shock Flashcards
what is it?
No standard definition - A syndrome in which tissue perfusion is inadequate for the tissue’s metabolic requirement
A state of cellular and tissue hypoxia due to either reduced oxygen delivery, increased oxygen consumption, inadequate oxygen utilisation, or a combination of these processes
what does normal tissue perfusion rely on?
o Cardiac Function
o Capacity of vascular bed
o Circulating blood volume
what is the imperfect estimation that is clinically used for tissue perfusion?
BP
what are the types of shock?
- Hypovolaemic
- Cardiogenic
- Distributive
- Obstructive
- (Endocrine)
how does hypovolaemic shock happen?
- An acute haemorrhage or fluid deplete states – severe dehydration or burns
- Volume depletion – leading to reduced SVR
- Reduced volume returning to heart – reduced pre-load and hence reduced CO.
how does cardiogenic shock happen?
Pump failure” – reduced CO
o Reduced contractility – “stroke volume”
o Reduced heart-rate
Primarily ischaemia induced myocardial dysfunction Also: cardiomyopathies, valvular problems, dysrhthmias
If due to MI – suggests that >40% of LV is involved.
what is the prognosis of cardiogenic shock?
Unless correctable pathology (E.g. valvular), mortality >75%
how does obstructive shock happen?
Mechanical obstruction to normal cardiac output in an otherwise normal heart Direct obstruction to cardiac output o PE o Air/Fat/Amniotic fluid-embolism Restriction of cardiac filling o Tamponade o Tension pneumothorax
how does distributive (vasopleic) shock happen?
‘hot’ shock
septic, anaphylaxis, acute liver failure, spinal cord injuries
- happens because one of the above disrupt normal vascular autoregulation and cause profound vasodilatation
• Poor perfusion – despite increased CO
• Regional perfusion differences
• Alteration of oxygen extraction
how does endocrine shock happen?
- Severe uncorrected hypothyroidism, Addisonian crisis – both reduced CO and vasodilatation
- Paradoxically – thyrotoxicosis
What is the neuroendocrine response to shock?
- Release of pituitary hormones – adrenocorticotrophic hormone, anti-diuretic hormone, endogenous opioids
- Release of cortisol – fluid retention, antagonises insulin
- Release of glucagon
- Suggestion that some shock states (sepsis) blunts the response to ACTH
how does shock present?
pale
cold skin
prolonged capillary refill
what are different physiological processes which can indicate shock and poor tissue perfusion?
- Urine output – Sensitive indicator of renal perfusion
- Neurological – Disturbed consciousness a good indicator of cerebral hypoperfusion
- Biochemical – Acidosis, lactate levels
- Blood pressure – either cuff, or invasive with arterial line
- Central Venous Pressure – Value in itself rarely useful, can be useful to assess “fluid responsiveness”
what are pulmonary artery pressures and how are they useful in shock monitoring?
o Pulmonary capillary wedge pressures (surrogate for LA pressure)
o Rarely used in mainstream practice – due to risks of devices, and lack of familiarty with equipment/interpreting results.
how is cardiac output monitoring done in shock?
o Gold standard – Thermodilution with a PA catheter – Again rarely used outside specialist units
o Pulse contour analysis
o Doppler ultrasonography
basic principles of shock management?
- Prompt diagnosis, and treatment critical
- ABC approach
- Establishment of reliable, wide bore IV access and resuscitate while investigating
- Identify – and treat – underlying cause
- Fluid management
how is fluid managed in shock?
increase pre-load
rapid fluid replacement (minutes) - have to balance this with risk of fluid overload
shocked patients are more at risk of pulmonary oedema because of microvascular dysfunction
o Crystalloids – Convenient, cheap, safe But: Rapidly lost from circulation to extravascular spaces, need significantly larger volumes than loss.
o Colloids – Cheap(ish), reduce volumes required But: Can cause anaphylaxis, no evidence of benefit
o Blood – oxygen carrying capacity, will stay in circulation. But: a scarce resource, and multiple risks
what drugs can be given if fluids alone aren’t working?
Need to be administered in a critical care environment (HDU +)
- Adrenaline (Epinephrine) – alpha/beta adrenergic agonist, but at low dose primarily beta (Inc. heartrate, contractility, vasodilatation)
- Noradrenaline (Norepinephrine) – predominantly alpha agonist (vasoconstriction)
- Vasopressin (ADH)
- Dopamine – Natural precursor to the above. Complex dose-dependent effects
- Dobutamine/Dopexamine
how is hypovolaemic shock managed?
o Assessment of bleeding – estimation of volume loss, and speed of ongoing loss.
o Establish source – may require imaging if stable
o Temporisation – Direct pressure, tourniquet’s
o Damage limitation resuscitation – until definitive control
o Damage limitation surgery
how should de-escalation/de-resuscitation take place once the patients shock has resolved?
o Importance of removing extra fluid from a patient once their shock has resolved.
o Growing body of evidence associating gross positive balances in the recovery phase with increased morbidity/mortality
o Mortality benefit in getting patients “dry” as early in their hospital stay as possible.
o Various means: Spontaneous, Diuretic, Dialysis
