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Tuesday, November 17, 2020

What is Shock? Types and management


Shock is a clinical condition characterized by failure to adequately perfuse and oxygenate vital organs. Clinically, shock is recognized by:

  • Hypotension: Generally considered to be systolic BP <90 mmHg (in adults ), but values may be higher in young, fit or previously hypertensive patients. Associated tachycardia (>100/min) is common, but may not be present in patients with cardiac or neurological causes or in those taking B-blockers. A few patients with hemorrhagic shock have a paradoxical bradycardia. 
  • Altered consciousness and fainting (especially on standing or sitting up) may result from decreased cerebral perfusion. 
  • Poor peripheral perfusion Cool peripheries, clammy/sweaty skin, pallor, decreased capillary return, but note that in the early phase of endotoxic septic shock there may be vasodilatation with warm peripheries. 
  • Oliguria decreased renal perfusion with urine output <50 mL/hr ( in adults)
  • Tachypnoea
Classification of shock

Traditional classification of types of shock is artificial -mixed aetiologies are common. 

Hypovolemic shock 

  • Blood loss: trauma gastrointestinal bleed, ruptured abdominal aortic aneurysm, ruptured ectopic pregnancy. 
  • Fluid loss/redistribution (third spacing): burns, GI losses (vomiting, diarrhoea ), pancreatitis, sepsis. 
Cardiogenic shock

  • Primary: myocardial infarction (MI), arrhythmias, valve dysfunction, myocarditis. 
  • Secondary: cardiac tamponade,  massive pulmonary embolus, tension pneumothorax. 
Septic shock

More common at the extremes of age, in patients with diabetes mellitus, renal/hepatic failure and the immunocompromised ( eg HIV infection, underlying malignancy, post-splenectomy, steroid therapy ). Note that fever rigors and increased white cell count (WCC) may not be present. 

  • Organism responsible include Gram +ve and Gram -ve, especially Staph, aureus, strep, pneumonia, N meningitidis, coliforms including enterococci and Bacteroides ( especially in patients with intra-abdominal emergencies, such as a ruptured diverticular abscess ). In the immunocompromised, pseudomonas, virus, and fungal may cause septic shock. 
Anaphylactic shock

Anaphylaxis is a generalized immunological condition of sudden onset, which develops after exposure to a foreign substance. The mechanism may. 

  • Involve an IgE-mediated reaction to a foreign protein ( stings, foods, streptokinase), or to a protein-hapten conjugate (antibiotics ) to which the patient has previously been exposed. 
  • Be complement-mediated (human proteins eg blood products)
  • Be unknown 
Irrespective of the mechanism, mast cells and basophils release mediators (eg histamine, prostaglandins, thromboxanes, platelet-activating factors, leukotrienes) producing clinical manifestations. Angio-oedema caused by ACE inhibitors and hereditary angioedema is not usually accompanied by urticaria and is treated with C1 esterase inhibitor. 

Other causes include Neurogenic, poisoning and addison disease 

Management of shock

Investigation and treatment should occur simultaneously. 

  • Address the priorities -ABC
  • Give high flow O2 by mask
  • Secure adequate venous access and take blood for FBC, U&E, glucose, liver function tests (LFTs) , lactate, coagulation screen, and if appropriate, blood cultures.
  • Monitor vital signs, including pulse, BP, SpO2 respiratory rate
  • Check ABG
  • Monitor ECG and obtain 12 lead ECG and CXR.
  • Insert a urinary catheter and monitor urine output hourly.
  • For shock associated with decreased effective circulating blood volume, give IV crystalloid (0.9% saline) 20mL/kg as bolus. Give further IV fluids including colloid may blood (aim for hematocrit (Hct) >30%) according to aetiology and clinical response ( and in particular, pulse, BP, central venous pressure, and urine output). Use caution with IV fluid infusion in shock related to cardiogenic causes, and in ruptured or dissecting aortic aneurysm. 
  • Look for, and treat specifically, the cause of the shock, Echocardiography, USS, CT, and surgical intervention may be required. Specific treatments include :
    • Laparotomy: ruptured abdominal aortic aneurysm, splenic and liver trauma, ruptured ectopic pregnancy, intra-abdominal sepsis. 
    • Thrombolysis/angioplasty :MI
    • Thrombolysis: PE
    • Pericardiocentesis/cardiac surgery : cardiac tamponade, aortic value dysfunction. 
    • Antidote: for certain poisons
    • Antibiotics: sepsis. The choice of antibiotic will depend upon the perceived cause and local policies. Where there is no obvious source, empirical combination therapy is advised
    • Inotropic and vasoactive therapy, assisted ventilation are often needed as part of goal-directed therapy. 

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