icu intro lecture hypoxia

• related: ICU
• tags: #icu

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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