Abstract
Background:
In ARDS recruitment requires a threshold opening pressure (the clinical correlate being plateau pressures or Pplat) that progressively increases from non-dependent to dependent lung over a range of 20-60 cm H2O. 1, 2 Three recruitment nodal points signifying these anatomic transitions (mid-to- dorsal lung) have been identified as 30, 35 and 45 cm H2O. 1 Because the ARDSNet ARMA protocol goal is Pplat < 30 cm H2O, lung-protection maybe at odds with stabilizing oxygenation. We examined the frequency in which this occurred in subjects managed with the ARMA protocol.
Methods:
Our ARDS quality assurance database contained 1, 287 subjects managed with the ARMA protocol with reference period ventilator data on the day following protocol initiation. Calculations included: 1) median and 75th percentile Pplat, 2) percentage of Pplat that met each recruitment nodal point, 3) percentage of subjects with severe ARDS (arterial oxygen tension-to- inspired oxygen fraction or PaO2/FIO2< 100 mm Hg), 4) percentage requiring a toxic FIO2 (> 0.7), 5) median and 75th percentile of tidal volume (VT) and 6) driving pressure (Pplat-PEEP).
Results:
At PEEP > 10 cm H2O, substantial and increasing numbers of subjects met severe ARDS criteria and required a toxic FIO2. Moreover, until PEEP reached 18 cm H2O, the majority of subjects did not cross any of the nodal points associated with alveolar recruitment; particularly those associated with dorsal lung recruitment (ie, Pplat > 35 cm H2O) (Table). Reasonable lung-protection (particularly at higher PEEP levels) was maintained as noted by median and 75th percentiles for both VT driving pressure.
Conclusions:
Increasing PEEP to stabilize oxygenation using the ARMA protocol often does not achieve sufficient Pplat to reverse dependent atelectasis. Depending upon PEEP and severity of hypoxemia, reasonable alternatives include increasing PEEP to increase Pplat, prone position (which increases dorsal transpulmonary pressure) or recruitment maneuvers.
1. Crotti S, et al. Recruitment and derecruitment during acute respiratory failure: a clinical study. Am J Respir Crit Care Med 2002;164:131-140. 2. Borges JB, et al. Reversibility of lung collapse and hypoxemia in early acute respiratory distress syndrome. Am J Respir Crit Care Med 2006;174:268-278.
† data reported as median [75%] to refine assessment of lung injury risk View all access options for this article.
PEEP (cmH2O)
5
8
10
12
14
16
18
20+
Pplat (cmH2O)†
19 [24]
21 [25]
23 [26]
25 [28]
28 [31]
29 [32]
33 [36]
35[40]
% Pplat 30-34
5%
6%
8%
13%
29%
34%
36%
38%
% Pplat 35-44
0%
3%
2%
2%
7%
10%
31%
54%
% Pplat > 45
2%
0%
0%
1%
0%
1%
3%
5%
% PaO2/FiO2 < 100 mmHg
4%
3%
9%
24%
34%
39%
53%
46%
% FiO2 > 0.70
5%
4%
9%
24%
50%
60%
68%
86%
VT (mL/Kg)†
6.1 [6.6]
6.2 [6.6]
6.1 [6.5]
6.1 [6.7]
6.1 [6.6]
6.1 [6.4]
6.2 [7.0]
6.1[6.7]
Pplat-PEEP (cmH2O)†
14 [19]
14 [17]
13 [16]
13 [16]
13 [17]
13 [16]
15 [18]
14 [18]
Get full access to this article