Wet, Dry, or Even?Some Ways of Looking at Volume Status without

a Pulmonary-Arterial Catheter

Anne K. Sutherland, MDCritical Care MedicineSt. Barnabas Hospital

March 27, 2010

Pulmonary Arterial Catheter

PACs Pulmonary Artery Catheters are no longer

deemed to be an effective tool for monitoring the volume status of the vast majority of critically ill patients.

SUPPORT was an observational study of critically ill patient by Conners et al that showed PACs to be associated with increased mortality and increased utilization of resources. (JAMA 1996)

Harvey et al in the PAC-Man trial showed that there was no difference in the mortality of patients managed either with or without a PAC. (Lancet, 2005)

FACTT The FACTT trial showed that PAC-guided therapy

did not improve survival or organ functions but was associated with more complications than CVC-guided therapy.

No difference in mortality between the liberal and conservative fluid management

Conservative strategy improved lung function, increased ventilator and ICU free-days

PAOP and CVP: No better than flip of a coin

Osman et al CCM Jan 2007 Retrospective study of all fluid challenges in 96

mechanically ventilated patients with severe sepsis or septic shock between 2001 and 2004 who were being monitored with a pulmonary arterial catheter.

Patients were given a volume challenge of 500 cc of 6% hydroxyethyl starch based on clinical signs of hypoperfusion.

Patients were divided into groups of responders and non responders based on whether or not the cardiac index increased by 15%.

Results of Osman

Physical Exam

Orthostatic hypotension – postural pulse increase of >30 beats/min has a specificity for hypovolemia of 96% (McGee, JAMA, 1999)

Postural hypotension occurs in up to 10% of normovolemic patients

Supine tacycardia is specific (96%), but insensitive (~10%)

Supine hypotension is also specific and insensitive

(McGee, JAMA, 1999)

The problem: How do I decide if my hypotensive septic patient needs fluids, pressors, or an inotrope?

Septic patients require volume Giving pressors to an under-resuscitated

patient can cause tissue hypoxemia and ischemia

However, giving too much fluid may lead to prolonged ventilatory support

Giving fluid is deleterious when the patient will not respond to the fluids with an increase in Cardiac output

The Perfect Volume Status Monitor

Fast Easy to learn Validated in all critically ill patients. (medical,

surgical, trauma, neurosurgical on and off positive pressure ventilaiton)

Available outside of the ICU, not require any highly specialized equipment

Give an easy answer

Dynamic Methods to look at Hemodynamics and Volume Status

in the MICU Take advantage of the Heart-Lung interactions

during positive pressure ventilation. Arterial Line Monitoring with dynamic analysis

of the wave form and pulse pressure variability Echocardiography to predict volume

responsiveness (not going to be covered in this 20 minute talk!)

LV, IVC, SVC

Fluid Responsiveness

A patient who is fluid responsive will have a significant (>15%) increase in CO in response to a fluid challenge.

This indicates that the heart is on the steep portion of the Frank-Starling Curve

Volume Responsiveness in Critically Ill patients

Many of our critically ill, hypotensive patient are on positive pressure ventilation

PPV causes changes in venous return, which is accentuated in hypovolemic patients

It is possible to take advantage of the swings in venous return in order to determine the fluid responsiveness of hypotensive patients

2 major tools to look at this: Echo Arterial Line – looking at changes in the pulse

contour, and in the pulse pressure

Positive Pressure and Venous Return – Taking advantage of

Heart-Lung InteractionsIn a volume

resuscitated patient: Venous return does not

fall during inspiration on PPV

Intrathoracic pressure is positive

Intrabdominal pressure also rises

Pressure gradient between the abdomen and thorax is maintained

Positive Pressure and Venous Return – Taking Advantage of

Heart-Lung InteractionsIn volume depleted patient on PPV:Collapse of intra-abdominal veins and SVC occurs as a result of positive intrathoracic pressureThis results in a fall in venous return RV stroke volume, LV preload and cardiac output

Maximum SBP occurs during inspiration in PPV

Maximum RV pre-load occurs during expiration There is a lag secondary to pulmonary transit time,

which results in increased LV stroke volume during inspiration

Additionally, there is an increased return of blood from the lung to the LV during inspiration Pulmonary blood vessel compression Decrease in left ventricular after-load

Interventricular effects: A decrease in RVSP in inspiration leads to increased

LV compliance which leads to an increase in LV pre-load

Min SBP occurs during expiration in PPV

Positive pressure during inspiration causes a decrease in venous return, which results in decreased right ventricular stroke volume

There is a lag of 2-3 heart beats secondary to pulmonary transit time, which leads to the decreased LV SV during expiration

Michard 2000 cont. The magnitude of

respiratory changes in LV stroke volume and pulse pressure should be an indicator of biventricular pre-load dependence

40 septic, hypotensive patients with a-lines were studied on positive pressure ventilation

Michard, AJRCCM, 2000

Michard 2000 cont. The effects of volume

expansion upon CI as measured with a PAC was analyzed

Patients with a baseline ΔPp >13% were very likely to respond to VE by increasing CI by >15% (ppv 94%)

Michard 2000 cont.

Michard – they used PPV as calculated themselves by looking at the wave form, with their own analysis

In the 40 patients studied, 9 patients were paralyzed, and 8 more had to be temporarily paralyzed for the readings.

Pulse Pressure Relationship to Stroke Volume

The compliance of the aorta is not a linear relationship between pressure and volume

The same PPV may theoretically result from large swing in volume in a patient with compliant arteries, or smaller swings in SV in stiff arteries

Wave reflection – pulse pressure from an a-line is the combination of the incident pressure wave and reflected wave from the periphery

Damping Aortic flow during systole – outflow tends to be more

continuous. SVV measured from pulse contour analysis

Devices to Automatically analyze waveforms – for SVV and PPV

PiCCO LiDCO/Pulse Plus Flotrac/Vigilo

PiCCO PiCCO is a device made by Phillips that enables

continuous hemodynamic monitoring using a femoral or axillary thermodilution a-line (proprietary) and a central venous line.

Looks at both static and dynamic parameters:1. Fluid responsiveness: SVV and PPV2. CO measurement - transpulmonary thermodilution and

pulse contour analysis3. Extravascular Lung Water Index4. Global End-diastolic volume index5. Cardiac Index

Requires calibration with a thermal bolus, and thus needs a special femoral a-line to determine CO using transpulmonary dilution

PiCCO

PPV – Pulse Pressure Variability – the difference between systolic and diastolic pressure throughout the respiratory cycle has been shown to be able to predict fluid responsiveness

An index of 13% discriminates between fluid resonders (an increase in CO of >15%) and non-responders

PPV has been shown to predict fluid responsiveness in CABG patients, patients with septic shock and ALI

On a PiCCO Monitor

PiCCO

SVV – determined by analysis of the continuous arterial pulse contour – uses the area under the systolic curve for beat-to-beat determination of stroke volume and their variation over the respiratory cycle – can also use for determining volume responsiveness

> 10% is considered to be responsive

PiCCO

Marx et al in 2004 – with 10 septic patients used PiCCO's calculation of SVV to determine whether or not to volume load a patient. (all patients were in sinus rhythm)

PiCCO was just as good as PAC as determining whether or not a patient would respond to a fluid bolus

LiDCO

Made by the LiDCO group in London Measures Cardiac output using a small dose of

lithium injected in the periphery and then generating a arterial lithium concentration-time curve by withdrawing blood past a lithium sensor attached to the patient's a-line

It then uses proprietary software to calculate continuous beat-to-beat cardiac output, by analysis of the arterial blood pressure tracing.

FloTrac/Vigileo

No calibration needed, derives measurements based on compliance and patient characteristics (gender, age, height and weight – derived from experimental cadaver data)Measures the pulsitility of the arterial waveform by calculating the standard deviation of the arterial pressure wave over a 20s period – multiplied by the compliance

The initial software autocalibrated every 20 minutes, leading to bad ROC when compared to PACs – however it now autocalibrates every minute.

FloTrac and Cardiac Output

FloTrac has been proven to be an acceptable way of monitoring CO in patients undergoing CABG (de Waal, CCM, 2007)

SVV as measured by FloTrac has been shown to be higher in patients who responded to fluid loading: 18 vs 4 (p <0.001) (Cannesson, Eur J of Anesth, 2007)

Using FLoTrac to Guide Goal Directed Therapy in High-Risk Elective Surgical Patients

Mayer et al. Critical Care 2010 Randomized, Single-Center Study of 60 patients

Intra-operative GDT using a protocol based on enhanced hemodynamic variables derived by the Flo-Trac/Vigileo device reduced the LOS in high-risk patients undergoing major abdominal surgery compared with a standard management protocol.

Both groups received the same amount of fluids, but the intervention group received more colloid.

The incidence of complications was reduced in the enhanced monitoring group.

No difference between the standard and enhanced monitoring protocol groups was found with regard to ICU stay.

PULSE Study GroupPAC/PiCCO Use and Likelihood of Success Evaluation

Uchino et al 2006

Multi-center observational study of 331 patients with either a PAC or PiCCO (192 PiCCO 150 PAC, 11 with both)

No difference in outcomes either way (although the PiCCO patients tended to be in positive fluid balance, and to be on the vent longer)

Demonstrates the difficulty in studying the effect of a tool on outcomes – how you get data is important – but what you do with it actually affects patient outcome.

Invasive Intermittent CO

Contin. CO

Addit'l Variables Limits

PiCCO Plus

Femoral thermistor-tipped catheter

Transpulm. thermodilution

Every 3s

GEDV, EVLW, SVV, PPV

Severe Vasc. Disease, IABP, arrythmias

PulseCO/LiDCO

Regular a-line

Transpulm. thermodilution

Beat to Beat SVV

SVV/PPV, IABP, arrythmias

FloTrac/Vigelo

Regular a-line None Every

20s SVV

Spont. Breathing, IABP arrythmias

Problems with Dynamic Measurements

Mechanical problems with a-line (dampening, air bubbles, etc)

Arrhythmias – variation no longer a reflection of changes due to mechanical ventilation (esp. with patients with a-fib or frequent PVCs)

Small pleural pressure changes – ie in patients with low tidal volumes, spontaneously breathing or open chests.

Just because the patient has increased SVV or PVV does not mean that she needs volume expansion.