Mechanisms of changes in nitrogen washout and lung volumes after saline infusion in humans

Evaluation of respiratory inductive plethysmography in controlled ventilation: measurement of tidal volume and PEEP-induced changes of end-expiratory lung volume

STUDY OBJECTIVE

To determine the accuracy of respiratory inductive plethysmography (RIP) with a respiratory monitor (Respitrace Plus; NIMS Inc., Miami) operating in the DC-mode for the measurement of tidal volumes (VT) and positive end-expiratory pressure (PEEP)-induced changes of end-expiratory lung volume (deltaEELV) in patients with normal pulmonary function, acute lung injury (ALI), and COPD during volume-controlled ventilation.

DESIGN

Prospective comparison of RIP with pneumotachography (PT) for assessment of VT and with multibreath nitrogen washout procedure (N2WO) for determination of deltaEELV as reference methods.

SETTING

Mixed ICU at a university hospital.

PATIENTS

Thirty-one sedated and paralyzed patients: 12 patients with normal pulmonary function mechanically ventilated after major surgery, 10 patients with respiratory failure due to ALI, and 9 patients with a known history of COPD ventilated after surgery or because of respiratory failure due to bronchopulmonary infection.

INTERVENTIONS

Stepwise increase of PEEP from 0 to 5 to 10 cm H2O and reduction to 0 cm H2O again. On each PEEP level, N2WO was performed.

MEASUREMENTS AND MAIN RESULTS

The baseline drift of RIP averaged 25.4+/-29.1 mL/min but changed over a wide range even in single patient measurements. Determination of VT for single minutes revealed that 66.5% and 90.0% of all values were accurate within a range of +/-10% and +/-20%, respectively. The deviation for VT measurements between RIP and PT in patients with COPD was significantly (p<0.05) higher compared to patients with ALI or normal pulmonary function. The difference of deltaEELV between RIP and N2WO was 11.6+/-174.1 mL with correlation coefficients of 0.77 (postoperative and COPD patients) and 0.86 (ALI patients). However, just 25.8% and 46.2% were precise within +/-10% and +/-20%, respectively. deltaEELV determination in COPD patients differed more between RIP and N2WO than in the other groups, but this was not significant.

CONCLUSION

In a mixed group of patients undergoing controlled ventilation, RIP using the Respitrace Plus monitor was not consistently precise enough for quantitative evaluation of VT and EELV when compared to our reference methods. This was most evident in patients with COPD. For long-term volume measurements, a better control of the baseline drift of RIP should be achieved.

Bronchial hyperresponsiveness in patients with chronic congestive heart failure

To investigate the relationship between pulmonary congestion and bronchial responsiveness, we measured bronchial responsiveness to acetylcholine in 51 patients with left heart disorders. The measurement of bronchial responsiveness was performed by inhaling doses of acetylcholine chloride (0.08 to 20 mg/ml) and calculating the PC20-FEV1. The median value for PC20-FEV1 was above 20 mg/ml in the subjects without history of congestive heart failure (n = 18), was 5.29 mg/ml in the subjects with clinical evidence of congestive heart failure in the past days (n = 18; p less than 0.01), and was 5.74 mg/ml in the subjects with clinical evidence of congestive heart failure at the time of study (n = 15; p less than 0.01). The hemodynamic variables by cardiac catheterization and the clinical symptoms were not correlated with the grade of bronchial responsiveness. These results suggest that the bronchial responsiveness was increased in most of the patients with chronic congestive heart failure. We concluded that continuous pulmonary congestion may contribute to the pathogenesis of bronchial hyperresponsiveness.