Table 2.

Conditions biasing inferior vena cava ultrasound findings.

	IVC CI	IVCmax	Comments
Underestimate intravascular volume
Increased tidal volume (ventilated)	Increased?	No change?
Increased inspiratory effort moving probe “in & out” of field (diaphragmatic breathing) [18]	Increased	No change	Midaxillary or midclavicular line views [23]. Cross-sectional view [18]
Increased inspiratory effort/deep breathing (sniff) [22, 28, 35]	Increased	No change	Large IVCmax with no collapse indicates being not hypovolemic
Valsalva maneuver [19]	Increased	Decreased	Large IVCmax with no collapse indicates being not hypovolemic
Intra-abdominal HTN [23, 36]	?	Decreased	Large IVCmax with no collapse indicates being not hypovolemic.
Off-center scan (cylinder tangent effect) [37]	Minimal changes	Decreased	Attempt to maximize IVC diameter. Cross-sectional view [18]
Overestimate intravascular volume
Cardiac tamponade	Decreased	Increased	Preload dependent
Severe valvular stenosis	Decreased	Increased	Preload dependent
Massive pulmonary embolism [18]	Decreased?	Increased	Preload dependent
Right ventricular myocardial infarction [38]	Decreased	Increased	Preload dependent, decreased venous return to LV
Severe tricuspid regurgitation	Decreased	Increased
High PEEP [39]	Minimal change	Increased	No difference between PEEP 0 and 5 cm H20[39]
Decreased tidal volume	Decreased	No change?
Decreased inspiratory effort/shallow breathing [22, 40]	Decreased	No change?	Highly collapsible IVC indicates being not hypervolemic

IVC = inferior vena cava, IVC CI = IVC collapsibility index, IVCmax = IVC maximum diameter, PEEP = positive end-expiratory pressure, LV = left ventricle, and HTN = hypertension, cm H₂0: centimeters of water.