Authors: Mark Winstanley, Andy Neill, Dave McCreary, Chetan Trivedy, Sarah Edwards, Becky Maxwell, Chris Connolly / Codes: IP1, IP3, MaC1, MaC3, MaP1, MaP3, SLO1, SLO3, TC2, TP7 / Published: 01/07/2020

Clinical Question:

Does the sensitivity of blood cultures really decrease after giving antibiotics?

Title of Paper:

Blood Culture Results Before and After Antimicrobial Administration in Patients with Severe Manifestations of Sepsis

Journal and Year:

Annals of Internal Medicine. 2019.

Lead Author:

Matthew Cheng, MD


– You may have heard that we like antibiotics to be given early in sepsis, yes?
– Surviving sepsis says cultures should be drawn before giving antibiotics, but allow 45 minutes grace as acceptable delay

Study Design:

– The FABLED (eFfect of Antimicrobial administration on BLood culture positivity in patients with severe manifestations of sepsis in the Emergency Department) study – now even as tenuous study acronyms go, that’s a stretch
– Patient-level, single group, diagnostic study
– Seven urban EDs in North America

Patients Studied:

– Adult ED patients with ‘severe manifestations of sepsis’
– SIRS plus source
– Severity: SBP <90mmHg, lactate ≥ 4
– Had 2 sets of cultures before starting abx
– And were able to have additional sets drawn within 2 hours of empirical abx administration

What they did:

– 2 sets of cultures from two sites before abx
– Second sets varied by hospital protocol
– Additional sets collection method varied by sites
– Initial protocol aimed for additional sets to be taken at 30-120 minutes
– This was extended to 240 minutes after difficulties meeting their protocol


Primary: Sensitivity of blood cultures within 120 minutes of abx administration

– Reference standard for bacteraemia was pre-antimicrobial cultures
– Non-contaminant organism in pre-abx cultures but absent from post-abx cultures = **discordant result**
– Post-abx cultures growing same organism as pre abx = **concordant result**

Secondary: Sensitivity of postabx cultures in the context of micro results from other anatomical sites

Summary of Results:

– 325 patients final analysis
– 264 patients had second sets taken between 30 & 120 minutes – PP analysis

– 43% had lactate ≥4
– 38% had SBP ≤90mmHg

– 60% got B-lactam abx including Pip-Taz
– 23% got 3rd generation cefalosporin
– 5% got a carbapenem

– Median time to repeat cultures 70 minutes (50-110)
– Pre abx positive cultures = 102 / 325 (31.4%)
– Post abx positive cultures = 63 / 325 (19.4%)
– 12% absolute difference (ITT), 10.6% (PP population)

Primary Outcome

Sensitivity of post abx blood cultures = 52.9% (ITT) & 56.3% (Per protocol population)

Secondary Outcome

When adding micro results from all samples – sensitivity of post abx BCs increased to 67.6% (68.8% in PP).

Discussion Points

> “Our results suggest that obtaining blood cultures after initiation of emperical treatment reduces sensitivity by approximately 50%”

> “Microbial diagnosis is key to optimising the effectiveness of antimicrobial treatment as well as its safe deescalation”

> “One in 6.7 patients would have had a false negative as a result of delayed draw”

Authors’ Conclusion:

> “Blood culture sensitivity decreased after initiation of empirical antimicrobial therapy. These findings are important in considering the optimal balance between prompt antimicrobial administration and the need for accurate microbiological data in the care of patients with sepsis.”

Clinical Bottom Line:

Surviving sepsis are probably correct in their suggestion that we should aim for blood cultures to be taken before abx administration.

I think it’s something that takes extra cognitive effort in ED management as it’s not going to help ***us*** in our resuscitation, but culture results are obviously incredibly helpful for patient care and antimicrobial stewardship down the line.

Dr Chetan Trivedy @TulsiF
Dr Sarah Edwards @drsarahedwards

Dr Trivedy is an Emergency Physician who has a long term interest in the management of maxfax/dental emergencies presenting to the ED. He originally trained as a Dentist with the plan to do Max Fax. During his medical training he fell in love with EM and has stayed since.

Facial injuries make up to 5% of the total of ED Workload
Over 1 million presentations to the ED

This month we’re looking at an RCEM guideline on FICB for analgesia in ED.

Published as a best practice guideline in May 2020

So why block?

Analgesia is great from these when they work. They can be opiate sparing, opiates in the elderly population can increase hospital acquired delirium, increase vomiting, reduce respirations to name a few.

Nerve Blocks provide a bridge to theatre.  If you use bupivacaine you can see a block that lasts from ED to pretty much time of theatre.

We’re such believers that there is almost no patient who comes through our doors with a broken hip that doesn’t get a FICB – exceptions would be those who are so agitated they’d require chemical restraint to permit blockade.


LA toxicity:  rare –The guideline suggests reducing the dose in lower body weight patients.  We have weight based dosing guide at our place and use 2mg/kg of levobupivacaine.  Make sure you know where the Intralipid is in your department.

‘US guidance is possible’ – we believe it is the most appropriate way to do them.  When you are feeling for a “pop-pop” in the elderly there so much calcified soft tissue that you can get “pop pop” just going thought a couple of layers of skin and muscle.  You need to see where you’re going, into the right space.

Anticoagulated patients:  the document suggests bleeding is reduced by avoiding blocking patients on a DOAC/warfarin.  We suggest that the broken bone will bleed loads more than you using a tiny needle to inject them.  US guidance will let you know you aren’t hitting a vessel.  The AAGBI has a list of risk for the patient with abnormal clotting.  Fascial plane block sits above digital nerve block but below femoral nerve block.

Infection:  take sterile precautions like you would for a haematoma block or a digital nerve block.

Where do you perform them? 

Must have cardiac monitor during procedure and following procedure have regular obs at at 5, 15 and 30mins.

Who don’t you perform nerve blocks on There’s an example proforma in the guideline with contraindication of confusion/dementia/inability to describe pain – Chris and Becky debate this in the podcast as we believe those who should not have a block should be those that require physical or chemical restraint. Just because they can’t complain about pain doesn’t mean they aren’t suffering, and their risk of delirium related to pain will be higher. Opiates cause constipation, constipation causes delirium, reducing the risk of both is definitely the way to go.

Other points to consider:

Training of those who perform blocks – need for training package when new doctors start in ED?

Use of a formal proforma for blocking – remember to ‘stop before you block’ consider WHO Checklist

RCEM Safety Alert – death of a patient who had been given opiates then had a FICB that worked well enough to remove painful stimulus and the patient then became apnoeic.  Must be mindful of what they’ve had before, their ability to clear opiates and an appropriate period of monitoring.


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