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Hypoxia

Rudyanto SedonoArif HM Marsaban

Department of Anesthesiology and Intensive TherapyFaculty of medicine University of IndonesiaDr Cipto Mangunkusumo General Hospital

Jakarta

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Topic related

Hypoxia definition Oxygen transport Type of hypoxia

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Hypoxia

Hypoxemia

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Insufficient oxygen at the cellular level (mitochondria)

Inadequate cellular oxygen uptake and utilization

Reduce oxygen for tissue respirationOxygen tension at cellular level is inadequate

Hypoxia

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Hypoxemia

Decreased oxygen partial pressure in arterialRelative deficiency of oxygen in the arterial

bloodDecreased oxygen concentration in the arterial

blood

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Oxygen is important for maintain aerobic metabolism in cellular level of the body, through oxidative phosphorylation in the mitochondria, the end result CO2 & H2O

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Aerobic metab becomes anaerobic metab when there is cessation of oxidative phosphorylation because decrease of PO2 in mitochondria

Anaerobic metab produce H+ + Lactate cumulates in blood, causes base deficit

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Oxygen transport

1. Convection2. Diffusion3. Chemical reaction

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Oxygen transport from air to the cell

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ALVEOLUS

Lung capillary

AIR :

PiO2 : 20.9 % x 760 = 159 mmHg

PiCO2 : 0.04 % x 760 = 0.3 mmHg

PiN2 : 78.6 % x 760 = 597mmHg

PiH2O : 0.46 % x 760 = 3.5 mmHgN2 H2O

O2

PAO2:104 mmHg

CO2

PACO2:40 mmHg

O2

PaO2: 40 mmHg

O2PaO2: 104 mmHg

CO2PaCO2: 45 mmHg

CO2PaCO2: 40 mmHg

PAN2:573 mmHg

PAH2O:47 mmHg

Diffusionprocess

Convection process

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Chemical reaction process of oxygen bound to haemoglobin

Rule of hemoglobin affinity to oxygen.Describe as oxygen dissociation curve

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Fick : DO2 ( ml/min ) = 10 x CO ( L/min ) x CaO2

CaO2 = 1.34 x Hb x SaO2 + 0.003 x PaO2

Normal DO2 ≈ 1000 ml/minCO ≈ 5 L/minHb = 15 gr/100mlSaO2 100%

Convection process of oxygen from heart-lung to capillary level

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Diffusion process of oxygen from capillary to cell

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Hypoxia

1. Hypoxic hypoxia2. Circulatory hypoxia3. Anemic hypoxia4. Cytophatic hypoxia

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Hypoxic hypoxia

Blood flow to capillary is held constant but oxygen saturation is decreased

Refers to the steps that depend on diffusion of oxygen

Diffusion from the lungs into arterial bloodDiffusion from oxygenated capillary blood into

the tissuesLow PO2 is the hallmark of hypoxic hypoxia

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Caused of hypoxic hypoxia

1. Diffusion limitation2. Hypoventilation3. Decreased Fraction Inspiration of Oxygen4. Shunting5. V / Q mismatch6. Contribution of low Mixed Venous Oxygen

Saturation

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Circulatory Hypoxia

Blood flow into a capillary is decreased while the arterial PO2 remains constant

Depend on cardiovascular systemStimulating the peripheral chemoreceptorTachycardia, bradycardia, peripheral

vasoconstriction or vasodilatation

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Anemic Hypoxia

The arterial hemoglobin concentration ( hematocrit ) decreasedDecreased oxygen deliveryPerioperative period hematocrit 30% as

optimal

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Physiologic response to anemic hypoxia

1. Cardiac output response to hemodilution - Increased stroke volume - Increased heart rate - Decreased peripheral vascular resistance

1. Blood oxygen extraction ratio - Systemic and microcirculatory level

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Cytopathic Hypoxia

Impaired production of ATP despite adequate availability of O2 in the cell

Sepsis conditionImpaired mitochondrial function such as

in sepsis

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Cardiovascular response to hypoxia

1. reflex response : neural & humoral 2. direct

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Reflex response : occurs first, excitory & vasoconstriction

• Neuro reflex is the response from Aorta & Carotid chemo, baroreceptor & central stimulation

• Humoral is the release of catecholamine & renin-angiotensin

Clinical signs : increase HR, BP, vasoconstr

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Direct response : occurs late, causes inhibitory & vasodilatation

The degree of hypoxia determines the balance of inhibitory & excitory response

Decrease of O2Sat < 80% : excitory 60 – 80% : vasodilation, BP , but

HR because baroreceptor < 60% : inhibitory

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If you are not confused, you

are not conscious