Autonomic dysreflexia (AD) is a potentially life-threatening condition that can affect people with established spinal cord injuries (SCIs) above the level of T6. It is triggered by a stimulus below the level of injury, resulting in an unopposed activation of the sympathetic nervous system with a sustained rise in blood pressure of 20 mmHg or more above baseline. If left untreated, it can lead to intracerebral haemorrhage, seizures and pulmonary oedema (Morgan, 2020).
In Ireland and the UK, over 60000 people are paralysed as a result of SCI (Spinal Research, 2023). In people with established spinal cord injuries, between 50–90% are susceptible to AD (Morgan, 2020). One study demonstrated that 26 out of 28 participants suffered from episodes of AD in a 12-hour period (Lee and Joo, 2017). Patients who suffer from a complete spinal cord injury – that is, no motor reflexes or sensation below the level of injury, have a much higher incidence of AD than incomplete injury (91% vs 27%) (Curt et al, 1997). A study from New Zealand showed that 40% of emergency department staff could not answer any questions at all about autonomic dysreflexia, highlighting the need for training into its recognition and management (Jackson and Acland, 2011). As paramedics are often the first healthcare professionals to encounter a patient suffering from AD, they play a vital role in identifying and managing this condition in the prehospital environment. This is even more important in rural areas, where ambulance transport times may be delayed.
Presented within this is article is a proposal to include training on the recognition and management of AD by paramedics in future training and education standards, and a draft clinical practice guideline for consideration.
What is autonomic dysreflexia and why can it be dangerous?
The peripheral nervous system in the body is divided into two parts: the autonomic (automatic) and the somatic (conscious) nervous systems (Waugh and Grant, 2018). Here, we are concerned with the autonomic, which is further divided into the sympathetic nervous system (the fight-or-flight response) and the parasympathetic nervous system (the rest-and-digest response). Put simply, one activates the body's responses and the other deactivates them; these work in tandem in a kind of balancing act.
Important for understanding AD is an insight into where these nerves originate. The sympathetic nerves arise from the thoracolumbar region of the spinal cord and the parasympathetic nerves arise from the craniosacral region (Figure 1). However, what happens when there is a spinal cord injury from T6 and above? It means there is a break in the signal. T6 is important because the nerves that innervate the adrenal medulla (releasing adrenaline) are located below the level of T6; if there is a break in the signal here, blood vessels below this level are cut off from descending control pathways. This means that the parasympathetic nervous system can not get through to bring the sympathetic nervous system back to normal (Eldahan and Rabchevsky, 2018).
If there is a noxious stimuli such as a urinary tract infection or a blocked catheter, the signal still reaches the thoracolumbar region of the spinal cord, causing a sympathetic response. Normally, the parasympathetic system engages to balance the scales. Here, the signal can not get through the part of the cord that is damaged. This means that there is an uncontrolled sympathetic response without the parasympathetic system stepping in to put on the brakes (Eldahan and Rabchevsky, 2018) (Figure 2).
Signs and symptoms
The hypertension induced by the sympathetic response is picked up by the carotid baroreceptors, which activates the vagus nerve. This can stimulate a reflex bradycardia and vasodilation – a parasympathetic response. Because the signals can not breach the level of injury, you have parasympathetic nervous system activation above it, and sympathetic nervous system activation below it. This is why the skin may look different above and below the injury. Above the injury may be flushed as the blood vessels are dilated, and below may be pale, cool and clammy owing to constriction of the blood vessels. Hypertension then, along with the vasodilation above the level of injury can lead to a headache. Sweating may also occur because of the dysregulated response. If the noxious stimuli is not removed or dealt with, and blood pressure is not reduced, this could lead to fatal consequences (Caroline, 2014; Eldahan and Rabchevsky, 2018; Morgan, 2020). Hypertension may be severe enough to cause a hypertensive crisis, with complications such as stroke, pulmonary oedema, retinal detachment, seizures and death. The reflex bradycardia may even lead to cardiac arrest (Lakra et al, 2021). It is also worth noting that an episode of AD can trigger a myocardial infarction (MI), especially in those with concurrent coronary artery disease (Allen and Leslie, 2023; Konstantinidis et al, 2023). These patients may not experience typical MI symptoms such as chest pain radiating into the neck and arm owing to the disrupted nerve pathways from their spinal cord injury (Ho and Krassioukov, 2010).
Causes: the 6 Bs
The causes of AD are (Allen and Leslie, 2023):
Non-pharmacological treatment
Treatment should begin first with non-pharmacological management, moving onto rescue medications if initially unsuccessful.
Initial management involves getting the patient into a sitting position with legs positioned in the direction of gravity. This is to induce orthostatic hypotension. Remove any tight or restrictive clothing. Investigate for possible causes using the 6 Bs as a reference. Remember, in about 85% of cases, the cause is a from a urinary or catheter source (Allen and Leslie, 2023).
If this is the case, consideration should be given to utilising paramedics with extended scope that includes catheter management. In Ireland, this may be a community paramedic or the Pathfinder Service. In the UK, this may a paramedic working in primary and urgent care.
Pharmacological treatment
If this does not work, the patient should take their own Nifidipine (if not taken already) as a rescue medication to induce smooth muscle relaxation and reduce hypertension (National Spinal Injuries Centre, 2013).
If the patient is unable to access their own Nifidipine because of issues with immobility, they should be assisted in this regard. The patient may be able to instruct the paramedic where to retrieve it from. If Nifidipine is not available, or the patient is unresponsive to it, sublingual glyceryl trinitrate (GTN) therapy may be given. Queensland and Ambulance Victoria clinical practice guidelines state that GTN can be given when blood pressure is ≥160 mmHg (Queensland Ambulance Service 2022; Ambulance Victoria 2023). However, the patient might have AD with a relative hypertension for them, an increase of 20 mmHg or more. Bear in mind that normal blood pressure in patients with an SCI can be around 90 to 110 mmHg. Therefore, even a reading of 120/80 mmHg can be considered elevated in these patients and a high index of suspicion for AD is recommended (Gall and Turner-Stokes, 2008; Popa et al, 2010; Christopher and Dana Reeve Foundation, 2023).
Therefore, we should consider GTN in the SCI patient that is symptomatic with a blood pressure above their baseline, and not just an arbitrary number of 160 mmHg. GTN here is being used as a substitute for the parasympathetic nervous system. Caution is advised however as many male patients with an SCI are prescribed medications such as sildenafil (Viagra) for erectile dysfunction (National Spinal Injuries Centre, 2013; Morgan, 2020).
If the patient is still unresponsive to these measures, consideration may be given for intravenous (IV) analgesia. This may include medications such as paracetamol and opioids such as morphine and fentanyl. There is a lack of research into opioid use and management of AD, with many guidelines and reviews not having it as part of their protocol (National Spinal Injuries Centre, 2013; Woller and Hook, 2013; State Rehabilitation Service, 2016; Allen and Leslie, 2023; Sarhan and Sarhan, 2023). In-hospital treatment suggests other medications such as GTN paste and antihypertensive such as Captopril and Clonidine (Allen and Leslie, 2023), but these are unavailable to prehospital staff.
Despite this, treatment must follow a step-wise approach and, although opioids are not contraindicated for treating pain, consideration must be given to this patient group owing to the lack of research on the topic, and the relative risk of dependence if given regularly during episodes of AD.
Current management and research issues
Currently, there are no guidelines on the prehospital management of AD in the community for paramedics and prehospital staff in neither Ireland, nor the UK.
At the time of writing, there appears to be no published research in relation to prehospital treatment of AD. Potential areas of interest include research of a qualitative and quantitative nature. The views and experiences of patients with SCI suffering from AD in the prehospital environment are fundamental for developing suitable guidelines for management of the condition. As of yet, we do not know the extent of the issue facing patients and paramedics regarding the treatment of AD in Ireland and the UK.
Prehospital treatment priorities
The following should be prioritised:
A draft clinical practice guideline for paramedics can be seen in Figure 3.
What others are doing
Ambulance Victoria, Queensland Ambulance Service and St. John Ambulance Western Australia have established autonomic dysreflexia clinical practice guidelines (Queensland Ambulance Service, 2022; St John Ambulance Western Australia, 2022; Ambulance Victoria, 2023). Ambulance Victoria suggests GTN administration if the patient is hypertensive, whereas Queensland and St John advocate for further escalation of pain management such as opioids if needed.
Patient perspective
‘As a C7 complete spinal cord injury sufferer since October 2020, I know the fear of having an episode of autonomic dysreflexia. To know my colleagues are aware of and able to help treat the issue is very reassuring. If selfadministration of Nifedipine hasn't happened, to know a paramedic can start with GTN and pain relief to reduce blood pressure and pain due to the stimulus is comforting. Also having the back up of an advanced paramedic with morphine and fentanyl is great, as having suffered a blood pressure of 225 systolic due to a severely blocked catheter, it's something I'd hope to never have to experience again. It's a feeling of impending doom when your blood pressure is so high you can't communicate.’
Olivia Lane, second author, paramedic and patient with C7 spinal cord injury
Conclusion
This article describes autonomic dysreflexia as a complication for patients with spinal cord injury, including its signs and symptoms, causes and pathophysiology. No guidelines exist currently for prehospital treatment by paramedics in Ireland or the UK. Potential treatment options include employing non-pharmacological options and removal of the noxious stimulus, before moving on to GTN and analgesia such as IV opioids. Research is lacking in paramedic treatment of AD. As such, there is potential for meaningful studies to be undertaken in this area.
Final remarks from lead author
To have my friend and colleague suffer from autonomic dysreflexia has been the stimulus for this proposal. Having a dedicated guideline and an educational programme for paramedics would be of massive benefit and importance to all patients with spinal cord injury in Ireland and the UK as potential sufferers of AD. It is time that we respond to the needs of this very important patient group.