Increase In Positive End-expiratory Pressure Research Articles

End-Expiratory Occlusion Test Predicts Preload Responsiveness Independently of Positive End-Expiratory Pressure During Acute Respiratory Distress Syndrome

A 15-second end-expiratory occlusion increases cardiac preload and allows detection of preload dependence. We tested whether the reliability of this test depends upon positive end-expiratory pressure. : Prospective study. Medical ICU. Thirty-four patients presenting with acute circulatory failure and acute respiratory distress syndrome ventilated with a tidal volume of 6.7 mL/kg (interquartile range, 6.3-7.1). At positive end-expiratory pressure = 5 cm H2O, we measured the changes in cardiac index induced by end-expiratory occlusion and a passive leg raising test. Preload dependence was defined by a passive leg raising-induced increase in cardiac index greater than or equal to 10%. Positive end-expiratory pressure was increased to a plateau pressure of 30 cm H2O, and end-expiratory occlusion and passive leg raising were performed again. At positive end-expiratory pressure = 5 cm H2O, 29% of patients were passive leg raising responders. An end-expiratory occlusion-induced increase in cardiac index greater than or equal to 5% detected a passive leg raising-induced increase in cardiac index greater than or equal to 10% with a sensitivity of 90% (95% CI, 56-100) and a specificity of 88% (95% CI, 68-97). At higher positive end-expiratory pressure (15 cm H2O [interquartile range, 13-15]), the plateau pressure - positive end-expiratory pressure difference did not change (15 mm Hg [14-17] vs 15 mm Hg [13-18] before the positive end-expiratory pressure increase). Increasing positive end-expiratory pressure significantly reduced cardiac index in passive leg raising responders (-27% [interquartile range, -6 to -56]) but not in other patients. At high positive end-expiratory pressure, passive leg raising increased cardiac index to a larger extent than at positive end-expiratory pressure = 5 cm H2O (19% [interquartile range, 15-34] vs 16% [interquartile range, 13-23], respectively). The proportion of passive leg raising responders significantly increased (34 vs 29%, respectively), meaning preload dependence had increased. At higher positive end-expiratory pressure, an end-expiratory occlusion-induced increase in cardiac index greater than or equal to 6% detected a passive leg raising-induced increase in cardiac index greater than or equal to 10% with a sensitivity of 100% (95% CI, 75-100) and a specificity of 90% (95% CI, 70-99). The end-expiratory occlusion test is reliable for detecting preload dependence whatever the positive end-expiratory pressure during acute respiratory distress syndrome.

Functio laesa: the consequences of the fifth cardinal sign of inflammation in preterm infants

<i>Functio laesa</i>: the consequences of the fifth cardinal sign of inflammation in preterm infants

Intrauterine inflammation alters cardiopulmonary and cerebral haemodynamics at birth in preterm lambs

Intrauterine inflammation is associated with preterm birth and poor long-term cardiopulmonary outcomes. We aimed to determine the effect of intrauterine inflammation on the cardiopulmonary and cerebral haemodynamic transition at birth, and the response to subsequent haemodynamic challenge. Fetal instrumentation was performed at ∼112 days gestation (term is 147 days) for measurement of cardiopulmonary and cerebral haemodynamics. At 118 days, inflammation was induced by intra-amniotic administration of lipopolysaccharide (LPS; n = 7); controls (n = 5) received intra-amniotic saline. At 125 days lambs were delivered and mechanically ventilated. Arterial blood gases, pulmonary and systemic arterial blood pressures and flows were measured during the perinatal period. At 10 min a haemodynamic challenge was administered by increasing positive end-expiratory pressure. During the first 10 min after birth, LPS-exposed lambs had higher pulmonary vascular resistance and lower pulmonary blood flow and left ventricular output than controls. Carotid arterial blood flow was higher in LPS-exposed lambs than controls between 3 and 7 min after delivery, and cerebral oxygen delivery was higher at 5 min. During the haemodynamic challenge, pulmonary blood flow and left ventricular output were reduced in controls but not in LPS-exposed lambs; a transient reduction in brachiocephalic arterial pressure occurred in LPS-exposed lambs but not in controls. Intrauterine inflammation altered the cardiopulmonary and cerebral haemodynamic transition at birth and reduced the cardiopulmonary response to a haemodynamic challenge after birth. The transient reduction in brachiocephalic arterial pressure suggests intrauterine inflammation may alter cerebrovascular control following an increase in positive end-expiratory pressure.

The influence of positive end-expiratory pressure on central venous pressure in patients with severe craniocerebral injury

To observe the impact of positive end-expiratory pressure (PEEP) on central venous pressure (CVP) in mechanically ventilated patients with severe craniocerebral injury. A prospective, interventional, self-control study was conducted. Thirty severe craniocerebral injury patients with central respiratory failure were enrolled. The changes in CVP, mean arterial pressure (MAP), heart rate (HR) and pulse oxygen saturation [SpO2] were monitored at different PEEP levels [0, 3, 6, 9, 12, 15 cm H2O; 1 cm H2O=0.098 kPa] during mechanical ventilation and after weaning of mechanical ventilation. The influences of PEEP and its discontinuance on haemodynamics and oxygenation were analyzed. The values of CVP [cm H2O] were increased when PEEP increased (from 7.9±3.1 to 13.1±3.7), a linear correlation was found (R=0.509, P=0.000), and linear regression equation was CVP [cm H2O]=7.774+0.368×PEEP [cm H2O]; CVP was elevated about 0.368 cm H2O when PEEP increased 1 cm H2O. CVP values significantly decreased during discontinuance of mechanical ventilation, as compared to those measured at different PEEP levels during mechanical ventilation (F=24.429, P=0.000). The values of MAP, HR and SpO2 showed no significant change with increase of PEEP levels [MAP (mm Hg, 1 mm Hg=0.133 kPa): from 81.6±10.4 to 85.6±10.6; HR (beats per minute): from 79.9±13.5 to 88.1±15.4; SpO2: from 0.968±0.036 to 0.975±0.033, all P>0.05] in mechanically ventilated patients, but discontinuance of mechanical ventilation could significantly increase the levels of MAP and HR (95.3±8.4 and 94.9±10.3, respectively) and lower SpO2 levels (0.928±0.036, all P=0.000). CVP values were overestimated during an increase in PEEP in mechanically ventilated patients with severe craniocerebral injury. CVP was increased about 0.368 cm H2O following an increase of PEEP of 1 cm H2O, whereas the values of MAP, HR and SpO2 showed no significant change with increase in PEEP levels. This study could offer a theoretical base in the correct assessment of CVP values at different PEEP levels without discontinuation of mechanical ventilation.

Tidal Volumes during General Anesthesia

Tidal Volumes during General Anesthesia

Mechanical ventilation with positive end-expiratory pressure in critically ill patients: comparison of CW-Doppler ultrasound cardiac output monitoring (USCOM) and thermodilution (PiCCO)

Background Aggressive mechanical ventilation can markedly and unpredictably aff ect cardiac function. The fall in cardiac output (CO) is due to a reduction in left ventricular stroke volume (SV). The aim of the present pilot study was to assess the eff ects of diff erent positive end-expiratory pressure (PEEP) levels on circulatory function and to compare them with continuous wave (CW)-Doppler ultrasound cardiac output monitoring (USCOM) and a thermodilution-based haemodynamic monitoring system (PiCCO).Methods Twenty mechanically ventilated (PEEP ≤10 mbar) adult patients (female n = 6, male n = 14, mean age 62 years, mean SAPS II-score 48.5), the majority with pneumonia and septic shock) were followed with USCOM and PiCCO at stepwise increased PEEP-levels from 0-10 mbar (1 mbar steps). The changes in CO/SV were recorded.Results With both methods, an increase of PEEP resulted in a decrease of SV and CO. Although the absolute decrease was consistently higher by USCOM, the changes of the parameters were qualitatively comparable. CO fell from 8.83 L/min (± 2.39) by 0.4 L/min to 8.49 L/min (± 2.48) with PiCCO and from 9.3 L/min (± 3.43) by 1.0 L/min to 8.3 L/min (± 3.2) with USCOM. The median CO/SV fell by 4.5%/5.2% with PiCCO and 10.8%/9% with USCOM, respectively. Correlation of CO values with the two methods by Bland-Altman yielded comparable results (mean percentage error at PEEP 0 mbar 13%, PEEP 10 mbar 18%). An adequate fl ow signal with USCOM was achieved in all patients.Conclusions A signifi cant infl uence of mechanical ventilation with PEEP on haemodynamic parameters was evident both with USCOM and PiCCO. While thermodilution methods like PiCCO are well established but time-consuming and invasive, CW-Doppler based USCOM constitutes an important tool for easy, rapid and reliable diagnosis and haemodynamic monitoring of critically ill patients.

Echocardiographic Measures of Diastolic Function Are Preload Dependent during Triggered Positive Pressure Ventilation: A Controlled Crossover Study in Healthy Subjects

Background. The use of echocardiography in intensive care settings impacts decision making. A prerequisite for the use of echocardiography is relative resistance to changes in volume status and levels of positive pressure ventilation (PPV). Studies on indices of diastolic function report conflicting results with regard to dependence on volume status. Evidence is scarce on PPV. Methods. Ten healthy subjects were exposed to 6 levels of positive end-expiratory pressure (PEEP) and pressure support (PS) following a baseline reading. All ventilator settings were performed at three positions: horizontal, reverse-Trendelenburg, and Trendelenburg. Echocardiography was performed throughout. Results. During spontaneous breathing, early diastolic transmitral velocity (E) changed with positioning (P < 0.001), whereas early diastolic velocity of the mitral annulus (e′) was independent (P = 0.263). With PPV, E and e′ proved preload dependent (P values < 0.001). Increases in PEEP, PS, or a combination influenced E and e′ in reverse-Trendelenburg- and horizontal positions, but not in the Trendelenburg position. Discussion. The change towards preload dependency of e′ with PPV suggests that PPV increases myocardial preload sensitivity. The susceptibility of E and e′ to preload changes during PPV discourages their use in settings of volume shifts or during changes in ventilator settings. Conclusion. Positioning and PPV affect E and e′.

Lung sound analysis correlates to injury and recruitment as identified by computed tomography: an experimental study

The aim of this study is to assess how analysis of the spectral characteristics of lung sounds can help in detecting lung injury and subsequent recruitment as verified by computed tomography (CT). Lung sounds were recorded at four locations (ventral and dorsal on right and left side) in six ventilated pigs before and after unilateral oleic acid-induced lung injury during sequential increase of positive end-expiratory pressure (PEEP) from 0 to 20 cmH(2)O. CT scans of the chest were used for comparison with lung aeration. Sound characteristics were compared by computer-aided analysis in the time and frequency domain as well as by clinicians. The presence of lung injury and its location were detected by substantial acoustic spectral components above 500 Hz (frequency) and -70 dB (amplitude). Application of increasing PEEP gradually reduced the pathological components as CT analysis verified recruitment. At 20 cmH(2)O PEEP there was no further tidal recruitment of injured lung and the pathological sounds had disappeared, rendering the lung sounds of the injured lung similar to those of the control lung. This was mirrored by the clinicians' characterization of the sounds. Computer-aided analysis of lung sounds is suitable for detection of pathological lung sounds and may guide in detection and recruitment of poorly/nonaerated lung.

Unintentional variation in positive end expiratory pressure during resuscitation with a T-piece resuscitator

Introduction The ability of T-piece resuscitators to deliver consistent peak inspiratory pressure (PIP) and positive end expiratory pressure (PEEP) during real and simulated neonatal resuscitation has been well described. The Neopuff (Fisher & Paykel Healthcare, Auckland, New Zealand) has been the device used for nearly all of these comparisons. Methods All high risk resuscitations were carried out in our dedicated resuscitation room, and were recorded on video tape for quality assurance purposes. 1 In addition to the audio and video recording, physiologic signals and resuscitation parameters, including oxygen saturation, pulse rate, airway pressure, FiO 2, and others signals as appropriate were also captured. These recordings were reviewed on a biweekly basis as part of a continuing quality review process. Resuscitations were graded for standard of care and the resuscitation checklist was reviewed to determine if the team had any unresolved issues that needed to be addressed. Results In the year between April of 2009 and March 2010, a period when we fully reviewed approximately 120 videos, we recognized visually obvious PEEP changes on 8 different occasions in ELBW infants. Our target PEEP was 5 cm H20. We observed rapid changes in the PEEP to as high as 15 cm H20 during resuscitation. Conclusion Based on our single-center experience, a T-piece resuscitation device which has the adjustment for the PEEP level and the orifice which is occluded to deliver a breath in the same location has the potential to cause an inadvertent and potentially toxic increase of PEEP which might not be noticed by the operator.

Study of the effects of mechanical ventilation on the heart function of patients with echocardiography

To study the effects of different positive end expiratory pressure (PEEP) levels on the heart function of patients undergoing mechanical ventilation (MV) with echocardiography. Thirty six critical patients with respiratory failure undergoing MV were divided into two groups according to the cardiac index (CI). The left heart function was measured with echocardiography at different PEEP levels (0, 4, 7, 10, 14 cm H(2)O, 1 cm H(2)O=0.098 kPa). In the normal cardiac function group (CI≥2.0 L×min(-1) ×m(-2) , n=17), an increase in PEEP had no significant effects on left ventricular systolic function [left ventricular end systolic volume (LVESV), left ventricular end diastolic volume (LVEDV), cardiac output (CO), ejection fraction (EF)]. The increase in PEEP had no significant effect on left ventricular diastolic function [mitral early diastolic filling velocity (E), late diastolic filling velocity (A), the ratio of E/A, early diastolic velocity (Ve), late diastolic velocity (Va), the ratio of Ve/Va, left ventricular end diastolic pressure (LVEDP)]. In the poor cardiac function group (CIP<2.0 L×min(-1) ×m(-2), n=19), when PEEP was increased to 10 cm H(2)O and 14 cm H(2)O, compared with PEEP 0, left ventricular systolic function indexes including LVESV (ml: 21.2±1.2 vs. 18.2±1.4 as 10 cm H(2)O) was significantly higher, i.e. LVEDV (ml: 42.6±2.4, 40.1±1.9 vs. 44.5±3.5), CO (L: 2.3±0.6, 2.1±0.7 vs. 2.6±0.7), EF (0.40±0.02, 0.39±0.02 vs. 0.42±0.02) were decreased (all P<0.05); left ventricular diastolic function indexes including A (cm/s: 88.5±15.2, 93.2±18.7 vs. 76.0±9.0), Va (cm/s: 14.3±4.5, 15.8±5.3 vs. 12.0±1.2), LVEDP [mm Hg (1 mm Hg=0.133 kPa): 15.3±2.0, 16.9±2.8 vs. 10.7±2.5] were significantly higher; E (cm/s: 73.6±15.4, 63.2±16.4 vs. 83.1±20.1), the ratio of E/A (0.83±0.10, 0.68±0.20 vs. 1.10±0.20), Ve (cm/s: 11.7±1.8, 10.4±2.0 vs. 13.8±2.8), the ratio of Ve/Va (0.8±0.1 , 0.6±0.2 vs. 1.2±0.2) were decreased (all P<0.05). Under the same condition of MV, change in PEEP levels (0-14 cm H(2)O) do not produce any obvious effect in the normal cardiac function group, on the other hand when PEEP≥10 cm H(2)O left heart function is significantly lowered in the poor cardiac function group. Optimal PEEP may improve the cardiac function.

Quantitative imaging of alveolar recruitment with hyperpolarized gas MRI during mechanical ventilation.

The aim of this study was to assess the utility of (3)He MRI to noninvasively probe the effects of positive end-expiratory pressure (PEEP) maneuvers on alveolar recruitment and atelectasis buildup in mechanically ventilated animals. Sprague-Dawley rats (n = 13) were anesthetized, intubated, and ventilated in the supine position ((4)He-to-O(2) ratio: 4:1; tidal volume: 10 ml/kg, 60 breaths/min, and inspiration-to-expiration ratio: 1:2). Recruitment maneuvers consisted of either a stepwise increase of PEEP to 9 cmH(2)O and back to zero end-expiratory pressure or alternating between these two PEEP levels. Diffusion MRI was performed to image (3)He apparent diffusion coefficient (ADC) maps in the middle coronal slices of lungs (n = 10). ADC was measured immediately before and after two recruitment maneuvers, which were separated from each other with a wait period (8-44 min). We detected a statistically significant decrease in mean ADC after each recruitment maneuver. The relative ADC change was -21.2 ± 4.1 % after the first maneuver and -9.7 ± 5.8 % after the second maneuver. A significant relative increase in mean ADC was observed over the wait period between the two recruitment maneuvers. The extent of this ADC buildup was time dependent, as it was significantly related to the duration of the wait period. The two postrecruitment ADC measurements were similar, suggesting that the lungs returned to the same state after the recruitment maneuvers were applied. No significant intrasubject differences in ADC were observed between the corresponding PEEP levels in two rats that underwent three repeat maneuvers. Airway pressure tracings were recorded in separate rats undergoing one PEEP maneuver (n = 3) and showed a significant relative difference in peak inspiratory pressure between pre- and poststates. These observations support the hypothesis of redistribution of alveolar gas due to recruitment of collapsed alveoli in presence of atelectasis, which was also supported by the decrease in peak inspiratory pressure after recruitment maneuvers.

Hemodynamic impact of a positive end-expiratory pressure setting in acute respiratory distress syndrome: Importance of the volume status*

The hemodynamic impact of positive end-expiratory pressure in acute respiratory distress syndrome and the underlying mechanisms have not been extensively investigated during low stretch ventilation. Our aim was to evaluate the hemodynamic effect of increasing positive end-expiratory pressure when tidal volume and the plateau pressure are limited and to explore the underlying mechanisms. Prospective study. Medical intensive care unit. Twenty-one acute respiratory distress syndrome patients ventilated with a tidal volume of 6.0 +/- 0.5 mL/kg of predicted body weight. Positive end-expiratory pressure was significantly increased from 5 +/- 1 cm H2O to 13 +/- 4 cm H2O for reaching a plateau pressure of 30 +/- 1 cm H2O. At high positive end-expiratory pressure, passive leg raising was performed for increasing the central blood volume. We performed echocardiography and pulmonary artery catheterization during positive end-expiratory pressure increase and during passive leg raising at high positive end-expiratory pressure. With positive end-expiratory pressure elevation, the cardiac index decreased by 13% +/- 9%. The right ventricular end-diastolic area, right atrial pressure, and pulmonary vascular resistance increased by 13% +/- 20%, 34% +/- 24% and 32% +/- 31%, respectively (p < .01; p = .04; and p < .01 vs. baseline, respectively). The transpulmonary pressure difference (mean pulmonary artery pressure--pulmonary artery occlusion pressure) increased (p < .05). Both at low and high positive end-expiratory pressure, an acute cor pulmonale was observed in the same three (14%) patients. At high positive end-expiratory pressure, the passive leg raising significantly increased the right and left ventricular end-diastolic areas and right atrial pressure. Passive leg raising also decreased the transpulmonary pressure difference (p < .05), increased the cardiac index by 14% +/- 10%, and decreased the pulmonary vascular resistance by 21% +/- 20% (both p < .01 vs. baseline). In acute respiratory distress syndrome patients, a positive end-expiratory pressure increase with limited tidal volume and plateau pressure reduced cardiac output by increasing the right ventricular afterload. Passive leg raising restored cardiac output by reducing the transpulmonary pressure difference and the pulmonary vascular resistance. This suggests that some pulmonary microvessels were collapsed by positive end-expiratory pressure elevation and were recruited by increasing the central blood volume.

Positive end-expiratory pressure affects the value of intra-abdominal pressure in acute lung injury/acute respiratory distress syndrome patients: a pilot study.

IntroductionTo examine the effects of positive end-expiratory pressure (PEEP) on intra-abdominal pressure (IAP) in patients with acute lung injury (ALI).MethodsThirty sedated and mechanically ventilated patients with ALI or acute respiratory distress syndrome (ARDS) admitted to a sixteen-bed surgical medical ICU were included. All patients were studied with sequentially increasing PEEP (0, 6 and 12 cmH2O) during a PEEP-trial.ResultsAge was 55 ± 17 years, weight was 70 ± 17 kg, SAPS II was 44 ± 14 and PaO2/FIO2 was 192 ± 53 mmHg. The IAP was 12 ± 5 mmHg at PEEP 0 (zero end-expiratory pressure, ZEEP), 13 ± 5 mmHg at PEEP 6 and 15 ± 6 mmHg at PEEP 12 (P < 0.05 vs ZEEP). In the patients with intra-abdominal hypertension defined as IAP ≥ 12 mmHg (n = 15), IAP significantly increased from 15 ± 3 mmHg at ZEEP to 20 ± 3 mmHg at PEEP 12 (P < 0.01). Whereas in the patients with IAP < 12 mmHg (n = 15), IAP did not significantly change from ZEEP to PEEP 12 (8 ± 2 vs 10 ± 3 mmHg). In the 13 patients in whom cardiac output was measured, increase in PEEP from 0 to 12 cmH2O did not significantly change cardiac output, nor in the 8 out of 15 patients of the high-IAP group. The observed effects were similar in both ALI (n = 17) and ARDS (n = 13) patients.ConclusionsPEEP is a contributing factor that impacts IAP values. It seems necessary to take into account the level of PEEP whilst interpreting IAP values in patients under mechanical ventilation.

Lung Opening and Closing during Ventilation of Acute Respiratory Distress Syndrome

The effects of high positive end-expiratory pressure (PEEP) strictly depend on lung recruitability, which varies widely during acute respiratory distress syndrome (ARDS). Unfortunately, increasing PEEP may lead to opposing effects on two main factors potentially worsening the lung injury, that is, alveolar strain and intratidal opening and closing, being detrimental (increasing the former) or beneficial (decreasing the latter). To investigate how lung recruitability influences alveolar strain and intratidal opening and closing after the application of high PEEP. We analyzed data from a database of 68 patients with acute lung injury or ARDS who underwent whole-lung computed tomography at 5, 15, and 45 cm H(2)O airway pressure. End-inspiratory nonaerated lung tissue was estimated from computed tomography pressure-volume curves. Alveolar strain and opening and closing lung tissue were computed at 5 and 15 cm H(2)O PEEP. In patients with a higher percentage of potentially recruitable lung, the increase in PEEP markedly reduced opening and closing lung tissue (P < 0.001), whereas no differences were observed in patients with a lower percentage of potentially recruitable lung. In contrast, alveolar strain similarly increased in the two groups (P = 0.89). Opening and closing lung tissue was distributed mainly in the dependent and hilar lung regions, and it appeared to be an independent risk factor for death (odds ratio, 1.10 for each 10-g increase). In ARDS, especially in patients with higher lung recruitability, the beneficial impact of reducing intratidal alveolar opening and closing by increasing PEEP prevails over the effects of increasing alveolar strain.

CENTRAL AIRWAY OCCLUSION UNDERESTIMATES INTRINSIC POSITIVE END-EXPIRATORY PRESSURE: A NUMERICAL AND PHYSICAL SIMULATION

Intrinsic positive end-expiratory pressure (PEEP) occurs when airway outflow is higher than zero at end-expiration. Differences in the time constant among alveolar units may result in an uneven distribution of intrinsic PEEP. The authors conducted a computer simulation of a 2-compartment respiratory system and calculated intrinsic PEEP for each alveolar unit and confirmed it with a test-lung experiment. Ventilator settings, including respiratory rate, inspiratory time, pause time, and external PEEP, were tested at various values in combination with various airway resistance and alveolar compliance values. The simulation was performed by calculating the flow, pressure, and volume every millisecond. The data demonstrated that the larger the difference of time constant between 2 respiratory units, the greater the difference in intrinsic PEEP between the units. A higher respiratory frequency and a larger percentage of inspiratory time resulted in an increase in the intrinsic PEEP at the central airway, as well as a wide difference in the intrinsic PEEP between airway units. These phenomena were confirmed by a 2-compartment test-lung study. The authors demonstrated and verified an uneven distribution of intrinsic PEEP in 2 different experiments, which raised a warning that some respiratory units might have much higher intrinsic PEEP than the intrinsic PEEP measured clinically.

Lung volume recruitment maneuvers and respiratory system mechanics in mechanically ventilated mice

The study aim was to establish how recruitment maneuvers (RMs) influence lung mechanics and to determine whether RMs produce lung injury. Healthy BALB/c mice were allocated to receive positive end-expiratory pressure (PEEP) at 2 or 6 cmH(2)O and volume- (20 or 40 mL/kg) or pressure-controlled (25 cmH(2)O) RMs every 5 or 75 min for 150 min. The low-frequency forced oscillation technique was used to measure respiratory input impedance. Large RMs resulting in peak airway opening pressures (P(ao))>30 cmH(2)O did not increase inflammatory response or affect transcutaneous oxygen saturation but significantly lowered airway resistance, tissue damping and tissue elastance; the latter changes are likely associated with the bimodal pressure-volume behavior observed in mice. PEEP increase alone and application of RMs producing peak P(ao) below 25 cmH(2)O did not prevent or reverse changes in lung mechanics; whereas frequent application of substantial RMs on top of elevated PEEP levels produced stable lung mechanics without signs of lung injury.

Visualization of alveolar recruitment in a porcine model of unilateral lung lavage using3He-MRI

In the acute respiratory distress syndrome potentially recruitable lung volume is currently discussed. (3)He-magnetic resonance imaging ((3)He-MRI) offers the possibility to visualize alveolar recruitment directly. With the approval of the state animal care committee, unilateral lung damage was induced in seven anesthetized pigs by saline lavage of the right lungs. The left lung served as an intraindividual control (healthy lung). Unilateral lung damage was confirmed by conventional proton MRI and spiral-CT scanning. The total aerated lung volume was determined both at a positive end-expiratory pressure (PEEP) of 0 and 10 mbar from three-dimensionally reconstructed (3)He images, both for healthy and damaged lungs. The fractional increase of aerated volume in damaged and healthy lungs, followed by a PEEP increase from 0 to 10 mbar, was compared. Aerated gas space was visualized with a high spatial resolution in the three-dimensionally reconstructed (3)He-MR images, and aeration defects in the lavaged lung matched the regional distribution of atelectasis in proton MRI. After recruitment and PEEP increase, the aerated volume increased significantly both in healthy lungs from 415 ml [270-445] (median [min-max]) to 481 ml [347-523] and in lavaged lungs from 264 ml [71-424] to 424 ml [129-520]. The fractional increase in lavaged lungs was significantly larger than that in healthy lungs (healthy: 17% [11-38] vs. lavage: 42% [14-90] (P=0.031). The (3)He-MRI signal might offer an experimental approach to discriminate atelectatic vs. poor aerated lung areas in a lung damage animal model. Our results confirm the presence of potential recruitable lung volume by either alveolar collapse or alveolar flooding, in accordance with previous reports by computed tomography.

Impact of acute hypercapnia and augmented positive end-expiratory pressure on right ventricle function in severe acute respiratory distress syndrome

To evaluate the effects of acute hypercapnia induced by positive end-expiratory pressure (PEEP) variations at constant plateau pressure (P (plat)) in patients with severe acute respiratory distress syndrome (ARDS) on right ventricular (RV) function. Prospective observational study in two academic intensive care units enrolling 11 adults with severe ARDS (PaO(2)/FiO(2) <150 mmHg at PEEP >5 cmH(2)O). We compared three ventilatory strategies, each used for 1 h, with P (plat) at 22 (20-25) cmH(2)O: low PEEP (5.4 cmH(2)O) or high PEEP (11.0 cmH(2)O) with compensation of the tidal volume reduction by either a high respiratory rate (high PEEP/high rate) or instrumental dead space decrease (high PEEP/low rate). We assessed RV function (transesophageal echocardiography), alveolar dead space (expired CO(2)), and alveolar recruitment (pressure-volume curves). Compared to low PEEP, PaO(2)/FiO(2) ratio and alveolar recruitment were increased with high PEEP. Alveolar dead space remained unchanged. Both high-PEEP strategies induced higher PaCO(2) levels [71 (60-94) and 75 (53-84), vs. 52 (43-68) mmHg] and lower pH values [7.17 (7.12-7.23) and 7.20 (7.16-7.25) vs. 7.30 (7.24-7.35)], as well as RV dilatation, LV deformation and a significant decrease in cardiac index. The decrease in stroke index tended to be negatively correlated to the increase in alveolar recruitment with high PEEP. Acidosis and hypercapnia induced by tidal volume reduction and increase in PEEP at constant P (plat) were associated with impaired RV function and hemodynamics despite positive effects on oxygenation and alveolar recruitment ( ClinicalTrials.gov #NCT00236262).

Evaluation of the Efficiency of Alveolar Opening in Cardiosurgical Patients with Low Left Ventricular Ejection Fraction

Objective: to determine the optimum alveolar opening parameters for the improvement of postoperative pulmonary oxygenizing function in patients with a left ventricular ejection fraction (LVEF) of less or more than 40% after aortocoronary bypass surgery (ACBS). Subjects and methods. Twenty patients with a LVEF of less than 40% after ACBS and with postoperative pulmonary oxygenizing dysfunction (PaO2/FiO2 less than 250) (Group 1) were examined. A control group consisted of 20 patients with a LVEF of more than 40% (Group 2). Gas exchange, respiration biomechanics, and central hemodynamic (CH) parameters were monitored (a Vigilance monitor (Edvard LifeScience)). Alveolar mobilization was carried out on Drager Evita-2 apparatuses in the BIPAP mode, by taking into account the previous artificial ventilation (AV) parameters. The low pressure phase corresponded to the positive end-expiratory pressure (PEEP) with volume AV, the high pressure phase was Pplato; the duration of both phases — that of inspiration and expiration (the high pressure phase was inspiration time; the low pressure phase was expiration time). Then the values of Pplato and PEEP were simultaneously increased by 2 cm H2O with a duration of 10 breathing cycles, by continuously monitoring Vt and SaO2 over this interval. By continuously monitoring Vt, a stepwise increase in PEEP and Pplato was continued until there was a Vt reduction or a negative impact of AV on CH. All alveoli were considered to be open when the maximum Vt and SaO2 were achieved. Conclusion. In Group 1 patients with Pinsp of 27—30 cm H2O, PEEP of 10—12 cm H2O, there are increases in PaO2/FiO2 and Cst. In Group 2, the increase of PaO2/FiO2 and Cst is observed with Pinsp of 30—35 cm H2O and PEEP 12—14 cm H2O. With these AV indices, there is an allowable hemodynamic reduction that results in no negative consequences and development of cardiovascular events. After switching to AV in an individually chosen mode, all hemodynamic parameters return to the baseline level. Consequently, the proposed AV mode and ventilation parameters are safe and effective for the prevention of early postoperative respiratory failure in cardiosurgical patients. Key words: recruiting ventilation, positive end-expiratory pressure, alveolar opening.

Performance of three minimally invasive cardiac output monitoring systems

We evaluated cardiac output (CO) using three new methods - the auto-calibrated FloTrac-Vigileo (CO(ed)), the non-calibrated Modelflow (CO(mf) ) pulse contour method and the ultra-sound HemoSonic system (CO(hs)) - with thermodilution (CO(td)) as the reference. In 13 postoperative cardiac surgical patients, 104 paired CO values were assessed before, during and after four interventions: (i) an increase of tidal volume by 50%; (ii) a 10 cm H(2)O increase in positive end-expiratory pressure; (iii) passive leg raising and (iv) head up position. With the pooled data the difference (bias (2SD)) between CO(ed) and CO(td), CO(mf) and CO(td) and CO(hs) and CO(td) was 0.33 (0.90), 0.30 (0.69) and -0.41 (1.11) l.min(-1), respectively. Thus, Modelflow had the lowest mean squared error, suggesting that it had the best performance. CO(ed) significantly overestimates changes in cardiac output while CO(mf) and CO(hs) values are not significantly different from those of CO(td). Directional changes in cardiac output by thermodilution were detected with a high score by all three methods.