5 | Organ and tissue DBD: anaesthetic staff

Role of the anaesthetist

During the donor surgery, donor physiology is managed in the operating theatre by an anaesthetist.

When the New Zealand thoracic team is retrieving heart and/or lungs, an anaesthetist is provided by that team. For all other donations, including heart and lung donation by most Australian thoracic teams, an anaesthetist from the donor hospital is required.

An anaesthetic technician from the donor hospital is required for all organ donation surgery.

The anaesthetist should aim to maintain stability in the donor until aortic cross-clamp to ensure that the organs being donated are in optimal condition at the time of procurement and will function well in recipients following transplantation. See Section 5.3 for information on physiological support in brain death.

What monitoring and instrumentation are necessary?

The anaesthetist should ensure that there is adequate monitoring and intravenous access.

• Multi-lumen central venous line (not femoral for thoracic donations)
• Arterial line (preferably not femoral)
• One large (16 or 14 gauge) peripheral IV line for rapid fluid infusion
• ECG (three or four leads)
• External defibrillator pads for thoracic donations
• Pulse oximetry
• Core temperature (rectal or oesophageal)
• Nasogastric tube
• Urinary catheter

The donor coordinator will have requested the ICU to cross-match four units of RBC for the donor surgery.

Spinal movements and sympathetic responses

Spinal reflexes in the limbs can be distressing for observers and could potentially lead to contamination of the operative field. Excessive sympathetic responses can also be distressing for observers and could result in myocardial injury or excessive bleeding, with subsequent haemodynamic instability and detrimental effects on graft function.

It is usual to administer a neuromuscular blocking drug and a volatile agent and sometimes an opioid. These treatments are recommended in the ANZICS Statement and by ODNZ. See Section 5.2 for information on observations compatible with brain death.

These agents prevent spinal reflex motor responses and ablate spinal sympathetic responses (tachycardia and hypertension) that can occur during the donor surgery.

It is important for operating theatre staff to understand that the patient is not receiving “an anaesthetic” as such. “Anaesthesia” is not required in individuals who are brain dead as they lack consciousness and cannot experience pain.

What other medications are required?

Intravenous heparin 300 IU/kg. This is administered five minutes before aortic cross clamp. The surgeon will tell the anaesthetist when this is to be given.

DDAVP (desmopressin) to control diabetes insipidus.

Noradrenaline infusion to maintain adequate blood pressure.

Insulin infusion to prevent glycosuria.

Esmolol to control hypertensive surges from spinal reflexes.

What laboratory testing is required?

Blood gases (including haemoglobin), serum sodium, potassium, urea, creatinine and glucose (some of these may be measured as part of the blood gas analysis) should be measured and reviewed as appropriate.

Blood samples

The donor coordinator will request blood samples to be taken for Epstein-Barr virus and strongyloides testing as well as retrospective tissue typing. The donor coordinator will provide the blood tubes for these samples and is responsible for sending the samples to the laboratories.

Additional blood samples will be requested when an organ is being transplanted in Australia.

Aortic cross-clamp

Fluids, mechanical ventilation and monitoring cease after aortic cross-clamp and commencement of the cold perfusion. The role of the anaesthetist is complete. The aortic cross clamp time is recorded by the donor coordinator as this is start of the cold ischaemic time for the organs.

There are a number of observations which are sometimes found in patients with deep coma. Some are compatible with brain death and must be distinguished from those that are not.

Some of these observations can occur during clinical examination. It is important to be able to explain these observations and their significance to healthcare workers and to family members who might observe them at the bedside or during clinical examination.

Observations compatible with brain death

Observations compatible with brain death include:

• spinal reflexes
• sweating, blushing or tachycardia
• normal blood pressure without the need for pharmacological support
• absence of diabetes insipidus (DI)
• having an ICP<MAP.

Spinal reflexes

Spinal reflexes do not occur in the motor distribution of the cranial nerves or in response to stimulation within the cranial nerve distribution.

Spinal reflexes can be either spontaneous or elicited by stimulation, such as:

• a painful stimulus applied to limbs or sternum
• tactile stimulation applied to palmar or plantar areas
• neck flexion
• limb elevation
• hypoxia during ventilation disconnection.

Spinal reflexes should not be confused with abnormal flexor or extensor responses.

It should be explained to family members that spinal reflexes involve only the spinal cord, not the brain. Spinal reflexes should be explained to healthcare workers as occurring as a result of connections within the spinal cord between an afferent (sensory) limb and an efferent (motor) limb of a spinal reflex.

Spinal reflexes may include:

• extension-pronation movements of the upper limbs
• undulating toe reflex (plantar flexion of the great toe, followed by brief plantar flexion sequentially of second to fifth toes)
• Lazarus sign (bilateral arm flexion, shoulder adduction, hand raising to above the chest, and may include flexion of trunk, hips and knees)
• deep tendon reflexes
• plantar responses (either flexor or extensor)
• respiratory-like movements (shoulder elevation and adduction, back arching or intercostal expansion) without significant tidal volume
• head turning.

ODNZ can help with identification of these movements. If there is any doubt as to the origin of the movement a cerebral blood flow study must be performed.

Observations incompatible with brain death

Observations incompatible with brain death include:

• decerebrate or decorticate posturing
• true extensor or flexor motor responses to painful stimuli
• seizures
• limb movement elicited by stimulation in the cranial nerve distribution
• facial movement elicited by stimulation in the torso/limbs.

Brain death is associated with specific physiological changes which should be treated early to avoid instability. Inadequate treatment can jeopardise organ function, thereby reducing the number of organs that might be donated or impair their early function in recipients. Treatment which prevents these problems is usually straightforward and within the capability of every anaesthetist.

The ODNZ Guidelines are designed to assist the anaesthetist to maintain stability following brain death until organ removal. An ODNZ medical specialist is available 24 hours for advice and assistance on these matters and can be contacted through the donor coordinator on call. If there is physiological deterioration outside of the recommended parameters, please discuss with the donor coordinator.

Temperature maintenance

It is much easier to prevent hypothermia than to treat it in the brain dead patient. Do not allow hypothermia to develop. Prevent heat loss from warm polyuria by quickly recognising and controlling diabetes insipidus with DDAVP or vasopressin.

Aim for: Core temperature of 36–38°C.

Respiratory support

Lung function is commonly abnormal in brain dead patients who may have had direct lung injury (lung contusion or aspiration), or pulmonary oedema (non-cardiogenic, neurogenic, cardiogenic or fluid overload). Further deterioration can develop due to atelectasis or pneumonia.

Bronchoscopy is sometimes performed in OT by the thoracic team before the commencement of the donor surgery.

Aim for:

• SpO₂ of 92–97%
• PaCO₂ 35–45 mmHg or 4.7–6.0 kPa

Circulatory support

When brain death occurs, there is often a period of sympathetic hyperactivity followed by loss of sympathetic outflow, resulting in vasodilatation affecting both the capacitance vessels (great veins) and the arterial system. Relative hypovolaemia should have been corrected by the ICU staff but further correction with resuscitation fluids may be required by the anaesthetist. Even after hypovolaemia has been corrected, inotropic support (noradrenaline is preferred) is usually required to maintain adequate MAP.

Aim for:

• MAP of 70 – 90 mmHg
• good perfusion (including peripheral perfusion and absence or resolution of acidosis)
• urine output 1mL/kg/hr (acceptable range 0.5-2mL/kg/hr)

Haemoglobin (or red blood cells)

Red cell transfusion is rarely required but four units of RBC will have been ordered by ICU staff.

Aim for: Hb >70 g/L.

Fluids and biochemistry

Diabetes insipidus, due to the loss of anti-diuretic hormone (ADH, vasopressin) occurs in ~85% of brain dead patients. Untreated, this results in dilute polyuria with loss of water in excess of sodium. Urine output is typically greater than 3 mL/kg/hr and can sometimes be very large (eg >500 mL/hr). If diabetes insipidus is not recognised and treated promptly, progressive hypernatraemia (hyperosmolality) can quickly occur. Hypernatraemia in the donor has been associated with worse outcomes for liver transplant recipients.

Hyperglycaemia can also contribute to polyuria by producing an osmotic diuresis.

Aim for:

• serum Na+ 135 – 150 mmol/L
• serum K+ 4.0 – 4.9 mmol/L
• blood glucose <12 mmol/L