How to operate a ventilator

A ventilator is a medical device that assists or completely controls a patient's breathing so that the patient can receive enough oxygen to maintain respiratory function. However, incorrect use may lead to serious complications and even worsen the patient's condition. Let’s summarize a few points on how to operate a ventilator:

1. Assisted controlled ventilation

Assisted controlled ventilation (ACV) is a combination of assisted ventilation (AV) and controlled ventilation (CV). When the patient's spontaneous breathing frequency is lower than the preset frequency or is unable to reduce the airway pressure or generate a small amount of airflow, the ventilator is triggered to deliver air. When the ventilator is activated, the ventilator performs positive pressure ventilation at the preset tidal volume and ventilation frequency, that is, CV; when the patient's inspiratory force can trigger the ventilator, ventilation is performed at any frequency higher than the preset frequency, that is, AV. The result , it is assisted ventilation when triggered, and controlled ventilation when not triggered.

parameter settings
Volume switching A-C: trigger sensitivity, tidal volume, ventilation frequency, inspiratory flow rate/flow rate waveform
Pressure switching A-C: trigger sensitivity, pressure level, inspiratory time, ventilation frequency

Features: A-C are common modes of mechanical ventilation for ICU patients, which can provide ventilation that is basically synchronized with spontaneous breathing. However, when the patient cannot trigger the ventilator, CV can ensure the minimum commanded minute ventilation volume to ensure ventilation for patients with unstable spontaneous breathing. Safety.

2. Synchronized intermittent mandatory ventilation

Synchronized intermittent mandatory ventilation (SIV) is a breathing mode that combines spontaneous breathing and controlled ventilation. Within the trigger window, the patient can trigger mandatory positive pressure ventilation synchronized with spontaneous breathing. The patient is allowed to breathe spontaneously between two mandatory ventilation cycles. Breathing can be performed with a preset volume (volume-controlled SIMV) or a preset pressure (pressure-controlled SIMV).

Parameter settings: tidal volume, flow rate/inspiratory time, control frequency, trigger sensitivity. When pressure is used to control SIMV, the pressure level and inspiratory time need to be set.

Features: Ensure the lowest minute volume by setting the frequency and tidal volume of IMV; SIMV can cooperate with the patient's spontaneous breathing, reduce the antagonism between the patient and the ventilator, reduce the hemodynamic negative effects of positive pressure ventilation, and prevent potential Complications, such as barotrauma, etc.; changing the level of respiratory support by changing the preset IMV frequency, that is, from full support to partial support, can be used to wean patients who have been on the machine for a long time; because the patient can use more respiratory muscles group, so it can reduce respiratory muscle atrophy; inappropriate parameter settings (such as low flow rate) increase the work of breathing, leading to excessive fatigue of respiratory muscles or respiratory alkalosis due to hyperventilation, and dynamic excessive lung expansion in COPD patients.

3. Pressure support ventilation

Pressure support ventilation (PSV) is a partial ventilation support mode. It is a mechanical ventilation mode that is triggered by the patient, pressure target, and flow switched. That is, the patient triggers ventilation and controls the respiratory rate and tidal volume. When the airway pressure reaches the preset pressure support level, and when the inspiratory flow rate decreases below the threshold level, the inspiratory phase is switched to the expiratory phase.

Parameter settings: pressure, trigger sensitivity, some ventilators have pressure rise speed, expiration sensitivity (ESENS).

Features: If the setting level is appropriate, there will be less man-machine confrontation, which can effectively reduce the work of breathing and increase the effectiveness of the patient's inspiratory effort. This kind of ventilation assistance with constant pressure and flow rate waveform can meet the needs of the patient and the ventilation provided by the ventilator. It is not ideal in terms of complete coordination; it has little impact on hemodynamics, including in patients after cardiac surgery; some studies believe that PSV of 5 to 8 cmH2O can overcome the resistance of endotracheal tubes and ventilator circuits, so PSV can be used for weaning During the machine process; the tidal volume of PSV is determined by the compliance and resistance of the respiratory system. When the mechanics of the respiratory system change, it will cause changes in tidal volume. The support level should be adjusted in time. Therefore, for patients with severe and unstable respiratory failure or those with bronchitis Patients with spasms and a lot of secretions should be particularly careful when using it. Aerosol inhalation treatment can lead to insufficient ventilation; if there is a large amount of gas leakage in the circuit, it can cause continuous inspiratory pressure assistance, and the ventilator cannot switch to the expiratory phase; breathing Patients with central drive dysfunction can also cause changes in minute ventilation, or even apnea and suffocation. Therefore, background ventilation needs to be set up.

4. Continuous positive airway pressure

Continuous positive airway pressure (CPAP) means that under spontaneous breathing conditions, the airway maintains positive pressure during the entire respiratory cycle (during inhalation and expiration), and the patient completes all the work of breathing. It is called positive end-expiratory pressure (PEEP). Special techniques under spontaneous breathing conditions.

Parameter settings: just set the CPAP level

Features: CPAP has various advantages and effects of PEEP, such as increasing intra-alveolar pressure and functional residual capacity, increasing oxygenation, preventing collapse of airways and alveoli, improving lung compliance, reducing respiratory work, and combating endogenous PEEP; Excessive CPAP pressure increases airway peak pressure and average airway pressure, reduces cardiac blood volume and blood perfusion of important organs such as liver and kidneys. However, during CPAP, spontaneous breathing can make the average intrathoracic pressure slightly lower than the same PEEP. .

5. Bilevel positive airway pressure ventilation

Bilevel positive airway pressure (BIPAP) refers to giving two different levels of positive airway pressure alternately during spontaneous breathing, switching regularly between high pressure level (Phigh) and low pressure level (Plow), and the high pressure time , low-pressure time, high-pressure level, and low-pressure level are each independently adjustable, taking advantage of the reduction in functional residual capacity (FRC) when switching from Phigh to Plow to increase exhaled air volume and improve alveolar ventilation.

Parameter settings: high pressure level (Phigh), low pressure level (Plow) i.e. PEEP, high pressure time (Tinsp), respiratory rate, trigger sensitivity

Features: During BIPAP ventilation, the airway pressure periodically switches between high pressure levels and low pressure levels. At each pressure level, the time ratio of the two-way pressure is independently adjustable. If the Phigh to Plow time is different, it can be changed to an inverse ratio BIPAP or airway. Airway pressure release ventilation (APRV); the patient's spontaneous breathing is less disturbed and inhibited during BIPAP ventilation, especially when the two pressure phases last for a long time, the application of BIPAP has a more obvious effect on increasing the patient's oxygenation than CPAP; During BIPAP ventilation, it is possible to transition from controlled ventilation to spontaneous breathing without changing the ventilation mode until offline. This is the concept of modern ventilation treatment.

2. Setting of tidal volume

In the volume-controlled ventilation mode, the tidal volume should be selected to ensure adequate gas exchange and patient comfort. It is usually selected from 5 to 125ml/Kg based on body weight, and adjusted based on the compliance and resistance of the respiratory system; based on the lung mechanical parameters , to maintain VT when the airway pressure is lowest, the maximum pressure should be lower than 30-35cmH2O to avoid barotrauma and ventilator-related lung injury (VILI); in the pressure-controlled ventilation mode, the tidal volume is determined by the selected target It is determined by the pressure, the resistance of the respiratory system and the patient's spontaneous breathing method; VT is set at the steep section of the P-V curve based on the P-V curve.
According to the lung mechanical parameters, in order to maintain VT at the lowest airway pressure, the highest pressure should be lower than 35cmH2O. The final adjustment should be based on plasma PaCO2 based on blood gas analysis.

3. Setting of respiratory rate

The selection of respiratory frequency is determined based on the ventilation mode, dead space/tidal volume ratio, metabolic rate, target PCO2 level and spontaneous breathing intensity. It should be determined based on the selected mode, tidal volume, dead space/tidal volume, metabolic rate, target PaCO2, etc. ,In principle:
Adults are usually set to 12 to 20 times/min. In acute/chronic restrictive pulmonary disease, it can also exceed 20 times/min based on minute ventilation and target PCO2 level. However, excessive respiratory rate should be avoided to cause gas trapping and increase in PEEPI. Clamp, otherwise in order to overcome the excessively high PEEPI, which will increase the work of breathing and lead to barotrauma, etc., the final precise adjustment of the respiratory frequency should be based on the changes in PH, PaCO2 and PaO2, and comprehensively adjust VT and f.

4. Flow rate adjustment

The ideal peak flow rate should be able to meet the patient's inspiratory peak flow rate needs. The commonly used flow rate for adults can be set between 40 and 60L/min. It is adjusted according to the minute ventilation volume, the resistance of the respiratory system and the compliance of the lungs. When controlling ventilation, due to The inspiratory time is limited and the peak flow rate can be lower than 40 L/min. In the pressure-controlled ventilation mode, the flow rate is determined by the selected pressure level, airway resistance and the patient's inspiratory effort. The flow velocity waveform is commonly used clinically as constant flow (square wave) or deceleration wave or square wave.

5. Inspiratory time/I:E setting

The selection of I:E is based on the patient's hemodynamics, oxygenation status and spontaneous breathing level. Appropriate settings can maintain good human-machine synchronization. The inspiratory time is selected based on hemodynamics, oxygenation and spontaneous breathing. Or the inhalation-to-exhalation ratio. Patients with spontaneous breathing usually set the inhalation time to 0.8 to 1.2 seconds or the inhalation-to-exhalation ratio to 1:1.5 to 2. For patients with controlled ventilation, in order to increase the average airway pressure and improve oxygenation, the inhalation time and Inhalation-to-exhalation ratio, but attention should be paid to patient comfort, monitoring of PEEPI and the impact on the cardiovascular system.

6. Trigger sensitivity adjustment

Under normal circumstances, the pressure trigger is usually -0.5~-1.5cmH2O, and the flow rate trigger is usually 2~5L/min. Appropriate trigger sensitivity settings will obviously make the patient more comfortable and promote human-machine coordination; some studies show that flow rate trigger is better than pressure trigger It can significantly reduce the patient's breathing work; if the trigger sensitivity is too high, it will cause automatic triggering regardless of the patient's exertion; if the trigger sensitivity is set too low, it will significantly increase the patient's inspiratory load and consume additional breathing work.
Under normal circumstances, the pressure trigger is usually -0.5~-1.5cmH2O, and the flow rate trigger is usually 1~3L/min. Appropriate trigger sensitivity settings will obviously make the patient more comfortable and promote human-machine coordination.

7. Inhaled oxygen concentration (FiO2)

In the initial stage of mechanical ventilation, high FiO2 (100%) can be given to quickly correct severe hypoxia. Later, based on the target PaO2, PEEP level, MAP level and hemodynamic status, the set FiO2 can be lowered to less than 50% as appropriate and try to maintain it. SaO2>90%, if the above goal cannot be achieved, PEEP can be added, the mean airway pressure can be increased, and sedatives or muscle relaxants can be used; if appropriate PEEP and MAP can make SaO2>90%, the lowest FiO2 should be maintained.

8. PEEP setting

The function of setting PEEP is to recruit collapsed alveoli, increase mean airway pressure, improve oxygenation, reduce blood return to the heart, reduce left ventricular afterload, and overcome the increase in respiratory work caused by PEEPI. PEEP is often used in type I respiratory failure represented by ARDS. PEEP is set based on the target PaO2 and oxygen delivery, and is considered jointly with FiO2 and VT. Although there is no consensus on the upper limit of PEEP setting, the lower limit is usually at the P-V curve. Low inflection point (LIP) or 2cnH2O above LIP; PEEP adjustment can also be guided according to PEEPI. When the exogenous PEEP level is approximately 80% of PEEPI, the total PEEP will not be increased.