Table 1. Normal values and critical values for Hb, SO₂ and flow.

	Normal values	Critical values
Hb	35–90 AU	<15 AU or >90 AU
SO2	20–50%	<10%
Flow	10–50 AU	<5 AU

Abbreviations: AU=arbitrary unit; Hb=haemoglobin content; flow=microvascular blood flow; SO₂= venous oxygen saturation.