Changes in Hemodynamic Values With Posture
Condition: Blood Pressure
Study type: Observational

Summary: 
      The study is designed as a prospective observational study. Each participant will have their
      BP, CVP, PAP, and CO measured by their clinical nurse using indwelling catheters placed for
      routine patient monitoring. Measurements will be recorded on an hourly basis during the day
      and for as many days as possible if the required measurements are being made for clinical
      care.

      Sixty patients between 18 and 85 years of age will be recruited in HVICU by means of
      convenience sampling. Data will be analyzed using a test of equivalence on the initial
      measurements (test of equivalence between two means) and then over time (repeated
      measurements) with a linear mixed-effects model.
    

Detailed description: 
      Invasive monitoring is a common method used in intensive care units to measure cardiovascular
      status. These parameters include central venous pressure (CVP), pulmonary artery pressure
      (PAP) cardiac output (CO) and arterial blood pressure (BP). There is a general understanding
      that these parameters vary with the position of the patient with the expectation that, as the
      patient goes from supine to sitting, these parameters decrease to some extent due to
      decreased venous return to the heart. Furthermore, the extent to which a patient might be
      reclining in bed can vary greatly from just having the head slightly raised to being totally
      upright. Different policies exist with respect to patient position when these measurements
      are made. The policies vary from no specified position to placing them completely flat for
      making the measurement and then returning them to a more upright position, usually 30 or 45
      degrees. Decisions are based upon the supine measurements despite no clear correlation to the
      patient's usual position. This study will investigate the correlation between position and
      these parameters.

      Patients in the HVICU will be approached by a member of the research team and asked for their
      verbal approval to record measurements made by their nurse. After receiving verbal consent to
      record the measurements, a member of the study team will record BP. CVP, PAP and CO as
      measured by the patient's nurse. These measurements will be recorded with the patient lying
      on the bed with the back of the bed raised to 30o and with the patient supine when the back
      of the bed is at 0o. The transducers will be leveled with the anterior axillary by zeroing of
      the transducer. After each position change, the team member will ask the nurse to wait 5
      minutes to allow stabilization of these parameters before measuring and recording the
      parameters at that position. These parameters will be recorded on an hourly basis using the
      day for as many days as the required measurements are being made for clinical care. Other
      patient information recorded will be date, ejection fraction, BMI, height, weight, age, and
      PEEP, if the patient is intubated.

      Sixty patients between 18 and 85 years of age will be recruited in HVICU by means of
      convenience sampling. The sample size was calculated based on the initial measurement of CVP
      where our preliminary data shows a mean difference 1.28±2.93 mmHg, and assuming that values
      with a difference < 3 are equivalent, with an α = 0.05 and a power of 90. The calculation was
      done at the following website: http://www.sealedenvelope.com/power/continuous-equivalence.
      Data will be analyzed using a test of equivalence on the initial measurements (test of
      equivalence between two means) and then over time (repeated measurements) with a linear
      mixed-effects model.
    

Observational model: Cohort
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        Patients at Hershey Medical Center having CABG and aortic valve surgery
      
Keywords: Hemodynamics; Central Venous Pressure; Pulmonary Artery Pressure; Cardiac Output