Introduction

Coronary artery bypass graft (CABG) surgery has emerged as the gold standard therapy for advanced coronary artery disease, predominantly performed using cardiopulmonary bypass (on-pump). The perioperative and in-hospital mortality rates associated with CABG surgery are estimated at approximately 1% for elective patients at the lowest risk, while ranging from 2 to 5% across all patient categories [1,2,3].

In an effort to optimize postoperative recovery and decrease intensive care unit (ICU) length of stay (LOS), a “fast-track” approach for patients undergoing cardiac surgery emerged in the early 1990s. It most notably included the optimization of anesthesia protocols as well as early extubation within anywhere between 7 and 12 h after surgery [4, 5]. Early studies on patients undergoing CABG surgery managed to demonstrate the fast-track approach to both be safe and lead to a decrease in ICU and hospital LOS [6, 7].

The subsequent introduction of enhanced recovery after surgery (ERAS) protocols in 1997 [8] marked a pivotal shift towards optimizing pre-, peri-, and postoperative patient management, aiming to accelerate postoperative recovery. This multimodal and interdisciplinary concept has been crucial in significantly reducing postoperative complications, mortality rates, and the duration of hospital stays [9, 10]. However, despite the demonstrated benefits, the adoption of ERAS protocols in cardiac surgery has been slow, with a majority of the studies highlighting their efficacy conducted within the recent 2 to 3 years [11,12,13]. These studies have shown that ERAS programs can decrease both the duration of hospitalization and postoperative morbidity in cardiac surgery [13, 14].

Nonetheless, the prevailing practice in many hospitals has remained to keep patients intubated rather than pursuing extubation within 6 h after on-pump CABG surgery as recommended by Engelman [15]. The onset of the coronavirus disease 2019 (COVID-19) pandemic underscored the critical need for efficient patient management strategies, such as early extubation, to optimize ICU bed availability for COVID-19 patients [16]. Early reports during the pandemic indicated that up to 20% of individuals with a COVID-19 infection developed severe illness requiring hospitalization [17,18,19], with a significant fraction of these patients necessitating ICU care [20, 21]. The variability in ICU admission rates in both the USA and Canada, ranging from 5 to 81% [22,23,24], along with the heightened demand for ICU beds, pressured hospitals during the COVID-19 pandemic to devise new strategies to alleviate healthcare system strains [25, 26]. Currently, hospitals are no longer under such strain [27].

In response, hospitals have sought to reduce the length of hospital stays for elective surgeries and implemented early extubation protocols to expedite discharge, thereby facilitating better management of surgical patients during the pandemic. This shift towards early extubation in cardiac surgery aims at shortening ICU stays and decreasing the reliance on prolonged invasive mechanical ventilation, reflecting a broader adaptation to the challenges imposed by the pandemic.

Therefore, this retrospective study was conducted to assess the feasibility and safety of extubating patients in the operating room immediately after on-pump CABG surgery, and to evaluate its impact on reducing hospital and ICU LOS, ICU readmissions, as well as ICU and hospital mortality rates.

Materials and methods

In this retrospective study, clinical data were collected and analyzed from 2019 to 2022 for patients who underwent on-pump CABG surgery at the University Hospital Aachen, Germany. The local ethics committee approved the study protocols, with approval granted on November 13, 2023 (EK 23-331), which permitted the inclusion of data from 2019 to 2022.

Patients

Eligibility for the study was based on the following inclusion criteria: (1) age of 18 years or older and (2) undergoing elective on-pump CABG surgery. Patients were excluded if they required CABG surgery due to acute conditions such as ST-elevation myocardial infarction (STEMI) or non-ST-elevation myocardial infarction (NSTEMI), underwent CABG in combination with other procedures (e.g., aortic valve replacement), receiving a type of CABG other than on-pump with cardioplegia (e.g., off-pump CABG), needed postoperative extracorporeal membrane oxygenation (ECMO), or had other cardiac pathologies like aortic valve stenosis or heart failure. Extubation in the operating room was defined as extubation directly after surgery on the operating table, instead of delaying extubation until after the transfer to the ICU.

The anesthesia regimen in cardiothoracic surgery is standardized. For induction, patients received sufentanil, propofol, and rocuronium, while sevoflurane and sufentanil were used for maintenance.

Patients were divided into two groups. The first group (EXT group) consisted of patients who were extubated immediately after on-pump CABG surgery on the operating room table, provided they were hemodynamically stable (norepinephrine <0.2 μg/kg/min, epinephrine < 0.1 μg/kg/min) and had less than 200 ml of chest tube drainage (time from chest closure until extubation). Patients also had to meet the general extubation criteria [28]. Extubation was postponed in cases of anesthesiological or surgical complications, hemodynamic instability, or pulmonary impairment. The second group (ITN group) included patients who underwent on-pump CABG surgery but were not immediately extubated post-surgery. The EXT group exclusively comprised patients from the COVID-19 pandemic years (2020–2022), while the ITN group included patients from 2019, the year before the pandemic.

Between 2019 and 2022, 600 patients underwent on-pump CABG surgery (Fig. 1). Of these, 57 patients had to be excluded due to incomplete data. An additional 38 were excluded because they received concurrent surgeries (e.g., surgical aortic valve replacement) alongside the on-pump CABG surgery. Further, 204 patients were excluded for having been diagnosed with NSTEMI or STEMI at the time of their on-pump CABG surgery. Nineteen patients were excluded due to receiving a type of CABG other than on-pump with cardioplegia (e.g., off-pump CABG). This resulted in a cohort of 282 patients, from which another 2 were excluded due to the necessity of postoperative ECMO support. Of the remaining 280 patients, 54 were extubated immediately after surgery, while 226 remained intubated. In this study, the ITN group includes only patients from before the COVID-19 pandemic, while the EXT group includes only patients from during the pandemic. Consequently, additional patients had to be excluded based on these criteria: Therefore, 176 patients from the ITN group who underwent on-pump CABG surgery during the COVID-19 pandemic, rather than before, were excluded, resulting in a final count of 50 patients for this group. Similarly, 7 patients from the EXT group who had their surgeries before and not during the pandemic, were also excluded, leaving a total of 47 patients in that group.

Fig. 1
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Flow chart of patient selection

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Study endpoints

The co-primary outcomes for comparing the two groups were ICU LOS, ICU readmission, and ICU mortality. Secondary outcomes included hospital LOS, hospital mortality, rate of reintubation, and the incidence of postoperative pneumonia.

Statistical analysis

Statistical analyses and graph design were conducted using GraphPad Prism software (Version 9.3.1, GraphPad Software, San Diego, CA, USA). A p value of less than 0.05 was considered statistically significant. Data were presented as median (first quartile–third quartile) or number (percentage). The Shapiro-Wilk test was used to assess normal distribution. For normally distributed data, an unpaired t-test was applied, while the Mann-Whitney test was used for data that were not normally distributed. Additional statistical data can be found in Supplementary Table 1. Outcome analysis was performed by using log-rank test with hazard ratios calculated with the Mantel-Haenszel method. Kaplan-Meier curves were used to illustrate the analysis.

Results

Baseline clinical characteristics of patients undergoing elective on-pump CABG surgery

Ninety-seven patients who met the inclusion criteria were included in this study. They were predominantly male (80%) with a median age of 66 years (61–71) (Table 1; Supplementary Table 1). The clinical characteristics of patients who were extubated in the operating room after surgery (EXT group) were comparable with those who remained intubated (ITN group), except for the duration of invasive mandatory ventilation (i-MV), which was longer in patients in the ITN group (8 h (6–11.6 h) vs. 0 h (0–0)), p < 0.01). The time spent during the surgery was not included in the total time calculated for invasive mechanical ventilation (i-MV). Notably, 6 out of 50 patients in the ITN group were extubated within 6 h after surgery.

Table 1 Baseline clinical characteristics of patients undergoing on-pump CABG surgery
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Clinical characteristics 24 h after on-pump CABG surgery

At 24 h after on-pump CABG surgery, the EXT group required a significantly lower concentration of norepinephrine (0.000 μg/kg/min (0.000–0.000)) compared to the ITN group (0.000 μg/kg/min (0.000–0.012)), with a significant difference (p < 0.01) as shown in Table 2. The concentration of epinephrine needed at 24 h post-surgery was similar between both groups. The analysis also indicated that the duration for which norepinephrine or epinephrine was administered did not significantly differ between intubated and extubated patients as depicted in Fig. 2A and B (norepinephrine: p = 0.15; HR (hazard ratio), 1.4; CI, 0.9–2.1; epinephrine: p = 0.69; HR, 0.8; CI, 0.3–2.1). Furthermore, there were no significant differences in mean arterial pressure (MAP) and pulmonary oxygenation (PaO2/FiO2 ratio) between the groups at 24 h after surgery. The incidence of postoperative complications, such as delirium and atrial fibrillation, as well as the rate of reintubation, showed no significant difference between the ITN and EXT groups.

Table 2 Clinical characteristics 24 h after on-pump CABG surgery and incidence of postoperative complications
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Fig. 2
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Percentage (%) of patients in the EXT and ITN group with the duration of norepinephrine administration (A) and duration of epinephrine administration (B). EXT, group of patients extubated in the operating room after surgery; ITN, group of patients who remained intubated post-surgery. There was no significant difference in the discontinuation rates of norepinephrine or epinephrine between the EXT group and the ITN group

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Primary and secondary outcomes

No significant differences were observed in ICU or hospital LOS, mortality, reintubation rates, ICU readmission rates, or the incidence of postoperative pneumonia between the groups, as shown in Table 3. Cox regression analysis revealed no significant association between the groups (intubated vs. extubated) regarding LOS in ICU (p = 0.63; HR, 0.9; CI (confidence interval), 0.6–1.4) or LOS in hospital (p = 0.67; HR, 0.9; CI, 0.6–1.4), as shown in Fig. 3A and B.

Table 3 Primary and secondary outcomes
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Fig. 3
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LOS in hospital and in the ICU of patients in the EXT and ITN group. A LOS in the hospital of patients in the EXT and ITN group. B LOS in the ICU of patients in the EXT and ITN group. LOS, length of stay; EXT, group of patients extubated in the operating room after surgery; ITN, group of patients who remained intubated post-surgery. Cox regression analysis showed that there was no significant association between the ITN and EXT groups regarding the rate of discharge from the ICU or hospital

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Discussion

This study evaluates the outcomes of patients undergoing on-pump CABG surgery, focusing on the effects of immediate extubation in the operating room versus conventional practices of remaining intubated post-surgery. We retrospectively collected and analyzed data from patients treated during the 2019–2022 period, including the COVID-19 pandemic years, to investigate the impact of extubation protocols on post-surgical recovery and the use of healthcare resources.

Patients who were extubated in the operating room immediately after on-pump CABG surgery (EXT group) demonstrated a shorter duration of invasive mandatory ventilation and significantly lower norepinephrine levels 24 h post-surgery compared to those who remained intubated (ITN group). There were no significant differences in ICU and hospital LOS, mortality, reintubation rates, ICU readmission rates, or the incidence of postoperative pneumonia between the two groups.

In the ITN group, 6 out of 50 patients were not extubated directly in the operating room but were extubated within 6 h postoperatively, as recommended by current ERACS (enhanced recovery after cardiac surgery) guidelines [15]. However, 44 out of 50 patients remained intubated for longer than 6 h, which does not meet these guidelines. It is important to highlight that the primary focus of this study was to explore the potential benefits of immediate on-table extubation, rather than extubation within the 6-h window recommended for post-cardiac surgery.

In addition, during the COVID-19 pandemic, ICU capacity constraints led to the implementation of direct extubation in the operating room after elective cardiac surgery to accommodate the increased need for ICU beds for COVID-19 patients. Before the pandemic, direct operating room extubation was not practiced; instead, patients were typically extubated several hours later in the ICU. Consequently, there were only very few patients meeting the criteria for the EXT group in the pre-pandemic era. Similarly, selecting intubated patients from the pandemic period would have introduced bias, as those who remained intubated were often patients with specific medical conditions requiring prolonged ventilation.

Further, none of the patients in the EXT group had a confirmed COVID-19 infection before, during, or after the CABG surgery, as all tested negative for severe acute respiratory distress syndrome coronavirus 2 (SARS-CoV-2). Since the patients in the ITN group were operated on in 2019, before COVID-19 testing was available, no data on their COVID-19 status is available.

Evidence suggests that on-table extubation [29, 30] or early extubation within 6 h post-cardiac surgery can decrease the rate of postoperative complications compared to prolonged intubation [31]. While one clinical trial found no difference in the incidence of reintubation, stroke, and renal failure between early and late extubation [31], other studies have indicated potential benefits, including reduced risks of postoperative atrial arrhythmia when extubated within 1 h after ICU arrival [32], and lower risks of pneumonia and bacteremia [33]. Meta-analyses have further supported that early extubation, within 8 h, is not associated with increased morbidity or mortality [34, 35]. Early extubation benefits include enhanced pulmonary secretion clearance, earlier mobilization, and improved cardiac performance, while prolonged mechanical ventilation is associated with higher rates of bacterial colonization and hospital-acquired pneumonia, as well as an increased risk of postoperative delirium, which has been linked to increased mortality and prolonged hospital LOS [36, 37]. Another study demonstrated that several factors are associated with early extubation, such as younger age and lower body mass index (BMI) [38]. Finally, e Silva and Badhwar et al. explored the financial implications of extubation practices, revealing that extubation in the operating room can significantly reduce hospital costs by minimizing the need for prolonged ICU monitoring and associated staffing costs, in addition to reducing ventilator-associated complications [39, 40].

At our hospital, patients were not extubated immediately after cardiac surgery per protocol but were transferred to the ICU while still intubated. The pandemic necessitated a shift in practice, with anesthesiologists opting to extubate patients to reduce ICU stays and make room for COVID-19 patients requiring intensive care. This study included 47 patients in the EXT group, with a similar number from 2019 selected for the ITN group to ensure comparable baseline characteristics, revealing no significant differences between the groups in this regard.

Notably, patients in the ITN group required significantly higher doses of norepinephrine compared to those in the EXT group. This difference is likely attributable to the need for sedation in intubated patients, as sedative agents can significantly impact hemodynamic stability. Consequently, additional vasopressors are often necessary to maintain adequate MAP.

Prior to the COVID-19 pandemic, routine on-table extubation was not a common practice from the perspective of cardiac surgeons and was not considered a standard approach (“lex chirurgica”). As a result, it was not a topic of serious discussion within our institution. However, the pandemic brought increased restrictions and a persistent shortage of ICU beds, which led to a significant shift in mindset. This situation prompted the initiation of an early extubation program, during which cardiac surgeons began to recognize the advantages of early extubation.

As the pandemic subsided, the benefits of early extubation became widely accepted among cardiac surgeons, who advocated for it to become the new standard of care. The primary adjustment during this period was the implementation of on-tabula extubation. Additionally, adjustments were made in anesthetic management, such as switching from intraoperative sufentanil to remifentanil and introducing intraoperative dexmedetomidine to reduce the use of sevoflurane and potentially lower the risk of postoperative cognitive deficits.

These changes, initially driven by the pandemic, have demonstrated benefits that extend beyond the immediate crisis and have now been integrated into current practice.

Limitations

It must be acknowledged that this study is subject to limitations. First, the retrospective design introduces potential biases, including selection bias and the retrospective collection of data, which may affect the reliability of the outcomes observed. The method of data collection and analysis relies on the accuracy and completeness of medical records, which might not capture all nuances of patient care or subtle clinical indicators that could influence outcomes.

Secondly, the study cohort was drawn from a single institution, which may limit the generalizability of the findings to other settings. Practices, patient demographics, and healthcare resources can vary significantly across different institutions and geographical locations, potentially influencing the applicability of the results to broader populations. The unique protocols and patient management strategies of the participating hospital may not be representative of those employed in other hospitals or cardiac surgery centers.

Another critical limitation is the selection of patients for the ITN group from the year 2019, exclusively before the COVID-19 pandemic, as opposed to the EXT group where patients were selected from the pandemic period (2020–2022). This distinction is pivotal as patients who remained intubated during the pandemic likely did so out of necessity, such as deteriorating gas exchange, which could inadvertently introduce a higher risk of selection bias into the study. Despite these challenges, a thorough comparison of baseline characteristics—including age, gender, BMI, comorbidities like pulmonary disease or diabetes mellitus, Sequential Organ Failure Assessment score (SOFA score), and European System for Cardiac Operative Risk Evaluation (Euro SCORE II)—revealed no significant differences between the groups, thereby facilitating a robust comparative analysis.

The relatively small sample size of this study of 97 patients limits the statistical power to detect small but clinically significant differences between groups. This limitation is particularly relevant for outcomes that occur infrequently, where a larger sample size might have provided the necessary power to observe significant differences. The inclusion criteria, designed to select patients during the COVID-19 pandemic for the EXT group, further constrained the ability to increase the sample size of this study, as it was limited by the number of eligible patients treated during this specific period.

Additionally, our analysis did not include a power calculation, primarily because we included all eligible patients for the EXT group from the pandemic period. Given that our study was conducted at a single center, we were unable to expand our patient sample size beyond those who met our inclusion criteria during the specified timeframe.

Lastly, the focus on short-term outcomes, such as ICU and hospital stay, without assessing longer-term effects or patient-reported outcomes, limits the scope conclusions of the study. Long-term recovery, quality of life post-surgery, and patient satisfaction are critical dimensions of surgical success that were not addressed in this analysis.

Future research should aim to address these limitations by employing prospective, multicenter study designs with larger, more diverse patient populations to strengthen the reliability and generalizability of the findings.

Conclusion

In conclusion, although immediate extubation in the operating room following on-pump CABG surgery did not show significant differences in ICU or hospital LOS, mortality, or ICU readmission rates compared to conventional intubation practices, it may still offer potential benefits, such as reduced norepinephrine use. Future multicenter randomized controlled trials are necessary to determine the optimal timing of extubation after cardiac surgery to enhance patient outcomes and healthcare efficiency.