Respiratory muscle workload in intubated,spontaneously breathing patients without COPD: pressure support vs proportional assist ventilation

OBJECTIVE: To compare the respiratory muscle workload associated with pressure support ventilation (PSV) and proportional assist ventilation (PAV) in intubated and spontaneously breathing patients without COPD. DESIGN AND SETTING: Prospective study, intensive care unit university hospital. INTERVENTIONS: Twenty intubated patients, during early weaning, PSV settings made by clinician in charge of the patient, and two levels of PAV, set to counterbalance 80% (PAV 80) and 50% (PAV 50) of both elastic and resistive loads, respectively. The patients were ventilated in the following order: 1) PSV; 2) PAV 50 or PAV 80; 3) PSV; 4) PAV 80 or PAV 50; 5) PSV. PSV settings were kept constant. MEASUREMENTS: Arterial blood gases, breathing pattern and respiratory effort parameters at the end of each of the five steps. MAIN RESULTS: PSV and PAV 80 had the same effects on work of breathing (WOB). The pressure-time product (PTP) was significantly higher during PAV 80 than during PSV (90+/-76 and 61+/-56 cmH(2)O.s.min(-1), respectively, P <0.05). Tidal volume was comparable, albeit more variable with PAV 80 than with PSV (variation coefficient, 43% vs 25%, respectively, P <0.05). PAV 50 entailed a higher respiratory rate, lower tidal volume, and higher WOB and PTP than PSV and PAV 80. PaO(2)/FiO(2) and SaO(2) were lower with PAV 50 than with PSV and PAV 80. CONCLUSION: In a group of intubated spontaneously breathing non-COPD patients, PAV 80 and PSV were associated with comparable levels WOB, whereas PTP was higher during PAV 80. PAV 50 provided insufficient respiratory assistance.     

比例辅助通气治疗幼兔胎粪吸入的肺组织病理观察

目的观察比例辅助通气(PAV)治疗幼兔胎粪吸入的肺组织病理变化。方法将30只日龄20～30d的幼兔随机分为灌入胎粪后实施比例辅助通气组(PAV组)、灌入胎粪后实施同步间歇指令通气组(SIMV组)、灌入胎粪后不予通气组(MAS对照组)以及灌生理盐水不予通气组(空白对照组),各组分别于灌后8h处死。观察湿干重比及病理大体评分,光镜下观察肺损伤程度。结果 (1)四组间肺组织湿干重比的比较,差异有统计学意义(F=47.900,P=0.000),PAV组湿干比较MAS组低,差异有统计学意义(P<0.05);PAV组湿干重比较SIMV组低,差异有统计学意义(P<0.05);SIMV组与MAS组湿干重比较,差异无统计学意义(P=0.895);(2)四组之间肺损伤病理评分比较,差异有统计学意义(F=118.125,P<0.05)。SIMV组与MAS组肺损伤病理评分比较,差异无统计学意义(P=0.093),PAV组评分较SIMV组低,差异有统计学意义(P<0.05),PAV组评分较MAS组低,差异有统计学意义(P<0.05)。结论兔胎粪吸入机械通气治疗应用PAV时所致的肺损伤程度较应用SIMV时小。     

Prolonged partial liquid ventilation in spontaneously breathing awake animals.

OBJECTIVE: To date, studies of partial liquid ventilation (PLV) have examined its effects acutely in anesthetized and mechanically ventilated subjects. We set out to develop a model of prolonged PLV in awake, spontaneously breathing animals. DESIGN: Animal case series SETTING: Cardiopulmonary physiology laboratory. SUBJECTS: Fifteen New Zealand white rabbits (3.2+/-0.39 kg). INTERVENTIONS: Animals were anesthetized and instrumented with a novel technique allowing percutaneously assisted placement of an intratracheal catheter with a subcutaneously tunneled externalized free end. After anesthetic recovery, PLV was performed in spontaneously breathing unsedated animals. MEASUREMENTS AND MAIN RESULTS: Evaporative losses were determined using a single 10 mL/kg perflubron dose (n = 5); hourly radiographs were obtained until residual perflubron was minimal. For prolonged PLV (n = 10), a 10-mL/kg initial perflubron dose was followed every 4 hrs with 5-mL/kg supplements. Radiographs were obtained immediately before and after perflubron administration and were scored (0-5) by a radiologist blinded to dosing regimen and time interval. Data were analyzed with ANOVA and Student's t-test with correction for multiple comparisons. Initial filling was nearly complete (score = 4.8+/-0.42); lungs were maintained approximately half-filled through 4 hrs (score = 2.53+/-0.71). By 6 hrs, the majority of perflubron had evaporated (score = 1.75+/-0.53). Over 24 hrs, radiographs documented continuous perflubron exposure (postffill = 4.53+/-0.64, prefill = 3.40+/-0.71, average = 3.97+/-0.43); scores were comparatively higher after filling (after = 4.53+/-0.64, before = 3.4+/-0.71, p< .001). Left and right lung volumes were equivalent (left = 4.06+/-0.47, right = 3.89+/-0.39, p = .027). All animals survived the 24 hrs of PLV. CONCLUSIONS: Percutaneously assisted intratracheal cannulation with catheter exteriorization permits prolonged PLV in spontaneously breathing, unsedated animals. Continuous perfluorocarbon exposure with this method is reproducible, consistent, and well tolerated for 24 hrs in uninjured animals.     

Evaluation of work of breathing in spontaneously breathing animals during partial liquid ventilation.

BACKGROUND: Partial liquid ventilation improves lung mechanics and gas exchange in paralyzed mechanically ventilated animals. OBJECTIVE: Examine the work of breathing (WOB) in a spontaneously breathing animal model during partial liquid ventilation with and without the use of pressure-support ventilation (PSV). METHODS: This was a prospective study including 6 lambs (mean weight 10.9 +/- 1.3 kg). Baseline measurements, including total work of breathing (WOB(T)), elastic work of breathing (WOB(E)), and resistive work of breathing (WOB(R)), were obtained using pressure-controlled synchronized intermittent mandatory ventilation with positive end-expiratory pressure of 5 cm H(2)O at PSV levels of 0, 5, and 10 cm H(2)O. The animals' lungs were filled with perflubron through an endotracheal tube, in 10-20 mL aliquots, until filled, approximately 30 mL/kg or functional residual capacity. Repeat measurements were obtained at 10 mL/kg, 20 mL/kg, and full. Perflubron was then allowed to evaporate from the lungs and repeat measurements were obtained 3 additional times, with at least a 1 hour separation between phases, for up to 7 hours after the lungs were filled. RESULTS: No differences were detected in WOB(T), WOB(R), or WOB(E) between the gas-filled lung and the lung filled to functional residual capacity with perflubron. However, compared to the gas-filled lung, WOB(T) and WOB(R) were higher during the filling (p < 0.05) and evaporative phases (p < 0.05). The PSV level affected WOB. Work of breathing was least at PSV 10 cm H(2)O. CONCLUSION: In this pilot study of healthy animals breathing spontaneously with perflubron-filled lungs, there was an acceptable amount of WOB, which decreased with the addition of PSV. However, WOB increased when the perflubron level was not maintained at functional residual capacity.     

New modes of mechanical ventilation: proportional assist ventilation,neurally adjusted ventilatory assist,and fractal ventilation

Increased knowledge of the mechanisms that determine respiratory failure has led to the development of new technologies aimed at improving ventilatory treatment. Proportional assist ventilation and neurally adjusted ventilatory assist have been designed with the goal of improving patient-ventilator interaction by matching the ventilator support with the neural output of the respiratory centers. With proportional assist ventilation, the support is continuously readjusted in proportion to the predicted inspiratory effort. Neurally adjusted ventilatory assist is an experimental mode in which the assistance is delivered in proportion to the electrical activity of the diaphragm, assessed by means of an esophageal electrode. Biologically variable (or fractal) ventilation is a new, volume-targeted, controlled ventilation mode aimed at improving oxygenation; it incorporates the breath-to-breath variability that characterizes a natural breathing pattern.     

Partial liquid ventilation with surfactant: effects on gas exchange and lung pathology in surfactant-depleted piglets

Objective: To evaluate the effects of 24 h partial liquid ventilation (PLV) with and without surfactant (S) treatment on gas exchange and lung injury in a newborn animal model of S deficiency.¶Design: A prospective, controlled, in vivo animal laboratory study.¶Setting: Research laboratory in a university setting.¶Subjects: Twenty-four pathogen-free, male piglets (mean weight 1.9 kg, age 1–3 days).¶Interventions: The animals were randomised in four groups: PLV with FC-77 combined with conventional ventilation (PLV/CV) versus S + PLV/CV and PLV combined with high frequency oscillatory ventilation (PLV/HFOV) versus S + PLV/HFOV. The piglets were anaesthetised, intubated and instrumented with vascular catheters. Thirty minutes after lung injury had been induced with repeated saline lavage, S animals received natural S. Thirty minutes after surfactant substitution PLV with FC-77 was started. The oxygenation index (OI), PaO₂/FIO₂ ratio, PaCO₂ and the ventilatory efficacy index were determined before and during PLV. After 24 h the lungs were removed for histopathological examination.¶Measurements and main results: Within 60 min after the initiation of PLV, all animals demonstrated improvements of the OI and PaO₂/FIO₂ ratio compared to the values after lung injury. However, at 18 and 24 h of PLV, the OI and PaO₂/FIO₂ ratio were significantly worse in the S + PLV/CV and S + PLV/HFOV groups compared to the groups without S. PaCO₂ was higher at 18 and 24 h when S was used in PLV/HFOV (p < 0.05). A semi-quantitative lung injury score revealed most severe lung damage in the S + PLV/HFOV group.¶Conclusion: The combination of S and PLV with FC-77 led to an impaired gas exchange and did not further protect the animal from lung injury.     

Compliance and resistance levels and unloading in proportional assist ventilation

During proportional assist ventilation (PAV), resistive and elastic unloading relieve the work of breathing. Excessive unloading, however, results in resonant oscillations and runaway pressures. Our aim was to determine the appropriate levels of unloading that could be applied to clinical practice. A lung model, resistance (50 or 150 cmH(2)O l(-1) s(-1)) and compliance (0.4 or 0.8 ml/cmH(2)O), was used. The volumes and airway pressures delivered by the ventilator at varying levels of resistive and elastic unloading and simulated breaths were recorded. Oscillations in airway pressure only occurred when the level of resistive unloading exceeded the model's resistance. When the level of unloading fully compensated for the model's compliance, peak inflating pressures greater than 40 cmH(2)O were delivered; peak pressure limits of 20 cmH(2)O, however, resulted in very short (0.2 s or less) inflation times. High peak pressures were not delivered if the level of elastic unloading used was limited to that which reduced the model's elastance to that of a 'normal lung'. In conclusion, these results suggest that when using PAV, it is important to assess the compliance and resistance of the infant and endotracheal tube, so that levels of unloading that fully compensate for the resistance and compliance levels can be avoided.     

Effects of prolonged partial liquid ventilation, high frequency ventilation and conventional ventilation on gas exchange and lung pathology in newborn surfactant-depleted piglets

Partial liquid ventilation (PLV) improves oxygenation in various animal models of respiratory insufficiency. The aim of this study was to compare the effects of conventional ventilation (CV), high frequency oscillatory ventilation (HFOV), and PLV combined with CV or HFOV on gas exchange and histopathology. Thirty anaesthetised newborn piglets (mean weight 1.94 kg, age 1-3 days) were randomized in five groups of six animals: CV, CV + surfactant (S), HFOV+S, PLV/CV, and PLV/HFOV. Thirty min after lung injury had been induced with repeated saline lavage, specific ventilatory treatment was initiated. Three animals of the CV group died within the 24 h study period, whereas none died in any of the other groups. The oxygenation index (OI) and the PaO2/FIO2 ratio improved significantly within 30 min in all groups, but not in the CV group. After 24 h all oxygenation parameters were better in the PLV groups than in CV or CV+S (P < 0.05). No differences in gas exchange were noted between HFOV+S and PLV/CV. The combination of PLV with HFOV led to an increased PaO2/FIO2 ratio when compared with PLV/CV and with HFOV+S (P < 0.05). All PLV treated animals had significantly less lung injury in the upper and lower lobes compared with gas-ventilated animals by histologic semi-quantitative lung injury score (P < 0.01) and in the lower lobes by morphometry (P < 0.001). In conclusion, HFOV+S and PLV either with CV or HFOV are effective techniques to provide adequate gas exchange in S-deficient lungs compared with CV with and without S. However, lung injury was significantly improved in both PLV treated groups compared with HFOV+S and the CV groups.     

Noninvasive pressure support versus proportional assist ventilation in acute respiratory failure

Background Although conventional pressure ventilation (PSV) decreases the rate of intubation in acute respiratory failure, patient-ventilator dyssynchrony is a frequent cause of failure. In proportional assist ventilation (PAV), pressure is applied by the ventilator in proportion to the patient-generated volume and flow; therefore, there is automatic synchrony between the patient's effort and the ventilatory cycle.Objective The aim of this study was to compare the effects of PSV and PAV during noninvasive ventilation in the treatment of acute respiratory failure.Design Prospective randomised study.Setting A multidisciplinary 24-bed intensive care unit of an acute-care teaching hospital in Alicante, Spain.Patients This study included 117 consecutive adult patients with acute respiratory failure randomised to noninvasive ventilation delivered by PSV (n = 59) or PAV (n = 58).Measurements and results There were no statistically significant differences between patients assigned to each mode of ventilation with regard to baseline parameters and aetiological diagnoses of acute respiratory failure. With regard to outcome data, no significant differences were observed between PSV and PAV in the frequency of intubation (37% vs 34%), mortality rate (29% vs 28%), and mean length of stay. Subjective comfort (0–10 visual analogue scale) was rated higher and intolerance occurred less frequently (3.4% vs 15%, P = 0.03) in the PAV than in the PSV mode.Conclusions Although PAV seems more comfortable and intolerance occurred less frequently, no major differences exist in terms of physiological improvement or in terms of outcomes when comparing PSV and PAV.An editorial regarding this article can be found in the same issue ()     

Respiratory comfort and breathing pattern during volume proportional assist ventilation and pressure support ventilation: a study on volunteers with artificially reduced compliance

OBJECTIVE: To assess respiratory comfort and associated breathing pattern during volume assist (VA) as a component of proportional assist ventilation and during pressure support ventilation (PSV). DESIGN: Prospective, double-blind, interventional study. SETTING: Laboratory. SUBJECTS: A total of 15 healthy volunteers (11 females, 4 males) aged 21-31 yrs. INTERVENTIONS: Decreased respiratory system compliance was simulated by banding of the thorax and abdomen. Volunteers breathed via a mouthpiece with VA and PSV each applied at two levels (VA, 8 cm H2O/L and 12 cm H2O/L; PSV, 10 cm H2O and 15 cm H2O) using a positive end-expiratory pressure of 5 cm H2O throughout. The study was subdivided into two parts. In Part 1, volunteers breathed three times with each of the four settings for 2 mins in random order. In Part 2, the first breath effects of multiple, randomly applied mode, and level shifts were studied. MEASUREMENTS AND MAIN RESULTS: In Part 1, the volunteers were asked to estimate respiratory comfort in comparison with normal breathing using a visual analog scale. In Part 2, they were asked to estimate the change of respiratory comfort as increased, decreased, or unchanged immediately after a mode shift. Concomitantly, the respiratory pattern (change) was characterized with continuously measured tidal volume, respiratory rate, pressure, and gas flow. Respiratory comfort during VA was higher than during PSV. The higher support level was less important during VA but had a major negative influence on comfort during PSV. Both modes differed with respect to the associated breathing pattern. Variability of breathing was higher during VA than during PSV (Part 1). Changes in respiratory variables were associated with changes in respiratory comfort (Part 2). CONCLUSIONS: For volunteers breathing with artificially reduced respiratory system compliance, respiratory comfort is higher with VA than with PSV. This is probably caused by a better adaptation of the ventilatory support to the volunteer's need with VA.     

Noninvasive proportional assist ventilation compared with noninvasive pressure support ventilation in hypercapnic acute respiratory failure

OBJECTIVES: To compare short-term administration of noninvasive proportional assist ventilation (NIV-PAV) and pressure support ventilation (NIV-PSV). DESIGN: Prospective, crossover, randomized study. SETTING: Medicosurgical intensive care unit in a nonteaching hospital. PATIENTS: Twelve chronic obstructive pulmonary disease patients admitted for hypercapnic acute respiratory failure. INTERVENTION: NIV-PSV and NIV-PAV given in a randomized order after baseline evaluation in continuous positive airway pressure. Using a flow-triggering ventilator, NIV-PAV was adjusted using the runaway method and compared with NIV-PSV at similar peak inspiratory airway pressure. MEASUREMENTS AND MAIN RESULTS: Flow, airway pressure, and changes in esophageal pressure were measured and the tidal volume, the patient's inspiratory work of breathing, and the esophageal pressure--time product were calculated. Arterial pH and PaCO(2) were measured and breathing comfort was assessed using a visual analogic scale. Peak inspiratory airway pressure (17 +/- 3 cm H(2)O) and tidal volume were similarly increased with the two modalities with no change in respiratory rate. The change in esophageal pressure was similarly decreased (from 20 +/- 8 cm H(2)O in continuous positive airway pressure to 12 +/- 7 in NIV-PSV and 10 +/- 5 cm H(2)O in NIV-PAV) as well as inspiratory muscle effort indexes. Arterial pH and PaCO(2) were similarly improved. Breathing comfort was significantly improved in NIV-PAV (+38 +/- 38%) but not in NIV-PSV (+11 +/- 23%). The tidal volume was more variable in NIV-PAV (89 +/- 18%) than in NIV-PSV (15 +/- 8%) and changes in tidal volume variability were significantly correlated (p =.02) with changes in breathing comfort. CONCLUSIONS: In chronic obstructive pulmonary disease patients with hypercapnic acute respiratory failure, NIV-PAV was able to unload inspiratory muscles similarly to NIV-PSV but may be more comfortable than NIV-PSV.     

比例辅助通气治疗新生儿呼吸衰竭的护理

目的 探讨比例辅助通气（PAV）时护理措施,提高新生儿呼吸衰竭（NRF）的救治质量.方法 对采用PAV技术治疗的56例NFR患儿的临床护理资料进行回顾性分析总结.结果 所有56例患儿均痊愈出院,平均机械通气时间为（74.1±11.2）h;平均吸氧时间为（5.3±2.1）d;平均住院时间为（12.6±3.5）d,呼吸机相关肺炎（VAP）发生率为12.5％,无气漏和血压下降等并发症出现.结论 规范的新生儿PAV护理措施能减少VAP的发生率,缩短机械通气时间,提高NRF的救治质量.     

Effect of hypothermia on ventilation in anesthetized, spontaneously breathing rats: theoretical implications for mechanical ventilation

Objective: To test if hypothermia, induced by a sustained pentobarbital anesthesia, in rats can reduce ventilatory demands without compromising pulmonary gas-exchange efficiency. Design: Prospective study. Setting: Research laboratory in a hospital. Subjects: One group of 11 female Sprague Dawley rats. Interventions: The rats were anesthetized with 45 mg/kg pentobarbital, tracheostomized and intubated; their femoral veins and arteries were cannulated. After surgery, anesthesia and fluid balance were maintained (10 mg/kg per h pentobarbital, and 5 ml/kg per h saline, i. v.). Rectal temperature, mean arterial blood pressure (MAP), and heart rate (HR) were continuously monitored. The respiratory variables and gas-exchange profiles were determined at 38 °C (normothermia), and during stepwise hypothermia at 37, 35, 33, 31 and 29 °C. The arterial pressure of carbon dioxide (PaCO₂₎, pH and arterial pressure of oxygen (PaO₂) during hypothermia were corrected at body temperature. Measurements and results: Graded systemic hypothermia, with maintained anesthesia, produced a strong correlation between reduction in the respiratory frequency and rectal temperature (r ² = 0.55; p < 0.0001; n = 66). The minute volume was significantly reduced, starting at 35 °C, without significant changes in the tidal volume (repeated measures of analyses of variance followed by Dunnett multiple comparisons test). No significant changes occurred in the PaCO₂, pH, PaO₂, hemoglobin oxygen saturation, the calculated arterial oxygen content and estimated alveolar-arterial oxygen difference during mild hypothermia (37–33 °C). The P_aO₂, however, was significantly reduced below 31 °C. The MAP remained stable at different levels of hypothermia, whereas HR was significantly reduced below 33 °C. Conclusions: Mild hypothermia in rats, induced by a sustained pentobarbital anesthesia, reduces ventilation without compromising arterial oxygenation or acid-base balance, as measured at body temperature. Theoretically, our observations in spontaneously breathing rats imply that a combination of mild hypothermia with anesthesia could be safely utilized to maintain adequate ventilation, using relatively low minute ventilation. We speculate that such a maneuver, if applied during mechanical ventilation, may prevent secondary pulmonary damage by allowing the use of lower ventilator volume-pressure settings. Received: 19 August 1999 Final revision received: 2 December 1999 Accepted: 20 January 2000     

Continuous positive airway pressure vs. proportional assist ventilation for noninvasive ventilation in acute cardiogenic pulmonary edema

Objective To compare continuous positive airway pressure (CPAP) and proportional assist ventilation (PAV) as modes of noninvasive ventilatory support in patients with severe cardiogenic pulmonary edema. Design and setting A prospective multicenter randomized study in the medical ICUs of three teaching hospitals. Patients Thirty-six adult patients with cardiogenic pulmonary edema (CPA) with unresolving dyspnea, respiratory rate above 30/min and/or SpO₂ above 90% with O₂ higher than 10 l/min despite conventional therapy with furosemide and nitrates. Interventions Patients were randomized to undergo either CPAP (with PEEP 10 cmH₂O) or PAV (with PEEP 5–6 cmH₂O) noninvasive ventilation through a full face mask and the same ventilator. Measurements and results The main outcome measure was the failure rate as defined by the onset of predefined intubation criteria, severe arrythmias or patient's refusal. On inclusion CPAP (n = 19) and PAV (n = 17) groups were similar with regard to age, sex ratio, type of heart disease, SAPS II, physiological parameters (mean arterial pressure, heart rate, blood gases), amount of infused nitrates and furosemide. Failure was observed in 7 (37%) CPAP and 7 (41%) PAV patients. Among these, 4 (21%) CPAP and 5 (29%) PAV patients required endotracheal intubation. Changes in physiological parameters were similar in the two groups. Myocardial infarction and ICU mortality rates were strictly similar in the two groups. Conclusions In the present study PAV was not superior to CPAP for noninvasive ventilation in severe cardiogenic pulmonary edema with regard to either efficacy and tolerance. T. Rusterholtz and P.-E. Bollaert contributed equally to this study. This work was supported in part by Respironics Inc., Murrysville, PA, USA.     

Distribution of lung ventilation in spontaneously breathing neonates lying in different body positions

Objective

The aim of our study was to determine the effect of the irregular spontaneous breathing pattern and posture on the spatial distribution of ventilation in neonates free from respiratory disease by the non-invasive imaging method of electrical impedance tomography (EIT). Scanning of spontaneously breathing neonates is the prerequisite for later routine application of EIT in babies with lung pathology undergoing ventilator therapy.

Design

Prospective study.

Setting

Neonatal intensive care unit at a university hospital.

Patients

Twelve pre-term and term neonates (mean age: 23 days; mean body weight: 2,465 g; mean gestational age: 34 weeks; mean birth weight: 2,040 g).

Interventions

Change in body position in the sequence: supine, right lateral, prone, supine.

Measurements and results

EIT measurements were performed using the Göttingen GoeMF I system. EIT scans of regional lung ventilation showing the distribution of respired air in the chest cross-section were generated during phases of rapid tidal breathing and deep breaths. During tidal breathing, 54.5±8.3%, 55.2±10.5%, 59.9±8.4% and 54.2±8.5% of inspired air (mean values ± SD) were directed into the right lung in the supine, right lateral, prone and repeated supine postures respectively. During deep inspirations, the right lung ventilation accounted for 52.6±7.9%, 68.5±8.5%, 55.4±8.2% and 50.5±6.6% of total ventilation respectively.

Conclusion

The study identified the significant effect of breathing pattern and posture on the spatial distribution of lung ventilation in spontaneously breathing neonates. The results demonstrate that changes in regional ventilation can easily be determined by EIT and bode well for the future use of this method in paediatric intensive care.

     

Patient-ventilator interaction and sleep in mechanically ventilated patients: pressure support versus proportional assist ventilation

OBJECTIVES: To understand the role of patient-ventilator asynchrony in the etiology of sleep disruption and determine whether optimizing patient-ventilator interactions by using proportional assist ventilation improves sleep. DESIGN: Randomized crossover clinical trial. SETTING: A tertiary university medical-surgical intensive care unit. PATIENTS: Thirteen patients during weaning from mechanical ventilation. INTERVENTIONS: Patients were randomized to receive pressure support ventilation or proportional assist ventilation on the first night and then crossed over to the alternative mode for the second night. Polysomnography and measurement of light, noise, esophageal pressure, airway pressure, and flow were performed from 10 pm to 8 am. Ventilator settings (pressure level during pressure support ventilation and resistive and elastic proportionality factors during proportional assist ventilation) were set to obtain a 50% reduction of the inspiratory work (pressure time product per minute) performed during a spontaneous breathing trial. MEASUREMENTS AND MAIN RESULTS: Arousals per hour of sleep time during pressure support ventilation were 16 (range 2-74) and 9 (range 1-41) during proportional assist ventilation (p = .02). Overall sleep quality was significantly improved on proportional assist ventilation (p < .05) due to the combined effect of fewer arousals per hour, fewer awakenings per hour (3.5 [0-24] vs. 5.5 [1-24]), and greater rapid eye movement (9% [0-31] vs. 4% [0-23]), and slow wave (3% [0-16] vs. 1% [0-10]) sleep. Tidal volume and minute ventilation were lower on proportional assist ventilation, allowing for a greater increase in Paco2 during the night. Patient-ventilator asynchronies per hour were lower with proportional assist ventilation than with pressure support ventilation (24 +/- 15 vs. 53 +/- 59; p = .02) and correlated with the number of arousals per hour (R = .65, p = .0001). CONCLUSIONS: Patient ventilator discordance causes sleep disruption. Proportional assist ventilation seems more efficacious than pressure support ventilation in matching ventilatory requirements with ventilator assistance, therefore resulting in fewer patient-ventilator asynchronies and better quality of sleep.     

早期比例辅助通气救治急性心源性肺水肿的疗效分析

目的：评价急救中早期比例辅助通气（PAV）治疗急性心源性肺水肿（ACPE）的临床效果。方法：60例ACPE患者随机分为对照组、PAV组和双水平正压通气（BiPAP）组,每组各20例。对照组给予吸氧、吗啡、利尿剂、血管扩张剂、洋地黄类强心剂和氨茶碱等常规治疗,PAV组和BiPAP组分别给予PAV＋常规治疗和BiPAP＋常规治疗。比较3组治疗前和治疗后2h各项生理参数、动脉血气、视觉模拟评分（VAS）、气道峰压（PIP）和气管插管率的变化。结果：3组治疗后的各项生理参数均较治疗前改善（P〈0.05）,与对照组比较,PAV组和BiPAP组的心率、呼吸频率和气管插管率均减低（P〈0.05）,氧分压和动脉血氧饱和度明显升高（P〈0.05）,PAV组的VAS评分和PIP低于BiPAP组（P〈0.05）。结论：尽早应用PAV和BiPAP均可迅速改善ACPE患者的生理参数和动脉血气指标,缓解呼吸困难;PAV气道峰压较低、同步性和舒适性好,安全、有效,更易为患者接受。     

Effects of pressure support ventilation, bi-level positive airway pressure, and volume-proportional assist on breathing with elevated respiratory system elastance

Fully awake subjects preferred ventilatory assist modes supporting every breath, like PS or PA., to the potentially unsynchronous BIPAP. — In pure volume-proportional assist, the relatively high P_AO at end-inspiration seemed to contribute to discomfort with high assist levels. So the addition of a flow-proportional component, which would tend to come into effect earlier in inspiration, might allow higher levels of PA with equal patient comfort.     

Partial liquid ventilation provides effective gas exchange in a large animal model

:The purpose of this study was to show the ability of partial liquid ventilation (PLV) to sustain gas exchange in normal large (50 to 70 kg) adult animals.:Ten adult sheep (53.7 ± 2.8 kg) were anesthetized and mechanically ventilated. Sequential dosing of perflubron (LiquiVent, Alliance Pharmaceutical Corp, San Diego, CA) was performed to cumulative doses of 10 mL/kg, 20 mL/kg, 40 mL/kg, and 60 mL/kg. Physiological data were assessed at baseline and after each dose. Five animals were rotated through the left decubitus, right decubitus, supine, and prone positions while five animals remained prone throughout the experiment.:PaO₂ and PaCO₂ did not change significantly from baseline during administration of perflubron except for the PaO₂ in rotated animals when supine (rotated-supine PaO₂: baseline = 519 ± 64 mm Hg; 60 mL/kg = 380 ± 109 mm Hg, P = .0131). In both groups, static lung compliance (C_T) decreased steadily with each successive perflubron instillation (nonrotated C_T: baseline = 1.55 ± 0.22 mL/cm H₂O/kg; 60 mL/kg = 0.52 ± 0.10 ml/cmH₂O/kg, P =.0003).:These data show that during PLV in this normal animal model, effective gas exchange is sustained and C_T decreases with increasing perflubron dose.