Lung-protective Ventilation Saves Lives: Why Aren't We Using It?
Abstract & Commentary
By David J. Pierson, MD, Editor, Professor, Pulmonary and Critical Care Medicine, Harborview Medical Center, University of Washington, Seattle, is Editor for Critical Care Alert.
Synopsis: In this cohort of patients who met accepted criteria for the diagnosis of ALI-ARDS, chart review showed that the majority did not receive lung-protective ventilation, in some cases even when it had been ordered. Prominent among the reasons given for not using it was diagnostic uncertainty about the presence of ALI-ARDS in the patient.
Source: Mikkelsen ME, et al. Respir Care. 2008;53(4):455-461.
Starting 4 months after publication of the ARDS Network's landmark study showing improved outcomes in patients with acute lung injury (ALI) or the acute respiratory distress syndrome (ARDS) when low-tidal-volume, lung-protective ventilation (LPV) was used,1 investigators at the University of Pennsylvania prospectively identified 88 patients who met the accepted American-European Consensus Conference definition of ALI-ARDS.2 These patients were previously described,3 as one of several studies that have documented a low rate of use of LPV for ALI-ARDS in the first several years following publication of the initial ARDS Network findings. The present article by Mikkelsen et al is an in-depth, retrospective examination of physician documentation in the 75 patients out of the original 88-patient cohort whose medical records were available and who were mechanically ventilated for at least 48 hours.
The 75 patients (mean age 50 years, 71% male, 38% mortality at 30 days) all met diagnostic criteria for ALI-ARDS, and had predisposing conditions including sepsis (31/75), pneumonia (15/75), and aspiration (19/75). In the medical records of 33 of these 75 patients (44%), no mention was made of the physician's intention to use LPV. Among the 42 (56%) in whose management it was used or was intended to be used, 6 never actually received LPV (defined here as never being on a tidal volume of 7.5 mL/kg predicted body weight or less) during the first 48 hours of mechanical ventilation, and 12 others received it only transiently.
In 21 of the 33 ALI-ARDS cases in which LPV was not attempted or intended, the physicians recorded concerns or clinical criteria that the authors interpreted as reasons not to use it. These reasons included the assumption that a different condition other than ALI-ARDS was responsible for the findings (14 patients), improvement in oxygenation after initially meeting the ALI-ARDS diagnostic threshold (4 patients), the presence of relative contraindications to LPV (2 patients), and a switch in the goals of care to comfort-only (1 patient). In half (6/12) of the instances in which LPV was used only transiently, physician diagnostic uncertainty was noted.
Commentary
This study found that over half of all patients with ALI-ARDS who were managed at the authors' institution never received LPV, even briefly. Given that LPV, including limiting tidal volume to about 6 mL/kg and end-inspiratory plateau pressure to less than 30 cm H2O, is now the standard of care for ALI-ARDS, these results are disturbing. They are also consistent with the findings of several other studies on actual ventilator management for ALI-ARDS outside of clinical trials-even in ARDS Network-participating centers.
One of the main reasons for non-use of LPV in patients with ALI-ARDS is that physicians fail to make this diagnosis. In the study by Rubenfeld et al4 to determine the incidence of ALI-ARDS in a region served by 19 general hospitals, using specially trained screeners and accepted international diagnostic criteria, over half of all identified cases never had this diagnosis mentioned in the chart by the physicians caring for the patients. Such diagnostic uncertainty was also found to be common in the present study.
If clinicians only consider using LPV in patients whom they identify as having ALI-ARDS, and if they fail to make that diagnosis in half of the patients who actually have it, maybe it would be better for patients if everyone with acute respiratory failure were managed using LPV. This concept has been advocated by some prominent authorities in mechanical ventilation,5 and is attractive for several reasons:
- Failure of ALI-ARDS to be recognized when present
- Reduced risk of developing ALI-ARDS in patients at risk
- Less risk of developing dynamic hyperinflation and intrinsic PEEP
- Less likelihood of adverse hemodynamic effects of positive-pressure ventilation
- Absence of evidence for clinical harm
On the last of these points, there is some evidence that atelectasis (as commented upon by radiologists interpreting routine chest radiographs) is more likely to occur when patients without ALI-ARDS are managed with low tidal volumes,6 but there is little indication that this is clinically important.
One reason given in the present study for not using LPV was that the patient got better. That is, the PaO2/FIO2 ratio initially meeting the diagnostic threshold for ALI (<300 mm Hg) or ARDS (<200 mm Hg) subsequently improved so that the patient no longer met that criterion. However, patients do not need to meet the initial diagnostic criteria continuously following the diagnosis in order to warrant management with LPV. In the ARDS Network studies, there has been no provision for discontinuing LPV in patients whose oxygenation improved after study enrollment—and many of the enrolled patients have in fact so improved. Thus, if a patient initially meets the diagnostic criteria for ALI-ARDS, he or she should be managed with LPV until the criteria are met for weaning from ventilatory support.
References
- The Acute Respiratory Distress Syndrome Network: Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. N Engl J Med 2000; 342: 1301-1308.
- Bernard GR, et al. The American-European Consensus Conference on ARDS. Definitions, mechanisms, relevant outcomes, and clinical trial coordination. Am J Respir Crit Care Med. 1994 Mar;149(3 Pt 1):818-824.
- Kalhan R, et al. Underuse of lung protective ventilation: analysis of potential factors to explain physician behavior. Crit Care Med. 2006 Feb;34(2):300-306.
- Rubenfeld GD, et al. Incidence and outcomes of acute lung injury. N Engl J Med. 2005;353(16):168-193.
- Steinberg KP, Kacmarek RM. Respiratory controversies in the critical care setting. Should tidal volume be 6 mL/kg predicted body weight in virtually all patients with acute respiratory failure? Respir Care. 2007;52(5):556-564;discussion 565-567.
- Wongsurakiat P, et al. Changing pattern of ventilator settings in patients without acute lung injury: Changes over 11 years in a single institution. Chest. 2004;126(4): 1281-1291.
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