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Consent in Interventional Radiology

F. Coccia and J. S. Freedman

Contents

1 Introduction.......................................................................... 19

2 What is Consent?................................................................. 19

2.1 Implied and Express Consent ............................................... 20

2.2 Voluntariness of Consent ...................................................... 20

2.3 Information to be Provided ................................................... 20

3 Capacity to Consent ............................................................ 21

3.1 Assessing Capacity ................................................................ 21

3.2 Supporting Patients to Make Decisions................................ 21

3.3 Patients Refusing Treatment ................................................. 22

3.4 Proxy Decision Makers ......................................................... 22

3.5 Considering Options Available............................................. 23

4 Practicalities ......................................................................... 23

4.1 Who Should Take Consent? ................................................. 23

4.2 When Should Consent be Taken?......................................... 23

4.3 Where Should Consent be Taken? ....................................... 23

5 Withdrawing Consent ......................................................... 23

6 Special Circumstances......................................................... 24

6.1 Consent in Children............................................................... 24

6.2 Consent to Research .............................................................. 24

6.3 Criminal Justice and Mental Health Legislation.................. 24

7 Conclusion ............................................................................ 24

References...................................................................................... 24

Abstract

Taking consent for Interventional Radiology procedures

can be difﬁcult, and requires consideration of the

patient’s general medical condition and their capacity

to consent. Standards for acquiring informed consent are

underpinned by legislation in many countries. Special

circumstances including consent in children, research

and patients detained in mental health or correctional

facilities require further knowledge of local legislation.

This chapter examines the current legislation and

provides a framework to establish capacity and ensure

informed consent.

1 Introduction

This chapter will provide an overview of the legal and

ethical principles related to consent in Interventional

Radiology (IR). It will draw on guidelines provided by

various medico-legal bodies within the United Kingdom

and make reference to the Convention on Human Rights

and Biomedicine. There will be a discussion relating to the

capacity to consent which will draw predominantly on

English legislation. Given the complexity of circumstances

that arise in capacity and consent settings, we will make use

of case vignettes to illustrate some common situations that

may arise.

2 What is Consent?

Article 5 of the Biomedicine Convention Patient Rights

states: ‘‘Anintervention inthe healthﬁeld mayonly be carried

out after the person concerned has given free and informed

consent to it. The person shall beforehand be given appro-

priate information as to the purpose and nature of the inter-

vention as well as on its consequences and risks. The person

concerned may freely withdraw consent at any time’’.

F. Coccia

Birmingham and Solihull Mental Health

NHS Foundation Trust, The Barberry, 25 Vincent Drive,

Edgbaston, Birmingham B15 2FG, UK

J. S. Freedman (&)

Heart of England NHS Foundation Trust,

Heartlands Hospital, Bordesley Green East,

Birmingham, B9 5SS, UK

e-mail: jonathan.freedman@heartofengland.nhs.uk

M. G. Cowling (ed.), Vascular Interventional Radiology, Medical Radiology. Diagnostic Imaging,

DOI: 10.1007/174_2011_531,  Springer-Verlag Berlin Heidelberg 2012

https://t.me/med1917

It is therefore a legal requirement that consent be

obtained from a patient before any medical care can be

provided, with the exception of emergencies where consent

cannot be obtained. In these situations Article 8 of the

European Convention dictates. ‘‘When, because of an

emergency situation, the appropriate consent cannot be

obtained, any medically necessary intervention may be car-

ried out immediately for the beneﬁt of the health of the

individual concerned’’.

For consent to be valid the patient must have information

regarding the treatment concerned, must be competent to

give consent and the consent must be voluntarily given.

Consent should be given in a timely manner to allow the

patient to make an informed decision about the treatment or

procedure being offered to them. The three components of

consent: voluntariness, information and capacity will be

discussed later on in this chapter.

2.1 Implied and Express Consent

2.1.1 Implied Consent

When patients attend for low risk procedures consent is

often implied and has been taken by the referring clinician

on behalf of the reporting clinician prior to the patient

arriving in the radiology department. For example a patient

with suspected pneumonia attends for a chest radiograph

after his physician has discussed the need for additional

investigation. As this investigation is part of the examina-

tion process, no additional consent is usually required,

although the radiographer may take verbal conﬁrmation

(Royal College of Radiologists 2005).

2.1.2 Express Consent

Where a more complex procedure is involved express

consent is required. It may be appropriate for this to take the

form of verbal consent, as long as the discussion and

granting of consent are documented in the patient notes. An

example may be a patient attending for a peripherally

inserted central catheter or nephrostogram (Royal College

of Radiologists 2005).

The General Medical Council of the United Kingdom

(GMC 2008) requires written consent to be obtained in the

following circumstances:

• The investigation or treatment is complex or involves

signiﬁcant risks

• There may be signiﬁcant consequences for the patient’s

employment, social or personal life

• Providing clinical care is not the primary purpose of the

investigation or treatment

• The treatment is part of a research programme or is an

innovative treatment designed speciﬁcally fortheirbeneﬁt.

2.2 Voluntariness of Consent

To be valid, consent should be given freely without undue

inﬂuence to either accept or refuse treatment. Patients may

be under pressure to consent to medical care from relatives,

carers or employers. Doctors themselves may exert undue

pressure on patients especially if the patient’s wishes do not

agree with the views of the doctor. There is anecdotal

evidence to suggest that clinicians are more likely to

question a patient’s capacity to consent if the patient

declines the medical treatment being offered. Doctors

should be aware of pressures being exerted on the patient

and should consider taking consent from the patient alone.

2.3 Information to be Provided

There is no clear guidance from the Biomedicine Conven-

tion on what information should be provided to a patient

before they undergo any procedure. The GMC recommends

the following information be provided to the patient

(GMC 2008):

• The diagnosis and prognosis

• Options for treating or managing the condition, including

the option not to treat

• The purpose of any proposed investigation or treatment

and what it will involve

• The potential beneﬁts, risks and burdens, and the likeli-

hood of success, for each option; this should include

information, if available, about whether the beneﬁts or

risks are affected by which organisation or doctor is

chosen to provide care

• Whether a proposed investigation or treatment is part of a

research programme or is an innovative treatment

designed speciﬁcally for their beneﬁt

• The people who will be mainly responsible for and

involved in their care, what their roles are, and to what

extent students may be involved

• Their right to refuse to take part in teaching or research

• Their right to seek a second opinion

• Any bills they will have to pay

• Any conﬂicts of interest that you, or your organisation,

may have

• Any treatments that you believe have greater potential

beneﬁt for the patient than those you or your organisation

can offer.

The GMC advises that doctors discuss these matters with

patients, encourage them to ask questions, listen to their

concerns and ask for and respect their views.

Explanatory literature should be clear and concise and

designed for patients (Royal College of Radiologists

2005). Many radiologists make use of patient information

20 F. Coccia and J. S. Freedman

https://t.me/med1917

booklets compiled by professional societies such as The

Cardiovascular and Interventional Radiological Society of

Europe (CIRSE) or British Society of Interventional

Radiology (BSIR), which go some way to provide stand-

ardised complication rates for common procedures. The

RCR has also developed a number of template information

pamphlets for common IR procedures.

3 Capacity to Consent

Not all European countries have legislation regarding

capacity, so English law will be used to guide readers

through the process. The Mental Capacity Act 2005 of

England is underpinned by ﬁve statutory principles:

• All persons are assumed to have capacity unless the

contrary is demonstrated

• All practicable steps must be taken to assist the person in

making a decision

• The person should not be considered to lack capacity if

they choose to make an unwise decision

• Any decision made or act done under the legislation on

behalf of a person lacking capacity should be in that

person’s best interests

• Any act done or decision made should be the least

restrictive possible that would ensure a good outcome.

Together with the GMC guidelines the Mental Capacity

Act emphasises the need for doctors to assume that patients

have the capacity to accept or decline a treatment or

intervention, unless it can be demonstrated that the person

in question lacks capacity.

3.1 Assessing Capacity

It is important to remember that a person does not have or

lack capacity in general. Capacity assessments should

establish whether the person in question has capacity to

make a speciﬁc decision at a speciﬁc time. Someone may

have the capacity to agree to be washed on the ward, but not

to angiography, as the process of the latter is more complex

and risky and involves greater mental processing abilities.

In order to ascertain if a patient has the capacity to consent

the following areas should be explored (Medical Protection

Society 2011):

• Does the person have a general understanding of what

decision they need to make and why they need to make

it?

• Does the person have a general understanding of the

likely consequences of making or not making this

decision?

• Is the person able to understand, retain, use and weigh up

the information relevant to this decision?

• Can the person communicate their decision (by talking,

using sign language or other means)?

• Would the services of a professional (such as a speech

and language therapist) be helpful?

• And in more complex or serious decisions: Is there a need

for a more thorough assessment (perhaps by involving

another professional expert)?

Capacity to consent is best established by the clinician

offering the proposed intervention, as they will have sufﬁ-

cient knowledge of the risks and beneﬁts involved. For

more complex procedures or where there is an underlying

illness contributing to difﬁculties in reasoning (e.g.

dementia) it may be of beneﬁt to work in collaboration with

expert colleagues (e.g. psychiatrists).

3.2 Supporting Patients to Make Decisions

Before a patient can be deemed lacking capacity to make a

decision, all practicable steps should be taken to support the

person in question to make the decision. Using interpreters,

family members or speech and language therapists may be

of assistance. It should also be considered whether the

treatment offered can safely be delayed in order to allow the

patient to regain capacity to make the decision.

Case 1

Mr. Johnson is a 75-year-old man with vascular

dementia and a non-healing ulcer on his left ankle.

Doppler ultrasound showed a short superﬁcial femoral

artery occlusion amenable to angioplasty. Dr Khum-

alo meets Mr. Johnson on the ward to take consent for

the procedure. He provides the information using a

patient information leaﬂet which includes simple

images. He allows Mr. Johnson to ask questions and

notes that the patient repeatedly asks the same ques-

tions about the purpose of the procedure. Dr Khumalo

concludes that Mr. Johnson is not able to retain the

information provided and therefore does not have the

capacity to consent to angioplasty.

Case 2

Mr. O’Sullivan is a 70-year-old man with peripheral

vascular disease. He presents to the emergency

department with confusion, from his residential home,

where he is independent but needs assistance with

personal care. The staff have reported that his toes

have become black over the past few weeks. On

clinical examination he is found to have a lobar

pneumonia, conﬁrmed on a chest radiograph, and dry

Consent in Interventional Radiology 21

https://t.me/med1917

3.3 Patients Refusing Treatment

Doctors may be faced with patients who choose not to

accept the treatment offered to them. Patients have the right

to make unwise decisions even when turning down treat-

ment may lead to their deaths. (M

S B V AN NHS Hospital

Trust 2002). In these cases the discussion with the patient

and the assessment of capacity must be clearly documented

in the patient’s notes. If the patient later loses the capacity

to make the same decision, the clinician cannot then per-

form the procedure in the patient’s best interests. This

would be a breach of Article 9 of the Biomedicine Con-

vention which stated ‘‘The previously expressed wishes

relating to a medical intervention by a patient who is not, at

the time of the intervention, in a state to express his of her

wishes shall be taken into account’’. Where a patient refuses

consent, this should be clearly and contemporaneously

recorded in the patient’s notes, preferably witnessed by a

third party (Royal College of Radiologists 2005).

3.4 Proxy Decision Makers

When patients do not have the capacity to decide on a

medical treatment offered to them, the treating clinician

may lawfully treat the patient in their best interests. In order

to do so, clinicians should consider the previously expressed

views of the patient, encourage participation of the patient

as far as possible and consult as may other people as pos-

sible: relatives, carers, other clinicians and professionals

involved in providing care.

Prior to acting in the patient’s bests interests clinicians

should establish if a proxy decision maker has been

appointed. Under English law people may designate a

Lasting Power of Attorney (LPA) for welfare as well as

ﬁnancial decisions. Should an LPA have been appointed

then any care intended for the person should be agreed by

the LPA. Clinicians are directed to the Mental Capacity Act

Code of Practice for details on the roles of LPAs. Seeking

legal advice from employment lawyers or protection soci-

eties is recommended if clinicians are unclear about how to

proceed.

gangrene of three toes on his right foot. The surgical

team has requested an angiogram prior to amputation.

Dr Patel sees Mr. O’Sullivan on the ward to take

consent and concludes that in his current state of

confusion the patient is unable to consent to angiog-

raphy. After discussion with the residential home

staff, the respiratory physician and the surgeon, the

team agree to delay the angiography until the proba-

ble cause of delirium, the pneumonia, has been trea-

ted. The team hopes that Mr. O’Sullivan will regain

his capacity to make an informed decision.

Case 3

Mrs. Meyer is 53 years old and has advanced endo-

metrial carcinoma. She undergoes a post-chemother-

apy restaging CT scan that shows no response in the

primary tumour and identiﬁes bilateral hydroneph-

roses. The urology consultant requests urgent bilateral

nephrostomies to preserve Mrs. Meyer’s renal func-

tion. Dr Broia meets with Mrs. Meyer to take consent.

He provides the information using a patient infor-

mation pamphlet and allows Mrs. Meyer to ask

questions. She asks what the outcome will be if she

does not undergo the procedure. He advises her that

she is likely to die of renal failure which may be

sooner than if nephrostomies were in place. Mrs.

Meyer is able to have an in-depth discussion with

Dr Broia regarding the risks and beneﬁts of the pro-

cedure and is clearly able to weigh up the information

provided. She tells Dr Broia that she does not wish to

undergo the procedure. Dr Broia asks the urology

consultant to conﬁrm this decision with her and they

document their discussions in the clinical notes. Mrs.

Meyer is discharged from hospital to a hospice under

the care of her gynaecology oncologist.

Case 4

Mr. Larsen is 52-year-old man with a 15-year history

of Huntington’s Disease. He is admitted from his

home with signiﬁcant weight loss due to poor swal-

lowing. The neurologist requests that a radiologically

inserted gastrostomy (RIG) be performed. Dr Dudas

goes to see Mr. Larsen on the ward. While discussing

the procedure with him, Dr Dudas notices the

Mr. Larsen gives inconsistent responses to the ques-

tions she asks him. She uses the diagrams in the rel-

evant patient information pamphlet, but there is little

improvement. She concludes that Mr. Larsen is

unable to process the information provided to him

reliably and therefore lacks capacity to consent to the

procedure. Dr Dudas discusses the matter with the

neurologists who feel that Mr. Larsen’s quality of life

22 F. Coccia and J. S. Freedman

https://t.me/med1917

3.5 Considering Options Available

When clinicians are required to provide care for an indi-

vidual who lacks capacity to consent to a particular proce-

dure, they should do so in the least restrictive manner

possible. To do otherwise would be a breech of Article 5 of

the European Convention on Human Rights.

4 Practicalities

4.1 Who Should Take Consent?

Ideally the person providing care should be taken consent

from the person for the procedure. This may not always be

possible and can be delegated to another person, not nec-

essarily a clinician of the same profession. This requires the

delegated individual to have sufﬁcient knowledge of the

procedure and that the clinician performing the procedure

be satisﬁed that consent has been appropriately taken.

(Medical Protection Society 2011). The ﬁnal conﬁrmation

of consent, done at the time of the procedure, remains the

responsibility of the doctor performing the procedure

(Royal College of Radiologists 2005).

4.2 When Should Consent be Taken?

For non-urgent procedures consent should be taken at least

24 h prior to the procedure (O’Dwyer et al. 2003) to allow

the patient to consider the options available to them and

change their minds if they wish to. There is no speciﬁc time

limit on capacity as long as the information provided to the

patient has not changed with the passage of time. Where

there is a delay between the initial giving of consent and the

procedure itself, the patient must conﬁrm their continued

consent.

4.3 Where Should Consent be Taken?

It is widely considered good practice to take consent prior to

the patient entering the operating room. Otherwise the

patient’s voluntariness may be impaired and consent

becomes invalid. Ideally the environment should be quiet

and private with sufﬁcient time allowed for the patient to

understand the information provided and to ask questions of

the clinician.

5 Withdrawing Consent

Between taking consent and conﬁrming it, the patient may

change their mind and decline to give consent at the time of

the procedure. The doctor should explore the patient’s

decision without being coercive and provide any support or

information that the patient requires. This discussion and

the withdrawal of consent should be clearly documented in

the patient’s notes. Patients may occasionally withdraw

consent during a procedure. If asked to stop the doctor

will be improved if the RIG is inserted and it is

therefore in his best interests. Given his condition,

Mr. Larsen is unlikely to regain his capacity.

Dr Dudas speaks to Mr. Larsen’s daughter and

establishes that there is no proxy decision maker, but

that many years ago Mr. Larsen told his General

Practitioner that he would in the future consider ent-

eral feeding. Dr Dudas contacts the GP who conﬁrms

that this conversation was documented in the clinical

notes. Dr Dudas then agrees to perform the procedure.

Case 5

Miss Kirros is a 40-year-old woman with Down’s

syndrome who is referred to the gynaecology outpa-

tients department with menorrhagia. She has in the

last six months required transfusion as a result of her

bleeding. MRI shows a multi-ﬁbroid uterus with a

dominant ﬁbroid of 10 cm in diameter. The gynae-

cologist offers her a hysterectomy and as part of the

consent procedure makes her aware of uterine ﬁbroid

embolisation. Miss Kirros’ mother brings her daugh-

ter to consult Dr Millet about embolisation. During

the discussion with Miss Kirros, Dr Millet notices that

she is struggling to compare the beneﬁts and risks of

each of the treatment options available. Dr Millet

concludes that Miss Kirros does not have the capacity

to make the decision. He establishes that Miss Kirros’

mother is not legally a proxy decision maker. He

explains that reducing the menorrhagia would

improve Miss Kirros’ quality of life and that it is

therefore in her best interest to treat her. He explains

to Miss Kirros’ mother that a hysterectomy would be

a deﬁnitive treatment, but would require lengthy

surgery and longer recovery time. In discussion with

the patient’s mother and the gynaecologist, Dr Millet

agrees that while the response to UAE may be vari-

able, it is less restrictive than hysterectomy and

should be attempted ﬁrst.

Consent in Interventional Radiology 23

https://t.me/med1917

should immediately stop the procedure (even temporarily)

and ﬁnd out the concerns of the patient. The doctor should

take into consideration that medication or pain may affect

the patient’s capacity to make this decision. However, if the

patient wishes the procedure to end their wishes should be

respected unless the patient is likely to come to immediate

harm. (Royal College of Radiologists 2005).

6 Special Circumstances

6.1 Consent in Children

Doctors should assess the competence of children to give

consent to a procedure. Children should be able to under-

stand the nature of the procedure. Children under 16 (in

England) may refuse a treatment, but parental responsibility

(or a court) may authorise a procedure in the child’s best

interests. This differs in Scotland and may in other parts of

Europe, so it is advisable to seek legal advice.

6.2 Consent to Research

Consent to participate in research should always be taken in

writing. Information should cover all the following aspects

of the research (Department of Health 2009):

• The nature, extent and duration of the procedures

involved, in particular, details of any burden imposed by

the research project

• The available preventive, diagnostic and therapeutic

procedures

• The arrangements for responding to adverse events or the

concerns of research participants

• The arrangements to ensure respect for private life and

ensure the conﬁdentiality of personal data

• The arrangements for access to information relevant to the

participant arising fromthe research andto its overall results

• The arrangements for fair compensation in the case of

damage

• Any foreseen potential further uses, including commer-

cial uses, of the research results, data or biological

materials

• The source of funding of the research project.

6.3 Criminal Justice and Mental Health

Legislation

Patients who are in detained by the Police, Criminal Justice

systems and Immigration Authorities and those detained

under Mental Health legislation may be particularly vul-

nerable to coercion. Doctors should ensure that patients

understand their rights to refuse or withdraw consent.

Patients who are detained under Mental Health legislation

can be given compulsory treatment for their mental illness

but not physical illness. Where mentally ill people also lack

capacity to consent to interventions, the advice above

should be followed.

7 Conclusion

It is the responsibility of the clinician to empower his patients

in the decision-making process when taking consent for

IR procedures. In order to ensure this, consent should be

voluntary and based on adequate information provided in a

suitable environment. Patients should know that they can

withdraw their consent at any time. There is recent evidence

that clinicians frequently overestimate the capacity of

patients, especially those of advanced age and the acutely

unwell. This has the potential to lead to poor outcomes for

and inadequate protection of patients (Lepping 2011).

Although not formally legislated in all countries, the

assessment of capacity and process of consent are under-

pinned by the Convention on Human Rights and Biomedi-

cine. The English Mental Capacity Act, outlined above,

provides a helpful framework to guide clinicians through this

often-complex process.

References

The Board of the Faculty of Clinical Radiology (2005) The Royal

College of Radiologists standards for patient consent particular to

radiology. The Royal College of Radiologists, London

Convention for the protection of Human Rights and Dignity of the

Human Being with regard to the Application of Biology and

Medicine: Convention on Human Rights and Biomedicine (1997)

Oviedo 4. http://conventions.coe.int/Treaty/Commun/ListeTraites.

asp?CM=8&CL=ENG,Ets 164

Department of Health (2009) Reference guide to consent for exam-

ination or treatment (Department of Health)

General Medical Council, Consent: Patients and Doctors making

decisions together (June 2008)

Lepping p (2011) Overestimating Patients’ Capacity. Bri J Psychiatry

199:355–356

Medical Protection Society (2011) Consent to Medical Treatment in

the UK. MPs

Mental Capacity Act 2005: Code of practice. www.publicguardian.

gov.uk/mca/code-of-practice.htm

Ms B v An NHS Hospital Trust (2002) 2 All ER 449

O’Dwyer HM, Lyon SM, Fotheringham T, Lee MJ (2003) Informed

consent for interventional radiology procedures: a survey detail-

ing current European practice. Cardiovasc Interv Radiol 26:

428–433

24 F. Coccia and J. S. Freedman

https://t.me/med1917

Drugs Used in Vascular Interventional Radiology

Gordon Dent and Mark G. Cowling

Contents

1 Introduction.......................................................................... 25

2 Drugs Used During Procedures ......................................... 26

2.1 Sedatives ................................................................................ 26

2.2 Local Anaesthetics................................................................. 26

2.3 Spasmolytics .......................................................................... 26

2.4 Antimuscarinics ..................................................................... 27

2.5 Anticoagulants, Antiplatelet Drugs and Fibrinolytics .......... 27

2.6 Contrast Media ...................................................................... 29

3 Drugs Used in Management of Patients Before

and After Procedures .......................................................... 29

3.1 Oral Anticoagulants ............................................................... 29

3.2 Oral Hypoglycaemics ............................................................ 30

3.3 Insulin .................................................................................... 30

3.4 Statins..................................................................................... 30

3.5 Antihypertensives .................................................................. 31

4 Conclusion ............................................................................ 31

References...................................................................................... 31

Abstract

With the growing complexity of vascular interventional

radiology, a larger array of drug treatments is employed

by practitioners undertaking these procedures. Further-

more, patients attending for treatment are likely to be on

combinations of drugs which may interact with medica-

tions employed during endovascular procedures. This

chapter describes the mechanisms of action of drugs

commonly used in this patient group and illustrates the

likely interactions that may be encountered during

endovascular procedures.

1 Introduction

Interventional radiologists use a variety of drugs during

vascular procedures. Equally signiﬁcantly, patients under-

going procedures are likely to be taking medication for the

conditions that indicate vascular intervention. It is impor-

tant, therefore, for the vascular interventional radiologist to

be aware of the actions of the drugs she/he uses, their

anticipated effects during and after the procedure, and the

possibility of interactions with the patient’s other medica-

tions. The interventionist should also consider the actions of

concurrent medications and their possible effects on the

procedure as well as on the patient’s reactions to drugs used

during intervention.

Vascular disease is most commonly associated with

atherosclerosis—itself associated with hypercholesterola-

emia—and concomitant intravascular coagulation. Conse-

quently, many patients are receiving treatment with drugs to

reduce plasma low-density lipoprotein (LDL) and triglyc-

eride levels, and to inhibit blood clotting. Many patients

will have additional cardiovascular conditions, such as

hypertension or arrhythmia, and may be taking several

medications to manage these. The vascular risks associated

with these conditions are exacerbated by diabetes mellitus,

G. Dent (&)

Institute of Science and Technology in Medicine,

Keele University, Keele, Staffordshire ST5 5BG, UK

e-mail: g.dent@hfac.keele.ac.uk

M. G. Cowling

University Hospital of North Staffordshire,

Newcastle Road, Stoke-on-Trent,

Staffordshire ST4 6QG, UK

M. G. Cowling (ed.), Vascular Interventional Radiology, Medical Radiology. Diagnostic Imaging,

DOI: 10.1007/174_2012_610, Ó Springer-Verlag Berlin Heidelberg 2012

https://t.me/med1917

which means that a large proportion of patients undergoing

interventions will also be receiving treatment for diabetes.

Contrast agents are used in many interventional proce-

dures. While these are not generally considered to have

pharmacological actions, they do have the potential to

interact with other medications. Finally, as invasive proce-

dures, vascular radiological interventions are sometimes

indications for sedation; the actions of the drugs used and

their potential interactions must be considered.

2 Drugs Used During Procedures

2.1 Sedatives

Where sedation is required a benzodiazepine, such as

midazolam, will be used. Benzodiazepines suppress anxiety

and reduce alertness, while having the additional beneﬁt of

producing anterograde amnesia which reduces the patient’s

subsequent recall of the procedure. These effects are med-

iated by an action on the GABA

receptor for the inhibitory

central nervous system neurotransmitter, c-aminobutyric

acid (GABA). The GABA

receptor is a typical ionotropic

receptor, with ﬁve protein subunits arranged around a cen-

tral pore which forms a ligand-gated chloride channel.

Binding of GABA to the a/b subunits of the receptor pro-

duce a conformational change that increases Cl

inﬂux,

leading to hyperpolarization of the neurone and reduced

neural activity. Binding of benzodiazepines to the c subunit

increases the frequency of channel opening in response to

GABA, thereby potentiating the neurotransmitter’s inhibi-

tory actions (Olkolla and Ahonen 2008).

Midazolam is an ultra short-acting drug, with a plasma

half-life (t



) of less than 4 h and a typical duration of action

of less than 6 h. It can produce sufﬁcient CNS inhibition to

allow invasive procedures—including endoscopy and

angioplasty—without full general anaesthesia. Benzodi-

azepines carry a signiﬁcantly lower risk of respiratory

depression than general anaesthetics; although this can be

increased in the presence of other drugs (see below). In the

event of respiratory depression arising, the effects of ben-

zodiazepines may be reversed rapidly by the intravenous

administration of the antagonist, ﬂumazenil (Smith 2010).

Where more profound sedation or additional analgesia is

required, opioidssuchas fentanylmay beused. Opioidsact by

mimicking the actions of endogenous opioid peptides (Met/

Leu-enkephalin, b-endorphin and dynorphin) on speciﬁc G

protein-coupled receptors classiﬁed as l (MOR), d (DOR)

and j (KOR) opioid receptors. Actions on MOR mediate

analgesia at a brain level, by activating descending pathways

that inhibit pain signal transmission in the dorsal root of the

spinal cord, while actions on MOR, DOR and KOR mediate

analgesia at a spinal level by directly suppressing neural

transmission between primary afferent nociceptive neurones

and spinothalamic neurones. MOR agonists additionally

produce euphoria and relief of anxiety through adisinhibition

of GABA release from inhibitory neurones throughout the

brain (Schlicker and Kathmann 2008).

In common with other CNS depressants, fentanyl pro-

duces respiratory depression which becomes life-threaten-

ing in overdose. Owing to the overlap of their mechanisms

of action, opioids and benzodiazepines interact to produce

additive or synergistic brainstem inhibition, potentially

leading to respiratory failure. Caution must be exercised

when using these drugs in combination, with ﬂumazenil

and/or the opioid receptor antagonist naloxone available for

rescue (Smith 2010). The use of opioids such as morphine

and pethidine for postprocedure pain relief—e.g. after an

embolisation procedure—requires similar caution. Such

systemic analgesia is rarely required during routine vascular

procedures. In addition signiﬁcant impairment of con-

sciousness can be a signiﬁcant disadvantage. For example,

it can make it more difﬁcult for patients to cooperate with

suspending respiration during angiographic runs. In addi-

tion, opioid analgesia may mask the pain caused by

impending vessel rupture during angioplasty.

2.2 Local Anaesthetics

Percutaneous procedures are usually performed with surface

or inﬁltration anaesthesia of the access site, with intrader-

mal injection of lidocaine the recommended procedure for

arterial puncture (Hudson et al. 2006). Lidocaine and other

local anaesthetics produce use-dependent blockade of axo-

nal sodium channels (i.e. they produce greater blockade of

channels in rapidly ﬁring neurones), thereby inhibiting

propagation of impulses. They selectively affect ﬁne and

unmyelinated axons, with nociceptive sensory ﬁbres and

postganglionic sympathetic ﬁbres exhibiting greater sensi-

tivity than broader somatosensory and mechanoceptive

ﬁbres and myelinated motor ﬁbres.

The use dependence oflidocaine, which involves selective

binding to Na

channels in their refractory state, may also

affect cardiac rhythm when the drugs are administered sys-

temically (Weirich and Antoni 1998). While this action has a

therapeutic application in arrhythmias, there is potential for

lidocaine to interact with other cardioactive drugs. Given the

very low total doses administered for cutaneous anaesthesia,

however, this is unlikely to present a signiﬁcant risk.

2.3 Spasmolytics

In procedures involving renal artery or ﬁstula interventions,

as well as below knee vascular procedures on patients with

26 G. Dent and M. G. Cowling

https://t.me/med1917

intermittent claudication, administration of spasmolytic

drugs may be indicated. Relaxation of vascular smooth

muscle may be achieved using intra-arterial nitrates—typ-

ically glyceryl trinitrate or isosorbide dinitrate—or a-adre-

noceptor antagonists such as doxazosin.

Organic nitrates act as nitric oxide (NO) donors, mim-

icking the vasodilatory actions of endothelium-derived NO.

NO activates a soluble guanylyl cyclase enzyme in vascular

myocytes, stimulating the production of guanosine 3

-cyclic monophosphate (cyclic GMP) from guanosine

triphosphate (GTP). Cyclic GMP activates intracellular

effectors, such as cyclic nucleotide-dependent protein

kinases, to reduce the availability of cytosolic calcium ions,

which are required for contraction mechanisms (Coggins

and Bloch 2007).

a-Blockers antagonise the action of noradrenaline and

adrenaline on a-adrenoceptors on vascular smooth muscle

cells, thereby reducing sympathetically mediated vascular

tone. Under normal physiological conditions, sympathetic

tone in resistance arteries of skin and visceral organs is

balanced by the vasodilator action of parasympathetically

and shear stress-mediated NO release from the endothelium.

In the presence of a-blockers the muscle tone is reduced,

leading to dilation of the vessels. Smooth muscle tone in

vessels supplying the skeletal muscles, myocardium and

brain is not dependent upon sympathetic innervation:

patency of these vessels is regulated principally by local

metabolites, such as thromboxane A

, lactate and adeno-

sine, with circulating adrenaline having a b

adrenoceptor-

mediated vasodilator action on skeletal muscle vessels.

a-Blockers therefore have no effect on these vessels

(Duncker and Bache 2008).

Spasmolytics, by the nature of their mechanism of

action, produce hypotension. Organic nitrates associate with

the vascular endothelium and liberate short-lived NO,

which limits both the extent of their distribution and the

duration of their action. They are also extensively metab-

olised on ﬁrst pass through the liver. Their systemic effects

are therefore less marked than those of a-blockers. How-

ever, they frequently cause headaches, which may be

severe, and can produce postural hypotension. a-Blockers

commonly cause postural hypotension and may also pro-

duce ankle oedema due to increased blood ﬂow into capil-

lary beds in the lower legs. They also exacerbate urinary

incontinence through dilation of the prostatic urethra.

2.4 Antimuscarinics

Percutaneous coronary angioplasty and subsequent proce-

dures, in particular femoral arterial sheath removal, may

evoke excessive vagal tone, evident as bradycardia, miosis

and salivation (Mager et al. 1994). Bradycardia presents

a clinical problem, commonly leading to syncope. The

excessive vagal activity may be controlled acutely by

intravenous administration of glycopyrrolate (glycopyrro-

nium), an antagonist of muscarinic acetylcholine receptors.

Glycopyrrolate does not exhibit major interactions with any

other drugs covered in this chapter, although its inhibition

of salivation may impair the absorption of sublingual nitrate

vasodilators.

2.5 Anticoagulants, Antiplatelet Drugs

and Fibrinolytics

The insertion of foreign objects, such as sheaths and

angiographic catheters, into blood vessels naturally pro-

vides a trigger for blood clotting, as well as presenting a risk

of atheromatous plaque rupture (Rao and Ohman 2010).

Although materials have been developed to reduce the

thrombogenicity of vascular catheters, if a cannula remains

in the circulation for signiﬁcant periods the risk of clotting

and formation of pericatheter thrombus must be addressed.

Additionally, patients may already have intravascular clots

and may have heightened risk of clot formation, making the

issue of anticoagulation particularly important.

Intravascular (usually intra-arterial although it may be

administered intravenously) heparin is routinely adminis-

tered to patients undergoing vascular interventions. Heparin

is a sulphated glycosaminoglycan derived from mast cells.

It is a highly anionic molecule, which confers an afﬁnity for

positively charged surfaces. Heparin associates with the

endothelial cell surface, where it exerts its anticoagulant

action by forming a complex with a circulating liver-derived

serine protease inhibitor (serpin), antithrombin

III (ATIII).

Heparin in the complex binds positively charged domains on

thrombin and activated factor X (Fig. 1a), whose activity is

then neutralised by AT

III (Chang et al. 1996).

In common with other anticoagulants, heparin carries

a risk of haemorrhage and bruising that is increased in

patients with thrombocytopaenia or severe renal impair-

ment. Peptic ulcer disease presents a particular risk of GI

bleeding following heparin treatment, while hepatic

impairment presents complications that require expert

assessment prior to its use. Excessive anticoagulation may

be corrected with protamine sulphate, a strongly cationic

protein that forms an inactive complex with heparin (Lemon

and Crannage 2011).

In addition to receiving heparin during the procedure,

patients with cardiovascular disease should also be taking

oral aspirin. Interventionists may also request patients to

take additional oral antiplatelet drugs for 3 days prior to

their appointment and for several days afterwards to reduce

the risk of intravascular coagulation. The most commonly

used drug for this purpose is clopidogrel.

Drugs Used in Vascular Interventional Radiology 27

https://t.me/med1917

Aspirin is an irreversible inhibitor of cyclooxygenase

enzymes. Cyclooxygenase catalyses the oxygenation of cell

membrane-derived arachidonic acid to form a cyclic

endoperoxide (prostaglandin H

), which is, in turn, con-

verted by a variety of synthase enzymes to the biologically

active molecules prostaglandin D

(PGD

), prostaglandin

(PGE

), thromboxane A

(TXA

) and prostacyclin

(PGI

). At high doses, aspirin signiﬁcantly inhibits forma-

tion of all of these products. At lower doses, however,

aspirin produces a selective reduction in the formation

of TXA

(Fig. 1c). This occurs because thromboxane

A synthase is principally expressed in platelets (Vitrat et al.

2000), while the other synthases are expressed in nucleated

cells with functioning protein synthesis. Consequently,

irreversible inhibition of the enzyme leads to an extensive

loss of TXA

production in platelets while prostaglandin

and prostacyclin production in nucleated cells is rapidly

restored by de novo synthesis of active synthase enzyme.

TXA

is produced by activated platelets and acts in an

autocrine/paracrine fashion to cause platelet aggregation,

which is a crucial component of blood clotting. Inhibition

of TXA

synthesis by aspirin and other non-steroidal

Fig. 1 Mechanisms of action of anticoagulants and antiplatelet drugs.

a Heparin and low molecular-weight heparins (LMWH) bind to

endothelium and recruit antithrombin

III (ATIII). ATIII binds and

inactivates activated factor X (Xa), while the heparin/AT

III complex

also binds and inactivates thrombin (IIa). Dabigatran directly inhibits

the conversion of ﬁbrinogen to ﬁbrin by thrombin; rivaroxaban

directly inhibits the conversion of prothrombin to thrombin by factor

Xa. b Warfarin inhibits hepatocyte vitamin K reductase, preventing

the post-translational c-carboxylation of factors II (prothrombin), VII

(tissue factor), IX and X, thereby making them unable to form enzyme

complexes on the surface of activated platelets. c Thrombin activates

platelets via an action on a protease-activated receptor (PAR), leading

to synthesis of adenosine diphosphate (ADP) and thromboxane

(TXA

), which act on P

and TP receptors, respectively, to

stimulate platelet aggregation. Clopidogrel antagonizes the action of

ADP at P

receptors while aspirin blocks the synthesis of TXA

inhibiting cyclooxygenase. Dabigatran inhibits the action of thrombin

on PAR. AA arachidonic acid, ATP adenosine triphosphate

28 G. Dent and M. G. Cowling

https://t.me/med1917

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