Shock
Shock is a very serious condition in which there is a dramatic reduction in blood flow throughout the body. More precisely it is a failure of the micro-circulation (basically the capillary network) to provide an adequate blood supply to the tissues, resulting in a multi-system disorder. In this situation cells are deprived of oxygen and nutrients, and waste products are not removed. Local cellular death will eventually occur, followed by death of the animal. Various categories of shock can be recognised, but of most practical importance is hypovolaemic shock (“low volume shock”) due to loss of blood, plasma, or just water and electrolytes. This can be caused, for example, by severe haemorrhage or dehydration. Other causes include severe wound infection, peritonitis, abscesses in internal organs etc – in which cases it is known as “septic shock”. In rare cases shock may even result from an adverse reaction to anaesthetic drugs. Whatever the cause, the main effect is insufficient liquid in the blood vessels to keep capillaries open and functioning, and if treatment is delayed too long, damage to cells is irreversible resulting in death.
Animals suffering from lesser degrees of fluid or blood loss may not actually be in shock as various adjustments in the body’s fluid distribution will have been made to compensate for these losses to maintain the microcirculation. However, they are at risk of developing shock – particularly when anaesthetic drugs are administered – and such losses should be replaced. In other words, the best way to deal with shock is to prevent it from occurring.
Dehydration should be suspected if the eyes are sunken, the mucous membranes dry and the skin lacks elasticity (not returning to normal position within 2-3 seconds of pulling up a patch of loose skin).
Signs:
Weak and rapid pulse which may also be irregular, low blood pressure, pale or cyanotic (bluish) mucous membranes with prolonged capillary refill time, rapid heartbeat, hyperventilation or shallow sporadic breathing, cold extremities, hypothermia.
Action:
- Correct any obvious cause, e.g., stop any haemorrhage, stop gas anaesthesia and/or reverse injected anaesthetic agents (but be aware of safety implications).
- Place in lateral recumbency with the head low, airway clear and hindquarters a little higher than the head.
- Give intravenous fluids rapidly.- 40 ml/kg of crystalloid solution such as lactated Ringers solution. If dehydration is severe, up to 100 ml/kg can be given. Use a large bore needle and the large veins such as jugular or femoral. Ideally, in addition give 10 ml/kg colloidal solution (i.e. plasma substitute)
- If it is impossible to give fluids intravenously, it is still advantageous to give them subcutaneously, although the effect will not be as rapid.
- Give broad spectrum antibiotics at standard doses. (Shock impairs the integrity of the gut lining which can result in bacteraemia).
- Give dexamethasone at 5 mg/kg by slow intravenous administration over 30 seconds.
- Maintain body temperature – cover in a blanket or thermally insulated material.
- Provide oxygen if available.
- Monitor vital signs very closely – especially capillary refill time and pulse rate and quality.
