Massive alveolar collapse and significant reduction in lung volume are important pathophysiological features of acute respiratory distress syndrome (ARDS). The combination of controlled lung expansion (SI) and small tidal volumes combined with optimal positive end-expiratory pressure (PEEP) is the core component of the currently proposed lung opening and protective ventilation strategy in ARDS. Studies have shown that this ventilation strategy is beneficial for improving ARDS oxygenation and reducing ventilator-associated lung injury. However, the effect of SI and PEEP on lung resuscitation and the criteria and methods for selecting the best PEEP need to be investigated in clinical and experimental studies 医学教育网收集整理 . It is important to compare the retension volume before and after SI and different levels of tidal volume, and to explore the relationship between the low turning point pressure (LIP) of the lung pressure-volume curve (P-V) and lung retension volume in ARDS, which is an important guiding significance for rational mechanical ventilation in ARDS. I. Comparison of methods for determination of pulmonary volumes in acute respiratory distress syndrome Pulmonary volumes are generally determined by the classical P-V curve method, but this method is relatively cumbersome and is currently used mainly in experimental studies. Recently, a relatively simple isobaric method has been proposed, but it is not clear how accurate the isobaric method is compared with the classical P-V curve method. Sheep with ARDS were studied to determine the retension volume of the same PEEP by P-V curve method and isobaric method, respectively. The results showed that the isobaric method gave immediate results, while the P-V curve method took 5-6 min to determine the volume. The retension volumes measured by the isobaric method and the P-V curve method were (25.79±20.48)ml and (63.26±54.57)ml, respectively, with no significant difference between the two groups (P>0.05=.) At PEEP of 10 and 15 cmH2O, the retension volumes measured by the isobaric method were (48.64±30.51)ml and (71.50±58.09)ml, respectively, while The isobaric pressure method measured a significantly smaller volume than the P-V curve (P<0.05), with a PEEP of 10 and 15 cmH2O, respectively. It can be seen that although the isobaric method is simple and time-saving, its accuracy is poor and it cannot replace the P-V curve to determine the volume of retension. The effect of tidal volume on pulmonary retension volume in acute respiratory distress syndrome Small tidal volume ventilation can avoid ventilator-related lung injury caused by alveolar hyperinflation, and is one of the lung-protective ventilation strategies in ARDS. However, due to massive alveolar collapse, the shear forces generated by the periodic closure and opening of alveoli with breathing can also aggravate lung injury. Therefore, it is also extremely important to reopen collapsed alveoli and increase lung volume in the treatment of ARDS. The size of the tidal volume may play an important role in the resuscitation of collapsed alveoli in ARDS, and it is worth exploring the effect of applying protective small tidal volume ventilation on the resuscitation of collapsed lungs. In sheep with ARDS, the P-V curve method was used to determine the volume of lung resuscitation. The changes in the volume of collapsed lungs with PEEP of 10 cmH2O and different tidal volumes (6 ml/kg, 10 ml/kg, 15 ml/kg) were observed. The results showed that under the condition that PEEP was fixed at 10 cmH2O, the volume of lung volumes increased gradually as the tidal volume increased from 6 ml/kg to 15 ml/kg (P<0.05=. The volume of resuscitation at a tidal volume of 10 ml/kg (148±85 ml) was higher than that at a tidal volume of 6 ml/kg (103±70 ml) and significantly lower than that at 15 ml/kg (230±87 ml) (P<0.05). The arterial partial pressure of oxygen increased significantly with increasing tidal volume, and the peak airway pressure and airway plateau pressure also increased significantly with tidal volume (P<0.05=. There was no significant change in hemodynamics at different tidal volumes (P>0.05). It can be seen that the size of tidal volume can affect the volume of pulmonary resuscitation, the larger the tidal volume the larger the resuscitation volume, and the application of small tidal volume may be detrimental to the resuscitation of collapsed alveoli in ARDS. SI is a method of pulmonary resuscitation operation, which can theoretically promote the resuscitation of collapsed lungs and improve oxygenation. However, some clinical indicators of blood gas changes are used to evaluate the effect of SI on pulmonary resuscitation, and there is a lack of studies on whether SI can promote pulmonary resuscitation and the degree of promotion of pulmonary resuscitation. In sheep with ARDS, the P-V curve method was used to determine the volume of pulmonary resuscitation before SI, 15 min after SI and lh after SI. The results showed that nine sheep showed an increase in arterial partial pressure of oxygen (PaO2) of more than 20% after SI compared with that before SI, and SI was considered effective. In the remaining 6 sheep, SI was not effective. 15 min after SI and 1 h after SI in the effective group were (95.9±44.7) ml and (107.7±53.6) ml, respectively, which were significantly higher than the pre-SI pulmonary volumes (45.2±28.2) ml (P<0.05=, PaO2 also improved significantly after SI (P<0.05), but The hemodynamics of sheep were not significantly changed after SI compared to before SI (P>0.05), while airway pressure was significantly lower and static compliance was significantly improved after SI (P<0.05=. No significant changes were observed in lung volumes and PaO2 after SI compared to before SI in the six sheep in the SI null group (P>0.05). Therefore, the combined application of SI and pulmonary protective ventilation strategy can induce the resuscitation of collapsed alveoli and increase the resuscitation volume in ARDS patients, which is conducive to improving the oxygenation and pulmonary compliance of patients. Moreover, SI is simple and easy to perform, safe for clinical application, and has obvious practical value, which is one of the effective treatments for ARDS. Fourth, the relationship between pulmonary resuscitation in acute respiratory distress syndrome and the low turning point of static lung pressure volume curve The application of PEEP can resuscitate collapsed alveoli in ARDS, avoid end-expiratory alveolar collapse and increase lung volume. However, there is no unified standard for the selection of PEEP during mechanical ventilation therapy in ARDS. Many scholars choose PEEP based on the LIP on the inspiratory branch of the static lung P-V curve, believing that LIP represents a large number of collapsed alveoli during inspiration, and therefore adjust PEEP with a pressure level slightly higher than LIP. Therefore, it may not be appropriate to use LIP to guide the choice of PEEP. The sheep ARDS model was replicated by continuous intravenous injection of endotoxin, the static lung P-V curve was traced by the low flow rate method, the LIP was determined by the linear regression method, and the sheep were divided into two groups, LIP and no LIP, according to the presence or absence of LIP. The P-V curve method was used to determine the lung resuspension volume at PEEP of 5, 10 and 15 cmH2O. Changes in hemodynamics, pulmonary gas exchange and mechanics were monitored at different PEEPs. The results showed that the pulmonary re-expansion volumes were (63.3±54.6) ml, (148.1±85.4) ml, and (322.9±148.4 m1) for PEEP of 5, 10, and 15 cmH2O, respectively, and increased significantly (P<0.05) as PEEP increased from 5 to 15 cmH2O levels. of 14 ARDS sheep , 7 sheep showed a significant LIP (7.8±4.4 cmH2O) in the inspiratory branch of their static lung P-V curves. As the PEEP level increased, the retension volume increased significantly (P<0.05) in both LIP and non-LIP groups. There was no significant difference between the two groups of sheep for the same PEEP level (P>0.05). The arterial oxygenation index (PaO2/FiO2) of sheep improved significantly with increasing PEEP, and the change in arterial oxygenation index was significantly correlated with the retension volume (r=O.557, P<0.05). In conclusion, alveolar resuscitation during inspiration is a continuous process, not an all-or-none phenomenon, and LIP does not represent the degree of pulmonary resuscitation in ARDS; changes in pulmonary resuscitation volume can reflect the process of pulmonary resuscitation. Therefore, it is inappropriate to select PEEP based on LIP. Obtaining optimal pulmonary resuscitation should be one of the goals of mechanical ventilation in ARDS. In clinical practice, the PEEP level can be adjusted by measuring the retension volume and combining it with the patient's specific situation. V. The effect of positive end-expiratory pressure on pulmonary resuscitation and oxygenation in acute respiratory distress syndrome The application of PEEP can prevent the collapse of ARDS alveoli at the end of expiration and avoid lung atrophy injury caused by repeated closure and opening of some alveoli with breathing, which is one of the protective ventilation strategies for ARDS. However, LIP does not represent the degree of pulmonary resuscitation in ARDS, and some ARDS patients do not have LIP on their static P-V curves, so it may be more objective and direct to select PEEP based on the magnitude of pulmonary resuscitation volume. Eleven patients with ARDS who were hemodynamically stable and received mechanical ventilation were studied, and the pressure-volume curve method was used to determine the pulmonary resuscitation volume with PEEP of 5, 10, and 15 cmH2O, and to monitor the arterial blood gas and pulmonary mechanics changes of the patients. The results showed that the retension volume was (40.2±15.3) ml at PEEP 5 cmH2O, (123.8±43.1) ml at PEEP 10 cmH2O, and (178.9±43.5) m1 at PEEP 15 cmH2O. The retension volume increased significantly with increasing PEEP (P<0.05). Arterial oxygenation index also increased with increasing PEEP level, and the change of arterial oxygenation index was positively correlated with retension volume (r=0.483, P<0.01). There was no significant change in patients' static pulmonary compliance with different PEEP conditions (P>0.05). Patients were divided into two groups, LIP and no LIP, according to the presence or absence of low turning point (LIP), and the retension volume increased with the increase of PEEP level in both groups, where the retension volume of patients in the LIP group at PEEP 15 cmH2O was greater than that in the no LIP group (P<0.05). It can be seen that the higher the PEEP level, the larger the pulmonary retension volume, and the increase in retension volume was positively correlated with the change in arterial oxygenation index. It may not be appropriate to select PEEP by LIP, and it may be more appropriate to select PEEP by measuring the retension volume. In summary, the isobaric method cannot replace the P-V curve for determination of pulmonary retension volume. SI is an important complement to the pulmonary protective strategy and is beneficial to the recovery of collapsed alveoli in ARDS, and it may be more appropriate to select PEEP by measuring the volume of recovery. PEEP may be more appropriate.