RESUMEN
In pediatric fluid therapy it would be preferable to describe distribution and elimination a fluid bolus based on repetitive hemoglobin (Hb) according to kinetic principles. Pulse CO-Oximetry is a recent advancement in patient monitoring that allows for the continuous noninvasive measurement of Hb (SpHb). The aim of this study was to describe the distribution and elimination of hydroxyethylstarch (HES) 130/0.4 in combination with crystalloids using a noninvasive Hb monitor in two cohorts of young children undergoing minor surgeries under general anesthesia. Two cohorts, 16 children aged 1-3 years and 12 aged 4-6 years, were investigated during anesthesia and minor surgical procedures. They were given a maintenance solution of lactated Ringer's and a fluid bolus of HES 130/0.4, 6 mL/kg over a period of 20 min. The whole procedure lasted 120 min, and SpHb values were measured every 10 min. The SpHb values were used to calculate plasma dilution, net volume, and mean residence time (MRT) of the infused fluid. A total of 377 measured SpHbs generated individual dilution plots that showed variability, particularly for the older cohort. Distribution and elimination rates of the infused fluid were calculated. Mean dilution plots were generated. There were no significant differences in dilution, net volume or MRT between groups. A non invasive Hb analyzer could be used to calculate fluid distribution. The variability in the data can probably be explained by reactions to anesthetic drugs, variability in measurement technique, variability in generating the complex capillary signals, and individual variability in baseline fluid status. The latter finding is important because this is a prerequisite for perioperative fluid planning for each individual.
Asunto(s)
Hemoglobinas/análisis , Hemoglobinas/química , Monitoreo Intraoperatorio/métodos , Anestesia General/métodos , Monóxido de Carbono/química , Niño , Preescolar , Humanos , Derivados de Hidroxietil Almidón/química , Lactante , Cinética , Procedimientos Quirúrgicos Menores , Monitoreo Fisiológico , Oximetría/métodos , Pediatría , Estudios Prospectivos , Reproducibilidad de los Resultados , Factores de TiempoRESUMEN
Peri-operative fluid therapy continues to be an exercise in empiricism, with nagging questions about efficacy and complications. Pharmacokinetics is used for studying the time dependency of administered drugs. Volume kinetics is a pharmacokinetic approach describing the peak effects and clearance of intravenously infused fluids. It clarifies the absorption, distribution, metabolism and excretion of an intravenous fluid bolus. This could possibly allow for more rational design of intravenous fluid paradigms to improve clinical fluid therapy. This chapter briefly summarizes currently accepted principles of fluid therapy, discusses the general approach to kinetic analysis of fluid therapy, reviews currently available data defining kinetic responses to fluid therapy, and speculates about future applications of this approach.
Asunto(s)
Fluidoterapia , Farmacocinética , Anestesia , Humanos , Modelos BiológicosRESUMEN
BACKGROUND: Conventional concept suggests that infused crystalloid fluid is first distributed in the plasma volume and then, since the capillary permeability for fluid is very high, almost instantly equilibrates with the extracellular fluid space. We challenge whether this view is consistent with findings based on volume kinetic analysis. METHODS: Fifteen volunteers received an IV infusion of 15 mL/kg of lactated Ringer's solution during 10 min. Simultaneous arterial and venous blood hemoglobin (Hgb) samples were obtained and Hgb concentrations measured. The arteriovenous (AV) difference in Hgb dilution in the forearm was determined and a volume kinetic model was fitted to the series of Hgb concentrations in arterial and venous blood. RESULTS: The AV difference in plasma dilution was only positive during the infusion and for 2.5 min thereafter, which represents the period of net flow of fluid from plasma to tissue. Kinetic analysis showed that volume expansion of the peripheral fluid space began to decrease 14 min (arterial blood) and 20 min (venous blood) after the infusion ended. Distribution of lactated Ringer's solution apparently occurs much faster in the forearm than in the body as a whole. Therefore, the AV difference in the arm does not accurately reflect the distribution of Ringer's solutions or whole-body changes in plasma volume. CONCLUSIONS: The relatively slow whole-body distribution of lactated Ringer's solution, which boosts the plasma volume expansion during and for up to 30 min after an infusion, is probably governed by a joint effect of capillary permeability and differences in tissue perfusion between body regions.