How to measure CVP (Central Venous Pressure)
I walk through the halls of the hospital confidently. Today is such a fine day. The sun is shining brightly outside, people are getting on with their own business, a smile here and there. I think to myself, “Today is going to be one good day.” I continue on with my good mood as I entered the ICU complex. I greeted my co-workers and fellow nurses good morning and checked for my patient assignment. So, I get assigned to patient 1. Not intubated. Good. Numbers of IV lines connected to my patient. It’s okay. I smile as I open the chart and kardex, checking everything from doctors’ orders to due medications. Everything was just going right when I glance at the note located at the special procedures part. “Vital signs monitoring every hour. Check CVP Q2H”.
CVP? How do you measure CVP? And wait, what? Every two hours? I don’t even fully understand the concept of CVP and here I am receiving a patient who’s CVP must be monitored every 2 hours. Why oh why? Can I do this? Can I survive this? I don’t even know.
A glimpse at CVP
Central Venous Pressure or CVP in short, is defined as the pressure in the central veins (internal jugular, subclavian or femoral). Basically, it is referred to as the blood pressure in the proximal SVC, near the junction with the right atrium. The normal value for CVP ranges from 0-6mmHg in a spontaneously breathing non-ventilated patient.
Usually, measurement of CVP is recommended for patients with hypotension who are not responding to basic clinical management; has continuing hypovolaemia secondary to major fluid shifts or loss and those who require infusions of inotropes. CVP may also be used to diagnose right ventricular infarction, PE, ARDS, cor pulmonale and tamponade. However, it cannot be used to assess fluid responsiveness as there is very poor relationship between CVP and blood volume, and CVP/DeltaCVP is a poor predictor of the hemodynamic response to a fluid challenge.
How to measure CVP
The thought seems complicated and difficult. Some would back out and think that they couldn’t do it. What they do not know is measuring CVP isn’t actually that complicated. Actually, if you take time to try to learn and understand the steps, you would realize that it can be easily done like a boss.
It can be measured using an indwelling central venous catheter and either manually using a pressure manometer or electronically using a transducer. Usually, the manometer is used especially in wards. But in both ways, it must be ‘zeroed’ at the level of the right atrium. You may do this by taking it at level of the 4th intercostal space in the mid-axillary line while the patient is lying supine, each time at the same zero position.
But before that, you must check the patency of the IV. If the IV fluid is not running, ensure that the CVC is patent by flushing the catheter. Then place the patient flat in a supine position if possible. Alternatively, measurements can be taken with the patient in a semi-recumbent position. The position should remain the same for each measurement taken to be sure that an accurate comparable result is derived.
For the manometer
Here, a 3-way tap is used to connect the manometer to an intravenous drip set on one side, and, via extension tubing filled with intravenous fluid, to the patient on the other. First, line up the manometer arm with the phlebostatic axis. This is done to ensure that the bubble is between the two lines of the spirit level. Make sure that no air bubbles are present in the tubings. Also, check if the tubings are either kinked or blocked. If the latter is the case, flushings can be done.
Zero the manometer by moving the manometer scale up and down. This procedure allows the bubble to be aligned with zero on the scale.
The 3-way tap is then turned so that it is open to the fluid bag and the manometer but closed to the patient, allowing the manometer column to fill with fluid. However, be careful not to overfill the manometer column. Usually, you can fill the manometer up to a level higher than the accepted CVP.
Then, turn off the flow from the fluid bag and open the three-way tap from the manometer to the patient. The fluid level within the manometer column will fall to the level of the CVP or when the gravity equals the pressure in the central veins, the value of which can be read on the manometer scale which is marked in centimeters, therefore giving a value for the CVP in centimeters of water (cmH2O)
When the fluid stops falling, you may now read the CVP measurement. In cases where the fluid moves with the patient’s breathing, read the measurement from the lower number. Close the manometer then record your measurement.
Using a transducer
As for the transducer, which is fixed at the level of the right atrium and connected to the patient’s CVP catheter via fluid filled extension tubing, similar care must be taken in order to avoid bubbles and kinks and many more same as mentioned with measuring via manometer.
Zero the transducer to atmospheric pressure by turning its 3-way tap so that it is open to the transducer and to room air, but closed to the patient. You may do this by removing the cap from the 3-way port opening the system to the atmosphere. Press the zero button on the monitor and wait while calibration occurs.
Then, as the monitor displays “zeroed,” turn the 3-way tap so that it is now closed to room air and open between the patient and the transducer. A continuous CVP reading, measured in mmHg rather than cmH2O, can be obtained.
At times, nurses get too caught up with their own fears of learning a new procedure that their hesitancy to learn overshadows their need to learn. With such, we don’t only become fearful and afraid of change, but we also remain clueless of what’s really happening with our patients. Let us face those fears and try to dive in the sea of opportunities and new knowledge. Not only will we feel satisfied after accomplishing something, but we will also be able to formulate the most appropriate and effective treatment plans that would lead our patients to the road of recovery.