Wet, Dry, or Even? Some Ways of Looking at Volume Status without a Pulmonary-Arterial Catheter

1. Anne K. Sutherland, MD Critical Care Medicine St. Barnabas Hospital March 27, 2010 Wet, Dry, or Even?Some Ways of Looking at Volume Status without a Pulmonary-Arterial Catheter

2. Pulmonary Arterial Catheter

3. 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)‏

4. 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

5. 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%.

6. Results of Osman

7. 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)‏

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

18. 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

19. 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%)‏

20. 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.

21. 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

22. Devices to Automatically analyze waveforms – for SVV and PPV • PiCCO • LiDCO/Pulse Plus • Flotrac/Vigilo

23. 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: • Fluid responsiveness: SVV and PPV • CO measurement - transpulmonary thermodilution and pulse contour analysis • Extravascular Lung Water Index • Global End-diastolic volume index • Cardiac Index • Requires calibration with a thermal bolus, and thus needs a special femoral a-line to determine CO using transpulmonary dilution

24. 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

25. On a PiCCO Monitor

27. 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

28. 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

29. 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.

30. 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.

31. 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)‏

32. Using FLoTrac to Guide Goal Directed Therapy in High-Risk Elective Surgical PatientsMayer 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.

33. PULSE Study GroupPAC/PiCCO Use and Likelihood of Success EvaluationUchino 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.

35. 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.