ANESTHESIA 101

Desiree Persaud MD FRCPC

Assistant professor University of Ottawa

Resident Coordinator

Dept of Anesthesiology

The Ottawa Hospital Civic Campus

Overview History Facts/Fiction Case presentations

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

Anesthesia 1846: ether anesthesia

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

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

General Anesthesia

x Not an On/Off Switch

Suppression of consciousness with profound systemic effects Lipid theory Protein theory

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

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

Adjuncts - continued Muscle relaxants

Succinyl choline, rocuronium Block NMJ Skeletal muscle paralysis

Problems: Inability to reverse Awareness

Adjuncts – cont. Induction agents:

Propofol, pentothal, ketamine Narcotics:

Fentanyl, remifentanil Non-narcotic analgesics:

Ketorolac, lidocaine, magnesium Anti-emetics

Dexamthasone, ondansetron

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

Spinal

Pros: Quick on set Dense surgical anesthesia

Cons: Limited duration - < 4 hours Limited cephaled spread Rapid sympathectomy Limited post op analgesia

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

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

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

Appendectomy 4 cases scenarios Patients/pathology come in different

packages:

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)

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

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

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

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

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

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,

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

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

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

Emergence Reversal of anesthesia: just as risky as induction Patients: responsive, protect A/W Stable: BP/temp Adequate reversal

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

Post-operative care Monitoring:

LOC/hemodynamic/sats Pain control Nausea/Vomiting Ambulation/movement

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