Abstract
Background:
Expiratory cassettes (EC) often play a vital role in mechanical ventilation (MV).ECs serve as the brain of the MV, measuring pressures and flows, among other functions after gas is exhaled from the patient. To protect the EC, filters are placed before it to prevent internal damage. Cases of filters creating PEEPtot (intrinsic PEEP) have resulted from the presence of sodium or aerosol medication deposition in the filters. The amount of time it takes for filter blockages or EC malfunction, however, has not been studied.
Methods:
Two ventilators were used side by side this bench study. Both used heated wire circuits and a filter attached to the EC according to the manufacturer’s recommendations. No filters were added to the inspiratory side. Sterilized ECs were used for the trial. MV settings were consistent for both ventilators: VC/AC, VT of 120 mL, frequency of 15, PEEP of 5 cm H2O and 1 s i-time were used in this bench study. Both MV circuits were attached to a 1 L max VT test lung. A continuous solution of 0.9% normal saline (NSS) was ran through a syringe pump at 10 mL/h using a vibrating mesh nebulizer. This was chosen to simulate continuous albuterol nebulization used for critical pediatric asthma exacerbations, as albuterol is mixed with NSS. The first ventilator (V1) received expiratory filter changes every 4 h, while the second ventilator (V2) had no filter changes throughout the study to determine its impact on the filters, EC readings, and the ability to ventilate. The following parameters were assessed every 4 h: Vti, Vte, PIP, PEEP actual, intrinsic PEEP (PEEPtot), expiratory airway resistance (Re), EC percentage of life expectancy. The trial ran for 6 days.
Results:
V1 had no significant change in Vti, Vte, PIP, PEEPtot, compliance (Ces), or Re over a 6-day period. V2 began to see changes in PEEPtot within 24 h. It was also subjectively reported that within 24 h the expiratory flow took significantly longer to get back to baseline. At 24, 48, and 72 h, values for PEEPtot in cm H2O (5.5, 12, 16), Re (11, 76, 452), PIP cm H2O (13, 18, 23).
Conclusions:
While running continuous albuterol mixed with NSS, ventilators that require EC filters, must be changed more frequently than at 24 h intervals, to prevent external factors of expiratory resistance. This may lead to caregivers mistaking airtrapping within the circuit of the ventilator for increased airway resistance in a patient who is at risk for severe airway resistance, ultimately leading to care mismanagement and potential patient harm.
V2 no filter changes
Date
time
NSS 10ml/hr
syringe changed
VTI
VTE
MAP
PIP
PEEP actual
PEEPTOT
EC predicted life %
AutoPEEP Present
Ces
Re
5/13
0800
yes
no
121
124
5.5
13
4.6
4.6
83%
no
16.9
16
5/13
1200
yes
no
120
121
5.5
13
4.6
4.7
83%
no
16.9
16
5/13
1600
yes
yes
120
121
5.6
13
4.7
4.7
83%
no
17.2
16
5/13
2000
yes
yes
120
122
6.1
13
4.9
5
83%
no
18.2
16
5/14
0001
yes
no
120
123
6.5
13
5
5.1
83%
no
18.3
11
5/14
0400
yes
yes
120
124
6.8
13
5.1
5.3
83%
no
18.4
11
5/14
0800
yes
no
121
121
7.3
13
5.2
5.5
83%
yes
18.4
11
5/14
1200
yes
yes
121
119
8
14
5.7
6.1
83%
yes
18.4
14
5/14
1600
yes
yes
121
119
8.9
14
6.4
7
83%
yes
19.3
19
5/14
2000
yes
no
121
117
9.3
14
6.8
7.5
83%
yes
20.3
22
5/15
0001
yes
yes
121
117
9.7
15
7.2
7.9
83%
yes
20.6
25
5/15
0400
yes
yes
5/15
0800
yes
no
121
111
13
18
11
12
83%
yes
24
76
5/15
1200
yes
no
120
116
17
22
15
12
83%
yes
24
76
5/15
1600
yes
yes
119
114
20
29
15
17
83%
yes
26.3
244
5/15
2000
yes
no
119
114
19
28
13
16
83%
yes
10.5
5/16
0001
yes
no
121
110
16
20
14
16
83%
yes
29.8
416
5/16
0400
yes
yes
120
112
16
21
14
16
83%
yes
33.2
214
5/16
0800
yes
no
119
111
16
23
14
16
83%
yes
17.6
452
5/16
1200
yes
no
119
113
18
27
14
16
83%
yes
10.7
2264
5/16
1600
yes
yes
119
110
19
29
14
16
83%
yes
9.2
2264
5/16
2000
yes
no
120
111
20
30
14
17
83%
yes
9.1
2264
5/17
0001
yes
yes
121
117
20
31
14
17
83%
yes
8.7
2264
5/17
0400
yes
yes
120
115
21
32
15
17
83%
yes
8.2
2264
5/17
0800
yes
no
120
113
21
32
15
17
83%
yes
7.2
2264
5/17
1200
yes
yes
121
115
21
33
15
17
83%
yes
7.4
2264
5/17
1600
yes
no
120
118
22
34
15
18
83%
yes
7.3
2264
5/17
2000
yes
no
120
117
22
35
15
18
83%
yes
7.4
2264
5/18
0001
yes
yes
120
116
23
35
16
18
83%
yes
7.3
2264
V1 4 hour filter changes
Date
Time
NSS 10ml/hr
Syringe changed
VTI
VTE
MAP
PIP
PEEP actual
PEEPTOT
EC%
Auto PEEP
Ces
Re
5/13
0800
yes
no
121
117
5
12
4.6
5.4
98%
no
19.4
14
5/13
1200
yes
no
122
122
6
13
4.7
5.4
98%
no
19.9
16
5/13
1600
yes
yes
122
118
6
13
4.7
5.4
98%
no
19.3
16
5/13
2000
yes
yes
120
119
6
13
4.7
5.5
98%
no
20.9
16
5/14
0001
yes
no
123
119
6
13
4.8
5.5
98%
no
20.5
14
5/14
0400
yes
yes
122
118
5
12
4.7
5.4
98%
no
20.5
14
5/14
0800
yes
no
121
118
6
13
4.7
5.4
98%
no
20.1
15
5/14
1200
yes
yes
122
122
6
13
4.7
5.4
98%
no
20
15
5/14
1600
yes
yes
122
122
6
13
4.7
5.5
98%
no
19.5
15
5/14
2000
yes
no
123
120
6
13
4.7
5.5
98%
no
21.3
15
5/15
0001
yes
yes
122
121
6
13
4.7
5.5
98%
no
21.1
15
5/15
0400
yes
yes
122
120
6
13
4.7
5.5
98%
no
20.8
14
5/15
0800
yes
no
123
122
6
12
4.7
5.4
98%
no
21.6
13
5/15
1200
yes
no
122
128
6
13
4.8
5.4
98%
no
21.6
14
5/15
1600
yes
yes
122
119
5
12
4.7
5.4
98%
no
21.3
14
5/15
2000
yes
no
121
124
6
12
4.7
5.4
98%
no
21.4
14
5/16
0001
yes
no
122
124
6
13
4.7
5.4
98%
no
22.4
15
5/16
0400
yes
yes
123
125
6
13
4.7
5.4
98%
no
22.1
14
5/16
0800
yes
no
122
119
6
12
4.7
5.4
97%
no
21
14
5/16
1200
yes
no
122
129
6
12
4.7
5.4
97%
no
22.9
14
5/16
1600
yes
yes
122
122
5
12
4.7
5.4
97%
no
21.7
13
5/16
2000
yes
no
122
123
5
12
4.7
5.3
97%
no
22.6
13
5/17
0001
yes
yes
122
121
5
12
4.7
5.5
97%
no
23.2
13
5/17
0400
yes
y
122
120
5
12
4.7
5.5
97%
no
23.5
13
5/17
0800
yes
no
122
124
6
12
4.8
5.4
97%
no
22.8
14
5/17
1200
yes
yes
121
124
6
12
4.7
5.4
97%
no
21.9
14
5/17
1600
yes
no
122
122
6
12
4.8
5.5
97%
no
21.7
14
5/17
2000
yes
no
121
122
6
12
4.7
5.5
97%
no
22.3
14
5/18
0001
yes
yes
121
124
6
12
4.7
5.5
97%
no
22.3
14
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