ARDS and Decreasing Tidal Volume?

[as90]

Why do you want to decrease tidal volume in ARDS? Is it to increase dead space in alveoli?

Thanks

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[Phloston]

Why do you want to decrease tidal volume in ARDS? Is it to increase dead space in alveoli?

Thanks

I think the limitations are designed to prevent damage to the lungs. Ventilators are pretty harsh devices. If I recall correctly, tidal volume should be kept under 6 mL/kg (http://www.ncbi.nlm.nih.gov/pubmed/19741487), and FIO2 should be under 50%.

The USMLE is pretty obsessed with PEEP. Increasing PEEP is usually the answer when they ask you what to do. They'll say a guy is on FIO2 of 60 and high tidal volume but is still desaturated, and the answer is increase PEEP. I think you can go up to 15 mm Hg or something, but don't quote me there.

Another thing they like is asking what to do when the guy's saturations are normal and he's on ventilator. The answer is you wean from the ventilator, but always decrease FIO2 and tidal volume first before PEEP.

 

[as90]

I think the limitations are designed to prevent damage to the lungs. Ventilators are pretty harsh devices. If I recall correctly, tidal volume should be kept under 6 mL/kg (http://www.ncbi.nlm.nih.gov/pubmed/19741487), and FIO2 should be under 50%.

The USMLE is pretty obsessed with PEEP. Increasing PEEP is usually the answer when they ask you what to do. They'll say a guy is on FIO2 of 60 and high tidal volume but is still desaturated, and the answer is increase PEEP. I think you can go up to 15 mm Hg or something, but don't quote me there.

Another thing they like is asking what to do when the guy's saturations are normal and he's on ventilator. The answer is you wean from the ventilator, but always decrease FIO2 and tidal volume first before PEEP.

Thanks for the response. This was actually something they love pimping on in the wards. I will never understand vent settings lol. The reason you want to keep the tidal volume low is the prevent a pneumothorax? Or is that why you increase PEEP (to keep the alveoli open and puffed up?)

 

[Phloston]

Thanks for the response. This was actually something they love pimping on in the wards. I will never understand vent settings lol. The reason you want to keep the tidal volume low is the prevent a pneumothorax? Or is that why you increase PEEP (to keep the alveoli open and puffed up?)

Any type of pulmonary damage can occur from the ventilator. So yes, pneumothorax could occur.

PEEP just increases the time allowed for gas diffusion (by keeping some alveoli open longer).

 

[as90]

Any type of pulmonary damage can occur from the ventilator. So yes, pneumothorax could occur.

PEEP just increases the time allowed for gas diffusion (by keeping some alveoli open longer).

thank you!!!

 

[DrPettans]

Are "PEEP" (positive end-expiratory pressure) and "mechanical ventilation with low tidal volumes" different things?

 

[Instatewaiter]

Are "PEEP" (positive end-expiratory pressure) and "mechanical ventilation with low tidal volumes" different things?

Yes- Tidal volume and PEEP are different things.

Tidal volume is the volume of air pushed in with each breath. The pressure during inspiration will be determined by lung mechanics (as well as PEEP). This will be entirely independent from PEEP.
PEEP is the pressure at the end of inspiration

On a ventilator (for instance with AC volume control) you will set the tidal volume, the respiratory rate, PEEP and the FiO2

Also, attending physician is one finished with training. You should probably change that in your "status" tab.

 

[Instatewaiter]

I think the limitations are designed to prevent damage to the lungs. Ventilators are pretty harsh devices. If I recall correctly, tidal volume should be kept under 6 mL/kg (http://www.ncbi.nlm.nih.gov/pubmed/19741487), and FIO2 should be under 50%.

The USMLE is pretty obsessed with PEEP. Increasing PEEP is usually the answer when they ask you what to do. They'll say a guy is on FIO2 of 60 and high tidal volume but is still desaturated, and the answer is increase PEEP. I think you can go up to 15 mm Hg or something, but don't quote me there.

Another thing they like is asking what to do when the guy's saturations are normal and he's on ventilator. The answer is you wean from the ventilator, but always decrease FIO2 and tidal volume first before PEEP.

For ARDS you tend to shoot for 6-8 ml/kg (by ideal body weight, based on height).

You tend to get oxygen toxicity at or above an FiO2 of 60%. The link below shows you the PEEP/FiO2 combinations used in the ARDS protocol.

The degree of PEEP you can go up to is determined by the peak and plateau pressures (ie the lung mechanics).

When weaning a ventilator, you tend not to change the tidal volume. You tend to wean FiO2 and PEEP until you get to an FiO2 of 40% and PEEP of 5. Give them a CPAP trial and extubate.

For those interested, this link shows everything you need to know with regard to ARDS vent management. The specifics won't be on the boards but questions regarding PEEP and FiO2 management are easy when you know this. http://www.ardsnet.org/files/ventilator_protocol_2008-07.pdf