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Mechanical Ventilation 101

Updated: Mar 27, 2020

The priority during this time is to protect healthcare workers. Wear personal protective equipment such as a mask, face shield, gown, and gloves at a minimum. Utilize a negative-pressure room if at all possible.

What is Mechanical Ventilation? Mechanical ventilation is needed for critically ill patients who are unable to protect their airway, sustain enough oxygen levels, or maintain adequate ventilation by taking in oxygen during inhalation and excrete carbon dioxide during exhalation.

What is a Ventilator? A ventilator is a machine that aids in a patient’s ability to take in oxygen and remove carbon dioxide. Mechanical ventilation is an invasive procedure because it involves placing tube inside the patient’s airway. The use of this machine does not completely heal the condition of the patient. Rather, it helps the patient achieve a stable condition while medications and other treatments promote healing.

Ventilation Modes

  • Controlled: ventilator does the work of breathing for the patient.

  • Assist-control: patient and ventilator share work of breathing, 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, etc.

Ventilator Settings

  • Rate – number of breaths per minute, typically 8-20. Start at a rate of 16.

  • Tidal volume (Tv) – volume of air delivered with each breathe, typically 6-10 mL/kg. Tv in lung injury should be 4-8 mL/kg of predicted body weight.

  • Fraction of Inspired Oxygen (FiO2) – oxygen concentration, typically 21%-100%. FiO2 in lung injury should be enough oxygen to keep SaO2 of 88-95%.

  • Positive End-Expiratory Pressure (PEEP) – positive pressure applied at the end of expiration, typically 5-20.

  • Pressure support – positive pressure applied to keep airway open and facilitate inspiration, typically 6-18.

  • I:E ratio – inspiration to expiration ratio, typically 1:2, 1:1.5.

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.

Complications of Mechanical Ventilation

  • Decreased cardiac output due to increase intrathoracic pressure resulting from high PEEP.

  • Barotrauma or volutrauma due to over distension of the lungs from high inspiratory pressures or high PEEP that can cause a pneumothorax.

  • Hypo or hyperventilation which can lead to acid base imbalances.

  • Ventilator-associated pneumonia.

  • Fluid and electrolyte imbalances due to low cardiac output and low kidney perfusion.

Acute Lung Injury Settings

· Start at a rate of 16, tidal volume of 6 mL/kg, FiO2 of 50%, PEEP of 10, plateau pressure of 25 or lower.

Prone Positioning

· Mainstay in the management of ARDS.

· Prone period should be 16-18 hours.

Additional Care of the Mechanically Ventilated Patient

· Begin enteral nutrition and DVT prophylaxis early.

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