Congenital Cardiac Defects RTS473 - 2024 PDF

RTS473 - 2024 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 1 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 2  Incidence Most common birth defect in the United States Major developments in th...

RTS473 - 2024 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 1 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 2  Incidence Most common birth defect in the United States Major developments in the Improved postoperative care identification of children with all resulted in significant congenital heart disease improvements in mortality along with new surgical over the last two decades of techniques the twentieth century Many children with congenital heart disease are surviving well into adulthood Mortality has continued to decrease over the last decade Recent epidemiological studies have found that there are currently as many adults living with congenital heart disease as there are children Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 3 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 4  Cardiopulmonary Anatomy and Physiology (1 of 3)  Anatomy of the normal heart ⮚ Normal human heart has four chambers Two atria (right and left) and two ventricles (right and left) ⮚ Outflow from each ventricle contains a valve  The cardiac cycle consists ⮚ Myocardial contraction (systole) ⮚ Myocardial relaxation (diastole)  Cardiac output from the left and right sides of the heart depends on: ⮚ Preload, contractility, and afterload Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 5 5  Cardiopulmonary Anatomy and Physiology (2 of 3)  Blood flow of the normal heart ⮚ Deoxygenated venous blood that enters the RA→ into the RV via the tricuspid valve → into the pulmonary arteries → oxygen diffuses from inspired air into the plasma and red blood cells, and CO2 diffuses from plasma into the alveolus → Oxygenated blood returns to the heart via four pulmonary veins to → LA → LV → aortic valve → systemic blood flow to the entire body Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 6 6 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 7  Cardiopulmonary Anatomy and Physiology (3 of 3)  Structure of each cardiac chamber is tailored to its function  Walls of the atria are thin and compliant ⮚ Enables expansion in setting of variable systemic and pulmonary venous return ⮚ RV is thin-walled and operates under low pressure ⮚ Unable to tolerate acute increases in afterload  Left ventricle is typically thicker-walled ⮚ Muscular, concentric, and operates at a higher systemic pressure Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 8 8 Transition of Fetal to Extrauterine Life (1 of 3) ⬤ During fetal development ⮚ Gas exchange takes place through the placenta ⮚ Shunts exist to bypass the pulmonary circulation ⬤ In utero ⮚ Lungs are fluid-filled High resistance capillary bed Pulmonary blood flow (PBF) is limited ⮚ Systemic circulation includes the placenta Low resistance Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 9 9 Transition of Fetal to Extrauterine Life (2 of 3) ⬤ Shunts ⮚ Patent ductus arteriosus (PDA) Connects the pulmonary artery (PA) with the systemic circulation Majority of blood passing into the PA in utero shunts from the PA into the descending aorta Down the pressure gradient created by the differential capillary bed resistances ⮚ Patent foramen ovale (PFO) Low PBF creates a low LA pressure Facilitates flow from the RA to LA the PFO (a flap opening) Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 10 10 Transition of Fetal to Extrauterine Life (3 of 3) ⬤ Shortly after delivery ⮚ Anatomic and physiologic changes ⮚ Most dramatic changes occur during the first breath The neonate generates pressures in excess of 80mmHg ⮚ Reduction in PVR Air spaces fill with air instead of fluid Increases in PaO2 ⮞ Diminishes PVR ⮚ Increased left atrial pressure ⮚ Closure of the foramen ovale Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 11 11 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 12 Cardiopulmonary Interactions ⬤ Preload ⮚ The ventricular end diastolic volume ⮚ Describes how full the heart is ⮚ The volume needed for the pump to work ⬤ Afterload ⮚ The downstream pressure that the heart pumps against ⮚ The impedance to ventricular emptying ⮚ Related to myocardial oxygen demand Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 13 13  Respiratory Cycle (1 of 2) ⬤ Inspiration ⮚ Inspiration is an active process (in spontaneously breathing patient) ⮚ Respiratory muscles, diaphragm and intercostal muscles contract ⮚ Chest wall expands resulting in a negative (subatmospheric) intrapleural and pericardial pressure ⮚ Pressure gradient drives flow Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 14 14  Respiratory Cycle (2 of 2) ⬤ Expiration ⮚ Passive ⮚ Chest wall muscles relax and recoil ⮚ Intrapulmonary pressures to become positive ⮚ Air is expulsion Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 15 15  The Right Heart ⬤ Venous system operates at low pressure ⮚ Intrathoracic pressure changes during the respiratory cycle can have profound impact on venous return ⮚ Can affect blood volume received by the right side of the heart ⬤ During spontaneous breathing ⮚ Low pressure gradient causes flow from the systemic veins to the RA ⬤ During PPV ⮚ Intrathoracic/pericardial pressure increases relative to spontaneous breathing Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 16 16  The Left Heart ⬤ Preload to the left heart is dynamic throughout the respiratory cycle ⬤ During spontaneous breathing ⮚ Inspiration significantly increases pulmonary arteriolar capacitance ⬤ Afterload of the left ventricle is predominantly determined by impedance to systemic blood flow ⮚ Acute changes in LV afterload can occur during PPV Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 17 17 Classification of Cardiac Anomalies ⬤ Categorize heart disease functionally: ⮚ Acyanotic Normal systemic oxygenation Shunt typically flows left to right Left-to-right shunting may cause muscularization of the pulmonary arteries leading to increased PVR ⮚ Cyanotic Decreases systemic oxygenation Contain a right to left shunt Deoxygenated blood from the systemic veins must pass into the aorta Either the atrial or ventricular level, or both Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 18 18  Acyanotic Lesions ⬤ May exhibit: ⮚ A shunt (which typically flows left to right) ⮚ Valvar abnormalities ⬤ Shunt lesions ⮚ Blood flow that deviates from the normal flow pattern ⮚ Results from anomalous connections and differential pressure or resistance ⬤ Common shunt lesions ⮚ Patent ductus arteriosus (PDA), atrial septal defect (ASD), ventricular septal defects (VSD), complete atrioventricular canal (CAVC) defect Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 19 19  Patent Ductus Arteriosus (1 of 2) ⬤ Patent ductus arteriosus (PDA) ⮚ 48 hours after birth Decrease in PgE2 + increase in Pao2 = closure ⮚ Predisposing factors for PDA Prematurity (most common) Persistent pulmonary hypertension Respiratory distress syndrome (RDS) ⮚ As PVR decreases, aortic pressures exceed pulmonary artery pressures, resulting in a left-to- right shunt through the PDA, and increasing pulmonary blood flow Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 20 20  Patent Ductus Arteriosus (2 of 2) ⬤ Patent ductus arteriosus (PDA) ⮚ Clinical signs Tachypnea, tachycardia, and a continuous murmur Post-ductal desaturation Increased pulmonary blood flow may delay the ability to wean respiratory support ⮚ Management Indomethacin Surgical closure Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 21 21 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 22  Device Closure Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 23  Atrial Septal Defect (ASD) ⬤ Communication between the right and left atria ⮚ Left-to-right shunting ⮚ Blood flow at the atrial level is determined by the relative compliance of the two receiving ventricles LV is thicker-walled and has a higher systolic pressure Its compliance during ventricular diastole is slightly lower than that of the RV ⮚ Less than 10% of children with ASD develop symptoms before 2 years of age Spontaneous closure of small ASDs may occur within the first year of life ⮚ Surgical repair Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 24 24 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 25 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 26 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 27  Ventricular Septal Defect (VSD) (1 of 3) ⬤ Communication between the right and left ventricles ⮚ One of the most common congenital heart defects ⬤ Described in terms of their location ⮚ Perimembranous ⮚ Subpulmonary ⮚ Muscular ⮚ Inlet ⬤ Could be singular or multiple Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 28 28 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 29  Ventricular Septal Defect (VSD) (2 of 3)  The pathophysiology depends upon VSD size ⮚ Small May close spontaneously and remain asymptomatic ⮚ Large and unrestrictive Create a left-to-right shunting Pulmonary arterial hypertension ⮚ Eisenmenger’s syndrome Occurs when pulmonary vascular resistance nears that of the systemic vascular resistance Left-to-right shunt may reverse to right-to-left shunt Associated with high mortality Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 30 30 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 31  Ventricular Septal Defect (VSD) (3 of 3) ⬤ Therapy ⮚ Unrestrictive VSDs and symptoms of heart failure Surgical closure ⮚ Mild symptoms Treated with diuretics and digoxin ⮚ Percutaneous transcatheter closure ⮚ Early extubation should be expected post surgery if isolated VSD Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 32 32 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 33 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 34  Complete Atrioventricular Canal (1 of 3) ⬤ Complete atrioventricular canal (CAVC) or Atrioventricular septal defect (AVSD) ⮚ Defect always involves a common (singular) AV valve ⮚ Often involves abnormalities of the lower portion of the atrial septum ⮚ Most common congenital heart lesion in infants with Down syndrome (trisomy 21) ⮚ Partial AVSDs Characterized by a primum ASD and common AV valve, without a defect in the ventricular septum ⮚ Complete AVSDs Characterized by absence of a portion of the atrial septum and the ventricular septum, and the presence of a single, common atrioventricular (AV) valve Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 35 35 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 36 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 37  Complete Atrioventricular Canal (2 of 3) ⬤ Clinical manifestations Children with partial AVSD may not have obvious clinical manifestations initially. Partial AVSD may not have obvious clinical manifestations initially Complete AVSD usually develop signs of heart failure in early life Chest radiography usually reveals cardiomegaly and increased pulmonary vascular markings Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 38 38  Complete Atrioventricular Canal (3 of 3) ⬤ Treatment ⮚ Supplemental oxygen may be given judiciously Potential for oxygen to induce pulmonary vascular dilation and encourage more PBF ⮚ Diuretics and digoxin ⮚ Surgical repair Children with co-morbid conditions who are poor candidates for early repair may be palliated with banding of the pulmonary artery to stabilize and/or allow more growth Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 39 39 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 40 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 41  Valvar Anomalies (1 of 2) ⬤ Valvar abnormalities exist across: ⮚ Outflow tracts Semilunar valves: pulmonary and aortic ⮚ Atrioventricular valves Mitral or tricuspid valves ⬤ Result in regurgitation (leak) or stenosis (obstruction) ⮚ Regurgitant lesions result from valve incompetence allowing retrograde flow (in the opposite direction) ⮚ Stenotic lesions can occur at multiple levels, resulting from obstruction at the level of the valve (valvar) or in the region above (supra-valvar) or below (sub-valvar). Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 42 42  Valvar Anomalies (2 of 2) ⬤ Obstruction can be: ⮚ Complete (atresia) Allows no flow with obligate shunt to allow flow via alternate paths ⮚ Partial (stenotic) Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 43 43 Left Ventricular Outflow Tract (LVOT) Obstruction ⬤ Left ventricular outflow tract (LVOT) obstruction ⮚ Exist along a spectrum ⮚ Likely results from impaired flow through the left side of the heart in utero ⮚ Without blood flow, there is poor growth ⮚ Aortic stenosis, coarction of the aorta Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 44 44  Aortic Stenosis (AS) (1 of 2) ⬤ Narrowing of the aortic valve orifice itself ⬤ Clinical presentation ⮚ Determined by the degree of snenosis ⮚ If dependent on PDA flow for survival Cardiogenic shock with hypotension, poor perfusion, and metabolic acidosis Pulmonary edema A risk for bacterial endocarditis Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 45 45 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 46  Aortic Stenosis (AS) (2 of 2) ⮚ Emergency therapy Opening the PDA to provide systemic blood flow, mechanical ventilation to minimize oxygen demands, and the aortic balloon valvotomy ⮚ Surgical repair Aortic valvuloplasty, artificial aortic valve replacement, and replacement with a pulmonary valve autograft (Ross) ⮚ Hypertension should be aggressively controlled Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 47 47 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 48 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 49 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 50  Coarctation of the Aorta ⬤ A severe narrowing of the thoracic aorta at the insertion site of the ductus arteriosus ⮚ The aortic isthmus ⬤ Pathophysiology ⮚ Diminished systemic perfusion ⮚ Increase LV afterload ⬤ Clinical manifestations ⮚ Cardiomegaly and pulmonary congestion ⬤ Treatment ⮚ Emergent opening of the PDA ⮚ Surgical repair Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 51 51 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 52 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 53  Cyanotic Congenital Heart Lesions ⬤ Hypoplastic left heart syndrome (HLHS) ⬤ Total anomalous pulmonary venous return (TAPVR) ⬤ Tetralogy of Fallot (TOF) ⬤ Truncus arteriosus ⬤ Transposition of the great arteries (TGA) ⬤ Pulmonary atresia with intact ventricular septum (PA/IVS) Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 54 54  Hypoplastic Left Heart Syndrome (HLHS) (1 of 3) ⬤ Underdevelopment of most or all of the left heart structures: ⮚ The mitral valve, left ventricle, aortic valve, and aortic arch ⮚ Blood flow to the body must be supplemented or completely provided by the right ventricle ⬤ To accomplish this (prior to operative intervention in the neonate), there must be: ⮚ A left to right shunt for pulmonary venous return ⮚ A right to left shunt for systemic blood flow Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 55 55 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 56  Hypoplastic Left Heart Syndrome (HLHS) (2 of 3) ⬤ Often diagnosed prenatally or shortly after birth ⬤ Clinical manifestations ⮚ Premature closure of the PDA causes immediate hypoperfusion, metabolic acidosis, and circulatory collapse and death ⬤ Preoperative management of infants with HLHS is targeted at ensuring: ⮚ Adequate intracardiac mixing, right-to-left flow at the PDA, and balance between the pulmonary and systemic circulations Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 57 57  Hypoplastic Left Heart Syndrome (HLHS) (3 of 3) ⬤ Treatment ⮚ Patients with pulmonary edema and increased WOB may be supported using NIV and FiO2 of 0.21 If intubated, conservative measures to allow PVR to rise include permissive hypercarbia and lowering demand by sedation and paralysis ⮚ Prostaglandin E1 ⮚ Diuretics ⮚ Surgical repair Outcomes for infants with HLHS have improved dramatically since the introduction of the stage 1 palliation (S1P) Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 58 58 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 59 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 60 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 61 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 62  Total Anomalous Pulmonary Venous Return ⬤ Total anomalous pulmonary venous return (TAPVR) ⮚ Spectrum of abnormalities in which the pulmonary veins drain to the systemic venous circulation rather than the left atrium Supracardiac, in which the common pulmonary vein drains into the SVC through a vertical vein or left SVC Cardiac, in which the common pulmonary vein empties into the coronary sinus Infracardiac, in which the common pulmonary vein drains to the portal vein, ductus venosus, hepatic vein, or inferior vena cava Mixed type, in which there are several different sites of drainage Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 63 63 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 64 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 65  Total Anomalous Pulmonary Venous Return ⬤ Total anomalous pulmonary venous return (TAPVR) ⮚ Spectrum of abnormalities in which the pulmonary veins drain to the systemic venous circulation rather than the left atrium ⮚ HFOV or ECMO support and urgent surgical repair to relieve pulmonary vein obstruction ⮚ Chest radiograph usually reveals a normal heart size Lungs with a modest burden of pulmonary edema ⮚ Postoperative mechanical ventilation strategies should utilize applied PEEP Inhalational nitric oxide may be helpful Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 66 66  Tetralogy of Fallot (TOF) ⬤ The most common cyanotic congenital heart abnormality ⬤ Includes four components ⮚ (1) pulmonary artery stenosis, (2) ventricular septal defect, (3) overriding aorta to the right, and (4) right ventricular hypertrophy Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 67 67 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 68  Tetralogy of Fallot (TOF) ⬤ Infants with unrepaired TOF: ⮚ May exhibit hypercyanotic episodes Acute increases in RVOT obstruction result in decreased pulmonary blood flow and SpO2 Acutely life threatening, and must be treated with hyperoxia, opiates, knee chest position, and if necessary, pharmacologic agents which acutely increase SVR Characterized by (1) hyperpnea or exaggerated, deep spontaneous breathing; (2) irritability and prolonged crying; (3) cyanosis; (4) decreased intensity of the heart murmur; and (5) syncope. Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 69 69 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 70  Truncus Arteriosus ⬤ Rare defect in which a single great artery arises from the ventricles of the heart ⬤ Supplies both systemic and pulmonary circulations ⬤ Infants may develop early respiratory distress, congestive heart failure (CHF), or shock from systemic hypoperfusion ⬤ Patients undergo complete biventricular repair in the newborn period Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 71 71 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 72 Transposition of the great arteries (TGA) ⬤ The aorta arises from the RV ⬤ The pulmonary artery arises from the LV ⮚ Two circulations are in parallel rather than in series with each other ⬤ Surgical repair of TGA is the arterial switch operation Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 73 73 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 74 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 75 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 76 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 77 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 78 Pulmonary Atresia with Intact Ventricular Septum (PA/IVS) ⬤ Blood flow out of the right ventricle is obstructed because of atresia of the pulmonary valve ⬤ The RV is typically hypertrophied and the RV cavity is often hypoplastic ⬤ The left side of the heart receives blood from the right side via an ASD or patent foramen ovale ⮚ Pulmonary blood flow is ductal dependent ⬤ Treatment ⮚ Catheter-based dilation of the pulmonary valve, PDA stenting or surgical placement of a BTS Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 79 79 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 80 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 81 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 82 Clinical Monitoring of Patients with Cardiac Anomalies (1 of 2)  Hemodynamic monitoring ⮚ A narrowing of pulse pressure is suggestive of a low stroke volume  Pulse oximetry and Co-oximetry  Capnography ⮚ Decreased ETCO2 Endotracheal tube dislodgement or obstruction, air trapping, decreased pulmonary blood flow, low cardiac output, or hyperventilation ⮚ Elevated ETCO2 Hypoventilation, fever, or malignant hyperthermia Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 83 83 Clinical Monitoring of Patients with Cardiac Anomalies (2 of 2)  Capnography ⮚ Increases in the gradient between the PaCO2 and the ETCO2 Increased dead space, lower pulmonary blood flow, high airway pressures leading to alveolar overdistention, and pulmonary embolism ⮚ The magnitude of the ETCO2 tracing may be used as a surrogate of efficacy of CPR ⮚ A precipitous drop in the ETCO2 may indicate a loss of pulmonary blood flow as a result of shunt thrombosis Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 84 84 Elsevier items and derived items © 2010 by Saunders, an imprint of Elsevier Inc. 85