Mode Of Ventilatory Support Research Articles

Ventilation and Weaning Practices in Australia and New Zealand

Using a one-day prospective point prevalence design, this study aimed to characterise the current practice of mechanical ventilation and weaning in Australian and New Zealand intensive care units. During 2005, a bi-national one-day survey of 55 intensive care units found the point-prevalence of mechanical ventilation to be 284/491(58%). Common modes used were synchronised intermittent mandatory ventilation with pressure support, pressure support ventilation (each 116/284, 41%) and pressure-control modes (48/284, 17%). Relative to volume-control modes, pressure-control was more frequently used for patients with respiratory disease (odds ratio 4.7, 95% confidence interval 2.4 to 9.2, P <0.001) or greater severity of illness (odds ratio 1.7, 95% confidence interval 1.1 to 2.6, P = 0.01, per five-point increment in the maximum sequential organ failure score). Excluding cardiothoracic surgery patients, the Kaplan-Meier estimated median total ventilation duration was 1.9 days (interquartile range 0.8 to 6.8 days). Apart from 24/255 (9.4%) patients who received only pressure support ventilation, weaning methods (attempted in 255 patients, 29 prior deaths) included: change to pressure support ventilation (186/255, 73%), T-piece (31/255, 12%) or other methods (14/255, 5.5%). The point prevalence of mechanical ventilation was greater than comparable international studies. Australian and New Zealand intensive care unit ventilatory practices are similar, but differ substantially from published international survey results, due to a near absence of assist/control, prominent use of pressure-control modes and a preference forpressure support ventilation weaning as opposed to T-piece.

Metabolic and Respiratory Variables during Pressure Support versus Synchronized Intermittent Mandatory Ventilation

Background: Mechanically ventilated patients interact and respond differently to different modes of ventilatory support. Objectives: To assess changes in metabolic and respiratory variables during equivalent changes with either pressure support ventilation (PSV) or volume-cycled synchronized intermittent mandatory ventilation (SIMV) in non-tracheostomized patients without known obstructive pulmonary disease receiving short-term mechanical ventilation in the intensive care unit. Methods: Fourteen patients receiving volume-cycled SIMV at 12 breaths/min (SIMV_100%) were included in the study. The PSV level (PSV_100%) resulting in a minute volume and respiratory rate equivalent to that during SIMV_100% was determined for each patient. Then each patient underwent trials at 66% and 33% of initial ventilator support with volume-cycled SIMV (SIMV_66% and SIMV_33%) and PSV (PSV_66% and PSV_33%) in random order. At the end of each trial, oxygen consumption (v̇O₂), carbon dioxide production (v̇CO₂), measured energy expenditures (MEE), peak inspiratory flow, total respiratory frequency, tidal volume, minute ventilation, occlusion pressure (P_0.1) and inspiratory duty cycle (T_i/T_tot) were measured. Results: There were smaller changes in v̇O₂, v̇CO₂ and MEE when equivalent changes were applied with PSV (15.7 ± 4.4; 12.5 ± 2.2 and 15 ± 3.5%) compared with volume-cycled SIMV (32.7 ± 7.7; 23 ± 5.2 and 30.7 ± 6.8%; p < 0.05). P_0.1 and T_i/T_tot were significantly smaller during PSV (2.64 ± 0.28 and 0.38 ± 0.03 cm H₂O) than volume-cycled SIMV (4.01 ± 0.21 and 0.43 ± 0.02 cm H₂O; p < 0.05). Conclusions: Changes in the level of PSV resulted in smaller changes in metabolic and respiratory variables compared with equivalent changes in the level of volume-cycled SIMV support. PSV may be more suitable for progressive respiratory muscle reloading.

Influence on cardiac-pulmonary function of health and acute lung injury dogs by proportional assist ventilation and pressure support ventilation modes

Objective Comparing the influence on cardiac-pulmonary function of health and acute lung injury (ALI)dogs by proportional assist ventilation(PAV)and pressure support ventilation(PSV)modes.Methods Use intermittent positive pressure ventilation(IPPV)mode in health and ALI dogs,calculate elastance(Ers)and resistance(Rrs),then change to PAV,set the assist ratio 60%.Then change the mode into PSV,set the inspiratory pressure(IPAP)according to PAV,so that tidal volume(VT)and peak pressure(Ppeak)were the sanle as that of PSV respectively.Observe the changes of respiratory mechanics,blood gas analysis and hemodynamics during mechanical ventilation.Results For health dogs,compared with PAV,mean airway pressure(mPaw)and work of breath of ventilator(WOBv)of PSV was higher than those of PAV when VT were similar,the difference was remarkable;while the influence on hemodynamics was not different.For ALI dogs,compared with PAV,Ppeak,mPaw and pulmonary capillary wedge pressure(PCWP)of PSV was higher than those of PAV when VT were similar,the difference was remarkable.Conclusion For health and ALI dogs,compared with PSV,PAV has lower airway pressure and less influence on hemodynamies. Key words: Posotive-pressure respiration:Respiratory distress syndrome,adult; Canidae; Animal testing alternatives

Evaluation of pressure support ventilation with seven different ventilators using Active Servo Lung 5000.

In modern emergency and critical care, physicians tend to choose the mode of mechanical ventilation based on spontaneous breathing for the purpose of promoting discharge of pulmonary secretion and preventing atelectasis in patients with acute respiratory insufficiency. However, we often observe "differences in recovery" among patients treated using the same PSV settings beyond "differences in individual characteristics." We evaluated the Pressure Support Ventilation (PSV) mode aiming to certify the difference among 7 representative mechanical ventilators using the Active Servo Lung 5000 (ASL5000) respiratory simulation system. The following parameters were measured: The time delay that resulted in the lowest inspiratory pressure from the point at which the ventilator recognized spontaneous breathing (TD), the lowest inspiratory airway pressure (cmH2O) generated prior to the initiation of PSV (DeltaPaw), the work of breathing while triggering required to achieve the lowest inspiratory negative pressure from the beginning of inspiratory support (WOBtrig), and the inspiratory work of breathing (WOBi). The mean TD of the Puritan-Bennett type 840 (PB840) was signifi cantly shorter than those of other ventilators (p0.01). The WOBtrig of the PB840 was significantly lower than those of others (p0.01). However, the WOBi values of the Servo-I and T-Bird were greater than the others, with the Evita series showing the smallest WOBi of the 7 ventilators tested. According to this simulation study using ASL 5000, we concluded that PB840 was the most rapid response ventilator, but the Evita series was the gentlest mechanical ventilator among 7 ventilators from the standpoint of the total work of breathing during the inspiration phase in the setting of PSV.

Continuous positive airway pressure vs. proportional assist ventilation for noninvasive ventilation in acute cardiogenic pulmonary edema

To compare continuous positive airway pressure (CPAP) and proportional assist ventilation (PAV) as modes of noninvasive ventilatory support in patients with severe cardiogenic pulmonary edema. A prospective multicenter randomized study in the medical ICUs of three teaching hospitals. Thirty-six adult patients with cardiogenic pulmonary edema (CPA) with unresolving dyspnea, respiratory rate above 30/min and/or SpO2 above 90% with O2 higher than 10 l/min despite conventional therapy with furosemide and nitrates. Patients were randomized to undergo either CPAP (with PEEP 10 cmH2O) or PAV (with PEEP 5-6 cmH2O) noninvasive ventilation through a full face mask and the same ventilator. The main outcome measure was the failure rate as defined by the onset of predefined intubation criteria, severe arrythmias or patient's refusal. On inclusion CPAP (n=19) and PAV (n=17) groups were similar with regard to age, sex ratio, type of heart disease, SAPS II, physiological parameters (mean arterial pressure, heart rate, blood gases), amount of infused nitrates and furosemide. Failure was observed in 7 (37%) CPAP and 7 (41%) PAV patients. Among these, 4 (21%) CPAP and 5 (29%) PAV patients required endotracheal intubation. Changes in physiological parameters were similar in the two groups. Myocardial infarction and ICU mortality rates were strictly similar in the two groups. In the present study PAV was not superior to CPAP for noninvasive ventilation in severe cardiogenic pulmonary edema with regard to either efficacy and tolerance.

Ventilator-induced diaphragm dysfunction: the clinical relevance of animal models

Experimental evidence suggests that controlled mechanical ventilation (CMV) can induce dysfunction of the diaphragm, resulting in an early-onset and progressive decrease in diaphragmatic force-generating capacity, called ventilator-induced diaphragmatic dysfunction (VIDD). The mechanisms of VIDD are not fully elucidated, but include muscle atrophy (resulting from lysosomal, calpain, caspase and proteasome activation), oxidative stress, structural injury (disrupted myofibrils, increased numbers of lipid vacuoles, and abnormally small and disrupted mitochondria), myofiber remodeling and mitochondrial dysfunction. The major clinical implication of the VIDD is to limit the use of CMV to the extent possible. Partial (assisted) modes of ventilatory support should be used whenever feasible, since these modes attenuate the deleterious effects of mechanical ventilation on respiratory muscles.

Noninvasive Positive-Pressure Ventilation in Patients With Malignancy

Noninvasive positive-pressure ventilation (NIPPV) is now accepted as the treatment of choice for subgroups of patients with acute respiratory failure. Noninvasive positive-pressure ventilation has traditionally not been considered in the management strategy of patients with malignancy; however, this mode of ventilatory support may be appropriate in some specific situations. Noninvasive positive-pressure ventilation is the preferred initial mode of ventilatory support in patients with hematologic malignancies or after bone marrow transplantation who develop acute respiratory failure. In these patients, NIPPV should be initiated early; severe respiratory distress and altered mental status require conventional mechanical ventilation. Noninvasive positive-pressure ventilation should be considered in select patients with cancer who develop respiratory failure and have a do-not-intubate code status. In rare instances, NIPPV may have a role in treating patients with advanced cancer who have intractable dyspnea; however, NIPPV should not be used for the sole purpose of prolonging life in patients with terminal respiratory failure.

Weaning from mechanical ventilation

Weaning covers the entire process of liberating the patient from mechanical support and from the endotracheal tube. Many controversial questions remain concerning the best methods for conducting this process. An International Consensus Conference was held in April 2005 to provide recommendations regarding the management of this process. An 11-member international jury answered five pre-defined questions. 1) What is known about the epidemiology of weaning problems? 2) What is the pathophysiology of weaning failure? 3) What is the usual process of initial weaning from the ventilator? 4) Is there a role for different ventilator modes in more difficult weaning? 5) How should patients with prolonged weaning failure be managed? The main recommendations were as follows. 1) Patients should be categorised into three groups based on the difficulty and duration of the weaning process. 2) Weaning should be considered as early as possible. 3) A spontaneous breathing trial is the major diagnostic test to determine whether patients can be successfully extubated. 4) The initial trial should last 30 min and consist of either T-tube breathing or low levels of pressure support. 5) Pressure support or assist-control ventilation modes should be favoured in patients failing an initial trial/trials. 6) Noninvasive ventilation techniques should be considered in selected patients to shorten the duration of intubation but should not be routinely used as a tool for extubation failure.

Use of Respiratory Support in the Biphase Ventilation Airway Mode in the Newborn

Biphasic positive airway pressure (BIPAP) (also known as DuoPAP, BiLevel, BiVent, PCV+, SPAP) is a mode of ventilation with cycling variations between two continuous positive airway pressure levels. It is a mixture of pressure controlled ventilation and spontaneous breathing, which is unrestricted in each phase of the respiratory cycle. The volume displacement caused by the difference between Phigh and Plow airway pressure level. The phase time ratio (PTR — the BIPAP frequency) is calculated as the ratio between the durations of the two pressure phases, a PTR greater than 1:1 is called APRV (airway pressure release ventilation). In patients with ARDS maintained spontaneous breathing with BIPAP resulted in lower venous admixture and better arterial blood oxygenation as compared with A/C. Only a few studies with BIPAP have been performed in newborn and infants until now. We studied the use of BIPAP in newborn (body mass > 3kg) and randomised 40 patients with respiratory failure for ventilation with BIPAP (n=20) or conventional mechanical ventilatory support (assist-control A/C) — synchronised intermittent mandatory ventilation (SIMV)) (n=20). The Pediatric Risk of Mortality score (PRISM) were collected for each patient. Fentanyl, diazepam, GABA were used as sedatives and adjusted in accordance with the Cook scale. We compared ventilatory parameters, information pertaining to pulmonary function and oxygen delivery, cardiac output, additional descriptors of organ system functions, duration and complications of ventilation and number and dosages of sedatives administered. All the patients that we intended to ventilate with BIPAP were successfully ventilated, we can conclude that biphasic ventilatory support suitable mode of ventilation for newborn with a decreased need of analgetics and sedatives than A/C. Finally, BIPAP is an a effective safe, and easy to use for personal mode of mechanical ventilatory support in newborn.

Influence of respiratory efforts on b2-agonist induced bronchodilation in mechanically ventilated COPD patients: A prospective clinical study

Several in vitro studies have shown that at similar tidal volume (VT), bronchodilator delivery to target sites is significantly lower during controlled mechanical ventilation (CMV) than that during simulated spontaneous breathing. However, the influence of active respiratory efforts on the magnitude of b2-agonist induced bronchodilation in mechanically ventilated patients has not been examined. To examine the influence of controlled and assisted modes of ventilatory support on the bronchodilative effect induced by b2-agonists administered with a metered dose inhaler (MDI) and a spacer device in a homogeneous group of mechanically ventilated patients with acute exacerbation of chronic obstructive pulmonary disease (COPD). Prospective clinical study. Ten mechanically ventilated patients with acute exacerbation of COPD were prospectively randomized to receive 4 puffs of salbutamol (S, 100 micro g/puff) either with volume-controlled (VC) or pressure-support (PS) ventilation. On PS the pressure level was such that VT was comparable between ventilatory modes. After a 6-h washout period, patients were crossed-over to receive the drug by the alternative mode of ventilation. Static and dynamic airway pressures, minimum (R(int)) and maximum (R(rs)) inspiratory resistance, the difference between R(rs) and R(int) (DeltaR), end-inspiratory static compliance of the respiratory system (C(rs)), intrinsic positive end-expiratory pressure (PEEP(i)) and heart rate (HR) were measured before and at 15, 30, 60, 120, 180 and 240 min after S administration. S caused a significant decrease in dynamic and static airway pressures, PEEP(i), R(int) and R(rs). These changes were not influenced by the ventilatory mode and were evident at 15, 30, 60 and 120 min after S. HR, C(rs) and DeltaR did not change after S administration. Considering the use of propofol with its presumed bronchodilative properties as a shortcoming of our study, it is concluded that the magnitude of bronchodilation induced by salbutamol delivered by an MDI and a spacer device in mechanically ventilated COPD patients is not affected by the presence or absence of active respiratory efforts.

Effects of partial ventilatory support modalities on respiratory function in severe hypoxemic lung injury*

The early phase of acute respiratory distress syndrome (ARDS) is characterized by impaired respiratory mechanics, ventilation-perfusion mismatch, and severe hypoxemia. Partial ventilatory support can effectively unload the respiratory workload and improve pulmonary gas exchange with less hemodynamic compromise. The partial ventilatory support mode most indicated in early phases of ARDS has not been determined. This study compares the effects of assisted ventilatory techniques on breathing pattern, gas exchange, hemodynamic function, and respiratory effort with those of controlled mechanical ventilation in similarly sedated subjects. Prospectively randomized crossover animal study. Animal research laboratory. Eleven anesthetized and mechanically ventilated pigs. Acute lung injury was induced by lung lavage. Pressure-controlled ventilation (PCV), pressure-controlled assisted ventilation (P-ACV), bilevel positive airway pressure (BIPAP), and pressure support ventilation (PSV) with equal airway pressures and sedation were applied in random order. Gas exchange, respiratory effort, and hemodynamic function were measured, and ventilation-perfusion distributions were calculated by multiple inert-gas-elimination techniques. The results revealed that partial ventilatory support was superior to PCV in maintaining adequate oxygenation and hemodynamic function with reduced sedation. The effects of P-ACV, BIPAP, and PSV were comparable with respect to gas exchange and hemodynamic function, except for a more pronounced reduction in shunt during BIPAP. P-ACV and PSV were superior to BIPAP to reduce respiratory drive and work of breathing. PSV affected the pattern of breathing and deadspace to a greater degree than did P-ACV. In acute lung injury, P-ACV preserves oxygenation and hemodynamic function with less respiratory effort compared with BIPAP and reduces the need for sedation compared with PCV.

Adaptive Support Ventilation as the Sole Mode of Ventilatory Support in Chronically Ventilated Patients

Adaptive Support Ventilation as the Sole Mode of Ventilatory Support in Chronically Ventilated Patients

Clinical review: Patient-ventilator interaction in chronic obstructive pulmonary disease

Mechanically ventilated patients with chronic obstructive pulmonary disease often prove challenging to the clinician due to the complex pathophysiology of the disease and the high risk of patient-ventilator asynchrony. These problems are encountered in both intubated patients and those ventilated with noninvasive ventilation. Much knowledge has been gained over the years in our understanding of the mechanisms underlying the difficult interaction between these patients and the machines used to provide them with the ventilatory support they often require for prolonged periods. This paper attempts to summarize the various key issues of patient-ventilator interaction during pressure support ventilation, the most often used partial ventilatory support mode, and to draw clinicians' attention to the need for sufficient knowledge when setting the ventilator at the bedside, given the often conflicting goals that must be met.

Bedside waveforms interpretation as a tool to identify patient-ventilator asynchronies

During assisted modes of ventilatory support the ventilatory output is the final expression of the interaction between the ventilator and the patient's controller of breathing. This interaction may lead to patient-ventilator asynchrony, preventing the ventilator from achieving its goals, and may cause patient harm. Flow, volume, and airway pressure signals are significantly affected by patient-ventilator interaction and may serve as a tool to guide the physician to take the appropriate action to improve the synchrony between patient and ventilator. This review discusses the basic waveforms during assisted mechanical ventilation and how their interpretation may influence the management of ventilated patients. The discussion is limited on waveform eye interpretation of the signals without using any intervention which may interrupt the process of mechanical ventilation. Flow, volume, and airway pressure may be used to (a) identify the mode of ventilator assistance, triggering delay, ineffective efforts, and autotriggering, (b) estimate qualitatively patient's respiratory efforts, and (c) recognize delayed and premature opening of exhalation valve. These signals may also serve as a tool for gross estimation of respiratory system mechanics and monitor the effects of disease progression and various therapeutic interventions. Flow, volume, and airway pressure waveforms are valuable real-time tools in identifying various aspects of patient-ventilator interaction.

RESPIRATORY FAILURE FROM HANTAVIRUS PULMONARY SYNDROME TREATED WITH HIGH FREQUENCY OSCILLATORY VENTILATION

INTRODUCTION: Hantavirus Pulmonary Syndrome (HPS) may lead to respiratory distress, hemodynamic compromise, and noncardiogenic pulmonary edema. High-Frequency Oscillatory Ventilation (HFOV) is an alternative mode of ventilatory support for patients with severe adult respiratory distress syndrome (ARDS). We present a severe case of HPS who did not respond to conventional ventilation. He was treated with HFOV, and recovered.

New Modes of Neonatal Ventilation: Let There be Light

New Modes of Neonatal Ventilation: Let There be Light

Bench-to-bedside review: Weaning failure – should we rest the respiratory muscles with controlled mechanical ventilation?

The use of controlled mechanical ventilation (CMV) in patients who experience weaning failure after a spontaneous breathing trial or after extubation is a strategy based on the premise that respiratory muscle fatigue (requiring rest to recover) is the cause of weaning failure. Recent evidence, however, does not support the existence of low frequency fatigue (the type of fatigue that is long-lasting) in patients who fail to wean despite the excessive respiratory muscle load. This is because physicians have adopted criteria for the definition of spontaneous breathing trial failure and thus termination of unassisted breathing, which lead them to put patients back on the ventilator before the development of low frequency respiratory muscle fatigue. Thus, no reason exists to completely unload the respiratory muscles with CMV for low frequency fatigue reversal if weaning is terminated based on widely accepted predefined criteria. This is important, since experimental evidence suggests that CMV can induce dysfunction of the diaphragm, resulting in decreased diaphragmatic force generating capacity, which has been called ventilator-induced diaphragmatic dysfunction (VIDD). The mechanisms of VIDD are not fully elucidated, but include muscle atrophy, oxidative stress and structural injury. Partial modes of ventilatory support should be used whenever possible, since these modes attenuate the deleterious effects of mechanical ventilation on respiratory muscles. When CMV is used, concurrent administration of antioxidants (which decrease oxidative stress and thus attenuate VIDD) seems justified, since antioxidants may be beneficial (and are certainly not harmful) in critical care patients.

Necrotizing Tracheobronchitis as a Complication of High Frequency Oscillatory Ventilation

INTRODUCTION: High-frequency oscillatory ventilation (HFOV) is an alternative mode of ventilatory support for patients with severe adult respiratory distress syndrome (ARDS) failing conventional ventilation. Reported complications include pneumothorax, pneumomediastinum, and subcutaneous emphysema. While necrotizing tracheobronchitis (NTB) has been widely reported in the pediatric literature with a reported incidence between 4–44%, it is rare in adults. We report a case of NTB associated with HFOV.

Long versus short inspiratory times in neonates receiving mechanical ventilation

When intermittent positive pressure ventilation (IPPV) was introduced in newborn infants with hypoxic respiratory failure from hyaline membrane disease (HMD), mortality was high and air leaks problematic. This barotrauma was caused by the high peak inspiratory pressures (PIP) required to oxygenate stiff lungs. The primary determinants of mean airway pressure (and thus oxygenation) on a conventional ventilator are the inspiratory time (IT), PIP, positive end expiratory pressure and gas flow rates. In the 1970s uncontrolled studies on a small number of infants demonstrated a benefit in reducing barotrauma using a long IT and slow rates. This strategy was subsequently widely adopted. Current neonatal ventilators have been designed to minimise lung injury but rates of bronchopulmonary dysplasia (BPD) remain high. It is therefore important that the inspiratory time causing least harm is used. To determine in mechanically ventilated newborn infants whether the use of a long rather than a short IT reduces the rates of death, air leak and BPD. The standard search strategy of the Cochrane Neonatal Review Group (CNRG) was used. Searches of electronic and other databases were performed. These included MEDLINE (1966 - April 2004) and the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 4, 2003). In order to detect trials that may not have been published, the abstracts of the Society for Pediatric Research, and the European Society for Pediatric Research were searched from 1998 - 2003. All randomised and quasi-randomised controlled trials enrolling mechanically ventilated infants with or without respiratory pathology evaluating the use of long versus short IT (including randomised crossover studies with outcomes restricted to differences in oxygenation). The standard method of the Cochrane Collaboration and its Neonatal Review Group were used. Two authors independently assessed eligibility, and the methodological quality of each trial, and extracted the data. The data were analysed using relative risk (RR) and risk difference (RD) and their 95% confidence intervals. A fixed effect model was used for meta-analyses. In five studies, recruiting a total of 694 infants, a long IT was associated with a significant increase in air leak [typical RR 1.56 (1.25, 1.94), RD 0.13 (0.07, 0.20), NNT 8 (5, 14)]. There was no significant difference in the incidence of BPD. Long IT was associated with an increase in mortality before hospital discharge that reached borderline statistical significance [typical RR 1.26 (1.00, 1.59), RD 0.07 (0.00, 0.13)]. Caution should be exercised in applying these results to modern neonatal intensive care, because the studies included in this review were conducted prior to the introduction of antenatal steroids, post natal surfactant and the use of synchronised modes of ventilatory support. Most of the participants had single pathology (HMD) and no studies examined the effects of IT on newborns ventilated for other reasons such as meconium aspiration and congenital heart disease (lungs with normal compliance). However, the increased rates of air leaks and deaths using long ITs are clinically important; thus, infants with poorly compliant lungs should be ventilated with a short IT.

Respiratory system mechanics in acute respiratory distress syndrome.

Respiratory mechanics research is important to the advancement of ARDS management. Twenty-eight years ago, research on the effects of PEEP and VT indicated that the lungs of ARDS patients did not behave in a manner consistent with homogenously distributed lung injury. Both Suter and colleagues] and Katz and colleagues reported that oxygenation continued to improve as PEEP increased (suggesting lung recruitment), even though static Crs decreased and dead-space ventilation increased (suggesting concurrent lung overdistension). This research strongly suggested that without VT reduction, the favorable effects of PEEP on lung recruitment are offset by lung overdistension at end-inspiration. The implications of these studies were not fully appreciated at that time, in part because the concept of ventilator-associated lung injury was in its nascent state. Ten years later. Gattinoni and colleagues compared measurements of static pressure-volume curves with FRC and CT scans of the chest in ARDS. They found that although PEEP recruits collapsed (primarily dorsal) lung segments, it simultaneously causes overdistension of non-dependent, inflated lung regions. Furthermore, the specific compliance of the aerated, residually healthy lung tissue is essentially normal. The main implication of these findings is that traditional mechanical ventilation practice was injecting excessive volumes of gas into functionally small lungs. Therefore, the emblematic low static Crs measured in ARDS reflects not only surface tension phenomena and recruitment of collapsed airspaces but also overdistension of the remaining healthy lung. The studies reviewed in this article support the concept that lung injury in ARDS is heterogeneously distributed, with resulting disparate mechanical stresses, and indicate the additional complexity from alterations in chest wall mechanics. Most of these studies, however, were published before lung-protective ventilation. Therefore, further studies are needed to refine the understanding of the mechanical effects of lung-protective ventilation. Although low-VT ventilation is becoming a standard of care for ARDS patients, many issues remain unresolved; among them are the role of PEEP and recruitment maneuvers in either preventing or promoting lung injury and the effects of respiratory rate and graded VT reduction on mechanical stress in the lungs. The authors believe that advances in mechanical ventilation that may further improve patient outcomes are likely to come from more sophisticated monitoring capabilities (ie, the ability to measure P1 or perhaps Cslice) than from the creation of new modes of ventilatory support.