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1. Original Study Journal of Veterinary Emergency and Critical Care 24(4) 2014, pp 403–407
doi: 10.1111/vec.12197
Determination and validation of volume to be
instilled for standardized intra-abdominal
pressure measurement in dogs
Leilani Ireland Way, DVM, MS and Eric Monnet, DVM, PhD, DACVS, DECVS
Abstract
Objectives – The objectives of this study were to determine (1) most appropriate volume of saline to be
infused into the bladder prior to intra-abdominal pressure (IAP) measurement, (2) to determine if a difference
exists between IAP measurements before and after abdominal surgery, and (3) to assess the variability in IAP
measurements associated with different saline volumes.
Design – Prospective study.
Setting – University teaching hospital.
Animals – Fifteen female research dogs, 7 undergoing ovariohysterectomy (OHE), and 8 undergoing la-
paroscopy.
Interventions – All dogs had urinary catheters placed and 4 consecutive IAP measurements measured using
a different volume of instilled saline (0.25, 0.5, 1, and 2 mL/kg) at baseline. Measurements were repeated
intraoperatively in laparoscopy dogs and postoperatively in OHE dogs.
Measurements and main results – For both groups of dogs, the volume infused into the bladder significantly
affected IAP measurement. An instilled volume of 1 mL/kg of saline produced the best correlation (R2
= 0.44,
P = 0.04) between IAP measurement and laparoscopic insufflator pressure. The mean (±SD) preoperative IAP
(cmH2O) using 1 mL/kg instilled saline was 7.9 ± 1.4 and 9.6 ±1.9 for laparoscopy and OHE dogs, respectively.
There was no difference in IAP before and after surgery in the dogs undergoing an OHE (P = 0.58). The volume
of saline instilled into the bladder significantly affected the IAP (P = 0.0028).
Conclusions – One milliliter per kilogram instilled saline is recommended for standardized IAP pressure
measurement in dogs. IAP in clinically normal dogs was not affected by abdominal surgery.
(J Vet Emerg Crit Care 2014; 24(4): 403–407) doi: 10.1111/vec.12197
Keywords: abdominal compartment syndrome, canine, intraabdominal hypertension
Introduction
Abdominal compartment syndrome is characterized by
adverse physiologic consequences due to an acute in-
crease in intra-abdominal pressure (IAP).1
The clini-
cal importance of increased IAP, also known as intra-
abdominal hypertension, has been well documented in
human medicine.2–4
Intra-abdominal hypertension al-
ters regional blood flow and impairs tissue perfusion,
which may trigger the systemic inflammatory response
syndrome and multiple organ failure.1
From the Department of Clinical Sciences, College of Veterinary Medicine,
Colorado State University, Fort Collins, CO 80523.
The authors declare no conflicts of interest.
Address correspondence and reprint requests to
Dr. Leilani Ireland Way, 300 West Drake Road, Fort Collins, CO 80523, USA.
Email: lireland@colostate.edu
Submitted August 03, 2012; Accepted May 19, 2014.
Abbreviations
IAP intra-abdominal pressure
OHE ovariohysterectomy
The easiest method of IAP measurement in people
is obtained using the urinary bladder (intravesicular
technique), and provides consistent and accurate results
compared to direct invasive measurements.5
This tech-
nique was first described by Kron,6
and involves place-
ment of a Foley catheter into the urinary bladder and
infusion of saline into the bladder via the catheter. The
IAP is measured via a water manometer as the saline pas-
sively exits the urinary bladder. Although this technique
of IAP measurement correlates with direct IAP measure-
ment in dogs,7
the volume that should be infused into
the urinary bladder of dogs for accurate IAP estimation
has not been evaluated.
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Veterinary Emergency and Critical Care Society 2014 403

2. L. I. Way E. Monnet
The volume infused into the urinary bladder for IAP
measurement is important; if too much is infused the
detrusor muscle will contract and falsely elevate IAP
readings.8,9
In human medicine, this topic is controver-
sial and recent literature supports the use of minimal
instillation volume (2–10 mL) for IAP measurement.9,10
These lower volumes allow for passive emptying of the
bladder and accurate IAP estimation. Because dogs vary
in size and most are smaller than a typical person, it
would make sense that some dogs may require less in-
fusion volume, so as not to activate the detrusor muscle
or not to stretch the wall of the bladder.
The objectives of this study were to (1) quantify a dose
of saline in milliliter per kilogram required for accu-
rate IAP measurement, (2) determine if an abdominal
surgery affects IAP in dogs, and (3) assess for interac-
tions between the volume of saline instilled, and IAP
measurements made before and after surgery.
Materials and Methods
Fifteen female research dogs were enrolled into a
prospective study, including 7 research beagles under-
going ovariohysterectomy (OHE) and 8 research hound
dogs undergoing laparoscopy. The beagles were adopted
out at the end of the study. The hound dogs were part
of a continuing education laparoscopy lab and were hu-
manely euthanized at the end of the study. The Insti-
tutional Animal Care and Use Committee at the study
facility approved this protocol.
Dogs were sedated with a combination of atropine,a
an opioid,b,c
and occasionally acepromazine.d
Dogs
were induced with either ketaminee
and diazepamf
or propofolg
and diazepam. They were maintained on
isoflurane-inhalanth
anesthetic through their procedure.
Foley urinary cathetersi
(6–8 French) were placed and the
urinary bladder was emptied. An open urinary collection
system was connected to the Foley catheter with two
three-way stopcocks. The stopcock closest to the subject
had a water manometerj
attached to it. The second stop-
cock was attached to a 20 mL syringe and liter bag of 0.9%
sodium chloride, as previously described by Conzemius
et al.11
The urinary bladder was emptied completely be-
tween each measurement and the manometer was ze-
roed at the level of the pubic symphysis before each
measurement.
Four consecutive IAP measurements (each with a dif-
ferent volume of saline) were obtained by the primary
investigator (L.I.W.) at 2 timepoints: preoperatively in
all dogs (under sedation), immediately postoperatively
for the dogs in the OHE group (while the dogs were
still under general anesthesia), and during laparoscopy
in the dogs in the laparoscopy group. The first measure-
ment was obtained with instillation of 0.25 mL/kg of
Table 1: Correlation coefficients between direct (by laparoscopy
insufflator) and indirect (intravesicular) intra-abdominal pres-
sure measurements at different volumes of saline instilled into
the urinary bladder of 8 healthy female dogs
Volume of 0.25 0.5 1 2
intravesicular saline mL/kg mL/kg mL/kg mL/kg
R 2
0.016 0.328 0.441 0.239
P-value 0.73 0.08 0.04 0.15
saline, second with 0.5 mL/kg of saline, third with 1
mL/kg of saline, and final with 2 mL/kg of saline in-
stilled into the urinary bladder. Dogs in the laparoscopy
group were maintained in lateral recumbency. The ab-
domen was clipped and aseptically prepared for laparo-
scopic surgery. A cannula was placed percutaneously
into the peritoneal cavity and the automatic insufflator
was introduced. Carbon dioxide was then instilled into
the peritoneal cavity until the pressure transducer at-
tached to the insufflators indicated the desired pressure.
This pressure was maintained by the automatic insuf-
flator with additional carbon dioxide as needed. After
each saline aliquot was instilled into the bladder, simul-
taneous measurements were recorded from the water
manometer and pressure transducer on the insufflators.
Measurements were taken during the laparoscopic pro-
cedure. All measurements were obtained with the ani-
mals in lateral recumbency at the end of expiration. Base-
line IAP was defined as the IAP measured before OHE
or before laparoscopy.
Statistical Methods
Data were analyzed using a commercially available sta-
tistical software program.k
IAP was normally distributed
in this population. Linear regression was used to com-
pare the measured IAP to insufflator pressure in la-
paroscopy dogs. ANOVA for repeated measures was
used to evaluate the effect of abdominal surgery, volume
of saline injected, and the interaction between surgery
and volume of saline infused on IAP in the OHE group.
Data were reported as mean ± SD. A P-value of 0.05
was considered statistically significant.
Results
In the laparoscopy group, the best correlation between
measured IAP and insufflator pressure was obtained
when 1 mL/kg of saline was infused into the bladder
(R2
= 0.44, P = 0.04) (Tables 1 and 2). The mean preoper-
ative IAP in laparoscopy dogs using 1 mL/kg of instilled
saline was 7.9 ± 1.4 cmH2O. The mean preoperative IAP
in OHE dogs using 1 mL/kg of instilled saline was 9.6
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3. Standardized IAP measurement in dogs
Table 2: Individual laparoscopy intra-abdominal pressure mea-
surements (cmH2O) obtained by measuring intravesicular pres-
sure following instillation of varying amounts of saline (using a
water manometer), and the corresponding intra-abdominal pres-
sure measured by the laparoscopic insufflator device (WM, water
manometer; I, insufflator pressure) for each volume of saline in-
fused
0.25 0.5 1 2
mL/kg mL/kg mL/kg mL/kg
Volume of
intravesicular
saline WM I WM I WM I WM I
Dog 1 11.2 22.2 15.0 22.2 14.4 24.1 15.4 24.1
Dog 2 14.4 24.1 16.0 24.1 16.6 22.2 16.0 24.1
Dog 3 17.8 27.7 16.8 27.7 18.0 27.7 22.6 27.7
Dog 4 22.0 22.2 21.0 25.8 21.2 20.4 24.0 22.2
Dog 5 13.6 35.1 15.0 25.8 25.8 25.8 25.8 25.8
Dog 6 20.0 27.7 21.4 27.7 21.2 27.7 24.2 27.7
Dog 7 19.8 25.8 21.2 25.8 21.6 24.1 20.0 27.7
Dog 8 17.2 20.4 15.4 15.0 9.0 5.4 14.6 1.9
Table 3: Intra-abdominal pressure (cmH2O) measured before
and after ovariohysterectomy (OHE) in 7 healthy female dogs us-
ing different volumes of intravesicular saline instillation (mean
± SD)
Volume of 0.25 0.5 1 2
intravesicular saline mL/kg mL/kg mL/kg mL/kg
OHE Preoperative 7.2 ± 2.9 7.4 ± 2.8 9.6 ± 4.9 17.3 ± 16.8
Postoperative 6.8 ± 1.4 7.1 ± 1.1 8.9 ± 1.5 12.8 ± 4.2
±1.9 cmH2O. The mean baseline IAP for all dogs was 8.7
± 4.4 cmH2O.
For all 4 volumes of saline infused in the OHE group,
there was no significant difference between the IAP mea-
surement taken preoperatively and the IAP measure-
ment taken postoperatively (P = 0.58) (Table 3, Figure 1).
The volume of saline instilled into the bladder signif-
icantly affected the measurement of IAP (P = 0.0028)
(Figure 1). There was no interaction among volume of
saline instilled and the IAP measurements before and
after surgery (P = 0.72).
Discussion
One milliliter per kilogram was the most appropriate
volume of saline to instill into the urinary bladder to
evaluate IAP measurement in healthy dogs in this study.
This volume correlated significantly to laparoscopy in-
sufflator pressure and is similar to the volume that
has been reported in the veterinary literature for IAP
measurement.8,12–14
The mean resting IAP in this popu-
lation of dogs was between 7.9 and 9.6 cmH2O.
The mean preoperative IAP in this study is higher than
previously reported IAP in clinically normal dogs. In
1995, Conzemius et al11
measured IAP in 20 healthy dogs
undergoing elective OHE. They documented a mean IAP
of 4.5 ± 0.44 cmH2O and suggested a reference interval
for IAP in dogs between 0 and 7.5 cmH2O. However, they
did not report the volume of saline used for IAP mea-
surements and all dogs were under general anesthesia
for their measurements. More recent studies have also
documented higher IAP measurements in awake, hos-
pitalized dogs13
(mean 5.6 ± 1.2 cmH2O) and healthy
sedated and awake cats12
(median 7.21 cmH2O), using
1 mL/kg for measurement. This suggests that IAP in
healthy dogs may be higher than initially suspected, and
larger prospective studies should be performed to con-
firm this hypothesis. Higher IAP may also be due to
other factors, such as stress or anxiety; the OHE dogs
had urinary catheters placed and preoperative IAP mea-
surements were taken while awake, but under sedation.
The effect of sedation is difficult to know and not all
dogs in this study were sedated with the same drugs.
Measurements that are taken while animals are strug-
gling can also result in increased IAP value. The dogs in
this study were presumed healthy, but underlying dis-
ease that could lead to increased IAP was not ruled out.
The volume of saline that was instilled into the blad-
der significantly affected the IAP measurements. In this
study, 1 mL/kg gave the best correlation with the pres-
sure measured via the laparoscopy insufflator. The R2
–
value was only 0.44, therefore, there is a lot of variability
in the data collected. A study in people measured IAP in
patients undergoing laparoscopy and found that their di-
rect measurements correlated well with urinary catheter
measurements (R2
= 0.68) and concluded that intraves-
icular pressure closely approximates IAP.15
While indi-
vidual IAP measurements are important particularly in
high-risk patients, it also important to note that trends in
IAP may be clinically more relevant than any individual
IAP measurement. As the instilled volume of saline in-
creased, the IAP measurements also increased. The instil-
lation of too much volume will result in detrusor contrac-
tion and falsely elevated IAP readings.9
There is much
debate over the appropriate amount of saline to instill
for accurate IAP measurement in human medicine, with
reported volumes anywhere from 2 to 100 mL.9,10,16,17
These studies vary significantly in the technique used
for IAP measurement: water manometer versus pres-
sure transducer, awake versus under sedation, supine
versus prone body position, and pubic symphysis ver-
sus midaxillary zero point. In this study, all of the dogs
were in lateral recumbency and the intravesicular pres-
sure was measured with a water manometer. The most
recent consensus paper from human medicine states
that no more than 25 mL of saline be instilled for accu-
rate IAP measurement.18
This recommendation is based
on previous documentation that instillation volumes
greater than 50 mL resulted in increased IAP measured
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4. L. I. Way E. Monnet
Figure 1: Graph showing the relationship between the volume of saline (mL/kg) instilled into the urinary bladder and the measured
intravesicular intra-abdominal pressure measurements in 15 healthy female dogs.
indirectly through the urinary bladder although the di-
rect IAP measurements did not change.19
More recent
studies have shown that as little as 2 mL of saline could
be instilled for accurate IAP monitoring in people.10
The
variable results among different studies may be related to
decreased bladder compliance in the critically ill or to the
rate or temperature of the instilled saline.9,10
This study
did not determine a maximum volume that should be in-
fused, although 2 mL/kg appears to be too high a volume
to infuse. Additionally, there was not much variability in
the body weight and body condition of this sample pop-
ulation. The dogs undergoing OHE were all research bea-
gles of roughly the same weight and body condition; the
laparoscopy dogs were all research hounds of roughly
the same weight and body condition. Although 1 mL/kg
resulted in the best correlation for this study population,
this may not be the same in dogs that are smaller or larger
(10 kg or 30 kg). Clinically, it is likely more relevant to
follow trends in IAP measurements from an individual
patient.
There was no difference in the IAP measured before
and after OHE. This corroborates previous reports of
elevated IAPs (up to 15 cmH2O) post-OHE that were
transient and physiologically insignificant.11
The preop-
erative measurements were taken under sedation and
postoperative measurements were taken under general
anesthesia (Table 3). Some higher IAP results in the pre-
operative subjects may be related to measurements being
taken under sedation only and associated anxiety or dis-
comfort associated with restraint and urinary catheteri-
zation.
There was no interaction found between volume of
saline instilled and the IAP measurements made before
and after surgery, indicating that the same amount of
instilled saline produced the same IAP measurement be-
fore and after surgery.
Study limitations include a small sample population.
Also, only one investigator measured IAP; however, IAP
monitoring in dogs generally has low intraobserver and
interobserver variability.13
All measurements taken us-
ing 2 mL/kg of saline were significantly elevated, but the
SD was also very wide resulting in a wide range of IAP
measured preoperatively (7.5–55 cmH2O) and postoper-
atively (8.4–25.8 cmH2O). This could be due to detrusor
contraction, speed with which the saline was infused or
subject anxiety (preoperatively).
The correlation between measured IAP and insufflator
pressure was weak. Other factors than pressure of carbon
dioxide in the abdomen may have influenced the IAP
measured via the intravesicular technique. Contraction
of the abdominal wall may have an effect on the pressure
read by the insufflator that the water manometer could
not appreciate. The respiratory cycle (expiration versus
inspiration) could have influenced the IAP as the auto-
matic insufflator was not able to adjust its pressure read-
ings fast enough to measure variation from inspiration
to expiration; therefore, the intravesicular IAP may have
been higher than what the insufflator recorded. The tone
of the detrusor muscle could have influenced the IAP
measured with the intravesicular catheter but not the
pressure measured by the automatic insufflator. A larger
sample size would have allowed for a more homogenous
dataset and eliminate some of those effects. However,
we were mostly interested in the variation in the IAP
rather than an absolutely accurate IAP. The insufflator
measured the pressure of a gas in the abdominal cav-
ity while the water manometer measured the pressure
in a bladder containing saline. Also, insufflator pressure
measurements are not the gold standard for IAP mea-
surement; insufflator pressure has been shown to corre-
late to intravesicular IAP measurement in people, with
an R2
-value of 0.68, but it is not 100% accurate.15
This
study was performed in healthy research dogs under-
going elective abdominal procedures and thus this tech-
nique may not translate to clinical patients. In addition,
the effect of postoperative analgesia has also not been
standardized. Although the dogs in this study were pre-
sumed healthy, we did not perform diagnostic testing to
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5. Standardized IAP measurement in dogs
rule out underlying disorders that may cause increased
IAP. Overall the IAP measurements varied dramatically
between the different volumes of saline infused; how-
ever, within one volume the IAP measurements did not
vary from preoperative to postoperative measurements.
Thus, as long as the method of IAP measurement is con-
sistent the trends in IAPs may be more clinically signifi-
cant than the actual numbers. Future prospective clinical
studies are warranted to further investigate this.
In conclusion, IAP measurement in dogs using 1
mL/kg of instilled saline has the best correlation to IAP
measured by direct means. We recommend that future
studies utilize 1 mL/kg to allow for more direct com-
parisons among IAP studies in dogs. Measured IAP is
not affected by abdominal surgery in healthy dogs. Fur-
ther study is needed to prospectively evaluate IAP in
clinically ill dogs with intra-abdominal hypertension or
abdominal compartment syndrome.
Footnotes
a
Atropine, Hospira Inc., Lake Forest, IL.
b
Morphine, Baxter Healthcare Corporation, Deerfield, IL.
c
Hydromorphone, Mayne Pharma Inc., Paramus, NJ.
d
Acepromazine, Boehringer Ingelheim Vetmedica Inc., St. Joseph, MO.
e
Ketamine, Bioniche Pharma USA LLC.
f
Diazepam, Hospira Inc.
g
Propofol, Teva Paranteral Medicines Inc, Irvine, CA.
h
Isoflurane, Baxter Healthcare Corporation.
i
Six or eight French Foley urinary catheter, Mila International Inc, Erlanger,
KY.
j
Manometer, Cardinal Health, McGaw Park, IL.
k
JMP Statistical Software by SAS, Cary, NC.
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