Intrinsic PEEP Predicts Lung Reduction Success

Abstract & Commentary

Synopsis: Patients with preoperative intrinisic PEEP (PEEPi) less than 5 cm H2O failed to improve in dyspnea score or forced expiratory volume in one second (FEV1) when evaluated three months following lung volume reduction surgery (LVRS). Patients with PEEPi 5 cm H2O or more were likely to be improved following LVRS.

Source: Tschernko EM, et al. Anesth Analg 1999 (Jan);88:28-33.

Lung volume reduction surgery (lvrs) for severe emphysema awaits confirmation of clinical efficacy. It is known that some patients have dramatic, subjective, and measurable objective improvements following this radical surgical approach while others fail to obtain benefit. Preoperative predictors identifying appropriate candidates are being evaluated. Tschernko and associates studied 32 patients undergoing LVRS. Preoperatively, they measured total resistive work of breathing (WOB), mean airway resistance (Raw), and dynamic intrinsic PEEP (PEEPi), in addition to the usual monitors of the severity of chronic lung disease (FEV1, FVC, arterial blood gases, pulmonary artery pressures, chest CT, and ventilation/perfusion scans) in 32 patients. Using a video-endoscopic approach, 20-30% of each lung was removed, concentrating on the most abnormal lobes.

Two patients were excluded: one could not be weaned postoperatively and underwent lung transplantation, and another developed the acute respiratory distress syndrome (ARDS) and died of multiple organ failure. The 30 remaining patients were extubated within 24 hours and served as the test group. The average age was 56 years, and there were 18 men and 12 women. The group’s average FEV1 was 0.75 L, or 25% of predicted. The group’s PaO2 ranged from 54-90 mmHg, PaCO2 from 34-77 mmHg, and two-thirds of the patients were on chronic oxygen therapy. The following surgery improvements in most parameters were noted.

    Table
    Surgery Improvements_________________________
    Parameter
    Preoperative
    Postoperative
    FEV1
    0.75 L 
    1.18 L 
    WOB
    1.65 J/L
    0.93 J/L
    Raw 
    17.3 cm H2O/L/sec
    9.7 cm H2O/L/sec
    PEEPi
    6.3 cm H2O
    1.9 cm H2O
    ____________________________________________

Five patients failed to improve at all following surgery; the others improved objectively by at least 10% in FEV1. Using a variety of cut points for each of the parameters, PEEPi greater than or equal to 5 cm H2O was found to be the best predictor of improvement in FEV1 and dyspnea score postoperatively, demonstrating a sensitivity of 0.93 and a specificity of 0.88. This predicted at least a 40% increase in FEV1 postoperatively.

Comment by Charles G. Durbin, Jr., MD, FCCM

This study offers a cut point for clinical use in deciding who will benefit from LVRS. It also identifies those who may not. Tschernko et al defined a good result as an increase in FEV1 of at least 40%, the group average being 0.75 L preoperatively. This is a high expectation and, if it holds up in other patients, should result in unquestioned benefit. It is interesting to note that none of the other tested variables performed as well in predicting success as did PEEPi.

Using the suggestions of Tschernko et al, measurements must be made carefully during quiet breathing with an esophageal pressure balloon. Simple, reliable equipment was used (Bicore 100), and well-experienced clinicians must evaluate the obtained data. The other variables obtained also correlated with success but were not as good as PEEPi for separating success from failure.

This study only reports early, three-month success. Whether continued improvement persists for longer remains to be evaluated. It is too early to suggest that the PEEPi be used to deny patients access to LVRS, but advisable that any study of the outcome of these patients include this variable in the evaluation data set.