. 2005 Nov 22;9(6):566–572. doi: 10.1186/cc3927

Table 1.

Clinical caveats for hemodynamic variables

Type of hemodynamic variable	Parameter	Comments
Solitary	Blood pressure	Hypotension is always pathological
	Central venous pressure (CVP)	CVP is only elevated in disease
	Pulmonary artery occlusion pressure (Ppao)	Ppao is the back-pressure to pulmonary blood flow
	Cardiac output	There is no normal cardiac output, only an adequate or inadequate one
	Mixed venous oxygen saturation (SvO₂)	Decreasing SvO₂is a sensitive but nonspecific marker of cardiovascular stress
Dynamic	Volume challenge	Positive response defined as an increase in any of blood pressure, CVP, Ppao, cardiac output and/or SvO₂, or a decrease in heart rate
	Echocardiographic analysis of vena cavae collapse during positive pressure inspiration identifies CVP <10 mmHg if it detects	Complete inferior vena caval collapse^a
		>36% collapse in superior vena cava^a
	Defining preload responsiveness	≥13% pulse pressure variation during positive pressure ventilation^a
		>1 mmHg decrease in CVP during spontaneous inspiration^b

^aRequires a fixed tidal volume of 6–8 ml/kg and complete adaptation to the ventilator. ^bRequires a spontaneous inspiratory effort greater than -2 mmHg to be valid.