Objective To assess the risk factors associated with extubation failure in patients who had successfully passed a spontaneous breathing trial.Methods Patients receiving invasive mechanical ventilation for over 48 h were enrolled in the study，they were admitted into Emergency ICU of Zhongshan Hospital during May 2006 and Oct.2007.A spontaneous breathing trial was conducted by a pressure support of 7 cm H2O for 30 min.Clinical data were prospectively recorded for the patient receiving full ventilatory support before and after the spontaneous breathing trial.Regarding the extubation outcome，patients were divived into extubation success group and extubation failure group.Results A total of 58 patients with a mean（±SD） age of 69.4±12.7 years passed spontaneous breathing trial and were extubated.Extubation failure occurred in 11 patients（19%）.The univariate analysis indicated the following associations with extubation failure：elderly patients（78.1±7.9 years vs 67.4±15.1years，Plt;0.05），higher rapid shallow breathing index（RSBI） value（83±12 breaths·min-1·L-1 vs 68±19 breaths·min-1·L-1，Plt;0.05）and excessive respiratory tract secretions（54.5％ vs 21.3％，Plt;0.05）.Conclusion Among routinely measured clinical variables，elderly patients，higher RSBI value and amount of respiratory tract secretions were the valuable index for predicting extubation failure despite a successful spontaneous breathing trial.
Objective To investigate the correlation between dynamic intrinsic positive endexpiratory pressure ( PEEPidyn) and volume dependence of elastance and resistance of respiratory system ( Evd/Rvd) derived from nonlinear analysis of respiratory mechanics in COPD patients during pressure support ventilation ( PSV) . Methods Twenty-five COPD patients mechanically ventilated using mode of PSV were ventilated at a PSV level of no less than 20 cm H2O in a period of 15 minutes to attain so-callednear-relaxation state. The pressure( P) , flow( V′) and volume( V) data were analyzed by nonlinear mode of respiratory motion. PEEPidyn was determined by esophageal balloon-tipped catheter technique. The correlations between PEEPidyn and Evd, Rvd as well as Evd ×Rvd were analyzed. Results The correlation coefficients between PEEPidyn and Evd, Rvd as well as Evd ×Rvd were 0. 85,0. 80, and 0. 90, respectively. Conclusions Nonlinear mode of respiratory motion is suitable to analyze respiratory mechanics of COPD patients mechanically ventilated using mode of PSV. There are good correlations between PEEPidyn and Evd,Rvd as well as Evd ×Rvd which may be used to noninvasively monitor PEEPidyn in mechanically ventilated COPD patients using mode of PSV.
ObjectiveTo investigate the physiologic effects of different pressure assist (PA) on ventilatory status,oxygenation and work of breathing (WOB) when a new generation of proportional assist ventilation (PAV) is applied in patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD). MethodsA prospective,crossover randomized physiologic study was performed.80%PA,60%PA and 40%PA was sequentially randomized to be applied with the duration of 30 minutes,and pressure support ventilation (PSV) with the duration of 30 minutes was applied before each PA.Ventilatory status, oxygenation,dyspnea indexes in PSV and different PA were compared,and WOB of patients and ventilator were compared in different PA. ResultsTwenty-eight patients were recruited into the study.With the decrease of PA,peak inspiratory pressure (PIP),mean airway pressure (Pm),and tidal volume (VT) decreased gradually (P>0.05),respiratory rate (RR) increased gradually (P<0.05),while minute volume (MV),heart rate (HR),systolic blood pressure (SBP),mean arterial pressure (MAP),pH,arterial carbon dioxide tension (PaCO2),and arterial oxygen tension/inspired oxygen fraction (PaO2/FiO2) did not change significantly (P>0.05).Compared with PSV mode,PIP increased significantly in 80%PA (P<0.05),decreased significantly in 60%PA and 40%PA (P<0.05).Pm did not change significantly in 80%PA (P>0.05),decreased significantly in 60%PA and 40%PA (P<0.05).VT increased significantly in 80%PA (P<0.05),decreased significantly in 60%PA and 40%PA (P<0.05).RR did not change significantly in 80%PA (P>0.05),increased significantly in 60%PA and 40%PA (P<0.05).MV did not change significantly in 80%PA (P>0.05),decreased significantly in 60%PA and 40%PA (P<0.05).With the decrease of PA,Borg score and scale for accessory muscle use increased gradually (P<0.05).Compared with PSV mode,Borg score and scale for accessory muscle use did not change significantly in 80%PA (P>0.05),increased significantly in 60%PA and 40%PA (P<0.05).WOB of patients in 40%PA was significantly higher than that in 60%PA (P=0.000) and that in 80%PA (P=0.000),while which in 60%PA was significantly higher than that in 80%PA (P=0.000).On the contrary,WOB of ventilator in 40%PA was significantly lower than that in 60%PA (P=0.004) and that in 80%PA (P=0.000),while which in 60%PA was significantly lower than that in 80%PA (P=0.000). ConclusionThe new generation of PAV can safely and effectively provide respiratory support to patients with AECOPD.Respiratory pattern,levels of dyspnea and accessory muscle use in 80%PA are similar with those in PSV.With the decrease of PA,levels of spontaneous breathing and WOB increase and dyspnea worsens.PAV can promote spontaneous breathing and prevent respiratory muscle disuse atrophy even more, but easily lead to respiratory muscle fatigue with inappropriate use.
ObjectiveTo evaluate the accuracy of the new dynamic approach in the measurement of respiratory mechanics with different pressure support (PS) level during pressure support ventilation (PSV) via oral-nasal mask.MethodsThe Respironics V60 ventilator was connected to a ASL5000 lung simulator, which simulate lung mechanics in patients with chronic obstructive pulmonary disease ［system compliance (Crs)=50 mL/cm H2O, airway resistance (Raw)=20 cm H2O/(L·s), inspiratory time (TI)=1.6 s, breathing rate=15 beats per minute］. PSV were applied with different levels of PS ［positive end-expiratory pressure=5 cm H2O, PS=5/10/15/20/25 cm H2O) and back-up rate=10 beats per minute］. Measurements were conducted at system leaks with 25 – 28 L/min. The performance characteristics and patient-ventilator asynchrony were assessed, including flow, airway pressure, time and workload. Crs and Raw were calculated by using new dynamic approach.ResultsTidal volume (VT) was increased with increasing PS level ［(281.45±4.26)mL at PS 5 cm H2O vs. (456.81±1.91)mL at PS 10 cm H2O vs. (747.45±3.22)mL at PS 20 cm H2O, P<0.01］. Severe asynchronous was occurred frequently when PS is at 25 cm H2O. Inspiration cycling criterion (CC) was up-regulated accompanied by increasing PS level ［(15.62±3.11)% at 5 cm H2O, vs. (24.50±0.77)% at 20 cm H2O, P<0.01］. Premature cycling was always existed during PSV when PS < 20 cm H2O, which could be eliminated as PS level increasing. Delay cycling was found when PS was at 20 cm H2O, and cycling delay time was (33.60±15.91)ms (P<0.01). The measurement of Crs was (46.19±1.57)mL/cm H2O with PS at 10 cm H2O, which was closer to the preset values of simulated lung. The underestimate of Crs was observed during high level PS support. The calculation of inspiratory and expiratory resistance was approximate to 20 cm H2O/(L·s) when PS level was exceeded 15 cm H2O.ConclusionsThe new dynamic approach can continuously assess the respiratory mechanics during non-invasive ventilation, which is no need to interrupt the patient's spontaneous breathing. Higher inspiratory flow during PSV is beneficial for Raw measurement, whereas the accuracy of Crs was influenced by the value of actual VT.