measuring intrabladder pressure with the head of the bed elevated 30º.pdf

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Published online http://www.ajcconline.org 2011 American Association of Critical-Care Nurses

doi: 10.4037/ajcc2011744 2011;20:e80-e89Am J Crit Care

Melanie Horbal Shuster, L. Kathleen Sekula, John C. Kern and Jorge A. VazquezEvidence to Support a Change in PracticeMeasuring Intrabladder Pressure With the Head of the Bed Elevated 30:

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By Melanie Horbal Shuster, RN, PhD, L. Kathleen Sekula, RN, PhD, John C. Kern, PhD,and Jorge A. Vazquez, MD

Background A 30 head-of-bed elevation is recommended formost critically ill patients. Measuring intrabladder pressure withthe patient in this position is controversial.Objective To assess the feasibility of measuring intrabladderpressure with a 30 head-of-bed elevation.Methods A prospective, randomized, and experimental study.Patients had intrabladder pressure measured first while posi-tioned supine with a 30 head-of-bed elevation and 25 mL ofsaline instilled into the bladder and again after the patientswere randomly repositioned to supine without any head-of-bedelevation (flat) or with a 30 head-of-bed elevation while supineor in right lateral or left lateral position with either 25, 50, or200 mL of saline instilled into the patients bladder.Results Intrabladder pressures measured with the patient inall 3 head-of-bed elevated positions were higher than pressuresmeasured with patients supine and flat after instillation of 25mL of saline into the bladder, but intrabladder pressure didnot differ between the 30 head-of-bed elevated positions andthe supine and flat positions when 50 or 200 mL of saline wasinstilled into the bladder. Two-way analysis of variance showeda significant interaction between volume of saline instilled(P = .05), patients position (P = .007), and bladder instill volumeand position interaction (P = .004).Conclusion It is feasible to measure intrabladder pressure witha 30 head-of-bed elevation, and that position could be analternative to supine positioning of patients for measurementof intrabladder pressure. (American Journal of Critical Care.2011;20:e80-e89)

MEASURING INTRABLADDERPRESSURE WITH THE HEADOF THE BED ELEVATED 30:EVIDENCE TO SUPPORT ACHANGE IN PRACTICE

e80 AJCCAMERICAN JOURNAL OF CRITICAL CARE, July 2011, Volume 20, No. 4 www.ajcconline.org

2011 American Association of Critical-Care Nursesdoi: 10.4037/ajcc2011744

Evidence-Based Practice in Critical Care


Intra-abdominal pressure is most commonlymeasured indirectly by using the urinary bladdertechnique in critically ill patients who are positionedsupine and flat.13 Because most patients in the inten-sive care unit (ICU) assume positions with somedegree of head-of-bed elevation (HOBE) for routinecare, positioning the patient supine and flat 1 to sev-eral times a day solely for the purpose of measuringintrabladder pressure (IBP) increases nurses work-load and may increase the risk of equipment dislodg-ment and discomfort for the patient. Use of thesupine position in patients receiving mechanicalventilation increases the risk of aspiration pneumo-nia developing.14 To decrease the occurrence of ven-tilator-associated pneumonia, the Institute forHealthcare Improvement15 developed the ventilatorbundle with 1 of the 4 components being somedegree of HOBE. A number of ICUs have adoptedthe recommendations of the Institute for HealthcareImprovement16 as well as the recommendations ofthe Healthcare Infection Control Practices AdvisoryCommittee of the Centers for Disease Control,17 theVentilator-Associated Pneumonia Guidelines Com-mittee and the Canadian Critical Care Trials Group,18

and the Association of Medical Microbiology andInfectious Disease Canada Guidelines Committee.19

In addition, the recommendations of the CanadianCritical Care Clinical Practice Guidelines Committee20

and the American Society for Parenteral and EnteralNutrition21 are for use of HOBE for critically ill adultpatients who require enteral nutrition. Althoughthese recommendations and guidelines are specificto intubated, ventilator-dependent and enterally fedpatients, the 30 HOBE position has become thepreferred position for the vastmajority of critically ill patients.

Measuring IBP in patients posi-tioned with a 30 HOBE will avoidthe pulmonary pitfalls associatedwith the supine position and willbe in compliance with current rec-ommendations for the care of ICUpatients.17,20,21 No physiological,technical, or clinical rationale pro-hibits measurements of IBP withthe patient in the 30 HOBE posi-tion. Indeed previous studies ofhemodynamic measurements thatused a technique identical to IBP measurementhave shown that measurements taken in positionswith HOBE are technically feasible,22 reliable,23 andclinically relevant.24

One argument used to recommend against a30 HOBE position to measure IBP is that thisposition yields higher IBP values than when IBP ismeasured with the patient in the supine flat posi-tion.25-27 However, a higher pressure measurementin the 30 HOBE position compared with thesupine flat position is not by itself a strong enoughreason to prefer one position over another formeasuring IBP. Other considerations such as accu-racy and reproducibility of the measurement, pre-dictability of outcomes, and safety and conveniencefor the patient are just as important as the absolute

Intra-abdominal pressure is the pressure within the abdominal compartment. Observedintra-abdominal pressure measured in supine hospitalized patients ranges from 0 to12.5 mm Hg with a mean (SD) of 6.5 (3.3) mm Hg.1,2 By consensus, intra-abdominalhypertension is defined as an intra-abdominal pressure that exceeds 12 mm Hg.3

Increasing intra-abdominal pressure produces alterations in gastrointestinal,4 renal,5

cardiovascular,6 and respiratory physiology7 and multiple organ failures, which can manifestas oliguria,8,9 decreased venous return,9 and increased airway pressures.7 The clinical signs oforgan failure in 1 or more systems in association with intra-abdominal hypertension are rec-ognized as abdominal compartment syndrome (ACS).10 Therefore, routine monitoring of intra-abdominal pressure in critically ill patients is recommended to monitor for intra-abdominalhypertension and ACS.11,12

About the AuthorsMelanie Horbal Shuster is a nutrition clinical nurse spe-cialist and Jorge A. Vazquez is director of medical nutri-tion at West Penn Allegheny Health System in Pittsburgh,Pennsylvania. L. Kathleen Sekula is an associate professorin the School of Nursing and John C. Kern is an associateprofessor of statistics in the Department of Mathematicsand Computational Science at Duquesne University inPittsburgh, Pennsylvania.

Corresponding author: Melanie Horbal Shuster, 1307Federal Street, Suite 301, Pittsburgh, PA 15212 (e-mail:[email protected]).

www.ajcconline.org AJCC AMERICAN JOURNAL OF CRITICAL CARE, July 2011, Volume 20, No. 4 e81

No physiological,technical, or clinical rationaleprohibits meas-urements ofintrabladder pres-sure in the 30elevated position.


research interest, and prior research data. The Sposition was chosen because it is the traditionalposition used to measure IBP and the position rec-ommended by the American Association of Critical-Care Nurses (AACN)30 and the World Society of theAbdominal Compartment Syndrome (WSACS).3

The 30 HOBE position was chosen because it isthe recommended position for the prevention ofpneumonia in patients who require mechanicalventilation by the Centers for Disease Control17 andthe Canadian Critical Care Trails Group18 and is theposition recommended in the ventilator bundledeveloped by the Institute for Healthcare Improve-ment15 to prevent ventilator-associated pneumoniaregardless of concomitant administration of enteralnutrition20,21 and is of clinical nursing relevance.The RL-30 and LL-30 positions were chosen becausethey represent alternative positions recommendedto prevent complications of bed rest encounteredin intensive care such as pressure ulcers.31,32 A 45angled wedge positioning pillow (Hausmann Indus-tries Inc, Northvale, New Jersey) was used to sup-port the patients back while in the lateral positions.The 25- and 50-mL instillation volumes were cho-sen to represent the recommendations of WSACS13

and of AACN,30 respectively, and a 200-mL volumewas chosen to represent the larger instillation vol-ume previously used in research studies.33,34

The randomization scheme was prepared bythe statistician and delivered to the principal inves-tigator in sealed envelopes that were opened onlyafter signed informed consent was obtained. Patientsparticipated only once per ICU stay. All measurementswere taken by the principal investigator (M.H.S.).Once all measurements were obtained, the patientswere positioned in the most appropriate and com-fortable position on the basis of their medical con-dition and wishes.

IBP MeasurementIBP was measured by the method of Kron et al35

with modifications as described.36

StatisticsData were analyzed by using SPSS statistical

software (SPSS-15 SPSS Inc, Chicago, Illinois) andare presented as mean (SD). Normally distributeddata were analyzed by using a 1-way or 2-wayanalysis of variance with Neuman-Kuels test forpost hoc comparisons. Data that were not normallydistributed were analyzed by using Kruskal-Wallistest with Dunn post hoc analysis or the Wilcoxonsigned rank test. IBP measured in the initial studyconditions and compared with the conditions rec-

IBP value in deciding to select one position overanother when measuring IBP.

The aim of this study was to assess the feasibilityof measuring IBP in positions with a 30 HOBE,which are consistent with current best-practice rec-ommendations for care of ICU patients. Because therequisite volume of saline instilled into the bladderfor IBP measurement affects IBP,28,29 IBP measure-ments were taken after instillation of 1 of 3 differentvolumes of saline into the patients bladder, reflectingthe range of previously studied instillation volumes.

Materials and MethodsThe study was reviewed and approved by the

institutional review board, and signed informedconsent was obtained for all patients.

Selection of PatientsPatients admitted to any of 6 adult ICUs of

Allegheny General Hospital, West Penn AlleghenyHealth System, in Pittsburgh, Pennsylvania, werescreened to participate in the study regardless of the

patients sex, race, diagnosis, or hos-pital treatment. Inclusion criteriawere age at least 18 years and a clini-cal need for a urinary bladderdrainage catheter as determined bythe attending physician. Patients wereexcluded from the study if they wereunable to assume any of the 30HOBE body positions or if they hada neurogenic bladder, a bladder

tumor, or a perforation that would potentially influ-ence the muscular tone of the bladder or if they hadhematuria, which would potentially alter the meas-urement techniques.

Study DesignThe study was prospective, randomized, and

experimental. After informed consent was obtained,participants were positioned supine with a 30HOBE and an IBP measurement was taken with 25mL of saline instilled into the patients bladder (ini-tial study position). Participants were then random-ized to have a second IBP measurement taken in 1of 12 possible combinations of 4 body positionsand 3 volumes of instilled saline. The 4 randomizedpositions were supine and flat with a 0 HOBE (S),supine with a 30 HOBE (S-30), right lateral with a30 HOBE (RL-30), and left lateral with a 30HOBE (LL-30). The 3 randomized volumes of salineinstilled were 25 mL, 50 mL, and 200 mL.

The positions and instillation volumes chosenfor the study were based on clinical relevance,


The volume ofsaline instilled

into the bladderdoes affect intra-bladder pressure.


ommended by the AACN and the WSACS were ana-lyzed by means of a paired t test.

ResultsDescription of Study Population

Between April 2007 and December 2007, 280adult patients were screened to participate. Sixty-two(22.1%) declined to participate after a detailedexplanation of the study was given. Fifty-nine sub-jects (21.1%) did not meet inclusion criteria; somewere less than 18 years of age and others had anuria,hematuria, or neurogenic bladder. Eighteen patients(6.4%) were unable to participate for other reasons,for example, the urinary bladder catheter had beenremoved or orders for transfer from the ICU werewritten and adequate time to complete the studycould not be guaranteed. Seventeen patients (6.1%)were unable to give informed consent because ofsedation, and a surrogate decision maker was notavailable to give consent. Finally, 3 patients families(1.1%) declined participation, and 1 patient (0.4%)was not enrolled for an unknown reason. The remain-ing 120 subjects (42.9%) agreed to participate inthe study and were enrolled after a detailed expla-nation of the study was provided by the principalinvestigator and a signed written informed consentwas obtained.

Participants were from 18 to 93 years old, witha mean (SD) age of 63.5 (17.1) years. Sixty-six par-ticipants (55.0%) were male, and 111 (92.5%) werewhite. Body mass index (calculated as weight inkilograms divided by height in meters squared)ranged from 15.8 to 54 with a mean (SD) of 29.0(7.3). The length of stay in the ICU before IBPmeasurement was from 1 to 50 days, with a mean(SD) of 4.7 (6.8) days. Thirty-eight patients (31.7%)had IBP measured on the first day of admission, 56(46.7%) within 5 days of admission, and the remain-ing 26 (21.7%) more than 5 days after admission.A 1-way analysis of variance showed no significantdifference in length of stay among the 12 groups, butsignificant differences were observed for age (F= 2.5,R2 = 0.2, P= .007) and body mass index (F= 2.5, R2 = 0.2, P= .007). Subjects randomized to the supine30 HOBE position with 25 mL of saline instilled(see Figure, group 2) were a mean (SD) of 75.8 (6.8)years old and differed in age from the subjects ran-domized to the supine 0 HOBE position with 50 mLof saline instilled (see Figure, group 5; mean [SD]51.8 [15.5] years, P= .05). Subjects randomized tothe RL-30 HOBE position with 50 mL of salineinstilled (see Figure, group 7) had a mean (SD) forbody mass index of 35.5 (9.3) and differed fromsubjects randomized to the RL-30 HOBE position

with 200 mL of saline instilled (see Figure, group 11),who had a mean (SD) body mass index of 23.8(3.2) (P= .01). All other paired comparisons werenot significant.

Forty-eight patients (40.0%) were recruitedfrom the trauma unit, 25 (20.8%)from 2 neurosurgical ICUs, 18(15.0%) from the medical ICU, 15(12.5%) from the coronary careunit, and 14 (11.7%) from the sur-gical ICU. Eight patients (6.7%)were receiving mechanical ventila-tion, and 5 others (4.2 %) weretreated with biphasic intermittentpositive airway pressure. Twenty-five patients (20.8%) were in nega-tive fluid balance, ranging from-7661 to -73 mL, and 95 patients(79.2%) were in positive fluid balance, rangingfrom 1 to 35 497 mL.

IBP Measurements in the Initial Study PositionThe IBP measured in the S-30 position with 25

mL of saline instilled yielded values ranging from 1to 44 mm Hg with a mean (SD) of 11.6 (5.9) mm Hg.One hundred eighteen patients had values between1 and 25 mm Hg, and 2 patients had values greaterthan 25 mm Hg. Fifty-three participants (44.2%)had values of 12 mm Hg or greater.

IBP Measurements in the Randomized StudyPosition

One patient randomized to the supine positionwith 200 mL of saline instilled was unable to assumethe position because of respiratory distress and did notcomplete the study. The IBP measurements in the ini-tial study position and after randomization for eachindividual patient according to randomization groupare shown in the Figure, and the mean (SD) for IBPfor each randomized group is shownin the Table. The IBP measured inpatients randomized to the 3 differ-ent 30 HOBE positions with 25 or50 mL of saline instilled yieldedresults within the range of values pre-viously reported in critically illpatients who had IBP measured inthe supine position with 25 or 50 mLof saline instilled. The 200-mL instil-lation volume also yielded measure-ments in the expected range butoccasionally produced very high values (>40 mmHg), and a few participants complained of the urge tourinate. As a result, the absolute values and the inter-


Participants wererandomized into12 combinationsof positions andinstill volumes for a secondmeasurement.

There were nodifferences inintrabladderpressure with 25 mL or 50 mLwith HOBE 30.


measured with the patients in the LL-30 position weresimilar for the 25- and 50-mL instilled volumes (seeTable). One-way analysis of variance showed a signifi-cant volume effect for each body position. Post hocanalysis via the Dunn comparison test showed thatthe IBP measurements obtained with 200 mL ofsaline instilled into the patients bladder were sig-

patient variability of IBP with 200 mL of salineinstilled were higher than for the 25- and 50-mLinstillation volumes. For the supine and the RL-30positions, IBP progressively increased as the volumeof saline instilled increased. However, for the S-30,IBP was higher when measured with 25 mL ratherthan 50 mL of saline instilled, whereas the IBP values


Figure Paired intrabladder pressure (IBP) measurements for all patients (n=119). The left column of each graph is the IBPmeasured with the patient in the initial study position (supine with a 30 head-of-bed elevation [HOBE] with 25 mL ofsaline instilled into bladder) and each measurement is represented by a solid black square. The right column of each graphis the IBP measured with the patient in the randomized condition (one of 12 possible combinations of 4 body positions:supine flat [S], supine with a 30 HOBE [S-30], right lateral with a 30 HOBE [RL-30], left lateral with a 30 HOBE [LL-30]and 3 volumes of saline instilled into the bladder: 25, 50 and 200 mL). All groups had 10 patients, except for group 9,which had 9. Position is represented by shapes: downward-pointing triangle for supine and flat (S), upward-pointing trian-gle for S-30, diamond for RL-30, and circle for LL-30. The volume of saline instilled into the bladder is represented by color:red for 25 mL, yellow for 50 mL, and blue for 200 mL. The scale for IBP (y axis) for the graphs depicting the 200-mLinstilled volume (groups 9-12) differs from the scale for the graphs depicting the 25-mL (groups 1-4) and 50-mL (groups 5-8) volumes of saline instilled into the bladder.

Group 1

25

20

25

10

5

0

S-30 25 mL S 25 mL

IBP,

mm

Hg

Group 2

25

20

25

10

5

0

S-30 25 mL S-30 25 mLIB

P, m

m H

g

Group 3

25

20

25

10

5

0

S-30 25 mL RL-30 25 mL

IBP,

mm

Hg

Group 4

25

20

25

10

5

0

S-30 25 mL LL-30 25 mL

IBP,

mm

Hg

Group 8

25

20

25

10

5

0

S-30 25 mL LL-30 50 mL

IBP,

mm

Hg

Group 7

25

20

25

10

5

0

S-30 25 mL RL-30 50 mL

IBP,

mm

Hg

Group 6

25

20

25

10

5

0

S-30 25 mL S-30 50 mL

IBP,

mm

Hg

Group 5

25

20

25

10

5

0

S-30 25 mL S 50 mL

IBP,

mm

Hg

Group 9

120

160

80

40

0

S-30 25 mL S 200 mL

IBP,

mm

Hg

Group 10

120

160

80

40

0

S-30 25 mL S-30 200 mL

IBP,

mm

Hg

Group 11

120

160

80

40

0

S-30 25 mL RL-30 200 mL

IBP,

mm

Hg

Group 12

120

160

80

40

0

S-30 25 mL LL-30 200 mL

IBP,

mm

Hg


the patient supine.3 Patients who are unable toassume this position either forgo IBP measurementor are measured supine with some degree of HOBE,but the interpretation of the results is difficultbecause the degree of HOBE lacks standardization.Furthermore, positioning a patient supine from amore comfortable HOBE position solely for thepurpose of measuring IBP places the patient at riskfor aspiration pneumonia developing, increases therisk of equipment dislodgment, is inconvenient,and increases the nurses workload. Measuring IBPin a position that is rarely used by nurses when car-ing for critically ill patients truly does not reflect IBPwhen the head of the bed is elevated, and the IBPtaken when the patient is lying supine for a fewminutes does not reflect the abdominal pressurewhen the head of the bed is elevated. Would it notmake more sense to measure IBP with the patientin a safer, more comfortable and widely used posi-tion rather than in a position that is rarely used?

The advantages of measuring IBP with the patientsupine are standardization, familiarity, and the cur-rent universal acceptance of the definitions of intra-abdominal pressure and ACS. The present studydemonstrates that it is feasible to measure IBP witha 30 HOBE and to obtain results with similar inter-patient variability and absolute IBP values similarto values obtained with patients positioned supine.The mean values of the IBP measurements obtainedin the HOBE positions are within the range of valuesobtained in previous studies that have measuredIBP in mixed ICU populations with patients supineand 50 mL of saline instilled.37 Furthermore, when


nificantly different from the measurementsobtained after instillation of 25 and 50 mL for eachbody position, but IBP did not differ significantlywhen measured with 25 vs 50 mL of saline instilled,regardless of position.

One-way analysis of variance demonstrated a sig-nificant position effect with the 25- and 50-mLinstilled volumes but not with the 200-mL volume.The variability in IBP within the 200-mL BIV groupwas too great to appreciate any significance related toposition. Post hoc Newman-Keuls comparison testshowed a significant difference between the supineand all three 30 HOBE positions with 25 mL ofsaline instilled (P< .01 for all 3 comparisons). For the50-mL instillation volume, the only significant differ-ence was between the S-30 and RL-30 position (P .05).

To determine if body position and volume ofsaline instilled are independent determinants of IBP,we performed a 2-way analysis of variance. Becausethe 4 groups who had IBP measurements taken with200 mL of saline instilled exhibited massive inter-patient variability relative to the values taken with25 or 50 mL of saline instilled, model criteria werenot met and the data from those 40 patients wereomitted from this analysis. The 8 remaining groups(80 patients) were found to have similar variabilityby using a Brown-Forsythe test and therefore wereincluded in the analysis. Statistical significance wasfound for both position (P= .007), and volume ofsaline instilled (P= .05) as well as the interactionof position and volume of saline instilled (P= .004).

Comparison of AACN and WSACS Recommen-dations for IBP Measurements

To further explore the relationship between bodyposition and volume of saline instilled and IBP meas-urements, patients randomized to the 2 groups thatreflected the current recommendations of the AACNand WSACS for IBP measurement were comparedwith the initial study position (S-30 with 25 mL ofsaline instilled). The mean of the differences betweenthe initial study position and that recommended bythe AACN (ie, supine with 50 mL of saline instilled)was 0.9 mm Hg (95% confidence interval, -2.5 to 4.3,t= 0.6, P= .02; see Figure, group 5). The mean of thedifferences between the initial study position andthat of the WSACS (ie, supine with 25 mL of salineinstilled) was 5.2 mm Hg (95% confidence interval,3.9 to 6.4, t= 9.8, P= .002; see Figure, group 1).

DiscussionThe definition of intra-abdominal pressure and

ACS is based on IBP measurement obtained with

Table Mean (SD) of intrabladder pressuresfor each of the 12 randomized groups

Volume of saline instilled, mL

Positiona

RL-30S-30Supine flat LL-30

a Positions: supine and flat, supine with head of bed elevated 30 (S-30), right lat-eralwith head of bed elevated 30 (RL-30), left lateral with head of bed elevated 30(LL-30).

b P< .01 compared with patients who were supine and had 25 mL saline instilledinto the bladder.

c P< .05 compared with patients in the S-30 group who had 50 mL of salineinstilled into the bladder.

d P< .05 compared with patients in the same position who had 25 and 50 mL salineinstilled into the bladder.

25

50

200

5.8 (2.2)Group 1 (n = 10)

11.6 (4.8)Group 5 (n = 10)

26.2 (29.7)d

Group 9 (n = 9)

12.7 (2.7)b

Group 2 (n = 10)

9.8 (5.1)Group 6 (n = 10)

23.2 (12.8)d

Group 10 (n = 10)

12.2 (5.8)b

Group 4 (n = 10)

11.8 (4.7)Group 8 (n = 10)

31.8 (28.5)d

Group 12 (n = 10)

11 (3.7)b

Group 3 (n = 10)

15.1 (4.9)c

Group 7 (n = 10)

42.2 (45.5)d

Group 11 (n = 10)


did not describe the anatomic landmark used to levelthe transducer, McBeth et al25 and Cheatham et al27

leveled the transducer at the intersection of the iliaccrest and the midaxillary line, and in this study thetransducer was leveled at the symphysis pubis. Inaddition, McBeth et al25 and Vasquez et al26 did notrelevel the transducer after each position change.Conversely, in the study by Cheatham et al27 and inthe present study, the pressure transducer wasreleveled and rezeroed with each position change.These differences in experimental design are impor-tant because elevating the head of the bed maychange the relationship of the transducer to theanatomic reference landmark for zeroing and couldalter the IBP measurement.

Results of the present study add to the knowl-edge regarding IBP measurement in ICU patientsbecause this study included an evaluation of 2 lat-eral positions with a 30 HOBE that had not receivedadequate attention in earlier studies. These lateralpositions were chosen for investigation becauseafter the S-30 position they are the most commonpositions assumed by critically ill patients and thesepositions are recommended to prevent the compli-cations of immobility such as pressure ulcers.32,40

The RL-30 and LL-30 positions yielded higher val-ues than did the supine position when 25 mL ofsaline was instilled into the patients bladder butnot when 50 mL of saline was instilled (see Figureand Table). Interestingly, the LL-30 position wasless sensitive to the volume of saline instilled thanall other positions studied. Finally, IBP did not dif-fer significantly between the RL-30 and LL-30,regardless of the volume of saline instilled. As ofthis writing, researchers in only 1 other study41 havereported IBP data when patients were in lateralpositions. De Keulenaer et al41 measured IBP in 10ICU patients in a lateral position with no HOBEand then again immediately after the patients werepositioned supine. In that study, the measurementswere taken 3 times in a single day: morning, after-noon, and evening. As in the present study, De Keu-lenaer et al41 found that IBP measured with patientsin the lateral positions with 20 mL of salineinstilled was higher than IBP measured withpatients supine and that IBP measurements did notdiffer between the right and left lateral positions.

VolumeThe independent effect of the volume of saline

instilled noted in this study is in agreement withresults of 2 studies28,42 of the effect of volume ofsaline instilled on IBP measurements but differedfrom previous studies because the effect of saline

50 mL of saline was instilled in the patients blad-der in the present study, the values obtained withpatients supine did not differ significantly from thevalues obtained in any of the study positions with a30 HOBE (see Table).

The experimental design used in the presentstudy to a major extent reflects contemporary nursingpractice. That is, IBP was first measured in the S-30position and then patients were moved to the ran-domized positions. Transition from the S-30 positionto supine flat resulted in a mean decrease of 5.2 mmHg when 25 mL of saline was instilled (see Figure,group 1). This finding is consistent with other stud-ies25-27 that have shown increases of 4 to 6 mm Hgwhen patients were moved in the opposite direction,that is, from supine to 30 HOBE positions. Thehigher IBP values in HOBE positions are to beexpected because of the tension of the abdominalwall musculature and the gravitational effects of the

abdominal viscera on the bladder.38,39

Therefore, the difference in absoluteIBP values noted in HOBE positions isdue to the inherent physiologicalproperties of the abdominal compart-ment and reflects the sensitivity of IBPto detect changes in intra-abdominalpressure with position changes andshould not be construed as a reason toavoid HOBE positions when measur-ing IBP in critically ill patients.

PositionIn this study, we generated a large database of

IBP measurements taken by a single nurse when ICUpatients were in the S-30 position, which is of clinicalimportance because this position is the most commonposition assumed by critically ill patients. Furthermore,S-30 is the position recommended by critical careexperts on the basis of evidence obtained in ICU andreflects current practice guidelines and consensusstandards published by professional organizationsto prevent ventilator-associated pneumonia andaspiration pneumonia in critically ill patients.15,17,18,20,21

When the present study was designed, no reportof a study that used the S-30 position had been pub-lished. Since then, 3 studies25-27 have been reportedthat show data obtained with patients in this position.In all 3 studies, researchers found that the mean IBPis higher when measured with the patient in a 30HOBE position than with the patient supine. A majordifference between the present study and the previousstudies assessing the effect of HOBE on IBP is theposition and leveling of the pressure transducer atthe time of measurement. Vasquez et al26 and others


The effect of instilled volume

on intrabladderpressure is not as

pronounced inelevated positions.


volume instilled was assessed with patients in posi-tions other than supine. The present study demon-strated that regardless of patients position, instillationof 25, 50 and 200 mL of saline yielded IBP meas-urements in a range that was clinically expected(see Figure). However, instillation of 200 mL ofsaline was associated with larger interpatient vari-ability and produced a higher mean IBP value thandid instillation of 25 or 50 mL of saline. Further-more, IBP measurements did not differ significantlywhen 25 vs 50 mL of saline was instilled. Theseresults are consistent with results of previouslyreported studies28,42 that showed very little differencesin IBP when less than 150 mL of saline was instilled.The high variability in IBP observed in selectedpatients in the present study when 200 mL of salinewas used (see Figure, groups 9-12) is most likely dueto a lower bladder compliance and/or high residualbladder volume at the start of the study. Thus, toreduce variability in IBP measurements betweenpatients, high volumes of saline should not beinstilled. Based on these considerations, instillationof either 25 or 50 mL of saline appears to be appro-priate for IBP measurement, supporting the recom-mendations of the WSACS and the AACN, respectively.

Position and Volume InteractionAn important finding of the present study is that

both position of the patient and volume of salineinstilled at the time of IBP measurement independ-ently affect IBP, but of greater interest is the identifi-cation of an interaction between patients positionand volume of saline instilled that was not previ-ously recognized. This observation was made possi-ble because of the unique study design that allowedthese variables to be investigated simultaneouslyand interactively. By instilling 3 different volumesof saline into the bladder with patients in 4 differ-ent positions, we are able to confirm the effect ofvolume of saline instilled on IBP with patients supine,but additionally found that the effect of volume ofsaline instilled on IBP is not as pronounced whenthe head of the patients bed is elevated.

These findings clearly illustrate the volume-position interaction and show that either positionor volume of saline instilled can affect IBP measure-ment and further illustrate the need for both accuratepositioning of patients and instillation of a consis-tent volume of saline, both of which are paramountin obtaining interpretable IBP measurements. Thesefindings also highlight the need for all investigatorsto clearly define the position and the volume ofsaline instilled into the patients bladder whenreporting IBP measurements.

Clinical Implications and Future ResearchThe AACN and the WSACS recommend that IBP

be measured with patients supine only, but neitherof these organizations has provided evidence tosupport this recommendation. To provide suchvalidation, studies must be conducted where intra-abdominal pressure is measured directly in patientsby placement of intraperitoneal catheters.43,44 Thesetechniques are not standard practices in the ICU,and their use would significantly increase the riskto patients and cannot be ethically justified. The lackof direct measurement of intra-abdominal pressureis a limitation of the present study, as with all otherclinical studies assessing the effects of the volumeof saline instilled into the patients bladder andposition on IBP.26,27,37,42,45 Because of this limitation,recommendations may need to be made on thebasis of the quality of research data obtained withindirect IBP measurements.

The present study demon-strated that IBP measured withpatients in 3 positions with 30HOBE yielded results that arewithin the expected range of meas-urements obtained with patientssupine. Furthermore, our resultsindicate that repositioning patientsfrom the S-30 to the supine posi-tion solely to measure IBP yieldsIBP values that are significantlylower, by approximately 5.2 mmHg (see Figure, group 1). No signif-icant changes in IBP occurred when the patientswere repositioned from the S-30 to LL-30 or RL-30position. In addition, the supine position is moresensitive to changes in the volume of saline instilledthan are the other HOBE positions studied, asshown by progressive increases in IBP values as thevolume of saline instilled was increased. In contrast,when measurements were made with patients in theS-30 and the LL-30 positions, progressive increasesin IBP were not observed (see Table).

Finally, although this point was not directlyassessed in this study, keeping patients in the S-30position for IBP measurement is theoretically expectedto decrease nurses workload, reduce the risk of aspira-tion pneumonia developing and equipment beingdislodged, and indirectly increase patients comfortand safety. If current guidelines are followed forprevention of ventilator-associated pneumonia andaspiration pneumonia related to enteral nutrition,most patients are expected to have a 30 HOBE orgreater while positioned supine or lateral and wouldneed to be repositioned supine and flat for the sole


Repositioningpatients from 30 to the supineposition only tomeasure intra-bladder pressurelowers the valueby 5.2 mm Hg.


What is normal intra-abdominal pressure and how is itaffected by positioning, body mass and positive end-expi-ratory pressure? Intensive Care Med. 2009;35(6):969-976.

3. Malbrain ML, Cheatham ML, Kirkpatrick A, et al. Resultsfrom the International Conference of Experts on Intra-abdominal Hypertension and Abdominal CompartmentSyndrome: I, definitions. Intensive Care Med. 2006;32(11):1722-1732.

4. Diebel LN, Dulchavsky SA, Wilson RF. Effect of increasedintra-abdominal pressure on mesenteric arterial and intes-tinal mucosal blood flow. J Trauma. 1992;33(1):45-48; dis-cussion 48-49.

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7. Pinsky MR. Cardiovascular issues in respiratory care.Chest. Nov 2005;128(5 suppl 2):592S-597S.

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9. Richards WO, Scovill W, Shin B, Reed W. Acute renal failureassociated with increased intra-abdominal pressure. AnnSurg. 1983;197(2):183-187.

10. Malbrain ML, Chiumello D, Pelosi P, et al. Incidence andprognosis of intraabdominal hypertension in a mixed pop-ulation of critically ill patients: a multiple-center epidemio-logical study. Crit Care Med. 2005;33(2):315-322.

11. Malbrain ML, De Laet I, Viaene D, Schoonheydt K, Dits H.In vitro validation of a novel method for continuous intra-abdominal pressure monitoring. Intensive Care Med. 2008;34(4):740-745.

12. Gallagher JJ. Intra-abdominal hypertension: detecting andmanaging a lethal complication of critical illness. AACNAdv Crit Care. 2010;21(2):205-219.

13. Malbrain ML, De Laet I, Cheatham M. Consensus confer-ence definitions and recommendations on intra-abdominalhypertension (IAH) and the abdominal compartment syn-drome (ACS): the long road to the final publications, howdid we get there? Acta Clin Belg Suppl. 2007(1):44-59.

14. Drakulovic MB, Torres A, Bauer TT, Nicolas JM, Nogue S,Ferrer M. Supine body position as a risk factor for nosoco-mial pneumonia in mechanically ventilated patients: a ran-domised trial. Lancet. 1999;354(9193):1851-1858.

15. Institute for Healthcare Improvement. Implement the venti-lator bundle. www.ihi.org/IHI/Topics/CriticalCare/IntensiveCare/Changes/ImplementtheVentilatorBundle.htm AccessedApril 25, 2011.

16. Resar R, Pronovost P, Haraden C, Simmonds T, Rainey T,Nolan T. Using a bundle approach to improve ventilator careprocesses and reduce ventilator-associated pneumonia. JtComm J Qual Patient Saf. 2005;31(5):243-248.

17. Tablan OC, Anderson LJ, Besser R, Bridges C, Hajjeh R.Guidelines for preventing health-careassociated pneumo-nia, 2003: recommendations of CDC and the HealthcareInfection Control Practices Advisory Committee. MMWRRecomm Rep. 2004;53(RR-3):1-36.

18. Muscedere J, Dodek P, Keenan S, Fowler R, Cook D, Hey-land D. Comprehensive evidence-based clinical practiceguidelines for ventilator-associated pneumonia: prevention.J Crit Care. 2008;23(1):126-137.

19. Rotstein C, Evans G, Born A, et al. Clinical practice guidelinesfor hospital-acquired pneumonia and ventilator-associatedpneumonia in adults. Can J Infect Dis Med Microbiol. 2008;19(1):19-53.

20. Heyland DK, Dhaliwal R, Drover JW, Gramlich L, Dodek P.Canadian clinical practice guidelines for nutrition supportin mechanically ventilated, critically ill adult patients. JPENJ Parenter Enteral Nutr. 2003;27(5):355-373.

21. McClave SA, Martindale RG, Vanek VW, et al. Guidelines forthe Provision and Assessment of Nutrition Support Therapyin the Adult Critically Ill Patient: Society of Critical CareMedicine (SCCM) and American Society for Parenteral andEnteral Nutrition (A.S.P.E.N.). JPEN J Parenter Enteral Nutr.2009;33(3):277-316.

22. Cason CL, Lambert CW. Position and reference level for meas-uring right atrial pressure. Crit Care Nurs Q. 1990;12(4):77-86.

23. Groom L, Frisch SR, Elliott M. Reproducibility and accuracy

purpose of measuring IBP. After IBP measurement,patients would be repositioned to an HOBE of atleast 30, and it is unclear what the value is ofmeasuring IBP with patients in a position that israrely assumed in the ICU. When the technical aspectsof IBP measurement such as interobserver andintraobserver variability are considered in tandemwith nurses workload and patients safety and com-fort, the S-30 appears to be a more desirable positionto measure IBP than the supine position.

Serious consideration needs to be given to nurs-ing research that is devoted to developing protocolswhere the S-30 becomes the standard position formeasuring IBP or at least an acceptable alternativestandard position for patients who are unable toassume the supine and flat position. Because thediagnosis and prognosis of intra-abdominal hyper-tension and ACS are all based on IBP values meas-ured with patients supine and flat, accepting the S-30position for IBP measurement will require moreresearch to redefine the intra-abdominal pressurevalue that correlates with intra-abdominal hyperten-sion and ACS, thereby requiring a revision of thedefinitions of intra-abdominal hypertension and ACS.

Further studies are needed that compare thepositions of supine and flat and S-30 with outcomevariables rather than the absolute differences in IBP,which has been the only outcome variable assessed.For instance, it would be of interest to determine ifIBP when measured in the S-30 position is associatedwith less nursing time, less disruption of care, andbetter quality of life for critically ill patients as com-pared with the supine position. In addition, it wouldbe important to investigate the IBP that defines intra-abdominal hypertension in the 30 HOBE positionand if this position correlates better with other impor-tant outcomes such as mortality and need for abdom-inal decompression than does the supine flat position.

FINANCIAL DISCLOSURESFinancial support for the research was received from theAmerican Association of Critical Care Nurses andPhillips Medical Systems (Outcome for Clinical Excel-lence Research Grant), the Epsilon Pi Chapter of SigmaTheta Tau International at Duquesne University School ofNursing, and District 6 of the Pennsylvania State NursesAssociation.

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