Physiotherapy Management in Cardiorespiratory Dysfunction II

Mechanical Ventilation and Weaning

• Mechanical ventilation is a form of life support that mechanically assists or replaces spontaneous breathing.
• Indications for mechanical ventilation include:
  • Cardiac or respiratory arrest
  • Tachypnea or bradypnea with respiratory fatigue or impending arrest
  • Acute respiratory acidosis
  • Refractory hypoxemia
  • Inability to protect the airway associated with depressed levels of consciousness
• Principles of mechanical ventilation:
  • Inspiration may be generated by application of either a constant pressure or a constant flow of gas to the lungs
  • Expiration is allowed when either a set pressure has been reached, a set volume has been delivered, or a set time has passed

Modes of Ventilation

• Controlled Mandatory Ventilation (CMV):
  • Vent initiates all breaths at a pre-set rate and tidal volume
  • Patient has no control over ventilation
  • Used mainly in the OR for paralyzed and sedated patients
• Assist Control (A/C):
  • Vent will allow a patient to initiate a breath and then deliver a pre-set tidal volume
  • Machine set at a minimum rate so apnea will not occur if the patient does not initiate a breath
• Synchronized Intermittent Ventilation (SIMV):
  • Similar to A/C, but patients can take own breaths with their own tidal volume between mechanically assisted breaths
  • Can be used as a primary mode or a weaning mode
• Pressure Support Ventilation (PSV):
  • Also called “spontaneous mode”
  • Pt initiates breath & vent delivers a pre-set inspiratory pressure to help overcome airway resistance and keeps airways open
• Continuous Positive Airway Pressure (CPAP):
  • Positive airway pressure provided during both inspiration and expiration
  • Improves gas exchange and oxygenation in patients able to breathe on their own

Weaning Parameters

• Adequate oxygenation:
  • PaO2 > 60-70 on FiO2 0.4 to 0.5, PEEP 5-8 cmH2O
  • PaO2/FiO2 ratio > 150-200
• Adequate ventilation:
  • PaCO2 35-45 mmHg
  • pH 7.3 to 7.45
• Adequate respiratory mechanics:
  • Tidal volume
  • Respiratory capacity
  • Minute ventilation
• Hemodynamic stability

Weaning Process

• Spontaneous breathing trials (SBT) lead to extubation more quickly than those receiving pressure support and IMV for weaning purposes in patients who are mechanically ventilated for > 1 week
• Signs of distress during weaning:
  • Increased tachypnea (> 30)
  • Increased heart rate
  • Irregular breathing pattern or use of accessory muscles
  • Agitation or panic unrelieved by assurance
  • Decrease pH to less than 7.25-7.3 with increasing PCO2
• Problems encountered while weaning:
  • Impaired ventilatory drive
  • Upper & lower airway incompetence, obstruction, or secretions
  • Lung parenchymal fluid or infection
  • Pleural effusion or pneumothorax
  • Chest wall abnormality, instability, or respiratory muscle weakness
  • Electrolyte or nutritional problems
  • Cardiovascular insufficiency

Mobilizing the Patient

• Patients weaning from mechanical ventilation should be considered for mobility and strengthening exercises
• Mobilization requires teamwork with the entire medical team
• Steps to mobilization include:
  • Looking at baseline vitals
  • Looking at baseline vent settings
  • Locating all wires, tubes, etc.
  • Moving IV pole and lines to the side
  • Assisting patient to sitting at the side of the bed
  • Transferring to the chair while managing lines
  • Coordinating with the medical team to place on a portable vent if necessary
  • Organizing equipment and lines
  • Supporting lines, vent/IV pole, and vent tubing
  • Having a tech or nurse follow with a wheelchair for safety