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Department of Anaesthesiology; University of Bern, Inselspital; Bern, Switzerland (Kabon) Department of Outcomes Research; The Cleveland Clinic; Cleveland, OH; sessler{at}louisville.edu (Sessler)
In Response:
We are mystified by Dr. Tornero-Campello's assertion (1) that supplemental fluid "might lead to a reduced hematocrit" and that "it is unclear whether the results reported by Dr. Kabon et al. have anything to do with tissue oxygenation, or whether the study design assesses the influence of tissue oxygenation on postoperative outcome."
Postoperative hemoglobin concentrations in our small intravascular volume group (12.0 ± 1.8 g/dL) were virtually identical to those in the large volume group (12.2 ± 2.1 g/dL), indicating that hemodilution was not a factor. As noted in both the Introduction and Discussion of our report (2), we have previously demonstrated that the fluid regimen used in our current study improved tissue oxygenation: intraoperative tissue oxygen tension (PsqO2) was significantly greater in patients given supplemental fluid: 81 ± 26 vs 67 ± 18 mm Hg, P = 0.03. Furthermore, postoperative PsqO2 (77 ± 26 vs 59 ± 15 mm Hg, P = 0.03) and capillary blood flow (69 ± 12 vs 53 ± 12, P < 0.001) were also greater in the supplemental fluid patients (3). We thus had ample evidence that supplemental fluid improves tissues oxygenation, and is good justification for conducting our study using our chosen doses.
We were nonetheless unable to identify any statistically significant or clinically important differences in wound infection rate between our "large fluid management" and our "small fluid management" group. In contrast, Nisanevich et al. (4) report more complications in patients receiving "liberal" amounts of crystalloids versus "restricted" amounts of fluid during the intraoperative period (4). It is important to recognize, though, that the average amount of crystalloid in our "small fluid management" group was 3.1 L, which was similar to the "liberal group" with 3.6 L in the study of Nisanevich et al. Their "restricted" group received an average of only 1.2 L, which was far less than we gave. These studies are thus not directly comparable. Although there were slightly more infection-related wound complications in the liberal group in the study of Nisanevich et al. (14 vs 9), the study was not powered to detect wound infections, and the difference was not statistically significant.
Other simple, low-risk, and inexpensive interventions that increase tissue oxygenation such as providing supplemental oxygen (5) or maintaining normothermia (6) reduce the infection risk by a factor or two (5,7) or three (8). These interventions most likely similarly affect tissue oxygenation in the arm, surgical wounds, and the intestines (9); normally, tissue oxygenation in the arm (the traditional "surrogate wound" measurement site) correlates well with oxygenation adjacent to surgical wounds (10,11). But, as discussed in our article, supplemental intravascular fluid administration may influence these tissues differently, explaining why supplemental fluid in the doses we tested increases arm tissue oxygenation but has little, if any, effect on infection risk. Additional study is necessary.
REFERENCES
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