Infectious diseases and Microbiology (IBL-ICU 04092019)

Notes scribed and collated by Dr Natalie Appelbaum and reviewed by A/Prof Chris Nickson

Here are the notes from the IBL-ICU discussion of the daily questions on the topic of Infectious diseases and Microbiology: that took place on 4th September 2019 at ICU Junior Medical Staff Teaching.

Q1. Thursday (29/08): 
Review a patient who has had a fever in the last 24 hours. How do you define fever? What are the potential infectious and non-infectious causes of fever in ICU patients?

Body temperature is usually considered elevated when > 37.5C.

  • Core body temperature is normally lower in the morning and higher at night.
  • Elevated temperature in the morning is considered > 37.2C, and in the afternoon > 37.5C.
  • Body temp is higher after eating!

 From an Infectious diseases perspective, T > 38.3C is considered a fever (e.g. for the purpose of deciding whether to take a blood culture due to risk of bacteraemia).

What temperature is normal also depends on how it is measured (e.g. the site of temperature measurement).

  • transcutaneous measurement is common on the wards
  • Other options in critically ill patients include esophageal, urinary catheters, rectal, and pulmonary artery catheters.

Remember, fever  or pyrexia is an elevation of body temperature above the normal range due to an increase in the temperature regulatory set point – as distinct from other forms of uncontrolled hyperthermia where the set point is not altered.

Hot tip: remember that patients on extracorporeal circuits (CVVHDF, ECMO) are temperature controlled, which may mask and underlying fever!

EPIC II (2007) Study of ICUs worldwide

Common sites of infection:

  • Lung 64%, abdomen 20%, blood 15%, renal/GIT 14%.

Common organisms:

  • Gram -ve: Pseudomonas, E. coli
  • Gram +ve: S. aureus

Important sites of infection to consider:

  • Chest
  • Urinary
  • CNS
  • Line related: Venous stasis, TPN increase risk.
  • Catheter
  • Cutaneous
  • Intra-abdominal
  • Sinusitis (NGT high risk)
  • Cardiac (endocarditis)

Non-infectious causes of elevated temperature include:

  • Burns
  • Malignancy
  • Drugs (e.g. methylene blue, B-lactams, heparin, MABs).
  • Iatrogenic: Filter related hyperthermia and heating blankets, blood transfusion reactions
  • Illicit Drugs: e.g. Amphetamines
  • Autoimmune condition
  • Hyperthermia
  • Allergy
  • Pancreatitis
  • Acalculous cholecystitis
  • Malignancy

Q2. Friday (30/08): 
Review a patient who is being treated for an infection. How will you determine when to stop antibiotics?

In general terms, check the Therapeutic Guidelines and local protocols, and look for:

  • Clinical improvement
  • Reduction in sepsis biomarkers
  • Improvement in organ derangement/support
  • No fevers for 24-48h
  • Reduction in pressor / inotropic support

Duration of antibiotics has traditionally lacked a strong evidence base (i.e. based on number of digits on one or two hands and the number of days in a week!). But this is changing… Even the features listed above can be unreliable.

Two common mistakes in ICU:

  • Underdosing patients.
  • Extended courses: Cure rate is as good with shorter courses.

In general, we should aim for shorter courses of antibiotics, at higher doses.

For example:

  • Evidence showing a 5-8 day course can successfully treat most pneumonias. Alfred recommendation is 6 days.
  • Meningococcal Meningitis: 2 day protocol now used in the non-immunocompromised host.
  • STOP IT study: Intra-abdominal sepsis from surgical source: Randomised for standard of care (8 days Abx) and 4 day course irrespective of clinical progress. Standard to give 4 days of antibiotics post op and then stop.

Longer durations of antibiotics are typically used in the immunocompromised (more research needed!)

Other areas in development:

  • Increasing use of oral therapy for diseases we thought we needed to use IV therapy for (osteomyelitis/endocarditis).
  • Role of continuous infusions and therapeutic drug monitoring (e.g. BLING studies)
  • Duration of antibiotics in bacteraemia: 7 vs 14 days (BALANCE study)

Q3. Saturday (31/08): 
Review a patient who is being treated with antibiotics. How do you decide if the patient is failing to respond to treatment? What are the possible causes of failure to respond to antibiotic therapy?

Treatment failure is not uncommon (6-60% tin the literature).

Treatment failure may be suggested by:

  • Patient based: Death, persistent or worsening signs of sepsis (e.g. fever), worsening/progression organ dysfunction.
  • Treatment based: Change/addition antibiotics, admitted to ICU, additional organ support, requiring operative intervention.
  • Test based: Persistent elevation septic biomarkers, non-resolving/worsening.

The question of procalcitonin (PCT) came up – which we rarely use at the Alfred ICU (ni the context of a well established antibiotic stewardship programme):

  • PCT needs careful interpretation!
  • PCT is flawed in similar fashion to CRP – there is evidence that CRP is not helpful in ICU setting, e.g. it increases in nearly any inflammatory process.
  • PCT “goes up quicker and comes down quicker” than CRP
  • There are ICU studies of PCT showing survival benefit and studies showing higher mortality…
  • SAPS Study: Survival benefit from procalcitonin-guided therapy. Without this one open-label multi-centre , systematic reviews (e.g. Pepper et al, 2019) would show no benefit for PCT-guided discontinuation.
  • Mills et al (2016) Study: PCT was found to be a useful screening tool in the context of a meningococcal disease outbreak in New Zealand

If procalcitonin is used:

  • use multiple measurements of PCT
  • use only as a de-escalation tool
  • Never make decisions based on PCT in isolation, but can be used in conjunction with clinical assessment and other markers.

Why does sepsis fail to resolve? Consider these factors (see Unresolved Sepsis on LITFL for more detail):

  • Cause (correct diagnosis?, non-infectious causes versus wrong bug?, etc)
  • Drug (dose, route, site penetrance, etc)
  • Host (immune status, etc)
  • Bug (causative organism, etc)
  • Complications (abscess formation, etc)

Hot tips: remember that some ICU patients (e.g. young trauma patients) may have augmented renal clearance and a high output surgical drain is like have another kidney (e.g. increased clearance of beta-lactams)!

Q4. Sunday (01/09): 
Consider a patient who has been isolated for infection control. What are the different types of isolation and their indications?

In brief:

Contact precautions: Gloves and gown in addition to standard precautions.

  • Known or suspected risk of direct/indirect contact transmission not effectively contained by standard precautions alone.
  • C.Difficile/rotavirus/norovirus/hep A virus/shigella/E.coli (haemorrhagic 157:H7)
  • Abscess of draining wound that can’t be covered (MRSA or Group A Strep).
  • HSV/enterovirus meningitis

Droplet precautions: + PPE and surgical mask.

  • For patients known or suspected to be infected with agents transmitted over short distances by large respiratory droplets.
  • Meningococcaemia/meningococcal meningitis (first 24hr).

Airborne precautions: + Negative pressure and N95 mask.

  • Patients known or suspected to be infected with agents transmitted person-to-person by the airborne route.
  • LRTI (flu, TB, parainfluenza virus, adenovirus, influenza virus, human metapneumovirus).
  • Measles, VZV, HSV, smallpox.
  • TB meningitis.

Useful resources include:

Q5. Monday (02/09): 
Attend an ICU Micro round. How does the ICU micro round help patients? What strategies help reduce the emergence of resistant organisms?

ICU microbiology rounds/ antibiotic stewardship:

  • Improves patient outcomes
  • Ensures cost-effective therapy
  • Reduces adverse sequelae of antimicrobial use (resistance)
  • Must be part of the wider hospital quality improvement system

What strategies help reduce the emergence of resistant organisms?

  • Avoid unnecessary use of antibiotics
  • Reviews antibiotic after 48h and de-escalates with clinical improvement if appropriate
  • Promote the use of agents less likely to select resistance bacteria
  • Understand of local incidence of antibiotic-resistant pathogens
  • De-escalation plan: For when to stop antibiotics depending on organisms identified and nature of infection
  • Incorporates lab results to guide therapy in a timely fashion.
  • Dose optimisation and route transmission
  • Involves pharmacists
  • Drug expertise
  • Education
  • Minimise duration therapy
  • Ensure monotherapy in most cases
  • Audit and quality improvement measures

While we can help prevent antibiotic resistance in the ICU with the above measures, some things are out of our control! (community use of antibiotics, antibiotic use for livestock, etc)

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