The primary indication for ultrasound usage before central venous catheterization is to aid the choice of vessel. Advantages, disadvantages and (relative) contraindications for internal jugular, subclavian and femoral vein cannulation will be discussed here and how ultrasound could aid the physician’s choice.
Internal jugular vein
Advantages of internal jugular vein cannulation are the high success rate, low mechanical complication risk, the vessel is often easily visualized by ultrasound and, usually, has a large cross-sectional diameter.15 A disadvantage is the increased risk for infections compared to subclavian cannulation, especially for long-term indwelling catheters.11 Increased intra-cranial pressure is a relative contra-indication due to the possible obstruction of venous drainage. Pre-scanning of the internal jugular vein should be done to assess the anatomy – i.e. the anatomic relationship of the internal jugular vein and carotid artery – and the patency of the vessel.
A major advantage of subclavian vein cannulation is the low infection risk in comparison to internal jugular and femoral vein cannulation. Disadvantages are that insertion requires more experience and carries a higher mechanical complication risk (pneumothorax).11 Bilateral or contralateral lung abnormalities are, therefore, a relative contraindication. Pre-scanning of the subclavian vein should be done to assess the anatomy – sometimes the vein is overlapped by the subclavian artery – and patency of the vessel.
Advantages of femoral vein cannulation are the high success rate and the low mechanical complication rate. Disadvantages of femoral vein cannulation are the higher infection risk in comparison to internal jugular and subclavian vein cannulation and the mobility impairment of patients. It is, therefore, less suitable for mobile patients. Abdominal endovascular stent grafting is a relative contraindication. Pre-scanning should be done to assess the anatomic relationship with the femoral artery and check the patency of the vessel.
Acquisition is, following the I-AIM model, subdivided into patient, probe, picture and protocol considerations. These subdivision will be discussed here.
Positioning of the patient is critical in evaluating the central veins. The optimal position for evaluation of the internal jugular or subclavian vein is the Trendelenburg position. It utilizes the force of gravity to pool blood toward the head from the lower extremities and, in turn, increases the cross-sectional area of the veins above the diaphragm.16 Following this line of reasoning, the optimal position for evaluation of the femoral vein is the anti-Trendelenburg position.
A high frequency (10-12 MHz) linear probe is the optimal choice for the pre-scanning of the entry vein.