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Hemodynamic Changes During Cardiac Manipulation in
Off-CPB Surgery: Relevance in Brain Perfusion
(#2002-15534 ... March 15, 2002)
John M. Murkin, MD, FRCPC
Department of Anesthesiology
and Perioperative Medicine, University of Western Ontario, London, Ontario
ABSTRACT
The recent introduction of various cardiac stabilization
and positioning devices, alone or in combination with deep
pericardial traction sutures, has greatly increased the ability
to perform beating heart surgery to accomplish multi-vessel
coronary revascularization without the need for cardiopulmonary
bypass (CPB), with its associated risks. However,
positioning the heart for anastomosis of the circumflex (Cx)
and the posterior descending artery poses a risk of inducing
hypotension, impaired cardiac output, and generalized
hemodynamic instability with risk of cerebral compromise.
This report discusses clinical studies suggesting that compromised
right ventricular diastolic filling as a result of
direct ventricular compression, rather than impaired contractility
or ischemia, may be the primary mechanism for
producing hemodynamic instability during OPCAB surgery.
Foremost among measures to minimize ventricular compression
is optimal placement of the myocardial stabilization
device. Secondary measures include steep Trendelenburg
positioning, fluid loading, right-sided pleuro-pericardial
window that allows rotation of the heart by partial herniation
into the right pleural cavity, and possibly certain pharmacological
agents. This report also analyzes the effect that
variable degrees of hemodynamic disturbance accompanying
displacement of the heart for OPCAB surgery has on endorgan
perfusion and considers the effects of hypotensive
agents, direct cerebral dilators, and patient-specific factors
on cerebral blood flow. The role of the partial aortic occlusion
clamp and risk of stroke is also considered. We conclude
that for cardiac surgery patients considered at increased risk
of adverse central nervous system events, direct monitoring
of cerebral function and avoidance of aortic manipulation is
strongly recommended.
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