... might be meant here.

See https://www.gesundheit.gv.at/labor/laborwerte/blutgase-saeur... (scroll down to the table with a reference range of (-2)–(+2) mmol/l).

See also

http://www.sciencedirect.com/topics/medicine-and-dentistry/b...

http://www.globalrph.com/abg_analysis.htm
"B.E.
The base excess indicates the amount of excess or insufficient level of bicarbonate in the system. (A negative base excess indicates a base deficit in the blood.) A negative base excess is equivalent to an acid excess. A value outside of the normal range (-2 to +2 mEq) suggests a metabolic cause for the abnormality ..."

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Note added at 35 mins (2018-01-19 10:31:06 GMT)
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... or 'current base excess/deficit' to account for the fact that this value can be either positive or negative.

Compare https://www.proz.com/kudoz/german_to_english/medical_general... - 'Basenabweichung' seems to refer to the same value.