PICU Primer I: Understanding Hypoxia, Hypoxemia, and Oxygenation in Critical Care, Slides of Pediatrics

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PICU Primer I

The Primer Outline

 Physiology

• Hypoxia / Hypoxemia
• ABG’s and Acidosis
• Sodium and H 2 O metabolism
• Hemodynamics and Cardiopulmonary interactions

 ICU Care & Common Problems

• Head trauma
• Toxicology
• Postoperative issues
• Mechanical Ventilation

Oxygen and Hypoxemia

Define

• Hypoxemia
• Hypoxia

Hypoxemia

 Ventilation/Perfusion mismatch

 Hypoventilation

 Shunt

 Diffusion

 Decreased Ambient O 2

Shunt / Dead Space Spectrum

Shunt

Dead Space

V/Q = 0 V/Q = infinity

No amount of  O 2  difference

will fix between EtCO 2

and PaCO 2

Ventilation / Perfusion mismatch

 Blood  Pus  Air  Water  Atalectasis

 Quantitate using A – a Gradient

V

Q >>>

Cause for desaturations

Anesthesia – hypoventilation

Atalectasis – V/Q mismatch

Edema - V/Q mismatch

Asthma– dead space/ V/Q mismatch

Dysfunctional Hemoglobin

You may need a CXR and or ABG in

addition to H+P to answer the question

Non respiratory Physiologic causes of a low PaO 2 Causes Effect on P(Aa)O 2

Nonrespiratory Righttoleft intracardiac shunt Decreased PIO 2 Low barometric pressure Low FIO 2 Decreased R value Low mixed venous oxygen content Artifact Very high white blood cell count Patient hyperthermia*

Increased Normal

Normal Increased

Increased Increased

*Only in presence of increased venous admixture docsity.com

Oxygen Debt/ Oxygen Deficit

0

5

10

15

20

25

30

35

40

45

O2 in ml

10 20 30 40 50 60 Time (minutes)

O2 Deficit O2 Debt

MODS >

Death >?

Inadequate Resuscitation

Oxygen Content

Which has the biggest impact on O 2

delivery to the tissues?

• Hemoglobin, Sat, Cardiac Output, or PaO 2

Which patient has more oxygen in the

blood?

• Patient A, PaO 2 89, Sat% 97%, Hg 9.
• Patient B, PaO 2 60, Sat% 85%, Hg 13.

DO 2

CaO 2

CO

Sat %

PaO 2

Hg

HR

SV

Preload

Contractility

Afterload

“Normal” Values

CaO 2 = (Hg X 1.34 X Sat%) +

(PaO 2 X 0.003)

• 17-20cc O 2 /dL

DO 2 = CI X CaO 2

• 400-600 ml X min / M^2

VO 2 = CI X avDo 2

• 140-160 ml X min / M^2

Arterial sat 100% minus Consumption = Venous sat 75-80%

Questions?

NEXT UP

• ABG’s

and acidosis

Acidosis

 Respiratory vs. Metabolic?

• Anion gap or not?

 Acute vs. Chronic?

 Primary or Secondary?

 Rule

• every 10 torr change in PCO 2 should result in 0.08 change in pH
• Every HCO 3 drop you should see 1:1 increase in base excess