Internal Jugular Vein and Spinal-induced Hypotension

To visualize the internal jugular veins ( IJVs) a linear transducer with a 5-10 MHz linear probe was placed over the neck, and the IJV was measured just below the bifurcation of the sternal and clavicular heads of the muscle. The IJV measurements were performed on the transverse axis over a single respiratory cycle. Patients with evidence of IJV thrombosis were excluded. IJV measurements included the antero-posterior maximum diameter at the end of expiration (IJVmax), the antero-posterior mimimum diameter/area at the end of inspiration (IJVmin), the IJV collapsibility index (IJV-CI) during spontaneous, quiet, breathing, \[(IJVmax - IJVmin area)/IJVmax\] and the ratio (R) of IJVmax-to-IJV-CI.