Anaesthesia for off pump coronary artery bypass grafting
Anaesthesia for off pumpcoronary artery bypass grafting- the current concepts Presented- DR. SACHIN BANSAL Moderator- DR. ANJUM
DEFINITION Off-pump coronary artery bypass or "beating heart" surgery is a form of coronary artery bypass graft (CABG)surgery performed without cardiopulmonary bypass (heart-lung machine) as a treatment for coronary heart disease During most bypass surgeries, the heart is stopped and a heart-lung machine takes over the work of the heart and lungs. When a cardiac surgeon chooses to perform the CABG procedure off-pump, also known as OPCAB (Off-pump Coronary Artery Bypass), the heart is still beating while the graft attachments are made to bypass a blockage.
Historical aspects the first open heart surgery was performed by John Gibbon in 1952 us-ing cardiopulmonary bypass First successful OPCAB was per-formed in 1961 and Kolesov in 1964 performed the first successful anastomosis of left internal mammary artery to left anterior descending artery In 1967 Favalaro and Effler performed reversed saphenous vein grafting. In 1968 Green performed anastomosis of the internal mammary artery to the coronary artery .
Off pump coronary artery bypass grafting vs. onpump coronary artery bypass grafting Systemic inflammatory response syndrome (SIRS) -A combination of non pulsatile flow, myocardial ischaemia, hypothermia and contact of the patient blood with the artificial surface of the extra corporeal circuit is responsible for the inflammatory process. Coagulopathy-disruption of the coagulation system and haemodilution after cardiopulmonary by-pass is avoided in OPCAB.
Off pump coronary artery bypass grafting vs. on pumpcoronary artery bypass grafting Neurologic dysfunction-four major causes- embolization, inflammation, hypoperfusion and hyperthermia. Two type-1. death either due to stroke or hy-poxic encephalopathy,stuper n coma. Risk factors are diabetes mellitus, atherosclerosis in the proximal aorta and preexisting impairment of cerebral blood flow. Type-2- intellectual dysfunction, memory deficits, confusion or agitation are due to small micro emboli and inadequate perfusion
The incidence of stroke after OPCAB is about 1% when comparedto 9% after CABG•Myocardial injury:- myocardial injury as assessed by biochemical markers is much less after OPCAB when compared to CABG. •Pulmonary dysfunction: CABG pulmonary dysfunction may be caused by alveolar atelectasis, inflammation, increased shunting, and volume infu-sion. . The rate of renal failure is lower in patients undergoing OPCAB.
The goals of anaestheticmanagement Provision of safe anaesthesia using a technique that offers maximum cardiac protection and stability Maintaining haemodynamics in the intraoperative period by physical and pharmacological methods Allowing early emergence, ambulation Providing adequate pain relief in the postoperative period.
Preoperative anaestheticassessment Preoperative optimization of diabetes, hypertension and reactive airway is essential. Preoperative assessment of the carotid arteries is routinely carried out. Preoperative transthoracic echocardiography, chest X ray, and ECG serve as baseline investigations.
Preoperative anaestheticassessment Beta blockers should continue to receive it in the same dose Anti plate-let medications should be stopped atleast 1 week prior to surgery ACE inhibitors should be stopped 24 to 36 hours prior to surgery. The last dose of low molecular weight heparin should be 12 hours prior to surgery & unfractionated heparin 6 hours prior to surgery. review the coronary angiogram for a patient with poor left ventricular function coupled with small caliber coronary arteries.
Premedication Benzodiazepines, opioids and anticholinergic medications. 0.05mg.kg -1 of midazolam and 1µg.kg -1 of fentanyl are administered intramuscularly thirty minutes prior to surgery. provide supplemental oxygen.Before insertion of intravenous and arterial cannulae administer additional midazolam and fentanyl.
MonitoringElectrocardiogram (ECG)-well visualized P wave and QRS complex prior to commencing the surgery.Non invasive monitors- include pulse oximetry and capnography.Invasive blood pressure monitoring-By radial or femoral artery. The cannula-tion of the femoral artery not only permits access to the central arterial tree but provides access to quick insertion of an intra aortic balloon pump. If radial artery cannulation is planned the Allens test must be performed prior to performing cannulation.
Pulmonary artery catheter (PAC)-PAC is usually via the right internal jugular vein.Indication- Ejection fraction less than 0.4. Significant abnormality of the left ventricular wall motion. LVEDP greater than 18 mm Hg at rest. Recent MI and unstable angina.
Transesophageal echocardiography(TEE)Advantages- Identify myocardial ischaemia early by detecting regional wall motion abnormalities. assess left ventricular dysfunction intra operatively. assessing the improvement in myocardial function after the completion of revascularization.Dissadvantage- Inability to image the required part of the heart during grafting .Monitoring of urine output, oropharyngeal and rectal tem-perature is essential.
INDUCTION induction should be slow. induce general anaesthesia by inhalational technique by either sevoflurane or isoflurane in 1-2 minimal alveolar concentration. Neuromuscular blockade is achieved by injecting 0.7 mg.kg -1 of rocuronium intra-venously prior to intubation. Maintenance of is achieved with an infusion of fentanyl, atracurium and isoflurane.
Intraoperative management Hypotension- treated with volume loading. adequate heart rate in sinus rhythm. increasing afterload to maintain systemic perfusion pressures. Inotrope therapy should ,like dopamine, epinephrin & dobutamine by infusion. informing to surgeon for cotton packs under heart and the epicardial stabilizers should be repositioned. resting the heart in the pericardial cavity. If there is no improvement, an intra aortic balloon pump support can be instituted.
Intraoperative management Arrhythmia- Use lidocaine (without preservative) infusion if patient has arrhythmia caused by myocardial ischaemia. If arrhythmias caused by electrolyte imbalance then start an infusion of potassium chloride and magnesium chloride.
Intraoperative management Intraoperative heparinisation and neutralization- The dose of heparin is 2mg.kg -1 (200 units.kg -1 ) in-travenously.Activated clotting time( ACT) should be per-formed 3 minutes after administration. The goal is to keep the ACT between 250 - 300 seconds.
Intraoperative managementACT should be repeated hourly and repeat bolus of 5000 units intrave-nously is essential if the ACT value is less than 250 sec-onds.Heparin is reversed with protamine sulfate with dose 1 mg/1mg of heparin. Accept-able ACT is in the range of 130 to 140 seconds after protamine administration.A high ACT will require additional protamine in a dose of 25 to 50 mg.
Prevention of hypothermiaWarm blanket covers in the pre operative Period.Keep the operating theatre warm till induction and there after the temperature can be decreased gradually.The time taken for sterile preparation by painting and drap-ing by sterile sheets should be kept to the minimum.
Prevention of hypothermia Spillage of cold fluids on the patient is avoided by draping the patient with water-proof sheets. intravenous fluids intended for use are warmed by fluid warmers.Low fresh gas flows with carbon di oxide reabsorp-tion circuits.
Prevention of Myocardialischaemia Maintaining systemic blood pressure by keeeping mean arterial pressure of at least 70 mm Hg all times by administration of boluses intravenous fluid and Trendelenburg position. Reduction in myocardial oxygen consumption by avoiding tachycardia , using intraoperative beta- blockers or calcium channel blockers. Ischaemia during distal anastomosis can be prevented by using intraluminal coronary shunts .
IntracoronaryshuntsThese are doublelimb shunts that fitinto the proximaland distal ends ofthe open coronaryartery
Intracoronary shuntsBenefits:-Native coronary arterial blood flow is maintained preventing intraoperative ischaemia.Blood loss during coronary anastomosis is avoided or decreased.The coronary stent prevents embolization of carbon dioxide into the coronary arteries.
Intracoronary shunts shunt prevents the surgeon from taking a suture on the posterior wall of the coronary artery.Presence of the shunt assures a proper coro-nary anastomosis. insertion of intraluminal coronary shunts will reverse the changes caused by ischaemia like myocardial oedema, endothelial and contractile dysfunction.
Haemodynamic changes related toheart positionLifting and rotating the heart during OPCAB can alter the haemodynamics such as cardiac output, stroke work, left ventricular end diastolic pressure and right atrial pressure. During grafting of right coronary artery bradycardia can occure due to reduction in blood supply to the sinus and AV nodes, so if required use atropine and atrial pacing .
Haemodynamic changes related toheart position During grafting of the right coronary artery and obtuse marginal branches "verticalization" of the heart is required, so posterior pericardial stitches and a gentle retracting socket will greatly facilitate haemodynamic . Reduction in the dose of intravenous vasodilators can increase the haemodynamic changes. During such times it may be essential to reduce the dose of the vasodilator and add a vasoconstrictor.
Post operative management Get a 12 lead electrocardiogram for any fresh changes like ischaemia or myocardial infarction & treated with low molecular weight heparin, anti platelet medications, insertion of an intra aortic balloon pump or revision of grafting. During transfer of the patient continuous monitoring of ECG , pulse oximetery and invasive blood pressure is essential. Always carry prefilled syringes of diluted 1:200,000 adrenaline, 1.2mg of atropine and 100mg of lidocaine (preservative free) to treat a crisis during the transfer phase. cardiac index and partial pressure of oxygen is decreased and took almost 15 to 20 minutes to return to baseline.
I.C.U. managementPatients are connected to the ventilator:- parameters are as follows:- FiO2 of 0.8 tidal volume- 7-10 ml.kg -1 frequency -12- 15/min I:E ratio of 1:2, and controlled mode of ventilation.Arterial blood gas analysis is performed after thirty minutes. FiO2 is reduced to 0.4 if oxygenation, carbon dioxide elimination and tissue perfusion.
I.C.U. managementThirty minutes later a reassessment of- blood loss (not more than 10% of blood volume) fluid balance (not more than 10-15 ml.kg- 1 body weight) core tem-perature ( not less than 35 deg Celsius ), arrhythmias urine output (at least 1-2 ml.kg -1 .hr -1 ) are done.If the residual neuro-muscular blockade is present then reversed by injecting a combination of neostigmine and glycopyrrolate.
I.C.U. managementAfter confirming adequacy of reversal ventilatory mode is switched to the spontaneous modes of ventilation, such as pressure support, or continuous positive airway pressure.Thirty minutes after supported ventilation arterial blood gas analysis is repeated and If the analysis shows satisfactory values of oxygenation, carbon dioxide elimination and metabolism, the patients are extubated.
Fast track anesthesia Defined:- as tracheal extubation within 8 hours after cardiac surgery, early mobilization of patient and early discharge from the hospital. availability of short acting opioid medications have made it possible to subject the patients after cardiac surgery to fast track anaesthesia..
Fast track anesthesia Early extubation resulted in regaining the cough reflex and thus a lower incidence of atelectasis and pneumonia. All patients may not be suitable for fast tracking; presence of bleeding, dysrryhtmias and haemodynamic instability warrant ventilation till stability is achieved. Long acting sedatives should be avoided
Management of postoperativepain Epidural analgesia:- begin an epidural fentanyl infusion with Fentanyl 3000 mcg (60 ml), 0.5% bupivacaine 55ml and saline 155ml are added to make a final total volume 265 ml & start at a rate of 2ml.hour -1 Intravenous opioids:- Fentanyl 3000mcg and saline 215ml are added to make a final con-centration 11 mcg.ml -1 of fentanyl.