Hypertonic saline and dextran in normovolaemic and hypovolaemic healthy volunteers increases interstitial and intravascular fluid volumes

Abstract

Background: Hypertonic saline (HS) is increasingly used for fluid resuscitation in hypovolaemic patients. Although the effects of HS have been investigated in animal models, controlled studies in healthy human individuals are few.

Aim: The effects of i.v. hypertonic saline 75 mg.ml-1 in dextran 70, 60 mg.ml-1 (HSD) infusion on fluid shifts between the interstitial and intravascular fluid spaces, diuresis and haemodynamics were studied in normovolaemic and moderately hypovolaemic healthy volunteers.

Material and methods: Nine fasting subjects received 4 ml.kg-1 HSD as a 10-min infusion in a normovolaemic situation. Seven days later they served as their own controls in a hypovolaemic situation after 10% of the calculated blood volume had been withdrawn during a 15-min period. Before and after the HSD infusion, interstitial colloid osmotic pressure (COPi) and interstitial fluid hydrostatic pressure (Pi) were measured on the lateral part of the thorax. During the study, blood sampling and pressure measurements were performed through a radial artery cannula, and central venous pressure measured through a catheter in the cubital vein.

Results: In these awake and normovolaemic healthy volunteers, HSD infusion caused a transitory unpleasant sensation of headache and heat in the thorax up to the throat. A transitory haemodynamic effect was found with increased heart rate (HR), increased mean arterial pressure (MAP) from 77 +/- 5 mmHg to 92 +/- 13 mmHg (P < 0.05) and CVP increase from 5 +/- 1 mmHg to 8 +/- 1 mmHg (P < 0.05) after end of infusion. A haemodilution with increase in calculated blood volume lasting longer than the MAP increase was observed, with decreased COPi from 14.4 +/- 2.2 mmHg to 12.1 +/- 2.0 mmHg (P < 0.05). The diuresis measured at 180 min was higher in the normovolaemic than in the hypovolaemic situation. More pronounced effects of the infused fluid (HSD) on calculated blood volume, interstitial compartment and CVP were observed during moderate hypovolaemia.

Conclusions: HSD infusion resulted in increased calculated blood volume with increased HR, MAP, and CVP. These effects were greater in a hypovolaemic situation. The haemodilution was most likely caused by fluid shifts from the intracellular compartment to the interstitial and vascular fluid spaces, eventually increasing diuresis.