As prepared by Aidan Burrell, here are the practice written questions from a recent CICM Second Part exam practice session at The Alfred ICU, with recommended reading from LITF.com’s Critical Care Compendium and other FOAM sources:
In patients with severe ARDS, compare and contrast ARDSNet ventilation with APRV strategies.
Learn more here:
Overview: APRV is Airway pressure release ventilation: this is an inverse ratio, pressure controlled, intermittent mandatory ventilation strategy which allows for spontaneous breathing.
APRV goes by different names depending on the ventilator company
- Servo: Bivent
- Hamilton: APRV
- Puritan Bennett: Bilevel
|Volume control 6mls/kg predicted body weight or not greater than 30cmH20||Set the high pressure at the Pplateau (but not to exceed 30cmH20|
|PEEP/low airway pressure||Set as per Fio2 tables||Set 0-5cmH20|
|Cycling||As per I:E or inspiratory time||T high 4.5-6 seconds and T low 0.5-0.8 seconds|
|Ventilation||Less ventilation||Improved ventilation as P low is much lower than PEEP level, enabling more ventilation|
|Lung recruitment||Relies on PEEP||Time at P-high is longer than P-low (85-95%) with higher mean airway pressure, potentially leading to better recruitment and less atelectasis|
|Atelectrauma||Faster cycling with higher risk||Slower cycles potentially allowing alveolar units with slow time constants to fill – preventing over distention|
|Driving pressure||Lower||Potentially higher (large drop down to lower airway pressure)|
|AutoPEEP||Rarely an issue except|
|Spontaneous breathing||Not possible||Possible at high and low CPAP levels, which may lead to more diaphragm related recruitment of especially the dependent lung|
|Circulation||More impact from the higher peep||Less impact on splanchnic and systemic circulation|
|Sedation/Paralysis||Usually requires more||Potentially less as enables spontaneous breathing. Can titrate sedation to enable 10-30% contribution of minute ventilation|
- Improved alveolar recruitment
- Better oxygenation via higher mean airway pressures
- Enables spontaneous breathing
- Less sedation
- Protective lung effect
- Higher driving pressure
- Potential for autopeep and dynamic hyperinflation
- Potential increased WOB and energy expenditure from spontaneous breathing
- Potential for diaphragm induced lung injury during spontaneous breathing
- Worsening airleaks eg bronchopulmonary fistula
- Potentially worsening raised ICP
- Increased RV afterload
- Animal studies have shown improved oxygenation, improved lung recruitment, reduced lung injury without an increase in circulatory depression
- APRV vs ARDSNet ventilation RCT ICM Zhou 2018
- Single centre RCT of 138 patients
- Compared to ARDSNet, APRV had
- Better oxygenation, improved compliance, less sedation
- More ventilator free days, shorter ICU stay, and lower mortality
- Criticisms: Single center, unblended with high potential for bias.
- Need to replicate this strategy
- APRV is a ventilator approach with potential physiological advantages. However the clinical risk benefit profile has not been established in large multicentre RCTs, and therefore should not be routinely used outside of the research setting.
In regards to candidiasis:
- Define invasive candidial infection
- Name 4 common species of candidial infection seen in ICU patients
- Compare and contrast the use of azole drugs vs echinocanins for patients with invasive candidial infection
Learn more here:
Invasive candida infection occurs when candida is:
- (1) cultured in a blood culture (most common manifestation)
- (2) found in a sterile site
- (3) cultured from two non-continguous sites
- (4) identified species is a non-commensal
- (5) cultured from tissue or burn wound biopsy
This contrasts with the much more common colonization, where the fungae can be cultured in up to 3 non sterile sites without infection.
Candida Ablicans remains the commonest cause of candidaemia ICUs, but pathogenic shift (and azole prophylaxis in haem and lung transplant patients) has meant this has reduced from 90% of ICU infections to now more like 30-50. Non Ablicans species include Tropicalis, parapsilosis, glabrata, krusei
|Coverage/spectrum||Albicans, parapsilosis, tropicalis (NOT krusei or glabrata)||Superior activity against all candida compared to fluconazole (lower MICs)||All Candidia|
|Mechanism||Inhibits fungal P450||Inhibits fungal P450||Inhibits 1,3 glucan in fungal wall|
|Side effects||ALP/AST increase, GIT side effects, Prolonged Qtc||Transient visual disturbance 19%, renal impairment 10%, Rash 7%||Generally well tolerated. Caspo is hepatically clear (anidulofungin ok in liver disease)|
|Interactions||Tacromilus, midazolam.||Tacro and morphine||Cyclosporin and tacrolimus|
|Other||Good tissue penetration (CNS, concentrates in urine), reduce does in renal failure||IV only, needs TDM||IV only, has poor oral bioavailability|
See also Reboli NEJM 2007 found
- Anidulafungin was non inferior to fluconazole in invasive candidiasis. And was found to have a superior rate of clearance of infection 75 vs 60%
- Echinocandins are associated with improved outcomes in invasive candida infections
Discuss the use of low chloride containing fluids in the ICU.
Learn more here:
- Lower chloride containing crystalloid solutions have composition that are closer to plasma levels, and may be associated with reduced side effects, especially renal toxicity.
- Potentially reduced AKI
- High sodium chloride has been shown in animal studies to be sensed by the macula densa at the thick ascending limb/distal convoluted tubule leading to renal arteriole constriction and reduced GRF.
- Reduced rate of hyperchloraemic acidosis
- Potentially reduced cytokine release and inflammatory changes
- Reduced hypotension
- Cost is more expensive
- There may be a role for higher chloride (and saline) containing fluids in patients with TBI during the resuscitation phase, as balanced solutions may be relatively hypotonic, which could lead to rises in intracranial pressure.
- Some fluid contain potassium/lactate which may be avoided when these levels are high, or may be contraindicated with combined with other fluids (ie calcium and blood)
|SMART 2018 NEJM||SALT ED 2018 NEJM||SPLIT 2015 JAMA|
|Randomization in blocks||ICU||ED||ICU|
|No of centers||Single||Single||Multi (4)|
|Dose (Total Litres)||2.2||2.1||1.0||1.0||2.0||2.0|
|Separation at 25hours||Na 137.5
|Proposed clinical difference||12% difference in Death, new RRT, Cr>200% day 30||0.5 hospital free days||No clearly defined – novel design|
|Results||14.3%||15.4% (0.04)||25 days||25 days||9.6%||9.2%|
|Blinding||None||None||Blinded – but 2/3 clinicians could guess the fluid type|
|Population same as ours?||10.3%||11.1% (0.06)||Mortality 1.4%||Mortality 1.5%||Mortality 7.6%||Mortality 8.6%|
SPLIT trial JAMA 2015
- Phase II, multi centre, cluster, double cross over, RCT
- 2278 ICU patients
- Moderately sick – mortality 7.6 and 8.6%
- 2.0L (Plasmalyte) vs 2.0L (Saline) given
- Separation not assessed, no daily blood tests
- Double blinded
- Primary outcome AKI incidence not different
- No other secondary outcomes different
SMART Trial NEJM 2018
- Phase III, single US center, 5 ICUs, unblended, multiple cross over RCT
- ICU level randomization- either to balanced fluids or normal saline for even or odd months
- 15802 patients
- Saline or Ringers/plasma lyte A
- Primary outcome was differnet major renal adverse event at 30 days (death, new RRT, Cr>200)
- Power 14000 patients to detect a 12% difference to detect an alpha of 90%, with a baseline rate of 15%.
- Mostly ED patients (50%), MV rate 34%, Sepsis 14%, vasopressors 26%.
- Only on average of 1000mls was delivered to the patients
- 14.3 vs 15.4% (OR 0.91 – 0.84-0.99 P=0.04
- No mortality difference 10.3 vs 11.1% P=0.06
- No change in RRT 2.5 vs 2.9% P=0.08
- Balanced had lower chloride and higher HCO3 levels.
- Critique – Clinical difference of primary outcome is arguable, single center trial risk of bias and reduces generalisability, total volume of fluid low, no blinding of patients or staff.
- ANZICS CTG trial that is recruiting.
- 8800 Plasmalyte vs normal saline
- Primary outcome mortality at 90 days
- Due to be completed in next 3-4 years.
- There is currently no definitive evidence that a low chloride strategy for fluids in ICU is better over normal saline. Using low chloride fluids may be reasonable in certain groups, such as in TBI patients or in patients hyperchloraemic metabolic acidosis. We awake further phase III, high quality, externally validated, RCT evidence to guide therapy (Eg PLUS trial)
You can access all the previous practice questions since 2014 here:
See this link on INTENSIVE for exam resources: