Liégina Silveira Marinho

Influences of Duration of Inspiratory Effort, Respiratory Mechanics, and Ventilator Type on Asynchrony With Pressure Support and Proportional Assist Ventilation

BACKGROUND: Pressure support ventilation (PSV) is often associated with patient-ventilator asynchrony. Proportional assist ventilation (PAV) offers inspiratory assistance proportional to patient effort, minimizing patient-ventilator asynchrony. The objective of this study was to evaluate the influence of respiratory mechanics and patient effort on patient-ventilator asynchrony during PSV and PAV plus (PAV+). METHODS: We used a mechanical lung simulator and studied 3 respiratory mechanics profiles (normal, obstructive, and restrictive), with variations in the duration of inspiratory effort: 0.5, 1.0, 1.5, and 2.0 s. The Auto-Trak system was studied in ventilators when available. Outcome measures included inspiratory trigger delay, expiratory trigger asynchrony, and tidal volume (VT). RESULTS: Inspiratory trigger delay was greater in the obstructive respiratory mechanics profile and greatest with a effort of 2.0 s (160 ms); cycling asynchrony, particularly delayed cycling, was common in the obstructive profile, whereas the restrictive profile was associated with premature cycling. In comparison with PSV, PAV+ improved patient-ventilator synchrony, with a shorter triggering delay (28 ms vs 116 ms) and no cycling asynchrony in the restrictive profile. VT was lower with PAV+ than with PSV (630 mL vs 837 mL), as it was with the single-limb circuit ventilator (570 mL vs 837 mL). PAV+ mode was associated with longer cycling delays than were the other ventilation modes, especially for the obstructive profile and higher effort values. Auto-Trak eliminated automatic triggering. CONCLUSIONS: Mechanical ventilation asynchrony was influenced by effort, respiratory mechanics, ventilator type, and ventilation mode. In PSV mode, delayed cycling was associated with shorter effort in obstructive respiratory mechanics profiles, whereas premature cycling was more common with longer effort and a restrictive profile. PAV+ prevented premature cycling but not delayed cycling, especially in obstructive respiratory mechanics profiles, and it was associated with a lower VT.

Assessment of regional lung ventilation by electrical impedance tomography in a patient with unilateral bronchial stenosis and a history of tuberculosis

Bronchial stenosis can impair regional lung ventilation by causing abnormal, asymmetric airflow limitation. Electrical impedance tomography (EIT) is an imaging technique that allows the assessment of regional lung ventilation and therefore complements the functional assessment of the lungs. We report the case of a patient with left unilateral bronchial stenosis and a history of tuberculosis, in whom regional lung ventilation was assessed by EIT. The EIT results were compared with those obtained by ventilation/perfusion radionuclide imaging. The patient was using nasal continuous positive airway pressure (CPAP) for the treatment of obstructive sleep apnea syndrome. Therefore, we studied the effects of postural changes and of the use of nasal CPAP. The EIT revealed heterogeneous distribution of regional lung ventilation, the ventilation being higher in the right lung, and this distribution was influenced by postural changes and CPAP use. The EIT assessment of regional lung ventilation produced results similar to those obtained with the radionuclide imaging technique and had the advantage of providing a dynamic evaluation without radiation exposure.

Exercise Capacity Impairment Can Predict Postoperative Pulmonary Complications after Liver Transplantation

Background: Postoperative respiratory complications (PRCs) are common after liver transplantation (LT) and contribute significantly to the related morbidity and mortality. Objective: The aim of this paper was to determine the incidence of PRCs after LT and the value of simple exercise capacity measures as independent predictors of PRCs. Methods: We conducted a prospective cohort study of consecutive adults submitted to LT at a University Hospital in Fortaleza Brazil from March 2013 to March 2015. At baseline, exercise capacity was assessed with the 6-minute walk test (6MWT) and the 6-minute step test (6MST), lung function was tested by spirometry, and respiratory muscle strength was measured by maximal respiratory pressure. Additional relevant pre- and intraoperative data were collected through interview and chart review, and their association with the incidence of PRCs was evaluated. Results: The study included 100 subjects, 44% of whom presented at least 1 of the PRCs. In the univariate analysis, poor 6MST and 6MWT results and a longer preoperative cold ischemia time were associated with PRCs. The logistic regression analysis showed that PRCs were less likely to occur when preoperative walking distances were longer: the odds ratio (95% CI) was reduced to 0.589 (0.357-0.971) for each 50 m walked (p = 0.03). Likewise, PRCs were more likely to occur in patients with longer preoperative cold ischemia times: the odds ratio (95% CI) increased to 1.008 (1.002-1.015) for each minute (p = 0.01). Conclusion: The incidence of PRCs is high in LT patients. A prolonged cold ischemia time and preoperative 6MWT results were independent predictors of PRCs in this patient population.