The trusted source for
healthcare information and
ABSTRACT & COMMENTARY
Marik and colleagues recently reported a study comparing gastric intramucosal pH (pHi) changes after volume replacement with hydroxyethyl starch or with crystalloid in patients undergoing elective abdominal aortic aneurysm repair. Thirty patients were studied. Patients were randomly selected to receive intraoperative and postoperative fluid replacement with either crystalloid (Ringer’s lactate) or hetastarch. Patients could not receive in excess of 3000 mL of hetastarch (only 1500 mL intraoperatively). Ringer’s lactate was used if additional volume replacement was required. Volume replacement was titrated to maintain a pulmonary artery occluded pressure of between 10 and 14 mmHg and urine output of greater than 0.5 mL/kg/h. Dobutamine or dopamine was used in patients with a cardiac index of less than 2.2 L/min/m2 or in patients who remained oliguric. Hemodynamic, oxygenation, and pHi data were collected preoperatively, preclamp, before unclamping, at the end of the procedure, and postoperatively for 24 hours. Doctors managing the patients were blinded to the pHi measurements. Coagulation parameters were determined preoperatively and postoperatively for 24 hours.
The groups were well matched in terms of severity, preoperative cardiac index, coagulation, length of surgery, cross-clamping time, and operative blood loss. The intraoperative fluid balance was significantly greater in the crystalloid group than in the hetastarch group (4194 ± 1500 mL vs 2949 ± 1123 mL; P = 0.05). In addition, the reduction of pHi was significantly higher in the hetastarch group (the lowest pHi was 7,34 ± 0,02 in the hetastarch group compared with 7,30 ± 0,04 in the crystalloid group; P = 0.01). By multivariate analysis, the only variable that influenced the maximal decrease in pHi was the type of resuscitation fluid. However, there were no significant differences in hemodynamic- and oxygenation-derived variables or coagulation between the two groups of patients. Length of mechanical ventilation, intensive care unit, and hospital stay were also comparable between the two groups of patients.
Volume expansion is the mainstay of hemodynamic resuscitation. However, the role of crystalloid vs. colloid solutions for fluid resuscitation is still controversial, especially for clinical disorders associated with increased vascular permeability. The benefits of colloid are that similar hemodynamic responses can be achieved with smaller volumes, as this study confirms. However, no clinical trials have demonstrated the superiority of either form of fluid in terms of a better outcome.
In regard to this point, a prospective, randomized trial recently compared crystalloid and colloid fluid resuscitation with 5% human serum albumin in 107 patients receiving interleukin (IL)-2 therapy for metastatic cancer (Pockaj BA, et al. J Immunotherapy 1994;15:22-28). IL-2 administration is associated with a vascular leak syndrome and causes hemodynamic changes similar to those seen in patients with septic shock. Even in this situation, no differences were measured between patients receiving 5% human serum albumin or crystalloid resuscitation with regard to amount of therapy tolerated, weight gain, hemodynamic compromise (incidence of tachycardia and hypotension), pressor requirement, or hospital stay. In addition, synthetic colloids may have adverse effects such as hypersensitivity reactions and coagulopathies.
These side effects seem to be less common with hydroxyethyl starches. Moreover, data suggest that hydroxyethyl starch solutions may limit the microcirculatory abnormality in the "capillary leak syndrome" (Zikria BA, et al. Surgery 1989;105:625-631). On this basis, Marik et al hypothesized that volume replacement with hetastarch would result in less tissue edema, and therefore, better preserved tissue oxygenation than volume resuscitation with crystalloid solutions. The lower decrease in pHi observed in the hetastarch group seems to support their hypothesis. This result is in agreement with previous studies in septic patients showing that the decrease in pHi commonly observed in these patients is blunted by hydroxyethyl starch solution administration but not by human albumin infusion (Boldt J, et al. Anesth Analg 1996;83:254-261). Unfortunately, Marik et al were also unable to show that this phenomenon results in a better outcome. Further appropriately designed clinical trials are needed to elucidate whether the special properties of hydroxyethyl starch solutions are clinically relevant by evaluating the occurrence of multiple system organ failure and long-term outcome.