Controlled ventilation with best positive end-expiratory pressure (PEEP) and high level PEEP in acute respiratory failure (ARF)

We assessed hemodynamics, total lung and chest wall compliance (CT) and gas exchange using two different levels of PEEP during controlled ventilation in two different groups of patients with ARF; in the first group (Group 1, 12 patients) chest X-Rays showed a symmetrical pattern of bilateral alveolar infiltrates; in the second group (Group 2, 5 patients) chest X-Rays showed an asymmetrical pattern with unilateral lobar consolidation. A first level of PEEP (best PEEP=9±3 cm H₂O) produced an improvement in CT and in gas exchange with a slight decrease in cardiac index in both groups; but improvement in PaO₂ (from 64±33 to 122±76 torr, p<0.001 in Group 1, and from 76±39 to 91±33 torr, p<0.05 in Group 2) and decrease in QS/QT were not as well marked in Group 2 as in Group 1. A second level of PEEP (high level PEEP: 20±4 cm H₂O) produced a sharp decrease in CT and required hemodynamic support in each case (blood volume expansion with or without Dopamine infusion) to maintain cardiac index within a normal range. In Group 1 this high level PEEP produced a greater improvement in gas exchange (PaO₂ increased from 122±76 to 194±76, p<0.01) but in Group 2 it had a deleterious effect, producing a decrease in PaO₂ (from 91±33 to 76±41 torr, p<0.05), and an increase in ; with this higher PEEP we also noted an increase of alveolar dead space in Group 2.This study demonstrates the efficiency of high levels of PEEP to reduce in ARF but also shows its limitations: namely reduction in cardiac performance and in efficiency if the damage to one lung is significantly more pronounced than that to the other lung.Supported in part by a grant of the U.E.R. Paris-Ouest     

高呼气末正压加肺复张治疗急性呼吸窘迫综合征

目的 评价高呼气末正压(PEEP)加肺复张(RM)治疗急性呼吸窘迫综合征(ARDS)的临床疗效和安全性.方法 选择2008年6月至2010年5月贵阳医学院附属医院内科重症监护病房(MICU)收治的ARDS患者38例,按信封法随机分为RM组和非RM组,每组19例.两组均采用压力支持通气(PSV)模式行机械通气,尽可能在吸入氧浓度(FiO2)＜0.60时达到目标氧合的最小PEEP水平,限制平台压≤30 cm H2O(1 cm H2O=0.098 kPa).RM时FiO2调至1.00,压力支持水平调至0,将PEEP升至40 cm H2O,持续30 s后再降低,8 h 1次,连续5 d.记录基础状态和5 d内的机械通气参数、血气分析结果及生命体征,比较两组氧合改善和肺损伤指标变化,观察RM的不良反应和气压伤发生率.结果 ①两组患者基础状态及机械通气参数均无明显差异.②两组动脉血氧分压(PaO2)和氧合指数(PaO2/FiO2)均明显改善,且RM组明显优于非RM组[PaO2(mm Hg,1 mm Hg=0.133 kPa)2 d:85.8±21.3比73.5±18.7,3 d:88.6±22.8比74.3±19.8,4 d:98.8±30.7比79.3±19.3,5 d:105.5±29.4比84.4±13.8;PaO2/FiO2(mm Hg)4 d:221.8±103.5比160.3±51.4,5 d:239.6±69.0比176.8±45.5,均P＜0.05].③两组呼出气冷凝液(EBC)中过氧化氢(H2O2)和白细胞介素-6(IL-6)水平均呈下降趋势,RM组下降幅度更明显[5 d时H2O2(μmol/L):0.04±0.02比0.10±0.03;IL-6(ng/L):4.12±2.09比9.26±3.47,均P＜0.05].④两组均无气压伤发生,心率无明显变化,无心律失常发生,中心静脉压和平均动脉压无明显变化.结论 高PEEP加RM可增加气体交换,改善氧合,减少呼吸机相关性肺损伤(VALI).应用RM比较安全,耐受性好,临床观察未见低氧血症、气压伤和血流动力学异常.

Abstract：

Objective To investigate the clinical effects and safety degree of high positive endexpiratory pressure (PEEP) combined with lung recruitment maneuver (RM) in patients with acute respiratory distress syndrome (ARDS). Methods Thirty-eight patients in medical intensive care unit (MICU) of Affiliated Hospital of Guiyang Medical College suffering from ARDS admitted from June 2008 to May 2010 were enrolled in the study. With the envelope method they were randomized into RM group and non-RM group, with n= 19 in each group. All patients received protective ventilation: pressure support ventilation (PSV) with plateau pressure limited at 30 cm H2O (1 cm H2O=0. 098 kPa) or lower. PEEP was set at the minimum level with fraction of inspired oxygen (FiO2) ＜0. 60 and partial pressure of arterial oxygen (PaO2) kept between 60 and 80 mm Hg (1 mm Hg=0. 133 kPa). RM was conducted by regulating FiO2 to 1.00, support pressure to 0, PEEP increased to 40 cm H2O and maintained for 30 seconds before lowering, and this maneuver was repeated every 8 hours for a total of 5 days. Base status, ventilation parameters, blood gas analysis and vital signs were obtained at baseline and for the next 5 days. Oxygenation status and lung injury indexes were compared between RM group and non-RM group, the adverse effects of (PaO2/FiO2) were both increased in RM group and non-RM group, but the values were higher in RM group [PaO2 (mm Hg) 2 days: 85.8± 21.3 vs. 73. 5± 18. 7, 3 days : 88. 6± 22. 8 vs. 74. 3 ±19. 8, 4 days : 98. 8 ±30. 7 vs. 79. 3±19. 3, 5 days: 105.5±29.4 vs. 84. 4±13. 8; PaO2/FiO2(mm Hg) 4 days: 221.8±103. 5 vs.interleukin-6 (IL-6) concentration in exhaled breath condensate (EBC) decreased in both groups but lower in RM group with significant difference [5 days H2O(μmol/L): 0. 04 ± 0. 02 vs. 0.10 ± 0.03 ; IL-6 (ng/L):No significant changes in heart rate were found during RM. Central venous pressure and mean arterial pressure remained unchanged after RM. Conclusion High level PEEP combined with RM can improve gas exchange and oxygenation, decrease ventilator associated lung injury (VALI). RM was safe and had good tolerance, no hypoxemia, barotrauma and hemodynamic instability were observed.     

Partial liquid ventilation and positive end-expiratory pressure reduce ventilator-induced lung injury in an ovine model of acute respiratory failure

OBJECTIVE: To examine the isolated and combined effects of positive end-expiratory pressure (PEEP) and partial liquid ventilation (PLV) on the development of ventilator-induced lung injury in an ovine model. DESIGN: Prospective controlled animal study. SETTING: University-based cardiovascular animal physiology laboratory. SUBJECTS: Thirty-eight anesthetized supine sheep weighing 22.3 +/- 2.2 kg. INTERVENTIONS: Animals were ventilated for 6 hrs (respiratory rate, 15; FIO2, 1.0, inspiratory/expiratory ratio, 1:1) with one of five pressure-controlled strategies, expressed as peak inspiratory pressure (PIP)/PEEP: low-PIP, 25/5 cm H2O (n = 8); high-PIP, 50/5 cm H2O (n = 8); high-PIP-PLV, 50/5 cm H2O-PLV (n = 8); high-PEEP, 50/20 cm H2O (n = 7); and high-PEEP-PLV, 50/20 cm H2O-PLV (n = 7). MEASUREMENTS AND MAIN RESULTS: Compared with the low-PIP control, high-PIP ventilation increased airleak, shunt, histologic evidence of lung injury, neutrophil infiltrates, and wet lung weight. Maintaining PEEP at 20 cm H2O or adding PLV reduced the development of physiologic shunt and dependent histologic injury indexes. Neither higher PEEP nor PLV reduced the high incidence of barotrauma observed in high-PIP animals. CONCLUSIONS: We conclude that application of PLV or PEEP at 20 cm H2O may improve gas exchange and afford lung protection from ventilator-induced lung injury during high-pressure mechanical ventilation in this model.     

Effects of recruitment maneuvers in patients with acute lung injury and acute respiratory distress syndrome ventilated with high positive end-expiratory pressure

Objective: Positive end-expiratory pressure (PEEP) and recruitment maneuvers (RMs) may partially reverse atelectasis and reduce ventilation-associated lung injury. The purposes of this study were to assess a) magnitude and duration of RM effects on arterial oxygenation and on requirements for oxygenation support (Fio2/PEEP) in patients with acute lung injury and acute respiratory distress syndrome (ALI/ARDS) receiving ventilation with low tidal volumes and high levels of PEEP; and b) frequency of adverse respiratory and circulatory events attributable to RMs. Design: Prospective, randomized, crossover study. Setting: Thirty-four intensive care units at 19 hospitals. Patients: Seventy-two patients with early ALI/ARDS. Baseline PEEP and Fio2 were 13.8 +/- 3.0 cm H2O and 0.39 +/- 0.10, respectively (mean +/- sd). Interventions: We conducted RMs by applying continuous positive airway pressure of 35-40 cm H2O for 30 secs. We conducted sham RMs on alternate days. We monitored oxyhemoglobin saturation by pulse oximetry (SpO2), Fio2/PEEP, blood pressure, and heart rate for 8 hrs after RMs and sham RMs. We examined chest radiographs for barotrauma. Measurements and Main Results: Responses to RMs were variable. Greatest increments from baseline SpO2 within 10 mins after RMs were larger than after sham RMs (1.7 +/- 0.2 vs. 0.6 +/- 0.3 %, mean +/- SEM, p < .01). Systolic blood pressure decreased more +/- 1.1 mm Hg, p < .01). Changes in Fio2/PEEP requirements were not significantly different at any time after RMs vs. sham RMs. Barotrauma was apparent on first radiographs after one RM and one sham RM.Conclusions: In ALI/ARDS patients receiving mechanical ventilation with low tidal volumes and high PEEP, short-term effects of RMs as conducted in this study are variable. Beneficial effects on gas exchange in responders appear to be of brief duration. More information is needed to determine the role of recruitment maneuvers in the management of ALI/ARDS.     

Non-invasive positive pressure ventilation in acute respiratory failure: providing competent care

Non-invasive positive pressure ventilation (NPPV) has been used as an alternative strategy to provide ventilatory support for patients with acute respiratory failure. Most studies demonstrate that the use of NPPV in acute respiratory failure results in a reduction in the need for endotracheal intubation and an overall survival advantage. However, current evidence, in the form of randomized controlled trials, suggests that these benefits may be restricted to patients suffering from acute exacerbation of chronic obstructive pulmonary disease (COPD).

The clinical application of NPPV involves the development of competence in delivering the particular intervention. Clinical outcomes and thus valid comparisons with alternate methods of ventilatory support can only be made if attention is paid to the clinical indications for the application of NPPV and patient subgroups it is used to treat and the level of competence of care givers in its application and delivery. One essential element of competence is the establishment of an appropriate knowledge base and the development of clinical practice guidelines. This literature review identifies the current indications for NPPV and the relevant information for developing clinical practice guidelines for the management of this form of ventilatory support.     

The use of high positive end-expiratory pressure for respiratory failure in abdominal compartment syndrome

We report a case in which a non-trauma patient suffering hematemesis and undergoing massive volume resuscitation developed abdominal compartment syndrome (ACS). The abdominal distension severely compromised his pulmonary functioning: a chest radiograph showed low lung volumes and dense bilateral parenchymal opacities. His blood oxygen saturation reached as low as 32%. Because he was hemodynamically unstable and coagulopathic, decompressive surgery was not possible. We gradually raised the ventilator settings to reinflate the lungs (positive end-expiratory pressure [PEEP] was raised to 50 cm H(2)O, peak inspiratory pressure to 100 cm H(2)O, and plateau inspiratory pressure to 80 cm H(2)O) and continued fluid resuscitation, and within an hour his blood oxygen saturation increased to 100%. In this case high PEEP was beneficial in a situation in which decompressive surgery was not feasible, but we do not suggest that high PEEP necessarily improves survival or that high PEEP is better than surgical decompression. On the contrary, high-pressure ventilation can be harmful in the setting of acute lung injury and acute respiratory distress syndrome, so we do not advocate high PEEP for all patients with hypoxemia and ACS, especially considering that many of the conditions associated with ACS can also precipitate acute lung injury and acute respiratory distress syndrome. As well, high-pressure ventilation can increase the risk of hypotension by impairing venous return. However, our case suggests that high PEEP may temporize in certain situations in which ACS causes life-threatening hypoxia but surgical decompression is not possible.     

Effect of positive end-expiratory pressure on extravascular lung water in porcine acute respiratory failure

Recent studies of acute respiratory failure suggest that PEEP causes increased pulmonary interstitial fluid collection and therefore increased extravascular lung water (EVLW). We examined the effect of increasing levels of PEEP on EVLW in 20 to 25-kg pigs with acute respiratory failure induced by continuous infusion of live Pseudomonas aeruginosa (2 X 10(8) organisms/20 kg.min). Animals were intubated, paralyzed, and ventilated at 15 ml/kg tidal volume and an FIO2 of 0.4. Pigs in group 1 were given 4 ml/kg.h of iv fluid (lactated Ringer's solution) with no PEEP administered. Animals in groups 2 through 5 were given 0, 4, 17, and 44 ml/kg.h of lactated Ringer's solution, respectively, and PEEP was added at 5-cm H2O increments per half-hour, starting one hour after beginning P. aeruginosa infusion. EVLW in PEEP animals was less than or equal to that in controls despite variation in the administration of lactated Ringer's solution. This suggests that PEEP may slow EVLW accumulation over time and provide a protective effect that allows increased amounts of crystalloid fluids to be administered.     

Mechanical ventilation in fiberoptic-bronchoscopy: comparison between high frequency positive pressure ventilation and normal frequency positive pressure ventilation

High frequency positive pressure ventilation (HFPPV) was compared with normal frequency positive pressure ventilation (NFPPV) during diagnostic fiberoptic-bronchoscopy. HFPPV was achieved by a simple modification of the Minivent, and gave satisfactory alveolar ventilation and oxygenation. In all 11 patients and over periods of at least 40 min, HFPPV gave normal PaCO2 and high levels of PAO2. Arterial blood pressures were higher and the airway pressures were lower than during NFPPV.     

无创正压通气与有创正压通气治疗急性呼吸衰竭的比较研究

目的　比较无创正压通气 (NPPV)和有创正压通气 (IPPV)救治急性呼吸衰竭 (ARF)的临床效果 ,评估NPPV在ARF治疗中的作用。方法　将各种原因所致ARF 5 2例患者随机分为NPPV组 (2 6例 )和IPPV组 (2 6例 ) ,在给予病因治疗同时分别实施NPPV和IPPV。观察分析两组患者在治疗过程中动脉血气变化、并发症的发生率及治疗结果。结果　NPPV组有 7例 (2 6 .9% )治疗失败转为气管插管IPPV ,其中 4例 (15 .4 % )死亡。IPPV组死亡 5例 (19.2 % ) ,两组死亡率无显著差异 (P >0 0 5 )。两组治疗有效患者在分别接受NPPV和IPPV治疗后 6h动脉血气有相似的显著改善。NPPV组患者机械通气时间和住院时间短于IPPV组 (P <0 .0 5 )。NPPV组的并发症发生率低于IPPV组 (P <0 .0 5 )。结论　在经过选择的ARF患者中 ,应用NPPV治疗的临床效果与IPPV相似。实施NPPV可缩短机械通气和住院时间 ,减少并发症。且因为无创伤性 ,NPPV可作为经过选择的ARF患者首选的通气支持治疗手段。     

Prone position and positive end-expiratory pressure in acute respiratory distress syndrome

OBJECTIVE: To determine whether positive end-expiratory pressure (PEEP) and prone position present a synergistic effect on oxygenation and if the effect of PEEP is related to computed tomography scan lung characteristic. DESIGN: Prospective randomized study. SETTING: French medical intensive care unit. PATIENTS: Twenty-five patients with acute respiratory distress syndrome. INTERVENTIONS: After a computed tomography scan was obtained, measurements were performed in all patients at four different PEEP levels (0, 5, 10, and 15 cm H2O) applied in random order in both supine and prone positions. MEASUREMENTS AND MAIN RESULTS: Analysis of variance showed that PEEP (p <.001) and prone position (p <.001) improved oxygenation, whereas the type of infiltrates did not influence oxygenation. PEEP and prone position presented an additive effect on oxygenation. Patients presenting diffuse infiltrates exhibited an increase of Pao2/Fio2 related to PEEP whatever the position, whereas patients presenting localized infiltrates did not have improved oxygenation status when PEEP was increased in both positions. Prone position (p <.001) and PEEP (p <.001) reduced the true pulmonary shunt. Analysis of variance showed that prone position (p <.001) and PEEP (p <.001) reduced the true pulmonary shunt. The decrease of the shunt related to PEEP was more pronounced in patients presenting diffuse infiltrates. A lower inflection point was identified in 22 patients (88%) in both supine and prone positions. There was no difference in mean lower inflection point value between the supine and the prone positions (8.8 +/- 2.7 cm H2O vs. 8.4 +/- 3.4 cm H2O, respectively). CONCLUSIONS: PEEP and prone positioning present additive effects. The prone position, not PEEP, improves oxygenation in patients with acute respiratory distress syndrome with localized infiltrates.     

Non-invasive ventilation in acute respiratory failure: a randomised comparison of continuous positive airway pressure and bi-level positive airway pressure

Objectives: To determine whether there is a difference in required duration of non-invasive ventilation between continuous positive airway pressure (CPAP) and bi-level positive airway pressure (BiPAP) in the treatment of a heterogeneous group of emergency department (ED) patients suffering acute respiratory failure and the subgroup of patients with acute pulmonary oedema (APO). Secondary objectives were to compare complications, failure rate, disposition, length of stay parameters, and mortality between the treatments.

Methods: This prospective randomised trial was conducted in the emergency departments of three Australian teaching hospitals. Patients in acute respiratory failure were randomly assigned to receive CPAP or BiPAP in addition to standard therapy. Duration of non-invasive ventilation, complications, failure rate, disposition, length of stay (hospital and ICU), and mortality were measured.

Results: 101 patients were enrolled in the study (CPAP 51, BiPAP 50). The median duration of non-invasive ventilation with CPAP was 123 minutes (range 10–338) and 132 minutes (range 20–550) for BiPAP (p = 0.206, Mann-Whitney). For the subgroup suffering APO, 36 were randomised to CPAP and 35 to BiPAP. For this group the median duration of non-invasive ventilation for CPAP was 123 minutes (range 35–338) and 133 minutes (range 30–550) for BiPAP (p = 0.320, Mann-Whitney).

Conclusions: These results suggest that there is no significant difference in the duration of non-invasive ventilation treatment between CPAP and BiPAP when used for the treatment of acute respiratory failure in the ED. There was also no significant difference between the groups in secondary end points.

     

Hemodynamic and respiratory changes during lung recruitment and descending optimal positive end-expiratory pressure titration in patients with acute respiratory distress syndrome

OBJECTIVES: To investigate respiratory and hemodynamic changes during lung recruitment and descending optimal positive end-expiratory pressure (PEEP) titration. DESIGN: Prospective auto-control clinical trial. SETTING: Adult general intensive care unit in a university hospital. PATIENTS: Eighteen patients with acute respiratory distress syndrome. INTERVENTIONS: Following baseline measurements (T0), PEEP was set at 26 cm H2O and lung recruitment was performed (40/40-maneuver). Then tidal volume was set at 4 mL/kg (T26R) and PEEP was lowered by 2 cm H2O in every 4 mins. Optimal PEEP was defined at 2 cm H2O above the PEEP where Pao2 dropped by > 10%. After setting the optimal PEEP, the 40/40-maneuver was repeated and tidal volume set at 6 mL/kg (T(end)). MEASUREMENTS AND MAIN RESULTS: Arterial blood gas analysis was done every 4 mins and hemodynamic measurements every 8 mins until T(end), then in 30 (T30) and 60 (T60) mins. The Pao2 increased from T0 to T(end) (203 +/- 108 vs. 322 +/- 101 mm Hg, p < .001), but the extravascular lung water (EVLW) did not change significantly. Cardiac index (CI) and the intrathoracic blood volume (ITBV) decreased from T0 to T26R (CI, 3.90 +/- 1.04 vs. 3.62 +/- 0.91 L/min/m2, p < .05; ITBVI, 832 +/- 205 vs. 795 +/- 188 m/m2, p < .05). There was a positive correlation between CI and ITBVI (r = .699, p < .01), a negative correlation between CI and central venous pressure (r = -.294, p < .01), and no correlation between CI and mean arterial pressure (MAP). CONCLUSIONS: Following lung recruitment and descending optimal PEEP titration, the Pao2 improves significantly, without any change in the EVLW up to 1 hr. This suggests a decrease in atelectasis as a result of recruitment rather than a reduction of EVLW. There is a significant change in CI during the maneuver, but neither central venous pressure, heart rate, nor MAP can reflect these changes.     

Mechanical ventilation in children with acute respiratory failure

PURPOSE OF REVIEW: Acute respiratory failure requiring mechanical ventilation continues to contribute to mortality and affect long-term functional outcomes in patients admitted to the pediatric intensive care unit (ICU). Studies in adults with acute respiratory distress syndrome (ARDS) far outnumber those conducted in the pediatric age group, and pediatric intensivists are left with the task of carefully selecting and critically appraising relevant adult data and extrapolating results to their domain of practice. RECENT FINDINGS: The recent ARDSNet study reinforces the use of low tidal volumes. Administration of surfactant is safe, but once again its beneficial effect was not sustained in a randomized trial. Surfactant proteins A and D have been shown to be of prognostic value in cases of acute lung injury. The effect of inhaled nitric oxide (NO) in patients with ARDS can be enhanced by aggressive lung recruitment strategies such as can be achieved using high-frequency oscillatory ventilation (HFOV). A recent adult trial shows good response rates but no significant long-term outcome benefit from prone positioning in patients with ARDS. Routine scheduled assessments of readiness for weaning and extubation may be more important than specific weaning modes and weaning criteria for children. A recent meta-analysis suggests that prophylactic dexamethasone use may decrease postextubation stridor and possibly reduce the need for reintubation in selected patients. Outcome data in children requiring mechanical support is encouraging, especially for high-risk groups such as bone marrow transplant (BMT) recipients, and may guide ethically challenging decision-making for these patients. SUMMARY: Mechanical ventilation strategies aiming for optimal alveolar recruitment with the judicious use of positive end-expiratory pressure (PEEP) and low tidal volumes will remain the mainstay for managing respiratory failure in children. Dexamethasone may prevent postextubation stridor. Prone positioning, surfactant therapy, HFOV, and inhaled NO are used sporadically and need to be evaluated for their effect on mortality and duration of ventilation.     

Non‐invasive positive pressure ventilation in patients with acute respiratory failure

Non‐invasive positive pressure ventilation is an emerging modality in contemporary critical care practice. Perhaps the most widely utilized and familiar form of non‐invasive positive pressure ventilation is mask continuous positive airway pressure. Other common modes include mask Bi‐level positive airway pressure and mask pressure support ventilation. All feature the delivery of positive airway pressure via a mask (full‐face, naso‐oral or nasal), and a patient‐controlled respiratory cycle. The physiological benefits of non‐invasive positive pressure ventilation suggested by a number of studies include improved oxygenation, decreased work of breathing, improved ventilation and perfusion matching, decreased fatigue, and increased minute ventilation. The utilization of non‐invasive positive pressure ventilation has now been reported for a variety of clinical indications. In most, randomized trials are lacking, and the benefits and preferred mode of non‐invasive positive pressure ventilation are still to be elucidated. In general, in patients that are candidates for endotracheal intubation, non‐invasive positive pressure ventilation should be used as a way to possibly avoid endotracheal intubation rather than as an alternative to endotracheal intubation. Whilst the benefit of non‐invasive positive pressure ventilation appears to be established in patients with chronic obstructive airways disease with hypercapnic acute respiratory failure, one of the major unresolved issues is whether one modality is significantly better than the others. Unfortunately, the question of whether Bi‐level positive airway pressure is better than continuous positive airway pressure in this clinical scenario has not been satisfactorily addressed in any large randomized and controlled clinical trial. Further, there is no ‘gold standard’ for predicting success with non‐invasive positive pressure ventilation, although several studies have looked at this aspect.