RESUMEN
BACKGROUND: Intravenous fluids for perioperative infusion therapy should be isotonic to maintain the body fluid homeostasis in children. Modified fluid gelatin 4% in a balanced electrolyte solution has a theoretical osmolarity of 284 mosmol L-1 , and a real osmolality of 264 mosmol kg H2 O-1 . Because both values are lower than those of 0.9% saline or plasma, gelatin would be expected to be hypotonic in-vitro and in-vivo. AIM: We thus hypothesized that the infusion of gelatin would be expected to decrease plasma osmolality. We performed an in-vitro experiment and an in-vivo study to evaluate the impact of gelatin on the osmolality in children. METHODS: In the in-vitro experiment, full blood samples were diluted with gelatin 4% or albumin (50 g L-1 ) from 0% (pure blood) to 100% (pure colloid), and the osmolality was measured by freezing-point depression. In the in-vivo study, blood gas analyses from children undergoing major pediatric surgery were collected before and after gelatin infusion, and the osmolality was calculated by a modified version of Zander's formula. RESULTS: In the in-vitro experiment, 65 gradually diluted blood samples from five volunteers (age 25-55 years) were analyzed. The dilution with gelatin caused no significant changes in osmolality between 0% and 100%. Compared with gelatin, the osmolality in the albumin group was significantly lower between 50% and 100% dilution (p < .05). In the in-vivo study, 221 children (age 21.4 ± 30 months) were included. After gelatin infusion, the osmolality increased significantly (mean change 4.3 ± 4.8 [95% CI 3.7-4.9] mosmol kg H2 O-1 ; p < .01) within a normal range. CONCLUSIONS: Gelatin in a balanced electrolyte solution has isotonic characteristics in-vitro and in-vivo, despite the low theoretical osmolarity, probably caused by the (unmeasured) negative charges in the gelatin molecules contributing to the plasma osmolality. For a better evaluation of the (real) tonicity of gelatin-containing solutions, we suggest to calculate the osmolality (mosmol kg H2 O-1 ) using Zander's formula. TRIAL REGISTRATION: ClinicalTrials.gov (ID: NCT02495285).