What does a low pressure alarm on a Mechanical Ventilator (MV) indicate?

Low Pressure Alarm on Mechanical Ventilator: Causes and Response

A low pressure alarm on a mechanical ventilator indicates that the delivered airway pressure has fallen below the set threshold, most commonly due to a circuit disconnection, leak in the system, or loss of tidal volume delivery to the patient. 1

Primary Causes of Low Pressure Alarms

The low pressure alarm activates when inadequate pressure is generated during the ventilator cycle, signaling potential failure to deliver the prescribed breath. 1 The three main system components that can cause this alarm are:

1. Circuit Disconnections and Leaks

• Complete disconnection at any point between the ventilator and patient (most common cause) 1
• Partial leaks in the breathing circuit, including loose connections at the Y-piece, humidifier, or ventilator outlet 1
• Endotracheal tube cuff leak allowing gas to escape around the tube 2
• Chest tube air leak in patients with pneumothorax or bronchopleural fistula 3

2. Patient-Related Causes

• Extubation (accidental or self-extubation) 3
• Tube migration into the pharynx or esophagus 3
• Decreased respiratory effort in spontaneous modes when patient stops triggering breaths 1
• Apnea in pressure support or spontaneous modes 4

3. Equipment Malfunction

• Oxygen supply failure or low gas source 3
• Ventilator malfunction affecting pressure generation 3
• Exhalation valve problems preventing pressure buildup 1

Systematic Response Algorithm

When a low pressure alarm sounds, follow this three-limbed approach to rapidly localize the problem: 1

Immediate Actions (First 10-15 seconds)

1. Assess patient first: Look at the patient's chest rise, skin color, and level of consciousness 1
2. Check pulse oximetry: Verify oxygenation status 5
3. If patient is in distress: Disconnect from ventilator and manually ventilate with bag-valve-mask using 100% oxygen while troubleshooting 1

Circuit Inspection (Next 15-30 seconds)

1. Trace the circuit from ventilator to patient, checking all connections 1
2. Inspect the Y-piece and patient connection point for disconnection 1
3. Check humidifier and inline suction catheter connections 1
4. Verify endotracheal tube position and cuff integrity 3, 2

Ventilator Assessment

1. Check gas supply: Verify oxygen and air sources are connected and pressurized 3
2. Review ventilator settings: Ensure alarm thresholds are appropriately set 6
3. Assess for equipment failure: Look for error messages or malfunction indicators 3

Critical Pitfalls to Avoid

Do not assume the alarm is false - Studies show that equipment-related problems, particularly those involving ventilation and artificial airways, are the main cause of adverse events during mechanical ventilation. 3 While alarm fatigue is real (with <15% of alarms being clinically actionable), 6 low pressure alarms have high clinical relevance and should never be ignored.

Alarm-defeating circumstances can occur when: 1

• The low pressure threshold is set too low, missing significant leaks
• Multiple simultaneous faults exist (e.g., partial disconnection plus decreased patient effort)
• The alarm is silenced or disabled inappropriately

In spontaneous breathing modes (pressure support, CPAP), low pressure alarms may indicate: 4, 7

• Patient has stopped triggering breaths (apnea)
• Inadequate inspiratory effort to generate trigger pressure
• This requires different troubleshooting than controlled modes

Alarm Configuration Recommendations

Set low pressure alarm threshold at 5-10 cm H₂O below the typical peak inspiratory pressure for that patient. 6 This individualized approach (rather than default settings) reduces nuisance alarms while maintaining safety. 6

Essential alarm settings that must be functional include: 3

• Apnea alarm
• Circuit disconnect alarm
• Low gas source alarm
• High peak airway pressure alarm

For patients on mouthpiece ventilation, special considerations apply as disconnection alarms activate frequently during normal use - these require specific ventilator settings with appropriate tidal volume and inspiratory time combinations to prevent nuisance alarms. 7

When Manual Ventilation is Required

If the cause cannot be rapidly identified or corrected, default to manual bag-valve-mask ventilation with 100% oxygen until the problem is resolved. 1 This ensures patient safety while allowing time for systematic troubleshooting without compromising oxygenation or ventilation.