424 SECTION IV Pediatric Critical Care Cardiovascular adults may result from more effective transmission of the force of chest compression because of the higher compliance and greater deformability of[.]
424 S E C T I O N I V Pediatric Critical Care: Cardiovascular 80 Without epinephrine With epinephrine Epinephrine Norepinephrine 100 Entire heart Blood flow (mL/min/100 g) 40 % of prearrest anteroposterior diameter 60 * * 20 Chest relaxation position 80 Displacement 60 Chest compression position 40 20 Displacement 80 60 RV LV Septum 40 RV 20 LV Septum Prearrest 20 35 50 Duration of CPR (min) LSD • Fig 38.5 Piston position during chest compression and relaxation phases of the cycle, and net piston displacement expressed as a percent of prearrest anteroposterior chest diameter (12.0 0.3 cm) in piglets Note that displacement was essentially unchanged over the 50-minute duration, but marked deformation occurred during the relaxation phase by minutes and continued to further deform over the 50-minute period in the groups with or without epinephrine CPR, Cardiopulmonary resuscitation (Modified from Schleien CL, Dean JM, Koehler RC, et al Effect of epinephrine on cerebral and myocardial perfusion in an infant animal preparation of cardiopulmonary resuscitation Circulation 1986;73[4]:809–817.) * 10 20 30 40 50 Duration of CPR (min) • Fig 38.4 Top, Total myocardial blood flow during cardiopulmonary resuscitation (CPR) in piglets with and without epinephrine Asterisk indicates significant difference between groups at and 20 minutes Bottom, Blood flow to right ventricular free wall (RV, circle), left ventricular free wall (LV, squares), and interventricular septum (triangles) in the groups with and without epinephrine Standard error bars are omitted for clarity, but the least significant difference bar (LSD, derived from Duncan multiple-range test) is shown for comparisons among heart regions within an animal group (Means must differ by height of bar for P , 05.) LSD for comparing means between groups is twice that shown for within-group LSD Asterisk indicates that RV blood flow was greater than LV and septal blood flows at minutes in the group without epinephrine Flows in all three regions in the group with epinephrine were greater than those in the respective regions in the group without epinephrine at and 20 minutes (Modified from Schleien CL, Dean JM, Koehler RC, et al Effect of epinephrine on cerebral and myocardial perfusion in an infant animal preparation of cardiopulmonary resuscitation Circulation 1986;73[4]:809–817.) relaxation phase, leading to decreased cardiac filling A progressive decrease in the effectiveness of chest compressions to produce blood flow is seen in piglets receiving conventional CPR.60 Permanent deformation of the chest in this model approaches 30% of the original anteroposterior diameter Using a thoracic vest to limit deformation when performing CPR greatly decreased permanent chest deformation (3% vs 30%) but did not attenuate the deterioration of vital organ blood flow with time.61 The characteristics of chest geometry of animals may relate to that in humans Body weight, surface area, chest circumference, and diameter did not correlate with the magnitude of aortic pressure produced during CPR in a study of nine adults already declared dead.61 A direct comparison of adult and pediatric human CPR has not been performed The higher intravascular pressures and organ blood flow during CPR in infants compared with adults may result from more effective transmission of the force of chest compression because of the higher compliance and greater deformability of the infant chest Effects of Cardiopulmonary Resuscitation on Intracranial Pressure When chest compressions are applied, the increase in intrathoracic pressure is transmitted through the venous system of the head and neck to the intracranial vault, resulting in an increased intracranial pressure (ICP) Pressure is transmitted via the paravertebral veins and the cerebrospinal fluid during CPR in dogs.62 Large swings in ICP corresponding to chest compressions occur in children undergoing CPR.63 This transmission of intrathoracic pressure to the intracranial contents accounts for the low CPP by increasing the downstream pressure and cerebral blood flow during closed-chest CPR However, in a porcine model of CPR with an impedance threshold device, it was found that CPR done in a reverse Trendelenburg position (head up at 30 degrees) reduced ICP and improved cerebral perfusion, likely because gravity improved venous drainage and, thus, reduced impedance to forward flow.56 The relationship of ICP to intrathoracic pressure during CPR is linear In dogs receiving conventional CPR, ICP increased by one-third of the rise of intrathoracic pressure in a range from 10 to 90 mm Hg.62 However, some modes of CPR change the intrathoracic to ICP relationship In dogs, abdominal binding increases the transmission of pressure to the intracranial space to one-half of the rise of intrathoracic pressure.64 Open-chest CPR decreases the transmission of pressure and improves CPP compared with conventional CPR Thus, increasing intrathoracic pressure may decrease cerebral blood flow because of the increase in downstream pressure, the ICP In this regard, ACD-CPR and ACD-ITV-CPR may have an advantage over conventional CPR These techniques are designed CHAPTER 38 Physiologic Foundations of Cardiopulmonary Resuscitation to reduce intrathoracic pressure Lindner et al showed in a porcine model that cerebral perfusion is increased with ACD-ITVCPR compared with standard CPR.65 Using an adult porcine model of hypothermic VF arrest, the same group demonstrated by micro-dialysis techniques improved lactate/pyruvate ratios and reduced glucose accumulation in the ACD-ITV group compared with standard CPR.66 In a pediatric porcine model of resuscitation, Voelckel et al found that ACD-CPR with ITV provided superior cerebral blood flow compared with standard CPR.67 Newer Cardiopulmonary Resuscitation Techniques A recent Cochrane systematic review of 11 trials including 12,944 adult patients with use of mechanical chest compression devices for CPR has not suggested that these mechanical devices are superior to conventional therapy.68 Similar recent reviews have had the same findings.69 However, pediatric trials were not included in this review and the authors did conclude that mechanical devices are a reasonable alternative where consistent, high-quality manual chest compressions are not possible or dangerous for the provider Thus, simultaneous compression ventilation CPR, vest approaches, interposed abdominal compression CPR, and openchest modalities are discussed More recent approaches, including tourniquet-assisted CPR to augment myocardial perfusion, have been presented in limited animal case series and will be reserved for future editions.70 Simultaneous compression ventilation cardiopulmonary resuscitation (SCV-CPR) is a technique designed to increase blood flow during conventional CPR by increasing the thoracic pump mechanism contribution to blood flow Delivering a breath simultaneously with every compression, instead of after every fifth compression, increases intrathoracic pressure and augments blood flow produced by closed-chest CPR Survival has been shown to be equivalent or significantly worse in both animals and humans who received SCV-CPR compared with conventional CPR.55,59,60,71–74 No study has shown an increased survival rate with this CPR technique Interposed abdominal compression cardiopulmonary resuscitation (IAC-CPR) is the delivery of an abdominal compression during the relaxation phase of chest compression An extensive review by Babbs has been published.75 IAC-CPR may augment conventional CPR in several ways First, IAC-CPR may return venous blood to the chest during chest relaxation.76,77 Second, IAC-CPR increases intrathoracic pressure and augments the duty cycle of chest compression.76,78 Third, IAC-CPR may compress the aorta and return blood retrograde to the carotid or coronary arteries.77 IAC-CPR is an attractive alternative to some of the newer techniques of CPR because it requires no additional equipment for implementation However, it does require training and manpower Four randomized controlled trials have compared IAC-CPR with standard CPR The first trial, reported in 1985 by Mateer et al., was the largest and included 291 patients.79 IAC-CPR was applied in the field by paramedics until ambulance transport No differences in mortality were found The later trials involved a total of 279 hospitalized patients.80–82 The results from these trials are more positive; a meta-analysis of these studies found an increased likelihood of return of spontaneous circulation (ROSC) and intact survival to discharge with IAC-CPR versus standard CPR.75,83 Although no intraabdominal trauma was detected in 425 any of the 426 patients in these trials, one pediatric case report demonstrated direct pancreatic injury More recent studies evaluating IAC-CPR to standard CPR on end-tidal carbon dioxide (ETCO2) and ROSC demonstrated improvement in ETCO2 without a difference in ROSC.84 This suggests that IAC-CPR may indicate improved cardiac output via this method without clinical improvement Application of IAC-CPR is limited by the need for training and additional manpower Although it has not been studied in a pediatric group, with skilled personnel available, IAC-CPR could be considered for use with inpatient arrests Active compression-decompression cardiopulmonary resuscitation (ACD-CPR) involves a negative-pressure “pull” on the thorax during the release phase of chest compression using a hand-held suction device (Fig 38.6).85 This technique improves vascular pressures and minute ventilation during CPR in animals and humans.65,85–87 The mechanism of benefit of this technique is attributed to enhancement of venous return by the negative intrathoracic pressure generated during the decompression phase In addition, it reverses the chest wall deformation that accompanies standard CPR.88 Preliminary results in adults were promising, and a large multi-institutional study of ACD-CPR completed in Europe found that ACD-CPR was superior to standard CPR.87,89,90 In this study, a total of 750 patients were randomly assigned to receive standard CPR or ACD-CPR In the experimental group, 5% survived to year (12 patients with intact neurologic status) versus 2% (three patients with intact neurologic status) in the standard group.91 However, a number of other trials have not shown a difference between standard CPR and ACD-CPR, and a Cochrane Database Systematic Review concluded that there was no consistent benefit from use of this technique.92 The effectiveness of ACD-CPR appears to be relatively site specific Explanations for this variability have focused on the effectiveness of training for providers and intersite variation of on-scene advanced life support techniques.88 Use of ACD-CPR requires significantly more physical effort than conventional CPR; this requirement may have influenced outcome.93 No device is cleared for clinical use in the United States at this time Use of an ITV has been evaluated in attempts to improve the outcome with ACD-CPR.91,94 This technique involves the use of a valve placed between the ventilating bag and airway, which is designed to close when the tracheal pressure falls below atmospheric pressure, enhancing the development of negative intrathoracic pressure during ACD-CPR (Figs 38.7 and 38.8) Animal studies, including a young porcine model, showed improved organ perfusion, and brain micro-dialysis studies demonstrated decreased lactate accumulation and improved glucose utilization.66,67,95,96 In a small series of patients, diastolic pressure was raised along with CPP and ETCO2 release.97 These studies led to an inclusion of the technique as an acceptable alternative to standard CPR in the 2000 AHA guidelines and subsequent revised guidelines.47,49 Plaisance et al reported on a series of 400 patients randomly assigned to ACD-CPR with ITV or sham ITV Survival at 24 hours was significantly improved.98 There was a nonsignificant trend toward improved neurologic survival, with of 10 discharged patients having intact survival compared with of discharged survivors in the sham ITV group In a randomized controlled study by Wolcke et al.99 of 610 adults in cardiac arrest in the out-of-hospital setting, use of ACD-CPR plus the ITV was associated with improved ROSC and 24-hour survival rates when compared with CPR alone The addition of the ITV was associated with improved hemodynamics during standard CPR in one 426 S E C T I O N I V Pediatric Critical Care: Cardiovascular A B • Fig 38.6 Device for performing active compression-decompression cardiopulmonary resuscitation The upper part is a handle and the lower part is a suction cup (Courtesy AMBU Corporation.) No ventilation or CPR Active manual ventilation Chest compression or exhalation Chest Spontaneous decompression inhalation No airflow Ventilation port Silicone diaphragm Airflow Safety check valve Patient port • Fig 38.7 Schematic diagram of impedance threshold valve During positive-pressure ventilation, the valve is open and gas flows During chest compression or exhalation, air moves freely through the valve During chest decompression, airflow is impeded by the valve, decreasing intrathoracic pressure During spontaneous ventilation, the check valve opens, allowing gas flow CPR, Cardiopulmonary resuscitation (Modified from Lurie KG, Barnes TA, Zielinski TM, et al Evaluation of a prototypic inspiratory impedance valve designed to enhance the efficiency of cardiopulmonary resuscitation Resp Care 2003;48[1]:52–57.) clinical study.100 The ultimate role of this technique, which requires specialized equipment and significant resuscitator training, remains to be determined.91,101 Vest CPR uses an inflatable bladder resembling a blood pressure cuff that is wrapped circumferentially around the chest with phased inflation to increase intrathoracic pressure Because chest dimensions are changed minimally, direct cardiac compression is unlikely In addition, the even distribution of the force of compression over the entire chest wall decreases the likelihood of trauma to the skeletal chest wall and its thoracic contents In a human study, vest CPR increased aortic systolic pressure but had little effect on aortic diastolic pressure compared with conventional CPR.102 Despite its late application, vest CPR improved the hemodynamics and rate of ROSC in adult patients in another study.103 Evidence from a case control study of 162 adults documented improvement in survival to the emergency department when vest CPR was administered by adequately trained personnel to patients in cardiac arrest in the out-of-hospital setting.104 The lack of metallic parts has allowed vest CPR to be used experimentally during nuclear magnetic resonance spectroscopy to study brain intracellular pH.105 Clinically, the use of vest CPR depends on sophisticated equipment and remains experimental at this time Abdominal Binding Abdominal binders and military antishock trousers have been used to augment closed-chest CPR Both methods apply continuous CHAPTER 38 Physiologic Foundations of Cardiopulmonary Resuscitation 427 ACD CPR with Active Impedance Threshold Device +10 mm Hg mm Hg –10 mm HgP1 Positive pressure ventilation Compression Decompression ACD CPR with Sham Impedance Threshold Device +10 mm Hg mm Hg –10 mm Hg P1 • Fig 38.8 Example of intratracheal pressures, a surrogate for intrathoracic pressures, in a patient under- going cardiopulmonary resuscitation (CPR) with an automated compression device (ACD) with and without an impedance threshold device attached to a face mask CPR was delivered at 100 compression/ decompression cycles/min with a synchronized compression/ventilation ratio of 15:2 Note the absence of significant decreases in intratracheal pressures with a sham device With the active impedance threshold device, wide fluctuations in intratracheal pressure are seen with each compression and decompression (Courtesy M Lurie, MD, and Advanced Circulatory Systems, Inc.) compression circumferentially below the diaphragm Three mechanisms have been proposed for augmentation of CPR by these binders First, binding the abdomen decreases the compliance of the diaphragm and raises intrathoracic pressure Second, blood may be moved out of the intrathoracic structures to increase circulating blood volume Third, applying pressure to the subdiaphragmatic vasculature and increasing its resistance may increase suprathoracic blood flow These effects increase aortic pressure and carotid blood flow in both animals and humans.32,106 Unfortunately, as aortic pressure increases, the downstream component of CPP, namely, right atrial pressure, increases to an even greater extent, resulting in decreased CPP and myocardial blood flow.29 These techniques also lower the CPP by enhanced transmission of intrathoracic pressure to the intracranial vault, which raises ICP (the downstream component of CPP) Clinical studies have failed to show an increased survival when an abdominal binder or military antishock trouser suit was used to augment CPR Open-Chest Cardiopulmonary Resuscitation Use of open-chest cardiac massage has generally been replaced by closed-chest CPR Compared with closed-chest CPR, open-chest CPR generates higher cardiac output and vital organ blood flow.107 During open-chest CPR, there is less elevation of intrathoracic, right atrial, and intracranial pressures, resulting in higher coronary and cerebral perfusion pressures and higher myocardial and cerebral blood flows.108 Open-chest CPR is not a technique that can be applied by most health care personnel It can be used in the operating room, ICU, or emergency department equipped with the necessary surgical and technical equipment and personnel It is easily used in the operating room or ICU after cardiac surgery when the open chest can be easily accessed Open-chest CPR is indicated for cardiac arrest resulting from cardiac tamponade, hypothermia, critical aortic stenosis, and ruptured aortic aneurysm Other indications include cardiac arrest resulting from penetrating or crushed chest wall abnormalities that make closed-chest CPR impossible or ineffective.109 Open-chest CPR is indicated for select patients when closed-chest CPR has failed, although exactly which patients should receive this method of resuscitation under this condition is controversial When initiated early after failure of closed-chest CPR, open-chest CPR may improve outcome.110 When performed after 15 minutes of closed-chest CPR, openchest CPR significantly improves CPP and the rate of successful resuscitation.111 Cardiopulmonary Bypass and Extracorporeal Cardiopulmonary Resuscitation Because of the low rate of survival after prolonged CPR, more aggressive methods have been suggested to improve its success: cardiopulmonary bypass (CPB) and extracorporeal membrane oxygenation CPR (E-CPR).112 CPB is one of the most effective ways to restore circulation after cardiac arrest Animal studies show that CPB increases survival at 72 hours, increases recovery of consciousness, and preserves the myocardium better than does conventional CPR.113 In dogs, CPB resulted in better neurologic outcome than conventional CPR after a 4-minute ischemic period However, neurologic outcome was dismal in both groups when the ischemic period lasted 12 minutes.113 Some 90% of dogs survived 24 hours after 15 to 20 minutes of cardiac arrest, but only 10% survived when the arrest time was prolonged to 30 minutes when CPB was used for stabilization during defibrillation.114 CPB decreased myocardial infarct size in a model involving coronary artery occlusion compared with conventional CPR.115 In all animal models, CPB improves the success of resuscitation compared with conventional CPR Human experience with CPB for cardiac arrest outside the operating room is growing In the first major series of pediatric patients undergoing E-CPR, reported by Morris et al., 64 children underwent 66 extracorporeal membrane oxygenation (ECMO) 428 S E C T I O N I V Pediatric Critical Care: Cardiovascular runs initiated during active resuscitation with chest compressions or internal cardiac massage.116 Of these patients, 33 (50%) were decannulated and survived for more than 24 hours, 21 (33%) survived to hospital discharge, and 16 (26%) reportedly had no major changes in neurologic outcome The average duration of CPR before cannulation in the survivors was 50 minutes Of the surviving children who required more than 60 minutes of CPR before ECMO, had no apparent change in neurologic status During the same period, 73 children underwent standard CPR; 10 received CPR for more than 30 minutes, with no survivors Duncan et al reported a series of 18 pediatric cardiac surgical patients at the Boston Children’s Hospital who received ECMO during active chest compressions.117 Of the first patients, only 29% survived This led to the development of a rapid ECMO deployment strategy in which an ECMO pump is kept saline-primed in the ICU at all times, allowing initiation of extracorporeal support within 15 minutes Precannulation support times dropped from an average of 90 minutes but still remained high at an average of 50 minutes Of the remaining 11 patients, 10 were decannulated successfully, with long-term survivors, of whom were in New York Heart Association class I This rapid deployment strategy likely will become more commonplace in large pediatric centers Many subsequent pediatric and adult studies have shown both the feasibility and varied success of E-CPR Clear indications for its use include witnessed arrest in a biventricular circulation, while contraindications include inability to provide effective CPR There is uncertainty for the role of E-CPR in prolonged conventional resuscitation, as there are no guidelines on when to initiate or which patient population it would be best suited for This lack of criteria may explain the wide range of success of E-CPR, with survival ranging between 33% and 100%.118 Subgroup analysis from the Therapeutic Hypothermia after Cardiac Arrest In-Hospital trial demonstrated, in a univariate analysis of 56 children receiving open-chest CPR, that approximately one-half survived with good neurobehavioral outcomes at year from index hospitalization.119 On multivariate analysis, the use of ECMO or other extracorporeal therapies demonstrated worse survival at 12 months and worsened neurobehavioral outcomes However, this trial was designed to evaluate hypothermia as an intervention and many potential confounders may have biased these findings Conversely, Lasa et al compared 591 pediatric patients who received E-CPR versus 3165 that received CPR alone and showed that survival to hospital discharge and survival with a favorable neurologic outcome was more favorable with ECPR compared with CPR alone.120 Bembea et al linked data from the Extracorporeal Life Support Organization and AHA Get with the Guidelines–Resuscitation registries to determine risk factors related to unfavorable outcomes with E-CPR among 593 children.121 In this study, they found that odds of death were increased with a noncardiac diagnosis and preexisting renal insufficiency and that for each additional minutes of CPR prior to ECMO initiation, the odds risk of death increased by 1.04 Under the 2015 AHA guidelines, centers should consider E-CPR for in-hospital cardiac arrest refractory to standard resuscitation attempts if the condition leading to cardiac arrest is reversible or amenable to heart transplantation, if excellent conventional CPR has been performed after no more than several minutes of no-flow cardiac arrest, and if the institution is able to rapidly perform ECMO Long-term survival has been reported even after more than 150 minutes of CPR in select patients.49 Data are emerging involving the role of ECMO in persons with refractory VF.122 These data have solely been in the form of case reports but may represent a future direction for the care of patients with VF In 2006, Samson et al reported successful treatment of in-hospital VF in children with ECMO after cardiac arrest who had an initial rhythm of VF and immediate initiation of CPR.123 CPB and ECMO require a great deal of technical support and sophistication In units with preprimed circuits on standby, CPB can be implemented quickly and with moderate success in a population of children who would otherwise almost certainly die The success with some patients undergoing very long CPR times followed by ECMO use is encouraging and suggests the possibility of reversible myocardial injury as a cause of resuscitation failure in a subset of patients Transcutaneous Cardiac Pacing TCP is used as a method for noninvasive pacing of the ventricles for a relatively short period Emergency cardiac pacing is successful in resuscitation only if it is initiated soon after the onset of arrest In the absence of in situ pacing wires or an indwelling transvenous or esophageal pacing catheter, TCP is the preferred method for temporary electrical cardiac pacing Since 1992, the AHA Advanced Cardiac Life Support (ACLS) guidelines have recommended the early use of an external pacemaker in patients with symptomatic bradycardia or asystole.124 Since Zoll established TCP in 1952 as a clinically useful method of pacing adult patients during ventricular standstill (Stokes-Adams attacks) and bradycardia-associated hypotension, numerous anecdotal reports have supported its use for bradycardic or asystolic arrests.125 Zoll et al reported successful inhospital resuscitation of 12 of 16 patients with hypotensive bradycardia or asystole if TCP was initiated within minutes of the arrest.126 In contrast, if TCP was started between and 30 minutes after the arrest, only of 44 patients with either of these rhythms could be resuscitated.126 In two controlled clinical trials of prehospital TCP, no differences in the survival rate or success of resuscitation were observed in paced and nonpaced patients who had asystole or PEA.127,128 In patients with symptomatic bradycardia, TCP improved resuscitation and the survival rate.129 To date, the efficacy of TCP in resuscitation of children has not been studied Beland et al showed that effective TCP could be achieved in hemodynamically stable children during induction of anesthesia for heart surgery.130 They were successful in 53 of 56 pacing trials, and the patients experienced no complications.130 TCP is indicated for patients whose primary problem is impulse formation or conduction and who have preserved myocardial function TCP is most effective in patients with sinus bradycardia or high-grade atrioventricular block with slow ventricular response who also have a stroke volume sufficient to generate a pulse TCP is not indicated for patients in prolonged arrest because, in this situation, TCP usually results in electrical but not mechanical cardiac capture and its use may delay or interfere with other resuscitative efforts To set up pacing, one electrode is placed anteriorly at the left sternal border and the other posteriorly just below the left scapula Smaller electrodes are available for infants and children; adultsized electrodes can be used in children weighing more than 15 kg.130 Electrocardiographic leads should be connected to the pacemaker, the demand or asynchronous mode selected, and an ageappropriate heart rate used The stimulus output should be set at zero when the pacemaker is turned on and then increased gradually until electrical capture is seen on the monitor The output ... demonstrated improvement in ETCO2 without a difference in ROSC.84 This suggests that IAC-CPR may indicate improved cardiac output via this method without clinical improvement Application of IAC-CPR... suction device (Fig 38.6).85 This technique improves vascular pressures and minute ventilation during CPR in animals and humans.65,85–87 The mechanism of benefit of this technique is attributed... there was no consistent benefit from use of this technique.92 The effectiveness of ACD-CPR appears to be relatively site specific Explanations for this variability have focused on the effectiveness