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Diagnosis of shock

When we attempt to diagnose shock what we are really looking for are signs of failing organs due to inadequate perfusion. In other words, organ dysfunction. We can start this process from the end of the bed.

Respiratory rate: Tissue hypoxia will result in a metabolic acidosis. This will normally stimulate hyperventilation to create a compensatory respiratory alkalosis. If the respiratory rate is normal and there are no signs of respiratory distress (or other factors that could compromise the hyperventilatory response like head injury or opiates) then tissue hypoperfusion will be less likely.

On the flip site of this, a patient with a high respiratory rate does not necessarily have a respiratory problem (which is often the first assumption made in clinical practice). It may merely be a sign of metabolic distress and respiratory compensation.

Level of consciousness: If the patient is awake and lucid then brain function is probably OK suggesting adequate brain perfusion and oxygen delivery.

Skin colour: Pink would be reassuring, grey or mottled would be less so, suggesting poor perfusion.


We can then go onto gain information from touching the patient:

Peripheral temperature: If the patient is peripherally warm it would tend to suggest that skin perfusion is adequate and that marked vasoconstriction was absent. This would be reassuring. Capillary refill of less than 2 seconds would provide similar reassurance. As with all these signs, this should not be used in isolation. A patient with septic shock may well have warm peripheries.

Heart Rate: Tachycardia may signify an attempt to maintain CO in the face of decreasing SV.


Then we can look at other things:

Urine output: A healthy urine output of >0.5ml/kg/hr suggests adequate renal perfusion. It is a late sign of shock and can take some time to improve even after adequate resuscitation.

Blood pressure: Commonly measured before all the indices above but as we have seen, not necessarily always reassuring in isolation.

So, if the patient is alert, looks a normal colour, has a normal respiratory rate, is warm peripherally, has a normal heart rate and is passing adequate amounts of urine their oxygen delivery is most probably adequate and shock unlikely. If one or more of these signs are present then it is safer to assume shock than ignore it.

If suspicious, the next steps would be to observe closely for further deterioration and hunt for more evidence of inadequate perfusion. An excellent “next step” investigation would be to perform an arterial blood gas (ABG) looking for a metabolic acidosis (even better if the ABG included a lactate). A metabolic, and particularly a lactic acidosis would provide further evidence of organ failure and inadequate oxygenation. Making a diagnosis early is vital for survival. Indifying the source of sepsis, for example, allow early treatment with appropriate emperic antibiotics or source control (e.g. incision of abscess, debridement of infected tissues).

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