Autonomic dysreflexia (AD) is a clinical emergency in individuals with spinal cord injury (SCI). It commonly occurs in individuals with injury at level T6 and above (Mathias & Frankel 1988; Teasell et al. 2000; Mathias & Frankel 2002). An episode of AD is usually characterized by acute elevation of arterial blood pressure (BP) and bradycardia (slow heart rate), which, on occasion, may be replaced by tachycardia (rapid heart rate). Objectively, an increase in systolic BP greater than 20–30mmHg is considered a dysreflexic episode (Teasell et al. 2000). Individuals with cervical and high thoracic SCI have resting arterial BPs that are approximately 15 to 20 mmHg lower than able-bodied individuals (Mathias & Bannister 2002; Claydon et al. 2006). As such, acute elevation of BP to normal or slightly elevated ranges could indicate AD in this population. Intensity of AD can vary from asymptomatic (Linsenmeyer et al. 1996), mild discomfort and headache to a life threatening emergency when systolic blood pressure can reach 300mmHg (Mathias & Frankel 2002). Untreated episodes of autonomic dysreflexia may have serious consequences, including intracranial hemorrhage, retinal detachments, seizures and death (Yarkony et al. 1986; Pine et al. 1991; Eltorai et al. 1992; Valles et al. 2005).
It has been observed that the higher the level of the SCI, the greater the degree of clinical manifestations of cardiovascular dysfunctions (Mathias & Frankel 1992; Curt et al. 1997; Krassioukov et al. 2003). Another crucial factor affecting the severity of AD is completeness of spinal injury as only 27% of incomplete tetraplegics presented signs of AD compared to 91% of tetraplegics with complete lesions (Curt et al. 1997). AD is three times more prevalent in tetraplegics with a complete injury, in comparison to those with an incomplete injury (Curt et al. 1997). It is important to note, however, that although autonomic dysreflexia occurs more often in the chronic stage of spinal cord injury at or above the 6th thoracic segment, there is clinical evidence of early episodes of autonomic dysreflexia within the first days and weeks after the injury (Silver 2000; Krassioukov et al. 2003).
AD is most commonly triggered by urinary bladder or colon irritation. However, many other causes were reported in the literature (Teasell et al. 2000; Mathias & Frankel 2002). AD is caused by massive sympathetic discharge triggered by either noxious or non-noxious stimuli below the level of the SCI (Krassioukov & Claydon, 2005). Numerous reports of AD have been described in the literature: episodes are usually short-lived either due to treatment or being self-limiting. However, there are reports of AD triggered by a specific stimulus, which then continued to be present for a period of days to weeks (Elliott & Krassioukov 2006).
Numerous mechanisms have been proposed for the development of AD. It is known from animal studies that autonomic instability following SCI results from plastic changes occurring within the spinal and peripheral autonomic circuits in both the acute and chronic stages following injury (Mathias & Frankel 1988; Teasell et al. 2000; Mathias & Frankel 2002; Krassioukov 2005). The destruction of the descending vasomotor pathways results in the loss of inhibitory and excitatory supraspinal input to the sympathetic preganglionic neurons; this is currently considered the major contributor to unstable blood pressure control following SCI (Furlan et al. 2003). Furthermore, there is numerous animal and human data suggesting that plastic changes within the spinal cord (specifically spinal sympathetic neurons and primary afferents) underlies the abnormal cardiovascular control and AD following SCI. Altered sensitivity of peripheral alphaadrenergic receptors (receptors in the sympathetic nervous system) is one mechanism that may contribute to AD (Osborn et al. 1990; Arnold et al. 1995; Krassioukov & Weaver 1995, 1996; Karlsson 1999; Krassioukov et al. 1999; Krassioukov et al. 2002).
Table 1: Signs and Symptoms
Presently there is a well established protocol of management of AD developed by the Consortium for Spinal Cord Medicine (Consortium for Spinal Cord Medicine 1997). In patients with spinal cord injury, appropriate bladder and bowel routines, in addition to pressure sore prevention are the most effective measures for prevention of autonomic dysreflexia. However, for each individual, the identification and elimination of specific triggers for autonomic dysreflexia should also be employed to manage and prevent episodes of autonomic dysreflexia (Teasell et al. 2000; Mathias & Frankel 2002; Blackmer 2003).
When AD develops, the initial management of an episode involves placing the patient in an upright position to take advantage of an orthostatic reduction in blood pressure, and the loosening of any tight clothing (Consortium for Spinal Cord Medicine 1997). Throughout the episode, the blood pressure should be checked at 5 min intervals. It is then necessary to search for and eliminate the precipitating stimulus most commonly (in 85% of cases) related to either bladder distention or bowel impaction (Teasell et al. 2000; Mathias & Frankel 2002). The use of antihypertensive drugs should be considered as a last resort, but may be necessary if the blood pressure remains at 150 mmHg or greater following the steps outlined above (Consortium for Spinal Cord Medicine 1997). The goal of such an intervention is to alleviate symptoms and avoidthe complications associated with uncontrolled hypertension (Yarkony et al. 1986; Pine et al. 1991; Eltorai et al. 1992; Valles et al. 2005).
The most effective approach to AD is the prevention of occurrence of this disabling and life threatening condition (Braddom & Rocco 1991). This includes careful evaluation of individuals with SCI and early recognition of possible triggers that could result in AD. Improved clinician awareness of AD and greater attention on the need to eliminate noxious stimuli in individuals with SCI is a priority. Clinicians, family members, and care givers should be aware that increased afferent stimulation (e.g., via surgery, invasive investigational procedures, labour) to persons with SCI will increase the risk for development of AD. A variety of procedures can be used to prevent occurrence of episodes of AD.
Urinary bladder irritation or stimulation is the major trigger of AD following SCI (McGuire & Kumar, 1986; Linsenmeyer et al. 1996; Giannantoni et al. 1998; Teasell et al. 2000; Mathias & Frankel 2002). A bladder management program and continuous urological follow-up are important elements of the medical care of individuals with SCI (Waites et al. 1993a; Vaidyanathan et al. 1994; Vaidyanathan et al. 2004). An established bladder management program with intermittent catheterization or an indwelling Foley catheter allows individuals with SCI to plan for bladder emptying when convenient or necessary (Consortium for Spinal Cord Medicine 2006). However, there are no studies which specifically assess the effect of bladder management programs on occurrence of autonomic dysreflexia.
During the last decade, urological follow-up including annual urodynamic evaluations and cystoscopy (depending on the bladder management program), have decreased the frequency of urinary tract infections and development of renal failure in individuals with SCI (Waites et al. 1993a; Waites et al. 1993b; DeVivo et al. 1999). However, conservative management is not always successful and alternative strategies (e.g. application of Botulinum toxin, capsaicin, anticholinergics, sacral denervation and bladder and urethral sphincter surgery) are needed to decrease afferent stimulation from the urinary bladder to prevent development of AD. In addition, urodynamic procedures and cystoscopy are associated with significant activation of the urinary bladder afferents and have potential to trigger AD (Linsenmeyer et al. 1996; Dykstra et al. 1987; Snow et al. 1978; Chancellor et al. 1993) and thus also require strategies to reduce afferent stimulation during those procedures.
Injection of Botulinum toxin into the detrusor muscle is an effective method for treating urinary incontinence secondary to neurogenic detrusor overactivity.
Table 2: Botulinum Toxin and AD
Four pre-post studies (n=84)(Dykstra et al. 1988; Schurch et al. 2000; Chen et al. 2008; Kuo et al 2008) found the injection of Botulinum toxin into the detrusor muscle or bladder sphincter to be an effective method for treating urinary incontinence secondary to neurogenic detrusor overactivity and bladder sphincter dyssynergia. In these conditions, injections of the Botulinum toxin either allowed increased urinary bladder capacity (i.e., reduced overactivity of the bladder) or facilitated improved evacuation of urine (reduced bladder sphincter dyssynergia). The duration of effect was reported to last up to 9 months (Schurch et al. 2000). All studies were level 4 and showed positive effects. In fact, following treatment with Botulinum toxin, 3 individuals reported fewer episodes of AD (Kuo et al. 2008), 4 individuals reported decreased frequency and intensity of AD (Chen et al. 2008) and 3 individuals who experienced severe AD during bladder emptying reported disappearance of these symptoms altogether (Schurch et al. 2000).
Capsaicin is the pungent extract from red pepper and exerts a selective action on certain sensory nerves, most notably those involved in reflex contractions of the bladder after spinal cord injury.
One RCT (n=23)(Giannantoni et al. 2002) and one pre-post study (n=7)(Igawa et al. 2003) evaluated the effect of capsaicin. Capsaicin exerts a selective action on those sensory nerves involved in reflex contractions of the bladder after SCI. In their pre-post study, Igawa et al. demonstrated that intravesical capsaicin decreased episodes of AD in patients with SCI during catheterization, thereby suggesting the therapeutic potential of intravesical capsaicin for both AD and detrusor hyperreflexia in SCI patients (Igawa et al. 2003). Giannantoni et al.’s high quality RCT (PEDro=6) used an analogue of capsaicin (resiniferatoxin RXT) which is more than 1,000 times more potent in desensitizing C-fiber bladder afferents and found reduced episodes of AD (Giannantoni et al. 2002). In addition, investigators found that intravesical administration of resiniferatoxin was superior to that of intravesical capsaicin in terms of urodynamic results and clinical benefits in SCI patients within 60 days of treatment and did not cause the inflammatory side effects associated with capsaicin. Long-term effects of capsaicin or resiniferatoxin on AD, however, have not been evaluated.
Anticholinergics are a class of medications that inhibit the binding of the neurotransmitter acetylcholine to its receptors. Acetylcholine is released by the parasympathetic nerve fibers innervating the urinary bladder and contributes to detrusor contraction and activation of the bladder afferent. These afferent stimuli activate spinal sympathetic circuits that trigger AD. Anticholinergic agents may therefore, possibly decrease afferent activations, and consequently AD. However, only one study, employing an observational cross-sectional design (n=48), has examined the use of anticholinergics (Giannantoni et al. 1998). Giannantoni et al. (1998) did not observe a correlation between anticholinergic drugs and reduced incidence of AD, unless it resulted in detrusor areflexia.
When detrusor hyperreflexia post-SCI does not respond to conservative treatment, and patients are not eligible for ventral sacral root stimulation for electrically induced micturition, sacral bladder denervation may be considered as a stand-alone procedure to treat urinary incontinence and AD. Three level 4 studies (aggregate n=459) (Schurch et al. 1998; Hohenfellner et al. 2001; Kutzenberger 2007) with sacral denervation have reported conflicting results in response to this procedure. Hohenfellner et al. reported that sacral bladder denervation is a valuable treatment option for eliminating detrusor hyperreflexia and AD in all 9 of their subjects (Hohenfellner et al. 2001). However, in Schurch et al.’s 10 subjects, it was shown that complete bladder deafferentation does not abolish AD during bladder urodynamic investigations. In a review of 440 patients, Kutzenberger saw sacral deafferentation eliminate AD in 438.
The association between episodes of AD and the presence of detrusor sphincter dyssynergia, high intravesical pressure and urethral pressure has led to the development of surgical procedures to alleviate voiding dysfunctions and consequently AD. Three surgical studies (Barton et al. 1986; Sidi et al. 1990; Perkash 2007) included indicators of AD (e.g., blood pressure changes). An older study by Barton et al.(1986) demonstrated reduced AD with an external sphincterotomy. A recent long-term follow-up of patients treated with transurethral sphincterotomies showed the procedure provides subjective relief of AD and is correlated with a significant decrease in blood pressure (Perkash 2007). In addition, post-void residual urine decreased significantly after surgery (Perkash 2007). However, such procedures are now rarely performed as they are associated with significant risks, including hemorrhage, erectile dysfunction(Ahmed et al. 2006) and the need for repeat procedures (Secrest et al. 2003). Thus, alternatives including intraurethral stents and Botulinum toxin injections have been investigated, both showing some success (Ahmed et al. 2006; Seoane-Rodriguez et al. 2007). The augmentation enterocystoplasty has demonstrated long-term success based on urodynamic evaluation and has been found to reduce symptoms of AD (Sidi et al. 1990). Enterocystoplasty with a Mitrofanoff Procedure has become a more frequent choice of bladder augmentation in individuals with SCI, due to more favorable long-term outcomes.
Table 6: Bladder and Urethral Sphincter Surgery
The second most common cause of AD is pain or irritation within the colorectal area. Constipation, hemorrhoids, and anal fissures, all frequently observed in patients with SCI, contribute to episodes of AD (Teasell et al. 2000; McGuire & Kumar 1986; Hawkins et al. 1994; Teichman et al. 1998). Digital stimulation, a common component of bowel routines in individuals with SCI, can also trigger AD (Furusawa et al. 2007). In addition, rectosigmoid distension and anal manipulation are common iatrogenic triggers of AD (Cosman & Vu 2005).
Table 7: Treatments to Reduce AD during Anorectal Procedures
In two small RCTs (n=70) (Cosman & Vu 2005; Cosman et al. 2002), investigators compared the effect of topical with local anesthesia of the anorectal area for the prevention of AD during anorectal procedures. They found that anoscopy, which involves stretching the anal sphincters, was a more potent stimulus for AD than flexible sigmoidoscopy, which involves gaseous distention of the rectosigmoid. In one randomized, double-blind, placebo-controlled trial, AD was not abolished by topical lidocaine in the rectum during the anorectal procedure (Cosman et al. 2002). However, the same investigators in a later RCT demonstrated that intersphincteric anal block with lidocaine was effective in limiting anorectal procedure-associated AD (Cosman & Vu 2005). In one small RCT (n=25) (Furusawa et al. 2009) investigators found that topical lidocaine applied to the rectum prior to digital bowel stimulation significantly reduced systolic blood pressure and reports of AD over the duration of the bowel program when compared to the control group.
In North America, women represent a third of the SCI population (Ackery et al. 2004). Approximately 3,000 American women of childbearing age are affected by SCI (Cross et al. 1992). The ability of women to have children is not usually affected once their menstrual cycle resumes (Jackson & Wadley 1999). There are increasing numbers of women with SCI who have healthy babies (Cross et al. 1992). However, during labor and delivery, women with SCI are at high risk of developing uncontrolled AD (Sipski 1991; Sipski & Arenas 2006).
Recognition and prevention of this life threatening emergency is critical for managing labor in women with SCI (McGregor & Meeuwsen 1985). The majority of women with SCI above T10 experience uterine contractions with only abdominal discomfort, an increase in spasticity and AD (Hughes et al. 1991). Numerous observational studies, case reports and expert opinions recommend adequate anesthesia in women with SCI during labor and delivery despite the apparent lack of sensation. However, there are only five studies (n=59)(Cross et al. 1992; Hughes et al. 1991; Cross et al. 1991; Ravindran et al. 1981; Skowronski & Hartman 2008) with observational evidence recording the management specific to AD during labor. The American College of Obstetrics and Gynecology emphasized that it is important that obstetricians caring for these patients be aware of the specific problems related to SCI (American College of Obstetrics and Gynecology 2002).
Table 8: Prevention of AD during Pregnancy and Labour
As AD may be triggered by a host of somatic and visceral noxious or non-noxious stimuli below the level of injury, a variety of interventions focusing on decreasing afferent information to the spinal cord have been used, including peripheral anesthetic blocks, epidural anesthesia, general anesthesia, or even dorsal rhizotomy (McGregor & Meeuwsen 1985; Barton et al. 1986; Cosman et al. 2002; Cosman & Vu 2005; Kutzenberger et al. 2005). However, it is important to acknowledge that despite the partial or total loss of sensation below the level of injury, surgical procedures or manipulations can potentially initiate episodes of AD. Anesthesiologists and surgeons performing surgery on SCI patients must be aware of the interactions of the anesthetic and its effects on AD and how to prevent or manage AD during these procedures.
Table 9: Prevention of AD during Surgery
Two observational studies (Lambert et al. 1982; Eltorai et al. 1997) presented evidence that AD is a common complication during the general surgery in individuals with SCI. Up to 90% of individuals undergoing surgery with topical anesthesia or no anesthesia developed AD. Both studies concluded that patients at risk for AD could be protected by either general or spinal anesthesia.
Functional electrical stimulation (FES) is a widely-used modality in the rehabilitation of individuals with SCI ( Sampson et al. 2000; Wood et al. 2001). Similar to any non-noxious or noxious stimuli below the level of injury, however, FES may also lead to significant afferent stimulation and trigger the development of AD (Ashley et al. 1993; Matthews et al. 1997).
Table 10: Prevention of AD during FES Exercise
One RCT (n=7) assessed the effect of topical anaesthetic and placebo creams applied to the skin area over the quadriceps muscle 1 hr prior to FES on two different days (Matthews et al. 1997). As cardiovascular and AD responses during FES were unaffected by topical anaesthetic cream application at the stimulation site, the authors suggested that mechanisms other than skin nociception contribute to FES-induced AD.
Despite appropriate preventative strategies, AD remains common among individuals with SCI. As previously noted, especially in individuals with cervical or high thoracic injuries, episodes of AD with a significant increase in arterial blood pressure could be asymptomatic (Linsenmeyer et al. 1996; Ekland et al. 2007; McGillivray et al. 2006).The Guidelines of the Consortium for Spinal Cord Medicine for management of AD recommends employing non-pharmacological measures initially; if they fail, and systolic blood pressure continues to be at or above 150 mmHg in adults, 120 mmHg in children under 5 years old, 130 mmHg in children 6-12 years old, and 140 mmHg in adolescents, pharmacological agents should be initiated (Consortium for Spinal Cord Medicine 2006).
The initial management of an episode of AD involves placing the patient in an upright position to take advantage of an orthostatic reduction in blood pressure (Consortium for Spinal Cord Medicine 2001). While there are no studies that evaluate the effect of a sit-up position on blood pressure during the episodes of AD, significant decreases in resting blood pressure have been shown during a tilt or sit-up test from supine position in individuals with SCI (Claydon & Krassioukov 2006; Krassioukov & Harkema 2006; Sidorov et al. 2007). It is proposed that an upright posture will induce pooling of blood into the abdominal and lower extremity vessels as peripheral vasoconstriction is compromised or lost following SCI; thus arterial blood pressure is reduced. The next step is to loosen any tight clothing and constrictive devices (Consortium for Spinal Cord Medicine 2001). This procedure will also allow more blood to pool into the vessel beds below the level of injury as well as removal of a possible trigger of peripheral sensory stimulation. Blood pressure should be checked at a minimum of 5 min intervals until the individual is stable (Consortium for Spinal Cord Medicine 2001), at which time it is necessary to search for and eliminate the precipitating stimulus and in 85% of cases, can be found to relate to either bladder distention or bowel impaction (Teasell et al. 2000; Mathias & Bannister 2002). The use of antihypertensive drugs should be considered as a last resort and used if the blood pressure remains at 150 mmHg or greater following the steps outlined above (Consortium for Spinal Cord Medicine 2001). The goal of such an intervention is to alleviate symptoms and avoidthe complications associated with uncontrolled hypertension (Yarkony et al. 1986; Pine et al. 1991; Eltorai et al. 1992; Valles et al. 2005).
Episodes of AD in individuals with SCI can vary in severity, but in some cases can be asymptomatic and be managed by the individual once they are familiar with their own triggers and symptoms (Linsenmeyer et al. 1996). However, in some individuals it is difficult to find the trigger for the acute blood pressure elevation and immediate medical attention is required (Elliott & Krassioukov 2006). Antihypertensive drugs with a rapid onset and short duration of action should be used in management of acute episodes (Blackmer 2003). The Consortium for Spinal Cord Medicine recommends that if non-pharmacological measures fail and arterial blood pressure remains 150 mmHg or greater, pharmacological management should be initiated (Consortium for Spinal Cord Medicine 2001). However, the Consortium for Spinal Cord Medicine (2001) does not identify any particular medication for management of AD. Numerous pharmacological agents (e.g., Nifedipine, nitrates, captopril, terzaosin, prazosin, phenoxybenamine, Prostaglandin E2, sildanefil) have been proposed for management of episodes of AD (Consortium for Spinal Cord Medicine; Blackmer 2003; Naftchi & Richardson 1997). The majority of the recommendations are based on the clinical management of hypertensive crises in able-bodied populations. Characteristics and outcomes of studies assessing pharmacological interventions for the management of AD are presented in the following sections.
Nifedipine, a calcium ion influx inhibitor (Ca-channel blocker), selectively inhibits calcium ion influx across the cell membrane of cardiac muscle and vascular smooth muscle while maintaining serum calcium concentrations. In man, Nifedipine decreases peripheral vascular resistance and creates a modest fall in systolic and diastolic pressure (5-10mm Hg systolic although sometimes larger). Nifedipine is generally given using the "bite and swallow" method, in a dose of 10 mg.
Table 11: Nifedipine (Adalat, Procardia)
Five studies (n=59) (Steinberger et al. 1990; Lindan et al. 1985; Thyberg et al. 1994; Kabalin et al. 1993; Dykstra et al. 1987) have evaluated the effects of Nifedipine; two level 2 controlled but not randomized trials (Steinberger et al. 1990; Lindan et al. 1985), and three level 4 studies (Thyberg et al. 1994; Kabalin et al. 1993; Dykstra et al. 1987). Four of these five studies saw a reduction or alleviation of AD with nifedipine (Steinberger et al. 1990; Thyberg et al. 1994; Kabalin et al. 1993; Dykstra et al. 1987. In their non-randomized control trial, Steinberger and co-investigators (1990) reported that sublingual nifedipine decreased peak systolic, diastolic, and mean blood pressure in SCI individuals undergoing electroejaculation. In their study, Braddom and Rocco (1991) surveyed 86 physicians with an average of 16.8 years of experience in managing AD in patients with SCI. While pharmacologic treatment of AD varied greatly from physician to physician, antihypertensive medications were the most frequently used medications with Nifedipine being a drug of choice for 48% of physicians for minor AD cases and for 58% of physicians for severe symptomatic AD cases. Although nifedipine has been the most commonly used agent for management of AD in individuals with SCI (Thyberg et al. 1994; Dykstra et al. 1987; Esmail et al. 2002; Braddom & Rocco 1991), its use has declined recently (Frost 2002; Anton & Townson 2004). There have beenno reported adverse events from the use of nifedipine in thetreatment of AD (Blackmer 2003), although all studies had a very small sample size. However, a review of nifedipine for the management of hypertensive emergencies not specific to SCI found serious adverse effects such as stroke, acute myocardial infarction, death and numerous instances of severe hypotension (Grossman et al. 1996). Due to several reports of serious adverse reactions occurring after administration of immediate-release nifedipine, the Joint National Committee on Detection, Evaluation and Treatment of High Blood Pressure (1997) has discouraged use of this drug.
Nitrates are used for an acute episode of AD as they relax vascular smooth muscle, producing vasodilator effects on peripheral arteries and veins. Dilation of postcapillary vessels, including large veins, promotes peripheral pooling of blood and reduces venous return to the heart, thereby reducing left ventricular end-diastolic pressure (pre-load) and arterial blood pressure. On the other hand, arteriolar relaxation reduces systemic vascular resistance which leads to reduced arterial pressure (after-load). If sildenafil has been used within the last 24 hours in an individual with SCI presenting with acute AD, use of an alternative short-acting, rapid-onset antihypertensive agent is recommended. Nitrates are the second most commonly used agent after nifedipine for management of AD in individuals with SCI (Consortium for Spinal Cord Medicine 2001; Braddom & Rocco 1991). However, with the exception of one case report with intravenous use of nitroprusside (Ravindran et al. 1981) and expert opinions (Consortium for Spinal Cord Medicine 2001), no studies exist to support their use in SCI. There is level 5 evidence (clinical consensus) (Consortium for Spinal Cord Medicine 2001; Braddom & Rocco 1991), but no clinical studies which support the use of nitrates in the acute management of AD in SCI.
Captopril is a specific competitive inhibitor of angiotensin I-converting enzyme (ACE). During an episode of AD, 25mg of captopril is recommended to be administered sublingually.
From one pre-post study (n=26) (Esmail et al. 2002), captopril was safe and effective in 4 out of 5 episodes for AD management. This prospective open labeled study and numerous experts’ opinion suggest the use of the captopril as a primary medication in management of AD (Consortium for Spinal Cord Medicine 2001; Frost 2002; Anton & Townson 2004).
Terazosin is a long-acting, alpha-1adrenoceptor selective blocking agent. Selective alpha 1 blockade has been suggested as a good pharmacological choice in the management of AD because of its dual effect at the bladder level (inhibition of urinary sphincter and relaxation of the smooth muscles of blood vessels).
Regular doses of Terazosin over weeks or months were evaluated in three level 4 experimental studies (n=57) (Vaidyanathan et al. 1998; Swierzewski et al. 1994; Chancellor et al. 1994) in which it appears to be effective in preventing AD without erectile function impairment. Patients reported moderate to excellent improvement (Chancellor et al. 1994) or even complete termination of the dysreflexic symptoms (Vaidyanathan et al. 1998) during a 3-month period of Terazosin administration.
Prazosin, a postsynaptic alpha-1 adrenoceptor blocker, lowers blood pressure by relaxing blood vessels. Prazosin has a minimal effect on cardiac function due to its alpha-1 receptor selectivity.The recommended starting dose in adults is 0.5 or 1 milligram (mg) taken two or three times a day.
Table 14: Prazosin (Minipress)
In a small (n=15) (Krum et al. 1992), but high quality RCT, Prazosin bid was well tolerated and did not affect the baseline blood pressure; AD episodes were also less severe and shorter in duration over a 2 week period.
Phenoxybenzamine, a long-acting, adrenergic, alpha-receptor blocking agent, can increase blood flow to skin, mucosae, and abdominal viscera and lower supine and erect blood pressures. The initial dose is 10 mg of Dibenzyline (phenoxybenzamine hydrochloride) bid with increases once daily, usually up to 20-40 mg 2-3 times/days.
Table 15: Phenoxybenzamine (Dibenzyline)
Prostaglandin E2 is a group of hormone-like substances that contribute to a wide range of body functions including the contraction and relaxation of smooth muscle, the dilation and constriction of blood vessels and control of blood pressure.
Frankel and Mathias (1980) studied five subjects; 3 subjects underwent administration with and without Prostaglandin E2 and showed that the level of BP recorded during electrical ejaculation decreased with the drug.
Sildanefil inhibits phosphodiesterase type 5 (PDE5), relaxes smooth muscle, and increases levels of cGMP in and inflow of blood to the corpus cavernosum. Sildenafil at recommended doses has no effect in the absence of sexual stimulation. The recommended dose is 50 mg taken, as needed, approximately 1 hour before sexual activity, but may be taken anywhere from 4 hours to 0.5 hour before sexual activity. Sildanefil is known to enhance the hypotensive effects of nitrates. Thus, nitrates in any form are contraindicated with sildanefil use.
The effect of sildenafil on AD was reported in one small RCT with 13 subjects (Sheel et al. 2005). Although sildenafil decreased resting BP, no effect on magnitude of AD resulting from vibrostimulation in men with SCI was observed.
While other pharmacological agents have been used to manage AD in individuals with SCI and while their use have been reported in the literature (e.g., expert opinion, case report) they currently do not have sufficient evident to warrant recommendation. These include the use of Phenazopyridine for AD associated with cystitis (Paola et al. 2003), magnesium sulfate for AD associated with labour (Maehama et al. 2000) or life-threatening AD in intensive care (Jones & Jones 2002), Diazoxide (Hyperstat) (Erickson 1980) for acute AD episodes and intrathecal baclofen for AD associated with spasticity (Kofler et al. 2009). In addition, there have been reports of the use of beta blockers (Pasquina et al. 1998), Mecamylamine (Inversine) (Braddom & Rocco 1991) and Hydralzine (Apresoline) (Erickson 1980) for the general management of AD symptoms in individuals with SCI.
Table 18: Other Pharmacological Agents Tested for Management of AD