Table 4.

Advantages and disadvantages of the various dynamic parameters used to predict preload responsiveness.

Method	Advantages	Disadvantages
Respiratory changes in CVP	Most critically ill septic patients have an IJ or SC CVL	It requires that the inspiratory effort be significant—a fall in PAWP of ≥2 mmHg was used in the original study by Magder et al. [11]
	It can be used in spontaneously breathing patients
Respiratory changes in IVC diameter	It is non-invasive and requires an ultrasound with M-mode which is now becoming widely available	It is only reliable in mechanically ventilated patients who are receiving ≥8 mL/kg PBW tidal volume, are not making any significant respiratory efforts, and are in NSR
	It is easy to learn and teach	It may not be reliable in conditions associated with IAH, for example, obesity, massive ascites, abdominal compartment syndrome
	It can be easily repeated as often as necessary
Respiratory changes in SVC diameter	It is more accurate than respiratory change in IVC diameter	It is semi-invasive and requires TEE and expertise in using it
		It is not continuous
		It too is only reliable in mechanically ventilated patients who are receiving ≥8 mL/kg PBW tidal volume, are not making any significant respiratory efforts, and are in NSR
PPV	PPV can be calculated manually from a 30 sec printout of the arterial blood pressure waveform	It is invasive and requires an arterial line
		It is only reliable in mechanically ventilated patients who are receiving ≥8 mL/kg PBW tidal volume, are not making any significant respiratory efforts, and are in NSR
SVV-FloTrac Vigileo	It does not require frequent recalibration	It is invasive and requires an arterial line
	It provides additional data: SV, CO	It is only reliable in mechanically ventilated patients who are receiving ≥8 mL/kg PBW tidal volume, are not making any significant respiratory efforts, and are in NSR
SVV-PiCCO Plus	It provides additional data: SV, CO, TBV, and EVLW	It is invasive and requires an IJ or SC CVL and a femoral arterial line with a thermistor
		It requires frequent recalibration
		It is only reliable in mechanically ventilated patients who are receiving ≥8 mL/kg PBW tidal volume, are not making any significant respiratory efforts, and are in NSR
PVI	It is noninvasive	It is only reliable in mechanically ventilated patients who are receiving ≥8 mL/kg PBW tidal volume, are not making any significant respiratory efforts, and are in NSR
	It is easy to use	It is not reliable if peripheral perfusion is severely compromised
	It does not require calibration
		Semi-invasive and requires TEE or esophageal Doppler US and expertise in using it
		It is only reliable in mechanically ventilated patients who are receiving ≥8 mL/kg PBW tidal volume, are not making any significant respiratory efforts, and are in NSR
		It suffers from additional limitations:
Respiratory changes in aortic blood flow velocity	Esophageal Doppler US monitoring uses a smaller esophageal probe than TEE and therefore is less invasive; it can also be left in place for continuous monitoring; it also requires less training to use and is less expensive	Long learning curve with a lack of reproducibility
		Inability to obtain continuous reliable measurements
		Requirement for 24-hour availability
		Practical problems related to the presence of the probe in the patient's esophagus
		As esophageal Doppler probes are inserted blindly, the resulting waveform is highly dependent on correct positioning
Respiratory changes in brachial artery blood flow velocity	It is non-invasive and requires only a US with Doppler which is now becoming widely available in ICUs	It is only reliable in mechanically ventilated patients who are receiving ≥8 mL/kg PBW tidal volume, are not making any significant respiratory efforts, and are in NSR
	It is easy to learn and teach as demonstrated by a study where residents used it after learning the technique
PLR maneuver	It can be used in spontaneously breathing patients	It requires continuous CO monitoring by a technology with a rapid response time, for example, USCOM, NICOM, FloTrac Vigileo, PiCCO, or PAC with such capability
	It can be used in patients with arrhythmias
	It can be completely noninvasive if CO is measured by a noninvasive method, for example, USCOM or NICOM

CVP: central venous pressure, IJ: internal jugular, SC: subclavian, CVL: central venous line, PAWP: pulmonary artery wedge pressure, IVC: inferior vena cava, PBW: predicted body weight, NSR: normal sinus rhythm, IAH: intra-abdominal hypertension, SVC: superior vena cava, TEE: transesophageal echocardiography, PPV: pulse pressure variation, SVV: stroke volume variation, SV: stroke volume, CO: cardiac output, TBV: thoracic blood volume, EVLW: extravascular lung water, US: ultrasound, USCOM: ultrasonic cardiac output monitor, NICOM: noninvasive cardiac output monitor.