What is Shock? • Shock occurs when tissue perfusion is inadequate to meet cellular needs • There are four types of shock: – Hypovolemic – Obstructive – Cardiogenic – Distributive
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
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
What are we monitoring inShock?
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
These factors are interrelated
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
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)
Blood pressure /mean arterial pressure
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
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
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.
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
How do We monitorPatients in Shock?
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
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
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
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
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
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
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.
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
Complications • The potential complications of arterial lines include: – Thrombosis of artery – Distal ischemia of extremity – Local bleeding and hematoma – Local and systemic infections
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
Assessing cardiac output
Assessing Cardiac Output (CO) • There are several methods to assess cardiac output: – Laboratory monitoring – Catheter-based measurements – Ultrasound-derived measurements
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
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
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
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
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
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)
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
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
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.
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
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.
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
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)
Maximum - Minimum 0.5 x (Max. + Min.)
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%
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
Pulse pressure variation
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
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
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
Passive leg raise (PLR)
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
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.
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
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
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