The need for accurate assessment of intravascular volume in shock states is critical. Central venous pressure (CVP) is often cited as an essential parameter to institute aggressive resuscitation in distributive shock and to guide fluid therapy, based largely on its use in early goal directed therapy (EGDT).
As it turns out, high-quality evidence does not back continuous CVP monitoring in distributive shock. A 2008 meta-analysis by Marik et al. in Chest addressed this very topic: “Does Central Venous Pressure Predict Fluid Responsiveness, or A Systematic Review of the Literature and the Tale of Seven Mares.”
In Marik’s analysis (24 human studies with 803 patients total), the findings were remarkable:
1) Initial CVP did not predict blood volume.
2) Baseline CVP did not predict fluid responsiveness (per stroke index and cardiac index).
3) The change in CVP did not predict fluid responsiveness.
Bottom line: “The results from this study therefore confirm that neither a high CVP, a normal CVP, a low CVP, nor the response of the CVP to fluid loading should be used in the fluid management strategy of any patient.”
In case you were wondering about the ‘seven mares:’ This refers to the only study where CVP was shown to predict volume status – seven horses had blood removed (CVP decreased) and then reinfused (CVP then returned to initial value).
Over the past decade, CVP has assumed the role of the Swan-Ganz pulmonary capillary wedge pressure (PCWP) -- a theoretically useful surrogate for left-ventricle end-diastolic volume (LVEDV) not borne out by evidence.
Exactly how this happened is unclear, but it is important to note that CVP was not designed as an intervention in the original Rivers’ EGDT study. Rather, CVP monitoring was present in both the control and intervention arms of this study (thus making it impossible to isolate benefit due to CVP monitoring alone).
A current study seeks to rest the debate on CVP monitoring. The Protocolized Care for Early Septic Shock (ProCESS) trial from Pittsburgh has three arms – EGDT, usual care, and protocolized standard care. The protocolized standard care states that “Central venous catheters will only be used when standard IVs are unable to give the proper amount of fluid and medicines. Blood transfusions will be given according to currently recommended guidelines.” Translation: The ‘no CVP’ arm may be a game-changer if there is no validated benefit to CVP monitoring.
-- Jonathan Purcell, MD