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Small Animal Final Year > Cyanosis > Flashcards

Cyanosis Flashcards

1
Q

Define cyanosis

A

Cyanosis is the bluish discoloration of the skin and mucous membranes.

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2
Q

What causes cyanosis?

A

Many reasons

  • Due to insufficient oxygenation
  • Too much deoxygenated haemoglobin in circulation
  • Occurs due to an increased amount of reduced haemoglobin within the RBCs

Main reasons for cyanosis:

  • Not getting enough oxygen from environment
  • If oxygen not getting to lungs – URT obstruction
  • If oxygen not getting into blood but is getting to lungs – diffuse alveolar disease or pleural disease
  • If getting to blood, but shunting deoxygenated blood to systemic circulation – some form of Right to Left cardiac shunt
  • Oxygen cannot bind to haemoglobin – because abnormality of haemoglobin, might be toxic or inherited problem with haemoglobin.
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3
Q

What are the 2 broad categories of cyanosis?

A

•Causes of cyanosis can be described as central and peripheral causes

–Central cyanosis = desaturation of arterial blood or the presence of a Hb derivative.

–Peripheral cyanosis = desaturation of blood due to a regional reduction in blood flow.

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4
Q

What is the problem with indicating cyanosis?

A

•Insensitive indicator of the state of oxygenation because it is difficult to recognise until oxygen saturation of Hb in arterial blood reaches 80% or less.

–Animal is cyanosed is a clinical emergency, is saturation below 80% then partial pressure of oxygen is significantly low and wont see signs until it is quite low anyway – so need to act fast

•Therefore it is an emergency condition requiring early recognition and treatment

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5
Q

What can CO2 be like with cyanosis?

A
  • If cyanotic
  • Must be severely hypoxaemic

–May be normocapnic or hypercapnic or hypocapnic – CO2 can be high, low or normal

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6
Q

What are some factors that can affect detection of cyanosis?

A

Pigmented skin can make it difficult to recognise, artificial light can make it difficult to recognise, as can anaemia

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7
Q

Why can cyanosis be a poor indicator of hypoxia?

A

The more anaemic the animal, the more hypoxic it must be before cyanosis is detected. An anaemic animal has to be more hypoxic before body detects cyanosis – overwrites all other emergencies other than arterial bleeding really!

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8
Q

What is the threshold for cyanosis?

A

The threshold for cyanosis is a reduced hemoglobin content of 5 g/dL in the capillary, which can occur at varying values of arterial oxygen saturation (SaO2) and arterial hemoglobin content

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9
Q

What does the detection of cyanosis depend on?

A
  • The detection of cyanosis depends on the amount of Hb in the blood.
  • In the normal patient with a PCV of 45% would have an oxygen saturation of 78% or lower to show cyanosis, BUT an anaemic animal with a PCV of 18% would be dead before cyanosis would become apparent.
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10
Q

What can cause central cyanosis broadly?

A

•Hypoxaemia

–Might not be getting the oxygen in at all

  • Anatomic R to L shunting
  • Methaemoglobinaemia

–Congenital

–Acquired – oxidant intoxicants

–Ferric haem iron – cannot bind O2

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11
Q

What are some things that can cause hypoxaemia (that causes central cyanosis)?

A

–Reduced inspired PO2 - O2 source failure, altitude

–Alveolar hypoventilation - high CO2

  • Resp depression – central/muscular
  • Obstruction - laryngeal paralysis, foreign body, BOAS etc

–Diffusion impairment

•Interstitial diseases

–Pulmonary fibrosis – will cyanosis is severe enough

–Ventilation-perfusion mismatch

  • Pulmonary thromboembolism (PTE)
  • Pulmonary parenchymal disease

–Something in alveoli preventing ventilation

•Perfusing bits of lung that are not being ventilated – not perfusing ventilated lung

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12
Q

What are some things that can cause INTRACARDIAC right to left shunting (that causes central cyanosis)?

A
  • Tetralogy of Fallot
  • ASD / VSD with concurrent pulmonic stenosis

–Because of this stenosis, the RV pressure will be very high and this animal will shunt blood from R to L

•Pulmonary hypertension

–Animal with signifance L to R shunt, too much blood to pulmonary circulation, pulmonary hypertension will develop

–can get reversing of the shunting - rare

•Get a pulmonary artery that’s almost too small and an aorta that’s too big – so aorta sits over VSD, so blood from RV goes into aorta

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13
Q

What are some things that can cause EXTRACARDIAC right to left shunting (that causes central cyanosis)?

A
  • Reversed patent ductus arteriosus (rPDA) (rare)
  • Pulmonary arteriovenous fistulas (very rare)
  • Lung lobe consolidation – perfused not ventilated
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14
Q

Name some things that can cause peripheral cyanosis

A
  • If you have got peripheral cyanosis to an area, it is usually pretty obvious as to why! Some causes:
  • Central cyanosis
  • Decreased arterial supply
  • Peripheral vasoconstriction
  • Arterial thromboembolism

–Cat with thromboembolic disease, no arterial supply to back legs, footpads etc. will exhibit cyanosis and not enough cyanosis to that particular site

  • Low cardiac output
  • Obstruction of venous drainage

–E.g. bandage on too tight

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15
Q

When establishing the cause of cyanosis, what should you look for on physical exam?

A
  • Observe – respiration, all visible MM
  • Palpate – extremities/chest wall – apex beat in right place?
  • Auscultation – murmur
  • Auscultation – pulmonary/pleural space disease
  • Neurological exam

–If you suspect neuromuscular problem

•If breathless – is it URT, lung, pleural space or non-respiratory problem?

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16
Q

When establishing the cause of cyanosis, what diagnostic tests should you consider?

A
  • Is it central or peripheral?
  • Does patient require stabilisation?
  • Do not stress! Might be better off putting them in an oxygen rich environment and leaving them..
  • Is tentative diagnosis possible?

–URT obstruction, pleural disease, lung disease

  • Thoracic radiography
  • Blood gas analysis?
  • If you suspect pleural space disease – put an ultrasound probe on it to rule in or out presence of pleural effusion
  • IN AN EMERGENCY – OXYGENATE
17
Q

In dogs that have cyanotic congenital heart disease, what else do they often show?

What is a frequent clinical sign in these guys other than cyanosis?

A
  • Some of these dogs will show significant stunted growth – owners will go and look at litters and pick the smaller one as its sweet and more placid!
  • OFTEN STABLE AT REST – but find it difficult to exercise and may well collapse or faint
  • Exercise intolerance is a frequent clinical sign
  • Collapse / syncope is also common especially on hindlimbs a very common sign in dogs with rPDA
  • The owner may notice cyanosis
18
Q

What is a reverse patent ductus arteriosus?

A
  • The fetal ductus connecting the pulmonary artery and aorta (allows blood to bypass the lungs in utero) does not close after birth.
  • Due to the presence of pulmonary hypertension in the new born.
  • Blood continues to shunt from the pulmonary artery into the aorta.
  • Differential cyanosis occurs = deoxygenated blood is delivered to the caudal part of the body but oxygenated blood is delivered to the cranial portion of the body
  • WHY? – because of the anatomical location of the ductus
19
Q

Why do patients with reverse patent ductus arteriosus collapse on back legs and have blue MM but have pink MM cranial MM?

A

•Overcirculate pulmonary vessels – they thicken up and become damaged and eventually get hypertension because the RHS in systole is now going up, this PDA will reverse and blood will shunt from PA to aorta – so these animals will collapse on back legs and cranial MM will be pink and caudal ones will be blue

–Because carotid arteries leave the aorta arch before DA enters the aorta – so these dogs, collapse on back legs as deoxygenated blood from DA to back end – differential cyanosis

20
Q

Do reverse patent ductus arteriosus patients have a murmur?

What happens to S2?

A
  • These dogs may not have a murmur if they do they are often a low grade murmur of tricuspid regurgitation
  • May have a split S2 due to the presence of severe pulmonary hypertension
21
Q

What is differential cyanosis with regards to reverse patent ductus arteriosus?

A
  • Vulval or penile mucous membranes are cyanosed whilst the gingival mucous membranes are pink.
  • With exercise the oral mucous membranes can also become cyanotic
22
Q

What is tetralogy of Fallot?

A

a congenital heart condition involving four abnormalities occurring together, including a defective septum between the ventricles and narrowing of the pulmonary artery, and accompanied by cyanosis

23
Q

What are the 4 specific features of tetralogy of Fallout?

A

•Complex congenital heart disease composed of four specific features:

–Pulmonic stenosis

–Ventricular septal defect

–Over-riding aorta

–Right ventricular hypertrophy and dilation

24
Q

With tetralogy of fallout, where does blood shunt?

A
  • In these cases blood shunts from right to left, the proportion of which is determined by the severity of the defects, and hence the severity of the clinical signs.
  • Defect can be variable, most cases is quite severe and cyanosed and will be compromised and stunted by it
25
Q

What are some things you can do for the diagnosis of cyanotic heart disease?

A
  • Routine haematology
  • Routine biochemistry
  • Arterial blood gases
  • Echocardiography – will be the key thing
  • Thoracic radiographs

–Extreme care sedating these patients

•ECG

26
Q

What are some non-therapeutic management of cases of cyanotic heart disease?

A
  • Exercise restriction is important in these dogs
  • Cold weather can make these animals significantly worse due to pulmonary hypertension
  • Weight control is also important
27
Q

Why do animals with CHD get polycthaemia?

A

–If you have a R to L shunt, the kidneys are perfused with blood that doesn’t have enough oxygen in it, so they release a lot of erythropoietin so the PCV goes up – they come polycyhaemic. This causes a problem of perfusion of capillary beds

28
Q

How can you control the polycthaemia that you get with CHD and cyanotic heart disease?

A

•Control of the inevitable polycythaemia is important, this can be done by various methods:

–Regular blood letting

  • Phlebotomy
  • Leeches
  • 10-20ml/kg of blood to drop the haematocrit usually

–Chemotherapy

29
Q

To control the polycythaemia that you get with cyanosis and CHD, what can you do with regards to blood letting?

A
  • 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 haematacrit to a target level of 55%
  • Need to monitor protein levels carefully
30
Q

To control the polycythaemia that you get with cyanosis and CHD, what can you do with regards to drugs?

Which drug do you use?

A

•Hydroxycarbamide - chemotherapy drug

–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 and safety issues which owners need to be aware of

31
Q

What are some things that can cause no oxygen getting into the lungs?

A

Altitude

Supply failure

32
Q

What are some things that can means the patient cannot get oxygen to the lungs?

A

Chest damage

Muscle damage

URT obstruction

33
Q

What are some things that can means the patient cannot get oxygen into the blood?

A

Airway obstruction

Diffuse alveolar disease

Severe pleural space disease

34
Q

What are some things that can means the patient has reduced systemic oxygen?

A

R to L shunting

Tetralogy of Fallot

Eisenmengers physiology

35
Q

What are some things that can means oxygen cannot bind to Hb?

A

Haemoglobinopathy

Methaemoglobinaemia

Small Animal Final Year (317 decks)

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