Anaesthesia for organ donation in the brainstem dead — why bother? (2000)

‘Brainstem dead patients do not require analgesia or sedation …’ for surgery for the retrieval of donor organs. Thus begins the recommendation of the Intensive Care Society (UK) regarding Anaesthesia and Clinical Management During the Donation Operation as published in their booklet of June 1999. The booklet was published to facilitate the establishment of local guidelines for the management of the potential organ donor [1]. However, the relevant section of the document goes on to state that peri-operative neuromuscular blocking agents should be given to prevent reflex muscle contraction and that hypertension may be treated with sodium nitroprusside or a volatile anaesthetic agent such as isoflurane Some anaesthetists responsible for the clinical management during the donation operation may be uncomfortable with this guidance. Firstly, under few circumstances do we allow operative surgery with muscle relaxation and without analgesia or anaesthesia, leading to a psychological compulsion to provide anaesthesia. Second, the hypertension and tachycardia that accompanies the donation operation can be distressing for operating theatre personnel to witness and for this reason alone one should always administer anaesthesia or agents to control these reflexes. The procedure causes a mean increase in blood pressure of 31 mmHg and a mean heart rate increase of 23 beat.min−1 [2]. This haemodynamic response could be considered to represent an organism in distress and probably occurs at a spinal level, although we are unaware of EEG studies during organ collection to confirm this. Third, death is not an event but a process and our limited understanding of the process should demand caution before assuming that anaesthesia is not required. Historically, death was easily established by the presence of coma, apnoea and pulselessness. Failure of the cardiovascular or respiratory systems invariably led to a rapid failure of the other two. Recent technology has allowed the temporary maintenance of respiration and the circulation by artificial means even when there is irreversible loss of brain function. The concept of ‘brain death’ has emerged both to establish futility and to enable beating heart cadaveric organ donation. Initially, the definition of brain death required the loss of all function of the nervous system [3]; however, it was soon realised that the cerebral hemispheres and brainstem could die with persistent function of the spinal cord. To understand the concept of brainstem death, one must first consider the anatomy of the brainstem. The brainstem lies in the posterior cranial fossa; it consists of the midbrain, pons and medulla and contains the third to twelfth cranial nerves, the reticular formation, and the descending motor and ascending sensory tracts. It links the diencephalon superiorly (the thalami, hypothalamus, epithalamus and subthalamus), with the spinal cord below, and it is also connected to the cerebellum posteriorly. The reticular formation consists of over 100 scattered nuclear groups in the brainstem and the spinal cord, with neuronal connections to ascending and descending axons, and projections to thalamic nuclei and thereafter to the cerebral cortex. Stimulation of this system is associated with widespread cortical activity and wakefulness, and pressure on the midbrain leads to progressive stupor [4]. Two memoranda issued by the Conference of Medical Royal Colleges and their Faculties (UK) in 1976 and 1979 have been instrumental in defining brain death in the United Kingdom [5, 6]. The criteria require a defined context and stringent clinical evidence of permanent functional death of the brainstem. Firstly, the patient must be in unresponsive apnoeic coma and the condition must be due to irreversible brain damage of known aetiology. Second, potentially reversible causes of unconsciousness must be excluded, including drugs, hypothermia and circulatory, metabolic and endocrine dysfunction. Third, a series of simple clinical tests of the cranial nerves and the respiratory centre are performed sequentially. These tests should be carried out on two occasions, to reduce the risk of observer error, by at least two appropriately competent medical practitioners who are independent of the transplant team [1]. There is debate regarding the necessity of objective confirmatory tests such as electroencephalography (EEG), brainstem auditory evoked potentials, angiography or radioisotope studies. Although these tests are not required in the UK, they are required in some European countries and in about half of US hospitals [7, 8]. Whereas brainstem death is an acceptable definition of death in the UK, the position in the USA has been defined by a President's Commission and requires the ‘irreversible cessation of all functions of the entire brain, including the brainstem’. In the UK, the presence of cortical activity and/or perfusion is regarded as acceptable in the knowledge that the reticular formation will not be functional if the brainstem reflexes are absent and so the capacity for consciousness is irreversibly lost. There is an assumption that the activity of the reticular formation is lost either prior to or at the same time as loss of brainstem reflexes. Shann argues that brainstem death should not be a requirement for death. He suggests that it is theoretically possible for the reticular activating system and hence consciousness to be preserved despite the loss of brainstem reflexes, yet consciousness cannot be preserved without the cerebral cortex [9]. Objective evidence exists of continued function of the hypothalamus (adjacent to the brainstem), such as vasopressin secretion, in those fulfilling brainstem death criteria. In one study, 23% of brain dead adults did not have diabetes insipidus [10]. In a review of 611 patients diagnosed as brain dead, the EEG retained activity in 23% of cases [11]. But electrical activity of brain cells does not necessarily imply function that has significance for the organism as a whole. Grigg et al., however, showed 11 of 56 (20%) clinically brainstem dead patients had EEG activity and demonstrated sleep-like cortical EEG activity in 4% for as long as 7 days [12]. Brainstem auditory evoked potentials can also persist and were demonstrated by Machado et al. in eight of 30 (27%) and by Sasaki et al. in five of 19 (26%) clinically brainstem dead patients [13, 14]. Seventeen whole brain dead patients as defined by Italian law (relying on the absence of brainstem reflexes, apnoea and a flat EEG) underwent single proton emission tomography (SPECT) [15], a measure of tissue perfusion. A third of these patients had residual perfusion of the basal ganglia, thalamus and/or brainstem. The futility of continuation of artificial support for patients who are clinically brainstem dead is well recognised [11]. In 1981, a retrospective study of 609 neurosurgical patients (dating back to 1962) with a clinical diagnosis of brainstem death showed no survivors. Cardiac asystole occurred during ventilation in 54% after a median time of 30–40 h of ventilatory care, and ventilation was withdrawn in the remainder. The same study examined prospective data on 1003 survivors of severe head injury and determined that none of the patients satisfied the brainstem death criteria at any stage [16]. It is clear that the diagnosis of brainstem death supports the withdrawal of artificial support. One should remember that the consensus brainstem death criteria are arbitrary, and lack prospective validation [8]. It is probable that the UK brainstem death criteria have a specificity of 100% for loss of consciousness; however, it is more certain that appropriate alveolar concentrations of volatile anaesthetic agent produce unconsciousness. Faced with the knowledge of the persistence of higher brain and spinal function in some donors, the inability to test the reticular formation directly and the dramatic peroperative haemodynamic changes that occur, sedation and analgesia should be given with muscle relaxation for organ donation. It is imperative that public confidence is maintained in the transplant programme. The act of organ donation is a final altruistic one, and we should ensure the provision of general anaesthesia at least sufficient to prevent the haemodynamic response to surgery.