Clinical knowledge of ventilator parameter setting

Clinical knowledge of ventilator parameter setting

Ventilator is a commonly used instrument in clinic. You know how to set the parameters of the ventilator. Welcome to reading.

First, the tidal volume setting of ventilator

The setting of tidal volume is the first consideration of mechanical ventilation. In volume control ventilation, the goal of tidal volume setting is to ensure adequate ventilation and make patients more comfortable. Adult tidal volume is generally 5 ~ 15 ml/kg, and 8 ~ 12 mg/kg is the most commonly used range. The following factors should be considered in the setting of tidal volume: thoracic and pulmonary compliance, airway resistance, compressible volume of ventilator pipeline, oxygenation state, ventilation function and risk of barotrauma. Ventilator-related injuries, such as barotrauma, are caused by improper application of mechanical ventilation. In order to prevent air pressure injury during tidal volume setting, it is generally required that the pressure of airway platform should not exceed 35 ~ 1000 pxh2o. For pressure-controlled ventilation, tidal volume mainly depends on the preset pressure level, patient's inspiratory intensity and airway resistance. In general, the tidal volume level should not be higher than 8 ~ 12 ml/kg.

Second, the ventilator mechanical ventilation frequency setting

When setting the mechanical ventilation frequency of ventilator, ventilation mode, tidal volume, dead space rate, metabolic rate, target level of arterial carbon dioxide partial pressure and patients' spontaneous breathing ability should be considered. For Chengren, the frequency of mechanical ventilation can be set to 8 ~ 20 times/minute. For patients with acute and chronic restrictive ventilation dysfunction, a higher mechanical ventilation frequency (20 times/minute or more) should be set. After mechanical ventilation 15 ~ 30 minutes, the mechanical ventilation frequency should be adjusted according to arterial oxygen partial pressure, carbon dioxide partial pressure and pH value. In addition, the frequency of mechanical ventilation should not be set too fast to avoid lung gas retention and endogenous positive end-expiratory pressure. Once endogenous positive end-expiratory pressure is generated, it will affect pulmonary ventilation/blood flow, increase the patient's respiratory work and increase the risk of barotrauma.

Three, ventilator inspiratory flow setting

Many ventilators need to set inspiratory flow rate. When setting the suction flow, the following questions should be paid attention to:

1. During volume control/auxiliary ventilation, if the patient has no spontaneous breathing, the inspiratory flow rate should be lower than 40 liters/minute; If the patient has spontaneous breathing, the ideal inspiratory flow rate should just meet the needs of the patient's inspiratory peak flow. According to the patient's inspiratory intensity and ventilation per minute, the inspiratory flow rate is generally adjusted to 40 ~ 100 liter/minute. Because the inspiratory flow rate will directly affect the patient's breathing work and man-machine cooperation, it should be paid attention to by clinicians.

2. During pressure controlled ventilation, the peak inspiratory flow rate is determined by the preset pressure level and the inspiratory intensity of the patient. Of course, the maximum inspiratory flow rate is limited by the performance of ventilator.

Four. Setting of Breathing-Breathing Ratio of Ventilator

During mechanical ventilation, the inspiratory-expiratory ratio of ventilator should consider the influence of mechanical ventilation on hemodynamics, oxygenation state and spontaneous breathing level of patients.

1. For patients who breathe spontaneously, when the ventilator assists breathing, the ventilation of the ventilator should be coordinated with the inhalation of the patient to ensure synchronization. Generally, it takes 0.8 ~ 1.2 seconds to inhale, and the ratio of inhalation to exhalation is 1: 2 ~ 1: 1.5.

2. For patients with controlled ventilation, long inspiratory time and high inspiratory rate can increase the average airway pressure and improve oxygenation. However, to prolong the inspiratory time, we should pay attention to monitoring the hemodynamic changes of patients.

3. Inhalation time is too long, patients are not easy to tolerate, and often need to use sedatives or even muscle relaxants. Moreover, short expiratory time will lead to endogenous positive end-expiratory pressure, which will aggravate the interference to circulation. Attention should be paid in clinical application.

Five, fan airflow mode setting

Many ventilators have a variety of airflow modes to choose from. The common airflow modes are deceleration airflow, acceleration airflow, square wave airflow and sine wave airflow. The selection of airflow mode is only applicable to volume control ventilation mode. When pressure control ventilation is used, the ventilator provides deceleration airflow to make the airway pressure reach the set pressure level quickly. In volume controlled ventilation, there are few studies on airflow organization comparison. From the existing data, under the same tidal volume and inspiratory time/respiratory time, different airflow patterns have similar effects on patients' ventilation and ventilation function and respiratory work. Of course, when controlling ventilation by air volume, it is customary to set the airflow mode on the square wave airflow. The effects of different airflow patterns on patients should be further studied and observed.

Six, ventilator oxygen concentration setting

During mechanical ventilation, the setting of oxygen concentration absorbed by ventilator generally depends on the target level of arterial oxygen partial pressure, positive end-expiratory pressure, average airway pressure and the hemodynamic state of patients. Inhalation of high concentration of human oxygen can cause oxygen-induced lung injury, so it is generally required that the human oxygen concentration should be lower than 50% ~ 60%. However, in the choice of human oxygen concentration, we should consider not only the lung injury caused by high concentration oxygen, but also the lung injury caused by high airway and alveolar pressure. For patients with severe oxygenation disorder, the oxygen concentration should be set to make the arterial oxygen saturation >: 88%~90%.

Seven, ventilator trigger sensitivity settings

At present, the inspiratory trigger mechanism of ventilator has two kinds: pressure trigger and flow trigger. Because the ventilator and artificial airway will produce additional resistance, in order to reduce the extra work of patients, the trigger sensitivity should be set at a more sensitive level. In general, the trigger sensitivity of pressure trigger is set to -0.5 ~ -0.5~-37.5pxH20, while the sensitivity of flow trigger is set to 1 ~ 3 liters/min. According to the preliminary clinical study, compared with pressure trigger, flow trigger can further reduce the patient's breathing work and make the patient more comfortable. It is worth noting that when the trigger sensitivity setting is too sensitive, small changes in pressure and flow in the airway will cause automatic trigger, which will make patients feel uncomfortable.

Eight, ventilator positive end-expiratory pressure setting

The main purpose of positive end-expiratory pressure (PEEP) is to increase lung capacity, average airway pressure and improve oxygenation. In addition, positive end-expiratory pressure can also offset endogenous positive end-expiratory pressure and reduce the inspiratory trigger work caused by endogenous positive end-expiratory pressure. However, positive end-expiratory pressure can increase intrapleural pressure, resulting in venous reflux and decreased left ventricular preload. In theory, the setting of positive end-expiratory pressure level should choose the best positive end-expiratory pressure, that is, to obtain the maximum oxygen delivery level, which is difficult to apply in clinic. For ARDS patients, the selection of positive end-expiratory pressure level should be combined with inhalation oxygen concentration, inhalation time, arterial oxygen partial pressure level and target level, oxygen delivery level and other factors. With the development of pulmonary mechanics monitoring (pressure-volume loop), the choice of positive end-expiratory pressure is well-founded. It is generally believed that in the early stage of acute lung injury, the level of positive end-expiratory pressure should be slightly higher than the pressure level at the low turning point of lung pressure-volume ring. For patients undergoing thoracic or epigastric surgery, positive end-expiratory pressure of 3 ~ 125 pH20 during postoperative mechanical ventilation is helpful to prevent postoperative atelectasis and hypoxemia.

Nine, ventilator airway pressure monitoring and alarm settings

The ventilator monitors airway pressure through different parts, and its fundamental purpose is to monitor alveolar pressure. Common pressure measuring components are ventilator, Y-tube and carina. The farther the pressure measurement position is from the alveoli, the greater the difference between the measured pressure and alveolar pressure may be. When the patient inhales, the pressure in the ventilator, Y tube pressure, carina pressure and alveolar pressure decrease in turn, while when the ventilator breathes, the pressure in the ventilator, Y tube pressure, carina pressure and alveolar pressure increase in turn. Only when the air flow rate is zero, the pressure of each part is the same. The pressure measuring part of 900C ventilator is in the ventilator, while the pressure measuring part of Xingang and towing ventilator is in the Y tube.

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