e5 Abstract Shock is an acute state of circulatory or metabolic dys function that results in failure to deliver or use sufficient amounts of oxygen and/or other nutrients to meet tissue metabolic de m[.]
e5 Abstract: Shock is an acute state of circulatory or metabolic dysfunction that results in failure to deliver or use sufficient amounts of oxygen and/or other nutrients to meet tissue metabolic demands If prolonged, it leads to multiple-organ failure and death Shock can be caused by any serious disease or injury However, whatever the causative factors, it is always a problem of inadequate cellular sustenance Shock states can be classified into categories; however, any given patient may display features of multiple categories over time Fluid resuscitation, improvement of oxygen delivery, and minimization of oxygen consumption are the cornerstones of treatment of patients in shock Key Words: shock, oxygen delivery, oxygen consumption, cardiac output, fluid resuscitation, lactate 10 35 Chapter Title Pediatric Cardiopulmonary Bypass CHAPTER AUTHOR RICHARD M GINTHER JR AND JOSEPH M FORBESS PEARLS gain basic knowledge of thewhich development ofin the • To Cardiopulmonary bypass (CPB), originated theeye mid• To developcentury, essential understanding howfor abnormalities twentieth was designed to allow the repair of at congenvarious of Its development can arrest hamper normal ital heartstages defects history has since been or characterized by performation of the ocular structures and pathways petual technological advancements thatvisual have been instrumental in sustaining the momentum of clinical progress of this field • Because of the morbidity associated with the “time on pump,” many early surgeries were performed at profoundly hypothermic temperatures by using circulatory arrest • The current philosophy underpinning the use of pediatric CPB is to meet the metabolic demands of the patient throughout • To adequate information about of normal anatomy of theacquire repair while minimizing the impact associated nonphysithe eyeeffects and related structures and develop a strong foundation ologic for aspects the understanding common ocular and their • All of CPB haveofexperienced majorproblems technological imconsequences provements Circuits are miniaturized and cause less blood trauma, blood component therapy is highly directed, and onpump patient monitoring techniques have advanced • The progress of pediatric CPB has played a major role in the steady reduction of morbidity and mortality associated with cardiac surgery in children Pediatric mortality rates are now comparable to those in adult patients Background heart-lung machine to just this By the early 1950s, Dr Gibbon, in an interesting collaboration with International Business Machines Corporation (IBM), reported promising success in the laboratory using a heart-lung machine on cats and dogs.5–7 After a previous fatal attempt to repair an atrial septal defect (ASD) in a 15-month-old child in February 1952, Dr Gibbon successfully closed an ASD in an 18-year-old patient using his heart-lung machine on May 6, 1953.8 Unfortunately, Dr Gibbon was not able to repeat the same success with the heart-lung machine on subsequent cases, and his next four patients died Other surgical teams devised their own versions of CPB but were unable to replicate laboratory successes, and no other human survivors were reported It was theorized that perhaps these hearts were too sick to be repaired and that it was unrealistic to expect that these hearts could recover CPB became a widespread disappointment, and most investigators abandoned the technique While others were reporting their attempts using the heart-lung machine, however,9–12 Dr C Walton Lillehei and his colleagues at the University of Minnesota introduced a new approach for supporting patients during surgery: controlled cross-circulation During cross-circulation, the patient’s parent was used as the “heart-lung machine” and supported the patient during the operation (Fig 35.1) Considering the potential for a 200% operative mortality, this was a highly controversial technique However, using this method, Dr Lillehei was able to effectively close an ASD on March 26, 1954.13 Dr Lillehei and his colleagues14 continued a remarkable series of successes using cross-circulation by performing 45 operations for anomalies that included ventricular septal defect, atrioventricular canal, and tetralogy of Fallot, with an History Surgery for congenital heart disease has evolved into a relatively safe intervention considering its brief history and countless hurdles This historical journey is, of course, filled with triumphs and tragic failures, telling a story of progressive intuition and challenges steadily surmounted This has culminated in the generally successful model that is used today (Table 35.1) The early years of cardiac surgery spawned many novel techniques for operations that did not rely on cardiopulmonary bypass (CPB) as used today Surgeons initiated their efforts in cardiovascular surgery with attempts to repair extracardiac vascular anomalies such as patent ductus arteriosus and coarctation of the aorta On August 26, 1938, at the Boston Children’s Hospital, Dr Robert Gross performed the world’s first successful patent ductus arteriosus closure on a 7-year-old girl.1 Soon, exposing the heart and attempting to correct life-threatening cardiac defects became a reality In the early 1950s, surgeons began to explore several different approaches to repairing intracardiac defects One technique, popularized by Dr F John Lewis, used total body hypothermia and vena cava inflow occlusion to achieve direct visualization of atrial septal defects.2 Although this technique proved to be fairly safe for simple atrial septal defects, failure was often the result when more complex defects were attempted.3,4 Surgeons needed a way to safely perfuse the patient’s circulatory system and extend the “safe” surgical time In the late 1930s, Dr John Gibbon and his wife Mary, a nurse and research assistant, began developing a 363 364 S E C T I O N I V Pediatric Critical Care: Cardiovascular TABLE Successful Congenital Cardiac Surgery 35.1 Milestones Year Event Surgeon 1938 Patent ductus arteriosus ligation Gross 1944 Coarctation repair Crafoord 1944 Blalock-Taussig shunt Blalock, Taussig 1946 Potts shunt Potts 1947 Closed pulmonary valvotomy Sellors 1948 Atrial septectomy Blalock, Hanlon 1951 Pulmonary artery band Muller, Dammann 1952 Atrial septal defect closure using atrial well Gross 1952 Atrial septal defect closure using hypothermia Lewis 1953 Atrial septal defect closure using cardiopulmonary bypass Gibbon 1954 Ventricular septal defect closure using cross-circulation Lillehei 1958 Superior cavopulmonary shunt (Glenn shunt) Glenn 1958 Senning operation for transposition of great arteries Senning 1963 Mustard operation for transposition of great arteries Mustard 1968 Fontan procedure for tricuspid atresia Fontan 1975 Arterial switch for transposition of great arteries Jantene 1981 Norwood procedure for hypoplastic left heart syndrome Norwood 1985 Neonatal heart transplantation Bailey operative mortality of only 38% This progress with more complex lesions prompted investigators to rethink their options for supporting, repairing, and recovering these patients Two surgical camps ignited the resurgence of the artificial heart-lung machine: Dr Lillehei and his colleagues at the University of Minnesota and Dr John Kirklin and his colleagues at the nearby Mayo Clinic Dr Kirklin and colleagues15 reported a 50% mortality among eight patients using a modification of the Gibbon-IBM pump oxygenator in the spring of 1955 Months later, Lillehei and colleagues16 reported a 29% mortality among seven patients using their own heart-lung machine and the groundbreaking DeWall Bubble Oxygenator These two groups demonstrated that surgical repair of complex congenital defects could be performed in a more controlled environment than cross-circulation or inflow occlusion, with promising results What followed were many groups initiating open-heart programs primarily addressing congenital heart disease Despite significant improvements in survival rates, congenital cardiac repairs remained a daunting undertaking with significant risk Bypass circuits were enormous when compared with the patient blood volume, the systemic response was an extreme shock, and the understanding of the physiologic response to this “nonphysiologic” extracorporeal circulation was quite limited Investigators sought to use CPB but limit the actual cumulative time that nonphysiologic blood flow is provided to the patient—with its attendant risk The bypass circuit could be used to cool the patient down to profound hypothermia after a lengthy period of topical cooling The circulation of the patient could then be safely terminated for lengthy periods of time, allowing for complex cardiac repairs At the conclusion of the repair, the heartlung machine could be used to fully warm the patient These hypothermic circulatory arrest techniques with limited periods of extracorporeal circulation were popularized in the early 1970s by Dr Barratt-Boyes and proved to dramatically extend the “safe” period of support.17 Surgeons began to perform increasingly complex congenital heart repairs Pediatric cardiac surgical care was further refined over the subsequent several decades The development of smaller, more efficient, and customizable heart-lung machine hardware and components, as well as improvements in myocardial protection, have allowed surgical teams to move away from the concept of limited CPB and toward a more “full-flow” philosophy wherein the metabolic demands of the body are continuously met while the patient is on the heart-lung machine This chapter explores the concepts that form the basis of this philosophy and the techniques that surgical teams currently use to support pediatric patients during cardiovascular surgery Surgical Team The surgical team consists of highly trained specialists, each of whom plays a vital role in the safety and success of the surgical procedure This specialized team is led by the cardiac surgeon and typically includes an assistant surgeon or physician assistant, anesthesiologist, perfusionist, and several nurses, surgical scrub technologists, anesthesia assistants, and perioperative surgical assistants A perfusionist is a healthcare professional who specializes in all aspects of extracorporeal circulation The primary focus of a perfusionist is to support the cardiac surgical patient during CPB Because of this, the perfusionist’s clinical expertise is a critical component of operative success Perhaps the first perfusionist was Mary Gibbon, Dr Gibbon’s wife In addition to helping design the Gibbon-IBM heart-lung machine, she assembled and operated it as well The term perfusionist did not emerge until the early 1970s; in the early days of cardiac surgery, surgical groups would typically use any locally available combination of physiologists, biochemists, cardiologists, or surgical residents to help operate the heart-lung machine Now, cardiovascular perfusionists are highly trained, nationally certified (Certified Clinical Perfusionist), statelicensed allied health professionals The common scope of practice for a perfusionist consists of CPB, extracorporeal membrane oxygenation (ECMO), isolated limb/organ chemoperfusion, ventricular assist devices, autotransfusion, and intraaortic balloon counterpulsation Equipment and Preparation for Cardiopulmonary Bypass Heart-Lung Machine Console and Pumps The CPB machine, commonly referred to as the heart-lung machine, is the mechanical hardware that a perfusionist uses to support the patient during surgery Until the late 1950s, the CPB hardware and circuitry were typically handmade, and many of the components had to be handwashed and sterilized for reuse CHAPTER 35 Pediatric Cardiopulmonary Bypass 365 Sigmamotor pump Patient Donor Defect • Fig 35.1 Controlled cross-circulation (From Stoney WS Evolution of cardiopulmonary bypass Circulation 2009;119:2844–2853.) The hardware components were designed at that time with two objectives: to pump blood through the patient’s cardiovascular system and to successfully perform respiratory gas exchange, hence, the term heart-lung machine Unfortunately, this heartlung apparatus was large, difficult to move, had no safety features, and was not available to other institutions eager to operate Surgeons interested in these handcrafted devices would often visit the surgical groups at the University of Minnesota and Mayo Clinic, but few could replicate their expensive and intricate systems Eventually, industry developers began to commercially release heart-lung machines with hardware components consolidated onto a wheel-mounted console Interestingly, although cardiac surgery began with the pediatric patient population, heart-lung machines were developed as one-size-fits-all units and were not customizable for smaller patients Modern heart-lung machine consoles are mobile, offer many pump configuration options, are loaded with safety features, and seamlessly send intraoperative CPB data to the electronic medical record These design improvements allow for better configuration options for the pediatric surgical population An ideal heart-lung machine for pediatric CPB is customizable for circuit miniaturization and offers safety devices and hardware that accommodate both smaller tubing sizes and circuitry Customizations such as mast mounting pumps in various configurations and incorporating mini-roller pumps with shorter raceway lengths are two popular heart-lung machine configurations.18,19 Several different types of mechanical pumps have been used to substitute the function of the heart; interestingly, the roller pump has remained a standard pump mechanism since the beginning of CPB A roller pump functions by positive fluid displacement Tubing is placed in a curved raceway; as occlusive rollers rotate over the compressible tubing, blood is pushed forward, creating a continuous nonpulsatile flow The flow output is controlled by changing the revolutions per minute (RPMs) of the pump Roller pumps are the most commonly used arterial (heart) pump in pediatrics (Fig 35.2).20 While roller pumps are used as the arterial pump, the heart-lung machine console also holds several other roller pumps used for cardiotomy field suction, venting the heart, and cardioplegia delivery The centrifugal pump is another type of arterial pump that has gained significant popularity since the mid-1970s A centrifugal pump uses an impeller cone and rotational kinetic energy to propel the blood Because it is nonocclusive, it is thought to be safer and cause less hemolysis than roller pumps Centrifugal blood flow is controlled by the impeller cone RPMs and is also dependent on preload and sensitive to resistance distal to the pump Because the pump is not occlusive, any resistance or occlusion will result in a reduction or cessation of flow These pumps require the use of a flow probe to measure actual flow; the nonocclusive property is considered a safety feature in the event of cannula obstruction or accidental arterial line occlusion The use of centrifugal pumps during ECMO has become increasingly popular owing to the suggested hemolytic and safety benefits; however, these benefits have often been refuted.21–24 Roller pumps remain the main arterial pump type in pediatric CPB because they are simple, inexpensive, and, importantly, require a much smaller prime volume than centrifugal pumps 366 S E C T I O N I V Pediatric Critical Care: Cardiovascular Cardiopulmonary Bypass Circuit • Fig 35.2 Roller pump with ¼-inch tubing placed in the raceway The handmade circuits used on children in the mid-1950s were elaborate, and the large blood volume required to prime them was a burden on the blood bank Perfusionists would have to spend the evening of surgery assembling the circuit and then tackle the tedious task of dismantling, rewashing, and sterilizing the same circuitry after surgery Fortunately, manufacturers now offer a wide variety of disposable circuit components that are fairly simple to assemble The modern CPB circuit is a series of components consisting of cannulas, tubing, venous reservoir, filters, oxygenator, heat exchanger, hemoconcentrator, suction, and cardioplegia delivery system Deoxygenated blood from the superior vena cava (SVC) and inferior vena cava (IVC) travels down a venous line, usually pulled by simple gravitational siphon effect, and into a venous reservoir The deoxygenated blood in the reservoir is pumped through the oxygenator and then back to the patient’s aorta (or other major artery) via the arterial line (Fig 35.3) This blood pathway diverts blood away from the heart and lungs, creating a bloodless operative field In the adult patient population, where the circuit prime volume is typically no greater than 25% of the patient’s blood volume, a single circuit size can be used for almost all patient sizes The small circuit prime-to-patient blood volume ratio helps Venous line; gravity drainage mm Hg Temp 4°C Bubble sensor Oxygenator; heat exchanger; integrated arterial filter mm Hg Water heater/cooler Gas filter Field suction Field suction Vent; cardioplegia; mini roller pumps Arterial pump Isoflurane Arterial line 1:4 del Nido cardioplegia Cardiotomy; venous reservoir Hemoconcentrator Cardiotomy field suction Level sensor SVC & IVC bicaval cannulation Gas flow meter Blender Air O2 CO2 • Fig 35.3 Schematic of the cardiopulmonary bypass circuit at Children’s Health Dallas CO2, Carbon dioxide; IVC, inferior vena cava; O2, oxygen; SVC, superior vena cava; temp, temperature ... (Fig 35.1) Considering the potential for a 200% operative mortality, this was a highly controversial technique However, using this method, Dr Lillehei was able to effectively close an ASD on March... countless hurdles This historical journey is, of course, filled with triumphs and tragic failures, telling a story of progressive intuition and challenges steadily surmounted This has culminated... heart transplantation Bailey operative mortality of only 38% This progress with more complex lesions prompted investigators to rethink their options for supporting, repairing, and recovering