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ANESTHESIA 101
Desiree Persaud MD FRCPC
Assistant professor University of Ottawa
Resident Coordinator
Dept of Anesthesiology
The Ottawa Hospital Civic Campus
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Overview History Facts/Fiction Case presentations
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Surgery prior to Anesthesia The last resort Medieval torture chamber – restraints/gags Physical assault: blow to the jaw Plants: marijuana, belladonna Hypnosis, distraction Alcohol, opium
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Anesthesia 1846: ether anesthesia
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Definition Anesthesia: No sensation Types: Alone or in combo
General anesthesia Neuraxial anesthesia
Spinals and Epidurals – lower extremity/bowel surgery
Peripheral Nerve Blocks Paravertebral – breast surgery Femoral - knee replacement/muscle biopsies
Awake Unconscious
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Anesthetic principles Perioperative acute care physicians Direct manipulation of physiology Intricate knowledge of pharmacology Expert laryngoscopist/backup A/W methods Regional/invasive line placement/anatomy knowledge Equipment: ventilators/monitors/gas delivery systems
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General Anesthesia
x Not an On/Off Switch
Suppression of consciousness with profound systemic effects Lipid theory Protein theory
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General Anesthesia - continuedX Not “going to sleep” Is a chemically induced “coma”
Direct CNS system depression Lack of A/W reflexes Depression of the respiratory centres Direct CVS depression Multiple pharmacologic effects influencing every
system – gut/liver/renal/endocrine/neuromuscular
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General Anesthesia - adjuncts Volatile agent : the “gas”
Potent CVS depressant No analgesic effects
Nitrous Oxide: Not very potent Distends spaces – eg bowel
Narcotics Potent RESP depressant PONV
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Adjuncts - continued Muscle relaxants
Succinyl choline, rocuronium Block NMJ Skeletal muscle paralysis
Problems: Inability to reverse Awareness
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Adjuncts – cont. Induction agents:
Propofol, pentothal, ketamine Narcotics:
Fentanyl, remifentanil Non-narcotic analgesics:
Ketorolac, lidocaine, magnesium Anti-emetics
Dexamthasone, ondansetron
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Neuraxial anesthesia Neuraxis = spinal cord Benefits:
No direct CNS, Resp, CVS depression No need for muscle relaxants Provides analgesia
Problems: SNS blockade – hypotension Spinal hematoma - anticoagulants
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Spinal
Pros: Quick on set Dense surgical anesthesia
Cons: Limited duration - < 4 hours Limited cephaled spread Rapid sympathectomy Limited post op analgesia
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Epidural Similar to spinals Longer onset Catheter placed – can extend duration of block Most often used in combo with GA Post-op analgesia
Superior: bowel function preserved Less need for systemic narcotic
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Peripheral Nerve blocks Mainly for orthopedic and vascular surgery Unlike neuraxial—virtually no systemic side effects Provides superior post-op analgesia Takes time for placement and onset
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Pre-assessment: consults Pts with Hx of difficult intubation Personal/Family Hx of anesthesia problems Pts with uncontrolled resp disease Pts with unstable coronary disease Endocrinopathies – pheochromocytoma Pts on anticoagulants: plavix/ticlid/LMWH
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Appendectomy 4 cases scenarios Patients/pathology come in different
packages:
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Cases 25 yr old male for open appendectomy Issues:
Emergency case Acute abdomen – risk perforation/sepsis “full stomach” – aspiration risk Dehydration – Nausea and Vomiting General (or neuraxial anesthesia)
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Pre-anesthetic assessment Assess level of hydration:
General anesthesia will depress CVS reflexes Potential for hypotension
Assess for other comorbid conditions Resp/CVS
Assess Airway – aspiration risk
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Intra-op management Functioning IV – volume replacement Optimal airway positioning Rapid intubation with muscle relaxant and cricoid
pressure Narcotic, IV induction agent, relaxant
Maintain with volatile/narcotics Extubate reversed and awake
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Is an appendix always an appendix? Case: Change age to 75 yr old male Additional issues:
Compensatory mechanisms less More likely to have resp/CVS comorbidities More “sensitive” to CNS depressants Less tolerance of physiologic stressors
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Intra-operative management IV fluids – pre-op fluid hydration more careful and
essential Monitors include: ST seg monitoring Slow, titrated induction Minimize volatile – predispose to hypotension Great risk of hypotension while the surgeon is
scrubbing!!! Non-compliant vasculature – rapid swings of BP Delayed emergence possible
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Change approach to laparoscopic appendectomy?
Does it matter? Laparoscopy
Trocar: vessel/viscous perforation Relaxation, large IV
Pneumoperitoneum: Restrictive resp defect – high PAW, atelectasis Vagal efferent relfex Reduction in preload – hypotension Incr gastric pressure – aspiration risk S/C emphysema pneumothorax
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Laparoscopy considerations - cont. Carbon dioxide
SNS stimulant: BP, HR Pulmonary V/C – predispose to PH Cerebral V/D –ICP Acidosis – K, enzyme dysfunction Embolus – CV Collapse
Positioning: loss of Airway, lines,
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Intraoperative management Fluid hydration key—reduction in preload Trocar insertion – must ensure patient does not move:
COMMUNICATE Difficulty with trocar insertion
COMMUNICATE Avoid too high intrabdominal pressures Avoid too steep trendelenburg
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Change patient: morbidly obese for laparoscopic appendectomy BMI > 35 CNS: sensitive to depressants/apnea A/W: obstruction/difficult to secure Resp: restrictive defect/ PH CVS: HP, LVH, CAD GI: reflux Endo: DM
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Intraoperative management Meticulous airway positioning Prone to desaturation Trendelenburg poorly tolerated – ventilatory
difficulty: atelectasis-shunting Pre-existing PH: high CO2/low O2
Delayed emergence Prolonged PACU/overnight stay
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Emergence Reversal of anesthesia: just as risky as induction Patients: responsive, protect A/W Stable: BP/temp Adequate reversal
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Why are they so “slow”? Pre-operative assessment Difficult IV access – MO, cancer pt Epidural/Spinal placement Difficult A/W: positioning/adjuncts/awake intubation:
topicalizaton Hemodynamic instability: BP, HR, rhythm Line placement: CVP/A. line Delayed Emergence: excess
narcotics/relaxant/hypothermia
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Post-operative care Monitoring:
LOC/hemodynamic/sats Pain control Nausea/Vomiting Ambulation/movement
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Take home message
Anesthetics are tailored to both the patient and procedure Patients and procedures come in different packages General anesthesia is not an on/off switch General anesthesia is not going to “sleep” Multiple dynamic physiologic effects Time to induce/maintain/emerg Regional techniques have multiple advantages Communication is KEY