2-22
2-22. MECHANICAL VENTILATION
a. When a patient is unable to maintain appropriate levels of arterial oxygen and carbon dioxide by normal breathing, some sort of mechanical assistance becomes necessary. A mechanical ventilator is a positive pressure-breathing device that maintains respirations automatically. Ventilators may be used for complete or partial control of a patient's respirations.
b. Mechanical ventilators are used in three modes of operation: assist, control, and assist-control. Determination is made by the physician according to the needs of the patient.
(1) Control mode is used for the patient whose respiratory drive is absent or excessive. The ventilator initiates breathes at a pre-set rate and will not respond to any patient attempts to initiate a breath.
(2) Assist mode is used for the patient who is able to make an inspiratory effort, but is unable to inhale an adequate amount of air. The patient initiates each breath and the ventilator then augments the breath to achieve a preset volume of air.
(3) Assist-control mode is used for the patient who has an erratic respiratory pattern. The ventilator will function in assist mode as long as the patient maintains an adequate respiratory rate. If the patient's respiratory rate falls below a preset level, the machine will switch to control mode and initiate breaths. The ventilator will switch from assist to control as determined by the needs of the patient.
c. The ventilator settings are determined by the physician.
(1) Tidal volume--The amount of air delivered for each inhalation.
(2) Respiratory rate--The number of breathes per minute.
(3) Minute volume--The amount of air delivered each minute (tidal volume multiplied by respiratory rate).
(4) Oxygen concentration--Percentage of oxygen mixed with room air.
d. Management of the ventilator and the ventilator patient is normally done by a physician, a respiratory therapist, and specially trained professional nurses. Paraprofessional nursing personnel assigned to patient care areas where ventilator patients are managed will receive special training in the principles of mechanical ventilation.
