38075193 general anaesthesia

8/3/2019 38075193 General Anaesthesia

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Dr. Roshana Mallawaarachchi

01/06/2010


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Anesthesia is defined as the abolitionof sensation.

Analgesia is defined as the abolition ofpain.


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First public demonstration of ETHERanaesthesia was given in 1846 for theremoval of a vascular tumour.

Later in 1846, an American dentistadministered ETHER during a dental

extraction.


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Contemporary re-enactment of Morton's October 16, 1846, ether operation


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1. Regional (Local) Anaesthesia

2. General Anaesthesia


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What are the methods?

1. Local infiltration2. Nerve Block

3. Topical

4. Intravenous Blocks

5. Spinal Anaesthesia

6. Epidural anaesthesia


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ESTERS AMIDESProcaineBenzocaine

CocaineTetracaine

LidocainePrilocaine

RopivacaineBupivacaine


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1. Unconsciousness

2. Analgesia3. Muscle relaxation

A variety of drugs are given to thePatient that have above effects.


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1. Reduces intraoperative patient awareness and recall.

2. Allows proper muscle relaxation for prolonged periods oftime.

3. Facilitates complete control of the airway, breathing, andcirculation.

4. Can be used in cases of sensitivity to local anestheticagent.

5. Can be administered without moving the patient from thesupine position.

6. Can be adapted easily to procedures of unpredictableduration or extent

7. Can be administered rapidly and is reversible


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1. Requires increased complexity of care and associatedcosts.

2. Requires some degree of preoperative patientpreparation.

3. Can induce physiologic fluctuations that require activeintervention.

4. Less serious complications. Eg: nausea or vomiting,sore throat, headache and shivering.

5. Associated with malignant hyperthermia, a rare, some(but not all) general anesthetic agents results in acuteand potentially lethal temperature rise, hypercarbia,metabolic acidosis, and hyperkalemia.


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Aneasthesia machine

Management of the airway& maintenance of anaesthesia


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General Anaesthesia usually involvesthe administration of 3 different drugs:

1. Premedication

2. Induction of anaesthesia

3. Maintenance of anaesthesia


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Clinical assessment of the patient:

History/Examination/Investigation

Pre operative optimization:

Correction of anaemia , Hypovolaemia & Dehydration

Control of medical disease

Premedication


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2 main aims:

1. Prevention of theparasympathomimetic effects ofanaesthesia. Eg: Bradycardia/bronchial secretion

2. Reduction of anxiety and pain


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Anxiolytics: Relief from anxiety

Eg: Benzodiazepines

(Diazepam/Lorazepam/Midazolam)Analgesics: When there is existing pain or as a supplementto an anaesthetic agent.

Eg: Paracetamol, NSAIDs, Opiates

Parasympathetic blockers: (Anti Muscaranic)To reduce bronchial and salivary secretions

Eg: Atropine / Hyoscine / Glycopyrronium


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Acid aspiration prophylaxis

Eg: Cimetidine/Ranitidine

Antibiotic Prophylaxis

Eg: Invasive dental procedures

Antithrombotic Prophylaxis

Eg: Subcutaneous Heparin injection


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1. Intravenous anesthetics

Eg: Thiopentone / Propofol / Ketamine

2. Inhalational anesthetics

Eg: Halothane / Isoflurane / Desflurane / Sevoflurane /Nitrous Oxide


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1. Intravenous anesthetics are still the mostcommon method.

Eg: Thiopentone / Propofol / Ketamine

May be used either to induce or maintenance ofanaesthesia.

Anaesthetic effect once it reaches the centralnervous system (One arm brain circulation time)


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Advantages:

IV anesthesia include rapid and smoothinduction of anesthesia.

Less equipment requirement (syringes,needles, Cannula)

Easy administration of drugs.


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Gauge Color Code

14G Orange16G Grey

17G White

18G Green20G Pink

22G Blue

24G Yellow


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Disadvantages:

Difficult retrieval of drug once administered.

Less control of depth and duration ofanesthesia.

Lack of ventilatory support.

Poor tolerability.


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high therapeutic indexno toxic metabolites

potent, so small volume is required for anestheticinduction/maintenance

long shelf life and resistance to microbial contamination

compatible with other drugs

quick and smooth induction and recovery

reversible with specific antagonist

non-allergenic

no cardiopulmonary depressionindependent of liver and kidneys for metabolism and excretion

no effect on cerebral blood flow

no endocrinologic effect

no pain on injectioninexpensive


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The most widely used barbiturate.

Causes unconsciousness within 3045 second persistsfor about 4-7 mins.

It has no analgesic properties.

Strongly Alkaline; causes severe necrosis in accidentalextra-vascular administration. Inject through catheters toavoid this.

Thiopental is not used to maintain anesthesia in surgicalprocedures. Because it displays zero-order eliminationkinetics.


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Presented as powder and dissolved in water to

required concentration.


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Metabolism:

Initially distributed highly vascular tissues of the

brain and other organs.

Subsequently diffuses into fatty tissues.

This process terminate the pharmacological

effect.It is slowly but entirely metabolized in the Liver.


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Dosage:

Adults and Children 3-5mg/kg given slowly over

10-15 seconds.

Over dosage:

Respiratory depression - Assisted ventilation withoxygen may required.

Hypotension progressing to circulatory collapse Head of the table must immediately be tilted down.


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Contraindications:

Should not be used if there is doubt that a clear

airway can be maintained.

If allergy to barbiturates.

If severe cardiovascular disease or hypotension.


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Precausions:

Administered under supervision of an

experienced anaesthetist.

Equipment for resuscitation should be available.

Patient should lie supine because even a small

dose can cause hypotension.


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Adverse Effects:

Hypotension, Apnea, Airway obstruction (Due to

cardiovascular and respiratory depression)Arrythmias

Cough, Sneezing

Hypersensitivity reactions


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Drug Interations:

Antihypertensives / Diuretics mayaugment the hypotensive effect.


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Ketamine is used very rarely now.

It has good analgesic properties.

Anaesthesia persist for upto 15 mins.


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Advantages:

Does not induce Hypotension

Pharyngeal and Laryngeal reflexes are slightlyimpaired. (So airway may be less at risk)

Rarely induces bronchospasms.


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Disadvantages:

Does not produce muscle relaxation.

It tends to raise Heart rate and intracranial andintraocular pressure.

High incidence of Hallucinations. These can be

reduced by diazepam or midazolam.


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Indications:

Pediatric anesthesia

Asthmatics or patients with chronic obstructiveairway disease.

In emergency medicine in entrapped patientssuffering severe trauma.

Emergency surgery in field conditions in warzones.

Painful procedures Dressing of burns, Minor

orthopaedic procedures, Dental procedures


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Dosage:

Induction

1-2 mg/kg (IV)6-8mg/kg (IM)

Maintenance

Serial doses of 50% of IV dose or 25% of IM dose

As an analgesic -

0.5mg/kg IM or IV


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Contraindications:

Moderate to severe Hypertension

Congestive cardiac failure

History of Cerebrovascular accident

Acute and Chronic Alcohol intoxication

Intracerebral mass or Haemorrhage

Eye injury

Psychiatric Disorders

Pregnancy


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Associated with quick induction (30s) andrapid recovery (4 min)

Used both for induction and Maintenance.

Sometimes pain on intravenous injection,which can be reduced by IV lidocaine.


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Inhalational anesthetics are useful in youngchildren or needle phobic adults. This may also

used in patients at risk of Pulmonary aspiration.Halothane

Isoflurane

DesfluraneSevoflurane

Nitrous oxide


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It is a potent agent.Induction is smooth and pleasant.

Produces moderate muscle relaxation.Vapour is non irritant.


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Advantages:

Anaesthesia can be produced by 2-5min.

Does not augment salivary or bronchial secretions.Recovery is rapid and nausea and vomiting is low.

Disadvantages: (Adverse Effects)

Severe Hepatotoxity (1:50,000)

Respiratory depression results in raised in CO2 andcause arrhythmias.

Cardio depression causes Bradycardia


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Contraindications:

History of unexplained Jaundice.

Family history of malignant hyperthermia.

Precautions:

At least 3 months should be allowed to elapsebetween each re-exposure. (Minimize liverdamage)


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Isoflurane

Similar in action to halothane.

But less cardio depressant and unlikely to causehepatotoxity

Desflurane

Similar to isoflurane but is less potent

Sevoflurane -

More potent than desflurane and recovery are rapid.


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This is not potent enough to use for induction.

So it is used for maintenance of anaesthesia.

For anaesthesia:

a mixture with 70% gas and 30% oxygen

For analgesia:

A mixture of NO and oxygen containing 50% of each

Self administration in labour (Entonox)


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Adverse Effects:

Nausea and Vomiting

Repeated exposure can cause bone marrowdepression.

Storage:NO is supplied under pressure in cylinders.


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General anaesthesia is a procedure which isnever without risk (including the risk ofdeath). As a result, the General DentalCouncil in the UK recommends that "the

decision to refer a patient for treatment undergeneral anaesthesia should not be takenlightly.


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It's not recommended for routine dental work like

fillings.Laboratory tests, chest x-rays and ECG are oftenrequired before having GA, because of the greaterrisks involved.

Very advanced training and an anesthesia team arerequired, and special equipment and facilities areneeded.

GA does nothing to reduce dental anxiety.

It's expensive.


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38075193 general anaesthesia

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