ANAESTHESIA

ANAESTHESIOLOGY

It is that branch of medicine which

is concerned with the administration

of anaesthetics & the management

of the patient under anaesthesia.

WHAT DOES ANAESTHESIA MEAN?

The word anaesthesia is derived from the Greek: meaning insensible or without feeling.

ANAESTHETIC

also known as anaesthesiologist.

He is a doctor or a person specially trained in administering anaesthesia.

DEFINITION OF ANAESTHESIA

It is a pharmacologically induced and reversible state of amnesia, analgesia, loss of responsiveness, loss of skeletal muscle reflexes, decreased stress response, or all of these simultaneously.

These effects can be obtained from a single drug which alone provides the correct combination of effects, or occasionally a combination of drugs (such as hypnotics, sedatives, paralytics and analgesics) to achieve very specific combinations of results.

This allows patients to undergo surgery and other procedures without the distress and pain they would otherwise experience.

TOOLS OF ANAESTHESIA

1. Anaesthetic machine.

2. Monitoring system.

ANAESTHETIC MACHINE

1. Oxygen gas

supply.

2. Nitrous oxide gas

supply.

3. Flow meter.

4. Vaporizer specific

for every agent.

5. Mechanical

ventilator.

6. Tubes for

connection.

MONITORING

1. Pulse, ECG.

2. Blood pressure.

3. Oxygen saturation.

4. End tidal CO2.

5. Temperature.

6. Urine output, CVP, EEG, bispectral

index, muscle tone, ECHO, drug

concentration.

TYPES OF ANAESTHESIA

LOCAL ANAESTHESIA inhibits sensory

perception within a specific location on the

body, such as a tooth or the urinary bladder.

REGIONAL ANAESTHESIA renders a larger

area of the body insensate by blocking

transmission of nerve impulses between a

part of the body and the spinal cord. Two

frequently used types of regional anaesthesia

are spinal anaesthesia and epidural

anaesthesia.

GENERAL ANAESTHESIA refers to inhibition of sensory, motor and sympathetic nerve transmission at the level of the brain, resulting in unconsciousness and lack of sensation.

DISSOCIATIVE ANAESTHESIA uses agents that inhibit transmission of nerve impulses between higher centers of the brain (such as the cerebral cortex) and the lower centers, such as those found within the limbic system.

General anaesthetics are drugs that brings about areversible loss of all sensation and consciousness.

Cardinal signs of general anaesthesia:-

i. Loss of all sensation.

ii. Sleep and amnesia.

iii. Immobility and muscle relaxation.

iv. Abolition of reflexes.

CLASSIFICATION

1.INHALATIONAL

Gas Liquid

•Nitrous oxde •Ether

•Halothane

•Isoflurane

•Desflurane

2. INTRAVENOUS

Inducing agents Slower acting draugs

• Thiopentone sodium 1. Benzodiazepines:

Diazepam , Lorazepam ,

Midazolam.

• Methohexitone sod. 2. Dissociative anaesthesia:

Ketamine.

• Propofol 3. Opiod analgesia:

Fentanyl.

Mechanism of action

Exert their action by the activation of inhibitoryCNS receptors and their inactivation of CNSexcitatory receptors.

Ligated gated ion channels are the major targetsof anaesthetic action.

The GABA receptor gated chloride ion channel ismost important.

Many inhalational anaesthetics, barbiturates, BZDsand propofol potentiate the action of inhibitorytransmitter GABA to open chloride ion channels

Each one interacts with its own specific binding site on theGABA receptor Cl-complex.

Action of glycine in the spinal cord & medulla is augmentedby barbiturates, propofol & many inhalational anaesthetics.

This action may block responsiveness to painful stimuliresulting in immobility of the anaesthetic state.

Fluorinated anaesthetics & Barbiturates inhibit neuronalcation channel gated by nicotinic cholinergic receptor whichmay mediated analgesia & amnesia.

On the other hand N2O , Ketamine don’t affect GABA ,glycine gated Chloride channels.Rather they selectivelyinibit the excitatory NMDA type of glutamate receptor.

This receptor gates mainly Calcium ion selective cationchannels in the neurons & their inhibitor appears to be theprimary mechanism of anaesthetic action of ketamine aswell nitrous oxide.

Volatile anaesthetics have little action on this receptor.

1. INHALATION

2. INJECTION (Intravenous or Intramuscular)

Inhalation

Substances are either volatile liquids or gases , & areusually delivered using an:-

1. Anaesthesia machine.

An anaesthesia machine allows composing a mixture ofoxygen,anaesthetics & ambient air,delivering it to thepatient & machine parameters.

2. Anaesthetic chamber induction:-Uses sturdy, seenthrough containers.

Cautions-Small patients only difficult to monitor patientrisk of vomiting/regurgitation hyperthermia waste gascontamination of room & exposure of personnel.

3. Laryngeal mask airway.

4. Tracheal tube connected to some type of anaestheticvaporiser & an anaesthetic delivery system.

5. Mask induction suited for critical patients.

Caution: Prevention anaesthetic gas pollution of room use tight-fitting mask risk of stressing patient use pre-anaesthetic sedationmay be dangerous with animals with poor respiratory function.

6. Gases or vapors which produce general anaesthesia by inhalationare stored in gas cylinders & administered using flowmeters.

Liquid anaesthetics are vaporised in machine & are quitehydrophobic.

Ideal volatile anaesthetic agent offers:-

• smooth & reliable induction.

• maintainance of general anaesthesia with minimal effectson other organ systems.

• odourless or pleasant to inhale.

• safe for all ages.

• rapid in onset & offset.

• cheap to manufacture & easy to transport.

• store with long shelf life.

INJECTION

Injectable anaesthetics are used for the induction &maintainance of a state of unconsciousness.

Anaesthetics prefer to use intravenous injections , as theyare faster , less painful & more reliable than intramuscularor subcutaneous injections.

Standard dose is calculated , drawn into syringe injected asneeded directly into vein.

Techniques of Mandibular

Anesthesia

Mandibular AnesthesiaLower success rate than Maxillary anesthesia -

approx. 80-85 %

Related to bone density

Less access to nerve trunks

Mandibular Nerve BlocksInferior alveolar

Mental - Incisive

Buccal

Lingual

Gow-Gates

Akinosi

Mandibular AnesthesiaMost commonly performed technique

Has highest failure rate (15-20%)

Success depends on depositing solution within 1 mm of nerve trunk

Inferior Alveolar Nerve BlockNot a complete mandibular nerve block.

Requires supplemental buccal nerve block

May require infiltration of incisors or mesial root of

first molar

Inferior Alveolar Nerve BlockNerves anesthetized

Inferior Alveolar

Mental

Incisive

Lingual

Inferior Alveolar Nerve BlockAreas Anesthetized

Mandibular teeth to midline

Body of mandible, inferior ramus

Buccal mucosa anterior to mental foramen

Anterior 2/3 tongue & floor of mouth

Lingual soft tissue and periosteum

Inferior Alveolar Nerve BlockIndications

Multiple mandibular teeth

Buccal anterior soft tissue

Lingual anesthesia

Inferior Alveolar Nerve Block Contraindications

Infection/inflammation at injection site

Patients at risk for self injury (eg. children)

Inferior Alveolar Nerve Block10%-15% positive aspiration

Inferior Alveolar Nerve BlockAlternatives

Mental nerve block

Incisive nerve block

Anterior infiltration

Inferior Alveolar Nerve BlockAlternatives (cont.)

Periodontal ligament injection (PDL)

Gow-Gates

Akinosi

Intraseptal

Inferior Alveolar Nerve BlockTechnique

Apply topical

Area of insertion:

medial ramus, mid-coronoid notch,

level with occlusal plane (1 cm above),

3/4 posterior from coronoid notch to

pterygomandibular raphe

advance to bone (20-25 mm)

Inferior Alveolar Nerve Block Target Area

Inferior alveolar nerve, near mandibular foramen

Landmarks

Coronoid notch

Pterygomandibular raphe

Occlusal plane of mandibular posteriors

Inferior Alveolar Nerve BlockPrecautions

Do not inject if bone not contacted

Avoid forceful bone contact

Inferior Alveolar Nerve BlockFailure of Anesthesia

Injection too low

Injection too anterior

Accessory innervation

-Mylohyoid nerve

-contralateral Incisive nerve innervation

Inferior Alveolar Nerve BlockComplications

Hematoma

Trismus

Facial paralysis

March 5, 2007Faisal A. Quereshy, MD, DDS, FACS

March 5, 2007Faisal A. Quereshy, MD, DDS, FACS

Faisal A. Quereshy, MD, DDS, FACS

March 5, 2007Faisal A. Quereshy, MD, DDS, FACS

March 5, 2007Faisal A. Quereshy, MD, DDS, FACS

March 5, 2007Faisal A. Quereshy, MD, DDS, FACS

Long Buccal Nerve BlockAnterior branch of Mandibular nerve (V3)

Provides buccal soft tissue anesthesia adjacent to

mandibular molars

Not required for most restorative procedures

Buccal Nerve BlockIndications

Anesthesia required - mucoperiosteum buccal to

mandibular molars

Contraindications

Infection/inflammation at injection site

Buccal Nerve BlockAdvantages

Technically easy

High success rate

Disadvantages

Discomfort

Buccal Nerve BlockAlternatives

Buccal infiltration

Gow-Gates

PDL

Intraseptal

Buccal Nerve BlockTechnique

Apply topicalInsertion distil and buccal to last molarTarget - Long Buccal nerve as it passes

anterior border of ramusInsert approx. 2 mm, aspirateInject 0.3 ml of solution, slowly

- 25-27 gauge needleArea of insertion:

- Mucosa adjacent to most distal

Buccal Nerve Block

Landmarks

Mandibular molars

Mucobuccal fold

Buccal Nerve BlockComplications

Hematoma (unusual)

Positive aspiration

0.7 %

March 5, 2007Faisal A. Quereshy, MD, DDS, FACS

March 5, 2007Faisal A. Quereshy, MD, DDS, FACS

Mental Nerve BlockTerminal branch of IAN as it exits mental foramen

Provides sensory innervation to buccal soft tissue

anterior to mental foramen, lip and chin

Mental Nerve BlockIndication

Need for anesthesia in innervated area

Contraindication

Infection/inflammation at injection site

Mental Nerve BlockAdvantages

Easy, high success rate

Usually atraumatic

Disadvantage

Hematoma

Mental Nerve BlockAlternatives

Local infiltration

PDL

Intraseptal

Inferior alveolar nerve block

Gow Gates

Mental Nerve Block

Complications

Few

Hematoma

Positive aspiration

5.7 %

March 5, 2007Faisal A. Quereshy, MD, DDS, FACS

March 5, 2007Faisal A. Quereshy, MD, DDS, FACS

March 5, 2007Faisal A. Quereshy, MD, DDS, FACS

March 5, 2007Faisal A. Quereshy, MD, DDS, FACS

Incisive Nerve BlockTerminal branch of IAN

Originates in mental foramen and proceeds

anteriorly

Good for bilateral anterior anesthesia

Not effective for anterior lingual anesthesia

Incisive Nerve BlockNerves anesthetized

Incisive

Mental

Incisive Nerve BlockAreas Anesthetized

Mandibular labial mucous membranes

Lower lip / skin of chin

Incisor, cuspid and bicuspid teeth

Incisive Nerve BlockIndication

Anesthesia of pulp or tissue required anterior

to mental foramen

Contraindication

Infection/inflammation at injection site

Incisive Nerve BlockAdvantages

High success rate

Pulpal anesthesia w/o lingual anesthesia

Disadvantages

Lack of lingual or midline anesthesia

Incisive Nerve BlockComplications

Hematoma

Positive aspiration

5.7 %

LOCAL

ANAESTHESIA

Local anaesthesia is defined as a loss of sensation

in a circumscribed area of the body caused by a

depression of excitation in nerve ending or inhibition

of the conduction process in the peripheral nerves

It does not cause loss of consciousness.

CLASSIFICATIONINJECTABLE

LOW POTENCY, SHORT DURATION

Eg: Procaine, chloroprocaine

INTERMEDIATE POTENCY AND DURATION

Eg: lidocaine, prilocaine

HIGH POTENCY, LONG DURATION

Eg: tetracaine, bupivacaine

SURFACE

SOLUBLE

Eg: cocaine, lidocaine

INSOLUBLE

Eg: benzocaine, oxethazaine

MECHANISM OF ACTION

The local anaesthetics block nerve conduction by

decreasing the entry of Na+ ions during upstroke of

action potential. As the concentration of LA is increased,

the rate of rise of action potential and maximum

depolarization decreases causing slowing of conduction.

Finally, local depolarization fails to reach the threshold

potential and conduction block ensues.

TECHNIQUES

SURFACE ANAESTHESIA

INFILTRATION ANAESTHESIA

CONDUCTION BLOCK

SPINAL ANAESTHESIA

EPIDURAL ANAESTHESIA

SURFACE ANAESTHESIA

It is produced by topical application of surface

anaesthetics to mucous membranes and abraded skin.

Only the superficial layer is anaesthetized. Onset and

duration depends on site, drug, its concentration and

form.

It is used extensively in the eye, throat, urethra and anal

canal. Topical LA is occasionally applie din mouth for

stomatitis, ulcers.

INFILTRATION

ANAESTHESIA

Dilute solution of LA is infiltrated under the skin in area of

operation- blocks sensory nerve endings. Onset of action

is almost immediate.

It is used for minor operations, eg. Incisions, excisions,

some dental procedures etc when area to be

anaesthesized is relatively small.

Relatively large amount of LA is required but motor

function is not affected.

CONDUCTION

ANAESTHESIA

This includes:

1.FIELD BLOCK: Produced by injecting the LA

subcutaneously in a manner that all nerves coming to a

particular field are blocked.

It is done for dental procedures, appendicectomy,

operations on legs and forearms etc.

2.NERVE BLOCK:

It is produced by injection of the LA around the

appropriate nerve trunks or plexuses. The muscles

supplied by injected nerve are paralysed.

In dentistry 2 important nerve blocks are there

Maxillary nerve block

Mandibular nerve block

MAXILLARY NERVE

BLOCK

MAXILLARY NERVE BLOCK

It includes:

A. posterior superior alveolar blockB. middle superior alveolar blockC. anterior superior alveolar blockD. greater palatine blockE. infraorbital blockF. nasopalatine block

pulpal anesthesia: through anesthesia of each nerve’s dental branches as they extend into the pulp tissue (via the apical foramen)

periodontal: through the interdental and interradicular branches

palatal: soft and hard tissues of the palatal periodontium (e.g. gingiva, periodontal ligaments, alveolar bone)

PSA block: recommended for maxillary molar teeth and associated buccal tissues in ONE quadrant

MSA block: recommended for maxillary premolars and associated buccal tissues

ASA block: recommended for maxillary canine and the incisors in ONE quadrant

greater palatine block: recommended for palatal tissues distal to the maxillary canine in ONE quadrant

nasopalatine block: recommended for palatal tissues between the right and left maxillary canines

POSTERIOR SUPERIOR ALVEOLAR

BLOCK• target: PSA nerve

– as it enters the maxillar through the PSA foramen on the maxilla’s infratemporal service

– into the tissues of the mucobuccal fold at the apex of the 2nd maxillary molar mandible is extended toward the side of the injection, pull the tissues at the injection site until taut

– needle is inserted distal and medial to the tooth and maxilla

– depth varies from 10 to 16 mm depending on age of patient

• no overt symptoms (e.g. no lip or tongue involvement)

• can damage the pterygoid plexus and maxillary artery

MIDDLE SUPERIOR ALVEOLAR

BLOCKlimited clinical usefulness

can be used to extend the infraorbital block distal to the maxillary canine

can be indicated for work on maxillary pre-molars and mesiobuccal root of 1st molar

if the MSA is absent – area is innervated by the ASA

blocks the pulp tissue of the 1st and 2nd maxillary premolars and possibly the 1st molar + associated buccal tissues and alveolar bone

useful for periodontal work in this area

to block the palatine tissues in this area – may require a greater palatine block

target area: MSA nerve at the apex of the maxillary

2nd premolar mandible extended towards injection

site

stretch the upper lip to tighten the

injection site

needle is inserted into the mucobuccal

fold

tip is located well above the apex of the

2nd premolar

harmless tingling or numbness of the upper lip

overinsertion is rare

ANTERIOR SUPERIOR ALVEOLAR

BLOCK

can be considered a local infiltration

used in conjunction with an MSA block

the ASA nerve can cross the midline of the maxilla onto the opposite side!

used in procedures involving the maxillary canines and incisors and their associated facial tissues

pulpal and facial tissues involved –restorative and periodontal work

blocks the pulp tissue + the gingiva, periodontal ligaments and alveolar bone in that area

target: ASA nerve at the apex of the maxillary canine

at the mucobuccal fold at the apex of the maxillary

canine

harmless tingling or numbness of the upper lip

overinsertion is rare

INFRAORBITAL NERVE BLOCK

anesthetizes both the MSA and ASA

used for anesthesia of the maxillary premolars, canine and incisors

indicated when more than one premolar or anterior teeth

pulpal tissues – for restorative workfacial tissues – for periodontal work

also numbs the gingiva, periodontal ligaments and alveolar bone in that area

the maxillary central incisor may also be innervated by the nasopalatine nerve branches

target: union of the ASA and MSA with the IO nerve after the IO enters the IO foramenalso anesthesizes the lower eyelid, side of nose and upper lipIO foramen is gently palpated along the IO rim

move slightly down about 10mm until you feel the depression of the IO foramen locate the tissues at the mucobuccal fold at the apex of the 1st

premolarplace one finger at the IO foramen and the other on the injection site –figure 9-17locate the IO foramen, retract the upper lip and pull the tissues tautthe needle is inserted parallel to the long axis of the tooth to avoid hitting the bone

GREATER PALATINE BLOCKused in restorative procedures that involve more than two maxillary posterior teeth or palatal tissues distal to the canine

also used in periodontal work – since it blocks the associated lingual tissues

anesthetizes the posterior portion of the hard palate – from the 1st premolar to the molars and medially to the palate midline

does NOT provide pulpal anesthesia – may also need to use ASA, PSA, MSA or IO blocks

may also need to be combined with nasopalatineblock

• target: GP nerve as it enters the GP foramen located at the junction of the maxillary alveolar process and the hard palate – at the maxillary 2nd or 3rd molar

• palpate the GP foramen –midway between the median palatine raphe and lingual gingival margin of the molar tooth

• can reduce discomfort by applying pressure to the site before and during the injection-produces a dull ache to block pain impulses

-also slow deposition of anaesthesia will also help

• needle is inserted at a 90 degree angle to the palate

NASOPALATINE BLOCKuseful for anesthesia of the bilateral portion of the hard palate

from the mesial of the right maxillary 1st premolar to the mesial of the left 1st premolar

for palatal soft tissue anesthesia periodontal treatment

required for two or more anterior maxillary teeth

for restorative procedures or extraction of the anterior maxillary teeth – may need an ASA or MSA block also

blocks both right and left nerves

target: both right and left nerves as they enter the incisive foramen from the mucosa of the anterior hard palate

posterior to the incisive papilla

injection site is lateral to the incisive papilla

head turned to the left or right

inserted at a 45 degree angle about 6-10 mm –gently contact the maxillary bone and withdraw about 1mm before administering

can reduce discomfort by applying pressure to the site before and during the injection

produces a dull ache to block pain impulsesalso slow deposition of anesthesia will also help

can anaesthetize the labial tissues between the central incisors prior to palatal block

can block some branches of the nasopalatine prior to injection

Anatomy. Skin

Subcutaneous fats

Supraspinous ligament

Interspinous ligament

Ligamentum flavum

Epidural space

Dura

Subarachnoid space

The spinal cord usually ends at the level of L1in adults and L3 in children.

Dural puncture above these levels is asso with

a slight risk of damaging the spinal cord

and is best avoided.

An important landmark to remember is that

a line joining the top of the iliac crests is

at L4 to L4/5

Mechanism of action

Local anaesthetic solution injected into the subarachnoid

space blocks conduction of impulses along all nerves with

which it comes in contact, although some nerves are more

easily blocked than others. There are three classes of nerve:

motor, sensory and autonomic. Stimulation of the motor

nerves causes muscles to contract and when they are blocked,

muscle paralysis results. Sensory nerves transmit sensations

such as touch and pain to the spinal cord and from there to

the brain, whilst autonomic nerves control the calibre of

blood vessels, heart rate, gut contraction.

Indications

Spinal anaesthesia is best reserved for

operations below the umbilicus e.g. hernia

repairs, gynaecological and urological

operations and any operation on the perineum or genitalia.

Older patients and those with systemic

disease such as chronic respiratory disease,

hepatic, renal and endocrine disorders such as diabetes.

It is suitable for managing patients with trauma

In obstetrics, it is ideal for manual removal of

a retained placenta (again, provided there is no hypovolaemia).

Advantages

1.Cost

2.Patient satisfaction

3.Respiratory disease

4.Diabetic patients

5.Muscle relaxation

6.Blood loss during operation is less

Contra-indications to Spinal Anaesthesia:-

Absolute:

1.Inadequate drugs and equipment

2.Coagulopathy or other bleeding disorders

3.Severe hypovolaemia(Shock)

4.Patient refusal

5.Increased Intracranial Pressure

6.Severe aortic stenosis

7.Severe Mitral stenosis

Local Anaesthetics for Spinal Anaesthesia:-

Local anaesthetic agents are either heavier

(hyperbaric), lighter (hypobaric), or have the

same specific gravity (isobaric) as the CSF.

Hyperbaric solutions tend to spread below the

level of the injection, while isobaric solutions

are not influenced in this way. It is easier to

predict the spread of spinal anaesthesia

when using a hyperbaric agent. Isobaric

preparations may be made hyperbaric by the

addition of dextrose.

Bupivacaine (Marcaine):- 0.5% hyperbaric (heavy) bupivacaine is the best agent to use if it is available. 0.5% plain bupivacaine is also popular. Bupivacaine lasts longer than most other spinal anaesthetics: usually 2-3 hours.

Lignocaine (Lidocaine/Xylocaine):- Best

results are obtained with 5% hyperbaric

(heavy) lignocaine which lasts 45-90 minutes.

Cinchocaine (Nupercaine, Dibucaine, Percaine, Sovcaine):- 0.5% hyperbaric (heavy) solution is similar to bupivacaine.

Amethocaine (Tetracaine, Pantocaine,

Pontocaine, Decicain, Butethanol, Anethaine,

Dikain):- A 1% solution can be prepared with

dextrose, saline or water for injection.

Mepivacaine (Scandicaine, Carbocaine,

Meaverin) :- 4% hyperbaric (heavy)

solution is similar to lignocaine.

Pre-loading :-

All patients having spinal anaesthesia must have a

large intravenous cannula inserted and be given

intravenous fluids immediately before the spinal.

The volume of fluid given will vary with the age of the

patient and the extent of the proposed block. A

young, fit man having a hernia repair may only need

500 mls. Older patients are not able to compensate

as efficiently as the young for spinal-induced

vasodilation and hypotension and may need 1000mls

for a similar procedure. If a high block is planned,

at least a 1000mls should be given to all patients.

The fluid should preferably be normal saline or ringer lactate.

5% dextrose is readily metabolised and so is not effective in maintaining the blood pressure.

Position:-

1.Lateral ( Lt lateral )

2.Sitting

Males tend to have wider shoulders than hips and so

are in a slight "head up" position when lying on their

sides, whilst for females with their wider hips, the

opposite is true.

LEFT LATERAL POSITION

SITTING POSITION

The sitting position is preferable in the obese

whereas the lateral is better for uncooperative or

sedated patients.

Complication

1.Immediate complication

- Hypotension and Cardiac arrest.

- Total spinal block leading to respiratory arrest.

- Urinary retention.

- Epidural hematoma, Bleeding.

2.Late complication

- Post dural puncture headache (PDPH)

- Backache

- Bacterial meningitis

Treatment of spinal headache:

1.Remain lying flat in bed as this relieves the pain.

2.They should be encouraged to drink freely or,

if necessary, be given intravenous fluids to maintain adequate hydration.

3.Simple analgesics such as paracetamol, aspirin or codeine may be helpful.

Caffeine containing drinks such as tea, coffee or Coca-Cola are often helpful.

Prolonged or severe headache may be treated with epidural blood patch performed by aseptically injecting 15-20ml of the patient's own blood into the epidural space. This then clots and seals the hole and prevents further leakage of CSF.

It used to be thought that bedrest for 24 hours following a spinal anaesthetic would help reduce the incidence of headache.

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