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Aortic X Clamp - CVS changes and strategies for maintaining perfusion…
Aortic X Clamp - CVS changes and strategies for maintaining perfusion
Clamping - CVS changes
Increased preload
Increased CVP
Increased PCWP
Due to passive recoil distal to clamp and increased catecholamines
Increased afterload
Increased BP
Increased myocardial wall tension
Increased myocardial O2 demand
Due to increased impedence to aortic flow and increased catecholamines
Net result on CO depends on whether coronary flow and increased contractility:
CO increases if coronary flow and contractility both increase
CO reduces if coronary flow and contractility do not increase
Increased blood flow above the clamp
Muscles, lungs, intracranial, coronaries
Reduced blood flow below the clamp
Reduced renal blood flow
Maintenance of organ perfusion
Invasive monitoring ART, CVC to guide therapy
Afterload reduction
SNP
Epidural or inhaled anaesthetics
Discussion with surgeons regarding shunts and partial L heart bypass (LA to fem/distal aorta)
Preload normalisation
Limit IVT prior to clamping
GTN - will also assist by dilating coronary vasculature
Controlled volume depletion i.e. phlebotomy
Maintenance of CO - may require inotropes
Discussion with surgeons regarding technique for renal protection
Minimise cross clamp time (best predict postop renal dysfx)
Partial L heart bypass
Endovascular repair
Hypothermic renal perfusion
Selective renal artery perfusion
Discussion with surgeons regarding technique for spinal cord protection
Minimise cross clamp time (safe <30min, spinal cord injury certain > 60mins)
Partial L heart bypass
Reimplantation of segmental arteries
Shunts to distal aorta (Gott shunt)
Unclamping - CVS changes
Reduced BP
Reduced contractility
Reduced CVP
Reduced CO
Mechanisms
Hypoxic vasodilation - reduced SVR
Hypovolaemia
Release of vasoactive and myocardial depressant mediators (Lactate, Potassium)
Maintenance of organ perfusion
Cease vasodilators prior to unclamping
Fluid loading - 500ml immediately prior to release of infrarenal clamp (more if supracoeliac)
Reduced inhaled anaesthetics
Talk to surgeons about gradual release of aortic clamp
Allows for volume replacment
Slow washout of vasoactive and cardiodepressant mediators
Reduced degree of abrupt oxygenation - reduced production of O2 free radicals
Vasoconstrictors
Severe hypotension may necessitate partial reclamping