Wet, Dry, or Even? Some Ways of Looking at Volume Status without a Pulmonary-Arterial Catheter Anne K. Sutherland, MD Critical Care Medicine St. 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 Interactions In 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 Interactions In volume depleted patient on PPV: Collapse of intra-abdominal veins and SVC occurs as a result of positive intrathoracic pressure This 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 PPV 2. CO measurement - transpulmonary thermodilution and pulse contour analysis 3. Extravascular Lung Water Index 4. Global End-diastolic volume index 5. 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)‏

Usin g 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 Group PAC/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. thermodiluti on Every 3s GEDV, EVLW, SVV, PPV Severe Vasc. Disease, IABP, arrythmias PulseCO/ LiDCO Regular a- line Transpulm. thermodiluti on 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.