Editing Shock

''Shock is acute circulatory failure, with inadequate tissue perfusion causing cellular hypoxia''

* ''Can't be defined using systemic parameters, as it is possible to have inadequate perfusion with normal blood pressure''

== Aetiology ==

=== Hypovolaemia ===

** Haemorrhage
** Fluid loss
** Dehydration

=== Cardiogenic ===

** MI
** Heart failure
** Arrhythmia

=== Obstructive ===

** PE
** Cardiac tamponade
** Pneumothorax

=== Distributive ===

** Sepsis
** Neurogenic
** Anaphylaxis
** Adrenal insufficiency

== '''Pathophysiology''' ==

=== '''Haemorrhagic/hypovolaemic''' ===

** Tachycardia and increase in cardiac contractility - attempt to preserve cardiac output (usually first signs)
** Endogenous catecholamines increase PVR, which increases DBP and reduces pulse pressure, but does not increase tissue perfusion
** Vasoconstriction of cutaneous, muscular and visceral circulation - preserve flow to kidneys, heart and brain - increases PVR
** Contraction of volume of blood in venous system
** Shift to anaerobic metabolism - lactic acid forms, and metabolic acidosis - which can progress to end-organ damage/MODS
** Stress hormone activation
** Systemic inflammatory response from wounds, treatment, stress hormones

=== '''Cardiogenic''' ===

** Primary cardiac disorder characterised by low cardiac output resulting in end-organ hypoperfusion and tissue hypoxia
** Myocardial ischaemia results in depressed myocardial contractility, reducing cardiac output and blood pressure
** Compensatory action of the SNS leads to peripheral vasoconstriction, preserving coronary perfusion at the cost of increased afterload
** Tachycardia increases myocardial oxygen demand

=== '''Obstructive''' ===

** Tamponade
*** Rapid accumulation of pericardial fluid results in compression to cardiac chambers and subsequent diastolic failure (reduced preload)
*** Cardiac output reduces
*** Compensatory tachycardia to attempt to overcome the reduced output
** Tension pneumothorax
*** Increased intra-thoracic pressure compresses the mediastinal structures and prevents filling of SVC and IVC, leading to reduced preload
*** There is also increased pulmonary vascular resistance
*** Cardiac output is compromised
** PE
*** Increased pulmonary vascular resistance due to a combination of mechanical obstruction and hypoxic vasoconstriction
*** Increased right ventricular afterload compromises right-sided output, and prevents downstream left ventricular filling, which results in reduced overall cardiac output

=== '''Distributive''' ===

** Sepsis/anaphylaxis
*** Inflammatory cytokines induce systemic vasodilation and capillary leak, and sometimes a direct cardiomyopathy
*** See separate topic 'Sepsis/SIRS'
** Neurogenic
*** Loss of sympathetic outflow beneath the level of injury means reduced catecholamine delivery and subsequent vasodilation
*** Similar condition can be seen with epidurals
*** ''Differentiate from spinal shock - a neurological phenomenon where there is immediate temporary loss of power, reflexes and sensation below the level of the injury''
** Adrenal insufficiency
*** Decreased alpha-1 receptor expression on arterioles secondary to cortisol deficiency, resulting in vasodilation
*** Seen with sudden withdrawal of chronic steroids
** Common pathway
*** Reduced venous return and reduced cardiac output
*** Reduced perfusion to vital organs

== Clinical features of subtypes of shock, in addition to generic features of hypo-perfusion ==

* Cardiogenic
** Similar to hypovolaemic shock
** Elevated CVP or JVP and pulmonary oedema, but low arterial pressure
* Obstructive
** Tachycardia
** Elevated JVP
* Septic
** Warm peripheries early
** Lower SVR meaning lower diastolic pressure
** Tachycardia
** Confusion
* Hypovolaemic
** Tachycardia
** Cool peripheries
** Decreased pulse pressure

== Clinical features of decreased tissue perfusion ==

* Cool peripheries
* Poor filling of peripheral veins
* Increased RR
* Increased core-peripheral temperature gradient
* Prolonged CRT
* Poor signal on pulse oximeter
* Poor urine output (<0.5mL/kg/hr)
* Anxiety/restlessness
* Decreased consciousness level
* Metabolic acidosis or raised serum lactate

== Treatment ==

* Diagnose and treat the underlying cause
* For hypovolaemic/vasodilatory shock:
** 10mL/kg crystalloid if normotensive
** 20mL/kg crystalloid if hypotensive
** Oxygen in high flow via non-rebreather bag
* Venous access
* IDC
* ECG monitoring
* Pulse oximetry monitoring
* CVC
* Assess response after 30 minutes, and change plan if the patient is not improving



[[Category:Critical care]]
[[Category:Intern education]]