What are the steps and rationale for inducing anesthesia in patients?

From the Guidelines

Inducing anesthesia in patients involves a careful sequence of steps, starting with premedication, followed by induction with propofol (1.5-2.5 mg/kg IV) and a neuromuscular blocking agent like rocuronium (0.6 mg/kg IV), to ensure patient safety and maintain vital functions throughout the surgical procedure. The process begins with a thorough pre-anesthetic assessment, where the anesthesiologist evaluates the patient's medical history, current medications, allergies, and physical condition to determine the appropriate anesthetic approach and identify potential risks 1. Before induction, patients typically receive premedication such as midazolam (1-2 mg IV) to reduce anxiety and sometimes anticholinergics like glycopyrrolate (0.2-0.4 mg IV) to decrease secretions.

Key Steps in Induction

• Preparation of the patient, including intubation and ventilation in volume-controlled mode with FiO2 = 1, as outlined in guidelines from the French Intensive Care Society and the French Society of Anaesthesia and Intensive Care Medicine 1.
• Induction of anesthesia using propofol (1.5-2.5 mg/kg IV) for its rapid onset and minimal side effects, often combined with an opioid like fentanyl (1-2 mcg/kg IV) for pain control.
• Administration of a neuromuscular blocking agent such as rocuronium (0.6 mg/kg IV) to facilitate endotracheal intubation, which secures the airway and allows for mechanical ventilation.
• Maintenance of anesthesia using inhaled agents like sevoflurane or desflurane at 0.8-1.2 MAC (Minimum Alveolar Concentration), or through continuous IV infusions of propofol (100-200 mcg/kg/min) and remifentanil (0.05-2.0 mcg/kg/min), as recommended by recent guidelines for perioperative care in emergency laparotomy 1.

Considerations for Patient Safety

• Continuous monitoring of vital signs, including heart rate, blood pressure, oxygen saturation, end-tidal CO2, and temperature, to maintain physiological stability throughout the procedure.
• Use of rapid sequence induction and intubation (RSII) to minimize the risk of aspiration, particularly in patients undergoing emergency laparotomy, as recommended by the European Society of Anaesthesiology and Intensive Care 1.
• Consideration of the use of ketamine in patients with head injury, as its sympathomimetic effects may have disadvantages in certain cases, but it is now frequently used in pre-hospital trauma care due to its relative haemodynamic stability 1.

Post-Induction Care

• Discontinuation of anesthetic agents at the conclusion of surgery, and administration of reversal agents like sugammadex (2-4 mg/kg IV) to counteract neuromuscular blockade.
• Careful monitoring of the patient during emergence from anesthesia until they regain consciousness and protective reflexes, at which point they are transferred to a recovery area for continued observation.

From the FDA Drug Label

When used for sedation/anxiolysis/amnesia for a procedure, dosage must be individualized and titrated. Midazolam should always be titrated slowly; administer over at least 2 minutes and allow an additional 2 or more minutes to fully evaluate the sedative effect. For induction of general anesthesia, before administration of other anesthetic agents. Individual response to the drug is variable, particularly when a narcotic premedication is not used. The dosage should be titrated to the desired effect according to the patient’s age and clinical status Unpremedicated Patients: In the absence of premedication, an average adult under the age of 55 years will usually require an initial dose of 0.3 to 0. 35 mg/kg for induction, administered over 20 to 30 seconds and allowing 2 minutes for effect. Propofol injectable emulsion should be titrated (approximately 40 mg every 10 seconds) against the response of the patient until the clinical signs show the onset of anesthesia Most adult patients under 55 years of age and classified as ASA-PS I or II require 2 mg/kg to 2. 5 mg/kg of propofol injectable emulsion for induction when unpremedicated or when premedicated with oral benzodiazepines or intramuscular opioids.

The steps for inducing anesthesia in patients are:

• Titration: Midazolam and propofol should be titrated slowly to the desired effect, with careful consideration of the patient's age, clinical status, and any premedications.
• Initial Dose: The initial dose of midazolam for induction of general anesthesia is typically 0.3 to 0.35 mg/kg for unpremedicated adults under 55 years, while propofol typically requires 2 mg/kg to 2.5 mg/kg.
• Administration: Midazolam should be administered over 20 to 30 seconds, with a 2-minute wait to evaluate the sedative effect. Propofol should be titrated approximately 40 mg every 10 seconds until clinical signs of anesthesia are observed.
• Monitoring: Patients should be closely monitored for clinical signs of anesthesia, and the dosage should be adjusted accordingly.
• Premedication Considerations: The presence of premedications, such as narcotics or benzodiazepines, can influence the required dose of midazolam or propofol for induction. 2 and 3

From the Research

Steps for Inducing Anesthesia

• Administering fentanyl to reduce the catecholaminergic response to orotracheal intubation, allowing for a reduction in the dose of propofol 4
• Using a combination of fentanyl, midazolam, and propofol to provide better intubating conditions without the need for neuromuscular blocking agents 5
• Considering the use of rocuronium, with its interaction with anesthetics such as etomidate, fentanyl, midazolam, propofol, thiopental, and isoflurane, to achieve a constant 90% neuromuscular block 6
• Monitoring hemodynamic variables during anesthetic induction to assess the relative contribution of various mechanisms to hypotension, such as reduced myocardial contractility, venous dilation, or arterial dilation 7
• Using a midazolam-fentanyl-rocuronium protocol for pre-hospital anesthesia, with consideration of the potential for haemodynamic changes, including reductions in systolic blood pressure and the occurrence of new hypotension or hypertension 8

Rationale for Inducing Anesthesia

• To reduce the risk of severe propofol dose-dependent hypotension by coadministering fentanyl 4
• To provide adequate conditions for tracheal intubation without the need for neuromuscular blocking agents, using a combination of anesthetics such as fentanyl, midazolam, and propofol 5
• To quantify the interaction of rocuronium with various anesthetics, allowing for more effective use of these agents in anesthesia induction 6
• To understand the mechanisms contributing to hypotension after anesthetic induction, including the role of arterial dilation and reduced systemic vascular resistance 7
• To develop effective protocols for pre-hospital anesthesia, including the use of midazolam, fentanyl, and rocuronium, with consideration of the potential for haemodynamic changes 8

Considerations for Patient Care

• Patients over 55 years may experience greater hypotension when the time between fentanyl and propofol administration is increased 4
• Patients with high bronchoaspiration risk, difficult airway, hemodynamic instability, or anesthetic allergies may require alternative approaches to anesthesia induction 4
• The use of neuromuscular blocking agents, such as rocuronium, may be necessary in some cases to achieve adequate intubating conditions 6
• Continuous monitoring of hemodynamic variables is essential during anesthetic induction to quickly identify and respond to any changes in the patient's condition 7
• Adherence to recommended doses of anesthetics, such as midazolam, fentanyl, and rocuronium, is crucial to minimize the risk of adverse effects 8