Cyanosis
CYANOSIS
- “Bluish discoloration of skin/mucous membrane”.
- Caused by deoxygenated/altered hemoglobin in sufficient concentration in blood.
- Deoxygenated hemoglobin color is bluish purple.
- Contrastly, oxyhemoglobin is reddish color.
Condition required for cyanosis:
- Presence of at least 5 gm% (4-5 gm/dl) of deoxyhemoglobin in capillary blood.
Common sites of where cyanosis is seen,
- Lips.
- Nail beds.
- Earlobes.
- Cheeks.
- Mucous membranes of oral cavity.
TYPES:
- Two types,
- Central cyanosis.
- Peripheral cyanosis.
1. Central cyanosis:
- Cuased by generalized disorder of oxygenation of blood.
- Due to decreased arterial PO2.
- Hence, any cause of hypoxic hypoxia can cause central cyanosis.
- Due to defective oxygenation in hypoxic hypoxia.
- Apparent all over body including mucous membrane of oral cavity.
2. Peripheral cyanosis:
- Due to blood stagnation.
- Leading to greater oxygen extraction in peripheral areas.
- Eg: in nail beds, nose tip & earlobes.
Causes:
- Any cause of stagnant hypoxia (CHF, shock).
- Cutaneous vasoconstriction.
CYANOSIS PRESENTATION IN VARIOUS TYPES OF HYPOXIA:
1. Hypoxic Hypoxia:
- Cyanosis is seen.
- Yet, only in severe hypoxia.
- Because at PO2 of 60mm Hg & above,
- Hemoglobin saturation is 90% & above.
- Cyanosis appears at saturation <85%.
- Hence, in mild hypoxia with insufficient deoxygenated hemoglobin can’t produce cyanosis.
- Thus, cyanosis considered as “Late sign of hypoxia in trauma patients”.
2. Anemic hypoxia:
- No cyanosis observed.
- Due to severe anemia causing hypoxia,
- Insufficient deoxygenated hemoglobin can’t produce cyanosis.
- Note: If out of low hemoglobin anemia more than 5g/100 ml is in deoxygenated form, the patient is already dead.
In CO poisoning,
- CO-Hb color – cherry red.
- No cyanosis is seen in CO poisoning.
- Because of less rapidly dissociating HbO2.
3. Stagnant hypoxia:
- Cyanosis is seen.
- Due to excess extraction of O2 from blood due to stasis.
- Hence, excessive deoxygenated hemoglobin produced.
4. Histotoxic hypoxia/”Cyanide poisoning”:
- Cyanosis is not seen.
- Because tissues cannot utilize O2.
- Hence, capillaries have more oxygenated hemoglobin & less deoxyhemoglobin.
UNCOMMON CAUSES OF CYANOSIS:
- Cyanosis is present,
- When capillary blood contains 5g% of deoxygenated hemoglobin.
- Yet, smaller concentration of other altered hemoglobin forms produces cyanosis,
- Eg: Sulphaemoglobin & Methaemoglobin.
- Due to very dark blood pigments.
Required levels to produce cyanosis:
- Methaemoglobin concentration of ≥ 1.5 gm/dl.
- Sulphaemoglobin concentration of ≥ 0.5 gm/dl.
Exam Question
CYANOSIS
- Presence of at least 5 gm% (4-5 gm/dl) of deoxyhemoglobin in capillary blood is essential to produce cyanosis.
- Common sites – Lips, nail beds, earlobes, cheeks, & mucous membranes of oral cavity.
Central cyanosis:
- Due to generalized disorder of oxygenation of blood due to decreased arterial PO2.
- Hence, any cause of hypoxic hypoxia can cause central cyanosis.
Peripheral cyanosis:
- Due to blood stagnation leading to greater extraction of oxygen in peripheral areas like nail beds, nose tip & earlobes.
- Any cause of stagnant hypoxia (CHF, shock) & cutaneous vasoconstriction can cause peripheral cyanosis.
In Hypoxic Hypoxia:
- Cyanosis is seen – Yet, only in severe hypoxia.
- Note: Cyanosis appears at saturation <85%.
- Thus, cyanosis considered as “Late sign of hypoxia in trauma patients”.
In Anemic hypoxia:
- No cyanosis observed.
- Because in case of severe anemia causing hypoxia, there will not be enough deoxygenated hemoglobin to produce cyanosis.
- In CO poisoning, CO-Hb color – cherry red.
- No cyanosis is seen in CO poisoning.
In Stagnant hypoxia:
- Cyanosis is seen.
- In Histotoxic hypoxia/”Cyanide poisoning”:
- Cyanosis is not seen.
- Uncommon causes of cyanosis due to,
- Sulphaemoglobin & Methaemoglobin.
Required levels to produce cyanosis:
- Methaemoglobin concentration of ≥ 1.5 gm/dl.
- Sulphaemoglobin concentration of ≥ 0.5 gm/dl.
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