icu intro lecture hypoxia

causes of hypoxemia

  • Low FiO2 or PiO2
  • Hypoventilation
    • apneic patient
  • Diffusion gradient
    • pulmonary edema, ARDS, fibrosis
  • Dead space: ventilated but not perfused. V/Q = infinity
  • Shunt: perfused but not ventilated. V/Q = 0

Shunt

  • causes of shunt: anything that causes collapsed alveoli
    • atelectasis
    • ARDS
    • surfactant missing
    • mucous plugging
  • in normal patients, hypoxemic pulmonary constriction limits shunt
  • medications make constriction and shunt worse: nitrates, CCB, PDE I, inhaled anesthetics.

Treatment

Increase PEEP

  • increase mean airway pressure to recruit more alveoli
  • Increase in PEEP will increase mean airway pressure

  • Increase in PEEP can obstruct blood flow and cause decreased CO, more acidosis. Give fluids to increase more volume to left side.

APRV

  • Alternatively, increase mean airway pressure by spending more time in PIP
  • AKA APRV
  • Downside:
    • not comfortable
    • hurt ventilation because not enough time spent exhaling
    • adding PSV decreases blood flow

40-40 Maneuvers

  • 40-40 maneuvers: PEEP for 40 cm for 40 sec

Prone Ventilation

  • Improves oxygenation but not ICU stays or mortality
  • PROSEVA

JET ventilation

  • Good for a lot of chest tubes

High frequency oscillating ventilation

Overview

  • Increase I time increases time spent with higher pressure, more recruitments