May 2013

Review of Current Articles

Dr Joy Roach – Clinical Fellow Neurocritical Car Dr Roger Lightfoot – Consultant in Anaesthesia and Neurocritical Care University Hospitals of Southampton NHS Trust Neurocritical Care New Trends in Hyperosmolar Therapy  Diringer MN. New trends in hyperosmolar therapy? Curr Opin Crit Care. 2013 Apr;19(2):77-82  It is common place to encounter osmotic therapy in the neurocritical care setting for the management of raised intracranial pressure (ICP). It remains a controversial subject with many studies on single dosing as opposed to continuous infusions of osmotic agents. A ‘gold standard’ study reviewing the long term outcomes of osmotic therapy in this setting has yet to be published. In the fully functioning blood-brain barrier (BBB) the movement of water across the membrane obeys Starling forces. However in brain injury, be it from subarachnoid haemorrhage or traumatic brain injury the BBB is disrupted increasing its permeability to solutes leading to cerebral oedema. What is interesting to note is that although single doses of osmotic agents such as mannitol or hypertonic saline result in a hyperosmolar state and a subsequent reduction in ICP, continuous infusions lead to a regulatory response that sees the cells return to their original size. As a result, when the hyperosmolar state is reversed, a rebound cerebral oedema can occur. The two main osmotic agents are mannitol and hypertonic saline (1.25 – 23.4%). Benefits of using a hypertonic saline are the sustained volume expansion in comparison to mannitol which results in a dieresis and secondary hypovolaemia. A meta-analysis in 2011 found that hypertonic saline was more effective at treating episodes of raised ICP (difference in ICP of 2.0mmHg). Similarly in 2012 another meta-analyses found comparable results but failed to include a key study by Sakellaridis showing no difference between the use of mannitol and hypertonic saline. Studies investigating the complications of hypertonic saline infusions have failed to find a significant difference between its use and mannitol. The authors have made valid conclusions that from a review of the literature there are no studies with clear evidence pointing to the benefit of either mannitol versus hypertonic saline or single dosing versus continuous infusions. Choice remains centre and consultant dependent pending further studies. Hormonal Dysfunction in Neurocritical Patients Vespa PM. Hormonal dysfunction in neurocritical patients. Curr Opin Crit Care. 2013 Apr;19(2):107-12.  Dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis is common following brain injury. This literature review focuses on the systemic effects, consequences and management of alterations in endocrine function in three common disease states encountered in neurocritical care; subarachnoid haemorrhage (SAH), traumatic brain injury (TBI) and brain death. The pituitary gland is vulnerable to injury in TBI from shearing forces, in SAH from hypothalamic ischaemia secondary to vasospasm, and more generally in neurological/neurosurgical patients in states of cerebral oedema and raised intracranial pressure. Neuroendocrine dysfunction can also be precipitated by propofol, barbiturates and etomidate, all commonly used drugs in the management of TBI. The authors found six studies on the HPA axis in acute SAH that noted deficiencies in gonadotrophin, growth hormone, ACTH and thyroid stimulating hormone. Sodium dysregulation in subarachnoid haemorrhage occurs in approximately 40-80% of these patients but is not the focus of the article. They also found a number of interesting studies on SAH patients noting a correlation of the secretion of BNP, with the onset of vasospasm and delayed cerebral ischaemia suggesting that ischaemia may actually be the stimulus for BNP release. One study on TBI found as many as 70% of these patients had hypopituitarism on diagnostic testing which led to worse long term outcomes. The development of a state of brain death goes hand in hand with abnormalities in neuroendocrine function, most commonly diabetes insipidus. The importance in the management of this dysfunction lies primarily in the vasopressor refractory hypotension that results in the period before organ donation occurs and can have a detrimental effect on donation. Options for hormonal replacement include corticosteroids, mineralocorticoids, sodium supplementation either orally or with hypertonic saline infusions and early enteral feeding. There has been a study in TBI with early enteral feeding demonstrating reduced downregulation of thyroid related hormones and reduced elevation of cortisol levels. However there was no difference in mortality in the study group. The underlying message from the authors of this literature review highlights the need to consider hormone replacement in all patients with acute brain injury as dysfunction of the hypothalamic-pituitary-adrenal axis in the acute phase can have longer term consequences. Haemoglobin management in acute brain injury LeRoux P. Haemoglobin management in acute brain injury. Curr Opin Crit Care. 2013 Apr;19(2):83-91 Article Summary: Anaemia in the critical care setting and when to transfuse has been the subject of many recent studies. Generally in stable, hospitalised patients the recommended threshold is Hb 7-8g/dl and in those with cardiac disease the threshold level is slightly higher. However, in the acutely injured brain there are less clear guidelines on transfusion thresholds. This article reviews the literature surrounding this in the hope of obtaining a consensus view for transfusion in neurocritical patients. In the injured brain as a result of subarachnoid haemorrhage (SAH), traumatic brain injury (TBI) or acute ischaemic stroke (AID) anaemia can result in secondary insults to the brain. In anaemic states the oxygen content of blood is reduced and compensatory mechanisms takeover. In the injured brain anaemia results in cerebral vasodilatation, from nitric oxide, which causes a subsequent rise in intracranial pressure and the development of cerebral oedema with tissue hypoxia. It has been shown that cognitive impairment develops with an Hb <7g/dl. There are several studies looking at TBI outcome with anaemia showing mixed results. The large CRASH and IMPACT studies demonstrated worse outcomes with an Hb <7g/dl. In SAH, anaemia is commonplace occurring in 40-50% of patients. Observational studies suggest that again anaemia is associated with worse outcome but there are some studies that also suggest that red blood cell transfusion is associated with worse outcome. This may be because transfusion only occurred following delayed cerebral ischaemia or it may be a marker of disease severity rather than an actual cause of worse outcome. In SAH, transfusion has been shown to be a more effective treatment for delayed cerebral ischaemia than hypertension, hypervolaemia or angioplasty. In AIS the risks of anaemia and having a low haematocrit that reduces oxygen transport against a higher haematocrit and subsequent increase in blood viscosity and its effect on the microcirculation need to be weighed up. The proposed transfusion threshold in these patients is <10g/dl. This literature review certainly raises a lot of unanswered questions surrounding the role of anaemia in disease outcome and the use of transfusion to modify this. There remains a lack of clear, agreeable evidence on appropriate thresholds for transfusion in neurocritical care patients. Neuroanaesthesia A comparison of two doses of mannitol on brain relaxation during supratentorial brain tumor craniotomy: a randomized trial. Quentin C, Charbonneau S, Moumdjian R, Lallo A, Bouthilier A, Fournier-Gosselin MP, Bojanowski M, Ruel M, Sylvestre MP, Girard F. Anesth Analg. 2013 Apr;116(4):862-8. This simple study compared 2 groups of 20% mannitol administration in patients undergoing supratentorial tumour resection. The reason for this is to improve brain relaxation and therefore inmprove the surgical field.  The quality of the field was described by the surgeon in a 4 point scale from bulging brain to perfect relaxation. The doses of mannitol were 0.7g.Kg-1 and 1.4g.Kg-1. This was tested in a total sample of 80 patients. The results suggest that there is no benefit in giving the larger dose of mannitol to patients to improve the surgical field. However if there is midline shift prior to resection then the larger dose of mannitol does signicantly produce a better surgical field. This type of study is always enjoyable to read because it is easy to translate in to everyday clinical practice. Certainly using a weight based administration of 20% mannitol in the elctive sitaution is not always practiced. This could allow the lowest possible dose to be administered whilst offering the best clinical field for the surgeon. Of course this will hopefully avaoid the massive diureisis expereinced with mannitol and potential subsequent cardiovascular instability. The incidence and risk factors for postoperative urinary retention in neurosurgical patients Mohammed Alsaidi, Joanne Guanio, Azam Basheer, Lonni Schultz, Muwaffak Abdulhak, David Nerenz, Mokbel Chedid, Donald Seyfried Surg Neurol Int. 2013; 4: 61 This study prospectively assessed the Post Operative Urinary Retention (POUR) in neurosurgical patients undergoing elective neurosurgical operations. Over a two month period 137 patients were recruited. The definition of POUR was a residual volume of greater than 250 mls 6 hours after removal of the urinary indwelling catheter (which was inserted at the time of the operation). For this study population the POUR was 39%. The management of this situation was to have a straight catheterisation and then immediate removal of catheter. This was done every 6 hours and on the third time a long term indwelling urinary catheter was inserted. This is practice I have not experienced in either theUKorAustralia. Risk factors for POUR were identified including inceasing age, male sex, spinal surgery and increasing duration of anaesthesia. Not unsurprisingly there was an increased duration in stay for those patients who ended up being recatheterised. The issue of POUR is not the most exciting but certainly is very uncomfortable and distressing for the patient. Interestingly the reinsertion of the catheter and then removal lead to patient refusal to further attempts in some circumstances. This raises questions on the technique adopted for this study. The recatheterisation rate seems to be particularly high when all patients are being catheterised at the time of surgery. Therefore the use of just residual volume as an indicator to recatheterise has to be questioned. Overall the study tried to amnswer the simple clinical question but by using a method far removed from standardUKpractice made it hard for me to translate or influence my current practice. The Effect of Gabapentin Premedication on Postoperative Nausea, Vomiting and Pain in Patients for Preoperative Dexamethasone Undergoing Craniotomy for Intracranial Tumors Misra S, Parthasarathi G, Vilanilam GC J Neurosurg Anaesthesiol, 2013 April 17 [Epub ahead of print] Post operative pain and nausea and vomiting for patients undergoing neurosurgical operations is reported as being somewhere between 55 – 70 percent for nausea and 60 -80% for moderate to severe pain. This simple study looked at whether the use of 600mg of gabapentin alongside dexamethasone could reduce the incidence of nausea, vomiting and pain compared to dexamethasone alone. The outcome was a little surprising in that there was no reduction in post operative pain in the gabapentin group but there was a siginificant reduction in the nausea and vomiting. Gabapentin has certainly started to emerge as a drug that can be used successfully in the management of chronic pain patients in the perioperative period. Its beneficial effect of reduction in nausea may be enough to use it for this alone.