Cardiac arrest is one of the leading causes of death in Europe (1). Patients with cardiac arrest must be treated immediately with basic life support to minimize no-flow time. Basic life support includes chest compressions with ventilation of the lungs, defined as cardiopulmonary resuscitation (CPR), and early defibrillation (2, 3). Early detection of cardiac arrest, high-quality CPR, and prompt defibrillation are crucial for patients’ survival with favorable neurological outcomes (4, 5). To ensure a favorable outcome, reversible causes of cardiac arrest—referred to by the mnemonic H’s and T’s—must be diagnosed and treated (4). Intraoperative cardiac arrest is a unique form of in-hospital cardiac arrest (IHCA) (6–8) and is feared by patients undergoing anesthesia (9). The limited data that exist suggest that the incidence of perioperative cardiac arrest is between 0.5 and 3 per 10,000 procedures for adult patients (10–13) and between 0.5 and 10 per 10,000 procedures for pediatric patients (14–18).

Patients undergoing anesthesia are considered highly monitored, which may contribute to early detection of cardiac arrest triggering the start of the chain of survival (6, 19). Furthermore, the personnel and equipment needed to provide advanced life support are assumed to be on site already, further accelerating proper resuscitative efforts. On the other hand, there has been a demographic change in patients undergoing anesthesia over the last decades. Nowadays, patients are older and present with a higher BMI and American Society of Anesthesiologists (ASA) physical status score (20), which contributes to a higher baseline risk for cardiac arrest (13).

A registry study with data collected from 2008 until 2012, including more than 1.8 million non-cardiac operations, identified ASA physical status, anesthesia technique, case urgency, type of surgery, and systemic inflammatory response syndrome (SIRS)/sepsis as the strongest predictors of intraoperative cardiac arrest (10). The in-hospital mortality after intraoperative cardiac arrest was reported to be around 35%, and 30-day mortality was up to 71% (21, 22). Some reports suggested that incidence is negatively associated with the higher resource areas (13, 23).

Data on the characteristics of intraoperative cardiac arrest are scarce. Furthermore, most published studies focused only on survival and did not investigate neurological outcome. Therefore, the sequela of intraoperative cardiac arrest for patients regarding neurological outcomes and health-related quality of life is underreported. Thus, we conducted our study to bridge this knowledge gap.

We screened 228,712 departmental anesthesia procedures, 6,245 of which were labeled with the header “severe cardiopulmonary instability” or “resuscitation” in the electronic medical record. Last, we included 195 patients with intraoperative cardiac arrest in this analysis, as displayed in Figure 1.

Patients’ baseline characteristics are summarized in Table 1. The median age was 70.5 [60.0; 79.4] years, and two-thirds of patients (n = 135; 69.2%) were male. Most patients had an ASA physical status ≥IV (IV; n = 83; 42.6% and V, n = 47; 24.1%). Cardiac arrest occurred more frequently (n = 103; 53.1%) during emergency procedures than elective ones (n = 92; 46.9%). The responsible surgeon classified almost one-third of the procedures (32.3%; n = 63) as immediate urgent intervention (Supplemental Tables S1, S2). The overall annual incidence of intraoperative cardiac arrest was 90 (CI 95% 78–103) in 100,000 procedures, with 24 (CI 95% 10–50) in children and 100 (CI 95% 86–115) in adults, respectively. The estimated annual incidence of intraoperative cardiac arrest was 58 (CI 95% 47–71) in 100,000 for elective and 175 (CI 95% 143–213) in 100,000 for emergency procedures.

This retrospective single-center study assessed characteristics and neurological survival following intraoperative cardiac arrest over 7 years. The overall incidence of intraoperative cardiac arrest was 80 (CI 95% 69–92) in 100,000 procedures. Pulseless electrical activity was most often the first rhythm in this cohort. Most patients had ROSC at least once over a one-minute period and sustained ROSC over 20 min. Over half of the patients had 30-day survival, most with a favorable neurological outcome (CPC 1 and 2). The health-related quality of life assessed 3 months after the cardiac arrest with the SF-12 was lower in the physical component score but higher in the mental component score than the average Swiss population.

Our study’s cardiac arrest incidences were comparable to previously reported pediatric data (10–13) but higher for adult (14–18) patients. The higher incidence in adult patients might be explained by including cardiac and vascular surgery. However, incidences vary in their classification (e.g., cardiac and vascular vs. non-cardiac surgery or elective vs. emergency procedures) and might be a problem of definition (1). Cardiac arrest in our presented cohort occurred more frequently during emergency procedures, similar to earlier reports (10). These patients are likely underdiagnosed regarding their co-morbidities and risks for cardiac arrest compared to elective patients, who can be clinically assessed in more detail in the pre-anesthetic visit and optimized if needed (28). Thus “prevention”—identified as a crucial step to avoid or indicate preparations in case of a cardiac arrest—is often limited in emergency patients (3). Furthermore, several emergency patients, especially those with highly urgent surgery, are considered to have severe trauma (e.g., polytrauma) or non-trauma (e.g., acute aortic dissection or a diagnosis of sepsis) are not expected to survive without surgery, as reflected by the high proportion of ASA physical status V.

Pulseless electrical activity was a leading non-shockable first rhythm in the presented cohort, and might be related to hypovolemic or distributive shock. Intraoperative hypovolemic or distributive shock is characterized by reduced circulating blood volume, and can be diagnosed by severe hypotension as a surrogate. While intraoperative hemorrhage might be the most significant and obvious cause during procedures, as reflected by the high number of red blood cell transfusions in this cohort, blood loss should be carefully monitored. Investigations (e.g., measurement of hemoglobin values and hemostasis) should be undertaken to identify appropriate treatment (36). Pre-existing conditions (e.g., sepsis), pre-existing illness (e.g., renal or liver failure), and pharmacological treatment (e.g., antihypertensive, antithrombotic, or anticoagulation) can contribute to intravascular hypovolemia or vasoplegia and should be anticipated early. Avoiding perioperative hemodynamic imbalance is also a key message underlined in the European Society of Cardiology guidelines to improve patients’ outcomes in non-cardiac surgery (28). Severe anaphylaxis from medication (e.g., antibiotics, neuromuscular blocking agents) or material (e.g., latex, prosthesis) used (37), or a patient’s position during the procedure (e.g., extreme reverse Trendelenburg or beach chair positions) should also be taken into account as a cause for cardiac arrest. The anesthesiologist’s task is to prevent the relative hypovolemia caused by vasodilation due to anesthesia overdose by monitoring anesthetic depth with a patient-centered electroencephalogram, and by being vigilant concerning absolute hypovolemia by treating volume loss and hypotension at an early stage.

An analysis of more than 700 episodes of pulseless electrical activity during CPR for patients with in-hospital cardiac arrest showed that it was the primary rhythm in around 60% (n = 423) of their included episodes (38). ROSC was recorded in over half of these episodes, with initial pulseless electrical activity (n = 230). However, only 9% of these patients survived until hospital discharge. In a recent registry data analysis of over 3,400 in-hospital cardiac arrest patients, an initial shockable rhythm was associated with an increased probability of 30-day survival (RR 2.31; CI 95% 2.02–2.64) compared to a non-shockable rhythm (39). In this registry analysis, only 16% of the patients with a non-shockable rhythm survived until 30 days (39). In contrast, in our analysis, the corresponding risk ratio for 30-day survival was 1.2 (95%-CI: 0.87–1.68) with an initial shockable rhythm. In our cohort, 30-day survival was higher than reported by Stankovic et al. (39) and significantly higher than reported in the registry analysis (22). Unfortunately, all studies (22, 38, 39) did not report the neurological outcome of the patients.

Furthermore, we can add that most survivors had favorable neurological outcomes. We hypothesize that this resulted from early resuscitative interventions based on mandatory high-quality education spaced over time for the entire anesthesia team. The health-related quality of life was in line with the findings of another in-hospital cardiac arrest cohort outside the operating room from our research group (8).

Compared to cardiac arrest registry data, our study showed real-life data on intraoperative cardiac arrests derived from a large Swiss University Hospital, including cardiac and vascular surgery, an adjunct emergency room for all ages, a cardiac arrest center, and intensive care units.

Intraoperative cardiac arrest is rare but is more likely in older patients, patients with ASA physical status ≥IV, cardiac and vascular surgery, and emergency procedures. Patients often present with pulseless electrical activity as the initial rhythm. ROSC can be achieved in most patients. Over half of the patients are alive after 30 days, most with favorable neurological outcomes, if treated immediately.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by the study protocol was approved by the Ethics Commission of the Canton of Bern (BASEC 2021-02330). According to Swiss Law, participants gave general consent for analyzing their health-related data in the retrospective part of the study and written informed consent for the neurological follow-up. Written informed consent to participate in this study was provided by the participants’ legal guardian/next of kin.

AF and LF helped with the study design, conduct, patient recruitment, analysis, manuscript writing, and funding. MC-C and MK helped with the study conduct, patient recruitment, and manuscript finalization. ND and UP helped with the study design, analysis, and manuscript finalization. MH helped with the study design, statistical analysis, and manuscript writing. TR and RG helped with the study design, conduct, analysis, manuscript writing, and supervision. All authors contributed to the article and approved the submitted version.

This study was funded by a grant from the Burgergemeinde Bern (2022–1029) and the Department of Anaesthesiology and Pain Medicine, Inselspital (FUAD-2-22). The article processing charges were covered by the University of Bern. Open access funding by University of Bern.

RG is the European Resuscitation Council (ERC) Board Director of Guidelines and ILCOR, and the ILCOR Education, Implementation and Team Task Force Chair.

The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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