General Anesthesia

General Anesthesia

• Controlled by a reversible irregular paralysis of cells of the central nervous system

• ALL modalities of sensations are lost, including consciousness

• Depression must be REVERSIBLE, since full recovery is very importnant

ARMAMENTARIUM

GAS MACHINES

PURPOSE

General anaesthesia has many purposes including:

• Analgesia — loss of response to pain,• Amnesia — loss of memory,• Immobility — loss of motor reflexes,• Unconsciousness — loss of

consciousness,• Skeletal muscle relaxation.

Sequence of Depression in CNS when G.A. is administered

1. Cerebrum Cerebral cortex – memory,

judgement, consciousness

2. Cerebellum Basal Ganglia – muscle

coordination

3. Spinal Cord Motor and sensory impulses

4. Medullary Centers Medullary centers

CEREBRUM

• Most highly developed area of the CNS

• First to be depressed• Produces loss of memory,

impairment of judgement, obtunding of the special senses, unconsciousness

• Patient will still react, however, to painful stimuli with somewhat coordinated muscular movements

CEREBELLUM & BASAL GANGLIA

• Patient loses muscles coordination and mat exhibit only purposeless movements in response to painful stimuli.

• As the amount of anesthetic agent increased, the irregular descending depression will manifest itself as the medullary centers of respiration and circulation are bypassed and he spinal cord are depressed.

SPINAL CORD

• Patient has now lost the ability to convey motor & sensory impulses and thus cannot respond to painful stimuli by any muscular movements

MEDULLARY CENTERS

• Depressed until, if the depression is allowed to continue, respiration and then the circulation will cease.

THEORIES OF GENERAL

ANESTHESIA

ANOXIC THEORIES

• Use ANOXIA as their basis no doubt predicated on the intimate relationship commonly exhibited between he effects of anoxia an those of anesthetics

• In effect, they stated the various anesthetic agents inhibited the oxidative of the cells on the CNS

LIPID THEORY

• States that there is a parallelism between the oil-water distribution coefficient of an anesthetic agent and its potency.

• Evidence for this theory has been strengthen with the fact that the lipid solubility coefficient of anesthetic agents compares favorably with their anesthetic potency.

• Suggests that the anesthetic acts nonspecifically on the lipid portions of the neuronal membrane to cause a general disturbance that causes the ion channels to change structure thereby changing their function

• Interactions here cause a physical change in the membrane

SURFACE TENSION THEORY

• It is based on the ability of the anesthetic agents to lower surface tension, on which their potency depends

• This property enables the agents possesing it to interfere with the permeability, polarization and metabolic processes of the cells

ADSORPTION THEORY• Based on the concept of surface

tension• It assumes that anesthetic agent

thus retarded the adsorption of other substances.

• The theory was substantiatedby the finding of much lower concentrations of anesthetic agent were needed to influence the activity of enzymes in cellular structures with large surface area than were needed in structure free fluids

CELLULAR PERMEABILITY THEORY

• Is an extension of the adsorption theory.

• It states that reversible paralysis is produce by a reversible decreased of cell lipid membrane.

• The decreased permeability for fat soluble substance seems to be increased.

COAGULATION THEORY

• It is the earliest of all the theories of anesthesia

• Anesthesia results from the reversible coagulation of proteins which is indeed true for a limited number of agents.

DEHYDRATION THEORY

• Based on the assumption that anesthesia is produced by dehydration of the cells in the CNS.

• It supposes that he brain loses some of its water content under anesthesia

MICROCRYSTAL THEORY

• Based on the molecular properties of anesthetic agent and aqueous molecular structure of nervous tissue.

• The theory involves the interaction of molecules of the anesthetic agent and water molecules of the brain, which is 78% water rather than lipid molecules

• It suggests that consciousness is loss when submicroscopic crystals are formed in the aqueous part of the brain subtance.

ADMINISTRATION OF GENERAL ANESTHESIA

To obtain general anesthesia

Reach the susceptable areas of the central nervous system

Exerts its depressant effect on the cells

Unconsciousness and other manifestations of GA developed

What must be maintained for a satisfactory result of

GA?Sufficient concentration of the

anesthetic agent.Enough oxygen to supply the

patients metabolic needsAn efficient elimination of Carbon

Dioxide

ROUTES OF ADMINISTRA

TION

Inhalation Route

• Anesthetic agent is given as GAS, VAPOR, or LIQUID– vaporized through a mask so that it is

eventually taken into the lungs then transmitted into the blood stream

Inhalation Route

• Transmission is dependent on a gradient or pressures between the concentration of anesthetic in the lungs and that in the blood stream

5 Different Methods of Inhalation Route

1. OPEN DROP– A suitable mask or gauze stucture is

needed for penetration and vaporization of volatile anesthetic agent

– No other cloth or confining covering is used

2. SEMI-OPEN DROP Same as the open drop method except

that a confining wrapper or covering is used to uncrease the concentration of anesthetic vapor more readily within the area.

Confining wraper or covering also prevents the entrance of atmospheric air and the exit of carbon dioxide

3. INSUFFALATION Done by vaporizing a volatile

anesthetic agent by air or oxygen under pressure.

Resultant mixture is brought by a catheter into the upper respiratory passeges

4. SEMI-CLOSED Done by using an anesthetic apparatus

where in controlled amounts of anesthetic agent and oxygen are delivered by meanes of gauges, vaporizers, breathing tube and masks.

Exhalation are blown into the atmosphere, which maintains equilibrium of gasses, reduces mechanical dead space and affords an efficient elimination of carbon dioxide.

5. CLOSED Done in the same manner as that of

the semi-closed to a closed system Difference with semi closed is that the

exhalations are confined to a closed system

Anesthetic machine and the external part of the respiratory system are in one continuous circuit where exhalations or inhalations are routed through a chemical compound (soda lime)

May be accomplished by using:

CIRCLE FILTER - gasses pass over the canister with soda only during inhalation

To-and-fro System – gasses pass over the soda lime during both exhalation and inhalation

ROUTES OF ADMINISTRATION (cont.)

Quizon, Lhajean May

INTRAVENOUS ROUTE• Most direct route

for inducing unconsciousness

• Anesthetic agent: carried directly into the venous circulation

2 techniques:

a. INTERMITTENT TECHNIQUE An intravenous agent is injected

slowly into the bloodstream until desired plane of anesthesia is reached

Patient watched carefully as the signs of anesthesia are observed

Additional intravenous agent is administered when necessary to maintain the proper level of anesthesia

b. CONTINUOUS DRIP TECHNIQUE Employs the anesthetic

agent in a much weaker concentration and allows it to drip constantly into the venous circulation

Rate of the drip is increased or decreased as desired to maintain the proper plane of anesthesia

Inhalation and Intravenous

• Most frequent routes used to secure anesthesia for dental and oral surgery

• Afford the anesthesia a fairly accurate control of the degree of depression of the central nervous system

RECTAL ROUTE• Anesthesia is administered

rectally in a single dose and is absorbed onto the bloodstream to elicit it effects

• Anesthetist does not have minute to minute control over the depth of anesthesia

• Often used when basal narcosis is needed and is supplemented by inhalational anesthesia

INTRAMUSCULAR ROUTE

• Anesthetic drug or agent is injected into the muscle tissues and then absorbed into the bloodstream to produce the desired effect

• Provides the anesthetist little control of the drug one it is administered

• Used primarily for premedication

• 90° positioned

INTRAORAL ROUTE• Patient is instructed to

swallow a previously calculated dose

• Provides the anesthetist little control of the drug one it is administered

• Used primarily for premedication purposes

• Method of choice of most dentists for premedication for the reason of convenience of the administration

Mode of Action

• First type of body tissue to be depressed = brain

• Brain: more readily susceptible to the depressant action of anesthetic agents

: receive a proportionately higher percentage of circulating blood volume

• General anesthetic agents:– Depress brain tissues

in advance of other body tissues

– Selectively depress specific cells of brain so that the ital functions are lost in a predetermined manner

– Dissolved in the circulating blood and transported by this means to the circulatory system

• What happens when in the circulatory system?– During each circuit of

the blood‚ a certain proportion of the dissolved agent is:

Carried to the brain Carried to the other

tissue Being excreted

– Remained in the circulating blood to reinitiate the previous action

– This action continues with the direction of diffusion:

• Higher concentration in the bloodstream→ lower concentration in the tissues

– When concentration in bloodstream ‹ tissues= direction of diffusion is reversed

• Result: – Exertion of a

depressant action– Reversal of the

temporary paralysis– Return of the ell to the

normal– Why would the

concentration in the bloodstream fall?

Detoxification Elimination Reduced administration

• Control of the anesthetic in the bloodstream depends on :– Rate of uptake of the anesthetic agent– Excretion from the circulating blood

• Excretion via: lungs ‚kidneys and liver

GENERAL ANESTHESIA IN DENTAL PROCEDURES

Patient’s level of fear is usually a more important factor than the nature of the procedure

High levels of preoperative anxiety lengthy and complex procedures and need for a pain free operative period ay be indications for general in anesthesia in healthy adults and young children

At least 3 professionals are required:Operating dentistA professional responsible for observing and

monitoring the patientAssistant of the operating dentist

INDICATIONS FOR GENERAL ANESTHESIA

1. Children who are too young to cooperate2. Lancing abscesses3. Adults who are abnormally fearful of

needle4. Extraction of teeth in the early stage of

suppurative infection5. Multiple‚ uncomplicated extractions6. In its analgesic stage for preparation of

sensitive teeth for fillings7. Treatment of peridental disease

CONTRAINDICATIONS FOR GENERAL ANESTHESIA

1. Presence of persistent thymus glands in children(status lypmhaticus)2. Exopthalmic goiter‚ diabetes or other disturbance of endocrine

function3. Abnormally high blood pressure4. Uncompensated valvular lesions of the

heart‚ myocarditis‚ pronounced cardiac arrhythmia5. Inflammations of the respiratory system‚ including pulmonary

tuberculosis6. Grave primary or secondary anemia7. Patients addicted to the excessive use of alcohol‚ tobacco‚ coal tar

derivatives and narcotic drugs8. Advanced pregnancy9. Obesity10. Children with greatly enlarged tonsils11. Operations requiring prolonged anesthesia12. Senility

Yasi –anaesthetic agent

STAGES OF ANESTHESIA

Kamran

• The Guedel's classification by Arthur Ernest Guedel described four stages of anaesthesia in 1937. Despite newer anaesthetic agents and delivery techniques, which have led to more rapid onset and recovery from anaesthesia, with greater safety margins, the principles remain.

• Stage 1• Stage 1 anaesthesia, also known as the "induction", is the

period between the initial administration of the induction agents and loss of consciousness. During this stage, the patient progresses from analgesia without amnesia to analgesia with amnesia. Patients can carry on a conversation at this time.

• Stage 2• Stage 2 anaesthesia, also known as the "excitement

stage", is the period following loss of consciousness and marked by excited and delirious activity. During this stage, respirations and heart rate may become irregular. In addition, there may be uncontrolled movements, vomiting, breath holding, and pupillary dilation. Since the combination of spastic movements, vomiting, and irregular respirations may lead to airway compromise, rapidly acting drugs are used to minimize time in this stage and reach stage 3 as fast as possible.

• Stage 3• Stage 3, "surgical anaesthesia".

During this stage, the skeletal muscles relax, vomiting stops, and respiratory depression occurs . Eye movements slow, then stop, the patient is unconscious and ready for surgery.

It has been divided into 4 planes:

• eyes initially rolling, then becoming fixed

• loss of corneal and laryngeal reflexes

• pupils dilate and loss of light reflex• intercostal paralysis, shallow

abdominal respiration

• Stage 4• Stage 4 anaesthesia, also known as "overdose", is the

stage where too much medication has been given relative to the amount of surgical stimulation and the patient has severe brain stem or medullary depression. This results in a cessation of respiration and potential cardiovascular collapse. This stage is lethal without cardiovascular and respiratory support.

• Phases of General Anesthesia:• 1. Preanesthesia• 2. Induction• 3. Maintenance

• Preanesthesia:• The stage from full consciousness to a state of sedation or

tranquilization with varying degrees of muscle relaxation

and immobilization. 

Reasons for preanesthesia:

· Induce sedation· Calm patient· Reduce general anesthetic drug requirements· Provide analgesia and muscle relaxation· Decrease airway secretion, salivation, gastric fluid

volume and acidity · Suppress vomiting or regurgitation· Obtund autonomic reflexes· Promote smooth and rapid induction and recovery

phases

Preanesthesia Drugs:

· Anticholinergics  e.g. Atropine, glycopyrrolate

· Tranquilizers  e.g. Acepromazine· Sedatives  e.g. Diazepam

Induction:· The stage following the preanesthetic stage

characterized by a loss of consciousness and complete muscular relaxation and immobilization.

· Typically a very short phase (5-10 minutes)· Often associated with an excitement phase

prior to achievement of general anesthesia · Both injectable and inhalant drugs are

available

Induction drugs

· Barbituates  e.g. Thiopental, thiamylal, methohexital

· Alkylphenol  e.g. Propofol· Inhalant gases  e.g. Isoflurane,

halothane

Maintenance:

· A plane of general anesthesia that is achieved prior to surgical intervention.

· Associated with the greatest physiological impact (hypothermia, hypotension, depression of cardiopulmonary parameters).

Maintenance Drugs: 

Examples: · Inhalant gases (isoflurane, halothane)· Barbituates (pentobarbital) · Neuroleptanalgesics (fentanyl-fluanisone,

Hypnorm® · Tribromoethanol (Avertin®)· Drug combinations (e.g.ketamine, xylazine

and acepromazine)

NOUGHANCHI SABET,MAHDIEH

Signs of anesthesiaDDB

Respiratory signs

• Preparatory stage: Rate &volume: usually normal or depressed Character: normal Rhythm: not significant

• Chemanesia stage: Rhythm : irregular or uncertain Depend on patient’s preoperative emotional & physical

state as well as preanesthetic medication

• Surgical stage:• Rhythm: regular rhythmic onset of respiration• Inhalation_ volume: greater than normal• Rate: slightly increased caused by the

shortening of the pause that follows expiratory phase• Intravenous_ volume and rate : • slightly decreased and depressed with a prolongation of the pause that follows

expiration

Optic (eye) signs

• Subdivided into:a) Lid reflexb) Eyeball movementsc) Tearingd) Pupillary reactions

a. Lid reflex :• Earliest to be eliminated• Absent by the time patient enters coordinated

plane of 2nd stage (except Vinethene)

b . Eyeball movement :Inhalation : more active than when intravenous

agents are administeredChemanesia stage : in both coordinated and

uncoordinated planes , the eyeballs oscillate because of an imbalance in the tone of the ocular muscles

• c. Tearing :

• Surgical stage: Lighter plane : eyeball is moist tearing is sometimes evident

(particularly in second stage) Depressed plane : eyeball loses

its luster (more so with administration of

agents than with intravenous agents.)

d.Pupilary reactions:• Maybe the extreme interest during the various

stages of anesthesia.• Pupils ability to dilate and contract is altered by

various drugs and conditions.• Iris: Circular fibers or sphincter papillae :

parasympathetic _

contraction Radiating fibers or dilator papillae : sympathetic

_ dilation

• Preparation stage : normal unless premedication is given .

Morphine _ constricts Atropine _ dilates• Chemanesia stage : pupil reacts to sympathetic stimulation

and also to the excitation of the antagonistic cortical centers of the parasympathetic fibers.

• Surgical stage : greately constricted particularly when morphine has been used for medication.

Miosis is also characteristic of the more potent inhalation agents (probabely due to the paralysis of the antagonistic cortical centers of theparasympathetic fibers.As a result ,the fibers accompanying the oculomotor nerve are no longer inhibited and have a decided predominance over the dilation fibers of the cervical sympathetic system.)

Moderate or depressed plane: pupil begins to dilate.

Muscular signs :

• Degree of skeletal muscle not required or desired

• manifestation: degree of relaxation of skeletal

muscle absence or presence of certain

reflexes (pharyngeal reflex,laryngeal reflex,swallowing reflex,and the vomiting reflex.)

NEUROLEPTANALGESIA

• In 1949 Laborit challenged the idea that general anesthesia can protect an organism from surgical pain by depression of cortical and subcortical centers alone. He introduced a concept based on selective blocking of the cerebral cortex and other cellular , autonomic, and endocrine mechanisms activated as a response to stress.

• Drug combinations consisting of chlorpromazine , promethazine and meperidine were used to produce this state.

• Marked circulatory depression often resulted from this induced homeostatic imbalance, which may explain why yhe technique never become popular.

• Recently compounds have been made available that depress subcortical and central autonomic activity with a minimum of toxic effects. These butyrophenone derivatives are potent psychosedatives and are also alpha_adrenergic blocking agents. When they are combined with a potent narcotic, a state, not unlike that of laborit , of neuroleptanalgesia may be produced in which the patient lies at rest and is completely passive.With the possible exception of respiratory depression , vital signs are remarkably stable.

• The search for improved means of selectively blocking afferent systems involved in surgical led to increased stress led to increased emphasis on analgesia.Fentanyl , a meperidine derivative, has been found to produce analgesia (it is reported to be 150 times as potent as morphine) without certain of the central nervous system that are blocked by orthodox anesthesia.

• The most popular drug combination used to produce neurolept analgesia today consist of a fixed mixture of 2.5 mg. droperidol ( inapsine) and 0.05 mg. fentanyl (sublimaze ) per ml.

• Introduction is carried out by administering 1 to 2 ml. per 20 pounds of body weight intravenously. During maintenance phase additional fentanyl is administered whenever signs if surgical stress occur.

Nitrous oxide and oxygen mixture is administered after completion if the intravenous injection , or the surgery maybe performed under regional analgesia if practical . Anesthesia is terminated by discontinuing the nitrous oxide and oxygen and allowing the patent to breathe room air ,which results in immediate awakening of the patient.

Advantages of neuroleptanalgesia:

1. Simple , safe,nonexplosive,economical2. Low toxicity of agent used 3. Profound analgesia produced without

cardiovascular and cortical depression4. Total amnesia for the

induction,maintenance, and early recovery phases

5. Nausea and vomiting rarely seen

Disadvantages of neuroleptanalgesia:

1. Profound respiratory depression possible after completion of intravenous injection

2. Poor skeletal muscle relaxation3. Possible lead-pipe chest wall rigidity , which

may be easily overcome by administrating neumuscular blocking agents and then providing artificial ventilation

4. Not suitable for outpatients because of the long action of droperidol (6 hours and more)

Dissociative anesthetics:

• a unique anesthesia characterized by analgesia and amnesia with minimal effect on respiratory function. The patient does not appear to be anesthetized and can swallow and open eyes but does not process information. This form of anesthesia may be used to provide analgesia during brief, superficial operative procedures or diagnostic processes. Ketamine hydrochloride is a phencyclidine derivative used to induce dissociative anesthesia. Ketamine is used for trauma patients with very unstable, low blood pressure or for elderly patients. Emergence may be accompanied by delirium, excitement, disorientation, and confusion.

Advantages of dissociative anesthesia:

1. Pleasant induction possible by the intravenous or intra muscular route.

2. With margin of safety3. May be used asan induction technique

prior to the administration of inhalation agents

4. Produces good analgesia

5. Pharyngeal and larengeal reflexes active, the patient maintaining own airway in a patent state

Disadvantages of dissociative anesthesia:

1. Heightened muscular tone andactive oral and pharyngeal reflexes

2. Recovery time longer ,which discourages use in ambulatory patients

3. Irrational behaviour occasionally seen during recovery

4. Actives pharyngeal reflexes, possible laryngospasm

5. Vivid dreams during emergence

COMMON SIDE EFFECTS

Regalado, Liel Marie

Common side effects• Nausea and vomiting after surgery (also called postoperative nausea and vomiting)

How common is it?Post-operative nausea and vomiting (PONV for short) is one of the most common side-effects that occurs in the first 24 hours after your surgery. It affects 20-30% of patients. However, nearly half of all patients who do not have PONV in the hospital, experience nausea and/or vomiting in the first few days after discharge.

Who is at risk?

For adults, there are many factors that increase the risk of having PONV. Firstly - being female, not smoking (the only benefit from smoking, but definitely not worth it!) and having a history of motion sickness or PONV after a previous surgery. 

Then some anesthetic drugs and painkillers - most commonly those gases that keep you asleep, the morphine-like painkillers (called opioids in medical terms) and laughing gas (called nitrous oxide in medical terms). The morphine-like painkiller’ used for pain relief after surgery (commonly used by the acute pain service) do a good job in relieving pain, but are a common reason for nausea on the first and second day after surgery. 

Lastly, some surgeries are known to carry a high risk for PONV. These include surgery on the ear or intestines and laparoscopic surgery (key-hole surgery) for operations on the female organs. 

•  Sore throat 

How common?

Sore throat and hoarseness in the first hours to days after anesthesia occurs in up to 40% of patients (13).

Who is at risk?

The following increase your risk:. Being female; younger than 50 years old and having a general anesthetic lasting more than 3 hours.

Can it be prevented and/or treated?

Having a regional anesthetic (link bold word to regional anesthesia) will completely prevent this problem. However, if you need a general anesthetic, your anesthetist may chose a smaller size for the device used to help you breath during surgery. Some drugs have also been proven to be beneficial, such as a freezing medication or an anti-inflammatory medication. In addition, the use of some over the counter substances such as Tantum or Strepsils can help alleviate acute sore throat pain. 

• Teeth damage

How common is it?

Teeth damage is a rare but very unfortunate complication of general anesthesia, roughly occurring in 1:2000-cases. The most frequently injured teeth are the upper front ones (the upper incisors) (25;26).

Who is at risk?

Patients mostly at risk for dental injury are those with poor dental health and where the anesthetist have had difficulty to ‘get the breathing tube down’ (called a ‘difficult intubation). 

Can it be prevented?

Although the anesthetists are always very careful, prevention of dental damage is not always possible. Several devices have been used such as mouth-guards and bite-blocks but provide no guarantee. Moreover, these devices may make it more difficult to place to place the breathing tube.

•  Shivering/Chills 

How common is it? Shivering after an anesthetic is an occurs in the early recovery phase after anesthesia in approximately 25-50% of patients.

Who is at risk?

Cooling down is the most common cause. Other causes including include pain, fever and stress after surgery. It seems to be more common in males and after longer surgeries, but it is quite rare in elderly patients.

Can it be prevented and/or treated?

While we try to reduce the drop in body temperature, is itit is impossible to completely prevent it. There are also a few drugs that can be used either to prevent and/or to treat post-operative shivering.

Goals of General Anesthesia

• Hypnosis (unconsciousness)• Amnesia• Analgesia• Immobility/decreased muscle tone

– (relaxation of skeletal muscle)• Inhibition of nociceptive reflexes• Reduction of certain autonomic

reflexes– (gag reflex, tachycardia, vasoconstriction)

Desired Effects Of General Anesthesia (Balanced Anesthesia)

• Rapid induction• Sleep• Analgesia• Secretion control• Muscle relaxation• Rapid reversal