Cardiac output is determined by the product of heart rate and left ventricular stroke volume. The contribution of both atrial and ventricular contraction to the stroke volume underlies the significance of normal cardiac rhythm and conduction in the generation of cardiac output. Bradycardia may result in an insufficient rate to sustain cardiac output and hence oxygen delivery to tissue beds. This is particularly so in the case of young children in whom cardiac output is more affected by changes in heart rate than stroke volume. In older patients bradycardia may reflect an ischaemic myocardium which is unable to maintain a stable electrical rhythm as a result of systemic hypotension or hypoxaemia. A prompt appropriate response to bradycardia under anaesthesia is important as some causes are rare and/or obscure and homeostatic mechanisms may be impaired by anaesthetic agents. It was decided to examine the role of a structured response to bradycardia under anaesthesia as there are many potential causes and associated conditions.

In 1993 a “core” crisis management algorithm represented by the mnemonic COVER ABCD–A SWIFT CHECK (the AB precedes COVER for the non-intubated patient) was proposed as the basis for a systematic approach to any crisis during anaesthesia where it is not immediately obvious what should be done or where actions taken have failed to remedy the situation.¹ This was validated against the first 2000 incidents reported to the original Australian Incident Monitoring Study (AIMS). AIMS is an ongoing study which involves the voluntary anonymous reporting of any unintended incident which reduced or could have reduced the safety margin for a patient.²

It was concluded that, if this algorithm had been correctly applied, a functional diagnosis would have been reached within 40–60 seconds in 99% of applicable incidents, and that the learned sequence of actions recommended by the COVER portion would have led to appropriate steps being taken to handle 60% of problems relevant to this portion of the algorithm.¹ This study also showed that the 40% of problems represented by the remainder of the algorithm ABCD–A SWIFT CHECK were not always promptly diagnosed or appropriately managed.^1–3 It was decided that it would be useful for these remaining problems to develop a set of sub-algorithms in an easy-to-use crisis management manual.⁴ This study reports on the potential place of the COVER ABCD–A SWIFT CHECK algorithm in the diagnosis and initial management of bradycardia, provides an outline of a specific crisis management sub-algorithm for bradycardia during anaesthesia, and provides an indication of the potential value of using this structured approach.

METHODS

Of the first 4000 incidents reported to AIMS, those which made reference to bradycardia or bradydysrhythmia were extracted and analysed with respect to the following criteria: anaesthetic technique, patient’s ASA grading, phase of anaesthesia at the time of presentation, presenting features (cardiac rhythm, blood pressure, oxygen saturation), presumed precipitating cause, management and outcome. The algorithm COVER–A SWIFT CHECK algorithm, described elsewhere in this series of articles,⁴ was applied to each relevant report to determine the stages at which the problem might have been diagnosed and to confirm that activating the COVER portion would have led to appropriate initial steps being taken.

As bradycardia is not adequately dealt with by this algorithm, a specific sub-algorithm for bradycardia was developed (see fig 1) and its putative effectiveness was tested against the reports. How this was done is described elsewhere in this series of articles.⁴ The reports were used in conjunction with contemporary guidelines on resuscitation^5–9 to generate a differential diagnosis and management algorithm which was especially relevant to anaesthesia. The potential value of this structured approach—that is, the application of COVER ABCD–A SWIFT CHECK to the diagnosis and management of the problem followed by the application of the bradycardia sub-algorithm—was assessed in the light of the AIMS reports by comparing its potential effectiveness for each incident with that of the actual management as recorded in each report. In addition to determining a difference between the two approaches with respect to likelihood of correct diagnosis and management, it was of particular interest during this part of the project to evaluate if delays in diagnosis and overall outcome could be improved with the application of the sub-algorithm.

RESULTS

Of the first 4000 incidents reported to AIMS, there were 265 reports which contained the words “bradycardia” or “bradydysrhythmia”; what constituted an incident was a decision made by the original reporter. These incidents occurred across a wide range of surgical groups. The patients’ ASA grades were available in 254 reports (table 1).

Bradycardia occurred during all phases of anaesthesia, but most commonly during the maintenance phase (table 2).

Aetiology

The attributed causes of bradycardia are shown in table 3. Overall, a total of 319 causative events were described for the 265 incidents involving bradycardia. The most common causes of bradycardia were drug events (28%), problems with the airway or ventilation (16%), autonomic reflexes (14%), and epidural or spinal anaesthesia (9%). A putative cause was not determined in 26 cases (8%). In addition, all cases of bradycardia are compared with subgroups based on associated blood pressure and are also cross referenced with datasets from the AIMS data relating to all cases of hypotension (table 3). The aim of this was to identify patterns which may indicate treatment when bradycardia coincided with abnormalities of blood pressure. Airway related events appear more likely to be associated with normotension, and neuraxial blockade appears more likely to be associated with hypotension. It also appears that cardiopulmonary events causing bradycardia are more likely than other causes to be associated with cardiac arrest.

Drug events were reported as a likely cause in 89 reports. In many cases it was not possible to clearly distinguish the specific contribution of any particular drug when drugs were given in combination. In this event, each drug was described as a drug event. Overall, 129 drug events were nominated. A breakdown of drug related bradycardia is shown in table 4.

The most commonly cited drugs were inhalational agents (n = 34), opiates (n = 20), intravenous induction agents (n = 18), and suxamethonium (n = 12). Enflurane and thiopentone were the most commonly described inhalational and intravenous agents, respectively. The time of collection of reports predated the wider usage of newer agents. Fentanyl was the most commonly described opiate. Its use was described in combination with other agents on all but two of a total of 11 occasions. Suxamethonium caused bradycardia after a repeat dose in 50% of cases. Drug errors and vaporiser incidents accounted, respectively, for nine and two of the total drug events described. A drug error was defined as the inadvertent administration of an agent and included syringe and ampoule swaps and residual agents in intravenous lines. Vaporiser incidents were identified whenever the reporter was unaware that an agent was being administered at all or in the concentration detected. This included incorrect settings and administration of multiple agents due to the absence of interlock devices.

Problems with the airway or ventilation were described in 58 reports. These included desaturation on pulse oximetry, difficulty with ventilation, clinical cyanosis, or symptoms of dyspnoea. On eight occasions no specific cause of the problem could be found with the airway; it is possible that the desaturation represented an artefact or true desaturation resulting from altered ventilation-pulmonary blood flow matching. The remaining 50 cases were associated with real airway abnormalities. This represented 19% of all reports describing bradycardia and 16% of total causes described when multiple causes were accounted for. The specific nature of these airway events is shown in table 5.

Importantly, no factors emerged which would enable the reporter to differentiate those caused by artefact (such as monitor malfunction) from real airway events without a formal assessment of the airway.

Vagal reflexes were considered to have contributed to bradycardia in 45 reports, which represented 14% of the 319 causes described. These reflexes were surgically induced in 36 cases. The majority of these were attributed to either vagal stimulation in the abdominal cavity or pelvis (n = 13) or the oculocardiac reflex (n = 12). Anaesthetic causes included laryngoscopy (n = 4) and intravenous cannulation (n = 2).

Surgical events were associated with 13 reports (5%). These included reaming, cementing or manipulating fractured hips (n = 4), manipulation of wires or catheters in central veins (n = 4), and pneumoperitoneum (n = 2).

Diagnosis

Bradycardia was described with abnormalities of blood pressure in 202 reports (76%). Bradycardia in association with a state of cardiac arrest, as defined by the absence of a peripheral pulse or the presence of a cardiac rhythm incompatible with a cardiac output (sinus arrest, asytole), was described in 67 reports (25%). Within this group, 24 cases involved degeneration from an initial state of hypotension into a pulseless state. Bradycardia was associated with hypotension in 134 cases (51%) and hypertension in one (<1%). There was no significant change in blood pressure in the remaining 63 cases (24%).

The prevailing rhythm when bradycardia was detected was specifically described as sinus rhythm in 74 reports. In another 135 reports sinus bradycardia was inferred from the narrative (table 6). Together, these account for 79% of cases.

Bradycardia degenerated into asystole in 19 cases. However, on a number of occasions the narrative suggested that sinus arrest was the actual rhythm. The reported rhythm was recorded on these occasions. The remaining 56 cases (21%) specified a non-sinus rhythm.

Management

The management of bradycardia as described in the narrative of the reports was classified as either conventional or non-conventional based upon the guidelines of the American Heart Association (AHA),⁵ the International Committee on Resuscitation,⁶ and the Australian Resuscitation Council (ARC).^7–9 It was subdivided into five grades which ranged from simple supportive measures to tertiary management (table 7)

Management was specified in 225 cases; in 25 of these it was classified as non-conventional. The most common reasons for this related to resuscitation with agents no longer recommended by AHA or ARC. Examples included the use of calcium (n = 5) and isoprenaline (n = 7), the omission of adrenaline when indicated (n = 9), an excessive dose or inappropriate route of administration of atropine (n = 2), and DC cardioversion for asytole (n = 1). Vasopressors were used in nine cases of cardiac arrest and 36 cases of hypotension. The most commonly used vasopressors were ephedrine (n = 17), metaraminol (n = 15), or a combination of the two (n = 4). External cardiac compression (ECC) was specified as given in only 45 of the 67 reports describing cardiovascular collapse. It was assumed to have been given whenever the report specified either the use of “resuscitation” or “cardiac life support”. The remaining cases were non-conventional by definition on the basis of AHA⁵ and ARC^7,9 resuscitation guidelines for management of pulseless patients. It is acknowledged that, on some occasions, ECC may have been instituted but not reported.

Outcome

The outcome from bradycardia is shown in table 8; 37% of reports described a poor outcome. Reports were considered to have a poor outcome if they were not resolved by the completion of the normal recovery period. An exception to this was ECG evidence of myocardial ischaemia or other cardiac events which may have resolved but often resulted in overnight monitoring.

Paediatric cases

Bradycardia occurring in children under the age of 14 years was described in 43 reports (16% of all reports). The distribution of ASA grading was similar to that of adults. Airway and drug events were responsible in 47% and 28% of paediatric cases, respectively. The haemodynamic profile was different in children than in adults. In 51% of cases there was no abnormality of blood pressure. This was attributed to the high incidence of airway events in which event hypoxaemia was associated with rapid deterioration in heart rate. This pattern has been identified in earlier studies.⁸ A smaller percentage of cases was associated with hypotension (21%). In contrast, cardiac arrest was described in 32%. In this group, drug events and a pre-existing condition were the most common causes. Non-sinus rhythms were reported in 12% of children (n = 7) compared with 16% overall. A good outcome was reported in only 48% of cases compared with 63% overall. However, there was a higher percentage of outcomes not specified in children (25%) than in the total group (12%).

Verification of the sub-algorithm

When COVER ABCD–A SWIFT CHECK was applied to each report it was considered that the problem would have been detected in all cases either at the C1 stage of COVER or at C of ABCD. Fifty three cases (20%) were diagnosed of which 45 (85%) would also have received correct management as a result of applying the core algorithm COVER. The majority of these dealt with circuit problems V1 (n = 3), vaporiser incidents V2 (n = 34), problems arising from monitors R1 (n = 5), equipment malfunction or errors with non-anaesthetic drugs R2 (n = 11). The remaining cases required completion of the sub-algorithm for bradycardia; this failed to provide a diagnosis or appropriate corrective management in two cases. Asymmetrical radial pulses and an under-reading central venous pressure monitor were responsible in these situations. It was felt that the algorithm performed better than the reporter in 11 cases (4%): missed or delayed diagnoses (n = 7), inappropriate use of drugs (n = 3), and failure to improve monitoring (n = 1). Non-conventional management was not included here unless it was felt to have adversely affected the outcome.

DISCUSSION

The specific sub-algorithm for bradycardia is shown in fig 1. It draws heavily upon the differential diagnosis and management strategies presented in the reports because they specifically deal with bradycardia within the context of anaesthesia.

Analysis of the AIMS reports shows that, in the majority of cases, bradycardia is managed appropriately. It is clear, however, that deficiencies in problem solving which have been identified in other arenas also exist in anaesthesia. For example, ARC guidelines on basic and advanced cardiac life support are clear on the institution of ECC in pulseless states. On a number of occasions in the reports there was a failure to interpret loss of peripheral pulses as a cardiac arrest. Not enough information was available to attempt to associate this with a poor outcome. However, it was interesting to observe that, in approximately half of the cases of cardiac arrest in which ECC was not described, cardiovascular collapse followed an initial presentation of bradycardia with hypotension. The conventional management of asystole includes early adrenaline. Atropine is recommended as a second line agent in refractory asystole or in the initial management of bradycardia associated with hypotension. The AIMS reports describe several cases of cardiac arrest in which a successful outcome was achieved with the use of atropine instead of adrenaline. Atropine without ECC was used successfully in five cases of reflex induced sinus arrest. If necessary, cardiac pacing should be instituted.¹⁰

The sub-algorithm begins with a reconsideration of the core algorithm COVER ABCD–A SWIFT CHECK as an initial response, as the causes of 20% of cases of bradycardia can be expected to be diagnosed as a result. The high incidence of airway or ventilation related events lends further support to this approach. It is easy to visualise the difficulties and delays one might encounter in managing a crisis situation in which it is not clear whether the primary problem is airway, heart rate, or blood pressure. COVER ABCD–A SWIFT CHECK enables cross referencing with airway related problems which are represented on other pages of the crisis manual. This establishes a system by which airway problems can be diagnosed and managed definitively at the same time that supportive measures to restore heart rate and blood pressure are instituted. This is important because aggressive resuscitation of the cardiovascular system may follow an episode of hypoxaemia and the possibility of multiple causes for bradycardia will always need to be considered.

In a similar manner to the airway, there is the potential for concentration on one component of the problem to the neglect of the wider problem when bradycardia occurs with either hypotension, hypertension, or cardiac arrest. Even when using an algorithm-based approach, the question may be raised “On which page do I start?” The AIMS reports were analysed in an attempt to identify presentation profiles from which high yield diagnostic and management pathways could lead. Several conclusions were drawn.

It is not possible to predict whether bradycardia is the primary or secondary event from the outset. This is a retrospective diagnosis made on the understanding of the pathophysiology after a diagnosis has been made. In some instances it is never possible to determine, for example, sepsis, bone cement and cardiopulmonary events.

The significance of any decrease in heart rate will be determined by the associated blood pressure rather than the absolute heart rate. When bradycardia occurs and the patient is pulseless, then go to the cardiac arrest algorithm because early aggressive management is required (table 4). If the rhythm is reflex induced sinus arrest, then the most effective treatment is to cease the precipitating event. If the patient is hypotensive it is worth noting the causes of hypotension and considering the use of vasopressors and aggressive fluid therapy. This is equally important in the context of spinal, epidural,¹¹ or regional blockade (especially interscalene block¹²). This can be achieved by reviewing the hypotension sub-algorithm. However, it should remain a problem of rate until the diagnosis has been made because of the important role of atropine and tertiary management options which include transvenous pacing. If the patient is hypertensive, then the problem should be managed according to the hypertension sub-algorithm.

Another issue which has the potential to complicate the problem is whether the prevailing cardiac rhythm should be diagnosed early. Sinus and non-sinus rhythms were compared with respect to ASA grading, haemodynamic status at the time of diagnosis, management. and outcome. This was done in an attempt to determine whether an early diagnosis of rhythm would be of value in the overall management of the problem. No differences were apparent. Analysis of cardiac rhythm should therefore not be pursued to the exclusion of supportive therapy or diagnosis of possible causes.