DOI: 10.1097/CCM.0b013e31821909b6

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PMID: 21685768

Issn Print: 0090-3493

Publication Date: 2011/07/01


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Fluids after cardiac surgery: Do all cardiac surgical patients behave similarly?

Anita Sugavanam; Sian Jaggar

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We were very interested to read the Canadian study by Madger et al (1). The authors state that they believe a flow-based protocol is the only way to assess volume-responsiveness of cardiac function, and indeed, any effects on cardiac output that are unrelated to volume, as has been suggested for colloids. They utilized an appropriately powered, double-blinded randomized controlled trial method in patients requiring Swan-Ganz catheters for their surgery, making prudent efforts to exclude actively bleeding patients. Appropriately, changes in filling pressures and cardiac outputs rather than absolute values were used to guide fluid resuscitation. Since colloids and crystalloids have different effects in different types of shock (2, 3), the authors looked specifically at cardiac surgery patients in an attempt to minimize confusion.
Unfortunately, the patients were undergoing a range of both closed (coronary artery bypass grafts) and open (valve) cardiac surgery. Although these are all within the realms of “cardiac surgery,” there is a fundamental difference in those operations where the heart is opened and those where it is not. This is particularly pertinent as the chosen primary outcome was catecholamine use the morning after surgery. It is possible, not to say probable, that those patients in whom there was direct manipulation of the open heart would require catecholamine support for longer, regardless of optimal volume status. Despite this flaw, it was interesting to note that less fluid was given to patients using colloids to achieve the same cardiac output goals. Furthermore, when colloid was given off protocol, this advantage of catecholamine use was eliminated.
A second issue arises since it is not clear from the paper whether all patients had been on bypass, or whether some were managed using an “off-pump” technique. Patients who have been on cardiopulmonary bypass may in some units be separated from bypass in a relatively “empty” state to aid function. Such patients will often require more intravascular fluid resuscitation, whatever fluid resuscitation protocol is utilized.
Nonetheless, this was a well-designed proof-of-principle study demonstrating no adverse effects of colloids. Indeed, the authors comment upon “a tendency” toward less arrhythmias, less need for pacing, and fewer mediastinal infections, which they explained by the reduced need for volume resuscitation and therefore less right ventricular load. The increased “tendency” toward bleeding and plasma transfusion that the authors note remains a concern, particularly since transfusion-related acute lung injury might be expected to further affect lungs at risk of damage due to cardiopulmonary bypass. Larger trials will be needed to further elucidate these issues.
In modern practice, most intensivists utilize flow-based alterations, giving aliquots of fluid to postoperative cardiac patients and looking at trends in filling pressures, cardiac output, and urine output to guide further treatment. However, there is variability in the type of fluid used and this study may have some influence on that.
The authors have not disclosed any potential conflicts of interest.

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