Emergency lectures - Monitoring patients in shock
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Emergency lectures - Monitoring patients in shock Presentation Transcript

  • 1. Monitoring the Patient in ShockHaney Mallemat, MDDepartment of Emergency MedicineDepartment of Critical CareUniversity of Maryland School of MedicineBaltimore, MD USA
  • 2. Outline • Why do we monitor patients in shock? • What are we monitoring in shock? • How do we monitor patients in shock?
  • 3. Why do We monitorPatients in Shock?
  • 4. What is Shock? • Shock occurs when tissue perfusion is inadequate to meet cellular needs • There are four types of shock: – Hypovolemic – Obstructive – Cardiogenic – Distributive
  • 5. Why Monitor Patients in Shock? • We monitor patients in shock to ensure adequate tissue perfusion • Tissue perfusion is important for oxygen delivery • Oxygen delivery is important for normal cellular function and metabolism
  • 6. Why is Perfusion Important? • Shock results in a low-flow state and reduced tissue perfusion • Reduced tissue perfusion results in: – Anaerobic Metabolism – Lactic Acidosis – Cellular Dysfunction
  • 7. What are we monitoring inShock?
  • 8. 3 Things Determine Perfusion: 1. Cardiac Output: – The heart is a pump that delivers blood to tissues 2. Blood Pressure: – Is the driving force for organ perfusion 3. Cardiac Preload: – The heart must be adequately filled to produce an effective stroke volume – Certain types of shock result in a reduction of cardiac preload and this must be corrected
  • 9. These factors are interrelated
  • 10. Cardiac output
  • 11. Cardiac Output (CO) • Cardiac Output = Heart Rate X Stroke Volume • Typically, we can only increase cardiac output by increasing stroke volume • Stroke volume is determined by two things: – Increasing ventricular volume – Increasing myocardial contractile strength • Heart rate usually increases by sympathetic stimulation during shock
  • 12. How to Increase CO • Increase ventricular filling by increasing cardiac preload – This is the reason we give fluid boluses during shock • Increase myocardial contractility (called ionotropy) – Fluid boluses produce better myocardial fiber overlap and better cardiac contractility – We can also use ionotropes (Dobutamine)
  • 13. Blood pressure /mean arterial pressure
  • 14. Blood Pressure • Blood pressure is the “driving pressure” to perfuse organs and it is directly related to cardiac output – MAP = CO x SVR • Mean arterial pressure (MAP) is the parameter measured during shock – DP = Diastolic Pressure – SP = Systolic Pressure
  • 15. Monitoring MAP • There is no “normal” MAP • A “normal” MAP is relative to each patient and exists when organs are adequately perfused • Certain patients may need higher MAPs – Example: patients with chronic hypertension • However, there has never been a benefit shown for a MAP >65 when patients are in shock
  • 16. Cardiac preload
  • 17. Cardiac Preload • Not every hypotensive patient will improve with fluid boluses so we need to determine who will benefit. • Assessing preload responsiveness determines which patients will increase their stroke volume in response to a fluid bolus.
  • 18. Preload responsiveness • During resuscitation, we always want S EC TIO N I RES U S C ITATIO N S KILLS AN D TEC H to be on the steep portion of curve – Increasing end-diastolic volume Stroke volume means big increase in stroke volume • We do not want to be on the flat portion of the curve End-diastolic volume F ig. 4. 2 Frank-S tarling c urve demons trating the relations hip – Increasing end-diastolic volume between end-dias tolic pres s ure (preload) and s ys tolic performanc e (s troke volume). results in little increase in stroke B OX 4. 1 Hins haw and C ox C las s i fi c ation of C irc ulatory S hoc k volume Hypovolemic H e m o rrh age Th ird s p ac ing o f flu id s • Ile u s • B u rns • Pancre atitis C ardiogenic
  • 19. How do We monitorPatients in Shock?
  • 20. Assessing overallperfusion
  • 21. Assessing Overall Perfusion • Physical exam can assess overall tissue perfusion: – Assess mental status • Are patients confused?, dizzy?, drowsy? – Assess skin • Is the skin cool or mottled? – Assess kidney perfusion • Is urine output less than 0.5 mL/kg/hour? • However, use of these signs is limited because they may be absent early in shock • None of these signs specifically reveals which of the three parameter needs to be augmented
  • 22. Assessing Overall Perfusion • Laboratory testing can be used to assess perfusion: – Elevated serum creatinine • This signifies reduced organ perfusion – Elevated liver function tests • This signifies reduced organ perfusion – Elevated Lactate • We can use either arterial or venous samples – Oxygen saturation of venous blood • SVO2
  • 23. Serum Lactate • Lactate is a marker of anaerobic metabolism secondary to reduced tissue perfusion – A normal lactate is less than 2 mmol/L • Lactate must be serially tested to assess whether patients are improving or getting worse – A reduction in lactate by 10% every two hours signals an improving clinical status Jones, A. Lactate clearance vs central venous oxygen saturation as goals of earlysepsis therapy: a randomized clinical trial. JAMA. 2010 Feb 24; 303(8): 739-46
  • 24. Venous Oxygen Saturation • De-oxygenated blood normally returns to the right atrium 70% saturated or to the pulmonary artery 65% saturated • A venous oxygen saturation less than these levels suggests that peripheral tissues are extracting extra oxygen secondary to reduced tissue perfusion • Venous oxygen saturation can be used as a surrogate for cardiac output and hence systemic perfusion
  • 25. Assessing bloodpressure
  • 26. Assessing Blood Pressure • Manual blood pressure cuffs are the standard method to assess perfusion pressure or Mean Arterial Pressure • There are problems with using manual blood pressure cuffs: – It takes time to perform and is labor intensive – During shock, MAP assessments are needed every few minutes and sometimes every minute when patients are unstable
  • 27. Automated BP Cuffs • A computer activates, controls, and records the MAP • The advantages of automated cuffs are: – It is a non-invasive monitor and calculates the MAP – It is easy to apply to and perform on patients – It automatically produces multiple pressure readings • The disadvantages of automated cuffs are: – It overestimates the MAP in low-flow states – Results can be inaccurate if cuff is improperly applied – Ambient noise makes measurement inaccurate – It is not provide continuous measurements
  • 28. Invasive Arterial Lines • Arterial lines are catheters placed in arteries to directly measure the MAP • The advantages of an arterial line are: – It provides continuous blood pressure measurements – It provides immediate access to arterial blood for lab draws and measures the partial pressure of oxygen – It allows for hemodynamic assessments, such as pulse pressure variation; to be discussed later.
  • 29. Invasive Arterial Lines • The disadvantages of an arterial line are: – It requires an invasive catheter – It may be uncomfortable and painful – It must be placed under sterile conditions and may be time consuming to place – Several complication may occur
  • 30. Complications • The potential complications of arterial lines include: – Thrombosis of artery – Distal ischemia of extremity – Local bleeding and hematoma – Local and systemic infections
  • 31. Invasive Arterial Lines • Potential insertion sites: – Radial artery (most common) – Femoral artery – Axillary artery – Dorsalis pedis artery • The artery can be identified with: – Palpation method – Ultrasound for localization and guidance during placement • Techniques will be discussed in afternoon workshops
  • 32. Assessing cardiac output
  • 33. Assessing Cardiac Output (CO) • There are several methods to assess cardiac output: – Laboratory monitoring – Catheter-based measurements – Ultrasound-derived measurements
  • 34. Determine CO by Labs • Either central venous saturation (ScVO2) or mixed venous saturation (SVVO2) can be used as a surrogate for cardiac output; 65-70% is normal • When saturations are low, consider increasing cardiac output to improve perfusion (remember Starling curve). We can increase either: – Filling of the heart, also known as cardiac preload – Ionotropy, also known as contractility
  • 35. Determine CO by Catheter Assessment • The Swan-Ganz catheter uses the method of thermodilution to measure blood flow through the heart • A Swan-Ganz catheter can be used to assess: – Left-ventricular function • Cardiac output / Stroke volume • Venous oxygen saturation • Central venous pressure • Pulmonary artery occlusion pressure – Right-ventricular function
  • 36. Swan-Ganz Catheter • The advantages are: – It provides continuous hemodynamic monitoring – This catheter is relatively easy to place – It is still considered the standard hemodynamic tool • The disadvantages are: – It is invasive and potentially harmful – It has never been shown to demonstrate clinical benefit – It requires training to interpret waveforms and pressures – It requires knowledgeable and continuous nursing care
  • 37. Ultrasound Assessment of CO • The technique will be discussed during the afternoon workshops • The advantages of ultrasound are: – It can determine stroke volume and cardiac output – It provides non-invasive measurements – The measured results are reproducible • The disadvantages of ultrasound are: – It requires specialized training to perfect the skill – Must be performed each time new data is needed – Ultrasound views might not be obtainable in all patients
  • 38. Assessing CardiacPreload
  • 39. Cardiac Preload • Stroke volume can be maximized by increasing cardiac preload in certain patients • There are two ways to evaluate cardiac preload (also known as preload responsiveness) S EC TIO N I RES U S C ITATIO N S KILLS AN D TEC H N IQ U – Static measurements – Dynamic measurements Stroke volume End-diastolic volume F ig. 4. 2 Frank-S tarling c urve demons trating the relations hip
  • 40. Static Measurements • Static measurements are pressures that indirectly assess left-ventricular filling pressures • Low-filling pressures suggest preload responsiveness • High-filling pressures suggest a lack of preload responsiveness • The most common static measurements are: – Central Venous Pressure (CVP) – Pulmonary Artery Occlusion Pressure (PAOP)
  • 41. Central Venous Pressure (CVP) • CVP is recommended by the Surviving Sepsis Guidelines for sepsis resuscitation • CVP is measured by an internal jugular or subclavian central line – Pressures less than 8 mmHg suggest that stroke volume will increase if a bolus is given – Pressures greater than 8 mmHg suggest that stroke volume will not improve if a bolus is given
  • 42. Pulmonary Artery Occlusion Pressure • It requires the placement of a Swan-Ganz catheter into the pulmonary artery – Pressures less than 12 mmHg suggest that stroke volume will increase if a bolus is given – Pressures greater than 12 mmHg suggest that stroke volume will not improve if a bolus is given
  • 43. Static pressures are notalways reliable • Certain factors make static pressures inaccurate: – Arrhythmias – Positive pressure ventilation – Right-ventricular disease – Improper pressure transducer calibration – Incorrectly interpreted waveforms • Static pressures used for preload responsiveness have been proven inaccurate by several authors Marik, P. et al. Does central venous pressure predict fluid responsiveness? A systematic review of the literature and the tale of seven mares. Chest. 2008 Jul;134(1):172-8.
  • 44. Measuring CVP by Ultrasound • IVC variation in a spontaneously breathing patient is a static measurement and only estimates central venous pressure • Several authors believe that CVP by ultrasound is a not a useful measurement of cardiac preload • This technique will be discussed in the afternoon workshops
  • 45. Table 4. 4 E s timation of Right Atrial Pres s ure FromMeas urement of the Inferior Vena C ava IVC S IZ E ON RA PRE S S URES IZ E OF IVC INS PIRA TION (mm hg)<1 .5 c m N e arly to tal 0-5(s m all) c o llap s e1 .5-2.5 c m D e c re as e >50% 5-1 0(no rm al)1 .5-2.5 c m D e c re as e <50% 1 0-1 5>2.5 c m D e c re as e <50% 1 5-20IVC and N o c h ange >20h e p atic ve ind ilatio nIVC , Infe rio r ve na cava; RA, right atrial.
  • 46. Dynamic Methods of Preload Assessment • These measurements rely on the interaction between the cardiac and pulmonary system • These methods are more reliable than static measures for preload assessment • There are several dynamic methods of preload responsiveness: – Pulse-pressure variation – Distensibility index – Passive-leg raise with Doppler
  • 47. Distensibility index
  • 48. Distensibility Index • Ultrasound is used to measure the variation of the inferior vena cava (IVC) during a respiratory cycle • The diameter of the IVC is measured when it is fully distended (during a positive pressure breath) • The diameter of the IVC is measured when it is in its smallest diameter (during release of that breath)
  • 49. Maximum - Minimum 0.5 x (Max. + Min.)
  • 50. Distensibility Index • Distensibility index >13% suggests that patients will increase their cardiac output if a fluid bolus is given • Distensibility index <13% suggests that patients will not increase their cardiac output if a fluid bolus is given • You can use this method for patients in shock to assess the need for fluid boluses by giving boluses until the distensibiltiy index is less than 13%
  • 51. Distensibility Index • Certain assumptions are necessary before using distensiblity index: – Patient must be in sinus rhythm – Patient must be on positive pressure ventilation – Patient cannot be taking spontaneous breaths – The tidal volume must be 8cc/kg ideal body weight
  • 52. Pulse pressure variation
  • 53. Pulse Pressure Variation • A dynamic method of measuring preload responsiveness that requires an arterial line • The pulse pressure is measured over a respiratory cycle. • Must measure the maximum and the minimum pulse pressure and calculate as seen below S EC TIO N I RES U S C ITATIO N S KILLS AN D TEC H N IQ U ES Paw End-expiratory pause ∆PP = 100 x (PP max – PPmin)/[(PP max + PPmin)/2] PPmax Pa PPmin
  • 54. Pulse Pressure Variation • A measurement more than 18% suggests the patient will respond to a fluid bolus • A measurement less than18% suggests the patient will not respond to fluid boluses • This method Scan beS KILLS AN Dto giveUfluid boluses until the the variation S ECTIO N I RES U C ITATIO N used TEC H N IQ ES is less than 18%, suggesting no more benefit to boluses Paw End-expiratory pause ∆PP = 100 x (PP max – PPmin)/[(PP max + PPmin)/2] PPmax Pa PPmin
  • 55. Pulse Pressure Variation • Certain assumptions must be made before using pulse pressure variation, these are: – Patient must be in sinus rhythm – Patient must be on positive pressure ventilation – Patient cannot be taking spontaneous breaths – The tidal volume must be 8cc/kg ideal body weight
  • 56. Passive leg raise (PLR)
  • 57. Passive Leg Raise • This is the only dynamic method shown for spontaneously breathing patients • There is 300mL of blood in a patient’s lower extremities and it is used as a bolus • This technique avoids patients receiving excess fluid boluses which may be harmful in the long-term
  • 58. Passive Leg Raise • This technique uses ultrasound to assess changes in cardiac output with a change in patient position • The first step is to obtain an apical 5-chamber view when the head is 45 degrees upright • Place a Doppler cursor in LVOT and trace the peak aortic VTI seen here.
  • 59. Passive Leg Raise • Then recline the patient’s legs 45 degrees above the horizontal • Ultrasound is used again to determine the peak aortic VTI • If the increase in VTI is >8-10%, this suggests that a patient will respond to a fluid bolus. • Be away that there are other ways to determine a positive change with recombency
  • 60. Summary• The purpose of monitoring patients in shock is to ensure adequate tissue perfusion and cellular function.• There are three interrelated parameters to monitor when patients are in shock: – Blood pressure or Mean Arterial Pressure – Cardiac Output – Cardiac preload or preload responsiveness
  • 61. Summary• Blood pressure can be measured invasively by a catheter or non-invasively by automated cuffs. Each technique has limitations.• Cardiac output can be measured invasively by catheters or non-invasively using ultrasound• Preload responsiveness can be measured invasively using catheters or non-invasively using ultrasound with or without PLR
  • 62. Email: Haney.mallemat@gmail.comTwitter: @criticalcarenow