Mask mechanics and leak dynamics during noninvasive pressure support ventilation: a bench study

OBJECTIVE: To study the mask mechanics and air leak dynamics during noninvasive pressure support ventilation. SETTING: Laboratory of a university hospital. DESIGN: A facial mask was connected to a mannequin head that was part of a mechanical respiratory system model. The mask fit pressure (P(mask-fit)) measured inside the mask's pneumatic cushion was adjusted to 25 cmH(2)O using elastic straps. Pressure support (PS) was set to ensure a maximal tidal volume distal to the mask (VT(distal)) but avoiding failure to cycle to exhalation. MEASUREMENTS: Airway pressure (P(aw)), P(mask-fit), mask occlusion pressure (P(mask-occl)=P(mask-fit)-P(aw)), VT proximal (VT(prox)), distal to the mask (VT(distal)), air leak volume ( Leak=VT(prox)-VT(distal)), and inspiratory air leak flow rate (difference between inspiratory flow proximal and distal to the mask) were recorded. RESULTS: PS 15 cmH(2)O was the highest level that could be used without failure to cycle to exhalation (VT(distal) of 585+/-4 ml, leak of 32+/-1 ml or 5.2+/-0.2% of VT(prox), and a minimum P(mask-occl) of 1.7+/-0.1 cmH(2)O). During PS 16 cmH(2)O the P(mask-occl) dropped to 1.1+/-0.1 cmH(2)O, and at this point all flow delivered by the ventilator leaked around the mask, preventing the inspiratory flow delivered by the ventilator from reaching the expiratory trigger threshold. CONCLUSION: P(mask-fit) and P(mask-occl) can be easily measured in pneumatic cushioned masks and the data obtained may be useful to guide mask fit and inspiratory pressure set during noninvasive positive pressure ventilation.     

Trigger performance of mid-level ICU mechanical ventilators during assisted ventilation: a bench study

OBJECTIVE: To compare the triggering performance of mid-level ICU mechanical ventilators with a standard ICU mechanical ventilator. DESIGN: Experimental bench study. SETTING: The respiratory care laboratory of a university-affiliated teaching hospital. SUBJECT: A computerized mechanical lung model, the IngMar ASL5000. INTERVENTIONS: Ten mid-level ICU ventilators were compared to an ICU ventilator at two levels of lung model effort, three combinations of respiratory mechanics (normal, COPD and ARDS) and two modes of ventilation, volume and pressure assist/control. A total of 12 conditions were compared. MEASUREMENTS AND MAIN RESULTS: Performance varied widely among ventilators. Mean inspiratory trigger time was <100 ms for only half of the tested ventilators. The mean inspiratory delay time (time from initiation of the breath to return of airway pressure to baseline) was longer than that for the ICU ventilator for all tested ventilators except one. The pressure drop during triggering (Ptrig) was comparable with that of the ICU ventilator for only two ventilators. Expiratory Settling Time (time for pressure to return to baseline) had the greatest variability among ventilators. CONCLUSIONS: Triggering differences among these mid-level ICU ventilators and with the ICU ventilator were identified. Some of these ventilators had a much poorer triggering response with high inspiratory effort than the ICU ventilator. These ventilators do not perform as well as ICU ventilators in patients with high ventilatory demand.     

Adult ICU ventilators to provide neonatal ventilation: a lung simulator study

Background

Traditionally, specific ventilators have been manufactured to only provide neonatal mechanical ventilation. However, many of the current generation of ICU ventilators also include a neonatal mode.

Methods

Using the IngMar ASL5000 lung simulator the Puritan Bennett 840, the Maquet Servo i, the Viasys AVEA, the GE Engström, the Drager Evita XL and Babylog 8000 Plus were evaluated during assisted ventilation in the pressure assist/control mode. Three lung mechanics were set: resistance 50 cmH₂O/L/s, compliance 2 mL/cmH₂O; resistance 100 cmH₂O/L/s, compliance 1 mL/cmH₂O; and resistance 150 cmH₂O/L/s, compliance 0.5 mL/cmH₂O. A maximum negative pressure drop of 4 and 7 cmH₂O was achieved during simulated inspirations. Each ventilator was evaluated with PEEP 5 cmH₂O, peak pressure 20 cmH₂O and inspiratory time 0.3 s and with PEEP 10 cmH₂O, peak pressure 30 cmH₂O and inspiratory time 0.4 s. Each ventilator setting was then repeated with a leak of 0.3 L/min at a constant pressure of 5 cmH₂O.

Results

Overall each of the 5 ICU ventilators responded faster or greater than the Babylog with respect to: pressure to trigger (except the Servo i), time to trigger (except the Evita XL), time between trigger and return of pressure to baseline, time from start of breath to 90% of peak pressure (except the Avea) and pressure time product of breath activation. Expiratory tidal volume was also greater with all ICU ventilators except the Avea. Variation in mechanics, leak, PEEP and muscular effort had little effect on these differences.

Conclusion

All ICU ventilators tested were able to at least equal the performance of the Babylog 8000 Plus on all variables evaluated.

     

Impact of the humidification device on intubation rate during noninvasive ventilation with ICU ventilators: results of a multicenter randomized controlled trial

Purpose

The use of heat and moisture exchangers (HME) during noninvasive ventilation (NIV) can increase the work of breathing, decrease alveolar ventilation, and deliver less humidity in comparison with heated humidifiers (HH). We tested the hypothesis that the use of HH during NIV with ICU ventilators for patients with acute respiratory failure would decrease the rate of intubation (primary endpoint) as compared with HME.

Methods

We conducted a multicenter randomized controlled study in 15 centers. After stratification by center and type of respiratory failure (hypoxemic or hypercapnic), eligible patients were randomized to receive NIV with HH or HME.

Results

Of the 247 patients included, 128 patients were allocated to the HME group and 119 to the HH group. Patients were comparable at baseline. The intubation rate was not significantly different: 29.7 % in the HME group and 36.9 % in the HH group (p = 0.28). PaCO₂ did not significantly differ between the two arms, even in the subgroup of hypercapnic patients. No significant difference was observed for NIV duration, ICU and hospital LOS, or ICU mortality (HME 14.1 vs. HH 21.5 %, p = 0.18).

Conclusions

In this study, the short-term physiological benefits of HH in comparison with HME during NIV with ICU ventilators were not observed, and no difference in intubation rate was found. The physiologic effects may have been obscured by leaks or other important factors in the clinical settings. This study does not support the recent recommendation favoring the use of HH during NIV with ICU ventilators.     

Accuracy of the dynamic signal analysis approach in respiratory mechanics during noninvasive pressure support ventilation: a bench study

ObjectiveTo evaluate the accuracy of respiratory mechanics using dynamic signal analysis during noninvasive pressure support ventilation (PSV).MethodsA Respironics V60 ventilator was connected to an active lung simulator to model normal, restrictive, obstructive, and mixed obstructive and restrictive profiles. The PSV was adjusted to maintain tidal volumes (V_T) that achieved 5.0, 7.0, and 10.0 mL/kg body weight, and the positive end-expiration pressure (PEEP) was set to 5 cmH₂O. Ventilator performance was evaluated by measuring the flow, airway pressure, and volume. The system compliance (C_rs) and airway resistance (inspiratory and expiratory resistance, R_insp and R_exp, respectively) were calculated.ResultsUnder active breathing conditions, the C_rs was overestimated in the normal and restrictive models, and it decreased with an increasing pressure support (PS) level. The R_insp calculated error was approximately 10% at 10.0 mL/kg of V_T, and similar results were obtained for the calculated R_exp at 7.0 mL/kg of V_T.ConclusionUsing dynamic signal analysis, appropriate tidal volume was beneficial for R_rs, especially for estimating R_exp during assisted ventilation. The C_rs measurement was also relatively accurate in obstructive conditions.     

Comparison of the effects of pressure support ventilation delivered by three different ventilators during weaning from mechanical ventilation

Objective To compare the effects of pressure support ventilation (PSV) delivered at the same level by three different ventilators on patients' work of breathing (WOB), breathing pattern and gas exchange.Design Prospective, self-controlled clinical study.Setting Intensive care unit of a tertiary university hospital.Patients Nine intubated adult patients during weaning from mechanical ventilation.Interventions Patients were randomly connected to one of three ventilators: the Siemens Servo 900 C (SC), the Ohmeda CPU 1 (CPU), and the Engström Erica (EE) during both zero cmH₂O PSV and 15 cmH₂O PSV.Measurements and results During zero PSV, there was no significant difference in terms of WOB, V_T, V_E, or auto-PEEP among the three ventilators, although there was a trend towards higher levels of WOB with EE. During 15 cmH₂O PSV, WOB was significantly less with SC than with EE or CPU (0.47±0.48 J/l for SC, 1.0±0.48 for EE and 0.78±0.51 for CPU 1,p=0.003). WOB was 64% less than at zero PSV with SC but only 38% less with EE. This was associated with a different pressurization shape, as assessed by the interior surface of Paw-V_T loops (1.23±0.09 J/l for SC, 0.9±0.02 for EE, and 0.79±0.18 for CPU;p<0.001). At 15 cmH₂O PSV, auto-PEEP was significantly lower with SC than with EE (1.7±2.1 cmH₂O for SC, 4.7±3.6 for EE, and 2.8±0.3 for CPU;p=0.04). External expiratory resistances, in cmH₂O/l/s, were significantly higher with EE than with CPU or SC (12.9±3.2 EE, 7.5±2.4 CPU, 5.9±0.5 SC;p<0.001).Conclusion During PSV, the different working principles of different mechanical ventilators profoundly affect patient's WOB. Among the various factors, velocity of pressurization of PSV may play a role in its efficacy in unloading the respiratory muscles.     

Bench testing of pressure support ventilation with three different generations of ventilators

OBJECTIVE: The new generations of intensive care ventilators tend to be more innovative and sophisticated than previous ones, but little is known about their respective performance for delivering pressure support ventilation (PSV) and how they compare to previous generations. DESIGN: Active lung model bench test. APPARATUS: Twenty-two commercially available ventilators classified into three categories: new generation ventilators (after 1993, n=7), previous generation (before 1993, n=6), and recent piston or turbine-based ventilators ( n=9). MEASUREMENTS AND RESULTS: During PSV, the unloading efficacy of the assistance depends on the ventilator's ability to meet inspiratory flow demand. Three levels of flow (0.1 l/s, 0.6 l/s, and 1.2 l/s) were used to simulate inspiratory demand and the net area of the inspiratory airway pressure-time trace was calculated over the first 0.3 s, 0.5 s, and 1 s (Area (0.3), Area (0.5), and Area (tot)) with three levels of PSV (5 cmH(2)O, 10 cmH(2)O, and 15 cmH(2)O). To assess the respective role of pressure support delivery and triggering function, triggering sensitivity was assessed independently by measuring the time delay ( TD (tg)) and the pressure fall (Delta Paw (tg)) with two levels of inspiratory drive. All the new generation ventilators exhibited significantly better results than most of the previous generation ventilators regarding Area (0.3) and TD (tg), indicating large improvements in terms of triggering and pressurisation. CONCLUSION: Regarding PSV and trigger performance, the new generation ventilators - but also some piston and turbine-based ventilators - outperform most of previous generation ventilators.     

Heliox delivery with noninvasive positive pressure ventilation: a laboratory study

BACKGROUND: There is clinical interest in the use of heliox (helium-oxygen mixture) during noninvasive positive pressure ventilation (NPPV), but delivery of heliox with ventilators designed for NPPV has not been reported. We studied helium concentration ([He]) when an 80%:20% helium:oxygen mixture (heliox) was used with 5 NPPV ventilators (Knightstar, Quantum, BiPAP S/T-D30, Sullivan, and BiPAP Vision). METHODS: A simulated spontaneous breathing lung model was connected to the ventilators with a circuit incorporating a standard leak. Heliox flows of 0, 5, 10, and 18 L/min and oxygen flows of 0 and 10 L/min were titrated into the system at either a proximal position near the lung model or a distal position near the ventilator (titration method). Because the BiPAP Vision has an oxygen delivery module, it was also studied using heliox connected to the air inlet of an oxygen blender, with the blender outlet connected to the oxygen module of the ventilator (blender method). All ventilators were evaluated in spontaneous/timed mode at inspiratory/expiratory pressures of 10/5, 15/5, and 20/5 cm H(2)O. After 5 minutes, [He], oxygen concentration, and pressure in the lung model were recorded. RESULTS: Heliox flow, NPPV settings, site of heliox infusion, and type of ventilator significantly (p < 0.05) affected [He]. [He] was > 60% when heliox flow was 18 L/min in some combinations of settings. The BiPAP S/T-D30 and Quantum occasionally functioned erratically. The BiPAP Vision (blender method) ventilator performed erratically with heliox unless the exhalation port test was bypassed on startup. The addition of heliox flow had no important effect on inspiratory or expiratory positive airway pressure on those breaths during which the ventilators functioned correctly. CONCLUSION: Heliox flow was the most important determinant of [He] when using heliox with NPPV. With heliox there was a potential for ventilator malfunction in some conditions. The clinical implications of these findings remain to be determined.     

Bench test evaluation of volume delivered by modern ICU ventilators during volume-controlled ventilation

Purpose

During volume-controlled ventilation, part of the volume delivered is compressed into the circuit. To correct for this phenomenon, modern ventilators use compensation algorithms. Humidity and temperature also influence the delivered volume.

Methods

In a bench study at a research laboratory in a university hospital, we compared nine ICU ventilators equipped with compensation algorithms, one with a proximal pneumotachograph and one without compensation. Each ventilator was evaluated under normal, obstructive, and restrictive conditions of respiratory mechanics. For each condition, three tidal volumes (V _T) were set (300, 500, and 800 ml), with and without an inspiratory pause. The insufflated volume and the volume delivered at the Y-piece were measured independently, without a humidification device, under ambient temperature and pressure and dry gas conditions. We computed the actually delivered V _T to the lung under body temperature and pressure and saturated water vapour conditions (BTPS).

Results

For target V _T values of 300, 500, and 800 ml, actually delivered V _T under BTPS conditions ranged from 261 to 396 ml (?13 to +32%), from 437 to 622 ml (?13 to +24%), and from 681 to 953 ml (?15 to +19%), respectively (p < 0.01). Respiratory system mechanics and application of an inspiratory pause significantly affected actually delivered V _T. Assuming a set V _T of 6 ml/kg of predicted body weight, a difference of 1–2 ml/kg with actually delivered V _T would be commonly observed.

Conclusion

The difference between preset V _T and actually delivered V _T is clinically meaningful and differs across modern ICU ventilators.     

无创正压通气时不同压力水平对呼吸衰竭患者呼吸生理学参数和人机同步的影响

目的 研究慢性阻塞性肺疾病急性加重期(AECOPD)呼吸衰竭患者无创机械通气时不同压力支持(PS)水平对呼吸生理学参数、人机同步性的影响.方法 入选15例住呼吸科重症监护病房(RICU)的AECOPD呼吸衰竭患者,均需无创机械通气.分别随机给予受试者5、10、15 cm H2O(1 cm H2O=0.098 kPa)水平的PS,在每个PS水平通气30 min后进行2 min的连续参数测量,取其均值.记录每个水平的生理学参数,并计算无效触发指数.结果 15例AECOPD患者,高PS水平(15 cm H2O)的无效触发指数、潮气量(VT)、分钟通气量(VE)、VT变异率、呼吸机吸气时间(TI)、呼气时间(TE)、漏气量(leak)均显著高于低PS水平[5 cm H2O,无效触发指数:(33.8±9.1)%比(8.0±6.0)%,VT(ml):626±203比339±115,VE(L/min):11.1±4.7比7.7±2.7,VT变异率:(32.6±15.5)%比(11.3±6.9)%,TI(s):1.14±0.31比0.76±0.15,TE(s):2.49±0.44比1.87±0.28,leak(L/min):8.28±4.86比2.22±1.58,均P<0.05],而高PS水平时呼吸机呼吸频率(RRvent,次/min)显著低于低PS水平(17±3比23±3,P<0.05);在低水平PS支持下,无效触发指数与TI呈显著正相关(r=0.62,P<0.05).PS水平由低至高变化时,无效触发指数变化率(Δ无效触发)的回归分析显示:Δ无效触发与ΔTI呈显著正相关,与ΔVT呈显著负相关(R2=0.88,P=0.000).结论 ①低水平PS时,患者的无效触发主要与TI延长有关.②高水平PS可显著增加患者的VE、VT,降低RRvent,同时无效触发显著升高;无效触发指数的增加可以通过患者TI的延长、VT变化的个体差异得到解释,而与leak无关.③即使使用Shape-signal切换机制,高水平无创压力支持通气下的AECOPD患者仍保持较高的无效触发指数.     

Health technology assessment in the ICU: noninvasive positive pressure ventilation for acute respiratory failure

Critical care practitioners have a number of health-related technologies at our disposal to provide the best possible care for our critically ill patients. Although certain technologies may improve outcomes in the intensive care unit (ICU), many technologies are disseminated without rigorous evaluation. Health technology assessment (HTA) in critical care is a complex and dynamic process, which is a powerful tool to assess a health technology for its initial use or continued application in the ICU. This article applies an HTA framework to the use of noninvasive positive pressure ventilation (NPPV) for patients with acute respiratory failure (ARF). The strongest evidence to date supports the use of NPPV in patients with ARF caused by exacerbations of chronic obstructive pulmonary disease (COPD); the benefit for patients with acute nonhypercarbic, hypoxemic respiratory failure is less clear. The success of NPPV technology depends on operator education and experience. The cost effectiveness of NPPV has been evaluated in patients with ARF caused by COPD, and cost reduction is attributed to the prevention of ventilator-associated pneumonia by avoiding endotracheal intubation. An HTA framework can help health care practitioners make important decisions regarding the acquisition of new technologies and the evaluation of current technologies. Careful evaluation of health technologies in the ICU should be an ongoing priority.     

Prehospital noninvasive pressure support ventilation for acute cardiogenic pulmonary edema.

Severe acute cardiogenic pulmonary edema (ACPE) can successfully be treated with noninvasive pressure support ventilation (NIPSV) in a clinical setting. Whether prehospital NIPSV starting early at patients' home and being continued until hospital arrival is feasible and improves ACPE emergency care is examined in this study. End points of the study were oxygen saturation at hospital admission and clinical outcome. Twenty-three patients suffering from severe cardiac pulmonary edema with severe dyspnea, an oxygen saturation of less than 90% and basal rales were included in this controlled prospective randomized trial. All patients received standard medical treatment and 10 patients were additionally treated with NIPSV (pressure support level, 12 cmH2O; positive endexpiratory pressure, 5 cmH2O; FiO2, 0.6) whereas the other patients received oxygen (8 l/min) via Venturi face mask. Improvement in oxygen saturation was significantly faster in the NIPSV group and oxygen saturation was higher at the time of the hospital admission (NIPSV=97.3+/-0.8%; standard=89.5+/-2.7%, P=0.002). A trend toward higher troponin T levels was seen in the standard treatment group. The need for intensive care treatment did not differ, and one patient of each treatment group died in hospital. No complications were noted during the treatment with NIPSV. Prehospital NIPSV is feasible and able to improve emergency management of ACPE.     

Efficacy of a heated passover humidifier during noninvasive ventilation: a bench study

BACKGROUND: Noninvasive positive-pressure ventilation (NPPV) delivers air at a high flow, which is associated with airway mucosal drying and impaired airway functioning. OBJECTIVES: To examine the effects of mechanical ventilation parameters on relative humidity and absolute humidity during NPPV, and to evaluate the effect of a heated passover humidifier on relative humidity, absolute humidity, and ventilator performance during NPPV. METHODS: We performed a bench study to assess the effects of inspiratory positive airway pressure (IPAP) of 10 cm H(2)O, 15 cm H(2)O, and 20 cm H(2)O, respiratory rates of 12 breaths/min and 24 breaths/min, and inspiratory-expiratory ratios of 1:2 and 1:3 on relative and absolute humidity. The measurements were obtained on room air and with a heated humidifier at medium and maximum heater settings. RESULTS: Without humidification, the relative humidity in the NPPV circuit (range 16.3-26.5%) was substantially lower than the ambient relative humidity (27.6-31.5%) at all ventilatory settings. Increasing the IPAP decreased the relative humidity (Spearman's rho = 0.67, p < 0.001). Changing the respiratory rate or inspiratory-expiratory ratio had no significant effect. Both relative and absolute humidity increased with humidification, and the air was fully saturated at the maximum heater setting. Delivered IPAP was reduced by 0.5-1 cm H(2)O during humidification. CONCLUSIONS: NPPV delivers air with a low relative humidity, especially with high inspiratory pressure. Addition of a heated humidifier increases the relative and absolute humidity to levels acceptable for nonintubated patients, with minimal effect on delivered pressure. Consideration should be given to heated humidification during NPPV, especially when airway drying and secretion retention are of concern.     

Assessment of respiratory system compliance with electrical impedance tomography using a positive end-expiratory pressure wave maneuver during pressure support ventilation: a pilot clinical study

Introduction

Assessment of respiratory system compliance (C_rs) can be used for individual optimization of positive end-expiratory pressure (PEEP). However, in patients with spontaneous breathing activity, the conventional methods for C_rs measurement are inaccurate because of the variable muscular pressure of the patient. We hypothesized that a PEEP wave maneuver, analyzed with electrical impedance tomography (EIT), might be suitable for global and regional assessment of C_rs during assisted spontaneous breathing.

Methods

After approval of the local ethics committee, we performed a pilot clinical study in 18 mechanically ventilated patients (61 ± 16 years (mean ± standard deviation)) who were suitable for weaning with pressure support ventilation (PSV). For the PEEP wave, PEEP was elevated by 1 cmH₂O after every fifth breath during PSV. This was repeated five times, until a total PEEP increase of 5 cmH₂O was reached. Subsequently, PEEP was reduced in steps of 1 cmH₂O in the same manner until the original PEEP level was reached. C_rs was calculated using EIT from the global, ventral and dorsal lung regions of interest. For reference measurements, all patients were also examined during controlled mechanical ventilation (CMV) with a low-flow pressure-volume maneuver. Global and regional C_rs(low-flow) was calculated as the slope of the pressure-volume loop between the pressure that corresponded to the selected PEEP and PEEP +5 cmH₂O. For additional reference, C_rs during CMV (C_rs(CMV)) was calculated as expired tidal volume divided by the difference between airway plateau pressure and PEEP.

Results

Respiratory system compliance calculated from the PEEP wave (C_rs(PEEP wave)) correlated closely with both reference measurements (r = 0.79 for C_rs(low-flow) and r = 0.71 for C_rs(CMV)). No significant difference was observed between the mean C_rs(PEEP wave) and the mean C_rs(low-flow). However, a significant bias of +17.1 ml/cmH₂O was observed between C_rs(PEEP wave) and C_rs(CMV).

Conclusion

Analyzing a PEEP wave maneuver with EIT allows calculation of global and regional C_rs during assisted spontaneous breathing. In mechanically ventilated patients with spontaneous breathing activity, this method might be used for assessment of the global and regional mechanical properties of the respiratory system.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-014-0679-6) contains supplementary material, which is available to authorized users.     

Sequential use of noninvasive pressure support ventilation for acute exacerbations of COPD

Objectives: To compare the efficacy of noninvasive pressure support ventilation (NIPSV) in acute decompensation in chronic obstructive pulmonary disease (COPD) by means of a bi-level positive airway pressure support system (BiPAP) in a sequential mode with medical therapy alone; to assess the short-term physiologic effects of the device on gas exchange; and to compare patients successfully ventilated with NIPSV with those in whom NIPSV failed. Design: A prospective case series with historically matched control study. Setting: A general intensive care unit (ICU) of a university hospital. Patients: We evaluated the efficacy of administration of NIPSV in 42 COPD patients and compared this with standard treatment in 42 matched historical control COPD patients. Interventions: NIPSV was performed in a sequential mode, i. e., BiPAP in the spontaneous mode was used for at least 30 min every 3 h. Between periods of ventilation, patients could be systematically returned to BiPAP when the arterial oxygen saturation was < 0.85 or when the respiratory rate was > 30 breaths/min. Measurements and results: Success rate, mortality, duration of ventilatory assistance, and length of ICU stay were recorded. Eleven of the 42 patients (26 %) in the NIPSV group needed tracheal intubation compared with 30 of the 42 control patients (71 %). The 31 patients in whom NIPSV was successful were ventilated for a mean of 6 ± 3 days. In-hospital mortality was not significantly different in the treated versus the control group, but the duration of ventilatory assistance (7 ± 4 days vs 15 ± 10 days, p < 0.01) and the length of ICU stay (9 ± 4 days vs 21 ± 12, p < 0.01) were both shortened by NIPSV. BiPAP was effective in correcting gas exchange abnormalities. The pH values, measured after 45 min of BiPAP with optimal settings, in the success (7.38 ± 0.04) and failure (7.28 ± 0.04) patients were significantly different (p < 0.05). Conclusions: NIPSV, performed with a sequential mode, may be used in the management of patients with acute exacerbations of COPD. Received: 10 February 1997 Accepted: 14 July 1997     

压力支持通气与成比例压力支持通气模式对血流动力学状态的影响

目的　探讨压力支持通气 (PSV)与成比例压力支持通气 (PPS)不同通气模式对血流动力学的影响。方法　选择呼吸衰竭行机械通气及脉搏轮廓法持续血流动力学监护患者 2 6例。经治疗进入低辅助通气后比较在PSV、PPS两种通气模式下血流动力学及呼吸力学的差异。结果　PPS模式心输出量 (CO)、心指数 (CI)、每搏量 (SV)较PSV模式明显增加 (P <0 0 5 ) ,外周血管阻力 (SVR)无明显变化 (P >0 .0 5 ) ,气道峰压 (Ppeak)及内源性PEEP(PEEPi)明显下降 (P <0 .0 5 )。结论　PPS模式对机械通气患者的血流动力学状态影响最小 ,较适用于血流动力学不稳定患者。