Fluid responsiveness

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  • Body water is divided into several compartments –  circulatory, interstitial and intracellular
  • Changes in circulatory volume can result in changes in haemo-dynamic parameters such as pulse rate and blood pressure
  • Nonetheless, haemo-dynamic parameters can be also altered by other factors
  • The water is also in dynamic flux between compartments and governed by two main forces – Starling forces (between circulation and interstitium) and osmolality (between the interstitial and intracellular space
  • Pathological changes in capillary permeability from disease processes such as sepsis can alter this relationship further
  • This can be exacerbated by further damage to the glycocalyx layer at this interface by overzealous fluid administration
  • Therefore, fluid entering the circulation is not a static event
  • Volumes in the other compartments are also much harder to quantify
  • There are important impacts of excess fluid in the interstitium such as pulmonary oedema.

Clinical implications

  • In hypovolaemic shock, volume resuscitation is required because it addresses the pathophysiology, but in other forms of shock where there is capillary damage as in SIRS or sepsis, the clinician may need to limit the amount of fluid given
  • It is difficult to precisely determine at what point further fluid will actually result in deleterious effects.
  • It is also uncertain if it has any sustained haemo-dynamic benefit

Controversies and Challenges

  • The bedside use of JVP height or central venous pressure may not correlate with degree of fluid balance or fluid responsiveness
  • Invasive monitoring with Pulmonary Arterial Wedge Pressure also has potential limitations
  • Some proprietary systems using sophisticated analysis of invasive haemodynamic parameters to measure ‘Lung Water’ have been used
  • The most promising non-invasive advances are bedside echocardiography and electrical cardiometry (bio-impedance) methods of evaluating cardiac function in response to a fluid challenge

See Practical approach of treating Shock

Further reading

LITFL – Fluid bolus therapy
LITFL – Fluid responsiveness
LITFL – Fluid challenge

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