"improving intensive care in Scotland"

Shock

Clinical example

The bleeding patient: Acute blood loss leads to a loss of circulating volume. This will reduce venous return and therefore end-diastolic volume (pre-load). The Starling curve then dictates that the patient will move from right to left with a resultant drop in SV.

 

Shock starling

The Starling curve

The patient will attempt to compensate for this. The priorities is to maintain oxygen delivery and perfusion pressure.

  • DO2 = CO X [oxygen content]

To maintain flow the patient must maintain CO.

CO = HR x SV

As SV is dropping due to volume loss the only way to maintain CO is to increase the HR.

  • BP = CO x SVR

To maintain perfusion pressure the patient must maintain flow (as above) and resistance (vascular tone).

As CO will tend to fall as the HR compensation reaches its maximum the only way then to maintain BP is to increase SVR. This will result in peripheral vasoconstriction; cold peripheries.

So the bleeding patient will become tachycardic with cold peripheries! The other signs of increased respiratory rate, decreased urine output, grey skin colour, confusion will also become apparent if the problem is not corrected.

To reverse these effects we need to restore normal physiology. Fluid will increase pre-load, move us back towards the right of the Starling curve, SV will therefore increase. If the SV increases we will need less of a HR to maintain a similar CO. HR will therefore decrease (a good marker of improving volume status), Fig 8.

Of course giving fluid other than blood may increase flow but it will not increase oxygen carrying capacity. If a large amount of fluid is required (normally greater than 30% circulating volume) one should consider administering blood to maintain oxygen carrying capacity.

As CO improves, BP will be maintained with a lesser SVR. The patient will become warmer peripherally. In fact it is often useful to document at which point the patient becomes peripherally warm before you start resuscitation (wrist, elbow, mid humerus, shoulder). The improvement in this point can be used as a useful yardstick of adequate resuscitation.

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