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Bradyarrhythmia due to SND and to lesser extent AVB is relatively common after
orthotopic heart transplantation and leads to permanent pacemaker implantation in
up to 21 % of patients with SND and 4.5 % of patients with AVB (Grant et al. 1995 ).
Improvement in postoperative bradyarrhythmia may occur in signifi cant number of
patients. Rate of recovery is less common after complete AVB than SND (Merin
et al. 2009 ).
9.3.2 Pathogenesis
Postoperative bradyarrhythmias can be caused by incomplete washout of cardiople-
gia solution, antiarrhythmic drugs, or their toxicity. In addition, it may be caused by
trauma or surgical manipulation in the area of the AV node or bundle of His.
9.3.3 Prophylaxis
In order to reduce the incidence of postoperative conduction disorder, special atten-
tion to the anatomy of the conduction system, careful administration of sinus or AV
nodal blocking agents, and complete washout of cardioplegia solution are
warranted.
9.3.4 Management
According to the American College of Cardiology/American Heart Association
guidelines, “permanent pacemaker implantation is indicated for third-degree and
advanced second-degree AVB at any anatomic level associated with postoperative
AVB that is not expected to resolve after cardiac surgery” (Tracy et al. 2013 ).
Generally, it is recommended to implant a permanent pacemaker if symptomatic
complete AVB or SND persists longer than 5–7 days after cardiac surgery (Merin
et al. 2009 ). Any decision regarding timing of implantation of a permanent pace-
maker will be impacted by the stability of the temporary pacing system. Therefore,
patients with no intrinsic underlying rhythm or those with failure of temporary pac-
ing leads, permanent pacing may be performed even sooner. In patients with
resolved or resolving bradyarrhythmias, electrophysiological study or exercise
stress testing is useful to determine the need for permanent pacemaker
implantation.
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A. Dabbagh et al. (eds.), Postoperative Critical Care for Cardiac Surgical Patients,
DOI 10.1007/978-3-642-40418-4_10, © Springer-Verlag Berlin Heidelberg 2014
Abstract
CNS dysfunction after cardiac surgery is considered among the most important
etiologies for morbidities and mortalities after cardiac surgery, and patients
undergoing cardiac surgery might be affected by unwanted CNS complications;
this is a well-established fi nding in many studies.
Although postoperative period-related factors constitute only about one fi fth
(20 %) of etiologies of postoperative CNS complications of cardiac surgery, the
CNS complications are not usually seen intraoperatively; those CNS complica-
tions seen fi rst during the hospitalization period are usually encountered in ICU.
Two main classifi cations are used for categorizing postoperative CNS injuries
in cardiac surgery patients. The fi rst is mainly a clinical classifi cation (including
type I and type II disorders), while the second is a time-based classifi cation
(including early and late disease).
A. Dabbagh , MD
Department of Anesthesiology and Anesthesiology Research Center, Faculty of Medicine ,
Shahid Beheshti University of Medical Sciences , Tehran , Iran
e-mail: alidabbagh@yahoo.com, alidabagh@sbmu.ac.ir
1 0
Postoperative CNS Care
Ali Dabbagh
Contents
10.1 Classifi cation and Mechanisms of CNS Dysfunction After Cardiac Surgery .............. 246
10.1.1 General Considerations of CNS Dysfunction After Cardiac Surgery ............. 246
10.1.2 Classifi cation of CNS Injuries After Cardiac Surgery .................................... 246
10.1.3 Risk Factors of CNS Injuries .......................................................................... 248
10.1.4 Mechanisms and Potential Etiologies of CNS Injuries ................................... 248
10.2 Prevention Strategies ..................................................................................................... 252
10.2.1 Pharmacologic Neuroprotection ..................................................................... 252
10.2.2 CPB-Related Equipment ................................................................................. 253
10.3 Neurologic Monitoring ................................................................................................. 253
References ................................................................................................................................ 253
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Advanced age, high preoperative creatinine level, prior neurologic event,
prolonged cardiopulmonary bypass time, and female gender are considered as
early risk factors, while prior neurologic event, diabetes mellitus, unstable angina,
previous cerebral vascular disease, need for inotropic support, and postoperative
atrial fi brillation are considered as delayed risk factors. Aortic atherosclerosis is
considered as both an acute and a chronic risk factor. The underlying mechanisms
are classifi ed in 5 main classes: patient-related etiologies, intraoperative surgical
etiologies, intraoperative anesthetic etiologies, intraoperative extracorporeal cir-
culation (ECC) etiologies, and postoperative period-related etiologies; a number
of potential etiologies have been proposed in each class. Prevention strategies
include pharmacologic neuroprotection and CPB-related techniques. Novel and
older technologies are used to improve the CNS outcome.
10.1 Classification and Mechanisms of CNS Dysfunction
After Cardiac Surgery
10.1.1 General Considerations of CNS Dysfunction
After Cardiac Surgery
CNS dysfunction after cardiac surgery is considered among the most important eti-
ologies for morbidities and mortalities after cardiac surgery, and patients undergo-
ing cardiac surgery might be affected by unwanted CNS complications; this is a
well-established fi nding in many studies.
Postoperative cerebral dysfunction after cardiac surgery is one of the most dev-
astating complications and the least desired morbidity after cardiac surgery; it
would affect not only the short-term clinical outcome adversely but also the long-
term quality of life; in such a way that “ neurocognitive decline after cardiac surgery
might be seen in up to three quarters of patients at hospital discharge and persist in
a third of patients up to 6 months after surgery…and also, are associated with
decreased quality of life .” As the population of elderly undergoing cardiac surgery
increases, these complications are seen more frequently. Although postoperative
period-related factors constitute only about one fi fth (20 %) of etiologies of postop-
erative CNS complications of cardiac surgery, the CNS complications are not usu-
ally seen intraoperatively; those CNS complications seen fi rst during the
hospitalization period are usually encountered in ICU (Roach et al. 1996 ; Newman
et al. 2001 ; Sato et al. 2002 ; Hogue et al. 2008a , b , c ; Mathew et al. 2009 ; Lombard
and Mathew 2010 ; Hedberg et al. 2011 ; Bartels et al. 2013 ; Mashour et al. 2013 ).
10.1.2 Classification of CNS Injuries After Cardiac Surgery
Two main classifi cations are used for categorizing postoperative CNS injuries in
cardiac surgery patients. The fi rst is mainly a clinical classifi cation, while the sec-
ond is a time-based classifi cation.
A. Dabbagh
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247
10.1.2.1 Type I and Type II Injuries
Cerebral complications after cardiac surgery have been categorized as type I and
type II injuries (Roach et al. 1996 ; Newman et al. 2001 ; Carrascal et al. 2005 ;
Marasco et al. 2008 ; Liu et al. 2009 ; Lombard and Mathew 2010 ).
The incidence of type I injuries is not high, but its severity and poor outcome
could never be neglected; the incidence of stroke following CABG is about 1 %;
these injuries are usually neurologic defi cits and include the following:
• Fatal and nonfatal stroke (motor, sensory, or language defi cit or a combination of
them)
• Hypoxic encephalopathy
• Focal neurologic injury
• TIA (transient ischemic attack)
• Coma at discharge
• Stupor at discharge
Type I injury could happen in 1–4 % of closed chamber cardiac surgery and
8–9 % of open chamber cardiac surgery.
Type II injuries are neurologic disorders other than type I which are also more
common than the previous class of disorders and include the following:
• New deterioration of intellectual function.
• Confusion.
• Agitation.
• Memory defi cit.
• Seizures without evidence of focal injury.
• Disorientation.
• Problem solving ability defi cit.
• Attention and concentration impairment.
• Language problems.
• Psychomotor performance problems.
• Learning and memory problems.
• Mental processing speed defi cit.
• Intelligence defi cit.
• Usually, delirium is among the most common acute presentations of CNS disor-
ders (detailed discussion about postoperative delirium and its management is
presented in another chapter of the book titled “Cardiovascular Pharmacology”
(Chap. 2 )).
Type II injury could happen in over 50 % of the patients at the time of discharge
from hospital and about 30 % of the patients six times after operation.
10.1.2.2 Time-Based Classification of Postoperative CNS Injuries
Another classifi cation involves the time interval after surgery, based on the fact that
“early and delayed stroke differ in their related risk factors.” The risk factors for
early and late CNS disorders are discussed in the next section. Early postoperative
cognitive dysfunction is an important predictor of “late postoperative cognitive dys-
function” 5 years later after surgery. It has been mentioned that early stroke has
right cerebral hemisphere predominance rather than the left hemisphere, while
10 Postoperative CNS Care
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delayed stroke involves a uniform distribution. About one fi fth (20 %) of postopera-
tive CNS complications of cardiac surgery occur due to postoperative events, while
80 % are directly related to intraoperative events (Hogue et al. 1999 , 2008a , b , c ;
Nathan et al. 2007 ; Hedberg et al. 2011 ; Hedberg and Engstrom 2012 ; Bartels et al.
2013 ; Mashour et al. 2013 ).
10.1.3 Risk Factors of CNS Injuries
Usually, a time-based classifi cation is considered for classifi cation of the risk fac-
tors, having the following two categories for classifi cations of risk factors for post-
operative cerebral disorders after cardiac surgery (Hogue et al. 1999 ; Hedberg et al.
2011 ).
Early stroke risk factors are:
• Advanced age
• High preoperative creatinine level
• Prior neurologic event
• Aortic atherosclerosis area of involvement
• Longer duration of cardiopulmonary bypass
• Female gender with a seven-fold increased risk of early stroke and a 1.7-fold
increased risk of delayed stroke
Delayed stroke risk factors are:
• Prior neurologic event
• Diabetes
• Aortic atherosclerosis
• Unstable angina
• Previous cerebral vascular disease
• Need for inotropic support
• Atrial fi brillation in postoperative period (combined end points of low cardiac
output and atrial fi brillation)
• Low cardiac output (combined end points of low cardiac output and atrial
fi brillation)
• Female gender
10.1.4 Mechanisms and Potential Etiologies of CNS Injuries
One of the most prominent features in “post-cardiac surgery cerebral disorders” is
that their etiologies are not distinct, but a number of interrelated factors are respon-
sible in occurrence of these clinical disorders; however, a general classifi cation
could be as follows:
• Patient-related factors.
• Intraoperative surgical factors.
• Intraoperative anesthetic factors.
• Intraoperative extracorporeal circulation (ECC) factors.
A. Dabbagh
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• Postoperative period-related factors: about one fi fth (20 %) of postoperative
CNS complications of cardiac surgery occur due to postoperative events, while
80 % are directly related to intraoperative events.
• First of all, postoperative CNS complications after cardiac surgery are usually
ischemic type; less than 5 % of them have a hemorrhagic origin. However, “ CPB-
related infl ammation, microemboli, and hypoperfusion ” are related mainly to
acute (short-term) neurocognitive disorders, and “ underlying cerebrovascular
disease in CABG candidates ” is mainly responsible for the late neurocognitive
impairments (occurring 1–5 years postoperatively).
• There is a direct relationship between aortic atherosclerosis and postoperative
CNS problems: “ aortic atherosclerosis and cerebral atherosclerosis are con-
comitant pathologies .” Till now, the main possible etiology for postoperative
CNS complications is the underlying atherosclerotic process of the patient
involving all the arterial system including the coronary arteries and the cerebral
vascular system. Aortic atheroma (even when it is not as a plaque) is disrupted
during thoracic aortic manipulations, including aortic cannulation, aortic cross
clamping, and proximal anastomosis of grafts. Also, perfusion through the arte-
rial cannula of CPB has a “sandblasting effect” which increases the risk of CNS
injury; epi-aortic scanning is the most sensitive method for detecting aortic ath-
erosclerosis to fi nd appropriate place for cannulation, while palpation of the
aorta by surgeon’s fi nger is not as effective.
• CNS hypoperfusion during CPB is an important risk factor. MAP between 50 and
80 mmHg is a target blood pressure for maintaining cerebral autoregulation
functioning; the role of MAP is especially important in maintaining both cortical
end arteries and cerebral collateral arteries. However, patients undergoing car-
diac surgery usually have comorbidities; so, their cerebral autoregulation would
function in higher pressures, and upper limit of blood pressure for MAP during
CPB is considered more appropriate for these patients. Even in patients undergo-
ing off-pump cardiac surgery, any blood pressure derangement might have a
great impact on CNS outcome. It seems that cerebral oximetry could help us
control cerebral perfusion with much more exactness.
• Hypothermia during cardiac surgery has been used as an organ-protective strat-
egy; however, its effect on CNS outcome is yet to be defi ned since it has not been
demonstrated to be effective in protecting CNS. On the other side, hyperthermia
is a potent CNS risk factor usually occurring if slow rewarming strategies are not
used for CPB weaning: 2 °C difference of CPB perfusate temperature and naso-
pharyngeal temperature improve outcome compared with 6 °C.
• As mentioned earlier, time interval after surgery is another factor since the risk
factors of “early and delayed stroke” are different.
• The main CNS insult happens during the operation; however, about 20 % of the
strokes are the result of postoperative events , which mandates enough vigilance
during postoperative period.
• Particle emboli : Both macroemboli (atherosclerotic debris originating from the
thoracic aorta) and microemboli (fatty particles or gaseous emboli) are consid-
ered as important etiologies for cerebral injuries.
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• Microemboli are originated both from fatty nature of embolic particles and also
the presence of aluminum and silicone in the aspirates of the cardiotomy suction;
both types could occlude CNS end arteries. Lipid microemboli cause small capil-
lary and arteriolar dilatations (SCADs), generally in the range of 10–70 μm;
most of the lipid microemboli are shed into brain end arteries through cardiot-
omy suction.
• Using or avoiding CPB has been considered as a potential mechanism of injury
with extensive studies assessing its effects. From one aspect, off-pump surgery
has less aortic manipulations and prevents CPB-related microemboli and infl am-
mation. However, on the other hand, “ aortic manipulations by the surgeon dur-
ing proximal grafting ” and “ hypotension episodes at the time of cardiac
maneuvering for distal grafting ” are two possible mechanisms which could
cause CNS injury in off-pump patients. Possibly this is why no signifi cant
difference (regarding postoperative CNS events) has been demonstrated between
on- pump and off-pump groups. Finally, “ CPB alone does not cause enough
neuro-infl ammatory changes leading to increased long-term cognitive
dysfunction. ”
• Against the discussions related to on-pump and off-pump procedures, the time
interval for using extracorporeal circulation and CPB is considered as a real risk
factor for postoperative CNS dysfunction, since it boosts the infl ammatory
response.
• Tight glycemic control in diabetic and nondiabetic adult patients undergoing car-
diac surgery was considered as a neuroprotective strategy; however, during recent
years, evidence demonstrated “tight glycemic control” as an equivocal strategy
regarding patient outcome and mortality rate , compared with conventional glu-
cose management; a possible mechanism is the relatively high resistance against
insulin during cardiopulmonary bypass with latent hypoglycemia after CPB,
especially kin postoperative period which could induce cerebral hazards.
• Anemia is another major potential risk factor for postoperative CNS injury, espe-
cially if the hematocrit level during CPB is below 22 % in patients at risk of CNS
injury; in such a way that for each 1 % fall in the level of hematocrit, a 10 %
increase in CNS injury chance has been shown; the possible mechanism for this
fi nding is decreased cerebral oxygen delivery accompanied with increased
embolic load due to compensatory cerebral arterial dilatation; however, it is not
still proved that packed cell transfusion in order to compensate for anemia could
prevent CNS injury, so we have to weigh the risk and benefi t of transfusion in
such cases.
• Genetic predisposition is another potential mechanism explained in a number of
studies, including genetic variants of CRP and interleukin 6 and also apolipopro-
tein E (APOE) genotype.
• Atrial fi brillation is the most common arrhythmia in postoperative period of car-
diac surgery, occurring in >30 % of the patients and has a clear and direct rela-
tionship with postoperative CNS injury.
• Advanced age is “the main predictive factor which could foresee the occurrence
of permanent postoperative neuropsychological defects” (mainly type II injury).
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• Gender Female gender is associated with a 5- to 7-fold increased risk of early
stroke and a 1.5- to 2-fold increased risk of delayed stroke.
• Previous history of cerebrovascular events.
• Impaired left ventricular function : Heart failure is associated with impaired cog-
nitive function (primarily presented as delirium in hospitalized patients).
• Valvular surgery is an important risk factor for increased prevalence of postop-
erative cognitive decline than other cardiac procedures; it is possible that micro-
embolic events are the major reason for this fact.
• Postoperative neurocognitive disorders would affect the cortical white matter of
the brain mainly due to infl ammatory mechanisms with a number of markers like
“Alzheimer-associated amyloid-β.” (Table 10.1 )
Table 10.1 Proposed risk factors for post-cardiac surgery cerebral dysfunction
Patient-related factors
1. Risk factors related to patient pathophysiologic status
CPB-related infl ammatory response
Intraoperative hypoperfusion
Intraoperative cerebral oxygenation status
Intraoperative anesthetics used during operation
2. Risk factors related to underlying patient status
Perioperative comorbid states (diabetes mellitus, hypertension, atherosclerosis especially in
ascending aorta, previous cerebrovascular pathologies)
Preoperative cerebral blood fl ow (CBF) velocity, which demonstrates cerebral perfusion
status (even, preoperative left-sided hypoperfusion could be a risk factor)
Old age
Perioperative sleep status
Perioperative administration of medications
3. Risk factors related to patient social status
Underlying social class and social status
Postoperative administration of rehabilitation care
Underlying level of education
Gender
Ethnic differences
Procedure-related factors (intraoperative and postoperative surgical factors, anesthetic factors,
and extracorporeal circulation (ECC) factors)
Using cardiotomy suction (time of using suction during surgery, using cell saver and arterial
fi lter)
Duration of aortic cross clamp
Using hypothermia, optimal rewarming, severity and duration of hypothermia (especially if
using DHCA)
Hyperthermia after CPB
Deairing management during surgery
Type of surgery (especially valve surgery or involving the aortic root)
Intraoperative use of epi-aortic scanning by the surgeon for aortic cannulation
Unstable hemodynamic status before, during, or after CPB
Location of the possible side of hypoperfusion during operation (left vs. right carotid system)
Using or avoiding CPB (on pump vs. off pump)
(continued)
10 Postoperative CNS Care
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