Anesthetic Management of a Patient with Ischemic Heart Disease for Non-Cardiac Surgery
Preoperative Assessment
What is the prevalence of Coronary Artery Disease (CAD) and why is this knowledge important for an anesthesiologist?
A 2016 cross-sectional study in South India found the prevalence of CAD in males and females was 6% and 3% respectively, which is almost similar to that in the USA and UK. This means every anesthesiologist has to provide anesthesia every day to a patient with CAD, and for postgraduates, it is a definite question in practical as well as theory exams.
What specific things should you ask in the history of a patient with CAD and a stent?
While evaluating a patient with CAD and a stent, you should ask for:
- History of ongoing anginal pain
- History related to heart failure, such as dyspnea on exertion, orthopnea, paroxysmal nocturnal dyspnea, and peripheral edema or any abdominal pain
- History to assess the functional capacity of the patient
How do you assess a patient's functional capacity?
Functional capacity can be measured using METs (Metabolic Equivalent of Task). One MET is the oxygen consumption of a person at rest, equal to 3.5 ml of O2 per kg per minute.
Another method is the Duke's Activity Status Index, a validated questionnaire with 12 questions and a scoring from 0 to 58. A score of less than 34 indicates poor functional status. METs can be calculated from the Duke's score using the formula: (1.43 x Duke's score + 9.6) / 3.5.
A patient who can climb more than two flights of stairs has more than 4 METs, which is considered good.
Why is airway examination particularly important in a patient with CAD?
In a patient with ischemic heart disease, we should anticipate a difficult airway. If a difficult airway is present, we should plan accordingly so that the stress response can be decreased, ensuring the myocardial oxygen supply and demand balance can be adequately met. Difficulty with ventilation or intubation can trigger a stress response.
What are the factors affecting myocardial oxygen supply and demand?
Oxygen demand is mainly dependent on contractility, afterload, preload, and heart rate.
Oxygen supply is dependent on:
- Coronary perfusion pressure and coronary blood flow
- The diameter of the coronary vessels (which can be reduced by hypercapnia or hypocapnia, as they are vasoconstrictors)
- The oxygen-carrying capacity of the blood (hemoglobin and saturation)
Tachycardia is a double-edged sword: it increases contractility and demand while also reducing perfusion by decreasing diastolic time.
How is coronary circulation different from systemic circulation?
Coronary circulation is mainly dependent on the diastolic period, whereas systemic circulation depends on systole. Coronary perfusion pressure is the aortic diastolic pressure minus the left ventricular end-diastolic pressure. In the left ventricle, which has a thicker muscle mass, the coronary vessels are compressed during systole, so perfusion mainly occurs during diastole. The right ventricle is less affected, and perfusion takes place during both systole and diastole.
What are the anesthetic concerns regarding the patient's antiplatelet drugs?
The patient is on dual antiplatelet therapy (aspirin and clopidogrel) because they have undergone PCI and have a stent. This therapy is necessary to prevent stent thrombosis, which is a major concern. Aspirin should be continued on the day of surgery, while clopidogrel should be stopped 5 to 7 days before surgery.
What are the different types of stents and when can elective surgery be planned?
There are two main types of stents:
- Bare Metal Stent (BMS): Made of stainless steel. Surgery can be posted after 30 days of stent placement.
- Drug-Eluting Stent (DES): Has a coating of drug (e.g., sirolimus, paclitaxel, everolimus, zotarolimus) to prevent proliferation. Elective surgery should be planned after 12 months for acute coronary syndrome (ACS) or after 6 months for chronic coronary syndrome (CCS). For time-sensitive surgery, it can be planned after 3 months.
What is the relevance of various pre-operative tests for this patient?
- Hemoglobin: To evaluate for anemia, which can trigger the need for transfusion.
- Platelet count: To evaluate, as the patient is on dual antiplatelet therapy.
- PT/INR and APTT: To know the coagulation profile.
- Blood sugar: Diabetic patients are more prone to silent MI and end-organ damage.
- Electrolytes: Imbalances can predispose to perioperative MI.
- ECG: Recommended for patients with reduced functional capacity, recent MI, or symptoms of heart failure.
- Chest X-ray: To look for cardiomegaly or signs of pulmonary edema.
- Echo: Indicated for patients with poor functional status, new-onset dyspnea, or those undergoing high-risk surgery.
What are the scoring systems used for risk stratification in a CAD patient?
The Revised Cardiac Risk Index (RCRI) is commonly used. It includes six components: history of ischemic heart disease, cerebrovascular disease, congestive cardiac failure, diabetes on insulin, serum creatinine >2 mg/dL, and intraabdominal surgery. Another scoring system is the NSQIP (National Surgical Quality Improvement Program).
Preoperative Preparation and Optimization
What preoperative advice and drug management is planned for this patient?
- Beta-blockers: Should be continued to maintain myocardial oxygen supply, decrease demand, and prevent tachycardia.
- Statins: Should be continued.
- Aspirin: Can be continued.
- Clopidogrel: Should be stopped 5 to 7 days before surgery.
- ACE inhibitors/ARBs: If for hypertension, stop 24 hours before surgery to prevent hypotension. If for congestive cardiac failure with reduced ejection fraction, they should be continued.
- Calcium channel blockers and other antihypertensives: Should be continued on the day of surgery.
What is bridging therapy and when is it indicated?
Bridging therapy is used for patients at high risk of stent thrombosis. A long-acting antiplatelet (like clopidogrel) is stopped 5-7 days before surgery and replaced with a short-acting intravenous agent like cangrelor. Cangrelor requires stoppage only 3 hours before surgery and can be restarted after 8 hours.
What does the preparation of the patient on the day before surgery involve?
Preparation includes creating a psychological and emotional rapport with the patient, providing information regarding the surgery and anesthetic plan to reduce anxiety. Night sedation (e.g., alprazolam 0.5 mg) can be given.
What drugs are planned for the patient on the morning of surgery?
On the day of surgery, with a sip of water, the patient should take aspirin, metoprolol, and pantoprazole. A small dose of sedative may also be given to prevent tachycardia from anxiety.
Intraoperative Management
What is the proposed anesthetic plan for this laparoscopic cholecystectomy?
The plan is for general anesthesia with controlled ventilation using an endotracheal tube, along with a thoracic epidural.
What are the advantages of a thoracic epidural in this patient?
- Provides coronary vasodilation, improving coronary perfusion
- Decreases the sympathetic stress response
- Provides excellent analgesia intraoperatively and postoperatively
- Helps maintain hemodynamic stability
- Reduces overall anesthetic requirement
What is the induction agent of choice and how should it be administered?
Etomidate is a choice because it is cardio-stable. Titrated doses of propofol can also be used, but it can cause hypotension and bradycardia. In a CAD patient, any induction agent should be given in slow, titrated doses according to the hemodynamic response.
What monitors are placed pre-induction?
Pre-induction monitors include pulse oximeter, ECG with ST analysis, capnography, and non-invasive BP monitoring. Invasive BP monitoring is also placed pre-induction using local anesthesia to detect subtle changes in BP.
Besides monitoring BP, what is another advantage of invasive BP monitoring for this laparoscopic surgery?
It allows for easy arterial blood gas (ABG) analysis to detect and correct hypercarbia, which the patient is prone to during laparoscopy.
How do you blunt the sympathetic response to laryngoscopy and intubation?
- Give titrated doses of the induction agent
- Use IV preservative-free lignocaine (1.5 mg/kg)
- Use short-acting opioids
- Use inhalation agents if needed
- Perform a short and gentle laryngoscopy
- Spray the vocal cords with local anesthetic
What are the reasons for hypotension after induction and patient positioning?
- The cumulative effect of drugs given for induction and to blunt the stress response
- The head-up position with lithotomy for laparoscopy decreases venous return
How is intraoperative hypotension (BP 70 from a baseline of 120) managed?
Initially, IV fluids are given. If hypotension persists, phenylephrine is the vasopressor of choice.
What intraoperative complications are anticipated in this patient?
Complications include hypertension, hypotension, tachycardia, bradycardia, perioperative MI, and ectopics (especially ventricular).
How do you manage intraoperative ventricular ectopics?
Evaluate the cause: look for hypoxia, hypercarbia, or electrolyte imbalance and treat accordingly. If they are more than 6 per minute, in runs of three or more, or multifocal, IV lignocaine, NTG, or beta-blockers can be used.
Postoperative Management and Complications
What is the plan for reversal and extubation?
Reversal is achieved with neostigmine and glycopyrrolate. Extubation is performed when the patient is fully awake to reduce the risk of aspiration and to ensure the patient can control their airway. The stress response during extubation is reduced with IV lignocaine.
Why is extubation at a deep plane problematic in this patient?
In a patient post-laparoscopy, residual hypercarbia and hypoxia may be present. Extubating at a deep plane can lead to aspiration and hypoxia, which significantly impacts the myocardial oxygen supply.
What is the significance of maintaining normothermia postoperatively?
Hypothermia causes myocardial depression. Postoperative shivering, which can occur due to hypothermia, significantly increases oxygen consumption and demand, disrupting the myocardial oxygen supply-demand balance.
How would you manage a patient in the postoperative period complaining of chest discomfort with falling BP?
- Take a 12-lead ECG immediately
- Send cardiac biomarkers (high-sensitivity troponin I is most sensitive)
- Perioperative MI is most common within 72 hours post-surgery due to inadequate analgesia leading to stress response and tachycardia
- If biomarkers are elevated, consider perioperative MI, provide coronary vasodilators (e.g., nitroglycerin), and involve cardiology for a multidisciplinary discussion, balancing the risk of bleeding