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Thoughts From A Clinician

You want me to measure what?!

CVP Waveform

While central venous pressure (CVP) has been measured for generations within the ED and ICU, the routine use of this modality has been challenged over the past decade.  As transport providers, it is imperative that we understand the risks and benefits of each of the diagnostic and therapeutic interventions we perform.  With regard to CVP, do the purported benefits outweigh the risks?  Can we extrapolate research and the experience of controlled environments, such as the ED and ICU, to the uncontrolled and often chaotic world of transport medicine?  We know that out-of-hospital variables, such as temperature and altitude, as well as the undifferentiated nature of our patients all affect CVP readings.  We also know that the majority of transport agencies do not routinely measure CVP.  In addition, experts such as Dr. Paul Marik, who has studied the pros and cons of CVP measurement in transport medicine, concluded that there is generally no advantage to CVP measurement in the out-of-hospital environment.

So, should we ever measure CVP in transport medicine?  The honest answer is that it depends on your local policies, procedures, and guidelines.  If your agency does advocate the assessment of CVP during transport, you should be aware of its strengths and limitations, particularly in the out-of-hospital environment.  In theory, CVP tells us about volume status and preload, giving us some indication of fluid responsiveness.  The reality is that CVP is a poor predictor of responsiveness to fluid administration.  In addition, the value will vary greatly depending upon patient pathology and whether fluid is being actively administered.  We expect CVP values between 0-6mmHg in a spontaneously breathing patient.  Ideally, measurements are obtained at the end of expiration.  Recorded values will change dramatically at different points in the respiratory cycle, particularly in the mechanically ventilated patient.  In addition, the active administration of intravenous fluids can result in CVP values that are higher than would otherwise be reflected by the volume status of a hypovolemic patient.

So, the transport provider must consider the patient condition at the time of transport, reason for transport, and multiple variables regarding ongoing therapies before making a decision on the accuracy and utility of CVP monitoring.  The implications of various CVP values should be clear to justify taking the time to acquire this information.  And, as always, consider CVP monitoring to be another tool in the tool box rather than a definitive measurement of anything. 

Let us know what you think about this subject.  Do you monitor CVP in the transport environment?  Why or why not?  As always thanks for reading and remember to always think like a clinician!

**Picture taken from Life in the Fast Lane, 2015

Reference:

Marik PE, Baram M, Vahid B. Does central venous pressure predict fluid responsiveness? A systematic review of the literature and the tale of seven mares. Chest. 2008 Jul;134(1):172-8. doi: 10.1378/chest.07-2331. Review. PubMed PMID: 18628220.

Peer Review #1:

I agree that there are many variables that play into whether a patient may undergo CVP monitoring and there may still be certain situations where this is appropriate management.  Fluid therapy is still considered a key intervention in the care of many critically ill patients, including sepsis; however controversial this may be.  The majority of studies are now questioning the use of CVP in the guidance of fluid administration in these critically ill patients and for good reason.  It has been shown that only approximately half of patients respond to fluid administration with increases noted in their stroke volume or cardiac output.  CVP monitoring has been utilized in the past in attempts to determine which patients would be fluid responsive.  I do believe this is imperative information because studies have also demonstrated that fluid under- and overload in general can be associated with increases in overall morbidity and mortality; therefore, the struggle continues among providers to determine whether or not their patients would benefit from volume administration and just how much is necessary.  However, I do feel that there is no current evidence to support the use of CVP monitoring whether in-hospital or pre-hospital, to assess volume status or fluid responsiveness. 

CVP monitoring has occurred for years and we are all too aware that attempting to change practices that have been routine for so long can be a daunting task.  There are several current studies that have demonstrated less invasive yet more accurate ways to predict adequacy of volume resuscitation.  There is a very fine line between under- and over-resuscitating our patients.  Ultimately, I think it is more beneficial for providers, especially in the transport environment, to focus on integrating several end point parameters rather than focus on invasive hemodynamic monitoring.  A few of those parameters include: monitoring urine output, mean arterial pressure, BUN (kidney function), pulse pressure variation (PPV) in mechanically ventilated patients, HR, lactate, ABGs and mixed venous oxygen saturation (SCVO2).  These basic parameters can provide a lot of useful information regarding resuscitation of your critically ill patients.  Sometimes, the basics can be very beneficial.

Ashley Bauer, MSN, MBA, APRN, FNP-C, CFRN 

Peer Review #2:

To measure, or not to measure?  That is the question.  If the central venous catheter is in place and we have a device that can transduce the CVP, then why not?  Isn’t additional information always better?  It’s not as though we’re asking transport providers to insert the catheter en route to the next facility…

Or is there a down side to all of this information?  Paralysis by analysis?  Acquiring and documenting information that will not be used to impact patient care becomes extraneous at best…and distracting – or even misleading – at worst.  And placing this information in the patient care record becomes ammunition in the court of law, right?

We are moving through a time period in which many of the traditions and “sacred cows” of medicine are being questioned and challenged.  In some cases, this involves a clear risk-benefit analysis in which clinical outcomes are at stake.  In others, such as the decision regarding the acquisition of CVP data, may not be quite as dramatic but are important, nonetheless, in pointing us towards a more rational approach to clinical medicine.  Everything that we do – and all of the information we collect – should be justifiable, with clear parameters by which to guide subsequent actions.  Collecting data for the sake of “completeness” or to “paint a picture with more colors” is no longer enough.  However, if the information will be used to guide therapy, then it has value.  Until we in the medical community can better define the indications and implications for CVP across a spectrum of patients and clinical care environments, this decision must be made at an agency level or on a patient-by-patient basis.  And rather than a source of frustration, this should be seen as part of the process in the evolution of medicine…

Dr. Dan Davis, MD

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