Protect airway from gastric contents (e.g. unfasted patient) Use of muscle relaxants Need for tight control of blood gasses (neurosurgery) Restricted access to airway (maxillo-facial surgery)

Anaesthetics Flashcards by Emily Ross

Triad of anaesthesia

Analgesia
Hypnosis
Relaxation

GA: HYPNOSIS, relaxation, analgesia
Muscle relaxants: RELAXATION
Opiates: ANALGESIA, hypnosis
LA/RA: ANALGESIA, relaxation

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Main potential anaesthetic problems

R-eflux
O-besity
A-irway
R-airities (malignant hyperpyrexia, cholinesterase deficiency)
S-pine

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Investigations to be carried out as part of a pre-op assessment are determined by…

NICE guidelines
take into account…

ASA grade (1-6)
Co-morbidities
surgery grade

Examples: ECG, Exercise tolerance test, (stress) Echo, Myocardial perfusion scan, Cardiac catheterisation, CT coronary angiogram, Saturations, ABGs, CXR, Peak flow measurements, FVC/FEV, Gas transfer, CT chest

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Cardiac risk index, high risk of surgical complications if…

> 4 of…

High risk surgery
Ischaemic heart disease
Congestive heart failure
Cerebrovascular disease 
Diabetes
Renal failure

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Parts of a pre-op assessment

Assess (history, examination, investigations)
Identify high risk (various assessment tools)
Optimise health
Minimise risk
Inform and support patients’ decisions
Consent

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General anaesthesia works by…

Hyperpolarising neurones (largely by opening chloride channels) – prevents them from firing

((processes lost “from the top down”, reflexes relatively spared))

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Most common method of induction and maintenance for general anaesthetic

IV induction –> inhalational maintenance

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IV induction of general anaesthetic usually uses…

+ how can specific concentrations be achieved

Propofol

o Specific concentrations can be achieved using a Target Controlled Infusion (TCI) pump system (calculations based on patient’s age, sex and size)

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Inhalational induction of general anaesthetic uses…

+ what measurements are used to control the concentrations

Halogenated hydrocarbons, e.g. sevoflurane

Alveolar partial pressure ≈ arterial concentration
MAC = Minimum Alveolar Concentration to produce anaesthesia

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Risks to an unconscious patient

Airway (obstruction/ aspiration)
Temperature
Loss of protective reflexes (e.g. corneal)
VTE risk
Pressure areas
Consent/ identification

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Minimum monitoring of an unconscious patient requires…

SpO2 (peripheral capillary oxygen saturation)
ECG 
NIBP (non-invasive BP)
FiO2 (fraction of inspired oxygen)
ETCO2 (amout of CO2 in exhaled air)

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Extra monitoring of the unconscious patient may include…

Respiratory parameters
Temperature
Urine output
Invasive venous/ arterial monitoring
Processed EEG

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The triple airway manouvre

head tilt,
chin lift,
jaw thrust

(painful so unconscious if tolerated)

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Apparatus to maintain (keep open + unobstructed) the airway:

Anaesthetic face mask
Oropharyngeal (Guedel) airway
Laryngeal mask airway (e.g. i-gel)

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To PROTECT (not just maintain) the airway, you must use…

Endotracheal intubation
- Cuffed tube in the trachea protects the airway from contamination

((Inserted using a muscle relaxant and laryngoscope ))

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Reasons to intubate:

Protect airway from gastric contents (e.g. unfasted patient)
Use of muscle relaxants
Need for tight control of blood gasses (neurosurgery)
Restricted access to airway (maxillo-facial surgery)

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echanism of emergence/ awakening from IV / inhalational general anaesthetic

IV: Rapid recovery as drug leaves circulation

Inhalational: agent is breathed off due to reversal of concentration gradient

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Muscle relaxants are used in anaesthesia when…

Immobility is essential (e.g. microscopic surgery/ neurosurgery)

Body cavity surgery (relaxation allows access)

((requires ventilation and intubation))

Relaxation without hypnosis =

awareness

Function of intraoperative analgesia

e.g. Opiates

Contribute to the hypnotic effect of GA

Suppression of reflex responses to pain

Prevent arousal due to pain

Mechanism of action of local/ regional anaesthetics

Block Na+ channels, preventing axonal excitation

benefits of local/ regional anaesthetics compared to GA

Relative sparing of CVS and respiratory function compared to GA

Nociceptive (physiological/inflammatory) pain

Cause + characteristics

Caused by obvious tissue injury/ illness, Protective function

Sharp +/- dull, Well localised

Neuropathic pain

Cause + characteristics

Caused by:

Nervous system damage (e.g. nerve trauma, diabetic pain)
Nervous system dysfunction (e.g. chronic tension headache, fibromyalgia)

Burning, shooting +/- numbness, pins and needles, Not well localised

Paracetamol: advantages and disadvantages

Advantages: - cheap and safe - given orally, rectally, IV - good for mild pain alone/ moderate in combination Disadvantages: - liver damage in overdose

NSAIDs: examples, advantages and disadvantages

E.g. diclofenac, ibuprofen, aspirin Advantages: - cheap, generally safe - good for nociceptive pain - best with paracetamol (synergism) Disadvantages: - GI + renal side ADRs - bronchospasm in sensitive asthmatics

Mild opioids: examples, advantages and disadvantages

E.g. codeine, dihydrocodeine Advantages: - cheap + safe - mild-moderate, acute, nociceptive pain - best with paracetamol Disadvantages: - constipation - bad for chronic pain

Strong opioids: examples, advantages and disadvantages

E.g. morphine, oxycodone, fentanyl Advantages: - cheap, generally safe - given orally IV, IM, SC - moderate-severe acute nociceptive pain - chronic cancer pain Disadvantages: - constipation, resp depression in high dose - misunderstandings about addiction - 1st pass metabolism means oral dose must be 3x higher

Antidepressants used for pain relief: examples, mechanism, advantages and disadvantages

E.g. amitriptyline, duloxetine Mechanism: increases descending inhibitory signals Advantages: - cheap, safe in low dose - good for neuropathic pain Disadvantages: - anti-cholinergic side-effects

Anticonvulsants used for pain relief: examples and mechanism

E.g. gabapentin, carbamazepine, sodium valproate Mechanism: reduce abnormal firing of nerves (good for neuropathic pain)

Tramadol: composition, advantages and disadvantages

Composition: - mixed weak opiate + serotonin (5HT) / noradrenaline (NA) reuptake inhibitor Advantages: - less resp depression - can be used with opiates + simple analgesics Disadvantages: - nausea + vomiting - nasty withdrawal

Ketamine mechanism

NMDA receptor (glutamate receptor) antagonist | (often used in ED as doesn't drop BP)

Nefopam mechanism

Mixed: - NMDA receptor (glutamate receptor) antagonist - serotonin (5HT) / noradrenaline (NA) reuptake inhibitor

"other" analgesics.... | (not simple analgesics or opioids)

Antidepressants (e.g. amitriptyline) Anticonvulsants (e.g. gabapentin) Tramadol (mixed weak opiate + 5HT/NA reuptake inhibitor) Ketamine (NMDA receptor antagonist) Nefopam (mixed NMDA receptor antagonist + 5HT/NA reuptake inhibitor) Topical agents (e.g. Capsaicin)

WHO pain ladder for nociceptive pain:

Mild: paracetamol (+/- NSAIDs) Moderate: paracetamol (+/- NSAIDs) + codeine/ alternative Severe: paracetamol (+/- NSAIDs) + morphine ((ok to start at top of the ladder, but must move down through every rung))

Treatment of neuropathic pain | NOT responsive to WHO pain ladder

Use alternative analgesics (e.g. amitriptyline, duloxetine, gabapentin) Non-drug treatments ! - RICE - nursing care - surgery - acupuncture - massage - TENS - Psychological treatments

The RAT approach to pain management

R-ecognise A-ssess T-reat

Methods to assess severity of pain

``` Verbal rating score Numerical rating score (0-4) Visual analogue scale Smiling faces (paeds) Abbey pain scale (for confused patients) Functional pain ```

Types of respiratory failure:

o Type 1: oxygenation failure | o Type 2: oxygenation and ventilation failure

Management of respiratory failure in critical care

Heated humidified high-flow (HHHF) therapy/ high flow nasal oxygen (HFNO) Non-invasive ventilation (NIV) Intubation

Definition of shock

Acute circulatory failure* resulting in cellular hypoxia | (*Cardiac Output (CO) is hard to measure so BP is used as a marker)

Treatment of circulatory/ cardiovascular failure (shock)

1st line = fluids 2nd line = CV failure drugs - Vasopressors (cause vasoconstriction), E.g. metaraminol, noradrenaline - Inotropes (improve cardiac contractility), E.g. adrenaline, dobutamine

Potential causes of neurological failure:# + concerning features

 Metabolic (DKA)  Trauma  Infection  Stroke ((concerning features: - uneven pupils - Cushing’s reflex (response to ↑ICP: ↑BP, ↓HR, irregular RR) - Failure to maintain airway - GCS<8))