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Posts Tagged ‘central cyanosis’

Answer : Peripheral cyanosis  reduces or disappears  , while central cyanosis persist.

This is how , 99% of cardiology fellows answered in one of my  classes ! And they were quoting few  references for it .

Is that correct ? If so , what is the mechanism  of  oxygen response ?

Comments welcome . Discussion will start soon .

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During  clinical examination of cyanotic congenital heart disease(CHD) ,  the major  task is to differentiate conditions with reduced  or increased pulmonary blood flow .

When a child with  CHD  is presented in clinical examinations , students are often asked to arrive at  the diagnosis  from history , physical examination before going in for ECG, X ray  or  echocardiography.

History,  surprisingly can  suggest  the  correct diagnosis in many (Most ?)

Reduced pulmonary blood flow is often associated with

  • Cyanosis   appearing with  /or worsening with   exertion*
  • Hypoxic spells.(Almost always occur in reduced pulmonary  blood flow )
  • History of squatting( Majority in reduced pulmonary flow)

Relief  of dyspnea   by assuming squatting position  convey   important hemodynamic information. It implies  there is significant reduction in pulmonary blood flow in standing posture , that  gets corrected  in the squat position.For squatting to improve pulmonary blood flow there must be a communication between right and left heart .This is most often due to a large VSD, rarely an  ASD .

Related article : How squatting relieves hypoxia in TOF ?

*Note :  Cyanosis  is  not  specific for reduced pulmonary  blood flow. In fact , simple reduction in pulmonary blood flow per se , cannot result in significant cyanosis .There need to be admixture /or right to left to shunt to produce cyanosis .Cyanosis in  pure admixutre states like TGV, Single ventricle , Common AV canal , Common atrium TAPVC,  are less Dependant on the reduction of  pulmonary  flow. In these situations RVOT obstruction if  present  will aggravate the baseline cyanosis.

Examination

Apart  from direct evidence for reduced pulmonary blood flow , lack of evidence for increased pulmonary  flow could  often mean ,  we are  actually  dealing  with  reduced pulmonary blood flow.

The following are the clinical clues to suspect  reduced pulmonary blood flow.

  • A quiet precardium*
  • A inconspicuous pulmonary component of S 2
  • Generally if  S 2 is well split  and both components are well heard it is highly likely the  pulmonary  blood flow is not reduced.
  • Lack of  pulmonary  arterial pulsations
  • Absence of mid diastolic  flow murmurs  in AV valves
  • Presence  of continuous murmur in a patient with cyanotic CHD almost always mean   reduced pulmonary flow and the lungs are perfused by alternate arterial collaterals (MAPCA)

* A silent  heart is the hall mark of Tetrology of Fallot which constitutes 80% of all CHD with reduced pulmonary blood flow.

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How  central cyanosis occurs  in primary pulmonary hypertension ?

While , peripheal cyanosis*  is easily explained in PPH ,the mechanism of central cyanosis is not straight forward.

The following explanations are offered

  1. PFO**  getting  opened due to high mean RA pressure
  2. Pulmonary arterio venous channels.(Neogeneis or dormant channels activated )
  3. Altered QP/QS .This effectively means lung shunts some blood without oxygenation(A right to left to shunt within lungs )
  4. Associated lung pathology -like pneumonia resulting in pathological right to left shunt across the alveolar circulation.

* Peripheral cyanosis can occur in PPH with cardiac failure

**PFOs are often anatomically patent in 20 % of normal population , which gets functionally patent  when exposed to high RA pressure

Cyanosis -A brief  description .

Cyanosis occurs when the arterial saturation goes below 85 % . Cyanosis  manifests in two ways . Central and peripheral.The term peripheral  does not  denote  peripheral parts of the body  rather it is  peripheral  circulation.(Capillary) The mechanism of peripheral cyanosis is somewhat  different from central cyanosis . It is generally due to sluggish circulation ,  more  oxygen extraction and resultant bluish discoloration .

Peripheral cyanosis is seen in finger tips, lips etc . Peripheral cyanosis can not occur in warm areas of the body for the  simple reason warmth  causes vasodilatation , better tissue perfusion  which prevents stagnation of  deoxygenated blood.

Central oxygenation defect alone can not result in  classical central cyanosis .

For central cyanosis  to occur ,  there need to be mixing of  deoxygented and oxygenated blood somewhere in the  circulation.(Right to left shunt in the heart or lungs )

Since it is a defect in central  oxygenation it  manifests  in both warm mucous membranes as well as cold extremities.

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