Breathbybreath Differences
Breath-by-breath changes in patient-ventilator interaction could arise because of ventilator-related factors mode of ventilation 9 , patient-related factors intrinsic breath-by-breath variability 23 , or a combination of both 24 . Intermittent mandatory ventilation IMV was the first mode designed to provide graded levels of assistance. By design, this mode attempts to support some breaths mandatory while providing no support to intervening spontaneous, non-mandatory breaths 2 . Manyyears...
Effects of Deforming Stress on Cellular Structure and Function
Cells interact with their surroundings through adhesion receptors such as integrins which provide dynamic bidirectional links between the cytoskeleton and the extracellular matrix. 27,28 . The extracellular matrix provides the scaffold in which cells live and to which they must conform. In the lung, an increase in basement membrane surface area that accompanies a large tidal breath imposes a shape change on adherent alveolar epithelial and microvascular endothelial cells. This shape change...
Controlled Mechanical Ventilation
Immediately after sedation and intubation of the trachea, great care has to be taken when adjusting the ventilatory parameters. Sedation may per se diminish arterial blood pressure. However, a rapid respiratory rate, either delivered manually via an Ambu-bagorwith a mechanical ventilator, may also cause severe hypotension due to the increase in intrathoracic pressure associated with auto-PEEP 6 . This happens because, in the presence of highly compliant lungs, a high fraction of increased...
Evidence and Limitations of Recent Clinical Trials
The recent randomized clinical studies 1,2,46-48 on lung protective ventilation gave rise to much debate. Some important aspects require further comment in this chapter. Although the five studies addressed the consequences of the 'baby lung theory' by limiting the end-inspiratory pressure, only the Brazilian study applied a first-intention strategy to prevent cyclic collapse and reopening 1 . The chosen PEEP-titration method at the time was the inspiratorypressure volume curve. PEEP was set at...
The Spectrum of ARF
Failure of the respiratory system represents the final common pathway for a wide range of respiratory disorders. The spectrum of ARF varies widely Fig. 1 from the severest form, namely ARDS, with severely impaired oxygenation PaO2 FiO2 lt 200 mmHg, regardless of the level of positive end-expiratory pressure PEEP , bilateral pulmonary infiltrates on chest radiograph, and pulmonary-artery occlusion pressure PAOP lt 18 mmHg or no evidence of elevated left atrial pressure on the basis of chest...
Breath by Breath Variability
Breath by breath variability in Vt, timing, flow rate and Ve is a prominent feature of breathing in healthy alert subjects 61, 62 . Its magnitude varies with level of vigilance, being less pronounced during sleep and minimal under anesthesia 63 . Breath by breath variability decreases in patients with weak muscles and abnormal mechanics 64, 65 . When the abnormal mechanics are offset by PAV, breath by breath variability becomes evident again. Typically, the coefficient of variation in...
References Jra
1. Macklin MT, Macklin CC 1944 Malignant interstitial emphysema of the lungs and mediastinum as an important occult complication in many respiratory disease and other conditions an interpretation ofthe clinical literature in the light oflaboratory experiment. Medicine 23 281-352 2. Webb HH, Tierney DF 1974 Experimental pulmonary edema due to intermittent positive pressure ventilation with high inflation pressures. Protection by positive end-expiratory pressure. Am Rev Respir Dis 110 556-565 3....
Partial Liquid Ventilation PLV
The first successful use of liquid ventilation was performed by Kylstra et al. in 1966 23 . In this experiment, dogs were maintained under hyperbaric conditions with saline used as the ventilating media. Total liquid ventilation required that the fluid 'ventilating' the lung be pumped into and out of the lung and a mechanism for adding oxygen to, and removing CO2 from the fluidbe established. To date, no total liquid ventilation system has been used on adults. The use of saline in this original...
Evidence of Air Space Collapse in ALIARDS
The presence of inhomogeneous aeration in mechanically ventilated patients was first described in tomographic studies of normal subjects during anesthesia 4,5 . Animal studies proved that these consolidated areas were constituted by atelectatic tissue, with collapsed or folded lung units causing pulmonary shunt and impaired gas exchange 6,7 . Soon after, the same phenomenon was also observed in a larger extent in computerized tomography CT studies of ARDS patients 8 . The finding of non-aerated...
Setting of Inspiratory Flow And VT
When a patient is first connected to a ventilator, inspiratory flow is set at some default value, such as 60 l min. Many critically ill patients have an elevated respiratory drive and the initial setting of flow maybe insufficient to meet flow demands. As a result, patients will struggle against their own respiratory impedance and that of the ventilator, with consequent increase in the work of breathing. To minimize this likelihood, clinicians commonly employ a much higher flow, e.g., 80 to 100...
Introduction Ugo
The respiratory system is composed of the lung and the chest wall, and these two structures are mechanically in series. The chest wall is considered as any part of the body that surrounds the lung, and is composed by two structures in parallel the rib cage and the abdomen 1 . The sum of the pressures used to inflate the lung and the chest wall represents the total pressure required to inflate the respiratory system. It is assumed that the changes in volume of lung and chest wall are equal to...
Clinical Application of PSV In ALIARDS
Recent data support the possibility of using PSV safely and effectively in the course of acute respiratory failure. Cereda et al. demonstrated that PSV could be used Fig. 2. Main ventilatory and gas exchange parameters during continuous positive pressure ventilation CPPV white bars and pressure support ventilation PSV gray bars in the PSV success left histograms and failure right histograms groups. PaO2 FiO2 oxygen arterial tension to inspiratory oxygen fraction ratio PaCO2 carbon dioxide...
Possible Mechanisms of VILI
It is now clear that ventilation-induced pulmonary edema is essentially the result of severe changes in the permeability of the alveolar-capillary barrier. Small increases in microvascular transmural pressure may add their effects to those of altered permeability to enhance edema severity. Depending on the duration of the aggression, two different kinds of injury probably occur. Small animals very rapidly develop a severe permeability pulmonary edema as a consequence of acute extreme lung...
Approach to Turning Patients Prone
Some argue that turning patients prone is difficult and risky. This is not supported by any published series, and most centers experienced in turning patients feel quite the opposite. Detailed algorithms describing a step-by-step approach to the mechanics of turning patients from supine to prone have been published 23 . Factors determining which patients will respond have not yet been elucidated. The data from Chatte and colleagues 18 suggest that improvement does not relate to the duration of...
Autotriggering
One risk of the modern, highly sensitive, triggering systems is auto-triggering Fig. 1 . Transmission of cardiac oscillations in terms of flowor pressure can be sufficient to trigger the ventilator, and can result in dangerous hyperventilation in a sedated or even paralyzed patient 11 . Through a better control of expiration, inspiratory triggers have been made more and more sensitive to minimize the extra-work due to the triggering mechanisms. Among the new sensitive systems, whether some...
The Asthmatic Patient
Acute changes in lung mechanics experienced by patients with severe bron-chospasm due to asthma attacks are similar to those observed in COPD during acute exacerbations. However, the pathophysiology of asthma may differ substantially from that of COPD. Increased airway collapsibility due to destruction of the lung parenchyma and loss of lung elastic recoil is a main feature of COPD patients. In asthma, the increases inbronchomotortone, and inflammatory infiltration may Fig. 4. Same patient as...
Mechanisms of Aeration Loss and their Influence on VILI
The loss of aeration characterizing the ARDS lung is classically explained according to the 'sponge' model developed from CT scan studies performed on a single juxta-diaphragmatic CT section the increased tissue mass causes the lung to collapse under its own weight 46 creating a sternovertebral gradient of aeration. The validity of this hypothesis implies that the pulmonary edema remains purely interstitial because the presence of fluid within the alveolar space prevents alveolar collapse. It...
Assisted Mechanical Ventilation
In every assisted mode, the ventilator responds in front of a patient's inspiratory effort. With respect to pressure and flow triggering systems, modern mechanical ventilators offer a high performance of both systems. Although the differences between these two systems are small in terms of added work of breathing, flow triggering seems to be slightly superior to pressure triggering 19 . When COPD patients under volume controlled mechanical ventilation resume spontaneous inspiratory activity,...
Prone Position
In clinical practice the prone position is commonly used to improve the arterial oxygenation in ARDS patients 28 . However, the positive effect on gas exchange is present in only 60-70 of patients. From animal and human data several mechanisms have been proposed to explain how prone positioning may affect gas exchange. The first suggested mechanism was related to an increase in FRC passing from supine to prone position 29 . However, when the FRC was measured it was found not to change between...
Introduction Oel
Mechanical ventilation is the main supportive therapy to re-establish sufficient oxygen supply to peripheral organs in patients with acute respiratory distress syndrome ARDS . As with any therapy, mechanical ventilation may expose patients to side effects. Alveolar rupture and air leak, the so-called barotraumas, were recognized early as the main side effects of mechanical ventilation 1 . However, in 1974, Webb and Tierney showed that mechanical ventilation could also be responsible for...
Targets in Mechanical Ventilation for ARDS
The conventional aims of mechanical ventilation are to provide adequate oxygenation, carbon dioxide CO2 clearance and relieve work of breathing. An additional aim is the recruitment of lung tissue based on multiple animal experiments and some clinical experiments, although this could not be considered a conventional aim at present. A final aim is to prevent multiple organ failure and death, although the appropriate means or targets necessary to achieve this are not at this stage validated for...
References Cdo
1. Gattinoni L, Pelosi P, Pesenti A, et al 1991 CT scan in ARDS clinical and physiopathological insights. Acta Anaesthesiol Scand 35 Suppl 95 87-96 2. Gattinoni L, Caironi P, Pelosi P, Goodman LR 2001 What has computed tomography taught us about the acute respiratory distress syndrome Am J Respir Crit Care Med 164 1701-1711 3. Pelosi P, Goldner M, McKibben A, et al 2001 Recruitment and derecruitment during acute respiratory failure an experimental study. Am J Respir Crit Care Med 164 122-130 4....
Setting Ventilation Pressures and Tidal Volumes
Mechanical ventilation with PEEP titrated above the lower inflection pressure of a static pressure-volume V P curve and low Vt has been suggested to prevent tidal alveolar collapse at end-expiration and overdistension of lung units at end-inspiration during ARDS 58 . This lung-protective ventilatory strategy has been found to improve lung compliance, venous admixture, and PaO2 without causing cardiovascular impairment in ARDS 58 . Recently, a lung protective mechanical ventilation using Vt of...
Analysis of the Dynamic Pressuretime Curve during Constant Flow A Stress Index
We recently proposed that the use of the static PV curve could be replaced by the analysis ofthe dynamic airway opening pressure-time profile during constant-flow inflation 43 . In 19 patients with ALI we previously found that a downward concavity on the pressure-time profile during constant flowinflation corresponded to a static PV curve with a distinct LIP and a continuous increase in compliance i.e., progressive recruitment with inflating volume 15 . On the other hand, an upward concavity on...
Pulmonary Gas Exchange
Radiological studies have demonstrated that spontaneous ventilation is preferably directed to the dependent well perfused lung regions 15 . During spontaneous breathing, the posterior muscular sections of the diaphragm move more than the anterior tendon plate 15 . Consequently, in patients in the supine position, the dependent lung regions tend to be better ventilated during spontaneous breathing. If the diaphragm is relaxed, it will be moved by the weight of the abdominal cavity and the...
References Nwc
1.Webb HH, Tierney DF 1974 Experimental pulmonary edema due to intermittent positive pressure ventilation with high pressures. Am Rev Respir Dis 110 556-565 2. Tsuno K, Prato P, Kolobow T 1990 Acute lung injury from mechanical ventilation at moderately high airway pressures. J Appl Physiol 69 956-961 3. Parker JC, Hernandez LA, Longenecker GL, Peevy K, Johnson W 1990 Lung edema caused by high peak inspiratory pressures in dogs. Am Rev Respir Dis 142 321-328 4. Parker JC, Hernandez LA, Peevy KJ...
Recommended with Caution
NIV can be used to treat patients with upper airway obstruction such as that caused by glottic edema following extubation. In this situation, NIV can be combined with aerosolized medication and or heliox, but to date no controlled trials have con firmed the efficacy of this approach. If NIV is considered, patients should be selected with great caution and monitored closely because upper airway obstruction can lead to precipitous deteriorations. The inappropriate use of NIV in patients with...
Immediate Responses
The immediate first 1-2 breaths responses to changes in ventilator settings are useful in that they define the operation of fast mechanisms, namely reflex changes in respiratory muscle activity which have a latency of a fraction of a second , and purely mechanical effects related to changes in muscle length, which cause the muscle to generate a different pressure for the same activity through the force-length relation. This latter response is immediate 2, 3 . Responses related to changes in...
Conclusion Sui
NAVA is a new mode of mechanical ventilation that responds to central respiratory demand, via intrinsic neural, chemical, and mechanical feedback loops, such that if there is a change in metabolism, load, muscle function, stress physical or psychological , or presence of leaks, the assist will always act to compensate. By improving patient-ventilator interaction, during both invasive and non-invasive ventilation, NAVA has the potential to reduce ventilator-related complications, reduce the...
with Acute Cardiogenic Pulmonary Edema
Wiener et al. reported survival data in 44 patients with acute cardiogenic pulmonary edema associated with coronary artery disease, of whom 26 had acute myocardial infarction AMI 15 . The authors do not describe the frequency of mechanical ventilation. Hospital mortality was strongly influenced by the presence of AMI 12 of 26 patients 46 with AMI died in hospital compared to only 1 of 18 patients 6 in its absence p 0.006 . Of the 30 hospital survivors, 8 of 30 27 had died at 1 year and 21 of 30...
Carbon Dioxide as a Target
Mechanical ventilation has traditionally been utilized to assist in the appearance of carbon dioxide as a respiratory waste gas. Limitation ofVT or inspiratory pressure to protect the lungs against excessive mechanical stretch was introduced, initially by Wung et al. 9 for neonatal hypoxic respiratory failure, and subsequently by Hickling et al. 10, 11 . In these situations, the PaCO2 was allowed to become elevated, and the idea that mild to moderate hypercapnia was not necessarily a harmful...
References Wiv
1. Marini JJ 1993 New options for the ventilatory management of acute lung injury. New Horiz 1 489-503 2. Downs JB, Klein EF Jr, Desautels D, Modell JH, Kirby RR 1973 Intermittent mandatory ventilation a new approach to weaning patients from mechanical ventilators. Chest 64 331-335 3. Esteban A, Frutos F, Tobin MJ, et al 1995 A comparison of four methods of weaning patients from mechanical ventilation. Spanish Lung Failure Collaborative Group. N Engl J Med 332 345-350 4. Tobin MJ 2001 Advances...
What is PSV
PSV is a pressure-targeted mode of ventilation, that provides breath-by-breath patient-triggered support, synchronized with the patient's inspiratory effort 4 . Following the detection of patient's inspiratory effort, a demand valve allows the airway pressure to rise to a pre-set level, which is maintained until the detection of the patient's wish to expire. At this stage an expiratory trigger system stops the support and allows the airway pressure to drop down to the expiratory level....
The Computed Tomographic Assessment of Lung Aeration
CT of the whole lung allows the accurate assessment of lung volumes gas and tissue and lung aeration. With the last generation of CT scanners, contiguous CT sections can be obtained from the apex to the diaphragm in less than 10 seconds with a spatial resolution of CT images as high as 0.2 mm3. Overall lung volume gas tissue is computed as the number of voxels present in a given lung region. Because the lung parenchyma is composed of gas and tissue with physical density close to water density,...
The Distribution of Aeration Loss and Excess Tissue in Patients with ARDS
The diffuse injury of the alveolar-capillary membrane that characterizes the ARDS lung, produces a high-permeability type pulmonary edema. The resulting increase in lung tissue detected on CT 16 is distributed from the apex to the diaphragmatic cupola, predominant in the upper lobes and frequently associated with a massive loss of aeration 20 . In caudal parts of the lung, although the regional loss of aeration is always massive, the excess lungtissue is absent or minimum in one-third of lower...
Evidence for VILI
Ventilation of Intact Lungs High lung volume VILI Webb and Tierney were the first to demonstrate that mechanical ventilation could cause pulmonary edema in intact animals 8 . They were able to show in rats subjected to positive airway pressure ventilation that pulmonary edema was more severe and occurred more rapidly when the animals were ventilated with 45 cmH2O than with 30 cmH2O peak airway pressure. Animals ventilated for 1 hour with 14 cmH2O peak airway pressure did not develop edema. It...
VILI from Ventilation with High Volumes and High Pressures
Because dead space is increased in ARDS, the generous Vt approach was useful for maintaining near-normal PaCO2 and pH. Moreover, the generous Vt approach was also useful for preventing or decreasing atelectasis and reversing some of the intrapulmonary shunt caused by atelectasis or intraalveolar filling 13, 14 . However, much of the ARDS lung is not available for ventilation because of consolidation, atelectasis, and alveolar filling 15,16 . Therefore, most of the Vt is delivered to the less...
References Gav
1. Pride NB,MacklemPT 1986 Lung mechanics in disease. In Handbook of Physiology, Section 3, vol. III The Respiratory System. Mechanics of Breathing, part 2. American Physiological Society, Bethesda, pp 659-692 2. Kimball WR, Leith DE, Robins AG 1982 Dynamic hyperinflation and ventilator dependence in chronic obstructive pulmonary disease. Am Rev Respir Dis 126 991-995 3. Derenne J, Fleury B, Pariente R 1988 Acute respiratory failure of chronic obstructive pulmonary disease. Am Rev Respir Dis...
Jubran A. W. B. Van De Graaff And M. J. Tobin. 1995. Variability Of
1. Tobin MJ 2001 Advances in mechanical ventilation. N Engl J Med 344 1986-1996 2. Sassoon CSH, Gruer SE 1995 Characteristic of the ventilator pressure- and flow-trigger variables. Intensive Care Med 21 159-168 3. Marini JJ, Capps JS, Culver BH 1985 The inspiratory work of breathing during assisted mechanical ventilation. Chest 87 612-618 4. Aslanian P, El Atrous S, Isabey D et al 1998 Effects of flow triggering on breathing effort during partial ventilatory support. Am J Respir Crit Care Med...
Work of Breathing and Related Measurements
Assessment of respiratory muscle activity during PSV, can be achieved by measurements of WOB 43 and PTP 44 . However, both WOB and PTP require the correct positioning of an esophageal balloon to estimate pleural pressure, and, although extensively used in investigational studies, neither is commonly used in clinical practice. P0.1 has shown good correlation with WOB during PSV 6 , and may estimate the respiratory effort. Alternatively, an index of muscular activity, which we have named pressure...
Introduction Sva
During the last two decades, the dramatic evolution of surgical techniques and the use of innovative immunosuppressive strategies has extended the applicability of solid organ transplantation to an increased number of patients suffering from end-stage failure ofvarious organs. As a direct consequence, the survival rates after solid organ transplantation have dramatically improved. Despite this increase in the post-transplantation survival rate, respiratory complications are the principal cause...
Cardiovascular Effects
When cardiac function is normal, the filling of the right and left ventricle during diastole is the predominant determinant of the stroke volume and cardiac output. Positive pressure ventilation increases intrathoracic pressure, which in turn reduces the venous return to the heart 34 . In normo- and hypovolemic patients, this produces reduction in right- and left-ventricular filling and results in decreased stroke volume, cardiac output and oxygen delivery DO2 . To normalize systemic blood flow...
Inflation and Pulmonary Vascular Pressure
The vascular pathway from pulmonary artery to left atrium can be considered as a series of three functional segments arterial, 'intermediate' which includes alveolar capillaries and contiguous microvessels , and venous 1 . Under normal conditions, arterial and venous segments - which are entirely extra-alveolar - contribute most to overall pulmonary vascular resistance. The compliant intermediate segment however, is influenced primarily by alveolar pressures and as a consequence, influences the...
Respiratory Muscle Function
By adjusting the pressure support level it is possible to modulate the relative contribution of the patient and of the ventilator to the total WOB 33 . This is certainly a major advantage of PSV indeed, aside from the mandatory presence of an intact neural drive, an effective muscular function is necessary to initiate the PSV breath and at least participate in inspiratory WOB. A relatively simple method to assess muscular strength is the maximal absolute pressure that is generated against an...
Organ Perfusion
By reducing cardiac index and the venous return to the heart, mechanical ventilation can have a negative effect on the perfusion and functioning of extrathoracic organ systems. In the kidney, reduction in cardiac index and venous return causes, via a sympatho-adrenergic reaction, vasoconstriction of the afferent renal arterioles with reduction and redistribution of the renal blood flow from the cortical to the juxtaglomerular nephrons. This reduces the glomerular filtration rate and sodium...
TGI Systems
A number of different approaches to the establishment of TGI have been described 9 . Essentially, the TGI catheter can be directed toward the carina or toward the ventilator circuit 10 . There appears to be little difference in gas exchange enhancement between these approaches, but each effect has a different influence on the development ofpositiveend-expiratorypressure PEEP 10,11 . TGI flowdirected toward the carina creates an additional threshold to prevent exhalation, increasing total PEEP...
Suppression of Spontaneous Breathing
Suppressing spontaneous breathing activity during controlled mechanical ventilation can be achieved by hyperventilation, deep sedation or muscle relaxation. Hyperventilation in conjunction with respiratory alkalosis may result in a drop in cardiac output, cerebral vasoconstriction, increased oxygen consumption, bron-choconstriction and V Q mismatch 49-51 . Analgosedation sufficient to suppress respiratory efforts is known to cause significant cardio-vascular depression. In addition, it may take...
Info Npl
The mortality rates of mechanically ventilated patients have been described with widely varying results, likely due to heterogeneity of the populations included in the studies. Table 6 shows the mortality rates reported in recent observational studies that included a general and unselected population of patients. This mortality has been associated with baseline factors including age severity of disease or previous functional status coma, sepsis or ARDS as the reason of mechanical ventilation...
Complications Associated with Mechanical Ventilation
Barotrauma is a frequent complication of mechanical ventilation and is associated with increased morbidity and mortality 45,46 . Investigators have reported incidences of barotrauma as low as 0.5 in postoperative patients 47 and as high as 87 in patients with ARDS 45 . These variations in the reported incidence of ventilator-associated barotrauma may relate to differences in the patients' underlying disease. Barotrauma is increased in patients with severe underlying lung disease, especially in...
Nava Ventilation
Fig. 1. Description of the setup used for NAVA. Electrode array arrangement i , attached to a nasogastric tube ii normally used for feeding or other purposes. The electrode array is positioned in the esophagus at the level of and perpendicular to the crural diaphragm such that the active muscle creates an electrically active region around the electrode. Signals from each electrode pair on the array are differentially amplified iii and digitized into a personal computer, and filtered iv to...