Postoperative pulmonary complications (PPCs) are major contributors to both morbidity and mortality following noncardiac surgery [1, 2]. Although definitions differ among studies, PPCs typically include conditions such as respiratory failure, pneumonia, atelectasis, hypoxemia, pleural effusion, bronchospasm, and aspiration pneumonitis [3]. These events prolong hospitalization, increase healthcare expenses, and reduce long-term survival [4]. Reported incidence rates vary, ranging from 5% to 20% in major procedures [5, 6] and even reaching as high as 80% in some series [1], depending on the patient population, surgical type, and criteria used. Established risk factors include older age, high American Society of Anesthesiologists (ASA) physical status, obesity [7], smoking history, preexisting lung disease (e.g., COPD), cardiovascular comorbidities, upper abdominal or thoracic operations, emergency interventions, and the type of surgical anesthesia [5, 8]. Tools such as the ARISCAT score (or Assess Respiratory Risk in Surgical Patients in Catalonia score) have been developed and validated to predict individual PPC risk [3].

The advent of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic dramatically altered surgical care worldwide. Early in the outbreak, patients who contracted COVID-19 perioperatively experienced exceptionally high rates of pulmonary complications and death [9, 10]. This prompted concern over whether those who had recovered from COVID-19 faced a similar increasing risk. Pathophysiological mechanisms linking prior viral respiratory infection to increased perioperative pulmonary risk include persistent inflammation, endothelial damage, impaired mucociliary clearance, altered immune responses, and diffuse lung injury [11].

Initial reports suggested that COVID-19 infection increased the risk of PPCs [12], leading to guidelines that recommend postponing elective procedures for seven weeks [13]. However, subsequent investigations yielded mixed results [10, 14–16], emphasizing individualized decision-making on the basis of patient health status.To address this gap, we designed this prospective cohort study at an academic center in Lebanon to compare the incidence of PPCs among patients with PCR-confirmed prior COVID-19 and matched controls. Our objectives were to provide regional data on the incidence of PPC, examine the relationship between previous COVID-19 infection and pulmonary complications, and explore how infection-related factors, such as severity and timing, influence outcomes. We hypothesize that prior COVID-19 would independently increase the incidence of PPC, but less so in vaccinated individuals.

This cohort study was chosen to be prospective to minimize recall bias and observational and was conducted at one of the largest academic hospitals in Beirut, Lebanon: The Lebanese American University Medical Center-Rizk Hospital (LAUMC-RH). The study period for patient enrollment and data collection was from December 2021 to December 2022. This timeframe is relevant, as it coincides with the dominance of the Omicron variant of SARS-CoV-2 and increasing vaccination rates in the population [17]. Prospective data collection and imputation with propensity score matching were used to limit confounding and selection bias.

No formal power calculation performed; all eligible patients during the study period were included. The sample size was pragmatically based on all eligible patients during the study period. Adult patients aged 18 years or older scheduled for or undergoing either elective or emergency surgery were screened for eligibility. Patients were categorized into two groups:

The inclusion criteria were as follows:

The exclusion criteria were as follows:

All eligible patients who consented to participate (or whose next-of-kin consented in emergency situations) were enrolled consecutively during the study period until the target sample size was approached. The initial target was approximately 100 patients in the prior COVID-19 group; the final enrolled cohort size is reflected in the results.

Extensive perioperative data were collected prospectively for each enrolled patient by trained research personnel. Data were captured electronically and anonymized to ensure patient confidentiality. The collected dataset included the following:

Statistical analysis was performed via SPSS and R software. Descriptive statistics were used to summarize patient characteristics and outcomes. Continuous variables are presented as ^the mean ± standard deviation (SD) or median (interquartile range, IQR) depending on their distribution. Categorical variables are presented as frequencies and percentages.

Bivariate analyses were conducted to compare the characteristics and outcomes between the prior COVID-19 group and the control group. For categorical variables, chi-square tests or Fisher's exact tests were used. For continuous variables, independent samples t tests or Mann‒Whitney U tests were applied on the basis of the assumption of normality. Statistical significance was set at a two-sided p value of < 0.05.

A second analysis was performed post hoc via nearest-neighbor propensity score matching performed separately within each imputed dataset to form matched cohorts balanced on demographic characteristics and key medical comorbidities (cardiovascular, respiratory, renal, hepatic, metabolic, and neurological history), decreasing information bias. Consensus patients across imputed datasets were then selected for analysis. These tests are consistent across imputed datasets and matching, so no additional sensitivity analyses are needed. Beforehand:

The study protocol was reviewed and approved by the Institutional Review Board at the Lebanese American University. Informed consent was obtained from all participating patients prior to enrollment. In emergency cases where the patient was unable to provide consent, consent was obtained from the legally authorized next-of-kin. All the collected data were anonymized via unique study identifiers to protect patient privacy. Electronic data were stored securely in accordance with institutional policies. No biological samples were collected or banked as part of this study.

The study was conducted by a multidisciplinary research team comprising physicians from pulmonary and critical care medicine, anesthesiology, surgery, and internal medicine departments. The study was conducted without external funding, relying on institutional resources and the dedicated efforts of the research team. English proofreading and language integrity checks were provided using ChatGPT (OpenAI), under the supervision of authors.

A total of 217 adult patients who underwent surgery between December 2021 and December 2022 were evaluated for inclusion in the study. These were used to calculate summary statistics. After missing data were addressed, 186 patients were included in the analysis for the primary outcome and for propensity score matching. Of these, 77 patients had a history of PCR-confirmed COVID-19 infection prior to surgery, and 109 patients served as controls without a known history of infection. The infection-to-surgery period was estimated to be 13.86 ± 10.16 months, with a median of 12, 1st mode ~ mean, 2nd mode ~ 24, ranging from 1–36 months. Patients were followed up daily until their discharge but not for more than 7 days.

The baseline demographic characteristics and comorbidities are presented in Tables 1 and 2. Patient details on surgical and anesthetic techniques, among others, can be found in Supplement 1. Propensity score matching was then performed on the imputed datasets to create comparable groups across demographic variables and key medical comorbidities.

The primary outcome, the occurrence of any postoperative pulmonary complication within 7 days of surgery, was observed in 16 out of 186 patients, resulting in an overall incidence of 8.65%. Comparing the two groups:

The rate of complications per patient among those who experienced any complication was reported as 1.11 complications per patient overall. This rate was approximately 1 for patients with prior COVID-19 and 1.5 for control patients who developed complications.

However, chi-square tests comparing the incidence of the primary outcome between the prior COVID-19 group and the control group yielded an OR of 0.68 (95% CI 0.21–2.2, p = 0.6), indicating that there was no statistically significant difference in the overall incidence of PPCs within 7 days of surgery.

The incidence of specific postoperative complications within the study follow-up period is summarized in Table 3. Chi-square tests were used to compare the rates of the mentioned outcomes.

As shown in Table 3, none of the specific postoperative complications listed were significantly different in incidence between the prior COVID-19 group and the control group (all p > 0.05).

With respect to continuous outcomes, the median length of hospital stay (LOS) was 2 days for patients with prior COVID-19 and 3 days for control patients. The Mann‒Whitney U test for LOS yielded a p value of 0.082, which was not statistically significant, although it suggested a trend toward a shorter stay in the prior COVID-19 group. The duration of postoperative oxygen supplementation also showed no statistically significant difference between the groups according to the Mann‒Whitney U test (p = 0.822).

Univariate multiple regression analysis was performed for length of stay, and it did not demonstrate a significant association with either the duration from COVID-19 onset to surgery or the duration of postoperative oxygen supplementation. No significant correlation (Spearman’s) was found between the outcomes and the risk factors in either group (p > 0.05). On the basis of these findings, the decision was made not to proceed with multivariate analysis for any outcome to avoid "overanalysis", since no complex confounding structure necessitating multivariate modeling was evident in the preliminary analysis.

Propensity "nearest neighbor matching" was applied to the imputed datasets to create groups comparable in terms of baseline demographic variables and key medical comorbidities. Analysis using the consensus patients derived from this matching process did not reveal any significant added value compared with the main analysis for the primary or other binary outcomes. The only observed change highlighted was in the p value for the LOS comparison, which became 0.200.

The study assessed whether specific characteristics of prior COVID-19 infection were associated with postoperative outcomes within the COVID-19 group or the overall cohort. The factors evaluated included indices of severity during acute infection (requirement for oxygen, ICU admission, presence of complications such as PE/stroke/pneumothorax, findings on chest CT), the number of SARS-CoV-2 vaccine doses received, and the interval from the date of PCR-confirmed infection to the date of surgery.

The analysis revealed that none of these COVID-19-related factors were significantly correlated with the incidence of postoperative pulmonary complications within 7 days, the length of hospital stay, or the duration of postoperative oxygen requirement (all p > 0.05). This finding suggests that within this cohort, the severity of the prior infection, vaccination status, or the time elapsed since infection did not appear to modify the perioperative pulmonary risk.

Initial observational reports and expert consensus suggested that recent COVID-19 infections could increase the risk of PPC [12], leading professional bodies such as the ASA and Anesthesia Patient Safety Foundation (APSF) to advocate postponing elective procedures for at least seven weeks in unvaccinated patients after diagnosis [13]. These guidelines were largely based on expert opinions and early, retrospective data, which often included patients who underwent surgery soon after infection rather than prospective trials on optimal surgical timing.

Subsequent investigations into the optimal timing of surgery after COVID-19 diagnosis have yielded mixed results, with a main emphasis on individualized decision making on the basis of each patient’s health status [10, 16]. Variability stems from differences in study design (retrospective vs. prospective), patient cohort (elective versus urgent cases; comorbidity burden), infection severity and variant type, vaccination coverage, follow-up duration, and PPC definitions. While several studies continue to document elevated PPC rates when surgery is performed soon after infection [14, 15], others report that risk returns to baseline beyond a certain interval, resembling that of noninfected patients [16]. The specific interval required for the risk to subside remains a subject of ongoing debate and investigation.

Moreover, generalizing results from large, multinational cohorts to local settings can be problematic. Regional disparities in patient demographics, comorbidity prevalence, standard perioperative protocols, and healthcare resource availability may alter outcomes. Therefore, generating region-specific evidence is crucial for guiding local practice and refining broader guidelines.

This prospective cohort study investigated whether a history of PCR-confirmed COVID-19 was associated with an increased risk of postoperative pulmonary complications (PPCs) in patients undergoing surgery at the Lebanese American University Medical Center, Rizk Hospital. Our primary finding is that prior COVID-19 infection, within a period of 13.86 ± 10.16 months from surgery, did not significantly increase the PPC risk within 7 days post-surgery compared with that of controls, even after adjusting for relevant confounders. Moreover, COVID-19-related factors, including infection severity, vaccination status, and the interval between infection and surgery, were not associated with PPC risk or secondary outcomes (length of stay, oxygen requirement duration) in this cohort.

Our findings contribute to an evolving literature in which early alarms regarding perioperative risks in COVID-19 patients have given way to more heterogeneous results as the pandemic has progressed. Initial studies conducted during the prevaccine era, often involving patients with recent or ongoing infections, reported markedly elevated risks of pulmonary and overall complications. A meta-analysis (2) reported a perioperative mortality of 23.08%, with pulmonary complications (viz. Pneumonia (35.39%) and ARDS (14.3%) were the most common adverse events. Similarly, another analysis [20] reported a perioperative mortality of 20%, which was particularly high among emergency surgeries (29%), with pulmonary, thromboembolic, and infectious complications most commonly reported (14%). Importantly, both studies lacked direct comparisons with COVID-19-negative surgical patients.

In contrast, more recent data from the Omicron and postvaccination eras suggest a declining perioperative risk profile. A meta-analysis [21] comparing postoperative complication rates between pre-COVID-19 patients and COVID-19 patients revealed no significant differences across the Clavien‒Dindo grades [22, 23]. Large-scale population data from England [24] also revealed a decrease in 30-day mortality as the interval from SARS-CoV-2 infection to surgery increased, with mortality decreasing to 0.2% in patients who underwent surgery ≥ 7 weeks after infection, which was substantially lower than that reported during the first pandemic year but still higher than the prepandemic rate of 0.1% [25]. However, the interpretation of these data remains complex due to potential confounding factors and underdetection of infection status in historical cohorts.

Our results align with this more reassuring contemporary evidence. In contrast to earlier reports that led to recommendations for prolonged surgical delays [10, 19, 20, 26], we observed no increased PPC risk in patients with prior COVID-19, supporting the growing consensus that perioperative risk may no longer be markedly elevated in certain populations. Several factors likely account for this discrepancy with earlier data.

Timing is critical in mitigating postoperative risk. In our cohort, most patients underwent surgery well beyond the acute infection phase (≥ 1 month), likely allowing sufficient time for the resolution of pulmonary and systemic sequelae. Although current guidelines suggest a minimum 4-week delay for mild infections and longer for severe cases (2), our findings suggest that similar intervals, regardless of case severity, are associated with negligible residual risk.

The severity of initial COVID-19 strongly influences residual pulmonary risk. While we found no associations between prior infection severity markers (oxygen requirements, ICU stay, CT findings) and PPC risk, our cohort likely included few patients with severe disease. This contrasts with earlier studies in which higher proportions of patients experienced critical illness, which predisposes them to persistent lung injury [10, 19, 20].

Vaccination substantially reduces COVID-19 severity [27]. Although we found no direct correlation between the number of vaccine doses and PPC risk, the high vaccination rates in our prior COVID-19 cohort likely contributed to the predominance of mild or asymptomatic infections, thereby lowering the residual risk of perioperative complications.

Variants with distinct clinical profiles impact perioperative outcomes. Omicron, which was prevalent during our study period (Dec 2021–Dec 2022), is associated with reduced virulence for severe pulmonary disease compared with earlier variants such as delta [28]. Consequently, surgical patients recovering from Omicron-era infections are likely to face a lower PPC risk than those infected with prior strains.

Our secondary outcomes further support these conclusions. No significant differences were observed in individual PPC rates, including pneumonia and respiratory failure rates. Interestingly, trends toward a shorter length of stay and higher 30-day readmission in controls (although not statistically significant) suggest no clinically meaningful excess risk in the prior COVID-19 group. These findings are consistent with recent evidence indicating diminishing perioperative risk with time since infection [25, 26, 29].

The strengths of our study include its prospective design, minimization of recall bias, comprehensive data collection, and inclusion of detailed prior COVID-19 history. Importantly, our results inform local surgical decision-making in a highly vaccinated, Omicron-era population. Nevertheless, its limitations include a modest sample size, which may limit the power to detect small differences or rare events, and a 7-day follow-up window, which may miss later-developing PPCs. While we adjusted for key confounders, residual confounding cannot be excluded. Additionally, generalizability may be limited to similar populations and healthcare settings; findings may not apply to populations with lower vaccine uptake or differing variant exposures. Another limitation is the inclusion of a low number of emergency surgeries and severe COVID-19 infections, leading to an overall low rate of events. Further research should prioritize large, multicenter, longitudinal studies incorporating granular data on variant type, vaccination status, infection severity, and time since infection. Sophisticated analytical methods are needed to address time-varying confounding factors and isolate causal relationships. Importantly, long-term pulmonary function and quality of life in surgical patients with prior COVID-19 merit further study, as do outcomes in specific high-risk subgroups (e.g., patients with severe prior infection or who are undergoing high-risk surgeries).

In summary, our study provides reassuring evidence that in a predominantly Omicron, postvaccine population, prior PCR-confirmed COVID-19 infection does not significantly increase the PPC risk in patients undergoing surgery, particularly when the infection occurs remotely or is clinically mild. These findings support evolving guidelines advocating individualized surgical timing, rather than universal delay, for patients with prior COVID-19 infection.

In this prospective cohort study of 186 Lebanese patients who underwent surgery between December 2021 and December 2022, a history of PCR-confirmed COVID-19 infection was not associated with a statistically significant increase in the incidence of postoperative pulmonary complications within 7 days compared with patients without prior infection. Furthermore, the severity of prior COVID-19 illness or the interval from infection to surgery did not correlate with the observed outcomes. These findings, potentially influenced by the prevalence of SARS-CoV-2 variants and patient characteristics during the study period, suggest that in this specific setting, the risk of short-term postoperative pulmonary complications in patients with prior COVID-19 may not be significantly elevated.