Shock

Shock is a circulatory failure resulting in inadequate organ perfusion - basically, if you're not getting enough oxygen to the important bits and pieces, you're probably in shock. There are lots of different causes of shock but there are four important types of shock:

• Cardiogenic shock - your heart isn't pumping efficiently enough
• Hypovolaemic shock - literally "low-volume" shock i.e. there isn't enough blood
• Septic shock - due to a blood infection
• Anaphylactic shock - a life-threatening allergic reaction

There are other types of shock but these are much rarer. Endocrine failure due to Addison's disease or hypothyroidism. Neurogenic and iatrogenic shock (in anaesthetics and with antihypertensives) can also occur.

In shock, one of two thing has happened: the pump (i.e. the heart) or the peripheral circulation is in failure. Cardiogenic shock covers the first category but all the others generally fall into the "peripheral circulation failure" category. If in doubt assume hypovolaemic shock. The details of this are outlined below

Hypovolaemic shock

Definition

Shock due to reduction in the volume of circulating fluid. Generally, do something if the Systolic BP < 90 - that's never good.

Epidemiology

If you only learn one thing before you become an F1 learn to manage shock. It's common and people die from it so if we had bothered to make an "Common And Important" .jpg, it would have been specifically for this condition.

Pathophysiology

Often, the cause of the shock is unknown and you just have to engage in some general management. Hypotension affects two bits: the sympathetic nervous system and renin-angiotensin-aldosterone system. The sympathetic nervous system causes vasoconstriction. Renin, released in the JGA of the kidney in hypotension, causes angiontensin-converting enzyme to convert angiontensin I to angiotensin II, a vasoconstrictor. This in turn causes aldosterone release in the adrenal glands, which causes salt and water retention.

Clinical Features

Essentially, there are three bits to hypovolaemic shock which cause symptoms: tissue perfusion, increased sympathetic tone, metabolic acidosis.

• Inadequate tissue perfusion
  • Skin - cold, pale, blue, CRT>2s (capillary refill time), clammy
  • Kidneys - oliguria or anuria
  • Brain - drowsy, confused, irritable
• Increased sympathetic tone
  • pulse - tachycardic, weak
  • blood pressure - maintained initially but later hypotension, narrowed pulse pressure (systolic - diastolic <25mmHg)
  • sweating

Investigations

• ECG - to identify cardiogenic shock
• CXR
• FBC
• U+E
• ABG
• Blood glucose
• CRP
• Cross-match blood and check clotting
• Cultures - blood, urine
• Others: lactate, echo, abdominal CT, USS

Management

If BP unrecordable, call cardiac arrest team.

• ABC
  • Give high-flow 100% O₂
• Raise foot of bed - everybody always forgets this but it's quite important and can help
• IV access x 2 - wide-bore cannulae
• Treat cause
• Infuse 500ml 0.9% saline fast don't do this if you know it's cardiogenic shock

Then do all your investigations. Consider putting in arterial and central line and record urinary output with a bladder catheter. Replace fluids guided by BP, CVP and urine output and consider inotropic support in hypotension.