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HYPOXIA & HYPERCAPNIA
Zulkifli, dr., SpAn.Mkes
Dept of Anesthesiology & Reanimation
Medical FacultyUniversity of Sriwijaya
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Definition
Hypoxia :
A pathological condition in which the body is
deprived of adequate oxygen supply
Oxygenation is failure
Hypoxemia :
The oxygen concentration within the arterial
blood is abnormally low
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Symptoms
Signs of oxygenation failure:
Tachypnea
Alkalemia (acidemia if concurrent ventilatoryfailure)
Increased pulsus paradoxus
Cyanosis
AgitationSomnolence
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TYPES OF HYPOXIA
A. HYPOXEMIC HYPOXIA (INADEQUATE ARTERIAL OXYGEN
TENSION)
CAUSES:
B. ANEMIC HYPOXIA (DEFICIENT OXYGEN-CARRYING CAPACITYOF THE BLOOD)
CAUSES:A. ANEMIA (DECREASED HEMOGLOBIN)B. CARBON MONOXIDE POISONINGC. SULFHEMOGLOBIN AND METHEMOGLOBIN
A. V/Q MISMATCH (EX: COPD)B. SHUNT (EX: ATELECTASIS, PULM. EDEMA)C. HYPOVENTILATION (EX: DRUG INDUCED)
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TYPES OF HYPOXIA
C. CIRCULATORY HYPOXIA (DECREASE PERIPHERAL CAPILLARY
BLOOD FLOW)
CAUSES:
D. HISTOTOXIC HYPOXIA (DECREASED UTILIZATION OF OXYGEN
AT THE CELL LEVEL)CAUSES:
A. DECREASED CARDIAC OUTPUTB. VASCULAR INSUFFICIENCY (SEPSIS)
A. CYANIDE POISONINGB. ALCOHOL POISONING (RARE)
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Hypoxia - Etiologies
PaO2 = [FIO2(PI
PH2O)]
(PaCO2/ RQ)
(A-a gradient)
A-a gradient
V/Q mismatch
COPD
Pulmonary embolus
Pneumonia
Pulmonary edema
Anatomic shunt
Right to left intracardiac shuntsPulmonary AVMs
Impaired diffusion
Emphysema
Pulmonary fibrosis
FIO2
Suffocation
PI
High altitude
PaCO2
As above
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Overview of Gas Exchange in the Lungs
Adapted from: Costanzo, LS. Physiology, 1st ed. 1998.
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Mathematical Description of Gas Exchange
PaCO2Partial pressure of CO2in the arterial blood.
PACO2Partial pressure of CO2in the alveolar gas.
PaO2Partial pressure of O2in the arterial blood.
PAO2Partial pressure of O2in the alveolar gas.
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Oxygen Transport
Oxygen is carried in the blood in 2 forms:
Dissolved O2(~2% of total O2content)
O2bound to hemoglobin (~98% of total O2content)
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Oxygen Transport
Total O2content of blood (CaO2) =
+
Dissolved O2
O2bound to hemoglobin
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Oxygen Transport
Total O2content of blood (CaO2) =
PaO2 Solubility of O2in blood
+
O2binding
capacity of Hbx
x
x[Hb] O2sat
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Oxygen Transport
Total O2content of blood (CaO2) =
PaO2 Solubility of O2in blood
+
O2binding
capacity of Hbx
x
x[Hb] O2sat
(During Normal Gas Exchange)
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Oxygen Transport
Total O2content of blood (CaO2) =
100 mmHg 0.003mL O2___100mL blood mmHg
+
1.34mL O2
1g Hbx
x
x15g Hb
1dL blood0.98
(During Normal Gas Exchange)
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Oxygen Transport
Total O2content of blood (CaO2) =
0.3mL O2_100mL blood
+
19.7mL O2_
100mL blood
(During Normal Gas Exchange)
(Dissolved O2)
(Hb-bound O2)
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CONTENT VS TENSION (PaO2)A. CONTENT= TOTAL AMOUNT OF OXYGEN CARRIED IN BLOOD
NORMAL = 20.7 VOL%CALCULATION: CaO2 = [%sat x l.39 x content] + [PaO2 x 0.003]
EXAMPLES/NORMAL
NORMAL Hb% = 15 GM%, 0.9802 SAT = PaO2 = 100mmHg
[1.39 X 0.98 x 15] + [100 x 0.003] = 20.7 vol.%
NORMAL MIXED VENOUS CONTENT = 15%ARTERIAL VENOUS DIFFERENCE (A-V) = 5VOL%
ANEMIA Hb 10g%, %sat = 98%,PaO2 = 100mmHg
[1.39 x 0.98 x 10] + [100 x 0.003] = 14.2 vol.%
HYPOXEMIAHb% =15 gm%,%Sat=85%, PaO2=50mmHg[1.39 x0.85x 15] = [50 x 0.003] = 18.0vol%
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CONTENT VS TENSION (PaO2)
B. TENSION (PaO2) = AMOUNT OF OXYGEN DISSOLVED IN BLOOD
NORMAL = 100mmHg [100 x 0.003] = 0.3%
PaO2 = 1.5% OF THE TOTAL O2 CARRIED IN THE BLOOD ONLY
Hg O2 CONTENT CARRIES 19.2 VOL%VS
PaO2 CONTENT CARRYING 1.5 VOL%
AS YOU CAN SEE PaO2 ISN'T ALWAYS THE MOST
IMPORTANT OXYGENATION INDICATOR
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Pathophysiology
If oxygen delivery to cells is insufficient for thedemand (hypoxia) hydrogen will be shifted to pyruvic acid converting it
to lactic acid
This temporary measure (anaerobic metabolism)allows small amounts of energy to be produced
Lactic acid build up in tissues and blood is a sign of inadequate mitochondrial oxygenation
due to hypoxemia, poor blood flow (e.g., shock)
or a combination of both
If severe or prolonged it could lead to cell death.
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Hypercapnia
Respiratory failure manifesting as hypercapnia isknown as ventilatory failure.
Signs of ventilatory failure:
Tachypnea
Acidemia
Increased pulsus paradoxus
Hyperinflation
Somnolence / Decreased mental status
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Hypercapnia - EtiologiesVCO2x PI
RR (VTVD)PaCO2 =
VCO2 (Hypermetabolism)
Fever
SeizuresSepsis
Hyperalimentation
RR (Central hypoventilation)
Drugs
Brainstem lesions
Obesity-hypoventilation syndrome
VT
Skeletal muscle weakness
Impaired neuromuscular transmission Lung / chest wall compliance
Airway obstruction
COPD
Asthma
Obstructive sleep apnea
VD
Excessive PEEP
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Hypercapnia - Treatment
Treat the underlying process
Non-invasive positive pressure ventilation
Intubation and mechanical ventilation
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