What general guidelines will you use when administering a fluid challenge for hemodynamic instability to a critically ill patient? In your answers, list the parameters, which may be used to predict fluid responsiveness in critical illness.

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College Answer

This area remains controversial with, in reality, no single correct answer. Examiners expected and were prepared to accept a range of approaches (if reasonable)

a)  The type of fluid – crystalloid/colloid . No ideal fluid in all clinical settings.

In general no differences in mortality in critically ill patients, between crystalloids and colloids (SAFE study). However in subgroups, albumin may be useful (sepsis) whilst in neurotrauma, crystalloids may be preferable.

b)  Rate of fluid administration (250-500 ml of colloid /500-1000 ml of crystalloid or
20 ml/kg of crystalloid over 30 min.)
Again, no hard data exist to support either regime, but these are rules of thumb and recommended in the Surviving Sepsis Campaign Guidelines.

c)  A clear defined goal such as a MAP/Urine output or resolution of tachycardia –
commonly used goals in clinical practice.

d)  Defining safety limits – such as an upper limit or an increment of CVP/ PAWP Although no criteria for the above end points exist, an increment in CVP 2-5 mm Hg and PCWP 3-7 mm Hg in 30 min or earlier should be used as an indication to cease fluid challenge. In the absence of invasive monitoring, measurement of JVP and signs of pulmonary oedema should be looked for.

Parameters predicting fluid responsiveness

1)  Clinical endpoints such as collapsed veins and state of peripheral circulation not sensitive.
2)  CVP / PCWP changes poor predictors
Other end points have been proposed:
a)  Systolic pressure variation with respiration b)  Pulse pressure variation with respiration
c)  Stroke volume variation with respiration
d)  Aortic blood velocity variation with respiration e)  Intra-thoracic blood volume
f)   Respiratory variation in SVC / IVC diameter
g)  Haemodynamic responses to passive leg raising.

None of the above has been shown to be a reliable predictor, although the haemodynamic response to passive leg raising is thought to be more sensitive than the rest.  The reliability of some of these end points are also influenced by the presence of positive pressure ventilation

Discussion

There are no set guidelines for fluid administration. It sounds like the examiners were prepared to tolerate a range of wacky responses to this. A 2006 article by JL Vincent attempts to bring some sort of order into the lawless Mad Max wasteland of fluid resuscitation practice; another attempt was made in 2011 by Cecconi et al. I will use his suggestions in this answer.

In summary:

  • Which fluid?
  • How much fluid?
    • At least in sepsis, perhaps less fluid is better (FEAST study).
    • Conventional teaching recommends 500-1000ml of crystalloid, or (in other sources) 10-20ml/kg. This convention may be closely related to the usual fluid bag content.
  • How fast?
    • Rate of administration may be more important than the amount and type of fluid.
    • There is no scientific consensus as to how fast is fas enough.
    • Surviving Sepsis people recommend the fluids be given over 30 minutes.
    • Another technique is SV maximisation - a process where 250ml boluses are given over 5-10 minutes until stroke volume (as measured by invasive hemodynamic monitoring) stops increasing by 10-15% with each bolus
  • When to stop?
    • Though not based in any firm evidence, resuscitation endpoints have historically included the following parameter theresholds:
      • MAP > 65mmHg
      • CVP >8mmHg, or a change of over 7mmHg in response to the bolus
      • PAOP change of over 5mmHg in response to the bolus
      • Normal lactate (<2.0mmol/L)
      • Urine output >0.5ml/kg/hr
      • ScvO2~ 75mmHg
      • Resolution of clinical features of hypovolemia which had given rise to the decision to administer the fluid bolus.

As for the assessment of fluid responsiveness - it is a vast topic, and is dealt with in a chapter dedicated to its bewildering detail.

In brief summary:

References

Finfer, Simon, et al. "A comparison of albumin and saline for fluid resuscitation in the intensive care unit." N Engl j Med 350.22 (2004): 2247-2256.

Bunn, Frances, Daksha Trivedi, and S. Ashraf. "Colloid solutions for fluid resuscitation." Cochrane Database Syst Rev 7 (2012).

Raghunathan, Karthik, et al. "Association Between the Choice of IV Crystalloid and In-Hospital Mortality Among Critically Ill Adults With Sepsis." Critical care medicine (2014).

Maitland, Kathryn, et al. "Mortality after fluid bolus in African children with severe infection." New England Journal of Medicine 364.26 (2011): 2483-2495.

Vincent, Jean-Louis, and Max Harry Weil. "Fluid challenge revisited." Critical care medicine 34.5 (2006): 1333-1337.

Cecconi, Maurizio, B. Singer, and Andrew Rhodes. "The Fluid Challenge."Annual Update in Intensive Care and Emergency Medicine 2011. Springer Berlin Heidelberg, 2011. 332-339.

Gan, Tong J., et al. "Goal-directed intraoperative fluid administration reduces length of hospital stay after major surgery." Anesthesiology 97.4 (2002): 820-826.