Out of Hospital Management of Neurogenic Shock

212 words INTRODUCTION

In the following essay I will examine the evidence supporting the management of a critically injured patient in the out of hospital arena, specifically focusing on the out of hospital management of neurogenic shock, looking at the pathophysiology; current management and analgesia as well as critically analysing the data backing up the current practice; in addition, I will also look at the possible future management for the out of hospital practitioner.

PATHOPHYSIOLOGY

Shock is a potentially life-threatening illness, consisting of poor perfusion of tissues resulting in hypoxia of the cell and inadequate metabolic function.(Silverman, Adam and Wang, Vincent 2005). One of the dangers with shock is that as cells are damaged by the poor blood supply they release an inflammatory response increasing blood flow to the area but as the circulating volume is already lowered the increase in demand for blood supply can pull blood away from other parts of the body resulting in body wide organ failure. On the cellular level Mitochondria perform Anaerobic respiration, resulting in the formation of lactic acid, resulting in acidosis; As a result, the body attempts to become more alkaline, it does this by hyperventilating. As this is occurring the baroreceptors that exist in the arteries of the body react to the hypotension and release 2 important hormones: Epinephrine and norepinephrine (Guyton, Arthur and Hall, John 2006). Epinephrine is primarily responsible for increasing the heart rate, by increasing the rate of contractions within the heart more blood is ejected in the same period, increasing the pressure in the arteries and increasing blood pressure. Norepinephrine is mostly responsible for the constriction of the arterioles and veins, by reducing the internal diameter there is less space for the circulating volume, increasing resistance and therefore blood pressure. the body can also control where the constriction of blood vessels occurs allowing it to redirect blood flow away from the peripheries and towards the vital organs, such as the heart lungs and brain; by moving blood flow away from organs that are less vital, such as the gastrointestinal tract and kidneys. By reducing blood flow to the kidneys the amount of urine produced is decreased, allowing for a greater amount of water to remain in the circulating volume also increasing blood pressure (John P. Cunha, DO, FACOEP 2017). When the body is able to utilise these mechanisms to maintain blood pressure and organ perfusion in a state of lowered circulating volume, it is called compensated shock. When the body is unable to keep up with the loss of circulating volume and perfusion of vital organs is no longer maintained it is called decompensated shock (Kris, Kaull, B.S., NREMT-P, CCEMT-P et al. 2016). Neurogenic shock, the focus of this essay, falls under the category of ‘Distributive shock’ which is differentiated from other kinds of shock as it occurs even though the output of the heart is within normal bounds (r: Lalit K Kanaparthi, MD 2013). Neurogenic shock can occur after a traumatic injury to the central nervous system such as the brain, brain stem or, most notably, the spinal cord at the high thoracic or cervical level. The injury disrupts the autonomic pathways found with the nervous system, resulting in a loss of sympathetic tone leading to vasodilation and pooling in the extremities. It can also result in a bradycardia as a result of unopposed vagal activity (Piepmeier, Lehmann, and Lane 1985). Due to the loss of 2 of the body’s compensatory mechanisms neurogenic shock has an atypical presentation, which can include: hypotension, warm flushed skin and priapism due to the loss of sympathetic tone and resulting vasodilation; Bradycardia; depending on the location of injury to the spinal cord respiratory distress may be present, at C5 loss of control of the intercostal muscles results in diaphragmatic breathing. At C3 or above loss of control over the diaphragm will result in respiratory arrest.(Mallek et al. 2012) (Axelrad et al. 2013)

MANAGEMENT

The management of neurogenic shock in the prehospital field is limited, as the initial trauma cannot be reversed by a paramedic in the field and any attempt to treat the trauma would delay transfer to a major trauma centre, and delay treatment by a specialist spinal team. The goal of treatment is therefore to prevent or reduce the likely hood of secondary injury due to the hypotension produced as a result of the shock (Adam Fox, DPM, DO, FACS 2014). To prevent or reduce injury due to hypotension, the prehospital practitioner should aim to provide fluid resuscitation, a wide bore cannula (a 14 or 16 gauge) should be placed, flushed and secured. In London paramedic only carry crystalloid fluids but evidence exists that states colloid group fluids may reduce mortality. In a study that looked at the mortality of ICU patients in 57 hospitals from France, Belgium, North Africa and Canada, more than 5,000 patients studied. The outcome showed a 90 mortality of 30.7% in patients that received colloids and 34.2% in patients that received crystalloids(Annane D et al. 2013). The study used a large group size and many ICU’s from many countries reducing anomalous errors and a randomizer was used to select which type of fluid would be used further improving accuracy; however, the study focused on hemogenic shock as opposed to neurogenic shock and was based in ICU, so the results may differ in the prehospital arena and in neurogenic shock. From these results we can’t really conclude which fluid is better, while colloids had a marginally better 90 mortality rate it is statistically too close to draw any real conclusions, other factors need to be considered such as price versus efficacy, could the money on a 3.9% improvement in survival be spent better elsewhere to save more lives? We can also conclude that the study showed there is a further need for more investigations as to the difference in efficacy. Another study looked at the use of Methylprednisolone, a corticosteroid, in acute, blunt spinal cord injury; the study they sent a questionnaire to “clinical directors of emergency departments, spinal units, and neurosurgical units in the UK.” 187 emergency departments responded to the study(Frampton and Eynon 2006). The results showed 128, 68.4%, used methylprednisolone but 69% only did so on the advice of a specialist team while 31% gave steroids upon confirmation of acute, blunt spinal injury. The study looked at a relatively low number of A&E’s within the UK, 187, and once again the study did not focus on the prehospital arena, so the results may differ in paramedic practice; the study also focused on the incidence of use of methylprednisolone as opposed to the efficacy in acute, blunt spinal injury. To conclude from this study a more focused double blind should be performed to look at the efficacy of methylprednisolone. Another import step in treating acute spinal injury is to prevent worsening of the initial trauma, current practise for this is to use a rigid neck collar and a hard backboard to prevent excess movement; manual handling is important to consider as well, as excess movement can worsen the spinal injury(Multidisciplinary Association of Spinal Cord Injury Professionals. 2015). The ideal way of moving a patient onto a spinal board is the ‘log roll’ (Adam Fox, DPM, DO, FACS 2014). A retrospective study looked at the use of spinal immobilisation in penetrating trauma(Haut et al. 2010); 45,284 trauma patients were studied, 4.3% received spinal immobilization, overall mortality was 8.1% and the ratio of spine immobilized patients death was 2.06 (1.35-3.13) compared to nonimmobilized patients. The limitations of this study are mainly the limitations of retrospective studies, the data they received does “not report prehospital scene or transport times or differentiate urban versus rural care. Thus, we could not demonstrate that the excess mortality in patients who underwent spine immobilization was associated with delays in transport to definitive care.” Therefore, their conclusion that the reason for the increase in mortality is due to the extra time on-scene, and whilst it may account for some increase in the death rate it would be impossible to conclude if it is solely reasonable for the increase or if it is due to other factors such as the rise in intercranial pressure (ICP) due to placing the collar. This study should be viewed with scrutiny and a further study into why the mortality rate is higher, and investigate factors such as raised ICP using technology such as the intrascanner(Weigl et al. 2016). The prehospital practitioner should always undertake repeated primary surveys and manage problems as they occur, special attention should be paid to management of the airway, as placement of advanced airways can cause unnecessary movement of the spine, evidence exists that shows that video laryngoscopy is superior in this aspect (Robitaille et al. 2008) (Turkstra, Pelz, and Jones 2009).After managing the hypotension and ruling out other causes, such as catastrophic haemorrhage, the patient should be transported to the nearest major trauma centre, with a pre-alert in place, under 1B of the major trauma decision tree (London Trauma Office n.d.) if they are experiencing neurogenic shock or 2F due to suspected spinal trauma. If the patient is conscious and experiencing pain, due to the injury, analgesia should be provided for patient comfort.

ANALGESIA

Improving patient comfort should be a goal of every prehospital practitioner, therefore reducing the pain of the patient is important. Assuming the patient is conscious and complaining of pain; the WHO advises to follow a step wise treatment, as to use the most conservative, effective, form of relief. Non-opiate’s are considered the first form of treatment, in cases where the patient is not experiencing lowered levels of consciousness (Brown, S. N. et al. 2017). However in cases of lowered consciousness Entonox should not be given, therefore the next step would be intravenous drugs, such as a paracetamol infusion or morphine sulphate; however morphine has a side effect of lowering blood pressure (Mahinda, Lovell, and Taylor 2004), so in an already shocked patient further increasing the hypotension can have catastrophic effects, this leaves the patient with insufficient options for effective pain relief, however other drugs and treatments could be considered. Ketamine is used as an adjunct or in lieu of opiates in analgesia, it has the added benefit of not causing the same profound hypotension that morphine induces (Wong and Jenkins 1975). In a study on patients aged 18-55 with acute on set of pain, they measured the difference between doses of morphine and ketamine. The results showed that there was little difference in the pain reduce between morphine and ketamine, 4.1 vs 3.9 respectively. However, the study was limited in its small sample size of a single centre and small sample size, but good randomization and unbiasing protocols were in place. You can conclude from this study that ketamine can subjectively provide equal pain relief to morphine, but without the effects on cardiovascular stability. Another study was done as a comparison of ketamine versus morphine in prehospital trauma care. The study looked at 308 patients in rural Vietnam. The results showed both drugs had a similar incidence of pain relief, but ketamine had a lower incidence of vomiting, 5% compared to 19% for morphine, and ketamine was determined to carry a lower risk of airway problems. The study is limited as it was performed in rural Vietnam so comparison for London paramedics may offer different results, the sample size was adequate but could be improved, a good method of randomization was in place. You can conclude from this study that ketamine could be preferable to morphine in unstable patients who may need airway interventions.

CONCLUSION

In conclusion, the current management of spinal cord injuries and neurogenic shock in the UK is adequate but further research needs to be preformed on the benefits of colloid fluids for resuscitation and the benefits versus risk of spinal immobilization and rigid neck collars. It is this authors belief that ketamine is a superior analgesic option in the shocked patient and should be considered for use in the prehospital arena.