Management of shock
When shock is present, tissue oxygen demand is higher than oxygen delivery. The management of shock therefore, aims at improving oxygen delivery and reducing oxygen demand.
These should be done at the same time as trying to provide definitive treatment of the underlying cause, e.g. thrombolysis of massive pulmonary embolism or laporotomy for perforated large bowel.
It is also important to appreciate that the worse the degree of shock, the quicker we have to act to improve the situation.
1) Improving oxygen delivery
The basis of managing the shocked patient is similar to the approach to any sick patient – ABCDE.
By ensuring a patent airway, adequate breathing and oxygenation, and optimising cardiovascular performance one would hope to avoid shock, stop its progression or reverse it. Once we have diagnosed shock clinically, the exact cause of shock is not vital to determine in the initial stages. More important is to embark on a generic “shocked” patient treatment pathway that will ensure prompt reversal of the shocked state.
Lets go back to formula A & B:
DO2 = CO x ([Hb x saturations x constant]
If oxygen delivery is failing then this can really only be due to one or more of three things:
- A low cardiac output: for which the treatment will depend on the cause (low preload, low contractility or high SVR). A fluid challenge would be a reasonable empirical first intervention as this will tend to improve the majority of patients (low pre-load).
- Anaemia: For which we can give blood to increase the oxygen carrying capacity of plasma.
- Hypoxaemia (low saturations): For this we can try and improve oxygenation by optimising airway and breathing.
Key message 2
The management of shock starts with ensuring a patent Airway and adequate Breathing to ensure optimum oxygenation.
BP = CO x SVR
We must also optimise perfusion pressure. This we can do by ensuring adequate CO as above and SVR. Sepsis is probably the most common shocked state with a low SVR. Noradrenaline is frequently used to increase SVR and maintain an adequate BP.
A useful word of caution regarding noradrenaline: Noradrenaline has become the first line drug for hypotension in many ICUs. One has to remember that it is not an inotrope but a vasopressor. It will increase the SVR generating a “normal” blood pressure, but this may be at the expense of increasing after load and reducing the CO and hence oxygen delivery. A great example of a “normal” blood pressure being misleading and flow being equally important to pressure.
2) Reducing oxygen consumption
Another important strategy to address the imbalance in oxygen demand and delivery which is present in shock, is to reduce oxygen consumption. E.g. a patient who suffers cardiogenic shock immediately after an MI. Here intubation and ventilation might form part of the management strategy, as this reduces work of breathing (which can be significant) and therefore oxygen consumption.
Adequate sedation, especially if the patient is agitated, is another way to reduce oxygen consumption.
Figure 8. Management of shock.
Principles of shock management
|Optimise oxygenation by ensuring patent Airway and adequate Breathing of high oxygen concentration and flow|
|Replace Hb if low|
|Use vasopressors to improve BP e.g. septic shock|
|Use inotrope to improve contractility if required e.g. dobutamine for cardiogenic shock|
|Adrenaline is a vasopressor and inotrope and can be used if cause of shock is unknown|
|Vasodilators are also used to reduce afterload and offload the heart in cardiogenic shock|
|Reduce oxygen demand|
|Call for HELP sooner rather than later if you are unsure|
|Adhere to you local ICU policy for inotrope/vasopressor dilutions|