Fluid responsiveness

Patients on non-intensive care wards (such as our stroke unit) are not as simple to understand as a patient with arterial and central line, with ultrasound and more high tech equipment around every corner.

So assume a lady with advanced heart failure, medium size stroke and a decent aspiration pneumonia, who is raised to your attention by a stroke nurse that is worried about the blood pressure of 78/28 mmHg with a heart rate of 109/min (sinus rhythm). What do we have by way of judging her fluid status? More precisely, is she going to benefit from a decent fluid bolus (say 500 ccs of NS or LR)?

From all evidence-based reviews on the history and physical, we know that a hemorrhagic patient might be identifiable by postural hypotension, tachycardia and postural dizziness. But this might be hard to check in a patient who is not able to sit or stand such as ours. Even more, both history and physical fare just as badly as flipping a coin (an AUC of the ROC curve of 56%), at least in the hands of an intensivist… Jugular venous pressure might be interesting for cardiological reasons, but the connection to right ventricular preload is difficult to judge as we don’t know the compliance of the system.

What remains are dynamic studies of responses to fluid challenges, such as

  • Passive leg raising: flip the legs up to 45° and the trunk down to 0°, effectively keeping the standard angle of legs to trunk of about 30-45°, pushing about 400 ccs of blood up to the heart.
  • Controlled respiration with volumes high above the usual aim of 6 ml/kg and with proper pressures (this yields vast changes in pressures, volumes and fluid compartmentalization around the heart and thorax)
  • Saline bolus of 500 ccs.

So what are the physiological variables to monitor during such a maneuver? In order of increasing complexity and high-tech-yness

  • Blood pressure (MAP), or even better pulse pressure (syst – diastol)
  • Heart rate (if the carotid sinus reflex is intact and Bezold-Jarisch/Bainbridge keep quiet)
  • Perfusion measurement of your oxygen saturation monitor (reflecting stroke volume in the periphery, which is worse than central stroke volume, but better than most measures)
  • etCO2, if you happen to monitor it, reflecting minute volume
  • PPV or SVV if measured by pulse contour analysis (PICCO = LIDCO, both better than Vigileo)
  • Inferior vena cava diameter and collapsibility index
  • Stroke volume (if measured by TEE or pulmonary catheter)
  • Femoral artery (better carotid artery, but this hasn’t been studied) mean systolic velocity
  • NICOM (thoracic impedance boosted)
  • … many more devices I have never used

So on any normal ward with – say – a simple vital sign monitor, us Neurologists can do best with ultrasound of the IVC and the carotid artery and the pulse pressure plus (perhaps) heart rate during passive leg raise. But this isn’t too bad.

References:

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