During recent decades, several studies on postoperative cardiac arrest and anaesthesia-related mortality in different patient populations from different countries have been published.1–14 However, from Europe there are only few data from high-quality studies. So far, only one study from the 1990s analysed perioperative cardiac arrest.3 Two other French studies, and one study from The Netherlands analysed perioperative mortality.7,11,14 Recently, data from a large German database revealed a serious complication rate of 26.2 per million procedures and for those with possible direct anaesthetic involvement, 7.3 per million cases in patients classified as American Society of Anesthesiologists’ (ASA) physical status grades 1 or 2 undergoing elective procedures.15 However, to date, there is no information available from Europe on the incidence of anaesthesia-related cardiac arrest and risk factors for perioperative cardiac arrest from a large unselected patient population of all ASA physical status grades. Thus, in our analysis, we sought to assess the incidence of anaesthesia-related perioperative cardiac arrest and to identify possible risk factors in a large unselected patient population from a tertiary care university hospital, including cardiac surgery and paediatric heart surgery.
Patients and methods
We analysed data retrospectively from critical incident reports obtained from 169 500 anaesthesiological procedures from 1 January 2007 until 31 December 2012 from the Department of Anaesthesiology and Intensive Care Medicine at the University Hospital of Cologne (Germany). Ethics approval was waived by the local Ethics Committee of the University Hospital of Cologne due to the retrospective and anonymous nature of the study (Ethics Committee No. 16-473).
The University Hospital of Cologne is a 1400-bed tertiary care referral centre, including cardiac surgery and transplant surgery, with approximately 30 000 anaesthetic procedures per year. At our institution, it is mandatory to report perioperative complications on a critical incident report form. This report is compiled by the anaesthesia team involved in the case and the report is stored together with the anaesthesia report in a dedicated database. Furthermore, data from all anaesthetic procedures are stored separately in a database.
Critical incidents reports between 2007 and 2012 were screened, and reports on perioperative cardiac arrest within 24 h postoperatively were identified. A cardiac arrest was defined as absence of pulse, pulseless electrical activity, asystole or ventricular fibrillation requiring cardiopulmonary resuscitation with a necessity for chest compressions.
Critical incidents from the ICU were excluded from this analysis so as to focus on anaesthesia-associated problems.
The patient's anaesthesia and medical records and the critical incident report form on each cardiac arrest were analysed independently by two of the authors (J-NM and SAP).
Anaesthesia-related and anaesthesia-contributory cardiac arrest
A classification modified from the Australian system of classification by State-Based Anaesthesia Mortality Committees was used to categorise cardiac arrest16 (Suppl. Table 1, http://links.lww.com/MD/B828).
Anaesthesia-related cardiac arrest was defined as cardiac arrest that was caused directly by anaesthetic measures in the context of surgery or interventional procedures (Category 1). Anaesthesia-contributory cardiac arrest was defined as cardiac arrest caused by both surgical and anaesthesiological factors or in which there was some doubt whether cardiac arrest was entirely attributable to anaesthesia or other factors under the control of the anaesthetist (Categories 2 and 3).
Adverse events leading to cardiac arrest
The primary adverse events leading to cardiac arrest were further classified in a fashion similar to the categories used by Cheney et al.17: respiratory, cardiovascular, medication-related, equipment-related, block-related, procedural, iatrogenic and other not further classified incidents. Finally, cardiac arrests were classed by reviewers as definitely preventable, possibly preventable or not preventable.18
Risk factors for perioperative cardiac arrest
Univariate and multi-variate logistic regression analysis was used to identify pre-existing risk factors, which were independently associated with the endpoint (cardiac arrest). Patients with reported critical events within the same time period without cardiac arrest served as a comparison group to analyse which patients with perioperative critical incidents are at risk of sustaining cardiac arrest. For univariate analysis, the χ2 test was used. The level of significance was P less than 0.05. Results of logistic regression analysis are reported as odds ratio (OR) with 95% confidence intervals (CI). Risk factor analysis was carried out by comparing the incidence of cardiac arrest among groups. Significant variables of univariate analysis associated with cardiac arrest were included in multi-variate regression analysis. We developed one model with the endpoint cardiac arrest. Selection was performed by the forward method and confirmed by the backward method. Data were documented with Microsoft Excel (version 2013, Microsoft Corporation, Redmond, Washington, USA) and analysed with IBM SPSS (version 24.0; IBM SPSS Statistics, Armonk, New York, USA). All continuous parameters were calculated as mean or median, minimum, maximum and SD and categorical variables were calculated as numbers and percentage.
Between 2007 and 2012, 169 500 anaesthetic procedures were performed at the University Hospital of Cologne. Within this time period, we obtained data from 318 critical incident reports. Ninety-nine cardiac arrests in 99 patients within 24 h perioperatively were found in our database, a perioperative cardiac arrest rate of 5.8/10 000 anaesthetics (95% CI 4.7 to 7.0). The number of anaesthesia-related cardiac arrests was 12, which is a rate of 0.7/10 000 (95% CI 0.3 to 1.1). The incidence of cardiac arrest caused by factors which were at least anaesthesia-contributory (n = 29) was 1.7/10 000 (95% CI 1.1 to 2.3) (Fig. 1). Overall mortality from cardiac arrest within 24 h perioperatively was 41 of 99 cardiac arrests. This is a rate of 2.4/10 000 (95% CI 1.7 to 3.2) procedures. None of the patients with anaesthesia-related cardiac arrest died, which implies a true anaesthesia-related mortality rate of less than 5.9 per million (0.059/10 000). Four patients (13.8%) in the anaesthesia-contributory group did not survive cardiac arrest. This is a rate 0.2/10 000 (95% CI 0.01 to 0.47) anaesthetic procedures. Of 58 patients with cardiac arrest unrelated to anaesthesia, 37 (63.8%) did not survive.
The median age of all patients with cardiac arrest was 60 years (range 3 months to 92 years). Twenty-five patients with cardiac arrest were older than 75 years and 13 patients with cardiac arrest were 0 to 3 years old. Of these, six cardiac arrests occurred during heart surgery or cardiac catheterisation. Forty-three patients affected were women (43.4%) and 56 patients were men (56.6%). Forty cardiac arrests occurred outside regular working hours and 79 patients with cardiac arrest were ASA physical status at least 3. Thirty-nine cardiac arrest patients had a revised cardiac risk index at least 3, and 39 cardiac arrest patients had a New York Heart Association functional score at least 3. Fifty-four cardiac arrests occurred in patients classified as emergency. Nineteen patients with cardiac arrest had a BMI at least 30 kg m−2. In six cases, a resident within the first year of training was involved in the treatment. In 75 cases, a specialist anaesthetist was involved. Figure 2 shows the distribution of primary adverse events leading to perioperative cardiac arrest in the subgroups of anaesthesia-related and anaesthesia-contributory cardiac arrest. In the group of patients with anaesthesia-related cardiac arrest (n = 12), respiratory events contributed to cardiac arrest in 41% of the cases (n = 5). Anaesthesia-contributory cardiac arrest (n = 29) was in two-thirds of the cases (n = 19) related to cardiovascular adverse events.
Patient characteristics and adverse events leading to anaesthesia-related cardiac arrest are shown in Table 1. In four cases of cardiac arrest, the adverse event was definitely preventable. The first of these received an accidental bolus dose of remifentanil causing apnoea and bradycardia requiring a short period of cardiopulmonary resuscitation (CPR). In the second case, a connector for the external pacemaker was missing, leading to a CPR duration of 4-min. In the third case, a defibrillator which malfunctioned had not been checked properly prior to surgery, leading to a delay in termination of ventricular fibrillation during testing of an implantable cardioverter-defibrillator. In the fourth case (5 months old infant), a medication error (adult dose of eye drops was given) led to bradycardia. This case was classified as ‘surgical or other factors’. Eleven cases (11.1%) were classified as potentially preventable, and 84 cases (84.8%) of cardiac arrest as not preventable.
The main pre-existing risk factors for cardiac arrest identified from multi-variate analysis were ASA physical status at least 3 [P = 0.007, OR 2.59 (95% CI 1.29 to 5.19)], emergency surgery [P < 0.001, OR 4.00 (95% CI 2.15 to 7.54)] and pre-existing cardiomyopathy [P < 0.001, OR 17.48 (95% CI 6.18 to 51.51)] (Table 2).
To the best of our knowledge, this is the first study on perioperative anaesthesia-related cardiac arrest in a large unselected patient population from a European tertiary care university hospital, including all ASA groups and cardiac surgery patients.
The study focuses on a clearly defined important clinical endpoint and provides valuable insight into current perioperative cardiac arrest rates. Furthermore, our analysis identifies risk factors for cardiac arrest in patients with perioperative critical incidents in a large unselected hospital population. Recent studies revealed markedly varying rates of perioperative mortality and rates of perioperative critical incidents between different European countries.19,20 Thus, our data can potentially serve as a basis for local quality improvement measures and national benchmarking. So far, only one European study, from a French university hospital, evaluated perioperative cardiac arrest in a large cohort from 1989 to 1995 but this analysis did not include cardiac surgery, abdominal surgery, obstetrics or neurosurgery.3 Other studies from Europe focused on a different outcome (e.g. perioperative mortality).7,11,14
Incidence of perioperative cardiac arrest
The incidence of anaesthesia-related cardiac arrest reported in our study (0.7/10 000) was similar to that found in a recent US study, although different definitions of anaesthesia-related cardiac arrest were used, and the study period was up to 48 h postoperatively.5 Although the overall perioperative cardiac arrest rate in our population was lower and the incidence of anaesthesia-contributory cardiac arrest was slightly higher, the perioperative risk in both studies seems to be comparable. Thus, for the first time, our data show that incidences of perioperative cardiac arrest in a large German university hospital seem to be similar to that in a US tertiary care hospital.
In a recent systematic review and meta-analysis, an overall perioperative cardiac arrest rate of 7.19/10 000 anaesthetics was calculated for studies from the 1990s to the 2000s.1 In this analysis, the overall incidence of perioperative cardiac arrest varied from 6.59/10 000 anaesthetics in highly developed countries to 20.68/10 000 in less-developed countries.
A study from France reported a frequency of 1.1 cardiac arrests related to anaesthesia per 10 000 anaesthetics.3 The authors then divided the cases into totally or partly related to anaesthesia. However, this study included only orthopaedic, paediatric, urological, otorhinolaryngological and maxillofacial surgery. In a Brazilian study, cardiac arrest rates were identified prospectively, and the authors found an incidence of 3.35/10 000 perioperative cardiac arrests related to anaesthesia, 1.86/10 000 totally attributed and 1.49/10 000 partly attributed to anaesthesia.4 The differences in study design, observation periods and definitions of perioperative complications or outcomes limit the comparability of the different studies. Therefore, a consensus on documenting complications and defining anaesthesia-related mortality is needed.21
Notably, five of 12 cardiac arrests related to anaesthesia occurred in paediatric patients. In three paediatric cases, cardiac arrest was related to respiratory events (Table 1). It is well known that the incidence of perioperative cardiac arrest is higher in children than in adults, especially newborns and infants.22 In previous studies on perioperative cardiac arrest in unselected patient populations, the rate of paediatric anaesthesia-related cardiac arrest varied from 0 to 50% of all cardiac arrests.4,5,8 In a single-centre tertiary teaching children's hospital, a perioperative cardiac arrest rate of 8.5/10 000 anaesthetics was found, and respiratory events were the most common reason for anaesthesia-related cardiac arrest.23 A recent European multi-centre observational study revealed an incidence of severe perioperative critical incidents, including cardiac arrest higher than expected with a large variability between countries.19 These results stress the importance of educational measures and quality improvement in paediatric anaesthesia. At our institution, a specialised paediatric anaesthesia team and educational programmes were implemented after the study period. Thus, our results are a helpful basis for future local quality measurements.
Adverse events leading to cardiac arrest
Respiratory events and problems with airway management were the primary cause of anaesthesia-related cardiac arrest. These results are in line with data from a recent US study where the majority (64%) of anaesthesia-related cardiac arrests was due to complications with airway management.5 In a previous analysis by the same authors, airway management problems contributed to 40% of anaesthesia-related cardiac arrest.8 However, in both US studies, the adverse events leading to anaesthesia-contributory cardiac arrest are inconsistent. Whereas the earlier study found a high rate (40%) of medication-related events,8 the recent study described – similar to our results – cardiovascular events (70%) as a major problem in anaesthesia-contributory cardiac arrest.5 Although it is regarded as evident that respiratory and airway-related adverse events play a major role in anaesthesia-related fatal outcomes (death, cardiac arrest etc.), this was not confirmed in all studies. In a study of older patients, two-thirds of the anaesthesia-related cardiac arrests were due to medication-related problems,10 and in a study from France, anaesthetic overdose was the most frequent adverse event leading to anaesthesia-related cardiac arrest.3 Anaesthesia-related death rates due to airway management problems cover a wide range from 7.9 up to 80%.15
In our analysis, all patients with anaesthesia-related or anaesthesia-contributory cardiac arrest due to airway management problems survived. The differences found in the studies on this topic might be ascribed to differences in primary outcomes (e.g. cardiac arrest, death, coma), patient populations, observation periods and definitions of anaesthesia-related and anaesthesia-attributable adverse events. Furthermore, as perioperative cardiac arrest or death is an infrequent event, slight fluctuations of the numerator (adverse events) might have a considerable impact on the frequency of the reported adverse events in the different studies.
Risk factors for perioperative cardiac arrest
Finally, in our study, we analysed pre-existing risk factors associated with perioperative cardiac arrest (Table 2). Multi-variate analysis identified ASA physical status grade at least 3, emergency surgery and pre-existing cardiomyopathy as independent predictors of perioperative cardiac arrest. ASA physical status was also a major risk factor for anaesthesia-related cardiac arrest in previous studies.3,10 The results of our study confirm that patient physical status seems to be a good predictor of perioperative complications. Emergency surgery was also a risk factor in a previous study on perioperative cardiac arrest in older patients.10 To our knowledge, pre-existing cardiomyopathy with reduced left ventricular ejection fraction (<30%) has not been previously described as a predictor of perioperative cardiac arrest. Interestingly, the Revised Cardiac Risk Index was a significant risk factor in the univariate analysis, but this could not be confirmed in the multi-variate analysis.
Due to the retrospective nature of the study design and as we depend on reporting by our staff anaesthesiologists, it is possible that some critical incidents were missed. We chose a time period of 24 h postoperatively and probably not all postoperative complications in outpatients were captured. Therefore, we might have missed some incidents in the late perioperative period. However, our analysis focuses on cardiac arrest related to anaesthesia and most anaesthesia-related complications are likely to appear in the intraoperative or early postoperative periods. Furthermore, critical incident reports were reviewed by institutional members. Therefore, it is possible that not all incidents were classified correctly as related or unrelated to anaesthesia. Studies on perioperative mortality, complications, or cardiac arrest, use different definitions, classifications and observation periods and focus on different patient populations. Thus, reports from different countries and institutions are difficult to compare and there is a need for consensus on defining anaesthesia-related mortality.21
Finally, as a single-centre study, our results may not be generalisable. However, our data from a tertiary care university hospital with approximately 30 000 anaesthesia procedures per year represent a broad anaesthesiological spectrum and a typical hospital patient mix. Furthermore, risk factors were identified from the population of patients with critical incidents. Thus, we analysed a population of patients who were probably at risk of sustaining perioperative complications and the results may not necessarily be generalised to the entire population of 169 500 patients.
In summary, we found an overall perioperative incidence of cardiac arrest at our institution, slightly lower than those published in the literature. Rates of anaesthesia-related and anaesthesia-contributory cardiac arrest were comparable to those from other studies in highly developed countries. Most cardiac arrests related to anaesthesia were due to respiratory events as described in most of the other studies on this topic. ASA physical status at least 3, emergency surgery and pre-existing cardiomyopathy were revealed to be relevant independent risk factors for cardiac arrest in our study population. In our opinion, uniform standards for reporting perioperative complications and mortality could improve evaluation of the quality and safety of anaesthesia. The results of our study can serve as a basis for national benchmarking. Consensus on defining anaesthesia-related mortality could be important to make data from different institutions and even from different countries comparable.
Acknowledgements relating to this article
Assistance with the study: none.
Financial support and sponsorship: this study was supported by solely from institutional and/or departmental sources.
Conflicts of interest: AH received industrial funding for an investigator-initiated trial and he received payments and compensation for travels and lectures from CytoSorbents GmbH Europe.
Presentation: preliminary data for this study were presented as a poster presentation at the European Society of Anaesthesiology (ESA) Euroanaesthesia meeting in Berlin from 30 May to 2 June 2015.
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