Lecture 2.8

Pharmacology

What is a crash cart/emergency trolley and why is it important in an MRS department?

A crash cart is an essential emergency resource containing medications and equipment required for rapid management of patient deterioration.

Its purpose is to make emergency equipment and medicines immediately accessible when a patient develops an acute episode, reaction, deterioration or complication.

Where should a crash cart be located in an MRS department?

Location depends on the department's activities and likely emergencies.

• Contrast CT: generally in or immediately outside the CT room
• Cardiac stress testing: immediately accessible
• Large departments may require multiple crash carts
• MRI may require a dedicated MRI-compatible crash cart

The key principle is rapid accessibility during an emergency.

Why can crash-cart contents differ between healthcare facilities?

Crash-cart size and contents vary according to:

• Hospital vs outpatient setting
• Department type
• Procedures performed
• Likely emergencies
• Patient population/case mix
• Adult vs paediatric patients

An adult crash cart is organised differently from a paediatric crash cart.

What should an MRS professional know about the crash cart before an emergency occurs?

Medical radiation professionals should familiarise themselves with:

• Its location
• How it is organised
• Where important equipment/medications are stored
• How its contents are used
• Local emergency procedures

The lecture emphasises being prepared before deterioration occurs rather than trying to learn the cart during an emergency.

What medication-label information should be checked before administering an emergency medication?

Check the medication label for:

• Correct drug name
• Pharmaceutical form
• Total amount of drug
• Concentration
• Approved administration route(s)
• Expiry date
• Batch information where relevant

The lecturer particularly emphasised always checking the expiry date.

What does “single-use vial” mean?

A single-use vial is intended for one patient/use.

After drawing up the required amount:

• Do not save the remaining medication
• Do not use the remainder for another patient
• Discard the unused medication

Why is recognising the deteriorating patient particularly important for medical radiation professionals?

MRS professionals are often positioned to observe the patient before, during and after an examination or intervention.

This allows them to recognise subtle changes such as:

• Colour
• Breathing
• Cognition
• Speech/communication
• Sweating
• Behaviour
• Consciousness

These may provide the first indication of deterioration.

What general principle should be applied to sudden changes in a patient?

A sudden or unexplained change from the patient's previous state should be treated as a potential early warning sign.

The change may have a benign explanation, but if there is no obvious cause it requires attention and assessment.

What changes are considered early warning signs of patient deterioration?

Sudden changes in:

• Respiratory rate
• Heart rate/pulse
• Blood pressure
• Level of consciousness
• Mental status/cognition
• Ability to communicate
• Uncontrolled pain

Also important:

• Seizures
• Bleeding

What respiratory rate is an early warning sign according to the lecture?

A respiratory rate:



should trigger concern for deterioration.

What pulse rate is an early warning sign according to the lecture?

A pulse:



is an early warning sign requiring assessment and response.

What systolic blood pressure is an early warning sign according to the lecture?

A systolic BP:



should be recognised as an important warning sign.

What is the sequence for recognising and responding to deterioration?

Deteriorating patient
↓
Recognise early warning signs + understand the meaning of symptoms
↓
Recognise the problem and trigger a response

Then two processes can occur simultaneously:

• Call for help
• Initiate appropriate action

Does recognising deterioration mean the radiographer must diagnose the underlying condition?

No.

The important responsibility is to:

• Recognise that something is wrong
• Understand the significance of the signs sufficiently to identify deterioration
• Trigger an appropriate response

Recognition may simply mean realising: “This patient needs help.”

What immediate actions may be initiated for a deteriorating patient?

Depending on the situation and scope/protocol:

• Address danger
• Address life-threatening problems
• Stay calm
• Communicate
• Support/reassure the patient
• CPR
• Oxygen
• Emergency medication, where appropriate

Examples discussed include EpiPen, oxygen and CPR.

What should happen after emergency treatment is initiated?

Once an action is initiated:

Maintain appropriate care until help arrives.

When help arrives:

• Continue supporting the patient as required
• Assist the responding team
• Retrieve equipment or medications as requested
• Provide relevant information

Who may provide emergency assistance after deterioration is recognised?

Depending on the clinical setting:

• Medical support
• Hospital crash/resuscitation team
• Paramedics
• Radiologist/other medical staff
• Nursing staff

The available response varies considerably between large hospitals and smaller/private facilities.

Why does the clinical setting affect the MRS professional's role during an emergency?

In a major hospital, a crash team may arrive very quickly.

In a smaller/private clinic:

• Staff numbers may be limited
• A nurse may not be present
• The radiologist may not be immediately available
• Paramedics may be the main emergency response
• Help could take considerably longer to arrive

Therefore staff may need to support the patient for longer before help arrives.

Why should MRS professionals prepare for emergencies even though severe emergencies are uncommon?

Most days may involve no emergency at all, or only mild reactions.

However, assuming emergencies will not happen can leave staff unprepared when one does occur.

The lecturer's emphasis was to begin each clinical day knowing that acute deterioration could occur in any patient.

Can emergencies in an imaging department involve people other than the patient?

Yes.

An emergency may involve:

• The patient
• A relative
• Partner/carer
• Visitor

The lecturer described having performed CPR on a patient's accompanying loved one who arrested in the waiting area.

What three broad categories are used in the lecture to classify problems in a deteriorating patient?

The diagram groups problems into:

1. Episode
2. Reaction
3. Deterioration or complication

This helps recognise that deterioration in an imaging department is not automatically a medication or contrast reaction.

What types of acute episodes may occur in an MRS department?

Acute episodes include:

• General acute episodes
• Trauma
• Seizure
• Mental-health episodes

These may occur independently of medication or contrast administration.

What are the signs of a mild general acute episode?

• Nausea/vomiting
• Flushing
• Chills
• Headache
• Dizziness
• Anxiety
• Altered taste
• Warmth
• Double vision
• Back pain

What are the signs of a moderate general acute episode?

• Refractory/persistent nausea or vomiting
• Changes in blood pressure
• Isolated chest pain

What are the signs of a severe general acute episode?

• Arrhythmia
• Convulsion
• Seizures
• Hypertensive emergency

A general acute episode may ultimately become fatal.

What signs may indicate a seizure?

• Aura sensation
• Jerking/twitching
• Convulsion
• Loss of consciousness

Seizures may be pre-existing or associated with the patient's pathology/treatment.

What signs may indicate a traumatic episode?

• Pain
• Swelling
• Loss of function

Trauma can arise from the patient's original injury or from an incident such as a fall within the department.

What changes may indicate an acute mental-health episode?

• Anxiety
• Depression
• Agitation
• Confusion
• Mood changes
• Inappropriate behaviour

Severe anxiety, claustrophobia and needle phobia may become clinically significant during imaging.

What major reaction types may be encountered in the imaging department?

The lecture diagram includes:

• General reactions
• Anaphylactoid reactions
• Non-anaphylactoid reactions
• Hypersensitivity reactions
• Vasovagal reactions

Hypersensitivity and vasovagal reactions can then be classified by severity.

What are the signs of a mild hypersensitivity reaction in the lecture diagram?

• Urticaria/pruritus
• Cutaneous oedema
• Itchy throat
• Nasal congestion
• Sneezing
• Mild eye swelling
• Cough

What are the signs of a moderate hypersensitivity reaction?

• Diffuse urticaria/pruritus
• Diffuse erythema
• Facial oedema
• Throat tightness
• Wheezing
• Dyspnoea
• Tachycardia
• Bradycardia
• Hypotension
• Hypertension

What are the signs of a severe hypersensitivity reaction?

• Diffuse oedema
• Facial oedema with dyspnoea
• Diffuse erythema with hypotension
• Laryngeal oedema
• Bronchospasm
• Arrhythmia
• Progressive angioedema
• Cardiopulmonary arrest
• Anaphylactic shock

What are the signs of a mild vasovagal episode?

• Pale skin
• Dizziness
• Tunnel vision
• Blurred vision
• Nausea
• Feeling warm
• Fainting

A mild episode is generally self-limiting.

How are moderate and severe vasovagal episodes distinguished?

Moderate:
• Bradycardia
• Hypotension
• Dilated pupils
• Responds to treatment

Severe:
• Bradycardia
• Hypotension
• Resists treatment

What signs may indicate cardiac deterioration?

• Chest pain
• Palpitations
• Tachycardia
• Arrhythmia
• Dyspnoea
• Dizziness
• Cardiac arrest
• Unconsciousness

What signs may indicate respiratory deterioration?

• Tachypnoea
• Bradypnoea
• Hypotension
• Abnormal airway sounds
• Cyanosis
• Tachycardia
• Respiratory/cardiac arrest
• Unconsciousness

What signs may indicate neurological deterioration?

• Headache
• Dizziness
• Nausea
• Agitation
• Vision changes
• Poor balance
• Dysarthria
• Confusion
• Anxiety
• Amnesia

What signs of diabetic deterioration are identified in the lecture diagram?

• Tiredness
• Nausea
• Dizziness
• Headache
• Hypoglycaemia
• Erratic behaviour
• Argumentative behaviour
• Unconsciousness

Fasting patients with diabetes are particularly relevant in imaging.

What signs may indicate significant bleeding?

• Tachycardia
• Hypotension
• Tachypnoea
• Thirst
• Confusion
• Hypovolaemic shock
• Unconsciousness

What signs may indicate shock?

• Tachycardia with hypotension
• Bradycardia with fainting
• Pale, cool, clammy skin
• Nausea
• Confusion
• Anxiety

What allergic/hypersensitivity-type emergencies are particularly relevant to MRS?

Examples include:

• Anaphylaxis — e.g. contrast media
• Anaphylactoid reactions — e.g. monoclonal antibodies in lecture terminology
• Other allergic responses — e.g. radiopharmaceuticals/contact allergy
• Vasovagal responses associated with injections, although these are not allergic reactions.

What cardiovascular emergencies may occur in an MRS department?

• Cardiac arrest
• Shock
• Angina/chest pain
• Arrhythmias
• Pulmonary oedema
• Hypertensive states

They may arise:

• Spontaneously from underlying disease
• From therapy
• As a consequence of an imaging procedure, such as cardiac stress testing.

What respiratory emergencies may occur in an MRS department?

Respiratory emergencies may arise from:

• Asthma
• Chronic obstructive airways disease
• Allergic/hypersensitivity reactions
• Contrast reactions
• Imaging medications such as dipyridamole
• Pathology such as pulmonary embolism

What neurological emergencies are relevant to MRS?

Important examples include:

• Seizures
• Severe anxiety

These may be:

• Pre-existing
• Related to underlying pathology/treatment
• Exacerbated by the imaging procedure

Examples include claustrophobia and trypanophobia (fear of needles).

Why can anxiety exist on a spectrum from manageable symptom to emergency?

Mild anxiety may simply require reassurance or pharmacological assistance.

However, severe anxiety can:

• Prevent safe examination/treatment
• Cause severe agitation
• Produce significant physiological effects
• Become a neurological/behavioural emergency

The lecturer used claustrophobia as an example of this spectrum.

What endocrine emergencies may be encountered in medical imaging?

Important examples include:

• Hypoglycaemia, particularly in fasting diabetic patients
• Thyroid storm, associated with severe thyrotoxicosis

What fluid/electrolyte emergencies may occur in imaging patients?

Patients may develop fluid or electrolyte problems due to:

• Major blood loss
• Gastrointestinal bleeding
• Hypovolaemic shock
• Dehydration
• Fasting
• Heat/environmental conditions

How can trauma become an emergency within an imaging department?

Trauma may involve:

• A fall or incident occurring within the department
• A pre-existing injury worsening
• Imaging positioning aggravating an existing injury

MRS staff therefore need to recognise and respond to trauma even when it is unrelated to the original imaging indication.

How relevant are poisoning and overdose emergencies to MRS?

They are less likely than cardiovascular, respiratory or hypersensitivity emergencies but can still occur.

The transcript notes that some patients may present after overdose or substance use, and particular patient groups such as IV drug users may also have associated complications.

Why must crash-cart medications be organised for rapid access?

During an emergency:

• Medications must be readily accessible
• Staff need to identify the correct drug rapidly
• Drugs should be in forms that are easy to measure
• They must be capable of being dispensed/administered quickly

Crash-cart contents therefore reflect the emergencies most likely to occur.

Why may crash-cart drawers have tamper-evident seals?

The transcript explains that seals:

• Reduce the risk of medications/equipment being stolen
• Show whether a drawer has been opened
• Help determine whether the contents require rechecking

If a seal has been broken, the contents should be checked for stock and expiry according to local procedure.

What equipment categories may be organised around a crash cart?

The lecture diagram includes:

• Defibrillator
• CPR protocol/board
• Medications
• Airway: Guedel airways, endotracheal tubes, laryngoscopes
• Ventilation: bag, masks, oxygen tubing
• Vascular access: IV catheters and intraosseous needles
• Other equipment, including defibrillation pads/difficult-airway equipment
• Oxygen tank

What medication classes may be required on a crash cart?

• Anticholinergics
• Anti-arrhythmics
• Antihistamines
• Antihypertensives
• Vasodilators
• Vasoconstrictors
• Beta blockers
• Beta agonists
• Calcium-channel blockers
• Inotropic agents
• Adrenergic stimulants
• Diuretics
• Bronchodilators
• Analgesics
• Anxiolytics

Why can emergency medication use differ from routine medication use?

Both the drug selected and its dose may differ substantially when treating an acute emergency compared with ongoing management.

Emergency treatment requires medications with an appropriate speed and intensity of action.

Why are ACE inhibitors not ideal for emergency management of an acute hypertensive state?

According to the lecture, ACE inhibitors generally lack the immediate effect required for acute emergency management.

A medication useful for long-term hypertension is therefore not automatically appropriate for an acute hypertensive emergency.

Why is IV lignocaine an example of the difference between acute and ongoing medication management?

IV lignocaine can be useful as an acute anti-arrhythmic, but the lecture notes that it is not suitable for ongoing anti-arrhythmic management.

This illustrates that emergency medication choice is context-specific.

What cardiovascular effects does endogenous acetylcholine produce according to the lecture?

Acetylcholine (ACh) can produce:

• ↓ Heart rate
• ↓ Cardiac output
• Vasodilation
• Hypotension
• Arrhythmias

What is atropine's basic mechanism of action?

Atropine is an anticholinergic/muscarinic antagonist.

It competitively blocks acetylcholine at muscarinic receptors, opposing parasympathetic effects.

What cardiovascular effects can atropine produce?

By blocking muscarinic effects, atropine can produce:

• ↑ Heart rate
• Vasoconstriction
• ↑ Blood pressure

Its major emergency relevance is treatment of bradycardia.

What other physiological effects can muscarinic antagonists such as atropine produce?

• Smooth-muscle relaxation
• Bronchodilation
• ↓ Exocrine secretions — sweat, tears, saliva etc.
• Mydriasis
• ↑ Intraocular pressure
• Cycloplegia
• ↑ Body temperature

CNS effects may include depression, restlessness, agitation and hyperactivity.

What clinical uses of atropine are identified in the lecture?

Atropine may be used for:

• Sinus bradycardia
• Pre-anaesthetic purposes
• Sedative-related applications described in lecture
• Tremor
• Motion sickness
• Antispasmodic effects
• Mydriasis

Its main crash-cart relevance is acute bradycardia.

What atropine dose is listed for emergency bradycardia in the lecture?

Adult: 1 mg IV

Repeat every 3–5 minutes until:

• Target heart rate achieved, OR
• Maximum 3 mg

Paediatric: 20 micrograms/kg IV, maximum 1 mg.

What are the major endogenous catecholamines discussed in the lecture?

• Norepinephrine/noradrenaline
• Epinephrine/adrenaline
• Dopamine

Dopamine is a precursor in the synthesis of norepinephrine.

Through which receptors do catecholamines exert their major effects?

Catecholamines act through adrenergic receptors, principally:

• α (alpha) receptors
• β (beta) receptors

Their clinical effects depend on which receptor types are activated.

What is the major emergency role of norepinephrine?

Norepinephrine is primarily used to treat:

Severe hypotension and shock

The lecture summary characterises it predominantly as an adrenergic vasoconstrictor with relatively limited major cardiac effects compared with adrenaline.

Why is adrenaline especially useful in anaphylaxis?

Adrenaline addresses several components simultaneously:

• Cardiovascular support
• Vasoconstriction
• Positive cardiac effects
• Bronchodilation
• Reduced mast-cell mediator/histamine release

This makes it more useful in anaphylaxis than a drug producing vasoconstriction alone.

What does β₁ receptor activation do?

β₁ agonism produces:

• ↑ Heart rate
• ↑ Force of cardiac contraction
• ↑ Cardiac output
• ↑ Myocardial oxygen consumption

Excessive stimulation can contribute to arrhythmias.

What does β₂ receptor activation do?

β₂ agonism causes smooth-muscle relaxation, producing:

• Bronchodilation
• Vasodilation

It also:

• ↑ Glycolysis in liver and muscle
• ↓ Histamine release

What are the major actions of adrenaline listed in the lecture summary?

Adrenaline produces:

• Positive inotropic action
• Positive chronotropic action
• Vasodilation at lower doses
• Vasoconstriction at higher doses
• Bronchial smooth-muscle relaxation
• Mast-cell stabilising/reduced mediator-release effects

What are the pharmacokinetic features of adrenaline in the lecture summary?

• Rapid IV onset
• Duration: 2–5 min
• Infusion steady state: 10–15 min
• Half-life:

What adverse effects of adrenaline are listed in the lecture?

• Anxiety/restlessness
• Dyspnoea
• Hyperglycaemia
• Palpitations
• Tachycardia ± anginal pain
• Tremor
• Sweating
• Hypersalivation
• Weakness
• Dizziness/headache
• Cold extremities

Why is beta-blocker use important when adrenaline is required?

The lecture notes that patients taking beta blockers may have an impaired response to adrenaline, including when adrenaline is needed for anaphylaxis.

The interaction between alpha/beta effects can also be complex, with the lecture warning of possible severe hypertension.

What adrenaline preparations are listed on the emergency-medication table?

Adrenaline/epinephrine:

• 1 mg/1 mL (1:1000)
• 1 mg/10 mL (1:10,000)

EpiPen:

• Adult: 300 micrograms/0.3 mL
• Junior: 150 micrograms/0.3 mL

What is the EpiPen dose for anaphylaxis in the lecture?

>20 kg: 0.3 mg IM
10–20 kg: 0.15 mg IM

The lecture table states it may be repeated every 3–5 minutes if there is no response.

Where should an EpiPen NOT be administered according to the lecture?

Do not administer into:

• Buttock
• Digits
• Hands
• Feet
• Intravenously

The lecture states there are no absolute contraindications to EpiPen use in a life-threatening allergic situation.

What are the pharmacokinetic characteristics of an EpiPen/adrenaline IM?

• Rapid IM onset
• Short duration
• Half-life

What adverse effects may occur following an EpiPen?

Transient effects can include:

• Anxiety/overstimulation
• Restlessness
• Tremor
• Weakness/dizziness
• Sweating
• Tachycardia/palpitations
• Pallor
• Nausea
• Headache
• Respiratory difficulty

Ventricular arrhythmias can occur.

What norepinephrine dose is listed for hypotension/shock?

Start:

8–12 micrograms/min IV

Then titrate to:

2–4 micrograms/min maintenance

Maximum listed:

30 micrograms/min if hypotension is unresponsive to lower doses.

Paediatric: 0.02–0.1 micrograms/kg/min.

What precautions and contraindications are listed for norepinephrine?

Caution:

• Hypovolaemia
• Hyperthyroidism

Avoid:

• Hypertension

Treatment is titrated to effect.

What is dobutamine's receptor action and emergency role?

Dobutamine is a selective β₁ receptor agonist.

It acts as an inotropic agent/vasodilator and is used in the lecture for management of hypotension.

What are salbutamol and salmeterol's principal receptor actions?

They are predominantly selective β₂ receptor agonists.

β₂ activation relaxes bronchial smooth muscle, so these drugs are primarily used as bronchodilators.

What is adrenaline's relationship to beta receptors?

Adrenaline is a non-selective beta-receptor agonist, meaning it can activate both:

• β₁ receptors → cardiac effects
• β₂ receptors → bronchodilation/smooth-muscle relaxation

It also has important alpha-receptor activity.

How do beta blockers work?

Beta blockers are β-adrenergic receptor antagonists.

They competitively block the actions of endogenous catecholamines at beta receptors.

What are atenolol and metoprolol's receptor actions?

Atenolol and metoprolol are relatively β₁-selective beta blockers.

Their effects include:

• ↓ Heart rate
• ↓ Force of contraction
• ↓ Myocardial oxygen demand

The lecture also lists peripheral vasoconstriction and possible bronchospasm.

Why are beta blockers used clinically?

Their reduction of cardiac rate, contractility and oxygen demand makes them useful for:

• Hypertension
• Arrhythmias
• Angina
Adenosine

What is adenosine and what is its main cardiovascular role?

Adenosine is an endogenous purine nucleoside with important cardiovascular effects.

As an emergency medication it can:

• Depress sinus-node activity
• Slow AV conduction
• Temporarily interrupt AV-node-dependent tachyarrhythmias

It is particularly relevant to treatment of supraventricular tachycardia (SVT).

What are the four main adenosine receptor subtypes?

The four adenosine receptor subtypes discussed are:

• A₁
• A₂A
• A₂B
• A₃

Different receptor subtypes produce different cardiovascular and respiratory effects.

What effects are produced by A₁ adenosine receptor activation?

A₁ receptor activation:

• Inhibits adenylate cyclase
• Blocks AV conduction
• Reduces force of cardiac contraction
• Produces negative inotropic and chronotropic effects
• Produces cardiac depression
• Can cause bronchoconstriction

What effects are produced by A₂A adenosine receptor activation?

A₂A receptor activation produces:

• Potent vasodilation
• ↓ Blood pressure
• Bronchodilation

What are the effects of A₂B and A₃ adenosine receptors?

A₂B: stimulates release of mast-cell mediators

A₃: contributes to bronchoconstriction

These actions help explain some of adenosine's respiratory effects.

What are the principal agonists of the adenosine receptor system?

Principal agonists include:

• Adenosine
• Adenosine monophosphate (AMP)
• Adenosine diphosphate (ADP)
• Adenosine triphosphate (ATP)

How does dipyridamole interact with the adenosine system?

Dipyridamole acts as an indirect adenosine agonist.

It blocks adenosine metabolism, thereby:

↓ Adenosine metabolism → ↑ adenosine bioavailability → enhanced adenosine effects.

What is adenosine's mechanism as an anti-arrhythmic?

Adenosine:

• Depresses sinus-node activity
• Slows AV-node conduction

Its strong but extremely brief effect on AV conduction makes it useful for certain SVTs.

What are the key pharmacokinetic characteristics of adenosine?

• Rapid onset
• Peak:

What adverse effects can occur with adenosine?

Adverse effects include:

• Chest, neck, jaw or arm pain
• Headache
• Flushing
• Dyspnoea
• ECG changes
• Bronchospasm

Bronchospasm is particularly important in patients with asthma.

Why does caffeine intake matter when administering adenosine?

Caffeine and other xanthines interact with the adenosine receptor system and can oppose adenosine's effects.

Therefore recent consumption of strong coffee/caffeine may reduce the desired response to adenosine.

What is GTN and what are its major cardiovascular effects?

Nitroglycerin/glyceryl trinitrate (GTN) is a potent vasodilator.

It:

• Enhances oxygen delivery
• Reduces myocardial oxygen demand
• Produces prominent venodilation
• Dilates coronary/collateral vessels

How does GTN cause vascular smooth-muscle relaxation?

GTN increases exogenous nitric oxide (NO).

Vasodilation is associated with:

• ↓ Intracellular calcium concentration
• Dephosphorylation of myosin
• Vascular smooth-muscle relaxation

How does GTN reduce cardiac preload?

GTN causes venodilation, resulting in pooling of blood in the veins.

This causes:

↓ Venous return → ↓ preload → ↓ LV end-diastolic volume → ↓ myocardial oxygen demand

How does GTN improve myocardial oxygen supply?

GTN dilates:

• Coronary vessels
• Coronary collateral vessels

This can improve distribution of blood and oxygen to ischaemic myocardial tissue.