Thomas Luecke

Respiratory and haemodynamic changes during decremental open lung positive end-expiratory pressure titration in patients with acute respiratory distress syndrome

IntroductionTo investigate haemodynamic and respiratory changes during lung recruitment and decremental positive end-expiratory pressure (PEEP) titration for open lung ventilation in patients with acute respiratory distress syndrome (ARDS) a prospective, clinical trial was performed involving 12 adult patients with ARDS treated in the surgical intensive care unit in a university hospital.MethodsA software programme (Open Lung Tool™) incorporated into a standard ventilator controlled the recruitment (pressure-controlled ventilation with fixed PEEP at 20 cmH2O and increased driving pressures at 20, 25 and 30 cmH2O for two minutes each) and PEEP titration (PEEP lowered by 2 cmH2O every two minutes, with tidal volume set at 6 ml/kg). The open lung PEEP (OL-PEEP) was defined as the PEEP level yielding maximum dynamic respiratory compliance plus 2 cmH2O. Gas exchange, respiratory mechanics and central haemodynamics using the Pulse Contour Cardiac Output Monitor (PiCCO™), as well as transoesophageal echocardiography were measured at the following steps: at baseline (T0); during the final recruitment step with PEEP at 20 cmH2O and driving pressure at 30 cmH2O, (T20/30); at OL-PEEP, following another recruitment manoeuvre (TOLP).ResultsThe ratio of partial pressure of arterial oxygen (PaO2) to fraction of inspired oxygen (FiO2) increased from T0 to TOLP (120 ± 59 versus 146 ± 64 mmHg, P < 0.005), as did dynamic respiratory compliance (23 ± 5 versus 27 ± 6 ml/cmH2O, P < 0.005). At constant PEEP (14 ± 3 cmH2O) and tidal volumes, peak inspiratory pressure decreased (32 ± 3 versus 29 ± 3 cmH2O, P < 0.005), although partial pressure of arterial carbon dioxide (PaCO2) was unchanged (58 ± 22 versus 53 ± 18 mmHg). No significant decrease in mean arterial pressure, stroke volume or cardiac output occurred during the recruitment (T20/30). However, left ventricular end-diastolic area decreased at T20/30 due to a decrease in the left ventricular end-diastolic septal-lateral diameter, while right ventricular end-diastolic area increased. Right ventricular function, estimated by the right ventricular Tei-index, deteriorated during the recruitment manoeuvre, but improved at TOLP.ConclusionsA standardised open lung strategy increased oxygenation and improved respiratory system compliance. No major haemodynamic compromise was observed, although the increase in right ventricular Tei-index and right ventricular end-diastolic area and the decrease in left ventricular end-diastolic septal-lateral diameter during the recruitment suggested an increased right ventricular stress and strain. Right ventricular function was significantly improved at TOLP compared with T0, although left ventricular function was unchanged, indicating effective lung volume optimisation.

Effects of positive end-expiratory pressure on respiratory function and hemodynamics in patients with acute respiratory failure with and without intra-abdominal hypertension: a pilot study

IntroductionTo investigate the effects of positive end-expiratory pressure (PEEP) on respiratory function and hemodynamics in patients with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS) with normal intra-abdominal pressure (IAP < 12 mmHg) and with intra-abdominal hypertension (IAH, defined as IAP ≥ 12 mmHg) during lung protective ventilation and a decremental PEEP, a prospective, observational clinical pilot study was performed.MethodsTwenty patients with ALI/ARDS with normal IAP or IAH treated in the surgical intensive care unit in a university hospital were studied. The mean IAP in patients with IAH and normal IAP was 16 ± 3 mmHg and 8 ± 3 mmHg, respectively (P < 0.001). At different PEEP levels (5, 10, 15, 20 cmH2O) we measured respiratory mechanics, partitioned into its lung and chest wall components, alveolar recruitment, gas-exchange, hemodynamics, extravascular lung water index (EVLWI) and intrathoracic blood volume index (ITBVI).ResultsWe found that ALI/ARDS patients with IAH, as compared to those with normal IAP, were characterized by: a) no differences in gas-exchange, respiratory mechanics, partitioned into its lung and chest wall components, as well as hemodynamics and EVLWI/ITBVI; b) decreased elastance of the respiratory system and the lung, but no differences in alveolar recruitment and oxygenation or hemodynamics, when PEEP was increased at 10 and 15cmH2O; c) at higher levels of PEEP, EVLWI was lower in ALI/ARDS patients with IAH as compared with those with normal IAP.ConclusionsIAH, within the limits of IAP measured in the present study, does not affect interpretation of respiratory mechanics, alveolar recruitment and hemodynamics.

Setting mean airway pressure during High-frequency oscillatory ventilation according to the static pressure-volume curve in surfactant-deficient lung injury: A computed tomography study

Background Numerous studies suggest setting positive end-expiratory pressure during conventional ventilation according to the static pressure–volume (P-V) curve, whereas data on how to adjust mean airway pressure (Paw) during high-frequency oscillatory ventilation (HFOV) are still scarce. The aims of the current study were to (1) examine the respiratory and hemodynamic effects of setting Paw during HFOV according to the static P-V curve, (2) assess the effect of increasing and decreasing Paw on slice volumes and aeration patterns at the lung apex and base using computed tomography, and (3) study the suitability of the P-V curve to set Paw by comparing computed tomography findings during HFOV with those obtained during recording of the static P-V curve at comparable pressures. Methods Saline lung lavage was performed in seven adult pigs. P-V curves were obtained with computed tomography scanning at each volume step at the lung apex and base. The lower inflection point (Pflex) was determined, and HFOV was started with Paw set at Pflex. The pigs were provided five 1-h cycles of HFOV. Paw, first set at Pflex, was increased to 1.5 times Pflex (termed 1.5 Pflexinc) and 2 Pflex and decreased thereafter to 1.5 times Pflex and Pflex (termed 1.5 Pflexdec and Pflexdec). Hourly measurements of respiratory and hemodynamic variables as well as computed tomography scans at the apex and base were made. Results High-frequency oscillatory ventilation at a Paw of 1.5 Pflexinc reestablished preinjury arterial oxygen tension values. Further increase in Paw did not change oxygenation, but it decreased oxygen delivery as a result of decreased cardiac output. No differences in respiratory or hemodynamic variables were observed when comparing HFOV at corresponding Paw during increasing and decreasing Paw. Variation in total slice lung volume (TLVs) was far less than expected from the static P-V curve. Overdistended lung volume was constant and less than 3% of TLVs. TLVs values during HFOV at Pflex, 1.5 Pflexinc, and 2 Pflex were significantly greater than TLVs values at corresponding tracheal pressures on the inflation limb of the static P-V curve and located near the deflation limb. In contrast, TLVs values during HFOV at decreasing Paw (i.e., 1.5 Pflexdec and Pflexdec) were not significantly greater than corresponding TLV on the deflation limb of the static P-V curves. The marked hysteresis observed during static P-V curve recordings was absent during HFOV. Conclusions High-frequency oscillatory ventilation using Paw set according to a static P-V curve results in effective lung recruitment, and slice lung volumes during HFOV are equal to those from the deflation limb of the static P-V curve at equivalent pressures.

Chest wall mechanics and abdominal pressure during general anaesthesia in normal and obese individuals and in acute lung injury.

Purpose of reviewThis article discusses the methods available to evaluate chest wall mechanics and the relationship between intraabdominal pressure (IAP) and chest wall mechanics during general anaesthesia in normal and obese individuals, as well as in acute lung injury/acute respiratory distress syndrome. Recent findingsThe interactions between the abdominal and thoracic compartments pose a specific challenge for intensive care physicians. IAP affects respiratory system, lung and chest wall elastance in an unpredictable way. Thus, transpulmonary pressure should be measured if IAP is more than 12 mmHg or if chest wall elastance is compromised for other reasons, even though the absolute values of pleural and transpulmonary pressures are not easily obtained at bedside. We suggest defining intraabdominal hypertension (IAH) as IAP at least 20 mmHg and abdominal compartment syndrome (ACS) as IAP at least 20 mmHg associated with failure of one or more organs, although further studies are required to confirm this hypothesis. Additionally, in the presence of IAH, controlled mechanical ventilation should be applied and positive end-expiratory pressure individually titrated. Prophylactic open abdomen should be considered in the presence of ACS. SummaryIncreased IAP markedly affects respiratory function and complicates patient management. Frequent assessment of IAP is recommended.

predictors of mortality in Ards patients referred to a tertiary care centre : a pilot study

Background and objective: In order to identify parameters predicting intensive care unit mortality in patients transferred to a specialized tertiary centre because of progressive acute respiratory distress syndrome, an observational pilot study was carried out involving 94 patients. Methods and Results: Forty‐one patients (43.6%) died. Survival was defined as intensive care unit discharge. Survivors were younger (32.0 ± 11.8 vs. 39.1 ± 12.4 yr, P = 0.008), at admission they had a lower acute physiology and chronic health evaluation (APACHE) II score (21.7 ± 5.4 vs. 25.4 ± 5.2, P = 0.0009), higher PaO2/FiO2 (122 ± 79 vs. 79 ± 42 mmHg, P = 0.002), lower positive end‐expiratory pressure (10.6 ± 3.1 vs. 12.5 ± 3.7 cmH2O, P = 0.02) and a lower Murray score (2.8 ± 0.63 vs. 3.0 ± 0.62, P = 0.04). No differences were observed for tidal volumes and peak inspiratory pressures. Days of hospitalization and mechanical ventilation prior to transferral were not related to survival. Multivariate analysis of variables assessed on admission detected only differences for age (P = 0.014) and APACHE II (P = 0.005). Odds ratio was 1.06 (95% confidence interval (CI): 1.013–1.119) for age and 1.21 (CI: 1.059–1.381) for APACHE II. Multivariate analysis of changes in respiratory parameters, APACHE II and Murray score during the first 3 days after transferral revealed a significant difference only for positive end‐expiratory pressure (P < 0.008). Corresponding odds ratio was 2.40 (CI: 1.25–4.58) for an increase of 1 cmH2O/24 h. Conclusion: Age‐related mortality in this small, but highly selected group of patients with established ARDS increased early in life even in a population with an overall mean age of 35.1 yr. APACHE II was the only clinical predictor for mortality on admission. The need for a substantial increase in positive end‐expiratory pressure after transferral markedly reduced the chance to survive.

Computed tomography scan assessment of lung volume and recruitment during high-frequency oscillatory ventilation

Objective:This review describes how computed tomography has increased our understanding of the pathophysiology of acute respiratory distress syndrome. It summarizes current knowledge about lung volume changes and alveolar recruitment during high-frequency oscillatory ventilation (HFOV) assessed by computed tomography (CT), outlines potential problems when comparing HFOV with conventional ventilation (CV) as a result of the different pressure-time profiles, and describes future research directions. Data Source:CT allows accurate assessment of total lung volumes and differentiation between overinflated, normally aerated, poorly aerated, and nonaerated lung regions. It allows for classification of different patterns of consolidation and may be predictive for the potential for recruitment. Data summary:Experimental data suggest that HFOV at mean airway pressures (mPaw) set according to a static PV curve leads to effective lung recruitment but results in overall lung volumes that are considerably higher than those predicted from the PV relationship. In saline-lavaged sheep, similar changes in total lung volumes and subvolumes were observed during HFOV and CV. One single study specifically assessed lung volume recruitment during HFOV as compared with CV in eight patients with acute respiratory distress syndrome from pneumonia or sepsis. After 48 hrs on HFOV, total ventilated lung volume was significantly increased, whereas only a minor increase in overinflated lung volume was observed. These changes correlated with a significant improvement in gas exchange. Conclusion:CT is a valuable tool to quantify recruitment and overinflation during HFOV. Additional studies are needed to better characterize the specific effects of HFOV on lung volume and morphology.

Lung imaging for titration of mechanical ventilation.

Purpose of review Computed tomography (CT) has fostered pivotal advancements in the understanding of acute lung injury/acute respiratory distress syndrome and ventilator-induced lung injury. Apart from CT-based studies, the past years have seen fascinating work using positron emission tomography, electrical impedance tomography and lung ultrasound as diagnostic tools to optimize mechanical ventilation. This review aims to present the major findings of recent studies on lung imaging. Recent findings Patients presenting with a focal loss of aeration on CT may not be suitable candidates for recruitment maneuvers and high levels of positive end-expiratory pressure (PEEP) in supine position. PET/CT has provided valuable insights into the inflammatory response of the lung. Electrical impedance tomography has been used to assess lung recruitability and to titrate PEEP. Finally, lung ultrasound has proven to be reliable diagnostic tool for assessing PEEP-induced recruitment. Summary Whereas quantitative CT remains the gold standard to assess lung morphology, recruitment and hyperinflation of lung tissue at different inflation pressures, EIT and LUS have emerged as valuable, radiation-free, noninvasive bedside lung imaging tools that should be used together with global parameters like lung mechanics and gas exchange to acquire additional information on recruitability and ventilation distribution.

Effects of end-inspiratory and end-expiratory pressures on alveolar recruitment and derecruitment in saline-washout-induced lung injury – a computed tomography study

Background:  Lung protective ventilation using low end‐inspiratory pressures and tidal volumes (VT) has been shown to impair alveolar recruitment and to promote derecruitment in acute lung injury. The aim of the present study was to compare the effects of two different end‐inspiratory pressure levels on alveolar recruitment, alveolar derecruitment and potential overdistention at incremental levels of positive end‐expiratory pressure.

Pulmonary gas distribution during ventilation with different inspiratory flow patterns in experimental lung injury – a computed tomography study

Background:  There is still controversy about the optimal inspiratory flow pattern for ventilation of patients with acute lung injury. The aim of this study was to compare the effects of pressure‐controlled ventilation (PCV) with a decelerating inspiratory flow with volume‐controlled ventilation (VCV) with constant inspiratory flow on pulmonary gas distribution (PGD) in experimentally induced ARDS.

Open lung approach with low tidal volume mechanical ventilation attenuates lung injury in rats with massive brain damage.

IntroductionThe ideal ventilation strategy for patients with massive brain damage requires better elucidation. We hypothesized that in the presence of massive brain injury, a ventilation strategy using low (6 milliliters per kilogram ideal body weight) tidal volume (VT) ventilation with open lung positive end-expiratory pressure (LVT/OLPEEP) set according to the minimal static elastance of the respiratory system, attenuates the impact of massive brain damage on gas-exchange, respiratory mechanics, lung histology and whole genome alterations compared with high (12 milliliters per kilogram ideal body weight) VT and low positive end-expiratory pressure ventilation (HVT/LPEEP).MethodsIn total, 28 adult male Wistar rats were randomly assigned to one of four groups: 1) no brain damage (NBD) with LVT/OLPEEP; 2) NBD with HVT/LPEEP; 3) brain damage (BD) with LVT/OLPEEP; and 4) BD with HVT/LPEEP. All animals were mechanically ventilated for six hours. Brain damage was induced by an inflated balloon catheter into the epidural space. Hemodynamics was recorded and blood gas analysis was performed hourly. At the end of the experiment, respiratory system mechanics and lung histology were analyzed. Genome wide gene expression profiling and subsequent confirmatory quantitative polymerase chain reaction (qPCR) for selected genes were performed.ResultsIn NBD, both LVT/OLPEEP and HVT/LPEEP did not affect arterial blood gases, as well as whole genome expression changes and real-time qPCR. In BD, LVT/OLPEEP, compared to HVT/LPEEP, improved oxygenation, reduced lung damage according to histology, genome analysis and real-time qPCR with decreased interleukin 6 (IL-6), cytokine-induced neutrophil chemoattractant 1 (CINC)-1 and angiopoietin-4 expressions. LVT/OLPEEP compared to HVT/LPEEP improved overall survival.ConclusionsIn BD, LVT/OLPEEP minimizes lung morpho-functional changes and inflammation compared to HVT/LPEEP.