general anesthesia in OMFS

1. GENERAL ANAESTHESIA

2. CONTENT
1. INTRODUCTION
2. HISTORY
3. STAGES OF GENERAL ANAESTHESIA
4. MECHANISM OF ACTION OF G.A
5. PRE-ANESTHETIC EVALUATION
6. RECOVERY
7. COMPLICATIONS OF G.A
8. CONCLUSION

3. DEFINITION
General anaesthesia is defined as “an induced state of unconsciousness
accompanied by partial or complete loss of protective reflexes, including
the ability to independently maintain an airway and respond
purposefully to physical stimulation or verbal command.”
Reference: Clinical review of oral and maxillofacial surgery, 2008

4. INTRODUCTION
• General anesthesia is a reversible state of
unconsciousness characterized by loss of
reception and perception of stimuli.
• Triad of G.A
1. analgesia
2. amnesia
3. skeletal muscle relaxation
• General anesthesia is used for
performing complex surgeries.
Must be achieved during the administration of any
general anesthetic agent

5. SEDATION REDUCED
ANXIETY
AMNESIA
SKELETAL
MUSCLE
RELAXATION
SUPPRESION
OF
PROTECTIVE
REFLEXES
ANALGESIA
EFFECTS OF GENERAL ANESTHESIA

6. WHY THE CONCEPT OF G.A IS IMPORTANT FOR US?
Need for:
Unconsciousness
Analgesia
Muscle relaxation

7. • The techniques of anaesthesia evolved first with inhalation
anaesthesia, followed by local and regional anaesthesia, and
finally intravenous anaesthesia.
• The development of surgical anaesthesia is considered one of the
most important discoveries in human history.
HISTORY

8. HISTORY OF INHALATIONAL ANESTHETICS
• Because the hypodermic needle was not invented until 1855, the first
general anesthetics were inhalation agents.
• The three early inhalation anesthetics were
1. Ether
2. Chloroform
3. Nitrous oxide

9. • Ether was used for frivolous purposes (“ether
frolics”) and was not used as an anesthetic
agent in humans until 1842, when Crawford
Long and William Clark independently used it
on patients for surgery and dental extraction,
respectively.
ETHER

10. A new era had dawned when William Morton administered ether
vapour before a large audience to removed a tumour without any sign
of distress.

11. Nitrous oxide
• Joseph Priestley produced nitrous oxide in 1772, and Humphry
Davy first noted its analgesic properties in 1800.
• Nitrous oxide was the least popular of the three early inhalation
anesthetics because of its low potency and its tendency to cause
asphyxia when used alone.
• Interest in nitrous oxide was revived in 1868 when Edmund
Andrews administered it in 20% oxygen.
• Nitrous oxide is the only one of these three inhalational agents
still in widespread use today.

12. •Intravenous anesthesia required the invention of the hypodermic
syringe and needle by Alexander Wood in 1855.
•Barbiturates were the first induction agents synthesized in 1903.
•The first barbiturate used for induction of anesthesia was
diethylbarbituric acid (barbital).
•Thiopental synthesized in 1932 remained the most common agent
for intravenous induction of anesthesia for many years.
HISTORY OF INTRAVENOUS ANESTHETICS
1. INDUCTION AGENTS

13. •Benzodiazepine like diazepam, lorazepam, and
midazolam are used extensively for premedication,
conscious sedation, and induction of general
anesthesia.
•The release of propofol in 1986 was a major
advance in outpatient anesthesia because of its
short duration of action. Propofol is currently the
most popular agent for intravenous induction
worldwide.

14. Depolarization of nerve release of neurotransmitter Ach
Diffusion in the synaptic junction combine with Ach receptors
Opening of ion channels generation of muscle action potential
Muscle contraction
Neuromuscular blocking agents

15. 2. Neuromuscular blocking agents
•Succinylcholine was synthesized in 1949 and it became a
standard agent for facilitating tracheal intubation.
•Other neuromuscular blockers like gallamine, metocurine,
alcuronium, and pancuronium were subsequently introduced.
Unfortunately, these agents were often associated with side
effects.
•Recently introduced agents that more closely resemble an ideal
NMB include vecuronium, atracurium, rocuronium.
NON- DEPOLARIZING
DEPOLARIZING

16. 3. Opioids
• Morphine, isolated from opium in 1805,
was also tried as an intravenous anesthetic.
• Subsequently fentanyl and sufentanil were
developed.

17. BALANCED ANESTHESIA
Opioid for
analgesia
muscle relaxation

18. CLASSIFICATION
GENERAL ANAESTHESIA
INHALATIONAL INTRAVENOUS
GAS VOLATILE LIQUID
NITROUS OXIDE
ENFLURANE
DESFLURANE
HALOTHANE
ISOFLURANE
SEVOFLURANE
SLOWER ACTING
DISSOCIATIVE ANAESTHESIA
(KETAMINE)
OPIOID
BEZODIAZEPINES
INDUCING AGENT
THIOPENTONE
METHOHEXITONE
PROPOFOL
ETOMIDATE

19. Inhalational anaesthetics IV anaesthetics

20. STAGES OF GENERAL ANESTHESIA

21. INDUCTION
•The period of time from the onset of administration of the anesthetic to the
development of effective surgical anesthesia in the patient.
•Thus GA is normally induced with an I.V thiopental, which produces
unconsciousness within 25 seconds or propofol producing unconsciousness in
30 to 40 seconds after injection.

22. MAINTENANCE
• Maintenance is commonly provided with volatile anesthetics, which offer good
control over the depth of anesthesia.
• Opioids such as fentanyl are used for analgesia along with inhalation agents,
because the latter are not good analgesics.
• After administering the anesthetic, vital signs and response to stimuli are
monitored continuously to balance the amount of drug inhaled and/or infused with
the depth of anesthesia.

23. RECOVERY
• The time from discontinuation of administration of the anesthesia until
consciousness and protective physiologic reflexes are regained.
• For most anesthetic agents, recovery is the reverse of induction.
• The patient is monitored to assure full recovery, with normal physiologic functions
(spontaneous respiration, acceptable blood pressure and heart rate, intact reflexes,
and no delayed reactions such as respiratory depression)

24. Depth of anesthesia (GUEDEL’S SIGN)
• Guedel in the year 1937 described 4 stages with ether anaesthesia
and divided stage 3 into four planes.

28. MECHANISM OF ACTION

29. MECHANISM OF ACTION
• For inhalational anesthetics- MAC (Minimum alveolar concentration)
• For intravenous anesthetics – Drug Potency
• General anethetic drugs mainly act via interaction with membrane
proteins
• Different agents have different molecular mechanism
• Sites of action- ligand gated (not voltage gated)ion channels
POTENCY

31. Enhanced GABA
effect on GABA A
Receptors
• GABA – the major inhibitory
neurotransmitter in brain.
• Normally GABA-A receptor mediates
the effect of GABA

32. 2. Glycine- activates chloride channel in spinal cord and
medulla- barbiturates, propofol, halothane
3. NMDA- N- methyl D- aspartate type of glutamate
receptors – nitrous oxide and ketamine selectively inhibit
4. Block nicotinic receptor (produces analgesia)-
barbiturates

33. PRE-ANESTHETIC EVALUATION
• An interview with the patient or guardian to review medical,
anesthesia, and medication history
• An appropriate physical examination
• Review of diagnostic data (laboratory, electrocardiogram, radiographs,
consultations)
• Assignment of ASA physical status score (ASA-PS)

34. PURPOSE:
• information about the patient’s medical history and physical as well
as mental condition.
• need for a medical consultation and the kind of investigations
required.
• To educate the patient about anaesthesia
• To choose the anaesthetic plan to be followed, guided by the risk
factors uncovered by medical history.
• To obtain informed consent.

35. PRE ANESTHETIC EVALUATION
1. HISTORY:
• Review for history of difficult airway, success of specific techniques,
and intraoperative complications.
• Anesthesia history
a. History of malignant hyperthermia
b. Family history of malignant hyperthermia
c. History of postoperative nausea and vomiting (PONV)
d. History of difficult intubation

36. • Current medications
Special attention paid to anticoagulants, beta-blockers, antihypertensives, diuretics, oral
hypoglycemics, and antidepressants.
• Drug allergies (including latex)
• Examination of organ systems

37. 2. PHYSICAL EXAMINATION
• Vital signs are evaluated
• Airway examination for detecting difficulty in laryngoscopy

38. PRE OPERATIVE AIRWAY EXAMINATION
• The assessment of the patient's airway is an integral part of the
pre-operative workup. Its purpose is to predict potential
problems, allowing a management plan to be developed ahead
of time and avoid an unanticipated difficult airway.

39. MALLAMPATI SCORE
• This is assessed by asking the patient (in a sitting or upright position) to open his/ her mouth
and protrude the tongue maximally without phonation, with the observer being at eye level with the
patient. Visibility of faucial pillars, soft palate and uvula inside the patient's mouth will result in a
score between one and three

40. • Seshagiri Rao Mallampati (1941 – ) Indian born American
anesthesiologist.
• Eponymously affiliated with the Mallampati Score used to predict
the ease of endotracheal intubation
• Mallampati practiced to see whether the faucial pillars and uvula
were visible in every patient. He found that the clinical sign of the
concealment of the uvula and faucial pillars by the base of the
tongue was helpful in predicting the majority of difficult tracheal
intubations.
• He later hypothesized and verified this in a study published in
1985, dividing the patients into 3 classes
• Dr. Young’s later added the 4th class in the Mallampati scoring
system.

41. • Cervical spine mobility
• thyromental distance

42. American Society
of
Anesthesiologists
Physical
Classification
Status (ASA
scoring)
• I —healthy patient
• II —patient with mild systemic disease
• III —patient with severe systemic disease
• IV —patient with severe systemic disease
that is a constant threat to life
• V —moribund patient who is not expected
to survive without the operation
• VI —declared brain-dead patient whose
organs are being removed for donor
purposes

43. REVERSAL OF ANAESTHESIA
• The only component of anaesthesia that is truly reversible at the
conclusion of general anaesthesia is the effect of the nondepolarizing
muscle relaxant.
• The timing of the last dose of muscle relaxant is important and if it is too
near to the conclusion of surgery, adequate time must be allowed before
reversal is attempted.
• Nondepolarizing muscle relaxant is reversed by anticholinesterase drugs,
e.g. neostigmine sulfate (0.05-0.07 mg/kg).
• atropine sulfate (anticholinergic) is administered along with this to prevent
the muscarinic effects of neostigmine like bradycardia, profuse salivation
and bronchospasm.

44. COMPLICATIONS
• During anaesthesia:
Respiratory depression
Salivation, respiratory secretions
Cardiac arrhythmias
Fall in BP
Aspiration
Laryngospasm and asphyxia
Awareness
 Delirium and convulsion
After anaesthesia:
 Nausea and vomiting
 Persisting sedation
 Pneumonia
 Organ damage – liver, kidney
 Nerve palsies
 Emergence delirium
 Cognitive defects

45. CONCLUSION
• Needs staff with anesthetic experience
• Needs careful monitoring to prevent airway obstruction as airway has been
compromised
• Requires constant monitoring until completely stable
• May require intervention for pain, nausea or anesthetic complications like
sensitivity to opiates or adverse reactions to anesthetic drugs
• Need IV therapy for drug administration and IV fluids until able to take
orally
• Requires longer recovery time
• Takes longer to ambulate (walk)
• Should be carefully observed for duration of time spent in recovery room
• Requires more extensive documentation

46. CONCLUSION
• Morgan and Mikhail’s Clinical Anesthesiology
• Miller’s Anesthesia
• Textbook Of Oral And Maxillofacial Surgery by Malik Neelima
Anil