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Published on: November 25, 2017
Crystalloid strong ion difference determines metabolic acid-base change during acute normovolaemic haemodilution
Thomas J Morgan1, Balasubramanian Venkatesh, Jonathan Hall
1Adult Intensive Care Unit, Mater Misericordiae Hospital, Raymond Terrace, 4101 South Brisbane, Queensland, Australia. thomas_morgan@mater.org.au
Objective:
To study the acid-base effects of crystalloid strong ion difference (SID) during haemodilution.
Design:
Prospective in vivo study.
Setting:
University laboratory.
Subjects:
Anaesthetised, mechanically ventilated Sprague-Dawley rats.
Interventions:
Rats were studied in seven groups of three. Each group underwent normovolaemic haemodilution with one of seven crystalloids, with SID values from 0 to 40 mEq/l. Six exchanges of 9 ml crystalloid for 3 ml blood were performed.
Measurements And Main Results:
[Hb] fell from 142+/-17 to 44+/-10 g/l ( p<0.0001). Final plasma [lactate] was 1.1+/-0.6 mmol/l. Final standard base excess values ranged from -8 to +7 mmol/l, and were directly correlated with crystalloid SID (R(2)=0.91). By linear regression, the SID of a crystalloid balanced to maintain standard base excess=0 mmol/l was 23.7 mEq/l. Dilutions 2-5 produced similar results.
Conclusions:
There is a linear relationship between crystalloid SID and post-dilutional metabolic acid-base status. The SID of a crystalloid balanced for normovolaemic haemodilution is 24 mEq/l. These principles are applicable in designing fluids for volume resuscitation, acute normovolaemic haemodilution and cardio-pulmonary bypass.
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