Anesthesia in general means loss of sensation. It can be either in the form of Local, General or Regional Anesthesia.
General anesthesia is a treatment that puts a person into deep sleep so that you don’t feel pain during surgery. So, to define General Anesthesia is a drug induced loss of consciousness during which a patient is not arousable, even by painful stimulation. The ability to independently maintain the ventilatory function is often impaired. Patient often required assistance in maintaining a patent airway because of depression of neuromuscular function. Cardiovascular function is also impaired. Overall all the major systems of the body are impaired.
And the drugs that bring about this reversible loss of consciousness are known as General Anesthetics.
General Anesthesia is given to patients for the following purposes:-
1. Pain relief(Analgesia)
2. Blocking the memory of the procedure(Amnesia)
3. Producing unconsciousness
4. Inhibiting normal body reflexes to make surgery safe and easier to perform
5. Relaxing the muscles of the body.
Hence, Triad of General anesthesia is-
The exact mechanism by which these agents produce this reversible loss of consciousness is still not known. GA act on CNS by modifying electrical activity of neurons. At the molecular level, it acts by modifying the function of ion channels. Hence the ultimate site of action for GA is the ion channels.
These General anesthetics can directly bind to the ion channels or may disrupt the function of molecules that maintain these ion channels.
Voltage gated and ligand gated ion channels both channels are sensitive to anesthetic action but general anesthetics can block the voltage gated channels only at very high concentration.
Hence, the general anesthetics inhibit or block excitatory ligand gated channels and enhance the sensitivity of inhibitory ion channels such as GABAA receptor. Also, NMDA receptor blockage is also responsible for the anesthetics to work.
The action of GA depends primarily upon the selectivity of ion channels either they may inhibit release of presynaptic excitatory neurotransmitter or alter post synaptic responsiveness to the released neurotransmitter.
Stages of General Anesthesia
Anesthesia performed with general anesthetic occurs in four stages-
Stage 1- Stage of Analgesia/Induction- is the period between the initial administration of the anesthetic and loss of consciousness. During this stage, Pain is progressively abolished. Patient remains conscious, can hear and see, and feels a dream like state. Reflexes and respiration remain normal.
Stage 2- Excitement Stage/ Stage of Delirium- During this stage-
1. The patient may become violent. He may shout, struggle and hold his breath
2. Blood pressure rises and becomes irregular.
3. Breathing rate increases
4. Uncontrolled movements, vomiting and pupillary dilation occur.
5. Involuntary micturition or defecation may occur.
Stage 3- Surgical Anesthesia- During this stage, the skeletal muscles relaxes, vomiting stops, and respiratory depression occurs. Eye movements become slow, and then stop, the patient is unconscious and ready for surgery. It has been divided into 4 planes:
Plane 1- Eyes initially rolling, this plane ends when eyes fixed
Plane2- Loss of corneal and laryngeal reflexes
Plane3- Pupils dilate and loss of light reflex
Plane 4- Intercostals paralysis, shallow abdominal respiration
Stage 4- Overdose/ Medullary Paralysis- is the stage where too much medication has been given relative to the amount of surgical stimulation and the respiratory centres in the brain that control breathing stop to work. Death can occur at this point.
Classification of General Anesthesia
Agents can be either gases or volatile liquids that are can either be inhaled through a mask or a breathing tube or injected into a vein.
In general a combination of inhaled and intravenous anesthetic is delivered during general anesthesia.
General anesthetics are given by anesthetists who are the doctors with specialist training. While giving the anesthesia to the patient, following factors should be kept in mind:
Preanesthetic medication means the delivery of drugs before the general anesthetics are given.
Purpose of GA
1. To relieve anxiety, apprehension and to make the patient more comfortable.
2. Relief in salivary and mucous secretion.
3. To prevent undesirable side effects ( bradycardia, muscle spasms)
4. To be used as an adjunct with the general anesthetic and make the induction more smooth.
5. Relief from pain
Drugs which are given for Preanesthetic medication are listed as below
1. Opioids: Morphine 10 mg or Pethidine 50-100 mg i.m is given prior to anesthetic to relieve anxiety and pain control.
2. Antianxiety drugs: Benzodiazepines: like Diazepam 5-10mg oral, Lorazepam 2 mg i.m is given to produce tranquility and smooth induction. Midazolam is given to produce amnesia.
3. Sedative-hypnotics: Barbiturates like Pentobarbitone, Secobarbitone or Butabarbitone 100 mg oral have been used night before to ensure sleep and in the morning to calm the patient.
4. Anticholinergics: Atropine or hyoscine 0.6 mg i.m/i.v to reduce salivary and bronchial secretions.
5. H2 blockers: Patients undergoing prolonged operations, caesarian section, and obese patients are at increased risk of gastric regurgitation and aspiration pneumonia. Ranitidine 150 mg or famotidine 20 mg given night before and in the morning benefit by raising pH of gastric juice.
6. Antiemetic: Metoclopramide 10-20 mg i.m preoperatively is effective in reducing post operative vomiting.
Complications of General Anesthesia
1. Respiratory depression and hypercarbia.
2. Salivation, respiratory secretions – incidence of this is less now as non-irritant anesthetics are mostly used nowadays.
3. Cardiac arrhythmias
4. Fall in BP
5. Aspiration of gastric contents
7. Delirium, convulsions
8. Fire and explosion - rare now due to use of non-inflammable agents.
1. Nausea and vomiting.
2. Persisting sedation: impaired psychomotor function.
4. Organ toxicities: liver or kidney damage.
5. Nerve palsies - due to faulty positioning.
6. Emergence delirium.
The use of general anesthesia in dentistry is still questionable because of risk of death associated with its use. However the risk is not that great and is a small one. Moreover majority of the operative care in dentistry can be carried out using either Local anesthesia or Local anesthesia with conscious sedation. Hence the use of GA is limited. Before deciding whether to use GA or not, a dentist should keep following factors in mind-
1. The co-operative ability of the child
2. The perceived anxiety and how the child has responded to similar procedures
3. The degree of surgical trauma anticipated
4. The complexity of the operative procedure.
5. The medical status of the child.
Various Circumstances and Conditions Suitable for GA in Dentistry are Listed as Below
1. To manage pain and anxiety in patients for whom local anesthesia and lighter levels of sedation are ineffective or inappropriate especially for pre-cooperative or uncooperative children, developmentally delayed, autistic and physically challenged patients as well as for the elderly with cognitive deficits.
2. Simple dental extractions in children mainly aged 4- 10 years who have learning difficulties.
3. Severe pulpitis requiring immediate relief
4. Acute soft tissue swelling requiring removal of the infected tooth.
5. Surgical drainage of an acute infected swelling
6. Established allergy to local anesthesia.
7. Moderately traumatic or complex extractions e.g. ankylosed or infra-occluded primary molars, extraction of broken-down permanent molars.
8. Teeth requiring surgical exposure or removal.
9. Post operative hemorrhage requiring packing and suturing.
1. The oral intake (solids and liquids) is restricted. Patients cannot eat any solid foods after midnight, the night before anesthesia/surgery. This includes all foods and liquids, chewing tobacco, chewing gum, candy, mints, throat lozenges, etc.
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