The Pulmonary Artery Catheter in Critical Care
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Slide 1 :
The Pulmonary Artery Catheter in Critical Care
Slide 2 :
Central Venous Pressure Often used to assess volume status Has limited ability to accurately reflect preload Disease states alter relationships between pressure and volume making predictability of volume needs difficult based upon a single measurement Examples include: ARDS, cardiac tamponade, positive pressure ventilation, LV or RV dysfunction
Slide 3 :
Pulmonary Artery Catheter First incorporated into clinical practice in 1970 Allows for direct pressure measurements in: Right atrium (RA) Right ventricle (RV) Pulmonary artery (PA) Allows for measurement of mixed venous oxygen saturation (SvO2) Indirectly measures left heart pressures and cardiac output
Slide 4 :
PA Catheter and Acute Renal Failure Compromised renal perfusion felt to be an important etiology of acute kidney injury Accurately assessing volume status and cardiac function in at risk patients may be important in avoiding morbidity PA catheter allows for measuring cardiac function, volume status and tissue perfusion in an effort to avoid organ failures
Slide 5 :
PA Catheter Insertion Usually inserted via an internal jugular or subclavian vein into the PA outflow tract
Slide 6 :
The PA Catheter with its balloon in the PA outflow tract.
Slide 7 :
The Characteristic Waveforms as the PA Catheter is Advanced Through the Heart en route to the PA
Slide 8 :
With PA Catheter in Place Clinician able to monitor Cardiac output (CO) Intravascular pressures O2 saturation of blood in the PA Isolated numbers attained from the catheter must be interpreted carefully as the manipulation of a parameter and the patient’s response is more important than a single number
Slide 9 :
PA Wedge Pressure (PAWP) Estimates LV preload Left ventricular end diastolic volume (LVEDV) is also known as preload PAWP measures the pressure in the column of blood arising from the LV and extending retrograde from the LA to the PA This reflects the left ventricular end diastolic pressure (LVEDP), a surrogate for LVEDV
Slide 10 :
LVEDV or Preload An important parameter, along with contractility and afterload, for impacting cardiac output If preload is too high or too low, the cardiac myocytes are unable to generate adequate force due to less than ideal sarcomere length The Frank – Starling curve demonstrates this relationship graphically
Slide 11 :
Relationship Between Preload and Stroke Volume.
Slide 12 :
Cardiac Output Typically determined via thermodilution A change in temperature of a known volume of cooled infusate is used to calculate CO How quickly or slowly the cooled infusate mixes with blood determines the CO Accuracy altered by conditions affecting the mixing of infusate and blood Tricuspid regurgitation, intracardiac shunts, cardiac arrhythmias, positive pressure ventilation
Slide 13 :
Oxygen Utilization The difference between O2 content of arterial blood and blood obtained from PA port of PA catheter. Difference, also referred to as O2 extraction, provides insight into patient’s metabolic state and O2 delivery Elevated when delivery poor or metabolic rates high Allows for targets of therapy
Slide 14 :
PA Catheter Pressures Influenced by: Catheter tip location (West zones) Zone 1 – alveolar pressure exceeds PA and vein pressure Zone 2 – PA pressure exceeds alveolar pressure which exceeds venous pressure Zone 3 – PA and venous pressure both exceed alveolar pressure, making it most accurate location for the PA catheter Heart disease Pulmonary hypertension
Slide 15 :
The Effect of the Alveolus on Wedge Pressure Changes Depending Upon the Zone of the Lung Pa = pulmonary artery PA = alveolus Pv = pulmonary vein
Slide 16 :
PA Catheter Pressures Impacted by circumstances altering ventricular compliance Ischemia, LVH, hypertension, tamponade, AS PEEP applied during mechanical ventilation Once greater than 10 cm H2O pressures transmit across vasculature and elevate PAWP Changes during respiratory cycle Intrathoracic pressure varies with inhalation/ exhalation, impacting the PA catheter readings Measure readings at end – exhalation
Slide 17 :
Oxygen Delivery Adequacy of tissue oxygenation depends upon balance between O2 delivery and O2 utilization O2 transport or delivery (DO2): DO2 = cardiac output (CO) x arterial oxygen content (CaO2) DO2 = CO x ((1.36 x gm of hemoglobin x O2 saturation of blood) + (PaO2 x .003)) PaO2 = partial pressure of arterial oxygen
Slide 18 :
Oxygen Delivery Prolonged periods of time with deficient DO2 lead to organ dysfunction, lactic acidosis and ultimately death
Slide 19 :
Oxygen Consumption (VO2) O2 consumption is the amount of O2 extracted from the capillaries as blood passes to the venous side Dependent upon metabolic needs of tissues Determining in the ICU challenging and best accomplished via indirect methods
Slide 20 :
Oxygen Consumption (VO2) Indirectly calculated via the Fick equation O2 consumption equals the difference between arterial O2 delivery and venous O2 return Venous O2 return = venous return (VR) x venous oxygen content (CvO2) CvO2 = (hemoglobin x 1.36 x SvO2) + (PvO2 x .003) Note: PvO2 and SvO2 are drawn from the PA port of the PA catheter and are typically 40 mmHg and 75% in a normal, at rest human PvO2 = partial pressure of venous O2 aka mixed venous O2 tension
Slide 21 :
Oxygen Consumption (VO2) In a normal situation: CvO2 = (15 x 1.36 x 0.75) + (40 x .003) CvO2 = 15 ml O2/100 ml of blood VR in steady state = CO with normal VR = 5 l/min Normal venous O2 return: = 5 l/min x 15 ml/dl x 10 dl/l (correction factor) = 750 ml O2/min
Slide 22 :
Oxygen Consumption (VO2) Normal O2 delivery is 1000 ml O2/min O2 extracted = 1000 ml O2/min delivered - 750 ml O2/min returned O2 extracted = 250 ml/min This is expressed in equation: VO2 = (CO x CaO2) – (VR x CvO2) CO = VR in steady state VO2 = CO x (CaO2 - CvO2)
Slide 23 :
Blood Flow = Cardiac Output = 5 Lmin-1
Slide 24 :
Oxygen Extraction As tissues’ metabolic activity increases so must O2 delivery Accomplished via increase in flow Occurs globally via elevated CO Occurs locally by recruitment of capillary beds through auto regulation Tissues able to increase O2 extraction if delivery fails to meet the metabolic needs Manifest as lower SvO2
Slide 25 :
Oxygen Extraction The oxygen extraction ratio (O2 ER) is a simple measure of global O2 extraction O2 ER = VO2/DO2 Normally 24 – 28%
Slide 26 :
Trauma Victim with Hypovolemic Shock
Slide 27 :
PvO2 and SvO2 PvO2 is the most reliable, single physiologic indicator of overall balance between O2 supply and demand PvO2 is a mixture of venous effluent from all perfused capillary beds PvO2 and SvO2 correlate well with O2 reserve and tissue oxygenation when flow is distributed according to metabolic need PvO2 < 28 mmHg may correlate with decreased survival
Slide 28 :
Central Venous O2 Saturation (SCvO2) Measures O2 saturation in the superior vena cava May be measured continuously with available fiberoptic catheters or intermittently with venous blood gases More readily available as does not require a PA catheter Reflects CvO2 of blood returned from upper body SCvO2 typically higher than SvO2 but trend track in parallel
Slide 29 :
Continuous SCvO2 Utilized as part of resuscitation in sepsis Rivers et al demonstrated a survival advantage when incorporated into a sepsis resuscitation pathway with goal of > 70% Rivers et al, NEJM, 2001
Slide 30 :
Lactic Acid (LA) and PvO2 Lactic acidosis in critically ill a marker of poor prognosis The failure to clear lactate over time particularly troubling Lactic acidosis not always due to anaerobic metabolism
Slide 31 :
Lactic Acidosis LA levels represent balance between production and clearance May be altered in critical illness In sepsis: Increased glycolytic flux Impaired pyruvate utilization Absence of frank O2 deprivation Best predictor of anaerobiosis and hyperlacticacidemia is critical PvO2 of 27 mmHg
Slide 32 :
PvO2 and SvO2 Thresholds PvO2 below 28 torr and SvO2 below 50% imply severe O2 deficits and must be corrected if survival expected
Slide 33 :
Continuous SvO2 Monitoring Incorporated into PA catheter SvO2 changes rapidly when DO2 altered May allow for rapid interventions as patients’ condition changes
Slide 34 :
PA Catheter Use in ICU Utility and safety debated When evaluate studies, use not shown to have impact on mortality Incorporated when patients have refractory hypoxemia, persistent hypotension or shock, especially with renal and cardiac involvement
Slide 35 :
Diagnosis Group(No. of ICU’s with > 10 Patients)
Slide 36 :
Probability of PAC, Survival Probability, and Presence of Full-Time ICU Physician
Slide 37 :
What is prudent use of PA catheter in a critically ill patient? In septic shock with acute kidney injury when fluid management is particularly complicated, a PA catheter may help guide further resuscitative efforts
Slide 38 :
Newer Methodologies for Obtaining CO Data The arterial pressure wave form results from interactions of the vascular system and the ejected SV Analyzing the waveform allows for determination of SV CO then simply calculated by equation: CO = HR x SV
Slide 39 :
Newer Methodologies for Obtaining CO Data Stroke volume variation Determined with arterial pressure cardiac output monitors Shown to predict volume responsiveness in mechanically ventilated patients An algorithm utilizing this concept follows
Slide 40 :
Slide 41 :
Conclusion The PA catheter is a valuable tool for understanding physiology Oxygen delivery and utilization are important parameters in determining the management of critically ill patients Newer technologies exist and may help better understand the fluid responsiveness of a patient
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