Instrumentation for estimating pulmonary function in patients on positive end-expiratory pressure

For patients requiring PEEP during ventilation, e.g., patients with respiratory distress syndrome, performing traditional tests of lung function is a complicated problem. The pulmonary mechanics of these patients can change rapidly with potential for a negative impact on oxygenation. In an effort to address these problems, we designed a system with a three-way valve that permits the patient to be switched from the ventilator to a data collection system for the assessment of changes in the disease state. The short periods required for data collection (20 to 30 sec) do not interfere with patient care and are well within the limits of safety. A unique feature of the valved system is that it serves to maintain positive airway pressure during data collection. Tests show that, within the frequency range of interest, the mechanics of the measurement system are not altered by the DC pressures applied to the speaker and the valve itself does not contribute significantly to the serial impedance of the system.     

Low positive end-expiratory pressure does not exacerbate nebulized-acid lung injury in dogs

It is not clear if low end-expiratory pressures contribute to ventilator-induced lung injury in large animals. We sought to determine whether ventilation with a low level of positive end-expiratory pressure (PEEP) worsens preexisting permeability lung injury in dogs. Lung injury was initiated in 20 mongrel dogs by ventilating with nebulized 3N hydrochloric acid until a lower inflection point (LIP) appeared on the respiratory system pressure-volume loop. One group of 10 dogs was then ventilated for 4 hours with PEEP set below the LIP (low PEEP), whereas the remaining group of dogs was ventilated for the same time period with similar tidal volumes but with PEEP set above the LIP (high PEEP). We found histologic evidence of reduced alveolar volumes in the low-PEEP animals. However, there were no differences in neutrophil infiltration, lung lobe weights, pulmonary capillary hemorrhage or congestion, or arterial endothelin-1 concentration between the 2 protocol groups. In conclusion, we were unable to demonstrate that ventilation with PEEP set below the LIP exacerbates hydrochloric acid-induced lung injury in dogs.     

Noninvasive bilevel positive pressure ventilation in severe acute pulmonary edema

Severe acute pulmonary edema is a medical emergency that requires immediate action on the part of the health care provider. Endotracheal intubation and mechanical ventilation remain the primary method of respiratory support in the most severe cases when respiratory failure ensues. Two cases of respiratory failure resulting from severe acute pulmonary edema are presented in which mechanical ventilation was indicated but the patients were treated instead with noninvasive bilevel positive pressure ventilation, which subsequently reversed their inspiratory failure. The use of noninvasive bilevel positive pressure ventilation in the emergency treatment of respiratory failure secondary to severe acute pulmonary edema is discussed.     

双水平正压通气在急性心源性肺水肿中的应用

目的:探讨双水平正压通气治疗急性心源性肺水肿的疗效。方法:收集内科2003年1月至2007年8月收治的92例急性心源性肺水肿患者的临床资料并进行分析。治疗组46例在应用常规抗心源性肺水肿药物的同时联用BiPAPS/T30或BiPAP-Synchrony呼吸机进行无创通气治疗,对照组46例只应用常规药物治疗。结果:治疗组患者临床症状、体征明显改善,心率、呼吸频率、血压与治疗前比较显著降低,SaO2与治疗前比较显著增高(P<0.05),总有效率93.5%。对照组总有效率仅为82.6%。结论:双水平正压通气治疗急性心源性肺水肿疗效确切。     

Noninvasive continuous positive airway pressure in elderly cardiogenic pulmonary edema patients

Objective To compare the physiological effects and the clinical efficacy of continuous positive airway pressure (CPAP) vs standard medical treatment in elderly patients (75 years) with acute hypoxemic respiratory failure related to cardiogenic pulmonary edema.Design A prospective, randomized, concealed, and unblinded study of 89 consecutive patients who were admitted to the emergency departments of one general, and three teaching, hospitals.Intervention Patients were randomly assigned to receive standard medical treatment alone (n=46) or standard medical treatment plus CPAP (n=43).Measurements Improvement in PaO₂/FIO₂ ratio, complications, length of hospital stay, early 48-h and overall mortality, compared between the CPAP and standard treatment groups.Results Study groups were comparable with regard to baseline physiological and clinical characteristics (age, sex ratio, autonomy, medical history, cause of pulmonary edema). Within 1 h, noninvasive continuous positive airway pressure led to decreased respiratory rate (respiratory rate, 27±7 vs 35±6 breaths/min; p=0.009), and improved oxygenation (PaO₂/F_IO₂, 306±104 vs 157±71; p=0.004) compared with baseline, whereas no differences were observed within the standard treatment group. Severe complications occurred in 17 patients in the standard treatment group, vs 4 patients in the noninvasive continuous positive airway pressure group (p=0.002). Early 48-h mortality was 7% in the noninvasive continuous positive airway pressure group, compared with 24% in the standard treatment group (p=0.017); however, no sustained benefits were observed during the overall hospital stay.Conclusion Noninvasive continuous positive airway pressure promotes early clinical improvement in elderly patients attending emergency departments for a severe pulmonary edema, but only reduces early 48-h mortality.     

Haemodynamic effects of selective positive end-expiratory pressure after unilateral pulmonary hydrochloric acid-aspiration in dogs

We investigated 1) the effects of HCl-mediated acute left lung injury on regional juxtacardiac pressures and 2) the haemodynamic effects of different modes of ventilation before and after induction of left lung injury. The study was done in 7 mechanically ventilated, anaesthetized dogs. Juxtacardiac pressures and haemodynamic variables were recorded during 1) differential ventilation (DV) with zero positive end-expiratory pressure (PEEP=0) and 2) DV with general (G) PEEP and selective right (R) and left (L) lung PEEP. Left lung injury increased left, but not right pleural pressure or pericardial pressure. Pulmonary vascular resistance (PVR) and pulmonary artery pressure (PAP) were increased moderately. Cardiac output (CO) did not change. GPEEP reduced LV filling and cardiac output markedly and by approximately the same degree before and after lung injury. The haemodynamic effects of LPEEP were minor before as well as after the induction of lung injury. RPEEP, which had only moderate haemodynamic effects during control, caused a marked reduction in cardiac function after the induction of left lung injury. The transmission of airway pressure to the pleura was reduced in the diseased lung. These results suggest that serious haemodynamic side effects may be avoided by applying PEEP selectively to the diseased lung.     

Mechanical ventilation in acute respiratory failure: recruitment and high positive end-expiratory pressure are necessary

PURPOSE OF REVIEW: To review as best the critical care clinicians can recruit the acute respiratory distress syndrome (ARDS) lungs and keep the lungs opened, assuring homogeneous ventilation, and to present the experimental and clinical results of these mechanical ventilation strategies, along with possible improvements in patient outcome based on selected published medical literature from 1972 to 2004 (highlighting the period from June 2003 to June 2004 and recent results of the authors' group research). RECENT FINDINGS: In the experimental setting, repeated derecruitments accentuate lung injury during mechanical ventilation, whereas open lung concept strategies can attenuate lung injury. In the clinical setting, recruitment maneuvers improve short-term oxygenation in ARDS patients. A recent prospective clinical trial showed that low versus intermediate positive end-expiratory pressure (PEEP) levels (8 vs 13 cm H2O) associated with low tidal ventilation had the same effect on ARDS patient survival. Nevertheless, both conventional and electrical impedance thoracic tomography studies indicate that stepwise PEEP recruitment maneuvers increase lung volume and the recruitment percentage of lung tissue, and higher levels of PEEP (18-26 cm H2O) are necessary to keep the ARDS lungs opened and assure a more homogeneous low tidal ventilation. SUMMARY: Stepwise PEEP recruitment maneuvers can open collapsed ARDS lungs. Higher levels of PEEP are necessary to maintain the lungs open and assure homogenous ventilation in ARDS. In the near future, thoracic CT associated with high-performance monitoring of regional ventilation (electrical impedance tomography) may be used at the bedside to determine the optimal mechanical ventilation of ARDS patients.     

Selective positive end-expiratory pressure and cardiac function in dogs

Effects of general (G) versus selective (S) right (R) and left (L) positive end-expiratory pressure (PEEP) were compared during differential lung ventilation in 11 anaesthetized dogs in the supine position. GPEEP 20 cm H₂O decreased cardiac output (1 min^–1) from 2.9±0.2 (mean±SE) to 1.7±0.5 (p<0.05), RPEEP from 2.8±0.2 to 2.2±0.2 (p<0.05) while LPEEP caused no significant change in cardiac output. GPEEP increased pleural pressure more than SPEEP. Pleural pressure was asymmetric during SPEEP. Both SPEEP and GPEEP increased pericardial pressure uniformly, but the increase was less marked with SPEEP. During GPEEP 20 cm H₂O transmural left ventricular end-diastolic pressure (LVEDP) decreased markedly. SPEEP caused less marked reductions in transmural LVEDP. Qualitatively similar, but less marked changes were observed with PEEP 10 cm H₂O. In conclusion, cardiac output decreased less with selective PEEP than with general PEEP. This was explained by less increase in pleural and pericardial pressure, and accordingly less decrease in LV transmural filling pressure.     

Recruitment maneuver and high positive end-expiratory pressure improve hypoxemia in patients after pulmonary thromboendarterectomy for chronic pulmonary thromboembolism

OBJECTIVES: To investigate the effects of a recruitment maneuver and high positive end-expiratory pressure (PEEP) on oxygenation and hemodynamics in hypoxemic patients with pulmonary hypertension after pulmonary thromboendarterectomy for chronic pulmonary thromboembolism. DESIGN: Prospective, observational, clinical study. SETTING: A surgical intensive care unit in a national heart institute. PATIENTS: Fourteen consecutively admitted patients who developed acute lung injury (Pa(O2) <300 torr at F(IO2) 1.0) and pulmonary hypertension (mean pulmonary artery pressure >25 mm Hg) after pulmonary thromboendarterectomy for chronic pulmonary thromboembolism. INTERVENTIONS: The recruitment maneuver was an increase of PEEP to 30 cm H2O in one step for 1 min at F(IO2) 1.0. The level of pressure control ventilation during the recruitment maneuver was the same as before the maneuver. Subsequently, PEEP was decreased in 15-min intervals from 15 to 10, 5, and 0 cm H2O. MEASUREMENTS AND MAIN RESULTS: Hemodynamics and respiratory variables were analyzed before and during the recruitment maneuver and at each PEEP level. At F(IO2) 1.0, Pa(O2) increased from 240 +/- 62 torr to 470 +/- 83 torr at 15 cm H2O of PEEP and 469 +/- 75 torr at 10 cm H2O of PEEP after the recruitment maneuver (p < .001). At 15 cm H2O of PEEP, cardiac index decreased (from 2.7 +/- 0.6 at baseline to 2.2 +/- 0.3 L.min(-1).m(-2), p < .01) and mean blood pressure decreased (from 86 +/- 8 at baseline to 74 +/- 11 mm Hg, p < .05), but they returned to the baseline levels at 10 cm H2O of PEEP (2.5 +/- 0.4 L.min(-1).m(-2) and 83 +/- 9 mm Hg). There were no differences in mean pulmonary artery pressure at different levels of PEEP. CONCLUSIONS: In hypoxemic patients with pulmonary hypertension after pulmonary thromboendarterectomy for chronic pulmonary thromboembolism, oxygenation was improved by the recruitment maneuver followed by high PEEP. However, hemodynamics were transiently suppressed and overall oxygen delivery did not change.     

Alveolar edema dispersion and alveolar protein permeability during high volume ventilation: effect of positive end-expiratory pressure

Objectives To evaluate whether PEEP affects intrapulmonary alveolar edema liquid movement and alveolar permeability to proteins during high volume ventilation. Design and setting Experimental study in an animal research laboratory. Subjects 46 male Wistar rats. Interventions A ^99mTc-labeled albumin solution was instilled in a distal airway to produce a zone of alveolar flooding. Conventional ventilation (CV) was applied for 30 min followed by various ventilation strategies for 3 h: CV, spontaneous breathing, and high volume ventilation with different PEEP levels (0, 6, and 8 cmH₂O) and different tidal volumes. Dispersion of the instilled liquid and systemic leakage of ^99mTc-albumin from the lungs were studied by scintigraphy. Measurements and results The instillation protocol produced a zone of alveolar flooding that stayed localized during CV or spontaneous breathing. High volume ventilation dispersed alveolar liquid in the lungs. This dispersion was prevented by PEEP even when tidal volume was the same and thus end-inspiratory pressure higher. High volume ventilation resulted in the leakage of instilled ^99mTc-albumin from the lungs. This increase in alveolar albumin permeability was reduced by PEEP. Albumin permeability was more affected by the amplitude of tidal excursions than by overall lung distension. Conclusions PEEP prevents the dispersion of alveolar edema liquid in the lungs and lessens the increase in alveolar albumin permeability due to high volume ventilation. This research was supported by a grant from the French Académie Nationale de Médecine     

Mortality in acute cardiogenic pulmonary edema treated with continuous positive airway pressure

Objective  To investigate mortality in acute cardiogenic pulmonary edema (ACPE) patients treated with continuous positive airway pressure (CPAP) and to identify clinical and laboratory characteristics associated with mortality. Design  Observational, retrospective study. Setting  Emergency Medicine Department. Patients and participants  A total of 454 consecutive ACPE patients treated with CPAP. Measurements and results  Demographics, past medical history, clinical characteristics, laboratory evaluation, in-hospital mortality data were collected. Potential predictors of in-hospital mortality that were considered of clinical relevance and immediately accessible on admission were investigated by multivariable logistic regression. ACPE-related mortality rate was 3.8% (17/452 patients) and the in-hospital mortality rate was 11.4% (50/440 patients). Significant independent predictors of increased risk of in-hospital mortality were: advanced age (P = 0.012), normal-to-low blood pressure (P < 0.001), low PaO₂/FiO₂ ratio (P = 0.020), hypocapnia (P = 0.009) and anemia (P = 0.05). Conclusions  Values recorded within few minutes from arrival to the hospital can predict mortality in ACPE patients treated with CPAP who has been tested, for the first time, in a real life study. This can allow physicians to quickly recognize more severe ACPE patients treated with CPAP and plan for aggressive monitoring and treatment and for deciding the better site of care.     

Noninvasive pressure support ventilation vs. continuous positive airway pressure in acute hypercapnic pulmonary edema

Objective This study compared noninvasive pressure support ventilation (NIPSV) and continuous positive airway pressure (CPAP) in patients with acute hypercapnic pulmonary edema with regard to resolution time.Design and setting Randomized prospective study in an emergency department.Patients and participants We randomly assigned 36 patients with respiratory failure due to acute pulmonary edema and arterial hypercapnia (PaCO₂ >45 mmHg) to NIPSV (n=18) or CPAP through a face mask (n=18).Measurements and results Electrocardiographic and physiological measurements were made over 36 h. There was no difference in resolution time defined as clinical improvement with a respiratory rate of fewer than 30 breaths/min and SpO₂ of 96% or more between CPAP and NIPSV groups. Arterial carbon dioxide tension was significantly decreased after 1 h of ventilation (CPAP, 60.5±13.6 to 42.8±4.9 mmHg; NIPSV, 65.7±13.6 to 44.0±5.5 mmHg); respective improvements were seen in pH (CPAP, 7.22±0.11 to 7.37±0.04; NIPSV, 7.19±0.11 to 7.38±0.04), SpO₂ (CPAP, 86.9±3.7% to 95.1±2.6%; NIPSV, 83.7±6.6% to 96.0±2.9%), and respiratory rate (CPAP, 37.9±4.5 to 21.3±5.1 breaths/min; NIPSV, 39.8±4.4 to 21.2±4.6 breaths/min). No significant differences were seen with regards to endotracheal intubation and in-hospital mortality.Conclusions NIPSV proved as effective as CPAP in the treatment of patients with acute pulmonary edema and hypercapnia but did not improve resolution time.     

Left ventricular geometry during positive end-expiratory pressure in dogs

We evaluated changes in left ventricular (LV) geometry in ten dogs during intermittent positive-pressure ventilation (IPPV) with and without 10 cm H2O of positive end-expiratory pressure (PEEP). The dimensions during expiration and inspiration decreased in all three orthogonal axes during PEEP, consistent with decreased LV end-diastolic (ED) and end-systolic (ES) volumes. Within a respiratory cycle, the anterior-posterior (AP) ED dimension during inspiration increased with IPPV alone but decreased when PEEP was added, consistent with presumed differences in pulmonary venous return. This caused opposite changes in AP percent regional shortening. Septal-lateral free wall (SL) percent regional shortening decreased during inspiration with both IPPV and PEEP, but the respiratory variation was significantly less during PEEP. Thus, PEEP did not simply produce a smaller version of the same events seen during IPPV alone. The larger decreases with PEEP observed in ED compared to ES dimensions in the AP and SL axes suggest a dominant regional preload effect, whereas the larger fall in the long axis ES compared to ED dimension suggests a primary regional decrease in afterload. Measurements of the right ventricular SL axis in three dogs showed an overall reduction with PEEP, with the inspiratory dimensions being minimal during both IPPV alone and with PEEP. Thus, ventricular interdependence cannot account for the diminished LV SL dimension with PEEP during any part of the respiratory cycle. These findings suggest that the motion of the LV free wall influenced by changes in lung volume may be at least as important as septal motion in determining LV geometry with PEEP.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of proning and positive end-expiratory pressure in COVID-19

The novel coronavirus, which was declared a pandemic by the World Health Organization in early 2020 has brought with itself major morbidity and mortality. It has increased hospital occupancy, heralded economic turmoil, and the rapid transmission and community spread have added to the burden of the virus. Most of the patients are admitted to the intensive care unit (ICU) for acute hypoxic respiratory failure often secondary to acute respiratory distress syndrome (ARDS). Based on the limited data available, there have been different opinions about the respiratory mechanics of the ARDS caused by coronavirus disease 2019 (COVID-19). Our article provides an insight into COVID-19 pathophysiology and how it differs from typical ARDS. Based on these differences, our article explains the different approach to ventilation in COVID-19 ARDS compared to typical ARDS. We critically analyze the role of positive end-expiratory pressure (PEEP) and proning in the ICU patients. Through the limited data and clinical experience are available, we believe that early proning in COVID-19 patients improves oxygenation and optimal PEEP should be titrated based on individual lung compliance.