1 types of anaesthesia “general anaesthesia” “general anaesthesia”prpd/dn/11

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Types of AnaesthesiaTypes of Anaesthesia

““GENERAL ANAESTHESIA”GENERAL ANAESTHESIA”

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Choice of Anaesthesia

Selection of anaesthesia for a given surgical procedure is made by the patient, the anaesthesia

provider, and the surgeon.

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GENERAL ANAESTHESIAGENERAL ANAESTHESIA

G.A G.A is a reversible, unconscious state is a reversible, unconscious state characterized by: characterized by:

- Amnesia (sleep, hypnosis, or basal - Amnesia (sleep, hypnosis, or basal narcosis). narcosis).

- Analgesia (freedom of pain). - Analgesia (freedom of pain).

- Depression of reflexes. - Depression of reflexes.

- Muscle relaxation. - Muscle relaxation.

- Haemostasis or specific manipulation of - Haemostasis or specific manipulation of physiologic systems and functions.physiologic systems and functions.

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GENERAL ANAESTHESIAGENERAL ANAESTHESIA

PremedicationPremedication

- - Anaesthetists may give a pre-medicationAnaesthetists may give a pre-medication by by injection or by mouth anywhere from a couple injection or by mouth anywhere from a couple of hours to a couple of minutes before the of hours to a couple of minutes before the onset of surgery. The primary purpose is to:onset of surgery. The primary purpose is to:

1) induce drowsiness (sedation) 1) induce drowsiness (sedation) 2) relaxation (reduce anxiety).2) relaxation (reduce anxiety).

- The most common drugs used are narcotics - The most common drugs used are narcotics (Opioids such as Fentanyl) and sedatives (most (Opioids such as Fentanyl) and sedatives (most commonly benzodiazepines e.g., Midazolam)commonly benzodiazepines e.g., Midazolam)

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Premedication cont…

An anticholinergic such as atropine or glycopyrrolate may be used to:

prevent bradycardia in pediatric patients for controlling secretions in patients

undergoing oropharyngeal procedures, or

for controlling cardiac reflex that may cause bradycardia as during ophthalmic procedures.

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Premedication Premedication cont …cont …

may be administered either may be administered either intramuscularly, intravenously, or orally intramuscularly, intravenously, or orally with 15 to 30 ml of water. with 15 to 30 ml of water.

Oral premedication is usually preferred by Oral premedication is usually preferred by the patient; the absorption and uptake are the patient; the absorption and uptake are more predictable than that with an more predictable than that with an intramuscular injection; and the small intramuscular injection; and the small amount of water is readily absorbed amount of water is readily absorbed directly across the gastricdirectly across the gastric mucosa. mucosa.

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PremedicationPremedication cont…cont…

Often premedication Often premedication is not given to older is not given to older patients because patients because their anxiety levels their anxiety levels are lower, their are lower, their responses to responses to medications are medications are unpredictable, and unpredictable, and sedation can be sedation can be given IV in the given IV in the operating room if operating room if required.required.

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The Anaesthetic MachineThe Anaesthetic Machine

The transport and supply of anaesthetic The transport and supply of anaesthetic gases from their source in cylinders or a gases from their source in cylinders or a pipeline through the anaesthetic machine to pipeline through the anaesthetic machine to its outlet.its outlet.

The most popular anaesthetic machine in The most popular anaesthetic machine in common use is often referred to as Boyle’s common use is often referred to as Boyle’s machine, the model introduced in 1917 by machine, the model introduced in 1917 by Edmund Boyle, a London anaesthetist.Edmund Boyle, a London anaesthetist.

Modern anaesthetic machines are like ‘work Modern anaesthetic machines are like ‘work stations’ and include ventilators and stations’ and include ventilators and monitoring devices built into the machine.monitoring devices built into the machine.

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The Anaesthetic MachineThe Anaesthetic Machine

Boyle’s machineBoyle’s machine Modern anaesthetic Modern anaesthetic machinemachine

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Anaesthesia machine Anaesthesia machine includes:includes:

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GENERAL ANAESTHESIAGENERAL ANAESTHESIA cont…cont…

InductionInduction

- G.A is induced by IV injection, or breathing a - G.A is induced by IV injection, or breathing a volatile anaesthetic through a face mask volatile anaesthetic through a face mask (inhalation induction).(inhalation induction).

- Onset of anaesthesia is faster with IV - Onset of anaesthesia is faster with IV injection than with inhalation, taking about 10-injection than with inhalation, taking about 10-20 seconds to induce total unconsciousness.20 seconds to induce total unconsciousness.

- Commonly used IV induction agents include - Commonly used IV induction agents include propofol, sodium thiopental, etomidate and propofol, sodium thiopental, etomidate and ketamine.ketamine.

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Induction Induction cont…cont…

- - The most commonly-used agent for inhalational The most commonly-used agent for inhalational induction is sevoflurane because it causes less induction is sevoflurane because it causes less irritation than other inhaled gases.irritation than other inhaled gases.

An inhalational induction may be chosen by theAn inhalational induction may be chosen by the

anaesthetist where:anaesthetist where:

- IV access is difficult to obtain.- IV access is difficult to obtain.

- difficulty maintaining the airway is - difficulty maintaining the airway is anticipated.anticipated.

- due to patient preference (e.g. children).- due to patient preference (e.g. children).

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MaintenanceMaintenance

-- The duration of action of IV induction agents is generally The duration of action of IV induction agents is generally 5 to 10 mins, after which time spontaneous recovery of 5 to 10 mins, after which time spontaneous recovery of consciousness will occur.consciousness will occur.

- To prolong anaesthesia for the required surgery usually - To prolong anaesthesia for the required surgery usually achieved by allowing the patient to breathe a carefully achieved by allowing the patient to breathe a carefully controlled mixture of oxygen, nitrous oxide and a volatile controlled mixture of oxygen, nitrous oxide and a volatile anaesthetic agent. anaesthetic agent.

- Inhaled agents are frequently supplemented by - Inhaled agents are frequently supplemented by intravenous anaesthetics, such as opioids (usually intravenous anaesthetics, such as opioids (usually fentanyl or a fentanyl derivative) and sedative-hypnotics fentanyl or a fentanyl derivative) and sedative-hypnotics (usually propofol or midazolam).(usually propofol or midazolam).

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Maintenance Maintenance cont…..cont…..

- At the end of surgery the V.A is discontinued.At the end of surgery the V.A is discontinued.

- Recovery of consciousness occurs when the Recovery of consciousness occurs when the concentration of anaesthetic in the brain concentration of anaesthetic in the brain drops below a certain level (within 1-30mins drops below a certain level (within 1-30mins depending upon the duration of surgery).depending upon the duration of surgery).

-- Total Intra Venous Anaesthesia (TIVA), this Total Intra Venous Anaesthesia (TIVA), this involves using a computer controlled syringe involves using a computer controlled syringe driver (pump) to infuse propofol throughout driver (pump) to infuse propofol throughout the duration of surgery, removing the need the duration of surgery, removing the need for a volatile anaesthetic.for a volatile anaesthetic.

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Maintenance Maintenance cont…..cont…..

Purported advantages include faster recovery Purported advantages include faster recovery from anaesthesia, reduced incidence of from anaesthesia, reduced incidence of postoperative nausea and vomiting, and postoperative nausea and vomiting, and absence of a trigger for malignant hyperthermia.absence of a trigger for malignant hyperthermia.

Other medications will occasionally be given to Other medications will occasionally be given to anaesthetized patients to treat side effects or anaesthetized patients to treat side effects or prevent complications. This medications include: prevent complications. This medications include: antihypertensive, ephedrine and phenylephrine, antihypertensive, ephedrine and phenylephrine, albuterol, epinephrine or diphenhydramine, albuterol, epinephrine or diphenhydramine, glucocorticoids or antibiotics. glucocorticoids or antibiotics.

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ParalysisParalysis

The induction of paralysis with a neuromuscular The induction of paralysis with a neuromuscular blocker is an integral part of modern blocker is an integral part of modern anaesthesia. Paralysis allows surgery within anaesthesia. Paralysis allows surgery within major body cavities, major body cavities,

e.g., abdomen and thorax without the need for e.g., abdomen and thorax without the need for very deep anaesthesia, and is also used to very deep anaesthesia, and is also used to facilitate endotracheal intubation.facilitate endotracheal intubation.

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Paralysis Paralysis cont…..cont…..

Acetylcholine, the natural neurotransmitter Acetylcholine, the natural neurotransmitter substance at the neuromuscular junction, substance at the neuromuscular junction, causes muscles to contract when it is causes muscles to contract when it is released from nerve endings. Muscle released from nerve endings. Muscle relaxants work by preventing acetylcholine relaxants work by preventing acetylcholine from attaching to its receptor.from attaching to its receptor.

E.g., of skeletal muscle relaxants are E.g., of skeletal muscle relaxants are pancuronium, vecuronium, atracurium, pancuronium, vecuronium, atracurium, mivacurium and succinylcholine.mivacurium and succinylcholine.

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Paralysis Paralysis cont…..cont…..

- Paralysis of the muscles of respiration, i.e. Paralysis of the muscles of respiration, i.e. the diaphragm and intercoastal muscles of the diaphragm and intercoastal muscles of the chest requires that some form of the chest requires that some form of artificial respiration be implemented. artificial respiration be implemented.

- As the muscles of the larynx are also As the muscles of the larynx are also paralysed, the airway usually needs to be paralysed, the airway usually needs to be protected by means of an endotracheal protected by means of an endotracheal tube.tube.

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Airway managementAirway management

With the loss of consciousness caused by G.A, there With the loss of consciousness caused by G.A, there is loss of protective airway reflexes (such as is loss of protective airway reflexes (such as coughing), loss of airway patency and sometimes coughing), loss of airway patency and sometimes loss of a regular breathing pattern due to the effect loss of a regular breathing pattern due to the effect of anaesthetics, opoids or muscle relaxants.of anaesthetics, opoids or muscle relaxants.

To maintain an open airway and regulate breathing To maintain an open airway and regulate breathing within acceptable parameters, some form of within acceptable parameters, some form of “breathing tube” is inserted in the airway after the “breathing tube” is inserted in the airway after the patient is unconscious.patient is unconscious.

To enable mechanical ventilation, an endotracheal To enable mechanical ventilation, an endotracheal tube is often used (intubation), although there are tube is often used (intubation), although there are alternative devices such as face masks or laryngeal alternative devices such as face masks or laryngeal mask airways.mask airways.

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The Anaesthetic EquipmentThe Anaesthetic Equipment

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INDUCTION OF GENERAL ANAESTHESIAINDUCTION OF GENERAL ANAESTHESIA

Loss of consciousness Loss of consciousness and Intubationand IntubationPreoxygenationPreoxygenation

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INSERTION OF LMAINSERTION OF LMA

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GENERAL ANAESTHESIA GENERAL ANAESTHESIA cont…cont…

MonitoringMonitoringInvolves the use of several technologies Involves the use of several technologies to allow for a controlled induction of, to allow for a controlled induction of, maintenance of and emergence from maintenance of and emergence from general anaesthesia.general anaesthesia.

1.1. Continuous Electrocardiography (ECG):Continuous Electrocardiography (ECG):the placement of electrodes which the placement of electrodes which monitor heart rate and rhythm. This monitor heart rate and rhythm. This may also help the anaesthetist to may also help the anaesthetist to identify early signs of heart ischaemia.identify early signs of heart ischaemia.

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Monitoring Monitoring cont……cont……

2.2. Continuous pulse oximetry (SpO2):Continuous pulse oximetry (SpO2):The placement of this device (usually on one of The placement of this device (usually on one of the fingers) allows for early detection of a fall in the fingers) allows for early detection of a fall in a patient’s haemoglobin saturation with oxygen a patient’s haemoglobin saturation with oxygen (hypoxaemia).(hypoxaemia).

3.3. Blood Pressure Monitoring:Blood Pressure Monitoring:There are 2 methods of measuring the patient’s There are 2 methods of measuring the patient’s BP;BP;

(i) Most common, (i) Most common, Non-Invasive Blood PressureNon-Invasive Blood Pressure (NIBP) monitoring – placing a BP cuff around the (NIBP) monitoring – placing a BP cuff around the patient’s arm, forearm or leg. A BP machine patient’s arm, forearm or leg. A BP machine takes BP readings at regular, preset intervals takes BP readings at regular, preset intervals throughout the surgery.throughout the surgery.

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(ii) (ii) Invasive Blood PressureInvasive Blood Pressure (IBP) (IBP) monitoring – this method is reserved for monitoring – this method is reserved for patients with significant heart or lung patients with significant heart or lung disease, the critically ill, major surgery disease, the critically ill, major surgery such as cardiac or transplant surgery, or such as cardiac or transplant surgery, or when large blood losses are expected. when large blood losses are expected. The IBP monitoring technique involves The IBP monitoring technique involves placing a special type of plastic cannula placing a special type of plastic cannula in the patient’s artery – usually at the in the patient’s artery – usually at the wrist or in the groin.wrist or in the groin.

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4.4. Agent concentration measurement – Agent concentration measurement – common anaesthetic machines have common anaesthetic machines have meters to measure the percent of meters to measure the percent of inhalation anaesthetic agent used (e.g. inhalation anaesthetic agent used (e.g. sevoflurane, isoflurane, desflurane, sevoflurane, isoflurane, desflurane, halothane etc).halothane etc).

5.5. Low oxygen alarm – almost all circuits Low oxygen alarm – almost all circuits have a backup alarm in case the oxygen have a backup alarm in case the oxygen delivery to the patient becomes delivery to the patient becomes compromised. This warns if the fraction of compromised. This warns if the fraction of inspired oxygen drops lower than room air inspired oxygen drops lower than room air (21%) and allows the anaesthetist to take (21%) and allows the anaesthetist to take immediate remedial action.immediate remedial action.

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Monitoring Monitoring cont…cont…

6.6. Circuit disconnect alarm – indicates Circuit disconnect alarm – indicates failure of circuit to achieve a given failure of circuit to achieve a given pressure during mechanical ventilation.pressure during mechanical ventilation.

7.7. Carbon dioxide measurement Carbon dioxide measurement (capnography) – measures the amount (capnography) – measures the amount of carbon dioxide expired by the of carbon dioxide expired by the patient’s lungs. It allows the patient’s lungs. It allows the anaesthetist to assess the adequacy of anaesthetist to assess the adequacy of ventilation.ventilation.

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Monitoring Monitoring cont…cont…

8.8. Temperature measurement to discern Temperature measurement to discern hypothermia or fever, and to aid early hypothermia or fever, and to aid early detection of malignant hyperthermia.detection of malignant hyperthermia.

9.9. EEG or other system to verify depth of EEG or other system to verify depth of anaesthesia may also be used. This anaesthesia may also be used. This reduces the likelihood that a patient will be reduces the likelihood that a patient will be mentally awake, although unable to move mentally awake, although unable to move because of the paralytic agents. It also because of the paralytic agents. It also reduces the likelihood of a patient receiving reduces the likelihood of a patient receiving significant more amnesic drugs than significant more amnesic drugs than actually necessary to do the job. actually necessary to do the job.

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STAGES (DEPTH) OF GENERAL STAGES (DEPTH) OF GENERAL ANAESTHESIAANAESTHESIA

STAGE 1STAGE 1Also known as Also known as “induction”.“induction”. Is the period Is the period between the initial administration of the between the initial administration of the induction medications and loss of induction medications and loss of consciousness. consciousness.

During this stage the patient progresses During this stage the patient progresses from analgesia without amnesia to from analgesia without amnesia to analgesia with amnesia. Patients can analgesia with amnesia. Patients can carry on conversation at the time.carry on conversation at the time.

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cont…cont…

STAGE 2STAGE 2Also known as the Also known as the “excitement stage,”“excitement stage,” is the is the period following loss of consciousness and period following loss of consciousness and marked by excited and delirious activity. marked by excited and delirious activity.

During this stage, respirations and heart rate During this stage, respirations and heart rate may become irregular, there may be may become irregular, there may be uncontrolled movements, vomiting, breath uncontrolled movements, vomiting, breath holding, and pupillary dilation. holding, and pupillary dilation.

Since the combination of spastic movements, Since the combination of spastic movements, vomiting, and irregular respirations may lead to vomiting, and irregular respirations may lead to airway compromise, rapidly acting drugs are airway compromise, rapidly acting drugs are used to minimize time in this stage and reach used to minimize time in this stage and reach stage 3 as fast as possible.stage 3 as fast as possible.

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cont…cont…

STAGE 3STAGE 3Also known as Also known as “surgical plane,”“surgical plane,” follows the follows the excitement stage and is markedly by a excitement stage and is markedly by a return of regular respirations.return of regular respirations.

This stage is divided into 4 planes based on This stage is divided into 4 planes based on changes to eye reflexes, eye movement, and changes to eye reflexes, eye movement, and pupil size.pupil size.

The ideal plane is plane 3 where the patient The ideal plane is plane 3 where the patient has minimal use of the respiratory muscles.has minimal use of the respiratory muscles.

The main indicators of the stages of The main indicators of the stages of anaesthesia are the patient’s respiratory and anaesthesia are the patient’s respiratory and cardiovascular response to stimulation. cardiovascular response to stimulation.

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cont…cont…

STAGE 4STAGE 4

Also known as Also known as “overdose,”“overdose,” is the stage is the stage where too much medication has been where too much medication has been given and the patient has severe brain given and the patient has severe brain stem or medullary depression. This stem or medullary depression. This results in a cessation of respiratory and results in a cessation of respiratory and potential cardiovascular collapse.potential cardiovascular collapse.

This stage is lethal (danger stage) This stage is lethal (danger stage) without cardiovascular and respiratory without cardiovascular and respiratory support. Prepare for cardiopulmonary support. Prepare for cardiopulmonary resuscitation.resuscitation.

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EmergenceEmergence from GAfrom GA• VVaries in length and aries in length and

depends on the patient’s depends on the patient’s state and the depth and state and the depth and duration of anaesthesia. duration of anaesthesia. Starts as the patient Starts as the patient begins to “emerge” from begins to “emerge” from anaesthesia and usually anaesthesia and usually ends when the patient is ends when the patient is ready to leave the OR. ready to leave the OR.

• Intubation occurs during Intubation occurs during induction phase, and induction phase, and extubation is usually extubation is usually performed during performed during emergence.emergence.

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MORTALITYMORTALITY RATES RATES

Overall mortality rate for G.A is about Overall mortality rate for G.A is about five deaths per million anaesthetics five deaths per million anaesthetics administrations. administrations.

Death in anaesthesia is most Death in anaesthesia is most commonly related to surgical factors commonly related to surgical factors or pre-existing medical conditions or pre-existing medical conditions include major haemorrhage, sepsis, include major haemorrhage, sepsis, and organ failure (e.g. Heart, lungs, and organ failure (e.g. Heart, lungs, kidneys, liver)kidneys, liver)

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MORTALITY RATES MORTALITY RATES cont….cont….

Common causes of death directly Common causes of death directly related to anaesthesia include:related to anaesthesia include:

- Aspiration of stomach contents.- Aspiration of stomach contents.- Suffocation (due to inadequate airway - Suffocation (due to inadequate airway management).management).- Allergic reactions to anaesthesia - Allergic reactions to anaesthesia (specifically and not limited to anti-(specifically and not limited to anti-nausea agents) and other deadly nausea agents) and other deadly genetic predispositions.genetic predispositions.- Human error.- Human error.- Equipment failure. - Equipment failure.

THE ENDTHE END

1 types of anaesthesia “general anaesthesia” “general anaesthesia”prpd/dn/11

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