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Flashcards in Hypercapnia Deck (26)
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1

Hypercapnia is defined as a PaCO2 >?

PaCO2> 45 mmHg

2

How is PaCO2 calculated?

PaCO2 = (CO2 Production)/ (Alveolar ventilation)

3

Cause of Hypercapnia

Increased CO2 Production

Decreased CO2 Elimination

Rebreathing

4

Causes of Hypercapnia due to increased CO2 Production include:

Sepsis

Overfeeding

Malignant hyperthermia

Intense shivering

Prolonged seizure activity

Thyroid storm

Burns

5

Causes of Hypercapnia due to Decreased CO2 Elimination include:

Airway obstruction

Increased dead space

Increased  Vd/Vt

ARDS - COPD

Respiratory center depression

Drug overdose

Inadequate NMB reversal

6

Causes of Hypercapnia due to Rebreathing include:

Incompetent one-way valve

Exhausted soda lime

7

How does the body compensate for hypercapnia (i.e., respiratory acidosis).

Compensatory mechanisms

8

What are the Consequences of Hypercapnia?

Hypoxemia

Increased P50

Cardiac & Smooth Muscle Depression

SNS Stimulation

Increased Alveolar Ventilation

Increased [K+]

Increa sed [Ca+2]

Increased ICP

Depression LOC

9

How does Hypercapnia lead to Hypoxemia?

Displacement of alveolar 02

 

Remember the alveolar gas equation?

Alveolar nitrogen is inert - its concentration remains constant

Increased Alveolar CO2 displaces alveolar 02  --> arterial hypoxemia

10

Alveolar nitrogen is inert - How does this affect its concentration?

Remains constant

11

How does Hypercapnia lead to Increased P50?

Curve shifts to the right

Releases  more 02  to the tissues

Partially compensates for hypoxemia

12

How does Hypercapnia lead to Cardiac & Smooth Muscle Depression?

Acidosis

Acidosis  inside the muscle affects contractile protein and enzymatic function, which leads to

Myocardial depression

Vasodilation

13

How does Hypercapnia lead to SNS Stimulation?

Increased catecholamine release

CO2 activates the SNS and increases catecholamine release

Unless acidosis is severe, SNS stimulation offsets cardiac and smooth muscle depression

Tachycardia --> increased myocardial 02 consumption & decreased myocardial O2 delivery

Vasoconstriction --> increased SVR --> increased myocardial O2 consumption

Dysrhythmias

Prolonged QT interval

Oculo-cardiac reflex is more common  following precipitating event

14

How does Hypercapnia lead to Increased Alveolar Ventilation?

Respiratory stimulant

CO2 is a respiratory stimulant --> increased minute ventilation

15

How does Hypercapnia lead to increased [K+]?

Activates H+/ K+ pump

Buffers CO2 acid in exchange for releasing K + into the plasma

16

How does Hypercapnia lead to increased [Ca+2]?

Ionized Ca+2 competes with H+ for binding sites on plasma proteins

Acidosis --> plasma proteins buffer H + and release Ca+ 2  --> increased inotropy

Alkalosis --> plasma proteins release H+ and bind Ca+2 --> decreased  inotropy

17

How does Hypercapnia lead to increased ICP?

CO2 freely diffuses across the BBB

Decreased CSF pH --> decreased cerebrovascular resistance --> increased CBF & volume

18

How does Hypercapnia lead to Depression LOC?

CO2 narcosis when PaC02 > 90 mmHg

19

During respiratory acidosis, the kidneys excrete (1)----- and conserve (2)------- to return pH to normal

(1) hydrogen

(2) bicarbonate

20

During respiratory acidosis, the kidneys excrete hydrogen and conserve bicarbonate to return pH to normal. This process begins within which time frame?

Hours

21

During respiratory acidosis, the kidneys excrete hydrogen and conserve bicarbonate to return pH to normal. This process begins within hours, but it may require how much time for full compensation to occur?

Days (several)

22

You should be able to predict the pH or PaCO2 given a change in the other variable

In Acute Respiratory Acidosis, if PaCO2 increases by 10 mm Hg

A. pH Decreases 0.08

B. pH Decreases 0.03 (renal HC0 3- retention)

pH Decreases 0.08

23

You should be able to predict the pH or PaCO2 given a change in the other variable

In Chronic Respiratory Acidosis, if PaCO2 increases by 10 mm Hg

A. pH Decreases 0.08

B. pH Decreases 0.03 (renal HC0 3- retention)

pH Decreases 0.03 (renal HC0 3- retention)

24

You should be able to predict the pH or PaCO2 given a change in the other variable

In Acute Respiratory Acidosis, a pH decrease of 0.08 implies a PaCO2 increase of:

 

10 mm Hg

25

You should be able to predict the pH or PaCO2 given a change in the other variable

In Chronic Respiratory Acidosis, a pH decrease of 0.03 (renal HC0 3- retention) implies a PaCO2 increase of:

 

10 mm Hg

26

Reference:

 

Hagberg. Benumof and Hagberg's Airway Management. 3rd ed. 2013 . p. 153- 157 .