, or billing codes for SSI surveillance,
which may underestimate the incidence of SSIs.
In contrast, the NSQIP used in our study is unique,
in that the database uses standard definitions of infection based on criteria established by the Centers
for Disease Control and Prevention and clinical
nurse reviewers to perform chart reviews to clinically detect SSIs, making the program more aggressive and probably more accurate at reporting SSIs
retrospectively. This approach may account for
part of the difference between our SSI rate and
the rate reported in the current literature.
A study by Neumayer et al15 using data from the
Department of Veterans Affairs’ NSQIP program
reported an overall SSI rate of 4.3%. When the results of this study are broken down by procedure,
however, general surgery patients who underwent
procedures involving the stomach, intestine, appendix, biliary tract, or pancreas had an SSI rate
of 40.6% and patients undergoing vascular procedures an SSI rate of 15.5%.15
Another study, this one carried out by Dimick
et al,3 also used NSQIP data to assess postoperative
occurrences of general and vascular surgery
patients. This study reported an SSI rate of approximately 7%,3 further corroborating our rate of 8.2%.
At our institution, the development of an SSI
after a general or vascular surgical procedure
incurs additional costs in excess of $10,497 for
the hospital admission in which the procedure was
940 Boltz et al
Surgery
November 2011
Table V. Linear regression of factors affecting duration of stay with surgical site infection
Variable (N = 2,250)
Intercepty
Surgical site infection
Category
General surgery
Vascular surgery
Sex
Female
Male
Ethnicity
White
Nonwhite
Patient transferred from another institution
Patient admitted from their residence
No previous history of steroid use
Steroid use
ASA class 1
ASA class 2
ASA class 3 and 4
Wound class
Clean
Clean-contaminated
Contaminated and Dirty
Operative time, h
<4
4–8
>8
Nonemergent operation
Emergent operation
Parameter
estimate (d)
95% Confidence
interval
Lower
Upper
P value*
5.91
2.29
6.64
6.22
<.0001z
<.0001z
Reference
0.57
2.52
1.38
.5660
Reference
1.34
0.16
2.51
.0260{
0.23
4.92
.0740
5.04
8.99
<.0001z
0.85
5.14
.0060z
1.20
0.55
10.65
12.42
.1180
.0320{
0.79
0.54
2.58
3.86
.2980
.0090x
1.42
0.77
4.22
3.20
<.0001z
.2290
1.51
4.76
<.0001z
6.27
4.26
Reference
2.35
Reference
7.02
Reference
2.99
Reference
4.72
6.48
Reference
0.89
2.20
Reference
2.82
1.22
Reference
3.13
*Variables analyzed with a P value > .2 that are not shown in this Table include the following: age, diabetes, and smoking status.
yIntercept represents duration of stay for patients without surgical site infections.
zDenotes statistical significance of P < .0001.
xDenotes statistical significance of P < .01.
{Denotes statistical significance of P < .05.
R2 = .26. This indicates that the model explains approximately 26% of overall variation in duration of stay.
ASA, American Society of Anesthesiologists.
performed. Concomitantly, the DOS for a patient
who develops an SSI is increased by 4.3 days.
Importantly, our study highlights the financial
implications in treating an SSI in select subpopulations of patients. Nonwhite patients who developed a wound infection incurred additional costs
of $10,314, while it cost an additional $9,064 to
treat an SSI in patients with a history of steroid use.
Patients with an ASA class of 3 or 4 led to costs of
$20,647 more than procedures for patients with an
ASA class of 1, and operations exceeding 4 hours
caused additional costs close to $10,000. These
results demonstrate clearly the financial imperative
in addition to the patient care imperative for
decreasing the incidence of postoperative SSIs.
These financial analyses assist in decisions
whether to invest in potentially costly interventions
to prevent SSIs. For example, the 2% chlorhexidine/70% isopropyl alcohol preoperative scrub
decreases SSIs by 41% compared to the povidoneiodine preoperative scrub; chlorhexidine-alcohol
is also substantially more expensive than iodine
products.16 Data on the costs of SSIs and the
number of SSIs that may be prevented with
chlorhexidine-alcohol can be used to assess the
economic value of converting preoperative scrub
products.
Analyses must be undertaken with the understanding that no individual intervention will prevent all SSIs and that interventions implemented
outside a research setting may not achieve results
as dramatic as those obtained in a research setting.
Lee et al17 estimated that if 2% chlorhexidine/
70% isopropyl alcohol scrub led to a decrease in
Surgery
Volume 150, Number 5
SSIs by at least 10%, net cost savings would be demonstrated. Our medical center is in the process of
transitioning to chlorhexidine-alcohol as the standardized preoperative scrub primarily for efficacy
reasons, but this decision appears to be supported
by financial analyses.
Although the economic impact of SSIs is acknowledged, few studies exist to quantify the costs
to treat these infections or the financial determinants that contribute to those costs. In a literature
review of the last 6 years, Broex et al18 could find
only 16 articles that met their study criteria for
reporting SSIs and economic evaluations and costs
across all surgical disciplines. Studies specific to
general and vascular surgical procedures are even
rarer.
Dimick et al3 used their NSQIP database to examine costs associated with postoperative complications at a single academic medical center. They
demonstrated that their unadjusted total hospital
costs for infectious complications were increased
by $8,209, and DOS was increased by 4.0 days.3
When adjusted for complexity, patient variables,
and other complications, their findings decreased
to $1,398 of additional total hospital costs and
2.8 days for DOS; however, in their grouping of infectious complications, they included patients with
sepsis and wound dehiscence.
A study of SSIs in English hospitals by Coello
et al19 examined the economic impact of wound
infections in a number of different surgical procedures and specialties.19 They showed that superficial incisional SSIs were more common than
deep incisional or organ-space SSIs, but the impact
of organ-space SSIs on mortality was clinically important. In addition, all classes of SSIs contributed
to significantly greater DOS and increased costs in
every surgical procedure examined.
The most in-depth attempt at examining the
economic factors that contribute to the excess
costs incurred by SSIs was published recently by
Alfonso et al20 who found that 9% of their patients
developed SSIs and that almost all the SSIs were
concentrated in general, vascular, and cardiac
patients. The overall DOS for these patients was increased by 14 days, and excess hospital costs were
$10,232 per patient. Interestingly, in an attempt
to include all costs, including both direct health
costs and indirect social costs, incurred in treating
SSIs, these investigators projected the overall costs
of treating these infections from a societal perspective to be $97,433 in 2006 U.S. dollars.
While all of these studies use slightly different
study methods and surgical populations, they serve
collectively to highlight the economic impact these
Boltz et al 941
SSIs have on the cost of delivering quality surgical
care.
It should be noted that the most important
determinant of healthcare spending is the intensity
of services provided over the course of a hospital
stay. Therefore, the greatest driver of hospital costs
is DOS. It can be assumed that the same variables or
patient characteristics that contribute to greater
DOS, such as sex or ethnicity (male and nonwhite,
respectively, in our study), would also contribute to
greater hospital costs. In addition, extended DOS
relates to severity of illness. For example, a patient
transferred from another institution is monitored
constantly by healthcare staff and presents for an
emergency procedure sooner than the patient admitted from their residence.
Greater DOS is also affected by its surrogates of
comorbid diseases and socioeconomic status.21 For
example, Procter et al22 found that increased operative time is independently associated with a
greater postoperative DOS after adjusting for
type of procedure. One reason for this finding is
that surgical procedures of greater duration have
been shown clearly to induce major metabolic disorders that, in turn, cause postoperative morbidity.
Another reason is that procedures of greater duration and DOS may be linked with factors affecting
the patient’s underlying condition, such as nutritional status or other comorbid diseases.22
Although this study attempts to control for as
many surrogate measures as possible within the
confines of the dataset, future studies are needed to
determine characteristics associated with duration
of surgical procedures to identify modifiable variables and potentially decrease DOS and hospital
costs.
This study has several limitations. First, all of the
patients studied were from a single academic
medical center, and our results may not be representative of general and vascular surgery patients
who develop SSIs in other institutions. Second,
whereas this study addresses several patient factors
affecting DOS, it does not account for socioeconomic status, which may prolong a hospital stay. In
addition, the frequency of distribution of DOS can
be skewed by a few patients whose stay is markedly
prolonged. Nevertheless, DOS is a better reflection
of resource utilization than the health status of the
patient.
Finally, the additional cost of $10,497 per patient reflects only hospital costs incurred as a result
of the primary hospitalization. Total costs associated with SSI must include medical services, such
as clinic visits, additional antibiotic use, home
health services, readmission to the hospital, and
942 Boltz et al
additional procedures, as well as costs experienced
directly by the patient, such as lost wages, transportation costs, and other out-of-pocket expenses.
Therefore, our study almost certainly underestimates the real costs attributable to SSI for the
surgical patient.
Surgery
November 2011
11.
12.
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