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Vasovagal syncope and anaesthetic practice

Hosie, L.; Wood, J. P.; Thomas, A. N.

European Journal of Anaesthesiology: August 2001 - Volume 18 - Issue 8 - p 554-557
Clinical Letter

We surveyed anaesthetists working in North-West England and in North Wales concerning episodes of vasovagal syncope encountered in their practice. Eighty-eight anaesthetists described 109 such events occurring in either patients or their relatives and the estimated frequency of syncope was 1 in 5000 anaesthetic episodes. The patient syncopal episodes were triggered by venous cannulation in 16 instances and regional or local techniques in 20 instances. Thirty-three of the 53 patients were in the upright position when syncope occurred. Thirty-nine of the 56 relatives were male partners of female patients and four of these partners suffered some morbidity. The results of the survey are consistent with our current knowledge of the pathophysiology of vasovagal syncope, which is summarized, and also highlight the common anaesthetic scenarios where fainting is most likely to occur. Given this information anaesthetists will be in a better position to avoid such potentially harmful episodes in the future.

Department of Anaesthesia, Hope Hospital, Stott Lane, Salford M6 8HD, UK

Accepted December, 2000.

Correspondence to: J. P. Wood 12 Churchwood Road, Didsbury, Manchester M20 6TY, UK.

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Syncope is a transient loss of consciousness and postural tone caused by cerebral hypoperfusion, yet resulting in no permanent neurological damage [1]. The most common type of syncope is described as vasovagal syncope or ‘emotionally mediated fainting’.

Vasovagal syncope is a complex reflex arc with poorly understood efferent and afferent limbs, it is extremely common, and has been estimated to affect up to one-third of the general population at some time [2]. Although individual anaesthetists have encountered patients who suffer vasovagal syncope, the effects of this problem on anaesthetic practice have not been determined. The aim of this study was to survey anaesthetists in the North-West Region of the UK and in North Wales, to establish in which situations they were most likely to encounter patients or relatives suffering from vasovagal syncope.

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A structured questionnaire was distributed during anaesthetic audit meetings held in the North-West Region of the UK and in North Wales, after a short presentation which outlined the aims of the study and gave a brief description of the pathways involved in vasovagal syncope; it was hoped that this direct approach would produce a greater response rate than would have been expected from a postal survey.

The questionnaire asked for basic details about the anaesthetist's experience, grade, subspecialty interests and also asked for details of all occasions where the anaesthetist had experienced patients or relatives who have been subject to vasovagal syncope. The anaesthetist was then asked to recall details of the patient or relative's age, gender and history of previous vasovagal syncope, and also any situations where harm had come as a result of vasovagal syncope.

The relationship between the number of years in anaesthetic practice and the number of episodes of vasovagal syncope reported during these years was established using regression analysis.

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A total of 88 forms were returned from the 11 anaesthetic departments surveyed and 127 episodes of vasovagal syncope were reported. Attendance registers suggested a sample population of 150 anaesthetists, although some questionnaires were returned by anaesthetists who had not attended the audit meetings; therefore, the true response rate could not be calculated.

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Of the 88 respondents 49 were consultants, the remainder were in training or non-career grades. The respondents had been in anaesthetic practice for a mean of 15 years (SD 8 years) and 49 respondents declared at least one subspecialty interest (obstetric anaesthesia, 31; paediatric anaesthesia, 26; chronic pain, 22).

The number of respondents reporting each number of episodes is shown in Figure 1. More than half of the responders had not encountered more than one episode of vasovagal syncope, eight had experienced four or more episodes.

Figure 1.

Figure 1.

The number of years in anaesthetic practice and the total number of episodes of vasovagal syncope reported for each cohort are shown in Figure 2, there was no significant relationship between these two variables. We had asked that vasovagal syncope episodes in members of staff should only be reported if they resulted in some morbidity. No such morbidity was reported; however, 18 episodes of vasovagal syncope suffered by staff were reported anyway.

Figure 2.

Figure 2.

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Fifty-three episodes of vasovagal syncope were reported, 26 (49%) in male patients, the mean age of the patients was 35 years (SD 15). Twelve patients were reported as having a previous history of fainting, 40 patients were described as ASA grade I–II, one as ASA grade III and 12 were ungraded. Proceeding the faint 33 patients were sitting, eight lying and one standing; the anaesthetist was unable to recall the position of 12 patients. The procedures most commonly associated with vasovagal syncope are shown in Table 1. There was no reported morbidity associated with any of these episodes.

Table 1

Table 1

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Fifty-six episodes of vasovagal syncope were reported in relatives, mean age 30 years (SD 5) and 44 (79%) were in males. Two relatives were reported as having a previous history of fainting, 36 relatives were standing, 17 sitting and the position of three was not reported. Thirty-two relatives were male partners of pregnant women; one of these suffered a fractured skull, one myoclonic jerks and one a minor head injury. Twelve relatives were parents of paediatric patients (nine mothers, three fathers) and seven were partners of women having other procedures; one of these seven suffered a scalp haematoma. Of the remaining five relatives one was a sister-in-law, two were mothers of adults and the relationship of two were not known.

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Vasovagal syncope is a poorly understood reflex arc, the afferent components of which arise either centrally or peripherally [3]. Peripheral afferents receive impulses from mechanoreceptors in blood vessels and viscera [1,4] and are responsible for micturition syncope, fainting after long periods of standing and fainting after carotid sinus massage. Central afferents originate in the cerebral cortex and hypothalamus [3] and are triggered by environmental stimuli.

The factors that make individuals susceptible to particular stimuli are also not fully understood; of most relevance to anaesthetic practice are individuals with blood injury injection phobia (BII phobia), a phobia associated with high levels of anxiety caused by excessive fear and avoidance of blood or conceptually similar triggers [5]. Phobias are subject to positive reinforcement from repeated environmental triggers and there is a strong familial predisposition to their development; this is particularly true of BII phobia with up to two-thirds of patients having a family history of the same phobia [5]. BII phobia is also unusual for being so strongly associated with vasovagal syncope [5–7], that it can even be induced on the first exposure to a particular stimulus. Some authors believe the strong familial component of the phobia is a predisposition to vasovagal syncope, which is also genetically determined, rather than for the phobia itself [5]. In general, vasovagal syncope is most common in young adults [8]; however, there is no difference between males and females in the incidence of vasovagal syncope [5,8].

The efferent component of vasovagal syncope is probably diphasic, with an initial increase in sympathetic tone, followed by bradycardia and peripheral vasodilation [5,8]; the haemodynamic changes have been elegantly represented using continuous recordings of haemodynamic variables during an episode of vasovagal syncope [9]. The relative importance of the effects of bradycardia and peripheral vasodilation on cerebral perfusion probably vary between subjects [3]; however, the failure of a pacemaker to stop vasovagal syncope would suggest vasodilatation is the major factor in most patients [1]; the mechanisms causing such vasodilatation are also unclear. The demonstration of subtle sympathetic dysfunction in individuals prone to vasovagal syncope [2] suggests excessive β-receptor-mediated vasodilatation, and a role for acetylcholine has also been proposed [1,3].

What do the results of our survey tell us about vasovagal syncope in patients and relatives during anaesthetic practice? First, we should acknowledge the limitations of the study as a retrospective collection of data dependant on individual recall, and with a small total number of events. The results probably both over and under estimate the incidence of vasovagal syncope, as with most surveys we had a low response rate and it would seem reasonable that non-responders would have been less likely to have experienced patients with vasovagal syncope. The fact that only eight anaesthetists reported more than three episodes of vasovagal syncope and the lack of relationship between years in service and number of episodes reported also suggests responding anaesthetists may have under reported their true incidence of vasovagal syncope. Information concerning the exact placement of episodes of vasovagal syncope within an individual anaesthetist's time in practice was not part of the information collected, so we were unable to determine any relationship between the number of years in practice and the occurrence of vasovagal syncope events during this time.

The methodology of the paper did not allow calculation of the number of anaesthetics administered by each individual in a typical year. However, using current information from the websites of the Royal College of Anaesthetists and of the Association of Anaesthetists of Great Britain & Ireland, it is estimated that four million anaesthetics are administered by 8400 anaesthetists each year in the United Kingdom. This equates to 475 anaesthetics per physician per year, a figure consistent with current records taken from logbooks. Taking into account the number of years practised by each of the 88 respondents this gives 1163 anaesthetic years, and therefore a projected 552 500 anaesthetics administered to induce 109 episodes of vasovagal syncope, ultimately leading to an estimated frequency of vasovagal syncope of 1 in 5000 anaesthetic episodes.

The gender ratio of patients and ages of the patients would be predicted from our knowledge of syncope; however, the small number of previous episodes of vasovagal syncope may reflect different management strategies for patients with a previous history of syncope. Vasovagal syncope on first exposure to a stimulus is also well described in BII phobia [5]. The high incidence during epidural procedures probably reflects the posture of patients during this procedure; it has recently been suggested that the sitting position should not be used for establishing regional anaesthesia in patients with a history of vasovagal syncope [10]. Subarachnoid block is less commonly performed in younger patients who are most at risk from vasovagal syncope, this may explain the relatively low incidence of vasovagal syncope associated with this procedure.

We did not expect the large number of episodes of vasovagal syncope reported in relatives, and male partners of pregnant women represented by far the largest part of this group. This may reflect the intensity of their environmental stimulus or an additional input from mechanoreceptors, for example from wearing excessive layers of clothing or standing for long periods in the operating theatre.

In conclusion, the episodes of vasovagal syncope reported by anaesthetists fit within the current understanding of this condition. The high incidence of vasovagal syncope during the performance of epidural block demonstrates the importance of monitoring and anaesthetic assistance when performing this procedure in the sitting patient [10]. Partners of pregnant women who suffer vasovagal syncope should be reassured that they are not unusual in having suffered this reflex during their partner's pregnancy.

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We wish to acknowledge the numerous anaesthetic departments that allowed presentation of our study at their audit meetings, and those members who further responded to the study.

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© 2001 European Academy of Anaesthesiology