Scott Weingart has a fantastic two part video lecture on ventilator management that should be required material for anyone who deals with vents. It has been a great help to me and has changed the way I think about these patients and how they should be managed. Here are the links:
Scott breaks vent patients into two groups: those who have obstructive lung pathology and… everyone else. “Everyone else” is managed according to a lung injury/ARDS strategy on the assumption that if they are on a vent, that’s the safest way to treat them.
Very briefly, Scott’s recommendations are as follows.
- A/C volume
- Vt 6-8 cc/kg PBW; PPlat < 30
- F 18, titrate to CO2, but hypercarbia is permissible.
- FIO2/PEEP according to the ARDSnet recommendations (see below).
- IFR: 60-80; pt comfort.
- A/C volume
- Vt 8 cc/kg PBW
- F 10; aim for I:E of 1:4 or 1:5
- FIO2: titrate to SPO2 88-95%
- PEEP: 0
- IFR: 80-100
Predicted Body Weight (PBW) formula: [2.3 *(height in inches – 60) + 45.5 for women or + 50 for men]
The strategy for lung injury patients is low volume ventilation that will protect the lung from barotrauma while still providing adequate ventilation. Mild hypercarbia is tolerated, and may require aggressive sedation. Perhaps the most controversial aspect of this strategy is the relatively high PEEP recommendation. Scott talks about misconceptions regarding PEEP in the lecture; the most common one I find when talking with providers is the idea that high PEEP causes pneumothorax. In fact, PEEP combined with lower tidal volumes protects against the most common causes of ventilator induced lung injury. The chart shown was developed by ARDSnet and is supported by the evidence of their trials. See this Medscape article for more on PEEP and lung injury.
The strategy for patients with obstructive lung pathology is to maximize expiratory time. This is the rationale behind the relatively low respiratory rate and shorter inspiratory time/flow rate.
It is uncommon in my practice to arrive at the bedside and find a patient who is being managed according to these guidelines. I typically ask for a recent ABG before arriving at the bedside and evaluate the need for any changes based on that. Obtaining a recent ABG also will also allow you to correlate ETCO2 to pCO2.
In the arena of prehospital care or en route intubation, these guidelines provide an effective means for rapidly transitioning from manual ventilation to the vent.
A couple of notes on applying these guidelines to the LTV series ventilators: inspiratory flow is a dynamic value based on the inspiratory time and tidal volume. It is adjusted with the Insp. Time setting, and can be monitored in the display window. An inspiratory time of 0.8-1 works well for both strategies. To monitor PPlat, press and hold Insp Hold for a half second, and PPlat will be shown on the display window.
A note on ventilators in resuscitation:
Transport ventilators are approved for use during resuscitation by the AHA. According to the 2010 guidelines, automatic transport ventilators “may provide ventilation and oxygenation similar to that possible with the use of a manual resuscitation bag, while allowing the Emergency Medical Services (EMS) team to perform other tasks.”1 Ventilator use is classified a IIb intervention, meaning benefit is considered greater than or equal to risk. The 2005 guidelines offer the following recommendations. Though they have been removed from the 2010 guidelines, they may offer a reasonable starting point. Tidal volume should be “adjusted to make the chest rise (approximately 6 to 7 ml/kg or 500 to 600 ml), with breaths delivered over 1 second… Once an advanced airway is in place, the ventilation rate should be 8 to 10 breaths per minute during CPR.”2
On the LTV one additional step is required: The sensitivity setting must be dialed to 0 to effectively “turn off” patient triggered breaths. Otherwise, the slight air exchange caused by chest compressions may be detected by the vent as inspiration and prompt the delivery of a breath.