Anesthetic Management

Anesthetic Management

Important Points to Consider Before Anesthesia

• Reduced circulating blood volume- There is a loss of water and protein from the circulation, so IV fluids, both crystalloids and colloids, may be required.
• A fall in body temperature due to the loss of a large amount of skin.
• Anemia- Deep burns result in hemolysis of red blood cells.
• Hypotension may be associated with the hypovolemia and may also be due to the toxins released from the damaged tissues.
• Renal failure may follow hypovolemia and hypotension.
• There is a constant danger of infection in the burned patient. If infection occurs the patient becomes debilitated.
• Airway damage, which may involve the upper or lower airways. It may be due to the inhalation of hot gases, fumes, steam, smoke, etc. Upper airway obstruction will increase over 6 to 24 hours, so intubate the patient or consider early tracheostomy depending on nursing care facilities.
• Pulmonary edema may be caused by inhalation of noxious fumes especially if the patient was in a closed space. Face, neck, nose and mouth burns are commonly associated with this type of trauma. Pulmonary edema may also occur during resuscitation from fluid overload.
• Respiratory infection.
• The danger of hyperkalemia from administration of suxamethonium.
• Venepuncture is difficult,
• Using a mask is difficult in patients with facial burns.
• Maintaining a clear airway is difficult in patients with neck contractures.
• Monitoring is difficult in patients with burns to the upper half of the body.
• The problem of multiple anesthetics and the danger of repeated use of the same anaesthetic agents.
• Fear and depression. The anesthetist needs to establish rapport with the patient and reassure them.

Monitoring

• Monitoring for a major burn excision and grafting should be based on the knowledge of the patient's medical condition and the extent of the surgery.
• Vital signs (blood pressure, pulse rate, temperature and respiratory rate) and urine output measurement are considered the standard of care in the resuscitation assessment of the burn patient.
• Standard electrocardiogram pads may be placed under a dependant part of the body to provide a satisfactory electrocardigraphic signal in most patients.
• Sites for pulse oximeter readings are frequently difficult to find in the burn patient. Standard sites such as fingers and toes may be affected by the burn or unusable due to tourniquet placement. Alternative sites can be used with a standard pulse oximeter probe if the fingers are too severely burned to be used. These sites include the ear, nose, or tongue.
• Temperature monitoring is essential for any burn patient undergoing anesthesia because hypothermia is common and often difficult to prevent. The burn patient develops a hypermetabolic state in proportion to the severity of the burn injury. Ambient temperature has an important effect on the metabolic rate of the burn patient. A burn patient with a thermo neutral ambient temperature of 28-32ºC has a metabolic rate that is 1.5 times greater than in a non burned patient. If the burn patient's ambient temperature is decreased to 22-28ºC the metabolic rate is increased in proportion to the burn size. Therefore, in the burn unit and the operating room, the patient's temperature should remain thermo neutral to avoid further increases in the metabolic rate.
• A catheter should be placed in the patient's bladder to evaluate hourly urine output. Even with a severe burn to the genitalia, the catheterization can almost always be performed.
• Mechanical ventilation is required for patients with more extensive burns, inhalational injury, or respiratory complications.

General Anesthesia

Analgesics for Dressing and If the Patient Is in Pain

• Give the drugs IV, not intramuscularly. The muscle blood flow is reduced in the shocked patient.
• Use adequate doses of drugs. These patients often develop tolerance and have increasing requirements for opioids, which should not be withheld. Sedatives and anxiolytics may also be useful.
• Clean and manage the burn with a dressing or by open exposure. Ketamine 0.5- 1.0 mg/kg IV is useful for dressing changes.

Intubation With a Muscle Relaxant and IPPV

Endotracheal anesthesia is useful for surgery in the area of the head and neck. It is also useful for prolonged surgery and surgery performed in abnormal positions. It ensures adequate ventilation. Care is needed however with the use of muscle relaxants such as suxamethonium. Rapid sequence induction is not advised because of the dangers of suxamethonium. Once healing of burns has begun fibrosis and strictures may make laryngoscopy impossible. Tracheostomy is not desirable because of the danger of infection and awake intubation using local anesthesia may be necessary.

Ketamine is useful for debridement and grafting of facial burns, where the use of a mask is impossible. It is also useful for the division of neck contractures prior to intubation. The burned patient with neck contractures and therefore possible airway obstruction will have to be treated with special care. In a hemodynamically unstable patient, etomidate is a reasonable alternative to ketamine for the induction of anesthesia. Etomidate should not be used for frequent dressing changes due to the possible adrenocortical suppressive effects of the drug. In patients who are adequately resuscitated and not septic, thiopental or propofol may be used.

Inhalational anesthesia is useful for short procedures performed in the supine position, in a patient with a secure airway but may be difficult in patients with facial burns. Remember that peripheral vasodilatation increases heat loss and postoperative shivering may cause movement of the graft. However, peripheral vasodilatation may help with venepuncture.

Burn injury results in denervation of the tissue, which causes the entire skeletal muscle membrane to develop acetylcholine receptors. On administration of succinylcholine, an exaggerated number of acetylcholine receptors are depolarized, resulting in a massive efflux of potassium from the cell into the extracellular fluid. The hyperkalemia cannot be prevented by giving a defasciculating dose of nondepolarizer prior to the administration of the succinylcholine. The larger the TBSA of the burn is, the higher the likelihood of a hyperkalemia (Increased serum potassium concentration) response.

The potassium concentration increases within the first minute after succinylcholine administration, peaks within 5 minutes, and starts to decline by 10 to 15 minutes. The hypersensitivity to the succinylcholine begins 48 hours after the burn, and peaks at 1 to 3 weeks. The hyperkalemic response may persist for up to 2 years.

Nondepolarizing muscle relaxants (NDMRs) are often used during excision and grafting of burn patients. Patients with thermal injury are usually hyposensitive or resistant to the action of NDMRs. This effect may take up to a week to develop and may be observed for as long as 18 months after the burn has healed. A marked resistance to non depolarizing muscle relaxant occurs when the burn is greater than 30 to 40 percent TBSA.

Excisional treatment of burn wounds is usually associated with a large operative blood loss. An excision performed less than 24 hours after the injury usually has less bleeding than one performed 2 to 16 days after the injury. Peak hemorrhage appears to occur on days 5 to 12. Percent area of third degree burn is associated with greater blood loss, but the percentage of TBSA burned is not. It is difficult to predict blood loss, the estimation of blood loss during excision and grafting.

Appropriate fluid resuscitation is imperative to improving mortality, especially in the initial phase of treatment and during operative excision and grafting. Blood loss is usually replaced with crystalloids, colloids and blood products. The initial goal of the cardiovascular resuscitation during excision and grafting is to correct and prevent hypovolemia. Intravenous fluid is usually given in proportion to the percent of TBSA burned and is guided by the clinical assessment, vital signs, and urine output.

Burn patients often receive large volumes of fluid during their resuscitation and therefore develop significant soft-tissue edema. Tracheal extubation should always be delayed until the tissue edema resolves. During general anesthesia, the patients often receive large quantities of opioids and muscle relaxants, which can also delay emergence and extubation. The criteria for extubation of any trauma patient, including the burn patient, should include ability to follow commands, non combativeness, pain well controlled, appropriate cough and gag, ability to protect the airway from aspiration, no excessive airway edema, adequate tidal volume, vital capacity greater than 15 mL/kg, negative inspiratory force greater than 20cmH2O, and normothermic without signs of sepsis.

When planning to extubate the patient's trachea, it is important to wait until an air leak occurs around the endotracheal tube when the cuff is deflated before extubation. If the patient appears ready for extubation according to all other criteria and still has no air leak, then a direct laryngoscopy may be helpful to determine the extent of residual airway edema.

Before ending this session, we recommend you to say something about the repeated exposure to anaesthesia effect and special things about it.

E.g.

• Repeated exposure to halothane
• Repeated exposure to ant pains (opioids)
• Repeated exposure to procedures like intubation, ...etc