Patients who undergo surgery with significant blood loss often have problems with coagulation. However, not all coagulation deficits in surgical patients can be related to the use of blood. Colloid solutions have been reported to be responsible in many settings. These deficits are in addition to those expected purely from the dilution associated with large-volume resuscitation.
Few topics in anaesthesia and surgery have generated as much controversy as the relative merits of colloids and crystalloids for intraoperative fluid replacement and resuscitation. Numerous animal and human studies have been undertaken to prove that one or the other is superior. In most cases, the choice is based more on personal opinion and dogma rather than on scientific merit.
A meta-analysis (Velanovich, 1989) looked at mortality in eight published human trials in patients receiving either crystalloid or colloid for resuscitation. It showed an overall 5.7% decrease in mortality rate in patients resuscitated with crystalloid rather than colloid solutions. Subgroup analysis showed that trauma/sepsis patients had a 12.3% decrease in mortality when crystalloids were used. However, when crystalloids were used in patients undergoing elective surgery, there was a 7.8% increase in mortality.
The proposed explanation was that patients with trauma and sepsis have an increase in capillary permeability that allows the administered colloid to leak out of the vasculature, to be less effective as an intravascular volume expander and to slow resolution of oedema from the affected tissues. In patients undergoing elective procedures, the amount of capillary leak, in contradistinction to that in major trauma, is more discretely limited to the surgical site; thus, the use of colloids may be more efficacious in increasing intravascular volume. This study does not settle the controversy, but it does provide some insight into specific situations when one or the other may be preferable. Most colloid advocates do not recommend these substances as the sole resuscitative fluid. The usual protocol involves initial infusion of crystalloids, followed by the administration of colloids when large volumes are necessary to reduce the amount of crystalloids.
In general, crystalloids need to be administered in volumes that are approximately 2-3 times that of iso-oncotic colloid to obtain the same haemodynamic effect. When more concentrated colloid solutions, such as 25% albumin, are used, this ratio is no longer valid.
The most comprehensive evaluation of colloid therapy was presented in a 1991 workshop on the assessment of plasma volume expander. All of the pertinent clinical trials involving albumin, dextran and hydroxyethyl starch were carefully evaluated in terms of efficacy, cost, indications for use and complications. Little evidence was found for either a short-term or long-term benefit from the use of supplemental colloidal agents in blood loss, burns, cardiopulmonary bypass, pulmonary oedema, trauma and nutrition. No evidence suggested that serum albumin levels as low as 3.0 g/dl were deleterious, and even values as low as 2.0 g/dl have not been clearly shown to be problematic.
Of particular interest was the discussion relating to pulmonary oedema and the fact that administration of albumin in hypoalbuminaemic patients, by abruptly increasing pulmonary artery perfusion pressure, may produce the very complication it is designed to prevent -- interstitial and alveolar flooding.
A rise in colloid oncotic pressure a little above normal significantly impairs renal salt and water excretion. No congenital hyperalbuminaemic states are known, and the body reacts to transient elevations of albumin by immediately stopping production and accelerating catabolism. The adverse renal effects may be associated with the absence of naturally occurring states of excess albumin, whereas those in which the albumin level is low are common.
However, with one exception, in which albumin supplementation of 900g occurred over several days, no toxic effect of albumin therapy has been shown. The anticoagulant, antiplatelet and fibrinolytic effects of colloidal products have been mentioned.
• First generation - concern about the O2 binding characteristics
• Normal O2 content of blood is 20 vol%; for first generation it is 5 vol%
• Newer generation FH
• Still low O2 content effect
• Patients still need high FIO2
• May be hyperoncotic if haemoglobin is kept whole
• Haemoglobin has a tendency to dissociate into two-alpha unit or two-beta unit dimers that are quickly excreted in the urine
• Linking these two dimers into a tetramer increases the half life
Reference Velanovich V. Crystalloid versus colloid fluid resuscitation: A meta-analysis of mortality. Surgery 1989; 105: 65–71.
Prof M Mythen: Colloid vs Crystalloid