Category: Lightning rounds

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References

The Vortex website

Lightning rounds 48: Complete airway closure with Thomas Piraino

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We talk about the phenomenon of airway closure during mechanical ventilation, with Thomas Piraino, RRT, FCSRT, FAARC, adjunct lecturer for the Department of Anesthesia at McMaster University, editor of The Centre of Excellence in Mechanical Ventilation Blog, and a member of the editorial board of Respiratory Care.

Takeaway lessons

Airway closure occurs when airways, probably smaller ones (ie bronchioles) completely collapse at some point during expiration, causing flow to cease.
This creates a false understanding of the “PEEP,” which may actually be higher than the set PEEP (effectively an autoPEEP), and hence an incorrect understanding of the driving pressure and compliance. (This autoPEEP may or may not be effective, as at higher FiO2s, this trapped volume may rapidly absorp, causing absorption atelectasis.)
It may cause lung injury at the airway level from cyclic opening/closing, separate from more-discussed alveolar injury.
ARDS, pulmonary edema, and obesity are all risk factors. Post-cardiac arrest is a particularly common substrate. Obstructive diseases like asthma/COPD can probably see this as well, although the recent discourse has focused on the hypoxic conditions; the phenotype is probably different, caused by intrathoracic pressure, not by air-fluid interfaces and surfactant issues.
Probably 40% of at-risk patients may see this phenomenon occur. Its presence and the pressure where it occurs may be labile and dependent on the clinical condition. It should probably be checked at least daily in such patients.
It may cause hypercarbia by terminating expiration early, leading to air trapping. Prolonging the expiratory time will not help, as flow has ceased.
Plateau pressure may be elevated. Expiratory holds will not reveal this, however. A visible inflection point in continuous-flow VC breaths that has a different height (higher) than the gap between the peak and plateau pressure may be a rough suggestion of this as well.
Plateau pressures will be accurate, as the airways should be open at peak inspiration (or no breath would be delivered). Thus, increasing PEEP and seeing no change in plateau pressure may be a sign of airway closure, although it can also be due to alveolar recruitment.
Active patient effort during exhalation may worsen this phenomenon, particularly in the obstructive patient, due to increasing intrathoracic pressure.
The best test is a slow-flow inflation curve. Draeger and Hamilton should have this built in (Hamilton does this incrementally, not continuously, which may make it a little harder to identify the exact inflection point). It can be done manually as such (patient must be passive):
- Set VC mode
- Square wave flow
- Flow 5L/min
- Rate 5/min
- PEEP 5 (or higher if needed for oxygenation)
- Freeze the screen and inspect the pressure scalar during inspiration. The upramp should be steady and continuous. If there is a change in slope or inflection point, this suggests a change in compliance, probably due to airway opening. Use the vent to measure pressure at this point.
- A clever time to do this might be shortly after intubation, while patients are deeply sedated and paralyzed.
That this inflection represents airway opening can be proven by measuring the compliance up to that point (volume delivered vs pressure), which will usually be <3 cmH2O/ml, roughly the compliance of the ventilator circuit.
Inflection can occur from alveolar recruitment as well, but this is usually a less abrupt, steady change in slope. If present, it will occur above the airway closing pressure inflection.
In general, set the vent PEEP at the same level as the measured closing pressure. This will normalize your understanding of the driving pressure and probably limit cyclic collapse and lung injury. It may also facilitate expiration and hence ventilation.

Lightning rounds 47: Post-op care transitions

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We chat about the post-op transition of care from the OR to the ICU, including questions to ask, workflows, and pitfalls.

Bryan’s textbook: Concepts in Surgical Critical Care

Lightning rounds 46: Nick Ghionni on combating cognitive bias

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We chat with Nick Ghionni, pulm/crit attending at MedStar Baltimore Hospital, about identifying and combating cognitive biases in our clinical decision-making.

Lightning rounds 45: Noelia Bischoff on transitioning nursing roles

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We chat with Noelia Bischoff, recently off orientation in the medical ICU at Johns Hopkins as a nurse practitioner, about the transition from her role as a bedside ICU nurse.

Lightning rounds 43: AI in medicine, with Nawar Shara

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We explore the fascinating world of artificial intelligence and its role in medicine, with Nawar Shara (@NawarShara), PhD, Chief of Research Data Science at Medstar Health Research Institute and cofounding director of the AI Collab between Medstar and Georgetown.

Lightning rounds 42: Hospital chaplains, with Christine V. Davies

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We learn about the training, role, and benefits of hospital chaplains, with Christine V. Davies, MDiv, MSW, Director of Chaplaincy at Robert Wood Johnson University Hospital.

Lightning rounds 41: Respiratory therapy with Keith Lamb

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We explore the profession of respiratory therapy in the US, including their role and training and how to optimize our clinical relationships, with Keith Lamb (@kdlamb1), RRT, RRT-ACCS, FAARC, FCCM. Keith is an RT at the University of Virginia in Charlottesville, working clinically in neuro/surgical/trauma critical care, who has been active in research and has held a variety of leadership positions.

Lightning rounds 40: Critical care medicine fellowships with Nicholas Ghionni

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We chat about pulmonary/critical care medicine fellowship with recent graduate Nicholas Ghionni (@pulmtoilet), a first-year attending at the MedStar Baltimore Hospital system. He completed PCCM fellowship at MedStar Washington Hospital Center where he also served as chief fellow.

Lightning rounds 39: Understanding flight medicine with Jace Mullen

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We explore critical care transport medicine from both a clinical and career perspective, including helicopters (HEMS), fixed wing jet, and ground ambulance transports, with Jace Mullen, flight paramedic and airway educator out of Denver.