Relationship between blood culture collection method and

Report
SCH Journal Club
Lucy Hinds
29th January 2013
Clinical case
• You are looking after a 28/40 baby on the neonatal unit.
After 3 days on CPAP, she develops apnoeas and
temperature instability.
• The consultant requests a partial
septic screen.
What is the best method of taking a sample
for blood culture to minimise the risk of
contamination?
Current practice
• No specific guideline
• Jessop Wing induction teaches:
– Clean skin with 2% chlorhexidine
– Use either venepuncture or insert a new cannula to take sample
of blood for culture
– Clean top of the culture bottle
– Change needle before inoculating the bottle
Structured clinical question
• Is there an ideal way to collect blood cultures from
neonates to prevent contamination?
PICO
Population
Neonates
requiring blood
sample for
culture
Interventio
n Sample
taken from
peripheral
cannula at time
of insertion
Compariso
n Sample
taken from
umbilical
catheter/
arterial or
venous stab
Outcome
Proportion of
contaminated
blood cultures
Why does it matter?
• Blood culture is diagnostic gold-standard for septicaemia
• Positive results difficult to interpret due to sample
contamination
• Exposes patients to unnecessary investigations and
treatments
• Increases health care costs
• Method of collection influences likelihood of
contamination
Relationship between blood culture
collection method and proportion of
contaminated cultures in neonates
McLaughlin, L. et al 2013
Journal of Paediatrics & Child Health
(doi:10.1111/jpc.12088)
Aims
• To determine whether the proportion of contaminated
cultures varies according to the method of blood
collection
Preferred
methods
Non-preferred
methods
• Arterial puncture
• Venous puncture
• Umbilical catheter at
time of insertion
• Peripheral arterial or
venous cannula at
time of insertion
Methods
• Prospective data collection over 12 month period (2010)
• All blood cultures taken in NICU/SCBU
Image removed for copyright reasons
• Proforma completed
• Medical record number
• Method of sample collection
– Missing proformas completed retrospectively
Results
• 1064 samples for
culture
Results
Results
•
Difference between proportion of cultures contaminated after
collection via peripheral arterial/venous puncture (11.5%) and
proportion collected via peripheral arterial/venous cannulae at time of
insertion (2.1%) was statistically significant (p=0.03)
Limitations
• Not specified whether culture taken for suspected earlyonset or late-onset sepsis
• Likelihood of positive culture may be greater in late-onset
than early onset septicaemia
• Inability to control for
•
•
•
•
Volume of blood collected
Number of skin breaks required
Adherence to aseptic technique
Level of experience of blood collector
• Potential bias
• Staff aware that study underway
GATE Frame
Participants
Intervention
Outcome
Participants
Eligible population
Source population
Present
Expert
opinion
Absent
Comparison
Comparison
Patient choice,
clinical
consideration
& policy
Using the GATE frame
Participants
Intervention
Outcome
1064
1064
1064
Present
Preferred method
275
(25.4%)
Non-preferred
method
694
(65.2%)
Unknown
96
(9%)
Comparison
Expert
opinion
Absent
4.1%
NO SIGNIFICANT
DIFFERENCE
2.4%
Significant
difference when
comparing
arterial/venous
puncture AND
peripheral
cannula at time
of insertion
Conclusion
• Blood cultures taken via peripheral cannula at
time of insertion are less likely to be
contaminated than cultures taken via separate
vascular puncture
Application
• Will the results of the study help locally?
• Apply specifically to neonatal population
• E.g. umbilical catheters
• Could be extrapolated to older children
• Highlights important issue
• Method of collection influences likelihood
of blood culture contamination
• NB – ‘preferred method’ not always best option!
Discussion
Local data
• Total SCH blood cultures received in 2012
• 3890
• Positive 369 (9.5%)
• Staph. aureus 24 (all fluclox sensitive)
• Number of probable contaminated specimens (CAV)
• ~ 60 (actually 31 in six months)
• 60/3890 = 1.5%
Difficult to introduce guideline for best method of collection
due to differences in e.g. ED, M3, surgical wards
OK to use alcohol wipe for peripheral sample/chlorhexidine
for centrally accessed sample

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