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Diploma in Anaesthesia > Intravenous induction sequence > Flashcards

Intravenous induction sequence Flashcards

1
Q

What are the main advantages of IV induction of anaesthesia compared to inhalational induction?

A

The main advantages are that it enables anaesthesia to be achieved far more rapidly and smoothly.

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2
Q

A smooth, rapid and stable loss of consciousness is wanted in all cases of non-RSI IV induction. But why might the required end-point vary between cases?

A

FACE MASK
IV induction –> relatively light to enable spontaneous ventilation to continue for the introduction of inhalational agents.

LMA
Upper airway reflexes must be suppressed –> requires relatively deep level of anaesthesia (may well produce a short period of apnoea)

ETT
Muscle relaxation required to pass ETT. Short period of intense analgaesia required to suppress SNS response to laryngoscopy.

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3
Q

What is co-induction?

A

Although it is possible to induce anaesthesia using a single IV agent, a combination of drugs frequently produces a smoother induction. This is called co-induction.

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4
Q

Why is midazolam given? What is an appropriate preoperative dose of midazolam and in which patients is this most beneficial and in which patients are benzodiazepines best avoided

A

As part of co-induction, benzodiazepines have beneficial characteristics: Amnesia, airway reflexes, akinesia, anxiolytic.

1 - 3 mg IV

Benefit: Young and anxious

Avoid: elderly (postoperative confusion)

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5
Q

Describe the role of opioids in co-induction

A
  1. Short lived profound analgaesia (blunt laryngoscopy/intubation SNS response)
  2. Reduce airway reflexes (for LMA/ETT insertion)

Dose dependent respiratory depression

Minor anxiolytic

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6
Q

How should fentanyl dosing vary according to type of anaesthesia: FM/LMA/ETT

A

FM - low dose to maintain spontaneous ventilation for the uptake of inhalational agents

LMA - Higher dose to suppress airway reflexes for LMA insertion

ETT - Even higher dose for suppression of airway reflexes and suppression of SNS response to laryngoscopy

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7
Q

Are muscle relaxants considered co-induction agents?

A

No.

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8
Q

Give the sequence, agents and doses for drugs administered in a non-RSI intubation

A
  1. Oxygen (preoxygenation)
  2. Benzo:
    - Midazolam 1-3 mg IV
  3. Opioid
    - Fentanyl (SV) 0.5 - 1.0 ug/kg
    - Fentanyl (IPPV) 2 - 5 ug/kg

If ETT/IPPV

  • Vecuronium 0.1 mg/kg
  • Atracurium 0.5 mg/kg
  • Rocuronium 0.6 mg/kg
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9
Q

What is the end point for induction of anaesthesia?

A

Patient has lost consciousness and is unrousable to gentle verbal stimulation: “can you open your eyes”.

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10
Q

What is the usual cause for laryngospasm, coughing during induction and intubation

A

Under-dosing and stimulation of the patient whilst only lightly anaesthetized

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11
Q

List four situations when inhalational induction is preferred to IV induction

A
  1. Paediatric (co-operation/small veins)
  2. IV drug user (sclerotic veins
  3. Needle-phobic
  4. Stridor
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12
Q

Why is stridor an indication for inhalational induction?

A

In the presence of stridor, the airway is more than 50% narrowed and has the potential to fully obstruct if managed inappropriately.

Inhalation induction –> maintains spontaneous ventilation and anaesthesia can be reversed if the airway is compromised during induction

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13
Q

Why is co-induction an important concept

A

Co-induction is an important concept as it enables the anaesthetist to combine the beneficial effects from a range of drugs whilst minimizing the side-effects

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14
Q

What are the stages of stages of anaesthesia using a slow inhalational induction using ether. Compare this to inhalational induction with sevoflurane

A

ETHER (obselete)

Stage 1: Induction to loss of consciousness
Stage 2: LOC –> Excitatory phenomena –> regular breathing.
Stage 3: Surgical anaesthesia
Stage 4: Depression of the medulla oblongata –> death

SEVOFLURANE

Works much faster than ether so no all of these stages can be clinically observed

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15
Q

Are the stages of unconsciousness usually seen after an adequate dose of an intravenous anaesthetic agent?

A

No. Provided an adequate dose of intravenous anaesthesia has been administered, the patient should pass quickly to the surgical anaesthesia plane.

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16
Q

Are the physiological signs of Stage 2 ever seen after intravenous induction?

A

They can be. These are signs that the patient is starting to recover from the induction dose and adequate inhalational anaesthesia has not yet been achieved to replace it.

17
Q

Which drugs can affect the signs defining the stages of anaesthesia during inhalational induction?

A

Anticholinergics affect pupils, heart rate and reduce secretions.

Opioids may dampen laryngeal reflexes, affect pupils, respiratory rate and response to stimulation.

Benzodiazepines may alter the level of consciousness.

18
Q

Why is knowledge of the stages of anaesthesia relevant

A

Knowledge of these stages allows the clinical assessment of depth of anaesthesia, for example whether the patient is ‘too light’ or ‘too deep’, rather than just relying on monitors alone. A balanced anaesthetic can then be titrated against the patient’s physiological signs and the degree of surgical stimulation.

19
Q

Define and describe Stage 1 anaesthesia (Geudel classification)

A

From induction to LOC

Awake –> reducing response to pain –> hearing intact

20
Q

Define and describe Stage 2 anaesthesia (Geudel classification)

A

From LOC –> excitatory phenomena –> regular breathing

Excitation
Irregular breathing
Breath-holding/coughing
Dilated pupils
Movement/struggling
Hypertension
Tachycardia
21
Q

Define and describe Stage 3 anaesthesia (Geudel classification)

A

From regular breathing divided into four phases

  1. Regular breathing
  2. Eyes become static
  3. Progressive loss of muscle tone
  4. Gradual intercostal paralysis

Surgical anaesthesia

22
Q

Define and describe Stage 4 anaesthesia (Geudel classification)

A

Overdose of agent

Hypotension/bradycardia
Apnoea
Cardiac arrest
Death

23
Q

What clinical indicators exist to inform that the patient is ready for intubation (latter stage 3) without a muscle relaxant

A
  1. Regular diaphragmatic breathing
  2. Slow regular pulse
  3. Loss of muscle tone
  4. Dilated pupils
24
Q

Describe the different types of awareness and their approximate frequency

A

Explicit awareness with pain (1:3000)
- Memory of events with pain or paralysis

Explicit awareness without pain
- Memory of events but comfortable

Implicit awareness
- Not consciously recalled but affect behaviour subsequently

25
Q

What important counselling should occur if a regional technique with sedation is used

A

Patients may be aware of noise in the operating room during procedure –> communicate this beforehand

26
Q

What are the signs of awareness? Name an anaesthetic-related factor or drug that can mask each symptom of awareness

A

SNS activation

  • tachycardia (Atenolol)
  • hypertension (Epidural)
  • sweating (glycopyrrolate)
  • lacrimation (glycopyrrolate)
  • pupils dilated + reactive (Morphine)
  • Movement/tachypnoea (Atracurium)
27
Q

Name 3 causes for awareness

A

Human error

  • Failure to check
  • Failure to turn on vaporizer
  • Inaudible alarms - noisy theatre

Equipment failure

  • poor connection (push and twist)
  • Blocked gas sampling line
  • Intravenous disconnection (TIVA)

Anaesthesia factors

  • TIVA infusion integrity
  • Neuraxial anaesthesia masks HPT

Patient factors

  • Unstable patients: lower GA agent
  • Cardiac surgery: large dose opioid, minimal dose induction agent
  • Tolerant CNS (Chronic ETOH/hyperthyroidism)
28
Q

When is true explicit awareness a significant risk

A

When muscle relaxants are used

29
Q

How can ET Volatile agent be used to detect awareness

A

If ET VA is > 0.8 MAC then awareness is unlikely.

30
Q

What is the isolated forearm technique

A

An inflated cuff prevents NMB from reaching the arm - the patient can move their arm or obey commands if aware.

31
Q

How does a bispectral index monitor (BIS) assist with the detection of awareness?

A

The BIS gives a dimensionless number between 0 - 100. Adequate anaesthesia is between 40 - 60.

Sedation occurs between 60 -80

32
Q

What is an audio evoked potential (AEP)

A

Ear phones - click noises - electrodes detect EEG changes in the auditory cortex –> characteristic waveforms can be processed by a monitor to produce a depth of anaesthesia

Diploma in Anaesthesia (73 decks)

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