Material and Method: The study was designed as a prospective observational study. A total of 70 patients, 35 with a Covid-19 history, and 35 without, were included in the study. Researchers observed the patients in the postoperative intensive care unit and filled out patient information forms.

Results: Although the length of ventilation was longer in patients with a history of Covid-19, there was no significant difference between the groups (p >0.05). The median values of the length of spontaneous ventilation mode in patients with a history of Covid-19 were significantly higher (p <0.05). The ventilation length of those with a Covid-19 history and previous cardiac surgery history was significantly longer (p <0.05).

Conclusion: According to the results of this study, Covid-19 may affect mechanical ventilator weaning time and postoperative outcomes after cardiac surgery.

Covid-19 is an infectious disease caused by the SARS-CoV-2 virus, leading to severe acute respiratory distress syndrome⁴. Covid-19 infection can lead to variety of complications, including pulmonary issues such as acute respiratory distress syndrome, pulmonary fibrosis, pulmonary hypertension, pulmonary embolism, and pneumothorax⁵. SARS-CoV-2-induced damage to the lungs results in decreased capillary per-meability and leakage. One consequence of this pulmonary leakage is pulmonary edema, which impairs gas exchange and respiratory function. This condition intensifies respiratory drive, prompting patients to breathe deeply and rapidly, causing rises and shifts in pleural pressure and inadvertently harming the lungs⁶. Covid-19 patients with respiratory failure often require long-term MV support ⁷.

The postoperative management of ventilator dependence is multifactorial. Patients' characteristics, habits, diseases, and the complexity of the surgical procedure can all impact lung function following cardiac surgery, influencing the length of postoperative MV support⁸. A study found a statistically significant difference between short and long MV lengths in Covid-19 patients, with those experiencing shorter MV having shorter intensive care and hospital stay⁷. Additionally, preoperative patient characteristics such as hypertension, COPD, chronic kidney disease, and previous endocarditis may also be predictive of delayed extubation². Nevertheless, early extubation not only promotes early patient mobilization but has also been associated with shorter durations of intensive care and hospital stays; for instance, a study reported that patients who were extubated early (within <24 hours) demonstrated reduced time in intensive care and shorter hospital stays^8,9. Considering the impact of Covid-19 on lung functions, evaluating the duration of MV application in Covid-19 patients after cardiac surgery and understanding the factors affecting length and postoperative outcomes will contribute valuable insights to the literature.

A study was referenced to determine sample size¹⁰. The sample size was calculated by power analysis method (G*Power 3.1) using difference between two independent means. Accordingly, with 95% power analysis and 0.05% margin of error, a total of 34 patients, 17 with a history of Covid-19 and 17 without. Our study was to be completed with 70 individuals, with 35 having a Covid-19 history and 35 without. The inclusion criteria for patients were being over 18 years old, being able to communicate, having a planned surgery, and accepting to participate in the study voluntarily. Exclusion criteria were refusing to participate in the study, having received an intra-aortic balloon and extracorporeal membrane oxygenation therapy, under-going an urgent surgery, and having post-operative unconsciousness.

Data collection tools
The Patient Information Form was used to collect demographic characteristics (age, gender, educational status, etc.), clinical status (comorbidity, Covid-19 history, vaccination, previous surgery, etc.), and post-operative data (on-pump time, ventilation time, intensive care unit stay, mobilization time, etc.).

Data collection
The patients were visited by the researchers at the clinics where they were hospitalized one day before the operation. The aim of the study was explained, and their Covid-19 background was assessed. The first 35 patients with and without a Covid-19 history who were scheduled to have surgery were included in the research. As of the start of the study, if a patient could not be recruited from either group, the next patient from both groups was excluded and the process was repeated with the subsequent patients. For example, if the tenth patient with a Covid-19 history was not included in the study, the tenth patient without a Covid-19 history was also excluded, and the study proceeded with the eleventh patients. When the first 35 patients with a Covid-19 history and the first 35 patients without a Covid-19 history agreed to participate in the study, they were monitored in the cardiovascular surgery intensive care unit. The researchers recorded the responses to the questions.

Ethics
Ethics committee approval was obtained from Trabzon Kanuni Training and Research Hospital (Decision no: 12/09/2022-2022/49). Institutional permission was obtained from hospital. Written informed consent was received from the patients who agreed to participate in the study. Patients were informed that they could leave the study at any time.

Statistical analysis
The Kolmogorov-Smirnov test was used to examine the suitability of the data for normal distribution. Percentages, mean, and standard deviation were used in the evaluation of descriptive data. The chi-square test was used to compare the Covid and non-Covid groups with categorical independent variables (Covid vaccination status, previous surgery, smoking, alcohol, etc.), and Mann Whitney U and correlation test were used to compare continuous variables (on-pump time during operation, ventilation time, spontaneous ventilation, etc.) for those not normally distributed.

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Table 1: Distribution of Demographic Characteristics of Patients with and without a Covid-19 History (n =70).

Among the participants, 65.7% and 68.6% of those with and without a Covid-19 history had hypertension (HT), respectively. Data revealed that 91.4% of those with a Covid-19 history and 97.1% of those without a Covid-19 history had no history of respiratory tract infection. It was observed that 62.9% and 57.1 % of those with and without a Covid-19 history were non-smokers, respectively, and 97.1% and 94.3% of those with and without a Covid-19 history got vaccinated, respectively. Most patients in both groups underwent coronary artery bypass graft (CABG) surgery (Table 2).

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Table 2: Distribution of Clinical Characteristics of Patients with and without a Covid-19 History (n=70).

The median length of ventilation was 485 (415-535) minutes in patients with a Covid-19 history and 480 (390-580) minutes in the other group, and there was no statistically significant difference between the groups (p >0.05). The duration of spontaneous ventilation mode in patients with a Covid-19 history was 75 (55-110) minutes, which was significantly lower (p <0.05). A statistically significant difference was observed in the lengths of ventilation in patients with a Covid-19 history based on their previous surgery status (p <0.05) (Table 3).

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Table 3: Comparison of Postop Data of Patients with and without a Covid-19 History (n =70).

Ventilation was longer in patients with a history of both surgery and Covid-19. There was a positive correlation between ventilation length of patients with a Covid-19 history, and the length of intensive care hospitalization, as well as hospital discharge (r =0.399, p =0.018; r =0.362, p =0.033, respectively) (Table 4).

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Table 4: Comparison of Ventilation Duration of Patients with and without a Covid-19 History with Some Variables (n =70).

Reports in the literature have presented varied findings regarding the impact of a Covid-19 history on the lengths of ventilation and intensive care. Todi and Ghosh found no statistically significant difference in hospitalization time between those with and without a history of Covid-19, whereas El Moheb et al. reported statistically significant longer hospital stays for those with a history of Covid-19 ^10,12. In our study, there was no significant difference between patients with and without a Covid-19 history in terms of length of ventilation, intensive care, and hospitalization. However, there was a positive correlation between lengths of ventilation, intensive care, and hospital discharge time in patients with a Covid-19 history. Along with the results of our study, it is shown in the literature that when the ventilation period is prolonged, intensive care, and hospital discharge time may be extended. Therefore, it is thought that prolonged ventilation may indirectly contribute to extended intensive care and hospital discharge times in the context of Covid-19.

The study also explored the relationship between the length of cardiopulmonary bypass (CPB), spontaneous ventilation mode, previous surgery status, and ventilation. Although the length of CPB has been recognized as a risk factor for delayed extubation in previous research^2,8,11, our study found no significant difference between the groups regarding the length of CPB. However, patients with a history of Covid-19 were found to have longer CPB. Likewise, Sankar et al., found that a history of previous surgery was associated with prolonged MV. Surgical variables such as previous cardiac surgery and length of cardiopulmonary bypass, patient factors like critical preoperative condition, impaired left ventricular function, renal failure, and pulmonary hypertension, have been identified as risk factors for prolonged MV¹¹.

Limitations
This study has several limitations. Firstly, data collection was conducted in a single center, limiting the generalizability of the findings to a broader population. Additionally, the study had a relatively low sample size, which may impact the statistical power and reliability of the results. Furthermore, the Covid-19 history was obtained through self-reporting by of the patients, and individuals with silent Covid-19 (asymptomatic cases) could not be identified. The absence of symptomless cases might influence the comprehensive understanding of the impact of Covid-19 on the outcomes measured in the study. Moreover, the duration elapsed since the patients' Covid-19 infection could potentially influence the study results, and this factor was not explicitly addressed in the analysis. This study was mainly conducted to evaluate the extent to which Covid-19 disease affects MV weaning time when prolonged MV is already a significant complication after open heart surgery. Since prolonged MV might be induced by a variety of preoperative, intraoperative, and/or postoperative factors, the results are difficult to generalize. Therefore, further research is required to support the results of this research.

Disclosure
The authors report no conflicts of interest in this work.

Acknowledgement
The authors convey their special thanks to all the families that participated in the study.

Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.

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