Open Journal of Nursing, 2012, 2, 307-310 OJN
http://dx.doi.org/10.4236/ojn.2012.223045 Published Online November 2012 (http://www.SciRP.org/journal/ojn/)
Comparison of temperature measurements in bladder,
rectum and pulmonary artery in patients after cardiac
surgery
Hendrika Wollerich, Farouq Ismael, Maarten W. Nijsten, Willem Dieperink
Department of Critical Care, University of Groningen, University Medical Center Groningen, Groningen, Netherlands
Received 10 September 2012; revised 12 October 2012; accepted 25 October 2012
ABSTRACT
In many patients in the intensive care unit (ICU) con-
tinuous temperature monitoring is performed with
rectal probes. Currently there are more options to
measure temperature in critically ill patients. Since
bladder catheters are routinely used in the majority
of ICU patients, using bladder temperature (Tb)
could do away with rectal probes. In this prospective
study, we compared Tb, rectal temperature (Tr) and
pulmonary artery catheter temperature (Tpa) in pa-
tients who underwent cardiac surgery. We also eva lu-
ated if urinary production affected Tb. Patients ad-
mitted af ter cardiac surg ery with sensors in place for
measurement of Tr, Tb and Tpa upon arrival at the
ICU were included. Diuresis was recorded every hour.
Data were collected until 24 h after admission or until
ICU discharge. Nineteen consecutive patients (9 males;
mean age 61 years) were evaluated. Over a median
observation period of 17 hours 382 Tb, 333 Tr and
371 Tpa measurements were recorded. Linear corre-
lations (R) between Tb and Tr, between Tb and Tpa
and between Tr and Tpa were 0.95, 0.95 and 0.91 re-
spectively (P < 0.001). Bland-Altman analysis demon-
strated no relation between temperature and the (Tb-
Tr) offset. No relation of diuresis with (Tb-Tr) or
(Tb-Tpa) was observed. After cardiac surgery, blad-
der temperature performed as well as conventional
rectal probes with no interference of diuresis on blad-
der temperature measurement. Thus, the use of blad-
der temperature probes may be preferable to rectal
probes in patients after cardiac surgery.
Keywords: Intensive Care; Cardiac Surgery; Body
Temperature
1. INTRODUCTION
Accurate and precise measurement of body temperature
is important for in the timely detection of fever or hypo-
thermia in patients in the intensive care unit (ICU). No
uniform practice regarding temperature measurement
exists. A variety of devices are used to measure body
temperature at diverse anatomical locations in two possi-
ble temperature scales. Traditionally the temperature meas-
ured within the pulmonary artery (Tpa) with a the Swan-
Ganz catheter (PAC), that is typically only used in pa-
tients with complex hemodynamic problems, is consid-
ered the “gold standard” for the measurement of body
temperature [1].
Nevertheless, for routine clinical use in ICU patients,
using a PAC is clearly inapplicable.
In many ICU’s continuous rectal temperature meas-
urement (Tr) is standard practice [2]. Placement of ther-
mometers in the rectum is more invasive than in the
axilla or groin. A rectal probe can be distressing as well
as embarrassing for patients. Moreover, for inserting the
probe, patients must be placed on their side, a maneuver
that often requires two nurses to safely turn the patient.
The rectal temperature probe can also result in mucosal
injury, or even perforation of the rectum [3]. Tr can also
be affected by the passage of stools and the probe can
dislocate easily. On the other hand Tr is more accurate
than less invasive measurement methods such as at the
axilla or inguinal [4].
Urinary bladder temperature (Tb), measurement of
temperature with a specially designed temperature probe
embedded in a Foley urinary catheter, could be a favor-
able alternative to Tr in the ICU because rectal probe
insertion is not required without the need for additional
procedures [5,6]. In several patient groups it has been
established that Tb generally corresponds well to the Tpa,
the “gold standard” [7,8]. It has been suggested, that the
accuracy and precision of Tb might be influenced by the
urinary flow rate [5,9]. In 22 ICU patients in which tem-
perature was simultaneously monitored with PAC it has
been demonstrated that the reliability of Tb is higher than
either Tr or inguinal or axillary temperature measure-
ments [6,10].

H. Wollerich et al. / Open Journal of Nursing 2 (2012) 307-310 308
It is not known if the same holds true for the reliability
of Tb during the direct post-operative phase in patients
admitted after cardiac surgery. Cardiac surgery involves
the opening of the chest and frequently the use of a
heart-lung machine. Thus during and after such surgery
important swings in hemodynamics and temperature can
occur. This may be particularly relevant given the large
thermal gradients from core to periphery that occur dur-
ing anesthesia and cardiac surgery [5].
Objective
In a prospective study we tested the hypothesis that after
cardiac surgery Tb adequately reflects Tpa, and at least
as good as Tr. We also examined the effect of varying
urinary flow rate on the Tb.
2. METHODS
During a 10-month study period (June 2009 to March
2010) consecutive patients aged >18 years, who were
undergoing cardiac surgery and admitted to the depart-
ment of critical care were evaluated for this study. Pa-
tients, with a ileal conduit urinary diversion also known
as Bricker ileal conduit, or patients with suprapubic
catheters, or other patients where urethral catheterization
was contraindicated as well as patients who were under-
going renal replacement therapy were excluded.
Only patients with both a PAC, a urinary bladder
catheter with temperature probe (Tb) and a rectal tem-
perature probe (Tr) were included.
Tb was measured by a probe incorporated in a Foley
urinary catheter (DeRoyal, Powell, USA). Tpa was meas-
ured by a pulmonary artery catheter (PAC) (Edwards,
Irvine California). Tr was measured by a digital ther-
mometer probe (Esophageal/Rectal temperature probe
25˚C - 45˚C, Philips Medical Systems, Andover, USA)
designed for axillar and rectal use. The temperature sen-
sors and the PAC were respectively connected to a tem-
perature and cardiac output module of the bedside moni-
tor (MP70, Philips Medical Systems, Eindhoven, the
Netherlands). Temperature values were recorded in de-
grees Celsius every 30 minutes by the ICU nurses. The
urinary production in ml was recorded every hour. All
data were collected until 24 h after admission or until
ICU discharge if this took place within 24 h.
Tpa was considered the reference value. Thus Tb was
compared with Tpa, and Tr was compared with Tpa us-
ing regression and Bland and Altman analysis.
Since no additional interventions were performed in-
formed consent was not required for this anonymized
analysis of data. The institutional review board of the
University Medical Center Groningen approved this ob-
servational study (METc 2008/279).
3. RESULTS
During the study period, 19 consecutive patients admit-
ted to the department of critical care after cardiac surgery
were included. For 9 men and 10 women with a mean
age of 61 ± 13 (SD) years, we recorded temperatures
over a median observation period of 17 hours. A total of
382 Tb, 333 Tr and 371 Tpa measurements were ana-
lyzed (Table 1). We also recorded 291 diuresis meas-
urements.
Correlation coefficients between Tb and Tr, between
Tb and Tpa (Figure 1) and between Tr and Tpa were
0.95, 0.95 and 0.91 respectively (P < 10−9). The mean
offsets for expressed as (Tb-Tr), (Tb-Tpa) and (Tr-Tpa)
were −0.05˚C, +0.05˚C and +0.10˚C respectively, indi-
cating that Tr was the least reliable of the three meas-
urements.
Bland-Altman analysis demonstrated no relation be-
tween temperature and the (Tb-Tr) offset (Figure 2). No
relation of diuresis with (Tb-Tr) or (Tb-Tpa) was ob-
served. The two outlying values visible in Figures 1 and
2 concerned immediate post-operative patients with very
cold peripheries and consequently high temperature gra-
dients. For both these outliers Tr deviated more from Tpa
than Tb.
4. DISCUSSION
Measuring body temperature in critically ill patients is a
part of routine nursing care. However, it is still unclear
which method and device is ideal for measuring accurate,
reliable affordable, comfortable and safe body tempera-
ture. Nurses therefore must have the knowledge and
skills related to the various temperature measuring
Table 1. Patient characteristics.
Number of patients 19
Age, mean, SD, (range) 61.1 ± 13.4 (32 - 83)
Gender, male/female 9/10
Admission diagnoses:
Valve replacement, n (%)
CABG, n (%)
Cardiovascular other, n (%)
9 (47.3)
5 (26.3)
5 (30.3)
Height (cm), mea n , SD, (rang e ) 171.1 ± 8.2 (156 - 189)
Weight (kg), mean, SD, (range) 79.0 ± 16.2 (51 - 105)
BSA (m2), mean, SD, (range) 1.9 ± 0.2 (1.53 - 2.37)
APACHE IV score, me an, ±SD, (range) 44.8 ± 15.7
SAPS II score, mean, ±SD 30.5 ± 8.1
Diuresis, ml/hr, mean, ±SD, (range) 88 ± 79 (5 - 400)
SD = Standard Deviation, CABG = Coronary Artery Bypass Graft Surgery,
BSA = Body Surface Area, APACHE II = Acute Physiologic and Chronic
Health Evaluation, SAPS II = Simplified Acute Physiology Score.

H. Wollerich et al. / Open Journal of Nursing 2 (2012) 307-310 309
393837363534
39
38
37
36
35
34
PA C temperature
Bl a dder te mperatur e
Co rre la tion of bl a dder t e mpe ra tur e versus P A C te mpe ra tur e
R=0.95 (P<10-9)
Figure 1. Correlation plot of Tb versus Tpa showing high cor-
relation between the two temperature measuring methods.
393837363534
1
0
-1
-2
-3
MEAN OF BOTH METHO DS, degrees Celsius
DIFFERENCES BETWEEN METHODS, degrees Celsius
Blad der temperature versus PAC t emperature
Figure 2. Bland and Altman Plot of the data obtained from
paired samples of bladder and PAC temperature. Correlation R
= 0.95 (P < 10−9).
methods and associated devices to make good clinical
decisions. In the ICU, Tb measurement has gained in-
creased acceptance and is simplified by the fact that most
patients have an indwelling Foley catheter.
In many clinical studies Tpa is considered as the most
optimal representation of internal body temperature [8,
11,12]. However, for temperature measurement only, Tpa
is obviously not a practical technique as the invasive
pulmonary artery catheter is only required in a minority
of ICU patients. Inserting rectal thermometers is usually
uncomplicated, although it can occasionally cause mu-
cosal injury. However, these probes can be easily dislo-
cated by stool movements or by the application of sup-
positories and they are definitely associated with addi-
tional patient discomfort. At our ICU most patients have
bladder catheters, making the use of a catheter with an
incorporated temperature probe therefore not additionally
invasive. Thus Tb could be the preferred temperature
device in ICU patients.
The data in our study agree with those found in other
patient groups where neither Tb nor Tr exactly correlate
with Tpa [13-17]. However, bladder temperature gener-
ally did as well or better compared to Tr.
In spite of the fact that devices for Tb measurement
are more expensive than Tr devices, the overall costs for
Tb are lower because Tr probes must be changed more
often than Tb probes. Thus, although overall costs may
vary according to local circumstances, in our setting the
use of Tb is associated with reduced yearly cost decrease
of more than €4000 for our unit.
There are some limitations of the present study. First,
none of the CE-certified thermometers were tested or
compared with certified laboratory thermometers. On the
other hand, all equipment and materials in our hospital
are routinely monitored and checked regularly, and Tpa
is regarded as the gold standard.
Second, rectal temperature measurement could be af-
fected by the depth of inserting the probe, conditions
affecting local blood flow and the presence of stools.
These factors were not assessed in the our study since we
assumed that interference of stools or probe dislocation
would be less important, so early after insertion and sur-
gery. But if these factors come into play later on, we ex-
pect them to work particularly to the disadvantage of the
rectal temperature measurement, not the bladder meas-
urement.
And finally, we had a small number of measurements
in patients who were severely hypothermic or hyper-
thermic. Hence, further studies with larger sample sizes
including hypo and hyperthermic patients might further
strengthen the results of this study.
5. CONCLUSIONS
In conclusion, this study demonstrates that for post-
operative cardiac surgery patients, bladder temperature
measurement performs equal or better than rectal tem-
perature measurement. Diuresis did not interfere with
bladder temperature measurement.
We believe that both from the patient’s perspective
and from the nursing perspective, bladder temperature
measurement has sufficient advantages in terms of ac-
curacy, patient comfort and cost to be used in place of
the cumbersome rectal temperature measurements in
these patients.
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ABBREVIATIONS
CABG: Coronary artery bypass grafting;
ICU: Intensive care unit;
Tb: Bladder temperature;
Tpa: Pulmonary artery temperature;
Tr: Rectal temperature;
PAC: Pulmonary artery catheter;
SD: Standard deviation.