Sedation and anesthetic support

Conscious sedation

The first-in-man transcatheter aortic valve implantation (TAVI) was performed percutaneously by a French team led by Alain Cribier under conscious sedation (CS). Despite this precedent, the majority of subsequent early TAVI cases were performed under general anesthesia (GA) with guidance using transesophageal echocardiography (TEE). This was in part due to the time-consuming early learning curve, bulky early TAVI devices, and the need to assess for paravalvular regurgitation after valve deployment. However, with the rapid growth in TAVI experience and improvements in device design, as well as a reduction in procedural TEE dependency, there has been renewed interest in CS with local anesthesia to such an extent that this is now the principal anesthetic technique.

• CS is defined as a drug-induced state of depressed consciousness where airway intervention is not required and the patient is able to respond purposefully to verbal or tactile stimulation. This sedation plane is often referred to as “moderate sedation” in North America.

• There are multiple pharmacologic agents ( Table 8.1 ), each with their own profiles, which can be used in isolation or in conjunction to achieve this level of sedation.

  TABLE 8.1

  Anesthetic Drugs Used for Conscious Sedation

  	Dose	Half-Life	Contraindication	Advantages	Disadvantages
  Hypnotic Drugs
  Propofol	3–4 mg/kg/h	2–4 min	Egg allergies	Short half-life Antiemetic effect	Apnea Hypotension
  Remifentanil	1–2 μg/kg/h	3–4 min	Hypersensitivity to remifentanil or formulation	Short half-life Analgesia	Apnea Muscle rigidity Bradycardia
  Dexmedetomidine	0.2–1 μg/kg/h	6–10 min	Severe liver failure High-grade atrioventricular block Severe hypovolemia	Analgesia Low respiratory depression	Bradycardia Hypotension
  Midazolam	0.1–0.2 mg/kg	10–20 min	Myasthenia Myopathy	Anxiolytic effect	Neurologic disorders Long half-life
  Ketamine	0.2 mg/kg	10–15 min	Porphyria Neurologic or psychiatric disorders	Analgesia No respiratory depression Positive inotrope Bronchodilation	Neurologic disorders Hallucinations

• There is no clear consensus as to which approach is superior, and the choice of agent is at the discretion of the anesthetist and dependent on local protocols.

• CS in selected patients can confer several advantages during TAVI procedures ( Table 8.2 ) because the lighter plane compared with GA allows more rapid recovery and patient turnaround, as well as earlier postprocedural neurologic assessment.

  TABLE 8.2

  Advantages and Disadvantages of Conscious Sedation Versus General Anesthesia for TAVI Procedures

  	Advantages	Disadvantages
  Conscious Sedation	Improved hemodynamic stability Improved preload Early detection of complications Shorter procedure time Monitoring of neurologic status Cost effectiveness	Patient movement TEE guidance difficult Risk of emergency conversion to general anesthesia
  General Anesthesia	Allows TEE guidance Patient immobility Provides controlled apnea during valve deployment	Increased need for vasopressors/inotropes Postoperative nausea or vomiting May prolong the ICU stay More expensive

  ICU, Intensive care unit; TAVI , transcatheter aortic valve implantation; TEE, transesophageal echocardiography.

• By allowing the patient to breathe spontaneously and reducing the need for insertion of airway devices, patient preparation time is shorter and the anesthetic process simplified.

• CS also encourages early ambulation and can supplement fast-track pathways to complement patient recovery.

General anesthesia

• Despite the widespread use of CS, there will always be a small cohort of patients who need GA to tolerate TAVI procedures, either because of the chosen surgical approach, procedural requirements, or patient-related factors ( Table 8.3 ).

  TABLE 8.3

  Relative Contraindications to TAVI Under Conscious Sedation

  Airway	Severe obstructive sleep apnea
  Hemodynamic	Cardiogenic shock
  Positioning	Severe musculoskeletal disease or back pain Severe orthopnea
  Cooperation	Dementia Agitation Noncompliance
  Procedural	Surgical approach Need for TEE guidance

  TEE, Transesophageal echocardiography.

• The percutaneous transfemoral approach lends itself to CS as the associated discomfort can usually be adequately controlled with local anesthesia.

• The more invasive transapical or transaortic routes (and vascular cut-downs) are generally too painful to be safely tolerated under CS and necessitate the use of GA.

• CS is more challenging when transesophageal echocardiography is required for TAVI procedures, because the patient’s unsecure airway becomes shared and the echocardiography probe increases the risk of aspiration and interferes with facemask oxygenation and capnography. GA with intubation mitigates these risks and is more appropriate in these circumstances.

• Certain patients who are agitated and uncooperative (see Table 8.3 ) may also be unsuitable candidates for CS, as they may pose a risk to themselves or the operating team by moving at key moments during the TAVI procedure. GA is a safer option for these patients to ensure immobility.

• During induction, maintenance, and emergence from GA in TAVI patients, it is important to preserve myocardial oxygen delivery by maintaining mean arterial pressure, sinus rhythm, adequate diastolic time, and optimal preload for the noncompliant ventricle (by judicious use of intravenous fluids).

Monitoring

Patients requiring TAVI procedures are often frail and elderly with multiple comorbidities that demand careful monitoring.

General anesthesia versus conscious sedation

There is a paucity of randomized controlled trials (RCTs) and consequent debate as to which form of anesthesia is most suitable for TAVI patients. Most studies comparing the outcomes of GA and CS for TAVI patients are retrospective and observational, with multiple biases making interpretation difficult. Because of their nonrandomized methodology, the level of evidence is low. However, the retrospective observational data are consistent and show no significant difference between GA and CS TAVI patients in terms of mortality at 30 days and 1 year. Data from the ADVANCE and SOLVE RCTs, as well as large TAVI registry databases, concur. Furthermore, quality of life scores and neurocognitive outcomes following TAVI do not significantly differ between CS and GA groups.

Meta-analysis suggests significant procedural differences between GA and CS TAVI cases. Procedures under CS are associated with greater hemodynamic stability and reduced use of inotropes and blood cell transfusion. Surprisingly, CS TAVI patients were also found to have an increased risk of pacemaker insertion and prosthetic paravalvular leak. Conversely, CS TAVI patients use significantly less contrast and have reduced pulmonary complication rates. ^, Procedures are also quicker, less costly, and associated with shorter ICU and overall length of hospital stay. ^,

• In conclusion, careful consideration of the access route, TEE requirement, and patient-related factors is required when deciding the most appropriate mode of anesthesia for TAVI procedures.

• CS is associated with shorter procedural time, reduction in pulmonary complications, and a more favorable hemodynamic profile with reduced use of red cell transfusion and inotropic agents.

• Procedures under CS are much more challenging if TEE or vascular cut downs are required.

• GA is associated with lower incidence of pacemaker insertion and more appropriate in patients who are unable to lie still.

• Because multiple factors across different specialties influence the choice of anesthesia, it is important that the heart team includes an anesthetist to review prospective cases and determine the most appropriate anesthetic strategy.

• A flowchart describing anesthetic options for TAVI patients is shown in Fig. 8.1 .