By Charles Draznin, MD and Peter Keenan, MD
Imagine this possible scenario: A 70 year-old male with pneumonia and sepsis develops hypotension, and your team wants to place a central venous catheter to give pressors.
Femoral vein access is precluded by a candidal skin infection under the abdominal pannus. He cannot tolerate lying fully recumbent due to dyspnea and thoracic kyphosis, and has very collapsible internal jugular veins on your pre-procedure ultrasound scan. Additionally, he has a large beard, and it seems likely to be difficult to optimally sterilize the skin of the neck for an internal jugular cannulation. You decide to obtain subclavian access, and start reviewing the landmark approach with your residents, but they ask you if there is a better way. How can ultrasound assist the placement of a subclavian line? Is it better than the landmark technique, and if so, how? Is it faster? Does it have shortcomings? What evidence can guide your decision? Darn medical students...
There is a growing amount of literature on the ultrasound-guided subclavian central venous access. Factors such as traumatic injuries, thrombosis, and patient anatomy can make this site preferred over the internal jugular or femoral veins. There is some thought that the subclavian is less prone to collapsibility than the internal jugular due the support of surrounding structures. Multiple studies have evaluated the use of ultrasound in the placement of femoral and internal jugular venous access, but the literature regarding subclavian access is now expanding as well.
A recent systematic review and meta-analysis evaluated the use of ultrasound in the placement of subclavian central venous catheters. Ultrasound modalities used in the reviewed studies included dynamic 2D imaging (real-time guidance), static 2D imaging, and Doppler only. As a whole, these ultrasound modalities offer an improved safety profile compared to the landmark technique. A subgroup analysis evaluating the performance of dynamic 2D guidance (and discarding the studies with static imaging or Doppler only) found an even stronger safety profile. There did not necessarily appear to be a time-saving benefit with ultrasound, but real-time guidance led to fewer failed catheterizations (risk ratio 0.243 in the real-time group). There were fewer adverse events, such as pneumothorax (odds ratio 0.339), hemothorax (OR 0.235), arterial punctures (OR 0.341), and hematomas (OR 0.351) in the ultrasound group as a whole, and even fewer in the real-time guidance group. In general, complications were much less common in the real-time group compared to the landmark group (OR 0.298) (Lalu)
The vein can be approached from either an infraclavicular or supraclavicular approach. It is as of yet uncertain if one route is superior. A recent study compared ultrasound views obtainable for the infra- and supraclavicular approaches from both the right and left. In this study, the veins were not actually cannulated, but the physicians were asked to rate the perceived level of difficulty of each approach. The supraclavicular approach to the right subclavian vein ranked as most favorable, but it is not known if these findings would translate into an easier procedure or not.
The infraclavicular approach is performed using an in-plane approach enabling full needle visualization to avoid puncturing the subclavian artery and lung. This is done by placing the transducer just below the clavicle so the subclavian vein is visualized in long axis. The needle is then inserted laterally in the same plane until puncture of the vein is observed
The subclavian vein can also be approached from the supraclavicular approach. To gain supraclavicular access to the subclavian vein, the transducer is placed transversely on the neck and the subclavian vein is found by following the course of the internal jugular vein inferiorly.
Using your linear transducer, you and your residents pre-scan the right and left subclavian veins to determine your optimal approach. You settle on the left infraclavicular approach. You achieve first attempt success in the long axis. Your order for a portable chest x-ray is delayed as the x-ray technician is helping with a trauma patient, so you decide to confirm position with ultrasound. With the linear transducer, you scan the left and right internal jugular veins and the right subclavian, without seeing a malpositioned catheter tip. A quick scan of the anterior chest bilaterally reveals excellent lung sliding, ruling out iatrogenic pneumothorax. Switching to the phased array transducer, you look for the presence of a catheter tip in the right atrium or ventricle. No aberrant catheter tip is seen, so you inject agitated saline. You note the appearance of microbubbles with laminar flow in the right atrium, suggesting the catheter is correctly positioned in the inferior portion of the superior vena cava, and not in an artery or intra-atrial. The patient’s hemodynamics improve on pressors, and the intensivist thanks you for a central line well done.