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

`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 re ̄ex muscle contraction and that hypertension may be treated with sodium nitroprusside or a volatile anaesthetic agent such as iso ̄urane 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 re ̄exes. The procedure causes a mean increase in blood pressure of 31 mmHg and a mean heart rate increase of 23 beat. minÿ1 [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 con®rm 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 arti®cial 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 de®nition 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 ®rst 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 de®ning brain death in the United Kingdom [5, 6]. The criteria require a de®ned 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 con®rmatory 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 de®nition of death in the UK, the position in the USA has been de®ned 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 re ̄exes 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 re ̄exes. 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 re ̄exes, 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 ful®lling brainstem death criteria. In one study, Anaesthesia, 2000, 55, pages 105±106 .