Conventional ventilation modes include forced ventilation (CV), assisted ventilation (AV), forced/assisted ventilation (A/CV), intermittent command ventilation (IMV), synchronized intermittent command ventilation (SIMV), continuous positive airway pressure ventilation (CPAP), positive end-expiratory pressure ventilation (PEEP), deep breathing (SIGH), and manual ventilation (MV).
1.Pressure support ventilation
The patient receives positive pressure support in the airway through the ventilator by receiving an additional airflow from the on-demand valve set by the ventilator during spontaneous inspiration.PsV has a lower peak inspiratory pressure than intermittent positive pressure ventilation (IPPV), which is related to the negative thoracic pressure generated by spontaneous breathing.At the same pressure, the tidal volume of PsV is greater than that of IPPV, which helps to reduce the VD/vT ratio, improve alveolar ventilation, and PSV is a useful partial assisted respiratory mode to play a part in the patient’s voluntary breathing, but PSV requires certain central sensitivity and respiratory muscle strength, and PsV should be used with caution for those who have unstable respiratory mechanics or whose condition may change rapidly in a short period of time, and generally the combination of SIMV and PSV low-level pressure support is mostly used in clinical practice. The representative models are SIMENS 900C, PB840, DRAGER E-vITA series, NEwPORT E200 and BEAR 1000 ventilators, etc. In DRAGER EVITA series ventilators, advanced assisted autonomic respiratory pressure support (ASB) technology is also adopted, which can adjust the pressure rise time to change the pressure in addition to adjusting the pressure of support. In addition to adjusting the support pressure, the pressure rise time can also be adjusted to change the slope of the pressure support, making the pressure support more flexible.
2.Biphasic Positive Airway Pressure Ventilation
BIPAP is a pressure/time cycle ventilation mode, commonly known as “universal mode”, it is set by software program two different levels of CPAP, namely P1 and P2 and their execution time Tl and T2, the patient can breathe autonomously on two different levels of CPAP within the set time, the application of BIPAP mode has a more significant effect on increasing the oxygenation of the patient than the application of PAP. Recent experience in clinical applications shows that BIPAP mode can be used as a ventilatory aid to patient autonomy in all stages of the disease, and is simple, convenient and non-invasive to operate. However, it is generally believed that BIPAP and APRV are only suitable for mild to moderate respiratory failure, because the mechanical assistance it provides is not very high, and the representative models are DRAGER EVITA 4.
3.Airway pressure release ventilation
The patient is allowed to breathe autonomously under continuous intra-airway pressure with a brief pressure release. During the high pressure period of the patient’s autonomic inspiration, the ventilator provides a high flow of gas in the respiratory circuit to maintain an almost constant CPAP level, which maintains a higher lung volume than when the human body breathes autonomously at atmospheric pressure, and in order to assist breathing, the CPAP drops briefly to allow a momentary reduction in the functional residual volume (FRC). The physiological dead space is reduced in the APRV mode, and the gas is better distributed in the lungs during the prolonged inspiratory phase. this ventilation mode is suitable for patients with very poor gas exchange, and is not effective for patients with airway obstruction due to the desire to expel as much gas as possible during pressurization. the representative models are DRAGER EVITA4. among them BILEVEL of PB840, BIVENT of SIMENS SERVO 300/300A and DUOPAP of HAMITTON Galileo contain two modes of BIPAP and APRV.
4.Proportional assisted ventilation
Proportional assisted ventilation (PAV), also known as proportional pressure support (ees), ventilator according to the patient’s inspiratory volume, inspiratory flow, proportional change in the airway pressure, the volume provided by traditional positive pressure ventilation are fixed. The volume and airway pressure provided by PAV increases proportionally to the patient’s instantaneous inspiratory effort, resulting in a convergence between inspiratory effort and ventilation. Because PAV protects and strengthens the patient’s own control mechanism, the peak airway pressure during ventilation is reduced, the possibility of hyperventilation is reduced, mechanical injury is avoided, and respiratory effort is greatly reduced. Because PAV requires the patient’s voluntary respiratory effort, it is not effective in patients with central depression and abnormal forms of breathing (hyperventilation or hyperventilation). The representative models are PB 840 SERIES.
5.Inverse Ratio Ventilation
IRV is a form of ventilation in which the ratio of inspiration to expiration (I:E) is greater than 1:1 by gradually extending the inspiratory time. IRV provides a longer period of positive pressure during inspiration to further retract the atrophied alveoli, and this positive pressure also slowly inflates the alveoli, thus improving ventilation. IRV is mainly used for acute respiratory failure where PEEP treatment is ineffective, such as severe ARDS, because IRV imposes an unnatural breathing pattern on the patient, causing discomfort to the patient, more sedative or inotropic drugs need to be given to avoid the patient confronting the ventilator, and should be used with caution in patients with severe airway obstructive lung disease and cardiac insufficiency, the representative models are DRAGER EVI -TA4, t5EAR 1000.
6, volume assurance pressure support ventilation
VAPS is a mechanical ventilation mode that can not only provide pressure support ventilation synchronized with the patient, but also provide volume support ventilation with volume assurance, which can maintain the lowest level of tidal volume while having a good synchronization aid. This mode can be used in combination with multiple ventilation modes, represented by the BIRD 8400STI, and similar ventilation mode is the pressure augmentation (PA) in the BERR1000 ventilator.
7.Command ventilation per minute
MMV automatically increases mechanical ventilation only when the patient’s voluntary breathing is insufficient and below the preset minimum minute ventilation, and conversely, patients who regain their voluntary breathing ability will automatically have their ventilation level reduced without changing ventilator parameters. MMV should be used with caution for those patients with shallow fast breathing and insufficient alveolar ventilation, the representative models are DRAGER EVITA4, BEAR 1000.
8.Pressure-regulated volume control
PRVC is actually a kind of pressure-controlled ventilation, in which the ventilator continuously measures the patient’s compliance and achieves the selected tidal volume VT with the minimum airway pressure under the patient’s current lung compliance condition and avoids peak pressure, with good human-machine coordination and constant tidal volume in this mode, which can guarantee the safety of ventilation for patients with unstable autonomic respiratory mechanics.
Similar technologies include Adaptive Pressure Ventilation (APV) in the Hamitton Galileo ventilator, Automatic Flow (AUTO-FLOW) in the DRAGER EVlTA 4 ventilator and Volume Control (VC) in the PB-840 ventilator.
9. Autonomic breathing with target volume ventilation (VV+) including VC+ and VSVC+ is set by the physician for inspiratory time and target tidal volume, and the ventilator gives a conventional volume test breath at the beginning with deceleration wave and inspiratory plateau pressure. To determine the relevant compliance of the lungs, the relevant pressure needed to deliver the set tidal volume is calculated. When the plateau pressure is reached, the ventilator switches to pressure-controlled breathing, and if the delivered tidal volume is less or more than the preset value, the target pressure of the later breath is adjusted to correct the difference.
The VS delivery control is similar to VC+, but VS uses PS to regulate inspiratory flow instead of PC. If the patient breathes above the set volume, both VC+ and VS cause the ventilator to reduce support to control the tidal volume, and the target volume breathing approach reduces the work of breathing in patients with high ventilatory demand, increases patient comfort, reduces the risk of insufficient flow, and improves man-machine Synchronization, the representative models are SIM ENS300/300A.PB840 SERIES.
10.Adaptive Support Ventilation
ASV is a pilot ventilation provided by a physician who sets the ventilation volume per minute according to the weight and clinical situation. ASV ventilation simplifies the setting of parameters and the commissioning of the ventilation process, avoids excessive airway pressure and tidal volume, increases human-machine coordination to reduce mechanical ventilation complications, and can be adapted to various patients and different clinical situations. HAMITTON Galileo. There are also some new ventilation modes such as negative pressure ventilation, high-frequency ventilation, split-lung ventilation and other special ventilation modes, which are not widely used clinically, but have a certain range of application for specific patients.