Table 2.

Different methods of measuring CO or arterial blood flow velocity^∗ during PLR maneuver.

Invasive	Semi-invasive	Noninvasive
Thermodilution	US	US
PAC (transpulmonary thermodilution)	∗Esophageal Doppler	Transthoracic echocardiography
PiCCO (aortic transpulmonary thermodilution)		Transthoracic USCOM
Arterial BP waveform analysis		∗Femoral arterial Doppler
FloTrac Vigileo		Bioreactance
		NICOM

CO: cardiac output, PLR: passive leg raising, PAC: pulmonary artery catheter, US: ultrasound, USCOM: ultrasonic cardiac output monitor, NICOM: noninvasive cardiac output monitor.