HYD: Assessing Hydration Status (2007)


Fisher RD, Papoff PM, Fisher AS.  The interstitial fluid pressure monitor: a device to aid in the determination of patient fluid requirements.  J Am Board of Family Practice 1990; 3: 7-17.

Study Design:
Diagnostic, Validity or Reliability Study
C - Click here for explanation of classification scheme.
Quality Rating:
Negative NEGATIVE: See Quality Criteria Checklist below.
Research Purpose:

To verify that 1) interstitial fluid pressure could be recorded rapidly and reliably by a portable monitor, and that 2) IFP correlates with patients' assessed fluid status.

Inclusion Criteria:

Informed patient consent; Patients selected  if appeared that there was any acute change in clinical status influenced by accumulation or depletion in fluids which required assessment of fluid status

Exclusion Criteria:

none mentioned

Description of Study Protocol:

Recruitment: selected from community-based general med/surg practice; Hospital and ambulatory office patients; Classified as hypo-, hyper-, or normovolemic. 


Design: IFP recorded during 1st visit and whwever possible on subsequent visits as clinical status evolved.  IFP also recorded in healthy volunteers to establish normal measurement for technique.  Monitoring device used is electronic device constructed by research team - used with a catheter for insertion into subjects into L or R anterior chest wall; reading appearing on monitor at this position was IFP measurement, measurement took 10 min total (setup to recording).


Blinding used (if applicable): none


Intervention (if applicable) n/a


Statistical Analysis: (no formal description of statistical tests); examined correlation between fluid status suggested by IFP measurement and clinical classification; distribution means.


Data Collection Summary:

Timing of Measurements

 IFP measurement recorded at 1st visit and whenever possible at subsequent visits.

Dependent Variables

  • Fluid status

Independent Variables: IFP monitoring device & clinical classification


Control Variables


Description of Actual Data Sample:


Initial N: 7 healthy volunteers, 25 patients

Attrition (final N): n/a

Age: 63-89 yoa

Ethnicity: not mentioned

Other relevant demographics: various clinical and volemic status

Anthropometrics: not mentioned

Location: Depts of Family PRactice & Surgery, Walter O. Boswell Memorial Hospital, Sun City, AZ, USA


Summary of Results:



Healthy Volunteers

Distribution mean


Visual observation of independent rdgs and manually setting Gaussian cutoff range

Distribution mean (mm Hg)


Patients + Normal volunteers: Normovolemic

Distribution mean N=?


Distribution mean


Statistical Significance of Group Difference




(-2.0- -0.5)





not mentioned












Other Findings

 Consistent correlation between fluid status and clinical classification; normal range supported (-2.0- -0.5 mHg) for IFP.

Distribution mean of healthy volunteers had highest sensitivity (0.95). 

89% of the time, abnormal IFP reading correctly identified clinical status of patient  (specificity).

Author Conclusion:

IFP reflects patient fluid status (degree of hydration of the interstitial space), and can aid in the determination of patient fluid needs when added to other clinical information. 

Funding Source:
University/Hospital: Boswell Memorial Hospital, Standford University
Reviewer Comments:

Results were very hard to make sense of, but the encouraging sensititivity and specifity measurements may lend to the practicality of this application and warrant further investigation in humans.

Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) ???
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) ???
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? No
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? No
  2.2. Were criteria applied equally to all study groups? ???
  2.3. Were health, demographics, and other characteristics of subjects described? No
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
3. Were study groups comparable? ???
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) N/A
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? ???
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? No
4. Was method of handling withdrawals described? N/A
  4.1. Were follow-up methods described and the same for all groups? N/A
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) N/A
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? ???
5. Was blinding used to prevent introduction of bias? No
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) No
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? No
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? ???
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? No
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? Yes
7. Were outcomes clearly defined and the measurements valid and reliable? ???
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? N/A
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? No
  7.5. Was the measurement of effect at an appropriate level of precision? ???
  7.6. Were other factors accounted for (measured) that could affect outcomes? No
  7.7. Were the measurements conducted consistently across groups? ???
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? No
  8.1. Were statistical analyses adequately described and the results reported appropriately? No
  8.2. Were correct statistical tests used and assumptions of test not violated? No
  8.3. Were statistics reported with levels of significance and/or confidence intervals? No
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? No
  8.6. Was clinical significance as well as statistical significance reported? No
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? N/A
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? ???
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? No
  10.2. Was the study free from apparent conflict of interest? Yes