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Clinical review: Respiratory mechanics in spontaneous and assisted ventilation
Daniel C Grinnan, Jonathon Truwit
Critical Care , 2005, DOI: 10.1186/cc3516
Abstract: In humans ventilation involves movement of the chest wall to produce a pressure gradient that will permit flow and movement of gas. This can be accomplished by the respiratory muscles, by negative pressure ventilation (iron lung), or by positive pressure ventilation (mechanical ventilator). Measurements of respiratory mechanics allow a clinician to monitor closely the course of pulmonary disease. At the bedside, changes in these mechanics can occur abruptly (and prompt immediate action) or they may reveal slow trends in respiratory condition (and prompt initiation or discontinuation of mechanical ventilation). Here we focus on the mechanical measurements that can be used to help make clinical decisions.In respiratory physiology, lung compliance describes the willingness of the lungs to distend, and elastance the willingness to return to the resting position. Compliance is determined by the following equation: C = ΔV/ΔP, where C is compliance, ΔV is change in volume, and ΔP is change in pressure. The inverse of compliance is elastance (E ~ 1/C). Airway pressure during inflation is influenced by volume, thoracic (lung and chest wall) compliance, and thoracic resistance to flow. Resistance to flow must be eliminated if compliance is to be measured accurately. This is accomplished by measuring pressure and volume during a period of zero flow, termed static measurements. Therefore, compliance is determined by taking static measurements of the distending pressure at different lung volumes and can be done during inflation or deflation [1]. Plotting pressure measurements throughout the respiratory cycle allows a pressure–volume (PV) curve to be constructed (Fig. 1).The slope of this curve is equal to the compliance. The inspiratory and expiratory curves are separated on the PV curve; this area of separation is termed hysteresis. Hysteresis develops in elastic structures when the volume change from an applied force is sustained for some time after the force is removed [2]. I
Goal-Directed Mechanical Ventilation: Are We Aiming at the Right Goals? A Proposal for an Alternative Approach Aiming at Optimal Lung Compliance, Guided by Esophageal Pressure in Acute Respiratory Failure  [PDF]
Arie Soroksky,Antonio Esquinas
Critical Care Research and Practice , 2012, DOI: 10.1155/2012/597932
Abstract: Patients with acute respiratory failure and decreased respiratory system compliance due to ARDS frequently present a formidable challenge. These patients are often subjected to high inspiratory pressure, and in severe cases in order to improve oxygenation and preserve life, we may need to resort to unconventional measures. The currently accepted ARDSNet guidelines are characterized by a generalized approach in which an algorithm for PEEP application and limited plateau pressure are applied to all mechanically ventilated patients. These guidelines do not make any distinction between patients, who may have different chest wall mechanics with diverse pathologies and different mechanical properties of their respiratory system. The ability of assessing pleural pressure by measuring esophageal pressure allows us to partition the respiratory system into its main components of lungs and chest wall. Thus, identifying the dominant factor affecting respiratory system may better direct and optimize mechanical ventilation. Instead of limiting inspiratory pressure by plateau pressure, PEEP and inspiratory pressure adjustment would be individualized specifically for each patient's lung compliance as indicated by transpulmonary pressure. The main goal of this approach is to specifically target transpulmonary pressure instead of plateau pressure, and therefore achieve the best lung compliance with the least transpulmonary pressure possible. 1. Introduction Patients with severe respiratory failure exhibiting decreased respiratory system compliance with hypoxemia or carbon dioxide retention are often difficult to ventilate and or oxygenate with current guidelines that limit applied plateau pressure. Furthermore, applying mechanical ventilation while limiting plateau pressure without assessment of respiratory system mechanics may result in application of inappropriate positive end expiratory pressure (PEEP) and inspiratory pressures. Thus, while these guidelines recommend a certain limit of plateau pressure, they do not take into consideration chest wall mechanics, which can only be assessed by partitioning respiratory system into its components by esophageal balloon and assessment of pleural pressure. Without partitioning of the respiratory system into its components, one cannot ascertain and identify the factors contributing to low respiratory system compliance. Identifying the dominant factor affecting respiratory system compliance by measuring transpulmonary pressure may better direct and optimize mechanical ventilation. Thus, instead of limiting mechanical ventilation
A pilot study to determine whether external stabilisation of the chest wall reduces the need for mechanical ventilation in preterm infants
DE Ballot, PA Cooper, BJ Cory, J Mlandu, C Palmer
South African Journal of Child Health , 2008,
Abstract: Objectives. This was a pilot study to determine whether external stabilisation of the chest wall with a splint reduces the need for mechanical ventilation in preterm infants, within the first 7 days after study entry. Design. This was a non-blinded prospective randomised controlled study. After consent was obtained, babies were randomised into a chest splint or control group. Setting and time. The study was conducted in the neonatal units of Johannesburg and Chris Hani Baragwanath hospitals between January 2004 and December 2005. Subjects. Preterm infants with a birth weight above 1 000 g with respiratory distress syndrome requiring more than 25% supplemental oxygen to maintain oxygen saturation above 90% during the first day of life. Outcome measures. The primary outcome measure was the need for mechanical ventilation within 7 days of study entry; secondary outcome measures were survival at 30 days, air leak and intraventricular haemorrhage. Results. There were 40 infants enrolled, 19 randomised to the chest splint group and 21 to the control group. Demographic characteristics were comparable, although the splint group required significantly more supplemental oxygen at enrolment. Four of the 19 infants in the splint group and 5 of the 21 controls required mechanical ventilation (not significant). There was no air leak in any of the study subjects during the study period. Twelve infants in each group had cranial ultrasound scans: there was one grade 3 intraventricular haemorrhage, one periventricular echodensity and one germinal matrix cyst in each group. Three of the 21 controls and 2 of the 19 splint group infants died within the first 30 days; no death was related to the chest splint. There were no local complications related to the chest splint, such as skin rash or pressure sores. Conclusion. This small study did not demonstrate any reduction in the need for ventilation with the use of the chest splint. Use of the splint was not associated with any complications and therefore appears to be safe to use. Further studies with larger numbers are warranted.
Recruitment maneuvers and positive end-expiratory pressure/tidal ventilation titration in acute lung injury/acute respiratory distress syndrome: translating experimental results to clinical practice
Carmen Barbas, Gustavo de Mattos, Eduardo Borges
Critical Care , 2005, DOI: 10.1186/cc3800
Abstract: It is well known that the main phenomenon of hypoxemia in acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is the high shunt fraction caused by the nonaerated areas of the lungs. During the disease process, the volume of extravascular lung water and the lung weight increase and promote the collapse of peripheral airways and lung parenchyma, mainly in the gravitation-dependent lung regions (Fig. 1). This phenomenon can be exacerbated by anesthesia and conditions of chest wall impairment. The relationship between the nonaerated, poorly aerated, normally aerated and hyperinflated lung regions depends on the degree of heterogeneity of the ALI/ARDS and the net result of the interaction of the pressure applied to the lung parenchyma (airway pressure/end expiratory pressure) and chest wall mechanics, as illustrated in the report by Henzler and colleagues [1] appearing in this issue of Critical Care. The most important force is not the airway pressure or tidal volume itself but the stress and strain that this airway pressure/tidal volume generates and the duration of these stresses and strains. At the bedside, the rough equivalent of stress is transpulmonary pressure, and the rough equivalent of the strain is tidal volume/end expiratory lung volume [2].This modern and complex mechanical ventilatory approach of ALI/ARDS recruitment maneuvers and positive end-expiratory pressure (PEEP)/tidal ventilation titration is a meshwork of interdependent but heterogeneously affected lung subunits that are behave according to different and multiple pressure–volume envelopes of the respiratory system during mechanical ventilation, which in some cases can be represented by respiratory mechanics (depending on the heterogeneity and etiology of the ALI/ARDS and the net results of the mechanical configuration of the respiratory system and the applied inspiratory/expiratory pressure along the mechanical ventilatory support duration) [3]. In 1998, a Brazilian prospective, random
Radical resection of giant chondrosarcoma of the anterior chest wall  [PDF]
Stani? Vojkan,Vulovi? Tatjana,Novakovi? Marjan,Ristanovi? Aleksandar
Vojnosanitetski Pregled , 2008, DOI: 10.2298/vsp0801064s
Abstract: Background. Chondrosarcomas represent approximately 30% of primary malignant bone tumors, the most frequent of which is on anterior thoracic wall. Case report. We presented a case of 50-year-old man suffering from a slowgrowing, painless giant chondrosarcoma of the anterior chest wall. A wide resection was performed to excise the tumor including attached skin, right breast, ribs, sternum, soft tissues and parietal pleura. Mediastinum was not affected by the tumor. After resecting a 26 × 20 × 22 cm segment, the chest wall defect was reconstructed with a Marlex mesh and extensive latissimus dorsi myocutaneous flap pedicled on the right thoracodorsal vessels. Histopatology diagnosis was chondrosarcoma G 2 3. The mechanics of ventilation was not altered and respiratory function was normal from the immediate postoperative period. Three years after the operation postoperative results showed no local recurrence and excellent functional and aesthetic results were evident. Respiratory function remained unaltered. Conclusion. According to the results it can be concluded that the use of Marlex mash and myocutaneous flap is good method for stabilization of the chest wall and enough to avoid paradoxical respiratory movements in managing giant chondrosarcoma of the anterior chest wall.
Bench-to-bedside review: Chest wall elastance in acute lung injury/acute respiratory distress syndrome patients
Luciano Gattinoni, Davide Chiumello, Eleondra Carlesso, Franco Valenza
Critical Care , 2004, DOI: 10.1186/cc2854
Abstract: The respiratory system includes the lung and the chest wall, in series, and the overall mechanical behavior depends on the mechanical characteristics of its components and their interactions [1]. The common increase in the elastance (decrease in compliance) of the whole respiratory system in acute lung injury (ALI) and in acute respiratory distress syndrome (ARDS) has traditionally been attributed to the lung component. It has long been reported, however, that the chest wall elastance was also altered in many cases [2-5]. Recently, mainly due to the increased concern for the abdominal pressure, more attention has been paid to the chest wall mechanics in critically ill patients [6,7]. The problems of the mechanical impairment of the chest wall and its consequences are now widely recognized. The present review will focus on the dimension of these problems and their consequences in the critically ill patient.When partitioning the respiratory mechanics into its lung and chest wall components, it is convenient to refer to elastance instead of compliance. The total elastance of the respiratory system is the pressure required to inflate it 1 l above its resting position. This is, the applied airway pressure is spent in part to inflate the lung and in part to inflate the chest wall. The chest wall comprises the anterior and posterior thoracic cage walls and the diaphragm, which is the 'abdominal component'. Indeed, in static conditions, when the airway resistance is nil:Paw = Pl + Ppl (1)andEtot = El + Ecw (2)where Paw is the (static) airway pressure, Pl is the transpulmonary pressure, Ppl is the pleural pressure, Etot is the total respiratory system elastance, El is the lung elastance, and Ecw is the chest wall elastance.On the basis of these classical equations it is easy to grasp the mechanical interaction between the lung and the chest wall. First, however, it is important to recall that the concept of 'transmission' of alveolar pressure to the thoracic cavity is mislea
Clinical review: Intra-abdominal hypertension: does it influence the physiology of prone ventilation?
Andrew W Kirkpatrick, Paolo Pelosi, Jan J De Waele, Manu LNG Malbrain, Chad G Ball, Maureen O Meade, Henry T Stelfox, Kevin B Laupland
Critical Care , 2010, DOI: 10.1186/cc9099
Abstract: Patients with acute respiratory failure frequently require mechanical ventilation (MV). Unfortunately MV can further damage the lungs and worsen respiratory failure through a variety of mechanisms [1,2]. Prone ventilation (PV) by means of prone positioning (PP) has been proposed as a strategy that may rescue the sickest patient from refractory hypoxemia [1,3-6], although identifying a survival benefit has proven difficult [4,7-12]. PV may also ameliorate the underlying physical strain and generation of inflammatory mediators that compound ventilator-induced lung injury [13-16]. Further, as a technologically simple intervention, PV could conceivably benefit patients in countries where more expensive respiratory technologies are unavailable. There is therefore reason to further explore specific mechanisms and patient groups who might benefit [5,7,17-19].One of the most frequent causes of acute respiratory failure requiring MV is acute respiratory distress syndrome (ARDS), reflecting the more severe spectrum of acute lung injury (ALI) [20,21]. The initial consensus definitions recognized two inciting pathways for ALI/ARDS: pulmonary and extrapulmonary - reflecting either direct lung injury or indirect injuries to the pulmonary endothelium as mediated by the systemic inflammatory response [20,21]. In particular, the influence of the abdomen appears to differ between pulmonary and extrapulmonary causes, differently affecting chest wall mechanics [21-28] - with higher intra-abdominal pressure (IAP) in extrapulmonary ALI/ARDS often related to greater and more recruitable lung collapse [24,26].The World Society of the Abdominal Compartment Syndrome defines intra-abdominal hypertension (IAH) as sustained IAP ≥12 mmHg, and defines the abdominal compartment syndrome (ACS) as IAP >20 mmHg with new organ failure [29]. IAH is a condition that can complicate virtually any critical condition, greatly influences the respiratory system and associates with adverse clinical outcomes [3
Comparison of Chest Compression to Ventilation Outcome Ratio during Basic Life Support and CPR in 2009  [PDF]
E. Nasiri,M. Vahedi,H. Jafari,R. Nasiri
Pakistan Journal of Biological Sciences , 2010,
Abstract: The aim of this study was to compare the effect of a 40:2, 15:2 versus 30:2 Compression: Ventilation (C: V) ratio on rate of Chest Compression (CC), rescuer fatigue and satisfaction. We measured the BP and pulse. Fifty three persons performed BLS and CPR using C: V of 15:2, 30:2 and 40:2 on an adult resuscitation lardal manikin for 2 min. Two researchers measured the above mentioned variables. Data were analyzed by ANOVA, student's t-test or Mann-Whitney U test between groups. The value of p<0.05 was considered as significant. The results revealed fatigue after 2 min and satisfaction from the performed technique in the groups differed (p<0.05). Number of breathing in two minutes was 8.8±4.7(1-24). Total cardiac massage in 2 min. in the study groups was 131.7±40.6 (20-265), of this number in130.6±40.5 was done correctly. The number of compression per 2 min increased with C: V ratio of 40:2 than to other C: V ratio. Most of participants (71.7%) prefer using 30:2 ratios to achieve the primary goal of Cardiopulmonary Resuscitation (CPR). The PR and systolic, diastolic BP of rescuers before and 2 min after resuscitation had insignificant difference (p<0.001) and SBP differed between groups (p<0.04). Although the rescuers prefer to perform the C: V ratio 30:2, but number of CC is less than standard recommended by AHA. Alternative C: V ratio of 40:2 methods, is equal to the AHA recommended 80 compressions/minute and also highest number of CC is done in 2 min, While, in the other methods is less than the recommended number.
A importancia da press?o pleural na avalia??o da mecanica respiratória
Fernandes, Cláudia Regina;
Revista Brasileira de Anestesiologia , 2006, DOI: 10.1590/S0034-70942006000300009
Abstract: background and objectives: pleural pressure has to be known for the partitioning of respiratory system mechanical measurements into their lung and chest wall components. this review aimed at discussing alternative methods to obtain pleural pressure to calculate pulmonary mechanics, at reporting peculiarities of the esophageal balloon method for obtaining indirect pleural pressure, peculiarities of esophageal pressure measurement in sedated or anesthetized patients, at discussing direct pleural pressure and its correlation with esophageal pressure, in addition to reporting on the impact of peep on pleural and esophageal pressures. contents: esophageal pressure variation reflects pleural pressure variation and may be used as alternative to direct pleural pressure in the study of lungs and chest wall mechanics. esophageal pressure may be obtained with a delicate balloon placed inside the esophagus. method and technique were observed and validated in humans and animals in different conditions and body positions. peep is a consolidated method for patients under mechanically controlled ventilation, however there are controversies about the close correlation between esophageal and pleural pressure in patients ventilated with peep, which may result in wrong respiratory mechanics calculation based on the esophageal pressure. conclusions: the esophageal balloon is the most common method to obtain indirect pleural pressure. in sedated or anesthetized patients without major respiratory compliance changes, esophageal pressure variation corresponds to pleural pressure variation when peep is applied.
Evaluation of the safety of high-frequency chest wall oscillation (HFCWO) therapy in blunt thoracic trauma patients
Casandra A Anderson, Cassandra A Palmer, Arthur L Ney, Brian Becker, Steven D Schaffel, Robert R Quickel
Journal of Trauma Management & Outcomes , 2008, DOI: 10.1186/1752-2897-2-8
Abstract: Twenty-five blunt thoracic trauma patients were entered into the study. These patients were consented. Each patient was prescribed 2, 15 minute HFCWO treatments per day using The Vest? Airway Clearance System (Hill-Rom, Inc., St Paul, MN). The Vest? system was set to a frequency of 10–12 Hz and a pressure of 2–3 (arbitrary unit). Physiological parameters were measured before, during, and after treatment. Patients were free to refuse or terminate a treatment early for any reason.No chest tubes, lines, drains or catheters were dislodged as a result of treatment. One patient with flail chest had a chest tube placed after one treatment due to increasing serous effusion. No treatments were missed and continued without further incident. Post treatment survey showed 76% experienced mild or no pain and more productive cough. Thirty days after discharge there were no deaths or hospital re-admissions.This study suggests that HFCWO treatment is safe for trauma patients with lung and chest wall injuries. These findings support further work to demonstrate the airway clearance benefits of HFCWO treatment.Blunt thoracic trauma can result in a variety of bony and non-bony injuries [1]. These patients are often cared for in the intensive care unit (ICU), and frequently require some form of pulmonary support. Mechanical ventilation carries with it risk for additional complications such as atelectasis and ventilator associated pneumonia (VAP). Patients requiring intubation often require longer ICU stays [2]. Avoiding mechanical ventilatory support of patients who don't absolutely require it results in a better outcome for these patients [3]. Blunt thoracic trauma patients and patients with flail chest have been treated effectively with bilevel positive pressure (BiPAP), continuous positive airway pressure (CPAP), or intermittent positive pressure ventilation (IPPV), with improved outcomes resulting from BiPAP and CPAP [2,4]. A recent study of mucociliary clearance in ICU patients demo
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