Fluid responsiveness is about stroke volume, and not pulse pressure Yogi: the power of Doppler fluid management and cardiovascular monitoring

Abstract

Fluid infusion is one of the most common critical care interventions, yet approximately 50 % of all fluid interventions are unnecessary and potentially harmful. An improved approach to identification of fluid responsiveness is of clinical importance. Currently fluid responsiveness is most frequently identified by blood pressure (BP) measurements or a surrogate. However fluid responsiveness is simply the increase in stroke volume (SV) associated with volume expansion, and may not be reflected in BP or BP surrogates. Guyton demonstrated that BP = CO x SVR, and it is know that baroreceptor mediated autonomic nervous system regulation of SV and SVR to preserve BP may mask significant and critical changes in haemodynamics. Dr Pinsky in his recent J Clin Monit Comput Editorial evaluated the relative merits of pulse pressure variability (PPV) methods, a variant on BP measurement, for assessment of fluid responsiveness and promoted the use of physiologic challenges to augment the applicability of PPV. However this guidance is only half right. This letter reminds clinicians of the physiologic limitations of PPV as a measure of fluid responsiveness, even when combined with physiologic challenges, and recommends the replacement of BP with SV measurements. The combination of accurate Doppler measurement of SV and physiologic challenges, as Dr Pinsky recommends, is a physiologically rational and effective approach to identification of fluid responsiveness with established evidence. The direct monitoring of SV and SV changes has the potential to improve a long standing critical care and anaesthetic conundrum; when to give fluid and when to stop.

Carotid Doppler flowmetry correlates poorly with thermodilution cardiac output following cardiac surgery

“…The PulsePres var failed to predict the response to PLR in this study. Although unlikely, this result might have been influenced by the inclusion of some patients with a pressure support mode of ventilation, but the physiologically inherent limitations of pressure changes to predict flow changes offer a more obvious explanation …”

Volume responsiveness assessed by passive leg raising and a fluid challenge: a critical review focused on mean systemic filling pressure

“…The assumption of a low cardiac output indicating volume responsiveness is entirely dependent on the inotropic state of the heart, and where it is operating on the Frank–Starling curve, as only a low‐output state in the steep ascending portion of the curve is likely to be improved by fluid administration. Variations induced by positive pressure ventilation in arterial pressure, or related variables, have been investigated to guide volume therapy ; however, these are restricted by the inherent physiological limitations of pressure changes to predict flow changes and a number of prerequisite criteria that are rarely fulfilled in critically ill patients .…”

The cardiovascular effects of crystalloid administration in endoscopy patients

“…25 Or alternatively, 50% of a fluid boluses in this population are unnecessary and potentially harmful. 26 The common bedside approach of a fluid challenge of 250-500 ml and assessing clinical response is increasingly being challenged with so called 'mini boluses' of fluid of as little as 50-100 ml reliably increasing SV as measured with echocardiography. 27,28 This has the potential to at least reduce the dose of an unnecessary fluid challenge.…”