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Address correspondence and reprint requests to Donat R. Spahn, MD, FRCA, Professor and Chairman, Department of Anesthesiology, University Hospital Lausanne (CHUV), CH – 1011 Lausanne, Switzerland. Address e-mail to donat.spahn{at}chuv.ch.
Concerns have been expressed that over-hydration may result in pulmonary edema, cardiac complications, delayed recovery of gastrointestinal motility, compromised tissue oxygenation, wound healing problems, and blood coagulation impairment (1–3). Patients with a cardiac comorbidity undergoing major noncardiac surgery may be particularly vulnerable and, therefore, perioperative fluid restriction might appear to be beneficial.
However, there are at least 4 prospective randomized trials showing that a goal-directed perioperative plasma volume expansion decreases major postoperative morbidity and the duration of hospitalization significantly (4–7). In all these studies, stroke volume in the descending aorta was assessed by esophageal Doppler monitoring. Two hundred mL of colloids were given over 10 min and stroke volume was assessed every 15 min. This was repeated until no further increase in stroke volume was detected. Indeed, higher Doppler cardiac outputs were observed at the end of surgery in the goal-directed perioperative plasma volume expansion groups (4,5,7). Interestingly, the reduction of duration of hospitalization was 2 days in general surgery in relatively young and healthy patients (mean age, 55–60 yr) (4), 4 days in cardiac surgery in 65-yr-old patients (7), and 4 to 8 days in 75- to 85-yr-old patients undergoing proximal femoral fracture repair (5,6). Older age and increasing comorbidity thus does not seem to limit but rather to increase the benefit of a goal-directed perioperative plasma volume expansion.
It is important to note that, first, supplemental fluid was not just given on a routine basis but administered goal-directed, the goal being the optimization of the stroke volume as assessed by esophageal Doppler monitoring (4–7). Second, goal-directed fluid therapy reduces postoperative morbidity more when done with colloids than with crystalloids (8), potentially related to a lesser development of intestinal edema in patients treated with colloids (9). This appears to be particularly relevant in gastrointestinal surgery, where, in the context of "fast-tracking," intraoperative fluid restriction has become a hot topic (3). Crystalloid fluid restriction and the individualized goal-directed administration of colloids thus are not opposing but rather complementary strategies.
Esophageal Doppler monitoring used in the aforementioned studies is easy to learn, but it is not widely used and lacks validation. In contrast, arterial catheters are used extensively in daily practice, are easy to place, and are rarely associated with serious complications. They continuously display the arterial waveform on the screen. The differential pressure between systolic and diastolic values, the pulse pressure, and the area under the curve, both easy to evaluate by visually analyzing the curve, are proportional to the actual blood volume pulsed toward the periphery. Mechanical ventilation interferes with cardiac filling and induces variations in stroke volume (10). The degree of stroke volume variation is proportional to the degree of hypovolemia and has been shown to accurately forecast fluid responsiveness (10–13).
In contrast, central venous and capillary wedge pressures are poor markers of volume status because the relationship between pressure and volume, or compliance of the cardiac chambers, cannot be determined clinically (14). Moreover, the compliance curve is nonlinear. At low volume, filling pressure variations are minimal in comparison with volume changes; their sensitivity for hypovolemia thus is low. At high filling pressure, however, the relationship is clinically useful because volume changes are associated with significant pressure changes (Fig. 1); the measurement of filling pressures gives an accurate image of the upper limit of fluid administration in patients with cardiac dysfunction and may serve to avoid over-hydration once stroke volume has been optimized (Fig. 1). If cardiac compliance is abnormal, such as in diastolic dysfunction, the filling pressure will be much higher than expected for the same filling volume (Fig. 1). Most of the studies on invasive monitoring, such as Swan-Ganz catheters in noncardiac surgery, have given disappointing results because their populations have not been selected and because the retrieval of the monitored data has not been accompanied by a goal-directed protocol of fluid administration (15–17). In addition, more complications were observed in the group with invasive monitoring (18).
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The cardiac dysfunction in a given patient may be diastolic, systolic, or both. In each case, their optimal end-diastolic wall stress, or filling volume, has a relatively narrow range. Outside this range, their stroke volume and cardiac output decrease by insufficient wall stress in case of hypovolemia (Frank-Starling phenomenon), or by congestive failure in case of hypervolemia. In general, patients with a significant cardiac dysfunction are exquisitely sensitive to volume variations, which should be minimized.
How should we thus proceed practically? After anesthesia induction many patients are in a situation of functional hypovolemia or reduced effective preload from anesthetic vasodilatation and positive pressure ventilation (10). These patients are thus on the ascending limb of the Frank-Starling curve and will benefit from individualized goal-directed intravascular fluid administration (Fig. 1), which moves them to the right of their end-diastolic volume – stroke volume relationship close to their optimum stroke volume (Fig. 1). Once stroke volume has been optimized, this position needs to be maintained and filling pressure monitored to avoid over-filling resulting in severe complications such as pulmonary edema (2). In addition, optimum cardiac filling will prevent tachycardia from hypovolemia, which dramatically increases the myocardial oxygen consumption, and is particularly dangerous in patients with or at risk of coronary artery disease.
It needs to be stressed once more that advanced monitoring alone is neither sufficient nor beneficial. In contrast, such monitoring may be associated with complications in patients with cardiac comorbidities undergoing noncardiac surgery (15,18). Only combining monitoring with a clear management algorithm aiming at the optimization of the stroke volume with colloid boluses in the presence of a knowledgeable anesthesiologist (19) will improve the outcome of patients with concomitant cardiac disease undergoing noncardiac surgery.
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  W. J. Fawcett and N. F. Quiney Fluid Restriction and Major Surgery Anesth. Analg., December 1, 2006; 103(6): 1608 - 1608. [Full Text] [PDF]
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