Internal Jugular Vein
This is typically the most common location for central access. One can easily see vessel size and patency, spatial relation to the carotid artery, and compressibility. All of these can inform your decision-making and strategy for optimizing your chances of success. With the introduction of ultrasound, some researchers have looked at a few factors and how they impact vessel size, vessel alignment etc.
Optimizing Neck Position
With head rotation, one changes both vessel size and vessel alignment
Gwak et al compared both vessel size and IJ relationship to the carotid at 0º (neutral), 40º and 80º of head rotation
Vessel size increased rotating from 0º to 80º
Vessel overlap also increased during the same rotation
The authors recommend head rotation of about 40º to optimize size, but minimize vessel overlap
One might also pre-scan to ascertain the ideal head position prior to sterile prep and drape
Trendelenburg
There is a two-fold benefit to placing a patient in Trendelenburg:
Reduces likelihood of entrainment of an air embolism during the procedure
May increase vein size due to increased venous return, though Verghese et al found it less effective in infants
The authors suggested this may be due to decreased vessel compliance/elasticity in infants
Valsalva/PEEPIncreases intrathoracic pressure, which may obstruct venous flow and cause IJ enlargement
Valsalva: This can be simulated in an anesthetized patient by manually sustaining increased airway pressure
PEEP: 5-10cm H₂O may increase intrathoracic pressure and enlarge the IJ
Liver Compression
Compression of the liver causes increased VR, which in turn increases cross-sectional area of the IJ
While perhaps not the most effective, I find it particularly useful if I am having difficulty threading a wire once I have free flow during needle aspiration. With concurrent liver pressure, the vein may be briefly stented open long enough to slip a wire in.
Gwak, M.J., Park, J.Y., Suk, E.H. and Kim, D.H., 2010. Effects of head rotation on the right internal jugular vein in infants and young children. Anaesthesia, 65(3), pp.272-276.
Verghese, S.T., Nath, A., Zenger, D., Patel, R.I., Kaplan, R.F. and Patel, K.M., 2002. The effects of the simulated Valsalva maneuver, liver compression, and/or Trendelenburg position on the cross-sectional area of the internal jugular vein in infants and young children. Anesthesia & Analgesia, 94(2), pp.250-254.