|Year : 2007 | Volume
| Issue : 4 | Page : 334
Anaesthesia for off pump coronary artery bypass grafting - the current concepts
Murali R Chakravarthy1, Dattatreya Prabhakumar2
1 MD, DA, DNB, FICC, Wockhardt Hospitals, Bangalore, Karnataka, India
2 MD, Wockhardt Hospitals, Bangalore, Karnataka, India
|Date of Web Publication||20-Mar-2010|
Murali R Chakravarthy
Chief Consultant Anaesthesiologist, Wockhardt Hospitals, Bangalore 560076, Karnataka
Source of Support: None, Conflict of Interest: None
Keywords: Anaesthesia, Off pump coronary artery bypass surgery, Thoracic epidural anaesthesia, Coronary arteries, Bypass surgery
|How to cite this article:|
Chakravarthy MR, Prabhakumar D. Anaesthesia for off pump coronary artery bypass grafting - the current concepts. Indian J Anaesth 2007;51:334
|How to cite this URL:|
Chakravarthy MR, Prabhakumar D. Anaesthesia for off pump coronary artery bypass grafting - the current concepts. Indian J Anaesth [serial online] 2007 [cited 2020 Jun 3];51:334. Available from: http://www.ijaweb.org/text.asp?2007/51/4/334/61162
| Introduction|| |
Cardiovascular disease is considered a major problem in our society, and is one of the major causes of death among humankind ,. In the United States of America alone, more than 500,000 coronary artery bypass graft (CABG) revascularization procedures are performed annually  . CABG is one of the most commonly performed surgical procedures. Cardiac surgery has taken huge strides in the past 5 decades, ever since the first open heart surgery was performed by John Gibbon in 1952 using cardiopulmonary bypass  . Though coronary arteries are located on epicardium, hitherto cardiac surgeons were compelled to perform the coronary artery bypass graft (CABG) surgery using cardiopulmonary bypass, for want of better epicardial tissue stabilizers. The scenario changed after good epicardial stabilizers were available to cardiac surgeons, development of the crucial heart stabilizers in the past decade has paved way for the advent of off pump coronary artery bypass (OPCAB) surgery. OPCAB has gained in popularity globally because of absence of 'side effects' of cardiopulmonary bypass, which till recently were considered as necessary evil. Currently the risk benefit of OPCAB versus conventional CABG is debated widely in the medical literature. ,,
This article is a descriptive summary of anaesthetic techniques for off-pump coronary artery bypass (OPCAB) surgery, as seen and used by the author. The authors describe their management strategies to make it easy for novices.
With the popularity of OPCAB growing, the importance of the anaesthesiologist also grew. Some workers even call the anaesthesiologist the "first assistant" to the cardiac surgeon. The anaesthetic management for off pump coronary artery bypass surgery is a new topic and has recently been listed in major textbooks of anaesthesia. Anaesthesia for OPCAB is particularly demanding and requires an approach specifically tailored to the procedure. OPCAB cases require vigilant anticipation of surgical steps, skilled haemodynamic management and close communication with the cardiothoracic surgeon. Furthermore, optimal management in OPCAB surgery involves a considerable learning curve, for the surgeon, the anaesthesiologist and the entire cardiac team.
| Historical aspects|| |
The concept of off pump coronary artery bypass grafting (OPCAB) surgery is not new. In the early 1950s an attempt was made to increase the myocardial blood flow by inducing pericardial adhesions  . In 1951 Vineburg implanted the internal mammary artery into the myocardium . Although this procedure increased the myocardial blood flow, it was not adequate to allow the patient to lead a symptom free life. First successful OPCAB was performed 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 as we know it today  . In 1968 Green performed anastomosis of the internal mammary artery to the coronary artery  . Studies later showed better patency of the internal mammary artery when compared to the saphenous vein grafts  . Interest was renewed in OPCAB with numerous publications from SouthAmerica and India highlighting the advantages of OPCAB , .
The concept of fast track anaesthesia emerged in the mid 1990's focusing on early extubation, mobilization and ambulation .
| Off pump coronary artery bypass grafting vs. on pump coronary artery bypass grafting|| |
Several studies have shown beneficial effects of avoiding cardiopulmonary bypass. These are reduction in duration of ventilator support, length of intensive care unit stay and hospital stay.
There is evidence to suggest that patients with pre operative renal dysfunction may benefit from the avoidance of CPB (Magee MJ et al 2001  ). Mack MJ et al , Racz MJ et al  and Sabik JF et al have concluded that the rate of renal failure is lower in patients undergoing OPCAB.
- Systemic inflammatory response syndrome (SIRS): Inflammation during on pump coronary revascularization surgery is due to cellular and chemical elements. 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. This response is reduced with OPCAB. Studies have shown that the increase in markers for SIRS is reduced after OPCAB .
- Coagulopathy: The disruption of the coagulation system and haemodilution after cardiopulmonary bypass is avoided in OPCAB. This results in reduced perioperative blood requirements. However recent reports suggest a hypercoaguble state after OPCAB. This state is similar to that after noncardiac surgery. This has led to the use of clopidogrel and aspirin after OPCAB revascularization .
- Neurologic dysfunction: The four major causes of neurological and neuropsychological deficits after CABG are embolization, inflammation, hypoperfusion and hyperthermia. Central nervous system abnormalities after CABG are of two types. Type I injuries are defined as death either due to stroke or hypoxic encephalopathy, or at the time of discharge the patient is in a state of stupor, has a non fatal stroke or is in coma. The risk factors for type I injuries are diabetes mellitus, atherosclerosis in the proximal aorta and preexisting impairment of cerebral blood flow. Type II injuries are new onset injuries. These can manifest as intellectual dysfunction, memory deficits, confusion or agitation. The risk factors for type II injuries include small micro emboli and inadequate perfusion. During CABG cannulation of the ascending aorta, arterial jets due to cannulation and application of aortic cross clamp increases the chances of embolization and neurologic injuries. The incidence of stroke after OPCAB is about 1% when compared to 9% after CABG ,.
- Myocardial injury: The degree of myocardial injury as assessed by biochemical markers is much less after OPCAB when compared to CABG. In a retrospective study involving 17,000 patients undergoing OPCAB and CABG, Mack MJ et al  concluded that following OPCAB the degree of myocardial injury is much less. Al-Ruzzeh S et al  , Shennib H et al  and Ascione et al  have demonstrated that the degree of myocardial injury is lesser after OPCAB in patients with impaired LV function.
- Pulmonary dysfunction: Following CABG pulmonary dysfunction may be caused by alveolar atelectasis, inflammation, increased shunting, and volume infusion .
| Surgical aspects|| |
The patient is usually in the supine position. Incision for performing OPCAB is similar to conventional CABG; via midline sternotomy. Following sternotomy the left internal mammary artery is harvested. At the time of harvesting the left internal mammary artery, a few surgeons wish to administer half dose of heparin (1mg.kg-1) to the patient. Adequate lengths of saphenous vein and radial artery are harvested. Prior to commencement of grafting either proximal or distal, 'full heparinization' is achieved by administering 2-3 mg.kg-1 of heparin intravenously. Activated clotting time guides the adequacy and reversal of heparinization. Activated clotting time of more than 240 secs is considered adequate for performing OPCAB. At the author's institute, the surgeons prefer to perform the proximal anastomosis prior to distal. The ascending aorta is exposed. Apartial cross clamp is applied onto the aorta and a hole measuring 4 mm is punched in the ascending aorta; the 'proximal end' of the proposed conduit is anastomosed to aorta on this punched hole. Various other surgeons perform the distal anastomosis prior to proximal. Performing one technique or the other depends on the institutional protocol. Most surgeons anastomose the left internal mammary artery to left anterior descending artery first. Other grafts usually follow this. Heart is usually 'positioned' by placing a few 'mops' underneath it. The proposed artery is 'stabilized' by placing the epicardial stabilization device/s [Figure 1]. Commonly Octopus TM and or starfish™ are used by surgeons in India. Stabilizing the heart to expose left anterior descending artery and other anterior coronary arteries does not cause serious haemodynamic problems; however, positioning for viewing the lateral vessels (obtuse marginals) may cause haemodynamic changes requiring intravenous fluid boluses or use of infusion of inotrope agents. After completion of grafting, residual heparinization is reversed using protamine sulfate (1 mg for every mg of heparin). Modifications to this technique by using total arterial revascularization, repair of ventricular aneurysm, endarterectomy of coronary arteries have been reported using the OPCAB technique.
Other important techniques include bilateral internal mammary harvesting, performance of a "Y" anastomosis with the radial artery in the presence of atherosclerotic lesions on the aorta where clamping the aorta is dangerous or in the presence of tight lesions in the coronary artery.
| Anaesthetic considerations|| |
The goals of anaesthetic management include
A. Preoperative anaesthetic assessment
- 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.
A detailed history of medical illnesses, anaesthesia in the past, should be obtained. Co-morbid conditions such as diabetes mellitus, systemic hypertension and their effects on target organs such as liver, kidneys and heart should be evaluated. Anaesthesiologists should review the coronary angiogram and the information from it may help him to plan his anaesthetic technique. For example, OPCAB in a patient with poor left ventricular function coupled with small caliber coronary arteries may be high risk and supportive technologies such as intra-aortic balloon counter pulsation, cardiopulmonary bypass may be kept handy. Preoperative optimization of diabetes, hypertension and reactive airway is essential. Use of iodine dye during coronary angiogram may result in damage to kidneys, which may manifest as increasing levels of serum creatinine. Patients with such dye induced nephropathy are more prone to renal dysfunction. Preoperative assessment of the carotid arteries is routinely carried out at the author's institute. In patients more than 50 years of age, a possibility of carotid artery occlusions exists. Assessment of airway as in other cases requiring general endotracheal anaesthesia is important. Laboratory test to assess the functions of vital systems such as hepatic, renal, coagulation must be carried out prior to planning surgery. Preoperative transthoracic echocardiography, chest X ray, and ECG serve as baseline investigations. The presence of regional wall motion abnormalities is a matter of concern to anaesthesiologist, because such patients may develop acute deterioration of haemodynamic status and this may necessitate the requirement of cardiopulmonary bypass to complete the surgery. Patients receiving beta blockers should continue to receive it in the same dose. Anti platelet 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. If the patient is on unfractionated heparin the last dose should be atleast 6 hours prior to surgery. Serum electrolytes should be checked if the patient is on treatment with diuretics.
The goals of premedication are to reduce apprehension and fear, preemptive analgesia, and provide amnesia. There are a variety of drugs available that can be used for premedication. These can be administered either by orally or intramuscularly. It is common to include benzodiazepines, opioids and anticholinergic medications as premedication. At the author's institute, 0.05mg.kg -1 of midazolam and 1µg.kg -1 of fentanyl are administered intramuscularly thirty minutes prior to surgery. It is essential to provide supplemental oxygen after administration of premedication. It is wise to avoid use of drugs that are likely to cause tachycardia.
Immediately preceding insertion of intravenous and arterial cannulae, it is prudent to administer additional midazolam and fentanyl.
Monitoring electrocardiogram (ECG) perhaps is one of the most important monitoring devices in OPCAB. It is the practice at author's institute to stick the ECG leads on the back of the patient. By placing the leads on the back of the patients, dislodgement of the electrode in midst of surgery and disturbance during handling of chest does not occur. One must ensure a well visualized 'P' wave and QRS complex prior to commencing the surgery. It is common to notice disappearance of QRS complex in the midst of OPCAB due to change in cardiac axis caused by positioning of the heart.
Other standard non invasive monitors include pulse oximetry and capnography.
Radial or femoral arterial access is necessary to monitor changes in arterial blood pressure. At the author's institute, right femoral artery is cannulated. The cannulation of the femoral artery not only permits access to the central arterial tree(less susceptible to abnormal values during phases of hypotension) but provides access to quick insertion of an intra aortic balloon pump. The author has used this route in more than ten thousand patients over past eighteen years without complication. Alternatively, left femoral artery can be cannulated with same benefits.
If radial artery cannulation is planned the Allen's test must be performed prior to performing cannulation. The modified Allen's test screens for patients with inadequate palmar collateralization from the ulnar artery.
After insertion of arterial line, it is a common practice among anaesthesiologists to check the blood gases and activated clotting time.
Placement of a pulmonary artery catheter (PAC) routinely in all cardiac patients is controversial. The authors are of the opinion that PAC is beneficial when OPCAB is practiced. Insertion of the PAC is usually via the right internal jugular vein. Indications for PAC insertion are 
Transesophageal echocardiography (TEE) is another useful intra operative monitoring tool, because we can identify myocardial ischaemia early by detecting regional wall motion abnormalities. Apart from identifying this, TEE can also be used to assess left ventricular dysfunction intra operatively. TEE will also help in assessing the improvement in myocardial function after the completion of revascularization. Inability to image the required part of the heart during grafting is an inherent disadvantage of this technique. Inability to image occurs due to the presence of mops placed under the heart. 'Akinesia' of the heart caused by epicardial tissue stabilization should not be mistaken for myocardial dysfunction.
- 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
- Post MI complications
- LV aneurysm
- Mitral regurgitation
- Congestive cardiac failure
- Emergency surgery
- Combined procedures
Monitoring of urine output, oropharyngeal and rectal temperature is essential.
At the end of surgery, efforts should be made to assess the blood loss and replacement of blood loss by suitable blood products may be necessary.
D. Intraoperative management
Different regimens are described for the induction of anaesthesia for a patient planned for OPCAB. However one guiding principle is that induction of anaesthesia should be slow and titrated to the response of the patient. It is the practice of the anaesthesiologists at the author's institute to induce general anaesthesia by inhalational technique. Either sevoflurane or isoflurane are used in 1-2 minimal alveolar concentration. Neuromuscular blockade is achieved by injecting 0.7 mg.kg -1 of rocuronium intravenously prior to intubation. Other monitoring catheters such as urinary catheter, TEE probe are inserted after endotracheal intubation.
Maintenance of anaesthesia is achieved with an infusion of fentanyl, atracurium and isoflurane. Isoflurane can be safely used for maintenance of general anaesthesia, the fears regarding coronary steal associated with isoflurane have been recently dispelled with recent publications ,, .
Hypotension should be treated aggressively with volume loading, adequate heart rate in sinus rhythm and increased afterload to maintain systemic perfusion pressures. Inotrope therapy should be initiated; 5 to 10 mcg.kg1 .min -1 of dopamine infusion is the inotrope of choice at the author's institute. If there is no response to initiation of inotropic therapy, the surgeon should be informed of it and the cotton packs under heart and the epicardial stabilizers should be repositioned. Despite these measures if there is no improvement in arterial blood pressure, the heart should be rested in the pericardial cavity. Usually, the arterial blood pressure increases. If there is no improvement, an intra aortic balloon pump support can be instituted. Use of lidocaine (without preservative) infusion may be indicated if the patient has arrhythmia caused by myocardial ischaemia. A common cause of arrhythmias intraoperatively is electrolyte imbalance. It is a routine practice at the author's institute to start an infusion of potassium chloride and magnesium chloride and the rate of infusion is titrated to maintain the value of these electrolytes in normal range.
| Intraoperative heparinisation and neutralization|| |
The dose of heparin is 2mg.kg -1 (200 units.kg -1 ) intravenously. Prior to the injection of heparin one should aspirate the line to ensure the intravascular presence of the catheter and inject heparin. An ACT should be performed 3 minutes after administration. The goal is to keep the ACT between 250 - 300 seconds. ACT should be repeated hourly and repeat bolus of 5000 units intravenously is essential if the ACT value is less than 250 seconds.
Heparin is reversed after the completion of grafting with protamine sulfate. The dose for heparin neutralization is 1 mg/1mg of heparin. Protamine should be administered cautiously after a test dose. Following protamine administration the ACT should be checked. An acceptable ACT is in the range of 130 to 140 seconds. A high ACT will require additional protamine in a dose of 25 to 50 mg.
| Measures to avoid hypothermia|| |
Maintaining normothermia is one of the important, but difficult tasks during OPCAB surgeries. It is important to prevent heat loss rather than actively rewarm the patient. During CABG it is possible to maintain the temperature/ rewarm the patient by core-warming the patient using heat exchangers. However this is not possible during OPCAB. The various techniques that help in maintaining temperature include
Role of thoracic epidural anaesthesia (TEA): The author's institute has reported a large series of use of TEA during cardiac surgery .
- Warm blanket covers in the pre operative period: Blankets such as Bear Hugger® is handy in maintaining the patient's temperature during the preoperative period. Waiting in air conditioned preoperative waiting should be kept to minimum.
- Keep the operating theatre warm till induction and there after the temperature can be decreased gradually
- The time taken for sterile preparation of the patient by painting the patient with antiseptic solution and draping by sterile sheets should be kept to the minimum
- Warm blankets under the patient: It is not difficult to procure a blanket rendered warm by circulating it with warm water. Spillage of cold fluids on the patient is avoided by draping the patient with waterproof sheets
- Warm intravenous fluids: Various types of fluid warmers are available in the market and anyone could be used. At the author's unit, intravenous fluids intended for use are warmed by fluid warmers.
- Low fresh gas flows with carbon di oxide reabsorption circuits: Use of circle absorbers prevent heat loss.
Advantages of TEA include
- Antianginal effect
- Improves myocardial oxygen balance
- Attenuates the paradoxical vasoconstrictor response at the site of atherosclerotic lesions
- Increases the luminal diameter of dynamic stenosis of epicardial coronary arteries
- Reduces myocardial work
- Reduces the total dose of anaesthetic requirements in the intraoperative period
- Haemodynamic stability is achieved. It is common to note that heart rate, arterial blood pressure and pulmonary artery pressure remain steady during surgery.
- Provides excellent postoperative pain relief. Good pain relief produces many beneficial effects such as improved participation in physiotherapy activities, early ambulation, and good postoperative morale of the patient.
| Challenges faced in the intraoperative period|| |
1. Myocardial ischaemia
Recognition of certain risk factors preoperatively can prevent the development of intraoperative ischaemia . These include higher preoperative angina class, higher prevalence of preoperative myocardial ischaemia, cardiomegaly and lower body surface area. Intraoperative ischaemia is avoided by:
- Maintaining systemic blood pressure. A mean arterial pressure of at least 70 mm Hg should be maintained at all times. At times, this may not be feasible. A mixed venous oxygen saturation of at least 60% or more is suggestive of adequate tissue perfusion. This can be achieved by a combination of techniques. If the wedge pressure is low, administration of boluses of intravenous fluid and Trendelenburg position may help.
- Reduction in myocardial oxygen consumption can be achieved by avoiding tachycardia. This can be achieved by using intraoperative beta-blockers, TEA or calcium channel blockers. However one must be careful while using this drug in the presence of impaired left ventricular function. It is also prudent to avoid bradycardia. Bradycardia may decrease cardiac output. It may be easier and faster to correct bradycardia by electrically pacing the patient. Bradycardia may commonly be seen during grafting of right coronary artery.
- A certain degree of ischaemia will occur during distal anastomosis and can be prevented by using intraluminal coronary shunts [Figure 2]. These are double limb shunts that fit into the proximal and distal ends of the open coronary artery. The benefits of using the intracoronary shunts are as follows:
It has been demonstrated that periods of ischaemia as brief as 12 minutes can cause myocardial oedema, endothelial and contractile dysfunction. Studies have shown that the insertion of intraluminal coronary shunts will reverse these changes ,,,,,. Patients with poor left ventricular function and poor collateral circulation are likely to benefit maximum from the insertion of intraluminal coronary shunts  .At times, it may not be possible to insert even the smallest sized shunt; cardiac surgeons 'sling' the coronary arteries briefly to prevent blood loss. 2. Haemodynamic changes related to heart position: In order to visualize the coronary arteries, the cardiac surgeon may lift the heart, or place cotton mops and use various stabilizers. The role of anaesthesiologist is to anticipate these steps and treat the resultant haemodynamic problems. Lifting 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.
- Native coronary arterial blood flow is maintained, this plays a major role in preventing intra-operative ischaemia
- Blood loss during coronary anastomosis is avoided or decreased.
- The coronary stent prevents embolization of carbon dioxide into the coronary arteries ( "Blower Mister", Medtronic ™ TM is a device used to 'flush' the operative field with carbon dioxide to improve vision during anastomosis)
- Presence of the intra-coronary shunt prevents the surgeon from taking a suture on the posterior wall of the coronary artery.
- Presence of the shunt assures a proper coronary anastomosis
When surgery is performed on the arteries supplying the anterior wall of the heart - typically the left anterior descending artery and diagonal artery territory the repositioning is minimal. In these cases a pad is placed under the heart. The haemodynamic changes encountered are thus minimal. When the grafting of the right coronary artery and obtuse marginal branches are planned "verticalization" of the heart is required. This will cause haemodynamic compromise. In such a condition use of posterior pericardial stitches and a gentle retracting socket will greatly facilitate haemodynamic tolerance.
During anastomosis of the circumflex territory dissection of the right pericardium, opening of the right pleura and lifting the right half of the sternum will help preserve haemodynamics. Positioning of the heart during the grafting of the obtuse marginal territory may kink or partially obstruct the venous return and compress the right ventricle. At this time volume loading, use of the Trendelenburg position can help reduce the haemodynamic changes.
During grafting of the right coronary artery territory there can be bradycardia as there can be a reduction in the blood supply to the sinus and AV nodes. Treatment includes use of atropine and atrial pacing if required.
A 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. At times, it may be necessary to 'bail out' an impending cardiac arrest by injection of a strong inotropic agent. The agent of choice in the author's institute is 1:200,000 adrenaline, 4 to 5 ml bolus of it is injected intravenously.
| Fast track anesthesia|| |
Fast track anaesthesia has been variously defined; as tracheal extubation within 8 hours after cardiac surgery, early mobilization of patient and early discharge from the hospital. Prior to the 1990's high dose narcotics were the preferred agent in view of the minimal haemodynamic changes associated with it (overnight or two days of ventilation was not uncommon those days), but availability of short acting opioid medications have made it possible to subject the patients after cardiac surgery to fast track anaesthesia. Fast track anaesthesia is a logical extension of OPCAB, because of the improvements in anaesthetic techniques and better myocardial preservation strategies.
Prakash et al  and Klineberg et al  demonstrated safe extubation in less than 5 hours after cardiac surgery in the 1970s. Benefits of fast track anaesthesia are not only economical. 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. Poor left ventricular function is not a reason for subjecting to prolonged ventilation. It is important that the nursing staff in the post operative ward is well educated about fast tracking. Long acting sedatives should be avoided. Protocol driven management of extubation, mobilization, discharge from intensive care unit and hospital allow fast tracking in majority of patients. Cheng et al , in their numerous studies on fast tracking showed that the incidence of myocardial ischaemia was no more than those who underwent fast tracking after OPCAB in comparison to CABG, the rate of complications was lower. In the author's institution patients are extubated within 4 to 6 hours after OPCAB.
| The protocol followed in the author's institution is as follows|| |
Failed OPCAB requiring cardiopulmonary bypass for completion of surgery: At times, it may not be possible to complete the surgery by OPCAB technique. Some of the reasons for the inability are, intraoperative cardiac arrest, small caliber coronary arteries, elevation of pulmonary artery pressure coupled with persistent decreased systemic arterial pressure caused by the abnormal position of the heart, arrhythmias not responding to treatment.
- Patients are connected to the ventilator with FiO2 of 0.8. The other ventilatory parameters are as follows: 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, if oxygenation, carbon dioxide elimination and tissue perfusion (indicated by pH and mixed venous oxygen saturation) are adequate, FiO2 is reduced to 0.4
- Thirty minutes later, a similar assessment is performed with regard to the metabolic parameters mentioned above. At this juncture, 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 temperature ( not less than 35 deg Celsius and a raising trend of it), absence of arrhythmias, urine output (at least 1-2 ml.kg -1 .hr -1 ) are done. If the residual neuromuscular blockade is clinically obvious, reversal of it is performed by injecting a combination of neostigmine and glycopyrrolate. After confirming adequacy of reversal of residual neuromuscular blockade, ventilatory mode is switched to one of the supported, spontaneous modes of ventilation, such as pressure support, or continuous positive airway pressure or bilevel positive airway pressure ventilation.
- Thirty minutes after supported ventilation on FiO2 of 0.4, arterial blood gas analysis is repeated. If the analysis shows satisfactory values of oxygenation, carbon dioxide elimination and metabolism, the patients are extubated. Earliest possible extubation is extubation on the operation table, which can be considered in a few cases in the absence of haemodynamic instability, impairment of ventricular function, hypothermia and bleeding disorders. Montes F et al have demonstrated no significant benefit of tracheal extubation after CABG in the operating room 
It is thus important to always have a perfusionist present in the operating theatre who should be ready to assemble the CPB machine at very short notice. In the authors institute a case is not started unless the perfusionist and surgeon are present in the theatre. All necessary equipments to assemble a pump are kept in the theatre. A reservoir and oxygenator are always kept in readiness.
| Completion of surgery|| |
It is the unique practice at the author's institute to get a 12 lead electrocardiogram prior to transfer of patients to the surgical intensive care unit. If any fresh changes in the electrocardiogram suggestive of ischaemia or myocardial infarction are present, suitable treatment can be instituted early. Treatment can be use of low molecular weight heparin, anti platelet medications, insertion of an intra aortic balloon pump or revision of grafting.
Transport of critically ill patients, such as patients after cardiac surgery often represents a difficult problem. Cardiac surgical patients differ from other intensive care patients; they are more likely to require life support mechanisms such as intra-aortic balloon counter pulsation, mechanical ventilation and infusions of vaso-active medications (delivered by electrically driven syringe and infusion pumps). During transfer of such patients, one may encounter critical incidents such as haemodynamic changes, arrhythmias, ventilatory disturbances, disconnection of ventilation or drug delivery system and mechanical/ electrical failure of cardiac support systems  . During transfer of the patient continuous monitoring should be present. ECG monitoring, pulse oximetery and invasive blood pressure monitoring is essential. It is the practice in the author's institute to 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. In a study conducted in the authors institute during transfer of patients after OPCAB there were changes in the heart rate and mean arterial pressure; however the most significant finding encountered was a decrease in the cardiac index and partial pressure of oxygen in the arterial blood. Furthur these changes took almost 15 to 20 minutes to return to baseline. These finding along with other studies ,,, emphasize the need to use appropriate equipment, personnel and planning for transport of patients. This will minimize complications and ensure optimal benefit to the patient. The transport process should not occur in a random, haphazard manner but rather a routine efficient system should be developed.
| Management of postoperative pain|| |
Postoperative pain after cardiac surgery if not treated effectively can contribute to morbidity and mortality. Pulmonary mechanics are altered after cardiac surgery and take about one week or more after surgery to return to normal. Inadequate pain relief can not only result in increased pulmonary complications, but tachycardia, hypertension and vasoconstriction, precipitating myocardial ischaemia. Inadequate pain relief can disturb the patient emotionally. Pulmonary complications are common in patients who cannot participate in physiotherapy activities due to pain and it is difficult to ambulate them early.
| The options followed in the treatment of post operative pain in the author's institute are|| |
- Epidural analgesia: In the authors institute we begin an epidural fentanyl infusion in a Baxter Infusor TM . Fentanyl 3000 mcg (60 ml), 0.5% bupivacaine 55ml and saline 155ml are added to make a final total volume 265 ml. The final concentration of fentanyl 10.9 mcg.ml -1 . We start at a rate of 2ml.hour -1 and monitor VAS scores. The infusion is increased to 3 ml or 5 ml.hour -1 depending on the VAS score. The target VAS score is 4 to 5. Most patients are comfortable with 3ml.hour -1.
- Intravenous opioids: In the authors institute when an epidural is not in situ intravenous infusion of fentanyl is started in the Baxter Infusor TM pump. Fentanyl 3000mcg and saline 215ml are added to make a final concentration 11 mcg.ml -1 of fentanyl. The infusion is titrated to obtain VAS scores of 4 to 5. If TEA has failed, they are converted to intravenous analgesia group. In the event of inadequate analgesia after either TEA or intravenous opioids, supplements with intravenous tramadol and intramuscular diclofenac sodium are added.
| Conclusions|| |
OPCAB is rapidly emerging as an attractive alternative to CABG performed using cardiopulmonary bypass. It presents a unique challenge to the anaesthesiologist in the perioperative period to manage changes in the haemodynamic parameters (which occur at short notice) and fast track the progress of the patient. OPCAB like other new procedures poses a learning curve and the anaesthesiologist should be prepared to adopt to the changing scenario.
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