Introduction

Postoperative pulmonary complications (PPCs) after major surgery and general anaesthesia are an important cause of morbidity and mortality in the perioperative setting [1]. To minimize such adverse events, it is crucial to identify predisposing conditions [2] and assess the underlying pathophysiology to provide a lung protective ventilation strategy [3, 4]. Ventilatory monitoring in the operating room is routinely based on the analysis of pressure, volume, and flow data provided by the ventilator [3, 5,6,7,8].

However, perioperative medicine has advanced, allowing for a broader array of surgeries on patients with serious health issues, such as extreme obesity or critical injuries. These include complex procedures like extended robotic surgeries in extreme positions or prolonged one-lung ventilation. Additionally, technological advancements provide new tools to monitor patients' physiological responses in real-time.

Currently, we can perioperatively employ devices such as electrical impedance tomography (EIT) that analyses lung regional ventilation [9], oesophageal pressure (Pes) monitoring which reflects approximately the pleural pressure, allowing transpulmonary pressure (Ptp) estimation [10], and lung and diaphragmatic ultrasound (US) that enable us to assess the echogenicity of the different lung fields to quantify aeration [11] or to assess diaphragmatic functionality [12]. This raises the question of whether and when these advanced respiratory monitoring tools should be used to prevent PPCs.

This review aims to summarize the technical underlying principles and explore the existing evidence on the usefulness of such advanced respiratory monitoring in the perioperative setting, specifically to ascertain which patients might benefit from it. We carried out a search in the Pubmed and Embase databases with the following criteria: (“respiratory monitoring" OR "ventilator monitoring" OR "lung function monitoring”) AND (intraoperative OR perioperative OR anesthesia OR surgery)”. We searched papers from 2009 to 2024 in the English language.

Monitoring of Ventilatory Mechanics Through Common Ventilatory Parameters Analysis

Conventional data such as pressure and flow curves or capnography can be leveraged to gain further insight into respiratory mechanics [13], helping us to assess the recruitment capacity and adequacy of patient ventilation [13, 14]. For instance, lung hysteresis, a physiological feature resulting from the visco-elastic properties of lung parenchyma, causes the pressure–volume relationship to differ between inflation and deflation [15, 16]. It can be quantified by the area enclosed within the quasi-static Pressure–Volume (PV) loops generated during mechanical ventilation [13]. These PV loops reveal a critical point where a sharp increase in ventilator pressure corresponds with a slower rise in lung volume, signaling the end of lung recruitment which could include some overdistension, whereas a pressure drop paired with a slower volume decrease indicates the onset of alveolar collapse [13, 15, 16]. Understanding these patterns helps to assess lung recruitability, and identify risks linked to mechanical ventilation [13].

The dynamic pressure–time curve can also be used to assess respiratory mechanics. For instance, the stress index (SI) [17], that assesses the dynamic pressure–time curve during constant inspiratory flow to detect intratidal recruitment or hyperinflation. A threshold SI value of greater than 1.05 has shown a sensitivity of 0.88 and a specificity of 0.50 to indicate injurious ventilation, which was contrasted with aeration indices based on computed tomography in ARDS patients. The SI obtained from the ventilator indicates the SI of the respiratory system and correlates with the lung SI with reasonable accuracy [18, 19].

Furthermore, volumetric capnography (VCap) performs a continuous assessment of the respiratory dead space [20] using the modified Bohr equation, which includes the tidal volume (VT), the partial pressure of CO2 at the end of alveolar respiration and the partial pressure of CO2 at the end of expiration (EtCO2) [21]. VCap divides the capnogram into three phases: Phase I, representing the CO2-free exhaled gas from the airways; Phase II, where a mix of airway and alveolar gases is present; and Phase III, which represents the alveolar plateau where gas exchange occurs. By separating the volume of gas in the airways from that within the alveolar compartment, it allows for precise calculations of dead space on a breath-by-breath basis. The slope of Phase III (SIII) is particularly informative as it reflects the ventilation-perfusion distribution in the alveoli. An increased slope indicates heterogeneity in alveolar ventilation. VCap is a current tool for clinical research works, proving to be an adequate guide in the assessment of end-expiratory lung volume (EELV) changes induced by surgical procedures and has proven to be useful in individualizing the level of PEEP during laparoscopic surgery [21, 22].

Nitrogen and helium techniques, particularly the washin/washout method, are commonly used to measure (EELV) [23]. This method calculates EELV based on the baseline nitrogen content in the lungs, which inversely correlates with alveolar oxygen levels [23, 24]. This approach has been extensively applied in studies on intraoperative mechanical ventilation and lung strain, revealing a high prevalence of expiratory flow limitation and airway closure in obese patients during laparoscopic surgery [25, 26].

Additional ventilatory parameters are used to evaluate lung characteristics non-invasively. For instance, the PEEP test identifies expiratory flow limitation and the air-test and the recruitment-to-inflation ratio assess alveolar recruitability. The PEEP-test consists in abruptly dropping from 3 cmH2O to 0 cmH2O and observing if there is outflow of gases, if not, there is expiratory flow limitation [27, 28]. The air test in healthy lungs checks if gas exchange at an FiO2 of 21–25% maintains a SatO2 above 96%; failure to do so suggests significant atelectasis with a shunt exceeding 10% [29]. The recruitment-to-inflation ratio involves a single breath test where PEEP is abruptly reduced from 15 to 5 cmH2O to measure expired volume and compare it against predicted compliance at low PEEP. This comparison estimates the volume of alveoli recruited by the PEEP, from which the compliance of the recruited lung is calculated. This ratio mathematically reflects the proportion of volume distributed into the recruited lung relative to the already aerated 'baby lung'. A higher R/I ratio indicates a greater potential for lung recruitment. Conversely, values below 0.5 suggest a lower probability of recruitment, which may warrant a lower PEEP setting [30].

Finally, some hemodynamic management strategies, such as the PEEP-test and tidal volume challenge (TVC), have been developed by manipulating ventilatory parameters. These tests assess fluid responsiveness by increasing intrathoracic pressure through enhanced PEEP or VT, utilizing heart–lung interactions to gauge hemodynamic effects [31, 32].

Advanced Respiratory Monitoring Tools Pros and Cons

Electrical Impedance Tomography

EIT is a non-invasive technique for monitoring lung ventilation as well as ventilation-perfusion mismatches. Electrodes are placed on the chest and record the surface voltage after repeated application of a small amount of electrical current. It provides images based on the chest tissues’ electrical conductivity [33]. The changes in electrical impedance are displayed as colour-coded images, providing a pixelated mapping of regional lung ventilation, thus adding information about the homogeneity of lung ventilation on a breath by breath [34]. EIT assesses hypoventilation, overdistension and areas of heterogeneous ventilation, allowing the clinician to estimate lung recruitability [35]. This technique has been used intraoperatively to individualize ventilator settings such as PEEP and VT [36,37,38,39], and in the postoperatively to assess the distribution of ventilation and to identify atelectatic regions [40, 41]. A recent meta-analysis of randomized-controlled trials (RCTs) [42] compared the effect of using EIT or Pes to guide individualized PEEP compared to standard monitoring, so it showed an improvement in intraoperative oxygenation. However, EIT is mostly used for research purposes and there are certain limitations to its routine roll both perioperatively and in critically ill patients [9, 37, 43]. For instance, its resolution is lower than that of other imaging techniques, such as computed tomography [37]. Moreover, incorrect placement of the electrodes can modify the image, affecting its intrapatient reproducibility [44]. Also, it should not be used in patients with pacemakers or automatic defibrillators due to possible interference with such devices [37].

Oesophageal Manometry

During mechanical ventilation, the peak pressure (Ppeak) is the force applied to overcome the airways resistance and inflate the lungs [45]. By setting a brief pause during inspiration, ventilators measure the plateau pressure (Pplat), which helps differentiate the lung’s elasticity from the airway resistance. Thus, Pplat indicates the elasticity of the lung, and the difference with Ppeak is due to airway resistance. The driving pressure (ΔP) that pushes each breath’s VT is the difference between Pplat and the set positive end-expiratory pressure (PEEP) or the intrinsic PEEP if it does exist [45]. The ratio of VT to ΔP indicates the lung’s compliance (C), or its ability to expand, which is the opposite of elastance [45]. Furthermore, lung strain is defined as the lung tissue stretch during each breath and is calculated by comparing the VT per ideal body weight to the end-expiratory lung volume (EELV), largely determined by PEEP [46].

The respiratory system consists of two main parts: the lung component, where elastic fibers help in breathing out, and the chest wall component, which expands during inhalation due to muscular action, creating a negative pressure during spontaneous breathing that stretches the lungs [47]. In anaesthetized patients, the chest wall does not expand, leading to a generally positive pleural pressure (Ppl), and an increased chest wall elastance (Ecw) [48, 49]. Ppl is the external force on the lungs that can cause them to collapse, and by measuring it, we can differentiate between the lung and chest wall components of the respiratory system [47, 48, 50, 51]. This distinction allows us to calculate the Ptp, the real pressure that distends the alveoli [50, 52,53,54]. Changes in Ptp on each ventilation generate lung stress [46, 55]. Negative end-expiratory Ptp can lead to lung collapse [56], while excessively high end-inspiratory Ptp increases the risk of ventilator-induced lung injury (VILI) [53]. It is usually recommended to keep Ptp below 15 cmH2O in healthy lungs and up to 12 cmH2O in pathological lungs [10].

Measurement of end-expiratory Pes as a surrogate for end-expiratory Ppl is useful in determining the level of PEEP required to achieve positive end-expiratory Ptp. When Ptp falls below atmospheric pressure at the end of expiration, the lung units may collapse [10, 46]. End-inspiratory Ptp measurement can discern whether an apparently high Pplat is safe [46].

Pes monitoring faces specific challenges that limit its routine implementation in clinical practice [57]. The primary challenge is that it requires a significant amount of technical skill and knowledge for accurate interpretation [43, 53]. Furthermore, it does not provide information on regional stress or strain but global stress and does not allow for an adequate source of data in heterogeneous lungs [58]. The oesophageal balloon is positioned at a specific point in the mid-lower third of the intrathoracic esophagus, and measurements taken may not correspond to the real Ppl at distant points in both dependent and non-dependent lung regions [59]. The relevance of using a calibrated oesophageal balloon method has recently been published [60], thus Pes gets a more accurate estimation of absolute values and respiratory changes in Ppl. Indeed, the traditional uncalibrated approach can be unreliable in this setting, since artifacts related to the oesophageal wall or the balloon can misguide mechanical ventilation [60]. Pes monitoring may be also misinterpreted and misguide a ventilatory strategy if spontaneous inspiratory stimulus is present [43].

In conclusion, Pes measurement can be useful in conditions characterized by an increase in chest wall elastance that compromise ventilatory mechanics [43] such as obesity or elevated intraabdominal pressure (IAP), including scenarios like pneumoperitoneum with the Trendelemburg position.

Lung Ultrasound

Lung ultrasound (LUS) is a non-invasive, radiation-free method used to evaluate lung mechanics that enables bedside assessment of pulmonary recruitment [61, 62]. It is based on the varying balances of gas and fluid within the lung parenchyma. Accordingly, three patterns are identified: Pattern A indicates predominant aeration, Pattern B suggests the presence of fluid, and Pattern C occurs when the lung parenchyma is dense, indicating consolidation or collapse [62, 63]. In healthy lungs subjected to mechanical ventilation, this technique aims to differentiate between the amount of aeration and alveolar collapse after analysing all the lung fields, thus assessing recruitability [64] and guiding pulmonary recruitment [61]. LUS not only analyses the lung parenchyma but also assesses with high diagnostic accuracy the presence of other pleural contents, i.e., pleural effusion, or the absence of inter-pleural motion, i.e., pneumothorax, apnoea, selective intubation [63, 65]. The practice of LUS for the diagnosis of pneumothorax has become the method of choice among physicians who can perform bedside LUS [66].

LUS can help to identify lung atelectasis [11] whereas predicting lung overdistension is currently the focus of research [61, 67]. Several recent studies in intraoperative and critical care settings use LUS to guide mechanical ventilation, identifying the best PEEP level, showing better oxygenation, ventilatory mechanics, and less PPCs [68,69,70,71,72]. LUS main drawback is its operator dependency [73].

Enhanced vigilance and tailored care are imperative for patients transferred from the emergency department to the operating room. The use of US in this context is quite widespread, even for the detection of a full stomach [74, 75]. In the initial management of a polytrauma patient, US assessment protocols are successful identifying major alterations, not only respiratory but also abdominal effusion or cardiac disorders [65, 76]. However, some of these alterations may go unnoticed in the initial assessment, or may be minimal at that time. It should be noted that in the event of a major change in the ventilatory mechanics of a trauma patient, US can detect pneumothoraxes that have been exacerbated by prolonged mechanical ventilation and surgeries. In addition, they can also detect pleural effusions, haemothoraces and consolidations [63].

Diaphragm Ultrasound

Ultrasound evaluation of the diaphragm is a non-invasive tool that allows us to assess the functionality of this muscle at the bedside [77, 78]. Within the perioperative setting of major surgeries a decreased inspiratory diaphragmatic dome excursion has been validated as an index of diaphragmatic dysfunction, as it is related to increased PPCs. In critically ill patients, diaphragmatic ultrasound (DUS) plays an established role in the assessment of diaphragmatic function and movement in weaning from mechanical ventilation and to guide rehabilitation in critically ill patients.

Within locoregional anaesthesia, brachial and cervical plexus blocks are standard procedures and the phrenic nerve may be blocked during these techniques. The clinical impact of blocking this nerve depends significantly on patient-specific, for example, existing phrenic nerve paralysis on the opposite side or obesity [79, 80]. During the procedure ipsilateral phrenic nerve palsy may go unnoticed. However, either in the hospital [81] or at home due to early discharge, these patients may develop severe PPCs due to unilateral diaphragmatic paralysis. DUS can help us for an early detection of the absence of diaphragmatic contraction [82]. DUS has been used to classify hemidiaphragmatic paresis into 3 grades (none, partial and complete) following cervical plexus blocks [83]. Thickness index of the diaphragm muscle (inspiratory thickness/expiratory thickness) obtained by US can be used in clinical practice to assess diaphragmatic paresis. This index has a 90% correlation with a reduction in FVC or FEV1 equal to or greater than 20% in spirometry [84].

Table 1 shows recent clinical studies that have used advanced respiratory monitoring in the perioperative setting.

Table 1 Recent clinical studies using advanced respiratory monitoring perioperatively
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Clinical Settings

Laparoscopic and Robotic Surgery

Laparoscopic and robotic approaches are now standard procedures in hospitals for many surgical interventions [85, 86]. During laparoscopy carbon dioxide (CO2) insufflation creates an artificial space known as a pneumoperitoneum [87,88,89]. This procedure increases IAP, which in turn raises Ppl and can cause lung collapse [90, 91]. This reduces the respiratory system compliance (CRS), hampering positive pressure ventilation. Alveolar overdistension, atelectrauma and atelectasis can coexist in laparoscopic surgeries generating heterogeneity in regional ventilation distribution (Fig. 1) [90,91,92]. Moreover, steep Trendelenburg i.e. head-down, and anti-Trendelenburg, i.e., head-up, positions, are commonly used in laparoscopic and robotic surgeries to enhance surgeon visibility and access to the abdominal or pelvic areas [93, 94]. While the anti-Trendelenburg position aids in shifting the diaphragm downward to improve breathing mechanics, the Trendelenburg position compounds on respiratory challenge posed by the pneumoperitoenum, particularly in patients with pre-existing conditions like obesity or chest wall stiffness [93]. Several studies have demonstrated the detrimental effect of the combination of Trendelemburg and pneumoperitoneum on ventilatory mechanics [95, 96].

Fig. 1
figure 1

This figure presents a schematic diagram of cross-sectional views of lung fields from the same patient, illustrating the heterogeneity in regional ventilation distribution that can occur during laparoscopic surgeries. This heterogeneity is exacerbated under Trendelenburg positioning or obesity. The color coding represents alveolar ventilation, with lighter shades indicating less ventilation and darker shades indicating more ventilation. A: Cross-section of basal segments, where the alveoli are collapsed during both inspiration and expiration, indicating atelectasis. B: Cross-section of mid-lung segments. In addition to atelectasis, this section also shows, as highlighted in the enlargement, overdistended alveoli during inspiration and airway collapse during expiration, which prevents proper emptying. This condition can be explained by expiratory flow limitation mechanism. C: Cross-section of apical segments. The enlargement illustrates a phenomenon where alveoli are ventilated during inspiration but collapse during expiration. This is known as tidal recruitment

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A multicentre observational study analysed the incidence of PPCs after abdominal robotic surgery, finding an overall incidence of 19%. They used the Assess Respiratory Risk in Surgical Patients in Catalonia (ARISCAT) score and found that patients at high risk according to this score had 22.4% of PPCs compared to 12.7% of patients with a low score [97]. Indeed, when IAP is high or accompanied by additional factors such as comorbidities, positioning, or surgical manipulation, the incidence of PPCs increases [98, 99]. For the same positive inspiratory pressure, as Ppl increases, Ptp decreases and becomes negative, so mechanically caused atelectasis becomes more abundant [99,100,101]. We are unable to accurately estimate Ptp in these patients using ventilator data and airway pressure measurements alone [56, 102]. Therefore, individualization of the protective lung ventilation strategy is one of the most studied areas in this field, and advanced respiratory monitoring is common in these research studies [66,67,68, 78, 103].

Pes monitoring is a key tool for measuring Ppl and Ptp, which is crucial for tailoring lung protective ventilation strategies during laparoscopic or robotic surgeries [56, 102]. Its utility arises because the increased intra-abdominal pressures from pneumoperitoneum do not uniformly affect Ppl [104, 105]. This monitoring allows for continuous customization of alveolar distension pressures and PEEP, helping prevent atelectasis and shunt phenomena [102, 106, 107]. While Pes monitoring has been effectively used in various clinical studies to determine the optimal PEEP for preventing alveolar collapse, evidence showing improvements in patient-centered outcomes like postoperative pulmonary complications (PPCs) is still lacking. Nevertheless, several studies have documented benefits such as better intraoperative oxygenation [108] and improved ventilatory mechanics with reduced transpulmonary driving pressures [102, 109,110,111].

EIT can theoretically avoid two frequent issues during mechanical ventilation in the presence of pneumoperitoneum: atelectrauma and regional overdistension [90, 91, 112]. It has mainly been used to calculate the best PEEP. A recent RCT has shown that EIT-guided PEEP in laparoscopic surgery improves PPCs, ventilatory mechanics, and intraoperative oxygenation compared to standard PEEP [103]. However, in 2016 another RCT had non-statistically significant results in terms of intraoperative oxygenation and reduction of CPP. In the latter case, they compared EIT-guided PEEP with ideal compliance-guided PEEP [113]. Several articles have demonstrated the value of EIT in improving ventilatory mechanics and intraoperative oxygenation during robotic [114, 115] and laparoscopic procedures [103]. Both EIT and Pes have been shown to be superior to non-advanced monitoring in oxygenation measured by PaO2/FiO2 in the intraoperative setting [42].

Given the high incidence of alveolar collapse in these patients and the widespread availability of LUS, there is a growing focus on using this tool to customize intraoperative ventilation during laparoscopic procedures [68, 69]. The randomised clinical trials performed so far demonstrate improved PPCs and clinical outcomes with the use of LUS to guide mechanical ventilation and PEEP compared to conventional management in the laparoscopic approach [68,69,70, 116]. Only one randomized clinical trial showed improvement in ventilatory mechanics and oxygenation without a reduction in PPCs [117]. A recent systematic review with meta-analysis on the use of LUS to guide intraoperative mechanical ventilation in non-cardiac surgery [71] found beneficial effects on intra- and postoperative atelectasis when using LUS versus conventional management. They selected a total of 9 randomised clinical trials including paediatric and adult patients, in open and laparoscopic surgery.

To date, the main focus of research using these advanced monitoring tools in laparoscopy has been on atelectasis, regional ventilation, recruitment and PEEP. There are no clinical studies, to our knowledge, using these tools to assess other challenges of mechanical ventilation in laparoscopy such as its relevance on expiratory flow limitation or mechanical power (MP). The mechanical power concept emerges from the analysis of the modifiable variables of positive pressure ventilation to estimate how much energy the ventilator delivers to the respiratory system per minute [118]. Then, MP analyses the elastic-static forces, i.e. PEEP, the elastic-dynamic forces, i.e. ΔP and VT, and the resistive forces, i.e. the airway flow and resistance or RR [119]. MP acts on lung parenchyma, deforming the epithelial and endothelial cells anchored to it [120]. High MP is associated with a higher rate of PPCs [121, 122]. MP has been shown to be higher in one-lung ventilation (OLV) during thoracic surgery [123], during pneumoperitoneum, in the trendelemburg position and in obese patients [109]. To the best of our knowledge, only one study has been published in a perioperative setting analysing the impact on mechanical power of a ventilatory strategy based on advanced respiratory monitoring [124]. In this study, Crs-guided PEEP achieved lower values of MP than transpulmonary ΔP-guided PEEP. In critically ill patients, it has been studied whether EIT-guided mechanical ventilation can reduce MP [125]. More research is needed on this very recent outcome related to PPCs.

Thoracic Surgery

The key challenge during thoracic surgery reside in oxygenating and ventilating the dependent lung without causing harm [7]. By a double-lumen endotracheal tube (DLT) or Bronchial Blockers (BB) we isolate and collapse the operated lung. By ventilating the dependent lung with a DLT or BB through a relatively thin and long lumen, we can generate autoPEEP, which may be harmful [126]. Furthermore, setting VT and PEEP OLV is complex. High VT increases VILI risk, whereas low VT promote the development of atelectasis. Additionally, while increasing PEEP can help prevent collapse, it may also cause regional overdistension and increase alveolar dead space [127]. Current evidence suggests that protective ventilation strategy combining low VT and increased PEEP, i.e., 10 cmH2O or individualized PEEP, improves ventilatory mechanics and PaO2 without impairing neither ventilation/perfusion ratio nor hemodynamics [39, 128]. EIT has proven to be useful in several tasks in these procedures. Essentially, EIT has allowed titration of VT during one lung ventilation (OLV), based on ventilation distribution and oxygenation [38], and it has also been used to individualize PEEP to achieve better ventilatory mechanics and intraoperative oxygenation [38, 129]. Indeed it is also useful in detecting correct OLV for double-lumen tube by detecting pulmonary regional ventilation [130].

Furthermore, a matter of concern in thoracic surgery, as well as in any surgical procedure that might impact the phrenic nerve, is maintaining proper diaphragmatic function. DUS has been shown to be useful in assessing hemidiaphragmatic paralysis after thoracic surgery, which is associated with PPCs [12].

Obese Patients

This is a common comorbidity that hinders mechanical ventilation [131]. In particular, one of the challenges is to find out what is the real pressure generated by excess weight on Ppl in our patients [132]. It can be challenging to maintain lung protection parameters without accurately estimating the Ptp we are generating. In obesity, as in other restrictive pathologies such as scoliosis, chest wall compliance is lower than lung compliance, which means that airway pressures are easily transferred to other intrathoracic structures (e.g. large vessels and pericardium) [133,134,135]. Of course, these patients need positive pressure values capable of counteracting this increase in pleural pressure, and the sum of all these factors makes the proper management of these patients so complex [136, 137].

Pes monitoring, which allows the partitioning of the respiratory mechanics, is the unique way to assess the real alveolar distension pressures of these patients with reduced chest compliance [138]. Only then the clinician will be able to manage adequate transpulmonary pressures (as in laparoscopy) and to individualize the lung protection values [110]. Pes has been used in several clinical studies in obese patients on mechanical ventilation. By establishing a Pes-guided ventilatory strategy in obese patients, improvements in ventilatory mechanics (partitioning of ventilatory mechanics by observing improvements in lung strain and lung elastance) [107] and oxygenation [139] have been demonstrated.

EIT has a role to play both intra-operatively [140] and in the postoperative context as a non-invasive tool [41]. Intraoperatively, EIT-guided mechanical ventilation with MRI and individualized PEEP has been shown to improve ventilatory mechanics and oxygenation parameters, but has not been shown to maintain these improvements postoperatively [140]. EIT allows breath-by-breath monitoring after extubation to monitor the dyshomeogenisation of spontaneous lung ventilation, thus allowing early detection of patients who are candidates for ventilatory support and indicating the response to the applied therapy [141].

The only advanced monitoring technique that does achieve evidence support for PPCs reduction in these patients is LUS. A randomized clinical trial has used it intraoperatively in bariatric surgery to guide individualized PEEP, achieving a reduction in PPCs as well as improved clinical outcomes compared to standard PEEP strategy [69].

Obese patients are potentially one of the groups that can benefit the most from advanced monitoring, but more clinical studies are required to really prove whether the intraoperative use of these techniques has advantages for them in patient-centred outcomes [142].

Conclusions and Future Directions

Advanced respiratory monitoring tools offer both advantages and limitations: EIT effectively individualizes PEEP titration and assesses regional ventilation, although its lower resolution and dependency on correct electrode placement limit its routine clinical use. Pes helps tailor lung protective ventilation by measuring transpulmonary pressure (Ptp), which is crucial in conditions with increased chest wall elastance, despite its technical complexity and limitations in regional stress assessment. LUS aids in identifying lung atelectasis and guiding mechanical ventilation adjustments, although operator dependency remains a drawback. DUS is useful for assessing diaphragmatic function and detecting diaphragmatic paralysis, which is associated with PPCs.

Despite the theoretical benefits of advanced respiratory monitoring technologies, there is currently a lack of clinical studies that demonstrate a clear improvement in patient-centered outcomes with these methods. To address this gap, there is a pressing need for randomized clinical trials. Such studies would help determine whether patients at higher risk, particularly those undergoing procedures involving pneumoperitoneum and those who are obese, would benefit from the use of advanced respiratory monitoring technologies. Focusing research on these groups could provide valuable insights into optimizing ventilation strategies to enhance patient safety and outcomes.

Key References

  • Esposito T, Fregonese M, Morettini G, Carboni P, Tardioli C, Messina A, et al. Intraoperative individualization of positive-end-expiratory pressure through electrical impedance tomography or esophageal pressure assessment: a systematic review and meta-analysis of randomized controlled trials. J Clin Monit Comput. 2024 Feb;38(1):89–100.

    • This systematic review and meta-analysis of RCTs compared the effects of PEEP individualized by EIT or esophageal pressure vs. non-individualized PEEP on intraoperative PaO2/FiO2 ratios in abdominal or pelvic surgeries. Six RCTs (240 patients) showed better intraoperative oxygenation in the intervention group, with reduced heterogeneity after adjusting for BMI.

  • Tharp WG, Neilson MR, Breidenstein MW, Harned RG, Chatfield SE, Friend AF, et al. Effects of obesity, pneumoperitoneum, and body position on mechanical power of intraoperative ventilation: an observational study. J Appl Physiol Bethesda Md 1985. 2023 Jun 1;134(6):1390–402.

    • This study investigated the impact of obesity, pneumoperitoneum, and body position on mechanical power during robotic-assisted laparoscopic surgery. Using esophageal manometry, the study found that obesity and specific surgical positions significantly altered ventilation bioenergetics.