IVC - Mythbuster
Mythbusting - Dispelling Common Misconceptions
1. Myth
2. Must Reads
1. Myth
2. Must Reads
1. Myth
Prior to discussing the technicalities of IVC image acquisition and interpretation, it is of utmost importance to discuss what it CANNOT do.
The foremost misconception about the IVC is its popularized status as the panacea to "volume status" assessment. This cannot be any further from the truth.
In fact, it is quite difficult to interpret its hemodynamic significance in isolation and in stasis -- this has been proven time and again.
Consider the assessment for the height of the JVP via physical examination or POCUS, the purpose is to estimate the central venous pressure (CVP) via assessing the height of the column of blood -- a measurement of pressure. However, IVC assessment such as maximal diameter and collapsibility DO NOT measure pressure -- one INFERS the pressure.
Prior to discussing the technicalities of IVC image acquisition and interpretation, it is of utmost importance to discuss what it CANNOT do.
The foremost misconception about the IVC is its popularized status as the panacea to "volume status" assessment. This cannot be any further from the truth.
In fact, it is quite difficult to interpret its hemodynamic significance in isolation and in stasis -- this has been proven time and again.
Consider the assessment for the height of the JVP via physical examination or POCUS, the purpose is to estimate the central venous pressure (CVP) via assessing the height of the column of blood -- a measurement of pressure. However, IVC assessment such as maximal diameter and collapsibility DO NOT measure pressure -- one INFERS the pressure.
2. Must Reads
What the Inspiratory Collapse of the IVC is Telling Us: https://pulmccm.org/critical-care-review/inspiratory-collapse-inferior-vena-cava-telling-us/
The Fallible IVC: https://pulmccm.org/cardiovascular-disease-review/that-fallible-ivc/
The IVC collapsibility is complicated. You need to consider the venous return (how quickly is the tube being filled), compliance of the IVC vessel (what is the pressure to volume relationship of the vessel), the intra-abdominal pressure (what is the pressure being exerted onto the tube), the function of the right heart (how quickly can it clear the blood returning from the tube), and transmural pressure to the right heart during pleural pressure excursion from inspiration (changes right heart filling).
ALL
these variables yield IVC diameter and collapsibility during the sniff test, and amidst all that is venous return which represent the elusive "volume status".
However, I would like to direct you to the following excellent treaties by Dr. Jon-Emile Kenny of Heart-Lung.org
and PulmCCM.com
in hope that you gain an appreciation for its intricacies yet fostering the concepts to utilize this sonographic tool clinically.
What the Inspiratory Collapse of the IVC is Telling Us: https://pulmccm.org/critical-care-review/inspiratory-collapse-inferior-vena-cava-telling-us/
The Fallible IVC: https://pulmccm.org/cardiovascular-disease-review/that-fallible-ivc/
Take Home Messages:
- Sonographic IVC assessment is more visually-objective than the physical examination of the JVP
- Ultimately, both techniques intents to CRUDELY estimate CVP (to infer "volume status")
- IVC interpretation is VERY complex - superficial appreciation will result in clinical demise