[Thoracic epidural pressure and peripheral venous pressure in the lower extremity during supine hypotensive syndrome]

After induction of spinal anesthesia, thoracic epidural pressure and left saphenous venous pressure were monitored and recorded during supine hypotensive syndrome in 8 pregnant patients who underwent elective cesarean section.

A 22 G venous catheter was inserted into the left saphena, and an epidural catheter for 18 G needles was positioned 5 cm cephalad in the epidural space through a Tuohy needle at the T 11-12 intervertebral space. Each catheter was connected to a pressure transducer, and recording was started in a supine position immediately after induction of spinal anesthesia with 0.5% isobaric bupivacaine at the L 3-4 intervertebral space.

In all patients, epidural pressure and peripheral venous pressure synchronously increased as soon as they began to recover from hypotension and tachycardia regardless of uterine displacement to the left.

The synchronous increase in both pressures was late after the hypotension probably because sympathetic block with spinal anesthesia inhibited vasoconstriction of the lower extremity, a factor to compensate for supine hypotensive syndrome. Only collateral flow via epidural venous plexus emptying into azygos system could not compensate for decreased venous return to the right atrium from obstructed inferior vena cava, and differences in the degree of compression of the inferior vena cava by gravid uterus would affect the recovery from supine hypotension.