superior vena cava (SVC) obstruction

Introduction

the SVC is the main venous drainage of head, neck and upper limbs
the azygous vein drains posterior thorax and joins the SVC at level of right main bronchus
obstruction of the SVC is a medical emergency, and around 60% of cases are due to underlying intrathoracic neoplasm

mediastinal masses
- neoplasm esp. lung cancer, particularly adenocarcinoma
- retrosternal thyroid
mediastinal fibrosis
thrombotic complication of SVC central line access
aneurysm eg. syphilis
tuberculous mediastinitis

if obstruction is distal to the insertion of the azygous V into the SVC then:
- compensation occurs with minimal clinical features
if obstruction is proximal to the insertion of the azygous V into the SVC then venous flow is diverted to the high pressure IVC via internal mammary, vertebral and similar veins resulting in raised venous pressures to head, neck and upper limbs resulting in:
- oedema and plethora with cyanosis to face, neck, upper torso, upper limbs
  - periorbital oedema
  - exophthalmos
  - conjunctival injection
  - venous dilatation of fundi
  - distended non-pulsatile neck veins
  - neck oedema causing stridor, Horner's syndrome, hoarse voice
  - positive Pemberton’s sign
    - bilateral arm elevation results in facial plethora due to a nutcracker effect of movement of the clavicles creating pressure within a narrowed thoracic inlet ¹⁾
  - dilated venous collaterals on chest wall
  - pleural effusions
  - cardiac tamponade
- syncope
- headaches
- SOB, cough, hoarseness, dysphagia and chest pain

IV access in the IVC territory
be prepared for and Mx:
- cardiac tamponade
- airway obstruction from extrinsic compression from the aetiologic mass
  - if airway compromise, consider prone posture or on all fours to reduce mass effect on trachea
  - intubation may not relieve the airway obstruction if the mass effect is distal
- laryngeal dysfunction
- respiratory failure
diagnose cause:
- usual bloods - FBE, U&E, coagulation profile
- sputum culture
- CXR
- CT chest
treat the cause if not for palliation:
- Rx is usually specific to aetiology such as steroids, chemotherapy, surgical debaulking, etc if tumour
- in extremis, may need sternotomy

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