The impact of ultrasound-guided recruitment maneuvers on the risk of postoperative pulmonary complications in patients undergoing general anesthesia

Postoperative pulmonary complications (PPCs) are among the most common problems in perioperative care. The most frequent complications include respiratory failure, atelectasis, pneumothorax, pleural effusion, pneumonia, and acute respiratory distress syndrome (ARDS)⁽¹⁾. Numerous risk factors predisposing a patient to the development of anesthesia-induced respiratory failure have been reported – a significant correlation has been evidenced with such risk factors as age over 60 years, class 2 or higher according to the ASA (American Society of Anesthesiologists) Physical Status Classification System, chronic obstructive pulmonary disease (COPD), heart failure, and reduced exercise tolerance⁽²⁾. Additionally, the risk of PPCs is affected by factors associated with the employed surgical technique, the surgical site (mainly surgeries involving the chest and epigastrium), the anesthesia technique, and the method of mechanical ventilation used during the procedure^{(3, 4, 5)}.

It has been found that nearly 90% of patients undergoing general anesthesia (intubated with the use of neuromuscular blocking agents) who had been ventilated with positive pressures developed atelectasis, i.e., a pulmonary aeration disturbance^{(6, 7)}. In the majority of patients, the areas affected by atelectasis are clinically insignificant and become normally aerated upon a return to sufficient spontaneous respiration. In some patients, however, intraoperative atelectasis may be a predisposing factor for postoperative complications. Recruitment maneuvers are commonly employed for reducing pulmonary atelectasis. Various techniques for performing them have been described in the relevant literature^{(8, 9, 10, 11, 12)}.

The effectiveness of conventional recruitment methods in preventing PPCs has not been proven⁽¹³⁾. Moreover, they are associated with the risk of developing respiratory complications (barotrauma, volumotrauma, biotrauma) and may lead to hemodynamic destabilization due to significant intrapleural pressure changes during their performance. Their disadvantage is the lack of patient-based customization: irrespective of the extent of pathology and the response of the lungs to performed maneuvers, they are conducted identically in all patients.

As claimed by some authors (Tusman, Cylwik, Park), the application of lung ultrasound for monitoring the recruitment process appears to be of significant benefit for patients. Owing to the continuous ultrasound assessment of the pulmonary tissue affected by atelectasis during the recruitment process, it is possible to decrease ventilation pressures necessary to achieving a good effect in reducing atelectasis, while at the same time limiting potential complications associated with the procedure^{(14, 15, 16)}.

The aim of this study was to determine whether it was possible to positively impact the postoperative period and reduce the frequency of postoperative pulmonary complications (PPCs) via patient-based intraoperative ultrasound-guided recruitment maneuvers. The 7-day postoperative period was assessed, with particular emphasis on the length of hospitalization after surgery, the need for prolonged mechanical ventilation, the duration of stay in the postoperative ward, and the incidence of pneumonia.

PPCs constitute a serious problem in perioperative care. Appropriate preoperative management (e.g., introduction of respiratory rehabilitation), and then optimally performed anesthesia procedure, including protective ventilation, and intensive postoperative care may reduce the risk of PPC development. Recruitment maneuvers are one of the constituents of optimal intraoperative ventilation⁽¹⁷⁾. Their effectiveness has been extensively discussed in literature; however, even based on large meta-analyses the most optimal procedure for performing them has not been determined thus far^{(18, 19)}. Because of the risk of both respiratory and circulatory complications (mainly hypo-tension), it is justified to closely monitor their course, also with the application of imaging techniques. A number of studies have reported the usefulness of computed tomography^{(20, 21)} and electrical impedance tomography^{(22, 23)} for recruitment monitoring. However, these methods cannot be employed in the operating theater during general anesthesia. Ultrasonography is a universally available imaging method that can be easily used in the operating theatre in the bedside mode, without emitting adverse radiation. Its great advantage lies in the possibility of reexamination as often as the clinical situation dictates.

The major aim of this study was to determine whether it was possible to positively impact on the postoperative period of patients undergoing general anesthesia via patient-based optimized intraoperative ultrasound-guided recruitment maneuvers. To this end, available relevant literature was analyzed. A search of scientific databases was conducted, which yielded a total of 127 publications that were further examined (key words: lung ultrasound, recruitment maneuvers). Out of the selected publications, 101 papers were excluded since they were not directly relevant to the topic. Six studies were devoted to ultrasound-guided recruitment monitoring in patients with ARDS, 12 referred to ultrasound-guided monitoring of the conventional procedure, and 3 papers only evaluated PEEP. Finally, only 5 publications were identified that directly related to the discussed topic (Tab. 3).

Elshalzy et al. ⁽²⁴⁾, who examined the application of intraoperative bedside lung ultrasound in optimizing PEEP settings in obese patients undergoing laparoscopic bariatric surgeries, reported a significant reduction of developing PPCs. These conclusions are consistent with our results. What needs to be stressed, though, is that in the Elshalzy et al. study, the postoperative follow-up period as regards the development of postoperative complications was only 24 h, which may be definitely too limited for infectious complications.

In their study, Park et al.⁽¹⁶⁾ compared the efficacy of conventional lung recruitment maneuvers and ultrasound-guided procedure in reducing areas affected by atelectasis. They revealed a lower incidence of atelectasis in the ultrasound-guided recruitment group with a persistent postoperative effect. These authors also analyzed the postoperative period – no episodes of desaturation were revealed in the intraoperative ultrasound-guided recruitment group, while in the conventionally performed recruitment group desaturation occurred in 10% of patients. No statistically significant differences were revealed between the groups as regards the period spent in the postanesthesia care unit and total hospitalization. Out of 40 patients, only one from the ultrasound-guided recruitment group developed PPC. In this study, similarly to the previously discussed one, the follow-up period was relatively short and amounted to 48 h. Our results indicate a more evidently pronounced positive tendency concerning the postoperative period. This may be, however, correlative to a different research methodology. In our study, the control group consisted of patients for whom no intervention was performed, while in the study by Park et al. the control group underwent conventional recruitment. Additionally, the number of participants is of relevance in both these studies – 40 vs. 200 patients, which may also be the reason for the dissimilarity of the findings.

A good clinical effect of reducing atelectasis with ultrasound-guided alveolar recruitment maneuvers during general anesthesia was reported by Song et al. ^{(18, 25)}. These studies involved a pediatric population characterized by a different physiology of the respiratory system and much lower lung compliance as compared to adults. Therefore, the results of these studies cannot be comparatively interpreted with our study, but the positive effect of ultrasound-guided recruitment maneuvers in pediatric patients is nevertheless worth noting.

In our study published in 2021⁽¹⁵⁾, we reported that owing to ultrasound-guided recruitment maneuvers it was possible to achieve the persistent effect of reducing intraoperative atelectasis and determine patient-based PEEP values that prevented the recurrence of lung aeration disturbances. To our knowledge, this is the only study in which a significant reduction of pressures in the respiratory system necessary for the alveolar recruitment was revealed, resulting in the absence of respiratory tract complications.

In the present study, we observed a reduced need for prolonged postoperative mechanical ventilation in the group of patients who underwent ultrasound-guided pulmonary recruitment during general anesthesia, as well as a slightly reduced postoperative hospitalization period, and a smaller number of ICU admissions due to postoperative complications. We believe these results, despite their lack of statistical significance, to be very advantageous both for the patients involved and the hospital (economic factors, better capacity of departments). This positive effect concerns not only the recruitment procedure per se, but also applies the holistic ultrasound image of the organs within the chest (assessment of both the lungs and the heart). Pathologies such as atelectasis and pulmonary congestion can be detected ultrasonographically before the occurrence of clinical symptoms^{(26, 27, 28)}. The detection of a pathology may influence decisions made by the anesthesiologist, for instance, decisions concerning fluid therapy intra- and postoperatively^{(29, 30, 31, 32, 33, 34)}. The persistence of atelectasis, despite performing the recruitment process, resulted in the administration of high-flow nasal oxygen therapy after extubation, which definitively affected the results.

Ultrasound-guided intraoperative recruitment maneuvers have a favorable effect on the postoperative period and reduce the incidence of PPCs.