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| Dr Charles Knight trained
at Cambridge and Oxford
Universities and is currently a
consultant cardiologist at the
London Chest Hospital.
Dr Knight has a particular
interest in chest pain, acute
coronary syndromes and
hypertrophic cardiomyopathy.
He specialises in coronary
angioplasty and stenting and
has considerable experience in
interventional cardiology and
in the renal complications of
coronary artery disease and its
treatment. Dr Knight is Head
of Cardiology at Barts and
the London NHS trust. He is
Honorary Secretary Elect of the
British Cardiovascular Society
and serves as a specialist
advisor to NICE. |
Fasting and cardiac catheterisation -
should we be following the evidence?
James Rosengarten,
Muhiddin Ozkor, Charles Knight
Department of Cardiology, Barts and The London
NHS Trust, London, UK
Address for correspondence:
Dr Charles Knight
Department of Cardiology,
London Chest Hospital,
Bonner Road, London E2 9JX, UK
Tel: +44-(0)20-8983-2248 Fax: +44-(0)20-8983-2278
Email: charles.knight@bartsandthelondon.nhs.uk
Abstract
It is usual for food and fluids to be withheld for
variable periods before cardiac catheterisation. Fasting
is considered necessary to reduce the risk of aspiration
in the case of emergency surgery or cardiac arrest.
The risks involved are low compared with the greater
risk of complications associated with dehydration,
hypoglycaemia and omission of medication. Existing
guidelines do not give clear direction and are not
evidence based. We propose a less stringent approach
with unlimited clear fluids allowed until the time of the
procedure.
Introduction
Cardiac catheterisation can be a worrying experience
for a patient and the typical requirement to fast for
a variable period of time may increase the stress.
Patients often err on the side of caution and may
arrive at the hospital having fasted from midnight and
failed to take antihypertensive medication, in case this
constitutes food.(Ref: 1) By the time the patient reaches the
catheterisation laboratory, it may be 12 hours since
they last ate and perhaps 6 hours without any fluid
intake other than sips of water at best. Consequently,
the patient is likely to be dehydrated and possibly
hypoglycaemic. This may make arterial access more
difficult and increase the risk of contrast-induced
nephropathy (volume depletion is an important
predictor of CIN); in addition, uncontrolled hypertension
may lead to problems in removing the sheath.
We feel that there is little evidence to support the
current system and that a more radical approach should
be taken.
Historical perspective
Cardiac centres across the UK perform a variety of
diagnostic and interventional procedures every day, and
each hospital has a policy relating to pre-procedure
fasting for food and fluids. A period of fasting is
considered necessary before cardiac catheterisation
to minimise the volume of gastric contents in case
of emergency transfer for intubation and surgery or
unexpected cardiac arrest. It has been traditional in
the UK that surgical patients are 'nil by mouth from
midnight', and to some extent this surgical policy has
been adopted by cardiac laboratories.
Clinically significant pulmonary aspiration during general
anaesthesia is rare in healthy patients undergoing
surgery. In the largest study of over 200,000 anaesthetic
procedures, aspiration occurred in approximately one in 4,000 elective cases, increasing to one in 900 for
emergency procedures. Death from respiratory failure
occurred in three patients.(Ref: 2)
Historically, anaesthetic guidelines have differed.
Although the earliest books on anaesthesia did not
mention fasting, Lister recommended in 1883 that there
should be no solid matter in the stomach, although
patients should drink clear liquid until about 2 hours
before surgery.(Ref: 3) Most textbooks recommend a 6-hour
fast for solids and 2-3 hours for clear liquids. During
the 1960s, early studies in gastric physiology led to
the preoperative order 'nil by mouth after midnight',
applying to both solids and liquids.
In 1974, Roberts and Shirley suggested that the
presence of 0.4 ml/kg (25 ml in adults) of gastric
contents with pH <2.5 was associated with a high
risk of pulmonary aspiration. However, there was no
relationship between the volume in the stomach and
the volume aspirated into the lungs. The authors later
revealed that that they had drawn their conclusion
after instilling 0.4 ml/kg acid into the right mainstem
bronchus in only one experiment in a single monkey.(Ref: 4)
 |
| Figure 1. Gastric emptying varies with meal type. |
Modern physiological studies use a dual isotope
technique in which solids and liquids are tagged with
different radioactive isotopes. Figure 1 demonstrates
the exponential gastric emptying of clear liquids: 90%
empty within 1 and virtually all within 2 hours. Such
liquids do not contain particles >2 mm and therefore
pass immediately through the pylorus.(Ref: 5,6)
'Clear liquids' include water, apple juice, carbonated
beverages, clear tea and black coffee. Sugar and up to
10 ml (two teaspoons) of milk may be added to tea or
coffee. If any more milk is added, the effects of gastric
juice lead to the formation of a thick flocculate that is
treated as a solid and may remain in the stomach for
up to 5 hours. The pylorus prevents passage of particles
>2 mm, so digestible solids (bread, meat, boiled
potatoes) must be broken down to particles <2 mm
before they can pass into the small bowel. Total
emptying of the contents of the stomach after a meal
normally takes 3-5 hours. Large particles of indigestible
food, especially cellulose-containing vegetables, empty
by a different mechanism, taking 6-12 hours after the
stomach has emptied liquid and digestible food.(Ref: 5,6)
In 1983, Miller et al. reported no difference in gastric
fluid volume or pH between patients who received 'nil by
mouth after midnight' and those who had tea and toast
2-4 hours before surgery.(Ref: 7)
A Cochrane review of 38 randomised controlled
comparisons revealed there was no evidence to suggest
that a shorter fluid fast results in an increased risk of
aspiration, regurgitation or related morbidity compared
with the standard 'nil by mouth from midnight' fasting
policy. In fact, permitting patients to drink water
preoperatively resulted in significantly lower gastric
volumes.(Ref: 8)
Current practices
International
There is no mention of fasting before cardiac procedures
in either the latest joint American Heart Association/
American College of Cardiology or the European Society
of Cardiology guidelines.(Ref: 9,10)
UK
Current British Cardiovascular Intervention Society
guidelines do not mention pre-procedural fasting.(Ref: 11)
A telephone survey of UK angioplasty centres indicated
that all were aware of local fasting policies but that
these were not clearly evidence based. Results varied,
and Figure 2 highlights the heterogeneity.
Diagnostic angiography: With regard to food, 10% of
centres asked patients to fast for 1-4 hours, 59% for
4-6 hours, 12% for 6-8 hours and a further 12% for
8 or more hours; 6% did not require a food fast. For
fluids, 49% withheld fluids for 1-4 hours, 33% for
4-6 hours, 6% for 6-8 hours and 8% for 8 hours or
more; 12% required no fluid fast before diagnostic
procedures. The median duration of fasting before
angiography was 4 hours for food and 2 hours for fluids.
Percutaneous intervention: With regard to food, 10%
asked patients to fast for 1-4 hours, 60% for 4-6 hours,
12% for 6-8 hours, 14% for 8 hours or more and 4%
required no food fast. For fluids, 41% withheld fluids for
1-4 hours, 31% for 4-6 hours, 6% for 6-8 hours, 8% for
8 hours or more and 10% required no fluid fast before
percutaneous intervention. The median duration of
fasting before angioplasty was 4 hours for food and
3 hours for fluids.
Two centres had a 'no fasting' policy for either procedure.
One was able to cite (unpublished) audit data suggesting
that few cases needed emergency transfer to theatre and
that the time for transfer was over 2 hours. The other
centre had changed its policy recently but did not have
data to support the change, identifying problems of
dehydration and the apparent rarity of surgery as driving
forces. One other centre did not require fasting before diagnostic angiography but withheld food for 4 hours
and fluids for 2 hours before percutaneous intervention.
In addition, no relationship was seen between duration
of fasting and availability of cardiothoracic surgical
facilities or estimated time for transfer to emergency
surgery. Nor was there a relationship between duration
of fasting and the patient's place on the angiography list.
 |
| Figure 2. Fasting times for coronary intervention varied widely between centres. |
Aspiration and complications of cardiac catheterisation
Concerns relating to fasting become relevant in
situations when aspiration may occur. Recent data
suggest that emergency coronary artery bypass surgery
following complicated cardiac catheterisation is required
in between 0.15% and 0.4% of cases.(Ref: 12,13) The incidence
of cardiac arrest is less well documented but appears to
be under 1%.(Ref: 14)
In the cases of the ~1% of patients who experience
cardiac arrest or need emergency surgery, it is reassuring
to know that only approximately 4% of all emergency
(and therefore non-fasted) intubations outside of the
operating room show evidence of infiltrates suggestive of
pulmonary aspiration on chest radiography. In addition, only 0.11% demonstrate clinical aspiration requiring
respiratory support.(Ref: 2,15)
Therefore, the cumulative risk of complications of
aspiration associated with emergency surgery or DC
cardioversion in a non-fasted patient undergoing cardiac
catheterisation is in the order of 0.0015%, equivalent
to one case in 70,000. This is well below the 1:1000
risk typically quoted for myocardial infarction, stroke or
death in diagnostic angiography and the 1:100 risk in
percutaneous coronary intervention, and indeed below
the 14% risk of contrast-induced nephropathy.(Ref: 16)
Conclusion
We propose a less stringent approach to pre-procedure
fasting, according to which patients are not required to fast
before arriving at the cardiac unit and can drink water, fruit
juice and sweet, strong tea and coffee up to the time of
angiography. This would not only simplify the preadmission
procedure but also reduce the serious complication of
contrast-induced nephropathy, since volume depletion is
an important risk factor for this condition. Practical issues
surrounding medication, hypertension, hypoglycaemia and
associated complications would also be reduced.
Key Learning
• There is little evidence to support the current practice of withholding food and fluids for a variable period before
cardiac catheterisation
• Current US, European and UK guidelines do not specify pre-procedural fasting
• A telephone survey of UK centres showed that they have a fasting policy, but the duration varies widely
• The evidence suggests that the cumulative risk of complications of gastric aspiration is very low in a non-fasted
patient undergoing cardiac catheterization who needs emergency surgery or cardioversion
• A more relaxed policy is proposed according to which patients are allowed to eat until they arrive at the unit and to
drink clear fluids up to the time of the procedure |
References
1. Best C, et al. How 'nil by mouth' instructions impact on patient behaviour.
Nurs Times 2004;100:32-4.
2. Warner MA, et al. Clinical significance of pulmonary aspiration during the
perioperative period. Anesthesiology 1993;78:56-62.
3. Lister J. On anaesthetics. In: The collected papers of Joseph, Baron Lister, Vol 1.
Oxford: Claridon Press, 1909:172.
4. Roberts RB, et al. Reducing the risk of gastric aspiration during Cesarean
section. Anesth Analg 1974;53:859-68.
5. Minani H, et al. The physiology and pathophysiology of gastric emptying in
humans. Gastroenterology 1984;86:1592-610.
6. Collins PJ, et al. Gastric emptying in normal subjects - a reproducible
technique using a single scintillation camera and computer system. Gut
1983;24:1117-25.
7. Miller M, et al. Gastric contents at induction of anaesthesia. Is a 4-hour fast
necessary? Br J Anaesth 1983;55:1185-8.
8. Brady M, et al. Preoperative fasting for adults to prevent perioperative
complications. Cochrane Database of Systematic Reviews. Art. No.: CD004423.
DOI: 10.1002/14652858. CD004423.
9. ACC/AHA Guidelines for Percutaneous Coronary Intervention (revision of the
1993 PTCA Guidelines). J Am Coll Cardiol 2001;37:2239i-lxvi.
10. Dieker HJ, et al. ESC guidelines for percutaneous coronary interventions. Eur
Heart J 2005;26:804-47.
11. Dawkins KD, et al. Percutaneous coronary intervention: recommendations for
good practice and training. Heart 2005;91(Suppl 6):vi1-27.
12. Williams DO, et al. Percutaneous coronary intervention in the current era
compared with 1985-1986: The National Heart, Lung, and Blood Institute
Registries. Circulation 2000;102:2945-51.
13. Grayson AD, et al. Multivariate prediction of major adverse cardiac events after
9,914 percutaneous coronary interventions in the north west of England. Heart
2006;92:658-63.
14. Webb JG, et al. Incidence, correlates, and outcome of cardiac arrest associated
with percutaneous coronary intervention. Am J Cardiol 2002;90:1252-4.
15. Schwartz DE, et al. Death and other complications of airway management in
critically ill adults. Anesthesiology 1995;82:367-76.
16. McCullough PA, et al. Acute renal failure after coronary intervention: incidence,
risk factors, and relationship to mortality. Am J Med 1997;103:368-75. |
