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Detailed explanation of the working principle of the ventilator and the four major functions of the ventilator
2021-10-03
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Author:Frank

Detailed explanation of the working principle of the ventilator and the four major functions of the ventilator
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The ventilator is a lung ventilation device (Lungventilator), because it can only play the role of sending gas into and out of the lungs, and does not participate in the whole process of breathing. It cannot replace all the functions of the lungs (referring to Gas function). So some people think that it is more accurate to call it a ventilator. The function of the ventilator we are talking about actually refers to its ventilation function.

  The functions of the ventilator can be divided into several categories: main function, secondary function, special function, auxiliary function.

   (1) Main function
(1) Adjust the ventilation pressure or ventilation volume: the constant pressure type ventilator has priority to set the pressure, the ventilation volume is determined by the size of the ventilation pressure, and the fixed volume type ventilator has the priority to set the ventilation volume, and the size of the ventilation pressure is determined by the ventilation volume. size. The current higher-end multifunctional ventilators have both functions. However, the pressure in the airway remains constant when the constant-pressure ventilator is mechanically ventilated, and its ventilation volume is directly proportional to lung compliance. When there is secretion in the airway Or when airway spasm causes increased resistance, as well as lung consolidation or fibrosis with poor compliance, its ventilation volume is not constant enough and it is difficult to master it, and it has been gradually eliminated.

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   (2) Adjust the breathing frequency or breathing cycle: Most ventilators can directly set the ventilation frequency, but some ventilators can change the ventilation frequency by setting the ventilation cycle. Ventilation cycle refers to the total time required to complete an inhalation, exhalation and resting period. If the ventilation cycle is set to 3s, the breathing rate is 20 breaths per minute. At present, the breathing rate of some high-end ventilators can be adjusted quickly, reaching 100-3000 times/min, which is much higher than the normal human breathing rate. This function can cope with some special situations, such as difficult tracheal intubation and bronchoscopy. Examination, severe air leakage of artificial airway, patients after lobectomy and pneumothorax, etc.
(3) Adjust the inspiratory/expiratory ratio: the inspiratory/expiratory ratio during mechanical ventilation depends on three factors, namely, ventilation frequency, ventilation volume (or pressure), and inspiratory flow rate. Under the premise of setting ventilation frequency and ventilation volume, The inspiratory/expiratory ratio can be changed by adjusting the inspiratory flow rate. A more specific example is inverse proportional ventilation (IRV), that is, the inhalation time is longer than the expiration time. It is suitable for patients with pulmonary cirrhosis or fibrosis.
  (4) Adjust the sensitivity of assisted ventilation: The sensitivity usually depends on the negative pressure in the circuit during inhalation, so the greater the negative pressure, the lower the sensitivity, and vice versa. The sensitivity of adult assisted ventilation should be adjusted between 0~-3cm water column.

   (two) secondary function
(1) Adjust the oxygen concentration in the inhaled gas: Use an in-air oxygen mixer to mix 100% pure oxygen with compressed air. The inhaled oxygen concentration can be adjusted to 21-100%. The oxygen concentration adjusted by the device is constant. It is mostly used for indirect driving of ventilator; while for direct driving of ventilator, Venturi device is mostly used, that is, the speed of pure oxygen jet is used to inhale the surrounding air to reduce the oxygen concentration, but the adjusted oxygen concentration is not constant and must have oxygen concentration. Direct monitoring means to prevent oxygen poisoning.
(2) Humidify and warm the inhaled gas: Most ventilators use a thermal humidifier to heat the water to produce steam, which is mixed into the inhaled gas, mixed into the inhaled gas, and at the same time plays a role of heating and heating. The general adjustment temperature is 32~35℃. But some ventilators do not have a heating function.

   (three) special function
(1) Positive end-expiratory pressure (PEEP): This function can support the small airways and alveoli, keep the internal pressure higher than the atmospheric pressure at the end of expiration, and prevent the small airways and alveoli from collapsing. And can increase the functional residual capacity and lung compliance, thereby improving the diffuse function of the lungs. It is mostly used in patients with ARDS (Acute Respiratory Distress Syndrome) and atelectasis.
   (2) Continuous positive airway pressure (CPAP): Its effect is similar to PEEP, which can prevent and reverse the closure of small airways and alveolar collapse, increase intrathoracic pressure, save effort in inhalation, and feel comfortable.
(3) Pressure support (PSV): This is an auxiliary ventilation pressure function, that is, the patient triggers ventilation first, and the ventilator gives the patient a certain level of positive pressure support during exhalation to reduce the patient's work during inhalation. It is conducive to the recovery of respiratory muscle function and is easy for patients to accept. It can slow down the breathing rate and is a means of evacuating the ventilator.
   (4) Sigh function (SIGH): This function is only used for long-term intermittent positive pressure ventilation (IPPV), which can fully expand the alveoli, but is likely to cause barotrauma. It should be used with caution in patients with lung bullae.
   (5) Intermittent mandatory ventilation (IMV) and synchronized intermittent mandatory ventilation (SIMV): It can organically combine spontaneous breathing and IPPV to ensure the effective ventilation of patients, and patients with early respiratory failure are easy to accept SIMV and drones. Used with CPAP to treat ARDS. These two functions are generally used for patients with good spontaneous breathing, and are mostly used before weaning.
(6) Minute Mandatory Ventilation (MMV): This function guarantees the ventilation volume per minute. If the voluntary ventilation volume is lower than the set value, the insufficient part will be automatically replenished by the ventilator. If the voluntary ventilation volume is greater than the set value or equal to the set value Value, the ventilator automatically stops the gas supply. Most suitable for patients with unstable spontaneous breathing.
   (7) Ventilator instead of ventilation (BUV): When the ventilator is running, if its self-check system finds a systematic error or the ventilator's power supply voltage is lower than 90% of the rated voltage, it will automatically be converted to BUV. The ventilator substitute ventilation conditions are pre-set by the ventilator manufacturer. When the ventilator substitutes for ventilation, the ventilator automatically ventilates according to the set conditions.
   (8) Separate lung ventilation (DLV, ILV): Separate the two lungs with a double-lumen intubation, and give different forms of ventilation, called separate lung ventilation. It is mainly used for patients with severe pulmonary bullae or lung abscess on one lung, and patients with normal lung on the other side, and it is also mostly used in thoracotomy.
   (9) Bi-level positive airway pressure (BiPAP): Adjust two pressure levels and time respectively, both pressures are pressure controlled, and the air flow rate is variable. This is a relatively new way of ventilation, and the prospects for development are greater.
   (10) Safety valve opening (SVO): When the power supply is interrupted or the ventilator detects a serious error, the safety valve opens automatically, and the patient can still breathe air.

   (four) auxiliary function
(1) Monitoring function: Modern ventilators have relatively complete monitoring functions. In addition to monitoring the basic ventilation functions of the ventilator such as ventilator frequency, tidal volume, and airway pressure, it can also perform blood oxygen saturation, airway resistance, and lung ventilation. Compliance and vital capacity monitoring. The medical staff can grasp the working status of the ventilator and the patient's condition changes in a timely manner.
   (2) Alarm function: The multifunctional ventilator uses a combination of optics and acoustics to give an alarm. The alarm content generally includes power supply, air supply status, respiratory frequency, tidal volume; airway pressure, temperature, exhalation/inhalation ratio, etc.
(3) Recording function: The high-end multifunctional ventilator also has a recording function, which can be directly connected to a printer, can review and print important parameters, waveforms, trend graphs and charts of mechanical ventilation in the past 12 hours, and can be connected to the monitoring system To store, display and record clinical data. At present, the country has higher and higher requirements for environmental protection and greater efforts in link governance. This is a challenge but also an opportunity for PCB factories. If PCB factories are determined to solve the problem of environmental pollution, then FPC flexible circuit board products can be at the forefront of the market, and PCB factories can get opportunities for further development.