Perioperative care

Medical management of burn victims has been considered elsewhere, but some aspects require further discussion because of their importance in determining the success of surgical treatment. These issues include fluid balance, transfusion requirements, and body temperature control ( D.e.mJÍD.g„..§.D.d Lakood.®..1989i).

Traditional burn shock resuscitation, performed with the primary goal of maintaining urine output, is known to 'run patients dry' and may fail to maintain intravascular volume. Often, blood pressure and cardiac output are supported partially, and sometimes largely, by elevated circulating catecholamine levels, even after resuscitation is complete. With general anesthesia, sudden hypotension can occur as underlying volume deficits are revealed. Even when fluid administration is adequate, stabilization of blood volume and oxygen delivery may require a considerably longer period than that of formal resuscitation. Capillary 'leakage' may persist and, coupled with increased evaporative losses, continue the potential for hypovolemia days after injury. Bacteremia associated with excision of infected burn wounds can also produce hypotension.

The surgeon should secure large-bore intravenous lines prior to operation and consider arterial line placement for large procedures, particularly if surgery will limit access to extremities. To improve perfusion and stability in the early postburn period, some burn centers are resuscitating selected patients with the 'physiological' goals of maintaining ventricular filling pressures and normal or supranormal oxygen delivery. Monitoring pulmonary artery pressure and cardiac output can clarify fluid status, and can also help to prevent under- or over-resuscitation during surgery. Such monitoring should be considered when the patient is frail or elderly, or an unusually large excision is planned. Fluid administration should be continued during surgery at least as aggressively as preoperatively. The surgical team should anticipate blood loss (see below), and be prepared to infuse additional fluids to compensate for evaporative losses as they occur.

Heightened risks of disease transmission have caused a radical revision of transfusion practices in many burn centers. Surgeons should avoid 'routine' transfusions and may allow stable patients to develop significant anemia before red cells are replaced, particularly if aggressive infusion of crystalloids is performed before and during surgery. However, the surgeon should never permit patients to become or remain unstable because of reluctance to transfuse blood products. Over- and undertransfusion can be avoided by following blood counts regularly and by anticipating surgical blood loss. Hemoconcentration is common despite fluid resuscitation, and the finding of an elevated (or normal) hematocrit and/or platelet count may belie diminished red cell mass from hemolysis and the consumption of platelets and coagulation factors. As resuscitation is completed, a sudden fall in hematocrit and platelet count should be expected. The blood loss which accompanies major excisions can be predicted (Warden,. efa/ 1982; MyJlei eLaL 1996); if it exceeds 20 per cent of the circulating blood volume, blood replacement should be planned before instability develops.

A number of techniques can help to reduce blood loss and the need for transfusion. The use of tourniquets for excision of burned extremities provides improved visibility as well as reduced hemorrhage. Many centers infiltrate wounds prior to excision with crystalloid solution containing epinephrine (adrenaline) or phenylephrine—the so-called 'Pitkin' procedure. This technique is also valuable in reducing the blood loss from donor site harvesting. The punctate capillary bleeding produced by large tangential excisions can be difficult to control with cautery. Application of topical thrombin and epinephrine and use of hot (40 °C) packs are helpful in controlling this type of bleeding. For very large tangential excisions, some surgeons prefer a 'two-stage' procedure, in which excised wounds are wrapped snugly with moist bulky gauze dressings overnight and grafting is performed the following day. The two-stage technique helps to reduce bleeding and, by dividing the operation, permits a period of equilibration which limits the blood and heat loss from each half of the procedure, resulting in less overall stress for the patient.

Patients undergoing major burn excision are at high risk of developing hypothermia. The suppressed metabolism characteristic of the 'ebb' phase of injury is worsened by general anesthesia, and patient exposure, peripheral vasodilatation, and use of wet packs for hemostasis increase evaporative and conductive heat loss. Burn patients are often maintaining near-maximum energy expenditure and can be rewarmed only with great difficulty. The resulting hypothermia produces additional metabolic and cardiovascular stress, contributes to coagulation deficits, and impairs peripheral perfusion and skin graft 'take'. To prevent hypothermia, several routines should be adopted. Patients should go to surgery warm; dressing changes or hydrotherapy should not be performed for several hours preoperatively. The operating environment should be made as warm as possible; the patient should be surrounded by heating pads or blankets, radiant heaters, and heat lamps. All fluids should be infused through warmers, and fluids used for preparation for surgery and for packs should be warmed to 40 °C. Perhaps most importantly, the duration of surgical procedures should be limited to 2 to 3 h, and terminated if body temperature drops significantly. Performing major excision and grafting procedures in two stages, and limiting the extent of each excision to 20 to 25 per cent TBSA, also reduces the risks of hypothermia.

Successful surgery requires a team of experienced professionals. Transporting a severely burned patient to and from the operating room can be the most hazardous part of the operation and should be performed by team members. Surgery itself does not usually aggravate underlying pulmonary problems; excision of truncal eschar can improve ventilation, as can administration of some anesthetics. However, the addition of surgery to other stresses can precipitate or aggrevate pulmonary failure. The team may elect to intubate patients prior to transport, and each patient should be assessed carefully before extubation, with consideration given to the need for immobilization postoperatively and timing to next surgery. Enteral nutrition need not be withheld for surgery, and can be continued even in the operating room if necessary. Involvement of the intensive care unit staff can be helpful in co-ordinating postoperative care and in planning dressing changes and positioning, which can be complicated.

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