Anesthesia for Coronary Artery Bypass Grafting Surgery - An Overview

Introduction

An ideal anesthetic agent should produce reversible loss of consciousness and a painless experience throughout a surgery without affecting other systems in the body. It should also have a rapid recovery rate and not produce any postoperative complications. Therefore, every patient should be administered an appropriate anesthetic agent after assessing their health condition.

What Is Coronary Artery Bypass Grafting Surgery?

It is a surgical procedure performed during coronary artery disease called atherosclerosis, when the coronary arteries get blocked or narrowed by the deposition of fatty material called plaque around their walls, leading to a lack of supply of oxygen-rich blood and other vital nutrients to the heart. This surgery bypasses the narrowed portion of the artery by attaching another new, healthy blood vessel taken as a graft from another body part, like the chest, arm, or leg, above and below that narrowed portion. The blood travels through the graft vessel, and the heart's normal blood supply is restored.

What Types of Coronary Artery Bypass Grafting Surgery Are There?

1. On-pump Coronary artery bypass grafting surgery

It is a traditional procedure in which the heart is temporarily stopped during the surgery, and a heart-lung machine or a bypass machine takes over the heart's function, and blood is pumped into the heart. This procedure is called cardiopulmonary bypass.

2. Off-pump coronary artery bypass grafting surgery

In this type of cardiac surgery, no heart-lung machine is used. During the surgery, the heart will not be stopped. Therefore, it is a less invasive procedure. It is also called a beating heart procedure.

What Are the Anesthetic Considerations for Coronary Artery Bypass Grafting Surgery?

• Written consent should be received from the patient.

• To help the patient feel less worried, they should be given clear information about the procedure and how to heal after surgery.

• Any allergic reactions to any anesthetic agent should be considered. To evaluate this, any past surgical history should be thoroughly investigated.

• Most importantly, a skilled and experienced anesthesiologist should plan the surgical procedure carefully, considering the possible surgical complications and how to manage them effectively.

What Are the Anesthetic Agents Used for Coronary Artery Bypass Grafting?

They are classified into two types, as follows:

1. Inhalational anesthetics

• Isoflurane

  • It has minimal harmful effects on cardiac function. Hence, it is the most commonly used volatile agent.

  • It reduces the need for oxygen for the brain during surgery, thus protecting the brain.

  • It has pungency properties and can irritate the airway. So it is used along with an intravenous agent.

• Desflurane

  • It is similar to isoflurane.

  • It has a short duration of action, rapid recovery, and low potency of action compared to other volatile agents.

  • It is a pungent agent, so it causes coughing and laryngospasm. It is generally used as an intravenous agent.

• Sevoflurane

  • It is the newest volatile agent used. It is not a pungent agent and rapidly increases the concentration in the lungs.

  • It has a bronchodilatory effect similar to isoflurane.

  • It has negative effects on renal function.

• Nitrous oxide

  • It is called laughing gas.

  • Sometimes it is used in the pre-bypass period of adult cardiac surgery.

  • It carries the risks of air embolism, increased systemic vascular resistance, and chronic exposure that can cause bone marrow depression and neuropathy.

  • It is contraindicated in patients with pulmonary hypertension. It has a rapid onset and fast recovery and can increase the efficiency of other volatile agents.

• Halothane

  • It is a cheap anesthetic agent that is difficult to prepare and toxic to the liver.

  • The unique feature of halothane is that it decreases the heart rate.

  • It leads to arrhythmias, so along with halothane, epinephrine, and norepinephrine are also given.

  • Due to its bronchodilatory effects, it is used in asthma-induced bronchospasm.

• Enflurane

  • It is similar to other volatile agents. It is most similar to halothane.

  • The difference between enflurane and halothane is that enflurane increases the heart rate by decreasing systemic vascular resistance.

  • This agent increases cerebral blood flow and increases cerebrospinal fluid secretion.

  • To help the patient feel less worried, they should be given clear information about the procedure and how to heal after surgery.

2. Intravenous anesthetics

• Barbiturates

  • These agents lower the oxygen needed for cerebral blood flow and are, therefore, safe for the brain.

  • They do not have an analgesic effect, so they are always used with other agents.

• Ketamine

  • Ketamine produces dissociative anesthesia, meaning the patient will remain conscious but cannot respond to stimuli.

  • It raises the heart rate but can push the oxygen demand above the capacity of coronary blood flow.

  • It increases cerebral blood flow and should be used cautiously in patients with increased intracranial pressure.

  • It is useful for patients with asthma since it has bronchodilatory effects.

• Propofol

• It causes pain while injecting and should be avoided in patients who are hypersensitive to its components.

• It has a quick onset of action and a quick recovery time, allowing for early extubation.

• It can cross the blood-brain barrier.

• Etomidate

  • It has a great potency that is 25 times more effective than thiopental.

  • It does not affect cardiac function in healthy patients but can cause cardiac impairment in compromised patients.

  • It decreases intracranial pressure and is hence used to protect brain function.

• Benzodiazepines

  • Midazolam and lorazepam are commonly used benzodiazepines.

  • They reduce anxiety and provide an amnesic effect.

  • They are slow-acting drugs.

What Are the Main Goals of Anesthesia During Coronary Artery Bypass Grafting Surgery?

• To keep hemodynamic changes stable.

• To manage myocardial infarction if it occurs during surgery.

• To prevent ischemia by lowering oxygen demand and increasing oxygen supply.

• To maintain the body temperature of the patient.

• To prevent anemia postoperatively.

What Are the Preanesthetic Preparations for Coronary Artery Bypass Grafting Surgery?

1. A detailed patient's health history should be noted, including exercise tolerance, heart attack, chest pain, and other cardiac diseases.

2. Any other co-existing non-cardiac diseases like pulmonary function, renal function, vascular disease, diabetes, and anemia.

3. The current mediation should be assessed. Medications like calcium channel blockers, beta-blockers, and nitrates should be continued until the time of surgery. Anticoagulants or blood thinners like aspirin should be stopped 5-7 days before surgery.

4. A general physical examination of vital signs, such as blood pressure, pulse rate, cyanosis, lymphadenopathy, edema, and pallor, should be done.

5. A detailed cardiovascular system examination should be done, measured as heart sounds and murmurs.

6. Laboratory tests like ECG (Electrocardiogram) and an echocardiogram are done to know the ejection fraction, any wall abnormalities, the pressure gradient, and the location of the blockage in the coronary arteries.

How Is On Pump Coronary Artery Bypass Grafting Surgery Performed?

The entire surgical procedure is divided into three phases called as follows:

1. Pre-bypass:

• The period when the bypass machine is connected to the patient through arterial and venous cannulas is called the "pre-bypass period."

2.Monitoring:

• The following parameters are monitored continuously during the bypass surgery:

• Electrocardiography.

• Arterial blood pressure.

• Central venous pressure.

• Pulmonary artery pressure.

• Urinary output.

• Body temperature.

• Laboratory parameters: Blood gasses, hematocrit, calcium, serum potassium, and glucose levels.

• TEE: Transoesophageal echocardiography to visualize the cardiac anatomy and function.

• EEG: Electroencephalography to measure the depth of anesthesia during surgery.

3. Induction Period:

• Cardiac induction: The administration of an anesthetic agent should be smooth and stable. The surgery requires endotracheal intubation and monitored ventilation.

• The dosage of an anesthetic is variable and depends on the patient's tolerance. Patients with severely compromised health should be given anesthesia in small doses and increments.

• The blood pressure is monitored during induction. Any rise in blood pressure during intubation indicates the need for more doses of anesthetic. No change or a slight change indicates that the next stimulus can be given.

4. Post-bypass period:

• The cardiopulmonary bypass is terminated, and heart function is restored.

• Bleeding is controlled. Protamine is given.

• Anticoagulation is revered.

• The arterial cannulas are removed.

Conclusion

Successful anesthesia is very important for successful bypass surgery. Hence, it becomes important for strong communication and a better understanding of patients' medical status among anesthesiologists and cardiologists. Unfortunately, no single general anesthetic agent is efficient enough to bring about a complete analgesic state, but combining inhalation and intravenous agents is beneficial.