Overview
Definition:
Ventilator dyssynchrony, also known as patient-ventilator asynchrony (PVA), occurs when the patient's spontaneous respiratory effort is not aligned with the mechanical ventilator's delivered breath
This mismatch can lead to increased work of breathing, patient discomfort, prolonged mechanical ventilation, and potential lung injury.
Epidemiology:
The prevalence of PVA varies significantly based on the patient population, ventilator settings, and definitions used, but has been reported in up to 25-60% of mechanically ventilated patients
Surgical patients, especially those with complex pathologies, sepsis, or undergoing prolonged ventilation, are at high risk.
Clinical Significance:
For surgeons, recognizing and managing ventilator dyssynchrony is critical, particularly in the perioperative period and in the ICU
Untreated PVA can impede recovery, prolong ventilator dependence, increase the risk of ventilator-associated pneumonia (VAP), and contribute to patient morbidity and mortality, directly impacting surgical outcomes.
Clinical Presentation
Symptoms:
Patient-reported discomfort or pain related to breathing
Subjective feeling of breathlessness or inability to breathe adequately
Alarms on the ventilator frequently triggering
Patient fighting the ventilator
In sedated patients, it may manifest as increased agitation or restlessness.
Signs:
Visible struggle with the ventilator
Paradoxical chest wall movement
Increased respiratory rate and effort
Increased heart rate and blood pressure
Persistent hypoxemia or hypercapnia despite appropriate ventilator settings
Diaphragmatic fatigue evident on imaging.
Diagnostic Criteria:
No single universally accepted diagnostic criteria exist
However, diagnosis is typically made based on clinical observation of mismatch between patient effort and ventilator delivery, analysis of ventilator waveforms (flow, pressure, volume), and sometimes esophageal manometry
Key indicators include premature cycling, delayed cycling, auto-PEEP, and ineffective triggering.
Diagnostic Approach
History Taking:
Focus on the timeline of ventilator initiation and changes in patient status
Inquire about sedation levels and patient comfort
Review the patient's underlying surgical condition and potential complications contributing to respiratory distress
Assess for risk factors like obesity, COPD, or ARDS.
Physical Examination:
Systematic assessment of respiratory mechanics
Observe chest wall movement for synchrony with ventilator breaths
Auscultate lung fields for air entry and adventitious sounds
Monitor vital signs for signs of distress (tachycardia, hypertension)
Assess for peripheral edema and signs of fluid overload.
Investigations:
Ventilator waveforms: analyze inspiratory and expiratory flow, pressure, and volume curves for abnormalities
Arterial blood gases (ABGs): to assess oxygenation and ventilation status and response to changes
Chest X-ray: to rule out pulmonary complications
Esophageal manometry: to directly measure pleural pressure and diaphragmatic effort (gold standard for detecting dyssynchrony).
Differential Diagnosis:
Pulmonary edema
Pneumonia
ARDS
Bronchospasm
Pleural effusion
Pneumothorax
Sepsis
Anemia
Metabolic acidosis
Neuromuscular weakness
High airway resistance
Ventilator malfunction.
Management
Initial Management:
First, assess the patient-ventilator interface
Check for leaks or disconnections
Optimize sedation and analgesia to reduce patient's drive to fight the ventilator
Adjust ventilator settings cautiously
Identify and address any underlying physiological derangements (e.g., fever, acidosis).
Ventilator Setting Optimization:
Adjust mode of ventilation (e.g., assist-control to pressure support, or vice-versa)
Optimize tidal volume, respiratory rate, PEEP, and flow triggers
Consider inverse ratio ventilation or high-frequency oscillatory ventilation in select cases
Ensure appropriate trigger sensitivity and expiratory trigger sensitivity.
Addressing Specific Dyssynchrony Patterns:
Ineffective triggering: increase trigger sensitivity, ensure adequate flow, or switch to a different mode
Premature cycling: increase expiratory time or decrease tidal volume
Delayed cycling: decrease inspiratory time or adjust flow pattern
Auto-PEEP: decrease tidal volume, decrease respiratory rate, or use expiratory retard
Double triggering: increase peak inspiratory flow or decrease tidal volume.
Advanced Interventions:
Neuromuscular blockade: generally a last resort due to side effects but may be necessary in severe, refractory dyssynchrony
Phrenic nerve pacing: investigational for prolonged ventilation
Tracheostomy: may facilitate patient comfort and weaning in chronic dyssynchrony.
Complications
Early Complications:
Increased patient distress and anxiety
Diaphragmatic fatigue and injury
Increased work of breathing
Barotrauma and volutrauma
Ventilator-associated pneumonia (VAP).
Late Complications:
Prolonged mechanical ventilation and ICU stay
Muscle weakness and deconditioning
Difficulty weaning from the ventilator
Post-ICU syndrome
Increased mortality.
Prevention Strategies:
Close monitoring of patient-ventilator interaction
Individualized ventilator settings based on patient's respiratory mechanics and condition
Appropriate sedation management
Early identification and correction of underlying causes of respiratory distress
Consider lung-protective ventilation strategies.
Key Points
Exam Focus:
Understanding the different types of PVA (triggering, cycling, breath stacking)
Recognizing waveform abnormalities indicative of dyssynchrony
Knowing the common causes of dyssynchrony in surgical patients
The role of modes like PSV, AC, and PRVC in PVA
Management strategies for common dyssynchrony patterns.
Clinical Pearls:
Always start by assessing the patient, not just the ventilator
If the patient is fighting the ventilator, consider the patient first before blaming the machine
A good sweep of the ventilator waveforms can reveal much about the patient-ventilator interaction
Judicious use of sedation is key
over-sedation can mask dyssynchrony and lead to diaphragm deconditioning.
Common Mistakes:
Attributing dyssynchrony solely to ventilator settings without considering patient pathology
Over-reliance on sedation to suppress patient effort
Inadequate waveform analysis
Failing to recognize auto-PEEP as a cause of dyssynchrony
Delayed intervention for persistent dyssynchrony leading to complications.