VNSA11 Flashcards

1
Q

What does general anaesthesia provide?

A

Muscle relaxation
Analgesia
Unconsciousness

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2
Q

Define general anaesthesia

A

The reversible immobile state that induces amnesia

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3
Q

Name anaesthetic types

A

General anaesthetic
IV induction agents
Inhalation gases
Epidural
Local anaesthetic
Dissociative
Topical
Regional

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4
Q

Local anaesthesia

A

Used alongside GA
Temporarily blocks conduction in sensory nerve fibres preventing nociceptibe info to be received.

Mode of action - inhibits sodium channels in neuronal membranes, preventing influx of sodium ions into nerve axons.

Nervous function lost in order: pain, cold & warmth sensation, touch, deep pressure, motor function

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5
Q

Pharmacokinetics of local anaesthetics

A

Absorption: depends on dose, site on inj and if there’s a presence of a vasoconstrictor

Distribution: affected by degree of protein binding. Free drug exerts effects and is metabolised. Metabolism via liver and lungs, excreted via kidneys.
Local anaesthetic can cause vasodilation (often used with adrenaline to delay absorption and lengthen action). Vasoconstrictors can cause localised ischaemia so not used in distal areas as potential necrosis.

Effects: lipid soluble and low molecular weight (cross blood-brain barrier). At therapeutic range these are of great use (anticonvulsants, sedatives and analgesia) at high levels can induce seizures and cause CNS depression. Can slow myocardium conduction causing vasodilation, hypotension, bradycardia and cardiac arrest. Cats and exotics are more susceptible to this than dogs

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6
Q

Local anaesthetic drugs

A

Lidocaine: rapid onset of activity, good tissue penetration. Short duration of activity (45 mins without adrenaline & 1-2hrs with). Good for regional blocks and general surgery.

Proxymetacaine: topical analgesia of eye, rapid onset but duration only 15 mins. Causes less initial sting than other agents.

Bupivacaine: slow onset of activity (15 mins) but longer duration (6-8 hrs). Potency 4X stronger than lidocaine. Good for epidural analgesia and post-op. Don’t give IV as cardiac toxicity risk.

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7
Q

What is topical anaesthesia (local)

A

Eg sprays, drops, gel or cream
Limited to analgesia of nasal mucous membranes, eye, larynx, penis, vagina, rectum and urethra.

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8
Q

Perineural (regional) block
(Local anaesthetic)

A

Injected directly around the nerve, reduces motor side effects and risks of systemic absorption and subsequent toxicity.
Nerves must be palpable and easily accessible - use of nerve stimulators and ultrasounds
Eg:
Intercostal nerve block: injected caudal to ribs
Brachial plexus block: analgesia distal to elbow
Maxillary and mandibular nerve blocks: dental and jaw surgery, nerves blocked as exit jaw bones

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9
Q

Intra-articular block (local anaesthetic)

A

Local anaesthetics or opioids injected into the joint cavity following surgery or arthroscopy.
Used as part as multimodal analgesia
Asepsis to prevent introduction of infection into the joint.

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10
Q

Epidural (local anaesthetic)

A

Performed by vs only
22G needle, or a 17G/18G tuohy needle
Inserted 90 degrees into skin surface and advanced slowly, stylet removed as it nears epidural space.
Eg; lumbosacral epidural, analgesia to structures caudal to thoracolumbar junction.

Bupivacaine used as long duration of action. Preservative free morphine can be used for analgesia of 18-24hrs

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11
Q

Local infiltration block (local anaesthetic)

A

Intradermal or subdermal tissue infiltrated by injection of local anaesthetic agent.

Uses: minor procedures used with sedation and or restraint.

Sterile needle injected into area. Draw back on hub to ensure no accidental vascular access. Inject small amount of local, creating a wheel effect.

If each injection is made at the periphery of the previous site the patient will only feel 1 injection.

Adrenaline may be used to delay local absorption and lengthen duration of action

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12
Q

Intravenous regional anaesthetic (Bier block)
(Local anaesthetic)

A

For surgical procedures in the body’s extremities, eg; toe removal.
Local is injected IV into area below or between two tourniquets (Esmarch bandage) on a limb.
Rapid onset of local in this area

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13
Q

Dissociative anaesthesia

A

KETAMINE
Has minimal effect on the respiratory system whilst creating analgesia and amnesia.
Patient presents as not anaesthetised as can swallow and eyes remain open.
Used in brief, superficial procedures or diagnostic processes.
Can be used in trauma patients (low bp) or elderly patients.

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14
Q

Recovery symptoms of dissociative anaesthesia

A

On recovery patient may present with;
Hypersalivation
Hyperventilation
Tachycardia
Muscle twitches
Paddling of the legs
Curling of the tongue

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15
Q

Physiology of anaesthesia

A

Produces many effects on the autonomic nervous system
Effects the brain by the anaesthetic agents acting on the receptors in the CNS and cell membrane of neuronal cells.
Anaesthetic agents cause a reversible depression on the CNS function resulting in loss of consciousness.

Blood-brain barrier: this barrier restricts movement of molecules into brain (water, oxygen and carbon dioxide can cross easily others cross more slowly to not at all). This depends on particles molecular size and lipid solubility.
HIGH lipid solubility and SMALL molecular weight crosses EASILY
The EASIER they cross the barrier the MORE potent they are as anaesthetics.

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16
Q

General anaesthesia; effects on the cardiovascular system

A

Often causes cardiovascular depression due to
Drugs depressant effect on the brain & peripheral effects of the drug.

Reduction in cardiac output — reduction in blood flow around the body — potential for tissue hypoxia

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17
Q

General anaesthesia; effects on the resp system

A

CNS depression causes a central depression of resp system.
Leads to reduced sensitivity to blood carbon dioxide concentration and reduced resp drive

Hypercapnia = higher blood CO2 than normal
Hypoxia = inadequate O2 delivered to tissues.

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18
Q

General anaesthesia; effects on the liver

A

Blood reaches the liver via the hepatic artery and portal vein.
Inhalant anaesthetic agents reduce liver blood flow to a degree due to reduction in cardiac output which affects relationship between hepatic artery and portal vein.

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19
Q

General anaesthesia; effects on the kidneys

A

Kidneys receive ~20% cardiac output
Normal renal function is reliant on adequate renal blood flow
By reducing that blood flow, GA also decreases glomerular filtration rate, urine output and electrolyte function.
Parameters should return to norm ranges within a few hours of a short GA.

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20
Q

Define MAC

A

Minimum alveolar concentration

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21
Q

What is the minimum alveolar concentration (MAC)

A

Amount required to suppress movement to noxious stimulant in 50% of patients.

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22
Q

About MAC

A

A measure of anaesthetic potency
Potent inhalant agents have a lower MAC.

Dependent on: species, age, temp, disease, CNS depressant drugs, pregnancy

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23
Q

Drug MAC levels

A

Halothane 0.75%
Isoflurane 1.15%
Sevoflurane 2.05%
Desflurane 5-10%

Halothane = most potent

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24
Q

Halothane

A

BG 2-3 and MAC 0.75%
High solubility coefficient
Absorbed quickly into the blood, but doesn’t want to come out
Concentration in the brain rises slowly as the blood reaches the brain (slow induction results)
At the end there is an accumulation of drug in the blood and fat and other tissues
Levels fall slowly as agent is slowly released into alveoli and exhaled
Slow recovery results

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25
Isoflurane and sevoflurane
Low solubility coefficient Slower absorption into blood, but released readily into brain Rapid induction of anaesthesia Agents are eliminated quickly by lungs Rapid recovery
26
Drug blood-gas solubility
Halothane 2.3 Isoflurane 1.4 Sevoflurane 0.6 Desflurane 0.42 Halothane has a slow induction and Desflurane has quickest recovery
27
Soluble anaesthetic agents
Slow induction, slow recovery
28
Insoluble anaesthetic agent
Rapid induction, rapid recovery
29
Define critical tension
The necessary drug concentration needed in the brain to induce unconsciousness. (As levels fall below critical tension the animal will regain consciousness)
30
Define pain
A sensory or emotional experience associated with actual or potential tissue damage
31
Analgesia
A conscious sensation An adequately anaesthetised patient will not experience pain A noxious stimulus is damaging to tissues (thermal, mechanical and chemical) Nociception causes perception of pain (experienced during recovery) Activation of pain pathways may cause surrounding tissues to become painful. Sensitivity to pain heightens due to repeated activation of nociceptive pathways
32
What 3 categories is pain split into?
Physiological Inflammatory Neuropathic
33
Physiological pain
Early warning device of potentially painful stimuli Pain is proportional to stimulation Pain experienced is localised “Normal” pain pathway activation
34
Inflammatory pain
Pain associated with changes to pain pathway -heightened pain sensitivity -skin incision causes inflammation and tissue damage Control of disease process causing pain hypersensitivity
35
Neuropathic pain
Clinical pain caused by nervous system damage -peripheral nerve damage -“phantom limb” pain following amputation Clinical pain is associated with hypersensitivity (at site of tissue damage) Stimuli that wouldn’t normally activate pain pathways will cause other pain Stimuli normally activating pain pathways will cause a prolonged and larger pain (hyperalgesia)
36
Peripheral sensitisation
Noxious stimuli at site of tissue injury produces a more intense and prolonged pain response following clinical pain (primary hyperalgesia) Nociceptors at site of tissue injury becomes more excitable
37
Central sensitisation
Resulting in secondary hyperalgesia, allodynia and spontaneous pain Starts where peripheral nerve reaches spinal cord Causes sudden augmentation of noxious stimuli as transmitted to brain
38
Pre-emptive analgesia
Analgesia provided before noxious stimuli Prevents “sensitisation” or “wind-up” Analgesia that has taken place after this is less effective
39
Multimodal analgesia
Using multiple analgesic drugs Controlling pain at different levels and sites Synergism between drugs means lower levels of each is needed reducing side effects Adequate analgesia speeds recovery
40
Physiological effects of pain
Tachycardia Inc blood pressure Tachypnoea Changes in resp pattern Panting Pyrexia Salivation Pupillary dilation Shivering and shaking Assess patients behaviour and demeanour without interference = more accurate
41
Response to pain (Spinal, medullary, hypothalamic, cortical)
Spinal - receives the pain message transmitted from nociceptors which is then sent to the brain Medullary - once in the brain the pain message is processed and responded to Hypothalamic - releasing hormones which travel in the portal blood to the pituitary gland where ACTH is produced and released into the general blood system. Cortical - adrenal cortex release corticosteroids under the influence.
42
Routes for administration of analgesia
IV - rapid action, potent opioids IM - volume to inject and site considered. Painful. S/C - onset of action is slower than IV or IM. Transmucosal - as effective as IV administration of buprenorphine in cats. Some formulations are unpalatable Transdermal - “patches” used to provide long term non-invasive analgesia. Reservoir of drug, covered with membrane controlling absorption rate. Bioavailability varies (cats 34% and dogs 64%).
43
Analgesia in rabbits and rodents
Opioids - good analgesia (Buprenorphine), wide safety margin but causes a degree of sedation, can be administered orally, causes pica in rats. NSAIDs are very effective but higher doses required Ketamine and alpha-2 agonists used as part of anaesthetic protocols
44
Analgesia in birds
Opioids used (kappa opioids receptors more effective than uu) Response between species varies NSAIDs used - nephrotoxicity and gastric ulceration seen. Repeated doses are unadvisable.
45
Define tidal volume
The amount of air that moves in or out of the lungs with each respiratory cycle
46
Define minute volume
Amount of gas inhaled or exhaled from the lungs in 1 minute
47
Expiratory reserve volume (ERV)
Amount of air you can forcefully exhale past a normal tidal expiration
48
Inspiratory reserve volume (IRV)
Amount of air that can be taken into the lungs (above the tidal volume) upon forceful inspiration
49
Define residual volume
The volume of air remaining in the lungs after maximum forceful expiration
50
Define vital capacity
Maximum amount of air a person can expel from the lungs after a maximum inhalation (ERV + IRV + tidal volume)
51
Define total lung capacity
The amount of air the lung can contain at the height of maximum inspiratory effort (Residual volume + vital capacity)
52
Define functional residual capacity (FRC)
The volume in the lungs at the end expiratory position (ERV + residual volume)
53
Define physiological (anatomical) dead space
Volume of air in the respiratory zone that doesn’t take part in gas exchange (Tranches down to the terminal bronchioles)
54
Define equipment dead space
Dead space resulting from devices placed between the ET tube and the y-piece of the breathing circuit
55
Define compliance
Measurement of pressure in a breathing system. Affects the tidal volume of gas the patient receives. Increases in compliance can decrease tidal volumes.
56
What is the difference between a sedative and a tranquilliser?
Sedative - promotes calm and induces sleep Tranquilliser - reduces tension or anxiety but does not induce sleep
57
What is a narcotic?
Drug that in moderate doses dulls the senses, relieves pain and induces sleep but in excessive doses causes stupor, coma or convulsions
58
Define neuroleptanalgesia
Joint administration of a tranquilliser and an analgesic Relief of surgical pain
59
What is the anaesthetic sparing effect?
Some medical agents have the ability to reduce the need for the full anaesthetic agent dose. (Premeds and N20)
60
What is the second gas effect?
N2O is very insoluble in the blood but rapid absorption from the alveolus increases the speed of anaesthesia induction. The same happens when N2O is stopped, speeds up the removal of volatile agent Patient should be fed 100% oxygen for 5-10mins after nitrous oxide has been turned off Must be carefully scavenged
61
What is diffusion hypoxia?
When N2O is stopped it moves to alveolus in high concentrations diluting the alveolar air and therefore the amount of oxygen, if an animal breaths room air it can cause diffusion hypoxia. To avoid this the patient should have 100% oxygen for about 5-10mins after N2O is stopped.
62
What is the triad of balanced anaesthesia
-loss of consciousness -muscle relaxation -analgesia
63
What is so important about pre-medication
-calms the patient before induction -reduces amount of anaesthetic needed for induction and maintenance -contributes to the triad of anaesthesia -analgesia -smoother recovery
64
Neuroleptanalgesia
Most premeds are a combination of drugs (sedative and opiate analgesic) Benzodiazepine and opiate Phenothiazine and opiate Alpha-2 and opiate. Synergistic effect inc quality and depth of sedation Lower dose rates Minimises side effects In high doses there is sufficient CNS depression for minor surgical procedures
65
Dissociate anaesthetics
KETAMINE These drugs induce CNS depression characterised by feeling dissociated from surroundings Unconsciousness and analgesia but little muscle relaxation Animals keep their eyes open - consider eye protection Complicating monitoring
66
Define TIVA
‘’Total intravenous anaesthesia’’ No specialised equipment necessary Drugs can be given IV or IM Induction is rapid and stress free Little technique or experience needed No pollution hazard Once administered dose cant be altered - hard to regulate depth Drugs must be metabolised before recovery May experience peaks and troughs in plane of anaesthesia if not using CRI
67
Define PIVA
‘’Partial intravenous anaesthesia’’ Syringe driver often needed Both IV and inhalation agents used to maintain an adequate plane of anaesthesia Patients intubated Airway is protected and O2 administered Depth of anaesthesia can be monitored and controlled Recovery doesn’t rely on metabolism of the drug Good for small furries when a rapid recovery is desired Requires an anaesthetic machine and oxygen supply Staff training Provides control of anaesthetic vapour Potential pollution of environment - scavenging needed Damage to ozone layer
68
Define potency
Alveolar concentration of inhalation anaesthetic that prevents movement in 50% of animals in response to a noxious stimulus
69
Define volatility
Liquid at room temp but evaporate easily for administration by inhalation (Nitrous)
70
Define solubility in tissues
Measure of how an agent is taken into tissues or organs
71
Define flammability
A measure of how quickly a specific material is capable of catching fire and burning
72
Define chemical stability
The materials ability to withstand change from chemical contact Drugs ability to remain in the same chemical form when exposed to various environmental conditions.
73
Depth of anaesthesia
Depth depends on concentration in the brain. Most inhalant agents cross the blood brain barrier with ease as they’re lipid soluble.
74
Process of anaesthesia (anatomy)
1. Inhaled into lungs 2. Cross the alveolar membrane and pulmonary capillary endothelium 3. Dissolve in the blood and taken via pulmonary circulation to the left hand side of the heart and all body tissues 4. Cross blood-brain barrier 5. Exert their effect (unconsciousness)
75
Ideal properties of inhalation agents
-easily vaporised -low blood/gas solubility -MAC sufficiently low so that a high concentration of oxygen can be delivered -Non-irritant to mucus membranes -Good analgesic -little depression/effect on respiratory or cardiovascular system -good muscle relaxation -minimal or no metabolism -non-toxic to tissues -non-flammable and non-explosive -stable for storage -compatible with soda lime
76
Oxygen (carrier gas)
Essential for supporting life Administered at concentrations between 33-100% Explosive combination with flammable agents
77
Nitrous oxide (Carrier gas)
Weak anaesthetic agent Very good analgesic properties Lower concentration of inhalant agent needed - balanced triad of anaesthesia Minimal effect on cardiovascular and respiratory system Not to be used at concentrations greater than 70% of the inspired gas mixture Minimum 30% oxygen to prevent hypoxia Not removed by soda lime and not suitable for circle or “to and fro” circuits
78
Neuromuscular blocking agents (NMBA) what does it provide
Adequate muscle relaxation essential for surgery Cessation of movement Reduced amount of inhalant agent needed (reduces cardiovascular and respiratory side effects also) Without it causes increased tissue traction during surgery and pain and inflammation post op
79
How can muscle relaxation be provided ?
GA - marked muscle relaxation, but still potential of sudden movement Local anaesthetic - around a peripheral nerve - blocking conduction of nerve impulse Local anaesthetic into intrathecal or epidural space. NMBA
80
What caution is needed when using NMBAs
Careful monitoring (use peripheral nerve stimulation electrodes when redosing) Checking the plane of anaesthesia regular - may become light but cant respond Supportive ventilation with IPPV Superficial nerves used to check NMBA Ensure ventilation is normal before recovery
81
Depolarising agents VS non-depolarising agents
Depolarising - suxamethonium. Bind reversibly to ACh receptor and open channels. Not often used in veterinary. Muscle pain on recovery. Non-depolarising - Bind reversibly to ACh receptors but do not open channels. Ach cant bind so muscle doesn’t contract. Used in practice. Vecuronium: duration of action = 30 mins in dog and cat, non-cumulative, may induce tachycardia, replaced by atracurium. Atracurium: duration of action 30-40mins in dogs and cat. Breaks down spontaneously in body - used in patients with poor hepatic or renal function. Inactivated by alkaline solutions. Flush catheter before administering.
82
What are the 4 stages to anaesthesia?
Stage 1: voluntary excitement - induction to unconsciousness. Fear, stress, apprehension, disorientation, prominent muscle activity, may U and D, resp and heart rate. Stage 2: involuntary excitement - unconsciousness to unexcited and stable respiration. Howling, excessive movement/struggling, reflexes still present, eyes open and central but eyes dilated, respiration irregular then stable. Stage 3 plane 1 (light) - heart rate + pulse slightly reduced and regular, smooth regular resp pattern, head and limb movement absent other reflexes present but less, nystagmus can be seen, muscle tone present and responsive. Stage 3 plane 2 (medium) - heart rate regular but reduced, pulse strong and regular, decrease in tidal volume, muscle tone relaxed, palpebral reflex slow or absent. Pedal reflex slow then absent, corneal reflex present, no nystagmus. Stage 3 plane 3 (deep) - heart rate and blood pressure reduced further, pulses weak, decrease in tidal volume, only corneal reflex present, eye centrally fixed, 3rd eyelid in correct position, muscle tone greatly reduced or absent. Stage 4 (overdose) - ending with resp muscle paralysis, great reduced and irregular resp rate progressing to apnoea, reduced heart rate, CRT, pulses weak and slow, reflexes absent inc corneal, eyes central and fixed, pupils dilated and unresponsive to light, flaccid muscle tone
83
What is the pin index system?
On the anaesthetic machine Pin holes on cylinder and yoke Pins are placed in different positions for different gases to prevent them being attached to the wrong outlet
84
What is a schrader probe?
Used to connect to pipeline outlet Designed so will only connect with correct pipeline gas outlets. All the hoses have the same male bayonet fitting but each gas supply has a protruding indexing collar with unique diameter
85
What is a Boyle’s bottle?
Uncalibrated vaporiser “Draw over types” Vaporiser output cannot be predicted so rarely used Gas drawn over vaporiser by patients resp effort So higher the patients minute volume the more gas passes through the vaporiser so the higher the concentration of inhalation agent
86
Calibrated vaporiser
“TEC’ / Penlon” types Produce known anaesthetic vapour concentration regardless of temp and fresh gas flow rate Serviced annually Anaesthetic agent specific
87
Vaporisers
Modern day = temperature, level and flow compensated Temp = constructed of metal which acts as a reservoir and conductor for heat energy, thermostatic valve in the bypass chamber - changes the flow depending on the temp in chamber. Level = fibrous wicks so the agent climbs by capillary action, this increases the surface area for vaporisation, change in liquid level has no effect on vaporiser output. Flow = the path of the gas through the vaporiser means it remains close to the wicks for a longer period of time. Reduces effect of high gas flows through the vaporiser. Supported by a back bar. Locked Into position.
88
Name the low oxygen warning devices
Ritchie whistle = uses oxygen in the cylinder to sound alarm, sounds when oxygen supply is first connected. Howison oxygen failure alarm = sounds alarm and cuts off other gas supplies Bosun whistle = unreliable as whistle relies on nitrous oxide flow, risks due to environmental contamination
89
What is a oxygen-nitrous oxide proportioning device
Anaesthetic machines will not supply nitrous oxide without oxygen. Preventing supply of hypoxic mixture to patient
90
What is active scavenging
Preferred technique Uses extractor fans to create negative pressure Pressure break incorporated to prevent excessive negative pressure on patient (Barnsley receiver)
91
What is passive scavenging ?
Gases moved by the patients resp effort into activated charcoal system (gravity fed) Scavenging tube no longer than 1.5m and not kinked Canister weighed regularly (max weight 1.40kg) Doesn’t absorb nitrous
92
What is active-passive scavenging
Tubing is used as with the passive system but connected to a forced ventilation system. Gases must not be re-circulated to another area of the building
93
What is the full weight of an oxygen cylinder
137 bar
94
What is the weight of a nitrous oxide cylinder ?
44 bar
95
What are the 3 main functions of an anaesthetic machine?
To deliver oxygen rich carrier gas and anaesthetic vapour to the patient Carry carbon dioxide rich gas away from the patient Deliver potentially harmful waste anaesthetic gas to the scavenging system
96
Define resistance
The ability of the patient to be able to breathe through the circuit. Resistance can be caused by the valve, canisters and tube length. Lighter patients are more likely to encounter resistance
97
Define mechanical dead space
Too much equipment between the patient and the anaesthetic machine.
98
Define circuit drag
The part of the circuit that harbours gaseous space that is respired at every breath but doesn’t participate in gas exchange. Eg - heavy tubing, valves, canisters as this can lead to disconnection or extubation.
99
What is an open anaesthetic circuit?
Lint or gauze placed on the nose of the animal and volatile anaesthetic agent dropped onto the material.
100
What is a semi-open anaesthetic circuit?
Same as open but gauze is placed inside a mask and attached to oxygen
101
What is a semi-closed circuit?
The use of an anaesthetic circuit to deliver the agent, but doesn’t involve soda lime and is referred to as a non-re-breathing circuit. The gas flow has to be high enough to flush old gases out of circuit.
102
What is a closed circuit?
Same as a semi-closed circuit but soda lime is used to absorb carbon dioxide so the patient can re-breathe the same gas.
103
Semi-closed (non-rebreathing) circuits
Mapleson classification: categorised by appearance Deliver oxygen and anaesthetic agents and eliminate carbon dioxide Components- fresh gas flow, reservoir bag, breathing tubes, expiratory valve and patient connection. 5 basic types A-F but only A, D, E, F are used today.
104
What circuits are Mapleson A?
Magill and lack
105
What circuits are Mapleson D?
Modified Bain Modified Ayers T-piece (Has a bag and APL valve)
106
What types of circuits are Mapleson E?
Ayres-T (No bag and no APL)
107
What type of circuits are Mapleson F?
Modified Ayres-T (Jackson Rees modification) (Has a bag with a hole in it and no APL)
108
What are the indicators for soda lime?
Pink soda lime turns white when exhausted White soda lime turns purple when exhausted
109
Advantages and disadvantages of red rubber ET tubes
A - reuseable, wide range of sizes, autoclavable, pre moulded so easy to intubate D - expensive, perish with time, kink easily, can be irritant to the airway, unable to see contamination unless looking down, low volume and high pressure
110
Advantages and disadvantages of PVC ET tubes
A - cheap, can be reused, malleable when warm, fairly kink resistant, non-irritant, easy to place, easy to see contamination, high pressure and low volume available. D - designed to be disposable, limited sizes, cannot be autoclaved, connections can become loose once PVC becomes warm.
111
Advantages and disadvantages of silicone ET tubes
A - same as PVC but can be repaired and autoclaved D - expensive, do not have a moulded curve so may require stylet to intubate, only low volume high pressure
112
What is the Murphy eye in ET tubes?
An oval hole in the tube opposite the bevel which allows gases to enter and exit if occluded
113
Define ataractic
Reduce stress or tension without reducing mental capacity. (Another word for tranquilliser)
114
Define psychotropic
Drug that affects how the brain works, causes change in mood, awareness, behaviour, thoughts and feelings
115
Define agonist
(Opioid) A drug or substance that binds to a receptor inside a cell or on its surface and causes the same action as the substance that normally binds to that receptor
116
What are the aims of pre-med
To calm and control the patient for a smooth induction To provide analgesia throughout surgery To reduce the amount of induction and maintenance agent needed To reduce some of the unwanted side effects To reduce other side effects of anaesthesia To ensure a smoother recovery
117
Routes for pre-med administration
SC - good animal tolerance as less painful but slow uptake and not reliable in dehydrated patients IM - more reliable uptake, fairly good animal tolerance, good onset of action, painful IV - predictable, very quick onset of action, usually not painful on injection, more difficult to place catheter.
118
What history should be taken during pre-op checks?
Status of chronic diseases if diagnosed Changes in bw Changes in water or food consumption Shortness of breath, exercise intolerance, coughing Prev GA hx Vaccine status Temperament
119
What does haematology and biochemistry test for ?
Haem - anaemia and coagulation disorders Bio - metabolic disorders
120
ASA grade 1
Minimal risk Normal healthy animals with no underlying disease (Young fog presenting for neutering)
121
ASA grade 2
Slight risk Mild systemic disturbances with no clinical signs of disease bcs they are able to compensate Dog with low grade heart murmur not showing signs of cardiac disease
122
ASA grade 3
Moderate risk Animals showing signs of mild clinical signs associated with moderate systemic disease Dog with a heart murmur resulting in reduced exercise tolerance
123
ASA grade 4
High risk Animals with pre-existing systemic disease or severe system disturbances that is a constant threat to life Dog with cardiac arrhythmia causing severe circulatory compromise
124
ASA grade 5
Grave risk Animals with life threatening system disease Dog with GDV
125
Thiopental (barbiturate)
Made up from a crystalline powder using sterile water to produce a 1.25% or 2.5% solution for small animals. Can be kept in the fridge for 24hrs once made Rapid onset but short acting (single dose = 20 mins) Administer slowly IV Causes myocardial depression,hypotension, resp depression and compensatory tachycardia Can cause splenic enlargement Recovery = re-distribution from brain into body’s fat instead of metabolism. (Hangover) Not to be given in puppies and kittens under 3mths old
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Etomidate (carboxylated imidazole)
NOT licensed in animals 2 formulations: propylene glycol and another in a hyperlipid emulsion Suitable for animals with severe cardiovascular compromise as minimal effects on hr or inotropy Minimal effects on resp system. May cause muscle twitching at induction Inhibits cortisol production so animals may enter Addisonian crisis Rapid recovery vis redistribution and hepatic metabolism
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Propofol (phenol)
2 preparations: a preservative (benzoyl alcohol) enabling it to be used for 28 days after 1st use and one without a preservative to be discarded immediately. IV inj - rapid induction lasting 15-20 mins Rapidly metabolise by liver and other sites. Can be used as CRI but less suitable in cats as slower liver metabolism (causes oxidative injury to RBCs) Muscle twitching if used for long duration. After IV inj may experience drop in bp, cardiac output, resp and poss apnoea Short duration of action
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Alfaxalone (steroid)
Alfaxan 10mg/ml Suitable for cats and dogs Route = IM or slowly IV (to avoid resp depression/apnoea) Maintain anaesthesia through incremental inj or CRI 2 formulations - preservative and non-preservative Causes myocardial depression and a compensatory inc hr Recovery can be unpredictable if no premed given Very rapidly metabolised by liver
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Ketamine (dissociative anaesthetic)
Compatible = dogs, cats, rabbits and exotics Used in combination with alpha-2 agonists, opiate analgesics and benzodiazepines Administration - IV or IM Longer shelf life as has preservative Sch 2 CD Causes inc hr, minimal changes to cardiac output and resp system Can cause apneuristic breathing Eyes remain open and eyelid and corneal reflexes intact Do not give to patients with impaired renal or hepatic function. Inc inter-cranial pressure
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Halothane (fluothane) Halogenated hydrocarbon
MAC 0.75% and BG = 2.3 Clear, colourless, needs protection from light May cause myocardial and resp depression High levels of adrenaline circulating which may follow cardiac arrest 30% metabolised by liver Prolonged recovery with prolonged use Reduces liver blood flow - avoid with liver comprised patients
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Isoflurane Halogenated ether
MAC 1.15% BG = 1.4 Pungent smell - irritant to airways Rapid induction and recovery Causes resp and cardiovascular depression Reduced vascular resistance = vasodilation and a compensatory hr. Excreted via lungs minimal involvement w liver.
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Sevoflurane Halogenated ether
MAC 2.05% BG 0.6 Odourless, less irritating Rapid induction and recovery Allows rapid changes in anaesthesia depth Reduction in myocardial contractility and arterial bp - induces peripheral vasodilation Minimal liver metabolism - excreted from lungs Reacts with soda lime producing a chemical called compound A (toxic to rats) More expensive than iso
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Desflurane Halogenated ether
MAC 5-10% BG 0.42 Poor inhalation induction due to pungent smell - unsuitable for mask inhalation Very low solubility - most rapid induction and recovery Allows rapid changes in anaesthesia depth Myocardial contractility and resp depression Excreted by lungs - very little liver metabolism NOT licensed in animal species Vaporises very quickly at room temp Delivery requires a special vaporiser to electrically heat and pressurise gas Flammable at very high concentrations (>17%)
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What equipment/consumables are needed for anaesthesia induction?
Induction agent, reversal agent and analgesia Clippers and blade Scissors Vacuum Assistant Laryngoscope ET tubes Capnograph, anaesthetic machine, multi parameter, Doppler IVFT and infusion pump, giving set, extension set, t-connector Catheter, bung, flush Swabs and spirit.
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Define ‘ABC’ in terms of anaesthesia
AIRWAY - assist in intubating the patient and check the tube is positioned correctly BREATHING - watch chest and bag to check breathing. Often a short period of apnoea following induction of thiopental, propofol, alfaxalone). May need to ventilate until patient is spontaneous breathing. CIRCULATION - monitor hr, check for pulse (peripheral pulses give an accurate idea of the peripheral perfusion)
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How can you tell a patient is ready for intubation?
Jaw tone is relaxed Tongue can be pulled out of mouth with no resistance Attempts to introduce the ET tube don’t result in swallowing or gagging movements
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What is the formula for ET tube size?
(BW/4) + 4 = tube size Can also measure gap in-between nostrils Dogs = Canine teeth - point of shoulder Cats and brachycephalic = corner of mouth - point of shoulder
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What are the steps of intubation ?
An assistant holds the jaw by the lateral aspect of the mucous membrane under the lips Use of laryngoscope Identification of epiglottis Avoidance of laryngeal spasm Intubate the patient and check the ETT is correctly positioned Correct inflation of the cuff (20-30cm H20) Secure in position Connection.
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When can the ETT be removed in dogs and cats?
Dogs = remove on return of the gag or swallow reflex (in brachycephalic dogs leave as long as poss) Cats = remove before the swallowing reflex returns - look for signs of arousal; palpebral and pedal reflexes, tail, head and limb movements
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What are the normal values for respiration ?
Dog: 10-30 breaths per min Cat: 20-30 breaths per min
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Hypoventilation depth definition
Slows resp rate and a small tidal volume. Likely to result in hypercapnia and a reduction in O2 saturation.
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What is hyperventilation in anaesthesia depth?
Increase in the depth resulting in deep rapid breathing
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What is a respiratory monitor
Uses microphones to monitor the depth of breathing. The monitor produces a tone whose volume is proportional to the depth of breathing. Adv - both vet and nurse can hear any changes and take immediate action, cost effective
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Capnograph
Measures CO2 levels in the airway Stated as either a % or mmHg Normal levels: 35-45mmHg or 5-6% 50mmHg = significant respiratory acidosis (brachycephalics may tolerate 50-55mmHg)
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What does Wright’s resp monitor measure?
Tidal and minute volume
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Pulse oximeter
Measure the amount of saturated O2 in the blood. Probe shines lights through the tissue and measure the colour of arterial haemoglobin. >97% is norm
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How can the pulse ox be affected by?
Probe squashing tissue and preventing pulsatile blood flow Abnormal haemoglobin Intravenous dyes Patient moving Vasoconstriction Interference from ambient light Skin pigmentation Electrosurgical equipment
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Blood gas analysis
Measures arterial levels of oxygen and carbon dioxide Indicates the presence of respiratory and metabolic derangements: acid base, ventilation and oxygen
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Normal heart rate for dogs and cats.
Dogs: 70-140 beats per min Cats: 100-200 beats per min
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Name the central pulses
Femoral and carotid
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Name the peripheral pulses
Metacarpal Dorsal pedal Coccygeal Lingual Auricular Theses pulses are more helpful when assessing perfusion as they are more sensitised to changes
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Define regular and irregular heart rhythm
Regular - steady constant rhythm Irregular - variations in timing between beats. Caused by cardiac arrhythmias or inadequate ventricular contractions failing to open aortic semilunar valves.
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Reasons for abnormal pulse rates
Lowered rate = myocardial depression caused by drugs, systemic illness and deep anaesthetic Increased rate = light anaesthetic, stress, pain, pyrexia, hypoxia Weak = poor circulation, peripheral vasoconstriction, drug effects Strong and jerky = heart defects and hyper-dynamic states
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Define a bounding pulse
An extremely strong and powerful pulse experienced for short durations Aka as leaping or forceful pulse Sometimes can be seen pulsing under the skin Large pulse pressure difference and wide waveform Can be a sign of heart failure, chronic kidney failure and fluid overload
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Define a waterhammer pulse
Aka Corrigan’s, jerky and B-B shot pulse. Associated with increased stroke volume of the left ventricle and decrease in the peripheral resistance leading to wide pulse pressure. Pulse strikes the palpating finger with a rapid, forceful jerk and quickly goes. Caused by the artery suddenly emptying because some of the blood flows back from the aorta into the ventricle. Found in: aortic incompetence, hyperdynamic states: fever, anaemia and thyrotoxicosis.
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The haemoglobin-oxygen dissociation curve
Saturation of haemoglobin with oxygen varies with the partial pressure of oxygen. At high partial pressures of oxygen, Haemoglobin binds to oxygen to form oxyhaemoglobin (shifts to the left) As the red blood cells travel to tissues deprived of oxygen the partial pressure of oxygen will decrease and makes the oxyhaemoglobin release the oxygen to form Haemoglobin (shift to the right) This is affected by increased temp, CO2, lactic acid, DPG, and H (decreased pH)
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Where can the mucous membranes be checked?
The gingiva The conjunctiva The anus The vagina or penis
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What are the normal values for blood pressure?
Dogs and cats Systolic: 90-120 mmHg Diastolic: 55-90 mmHg MAP: 60-85 mmHg
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What causes slow CRT?
Hypotension Hypovolaemia Toxaemia Shock Haemorrhage Rough handling of viscera
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Oscillometric blood pressure monitoring (Non-invasive)
Only non-invasive method that measures MAP Placement: distal limb or tail Cuff is inflated to above systolic pressure, occluding the blood flow, pressure is then slowly reduced, allowing blood to pulse through the vessel, indicating systolic arterial blood pressure. A: non-invasive and simple to use. Repeated readings taken every few mins. Provides systolic, diastolic and mean blood pressures. D: less accurate than Doppler methods in smaller animals although newer machines very accurate
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Doppler method (blood pressure monitoring) Non-invasive
Probe placed on the palmar aspect of metacarpus, cuff is placed above elbow. The sphygmomanometer measures pressure in the cuff and the Doppler probe senses blood movement within the artery which can be heard. Cuff inflated to a pressure that occludes systolic pressure, so no pulsing is heard from the probe. Cuff is deflated, an audible pulsation returns, indicating systolic pressure at the cuff. A: non-invasive and more accurate than oscillometric. D: doesn’t provide a continuous reading, has to be manually taken. No accurate diastolic reading is obtained and no MAP.
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Invasive arterial reading
Catheter placed into an artery (commonly used - dorsal metatarsal, femoral and carotid) Catheter should be sutured in place and a 3 way tap attached, a manometer is then attached with another 3 way tap and then a pressure veil and aneroid manometer, the system is then filled with saline, once a reading is required a 20ml syringe filled with saline is attached to the 3 way tap and introduced until there is a pressure reading on the manometer. The fluid line needs to be flushed periodically to avoid clot formation at the site, this can be seen from the arterial trace wave.
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Central venous pressure blood pressure Invasive
The same as invasive arterial reading but only using the jugular vein and a venous manometer. The height of the manometer should be in line with the height of the right atrium. Filling pressure of the central venous reservoir at the level of the right thoracic vena cava Used to assess fluid balance, hypovolaemia or circulatory overload. Influenced by changes in intrathoracic pressure. Normal range 0-7cmH2O.
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Electrocardiography (ECG)
Detects electrical activity of the heart The monitor could produce a normal readout when cardiac output is zero, this is known as electromechanical dissociation (aka pulsless electrical activity PEA)
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Define the ECG waves
P: depolarisation atria PR: beginning of atrial depolarisation into ventricular depolarisation. Interval due to slow conduction through AV node. QRS: ventricular depolarisation T: repolarisation is hidden by QRS complex.
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Causes of arrhythmias
Cardiac disease (macro or microscopic) Autonomic imbalance Metabolic derangement (electrolytes) Drugs and toxins Sepsis Trauma
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What is abornomal ventricular complexes?
Abnormal rhythm Wide, often bizarre shape, no P waves and T wave obscure
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What are normal temp values? (Dog, cat, rabbit)
Dog - 38.3 - 39.2 Cat - 38.2 - 38.6 Rabbit - 38.5 - 40
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What causes hypothermia during anaesthesia?
A large surgical clip wet patient prep Lowered metabolic rate (old) Lack of movement Low ambient temp Insufficient external heat
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How can the level of consciousness be measured?
Eye position Muscle tone Cranial nerve reflexes Cardiovascular signs
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How can blood loss be measured?
Weight differential of dry and used swabs Suction bottle contents Visual observation Blood analysis Blood pressure
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Formula for calculating blood loss
10 X 10cm swab = 2g 2g X number of swabs used during surgery = dry weight Subtract dry weight from weight of blood soaked swabs to calculate weight of blood lost 1g of weight = 1ml blood Blood volumes: Dogs 88ml/kg Cats 66 ml/kg
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Tourniquets
Bier blocks - used in orthopaedic surgery Haemorrhage of limb or tail - used as last resort Max of 15 mins Potential toxic shock syndrome, haemolysis, ischaemia, muscle and nerve damage, tissue necrosis Removal of tourniquets leads to decrease in mean arterial bp (due to release of metabolites from ischemic limb into the circulation and dec in peripheral vascular resistance) Transient inc in EtCO2, dec in temp, central venous oxygen tension seen. Allowing blood flow back can induce a paradoxical extension of ischemic damage mediated by oxygen free radicals and is known as ‘reperfusion syndrome’ Acute resp distress syndrome, renal and cardiac injury Venous embolisation may occur (lower limbs especially)
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What’s signs should be reported during recovery?
Significant change since resp, pulse, pattern or rate Level of consciousness Significant blood loss Significant changes in bp Signs of pain/distress Changes in behaviour/appearance Temp changes
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What is an anaesthetic emergency and what could cause it?
Anything posing an immediate threat to your patients life around the anaesthetic period. -resp obstruction/dyspnoea -resp arrest/apnoea -bradycardia -tachycardia -arrhythmia -cardiac arrest -equipment failure
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List the Mu-agonists
Morphine Methadone Fentanyl Pethidine Alfentanil
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Name the partial mu-agonist
Buprenorphine
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Name the kappa agonist
Butorphanol
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Name the antagonist
Naloxone
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Define agonist
Combine with the receptors, activating them and inducing response
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Define partial agonist
Combine with receptors allowing for a partial response
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Define synergism
Increase action of 2 or more drugs (1+1=3)
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Define antagonism
A drug inactivates the action of another (1+1=0)
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Define antagonist
Combine with receptors but dont activate them, so blocking a response by stopping agonist using the receptor
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Phenothiazines (ACP)
Blocks dopamine receptors in the CNS, depressing the reticular-activating system. A = sedation and tranquillisation, not an analgesic but potentiates effects of analgesic drugs, anti-arrhythmic, anti-emetic, antihistamine, smooth muscle spasmolytic D = hypotension, decreases seizure threshold, unpredictable and lasts a long time, hypothermia, boxers are particular sensitive and less effective in cats.
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Benzodiazepines (diazepam, midazolam)
Bind to a number of receptors in CNS A = anti-anxiety effects, minimal CNS and resp effects, muscle relaxation, anticonvulsant, appetite stimulant, good adjunct to ketamine as offsets muscle hypertonicity. Reversal is flumazenil D = paradoxical state of excitement in healthy patients. Diazepam - thrombophlebitis in solutions containing propylene glycol, use syringes immediately after drawing up, painful and poorly absorbed if administered IM.
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Antimuscarinics
A = reduces saliva and bronchial secretions, blocks vagus nerve, prevents bradycardia, promotes bronchodilation D = cardiac arrhythmias, increases anatomical dead space, confusion, dry mouth, pupillary dilation which can trigger panic or acute glaucoma.
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Opioids
Bind to specific opioid receptors located in CNS A = sedation, analgesia, minimal cardiovascular effects, synergistic, anaesthetic sparing, reversal using naloxone D = dysphoria, CNS effects vary, resp depression, nausea and vomiting, bradycardia and hypotension, antitussive and urinary retention
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Alpha-2 agonists (Medetomidine, dexamedetomidine)
Bind to central and peripheral alpha-2 adrenergic receptors. A = potent sedation and hypnosis, analgesic effect, good adjunct to ketamine as offsets the muscle hypertonicity, reversal is atipamezole. D = profound cardiovascular effects, milder resp effects,, vomiting, diuresis, hyperglycaemia, premature parturition