Ch 52 Shock

CHAPTER 52

SHOCK

Outline: Definition Physiology Classification Signs and Symptoms Immediate treatment for shocked patients Specific treatment for hypovolaemic shock Anaesthetic management of the shocked patient Other forms of shock

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DEFINITION Shock is a state of inadequate tissue perfusion which may be caused by a reduction in the volume of circulating fluid, cardiac failure, neurogenic injury, sepsis, or a number of other causes. The danger of shock is that tissue perfusion (or the blood flow to the tissues) is severely reduced and the tissues are therefore damaged or die from lack of oxygen and nourishment. PHYSIOLOGY Three things are needed to maintain a normal blood pressure. A pump (in this case, the heart). The heart must contract efficiently. A circulating blood volume. The blood is pumped by the heart into the arteries and thence to the tissue capillaries. The veins collect the blood and return it to the heart. If the blood volume falls then the patient can go into shock. The peripheral resistance. This is the state of the small arteries (arterioles) and capillaries. If the peripheral resistance is high, it means that these small vessels are constricted. If the peripheral resistance is low, these vessels are dilated. A low peripheral resistance can result in low blood pressure. The blood tends to stagnate or pool in the dilated peripheral vessels. The volume of blood returning to the heart is reduced, so the blood pressure falls. Certain drugs, e.g. anaesthetic agents thiopentone and halothane, tend to lower blood pressure, mainly by causing peripheral vasodilatation. Sepsis may also induce shock by vasodilatation. CLASSIFICATION OF SHOCK Shock can be classified as follows: Hypovolaemic shock (a reduction in the circulating blood volume) caused by: • Loss of blood as in haemorrhage • Loss of plasma, as from burns • Dehydration, caused by: − Decreased input, e.g. fasting, especially in the very young and the very old. − Increased output from vomiting, diarrhoea, fistula, intestinal obstruction with accumulation of fluid in the gut.

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Septic (bacteraemic) shock caused by Systemic infection (usually by gram-ve organisms) and characterised by hypotension and altered organ function

Neurogenic shock (reduction in peripheral resistance) caused by • Spinal cord or brain stem injury Anaphylactic shock caused by • A hypersensitivity reaction to an antigen usually a drug Cardiogenic shock (failure of heart action) caused by • Heart disease, e.g. infarct, valve disease etc. • Drugs or toxins depressing the heart Very often more than one factor is involved, e.g. in septic shock there may be heart failure, hypovolaemia and a loss of peripheral resistance. SIGNS AND SYMPTOMS Cardiovascular • Poor peripheral circulation seen as pallor and cold extremities. • Poor filling of peripheral veins and nail beds is a better sign than a falling blood pressure (BP). • Rapid and thready pulse. • Fall in blood pressure. This is the least reliable sign. The blood pressure remains normal till all the compensatory mechanisms fail, then there is a dramatic fall after one third of the blood volume is lost. • Collapsed peripheral veins. The veins in the neck are the best guide. In severe shock, the veins collapse. They reappear as resuscitation progresses. The central venous pressure (CVP) is low. Respiratory • Respirations are rapid and shallow. Central nervous system • The mental state of the patient in shock varies. Often the patient is mentally alert. If the blood pressure is low enough to cause cerebral hypoxia, restlessness and confusion can occur. Don’t give sedatives or analgesics until you are sure that the patient's restlessness is due to pain. Gastro-intestinal • Nausea and vomiting may occur.

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Genito-urinary A fall in the urine output. A good urine output in the average adult patient is about 60ml/hr. A minimum acceptable output is 30ml/hr (i.e.0.5ml/kg/hour). In shock the urine output per hour is very low.

IMMEDIATE GENERAL TREATMENT (AIRWAY, BREATHING, CIRCULATION) FOR ALL SHOCKED PATIENTS Maintain respiration • Clear the airway. Suction may be required to remove any vomitus or secretions. • If the airway is obstructed, extend the head, lift up the chin and insert an airway if the patient will tolerate it. • Give oxygen by mask 6 L/min. • If the patient is not breathing adequately, ventilate with oxygen, using a mask or an ETT. Maintain circulation • An intravenous infusion is commenced. More than one infusion may be required. Give fluids - crystalloid or colloid (1-2 litres in an adult, 10-20ml/kg in a child) initially stat. while the cause is established. • Monitor the pulse, blood pressure, colour, urine output and CVP. CVP (if available) gives information on right ventricular filling pressures and also provides a means of giving inotropes many of which should be given centrally. CVP gives a rough guide of central blood volume. • Repeat fluid bolus if no improvement or inadequate improvement while the diagnosis is being made. Continue crystalloid infusion titrating rate to clinical setting. SPECIFIC TREATMENT FOR HYPOVOLAEMIC SHOCK This is a common form of shock but much of the treatment is relevant to other forms of shock. Insert two 16-gauge cannulae and begin two infusions. Use Hartmann’s solution or 0.9% saline until blood is available. The first few bottles can be given quickly (depending on the degree of shock). Monitor clinical parameters as above. In order to increase the rate of infusion: • Use a large needle or cannula • Elevate the bottle as high as possible • Use a pump set

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• Use a pressure bag Fluids available Crystalloid solutions. These are synthetic salt or dextrose solutions. Crystalloids distribute themselves readily throughout the extravascular space, therefore large volumes have to be given to expand the circulating blood volume. • Saline. Normal saline contains more chloride ions than blood. • Hartmann’s (Ringer lactate) solution contains sodium, chloride, lactate, potassium and calcium. It is considered a more physiological solution than normal saline, as the concentration of electrolytes resembles interstitial fluid. Hartmann’s solution is generally used in "shocked" patients until blood is available. If Hartmann’s solution is not available, normal saline can be used. Dextrose solutions must not be used in the treatment of hypovolaemic shock. Colloid solutions (plasma expanders). Colloid solutions contain large molecules which are not filtered by the kidney and do not diffuse through the capillary membrane but are retained in the circulation and therefore expand the circulating volume. Protein colloids. (Human plasma products). For a more detailed description see Chapter 49 (Blood transfusion). • Albumin (4.5% and 20%) is very expensive. Both these solutions have a prolonged half-life 5-10 days. They are both heat treated and carry a very small risk of hepatitis. 5% solutions are preferred for rehydration and intravascular volume expansion but are not ideal for rapid resuscitation and are more commonly used in hypo-proteinaemic states. Synthetic colloids • Haemaccel • Gelofusine These are gelatin preparations. They do not interfere with blood cross matching, nor is there any disturbance of haemostasis with their use but allergic reactions may occur. They have a half-life of 4-5 hours and are suitable for use in rapid resuscitation. • Hetastarch • Pentastarch (isotonic) Synthetic starches give longer plasma expansion with a half life of up to 17 days. • Dextran 70 (macrodex). This is a plasma substitute available as a 6% solution in either saline or dextrose. The particles may remain in

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solution for up to a week. It is associated with certain side effects and it is advisable not to use more than 1.5 L in any one patient.

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Disadvantages of Dextran Dextran interferes with blood cross-matching. Any samples of blood for cross matching must be taken before the dextran is administered. Anaphylactic reactions may occur. It may interfere with platelet function and therefore haemostasis. The danger of fluid overload and infection is common to all plasma expanders.

Blood (See Chapter 49) Blood may be available in the following forms: • • • • •

Fresh whole blood. This is the ideal as it provides clotting factors but it rarely available. Stored bank blood. This is the commodity usually available. Packed red cells. Volume replacement must be made at the same time. Un-cross matched blood. Group O negative. This should not be used except in life- threatening conditions. Type specific. This is considered much safer than using Group O negative blood. It takes 15-20 minutes to group the patient and get type specific blood (i.e. blood of the same ABO and Rh group as the patient).

Rate of transfusion of fluids In the patient with moderate to severe shock, the rate of transfusion must be rapid, e.g. 500ml in ten or fifteen minutes. As soon as a real improvement in the patient's pulse and blood pressure are noted then the transfusion must be slowed down. The danger of rapid transfusion is that of pulmonary oedema, especially in older patients. Generally speaking the dangers of inadequate volume replacement far outweigh the small risk of over hydration. Careful clinical monitoring is the key. To determine the rate of transfusion, re-evaluate frequently: • Pulse: Rapid pulse rate may indicate hypovolaemia. • Blood pressure: If the blood pressure is less than 90 mmHg in a normotensive patient or if it is significantly lowered in a hypertensive patient, further transfusion is necessary. • Urine output: A urine output of at least 0.5ml/kg/hour must be maintained. A smaller urine output may signify hypovolaemia. Urine output is an excellent guide to fluid resuscitation and the insertion of urinary catheter with an hourly measurement bag should always be considered.

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Central venous pressure: The normal central venous pressure is 8-12 cm water. See previous comments. General condition of the patient: Look for restlessness, thirst, dyspnoea, faintness, pallor and cold extremities which may suggest the need for further transfusion. Haematocrit is not useful in estimating the precise amount of blood lost until 12-24 hours have passed. However it is a useful guide in determining how much blood may be needed.

The use of drugs in hypovolaemic shock The main aim in treating shock is to restore tissue perfusion and oxygenation. If after adequate volume replacement there is still inadequate tissue perfusion a second diagnosis may be considered (e.g. cardiac failure, sepsis, etc.). Ongoing bleeding or volume loss must always be excluded. The use of drugs to support blood pressure in hypovolaemia is only a temporary measure until volume replacement occurs or there is a diagnosis of a secondary cause of the shock (e.g. cardiac failure, sepsis, tension pneumothorax, or neurogenic shock). Agents that can be used to restore blood pressure temporarily while replacement is taking place include metaraminol, noradrenaline, adrenaline, or dopamine. Noradrenaline and adrenaline require central access (CVP line). ANASTHETIC MANAGEMENT OF THE SHOCKED PATIENT • • • • • • •

Carefully assess the degree of hypovolaemia. Use the IV route for any drugs given to the shocked patient. Drugs given IM are poorly absorbed. Treat for shock as already outlined. Cross match blood and have it available for intra-operative use. The presence of head and neck injuries, chest and abdominal injuries, must be ruled out in traumatic shock. Treat shocked patients as you would a patient with a full stomach i.e. rapid sequence induction with cricoid pressure. Severely shocked patients may need ventilation after surgery.

Unless the patient requires life-saving surgery it is beneficial to delay surgery while resuscitation is undertaken and hypovolaemia, hypoxia and hypothermia treated.

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Technique of anaesthesia Use a general anaesthetic with a rapid sequence induction. • Pre-oxygenate for four minutes, then perform induction (awake intubation may be performed in moribund patients). In patients who have been adequately resuscitated use IV ketamine (1 mg/kg) or etomidate (150 micrograms/kg), then suxamethonium 1 mg/kg and cricoid pressure. • Intubate using an appropriate cuffed endotracheal tube. • Maintaining anaesthesia will depend on the patient's condition. If the patient is moribund, ventilate with 100% oxygen and a small dose of ketamine. If the patient shows evidence of being too lightly anaesthetised then nitrous oxide, a low concentration of ether (2- 3%) or a ketamine infusion may be introduced. The patient who is well resuscitated is ventilated with 50% oxygen, together with opiate and a volatile agent in low concentrations. Again, if there is evidence that the patient is light, the anaesthetic can be further supplemented. Shocked patients need small doses of drugs but a higher concentration of oxygen. The ketamine infusion and relaxant technique is an excellent one for the shocked patient. • Reversal using the routine reversal procedure. Patients who will require post-operative ventilation need not be reversed. OTHER FORMS OF SHOCK Specific treatment for septic or bacteraemic shock • • • • •

General airway measures and oxygen as described for immediate resuscitation. Restore the circulating blood volume as in hypovolaemic shock. Give antibiotics, after blood cultures have been taken. Give vasopressors/ inotropes for resistant hypotension. Surgical treatment if indicated to remove the source of infection.

Many patients with septic shock will require laparotomy for diagnosis and treatment of acute abdominal conditions. Many will also be hypovolaemic and pre-operative resuscitation should be attempted before anaesthesia is commenced. Management of anaesthesia should be as discussed for hypovolaemic shock with particular care being taken to avoid hypotension and hypoxia.

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Specific treatment for anaphylactic shock This occurs after administration of a drug or after the intake of food, to which the patient is sensitive. Drug anaphylaxis is further discussed in Chapter 6 and Chapter 62. • Stop administration of drug or food causing the reaction. • Maintain circulating blood volume. You may need large volumes of plasma expanders. • Give adrenaline 0.1-0.5 mg IV (0.1-0.5ml of 1:1000 solution or 1-5ml of 1:10,000 solution.) Adrenaline is the first line treatment in anaphylaxis. An infusion may need to be commenced. • Give salbutamol (250 micrograms IV) as a second line treatment of bronchospasm associated with anaphylaxis. Give aminophylline as a third line treatment for bronchospasm, although it is not nearly as effective as adrenaline or salbutamol. • Give an antihistamine- chlorpheniramine (Piriton) 10-20mg slowly IV. • Give steroids hydrocortisone 100- 300mg IV. These are of use in anaphylaxis, however there is a delayed onset of action (several hours) and therefore it is not a first line treatment. When anaphylactic shock occurs during anaesthesia any drugs which might have been responsible for the collapse should be discontinued and surgery abandoned or completed as quickly as possible. Oxygenation should be maintained by whatever method is already being used and the above measures instigated where appropriate. An attempt should be made after stabilization to identify the cause of the reaction even if no specialized laboratory testing is available. The patient should be informed about his condition and the occurrence and treatment documented in the medical notes. Specific treatment for cardiogenic shock This is most commonly seen after myocardial infarction, when the force of cardiac contraction has been reduced. The aim of the treatment is to increase cardiac output. • Maintain airway and breathing with supplementary oxygen. • Exclude and treat arrhythmias. • Begin treatment of myocardial infarction i.e. aspirin, thrombolysis (if available and indicated), heparin and nitrates. • Give dopamine, in a dose of 2-10 micrograms/kg/min, or dobutamine 2.5-10 micrograms/kg/min to increase the force and rate of cardiac contraction and also to increase renal blood flow. Adrenaline may also be used in severe cases or where other inotropes are unavailable.

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In the case of complete heart block, isoprenaline 0.5-10 micrograms/min by infusion may be used before the correction of the underlying cause with a pacemaker (if available). The use of these drugs has been discussed under the subject of management of anaesthetic complications in Chapter 46 and in Chapter 6 (Pharmacology)

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