UMEM Educational Pearls - By John Greenwood

Vent Management: Finding the AutoPEEP!

OK, so we all know not to, "...Fall asleep on Auto-PEEP" thanks to Dr. Mallemat's pearl that can be seen here.  But now the question is, how do you know if your patient is air-trapping?

There are 3 ways you can look for evidence of Auto-PEEP on the ventilator:

1. Do an end-expiratory hold:  If the measured PEEP is more than the PEEP set on the vent after a 2-3 second hold, the difference is your Auto-PEEP.


2. Look at the expiratory flow waveform:  If the waveform does not return to baseline (still expiring when inspiratory ventilation occurs), there's Auto-PEEP!


3. Compare the inspiratory vs. expiratory volumes.  If the inspiratory volumes are much higher then the expiratory volumes, consider Auto-PEEP.

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Ineffective triggering is the most common type of ventilator dyssynchrony.  The differential diagnosis includes:

• Auto peep (the most common cause) 
• Neuromuscular weakness 
• Improper ventilator settings

Auto peep is the most common cause of ineffective triggering and will often occur as a patient cannot create enough inspiratory force to overcome their own intrinsic peep (PEEPi).  Patients who are severely tachypnic or those with obstructive lung disease are at high risk for auto peep (not enough time to exhale).

Ineffective triggering can also occur if the patient cannot create enough of a negative inspiratory force to trigger the vent to deliver a positive pressure breath. Prolonged period of mechanical ventilation, over sedation, high cervical spine injuries, or diaphragmatic weakness are common causes.

Lastly, improper trigger sensitivities may make it difficulty for the ventilator to sense when the patient is attempting to take a spontaneous breath.  

For an example of a patient with ineffective triggering, check out: http://marylandccproject.org/2013/10/28/vent-problems1/

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Want to improve your chances of success in the resus room?  Download a metronome app on your smartphone and set it to a rate of 100-120 beats per minute.  There are a number of cheap (usually free) metronome applications for both iOS and Android devices.

A recent review looked at the evidence behind CPR feedback devices and found:

• Compared to baseline, chest compression rates and end-tidal CO₂ improved after activation of the metronomes.

So instead of going to iTunes and downloading the Bee Gees, go over to the App store and download a free metronome.  Your resus team will be able to stay on track with their compressions and even better - they won't have to hear you sing!

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Necrotizing Pneumonia
 

Necrotizing pneumonia is a rare, but potentially deadly complication of bacterial pneumonia.

It is characterized by the finding of pneumonic consolidation with multiple areas of necrosis within the lung parenchyma. Necrotic foci may coalesce, resulting in a localized lung abscess, or pulmonary gangrene if involving an entire lobe.

Most common pathogens: S. aureus, S. pneumoniae, and Klebsiella pneumonia.  
Others include S. epidermidis, E. coli, Acinetobacter baumannii, H. influenzae and Pseudomonas.

Contrast-enhanced chest CT is the diagnostic test of choice and is also helpful in evaluating  for parenchymal complications. 

Empiric antibiotic therapy should include:

• Broad spectrum coverage for commonly implicated pathogens (vancomycin, pseudomonal-dose piperacillin/tazobactam)
• PLUS either clindamycin or metronidazole to cover possibly involved anaerobes

Consider an early surgical evaluation for the patient with necrotizing pneumonia complicated by septic shock, empyema, bronchopleural fistula, or hemoptysis. 

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Bad brain, good lungs.... Right?

A recent retrospective study reviewed the incidence of acute respiratory distress syndrome (ARDS) in patients presenting with spontaneous intracerebral hemorrhage over a 10-year period.  After reviewing 1,665 patients, the authors found that:

• The development of ARDS occurred in approximately 27% of patients with spontaneous ICH (similiar to previous literature).
• The incidence ARDS after spontaneous ICH was similiar to other "high-risk" conditions such as sepsis, trauma, & aspiration.
• Modifiable risk factors include: high tidal volume ventilation, higher total fluid balance, & transfusion of PRBCs/FFP.
   

It's of particular importance to note that high tidal volume ventilation (>8cc/kg) was the single greatest modifiable factor for the development of ARDS.

Bottom line:  Try and use lung-protective ventilation strategies (6-8cc/kg ideal body weight) and avoid excessive volume resuscitation in your critically-ill patients whenever possible.  Even in cases of isolated intracerebral hemorrhage - where the patient's lungs may appear to be completely normal - traditional tidal volume settings may be harmful.

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