IT 17_ZUL Hypoxia

8/12/2019 IT 17_ZUL Hypoxia

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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


PaO2 Solubility of O2in blood

+

O2binding

capacity of Hbx

x

x[Hb] O2sat


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Oxygen Transport


PaO2 Solubility of O2in blood

+

O2binding

capacity of Hbx

x

x[Hb] O2sat

(During Normal Gas Exchange)


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Oxygen Transport


100 mmHg 0.003mL O2___100mL blood mmHg

+

1.34mL O2

1g Hbx

x

x15g Hb

1dL blood0.98



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Oxygen Transport


0.3mL O2_100mL blood

+

19.7mL O2_

100mL blood


(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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IT 17_ZUL Hypoxia

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