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In SIMV, full ventilatory support is provided when the patient is not attempting to breathe above the mandatory rate, and partial ventilatory support when any spontaneous ventilation is present. A number of modes are available that preset the maximum inflation pressure rather than a fixed Vt. Most widely used among these are pressure support ventilation PSV and pressure control ventilation PCV , illustrated in Figures 5 and 6.

With PSV, the patient breathes spontaneously and is assisted with every breath to a preset inspiratory pressure target. Although the technical aspects of its delivery are different, this is conceptually the same as intermittent positive-pressure breathing IPPB , used in the past as a means of ventilatory support but now primarily an adjunct to lung-expansion maneuvers for preventing or treating atelectasis. Pressure support can be combined with SIMV, so that when the patient takes a spontaneous breath, over and above the set frequency of mandatory volume-targeted breaths, inspiration is assisted to the set pressure support level.

Similar to CMV, in PCV the rate is fixed and cannot be increased by patient effort, but a difference is that it is the peak inflation pressure rather than the Vt that is set. Technically, the term for this mode is pressure-controlled continuous mandatory ventilation. This variant of PCV has been used in patients who have severe hypoxemic respiratory failure in an attempt to improve oxygenation, but its popularity has waned because of the high incidence of hemodynamic compromise and barotrauma.

Figure 5: Schematic depiction of changes in pressure at the airway opening, lung volume, and flow during pressure support ventilation PSV. Pressure support is essentially spontaneous breathing with a preset positive pressure boosting each inspiration. Patients on PSV receive no ventilation if apnea occurs. Figure 6: Schematic depiction of changes in pressure at the airway opening, lung volume, and flow during pressure control ventilation PCV. A key distinction between volume- and pressure-targeted modes relates to what happens when the mechanics of the patient-ventilator system change.

When a patient who receives volume-targeted ventilation develops a pneumothorax or partial airway obstruction by inspissated secretions, the same Vt is delivered as before, but at higher peak and static airway pressures. However, with pressure-targeted ventilation, maximal airway pressure is preset and cannot increase under these circumstances.

Instead, with obstruction in the airway or a decrease in compliance, the pressure stays the same and the delivered Vt decreases. Thus, the clinician needs to be aware that complications may be manifested differently in the different modes. When managing a patient whose pulmonary process may improve rapidly, as in acute asthma or pulmonary edema, the clinician needs to be prepared to make frequent ventilator adjustments when pressure ventilation is used. Most critical care ventilators of recent manufacture offer hybrid "modes" combining features of volume-targeted and pressure-targeted ventilation, in an attempt to avoid both the high peak airway pressures of volume ventilation and also the varying Vts that may occur with pressure ventilation.

Manufacturers have attempted to make these combinations unique to their own machines in a competitive market, and as a result several apparently new modes have appeared on the scene. Essentially, these combinations consist either of volume ventilation with high inspiratory flow and a limitation on peak pressure, or of pressure ventilation regulated to provide a preset minute ventilation. These same ventilators also offer volume support, a combined mode that consists of PSV with a preset target Vt or minute volume, which the ventilator achieves by adding mandatory breaths, the inspiratory pressures of which are varied as necessary to achieve the set volume goal.

Auto-mode combines dual-control breath-to-breath time-cycled breaths with dual-control breath-to-breath flow-cycled breaths, patient effort or the lack thereof determining how individual breaths are cycled. Each manufacturer features its own slightly-different blending of volume- and pressure-targeted modes. The operator enters the endotracheal tube diameter, and the ventilator applies positive pressure to overcome the desired proportion of calculated tube resistance via closed-loop control. All these so-called combined modes are intended to give market advantage to the ventilator models that feature them.

Overview of Mechanical Ventilation - Critical Care Medicine - Merck Manuals Professional Edition

None has been demonstrated to have a detectable effect on clinical outcomes such as survival, complications, or weaning time. Manipulation of inspiration by means of the phase variables and modes just discussed is one of the two main processes involved in mechanical ventilation. The other is manipulation of end-expiratory pressure, which may be kept equal to that of the atmosphere or deliberately raised to produce positive end-expiratory pressure PEEP. The application of PEEP has two primary purposes:. When PEEP is applied to the breathing circuit connected to the closed respiratory system of an intubated patient, all breaths start and end at a pressure above ambient.

Continuous pressurization of the system from which a patient breathes spontaneously is referred to as CPAP, a term applicable only during spontaneous breathing. Whenever positive pressure above the end-expiratory level is applied during inspiration, the term PEEP is used. As end-expiratory, end-inspiratory, and mean airway pressures are all increased in the presence of PEEP, the potential exists for a fall in cardiac output because of diminished venous return to the right side of the heart. Regional or generalized lung overdistention can also stretch pulmonary vessels, which reduces their caliber and increases pulmonary vascular resistance.

In the presence of a reduced cardiac output secondary to either or both of these mechanisms, any gain in arterial oxygenation may be offset, and tissue oxygen delivery may actually fall. In addition, the application of PEEP may increase end-inspiratory lung volume to the point at which individual lung units become overdistended and rupture alveolar membranes, which leads to clinical barotrauma. Ideally, only one variable—the amount of PEEP—is altered during the trial, with Vt, fraction of inspired oxygen FIO 2 , body position, and other factors that might affect oxygenation unchanged.

As the condition of the patient may change over time, to determine the effects of PEEP most clearly the intervals at each level must be kept short. As PEEP is increased, the occurrence cardiac impairment becomes progressively more likely. Direct measurement of cardiac output during the trial should be considered if any of the following circumstances exist:. Changes in cardiac output and lung compliance are likely to occur rapidly following an increase in PEEP, and should be sought within the first minutes at each level.

If a substantial increase in PaO2 occurs with no evidence of either cardiac impairment or alveolar overdistention as assessed using static compliance , that PEEP level can be maintained and the FIO 2 titrated downward to maintain the target PaCO 2. N Engl J Med 5 —, Yang M, Ahn HJ, Kim K, et al : Does a protective ventilation strategy reduce the risk of pulmonary complications after lung cancer surgery? A randomized controlled trial. Chest —, Mechanical ventilation is typically done with the patient in the semiupright position.

However, in patients with ARDS, prone positioning may result in better oxygenation primarily by creating more uniform ventilation. Uniform ventilation reduces the amount of lung that has no ventilation ie, the amount of shunt , which is generally greatest in the dorsal and caudal lung regions, while having minimal effects on perfusion distribution.

The study, which included a total of patients, identified lower and day mortality in the prone-positioning group without a significant incidence of associated complications 1. Prone positioning is contraindicated in patients with spinal instability or increased intracranial pressure. This position also requires careful attention by the ICU staff to avoid complications, such as dislodgement of the endotracheal tube or intravascular catheters. N Engl J Med 23 —, Although many patients tolerate mechanical ventilation via endotracheal tube without sedatives, some require IV administration of sedatives eg, propofol , lorazepam , midazolam and analgesics eg, morphine , fentanyl to minimize stress and anxiety.

These drugs can also reduce energy expenditure to some extent, thereby reducing carbon dioxide production and oxygen consumption. Patients undergoing mechanical ventilation for ARDS typically require higher levels of sedation and analgesia. The use of propofol for longer than 24 to 48 h requires periodic monitoring of serum triglyceride levels. There is evidence that continuously administered IV sedation prolongs the duration of mechanical ventilation. Thus, the goal is to achieve adequate but not excessive sedation, which can be accomplished by using continuous sedation with daily interruption or by using intermittent infusions.

Neuromuscular blocking agents are not used routinely in patients undergoing mechanical ventilation because of the risk of prolonged neuromuscular weakness and the need for continuous heavy sedation; however, one study did show reduced mortality at 90 days in patients with early, severe ARDS who received 48 h of neuromuscular blockade 1. Exceptions who may benefit from neuromuscular blockade include patients who fail to tolerate some of the more sophisticated and complicated modes of mechanical ventilation and to prevent shivering when cooling is used after cardiac arrest.

N Engl J Med —, The presence of an endotracheal tube causes risk of sinusitis which is rarely of clinical importance , ventilator-associated pneumonia see Hospital-Acquired Pneumonia , tracheal stenosis, vocal cord injury, and, very rarely, tracheal-esophageal or tracheal-vascular fistula. Complications of ongoing mechanical ventilation itself include pneumothorax , oxygen toxicity, hypotension, and VALI. Toxicity is both concentration- and time-dependent. Ventilator-associated lung injury VALI , sometimes termed ventilator-induced lung injury, is alveolar injury related to mechanical ventilation.

Possible mechanisms include alveolar overdistention ie, volutrauma and the shear forces created by repetitive opening and collapse of alveoli ie, atelectrauma , leading to release of inflammatory mediators resulting in increased alveolar permeability, fluid accumulation, and loss of surfactant. More commonly, however, hypotension is a result of sympathetic lysis caused by sedatives or opioids used to facilitate intubation and ventilation. An immediate improvement suggests a ventilation-related cause, and ventilator settings should be adjusted accordingly. Relative immobility increases the risk of venous thromboembolic disease, skin breakdown, and atelectasis.

Most hospitals have standardized protocols to reduce complications. All patients receiving mechanical ventilation should receive deep venous thrombosis prophylaxis, either heparin units sc bid to tid or low molecular weight heparin or, if heparin is contraindicated, sequential compression devices. To prevent GI bleeding, patients should receive an H 2 blocker eg, famotidine 20 mg enterally or IV bid or sucralfate 1 g enterally qid. Proton pump inhibitors should be reserved for patients with a preexisting indication or active bleeding.

Routine nutritional evaluations are mandatory, and enteral tube feedings should be initiated if ongoing mechanical ventilation is anticipated. The most effective way to reduce complications of mechanical ventilation is to limit its duration. From developing new therapies that treat and prevent disease to helping people in need, we are committed to improving health and well-being around the world. The Merck Manual was first published in as a service to the community.


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Add to Any Platform. In the PAV system the ventilator detects the inspiratory effort of the patient by precisely measuring the flow and volume leaving the ventilator toward the patient. Both parameters are conditioned by the inspiratory decrease in alveolar pressure which the patient generates through muscle contraction. The flow and volume are amplified by respective adjustable gain controls, and the sum of both constitutes the control signal that generates the pressure response of the ventilator. The latter reacts with the rapid delivery of flow in response to this control signal Fig.

Schematic representation of the PAV system. The PAV mode affords assistance proportional to effort through the continuous measurement of the flow and volume 1 leaving the ventilator toward the patient, conditioned to the muscle pressure Pmus generated by the patient and which leads to a decrease in alveolar pressure P alv. The flow and volume are amplified AF and AV by adjustable gain controls 2 , and the sum of both signals conforms the input control signal 3 that generates the pressure response of the ventilator motor. The latter drives the piston, causing the ventilator to respond with rapid flow delivery to the patient in proportion to his or her P alv , overcoming the elastic and resistive pressure.

The pressure-time and flow-time curves resulting from the mechanical cycle 4 show that the pressurization pattern is gradual, reaching the maximum value at the end of inspiration, and exhibiting proportionality at all times. Note that expiratory cycling coincides with the drop in inspiratory pressure, i.


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The proportionality of the assistance is determined by the motion equation of the respiratory system. During assisted ventilation, the total pressure is the sum of the pressure generated by muscle contraction of the patient P mus and the pressure generated by the ventilator P vent. The levels of flow and volume assistance are adjusted independently by the user. This requires an estimation of the passive mechanical characteristics, resistance and elastance, at the start of adjustment and on an intermittent basis. Once these are known, the pressure assist afforded by the ventilator is determined by the sum of the flow and volume assistance:.

Because of the changing nature of respiratory mechanics, the system requires frequent measurement of elastance and resistance. There is consequently a risk of excessive or insufficient assistance in cases of estimation error or a lack of concordance between the estimated and the actual values.

This mode offers two essential improvements: 1 the noninvasive and semi-continuous measurement of respiratory mechanics, allowing automatic closed-loop adjustment of the assist level. This measurement is made by introducing brief pauses ms at the end of inspiration every 8—15 respirations to estimate resistance 9 and elastance 10 ; and 2 the automatic adjustment of a single level of flow and volume assistance that becomes a constant fraction of the measured values of resistance and elastance.. The proportionality is simplified as follows:.

After activating the inspiratory trigger through pressure or flow, the inspiratory pressure progresses with the established proportionality, following a profile identical to that of P mus. The result is gradual pressurization, reaching the maximum pressure only at the end of inspiration. In the moment in which the effort of the patient begins to decrease, the delivery of flow also decreases—expiratory cycling therefore generally coinciding with the cessation of patient effort..

Many clinical studies have compared the physiological advantages of PAV versus conventional assist modes. Marantz et al. They found that during PAV, in the absence of limitations imposed by respiratory mechanics, the RCS of the patient determines the tidal volume V t and the frequency in response to variable assist levels. The patients tend to lower V t and to increase the frequency in order to maintain the chosen minute volume.

This results in a reduction of the inspiratory pressures.. With respect to pressure support ventilation RSV , PAV has shown similar muscle discharge 11—14 and better hypercapnia compensation. Xirouchaki et al. The PAV system depends on pneumatic triggering, and therefore has the same limitations for inspiratory cycling in patients with dynamic hyperinsufflation and intrinsic positive-end expiratory pressure PEEP as the traditional modes.

Although expiratory cycling, based on flow, accompanies the cessation of inspiratory effort, expiratory asynchronies have been described particularly with high assist levels. Compared with PSV, mainly in patients with chronic obstructive pulmonary disease COPD , PAV usually affords higher levels of tolerance, a better physiological response, and fewer complications. In addition to providing valuable evolutive information, it allows us to immediately assess the response to changes in the respiratory parameters or to quickly detect possible complications.

The system is also able to estimate and monitor Pmus, which is the only unknown factor of the motion equation. Knowing P mus , we in turn can calculate the work of breathing, helping to select an adequate assist level with a view to avoiding excessive muscle work or rest.

Neurally adjusted ventilatory assist NAVA is a new assisted ventilation mode synchronized and proportional to the effort of the patient that has become available only in the last few years. The latter is recorded via transesophageal electromyography using a modified nasogastric tube, also known as an EAdi catheter, which is similar in size and function to a conventional nasogastric tube but equipped with several microelectrodes at the distal tip for recording EAdi.

Correct positioning of the catheter is carried out using the transesophageal electrocardiographic signal recorded through the same electrodes as a guide. The operator can check correct positioning at the esophageal hiatus on the ventilator screen, based on a simple algorithm. The utilization of EAdi for control of the ventilator has a series of theoretical advantages.

In effect, EAdi is a signal that directly i. It is therefore the signal closest to the origin of the respiratory stimulus that current technology is able to offer.. During NAVA, inspiratory cycling is determined by the detection of the elevation of EAdi over the expiratory level, with a sensitivity threshold determined by the operator. This allows adjustment of the duration of the mechanical inspiratory and expiratory times to the neural inspiratory and expiratory times of the patient determined by the RCS, in a way which no other ventilatory mode is able to do.

This defines NAVA as the ventilatory mode which theoretically offers the greatest level of patient—ventilator synchrony.. A EAdi signal. The start of inspiration is given by the increase in EAdi activity first broken line from the expiratory activity, which under normal conditions is 0. The neural inspiratory time comprises the period between the two solid lines, and ends when EAdi reaches its maximum value. The mechanical ventilatory time comprises the period between the two broken lines inspiratory and expiratory cycling. Note that although minimal, there is a phase lag in the time between the neural and mechanical times due to the imposed cycling criteria.

B The curves corresponding to pressure, flow and EAdi of a cycle show the perfect inspiratory first broken line and expiratory cycling synchrony produced immediately after the start of the neural time of the patient, in relation to the cessation of inspiratory effort. In the same way as during PAV, the inspiratory assist is at all times proportional to the effort of the patient and is determined by a proportionality constant adjusted by the operator, called the NAVA level, which amplifies the instantaneous progression of EAdi during the inspiratory phase.

The pressure in the airway P aw over the level of PEEP, in each moment during inspiration, is expressed as follows:. Different methods have been proposed for adjusting the NAVA level, which theoretically should be that affording an adequate level of muscle discharge. Brander et al. The optimum NAVA level would be that coinciding with transition from an ascending phase to the plateau phase of the V t and P aw values. Roze et al. Several clinical studies have evaluated and compared the physiological response to NAVA.

These studies have consistently recorded significant improvement in patient—ventilator synchrony, a lesser over-assistance tendency, and greater variability of the respiratory pattern in comparison with PSV in different groups of patients. Patroniti et al. With NAVA, the patients maintained similar V t and respiratory frequency values, even with high assist levels, despite an increase in P aw , which corresponded to a decrease in EAdi. Effect of different NAVA levels and pressure support. Note that in NAVA, and in contrast to pressure support ventilation PSV , greater assist levels do not increase the tidal volume or decrease the respiratory frequency, and the pressure in the airway reaches a plateau with higher assist levels—corresponding to a decrease in EAdi.

The NAVA mode has been shown to facilitate assisted ventilation also in patients with seriously impaired respiratory function. In this respect, the NAVA mode reduced asynchrony in patients subjected to extracorporeal oxygenation support and with severely impaired lung distensibility 37 versus PSV, and achieved better auto-regulation of PCO 2 during weaning from extracorporeal oxygenation 41 —in both cases maintaining protective ventilatory parameters with low V t values..

Because of its operating characteristics, NAVA may be particularly interesting in the context of NIV, since it is not affected by leakages. In this regard, Piquilloud et al. The EAdi signal offers new and interesting possibilities in respiratory monitoring. By affording a direct and continuous measure of the central respiratory stimulus of the patient, the signal allows us to evaluate the response to changes in assist level, detect apneas, evaluate sedation effects, and also assess the neural respiratory stimulus.

EAdi is the best tool available for monitoring patient—ventilator synchrony, since it offers direct information on the neural inspiratory and expiratory times and their relation to the mechanical times. It allows us to determine the neural frequency the real frequency of the patient , thereby enhancing the value of this variable in determining the degree of patient stress or wellbeing.

Mechanical Ventilation

A number of indices derived from the EAdi signal have recently been described. In one same parameter it integrates information on the respiratory stimulus, diaphragmatic function, and respiratory loading, and has been shown to be a good predictor of weaning. Based on neuromechanical efficiency, Bellani et al. These modes encompass closed-loop control modes that incorporate algorithms and control rules which transfer physiological and clinical reasoning principles to automated assist protocols.

According to different physiological and clinical objectives, these modes automatically adjust the pressure or minute-volume levels administered to the patient, adapting to the needs of the latter over time. Adaptive support ventilation ASV performs cycle-to-cycle adjustments of tidal volume through changes in pressure and respiratory frequency, adapting them to changes in respiratory mechanics. The aim is to simulate clinical reasoning in order to avoid under- or over-assistance and to achieve a decrease of the automated support.. According to this principle, in order to reach one same alveolar ventilation level at very low frequencies, we require a greater V t , increasing the work to overcome the elastic load of the respiratory system.

In contrast, at high frequencies, the work of breathing must increase to overcome the resistive load, with a pattern characterized by rapid shallow breathing. Between these two extremes lies the optimum combination of frequency and volume for achieving the desired alveolar ventilation.. Unlike the other examined modes, ASV in fact is a mixed mode that can function as a controlled or assisted mode according to the contribution of the patient..

Figure 5 schematically represents the principles of the functioning and control system of ASV.

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The operator establishes a target percentage minute-volume based on the body weight of the patient. Functioning of ASV. Before starting, the clinician enters the data referred to patient weight, percentage minute-volume estimated a priori according to the patient and disease condition , FiO 2 , PEEP and the maximum inspiratory pressure limit P max. Analysis of the flow-volume curve determines the expiratory time constant, and minimum squares fitting is used to calculate the respiratory mechanics and the presence of intrinsic PEEP.

The closed-loop control algorithm of the ASV system adjusts the inspiratory pressure according to the iterative equation derived from Otis and Mead.

The combinations of target minute-volume and frequency are continuously adjusted to reach and keep the patient on the minute-isovolumetric curve IsoVM.. Accordingly, ASV incorporates the estimation of dead space in its algorithm, and which the system assumes to be 2. The ASV system then adjusts the level of pressure and respiratory frequency cycle-to-cycle, following its algorithm to maintain the ventilatory pattern according to the established target minute-volume, in consistency with the mechanical characteristics of the respiratory system and the spontaneous respiratory frequency of the patient.

Inspiratory cycling uses the conventional pneumatic trigger by pressure or flow, while expiratory cycling is by flow as in the case of PSV.. Most clinical studies have focused on examining ASV under passive ventilation controlled conditions, comparing it with other modes, and specifically evaluating whether ASV yields protective parameters low V t and P aw in an automated and efficient way..

As assist mode which is what interests us in this review , ASV has been studied mainly as a mode designed to facilitate weaning. It has been shown to be a safe and effective technique that simplifies the weaning process in the postoperative period of heart surgery 49—51 and in patients with COPD, 52 and is moreover associated with a lesser consumption of resources. In comparative studies, ASV has not been found to shorten the mechanical ventilation times in heart surgery, 50,51 though shortened times have been recorded in COPD patients, where Kirakli et al.

The best comparative clinical study to date on the effect of ASV upon patient—ventilator synchrony was published by Tassaux et al. The ASV mode has recently received improvements, with addition to the algorithm of closed-loop control for end-expiratory CO 2 etCO 2 55 and oxygen saturation. The control algorithm incorporates rules for action based on clinical reasoning, in an attempt to reproduce the PSV adjustments which the clinician would decide in the same context.. The control algorithm of the system uses the values of V t , respiratory frequency and etCO 2.

The system responds as follows: 1 it reduces the level of PSV in the case of diagnosed over-assist e. The aim is to move the patient toward a zone of respiratory wellbeing in order to start the weaning process. This zone of wellbeing is derived from the patient characteristics body weight, type of illness, size of the endotracheal tube, type of humidifier. The values are entered by the clinician in the ventilator, and determine the limits of V t , frequency and etCO 2 , and the PSV adjustments required.

The automated weaning protocol involves automated adaptation of the PSV level followed by an automated PSV reduction phase, and finally an automated spontaneous breathing test.. Variability is an intrinsic characteristic not only of the respiratory system but also of any complex biological system, and the loss of such variability is generally associated with functional impairment. Variable pressure support ventilation V-PSV introduces random variability in the levels of pressure support ventilation, resulting in a ventilatory pattern that is variable but independent of the demands of the patient and his or her inspiratory effort..

V-PSV noisy ventilation is based on the recurrent application of a set of pressure values generated on a random basis. Experimental studies have consistently shown beneficial physiological effects, such as improved gas exchange and respiratory mechanics. A relevant aspect is the possible benefits in terms of lung protection. Although an attractive mode, the lack of clinical data means that many questions still need to be answered before the true clinical usefulness of the technique can be established.

As an example, what pattern or level of variability would have been most appropriate for a given situation? In this respect, Spieth et al. These are very interesting times for mechanical ventilation. The constant technological advances have allowed the development of new assisted ventilation modes with the capacity to adapt to the changing patient needs. The new modes allow the patient a total control of the ventilatory process, causing the ventilator to act as an accessory muscle in synchrony with patient inspiratory effort.

New modes that incorporate increasingly complex closed-loop or knowledge-based control systems are paving the way toward gradual automatization of the mechanical ventilation process. It can be expected that such modes and automatization will gradually find their way into routine clinical practice. The results of future studies will help us to better define their advantages, indications and benefits in assisting patients subjected to mechanical ventilation.. The author serves as a consultant to Maquet Critical Care.. Med Intensiva.

ISSN: Previous article Next article. Issue 4. Pages May Update in Intensive Care Medicine: Mechanical ventilation. Download PDF. Corresponding author. This item has received. Article information. Show more Show less. Future clinical trials should improve our understanding of these modes and help determine whether the claimed benefits result in better outcomes.

Patient—ventilation synchrony. Palabras clave:. Introduction Mechanical ventilation MV is a life support measure that is used when the respiratory system of the patient is unable to meet the metabolic demands of the body. In this phase, which is referred to as assisted ventilation, the aim is to provide ventilatory support synchronized in time and magnitude with the inspiratory effort of the patient as the level of mechanical ventilation is gradually reduced. The challenges of assisted ventilation Assisted ventilation has the difficult task of harmonizing the operation of two complex systems, i.

As a result, patients subjected to assisted ventilation can develop complex respiratory patterns that affect interaction with the ventilator, thereby complicating mechanical assist. The voluntary system in turn can modulate the activity of the automatic system or directly activate the muscle pump. Figure 1. Figure 2. Figure 3. Adapted from Suarez-Sipmann et al. Figure 4. Adapted from Patroniti et al. The combinations of target minute-volume and frequency are continuously adjusted to reach and keep the patient on the minute-isovolumetric curve IsoVM. Figure 5. Adapted from Tassaux et al.

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Prog Neurobiol, 59 , pp. Thille, P.

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Rodriguez, B. Cabello, F. Lellouche, L. Patient—ventilator asynchrony during assisted mechanical ventilation. Intensive Care Med, 32 , pp. Thille, B. Galia, A. Lyazidi, L. Reduction of patient—ventilator asynchrony by reducing tidal volume during pressure-support ventilation. Intensive Care Med, 34 , pp. Proportional assist ventilation, a new approach to ventilatory support. Am Rev Respir Dis, , pp. Marantz, W.

Patrick, K. Webster, D. Roberts, L. Oppenheimer, M. Response of ventilator-dependent patients to different levels of proportional assist. J Appl Physiol, 80 , pp. Passam, S. Hoing, G. Prinianakis, N. Siafakas, J. Milic-Emili, D. Effect of different levels of pressure support and proportional assist ventilation on breathing pattern, work of breathing and gas exchange in mechanically ventilated hypercapnic COPD patients with acute respiratory failure.

Respiration, 70 , pp. Younes, J. Kun, B.