Question 15

Created on Thu, 12/17/2015 - 08:14
Last updated on Mon, 07/18/2016 - 19:16
Pass rate: 62%
Highest mark: 7.3

Other SAQs in this paper

Other SAQs on this topic

a)    Describe the ultrasound features that help differentiate the internal jugular vein and the carotid artery?    (70% marks)

b)    List the complications of central line insertion.    (30% marks)

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College Answer

a)

The IJ vein:

Has an elliptical shape Is larger

More collapsible with modest external surface pressure than the carotid artery (CA), which has rounder shape, thicker wall, and smaller diameter

A Valsalva manoeuvre will further augment their diameter

The IJ vein diameter varies depending on the position and fluid status of the patient and is particularly useful in hypovolemic patients.

Adding Doppler, if available, can further distinguish whether the vessel is a vein or an artery. Colour flow Doppler demonstrates pulsatile blood flow in an artery in either SAX or LAX orientation.

A lower Nyquist scale is typically required to image lower velocity venous blood flows. At these reduced settings, venous blood flow is uniform in colour and present during systole and diastole with laminar flow, whereas arterial blood flow will alias and be detected predominantly during systole (Figure 5) in patients with unidirectional arterial flow (absence of aortic regurgitation).

A small pulsed-wave Doppler sample volume within the vessel lumen displays a characteristic

Veins are thin walled and compressible and may have respiratory-related changes in diameter. In contrast, arteries are thicker walled, not readily compressed by external pressure applied with the ultrasound probe and pulsatile during normal cardiac physiologic conditions.

b)

Pneumothorax Air embolus

Haematoma Haemorrhage Thrombosis Stenosis

Arterial puncture / catheterisation Incorrect catheter tip position

Central vein perforation Tamponade

Cardiac arrhythmia

Embolised, fractured or irretrievable guide wires Infection

Discussion

From the central venous cannulation chapter, the complications of CVC insertion are as follows:

  • Immediate
    • Failure of procedure
    • Pneumothorax
    • Haemothorax
    • Retroperitoneal haematoma
    • Arterial puncture
    • Local haematoma
    • Guidewire-induced arrhythmia
    • Thoracic duct injury
    • Guide wire embolism
    • Air embolism
  • Early
    • catheter blockage
    • chylothorax
    • catheter knots
  • Late
    • Infection : 2.5 infections/ 1000 catheter days
    • catheter fracture
    • vascular erosion
    • vessel stenosis
    • thrombosis
    • osteomyelitis of clavicle (subclavian access)

This is the first time the college have asked about the ultrasound features which help us distinguish between different neck vessels. For most of us, the two are fairly easy to tell apart, but... if one were asked to articulate exactly how they differ, one might come to trouble. "Squishy" and "roundly pulsatey" are probably inappropriately loose terms to use in this context. Instead, please find the table below:

Ultrasonographic features
of the Internal Jugular Vein and the Carotid Artery
Features Internal Jugular Vein Carotid Artery
Shape Elliptical Circular
Size Larger Smaller
Wall thickness Thin Thick
Pulsatility Occasionally, might pulsate (eg. in severe TR) Always (should be ) pulsatile
Compressibility Compressible Non-compressible
Response to Valsalva Increases in diameter Remains unchanged with Valsalva
Colour Dopper May demonstrate pulsatile blood flow Should demonstrate pulsatile blood flow
Flow direction Flow should be laminar and present during both systole and diastole Flow should be laminar and present only during systole
Nyquist scale Low scale required (i.e. low velocity flow) High scale required (or, aliasing occurs)
     

References

Williams, William M. Vascular ultrasound of the neck: an interpretive atlas. Lippincott Williams & Wilkins, 2001.