Cyanosis and cyanotic heart disease Flashcards
What is cyanosis? Why does it occur?
= the bluish discolouration of the skin and mm
- it is an insensitive indicator of the state of oxygenation as it is difficult to recognise until oxygen saturation of Hb in arterial blood reaches 80% or less
– therefore, it is an emergency condition requiring early recognition and tx
- occurs due to an increased amount of reduced haemoglobin within the RBCs
What is central cyanosis?
- desaturation of arterial blood or the presence of a Hb derivative
What is peripheral cyanosis?
- desaturation of blood due to a regional reduction in blood flow
CS
- typically seen in breathless pts
– esp URT dyspnoea
– also severe lung dz / pleural space dz - mouth breathing (‘air hunger’)
Causes of cyanosis
No oxygen
- altitude
- supply failure
Can’t get oxygen to lungs
- chest damage
- muscle damage
- URT obstruction
- pleural space dz
Can’t get oxygen into blood
- interstitial lung dz
- diffuse alveolar dz
Reduced systemic oxygen
- R to L shunting
- tetralogy of fallot
- Eisenmenger’s physiology (ASD/VSD)
Oxygen can’t bind Hb
- haemoglobinopathy
- methaemoglobinaemia
Causes of central cyanosis
- reduced inspired PO2-O2 source failure, altitude
- alveolar hypoventilation - high Co2
- resp depression: central/muscular
- obstruction: laryngeal paralysis, FB, BOAS, etc - diffusion impairment
- interstitial/alveolar dz
- ventilation-perfusion mismatch
– pulmonary thromboembolism (PTE)
– alveolar dz - anatomic R to L shunting
- intracardiac
– tetralogy of fallot
– ASD/VSD with concurrent pulmonic stenosis
– pulmonary hypertension
- extracardiac
– reversed PDA (rare)
– pulmonary arteriovenous fistulas (v rare)
– lung lobe consolidation -> perfusion not ventilated - haemoglobinopathy
Peripheral cyanosis - cause
- central cyanosis
- decreased arterial supply
- peripheral vasoconstriction
- arterial thromboembolism
- low cardiac output
- obstruction of venous drainage
History q’s to establish a cause
- age & breed
- resp pattern
- resp noise
- cough
- neuro signs
- muscular weakness
- episodic weakness/collapse
- gait
- drug use
Physical exam to establish a cause
- observe: respiration, all visible mm
- palpate: extremities/chest wall - apex beat?
- auscultation: murmur
- auscultation: pulmonary/pleural space dz
- neuro exam
Emergency management
- oxygenate
Cyanotic congenital heart dz - CS
- some will show significant stunted growth
- often stable at rest
- exercise intolerance is a frequent CS
- collapse/syncope is also common
- O may notice cyanosis
What is Tetralogy of Fallot?
- Complex congenital heart disease composed of 4 specific features:
– pulmonic stenosis
– VSD
– over-riding aorta
– right ventricular hypertrophy & dilation - in these cases blood shunts from R to L, the proportion of which is determined by the severity of the defects, and hence the severity of CS
Diagnosis of cyanotic heart dz
- echocardiography
- thoracic radiographs give clues
– extreme care sedating these pts - ECG gives clues
Non-therapeutic management of these cases
- exercise restriction is important
- weight control is also important
Polycythaemia
- abnormally high RBC in blood
- also known as erythrocytosis
Tx
- animals with CHD and R to L shunts can’t be cured without surgery which is rarely possible, therefore tx relies on the management of CS
- control of inevitable polycythaemia is important, this can be done by
– regular blood letting -> phlebotomy, leeches
– chemotherapy
Blood letting
- phlebotomy is the most common although there are successful reports of the use of leeches in cats
- phlebotomy 10-20ml/kg of blood is removed in order to reduce the haematocrit to a target level of 55%
- need to monitor protein levels carefully
Chemotherapy tx
Hydroxycarbamide
- myelosuppressant drug
- reduces RBC production in the bone marrow
- needs careful monitoring for bone marrow suppression
- liquid or tablet form -> liquid has many significant health & safety issues which O needs to be aware of
