Accelerated lymph flow from infusion of crystalloid fluid during general anesthesia

Kinetic analysis of crystalloid fluid yields a central distribution volume (V_c) of the same size as the expected plasma volume (approximately 3 L) except during general anesthesia during which V_c might be only half as large. The present study examined whether this difference is due to influence of the intravascular albumin balance.

A population volume kinetic analysis according to a three-compartment model was performed based on retrospective data from 160 infusion experiments during which 1-2.5 L of crystalloid fluid had been infused intravenously over 20-30 min. The plasma dilution based on blood hemoglobin (Hb) and plasma albumin (Alb) was measured on 2,408 occasions and the urine output on 454 occasions. One-third of the infusions were performed on anesthetized patients while two-thirds were given to awake healthy volunteers.

The Hb-Alb dilution difference was four times greater during general anesthesia than in the awake state (+ 0.024 ± 0.060 versus - 0.008 ± 0.050; mean ± SD; P < 0.001) which shows that more albumin entered the plasma than was lost by capillary leakage. The Hb-Alb dilution difference correlated strongly and positively with the kinetic parameters governing the rate of fluid transfer through the fast-exchange interstitial fluid compartment (k₁₂ and k₂₁) and inversely with the size of V_c. Simulations suggest that approximately 200 mL of fluid might be translocated from the interstitial space to the plasma despite ongoing fluid administration.

Pronounced plasma volume expansion early during general anesthesia is associated with a positive intravascular albumin balance that is due to accelerated lymphatic flow. This phenomenon probably represents adjustment of the body fluid volumes to anesthesia-induced vasodilatation.