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[.]
Trang 1Abstract: 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-mands 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; Key Words: output, fluid resuscitation, lactateshock, oxygen delivery, oxygen consumption, cardiac
however, any given patient may display features of multiple cate-gories over time Fluid resuscitation, improvement of oxygen de-livery, and minimization of oxygen consumption are the corner-stones of treatment of patients in shock
Trang 210
Chapter Title
CHAPTER AUTHOR
PEARLS
• To acquire adequate information about normal anatomy of the eye and related structures and develop a strong foundation for the understanding of common ocular problems and their consequences.
• To gain basic knowledge of the development of the eye.
• To develop essential understanding how abnormalities at
various stages of development can arrest or hamper normal
formation of the ocular structures and visual pathways.
Background
History
Surgery for congenital heart disease has evolved into a relatively
safe intervention considering its brief history and countless
hur-dles This historical journey is, of course, filled with triumphs and
tragic failures, telling a story of progressive intuition and
chal-lenges 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
at-tempts 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
per-formed 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
ap-proaches to repairing intracardiac defects One technique,
popu-larized 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
heart-lung machine to do 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 rep-licate 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 Uni-versity 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 mor-tality, 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 perform-ing 45 operations for anomalies that included ventricular septal defect, atrioventricular canal, and tetralogy of Fallot, with an
35
Pediatric Cardiopulmonary Bypass
RICHARD M GINTHER JR AND JOSEPH M FORBESS
• Cardiopulmonary bypass (CPB), which originated in the
mid-twentieth century, was designed to allow for the repair of
congen-ital heart defects Its history has since been characterized by
per-petual technological advancements that 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
hypother-mic temperatures by using circulatory arrest.
• The current philosophy underpinning the use of pediatric CPB
is to meet the metabolic demands of the patient throughout
PEARLS
the repair while minimizing the impact of associated nonphysi-ologic effects.
• All aspects of CPB have experienced major technological im-provements Circuits are miniaturized and cause less blood trauma, blood component therapy is highly directed, and on-pump 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.
Trang 3364 SECTION IV Pediatric Critical Care: Cardiovascular
operative mortality of only 38% This progress with more
com-plex 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
col-leagues16 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
oc-clusion, 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
ex-treme 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 cu-mulative 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 heart-lung machine could be used to fully warm the patient These hy-pothermic 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 com-plex congenital heart repairs Pediatric cardiac surgical care was further refined over the subsequent several decades The develop-ment of smaller, more efficient, and customizable heart-lung ma-chine 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 con-tinuously 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, anes-thesiologist, perfusionist, and several nurses, surgical scrub tech-nologists, 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 per-fusionist 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
oper-ated 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), state-licensed allied health professionals The common scope of practice for a perfusionist consists of CPB, extracorporeal membrane oxy-genation (ECMO), isolated limb/organ chemoperfusion, ven-tricular 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
ma-chine, is the mechanical hardware that a perfusionist uses to
sup-port 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
TABLE
35.1 Successful Congenital Cardiac Surgery Milestones
Trang 4The 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 lung machine Unfortunately, this
heart-lung apparatus was large, difficult to move, had no safety features,
and was not available to other institutions eager to operate
Sur-geons 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
miniaturiza-tion and offers safety devices and hardware that accommodate
both smaller tubing sizes and circuitry Customizations such as
mast mounting pumps in various configurations and
incorporat-ing mini-roller pumps with shorter raceway lengths are two
popu-lar 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 pe-diatrics (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 ctrifugal pump uses an impeller cone and rotational kinetic en-ergy 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 re-sistance 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 cen-trifugal pumps
Patient
Sigmamotor pump
Donor
Defect
•Fig 35.1
Controlledcross-circulation.(FromStoneyWS.Evolutionofcardiopulmonarybypass.Circula-tion.2009;119:2844–2853.)
Trang 5366 SECTION IV Pediatric Critical Care: Cardiovascular
Cardiopulmonary Bypass Circuit
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 sim-ple to assemble The modern CPB circuit is a series of compo-nents consisting of cannulas, tubing, venous reservoir, filters, oxy-genator, 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 opera-tive 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
• Fig 35.2 Rollerpumpwith¼-inchtubingplacedintheraceway.
Field
suction
Cardiotomy
field suction
SVC & IVC
bicaval
cannulation
Venous line; gravity drainage
Temp 4°C
mm Hg
del Nido cardioplegia 1:4
Bubble sensor
Gas filter
Water heater/cooler
Blender
Air
CO2
Cardiotomy;
venous reservoir
Oxygenator;
heat exchanger;
integrated arterial filter
Field suction
Arterial pump Vent;
cardioplegia;
mini roller pumps
mm Hg
•Fig 35.3 Schematic of the cardiopulmonary bypass circuit at Children’s Health Dallas. CO 2, Carbon