Shock

Published on 23/06/2015 by admin

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2.5 Shock

Kevin Mackway-Jones

1 Shock is a syndrome that arises because of acute failure of the circulation resulting in inadequate tissue perfusion. It may result from hypovolaemic, cardiogenic, distributive, obstructive or dissociative causes.

2 The normotensive child may have profound compensated shock.

3 As tachycardia may be a non-specific sign and hypotension occurs late, it is crucial to recognise the early features of shock in a child by assessing indices of peripheral perfusion and alterations of end organ function.

4 The initial management of shock should be volume expansion with a bolus of 20 mL kg^–1 crystalloid. Further boluses are given according to clinical response. Occasionally, in the exsanguinating child, universal donor blood is indicated.

5 The ongoing management of the shocked child will depend on the specific cause and may include interventions such as: oxygenation, ventilation, glucose administration, cardioversion, broad-spectrum antibiotics, inotropic support, ductus arteriosus manipulation, adrenaline (epinephrine), atropine or surgical intervention.

Introduction

Shock, in the sense described in this chapter, is a syndrome that arises because of acute failure of the circulation. This acute circulatory failure results in inadequate tissue oxygenation and inability to remove the waste products of metabolism. Shock is a complex construct, having many causes and many expressions. The clinical diagnosis and management of shock is complicated by the fact that many organ systems become involved and because many of the ‘signs of shock’ actually arise because of the body’s attempts at homeostasis rather than because of the underlying process.

The adequacy of circulation (and thereby the adequacy of tissue perfusion) requires proper functioning of the heart, vessels and blood. The heart must pump enough blood to meet peripheral oxygen demand; the vessels that deliver the blood to both the lungs and the other organs must be patent (that is not obstructed), be regulated appropriately at a macro level to ensure delivery of blood at an appropriate pressure to the organs requiring oxygen, and must function appropriately in the periphery so as to allow oxygen diffusion without fluid loss. The blood must have sufficient oxygen carrying capacity and must maintain the ability to allow oxygen exchange. Failure of any aspect of this complicated system will result in inadequate peripheral tissue perfusion and therefore shock.

Conventionally shock is divided into the following five types:

• hypovolaemic

• cardiogenic

• distributive

• obstructive

• dissociative.

Hypovolaemic shock arises when there is circulatory volume inadequacy. This classically arises in trauma following haemorrhage or burns but it is also seen following gastrointestinal fluid losses such as diarrhoea and vomiting or third space losses such as in volvulus. Cardiogenic shock occurs when the heart fails to pump enough fluid. This can occur because the heart itself is failing secondary to infection, because the heart muscle has been injured (such as in cardiac contusion) or because of a problem with rhythm where the heart is beating too slow or too fast to achieve an adequate cardiac output. In distributive shock, peripheral vascular abnormalities result in failure to appropriately distribute pumped blood. This can be because of infection (as in the septic child), allergic reaction, spinal cord injury or drugs. Obstructive shock arises when there are abnormalities of flow. This can either be because particular vessels themselves are obstructed (such as in pulmonary embolus) or because of extra vascular abnormalities which obstruct the flow of blood (such as tension pneumothorax or cardiac tamponade). Finally, dissociative shock arises when the oxygen carrying capacity of the blood is too low (as in anaemia) or has been reduced as in carbon monoxide poisoning.

Diagnosis and assessment

In all ill children the first need is to recognise the seriousness, or impending seriousness of the condition. This requires a systematic approach to assessment that involves looking at the airway, breathing, circulation, neurological status and exposing the child.

Airway

The ability to speak or cry without stridor indicates a patent airway. The presence of adequate breathing as assessed by looking at chest wall movement, listening and feeling for exhaled air also indicates an adequate airway.

Generally, shock affects the airway by reducing conscious level. In acute allergic reaction, airway obstruction (by swelling in the upper airway) and shock due to changes in vascular tone, can both arise as part of the same process.

Breathing

The effort of breathing, efficacy of breathing and effects of inadequate respiration should be examined. Oxygen saturation and respiratory rate should be monitored.

Circulation

This is the crux of shock assessment since homeostatic mechanisms function particularly well in children and compensation for inadequate circulatory function is good. Consequently, in a child it can be difficult to detect circulatory failure until a late stage, hence one needs to be vigilant in detecting the earlier features of compensating shock.

Circulatory assessment should look at both circulatory status and also at the effects of inadequate circulation on other organ systems.

Heart rate and blood pressure are the classical measures of circulatory status but changes in skin perfusion (as shown by capillary refill and by skin pallor or temperature) can be more useful in detecting the early signs of compensated shock.

Heart rate

Tachycardia (relative to age norm) is a key sign of shock (see Chapter 1.1). This tachycardia is a homeostatic response to maintaining cardiac output. Bradycardia may occur pre-terminally in the child with overwhelming shock, and untreated will progress to asystole. The peripheral pulses may be weak, thready or absent.

Blood pressure

While it is true that a child with hypotension is shocked it is not true to say that a child that is normotensive is not shocked. This is because maintenance of blood pressure is the key end point of the homeostatic response, and decompensation (and thereby hypotension) occurs late and may be precipitous. The accurate measurement of blood pressure in a distressed child can be a challenge in itself and a judgement as to whether a particular blood pressure is normal or abnormal in a particular age group in any particular circumstances is also challenging. Many widely quoted normal ranges by age are broad – furthermore many of these were derived in the resting outpatient child rather than in the seriously ill or injured child.

Capillary refill

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