Summary of abstracts
Is there any hope in finding an answer to the crystalloid:colloid debate? Here is a concise summary of the controversy, with pointers to recent fairly substantial reviews. (You may also wish to briefly browse our editorial comment)
Crystalloid versus Colloid - the controversy rages
The debate over whether to use crystalloids or colloids (and which specific fluid in each group to use) continues to be a controversial point in trauma, surgical and acutely ill patients.
The shift towards fluid as opposed to blood products is based on the risks of blood product infusion and the fact that acute anaemias are tolerated better than tissue perfusion deficits.
The arguments for the use of one type of fluid over another are based on, amongst others: cost, risk of anaphylactoid reactions, effects on coagulation and post- operative organ function. The major point of contention however is based on the propensity of either fluid to cause pulmonary oedema.
What both groups do agree on is that hypovolaemia leads to cardiovascular decompensation, decreased cellular perfusion and oxygen delivery (DO2), increasing oxygen debt, lactic acidosis and ultimately, cell death. Fluid provision will decrease the amount of irreversibly damaged cells BUT this does not necessarily mean an improvement in DO2. Agreement is also reached that fluids should be warmed to prevent the further complications of hypothermia.
Some factors responsible for non-resolution of the crystalloid –colloid controversy are based on none of the studies having:
The number of studies done in this area and the failure to reach consensus indicates the poor nature of these studies.
1. Colloid vs Crystalloids in Fluid Resuscitation: A systematic Review
This review of all randomised clinical trials from 1966 to1996 looks at outcomes of pulmonary oedema, mortality and length of hospital stay in all those studies looking at crystalloid vs. colloid resuscitation. A total of 16 studies met the inclusion criteria and the overall results indicated no difference in any of the observed outcomes in the 2 clinical groups. There was however a statistically significant improvement in mortality in the crystalloid -treated subset of trauma patients.
There are numerous problems with this study review. Is mortality an appropriate outcome to be looking at in these trials? The methodology of the reviewed studies were rated on 8 variables from 0-2; i.e. A total score of 16. The range was 4-12, indicating poor study methodology. The total number of patients from the pooled data was insufficient and this affects the power of the study.
2. Distribution of Normal Saline and 5% Albumin infusions in septic patients
One of the major points of contention with type of fluid is the development of pulmonary oedema as a morbid complication. A study looking at distribution of colloid vs. crystalloid may give insight into the distribution of each fluid when infused.
This prospective randomised trial looks at distribution of NS and 5% albumin in 18 critically ill patients. Plasma and extracellular fluid volume were measured using I-131 albumin and S-35 sodium sulphate radio- isotope dilution techniques. Then interstitial fluid volume ISFV = ECFV-PV. From plasma counts, extrapolated zero time plasma counts for each isotope was calculated using linear regression. It was found that NS distributed in a ratio of 1:3 through PV and ISFV in the same volume as was infused. Albumin increased ECFV by twice the volume infused PV and ISFV increasing in equal proportions. The likely explanation is that leaky capillaries allow colloid to leak into the ISFV, where the colloid then draws in water from the intracellular compartment.
Problems with the study include:
However, this study still gives useful insights into the distribution of infused fluids, and the potential for development of interstitial and pulmonary oedema.
Although not a primary objective of the study, it was found that none of the fluid infused increased DO2, but this may be due to the study lacking statistical power due to the small number of study patients.
3. Fluid Replacement
This review highlights the fact that in the initial stages of trauma, it is not the type of fluid, but rather an amount appropriate to restore tissue perfusion that is important. As well as discussing the effects and side effects of the various crystalloids and colloids, other alternatives such as synthetic haemoglobin solutions are considered.
Due to the difficulty in assessing tissue perfusion, it is suggested that failure to supranormalise VO2I and DO2I is a predictor of the development of multi-organ failure, and that these should be considered goals of therapy. The other suggestion made is that in the later stages of critical illness, once `capillary leakiness` has occurred, the low molecular weight (MW) colloids e.g. Gelatins have no role and high MW colloids should be used in this setting. The review also looks at prehospital fluid management and the principles of permissive hypotention.
It is the lack of any proper studies in this field, which has led to the perpetuation of, and non-resolution of this specific controversy. At this time the, ideal fluid to use in resuscitation is most likely a combination of crystalloid and colloid, but, until an adequate study is produced, this is based not so much on evidence as on a middle road between the two sets of protagonists.