RESUMO
OBJECTIVES: To investigate the effects of ventilation mode and manual chest compression (MCC) application on the flow bias generated during positive end-expiratory pressure-zero end-expiratory pressure (PEEP-ZEEP) in mechanically ventilated patients. PEEP-ZEEP is an airway clearance manoeuvre with the potential to exceed the flow bias required to remove secretions. However, the ventilation mode applied during the manoeuvre has not been standardised. DESIGN: Randomised crossover trial. PARTICIPANTS: Nineteen mechanically ventilated patients. INTERVENTIONS: Patients were randomised to receive PEEP-ZEEP in volume-controlled and pressure-controlled modes, and with or without MCC. MAIN OUTCOME MEASURES: The difference in flow bias - assessed by the peak expiratory flow (PEF) and peak inspiratory flow (PIF) ratio and difference - between PEEP-ZEEP applied in both ventilation modes, and with and without MCC. RESULTS: The expiratory flow bias was significantly higher in the volume-controlled mode than the pressure-controlled mode. This result was caused by a lower PIF in the volume-controlled mode. PEEP-ZEEP applied in the pressure-controlled mode did not achieve the PEF-PIF difference threshold to clear mucus. Moreover, in the majority of cycles of PEEP-ZEEP applied in the pressure-controlled mode, an inspiratory flow bias was generated, which might embed mucus. PEF was 8l/minute higher with MCC compared with without MCC, which increased the PEF-PIF difference by the same amount. No haemodynamic or respiratory adverse effects were found. CONCLUSIONS: If applied in the volume-controlled mode, PEEP-ZEEP can achieve the flow bias needed to expel pulmonary secretions. However, this is not the case in the pressure-controlled mode. MCC can augment the flow bias generated by PEEP-ZEEP, but its application may be dispensable. CLINICAL TRIAL REGISTRATION: http://www.ensaiosclinicos.gov.br/rg/RBR-223xv8/.
