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Ростовский Государственный Медицинский Университет

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CHAPTER14 Anaesthesia:preoperative management

Quality ofresuscitation

The current standard of care is early excision of burn wounds. In some centres this may be done while the initial uid resuscitation is in progress or soon after. It is important to know if resuscitation eorts have been appropriate (avoiding over or under resuscitation) and if the patient is responding favourably. There are many formulas for guiding resuscitation of burn patients (see Chapter11 Fluid resuscitation in burns). These formulas can be used to estimate an appropriate volume of uid the patient should receive by a given time after injury. The rates of uid infusion estimated by these formulas are starting points and uid administration must be titrated based on the patient’s response. Intravascular volume expansion is maximized when the uid is infused over a period of time rather than as given as a bolus in a shorter interval. Some centres use an albumin solution to rescue patients who are requiring extra amounts of uid and/ or are developing oedema related complications. Quality of resuscitation can be determined from the patient’s physiological status as indicated by the volume of uid given, blood pressure, urine output, haematocrit, acid base status, and presence of oedema that could be associated with compartment syndromes.

Surgical plan

Preparation for perioperative anaesthetic management must be done within the context of the surgical plan. Blood loss and problems associated with patient positioning will depend on the surgical plan and these factors will inuence decisions regarding vascular access, monitoring and airway management.

• Surgical technique

• Tangential excision can be associated with bleeding that is copious and brisk

• Fascial excision of skin and subcutaneous tissue down to muscle fascia produces less bleeding than tangential but may also be associated with extensive haemorrhage

• Tumescent technique involves subcutaneous injection of dilute crystalloid solution with or without adrenaline to reduce bleeding and facilitate burn excision or donor site harvest; large volumes injected can add to uid volume given and hypertension resulting from systemic eects of adrenaline may need treatment (avoid interventions that impair ventricular contractility in this case)

• Positioning:If prone positioning is required extra consideration must be

given to securing the airway and vascular catheters

• Anticipated blood loss:Surgical blood loss from wound debridement

and donor harvest sites increases with time after injury and with wound infection. During the rst 24 hours surgical blood loss has been reported to be approximately 0.5mL per cm2 burn wound to be excised and grafted (where cm2 to be excised=total body surface area × % body surface area to be excised × 10,000cm2/ m2). This increases over the next 2 weeks and if the wounds also become infected approximately

1.25mL per cm2 blood loss can be expected

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Further reading

Bittner EA, Shank E, Woodson LC, Martyn JA. Acute and perioperative care of the burn- injured

patient. Anesthesiology 2015;122:448– 64.

Cancio LC. Initial assessment and uid resuscitation of burn patients. Surgical Clinics of North

America 2014;94:741– 54.

Woodson LC, Sherwood ER, Kinsky M (eds). Anesthesia for burned patients. In Herndon DN (ed.)

Total burn care, 5th edn. Edinburgh:Elsevier, 2018; pp. 131– 57.

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Chapter15

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Anaesthesia: intraoperative management ofpatients withacute burn injury

Selection of anaesthetic agents 126 Airway management 126 Monitors and vascular access 127 Fluid management 128 Thermal regulation 129 Postoperative care 129 Further reading 130

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CHAPTER15 Anaesthesia: Intraoperative management

Selection ofanaesthetic agents

No specic anaesthetic technique has been found to be superior for burn patients as long as consideration is given to the expected pathophysiological changes.

Airway management

If burn injuries do not distort airway anatomy, standard induction and intubation procedures are appropriate. In the absence of sepsis, gastric emptying is not delayed in patients with severe burns. At the time of admission following injury the patient may present with a full stomach when intubation is indicated. If rapid sequence induction is necessary the question of when it is safe to use succinylcholine arises. Owing to the risk of hyperkalaemic cardiac arrest it is recommended that succinylcholine be avoided after 48hours following burn injury until approximately 1year after healing. This is not an absolute contraindication, however. The hyperkalaemic response to succinylcholine is highly variable and treatable. If it appears that anoxic injury due to laryngospasm is imminent, the use of a small dose of succinylcholine to relieve laryngospasm is a matter of clinical judgement.

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MONITORS AND VASCULAR ACCESS

Monitors and vascular access

Special considerations for burn patients are necessary in applying minimum standard monitors recommended by the American Society of Anaesthesiologists and decisions regarding more invasive monitors:

• Pulse oximetry:Transmission oximetry sites may be burned or within

the surgical eld. When available, reectance oximetry may be used and at times pulse oximetry may be disrupted or unavailable

• Electrocardiogram:Standard gel electrodes will not adhere to burned

skin or in the presence of topical antibiotic ointments. Surgical staples with alligator clips are eective in these cases

• Foley catheter:Since general anaesthesia masks most symptoms of

transfusion reaction a Foley catheter is necessary if it is expected that blood products will be needed. Measurement of urine output is a common index of global perfusion. Bladder temperature is also a reliable measure of core temperature

• Venous access:Although central venous pressure (CVP) is not

considered a reliable measure of cardiac preload, when replacing large volumes of blood loss in potentially septic patients it is very helpful to know if the CVP is high or low. Venous catheters should be secured with sutures and when peripheral venous access is not available central venous catheters must be large enough to allow rapid uid ow. It is possible to place central venous catheters through burned skin but another choice is to ask the surgeon to debride the insertion site before placement

• Arterial catheter:In addition to conventional indications for placement

of arterial catheters, in burn patients extremities may not be available for non- invasive cus because they can dislodge fresh grafts or may be in the surgical eld. Radial artery catheters are dicult to maintain for extended periods in burn patients and the arms are often burned. Despite risks of femoral artery catheters this is often the preferred site when direct measurement of arterial pressure is necessary especially for prolonged periods

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CHAPTER15 Anaesthesia: Intraoperative management

Fluid management

Massive crystalloid volumes administered for the acute burn injury and the addition of further crystalloid often administered with tumescent techniques during surgery, can often lead to over- resuscitation. The following methods can be utilized to reduce the volume of intraoperative uid and blood products administered:

• Maintain spontaneous ventilation when possible. With reduced

intrathoracic pressure, preload can be maintained with less volume administered. In addition, securing the endotracheal tube can be dicult in the presence of facial burns and when spontaneous ventilation is maintained, dislodgment of the tube can be corrected with less urgency

• Use of colloid solutions to replace shed blood can reduce the total

uid volume needed. Since burn patients have reduced albumin levels,

2.5 % albumin usually has the same albumin concentration as plasma. Dilution of the patient’s haemoglobin with colloid solution during the initial excision reduces the red cell mass of surgically shed blood. This can reduce the amount of packed red cells needed to achieve a desired haemoglobin concentration after haemostasis is achieved

• Transfusion trigger depends on the individual patient’s physiological

status and co- existing diseases. With massive transfusion dilution of coagulation factors may result in coagulopathy. At our paediatric burn centre colloid solutions supplemented with packed red cells when needed are used until half the predicted total blood volume has been shed. If signicant blood loss is expected to continue we then begin to replace blood loss with packed red blood cells diluted 1:1 with fresh frozen plasma

• There is no single reliable physiological endpoint to titrate uid

replacement and it is necessary to monitor several variables:systolic blood pressure, arterial pressure wave form (when arterial pressure is monitored directly), central venous pressure, urine output, haemoglobin concentration, and acid– base balance. Adequate preload must be maintained but with attention to details this can be accomplished without overload

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POSTOPERATIVE CARE

Thermal regulation

Burn- related destruction of the major thermoregulatory organ (skin), a hypermetabolic response to large burns, and alterations in central thermoregulation including an increase in the set point (approximately 0.03°C per percent of total body surface area burned) make patients with large burns susceptible to hypothermia. This is exacerbated during surgery when the patient is completely exposed. Reduction in core temperature of burn patients, even below their elevated set point, results in a brisk hypermetabolic response. This is poorly tolerated as these patients already are experiencing an intensely catabolic stress from their wounds and the associated inammation. The following measures should be taken to avoid hypothermia.

• Before the patient arrives the operating room should be warmed

• Overhead warmers above the patient available for use when needed

• Intravenous uids should be warmed

• Cover areas outside the surgical eld when possible

• Use ‘bear huggers’ or warming blankets during surgery

Postoperative care

Several issues must be addressed before postoperative care is transferred to the burn unit or surgical ICU.

Continued bleeding

Continued bleeding at donor sites and excised wounds may be signicant and yet concealed by bulky dressings. This can be revealed by steady decreases in arterial and central venous pressures and changes in the arterial pressure wave form. When this is suspected, surgical advice should be sought immediately to determine if the patient requires a return to theatre to control bleeding and ICU personnel should prepare for any transfusion that may be required.

Temperature

Precautions must be taken to avoid heat loss during transport from the operating room to the burn unit. Transfer of the patient must include provisions to maintain temperature or to re- warm.

Pain

Burns are associated with intense pain. Poorly controlled pain increases anxiety, sympathetic tone, and catabolic stress. Burn pain often involves a component of neuropathic pain poorly controlled with morphine. Some patients develop rapid tolerance to morphine and experience an associated hyperalgesia. Methadone is more eective than morphine for neuropathic pain and has been found eective in burn patients tolerant to morphine and whose pain is poorly controlled by morphine. Alpha 2 adrenergic agonists (clonidine and dexmedetomidine) have also been found to facilitate analgesia in burn patients.

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CHAPTER15 Anaesthesia: Intraoperative management