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Anesthetics: Classification, types and uses.
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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!