One-lung ventilation (OLV) is an anesthesiological technique that is increasingly being used in thoracic surgery. This requires specific skills and knowledge about airway management, maintenance of gas exchange and prevention of acute lung injury. One lung ventilation (OLV) refers to mechanical separation of the lungs to allow ventilation of only one lung. OLV is a standard approach to facilitate surgical exposure for thoracic surgeries and may be used to isolate a pathology from a healthy lung to prevent soiling or to allow differential ventilation. OLV is used either to improve exposure to the surgical field in thoracic surgery, or to anatomically isolate one lung from a pathologic process of the other lung. During one-lung ventilation (OLV) for thoracic surgery, the management of ventilation is still challenging (1). To reduce the risk of atelectasis, hypoxemia, and mismatch of ventilation to perfusion ratio (V/Q), positive end-expiratory pressure (PEEP) is widely used to minimize the risks and prevent the alveoli from repeated opening and collapse, and thus improve oxygenation (2,3). However, inappropriate PEEP settings may increase pulmonary vascular resistance and shift blood flow to the non-dependent lung, which can lead to oxygenation impairment during OLV. So far, the optimal PEEP level and PEEP titrating strategy during OLV remains to be controversial (1,2), and processes of maintaining adequate gas exchange and minimizing lung injury may be contradictory at sometimes (4). For seeking the optimal PEEP value, we planned to apply different procedures of PEEP titration, to investigate the effects on oxygenation and respiratory mechanics during OLV. The various strategies to overcome hyoxemia during one lung ventilation which were widely proposed are use of PEEP in the dependent lung , CPAP in the non dependent lung , by vasoconstrictors and intermittent IPPV of TLV . In. patients under general anesthesia ,lung recruitment is easy to perform and prevents the alveolar collapse , decreased compliance and hypoxemia . A double-lumen tube (DLT) is an endotracheal tube designed to isolate the lungs anatomically and physiologically. Double-lumen tubes (DLTs) are the most commonly used tubes to provide independent ventilation for each lung. One-lung ventilation (OLV) or lung isolation is the mechanical and functional separation of the 2 lungs to allow selective ventilation of only one lung. The other lung that is not being ventilated passively deflates or is displaced by the surgeon to facilitate surgical exposure for non-cardiac operations in the chest such as thoracic, esophageal, aortic and spine procedures. It can also be used during minimally invasive cardiac surgery and in disease processes affecting one lung to prevent soiling from the contralateral lung. DLTs also allows bronchial toilet without interrupting ventilation(5). We hypothesized that application of Recruitment Maneuver and different decremental level of PEEP in the dependent lung should increase the PO2 during OLV. The main aim of the study was to evaluate the improvement in PaO2 levels during decremental PEEP levels in the dependent lung . Hypoxemia and atelectasis during OLV is widely reduced by giving PEEP , but the optimum PEEP required for improving the oxygenation during OLV is still unclear . Few studies have been done but still unclear . This study aim to investigate the various PEEP strategies on oxygenation during OLV .

After approval team the institutional ethical committee and review board informed consent was taken from each patient undergoing elective lung lobectomy surgeries through thoracotomy in lateral decubitus position . Clinical trials registration no. CTRI/2023/11/059998 . Adult patient above 18 yrs of age undergoing single lobectomy were included with OLV >60 minutes. Patients having hemodynamic instability , pneumonectomy ,FEV1 /FVC ratio <60% ,pleural disease , COPD were excluded . Upon their arrival in the operating room, standard monitoring were attached (electrocardiogram and pulse oximeter), radial/femoral artery was cannulated under local anesthesia (Radial Artery Catheterization Set) for IBP monitoring. I.V. fluids were managed by MAP and CVP(central venous pressure) values. Anesthesia was induced by Inj.Midazolam 0.15mg/kg, Inj.Fentanyl 2mcg/kg IPPV , Inj propofol 2mg/kg , Inj Rocuronium 0.9mg/kg. IPPV given for 3minutes .After induction, the trachea and left bronchus were intubated with a left double lumen tube (DLT) of the appropriate size under direct laryngoscopy. Correct DLT position was confirmed using fiber optic bronchoscopy and checked again after turning the patients in the lateral position by auscultation. Maintenance of anesthesia was by sevoflurane inhalation , atracurium, fentanyl. VENTILATION STRATEGY - Ventilation was set for a tidal volume (Vt) of 6–8 ml/kg Body Wt. respiratory rate (RR) of 12– 14 breath/min, I:E ratio is kept 1:2. Patients were initially ventilated using oxygen in air with an inspiratory oxygen fraction (FiO2) as needed to maintain the SaO2 > 95%. No PEEP was initially added. After the OLV (one lung ventilation) was commenced , the RR was increased and tidal volume was decreased to maintain the minute ventilation and other parameters were kept constant. STUDY PROTOCOL- When OLV was started, after assuring that patients were hemodynamically stable i.e. MAP >80 mmhg and heart rate >60 bpm, the recruitment manoeuver was applied selectively to the ventilated lung. The ventilator was switched to pressure-control ventilation with an inspiratory pressure of 20 cmH2O above PEEP. The maximal recruiting pressure of 40cmH2O (20 PEEP/20 driving pressure) was applied for 5 breaths. After a 3 min equilibration, PEEP was applied in steps of 5,10,15 and 20 cmH2O every five respiratory breaths. PEEP was stepwise reduced starting from 15cmH2O, by 2cmH2O every 2min. During decremental trial of PEEP , the serial ABGs were taken to assess the gas exchange parameters and PaO2 levels. Lung Compliance readings were also noted . The PEEP level corresponding to highest PaO2 during the decremental trial was identified as the “best PEEP”. Subsequently, the lungs were recruited again and the “best” PEEP was applied. The ventilator was then switched to volume-control ventilation maintaining the baseline settings, except that for the “best” PEEP level. This setting was maintained until the end of surgery. Hemodynamic parameters ( BP, HR,SPO2),and gas exchange measurements (by serial ABG) and respiratory mechanics measurements were obtained before surgery, on OLV and after resuming Two lung ventilation(TLV). STATISTICAL ANALYSIS Data was entered in excel sheet. Appropriate statistical test was applied.Continuous data was summarized in the form of Mean and Standard Deviation. Continuous data was expressed in the form of proportions and difference in proportion would be analysed using “chi-square test”. Multivariate analysis was done using logistic regression, for prediction of outcome on the basis of independent factors. The level of significance was kept 95% for all statistical analysis.

TABLE 1 - Demographic Parameters Age (mean±Sd) 42.58±14.98 Height (mean±Sd) 163.02±9.42 Weight (mean±Sd) 60.52±11.01 BMI (mean±Sd) 22.74±3.57 Sex (M/F) 40/10 SIZE OF DLT(Fr) (mean±Sd) 37.27±1.44 Table 2 (One Lung Ventilation duration in minutes) Mean 83.7 Median 72.5 Mode 60 Standard Deviation 40.76 The dataset includes One-Lung Ventilation (OLV) session durations measured in minutes for 50 cases. The average duration is 83.7 minutes, with a median of 72.5 minutes and a mode of 60 minutes. a FIGURE 1- Showing the duration of OLV in minutes TABLE 3- ABG analysis and respiratory variable at different level of PEEP on OLV ON PEEP 15 ON PEEP 13 ON PEEP 11 ON PEEP 9 ON PEEP 7 ON PEEP 5 p value PAO2 287.32±58.54 278.76±52.56 275.56±52.34 274.82±52.51 283.18±47.67 311.30±50.74 0.004 Cdyn 24.04±6.04 23.86±4.54 23.92±4.91 23.80±4.75 23.96±4.86 24.44±5.46 0.992 PaO2/FiO2 ratio 359.15±73.18 348.45±65.71 344.45±65.43 343.52±65.64 353.97±59.59 389.50±63.42 0.004 Ppeak 31.37±1.31 28.17±0.60 26.50±0.64 24.67±0.61 22.69±0.82 20.15±1.19 p<0.001 Pplat 29.59±0.61 27.44±0.61 25.80±0.51 23.48±0.90 21.76±0.86 19.02±1.24 p<0.001 pH 7.41±0.04 7.41±0.04 7.41±0.07 7.41±0.07 7.41±0.04 7.42±0.04 0.530 PaCO2 41.42±3.76 40.52±3.50 41.12±4.21 41.32±3.51 40.50±3.69 40.32±3.59 0.577 HCO3 21.26±2.75 20.24±2.58 20.92±2.61 21.04±2.70 20.88±2.60 21.56±2.60 0.210 TABLE 4 -Hemodynamic parameter at different level of PEEP on OLV ON PEEP 15 ON PEEP 13 ON PEEP 11 ON PEEP 9 ON PEEP 7 ON PEEP 5 p value MAP 86.66±13.96 79.22±16.76 78.10±17.00 84.90±13.11 87.76±13.33 88.50±10.57 0.0002 HR 95.48±17.59 90.32±20.46 87.48±17.80 92.28±10.36 92.84±12.07 92.38±9.77 0.158 SpO2 99.98±0.141 99.96±0.198 99.98±0.141 99.96±0.198 99.98±0.141 100.00±0.00 0.782 FIGURE 2 - The study investigated the relationship between Positive End-Expiratory Pressure (PEEP) settings and Partial Pressure of Arterial Oxygen (PaO2) levels in a cohort of 50 subjects for each PEEP level. The analysis revealed statistically significant differences in PaO2 levels across the varying PEEP settings (F = 3.438, p = 0.004). Specifically, the mean PaO2 levels displayed variability across the different PEEP levels, with PEEP 5 demonstrating the highest mean PaO2 (311.600 mmHg, SD = 50.740) and PEEP 9 showing the lowest mean PaO2 (274.820 mmHg, SD = 52.513). FIGURE 3 – Showing ratio of partial pressure of arterial oxygen to fraction of inspired oxygen i.e.PaO2/FiO2 Ratio. The study investigated the PaO2/FiO2 ratios across different Positive End-Expiratory Pressure (PEEP) levels. Results from 50 samples per PEEP setting showed varying mean PaO2/FiO2 ratios: PEEP 15 (359.150), PEEP 13 (348.450), PEEP 11 (344.450), PEEP 9 (343.525), PEEP 7 (353.975), and PEEP 5 (389.501). Statistical analysis indicated a significant difference between PEEP levels (F value = 3.438, p-value = 0.004). FIGURE 4 – showing Mean Arterial Pressure in mmHg. The study investigated Mean Arterial Pressure (MAP) across various Positive End-Expiratory Pressure (PEEP) levels. Significant variations were observed in MAP means (ranging from 78.100 to 88.500) among different PEEP settings. Maximum Mean arterial pressure is on PEEP 5 i.e. 88.500. Statistical analysis indicated substantial differences (F value = 4.876, p-value = 0.0002), affirming a strong association between PEEP levels and MAP.

One-lung ventilation (OLV) plays a pivotal role in thoracic surgeries, allowing for improved access and efficiency during procedures involving the lung, esophagus, aorta, or mediastinum. For instance, in lung surgeries like lobectomy or pneumonectomy, OLV enables surgeons to isolate and operate on one lung while maintaining ventilation and perfusion of the other. Similarly, in esophageal surgeries, OLV facilitates exposure and dissection of the surgical field, enhancing the surgeon's precision and maneuverability.[6] Lung compliance refers to the ease with which the lungs can expand and contract during breathing. It is influenced by factors such as the elasticity of lung tissue, the presence of surfactant, lung volume, and the compliance of the chest wall. During one-lung ventilation in surgery, lung compliance in the ventilated lung typically decreases due to factors like collapse, atelectasis, and reduced surfactant production. The non-ventilated lung may experience increased compliance due to overinflation or reduced resistance. These changes can affect gas exchange and may require adjustments in ventilation parameters to maintain adequate oxygenation and ventilation. Patients undergoing thoracic surgery also represent a unique population with physiologic and clinical circumstances that complicate the application of conventional lung-protective ventilation techniques.[7, 8]A proposed multi-hit model considers the unique challenges of OLV: (1) these patients often have baseline lung disease; (2) the deleterious effects of mechanical ventilation are exerted on a single lung tasked with the patient’s entire respiratory load; (3) surgical manipulation of the nondependent lung may result in direct injury; (4) obligate collapse and re-expansion of the nondependent lung represents widespread atelectotrauma and is related to systemic inflammatory cascades.[9-12] Due to the positioning for most thoracic surgery (i.e., lateral decubitus position), chest wall compliance is reduced and the ventilated lung is vulnerable to atelectotrauma as it experiences the weight of the mediastinum and abdomen.[10,12] Anesthesiologists have refined the use of double-lumen tubes (DLTs) to achieve effective OLV in these procedures. By employing DLTs, anesthesiologists can selectively ventilate one lung while simultaneously providing oxygenated blood flow to both lungs. A double-lumen endotracheal tube (DLT) is a specialized breathing tube used in anesthesia for one-lung ventilation during thoracic surgeries. It has two separate lumens—one for delivering oxygen to the lung being ventilated and the other for allowing the deflation of the lung not being ventilated. The primary role of a double-lumen tube in one-lung ventilation is to isolate and selectively ventilate one lung while collapsing the other. This enables better surgical exposure and access to the thoracic cavity while minimizing the risk of contamination from the non-operative lung. Additionally, it helps maintain adequate oxygenation and ventilation throughout the procedure by optimizing lung mechanics in the surgical field. However, challenges persist, particularly regarding oxygenation. [6] Research shows that hypoxemia, characterized by a drop in arterial hemoglobin oxygen saturation (SaO2) below 90%, occurs in 4-10% of cases during OLV, especially when the ventilated lung is exposed to high fractions of inspired oxygen (FIO2). This hypoxemia can jeopardize patient safety and surgical outcomes, underscoring the importance of proactive measures to predict, prevent, and promptly address oxygenation issues during OLV. [13-16] In this study to avoid hypoxia we use fio2 of 0.8. Recent retrospective studies have demonstrated a significant association between high ventilating pressures, high tidal volumes, and lung injury. [17,18,19] Some studies reported increased inflammatory proteins when high pressures and volumes were used. [20,21] Notably, one study found that even lungs that were not collapsed during the study period sustained inflammatory injury similar to or worse than collapsed lungs. [22] In another study, patients who received lower tidal volumes (6 ml/kg) had better postoperative outcomes, including Improved gas exchange, fewer postoperative complications, reduced atelectasis and acute lung injury (ALI) episodes.[23] The causes of perioperative acute lung injury (ALI) are multifactorial, but hyperinflation, repetitive inflation/deflation cycles, and excessive tidal volumes are thought to contribute to injury in susceptible patients. [24] So in this study we used low tidal volume for one lung ventilation. Lung compliance refers to the ability of the lungs to stretch and expand. In one-lung ventilation (OLV), where only one lung is ventilated while the other is collapsed or partially deflated, lung compliance becomes crucial as it affects gas exchange and ventilation efficiency. Factors affecting lung compliance include the elasticity of lung tissue, surface tension within the alveoli, and the flexibility of the chest wall. Positive end-expiratory pressure (PEEP) in OLV can help maintain lung compliance by preventing collapse and improving alveolar recruitment in the ventilated lung. [21,25,26,27] PEEP counteracts the decrease in compliance often seen in OLV by keeping the alveoli open and reducing atelectasis.[28] Low levels of PEEP (5 cm H2O) applied during thoracic surgery in healthy patients is hemodynamically well tolerated, but it does not improve oxygenation in all cases. [29] The level of PEEP needs to be adjusted according to the individual and their respiratory mechanics. In patients who have severe obstructive lung disease, the application of excessive PEEP may develop dynamic hyperinflation, and the air-trapping created needs to be considered as a potential cause of intraoperative hypotension. The ideal PEEP value should be low enough to prevent hemodynamic impairment and overdistension of the lung, but high enough to induce alveolar recruitment, keeping the lung more aerated at end expiration. [30] Michelet et al. conducted a study showing that moderate levels of positive end-expiratory pressure (PEEP), specifically 5 and 10 cmH2O, improved oxygenation similarly during one-lung ventilation (OLV). However, they observed that increasing PEEP to 15 cmH2O worsened oxygenation due to potential over-distension, leading to increased shunt by diverting pulmonary blood flow to non-aerated areas.[27] Additionally, the physiological and clinical effects of PEEP can vary when used alone versus in combination with alveolar recruitment maneuvers. While PEEP effectively prevents atelectasis, its optimal level may differ between patients. However, alveolar recruitment maneuvers are not routinely performed during OLV and are typically reserved for cases of hypoxemia.[26] Despite these findings, previous studies have yet to determine whether a standardized PEEP level or an individualized approach after an alveolar recruitment maneuver is superior during OLV.[12,26,27] Further research is needed to elucidate the optimal PEEP strategy for improving oxygenation and patient outcomes in thoracic surgeries. With this background to evaluate the relationship between PEEP and PaO2/FiO2 ratio in One Lung Ventilation in patients undergoing thoracic surgeries we assessed the improvement of arterial oxygenation (PaO2) by application of Different PEEP (Positive End Expiratory Pressure) in One Lung Ventilation by serial ABG (Arterial blood Gas) Analysis. Patient Characteristics: In the present study, the mean age of patients was 42.58±14.97 standard deviation in years with mean BMI of 22.736 ±3.569. Among these 50 patients 80% patients were male and 10% (5 cases) exhibit Diabetes Mellitus, while 90% (45 cases) do not show signs of this condition, for successful DLT insertion the majority (84.00%) attempted the task only once, while 12.00% attempted it twice, and 4.00% attempted it three times and average OLV duration was 83.7 ± 40.76 min. Partial Pressure of Arterial Oxygen (PaO2) We investigated the relationship between Positive End-Expiratory Pressure (PEEP) settings and Partial Pressure of Arterial Oxygen (PaO2) levels in 50 patients for each PEEP level. The analysis revealed statistically significant differences in PaO2 levels across the varying PEEP settings (F = 3.438, p = 0.004). Specifically, the mean PaO2 levels displayed variability across the different PEEP levels, with PEEP 5 demonstrating the highest mean PaO2 (311.600 mmHg, SD = 50.740) and PEEP 9 showing the lowest mean PaO2 (274.820 mmHg, SD = 52.513). In our study we found that lower PEEP levels (range 5–7 cmH2O) were able to improve oxygenation and lung mechanics. This optimum PEEP is applied to the ventilator throughout the surgery during one lung ventilation. Arterial oxygenation deteriorates during ventilation of one lung (OLV). It has been estimated that shunt values during this procedure can range from 20% to 40%, and it was postulated that intrapulmonary shunt originates from zones of total alveolar collapse and from zones of relative hypoventilation in both the dependent and the nondependent lung. Our study showed that the arterial oxygen tension (pao2) is improved after Alveolar recruitment maneuver followed by decremental PEEP trial during one lung ventilation maintaining the stable hemodynamic parameters. Our results are supported by Michelet et al. [26,27] and Ren Y.et al [31] They found that 5 and 10 cm H2O of PEEP improved oxygenation to the same degree, but 15cmH2O worsened oxygenation because over distension can increase shunt by diverting pulmonary blood flow to non-aerated areas. PaO2 / FiO2 ratio: An FIO2 of 1 is generally not recommended during OLV. A high FIO2 may, however, cause absorption atelectasis and potentially further increase the amount of shunt because of the collapsed alveoli. The use of an FIO2 less than 1 during OLV has the potential benefits of decreasing the risk of absorption atelectasis and, if N2O is used, may allow potent inhaled anesthetics to be used in lower concentrations. Some clinicians use an O2 80% and /N2O 20% mixture as long that the SpO2 is maintained in a safe range. In our study we used fio2 of 0.8. The study investigated the PaO2/FiO2 ratios across different Positive End-Expiratory Pressure (PEEP) levels. Results from 50 samples per PEEP setting showed varying mean PaO2/FiO2 ratios: PEEP 15 (359.150), PEEP 13 (348.450), PEEP 11 (344.450), PEEP 9 (343.525), PEEP 7 (353.975), and PEEP 5 (389.501). Statistical analysis indicated a significant difference between PEEP levels (F value = 3.438, p value = 0.004). In our study PaO2/FiO2 ratios was highest at PEEP level of 5 which was lowest in other PEEP levels. Results of our study is supported by Michelet et al. [26,27] in their study with fio2 0.4, PaO2/fio2 was highest (approx..250) at PEEP level 5 and 10 and Ren Y. [31] also showed that the beneficial effect of PEEP (5 and 10 cmH2 O) seemed similar on improving oxygenation, which is in accordance with our study. Peak airway pressure (P peak) and Plateau pressure (P plat): During one-lung ventilation (OLV), positive end-expiratory pressure (PEEP) influences both peak airway pressure (P peak) and plateau pressure (P plat). PEEP is applied at the end of expiration to maintain alveolar recruitment and prevent atelectasis in the ventilated lung. Its effect on P peak and P plat depends on various factors, including the level of PEEP applied and the compliance of the respiratory system. When PEEP is introduced during OLV, it helps maintain functional residual capacity (FRC) in the ventilated lung, thereby reducing airway resistance and improving lung compliance. As a result, P peak, which reflects the maximum pressure during inspiration, may decrease due to improved lung mechanics and reduced airway resistance. Similarly, P plat, which represents the pressure in the respiratory system when airflow ceases during an inspiratory pause, may also decrease with the application of PEEP during OLV. This reduction in P plat indicates improved alveolar recruitment and lung compliance, leading to more homogeneous ventilation distribution and lower overall lung pressures. However, excessive PEEP levels can lead to over-distension of the ventilated lung, potentially increasing both P peak and P plat. Over-distension can occur when PEEP exceeds the optimal level for maintaining alveolar recruitment, causing increased intrathoracic pressure and compromising lung mechanics. In our study Peak airway pressure was lowest with Peep 5 that was 20.15±1.19. The difference of Peak airway pressure at different PEEP was significant (p< 0.001). Plateau pressure was lowest with Peep 5 that was 19.02±1.24. The difference of plateau pressure at different PEEP was significant (p< 0.001). In previous study, Ren Y. et al also found that 10 cm H2O PEEP increased airway pressure (Ppeak and Pplat).[31] This might be partly explained by the fact that the PEEP was increased without changing the tidal volumes during OLV. Thus, strictly speaking, these results of Ren Y. et al support the idea that when the tidal volume is set as 8 ml/kg during OLV in patients with healthy lungs, 5 cmH2 O PEEP is enough to recruit the alveolar area of the dependent lung and there might be no need to apply a larger PEEP (such as 10 cmH2 O). The higher airway pressures might also increase the risk of ventilator-induced lung injury.[31] In another study Slinger et al found that oxygenation improvements would occur when the application of PEEP caused the plateau end-expiratory pressure to move toward the lower inflection point of the compliance curve.[32] Results of our study were also supported by Michelet et al.[26,27] and Christoph Boesing et al.[33] In their Study peak airway pressure and plateau pressure was lowest with PEEP 5 cmH2O. Dynamic compliance : The dynamic compliance was maximum with PEEP 5cmH2O in our study. Dian Xu[52] showed an improvement in dynamic compliance after applying PEEP and recruitment maneuver. Hemodynamics: Elevated intrathoracic pressures (due to higher PEEP) can diminish venous return and thus cause decreases in blood pressure, hemodynamic and ventilatory variables were monitored closely while performing the opening maneuver. If mean arterial pressure decreased by more than 15% from its initial value, the Alveolar recruitment strategy(ARS) was discontinued and 500 mL of crystalloids was administered. In our study significant variations were observed in MAP means (ranging from 78.100 to 88.500) among different PEEP settings. Statistical analysis indicated substantial differences (F value = 4.876, p-value = 0.0002), affirming a strong association between PEEP levels and MAP. Association between PEEP levels and MAP were also showed by Christoph Boesing et al. In their study Mean arterial pressure were significantly decreased as PEEP level increased.[33] But however it is not associated in another study by Michelet et al[26,27] . In our study the mean arterial pressure were decreased with increase in PEEP level. For heart rate some differences were observed at different PEEP settings, statistical analysis suggested these differences might not be statistically significant (F value = 1.609, p-value = 0.158). There were No significant relationship between PEEP levels and SPO2 changes was evident, indicating a stable and uniformly high SPO2 across all tested PEEP settings. Results of our study supported by Michelet et al.[26,27] and Christoph Boesing et al.[33] In their study there were no significant relationship between PEEP levels and SpO2 changes at different PEEP level.

This study investigated the effects of different Positive End-Expiratory Pressure (PEEP) levels on arterial oxygenation and lung mechanics during one-lung ventilation (OLV) in patients undergoing thoracic surgery. The results showed that lower PEEP levels (5-7 cmH2O) improved oxygenation and lung mechanics, while higher PEEP levels (9-15 cmH2O) worsened oxygenation due to overdistension. The optimal PEEP level was found to be 5 cmH2O, which improved arterial oxygen tension (PaO2) and PaO2/FiO2 ratios without compromising hemodynamic stability. Peak airway pressure and plateau pressure were also lowest at PEEP 5cmH2O, indicating improved lung compliance and reduced risk of ventilator-induced lung injury. The study's findings support the use of individualized PEEP titration to optimize oxygenation and lung mechanics during OLV, and highlight the importance of careful PEEP selection to avoid overdistension and hemodynamic impairment. In patients undergoing Thoracic surgeries, the alveolar recruitment strategy proved successful in augmenting arterial oxygenation during OLV. The PEEP at which the PaO2 is maximum in ABG is 5-7cmH2O in our study. ACKNOWLEDGMENT The authors extend their gratitude to the surgery and nursing teams of the Cardiothoracic and Vascular Surgery Department at S.M.S. Medical college , Jaipur. CONFLICT OF INTEREST The authors declare that there are no conflicts of interest among them. FUNDING This research did not receive any specific from public, commercial, or non -profit organisations.

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