Air leak or Air trapping?
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Respiratory Failure & Mechanical Ventilation
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69 years old with anoxic encephalopathy and acute right parietal infarct after cardiac arrest. On Volume control mode of ventilation with VT of 510 breathing
What do you think?
Age/gender : 54y/o male
📝 Diagnosed as ARDS, H1N1 positive, later found to have ICH
🗂️ Medical history : Nil
🏋🏻♂️ Adm wt.60kg, ht.168cm.
Current wt: 54.0
Mazen Kherallah
Feb 05
Interesting answers, it looks like this is a case of delayed cycling indicated by increase inspiratory flow at end of inspiration in every single breath. Notice the increase in volume at the same time. This may lead to double triggering if the inspiratory negative pressure continued and was at the level to trigger another breath. However, we need to rule out reverse triggering by applying expiratory hold and notice if these efforts disappear. If they disappear then the answer to the question would be resuming paralysis, if they did not then we need to shorten inspiratory time on the ventilator first and re-evaluate.
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How do you explain the the drop in the pressure indicated by the white arrows on the pressure/time scalar?
@Everyone
Please answer the question and provide your input in the comment section!
The drop in the pressure on the pressure waveform is caused by:
0%Ventilator malfunction
0%Double triggering
0%Patient’s inspiratory efforts
0%Early cycling
Mohammad Shaban
Jan 01
having this phenomena in each breath at the same time will trigger me to find if it is a type of reverse trigger or just additional inspiratory efforts that do not cause another trigger.
the scalar does not show if the initiation of the cycle is triggered by time or by the patient.
Reverse trigger may manifest by a nigative deviation in the pressure wave after the beginning of the inspiration by the ventilator. However, the initial trigger should be time.
I tried to compare the total frequency to the set frequency. They are not the same, 41 vs 24, which may indicate that its not time triggered but patient triggered. If this is true then it is not a reverse trigger.
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PRVC mode of ventilation with a targeted VT of 400, RR 26 and I:E ratio of 1:1.5. Notice the dynamic hyperinflation (autoPEEP) with persistent flow at end of expiration and the ineffective triggers.
Ventilator settings were adjusted to allow longer expiration by decreasing the rate to 20 per minute, and decreasing inspiratory time with I:E at 1:2.9. The volume was also increased to 450 ml.
Dynamic hyperinflation improved remarkably and now the ventilator is triggered with every inspiratory effort of the patient.
Noor Shah
Dec 29, 2023
•
In the first setting of ventilator, there were two issues discovered
1) Auto Peep due to low expiration time, leading to air trapping- Auto Peep, by decreasing RR expiration time increased lead to resolved the auto peep issue as shown in second picture.
2) The second issue discovered what I observed was “ Air Hunger or Starvation ” in flow time waves, which was resolved by increasing Tidal Volume or Peak flow.
Thanks Dr. Mazen for sharing such interesting articles.
Edited
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65 year-old male with acute respiratory failure secondary to pulmonary edema who was intubated and placed on mechanical ventilation. His course was complicated with left parietal occipital and temporal infarction. The following graphs have been observed;
Please identify the abnormality and answer the following question:
This patient-ventilator asynchrony is caused by:
0%Early cycling
0%Delayed cycling
0%Flow asynchrony
0%Malfunction
65 years old with submasdive pulmonary embolism, DVT, atrial flutter, and non-ischemic cardiomyopathy. Intubated and placed on mechanical ventilation at night (A/C mode VT 500, Flow of 50, RR 22 and PEEP 5). The following was observed during the morning round:
Based on the pressure over time waveform, how would you approach this case?
What would you do next?
0%Increase flow
0%Decrease flow
0%Increase tidal volume
0%Increase fentanyl
You can vote for more than one answer.
Please see comments for the answer!
Mazen Kherallah
Dec 05, 2023
And this is at 80 liters per minute then we increased fentanyl and much improved.
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Please notice the volume over time scalar as indicated by the light orange arrow and provide your feedback:
@Everyone
Please select your answer and you may provide your explanation in the comment section.
The noticed abnormality is caused by:
0%Leak
0%Auto-PEEP
0%Malfunction
Please see comments for explanation!
Mazen Kherallah
Dec 02, 2023
So the main problem in the first breath is that the exhaled volume is less than the inhaled, then you would ask where did the air go, has it leaked or trapped, then if you look at the second breath, you see that the exhaled volume is more the than the inhaled indicating that the patient exhaled the trapped air from the first breath. The expiratory phase of the second breath is prolonged and patient had an inspiratory effort during it but was ineffective as he did not reach the trigger threshold.
Now, if this is trapped air in the first breath, why the flow did not persist at end of expiration? The answer is that he has a high central respiratory drive from massive stroke and his inspiratory efforts every 2 seconds cut off his expiratory flow and decreased to zero and in fact reached 3.66 L/min as you see at the dot and was able to trigger the ventilator for the second breath.
So this is trapped air or auto-peep.
here is what happened when I decreased the tidal volume to 450 from 540!
Edited
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Double-triggering seen in flow and volume waveforms from volume-controlled ventilation. Continued subject effort during the second breath causes the airway pressure to drop below the trigger threshold, which initiates an additional “stacked” breath. Note the large increase in peak airway pressure caused by the stacked breath and the high peak expiratory flow following the stacked breath.
Cycling asynchrony on the ventilator assessed by expiratory muscle EMG (Transversus abdominis):
The above graph shows the relationship between the flow over time waveform and the activities of the expiratory muscles measure by EMG. The relationship of neural expiratory time to ventilator expiratory time was assessed by measuring the phase angle, expressed in degrees. If neural activity began simultaneously with the ventilator, the phase angle (0) was zero. Neural activity beginning after the offset (termination) of inflation by the ventilator resulted in a positive phase angle (60 degrees for subject 1). Neural activity beginning before the offset of inflation by the ventilator resulted in a negative phase angle (45 degrees for subject 2)
The second graph shows waveforms airway pressure (Paw), flow, and transversus abdominis electromyogram in a critically ill patient with chronic obstructive pulmonary disease receiving pressure control of 15 cm H2O. Expiratory muscle activity (vertical dotted line) began…
We performed an inspiratory hold and the plateau pressure is higher than the peak inspiratory pressure. How can that be explained for the patient who is not sedated.
ibrahim al-sanouri
Oct 06, 2022
Asynchronous breath with cough during the inspiration as shown with pressure scalar
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Left image showing delayed termination (cycling) asynchrony with inspiratory time of 1 second. Middle image, inspiratory time was decreased to 0.8 and asynchrony improved. However, patient started to have double triggering as shown in the right image.
Mohammad Shaban
Sep 09, 2022
The image on right is confusing Pressure-time curve looks like double trigger, but we know that in pressure modes it’s better to look at the flow -time curve to understand the real interaction between the patient and the ventilator…. Looking at the flow-time curve shows that in the third cycle it might not be double trigger. Clearly there was no positive flow during the second pressure wave of the third cycle, means there was no gas in So, I need more cycles like this to understand but looks like the patient immediately after starting the expiratory phase held his breath again and did not allow all the volume to be out freely. The expiratory flow shows that clearly Volume curve may help to understand more about this
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What change would you do on the ventilator to improve the asynchrony indicated by the green arrows?
Decrease Inspiratory time
Increase inspiratory time
Increase trigger threshold
Decrease trigger threshold
Mazen Kherallah
Sep 08, 2022
This patient has delayed cycling asynchrony indicated by the hump at the end of inspiration (expiratory efforts by the patient during inspiratory time of the ventilator breaths). Therefore, the answer is decreasing inspiratory time on the ventilator to allow synchrony with the patient's expiratory efforts.
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Delayed cycling (termination) indicated by early patient’s expiratory efforts!
Flow-time waveform from a patient receiving intermittent mandatory ventilation with pressure support. Large tidal volume (VT) during the mandatory breath prolongs expiratory time (lengthened time constant) that exceeds the patient’s neural timing mechanism. Additional patient efforts that fail to trigger the ventilator are evident in the expiratory flow waveform.
It illustrates the impact of large tidal volumes (VT) provided during the mandatory breaths and the impact on expiratory timing. Following the large mandatory breath, expiratory time is slightly prolonged and interferes with the patient’s internal timing mechanism, so the next inspiratory effort (seen as a sudden drop in the expiratory flow, to nearly zero) occurs prior to completion of exhalation. As in previous waveforms, this example illustrates the importance of carefully evaluating the flow waveform to identify additional patient efforts.
Flow, airway pressure (Paw), and esophageal pressure (Pes) in a patient with severe chronic obstructive pulmonary disease and ventilated with pressure support. The dotted lines indicate the beginning of inspiratory efforts that triggered the ventilator. The thin, black arrows indicate nontriggering inspiratory efforts. Notice the time delay between the beginning of inspiratory effort and ventilator triggering. Ineffective (nontriggering) efforts occurred during both mechanical inspiration and expiration. Those ineffective efforts can easily be identified on the flow waveform; ineffective efforts during mechanical inspiration abruptly increase inspiratory flow, whereas during expiration they result in an abrupt decrease in expiratory flow (open arrows in the flow waveform). The set respiratory frequency is 12 breaths/min, but the patient is making 33 inspiratory efforts per minute.
The second breath is an ineffective breath to trigger the ventilator as the patient’s efforts did not generate a flow to reach the trigger threshold on the ventilator setting, therefore it was wasted with minimal tidal volume!
The adequacy of flow during volume-controlled ventilation can be evaluated with the pressure-time waveform. Since the total work performed during the breath is the sum of the patient work and the ventilator work, we can evaluate the relative contributions of both by comparing the shapes of the pressure-time waveform during 2 different conditions: completely passive breathing, during which the waveform has a defined pattern based on the type of flow (constant-flow, descending-ramp, or sinusoidal) and patient-triggered breathing, during which the additional patient effort “dishes out” (ie, makes concave) the pressure waveform, relative to the amount of patient work performed. The hatched area illustrates the pressure-time product and represents the effort the patient contributed to the delivery of the breath.
Dynamic hyperinflation syndrome (auto PEEP) on volume/flow loop, note the persistent flow at the end of expiration and the tapped volume indicated by the yellow square.
The question is, what happens to the auto PEEP if settings on the ventilator are not corrected, does the lung continue to hyperinflate or what?
Mazen Kherallah
Aug 09, 2021
Double triggering in patients with ARDS on protective lung strategy (PLS). The added tidal volume with the second triggered breath results in a VT much larger than what is accepted for PLS (4-6 mL/kg of IBW). Paralysis would benefit this patient to stay within the range of protective lung strategy.
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Air leak as tidal volume drops after 3rd breath to zero.