What are the key concepts and techniques in Clinical Anesthesia?

Clinical Anesthesia: Essential Concepts and Techniques

Core Anesthetic State Components

General anesthesia requires simultaneous management of three fundamental elements: unconsciousness (hypnosis), analgesia (pain control), and muscle relaxation. 1, 2

• Unconsciousness is achieved through hypnotic agents administered intravenously (propofol, barbiturates) or by inhalation (sevoflurane), creating reversible loss of consciousness 2, 3
• Analgesia is primarily managed with potent opioids to inhibit pain transmission and suppress sympathetic/endocrine responses to surgical stimuli 1, 2
• Muscle relaxation facilitates tracheal intubation and surgical exposure through neuromuscular blocking drugs 2

Multimodal Anesthesia Strategy

Modern anesthetic practice employs multimodal techniques using multiple agents at lower individual doses to maximize desired effects while minimizing side effects, rather than relying on single high-dose agents. 1

• Balanced anesthesia combines different drug classes (hypnotics, opioids, adjuncts) to avoid sole reliance on any single agent 1
• Additional agents include dexmedetomidine (specific CNS target) and magnesium (less specific targets) to reduce opioid requirements 1
• The rational strategy focuses on controlling nociception intraoperatively and pain postoperatively by targeting different points in the nociceptive system 1
• Lower doses of hypnotics/inhaled agents are needed when effective antinociceptive agents are used 1

Airway Management Fundamentals

Supraglottic airway devices (SADs) revolutionized anesthesia practice and are now used in 56.2% of general anesthetics, with the laryngeal mask airway introduced in 1983 representing a cornerstone innovation. 4

Airway Assessment

Pre-anesthetic airway evaluation must identify factors associated with difficult airway management: 4

• History: Previous anesthesia problems, stridor, snoring, sleep apnea, advanced rheumatoid arthritis, chromosomal abnormalities 4
• Physical examination: Focused assessment of heart, lungs, and airway anatomy 4
• Positive pressure ventilation with or without intubation may be necessary if respiratory compromise develops during sedation 4

Modern Airway Devices

• Videolaryngoscopes and supraglottic airways are now routine equipment for new trainees 4
• Macintosh laryngoscope technique (1937): Blade tip placed in epiglottic vallecula, lifting the tongue base to expose the larynx 3
• Endotracheal tubes with cuffs (1932) enable positive pressure ventilation 3
• SADs can be used for procedures lasting up to 11 hours in contemporary practice 4

Cricoid Pressure Evolution

Current recommendations are that cricoid pressure should be applied during rapid sequence induction, but must be released rapidly if airway difficulty is encountered. 4

Monitored Anesthesia Care (MAC)

MAC is a planned procedure combining local anesthesia with sedation and analgesia, used in 10-30% of surgical procedures, with three fundamental purposes: safe sedation, anxiety control, and pain control. 5, 4

MAC Initiation in Adults

For MAC sedation initiation, use either slow infusion at 100-150 mcg/kg/min for 3-5 minutes OR slow injection of 0.5 mg/kg over 3-5 minutes, while closely monitoring cardiorespiratory function. 6

• Rapid bolus administration must be avoided in elderly, debilitated, or ASA-PS III/IV patients as it causes hypotension, apnea, airway obstruction, and oxygen desaturation 6
• Reduce dosage to 80% of usual adult dose in elderly, debilitated, or ASA-PS III/IV patients 6
• Most patients achieve adequate sedation when propofol is administered slowly over 3-5 minutes, minimizing cardiorespiratory effects 6

MAC Maintenance

Variable rate infusion (25-75 mcg/kg/min) is preferable over intermittent bolus dosing for MAC maintenance, as bolus technique increases respiratory depression risk, transient deep sedation, and prolonged recovery. 6

• Initial maintenance rates of 25-75 mcg/kg/min during first 10-15 minutes 6
• Decrease infusion rates over time to 25-50 mcg/kg/min, adjusted to clinical response 6
• Allow approximately 2 minutes for onset of peak drug effect when titrating 6
• If using intermittent bolus method, administer 10-20 mg increments titrated to effect 6

MAC Monitoring Requirements

Continuous monitoring during MAC includes: 4

• Level of consciousness: Responsiveness assessment 4
• Breathing/ventilation: Observation (color), auscultation, chest excursion 4
• Capnography: Continual end-tidal CO2 monitoring preferred over observation alone 4
• Pulse oximetry: Continuous oxygenation monitoring 4
• Hemodynamics: Blood pressure, heart rate, electrocardiography 4
• Dedicated monitor: Individual solely responsible for patient monitoring must be present 4
• Contemporaneous recording: Real-time documentation of all monitored parameters 4

General Anesthesia Induction and Maintenance

Propofol Induction Dosing

For healthy adult patients, propofol induction dose is 2-2.5 mg/kg IV; for elderly, debilitated, or ASA-PS III/IV patients, reduce to 1-1.5 mg/kg and avoid rapid bolus administration. 6

• Pediatric induction: 2.5-3.5 mg/kg for patients aged 3-16 years, 2-2.5 mg/kg for infants and children 1-2 months 6
• Cardiac anesthesia: Use slow rate of approximately 20 mg every 10 seconds until induction onset (0.5-1.5 mg/kg total) 6
• Rapid bolus induction must be avoided in cardiac patients 6

Propofol Maintenance Infusion

For general anesthesia maintenance in adults, propofol infusion rates of 100-200 mcg/kg/min with 60-70% nitrous oxide provide adequate anesthesia, with higher rates (150-200 mcg/kg/min) required during the first 10-15 minutes. 6

• Decrease infusion rates 30-50% during first half-hour of maintenance 6
• Target maintenance rates of 50-100 mcg/kg/min in adults to optimize recovery times 6
• Pediatric maintenance: 200-300 mcg/kg/min immediately following induction, then 125-150 mcg/kg/min after first half-hour 6
• Younger pediatric patients require higher maintenance rates than older children 6

Cardiac Anesthesia Considerations

Propofol causes dose-proportional decreases in blood pressure through reduced preload and afterload, with lower heart rates during maintenance possibly due to reduced sympathetic activity or baroreceptor reflex resetting. 6

• Anticholinergic agents should be administered when increases in vagal tone are anticipated 6
• When propofol is the primary agent, maintenance infusion rates should not be less than 100 mcg/kg/min and must be supplemented with continuous opioid administration 6
• When opioid is the primary agent, propofol maintenance rates should not be less than 50 mcg/kg/min, with care to ensure amnesia 6
• Propofol should not be administered with high-dose opioid technique as this increases hypotension likelihood 6
• Morphine premedication (0.15 mg/kg) with 67% nitrous oxide decreases necessary propofol maintenance rates compared to non-narcotic premedication 6

Procedural Sedation Guidelines

Fasting Requirements

Healthy patients undergoing elective procedures must fast according to ASA guidelines: clear liquids 2 hours, breast milk 4 hours, infant formula 6 hours, nonhuman milk 6 hours, light meal 6 hours, and fried/fatty foods 8 hours before sedation. 4

• These guidelines do not apply to women in labor 4
• Fasting periods apply to all ages 4
• Clear liquids include water, fruit juices without pulp, carbonated beverages, clear tea, and black coffee 4

Sedation Exclusions and Special Populations

The ASA moderate procedural sedation guidelines specifically exclude: 4

• General anesthesia 4
• Major conduction anesthetics (neuraxial anesthesia) 4
• Premedication administered before general anesthesia 4
• Obstetric procedures (labor and delivery) 4

Emergency Equipment and Medications

Immediate availability of emergency equipment and medications is mandatory, including individuals capable of establishing patent airway, positive pressure ventilation, and advanced life-support skills. 4

Required emergency medications: 4

• Cardiovascular: Epinephrine, ephedrine, vasopressin, atropine, nitroglycerin, amiodarone, lidocaine, beta blocker, adenosine 4
• Metabolic: Glucose (IV or oral) 4
• Allergic/inflammatory: Diphenhydramine, hydrocortisone, methylprednisolone, or dexamethasone 4
• Sedation reversal: Benzodiazepines 4

Required airway devices: 4

• Nasal cannula, face masks, specialized devices (high-flow cannula) 4
• Supraglottic airway (laryngeal mask airway) 4
• Individual present to establish intravenous access 4

Supplemental Oxygen

Supplemental oxygen should be administered during procedural sedation, with method of delivery (nasal cannula, face masks, or specialized high-flow devices) determined by patient needs. 4

Ketamine in Procedural Sedation

Ketamine combined with non-general anesthesia sedative/analgesics is an acceptable technique for procedural sedation, distinct from general anesthesia. 4

• Dissociative sedation with ketamine maintains protective airway reflexes, spontaneous respirations, and cardiopulmonary stability despite profound analgesia and amnesia 7
• Intramuscular ketamine (not causing respiratory/cardiovascular collapse) should be used when IV access is difficult in combative patients or those with IV drug abuse history 4
• Once sedated with IM ketamine, peripheral, central, or intra-osseous access can be established before proceeding with anesthesia 4

Pre-Hospital and Emergency Anesthesia

Sedation Before Rapid Sequence Induction

Non-pharmacological anxiety reduction methods should be attempted first: avoid crowding the patient, use single-face point of contact, and target sedation level where patient is quiet but responsive to verbal or painful stimuli. 4

• High-risk patients: Frail, elderly, critically ill, or those with concomitant drug use (opioids) 4
• IV route preferred: Titrate small doses (1-2 mg midazolam increments) to achieve desired effect 4
• Even smaller doses: Required in frail, elderly, hemodynamically unstable patients 4
• Dilution of sedative provides better dose control 4

Pre-Oxygenation and High-Flow Nasal Oxygen

Adequate pre-oxygenation is essential to prevent hypoxaemia, with high-flow nasal oxygen now recognized as an important technique in anesthesia practice. 4

• Judicious sedation facilitates establishment of monitoring and ensures adequate pre-oxygenation in confused, agitated, or combative patients 4
• Underlying anxiety, pain, and hypoxia can be exacerbated by failure to comply with oxygen administration 4

Regional Anesthesia and Ultrasound-Guided Blocks

Ergonomic Principles for Nerve Blocks

For ultrasound-guided regional nerve blocks, position the ultrasound machine in front of the operator (not perpendicular) and use in-plane needling ALONG the visual axis (needle insertion parallel to visual axis) to improve speed and accuracy. 4

• In-plane technique: Allows tracking of entire needle length on trajectory toward target 4
• Out-of-plane technique: Similar to central venous access but more complex for regional anesthesia due to needle tip identification challenges 4
• Dominant-hand needling: Recommended for novices, though visual-spatial aptitude is more relevant than hand dominance for experts 4
• Ultrasound probe should be held toward its base; avoid "pinch" grip 4

Nerve Block Phases

Each phase of ultrasound-guided nerve block has ergonomic challenges: 4

• Turning the trunk, turning the head 45° or more, and non-dominant hand needling are associated with fatigue and suboptimal block performance 4
• Needle must be steered within narrow ultrasound beam without losing view of needle tip 4
• Needle placed in close proximity to target without piercing it 4

Autonomic Nervous System Considerations

Pre-operative Autonomic Assessment

Diabetic patients must undergo cardiovagal function testing including heart rate variability during deep breathing, active orthostatism, and Valsalva maneuver, as recommended by the American Society of Anesthesiologists. 7

Additional indications for autonomic testing: 7

• Prolonged QTc interval >440 ms on ECG (increased risk of perioperative hemodynamic instability and vasopressor requirements) 7
• Neurodegenerative disease patients 7
• Orthostatic hypotension symptoms or episodes of unfelt hypoglycemia 7

Testing Conditions

Autonomic testing requires 3-hour fasting, avoidance of nicotine, caffeine, theine, or taurine-containing drinks on examination day, with continuous beat-to-beat blood pressure and ECG monitoring in quiet, temperature-controlled environment (21-23°C). 7

• Results must be interpreted using age-specific reference values due to physiological reduction in heart rate variability with aging 7

Intra-operative Management of Autonomic Dysfunction

Avoid drugs inducing orthostatic hypotension in patients with detected cardiac autonomic neuropathy (CAN), and titrate vasopressors carefully rather than using standard dosing, as requirements correlate with dysautonomia severity. 7

• Peripheral nerve blocks preferable: Avoid sympatholytic effects of neuroaxial blocks that compound parasympathetic hyperactivity 7
• Preoperative decrease in respiratory heart rate variability predicts perioperative hemodynamic instability 7
• Quantitative neuromuscular monitoring mandatory: Autonomic dysfunction can prolong recovery and mask residual paralysis 7
• End-tidal anesthetic concentration monitoring: Maintain >0.7 age-adjusted MAC with audible low-concentration alarms to prevent awareness 7

Elderly Patient Considerations

Elderly patients experience reduced beta-receptor responsiveness (effectively "beta-blocked"), limiting their ability to increase cardiac output or respond to fluid losses, compounded by baroreceptor dysfunction and reduced angiotensin II responsiveness. 7

• Age-related cardiac compliance reduction further limits physiological stress response 7
• Reduced organ reserve limits response to acute illness, anesthesia, and surgery 7
• Closing volume increases and ventilation/perfusion mismatch worsens when supine 7
• Age-related decline in oxidative capacity combined with cardiopulmonary changes increases perioperative myocardial and cerebral ischemia risk 7

Anaphylaxis Recognition and Management

Immediate Recognition

Cardiovascular collapse occurs in 50.8% of anaphylactic reactions during anesthesia and may be the sole clinical feature in 10% of patients, often without cutaneous signs—do not exclude anaphylaxis based on absence of skin manifestations. 8, 7

Clinical presentation: 8, 7

• Cutaneous signs: Present in 72% (flushing, urticaria) but absence does not exclude anaphylaxis 8
• Bronchospasm: Occurs in 39.8% of allergic anaphylaxis cases 8
• Bradycardia: Occurs in 1.3-10% of cases, not just tachycardia 8, 7
• Hypotension: May be sole feature in ~10% 8
• Timing: Symptoms typically develop within minutes but may be delayed up to one hour (latex, antibiotics, IV colloids, Cidex OPA) 8

Immediate Management Protocol

Administer intravenous adrenaline (epinephrine) immediately at 50 mcg (0.5 mL of 1:10,000 solution) for adults, repeated as needed, while simultaneously securing airway, administering 100% oxygen, and providing aggressive fluid resuscitation with normal saline, as recommended by the American Society of Anesthesiologists and American Heart Association. 8

Step-by-step protocol: 8

1. Call for help immediately and note the time 8
2. Stop all potential causative agents (IV colloids, latex, chlorhexidine, antibiotics); maintain anesthesia with inhalational agent only if needed 8
3. Secure airway and administer 100% oxygen—intubate if necessary and ventilate 8
4. Elevate legs if hypotension present to prevent orthostatic hypotension and improve venous return 8
5. Start CPR immediately if indicated according to Advanced Life Support Guidelines 8

Adrenaline Dosing

Repeat adrenaline 50 mcg IV boluses every few minutes as needed for severe hypotension or bronchospasm; start continuous IV infusion if multiple boluses required due to short half-life. 8

Infusion preparation: 8

• Standard preparation: 1 mg (1 mL of 1:1000) in 250 mL D5W = 4 mcg/mL, infuse at 1-4 mcg/min initially, titrate up to 10 mcg/min 8
• Alternative preparation: 1 mg in 100 mL saline (1:100,000), infuse at 30-100 mL/h (5-15 mcg/min) 8
• Pediatric IV dosing: 1 mcg/kg (0.1 mL/kg of 1:10,000 solution), titrated to response 8
• Pediatric preparation: 1 mL of 1:10,000 per 10 kg body weight; start with one-tenth of syringe contents 8

IM dosing (if IV access unavailable): 8

• >12 years: 500 mcg (0.5 mL of 1:1000) 8
• 6-12 years: 300 mcg (0.3 mL of 1:1000) 8
• <6 years: 150 mcg (0.15 mL of 1:1000) 8

Fluid Resuscitation

Administer normal saline 0.9% or lactated Ringer's at high rate through large-bore IV: adults require 1-2 L at 5-10 mL/kg in first 5 minutes (up to 7 L may be required); children require up to 30 mL/kg in first hour. 8

• Increased vascular permeability can transfer 50% of intravascular fluid to extravascular space within 10 minutes 8, 9
• Avoid dextrose solutions (rapidly extravasated); use normal saline preferentially 8

Secondary Medications

Adjunctive therapy: 8

• Chlorphenamine: 10 mg IV (adult dose) 8
• Hydrocortisone: 200 mg IV (adult dose) 8
• Alternative vasopressors: Metaraminol if blood pressure does not recover despite adrenaline infusion 8
• Persistent bronchospasm: IV salbutamol infusion, metered-dose inhaler if appropriate connector available, consider IV aminophylline or magnesium sulphate 8

Diagnostic Workup

Mast cell tryptase sampling requires three time points: first sample as soon as feasible after resuscitation starts (do not delay resuscitation), second sample 1-2 hours after symptom onset, third sample at 24 hours or in convalescence to establish baseline. 8

• Collect 5-10 mL clotted blood, label with time and date 8
• Some individuals have elevated baseline tryptase, making convalescent sample essential 8

Post-Resuscitation Care and Observation

Patients who experience severe initial anaphylaxis with cardiovascular collapse or hypotension require prolonged observation or hospital admission, as biphasic reactions can occur as late as 72 hours after initial reaction (most occur around 8 hours), as recommended by the Journal of Allergy and Clinical Immunology. 9

Risk factors for extended observation: 9

• Requirement for more than one dose of epinephrine during initial treatment (odds ratio 4.82 for biphasic reaction) 9
• History of previous biphasic anaphylactic reactions 9
• Protracted reactions may last up to 32 hours despite aggressive treatment 9

Discharge Criteria

Patients may be discharged only after complete resolution of all anaphylaxis signs and symptoms, completion of appropriate observation period (4-6 hours minimum, longer based on severity), and hemodynamic stability without ongoing interventions, as recommended by the NIAID and American Academy of Allergy, Asthma, and Immunology. 9

Post-discharge management: 9

• Continue treatment for 2-3 days with H1 antihistamine, H2 antihistamine, and corticosteroid 9
• Note: Corticosteroids do not prevent biphasic anaphylaxis 9
• Food-induced anaphylaxis may cause loose stools/diarrhea for 24 hours after reaction 9
• Recurrent urticaria may persist for 1-2 days after significant cutaneous reactions 9

Critical Pitfalls

Do not delay adrenaline administration—it is the definitive treatment with alpha-agonist (vasoconstriction), beta-agonist (inotropy, bronchodilation), and mediator release inhibition properties. 8

Common errors to avoid: 8

• Do not exclude anaphylaxis based on absence of cutaneous signs (28% lack skin manifestations) 8
• Do not assume tachycardia will be present (bradycardia occurs in 10% of cases) 8
• Do not use IM route when IV access is available in anesthesia setting (IV allows precise titration) 8
• Exclude equipment failure (misplaced tracheal tube) before attributing symptoms solely to anaphylaxis 8
• Neuraxial blockade exaggerates hypotension in anaphylaxis 8
• Tourniquet deflation may trigger anaphylaxis if allergen sequestered in limb 8
• Patients with pre-existing asthma may have more prominent bronchospasm 8

Consent and Patient Information

Information Disclosure Requirements

Anaesthetists must tell patients what procedures are intended and why, what significant foreseeable risks are and their consequences, and what alternatives exist including having no treatment, with information tailored to what the particular patient wants to know from their perspective. 4

Broad information categories: 4

• Common components: Fasting, premedication effects, transfer to anaesthetic room, cannula insertion, non-invasive monitoring, induction technique, intra-operative monitoring by anaesthetist, intra-operative drugs/fluids, awareness of procedure/surroundings if awake/sedated, transfer to recovery, return to ward, postoperative analgesia/anti-emetics/fluids 4
• Alternative techniques: Including backup plans if one technique fails (e.g., general anesthesia for caesarean section as alternative to regional anesthesia) 4
• Specific procedure-related aspects: Invasive monitoring and associated risks, recovery in critical care environment, sedation, intubation/tracheotomy 4
• Common/significant side-effects: Nausea and vomiting, sore throat, damage to teeth/lips, cognitive dysfunction, numbness/weakness/return of pain after local anaesthetic techniques, suxamethonium pains, post-dural puncture headache 4
• Serious side-effects: Nerve/eye damage, awareness during anaesthesia, death 4

Patient-Specific Risk Communication

Anaesthetists must make reasonable efforts to identify particularly significant risks or complications to individual patients, such as vocal cord damage risk from general anesthesia in professional singers, and provide estimates of risk incidence. 4

• All patients should be given opportunity to ask questions with honest answers provided 4
• Courts emphasize importance of recognizing consent as dialogue with patients, tailored to individual patient needs 4
• Anaesthetists should not provide information about surgical procedure beyond their capability 4

Documentation

A signed consent form is not necessary for anaesthetic procedures done to facilitate another treatment, as the consent process itself is important—the signed form is merely evidence that consent process occurred but does not validate or invalidate consent. 4

• Anaesthetic can be considered component of another treatment (anaesthesia for surgery) or part of larger interrelated process (epidural pain relief for childbirth) 4
• Whether consent is oral or written, clear documentation of patient's agreement to intervention and discussion content is essential 4

COVID-19 Pandemic Considerations

Universal Safety Measures

Universal safety measures must be implemented to protect staff and patients during resumption of surgical activity in the COVID-19 pandemic context, with dedicated circuits for patient flow and quality improvement processes. 4

• High-risk surgeries: Surgery with high risk of caregiver contamination by aerosolization (lung resection, ENT surgery, skull base neurosurgery, rigid bronchoscopy) 4
• Major surgery: High risk of postoperative critical care stay where perioperative respiratory risk is increased by SARS-CoV-2 infection 4

High-Risk Patient Identification

Patients at increased perioperative risk: 4

• Morbid obesity (BMI >30 kg/m²) 4
• Malignant haemopathy being treated 4
• Cirrhosis at least stage B of Child-Pugh classification 4

Benefit-Risk Assessment

Preoperative assessment and decision on intervention must include benefit/risk analysis specific to COVID-19 context, with patient information regarding pandemic-related risks and modalities of preanaesthetic consultation adapted to minimize exposure. 4

• 51 recommendations developed with 100% strong agreement after one round of expert scoring 4
• At least 70% of experts must express favorable opinion with less than 20% unfavorable to validate recommendation 4

Quality Improvement and Monitoring

Mandatory Monitoring Standards

Creation and implementation of quality improvement processes is essential for procedural sedation and anesthesia, with contemporaneous recording of all monitored parameters required. 4

• Presence of individual dedicated to patient monitoring is mandatory 4
• Consultation with medical specialist (physician anesthesiologist, cardiologist, endocrinologist, pulmonologist, nephrologist, obstetrician) when indicated 4

Depth of Anesthesia Monitoring

Depth of anesthesia may be monitored using automated electroencephalographic analysis (Bispectral Index), while myorelaxation must always be monitored using nerve stimulator, though pain/analgesia evaluation remains based on clinical signs of sympathetic stimulation. 2, 5

• Adequacy of neuromuscular recovery (ToF ratio >0.9) must be demonstrated and documented before awakening and extubation 7
• Effective multimodal anesthesia strategy requires simultaneous monitoring of antinociception and level of unconsciousness 1