Review article

Intravascular Volume Therapy With Colloids in Cardiac Surgery

To explore the effects of fluid therapy with the synthetic colloids hydroxyethyl starch (HES) and gelatin (GEL) on the incidence of acute kidney injury (AKI) and need for renal replacement therapy (RRT) in patients undergoing cardiac surgery.

Secondary analysis of a prospective observational study in cardiac surgical patients.

University hospital.

The study included 584 elective patients (excluding patients on preoperative dialysis).

Anamnestic and surgical core data, hemodynamics, and hemodynamic treatments were recorded intraoperatively and postoperatively. Postoperative kidney dysfunction was graded according to the Acute Kidney Injury Network criteria from perioperative changes in plasma creatinine and urine flow. Statistical analyses were performed descriptively, by logistic and probit regression, omitting inotropic and vasoactive medications as established renal risk factors. The incidence of AKI and new renal replacement therapy was 28.6% and 7.5%, respectively. Patients with AKI were older, had a higher additive Euroscore, lower preoperative glomerular filtration rates and hemoglobin level, and presented with a longer duration of cardiopulmonary bypass and surgery and higher postoperative drainage loss. HES (1 [0-2] units of 500 mL) and GEL (3 [2-5] units of 500 mL) were used in 317 and 563 patients, respectively. Crystalloids were used in all patients (4,560 [4,080-5,042] mL). Patients presenting with AKI or new RRT were treated with significantly higher amounts of GEL. The use of HES and crystalloids did not differ between these groups. Probit regression showed significant dose-response relationships between the amount of infused gelatin and the probability of AKI and new RRT. Probit regression showed significant (p = 0.0001 and 0.0003, respectively) dose-response relationships between the total units of gelatin polysuccinate infused and the probability of AKI and new RRT (Fig 1). Logistic regression revealed a statistically significant odds ratio (OR) of 1.9741 (95% CI: 1.3104-2.9740; p = 0.0011) for an association between the number of gelatin units infused and AKI (grade 1-3) but no direct association between the number of gelatin units administered and new RRT. No association between a decrease in kidney function and the application of HES was observed.

Taking into account the limitations of the small sample size and a low event rate, the nonconsideration of established renal risk factors such as inotropes and vasopressors, and potentially unmeasured confounders, these findings suggested that gelatin solutions may have deleterious effects on renal function in cardiac surgical patients. The adverse clinical effects of HES on kidney function observed in other studies may have been blunted by the restrictive use of this synthetic colloid.

This study assessed the effect of 2 types of hydroxyethyl starches (HES) on renal integrity and blood transfusion in cardiac surgery patients.

Retrospective investigation.

Patients from a single tertiary medical center.

Inclusion criteria included coronary artery bypass graft (CABG) and/or valve surgery that included cardiopulmonary bypass with aortic cross-clamping.

Intraoperative HES and blood product administration.

The study comprised 1,265 patients who met inclusion criteria. Of these patients, 70% received HES, and of these, 47% received<1,000 mL and 53% received≥1,000 mL. There was no difference in the development of acute kidney injury between the 2 groups. A parsimonious propensity model for colloids showed that combined CABG and valve surgery were less likely to be associated with HES administration than was CABG alone (OR 0.68, confidence interval [CI] 0.46-0.97; p = 0.04). Intra-aortic balloon pump use was less likely to be associated with HES administration (OR 0.57, CI 0.38-0.86; p = 0.007). Patients with chronic kidney disease, stages 3 to 5, were less likely to receive HES, with an OR of 0.56 (CI 0.38-0.84; p = 0.004); 0.51 (CI 0.20-1.33; p = 0.170); and 0.23 (CI 0.12-0.44; p<0.0001), respectively, for each stage. No difference was noted in red blood cell transfusion. However, fresh frozen plasma, cryoprecipitate, and platelet transfusions were significantly higher with larger volumes of HES, with an OR of 2.03 (CI 1.64-2.52; p<0.001); 1.60 (CI 1.30-1.97; p<0.000); and 1.62 (CI 1.21-2.15; p = 0.006), respectively. No differences in surgical mortality were found between the colloid and noncolloid groups.

This study showed no association of postoperative acute kidney injury and red blood cell transfusion between the colloid and noncolloid groups. Although the complication rate was higher with HES administration, there was no difference in surgery mortality between the 2 groups.

This study presents a magnetic hydrogel-based microgripper that can be wirelessly manipulated using magnetic fields. The proposed device can move freely in liquids when driven by direct current (dc) magnetic fields, and perform a gripping motion by using alternating current (ac) magnetic fields. The device is fabricated from a biocompatible hydrogel material that can be employed for intravascular applications. The actuation mechanism for gripping motions is realized by controlling the exposure dose on the hydrogel composite during the lithography process. The preliminary characterization of the device is also presented. The measurement results show that the gripping motion reached a full stroke at approximately 38 °C. By dispersing multiwall carbon nanotubes (MWCNT) into the material, the overall response time of the gripping motion decreases by approximately 2-fold. Device manipulations such as the gripping motion, translational motion, and rotational motion are also successfully demonstrated on a polyvinyl chloride (PVC) tube and in a polydimethylsiloxane (PDMS) microfluidic channel.