Osmotonicity of acetoacetate: possible implications for cerebral edema in diabetic ketoacidosis.
BACKGROUND
Rapid drops in blood glucose and sodium levels during treatment of diabetic ketoacidosis (DKA) can cause a drop in the osmotonicity of plasma, resulting in cerebral edema. Ketone bodies are assumed to move freely in and out of cells, so it is assumed that they do not contribute to the tonicity of plasma or influence fluid shifts. The assumption that ketone bodies do not contribute to osmotonicity has not been tested previously. The experiment described here was done to check if acetoacetate has osmotonicity.


METHODS
A modified erythrocyte fragility test was used to check the osmotonic and osmoprotective effects of the ketone body. Red blood cells were suspended in different test tubes containing distilled water, normal saline, glucose, urea and acetoacetic acid (lithium salt C4H5O3Li). All solutions (except the tube with distilled water) were made to match the osmolality of plasma. We hypothesized that solutions in which red cell hemolysis does not take place have greater tonicity than the tonicity of 0.45% saline.


RESULTS
Spectrophotometry showed that there was no hemolysis in the solutions of normal saline or solutions containing glucose or acetoacetate. Complete hemolysis was demonstrated in the tube with plain distilled water and also in the solutions containing urea.


CONCLUSIONS
This study shows that acetoacetate is functionally similar to glucose in that it contributes to increased osmotonicity. The drop in ketone body levels can produce a drop in the osmolar tonicity of plasma and precipitate cerebral edema.
Puliyel
Jacob M
JM
St Stephens Hospital, Tis Hazari, Delhi, India. puliyel@vsnl.com
D000090:Acetoacetates / Q000378:metabolism*; D001929:Brain Edema / Q000209:etiology / Q000378:metabolism*; D016883:Diabetic Ketoacidosis / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006801:Humans; D006982:Hypertonic Solutions; D007552:Isotonic Solutions; D009994:Osmolar Concentration; D009996:Osmotic Fragility; D012964:Sodium / Q000378:metabolism; D014508:Urea / Q000378:metabolism
D000090:Acetoacetates; D006982:Hypertonic Solutions; D007552:Isotonic Solutions; D014508:Urea; D012964:Sodium; D005947:Glucose