Understanding PAP Mode and Setting
Table of Contents
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PAP Machine Modes
There are two types of breathing modes in a typical non-invasive ventilator: one is pressure-controlled breathing mode (PCV) and the other is spontaneous breathing mode (PSV); the pressure-controlled breathing mode can be triggered by the patient or the machine, and the switch is through time. The spontaneous breathing mode is triggered and switched by the patient.
Therefore, most non-invasive ventilators have four modes.
Single-level mode-CPAP mode: continuous positive pressure mode.
Bi-level mode (BiPAP)-S mode: trigger mode (spontaneous), T mode: time control mode (timed), S/T mode: spontaneous breathing/time control automatic switching mode.
Spontaneous breathing
During spontaneous breathing, inhalation is negative pressure and exhalation is positive pressure.
S mode: trigger mode (spontaneous)
This mode is equivalent to the invasive PS+PEEP mode, which provides respiratory support during the inhalation phase. However, this mode must be used when the patient has strong spontaneous breathing. Each breath needs to be triggered by the patient. When the patient does not trigger, the PAP machine does not deliver air. As shown in the figure, the pressure drops before inspiration at A, which means that the patient triggers the delivery of air for this breath. B is the switching point between inspiration and exhalation, which is a spontaneous switch.
- Suitable for mild patients with stable spontaneous breathing. Breathing is completely triggered by the patient. In this mode, the PAP ventilator detects when the patient inhales and exhales, and can follow the patient’s spontaneous breathing frequency and provide appropriate pressure support.
- The trigger mode is used when the patient is able to trigger IPAP whether awake or asleep and does not have sleep apnea (without backup ventilation, the patient with sleep apnea stops breathing during sleep at night, resulting in an inability to trigger breathing, leading to suffocation). However, the patient can control breathing independently and can switch to EPAP independently. This mode is contraindicated for patients who have no spontaneous breathing, or whose spontaneous breathing is weak and cannot trigger the PAP ventilator to deliver air.
- The difference between the IPAP and EPAP settings determines the pressure support provided by the device.
T mode: time control mode (timed)
Time-triggered controlled ventilation, time trigger (C) time conversion (D), PAP machine completely controls the patient’s breathing, suitable for patients without spontaneous breathing or unable to trigger the PAP ventilator independently.
Characteristics of T mode: Breathing is completely determined by the PAP ventilator, and the breathing cycle is completely determined by the PAP machine.
- It is suitable for patients with weak breathing or no spontaneous breathing, but who are unable to undergo invasive PAP ventilation. If the patient has strong breathing ability, it is easy for a patient-machine conflict to occur due to asynchrony. Basically, this mode is not used alone, and the S/T mode is generally used.
- Time triggering is also called forced triggering, which means that the PAP machine will forcefully deliver air according to the respiratory rate you set. For example, if the respiratory rate is set to 20 times/minute, the ventilator will deliver air every 3 seconds, regardless of whether the patient needs to inhale at this time.
- The parameters that need to be set are: IPAP, EPAP, Ti (inspiratory time), and f (respiratory rate).
S/T mode: (spontaneous breathing/time control automatic switching mode)
The S/T mode is safer than the S mode and is the most commonly used mode. When the patient has no spontaneous breathing or weak spontaneous breathing, the T mode will be forced to start once. As shown in the figure, the pressure drops before the first two gas deliveries (A), which means that these two gas deliveries were triggered by the patient, and the inhalation and exhalation switch to spontaneous conversion (B).
However, the patient did not trigger it later, and the ventilator will start from the beginning of the previous gas delivery and wait until 60/f (if the respiratory frequency f is 12, the PAP machine ventilator will wait for 60/12, which is 5 seconds). If the patient has not triggered it at this time (that is, at point C), the PAP ventilator will force a gas delivery, that is, T mode, and the gas delivery time this time is the set Ti, and the inhalation and exhalation switch to time conversion (D).
Features of S/T mode:
- Triggering link: spontaneous triggering or forced triggering. That is when the patient can spontaneously inhale and trigger the PAP ventilator to deliver air within the set respiratory rate cycle, it is S mode. The PAP ventilator gives a higher pressure (IPAP) when the patient inhales and a lower pressure (EPAP) during the exhalation phase. If the PAP machine ventilator cannot be triggered to deliver air, the PAP machine will force ventilation, which is T mode. When the spontaneous breathing rate is greater than the frequency set by the PAP machine, the patient triggers the PAP machine to deliver air on his own. The actual breathing rate is related to the patient. At this time, the frequency and inhalation time set by the PAP machine do not take effect. When the spontaneous breathing rate is less than the frequency set by the PAP machine, the PAP machine is forcibly triggered to deliver air.
- Air supply link: Whether entering S mode or T mode, the PAP machine provides inspiratory positive airway pressure (IPAP) and expiratory positive airway pressure (EPAP) according to the set pressure. The difference is that when entering S mode, the respiratory rate, inspiratory time, and inspiratory-expiratory ratio are all controlled by the patient independently, and have nothing to do with the respiratory rate, inspiratory time, or inspiratory-expiratory ratio set by the PAP machine. When entering T mode, the respiratory rate is forced ventilation by the PAP machine at the set frequency, that is, the respiratory rate, inspiratory time or inspiratory-expiratory ratio set by the PAP machine are all effective.
- Switching link: In S mode, it is flow rate switching, and in T mode, it is time switching.
The advantage of S/T mode is that it allows spontaneous breathing triggering, has a backup respiratory rate, ensures minimum ventilation guarantee, and can increase tidal volume.
CPAP mode: (Continuous Positive Airway Pressure mode)
The CPAP machine only provides constant pressure, CPAP=IPAP=EPAP, and by increasing the pressure support during exhalation and inhalation, it opens the airway, reduces airway resistance, and ensures gas diffusion.
In CPAP mode, the CPAP machine provides the same pressure in both the inspiratory and expiratory phases. The entire ventilation process is completed by spontaneous breathing. In essence, the spontaneous breathing baseline with zero pressure as the baseline is moved up by a CPAP pressure, which is conducive to opening the airway.
It is mainly used for obstructive sleep apnea syndrome, pulmonary edema, etc. This mode does not provide inspiratory pressure support.
The characteristics of this mode are:
- It is suitable for mild patients with stable spontaneous breathing and is often used for patients with type I respiratory failure, pulmonary edema, and obstructive sleep apnea. These patients do not need to increase tidal volume.
- The patient needs to have strong spontaneous breathing, and all the breathing work is done by the patient. There is no triggering or switching during the operation of the ventilator. Instead, it continuously provides an identical pressure in the inspiratory and expiratory phases (i.e. CPAP=IPAP=EPAP), helping the patient reduce airway resistance and maintain an open upper airway.
Advantages: Patients can breathe freely and are comfortable
- Disadvantages: The tidal volume is not accurate and basically does not provide additional ventilation assistance
PAP Machine Adjustment Parameters
The common parameters and adjustments of non-invasive PAP ventilators follow the principle of “adjusting from low to high, step by step, and patient tolerance”. Common parameters of non-invasive ventilators include: Inspiratory Positive Airway Pressure (IPAP), Expiratory Positive Airway Pressure (EPAP), Rise Time, Inspiratory Time (Ti), Backup Respiratory Rate (f, also known as BPM, RR), Oxygen Concentration (FiO2), and Delayed Pressure Rise Time, but it is not commonly used.
Inspiratory Positive Airway Pressure (IPAP):
It represents the pressure output by the PAP machine during the patient’s inspiratory phase and refers to the high-pressure phase pressure delivered after the patient’s inspiratory trigger or the PAP machine triggers. Its function is that the higher the IPAP value is set, the greater the support output by the PAP machine, the higher the breathing work completed by the PAP machine, and the less breathing work the patient needs to complete independently; it is beneficial to increase the ventilation level and reduce the partial pressure of carbon dioxide, especially the higher the pressure support (PS) value (PS=IPAP-EPAP), the greater the support for the patient and the higher the tidal volume.
IPAP adjustment principles: commonly used range 4 ~ 40cmH20, the initial setting is usually IPAP 8 ~ 12 cmH2O (CPAP mode, can start from 4 cmH2O) increase once every 2 to 6 minutes, increase or decrease IPAP between 4 and 40cmH20 in increments of 0.5, when the Flex function is enabled, the maximum value should not exceed 25cmH20 to avoid causing gastric bloating, in order to obtain better human-machine coordination.
Expiratory positive airway pressure (EPAP):
It refers to the low-phase pressure that the PAP machine maintains in the expiratory phase after switching to the expiratory state, which is equivalent to the PEEP of invasive ventilators. Its function is to increase functional residual capacity, increase oxygenation, expand trapped alveoli, improve V/Q imbalance, and reduce the work of breathing; higher EPAP pressure can generate more flow at the expiratory port, which helps to discharge carbon dioxide in the circuit and prevent the potential danger of repeated inhalation.
EPAP adjustment principle: generally start from 4cmH20, the common range is: 4~25cmH20, generally EPAP of 4 cmH20 can effectively remove carbon dioxide from the mask and the tube. The higher the EPAP, the cleaner the carbon dioxide in the mask and the tube is removed during the exhalation phase, and the less repeated breathing.
Positive pressure support (PS) of bi-level machine:
This value is not set directly on the non-invasive PAP ventilator but is the difference between the inspiratory pressure (IPAP) and the expiratory pressure (EPAP) (i.e. PS = IPAP-EPAP). The larger the PS value, the larger the tidal volume, and vice versa. This is the most important factor affecting the tidal volume. The PS value affects the tidal volume. If it is a dual-level mode with different pressures, the PS value is generally required to be ≥5cmH20. If it is to better improve carbon dioxide retention, it is generally recommended that PS ≥10cmH20 is preferred.
Respiratory rate (RR, BPM, f):
In T mode, the respiratory rate set by the ventilator is the actual respiratory rate of the patient, which is generally set to 12 to 20 times/minute. In S/T mode, the set respiratory rate is the backup rate, which is generally set to 10 to 20 times/minute.
That is to say, if the patient breathes during the set respiratory cycle, this setting value will not work (or is called a backup effect). If the patient does not breathe or the breathing cannot trigger the breathing and air delivery during the set respiratory cycle, this setting value will work. If the respiratory rate is set too low, the minimum ventilation demand cannot be guaranteed, and if it is set too high, it may interfere with the patient’s spontaneous breathing.
- If the patient’s spontaneous breathing rate is basically normal (16-24 times/min) or significantly weakened, or even stopped. The breathing rate can be set at 16~20 times/min.
If the patient’s spontaneous breathing rate is significantly faster (>28 times/min), the initial breathing rate should not be set too low, otherwise the ventilator will resist and increase the work of breathing. The breathing rate can be set close to or slightly lower than the patient’s spontaneous breathing. Later, as the cause of the increase in spontaneous breathing rate is removed (hypoxia, metabolic acidosis, pain, mental tension, etc.), the breathing rate will be gradually reduced to a normal level.
For patients with obstructive pulmonary diseases with increased airway resistance, it is suitable to use a slow and deep breathing rate first. That is, a low breathing rate (12~15 times/min) and a high tidal volume.
For patients with restrictive lung disease, since the airway resistance is basically normal, and the main manifestations are decreased lung compliance and a decrease in effective gas exchange lung units, a slightly faster and deeper respiratory rate (18-24 times/min) should be used.
For patients with normal lung function, such as respiratory failure caused by respiratory center influence, ventilator paralysis or paralysis, the respiratory rate does not consider the above factors. Set it to 12-15 times/min (except for patients with too fast a rate).
In diseases with restrictive ventilation disorders such as ARDS, ventilation with a faster frequency supplemented by a smaller tidal volume is beneficial to reduce the work done to overcome elastic resistance and the adverse effects on the cardiovascular system.
Inspiratory time (Ti):
The Ti set by the PAP machine controls the patient’s inhalation time in T mode. It has no effect in S mode and is determined by the patient’s spontaneous inhalation time. The inhalation time of the PAP machine is generally set to 0.8 to 1.2 seconds. In special cases, it is adjusted accordingly according to the patient’s condition. In other words, it depends on the condition and the purpose of the PAP machine. If it is to reduce carbon dioxide, the inhalation time should be set shorter. If it is to improve hypoxia, it should be set longer. The longer the inhalation time, the longer the pressure platform is maintained. The longer the inflation time, the larger the tidal volume. This is the second most important factor affecting the tidal volume (ventilation volume).
Oxygen concentration (FiO2):
The minimum oxygen flow rate that can maintain oxygen saturation > 90% is generally required to be no less than 5L/min, so that oxygen can enter the pipeline more smoothly. Different connection methods for oxygen supply, oxygen flow rate, and patient breathing patterns will affect the actual FiO2. For patients with COPD and chronic type II respiratory failure, it is not recommended to adjust the oxygen concentration too high. It is generally required to evaluate the effect 1 to 2 hours after treatment. The basis for improvement is mainly based on clinical manifestations and blood gas analysis standards.
- When using a PAP machine for the first time, in order to quickly correct hypoxia, a higher concentration of FiO2 (>60%) can be used, but the time should be controlled within 30min~1h, and then FiO2 should be gradually reduced to a relatively safe level of <60%.
Generally stabilized at 40~50%.
For patients whose hypoxemia has not been completely corrected, hypoxia cannot be corrected by simply increasing FiO2. Other methods, or PEEP, etc., should be used.
For patients with obvious improvement in hypoxemia, it is best to set FiO2 at 40%~50%.
In short, the principle of Fio2 setting is to maintain the lowest FiO2 level under the premise of 60mmHg PaO2.
Precautions: Be alert to oxygen poisoning when >50%. At 100%, the duration should not exceed half an hour to one hour.
Pressure rise time (Rise Time):
It refers to the speed at which the pressure reaches the target pressure (i.e. IPAP) after triggering inspiration. Its purpose is to improve comfort and reduce the work of breathing. The pressure rise time is generally set to 2-3 levels (or 0.05-0.3s). If it rises too fast, the patient will feel a large airflow; if it rises too slowly, it will increase the patient’s work of breathing.
Pressure delay rise time: Different from “pressure rise time”, “pressure delay rise time” helps patients adapt to ventilation by gradually increasing the inspiratory and expiratory pressure (IPAP and EPAP/CPAP) from auxiliary treatment to the set pressure during the set interval. It is generally set to 5-30 minutes, and the ventilator gradually increases to the target pressure, which helps reduce the patient’s fear and intolerance when initially wearing the machine, but it is not suitable for use in severe dyspnea or rescuing patients.
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