IVC Collapsibility

We already mentioned that the IVC diameter (>2.5cm) correlates with high venous pressure. The collapsibility of the IVC during inspiration also helps semi-quantify the venous filling pressure. One study suggested that heart failure patients with larger IVCs and lower IVC collapsibility at discharge (i.e. high venous pressure) had a higher readmission rate for CHF at 30 days. 

(Goonewardena SN, et al. J Am Coll Cardiol Img, 2008; 1:595-601).

IVC maximum diameter

IVC minimum diameter during 'sniff'

IVC max measurement  approx 2 cm from IVC/RA junction

IVC min measurement

The collapsibility index is simply calculated as a percentage as follows:
 
(IVC maximum diameter-IVC minimum diameter during sniff)/IVC maximum diameter = %IVC collapsibility

IVC measured (cm)	% collapse IVC during inspiration	CVP  (mmHg)
< 1.5 cm	> 50%	0 - 5
1.5 – 2.5 cm	> 50%	5 - 10
1.5 – 2.5 cm	< 50%	10 - 15
> 2.5 cm	Poor phasicity	15 - 20