General Anesthetics

General AnestheticsBy Abril Santos

Universidad Popular Autónoma del Estado de PueblaInternational Intership Program

introduction

General anesthetics (GAs) are drugs

which:

• Reversible loss of all sensations and

consciousness.

• Loss of memory and awareness with

insensitivity to painful stimuli, during

a surgical procedure.

General Anesthesia

Need for unconsciousness

‘Amnesia-hypnosis’

Need for analgesia‘Loss of sensory and autonomic reflexes’

Need for muscle relaxation

• 1846 – Oliver Wendell Sr. “Anesthesia”meaning: Insensibility during surgery produced by inhalation of ether.

• William T. G. Morton (dentist) was the first to publicly demonstrate the use of ether during surgery.

• 1860 – Albert Niemann Cocaineas.

Types of Anesthesia• General anesthesia• Local and regional anesthesia

• Local Infiltration• Topical block• Surface anesthesia• Nerve Block• Spinal or subarachnoid anesthesia• Peridural anesthesia

Describes the multidrug approach to managing the patient needs.

Balanced Anesthesia

Beneficial effects Adverse Qualities

Intraoperative, an ideal anaesthetic drug:1. Would induce anesthesia smoothly, rapidly 2. Permit rapid recovery as soon as administration ceased.

*So a ‘balanced anesthesia’ is achieved by a combination of I.V and inhaled anesthesia and Pre-anaesthetic medications

General Anesthesia

Inhalational

Gas

Nitrous oxideZenon

Volatile liquids

EtherHalothaneEnfluraneIsofluraneDesfluraneSevoflurane

Methoxyflurane

Intravenous

Slower acting

Dissociative anesthesia

Ketamine

Opiod analgesia

Fentanyl

Benzodiazepines

DiazepamLorazepamMidazolam

Inducing agents

Thiopentone sod.Methohexitone sod.

PropofolEtomidateDroperidol

Stages of anesthesia

Guedel (1920) described four stages with ether anesthesia, dividing the III stage into 4 planes.

The order of depression in the CNS is:

1. Cortical centers

2. Basal ganglia

3. Spinal cord

4. Medulla

Surgical Period and GA protocol

Use pre-anesthetic medication↓

Induce by I.V thiopental or suitable alternative↓

Use muscle relaxant↓

Intubate↓

Use, usually a mixture of N2O and a halogenated hydrocarbon→maintain and monitor.

↓

Withdraw the drugs → recover

Pre-operative Period

• Meet the patient personally.• Choose the right technique by

the preferences, case and patient.

1. Patient’s History2. History of use of

anestheticsor drugs

3. Exploration 4. Pre-operative labsUse the ASA and GOLDMAN scale

for anaesthetic risk.

ASA score Use to measure risk for anaesthetic procedures.

Pre-anaesthetic Medications

Pre-anaesthetic MedicationsServe to

• Calm the patient, relieve pain• Protect against undesirable effects of the subsequently administered

anesthetics or the surgical procedure.• Facilitate smooth induction of anesthesia • Lowered the dose of anaesthetic required

Preanesthetic Medicine: • Benzodiazepines; midazolam or diazepam: Anxiolysis &

Amnesia.• Barbiturates; pentobarbital: sedation• Diphenhydramine: prevention of allergic reactions:

antihistamines• H2 receptor blocker- ranitidine: reduce gastric acidity.

Intraoperative Period

• Induction: Onset of anesthetic to the surgical anesthesia (I.V thiopental or inhalated halothane or sevoflurane)

• Maintenance: Volatile anesthetics = good minute-to-minute control over the depth. (halothane, isoflurane or fentanyl, morphine, pethidine + N.M blocking agents)

• Recovery: From discontinuation of anesthesia until • Consciousness • Protective physiologic reflexes

Regained.

Post-operative Period

• N.M blocking agents and Opioids worn off or reversed by antagonists.

• Regained consciousness and protective reflex restored• Relief of pain: NSAIDs• Postoperative vomiting: metoclopramide,

prochlorperazine

Drug Induction and recovery Main unwanted effects Notes

Thiopental Fast onset (accumulation occurs, giving slow recovery) hangover

Cardiovascular and respiratory depression

Used as induction agent declining. ↓ CBF and O2 consumptionInjection pain

Etomidate Fast onset, fairly fast recovery

Excitatory effects during induction adrenocortical suppression

Less cvs and resp depression than with thiopental, injection site pain

Propofol Fast onset, very fast recovery

Cvs and resp depression Pain at injection site.

Most common induction agent. Rapidly metabolized; possible to use as continuous infusion. Injection pain. Antiemetic

Ketamine Slow onset, after-effects common during recovery

Psychotomimetic effects following recovery, postop nausea, vomiting ， salivation

Produces good analgesia and amnesia. No injection site pain

Midazolam Slower onset than other agents

Minimal CV and resp effects. Little resp or cvs depression. No pain. Good amnesia.

Properties of Intravenous Anesthetics.

Drug Systemic BP Heart rate

Propofol ↓ ↓

Etomidate No change or slight ↓ No change

Ketamine ↑ ↑

Non-barbiturate induction drugs effects on BP and HR

Local Anesthetics

Order of sensory function block1. Pain2. Cold3. Warmth4. Touch5. Deep pressure 6. Motor

*Recovery in reverse order.

Vasoconstrictor

Vasoconstrictors decrease the rate of vascular absorption which allows more anesthetic to reach the nerve membrane and improves the depth

of anesthesia.

In Conclusion:• Type of surgical procedure

• Duration of surgical procedure• Type of anesthesia

• PATIENT• Risk vs Benefit

• ALWAYS monitor

References• American Society of Anesthesiologists (2011). Guidelines for patient care in

anesthesiology. Available online: http://www.asahq.org/For-Members/Standards-Guidelines-and-Statements.aspx.

• Dorian RS (2010). Anesthesia of the surgical patient. In FC Brunicardi et al., eds., Schwartz’s Principles of Surgery, 9th ed., pp. 1731–1752. New York: McGraw-Hill.

• Brown DL (2010). Spinal, epidural and caudal anesthesia. In RD Miller et al., eds., Miller's Anesthesia, 7th ed., pp. 1611–1638. Philadelphia: Churchill Livingstone.

• Handbook of Local Anesthesia 6th ed. Stanley F. Malamed, DDS iii Handbook of Local Anesthesia, 6th Edition

Thank You!