Controversial Issues Concerning Fluid Management In The Perioperative Setting
Fluid management in the perioperative setting remains an area of significant controversy. Poor fluid management can wreak havoc in a surgical patient’s physiological electrolyte and fluid balance and thus cause inadequate tissue oxygenation and perfusion. From a perioperative perspective, this is especially concerning in patient’s undergoing abdominal surgery because these patients must fast pre-operatively and are often not able to manage their own fluid consumption post-operatively. Therefore, the onus falls upon the perioperative clinician to administer fluid appropriately and safely to correct for any tissue hypo-perfusion. In order to do so, one must be very careful to not replace fluid excessively or insufficiently, even if the risk is relatively small in previously and otherwise healthy, low risk surgical patients. Nevertheless, it should be noted that even in these otherwise low risk patients, a tendency towards hypervolemia or hypovolemia is reasonable in the setting of recent abdominal surgery. To this end, extensive research on perioperative fluid management has been done comparing “liberal” fluid regimens with “restrictive” and “goal-directed” fluid regimens.
Historically, clinicians have tended towards a more liberal fluid regimen of up to 7 litres of crystalloid on the day of abdominal surgery. This was usually done to correct for perceived fluid deficits such as preoperative fasting (although some have argued that dehydration from preoperative fasting is negligible), vasodilation secondary to anaesthetic agents, and third space losses. This has been shown to decrease nausea, drowsiness and thirst in patients undergoing minor surgery. Unfortunately, overzealous replacement has been shown to cause tissue oedema with concurrent weight gain. Furthermore, accidentally causing a hypervolemic state could increase the risk of renal failure, pulmonary oedema, impaired wound healing and even sepsis. In recent years, there has been more support for fluid restriction. Whilst there have been some smaller studies that have demonstrated decreased hospital stays and fewer post-surgical complications secondary to a restrictive fluid regimen; the overall evidence for its use in abdominal surgery remains inconclusive. Moreover, accidentally causing a hypovolemic state could increase the risk of hypotension and decreased organ tissue perfusion leading to organ failure.
Whilst it is clearly advantageous to be managing a patient’s fluids after surgery, it remains very unclear just exactly how much fluid is the correct amount even though many trials have been done comparing various fluid management regimens. This has largely been due to significant variation on the exact definitions of a “liberal regimen” and a “restrictive regimen” as well as variation between studies on what kinds of crystalloids or colloids were used. Indeed, often there have been significant overlap between one studies liberal regimen compared to another studies restrictive regimen and this heterogeneity has meant that it has been very difficult to compare trials in a meaningful manner. As such, the simplest conclusion one can draw is that fluid management is complex and actual physiological requirement for fluid likely varies between individual patients and varying surgeries. This has led to the recommendation now for a third fluid management strategy known in literature as a “goal-directed” fluid regimen.
Goal-directed fluid regimens have been recommended by some as it eschews the provision of arbitrary volumes of fluid and instead recommends that fluid is titrated based on a measurable endpoint. In most trials, this has been done with an oesophageal doppler to estimate cardiac output in the perioperative period. In abdominal surgery specifically, using an oesophageal doppler-assisted goal-directed fluid regimen has been shown to reduce hospital length of stay and post-operative morbidity. This has led the National Institute of Health and Care Excellence in the UK to recommend the use of an oesophageal doppler routinely in colorectal surgery. Unfortunately, actual use of oesophageal doppler-assisted fluid management is far from routine in Australia and this is likely due to cost considerations, practicality of use and lack of clinician familiarity with the device.
Given all of this, a large, Australian-led, multi-centre, international trial (RELIEF) was published in June this year in an attempt to more conclusively compare liberal fluid regimens with restrictive fluid regimens, both with and without the assistance of an oesophageal doppler. It was found that among patients undergoing abdominal surgery, those who received a “modestly” liberal fluid regimen had a similar rate of disability-free survival at 1 year as a those who received a restrictive fluid regimen. However, those who received a restrictive fluid regimen demonstrated a considerably greater risk of acute kidney injury. Disappointingly, the clinicians administering the fluids in this trial were not blinded so there is a possibility for some bias which must be considered, although the pragmatic study design should diminish this bias somewhat.
The patient described in the scenario is relatively young and without significant comorbidities. He is however, about to have relatively major, abdominal, cancer surgery. In consideration of the above evidence, it would be fair to say a liberal fluid regimen is likely to be superior to no fluid management whatsoever but unlikely to be significantly more advantageous than a restrictive fluid regimen in the long term. The main advantage will be that he is significantly less likely to develop an acute kidney injury (and the morbidity associated with an acute kidney injury), although this does assume that he is not excessively fluid overloaded, which would also confer morbidity and mortality. Ultimately, fluid management remains a complex, multi-factorial challenge in the perioperative setting and a pragmatic approach must be considered to ensure the best possible patient outcomes in the long term.
