Dynamic Hyperinflation Syndrome in Severe Asthma

By Adem Lewis / in , , /

The clinical case that will be discussing today is dynamic hyperinflation syndrome So you have this patient who has been admitted to the intensive care unit with the diagnosis of severe asthma requiring intubation and mechanical ventilation He has been placed on Volume control mode of ventilation with a tidal volume of 620, his ideal body weight is 70 kilos His rate was set at 18 and inspiratory time of 1.7 his fio2 is at 40% and his saturation is 98% his pH is 7.48 and PCO2 is 30 So when you analyze his Ventilator graphics, we can easily appreciate that in expiration The expiratory flow is limited with a decreased peak expiratory Flow and limitation of the expiratory flow to the level that at the end of expiration the expiratory flow does not reach the zero point So there is a persistent flow at the end of expiration Notice that the next breath starts before we empty the lung completely, that means that there is air trapping inside the lung and this has hemodynamic consequences if it accumulates further So in order to deal with the problem Essentially what we need to do is, we need to allow more time in expiration for this patient So the expiratory flow will go down all the way to zero before the next breath There are multiple maneuvers that we can do for this patient to allow more expiratory time But first let’s start with his ventilation we given him 620, this is almost 9 ml per kg and His pH is 7.48 and The PCO2 is 30 so he’s getting more ventilation than what it is required for him I usually give those patients between 6 to 8 mL per kg of ideal body weight. So let’s start with that and it’s going down on the tidal volume To the level of 7 ml per kg we say that his 70 kilos, Of ideal body weight, so let’s give him 480 and See that the dynamic hyperinflation has improved slightly So we’ll put in less air into the lung of course that will be associated with a less air traping The second thing that we can do is his respiratory rate is slightly elevated And we can do go down on respiratory rate to 14 and by decreasing the response rate We are changing the I:E ratio, so we’re gaining more time in this exploration You can see how the dynamic hyperinflation syndrome is improving at the same time if you if you take a look on the inspiration you can see here that there is a Plateau that is not required, this patient has no problem with oxidation And I would rather use this time for expiration So let’s eliminate the plateau time and had this time to expiration so the way we eliminate it is by going down on the inspiratory time so we go down on the inspiratory time to the minimum required for this tidal volume to get it, and by doing this you can see that now we eliminated the plateau completely and the expiratory flow has improved reaching very Close to the zero point, but has not been eliminated completely So the next thing we do is let’s try to gain more of The expiratory time by decreasing the inspiratory time and the way we decrease the inspiratory time, and this is volume control mode of ventilation We can go up on the flow, let’s double the flow for this patient So let’s go up to 60 and By going up on the flow now. We can deliver the 480 faster. Let me just freeze it for you here, so you can see that the 480 ml has been delivered faster, so I gained more plateau time here that is not needed. I’m going to Take this From inspiration give it to expiration by decreasing the inspiratory time again so by going down on the inspiratory time To the minimum you can see that now, I’m using most of the time For expiration and I almost completely eliminated The Dynamic hyperinflation. Notice that the peak inspiratory pressure has increased, but this is Not a plateau pressure and the peak inspiratory pressure may not have much of the effects on the Lungs in terms of the barotrauma, so it would not be very much concerned about it at this point. So this way We went through the different maneuvers that Essentially aim to increase the expiratory time in order to improve the dynamic hyperinflation syndrome In addition to all those maneuvers of course the patient is on Beta-2 agonist as bronchodilators and steroids to improve his severe asthma Thank you very much

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