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juan carlos vidal

Permissive hypercapnia and Volume-targeted

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Hi all. I would like your experience in ventilation with guaranteed volume in premature babies under 750 grams.
In my ucin I have a drager vn500 ventilator and a sle5000.

Which one looks better ventilator  for this function?

What pco2 values do they tolerate?

How to manage hypercapnia with this strategy?

What maximum pressures do you tolerate at these weights before going into vafo?

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Great question, Juan Carlos.

I am partial to the VN500, but I'm sure both devices can deliver VG quite well. The problem is that babies don't like to be acidotic. Consequently, there is a problem with permissive hypercapnea in the first days of life in small preemies, because their kidneys are not able to compensate for respiratory acidosis. Therefore, the baby will try to generate a tidal volume sufficient to bring the PCO2 down and normalize the pH. As you know when the tidal volume exceeds the target value, PIP will come down and pretty soon, your baby may be on endotracheal CPAP with rising oxygen requirement (due to the drop in MAP), tachypnea and increased work of breathing. You would have to sedate the baby sufficiently to suppress their respiratory drive, which is a bad idea. People find all kinds of ways to reduce the support for the baby's effort, for example changing from AC to SIMV at a low rate, so the baby is unable to generate adequate minute ventilation and correct the acidosis. So, the baby is struggling, but the doctor is happy, because the PCO2 is where he or she wants it. If you can buffer the acidosis by adding some acetate to your TPN and get the pH up to near normal, you might be able to let the CO2 rise gradually. 

The focus needs to be on pH, not PCO2, because it's the pH that is the primary stimulus for respiratory drive.  Basically it is better to support the baby's effort to maintain normal pH and avoid the mistake of looking only at the PCO2. Ultimately, it is the perivascular pH that controls cerebral circulation, but unfortunately all studies keep focusing on PCO2 and ignoring pH. What we know is that rapid fluctuations in PCO2 confer the greatest risk of IVH. 

Once the baby is a bit older and the kidneys are more mature, it'a s lot easier to allow permissive hypercapnia if they still need mechanical ventilation.

I hope this helps, 

MK

 

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On 12/10/2019 at 1:37 PM, Martin.Keszler said:

Great question, Juan Carlos.

I am partial to the VN500, but I'm sure both devices can deliver VG quite well. The problem is that babies don't like to be acidotic. Consequently, there is a problem with permissive hypercapnea in the first days of life in small preemies, because their kidneys are not able to compensate for respiratory acidosis. Therefore, the baby will try to generate a tidal volume sufficient to bring the PCO2 down and normalize the pH. As you know when the tidal volume exceeds the target value, PIP will come down and pretty soon, your baby may be on endotracheal CPAP with rising oxygen requirement (due to the drop in MAP), tachypnea and increased work of breathing. You would have to sedate the baby sufficiently to suppress their respiratory drive, which is a bad idea. People find all kinds of ways to reduce the support for the baby's effort, for example changing from AC to SIMV at a low rate, so the baby is unable to generate adequate minute ventilation and correct the acidosis. So, the baby is struggling, but the doctor is happy, because the PCO2 is where he or she wants it. If you can buffer the acidosis by adding some acetate to your TPN and get the pH up to near normal, you might be able to let the CO2 rise gradually. 

The focus needs to be on pH, not PCO2, because it's the pH that is the primary stimulus for respiratory drive.  Basically it is better to support the baby's effort to maintain normal pH and avoid the mistake of looking only at the PCO2. Ultimately, it is the perivascular pH that controls cerebral circulation, but unfortunately all studies keep focusing on PCO2 and ignoring pH. What we know is that rapid fluctuations in PCO2 confer the greatest risk of IVH. 

Once the baby is a bit older and the kidneys are more mature, it'a s lot easier to allow permissive hypercapnia if they still need mechanical ventilation.

I hope this helps, 

MK

 

thank you very much for your reply
and in the narrow range of weight and gestational age, which values of ph make reference as the minimum objective

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