Optimizing the value of measuring inferior vena cava diameter in shocked patients

Abstract

Point-of-care ultrasound has been increasingly used in evaluating shocked patients including the measurement of inferior vena cava (IVC) diameter. Operators should standardize their technique in scanning IVC. Relative changes are more important than absolute numbers. We advise using the longitudinal view (B mode) to evaluate the gross collapsibility, and the M mode to measure the IVC diameter. Combining the collapsibility and diameter size will increase the value of IVC measurement. This approach has been very useful in the resuscitation of shocked patients, monitoring their fluid demands, and predicting recurrence of shock. Pitfalls in measuring IVC diameter include increased intra-thoracic pressure by mechanical ventilation or increased right atrial pressure by pulmonary embolism or heart failure. The IVC diameter is not useful in cases of increased intra-abdominal pressure (abdominal compartment syndrome) or direct pressure on the IVC. The IVC diameter should be combined with focused echocardiography and correlated with the clinical picture as a whole to be useful.

Keywords: Inferior vena cava diameter; Measurement; Point-of-care ultrasound.

Figure 1

A figure demonstrating the technique to measure the inferior vena cava diameter longitudinally. A small print convex array probe with a frequency of 3-5 MHZ is located in the mid-clavicular line at 90 degrees perpendicular to the skin. The marker is pointing proximally towards the head (arrow).

Figure 2

Three dimensional diagram showing the longitudinal ultrasound measurement of the antero-posterior diameter. Measurements depend on the site and angle at which it crosses the IVC. Section A is the proper one as it crosses the IVC vertically at the midpoint. Section B crosses the IVC vertically but peripherally and gives a false low measurement of the IVC diameter. Section C crosses the IVC obliquely and gives a false high measurement of the IVC diameter. IVC: Inferior vena cava.

Figure 3

Cross section of the abdomen on the left side of the figure showing the liver, inferior vena cava, and aorta. The B mode longitudinal ultrasound image will depend on the angle between the plane of the ultrasound section and the IVC. Three different planes are shown on the cross section (A-B-C) and the corresponding longitudinal IVC images are shown to the right. Longitudinal section A is the proper one as it crosses the IVC vertically at the midpoint. Section B crosses the IVC vertically but peripherally and gives a false low measurement of the IVC diameter. Section C crosses the IVC obliquely and gives a false high IVC diameter measurement. IVC: Inferior vena cava.

Figure 4

Inferior vena cava measurements in a 39-year-old man who was in septic shock and complete renal failure. The upper image is a transverse cross sectional B mode showing the aorta (yellow arrow) and the IVC (white arrow). The lower image is an M mode showing the IVC measurement (A-A) which is 59 mm indicating that the patient was hypovolemic. IVC: Inferior vena cava.

Figure 5

Two point five liters of crystalloids were given to the previous patient over 35 min and repeated measurements of the inferior vena cava diameter were performed. The upper image is a transverse cross sectional B mode showing the IVC (white arrow). The lower image is an M mode showing that the IVC increased to a maximum 1.55 cm with an IVC index of 9% [(1.55-1.41)/1.55]. A-A in the M mode represents the maximum IVC diameter while B-B represents the minimum IVC diameter. IVC: Inferior vena cava.

Figure 6

The patient’s blood pressure quickly improved without evidence of pulmonary oedema. Point A is when images in Figure 4 were taken while point B is when images in Figure 5 were taken.