Critical Care: Mechanical Ventilator Basics

I. MODES OF VENTILATION

  • Controlled: ventilator does the work of breathing (WOB) FOR the patient
  • Assist-control: patient and ventilator share WOB, patient initiates a spontaneous breath and a tidal volume is delivered
  • Synchronized Intermittent Mandatory Ventilation (SIMV): patient receives a preset tidal volume at a preset frequency, synchronous with the patient’s own breathing; patient can still breathe spontaneously in between ventilator breaths
  • Pressure support ventilation (PSV): positive airway pressure (PAP) applied during inspiration; patient must be able to initiate a spontaneous breath
  • Pressure-control inverse ratio ventilation (PC-IRV): prolonged PAP applied to increase inspiratory time and decrease expiratory time; normal inspiration/expiration (I:E) ratio is 1:2, with PC-IRV it is reversed to 2:3, 3:1, 4:1, etc1

II. VENTILATOR SETTINGS

  • Rate (f) – number of breaths per minute (usual: 6-20)
  • Tidal volume (Tv) – volume of air delivered with each breathe (usual: 6-10 mL/kg)
  • Fraction of Inspired Oxygen (FiO2) – oxygen concentration (usual: 21%-100%)
  • Positive End-Expiratory Pressure (PEEP) – positive pressure applied at the end of expiration (usual 5 cm H2O)
  • Pressure support – positive pressure applied to keep airway open and facilitate inspiration (usual: 6-18 cm H2O)
  • I:E ratio – inspiration:expiration ratio (usual: 1:2, 1:1.5), if IMV desired – 2:1, 3:1

III. VENTILATOR ALARMS

  • High pressure alarm: kinking of the tubing, patient biting on endotracheal (ET) tube, secretions pooling in tubing, patient “fighting” the ventilator, bronchospasms, pulmonary edema
  • Low pressure alarm: air leak from tube, ET tube cuff has deflated, total or partial extubation,

IV. PREVENTING VENTILATOR-ASSOCIATED PNEUMONIA (VAP)

  • Head-of-bed (HOB) elevated at minimum, 30-45 degrees
  • NO routine changes of ventilator circuit tubing
  • Use of an ET tube with dorsal lumen to facilitate suctioning
  • Hand hygiene

V. WEANING PARAMETERS

  • Negative Inspiratory Force (NIF) = 20-30
  • Minute ventilation (Ve) = < 10 L/min
  • Pressure of carbon dioxide (PaCO2) = 35-45 (or within normal limits [COPD patients])
  • Pressure of oxygen (PaO2) = 60+
  • Fraction of inspired oxygen (FiO2) = 50% or less
  • Positive end-expiratory pressure (PEEP) = < 5
  • Pressure support ventilation (PSV) = 10 or less

VI. COMPLICATIONS OF MECHANICAL VENTILATION

  • Decreased cardiac output due to increase intrathoracic pressure resulting from high PEEP
  • Barotrauma/volutrauma due to over distension of the lungs from high inspiratory pressures or high PEEP; can lead to pneumothorax
  • Hypo/hyperventilation which can lead to acid base imbalances
  • Ventilator-associated pneumonia (VAP)
  • Fluid and electrolyte imbalances due to low cardiac output, low kidney perfusion
Image Source.
Content derived from Medical-Surgical Nursing: Assessment and Management of Clinical Problems, 8th Edition.
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