Fluid resuscitation is required in situations where there is acute circulatory shock or intravascular volume depletion. The objective is to restore circulating volume and increase cardiac output, thereby restoring tissue perfusion and oxygen delivery.
In resuscitation situations, restoring intravascular volume is initially important, and any sodium or colloid-based fluid can be used to do this. Fluids that distribute throughout total body water (eg, glucose) do not restore intravascular volume and can exacerbate interstitial oedema in patients who are septic or suffering from other inflammatory conditions.
Practitioners should remember that any fluid (and its associated electrolyte load) administered during the resuscitation phase will have to be cleared or redistributed by the body. This may take several days or weeks in a patient with impaired homoeostasis.
Considering the complications associated with excessive NaCl load (see below), a crystalloid of a more “physiological” composition (eg, Hartmann’s solution) is preferred if large volumes of fluid are required.
Colloids vs crystalloids
Colloids allow fast restoration of intravascular volume, but there has been much debate about their safety and superiority over crystalloids. A recently updated Cochrane meta-analysis4 showed no difference in mortality between patients treated with colloids and those treated with crystalloids for fluid resuscitation. In the original Cochrane review, there was particular controversy regarding albumin infusions.
Subsequently, the SAFE study5, which compared albumin and saline for fluid resuscitation, demonstrated no difference in outcomes between albumin 4 per cent and NaCl 0.9 per cent for patients in intensive care.
With colloid infusions being significantly more expensive than crystalloid infusions, they are often less cost-effective. The use of albumin is now restricted in the UK to conditions where the synthesis of clotting factors is reduced (eg, severe hepatic failure). However, it is not in other countries (eg, Australia, New Zealand).
The lower overall volume load with colloids is often pointed out as an advantage. Regarding their ability to replenish the intravascular volume, 3L of a crystalloid solution is generally assumed to be equivalent to 1L of colloid solution. However, the SAFE study reported a ratio of 1.4L of normal saline to 1L of albumin.
Gelatin infusions have a similar molecular size to albumin and, therefore, may not allow a significant reduction in administered volume either. It may be possible to use smaller volumes of solutions of large starch molecules (eg, Voluven) to replenish intravascular volume.
In particular, in conditions where there is increased epithelial wall permeability (eg, sepsis, other inflammatory conditions, anaesthesia), starches may be more effective at reducing leakage into the interstitial space by increasing oncotic pressure.
A 2007 meta-analysis6 failed to show any difference in outcome between different types of colloids. However, a wide variety of studies were included and further research is required. Colloids are associated with their own adverse effect profiles, which should be taken into account when making choices for individual patients.
Until recently, all colloids contained considerable amounts of sodium, so their administration invariably resulted in patients receiving a substantial sodium load. However, Hextend, a starch infusion delivered in a more physiological solution (ie, with a lower sodium content), is now available and a similar gelatin-based product is expected to become available within a year.