Resuscitation in Hypovolaemic Shock

Hypovolaemic shock occurs when the volume of the circulatory system is too depleted to allow adequate circulation to the tissues of the body. The aim of resuscitation is to correct the hypovolaemia and hypoperfusion of vital organs such as the kidneys before irreversible damage occurs.

A healthy adult can withstand the loss of half a litre from a circulation of about 5 litres without ill effect but larger volumes and rapid loss cause progressively greater problems.
Risk is very much related to the degree of hypovolaemia and the speed of correction. In young adults the circulatory system is much better able to cope with the rigours of loss. The risk of morbidity and mortality is much greater as age increases. Pathology in the cardiovascular, respiratory and renal systems increases risk.

Symptoms

• The individual may feel cold, unwell, anxious, faint and short of breath.
• There may be faintness on standing or even sitting up due to postural hypotension.
• There may be symptoms related to the cause of the hypovolaemia such as pain from a bleeding ulcer, dissecting aneurysm, ruptured ectopic pregnancy, trauma or burns.
• Gut ischaemia can lead to nausea and vomiting but the significance is often overlooked.

Signs

• The patient will probably look pale and sweaty.
• There may be tachypnoea.
• The periphery will be cold from poor perfusion and capillary refill time will be prolonged. However, this may be a poor indicator of hypovolaemia.¹
• There will be tachycardia and a fall in blood pressure or postural hypotension. However, tachycardia is a later feature than the cold periphery and a fall in blood pressure occurs still later. This is particularly so in a young person, compared with an old person.
• Young people may show little rise in pulse rate and no fall in BP despite significant exsanguination. It is very easy to underestimate the severity of loss in a young person.
• Late features include confusion or even coma.

Pulse rate, BP and core temperature should be recorded. Heat exhaustion may be associated with a rise in core temperature requiring active cooling and extensive burns are associated with loss of thermoregulatory ability.² This means both excessive heat loss and reduced response of sweating when temperature rises.

The causes of hypovolaemic shock are:

• Loss of blood which may be revealed or occult.
• Trauma may lead to visible bleeding or rupture of an internal organ like spleen or liver. A fractured femur will bleed about half a litre and a fractured pelvis will lose about a litre of blood. The volume of haematemesis gives little indication of the degree of bleeding. Bleeding from ectopic pregnancy is also occult with little or no vaginal loss and 30% of ectopic pregnancies rupture before a menstrual period has been missed. It is important to maintain a high level of clinical suspicion.
• Leakage of plasma and often some blood as in burns.³
• Severe loss of water and salt. This may occur with vigorous exercise in a hot environment, poor intake, loss from diarrhoea and vomiting and inappropriate diuresis.

The surface area of burns should be estimated using the rule of 9s. The larger the area involved the more severe the problem, especially in children and the elderly. In children the rule of 9s does not apply but as a guide the child's palm represents about 1% of surface area. Children need relatively more fluid than adults.⁴
Severe diarrhoea and vomiting will cause marked loss of salt and water. In cholera, diarrhoea can be up to 20 litres a day. Exercise in extreme heat can cause serious loss of water and salt. As the rate of sweating rises the concentration of Na in the sweat rises so that the total loss of Na rises exponentially. Ability to remove Na from sweat improves with acclimatisation.
Other causes of shock include:

• Poor cardiac output as in massive myocardial infarction, ruptured aortic valve or massive pulmonary embolism.
• Septic shock and acute pancreatitis lead to a fall in vascular resistance.
• So too can a high transection of the spine or a high spinal anaesthetic.

• Check Hb, U&E and in haemorrhage and burns, group and cross match.
• Get coagulation screen.
• Blood gases may show a metabolic acidaemia from poor perfusion.
• Monitor urine output. This may require a catheter but if possible it is best avoided.

For adults the clinical staging relating to loss of blood volume can be classified as:

• Class 1 : 10 to15% blood loss; physiological compensation and no clinical changes appear.
• Class 2 : 15 to 30% blood loss; postural hypotension, generalised vasoconstriction and reduction in urine output to 20 to 30 ml/hr;
• Class 3 : 30 to 40% blood loss; hypotension, tachycardia over 120, tachypnoea, urine output under 20 ml/hr and the patient is confused;
• Class 4: 40% blood loss; marked hypotension, tachycardia and tachypnoea. No urine output and the patient is comatose.

Physiologically three stages of hypovolaemic shock are recognised:

• Compensated shock is when baroreceptor reflexes result in increase in myocardial contractility, tachycardia and vasoconstriction. They maintain cardiac output and blood pressure and lead to the release of vasopressin, aldosterone and renin.
• Progressive or uncompensated shock occurs with myocardial depression, failure of vasomotor reflexes and failure of the microcirculation with increase in capillary permeability, sludging and thrombosis resulting in cellular dysfunction and lactic acidosis.
• Irreversible shock means failure of vital organs with inability to recover.

These stages are also applicable to children but their cardiac reserve is less, so that uncompensated shock can progress more rapidly to the irreversible stage.

Non-Drug

• Oxygen should be given.
• Venous access must be secured early. It is more difficult to achieve once further circulatory collapse has occurred. There may be some concern that fluid replacement before arrest of haemorrhage may encourage further bleeding but maintaining adequate perfusion of vital organs is more important.⁵
• Resuscitation is usually started with crystalloid such as normal saline or Hartmann's solution although some people prefer colloids from the outset⁶. Studies have shown that there is remarkably little to choose between the two^{7 8} but albumin should be avoided in the seriously ill patient as it is associated with a worse outcome.⁹ In haemorrhage, blood should be given as soon as possible. Rapid infusion devices and autologous blood transfusion may be employed if blood loss is massive and fast.¹⁰
• A Central Venous Pressure line may be required. CVP is far more sensitive to the balance between loss and replacement than pulse or BP and in the elderly it can prevent over transfusion and pulmonary oedema. Particularly in young patients, there is a tendency towards over-replacement to prevent tissue ischaemia, although the evidence base is surprisingly scarce.⁸ In burns a high CVP may be required to maintain adequate output of urine.
• As a first aid measure in burns Clingfilm™ or some such polyethylene film is very useful both to prevent infection that can convert a superficial burn to full thickness and to reduce fluid and plasma loss.

Drugs

• Traditional teaching is that vasopressors have no part to play as they will only increase tissue ischaemia. However, there may be a place if there is failure to respond to volume replacement but the evidence is inconclusive.¹¹
• Vasodilator therapy is for the intensive care specialist. It is used more for septic shock. If hypovolaemia is the problem, volume should be replaced.
• If there is pain, analgesia must be given by the iv route as any other route will be ineffective. Pain increases metabolic rate and so aggravates tissue ischaemia.

Surgical

• If bleeding continues surgery may be needed to stem the flow. It is usual to resuscitate first to reduce the risk, especially as induction of anaesthesia can lead to collapse of a fragile circulation. In some cases like ruptured ectopic pregnancy and placenta praevia the rate of bleeding cannot be matched by transfusion and the cause must be treated before resuscitation can be effective.
• In trauma, first aid measures may help stem blood loss. In gunshot wounds look for not just the entrance but also the exit wound. The latter may be significantly larger than the former. If a high-powered weapon was used primary closure of the wound should not be attempted.

• Blood is directed away from the kidneys and gut. This can produce acute renal failure and complications of gut ischaemia.
• In obstetric shock, acute tubular necrosis can occur.
• Inadequate perfusion leads to hypoxia and metabolic acidosis.
• About 75% of the blood flow to the right ventricle and 100% to the left ventricle occurs in diastole. A fall in diastolic pressure will predispose to cardiac arrhythmias and even arrest. Upset of acid/ base balance, hypoxia and disturbance of electrolytes will aggravate the problem.
• In those who are susceptible, dehydration may lead to haemoconcentration and sludging of the circulation with such complications as venous sinus thrombosis.

Prognosis is worse in the elderly than the young. Physical fitness improves outcome. Rapid and adequate replacement of the circulating volume will prevent the complications of hypoperfusion, including renal failure, ischaemic damage to the gut, brain damage and cardiac arrest.

• Loss of circulating volume must be diagnosed and treated before the condition becomes critical. This is often difficult when bleeding is internal and hence occult. It is often poorly done.¹²
• Where the loss is simply salt and water, oral replacement will be adequate in the early stages.
• In other cases venous access and adequate replacement is required at an early stage.
• Small children are very susceptible to dehydration as are the elderly.
• Nowadays sportsmen are very much more aware of the problems of dehydration. Even slight dehydration has a marked adverse effect on fitness. Long distance races usually have water stations but this is a comparatively recent innovation. In 1952, Emile Zatopek ran the Olympic Marathon in Helsinki in a time of 2 hours, 23 minutes and 3 seconds. This may seem unimpressive by modern standards but he did this wearing plimsoles, without water stations and this was the first time he had ever run a marathon. He beat the world record holder Jim Peters who is unfortunately best remembered for his finish in the 1954 Empire Games in Vancouver. He was staggering, uncoordinated and disorientated from dehydration and was finally helped across the line. This led to his disqualification.