Modes of Mechanical Ventilation
A ventilator mode describes the manner in which a breath is delivered to a patient in order to meet physiological demands.7 It has been proposed that a ventilator mode can be classified by specifying the control variable, breath sequence, and targeting scheme.7,10 It incorporates variables that control, initiate, sustain, and terminate the breath (phase variables) as well as determine if a change in breath pattern is needed (conditional variables). The emergence of a new generation of microprocessor-based ventilators has resulted in advancements in triggering, monitoring, and safety at the cost of added complexity and expense.4,17,18 None of these newer modes of have been shown to reduce morbidity or mortality.4,17,18 Following are some of the common conventional and alternative modes of ventilatory support utilized in clinical practice (Table 18–3).
Table 18–3Commonly used ventilator modes. |Favorite Table|Download (.pdf) Table 18–3 Commonly used ventilator modes.
|Ventilator Modes ||Description ||Proprietary Name |
|Conventional Modes of Ventilation |
|CMV ||All breaths are mandatory and delivered at a predetermined frequency and inspiratory time. Ventilator triggers all breaths. Patients usually require deep sedation or paralysis, or do not have ventilatory drive. This mode has been replaced by the assist-control mode. ||CMV-VC, CMV-PC |
|ACV ||All breaths are mandatory and delivered at a predetermined minimum frequency. Breaths could be triggered by ventilator or patient. Preferred mode for primary support in most clinical settings. ||A/C VC, A/C PC |
|IMV ||Breaths are mandatory and delivered by the ventilator at a preset frequency. Mandatory breaths are triggered by the ventilator. In between mandatory breaths, patient can breathe spontaneously. ||IMV-VC, IMV-PC |
|SIMV ||Is a form of IMV but differs by ventilator's ability to detect patient effort during preset intervals and delivering a mandatory breath is in coordination with (ie, synchronized) patient's effort. If no effort detected, ventilator will deliver a mandatory breath at the scheduled time (ie, time triggered). SIMV has replaced IMV in clinical practice. Used for primary support and weaning. ||SIMV-VC, SIMV-PC |
|PSV ||All breaths are spontaneous. Patient determines the respiratory rate, inspiratory time, and VT. Patient-ventilator synchrony is enhanced. Used commonly as a weaning mode but can also be used for primary support or in combination with other modes such as SIMV. ||Pressure support |
|Dual-Control Modes of Ventilation |
|Dual control ||Pressure or volume delivered is controlled by the ventilator via a feedback loop. Ventilator regulation of the pressure or volume occurs within a breath, ie, intrabreath. VT is guaranteed by switching between PSV and VC. Breaths may be triggered by patient or ventilator. ||VAPS or PA |
| ||Pressure or volume delivered is controlled by the ventilator via a feedback loop. Ventilator regulation of the pressure or volume occurs breath to breath, ie, interbreath. VT is guaranteed by adjusting PS level. Breaths are all patient-triggered. ||VS or VPS |
| ||Pressure or volume delivered is controlled by the ventilator via a feedback loop. Ventilator regulation of the pressure or volume occurs breath to breath, ie, interbreath. VT is guaranteed by adjusting PC. Breaths may be triggered by patient or ventilator. ||PRVC, APV, Autoflow, VPC or VCV+ |
| ||Combines dual-control, breath-to-breath, time-cycled (mandatory), and flow-cycled (spontaneous) breaths into a single mode. Can switch between PRVC and VS, or PC and PS, or VC and VS. Breaths may be triggered by patient or ventilator. ||AutoMode |
| ||Combines dual-control, breath-to-breath, time-cycled (mandatory), and flow-cycled (spontaneous) breaths into a single mode. Ventilator chooses ventilator parameter based on clinician input of IBW and percent minute volume to meet minute ventilation target while minimizing WOB. Can switch between APC and PS, and SIMV-PC and PS. Breaths may be triggered by patient or ventilator. ||ASV |
|Nonconventional Modes of Ventilation |
|APRV ||Uses 2 levels of continuous airway pressure, high and low, with intermittent release to the lower level. Patients are able to take spontaneous breaths during any phase of the respiratory cycle. It is commonly used as an alternative modality in ARDS patients. ||APRV |
|PAV ||Continuous spontaneous ventilation in which pressure generated is proportional to patient's inspiratory effort (volume and flow). It enhances patient-ventilator synchrony. ||PAV |
|NAVA ||Continuous spontaneous ventilation in which pressure generated is proportional to the electrical activity of the diaphragm. It enhances patient-ventilator synchrony. ||NAVA |
|HFV ||Generates very small tidal volumes with respiratory rates > 100/min. Has been used in patients with ARDS. ||HFOV |
| ||Generates very small tidal volumes with respiratory rates > 100/min. Has been used in patients with ARDS, bronchopleural fistulas, burns with significant airway secretions, and patients with raised ICP. ||HFPV |
Conventional Modes of Ventilatory Support
Continuous Mandatory Ventilation
In the CMV mode, all breaths are mandatory and delivered by the ventilator at a predetermined frequency and inspiratory time (Figure 18–2). The breaths could either be volume or pressure targeted (or controlled), triggered by the ventilator (ie, time triggered), pressure, volume or flow limited, and time, flow, pressure, or volume cycled by the ventilator.19,20 Patients receiving this mode usually require deep sedation or paralysis, or do not have ventilatory drive.19 Most modern ventilators do not prevent patients from triggering a breath; therefore, this mode has been replaced by the A/C mode.19 In some ventilator brands, CMV and A/C modes are the same.
Continuous mechanical ventilation (CMV) using pressure-controlled breaths. All the breaths are triggered by the ventilator as depicted by the absence of a negative deflection on the pressure waveform (top waveform), flow limited (middle waveform), and time cycled. The bottom waveform shows the tidal volume that is being generated, which can be variable based on changes in the patient's compliance and resistance.
In assist-control ventilation (ACV) mode, breaths are mandatory and delivered by the ventilator at a predetermined minimum frequency. The breaths could be volume or pressure targeted (A/C VC or A/C PC), and are either ventilator, that is, time triggered based on a set rate, or patient triggered (using flow or pressure) depending on patient effort and set sensitivity (Figure 18–3). In this mode, assisted breaths (mandatory breaths that are patient triggered) can be delivered at the predetermined pressure or volume in between the ventilator triggered breaths. Similar to CMV, the breaths are also pressure, volume or flow limited and flow, volume, pressure, or time cycled by the ventilator.20 ACV is the preferred mode in most clinical settings, but common problems encountered include respiratory alkalosis in patients with a high respiratory drive, increased WOB by patients if the sensitivity and flow rates are inadequately set and dyssynchrony in awake patients.19,21
Assist control ventilation (ACV) using volume-controlled breaths. Some breaths are patient-triggered (depicted by the negative deflection on the pressure waveform [top waveform]), that is, assisted, and some breaths are ventilator-triggered (depicted by the absence of a negative deflection on the pressure waveform [top waveform]), that is, mandatory. The pressure generated can be variable based on changes in the patient's compliance and resistance, while the flow (middle waveform) and volume (bottom waveform) remain constant.
Intermittent Mandatory Ventilation and Synchronized Intermittent Mandatory Ventilation
In the IMV mode, breaths are mandatory and delivered by the ventilator at a set frequency, and are either volume or pressure targeted. Furthermore, the mandatory breaths are triggered and cycled by the ventilator. In between the mandatory breaths delivered, a patient can breathe spontaneously at a frequency and VT determined by the patient, irrespective of the set ventilator frequency. These spontaneous breaths are patient triggered and patient cycled, and may be augmented by pressure support.22,23,24,25,26 Nevertheless, the lack of coordination between spontaneous and mandatory breaths can result in breath stacking if a mandatory breath is triggered before the patient completely exhales a spontaneous breath. The SIMV mode (Figure 18–4) is a form of IMV in which mandatory breaths are delivered at a preset frequency with the patient taking spontaneous breaths in between. However, if the ventilator detects patient effort at the time a mandatory breath is to be triggered, the mandatory breath is delivered in coordination (ie, synchronized) with the patient's effort, that is, it becomes patient triggered instead of ventilator triggered.19 If no inspiratory effort is detected from the patient within a set interval (ie, synchronization window) at the time scheduled for a mandatory breath, then the ventilator will deliver a time triggered mandatory breath. Modern day ventilators provide SIMV rather than IMV. This mode of ventilation has been used for both primary support as well as weaning from mechanical ventilation, though there is evidence suggesting that its use as a weaning mode may contribute to prolonged weaning time.17 Additionally, the premise that mandatory breaths of SIMV allow respiratory muscles to rest has been questioned.27,28 It is felt that since the respiratory center does not anticipate when the ventilator will deliver the next breath, it continues to provide its output and stimulate respiratory muscle activity even during mechanically generated or supported breaths. Hence, the patient ends up performing as much WOB in spontaneous as in ventilator generated or supported breaths.
Synchronized intermittent mechanical ventilation (SIMV) showing both volume-controlled mandatory breaths triggered by the ventilator at a set frequency and spontaneous pressure supported breaths triggered by the patient in between the mandatory breaths.
Pressure Support Ventilation
Pressure support ventilation (PSV; Figure 18–5) is a spontaneous ventilatory mode in which a patient's inspiratory effort is assisted by the ventilator up to a predetermined inspiratory pressure level. Each breath is patient triggered, pressure limited, and flow cycled, thus the patient determines the frequency, inspiratory time and VT and thereby patient-ventilator synchrony is enhanced.26,29,30 This mode is often confused with PC ventilation which is patient or ventilator triggered, pressure limited, and time cycled (Figure 18–2). Inspiration in PSV ceases when the peak inspiratory flow rate decreases to a predetermined minimum level (eg, 5 L/min) or a percentage of the initial inspiratory flow (eg, 25%).19,31 The WOB related to this mode is a function of the selected pressure level, such that higher levels provide more ventilatory support and decrease the workload of the respiratory muscles.19 This is used commonly as a weaning mode, but can also be used for primary support or in combination with other modes, such as SIMV.29,31 It should not be used in patients with unstable respiratory drive.
Pressure support ventilation (PSV) in which all breaths are spontaneous and the patient's inspiratory effort is assisted by the ventilator up to a predetermined inspiratory pressure level. Each breath is patient triggered, pressure limited, and flow cycled; thus the patient determines the respiratory frequency, inspiratory time, and tidal volume.
Alternative Modes of Ventilatory Support
Changes in ventilatory support continue to occur as a result of microprocessor control of mechanical ventilators. This has led to the production of devices that are increasingly more complex. Some of the more common alternative modes are described below briefly.
Dual control is a mode of ventilation in which the pressure or volume delivered is controlled by the ventilator via a feedback loop.32 Ventilator regulation of the pressure or volume could occur within a breath, that is, intrabreath or from breath-to-breath, that is, interbreath. In the former, the ventilator switches from PC to VC during the breath, while in the latter the ventilator functions in either the PS or PC mode, adjusting the pressure limit to automatically maintain a predetermined VT.32
VAPS or pressure augmentation uses dual control within a single breath. The breath may be patient triggered or ventilator triggered. After a breath is triggered, the ventilator attempts to reach the predetermined pressure target, that is, the PS setting. This portion of the breath is the pressure-limited portion. As the pressure level is attained, the ventilator determines the adequacy of the VT delivered to the patient by comparing the volume delivered with the predetermined VT. If the ventilator senses that the desired VT will not be reached, inspiration continues (ie, increase in inspiratory time [TI]) according to the set peak flow, whereby the breath changes from a pressure limited to a volume limited mode. This assures the predetermined volume is delivered to the patient.19,32 However, if the delivered VT and predetermined VT are the same, the breath remains in the PS mode and is flow cycled. Consequently, VAPS combines the high initial flow of a pressure-limited breath with the constant volume delivery of a volume-limited breath.
Volume support ventilation (VS) or variable pressure support ventilation uses dual control from breath-to-breath (Figure 18–6). The breaths are pressure-limited and flow-cycled and are all triggered by the patient.19 The ventilator maintains VT by adjusting the PS, that is, VT is used as a feedback control for continuously adjusting the pressure support level for the next breath.33 Because all breaths are PS breaths, cycling occurs when the flow falls less than 25% of peak value.33 It is a combination of the positive attributes of PSV with the constant minute volume and VT seen with volume-controlled ventilation (VCV).
Volume support (VS) ventilation in which all breaths are triggered by the patient and are pressure supported. A constant tidal volume is maintained by the ventilator by adjusting the pressure support level, that is, variable pressure support.
PRVC uses dual control from breath-to-breath (Figure 18–7). It has also been described as adaptive pressure ventilation, autoflow, VCV+, variable pressure control, though small technical differences exist.10,33 The breaths are ventilator or patient triggered, pressure limited, and time cycled. In this mode of ventilation, the VT is used as the feedback control mechanism (conditional variable) for continuously adjusting the pressure limit.10,32 Initially, a series of test breaths are delivered to determine the inspiratory pressure required, based on the patient's respiratory mechanics, to deliver the desired VT within the chosen TI.29 This mode maintains a minimum peak pressure which provides a constant predetermined VT and an automatic reduction of inspiratory pressure as the patient's efforts increase or lung mechanics improve. Conversely, an increase in inspiratory pressure will occur on the next breath if a change in lung mechanics or patient effort causes the VT delivered to below the target VT.29,32 A major benefit of this mode is that the ventilator can adjust inspiratory flow according to the patient's demand while maintaining a constant minimum minute volume, thus making this mode more comfortable for the patient. Conversely, the fixed minute ventilation may result in alveolar overdistention in the face of varying compliance of the lung.34
Pressure-regulated volume control (PRVC) (ie, adaptive pressure ventilation) in which the breaths are currently being triggered by the ventilator and not the patient. The ventilator adjusts the pressure limit based on the patient's respiratory mechanics to guarantee the targeted tidal volume.
AutoMode ventilation combines dual control breath-to-breath time cycled breaths (PRVC) with dual control breath-to-breath flow-cycled breaths (VS) into a single mode. In this mode, the ventilator is able to switch from either PRVC to VS or vice versa based on whether the breaths are mandatory (time triggered, pressure limited, and time cycled) or spontaneous (patient triggered, pressure limited, and flow cycled). In a similar fashion, this mode can also switch from PS to PC (Figure 18–8) or from VS to VC if the patient is unable to sustain spontaneous breathing and requires mandatory breaths to be delivered.32,35
AutoMode ventilation combining pressure control and pressure support into a single mode. The ventilator is able to switch from either pressure control to pressure support or vice versa based on whether the breaths are mandatory (time triggered, pressure limited and time cycled) or spontaneous (patient triggered, pressure limited, and flow cycled). If the patient is unable to sustain spontaneous breathing, mandatory breaths are delivered.
Nonconventional Modes of Ventilatory Support
Airway Pressure Release Ventilation
Airway pressure release ventilation (APRV) is a pressure limited, time cycled (flow cycled in some ventilator brands) mode (Figure 18–9) that uses a high continuous airway pressure level (Phigh) with a periodic release to a low continuous airway pressure level (Plow).36,37 Patients are able to spontaneously breathe in both phases of the ventilator cycle, that is, during Phigh and Plow.36 Time spent at Phigh (Thigh) is usually longer than TI in conventional ventilation, thereby promoting adequate alveolar recruitment and oxygenation. However, the brief periodic expiratory release to Plow in addition to the patient's ability to breathe spontaneously allow for adequate ventilation. The VT generated is a function of the lung compliance, airway resistance, periodicity, and duration of the release phase.38 Recently, several studies and editorials have questioned the usefulness and safety of spontaneous breathing in the setting of ARDS.39
Airway pressure release ventilation (APRV) that is a pressure-limited and time-cycled mode that uses high and low levels of continuous airway pressure with a periodic release between the two. As is seen in this figure, patients are able to spontaneously breathe in both phases of the ventilator cycle that enhances oxygenation and further lung recruitment. However, this capability also increases the risk of producing higher tidal volumes than would be conventionally recommended.
Proportional Assist Ventilation
PAV is a ventilatory mode that amplifies a patient's effort without imposing predetermined targets such as flow or volume.40,41 The ventilator applies pressure in proportion to the patient's inspiratory effort.42,43,44 Unlike in PSV where the inspiratory pressure provided by the ventilator is constant, with PAV, the ventilator provides dynamic inspiratory pressure assistance in linear proportion to the patient-generated flow and volume as a result of the pressure generated by the respiratory muscles. The ventilator-applied pressure increases and decreases according to the proportion of the patient's effort and this results in better patient-ventilator synchrony.19 The ventilator amplifies the patient's instantaneous effort while leaving complete autonomy over the breathing pattern (such as tidal volume, inspiratory and expiratory duration, and flow) to the patient. The proportion of assist provided is determined by the continuous calculation of the resistive and elastic loads and this is amplified to assist the patient.19 Hence, the system functions by positive feedback (ie, mechanical unloading). In this mode, the proportionality between applied pressure and both flow and volume is selected, and this determines the magnitude of the decrease in both the resistive and elastic loads faced by the inspiratory muscles. The necessity of the accurate measurements of airway resistance and respiratory system elastance are limitations to the use of PAV. However, the development of PAV with load adjustable gain (PAV+) may have solved this, thereby facilitating broader clinical use.45,46
Adaptive Support Ventilation
ASV is a pressure-targeted closed loop mode of ventilation with optimal targeting schemes for VT, respiratory rate and V̇E, in response to changes in respiratory mechanics and spontaneous breathing (Figure 18–10).47 The ventilator determines the predicted V̇E (ie, 0.1 L/kg/min) based on the patient's ideal body weight (IBW) and estimated dead space (ie, 2.2 mL/kg), which represents 100% minute ventilation.10,48 The clinician then inputs the target percent of minute ventilation (%MinVol) that the ventilator will support. Subsequently, the ventilator automatically utilizes the Otis' equation to predict a VT and optimal frequency (f) combination that minimizes the WOB.49 The target VT is calculated as V̇E/f. If the patient is making respiratory efforts, ASV delivers PS breaths (patient triggered, pressure targeted, and flow cycled), and can only adjust the inspiratory pressure level and thereby VT, in order to maintain target V̇E. However, in the absence of respiratory efforts, ASV delivers adaptive pressure controlled breaths (ventilator triggered, pressure targeted, and time cycled) while still maintaining the target V̇E by being able to adjust both VT and f.10,47,50 The ventilator will continuously monitor WOB relative to selected %MinVol, by adjusting peak pressure, VT, and f accordingly. ASV has been used for weaning as it progressively and automatically decreases inspiratory pressure as the patient's respiratory mechanics improve and all breaths remain spontaneous.51
Adaptive support ventilation (ASV). The ventilator determines the predicted minute ventilation (V̇E) based on the patient's ideal body weight (IBW) that represents 100% minute ventilation and the clinician decides on the target percent of minute ventilation (%MinVol) that the ventilator will support. If the patient makes respiratory efforts, ASV delivers pressure support breaths (patient triggered, pressure targeted, and flow cycled). However, in the absence of respiratory efforts, as in this figure, ASV delivers adaptive pressure-controlled (APC) breaths (ventilator triggered, pressure targeted, and time cycled) so as to maintain the target V̇E.
Neurally Adjusted Ventilatory Assist
NAVA is a ventilator mode whereby positive pressure is applied to the airway opening in proportion to the electrical activity of the diaphragm (EAdi).52,53 This diaphragmatic activity is directly related to phrenic nerve impulse. A specially designed esophageal catheter with multiple electrodes is inserted to collect the EAdi.54 The use of EAdi to estimate respiratory center output needs the integrity of the respiratory center, phrenic nerve, and neuromuscular junction to be intact, and assumes the diaphragm to be the primary inspiratory muscle. This diaphragmatic electrical activity is picked up by the electrode, and acts as a trigger for a pressure support breath to be delivered by the ventilator (Figure 18–11). The pressure delivered by the ventilator is calculated by multiplying the EAdi by a proportionality factor called “NAVA level” (expressed as cm H2O/μV). Ultimately, the pressure delivered by the ventilator is cycled-off as the EAdi falls to 40% to 70% of the peak EAdi reached during inspiration.52,53 NAVA is said to represent the first form of assisted ventilation in which the patient's respiratory center can assume full control of the magnitude and timing of the mechanical support provided, in spite of changes in respiratory drive, mechanics, and muscle function. This results in a better patient-ventilator synchrony, reduction in the risk of iatrogenic hyperinflation, respiratory alkalosis, and hemodynamic impairment.52,53
Neurally adjusted ventilatory assist (NAVA) in which positive pressure is delivered in proportion to the electrical activation of the diaphragm (EAdi). Ventilatory support begins when the neural drive to the diaphragm starts to increase, such that as the EAdi progressively rises, inspiratory airway pressure also rises proportionally. The pressure delivered is reached by multiplying the EAdi by a proportionality factor called “NAVA level” (in this patient: 1.6 cm H2O/μV). The pressure delivered by the ventilator is cycled-off as the EAdi is terminated by the respiratory centers.
High-frequency ventilation (HFV) is a mechanical ventilatory technique that uses respiratory rates greater than 100 breaths/min along with the generation of small VT, that are smaller than traditional estimations of both anatomic and physiologic dead space and range from approximately 1 to 5 mL/kg.55,56 Three types of HFV exist, but the two types discussed are high-frequency oscillatory ventilation (HFOV) and high-frequency percussive ventilation (HFPV) whose waveforms are shown in Figure 18–12. In contrast to conventional ventilation where gas transport takes place by bulk delivery of gas, further theoretical mechanisms believed to enhance gas exchange in these forms of HFV have been described in the literature and include asymmetric velocity profiles, longitudinal (Taylor) dispersion, pendelluft, cardiogenic mixing, and molecular diffusion.55,57,58 There has been interest in the use of HFV in severe hypoxemic respiratory failure, however, studies have failed to demonstrate mortality benefit in adult patients.
The waveforms that can be generated in high-frequency oscillatory ventilation (HFOV) versus high-frequency percussive ventilation (HFPV). With HFPV, small volumes are delivered in a stepwise manner with scheduled interruptions that result in the formation of high- and low-frequency cycles. It has crudely been described as an amalgam of HFOV and pressure-controlled breaths into one.
HFOV is characterized by the generation of small VT as a result of the oscillation of a bias gas flow that result in pressure swings within the airway at frequencies ranging from 3 to 15 Hz (usually 3–6 Hz in adults). These pressure swings may be significant proximally, but become attenuated as they reach the distal airways and alveoli resulting in the low VT. The oscillations are produced by an oscillatory diaphragm/piston pump, and result in an active inspiratory and expiratory phase. The rapid oscillations of gas are delivered at pressures above and below a constant mean airway pressure (mPaw), which in addition to the fraction of inspired oxygen (FIO2), determine the level of oxygenation. Ventilation, on the other hand, is directly related to the pressure amplitude of oscillation (ΔP); that is, degree of displacement by the oscillatory diaphragm/piston pump, but inversely related to the set frequency.59 The combined effects of a high mPaw and small VT potentially result in improved recruitment of alveoli and gas exchange with an associated reduced risk of overdistention.60,61,62 Because of the low VT generated, it is considered to be lung protective. It has been used primarily in patients with ARDS in whom conventional ventilatory strategies have failed. However, recent trials have demonstrated that it has limited benefit for the treatment of these patients.63,64
HFPV is a pressure-limited, flow-regulated, and time-cycled ventilator mode that delivers a series of high-frequency (200-900 cycles/min) small volumes in a consecutive stepwise stacking manner resulting in the formation of low-frequency (4–30 cycles/min) convective pressure-limited breathing cycles (Figure 18–13).62,65,66,67 Gas exchange is a function of the percussion frequency, such that at average percussion frequencies (500-600 cycles/min) oxygenation and ventilation are augmented, while low percussion frequencies less than 500 cycles/min may be utilized in patients with deep-seated secretions so as to enhance clearance.62,67,68,69 The interplay of its control variables (ie, inspiratory and expiratory time, percussion frequency, PIP, pulsatile flow rate, and PEEP) either individually or in combination, play a role in determining the mPaw and degree of gas exchange.62,67,69 HFPV has been used as a rescue modality in patients with severe hypoxemic respiratory failure, such as those with ARDS in whom conventional ventilatory strategies have failed. It has also been used in patients who tend to have a significant amount of airway secretions and debris because of its pulsatile flow mechanism. There is a paucity of literature with regards to its use and it has not been demonstrated to bring about a reduction in mortality.
High-frequency percussive ventilation in which the breaths are pressure-limited, flow-regulated, and time-cycled, but are delivered at a high frequency (in this case 655 cycles/min) with very small volumes. These volumes are delivered in a consecutive stepwise stacking manner resulting in the formation of low-frequency (in this case 14 cycles/min) convective pressure-limited breathing cycles. Gas exchange is a function of the percussion frequency. The interplay of its control variables plays a role in determining the mPaw and degree of gas exchange. 1. Periodic scheduled interruptions signifying end of inspiration and onset of expiration. 2. Demand continuous positive airway pressure (CPAP). 3. Pulsatile flow during inspiration at 595 cycles/min. 4. Convective pressure-limited breath with low-frequency-cycle at 14 cycles/min. 5. Oscillatory CPAP. 6. Single percussive breath.
Adjuncts to Mechanical Ventilation
Nonventilatory strategies that have been used in conjunction with mechanical ventilation either to enhance oxygenation, patient comfort or maintain other goals of mechanical ventilation, include prone positioning, extracorporeal membrane oxygenation also called extracorporeal life support, use of neuromuscular blocking agents or inhaled vasodilators.70,71,72,73,74,75