Lung Protective Ventilation Strategies: Have We Applied Them in Trauma Patients at Risk for Acute Lung Injury and Acute Respiratory Distress Syndrome?

By Gillis, Robert C Weireter, Leonard J Jr; Britt, Rebecca C; Cole, Frederic J Jr; Et al

Lung protective ventilation strategies for patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are well documented, and many medical centers fail to apply these strategies in ALI/ARDS. The objective of this study was to determine if we apply these strategies in trauma patients at risk for ALI/ ARDS. We undertook a retrospective review of trauma patients mechanically ventilated for >/=4 days with an ICD-9 for traumatic pneumothorax, hemothorax, lung contusion, and/or fractured ribs admitted from May 1, 1999 through April 30, 2000 (Group 1), the pre- ARDS Network study, and from May 1, 2003 through April 30, 2004 (Group 2), the post-ARD S Network study. Tidal volume (VT)/kg admission body weight, VT/kg ideal body weight (IBW), and plateau and peak pressures were analyzed with respect to mortality. VT/Kg admission body weight and IBW were significantly reduced when comparing Group 1 with Group 2 (9.27 to 8.03 and 11.67 to 10.04, respectively). VT/kg IBW was greater (P < 0.01) for patients who died in Group 1 (13.81) compared with patients who lived (10.29) or died (9.89) in Group 2. Peak and plateau pressures were greater (P < 0.01) in patients who died in Group 1 than patients who lived or died in Group 2. A strict ARDS Network ventilation strategy (VT < 6 mL/kg) is not followed, rather a low plateau/peak pressure strategy is used, which is a form of lung protective ventilation. ACUTE RESPIRATORY DISTRESS syndrome (ARDS) was first described in 1967 and had an associated mortality rate that exceeded 95 per cent.1,2 Today, mortality rates are estimated to be as high as 50 per cent, and this number is even higher in patients with ventilator- associated lung injury.3-5 The reduction of mortality by the use of lung-protective ventilation strategies in patients at risk for ARDS and acute lung injury (ALI) has been well documented.6-10 The ARDS Network study recommends low tidal volume (VT) ventilation and is considered by some to be the standard for lung-protective ventilation for patients with or at risk for ALI/ARDS.5,8 Recently, several studies demonstrated that even though low VT ventilation is clearly advocated in patient populations at risk for ALI/ARDS, many clinicians failed to apply low VT lung-protective ventilation strategies in their clinical practice and still use VT that are too high and may cause further damage to this patient population.7,11,12 Thus, the objective of this study was to determine if ARDS Network lung protective ventilation strategies are applied in the trauma patient population at risk for ALI/ARDS.

Methods

A retrospective review to determine if we were in compliance with the ARDS Network study in using lung-protective ventilation strategies was conducted of all trauma patients mechanically ventilated for ^4 days admitted before the publication of the ARDS Network study (May 1, 1999 through April 30, 2000 = Group 1) and after the publication of the ARDS Network study (May 1, 2003 through April 30, 2004 = Group 2). Patients were further identified by those who had documented ICD-9 codes for traumatic pneumothorax, traumatic hemothorax, lung contusion, and/or fractured ribs. ICD-9 code identification of patients was conducted through our institutions trauma registry. VT (mL/kg) admission body weight (ABW), VT (mL/kg) ideal body weight (IBW), plateau pressure, and peak pressure were analyzed with respect to mortality. Ventilation data were collected and averaged over a patients’ entire intensive care unit course, i.e., if a patient was ventilated for 16 days, 16 days of ventilation data were averaged. Thus, means were calculated from data over the entire length of time the patient was mechanically ventilated. Data were analyzed by one-way analysis of variance followed by the Ryan-Einot-Gabriel-Welch mean separation test and are expressed as means +- SE. P

Results

In Groups 1 and 2, 235 patients were mechanically ventilated for >/=4 days. Of these, 33 from Group 1 and 48 from Group 2 met our ICD- 9 inclusion criteria. Medical records personnel were unable to locate six records from Group 1 and eight records from Group 2, for a total of 27 records from Group 1 and 40 records from Group 2. Patient characteristics did not differ when comparing Group 1 with Group 2 (Table 1). Ventilation data are shown in Table 2. VT, plateau pressure, and peak pressure were significantly decreased when comparing Group 2 with Group 1. All other ventilation data did not differ when comparing Group 1 with Group 2. VT/kg IBW and VT/kg ABW were significantly decreased when comparing Group 2 with Group 1 (Table 3). VT/kg ABW did not differ for patients who lived or died when comparing Group 1 with Group 2 (Table 4). VT/kg IBW was significantly higher for patients who died in Group 1 compared with patients who lived in Group 1 and patients who lived or died in Group 2 (Table 5). Peak and plateau pressures were significantly higher for patients who died in Group 1 compared with patients who lived in Group 1 and patients who lived or died in Group 2. Additionally, peak and plateau pressures were significantly lower for patients who lived in Group 2 compared with patients who died in Group 2 and patients who lived or died in Group 1 (Tables 6 and 7). VT was significantly higher for patients who died in Group 1 compared with patients who lived or died in Group 2 (Table 8).

TABLE 1. Patient Characteristics

TABLE 2. Ventilation Data

TABLE 3. Tidal Volume ml/Kg Body Weight

TABLE 4. Tidal Volume ml/Kg Admission Body Weight of Patients Who Lived or Died

TABLE 5. Tidal Volume ml/Kg Ideal Body Weight of Patients Who Lived or Died

TABLE 6. Peak Pressure (cm H2O) of Patients Who Lived or Died

Discussion

The use of lung-protective ventilation strategies has been well documented in patients with ALI/ARDS. The ARDS Network study was stopped after 861 patients were enrolled because of the efficacy of decreasing mortality by more than 20 per cent of patients treated with a VT of 6 mL/kg predicted body weight verses a higher VT of 12 mL/kg predicted body weight.6 Traditional ventilation can reach VT as high as 10 to 15 mL/kg. Although VT of this magnitude are effective at maintaining arterial PCO^sub 2^ and pH within normal limits, they are not without problems.5 ALI and ARDS reduce lung compliance, leading to elevated airway pressures with high VT mechanical ventilation.5, 13 Elevated pressures may over-distend normal aerated regions of the lung, resulting in alveolar rupture and cell injury, as well as causing damage via recruitment/ derecruitment of alveoli, leading to shear stress injury, all of which lead to inflammation and increased vascular permeability.5, 13 Additionally, these injuries may lead to a loss of surfactant, further complicating patient care.5 Recent publications challenge the actual application of these strategies in clinical practice, and the objective of this study was to determine if ARDS Network ventilation strategies are applied in the trauma patient population at risk for ALI/ARDS.

TABLE 7. Plateau Pressure (cm H2O) of Patients Who Lived or Died

We use a volume-targeted pressure control ventilation strategy as our usual ventilation management methodology. This allows us to control peak and mean airway pressures below thresholds thought deleterious to the alveolar space. Using the variable airflow in the pressure control mode, as opposed to the fixed air flow in the volume control mode, we believe we can minimize the flow dysynchrony experienced by some patients. This leads to improved patient comfort and facilitates the weaning process. Our performance improvement surveillance demonstrates excellent compliance and satisfactory results with this approach. Neither technique has been demonstrated to be superior in patients with ALI/ARDS.

According to ABW and IBW, ARDS Network lung protective ventilation strategies have not been completely applied in the trauma patient population. VT/ kg ABW and IBW were significantly reduced from Group 1 to Group 2 (9.27 to 8.03 and 11.67 to 10.04, respectively), but not to the standard suggested by the ARDS network of <6 mL/kg predicated body weight. Young et al.7 reported a similar finding in a study of over 900 ARDS patients at three different medical centers. They found a significant reduction in the VT/ kg predicated body weight from a pre-ARDS Network group to a post-ARDS Network group, but did not reduce the VT/kg predicated body weight to the goal of <6 mL/kg.

Although the strategy that we have adopted has not decreased VT/ kg body weight to ARDS Network standards, our approach has significantly decreased peak and plateau pressures from Group 1 to Group 2 (35.0 to 29.1 and 29.3 to 25.2, respectively). Furthermore, patients who lived in Group 2 had a significantly lower plateau and peak pressures than patients who died, which correlates well with the current literature in that decreased VT and plateau pressures lead to decreased mortality in patients with ALI/ARDS. Decreased plateau pressures are considered a form of lung-protective ventilation in a pressure-controlled ventilation system.14, 15 The ARDS Network further advocates a plateau pressure limit (<30 cm H2O) in addition to decreased VT.6 It may not be the decrease in VT per se that is important in the documented positive outcomes observed in the ARDS Network study. Rather, it could be the decrease in pressures (i.e., plateau and peak pressures) in the injured lung that result in the positive outcomes. By decreasing the VT, the pressures directly decrease in the noncompliant lung seen in ARDS patients. Therefore, by decreasing peak and plateau pressures, one should expect to achieve similar results as those observed in the ARDS Network study.

The main limitation of this study is the small sample size. This is a direct result of the number of patients admitted to the trauma service over the selected time period, as well as the ICD-9 codes used for inclusion. ICD-9 codes for inclusion into the study were chosen by which injuries increase the risk that a patient will develop ALI/ARDS. Other ICD-9 codes could have been included such as liver laceration, pelvic injuries, etc. However, this being a retrospective pilot study, decisions had to be made on where to cut the data set. This study was retrospective and thus had all the associated problems that come with a retrospective study. A prospective trial needs to be done to determine if decreased peak and plateau pressures lead to decreased mortality. Additionally, future studies should focus on patients diagnosed with ALI/ARDS, not patients at risk for ALI/ARDS.

We conclude that a strict ARDS Network lung-protective ventilation strategy (VT < 6 mL/kg) has not been followed, rather a low plateau/low peak pressure strategy has been adopted, which is a form of lung-protective ventilation in the trauma patient population at risk for ALI/ARDS.

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ROBERT C. GILLIS, PH.D., LEONARD J. WEIRETER, JR., M.D., REBECCA C. BRITT, M.D., FREDERIC J. COLE, JR., M.D., JAY N. COLLINS, M.D., L.D. BRITT, M.D., M.P.H.

From the Department of Surgery, Eastern Virginia Medical School, Norfolk, Virginia

Address correspondence and reprint requests to Leonard J. Weireter, Jr., M.D., Department of Surgery, Eastern Virginia Medical School, 610 Hofheimer Hall, 825 Fairfax Avenue, Norfolk, VA 23507.

Copyright Southeastern Surgical Congress Apr 2007

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