Patient- and ventilator-related factors that affect patient-ventilator interaction

Respiratory center output

  1. Factors that may decrease respiratory drive
    • Sedative, opioid, hypnotic medications
    • High level of ventilatory assistance
    • Metabolic alkalosis
    • Malnutrition
    • Sleep deprivation
    • Severe hypothyroidism
    • Idiopathic central hypoventilation syndrome
    • Severe bilateral brainstem injury of mid to lower medulla
  2. Factors that may increase respiratory drive
    • Chemoreceptor stimulation (hypoxemia, hypercapnia, acidosis states)
    • Increased ventilatory demand from
      • Increased metabolic states (pain, fever, shivering, overfeeding, sepsis, burns, trauma, hyperthyroidism, metabolic acidosis)
      • Underlying lung disease
    • Increased workload (weaning, stimuli that increase demand)
    • Pain, increased psychogenic stimuli or agitation
    • Medications (theophylline, doxapram, acetazolamide)


  1. Ineffective trigger
    • Excessive intrinsic positive end-expiratory pressure
    • Delayed termination dyssynchrony
    • Maladjusted sensitivity level
  2. Auto-cycling
    • Maladjusted sensitivity level
    • Excessive water in the circuit
    • Air leaks in endotracheal tube cuff, ventilator circuit, chest tube
    • Cardiac oscillations
  3. Double triggering
    • Premature termination dyssynchrony

Respiratory system mechanics

  1. Prolonged patient inspiratory time
  2. Shortened patient expiratory time
  3. Weak respiratory muscles, poor neuromuscular control,
    wean from high assist

Cycling off

  1. Inappropriately set cycling variable for patient

Disease states and conditions

  1. Obstructive pulmonary disease, dynamic hyperinflation states
    causing increased intrinsic positive end-expiratory pressure
  2. Acute respiratory distress syndrome
  3. Pain, splinting
  4. Body posture, abdominal distention
  5. Psychogenic behavioral stimuli causes agitation from
    • Pulmonary edema, pulmonary emboli, pneumothorax
    • Bronchospasm, retained airway secretions
    • ICU environment, fear, anxiety

Ventilator causes of patient agitation

  1. Ventilator disconnection
  2. System leak, circuit malfunction
  3. Inadequate fraction of inspired oxygen
  4. Inadequate ventilator support

Artificial airway in place

  1. Size, shape, narrowing of lumen by secretions
  2. Cuff leak
  3. Disconnection from circuit

Dead space

  1. Increased dead space in circuit causes increased work
    load and work of breathing


Mellot, K.G., Critical Care Nurse. 2009 December; 29(6): 41–55. DOI: 10.4037/ccn2009612.