Cardiovascular Anesthesia - Significance and Test Procedures

Introduction:

Cardiac anesthesia is a demanding specialty that requires a comprehensive understanding of the structural and functional aspects of the heart and in-depth knowledge of the pathophysiology and result of extracorporeal circulation. Earlier cardiac surgery was confined to repairing simple congenital heart defects until the emergence of coronary artery bypass graft (CABG) and later on to percutaneous coronary interventions (PCI). This broadened the scope of cardiac anesthetists to perform cardiac surgeries in larger volumes. With many comorbidities like pulmonary, cardiac, renal, endocrine, and systemic illnesses, these patients are frequently regarded as high risk. It takes extensive professional knowledge, skill, and expertise to manage these individuals.

How to Evaluate the Patient for Cardiovascular Surgery?

Cardiac risk assessment prior to surgery evolved a great deal for a successful outcome. The primary focus is on identifying the appropriate surgical procedures and patient-associated factors that increase the risk of complications during surgery.

• Preoperative Patient Evaluation: Cardiac evaluation is influenced by the patient's past medical history, physical examination, assessment of cardiovascular risk factors, functional capability, and associated risk assessment utilizing risk prediction methods or biomarkers. General anesthetic, operation duration, blood loss, hemodynamic changes, and surgical experience should all be taken into account when calculating surgical-specific risks.

• Perioperative Patient Evaluation: Presence or absence of clinical factors, including recent myocardial infarction history, congestive heart failure, severe aortic stenosis, significant non-cardiac organ failure or disease, the need for surgery right away, and old age.

What Are the Pre-medications Used?

These patients are usually anxious and aware of the potential risks of surgery. In order to reduce fear and anxiety, analgesia can be given prior to any painful procedures and amnesia to some extent. Pharmacological agents have been shown to prevent anginal episodes which are clinically silent preoperatively. Benzodiazepines - Diazepam, Midazolam, Morphine, Fentanyl (IM/IV) are used. The drug dosage is based on the age and physiological status of the patient, ensuring that these agents are given in the morning with sips of water.

How Is Anesthesia Induced?

Induction is a very critical step in the anesthetic management of cardiac patients. A cardiologist, along with the cardiopulmonary bypass, should be readily available during induction in case of hemodynamic changes. A gradual induction involves minimizing the degree of cardiovascular depression while maintaining an adequate anesthetic depth.

Agents helpful in the induction and maintenance of anesthesia in cardiac surgical patients include the following:

• IV opioids: Cause various degrees of vasodilation and bradycardia without any significant myocardial depression. Fentanyl (50 to 100 μg/kg) or Sufentanil (10 to 20 μg/kg) can be used as both the induction and primary maintenance agents. Alternatively, even lower doses (Fentanyl 10 to 25 μg/kg or Sufentanil 1 to 5 μg/kg) may be used in conjunction with other central nervous system depressants.

• Sedative Hypnotics and Amnestic: Benzodiazepines, Propofol, and Etomidate may be useful as co-induction agents. Etomidate causes very low myocardial depression.

• Volatile Inhalation Anesthetics: These are useful supplementary agents, especially in the treatment of hypertension.

• Muscle Relaxants: With minimal cardiovascular effects are commonly used (For example - Vecuronium, Cisatracurium, and Rocuronium). Pretreatment with a “priming dose” and early relaxant administration help to counteract chest wall rigidity.

• Succinylcholine: It is used for rapid sequence inductions for patients with stomach reflux. The parasympatholytic actions of Pancuronium can counteract the bradycardic effects of Opioids.

Anesthesiaconsists of hypnosis, analgesia, amnesia, and muscle relaxation. It is always advisable to use drugs in combination to achieve the desired effect. Prior to administration, preoxygenation, monitoring with pulse oximetry, electrocardiogram (ECG), non-invasive BP, and radial artery cannulation for arterial blood pressure monitoring (ABP) for high-risk patients with central venous catheters and pulmonary artery catheters. Titration of the drugs, with continuous monitoring of hemodynamic changes to avoid increasing oxygen consumption and decreasing oxygen supply.

The table shows the anesthetic effect of particular drugs. NC - no change.

Does Anesthesia Have an Effect on Cardiovascular System?

Both anesthesia and surgery have varied effects on the cardiovascular system. Even in healthy patients undergoing surgery, anesthetic agents can cause cardiac depression and hemodynamic instability. In patients with prior history of cardiac disease, these cardiovascular anesthetic effects become serious due to alterations in hemodynamic changes. These include loss of blood and changes in the volume, the release of various substances into the circulation, hypothermia, sudden changes in cardiac output, myocardial ischemia, and effects of drugs. Anesthesia frequently covers up the signs and symptoms of these surgical stresses.

This table shows the anesthetic effect on the cardiovascular system. NC - no change

How to Create Awareness in Cardiovascular Patients?

These patients have an increased risk for intraoperative awareness and recall due to deliberately stopping the cardiac depressant volatile anesthetics in the presence of hemodynamic instability, causing changes in the heart and great vessels, leading to light anesthesia periods. As volatile anesthetics have been proven to provide preconditioning before cardiopulmonary bypass (CPB), they began to have a major role in cardiac anesthesia protocols reducing the risk of awareness.

What are the Complications of Cardiovascular Surgery?

Patients with a previous history of cardiac disease are susceptible to complications after surgery. Complications are generally due to hypotension, hypertension, and dysrhythmias.

1. Hypotension - In patients with hypovolemia due to inadequate fluid administration or blood loss. In such patients, the administration of various blood products, along with vasopressors and inotropes, minimize damage to the end organs. Myocardial ischemia with acute heart failure and ventricular dysfunction can also lead to hypotension, tachycardia, and changes in the electrocardiogram.

2. Hypertension - Surgical trauma and pain can cause increased sympathetic tone leading to hypertension and tachycardia.

3. Arrhythmias - Arrhythmias are life-threatening and can sometimes cause cardiac arrest. A decrease in the heart rate can be due to vasovagal reflexes, residual effects of anticholinesterases, β-blockers, opioids, and myocardial infarction. Anticholinergic drugs should be given to patients with decreased heart rates.

Conclusion:

Patients with cardiac disease present for anesthesia every day. Each patient is different in the cardiac unit, and there is no clear-cut strategy to be recommended for all cardiac surgical patients. Identifying patients with high risk and the use of balanced anesthesia techniques, an anesthetist alert at all times will go a long way in preventing intraoperative complications. Anesthetists should be able to provide hemodynamically stable anesthesia because these operative procedures are associated with high morbidity and mortality rates.