Use of the SonoSite Probe for Measuring Jugular Venous Pressure

Overview

This prospective study will be performed in the Cardiothoracic (Chesterman) Department at Sheffield Teaching Hospitals NHSFT, Northern General Hospital. Pre-operative patients undergoing surgical valvular intervention, breathing both spontaneously and mechanically will be included in the trial. All patients will already have a central venous catheter inserted as part of their ongoing care. Patients will be eligible for the study irrespective of diagnosis or neck size. Patient demographical data will be recorded by Sam Jenkins following written consent, the day before the trial. The goal of this study is to determine if ultrasound assessment of Jugular Venous Pressure (JVP) accurately predicts Central Venous Pressure (CVP). Secondary objectives aim to identify if using the angle of Louis to approximate the location of the right atrium produces inaccuracies when measuring JVP. Comparing results in patients breathing spontaneously or under positive pressure ventilation will identify if the form of ventilation impacts on JVP and CVP recording. Correlating results between physical JVP examination and ultrasound assessment of JVP to measure CVP will conclude if ultrasound is a more appropriate tool, in an era where the physical examination of the cardiovascular system is becoming less valuable.

Initial exploratory investigations will compare left-sided and right-sided Jugular Venous Pressure (JVP) using ultrasonography. Should results show that they are the same, the central line is to be placed into the right internal jugular vein when required. To begin the trial and whilst the patient is spontaneously breathing, a physical examination of the right JVP will be performed. A central line will be inserted with the patient awake into the right internal jugular vein. Left-sided ultrasound of JVP and Central Venous Pressure (CVP) will be measured using the right-sided catheter will be recorded simultaneously. The tip of the catheter attached to the transducer (which is zeroed to the reference point) will be placed at the point of venous collapse, identified by ultrasonography, to identify if the JVP and CVP match. The tip of the catheter will then be placed at the angle of Louis. Measurement of the pressure difference between the angle of Louis and the reference point will identify if this value shows variability compared to previous approximations of 5cm above the right atrium. With the patient anaesthetised and mechanically breathing, left JVP and CVP will be measured once more. Twenty-four hours post-surgery, ultrasound of the JVP and CVP will be measured with the patient breathing spontaneously. The physical JVP examination will be recorded from the opposite side to the central venous catheter. The bed will be adjusted to an angle between 30 and 60 degrees, that most clearly identifies the collapsing vein. Differentiation between the JVP and the carotid pulse must be distinguished. Tangential lighting using a flashlight should be used to correctly identify and note the apex of the jugular venous pulsations. Recordings will be taken at end-expiration allowing the vertical distance between the venous meniscus and phlebostatic axis to be measured. JVP will be measured in millimetres of water. Ultrasound recordings will be made using the SonoSite ultrasound probe by Sam Jenkins. The equipment and gels required are used routinely on site and will be supplied by Sheffield Teaching Hospitals. The SonoSite probe will be calibrated prior to each use, based on the recommendations of the manufacturer. The angle of the bed is kept constant and the patient will remain in the same position following the physical JVP examination. Ultrasound gel will be applied, again on the opposite side to the central venous catheter. Locating the area of venous collapse will be identified following visualisation from both longitudinal and transverse planes. The apex of venous collapse at end-expiration will be marked using the longitudinal view. Corroboration of the correct position of the probe by looking at the transverse view will be performed prior to marking of venous collapse. CVP will be measured once the central venous catheter has been zeroed. The reference point of the transducer will be placed at the 4th intercostal space, mid-axillary line. The bed should still be kept at a constant angle for this measurement. The mean of the 'a' wave upon end-expiration will be taken. Converting the CVP from millimetres of mercury to millimetres of water will allow direct comparison to prior findings of JVP.