Summary of common ventilator alarm causes and solutions (Part 1)

The ventilator must have the function of issuing alarms for various events that require warning. The alarms include both voice-controlled alarms and light-controlled alarms.
The American Society for Respiratory Therapy recommends that ventilator alarms be divided into three levels according to their priority and urgency:
Level 1, immediately life-threatening situation;
Level 2, potentially life-threatening situations;
Level 3, conditions that are not life-threatening but may be harmful to the patient.
Most ventilators set the first-level alarm to a continuous screaming alarm, and set the second- and third-level alarms to intermittent, soft-sounding alarms. The alarm should be set in a state that is sensitive enough to detect critical events without causing false alarms.
1. Pressure alarm
The pressure alarm is an important protective device of the ventilator and is mainly used to monitor the pressure of the patient's airway. The setting of alarm parameters is mainly based on the patient's normal airway pressure level. The high-pressure setting is usually 10cmH2O higher than the actual inspiratory peak pressure, and the limit value generally does not exceed 45cmH2O. The low pressure is set at the lowest pressure level that can maintain inhalation, and is generally set to 5 to 10cmH2O lower than the peak inspiratory pressure.

2. Airway high pressure alarm
Common reasons:
(1) Ventilator. Abnormal operation (inhalation valve and/or exhalation valve failure, pressure sensor damage, etc.).
(2) Loop. Twisted, discounted, stressed, condensation accumulation.
(3) Artificial airway. The lumen is narrow, twisted, discounted, secretions blocked, artificial airway prolapsed, intubation is too deep, the end adheres to the wall, and the air bag is blocked.
(4) Patients. Cough, bronchospasm, airway secretions, reduced lung compliance, pneumothorax, pleural effusion, reduced chest wall compliance, human-machine incoordination, etc.
(5) Human factors. Improper setting, such as the high pressure alarm upper limit is set too low.
deal with:
The basic principle is to ensure ventilation and oxygenation of the patient and avoid complications. No matter what the cause of the high-pressure alarm is, you should first determine whether the patient's airway is unobstructed and whether there is basic ventilation and oxygen protection. To determine the cause of high pressure, attention should be paid to the combination of airway pressure, clinical manifestations of the patient, physical examination (auscultation of breath sounds) and observation of the ventilator waveform.
First, check whether the patient's vital signs are stable. If the vital signs are not stable, the ventilator should be disconnected and a simple respirator should be used to assist ventilation. If the ventilation is smooth and the pulse oxygen saturation (SPO2) remains normal, it means that the ventilator and circuit factors are the cause. Attention should be paid to solving the problems of the ventilator itself and the ventilator circuit. If ventilation is not smooth and SPO2 cannot maintain normal, it means that there is no problem with the ventilator itself and the circuit. The ventilator should be connected again, mechanical ventilation should be continued, and further physical examination should be carried out to find an artificial airway. and patient factors.
If the vital signs are stable, use the volume control/assist mode to observe the time pressure curve, conduct respiratory mechanics analysis, and observe the time pressure curve. If the airway peak pressure increases but the plateau pressure remains unchanged, the reason is an increase in airway resistance, and sputum should be suctioned in time. Use tube suction to remove secretions, blood clots, aspirated vomitus, etc., avoid twisting, discounting of the circuit artificial airway and accumulation of condensation water, relieve bronchospasm, and if necessary, use bronchoscopy to suction sputum and observe whether there are phlegm scabs, tumors, etc.; such as The airway peak pressure increases, and the plateau pressure also increases, indicating a decrease in compliance or an increase in PEEP. The lungs should be observed with a chest X-ray promptly, and thoracic and abdominal causes should be searched for.
When putting down the sputum suction tube, if the sputum suction tube extends >25cm and improves after sputum suction, it may be due to sputum blockage; if there is no improvement or the improvement is not obvious, attention should be paid to whether the patient's spontaneous breathing is antagonistic or inconsistent with mechanical ventilation, such as The ventilator is set to have a short inhalation time, but the patient has strong spontaneous breathing. At this time, the patient inhales, but the ventilator has started to exhale, causing human-machine confrontation, or due to patient anxiety, panic, pain, or other reasons ( Respiratory distress caused by hypovolemia, CO2 retention, shock, central nervous system lesions, etc.) forces human-machine confrontation or incoordination; sedation, analgesia, and ventilator parameters adjustment (increased inspiratory time, Increase ventilation and/or oxygen concentration), correct the primary cause, etc.; the suction tube cannot be extended >25 cm, as the tracheal tube may be blocked. Adjust the head position and observe whether the tracheal tube is bitten or the bronchoscope is blocked. There are no airway tumors, dry phlegm, etc., otherwise the patient will be reintubated.

3. Airway low pressure alarm
Common reasons:
(1) The ventilator circuit is leaking. The patient is disconnected from the ventilator, whether the pipe is broken, whether there is a needle hole, whether the circuit connection is loose, whether the water bottle is tightened, whether the humidifier water injection port is tightly capped, whether the humidifier temperature probe falls off, whether the exhalation valve is not tightly closed or improper installation.
(2) Airway leakage. If the air bag leaks, is under-inflated or ruptured, the cuff should be properly inflated or the tube should be replaced; the endotracheal tube is displaced to the supraglottic airway.
(3) Bronchopleural fistula and chest drainage catheter leakage.
(4) The patient’s inhalation force is too strong.
(5) Abnormal operation of the ventilator: Abnormal pressure sensor, air leakage inside the ventilator (exhalation valve leakage, such as valve rupture or leakage, loose sealing or improper connection).
(6) The lower alarm threshold is improperly set.
(7) Insufficient air source causes ventilation volume to decrease.

deal with:
When a low-pressure alarm occurs, you should first check to see if the patient is still being ventilated. If the patient does not receive basic ventilation guarantees, you should immediately remove the patient from the ventilator, replace the ventilator with a simple respirator or replace it with another ventilator. After promptly finding and removing the cause of air leakage, the alarm threshold should be reset and check whether the set threshold is appropriate. When air leakage is suspected, use the simulated lung to determine the location of the air leak. If the ventilator can ventilate normally when connected to the simulated lung, it means that the air leak may occur at the patient end. Otherwise, look for factors in the ventilator circuit.

4. Volume (exhaled air volume) alarm
Exhaled tidal volume low limit alarm
The alarm starts when the average tidal volume measured in 4 breaths is less than the set alarm lower limit.
Common reasons:
There is air leakage in the pipeline, the tidal volume is set too low, the alarm setting is too high, the patient's inspiratory force is weak in spontaneous breathing mode, the mode is improperly set, and the volume sensor is faulty.
deal with:
Check the pipeline to determine whether there is air leakage; if the patient's inspiratory strength is insufficient, increase the PSV pressure or change the A/C mode; set an appropriate alarm range according to the patient's weight; use a simulated lung to check the air supply of the ventilator; use a tidal gauge to monitor the air supply Tidal volume to determine whether the ventilator tidal volume sensor is accurate.

5. Exhaled tidal volume high limit alarm
This alarm is usually a third-level alarm, but if the alarm occurs more than three times in a row, it will become a first-level alarm.
Common reasons:
It is common in patients with enhanced spontaneous breathing, such as respiratory distress, severe metabolic acidosis, or when the patient's condition improves but ventilatory support is too high, etc. It often indicates that the patient may have resistance or incoordination between spontaneous breathing and the ventilator.
deal with:
For methods, see High Pressure Alarm. Also check whether the set ventilation mode, tidal volume, respiratory rate and other parameters are appropriate. Assess for changes in patient compliance or airway resistance.

6. Flow (exhaled air volume per minute) alarm
High limit or low limit alarm of exhaled air volume per minute: a high limit alarm indicates hyperventilation (automatic triggering of the machine or triggering by the patient too quickly); a low limit alarm may be due to apnea, patient circuit disconnection or hypoventilation.
Minute expiratory volume low limit alarm
Common reasons:
(1) Air leakage in the ventilator circuit or air bag: The exhaled tidal volume is significantly less than the preset (inhaled) tidal volume, indicating the existence of air leakage in the ventilator circuit.
deal with:
Extract the gas from the endotracheal tube balloon and re-inject it. If the balloon ruptures, replace the catheter; if the expiratory/inspiratory valve ruptures, replace it in time; if the cannula is in the wrong position, adjust the cannula position; and perform other symptomatic treatment.
(2) Patient's reasons: Such as multiple alarms caused by excessive inspiratory pressure (for example, patients with severe asthma have severe airway spasm when they are under control, and the peak airway pressure reaches 70-80cmH2O, making it difficult to blow air in); the patient's condition worsens and he becomes independent Breathing is weakened, trigger sensitivity is too low and does not trigger the ventilator; sputum obstruction.
deal with:
Relieve spasms, adjust trigger sensitivity or change modes, suction, etc.
(3) Human factors: The limit setting of the low limit alarm of exhaled volume per minute is too high; the ventilator mode and parameter settings are improper. For example, when applying PSV, SIMV or SIMV+PSV ventilation mode, the patient's breathing frequency is too slow and the tidal volume is set too high. Small, the low limit of minute expiratory volume may have intermittent alarm.
deal with:
Adjust parameters or change the breathing mode, and pay attention to appropriately increasing the inspiratory time, inspiratory flow rate, etc. according to the situation.
(4) Machine failure: such as damage to the expiratory flow sensor, failure of the potentiometer that controls the gas output, etc.
deal with:
Call maintenance personnel to check and eliminate corresponding faults.