Fluid Challenge

OVERVIEW

The fluid challenge (FC) aims at identifying patients in whom fluid administration improves haemodynamics (known as “fluid responsiveness”)

Vincent and Weil (2005) have described the TROL approach to safely perform a fluid challenge:

1. type of fluid (T)
2. rate of fluid administration (R)
3. objectives (O)
4. limits for safety (L)

Therapeutically, a positive FC suggests that fluid administration should be continued as long as the response to FC is positive, and the decision to stop fluid administration occurs when a negative response to FC occurs (Messina et al, 2017)

• The definition of a FC lacks standardisation, but most commonly involves infusing (Messina et al, 2017):
  • crystalloids or colloids
  • at a rate of 500 mL over 20-30 minutes, and
  • considering an increase in cardiac index ≥15% as a positive response
• The assessment and monitoring of fluid responsiveness is a controversial topic — particularly the assessment of a positive response — and there are numerous approaches described
• The main drawback of the FC is the risk of harm from fluid overload — particularly in patients undergoing repeated fluid challenges

INDICATIONS

Messina et al (2017) note that the most common indications for FC are:

• hypotension
• oliguria

and that these indications may not be due to reasons other than hypovolaemia and many not be fluid responsive!

TYPE OF FLUID

• dependent on the clinical situation
  • crystalloid is usually preferred (e.g. a balanced salt solution)
  • blood products may be used in patients with significant haemorrhage
• no differences in mortality in critically ill patients between saline and albumin (SAFE study)
  • albumin may be useful in sepsis, avoid in traumatic brain injury
• avoid HES (starch)
• consider avoiding excessive chloride administration (e.g. saline boluses resulting in excessive hyperchloraemia)

RATE OF FLUID ADMINISTRATION

• give 500mL over 20-30 minutes
• no hard data to support a particular regimen
• see fluid bolus therapy

OBJECTIVES

Options

• target MAP
  • 65mmHg usually OK, may need to higher for the hypertensive patient
• target urine output
  • e.g. 0.5mL/kg/h
• resolution of end-organ malperfusion
  • resolution of tachycardia, improved LOC, falling lactate, rising ScvO2 (aim > 70%)
• Ultrasound and echocardiography
  • optimal filling state (e.g. atrial pressures, IVC diameter, ventricular filling and EF)
• Cardiac output monitoring
  • e.g. cardiac index, stroke volume, stroke volume variation

Some of these are only surrogates for stroke volume and cardiac output, which is what we really want to assess.

• The utility of surrogates is controversial, many are poor indications of improved stroke volume
• Some would argue that if tachycardia settles and hypotension resolves during the fluid challenge then you don’t need to measure cardiac output

Problems

• in practice, FC is limited by the difficulty controlling for other factors that may affect the objective
• for example, blood pressure will increase if sedation is changed or the patient is suctioned

LIMITS FOR SAFETY

If the limit is reached before the objective, the FC is stopped

• upper limit or increment of CVP or PAWP
  • e.g. if CVP increases by 2-5mmHg or PCWP increases by 3-7mmHg, stop fluid challenge
  • however, CVP and “deltaCVP” correlate poorly with blood volume or fluid responsiveness
• if no invasive monitoring:
  • measure JVP and look for signs of APO
  • or use IVC ultrasound and lung ultrasound to assess for ‘fluid tolerance’

As with the surrogates used as objectives, the limits for safety are poorly validated for the most part

‘MINI-FLUID CHALLENGE’

The ‘mini-fluid challenge’  is an alternative approach described by the AzuRéa group (Muller et al, 2011)

• an infusion of 100 ml of colloid over 1 min predicts the fluid responsiveness (10% increase in VTI) of a full fluid challenge with an additional 400 ml given over the next 14 min
• sensitivity and specificity of 95% and 78%
• gold standard: 15% increase in VTI following 500 mL colloid bolus over 15 minutes (occurred in about 50% of patients with circulatory failure)
• Commentary and criticisms:
  • not validated
  • small study (39 patients)
  • used starch (HES)!
  • requires echocardiography (TTE) to measure subaortic velocity time index (VTI)
  • only deeply sedated mechanically ventilated patients studied, and arryhthmias were excluded

References and Links

LITFL

• CCC — Passive leg raise
• CCC — Fluid responsiveness

Journal articles

• Messina A, Longhini F, Coppo C, et al. Use of the Fluid Challenge in Critically Ill Adult Patients: A Systematic Review. Anesthesia and analgesia. 2017; 125(5):1532-1543. [pubmed]
• Muller L, Toumi M, Bousquet PJ, Riu-Poulenc B, Louart G, Candela D, Zoric L, Suehs C, de La Coussaye JE, Molinari N, Lefrant JY; AzuRéa Group. An increase in aortic blood flow after an infusion of 100 ml colloid over 1 minute can predict fluid responsiveness: the mini-fluid challenge study. Anesthesiology. 2011 Sep;115(3):541-7. [pubmed]
• Vincent JL, Weil MH. Fluid challenge revisited. Crit Care Med. 2006 May;34(5):1333-7. Review. [pubmed]
• Vincent JL. “Let’s give some fluid and see what happens” versus the “mini-fluid challenge”. Anesthesiology. 2011 Sep;115(3):455-6.[pubmed] [article]