It’s been a leisurely start to the new year, but so far 2012 is shaping up to be remarkably like its predecessor. I go to university, I do my work, and my desire to pack up and move to Scandinavia continues to grow with every passing day. I’m standing on the cusp of my “Adventures in GP-Land” (which, come to think of it, is a terrific idea for an illustrated public health campaign- watch this space). But before I unleash my unparalleled powers of clinical reasoning in primary care I have to get through my SSC poster presentation on Friday.
You might think, assessment looming as it is, that I would have spent this week preparing, getting my patter slicker than brylcreem and coaching myself to answer questions with a clarity that would make a bowl of consommé envious. No. Panettone, focaccia, poppy seed loaves- I’ve baked the lot. But today is a new day, so I’ve renounced my baking tins and sachets of dried yeast in favour of my favourite medical tomes in an effort to produce this blog post and stop myself consuming my weight in bread products by the weekend.
I’ve decided to cover a topic that I covered at some point last year, in an effort to firmly cement it in my mind. Happily, it covers some really basic physiology and I think it’s always helpful to review the basics.
I’m not talking about the shock that sets in just after you realise you’ve devoured a whole loaf of freshly baked bread 14 minutes after you liberated it from its tin (I like to call this “Loaf Shock”). No, the term “SHOCK” is used to describe acute circulatory failure with inadequately/inappropriately distributed tissue perfusion. This results in generalised cellular HYPOXIA and/or inability of cells to utilise oxygen.
Abnormalities of tissue perfusion may result from:
- Failure of the heart to act as an effective pump
- Mechanical impediments of forward flow
- Loss of circulatory volume
- Abnormalities of the peripheral circulation
Often shock can result from a combination of these factors
Eg, in SEPSIS, distributive shock is frequently complicated by hypovolaemia and myocardial depression.
CAUSES OF SHOCK
- Hypovolaemic Shock
- Exogenous losses (eg, haemorrhage, burns)
- Endogenous losses
- Cardiogenic (eg, ischaemic myocardial injury: MI, PE, valve rupture)
- Obstruction to outflow (eg, pulmonary embolus)
- Restricted cardiac filling (eg, cardiac tamponade, tension pneumothorax)
- Distributive (eg, sepsis, anaphylaxis)
- Vascular dilation
- Arteriovenous shunting
- Maldistribution of flow
- Myocardial depression
Clinically, shock is:
Persistently low blood pressure:
- Systolic <90mmHg
- Reduction in 30mmHg if previously hypertensive
- Altered end-organ function (eg, confusion, oligourea)
Aggressive shock management should prevent blood pressure falling, and remember:
LOW BLOOD PRESSURE IS A LATE SIGN OF SHOCK!
THE PATHOPHYSIOLOGY OF SHOCK
BP = CO x SVR
CO = HR x SV
BP= Blood Pressure, CO= Cardiac Output, SVR= Systemic Vascular Resistance, SV= Stroke Volume
So, if Blood Pressure is low, it must result from either:
1) DECREASE IN CO
As CO = HR x SV
HR increases to compensate for low CO => TACHYCARDIA
As BP = CO x SVR
SVR increases to compensate for low CO => COLD/CLAMMY PERIPHERIES (sweating and pallor)
BP is therefore normal until these mechanisms fail.
2) DECREASE IN SVR
Common causes of SVR changes include:
- Spinal shock (where there has been transection of the spinal cord)
3) DECREASE IN SV
Common causes: Fluid Loss
- Haemorrhage (into thorax/ abdomen/ pelvis)
- Diarrhoea/ vomiting
- Bowel obstruction
- Urinary loss (eg, DKA)
So, to summarise,
There are 3 indices that can cause shock:
1) Cardiac output (cardiogenic shock)
2) Systemic vascular shock (anaphylaxis, sepsis)
3) Stroke volume (fluid loss- hypovolaemic shock)
REMEMBER! Adrenocortical failure (Addisonian Crisis):
- Hyperpigmentation of palmar creases/ buccal mucosa
- Treatment should be given simultaneously with evaluation
- Patient should be supported with respect to fluid balance
- ESTABLISH A CAUSE- this will ultimately influence management.
ABC (PRIMARY SURVEY)
- AIMS: maintain patent airway
- Give 100% O2 (via mask)
- Gain access to circulation by cannulation
CRUCIAL INVESTIGATIONS AND SUPPORT
- Blood glucose
- Pulse oximetry
- Blood gases/ blood tests
Specific management of shock depends on the cause of shock.
Eg, Hypovolaemic shock will require fluids, whereas septic shock will ultimately require antibiotics