Dilution and redistribution effects of rapid 2-litre infusions of 0.9% (w/v) saline and 5% (w/v) dextrose on haematological parameters and serum biochemistry in normal subjects: a double-blind crossover study

Although hypoalbuminaemia after injury may result from increased vascular p ermeability, dilution secondary to crystalloid infusions may contribute sig nificantly. In this double-blind crossover study, the effects of bolus infu sions of crystalloids on serum albumin, haematocrit, serum and urinary bioc hemistry and bioelectrical impedance analysis were measured in healthy subj ects. Ten male volunteers received 2-litre infusions of 0.9% (w/v) saline o r 5% (w/v) dextrose over I h; infusions were carried out on separate occasi ons, in random order. Weight, haemoglobin, serum albumin, serum and urinary biochemistry and bioelectrical impedance were measured pre-infusion and ho urly for 6 h. The serum albumin concentration fell in all subjects (20% aft er saline; 16% after dextrose) by more than could be explained by dilution alone. This fall lasted more than 6 h after saline infusion, but values had returned to baseline I h after the end of the dextrose infusion, Changes i n haematocrit and haemoglobin were less pronounced (7.5% after saline; 6.5% after dextrose). Whereas all them water from dextrose was excreted by 2 h after completion of the infusion, only one-third of the sodium and water fr om the saline had been excreted by 6 h, explaining its persistent diluting effect. Impedances rose after dextrose and fell after saline (P < 0.001). S ubjects voided more urine (means 1663 and 563 ml respectively) of lower osm olality (means 129 and 630 mOsm/kg respectively) and sodium content (means 26 and 95 mmol respectively) after dextrose than after saline (P < 0.001). While an excess water load is excreted rapidly, an excess sodium load is ex creted very slowly, even in normal subjects, and causes persistent dilution of haematocrit and serum albumin. The greater than expected change in seru m albumin concentration when compared with that of haemoglobin suggests tha t, while dilution is responsible for the latter, redistribution also has a role in the former. Changes in bioelectrical impedance may reflect the elec trolyte content rather than the volume of the infusate, and may be unreliab le for clinical purposes.