Pleural Pressure Research Articles

An Improved Physical Lung Model for Teaching Lung Ventilation

This article describes an easily made physical lung model for teaching about lung ventilation. It has rectified some major shortcomings of the bell-jar balloon model by having a fluid-filled “pleural cavity,” a dome-shaped “diaphragm,” and an inflated “lung” at rest. The model can be used to tackle some misconceptions about ventilation as well as to learn some difficult concepts such as the negative pleural pressure and pneumothorax.

Pleural Pressure Pulse in Patients with Pleural Effusion: A New Phenomenon Registered during Thoracentesis with Pleural Manometry.

Pleural manometry enables the assessment of physiological abnormalities of lung mechanics associated with pleural effusion. Applying pleural manometry, we found small pleural pressure curve oscillations resembling the pulse tracing line. The aim of our study was to characterize the oscillations of pleural pressure curve (termed here as the pleural pressure pulse, PPP) and to establish their origin and potential significance. This was an observational cross-sectional study in adult patients with pleural effusion who underwent thoracentesis with pleural manometry. The pleural pressure curves recorded prior to and during fluid withdrawal were analyzed. The presence of PPP was assessed in relation to the withdrawn pleural fluid volume, lung expandability, vital and echocardiographic parameters, and pulmonary function testing. A dedicated device was developed to compare the PPP to the pulse rate. Fifty-four patients (32 women) median age 66.5 (IQR 58.5–78.7) years were included. Well visible and poorly visible pressure waves were detected in 48% and 35% of the patients, respectively. The frequency of PPP was fully concordant with the pulse rate and the peaks of the oscillations reflected the period of heart diastole. PPP was more visible in patients with a slower respiratory rate (p = 0.008), a larger amount of pleural effusion, and was associated with a better heart systolic function assessed by echocardiography (p < 0.05). This study describes a PPP, a new pleural phenomenon related to the cyclic changes in the heart chambers volume. Although the importance of PPP remains largely unknown, we hypothesize that it could be related to lung atelectasis or lower lung and visceral pleura compliance.

Expiratory Pressure Generation In Adult Survivors Of Preterm Birth

Adult survivors of preterm birth (PRE) have arrested lung development resulting in lower pulmonary function compared to their counterparts born at full term (CON). PRE have normal lung volumes, but lower expiratory airflow, which could be caused, in part, by a lesser driving (alveolar) pressure. During forced expiration alveolar pressure is the sum of pleural pressure, a function of respiratory muscle effort/strength, and lung recoil pressure. Whether or not PRE have normal respiratory muscle strength and/or lung compliance (CL) has not yet been explored. PURPOSE: The purpose of this study was to quantify respiratory muscle strength and CL in PRE and CON. Based upon the existing literature, we hypothesized that PRE and CON will have equivalent respiratory muscle strength and CL. METHODS: To date, n = 8 PRE and n = 5 CON, visited the lab on two occasions. First, subjects performed standard spirometry (e.g. fast and slow vital capacity maneuvers). Next, to assess respiratory muscle strength, subjects performed maximal inspiratory and maximal expiratory pressure maneuvers (MIP and MEP, respectively). For MIP, subjects inhaled maximally against an occluded mouthpiece at residual volume. For MEP, subjects exhaled exhale maximally against an occluded mouthpiece at total lung capacity. Each maneuver was performed 3-5 times. On the second visit, CL was measured. To do so, subjects were instrumented with an esophageal balloon catheter and performed quasi-static expiratory deflation curves (i.e., very slow exhalations from total lung capacity to residual volume). To test for differences in MIP, MEP, and CL between groups we computed multiple independent samples t-tests with significance set to p<0.05. RESULTS: We found no difference in MIP (-130.6 ± 29.3 vs. -106.5 ± 36.1 cm H2O; p = 0.24) or MEP (165.7 ± 42.9 vs.121.0 ± 51.6 cm H2O; p = 0.14) between CON and PRE, respectively. Likewise, CL was comparable between CON (0.29 ± 0.11 L/cm H2O) and PRE (0.33 ± 0.10 L/cm H2O; p = 0.53). CONCLUSION: Our data suggests no effect of birth status on the ability to generate expiratory pressure during forced expiration. Likewise, results suggest that the lower pulmonary function in PRE is not the result of a lesser driving pressure, but instead may be the result of excessive airflow resistance. Support: Hooper Undergraduate Research Award from NAU.

Awake prone positioning in COVID-19

In the absence of effective targeted therapies for COVID-19, optimisation of supportive care is essential. Lung injury with features of acute respiratory distress syndrome (ARDS) appears to be the principal...

Esophageal Manometry.

The estimation of pleural pressure with esophageal manometry has been used for decades, and it has been a fertile area of physiology research in healthy subject as well as during mechanical ventilation in patients with lung injury. However, its scarce adoption in clinical practice takes its roots from the (false) ideas that it requires expertise with years of training, that the values obtained are not reliable due to technical challenges or discrepant methods of calculation, and that measurement of esophageal pressure has not proved to benefit patient outcomes. Despites these criticisms, esophageal manometry could contribute to better monitoring, optimization, and personalization of mechanical ventilation from the acute initial phase to the weaning period. This review aims to provide a comprehensive but comprehensible guide addressing the technical aspects of esophageal catheter use, its application in different clinical situations and conditions, and an update on the state of the art with recent studies on this topic and on remaining questions and ways for improvement.

Comparison of pleural and esophageal pressure in supine and prone positions in a porcine model of acute respiratory distress syndrome.

Patients with moderate to severe acute respiratory distress syndrome (ARDS) benefit from prone positioning. Although the accuracy of esophageal pressure (Pes) to estimate regional pleural pressure (Ppl) has previously been assessed in the supine position, such data are not available in the prone position in ARDS. In six anesthetized, paralyzed, and mechanically ventilated female pigs, we measured Pes and Ppl into dorsal and ventral parts of the right pleural cavity. Airway pressure (Paw) and flow were measured at the airway opening. Severe ARDS [arterial partial pressure of oxygen ()/fraction of inspired oxygen () < 100 mmHg at positive end-expiratory pressure (PEEP) of 5 cmH2O] was induced by surfactant depletion. In supine and prone positions assigned in a random order, PEEP was set to 20, 15, 10, and 5 cmH2O and static end-expiratory chest wall pressures were measured from Pes (PEEPtot,es) and dorsal (PEEPtot,PplD) and ventral (PEEPtot,PplV) Ppl. The magnitude of the difference between PEEPtot,es and PEEPtot,PplD was similar in each position [−3.6 cmH2O in supine vs. −3.8 cmH2O in prone at PEEP 20 cmH2O (PEEP 20)]. The difference between PEEPtot,es and PEEPtot,PplV became narrower in the prone position (−8.3 cmH2O supine vs. −3.0 cmH2O prone at PEEP 20). PEEPtot,PplV was overestimated by Pes in the prone position at higher pressures. The median (1st–3rd quartiles) dorsal-to-ventral Ppl gradient was 4.4 (2.4–6.8) cmH2O in the supine position and −1.5 (−3.5 to +1.1) cmH2O in the prone position (P < 0.0001) and marginally influenced by PEEP (P = 0.058). Prone position narrowed end-expiratory dorsal-to-ventral Ppl vertical gradient, likely because of a more even distribution of mechanical forces over the chest wall.NEW & NOTEWORTHY In a porcine model of acute respiratory distress syndrome, we found that static end-expiratory esophageal pressure did not change significantly in prone position compared with supine position at any positive end-expiratory pressure (PEEP) tested between 5 and 20 cmH2O. Prone position was associated with an increased ventral pleural pressure and reduced end-expiratory dorsal-to-ventral pleural pressure (Ppl) vertical gradient, likely due to a more even distribution of mechanical forces over the chest wall.

Respiratory consequences of intra-abdominal hypertension.

Intra-abdominal hypertension (IAH) is a common complication in critically ill patients that may lead to multiorgan failure and is associated to worse outcome. Respiratory failure is among the most important consequences of IAH and it is originated by different mechanisms, such as chest wall elastance increase, functional residual capacity reduction, compression atelectasis and lung edema formation through reduction in lymphatic drainage. Many experimental studies showed that total lung capacity and functional residual capacity can be decreased by 40% during abdominal hypertension, while respiratory system and chest wall pressure-volume curves can be significantly shifted downward and to the right. Moreover, the relationship between intra-abdominal volume and airway pressure has been found to be exponential, meaning that small increases in volume can translate in dramatic increases in pressure. Clinical studies confirmed relevant atelectasis in dependent lung regions during IAH, with significant reductions in functional residual capacity and compromised oxygenation. Moreover, sepsis-related capillary leak and fluid overload may aggravate IAH and respiratory failure, thus establishing a dangerous vicious circle. Respiratory management of patients with IAH is challenging and there is no univocal answer. The measurement of intra-abdominal pressure and esophageal pressure (as a surrogate of pleural pressure) may be useful in assessing the condition and guiding mechanical ventilation. Positive end-expiratory pressure (PEEP) must be carefully selected to counteract IAH-related diaphragm displacement, but too high PEEP levels are associated with hemodynamic failure. Continuous negative extra-abdominal pressure is a promising approach, but its clinical application needs more investigation.

Manometry performed at indwelling pleural catheter insertion to predict unexpandable lung.

BackgroundThe finding of unexpandable lung (UL) at an early timepoint is of increasing importance in guiding treatment decisions in patients with malignant pleural effusion (MPE). Pleural manometry is the most common technique to delineate UL, however it has never been measured via an indwelling pleural catheter (IPC). To further the evidence base we analysed all patients in the IPC-PLUS study who had manometry performed during IPC insertion for the ability to predict substantial UL using manometry.MethodsAll patients enrolled in IPC-PLUS who had manometry performed at IPC insertion and radiographic assessment of UL at day 10 were included. Elastance curves were visually inspected for each patient. Initial pleural pressure, closing pleural pressure, and terminal elastance were analysed for their differences and predictive ability in those with substantial UL, defined as ≥25% entrapment on chest radiography.ResultsA total of 89 patients had manometry performed at IPC insertion with subsequent radiographic assessment of UL and interpretable elastance curves. Those with substantial UL had a significantly lower median closing pleural pressure (−15.00 vs. 0.00 cmH2O, P=0.012) and higher terminal elastance (12.03 vs. 8.59 cmH2O/L, P=0.021) compared to a combined group with no or partial UL. However, the predictive ability of these factors to discriminate substantial UL was poor, with areas under the receiver operating characteristic curves of 0.695 and 0.680 for closing pleural pressure and elastance respectively.ConclusionsOur results suggest that manometry is not useful in accurately predicting substantial UL when used via an IPC at the time of insertion.

Sex differences in the evolution of net respiratory muscle pressures during incremental exercise

The respiratory muscle pressure (Pmus) waveform lends insight into the patterns of net inspiratory v expiratory muscle recruitment under a wide variety of conditions, including mechanical ventilation, spontaneous breathing, and during exercise. On this last point, inspection of the Pmus waveform during incremental and constant work rate cycling reveals that inspiratory and expiratory muscle recruitment systematically increase with rising minute ventilations, and that the duration of post‐inspiratory inspiratory activity (PIIA) gradually disappears from low to high levels of respiratory motor output. In recent years, it has become increasingly evident that the work of breathing is systematically higher for women compared with men at a given minute ventilation during exercise. Yet, no study has examined the potential sex differences in the evolution of Pmus (and its components; e.g., PIIA) during exercise. Thus, a comprehensive assessment of the Pmus waveform during exercise between sexes is warranted.PurposeTo compare the evolution of inspiratory and expiratory Pmus between men and women during incremental cycling.MethodsThirteen men (21 ± yrs; 181 ± 5 cm; 82 ± 11 kg) and 10 women (21 ± 1 yrs; 165 ± 6 cm; 62 ± 6 kg) visited the laboratory on two separate occasions. The first occasion was used to obtain informed consent and to screen participants for normal pulmonary function (&gt;85% age‐predicted). On the second visit, participants were instrumented with an esophageal balloon catheter to estimate variations in pleural pressure (Ppl). Quasi‐static relaxation curves were obtained to measure chest wall recoil pressure (Pcw). Participants then completed an incremental cycling protocol until volitional exhaustion. Pmus was calculated at given minute ventilations during the exercise protocol as follows: Pmus = Pcw – Ppl.ResultsThe peak inspiratory Pmus were significantly greater in females compared with men at a given minute ventilation during incremental cycling (P &lt; 0.05), yet peak expiratory Pmus was similar between sexes. The average rates of change (slope) in Pmus during inspiration &amp; expiration were significantly faster in females than males at a given minute ventilation (P &lt; 0.05). Finally, the duration of PIIA (expressed as a fraction of expiratory time) gradually decreased with increasing minute ventilation during exercise (P &lt; 0.05). This reduction in PIIA was however similar between men and women.ConclusionThe primary finding of this study was that the pattern of respiratory muscle recruitment was different between sexes during incremental cycling, insofar as women displayed systematically larger inspiratory Pmus, and faster rates of net inspiratory &amp; expiratory pressure‐development compared with men at matched ventilations. However, no differences in PIIA between sexes were observed.Support or Funding InformationThis research was funded by preliminary data funds provided by Northern Arizona University (JWD). TJC was supported by the Irene Diamond Fund/American Federation for Aging Research Postdoctoral Transition Award during the time of this study.

Quantifying the work and power of breathing during exercise: a comparison of methods

The work and power of breathing (Wb &amp; Pb, respectively) have been extensively studied in humans during exercise. Through the measurement of the Wb &amp; Pb during exercise, we yield insight into the energetic demands of the respiratory muscles across a wide range of minute ventilations. It must be noted, however, that the methodological approach to quantifying Wb &amp; Pb is very inconsistent in the literature. The 3 most popular methods of calculating Wb &amp; Pb are: (1) the integrated pressure‐volume (PV) loop; (2) the Otis diagram; and (3) the Campbell diagram. Each of these methods are based on different theoretical assumptions and, as such, do not necessarily provide a consistent measure of Wb &amp; Pb. A comparison of the Wb &amp; Pb measured via these 3 methods during exercise is presently lacking.PURPOSETo compare values of the Wb &amp; Pb obtained during incremental exercise as determined by the integrated PV, Otis and Campbell methods.METHODSTwenty‐three young, healthy adults (10 women; 21 ± 1 yrs) visited the laboratory on two separate occasions. The first occasion was used to obtain informed consent and to screen participants for normal pulmonary function (&gt;85% age‐predicted). On the second visit, participants were instrumented with an esophageal balloon catheter to estimate variations in pleural pressure. Quasi‐static relaxation curves were obtained to measure chest wall recoil pressure. Participants then completed an incremental cycling protocol until volitional exhaustion. The total Wb &amp; Pb were computed according to the numerical procedures for the integrated PV, Otis and Campbell methods. The Wb &amp; Pb of each method were compared at standardized minute ventilations obtained during incremental.RESULTSThe total Wb &amp; Pb as determined via the Campbell method was systematically higher than the other two methods (integrated PV &amp; Otis) at any given minute ventilation during exercise (Figure 1A; P &lt; 0.05). Interestingly, the integrated PV method produced values for total Wb &amp; Pb that were lower than those of the Otis method for minute ventilations below 80 L·min−1, yet were higher at minute ventilations greater than 110 L·min−1 (Figure 1B; P&lt;0.05). When expressed as a percentage of the values obtained via the Campbell diagram, it was clear that the Otis method constituted a decreasing proportion of total Wb &amp; Pb as minute ventilation increased (Figure 1B; P&lt;0.05), whereas the integrated PV method yielded values that represented an increasing proportion during exercise (P&lt;0.05).CONCLUSIONThe Campbell method produced the highest values at any given minute ventilation. Importantly, however, the Otis method tended to progressively underestimate the total Wb &amp; Pb relative to the Campbell, while the opposite was true of the integrated PV method, as minute ventilation increased during exercise. Investigators must be cognizant of these differences when choosing a method to quantify the Wb &amp; Pb during exercise.Support or Funding InformationThis research was funded by preliminary data funds provided by Northern Arizona University (JWD). TJC was supported by the Irene Diamond Fund/American Federation for Aging Research Postdoctoral Transition Award during the time of this study.The power of breathing (Pb) determined by the integrated pressure‐volume (PV), Otis and Campbell methods.Values represent means ± 95% confidence intervals. The left panel (A) represents the total Pb values obtained via the 3 different methods. The right panel (B) illustrates the percentage of the Campbell method's total Pb that is constituted by the integrated PV and Otis methods, separately. Only portions where no significant differences (NS) were observed have been illustrated.Figure 1

Determinants of the esophageal-pleural pressure relationship in humans.

Esophageal pressure has been suggested as adequate surrogate of the pleural pressure. We investigate after lung surgery the determinants of the esophageal and intrathoracic pressures and their differences. The esophageal pressure (through esophageal balloon) and the intrathoracic/pleural pressure (through the chest tube on the surgery side) were measured after surgery in 28 patients immediately after lobectomy or wedge resection. Measurements were made in the nondependent lateral position (without or with ventilation of the operated lung) and in the supine position. In the lateral position with the nondependent lung, collapsed or ventilated, the differences between esophageal and pleural pressure amounted to 4.4 ± 1.6 and 5.1 ± 1.7 cmH2O. In the supine position, the difference amounted to 7.3 ± 2.8 cmH2O. In the supine position, the estimated compressive forces on the mediastinum were 10.5 ± 3.1 cmH2O and on the iso-gravitational pleural plane 3.2 ± 1.8 cmH2O. A simple model describing the roles of chest, lung, and pneumothorax volume matching on the pleural pressure genesis was developed; modeled pleural pressure = 1.0057 × measured pleural pressure + 0.6592 (r2 = 0.8). Whatever the position and the ventilator settings, the esophageal pressure changed in a 1:1 ratio with the changes in pleural pressure. Consequently, chest wall elastance (Ecw) measured by intrathoracic (Ecw = ΔPpl/tidal volume) or esophageal pressure (Ecw = ΔPes/tidal volume) was identical in all the positions we tested. We conclude that esophageal and pleural pressures may be largely different depending on body position (gravitational forces) and lung-chest wall volume matching. Their changes, however, are identical.NEW & NOTEWORTHY Esophageal and pleural pressure changes occur at a 1:1 ratio, fully justifying the use of esophageal pressure to compute the chest wall elastance and the changes in pleural pressure and in lung stress. The absolute value of esophageal and pleural pressures may be largely different, depending on the body position (gravitational forces) and the lung-chest wall volume matching. Therefore, the absolute value of esophageal pressure should not be used as a surrogate of pleural pressure.

Abstract 268: Evaluation of the Abdominal Aortic and Junctional Tourniquet as an Adjunct to Chest Compressions in a Swine Model of Out-Of-Hospital Cardiac Arrest

Introduction: Overall success in treating out-of-hospital cardiac arrest using traditional chest compressions is low. The abdominal aortic and junctional tourniquet (AAJT) is a device with a wedge-shaped air bladder that can be used to occlude the descending aorta at the level of bifurcation. In addition to shunting blood away from the lower extremities, this device may increase pleural pressures by inhibiting movement of the diaphragm during compressions. We have previously shown that the addition of an AAJT to mechanical chest compression leads to an increase in rate of survival in a model of traumatic cardiac arrest. Hypothesis: This study was designed to determine if application of the AAJT would lead to more effective chest compressions as measured by an increased rate of return of spontaneous circulation (ROSC) and hemodynamic parameters. Methods: Yorkshire swine (n=6 per group) underwent general anesthesia and instrumentation. Ventricular fibrillation was electrically induced using spinal needles placed in contact with the left ventricle. After eight minutes of arrest, chest compressions were initiated. Animals were then allocated into groups with or without the AAJT. Following a total of ten minutes of compressions, the animals entered into a ten-minute advanced cardiac life support phase. Results: A ROSC was not achieved in either group. No significant differences were observed with coronary perfusion pressure or end tidal CO 2 . However, the AAJT group had a significantly higher carotid diastolic pressure and higher blood flow in the carotid as compared with repeated-measures ANOVA (p = 0.016 and 0.028 respectively). Conclusion: The AAJT did not confer a survival advantage during chest compressions in our swine model of cardiac arrest. However, while the AAJT was in place, improvement was observed in some measures of CPR efficacy. Disclaimer: The views expressed are those of the authors and do not reflect the official views or policy of the Department of Defense or its Components. The experiments reported herein were conducted according to the principles set forth in the National Institute of Health Publication No. 80-23, Guide for the Care and Use of Laboratory Animals and the Animal Welfare Act of 1966, as amended.

Prone positioning in ARDS: physiology, evidence and challenges

Introduction: Prone position has been used since the 1970s as a rescue therapy to treat severe hypoxemia in patients with acute respiratory distress syndrome (ARDS). Despite numerous observational and randomized controlled trials showing the effectiveness of prone position in improving oxygenation, mortality benefit was demonstrated only recently in the PROSEVA study1. Intensivists taking care of patients with ARDS should be aware about the physiological changes during prone ventilation, the latest evidence available and challenges that can be encountered in managing such patients. Physiology of prone position ventilation: When a person is supine, the weight of the ventral lungs, heart, and abdominal viscera increase dorsal pleural pressure. This compression reduces transpulmonary pressure in the dorsal lung regions. The increased mass of the edematous ARDS lung further increases the ventral-dorsal pleural pressure gradient and reduces regional ventilation of dependent dorsal regions. The ventral heart is estimated to contribute approximately an additional 3 to 5 cm of water pressure to the underlying lung tissue. In addition to the weight of the heart, intraabdominal pressure is preferentially transmitted through the diaphragm, further compressing dorsal regions. Although these factors tend to collapse dependent dorsal regions, the gravitational gradient in vascular pressures preferentially perfuses these regions, yielding a region of low ventilation and high perfusion, manifesting clinically as hypoxemia. Placing a person in the prone position reduces the pleural pressure gradient from nondependent to dependent regions, in part through gravitational effects and conformational shape matching of the lung to the chest cavity2[Figure 1]. Clinical evidence: A few large randomized clinical trials, conducted over a period of 15 years, investigated the possible benefit of prone position on ARDS outcome [Table 1]. The improvements in oxygenation apparent in most trials were not associated with improvements in mortality, suggesting that oxygenation is not itself the source of improved survival with prone positioning. Most recently, the PROSEVA study group1 enrolled 466 subjects with moderate-to-severe ARDS. Mortality at 28 and 90 days was significantly lower with prone position versus supine position (16% vs 33%, respectively, p < 0.001, and 24% vs 41%, respectively, p < 0.001). Challenges: There are only a few absolute contraindications to prone positioning, such as unstable vertebral fractures and unmonitored or significantly increased intracranial pressure. Hemodynamic instability and cardiac rhythm disturbances are some of the relative contraindications. The common complications of prone positioning are pressure ulcers, ventilator-associated pneumonia and endotracheal tube obstruction. More serious fatal events such as accidental extubation is rare (zero to 2.4% prevalence). A recent meta-analysis of the safety and efficacy of the maneuver showed that it is safe and inexpensive but requires teamwork and skill. Reports in the literature suggest that the incidence of adverse events is significantly reduced in the presence of trained and experienced staff. Thus, centers with less experience may have difficulty managing complications, but nursing care protocols and guidelines can mitigate this risk4. Conclusion: Prone position ventilation in patients with moderate-to-severe ARDS improves hypoxemia, provides mortality benefit and is relatively safe.

FATAL CONSEQUENCES OF THERAPEUTIC THORACENTESIS IN PATIENTS WITH SYSTEMIC SCLEROSIS

SESSION TITLE: Global Case Report Posters SESSION TYPE: Global Case Reports PRESENTED ON: 10/23/2019 09:45 AM - 10:45 AM INTRODUCTION: Pulmonary complications are common and a leading cause of death in patients with systemic sclerosis (SSc). Pleural effusions, however, are rare. Thoracentesis is a common procedure, performed to reveal the cause of pleural effusion or to drain it and relieve dyspnea. Although generally considered a low-risk intervention, complications of thoracentesis can lead to increased morbidity and mortality. We Here by describe our experience with patients with SSc requiring therapeutic thoracentesis. CASE PRESENTATION: We describe three patients with SSc and symptomatic pleural effusion who required thoracentesis. All patients deteriorated shortly after the procedure and died. The patients all had advanced heart failure either from left heart disease and/or severe pulmonary hypertension. DISCUSSION: We assume that patients with SSc are at high-risk to develop complications after thoracentesis, most likely due to the low compliant lungs and the low elastance of the pleura, in addition to significant cardiac compromise as etiology for pleural effusions. CONCLUSIONS: Pleural effusion in patietns with SSc is associated with grave prognosis secondary to heart failure or pulmonary hypertension. In such patients thoracentesis should be done with caution, while measuring the pleural pressure, either invasively, or with noninvasive surrogates. Reference #1: Luo YF, Robbins IM, Karatas M, et al. Frequency of pleural effusions in patients with pulmonary arterial hypertension associated with connective tissue diseases. Chest 2011; 140:42-7. Reference #2: Thompsom AE and Pope JE. A study of the frequency of pericardial and pleural effusions in scleroderma. Br J Rheumatol 1998; 37:1320-3. Reference #3: Bouros D, Pneumatikos I, and Tzouvelekis A. Pleural involvement in systemic autoimmune disorders. Respiration 2008; 75:361-71. DISCLOSURES: no disclosure on file for Yair Levy; no disclosure on file for aiman Natur; no disclosure on file for Tsvi Sirotkin; No relevant relationships by ori wand, source=Web Response

Why Prone? Why Now? Improving Outcomes for ARDS Patients

The latest evidence I have seen is that proning more than 16 to 18 hours/day showed benefits. Was the 12-hour mark a new change?The current evidence suggests that patients should remain in the prone position for most of the day (&gt;16 h), if tolerated. Derecruitment of the lungs can occur when the patient is turned supine because of an increase in ventral-dorsal pleural pressure on the lungs. The greater than 12-hour mark is the recommendation from the American Thoracic Society/Society of Critical Care Medicine guidelines for patients with moderate to severe adult respiratory distress syndrome (ARDS) who are receiving mechanical ventilation. If no improvement is seen on initial prone positioning, consider a consecutive 48-hour trial, then stop if no improvement. Evidence of improvement includes fraction of inspired oxygen (Fio2) reduced by 0.10 or a 30-point increase in Pao2/Fio2 ratio. Discontinue proning if instability occurs or if the Pao2/Fio2 ratio is greater than 150 mm Hg and the Fio2 is less than 0.60.How do you determine whether prone positioning is best versus extracorporeal membrane oxygenation (ECMO)?Consider ECMO only after routine treatment strategies have failed, including the following:Are standards to place patients in the prone position quickly or within so many hours of diagnosis of ARDS?The time from lung injury to prone positioning should be less than 48 hours. Begin as soon as possible, if conventional ventilation is not meeting goals.How do you deal with hemodynamic instability during the 10 to 15 minutes after proning?For cardiovascular instability, adjust vasopressor dosage temporarily and then titrate back down as appropriate. For oxygen, repeat the hyperoxygenation until patients adjust. The body’s oxygen demand increases during a turn, so providing greater support may be enough to overcome the increase in demand. For life-threatening arrhythmias, return patients to the supine position immediately.

Assessment of Diaphragm Function and Pleural Pressures During Thoracentesis

This prospective observational study reports on diaphragm excursion, velocity of diaphragm contraction, and changes in pleural pressure that occur with thoracentesis. Twenty-eight patients with pleural effusion underwent therapeutic thoracentesis. Diaphragm excursion and velocity of diaphragm contraction were measured with M-mode ultrasonography of the affected hemidiaphragm. Pleural pressure was measured at each aliquot of 250mL of fluid removal. Fluid removal was continued until no more fluid could be withdrawn, unless there was evidence of nonexpandable lung defined as a pleural elastance greater > 14.5cm H2O/L and/or ipsilateral anterior chest discomfort. Twenty-three patients had expandable lung, and five patients had nonexpandable lung. Velocity of diaphragm contraction (mean ± SD) increased from 1.5 ± 0.4cm/s to 2.8 ± 0.4cm/s pre-thoracentesis and post-thoracentesis, respectively (CI, 0.93-1.61; P< .001) in subjects with expandable lung. Velocity of diaphragm contraction (mean ± SD) increased from 2.0 ± 0.4cm/s to 2.3 ± 0.4cm/s pre-thoracentesis and post-thoracentesis (P= .45) in subjects with nonexpandable lung. Diaphragm excursion was significantly increased in subjects with expandable lung at the end of thoracentesis; diaphragm excursion did not increase to a significant extent in patients with nonexpandable lung. The velocity of diaphragm contraction and diaphragm excursion increased in association with fluid removal with thoracentesis in patients with expandable lung, whereas it did not significantly change in patients with nonexpandable lung. This may derive from improvement in loading conditions of the diaphragm in patients with expandable lung related to its preload and length-tension characteristics.

A novel method for transpulmonary pressure estimation using fluctuation of central venous pressure.

The objective of the study is to develop a correction method for estimating the change in pleural pressure (ΔPpl) and plateau transpulmonary pressure (PL) by using the change in central venous pressure (ΔCVP). Seven children (aged < 15years) with acute respiratory failure (PaO2/FIO2 < 300mmHg), who were paralyzed and mechanically ventilated with a PEEP of < 10 cmH2O and had central venous catheters and esophageal balloon catheters placed for clinical purposes, were enrolled prospectively. We compared change in esophageal pressure (ΔPes), ΔCVP, and ΔPpl calculated using a corrected ΔCVP (cΔCVP-derived ΔPpl). cΔCVP-derived ΔPpl was calculated as κ × ΔCVP, where κ was the ratio of the change in airway pressure (ΔPaw) to ΔCVP during the occlusion test. cΔCVP-derived ΔPpl correlated better than ΔCVP with ΔPes (R2 = 0.48, p = 0.08 vs. R2 = 0.14, p = 0.4) with lesser bias and precision in Bland-Altman analysis. The plateau PL calculated using the cΔCVP-derived ΔPpl (17.6 ± 2.6 cmH2O) correlated well with the ΔPes-derived plateau PL (18.1 ± 2.3 cmH2O) (R2 = 0.90, p = 0.001). Our correction method can estimate ΔPpl and plateau PL from ΔCVP with a reasonable accuracy in paralyzed and mechanically ventilated pediatric patients with respiratory failure.

Experimentally Induced Open Pneumothorax in Horses

The objective of this study was to evaluate clinical and cardiovascular parameters and pleural and intra-abdominal pressures of horses after experimentally induced unilateral open pneumothorax. Prospective, experimental study—animals: seven healthy adult horses, 4 females and 3 males. Left hemithorax thoracotomy was carried out to create an open pneumothorax for 60 minutes. Pleural pressure (Ppl) was directly obtained at the midpoint of the left eighth intercostal space before thoracotomy. Esophageal pressure (Pes), arterial blood gas analysis, left ventricular function, and ultrasonographic assessment of pneumothorax extent/resolution were performed at the baseline, and 5, 10, 15, 30, 45, and 60 minutes after thoracotomy, and on the first, second, third, fifth, and seventh days postoperatively. Intra-abdominal pressure was only recorded while the pneumothorax was present. There was moderate correlation (Spearman's rs = 0.404; R2 = 0.8; P < .00001; Bland-Altman bias = −2.59; s.d. = 2.11) between Pes and Ppl. Esophageal pressure increased (P < .05) after open pneumothorax until the fifth day postoperatively. Partial pressure of oxygen in arterial blood reduced (P < .05) until the third day postoperatively when it returned to the baseline. No significant variations in PaCO2, pH in arterial blood, and in left ventricular function were appreciated. The extent of the pneumothorax was assessed by thoracic ultrasonography. Esophageal pressure, in association with blood gas analysis and thoracic ultrasonography, could be used to aid diagnosis of pneumothorax in horses. Horses tolerate open pneumothorax, with minimum cardiovascular impairment, even without aspiration of free air from within pleural space to restore thoracic wall integrity.

A Measurement System to Estimate the Pleural Pressure From the CVP for Respiratory System Monitoring

We present a technique to estimate the pleural pressure combining the information provided by the central venous pressure (CVP) and electrocardiographic signals (ECG) for respiratory system monitoring. We discuss the characterization of the proposed measurement method with theoretical modeling, numerical analysis, and experiments based on signals acquired from intensive care unit patients. The results confirm the validity of the proposal suitable to define a novel method for the continuous monitoring of the respiratory mechanics. Since mechanically ventilated patients are supposed to have a central venous catheter in position, the CVP filtering technique can results in an useful clinical approach to estimate the pleural pressure, avoiding additional invasive devices (i.e., balloon-tipped esophageal catheters).

Physiologic Basis of Symptoms in Pleural Disease.

Pleural effusions are commonly encountered and have a significant impact on the respiratory system. The reported effect of thoracentesis on physiologic parameters including oxygenation, lung volumes, and respiratory mechanics is variable likely owing to studies with a small, heterogeneous population of patients.Most patients who are short of breath from pleural effusion experience relief following drainage due to improvement in the length-tension relationship of the respiratory muscles. An observed increase in oxygenation following thoracentesis is likely due to improved ventilation and perfusion matching. Recent advances in methods of measuring pleural pressure provide a greater understanding of the impact of pleural effusion on pleural pressure and changes in pleural pressure with thoracentesis; however, there has been no demonstrated benefit of routine monitoring of pleural pressure to reduce complications from thoracentesis. Manometry does allow for the identification of patients with unexpandable lung which is useful when determining options for pleural palliation. The following article will review the pathophysiological effects of pleural effusion and thoracentesis.