Principles of General Anaesthesia

Definition

• Is a state produced when patient receives medication of amnesia, analgesia, muscle paralysis and sedation.
• An anaesthetized patient can be thought of as being in controlled, reversible state of unconsciousness.
• It enables patient to tolerate surgical procedures that otherwise inflict unbearable pain, potentiate extreme physiologic exacerbations, and result in unpleasant memories.

• Combination of anesthetic agents used for GA will leave patient with:

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• Unarousable even to secondary stimuli
• Unable to remember what happened (amnesia)
• Unable to maintain adequate airway protection and/or spontaneous ventilation from muscle paralysis
• Cardiovascular changes secondary to stimulant/depresant effects of anesthetic agent

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Disadvantages?

• Need increased complexity of care and associated costs
• Preoperative patient preparation
• Can induce physiologic fluctuations which require active intervention
• Associated with less serious complications such as nausea or vomiting, sore throat, headache, shivering, and delayed return to normal mental functioning

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Process?

• 1. premedication
• Goal is for patient to arrive in a calm, relaxed state of mind.

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• Eg, midazolam(short acting benzodiazepine)

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• 2. induction

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• transformation of a waking patient into an anesthetized one.
• D  rugs,
• A  irway equipment,
• M  achine,
• M  onitors,
• I  V,
• S uction).

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3. Maintenance phase: At this point, the drugs used to initiate the anesthetic are beginning to wear off, and the patient must be kept anesthetized with a maintenance agent.

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delivery of anesthetic gases (vapors) into the patient's lungs. These may be inhaled as the patient breathes spontaneously or delivered under pressure by each mechanical breath of a ventilator.

4.Emergence

• In advance of that time, anesthetic vapors have been decreased or even switched off entirely to allow time for them to be excreted by the lungs.
• Excess muscle relaxation is reversed using specific drugs and an adequate long-acting opioid analgesic to keep the patient comfortable in the recovery room.
• If a ventilator has been used, the patient is restored to breathing by himself, and, as anesthetic drugs dissipate, the patient emerges to consciousness.

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Concept of balanced anesthesia

Balanced Anesthesia

The concept of Balanced anaesthesia was introduced in 1926 by Lundy to consist of Thiopental for induction, nitrous oxide for amnesia, meperidine for analgesia and curare for muscle relaxation

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Balanced anesthesia allows us to minimize patient risk and maximize patient comfort and safety.  The objectives of balanced anesthesia are to calm the patient, minimize pain, and reduce the potential for adverse effects associated with analgesic and anesthetic agents.

Intraoperative Care of patient

Staffing requirements

1.1 All anaesthetists and anaesthetic assistants, including locum and agency staff, must undergo a proper induction process.

1.2 An appropriately trained and experienced anaesthetist must be present throughout the conduct of all general and regional anaesthetics and procedures requiring sedation by an anaesthetist.

1.3 Under the present system of healthcare provision in the UK, one anaesthetist cannot provide direct care for more than one patient receiving general or regional anaesthesia, or sedation.

1.4 As soon as the care of the patient is transferred to the anaesthetist, an anaesthesia assistant who is trained, competent and holds an appropriate national qualification must provide exclusive assistance to the anaesthetist.

1.5 The anaesthetic assistant must be immediately available throughout the entire anaesthetic procedure

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• Equipment
• General
• 2.1 Facilities for monitoring, ventilation of patients’ lungs and resuscitation including defibrillation must be available at all sites where patients are anaesthetised.
• 2.2 The following ancillary anaesthetic equipment must also be available at all sites where patients are anaesthetised:
• ■■ oxygen supply
• ■■ facemasks
• ■■ suction
• ■■ airways (e.g. ‘Guedel’)
• ■■ laryngoscopes
• ■■ tracheal tubes and connectors
• ■■ intubation aids (e.g. bougies, forceps etc)
• ■■ laryngeal mask airways

• ■ heat-moisture exchange filters
• ■■ self-inflating bag
• ■■ trolley/bed/operating table that can be rapidly
• tilted head-down.
• .

• 2.3 In each theatre suite there must be at least one portable storage unit with specialised equipment for management of the difficult airway. In addition,a fibre-optic laryngoscope should be readily available.
• 2.4 User manuals should be available as needed for anaesthetic equipment.
• 2.5 All anaesthetic equipment must be checked before use according to the AAGBI published guidelines.4
• Anaesthetic machine checks should be recorded in a logbook or on the anaesthetic chart.
• 2.6 No anaesthetic machines should be able to supply a hypoxic gas mixture.
• 2.7 All anaesthetists and anaesthetic assistants should receive systematic training in the use of new
• equipment.
• 2.8 A named consultant should oversee the provision of anaesthetic equipment.
• 2.9 There must be a planned maintenance and replacement programme for all anaesthetic equipment.12
• 2.10 Appropriate equipment must be available to minimise heat loss by the patient and to provide active warming.
• 2.11 Additional specialised equipment is needed for babies and young children.

Monitoring

• 2.12 The recommended standards of monitoring,
• instrumental or otherwise, must be met for every
• patient.1
• 2.13 The following equipment must be available to
• monitor the anaesthetic machine:
• ■■ oxygen analyser
• ■■ device to display airway pressure whenever
• positive pressure ventilation is used, with
• alarms that warn if the pressure is too high or
• too low
• ■■ vapour analyser whenever a volatile
• anaesthetic agent is in use
• ■■ capnograph.
• 2.14 The following equipment must be available to
• monitor the patient:
• ■■ pulse oximeter
• ■■ non-invasive blood pressure monitor
• ■■ electrocardiograph

• capnograph
• ■■ a means of measuring the patient’s
• temperature
• ■■ a nerve stimulator when a muscle relaxant is
• used.
• 2.15 Some patients will require additional monitoring
• equipment, such as invasive pressure which should
• be readily available, and cardiac output monitors to
• which there should be access.1
• 2.16 All monitors should be fitted with audible alarms

Role of anaesthesist

• Pre-op
• Intra-op
• Post op

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Pre-op

• Pre-op assessment. Fit for anaes? Probs?
• Explain procedure, type of anaes, adv + risk (consent)
• Premeds?
• Administration of anaes

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Intra-op

• Monitors patient → stable, pain free
• Pain management

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Post-op

• Monitor conditions
• Anaes effects reversed, consciousness returns
• Pain management in pain clinics → post op /chronic pain / palliative

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Types of Anaesthesia

Types of Anesthesia

• 1. General
• 2. Regional
• Spinal
• Epidural
• Peripheral nerve block

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3. Local

General Anaesthesia

• Drug-induced loss of consciousness with analgesia, amnesia and muscle relaxation
• Has different phases:
• Induction
• Maintenance
• Recovery
• Drugs can be administered intravenously, by inhalation or a combined approach
• Suppression of body functions, can cause bradycardia, hypotension, respiratory depression, risk of aspiration
• The only exception to side effects of GA drugs is ketamine, which raises blood pressure but can cause hallucination.

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Gas and Volatile Anaes

• Sevoflurane
• Desflurane
• NO
• Isoflurane
• Halothane

Local Anaesthesia

• Blockage of pain in a specific site of the body
• Drug is administered directly to site
• Usually used for minor surgeries
• LA drugs act in excitable tissues by blocking Na+ channels, stabilising the cell membrane and decreasing rate of depolarisation
• Can be given:
• Local infiltration
• Topical

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• Adverse effects; parasthesia, anaesthesia, toxicity causing anaphylaxis, CNS and CVS effects
• BEWARE IF LOCAL INFLAMMATION

Regional Anaesthesia

• Blockage of pain in a portion of the body
• Patient remains conscious during operation
• Usually used for surgery of the extremities, abdomen and pelvis
• Different types:
• Epidural anaesthesia
• Spinal anaesthesia
• Combined spinal epidural anaesthesia
• Peripheral nerve block
• Type C fibres carrying pain are affected more than Type A motor fibres

Regional anaesthesia

• Lignocaine
• Bupivocaine
• Ropivacaine
• Levobupivacaine
• Procaine
• Prilocaine
• Eutectic Mixture (EMLA)

Spinal Anaesthesia

• Administration of anaesthesics into the subarachnoid space
• Combination of local anaesthesia (lignocaine, bupivacaine) and opioids (morphine, fentanyl)
• Affects all dermatomes below site of injection
• Indications: Irritable airway e.g. asthma, unable to tolerate GA
• Contraindications: Patient refusal, raised ICP, site infection, allergy, coagulopathy, uncorrected hypovolemia, sepsis

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• Advantages: rapid onset, reduced risk of GA (DVT, bleeding, respiratory complications), simple to do
• Disadvantages: Hypotension, post-dural puncture headache, high spinal, side effects of drugs

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complications

• Toxicity- central nervous system toxicity – if at low blood concentration, there is numbness of the mouth and tongue, lightheadedness and tinnitus. At higher concentration- muscle twitching and generalized convulsions
• Severe hypotension and bradycardia
• Accidental intravenous injection
• Dural puncture- masssive spinal anesthetic and headache
• Others: leg weakness, shivering, atonic bladder, contraction of the small bowel, backache.

• Patient positioned in siting/ lateral position with knees to chest
• Site selected (L3/L4 or L4/L5 space ) and prepared, local infiltration with LA
• Introducer passed into site
• Spinal needle passed through introducer into subarachnoid space
• Aspirate CSF to confirm placement
• Anaesthetic administered
• Needle removed

Epidural anaesthesia

• Administration of anaesthesia into the epidural space at any level of the spine
• Combination of local anaesthesia (lignocaine, bupivacaine) and opioids (morphine, fentanyl)
• Affects dermatomes cranially and caudally to site of injection
• Indications: obstetric analgesia, surgical anaesthesia, postoperative analgesia, chronic pain relief
• Contraindications: Patient refusal, site infection, allergy, coagulopathy, uncorrected hypovolemia, sepsis

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• Advantages: controlled onset, reduced risk of GA (DVT, bleeding, respiratory complications), post-operative analgesia
• Disadvantages: Requires technical expertise, post-dural puncture headache, side effects of drugs

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Complications

• Toxicity- central nervous system toxicity – if at low blood concentration, there is numbness of the mouth and tongue, lightheadedness and tinnitus. At higher concentration- muscle twitching and generalized convulsions
• Severe hypotension and bradycardia
• Accidental intravenous injection
• Dural puncture- masssive spinal anesthetic and headache
• Others: leg weakness, shivering, atonic bladder, contraction of the small bowel, backache.

• Patient positioned in sitting/lateral position
• Site selected and prepared
• Epidural needle advanced between 2 spinal processes until enter ligamentum flavum
• Needle attached to syringe and advanced until loss of resistance to air/saline
• Catheter advanced through needle and needle removed
• Catheter secured at appropriate length
• Test dose given before loading dose

Assessment of neuromuscular blockage by Bromage score

Peripheral Nerve Block

• Injection of anaesthetic agent near a nerve to block pain in the body area supplied by that nerve
• Usually used for surgery of extremities
• Brachial plexus, axillary nerve, intrascalene, ankle block, femoral nerve block
• Contraindications: Patient refusal, site infection, allergy, coagulopathy
• Advantages: Inexpensive, no risks from GA, no hypotension, post-procedure headache
• Disadvantages: Neuropathy, takes time
• Can be single shot or continuous blockage

Types of Anaesthesia

Intensive care unit

Aim

• To support patients with threatened or definite organ failure whilst they recover (severely ill, medically unstable)
• Involves close monitoring by specially trained staff and more advanced machines and devices

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What is ICU?

Sections within a hospital that look after patients whose conditions are life-threatening and need constant, close monitoring and support from equipment and medication to keep normal body functions going.

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ICU beds are expensive & limited because they provide:

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• specialised monitoring equipment
• a high degree of medical expertise
• constant access to highly trained nurses (usually one nurse for each bed)

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In Malaysia……..

The first intensive care unit (ICU) in Malaysia was established in 1968.

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Since then, intensive care has developed rapidly and ICUs are now available in all tertiary care hospitals and selected secondary care hospitals in the Ministry of Health.

Levels of Care

A Department of Health report (UK) in 2000 entitled "Comprehensive Critical Care" defined 4 different levels of care encompassing patients in hospital.

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The definitions of these levels of care are:

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Level 0

Patients whose needs can be met through normal ward

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Level 1

Patients at risk of their condition deteriorating, or higher levels of care whose needs can be met on advice and support from the critical care team.

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Level 2

Patients requiring more detailed observation or intervention, single failing organ system or postoperative care, and higher levels of care.

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Level 3

Patients requiring advanced respiratory support alone or basic respiratory support together with support of at least two organ systems. This level includes all complex patients requiring support for multi-organ failure.

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High dependency can refer to level 1 or 2 whereas intensive care usually means level 2 or 3.

Examples of problems that may require the special and expensive care in an ICU

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1. Cardiovascular problems: very high blood pressure, very low blood pressure (shock), arrhythmia, myocardial infarction.

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• Respiratory problems: asthma, severe pneumonia, or pulmonary embolism (blood clots in the lung). Difficulty with breathing that is so severe that the patient may need a machine to help or take over breathing until the problem is corrected.

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• Electrolyte imbalances

4. Brain injury: including bleeding, stroke and head trauma, may cause coma. Patients who are in a coma or who are at a high risk of coma are often watched and treated in the ICU until stabilised.

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• Severe trauma: auto accidents, gunshot wounds and burns. These patients may have multiple injuries

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• Major surgery: Patients undergoing major surgery, who need special monitoring or who are at high risk of having problems after the operation. They may have other serious health problems that can complicate care after surgery.

ICU would seem a good place for patients to stay all the time they are in hospital because of the high level of care.

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This is not the case, however, for the following reasons…

1. Risks - getting new infections. Since severe infections are common in critically ill patients, the longer a patient stays in an ICU, the greater is the risk of picking up an infection from other patients. Also, consider antibiotic-resistant strains.

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• Expense - It is very expensive to provide constant nursing attention for patients who are getting better.