General Anesthesia: Comprehensive Clinical Approach
Core Definition and Components
General anesthesia is a reversible, drug-induced state characterized by loss of consciousness, amnesia, analgesia, immobility, and suppression of autonomic reflexes, achieved through hypnotic agents (intravenous or inhaled), opioids for pain control, and neuromuscular blocking agents for muscle relaxation. 1
The essential components include:
- Mental blockade (sedation and hypnosis/unconsciousness) 2
- Sensory blockade (analgesia and antinociception) 2
- Muscle relaxation to facilitate intubation and surgical access 1
- Suppression of noxious reflexes and autonomic responses 3
Mechanism of Action
General anesthetics do not act through a single unified mechanism but rather alter neuronal ion channels and neural communication at multiple sites within the neural nexus. 3
Primary mechanisms include:
- Enhancement of inhibitory transmission through GABA-A and glycine receptors (most inhaled agents, propofol, benzodiazepines) 3
- Depression of excitatory conduction by blocking nicotinic acetylcholine receptors 3
- NMDA receptor antagonism (ketamine, nitrous oxide) with additional opioid receptor enhancement 3
These effects occur at both spinal and supraspinal levels, affecting arousal centers and memory formation pathways. 3
Induction of Anesthesia
Intravenous Induction Agents
Propofol is the most commonly used induction agent due to its rapid onset and recovery profile. 4
- Induction dose: 1-2.5 mg/kg IV, administered slowly over 60 seconds to avoid respiratory depression and hypotension 5
- In elderly, debilitated, or ASA III-IV patients, rapid bolus administration must be avoided as it significantly increases cardiorespiratory depression including hypotension, apnea, airway obstruction, and oxygen desaturation 5
- Propofol reduces myocardial oxygen consumption and causes dose-dependent decreases in blood pressure and heart rate 5
Ketamine is recommended for induction or as an adjunct, particularly valuable because it maintains systemic vascular resistance and provides intrinsic analgesia. 4
- Induction dose: 1-4.5 mg/kg IV (average 2 mg/kg produces 5-10 minutes of surgical anesthesia) or 6.5-13 mg/kg IM 6
- Administer slowly over 60 seconds IV; rapid administration results in respiratory depression and enhanced vasopressor response 6
- Contraindicated in patients where significant blood pressure elevation would constitute serious hazard 6
- Transient increases in blood pressure, heart rate, and cardiac index frequently occur 6
- Administer an antisialagogue prior to induction due to potential for salivation 6
Etomidate is suggested as an alternative induction agent, particularly useful in hemodynamically unstable patients at 0.2-0.3 mg/kg. 4
Inhalational Induction
Sevoflurane is preferred for both induction and maintenance due to rapid onset and offset with less airway irritation, and is often the agent of choice for mask induction in pediatric patients due to its non-pungent odor. 4
Desflurane is not recommended as first choice due to higher environmental impact (significantly greater carbon footprint than sevoflurane), although it allows rapid emergence. 7, 4
Nitrous oxide is not recommended as a primary agent due to increased risk of postoperative nausea and vomiting, delayed bowel function, and substantial environmental concerns. 7, 4
Maintenance of Anesthesia
Continuous Infusion Technique
For propofol maintenance:
- Initial infusion rates of 150-200 mcg/kg/min for the first 10-15 minutes following induction 5
- Decrease rates by 30-50% during the first half-hour of maintenance 5
- Target maintenance rates of 50-100 mcg/kg/min in adults to optimize recovery times 5
- In pediatric patients, higher rates of 200-300 mcg/kg/min initially, then 125-150 mcg/kg/min are typically needed, with younger children requiring higher rates than older children 5
For ketamine maintenance:
- Slow microdrip infusion at 0.1-0.5 mg/minute maintains general anesthesia in adults 6
- Alternatively, repeat increments of one-half to full induction dose as needed 6
Balanced Anesthesia Approach
When propofol is used as the primary agent, maintenance infusion rates should not be less than 100 mcg/kg/min and must be supplemented with analgesic levels of continuous opioid administration. 5
When an opioid is used as the primary agent, propofol maintenance rates should not be less than 50 mcg/kg/min, with careful attention to ensuring amnesia. 5
Morphine premedication (0.15 mg/kg) with nitrous oxide 67% decreases necessary propofol maintenance infusion rates and therapeutic blood concentrations compared to non-narcotic premedication. 5
Inhaled Anesthetic Maintenance
Sevoflurane is preferred over desflurane or isoflurane due to lower environmental impact (significantly reduced carbon footprint per MAC-hour). 7, 4
Low fresh gas flow techniques should be employed when using inhaled anesthetics to reduce environmental impact and agent consumption. 7, 4
With equal clinical benefit, anesthesia professionals should prefer sevoflurane to desflurane or isoflurane and should not utilize nitrous oxide. 7
Neuromuscular Blockade
Non-depolarizing agents such as rocuronium, vecuronium, and cisatracurium are used to facilitate intubation and provide muscle relaxation, with intermediate-acting agents being preferred. 4
Succinylcholine is used for rapid sequence induction but should be avoided in patients with myopathies. 4
Complete reversal of neuromuscular blockade (TOF ratio ≥0.9) must be ensured before extubation using quantitative peripheral nerve monitoring. 8, 4
Adjunctive Medications
Benzodiazepines (midazolam 0.05-0.1 mg/kg) are used for premedication or as part of induction. 4
Alpha-2 agonists (dexmedetomidine, clonidine) provide sedation and analgesia with opioid-sparing effects. 4
Short-acting opioids (fentanyl, alfentanil, remifentanil) should be used during induction and maintenance. 8
Monitoring Requirements
Essential monitoring during general anesthesia includes:
- Pulse oximetry for oxygen saturation 7, 4
- Capnography for ventilation monitoring 4
- Continuous ECG and blood pressure monitoring 5
- Neuromuscular monitoring when muscle relaxants are used 4
- Depth of anesthesia monitoring (BIS targeting ~50) helps avoid excessive anesthesia depth, particularly important in patients over 60 years to reduce postoperative delirium and hypotension risk 8, 4
Monitor ventilation and circulation at regular intervals (every 5-15 minutes) until patients are suitable for discharge. 7
Airway Management
Emergency airway equipment must be immediately available whenever general anesthesia is administered. 6
When using sedative/analgesic medications intended for general anesthesia, practitioners must be able to reliably identify and rescue patients from unintended deep sedation or general anesthesia. 7
For patients receiving IV sedative/analgesics intended for general anesthesia, maintain vascular access throughout the procedure and until the patient is no longer at risk for cardiorespiratory depression. 7
In patients with airway pathology, consider spontaneous ventilation techniques with ketamine or sevoflurane. 4
Drug Administration Principles
Administer IV sedative/analgesic medications intended for general anesthesia in small, incremental doses or by infusion, titrating to desired endpoints. 7
Allow sufficient time between doses so the peak effect of each dose can be assessed before subsequent drug administration. 7
Knowledge of each drug's time of onset, peak response, and duration of action is essential as combinations of sedative and analgesic agents have propensity to cause respiratory depression and airway obstruction. 7
When drugs intended for general anesthesia are administered by non-IV routes (oral, rectal, IM, transmucosal), allow sufficient time for absorption and peak effect before supplementation. 7
Emergency Management
If patients develop hypoxemia, significant hypoventilation, or apnea:
- Encourage or physically stimulate patients to breathe deeply 7
- Administer supplemental oxygen 7
- Provide positive pressure ventilation if spontaneous ventilation is inadequate 7
Specific antagonists must be immediately available:
- Naloxone to reverse opioid-induced sedation and respiratory depression 7
- Flumazenil to reverse benzodiazepine-induced sedation and respiratory depression 7
Use reversal agents when airway control, spontaneous ventilation, or positive pressure ventilation is inadequate. 7
Basic and advanced life-support equipment should be immediately available, and an emergency response plan must be in place (e.g., activating code blue team or 911). 7
Special Population Considerations
Obstetric Patients
Consider selecting neuraxial techniques in preference to general anesthesia for most cesarean deliveries and postpartum tubal ligations. 7
General anesthesia may be most appropriate in specific circumstances including profound fetal bradycardia, ruptured uterus, severe hemorrhage, severe placental abruption, umbilical cord prolapse, and preterm footling breech. 7
Be aware that gastric emptying is delayed in patients who received opioids during labor. 7
Pediatric Patients
Sevoflurane is often preferred for mask induction in pediatric patients due to non-pungent odor, though higher maintenance doses are required. 4
Younger pediatric patients require higher maintenance infusion rates than older pediatric patients. 5
If general anesthesia is not being used in children, IV sedation should only be given by those trained in conscious sedation, airway management, and pediatric resuscitation, using full monitoring equipment. 7
Cardiac Patients
Careful titration of anesthetics is required in cardiac patients, with propofol used cautiously due to potential hypotension. 4
Propofol should not be administered with high-dose opioid technique as this may increase likelihood of hypotension. 5
Anticholinergic agents should be administered when increases in vagal tone are anticipated as propofol reduces sympathetic activity and may reset baroreceptor reflexes, resulting in lower heart rates. 5
High-Risk Patients
Patients taking GLP-1 receptor agonists may have increased risk of regurgitation and pulmonary aspiration during general anesthesia, requiring extended fasting times and additional precautions. 9
In obese patients, airway management should be carefully considered. 9
Environmental Considerations
With equal clinical benefit for the patient, anesthesia professionals should utilize either maintained general anesthesia by inhaled vapors or total intravenous general anesthesia by propofol, recognizing that inhaled agents have environmental impact through greenhouse gas emission while propofol is ecotoxic for water and soils. 7
During inhalational anesthesia, monitor depth of anesthesia in association with end-tidal anesthetic concentration to reduce consumption of anesthetic vapors. 7
During total intravenous general anesthesia, monitor depth of anesthesia to reduce consumption of anesthetic drugs. 7
Quality and Safety Processes
Create and implement a quality improvement process based on established national, regional, or institutional reporting protocols for adverse events and unsatisfactory sedation. 7
Periodically update the quality improvement process to keep up with new technology, equipment, or advances in moderate procedural sedation/analgesia. 7
Strengthen patient safety culture through collaborative practices including team training, simulation drills, and development and implementation of checklists. 7
Critical Pitfalls to Avoid
Overdosing must be avoided by careful titration to prevent prolonged recovery and respiratory depression, especially in elderly or debilitated patients. 4
Inadequate monitoring is unacceptable—appropriate monitoring including pulse oximetry, capnography, and neuromuscular monitoring is mandatory. 4
Awareness risk exists, especially with TIVA techniques—depth of anesthesia monitoring is recommended. 4
Rapid bolus administration in elderly, debilitated, or ASA III-IV patients significantly increases cardiorespiratory complications including hypotension, apnea, airway obstruction, and oxygen desaturation. 5
The 100 mg/mL concentration of ketamine must not be administered IV without proper dilution (dilute with equal volume of sterile water, normal saline, or D5W). 6
Ketamine is not recommended for use in patients who have not followed nil per os guidelines due to potential for vomiting and aspiration despite some degree of airway protection from active laryngeal-pharyngeal reflexes. 6
Incomplete reversal of neuromuscular blockade before extubation is a preventable complication—ensure TOF ratio ≥0.9. 4