Effect of reducing inhaled oxygen concentration on lung injury in rabbits during one-lung ventilation

【Abstract】 Objective To observe the effect of reducing the concentration of inhaled oxygen (FiO2) on lung injury in rabbits during single lung ventilation (OLV). Methods Thirty New Zealand white rabbits were randomly divided into three groups: 60% FiO2 group (L group), 100% FiO2 group (H group) and control group, double lung ventilation (TLV) group (C group, 60% FiO2). . L group and H group TLV 30 min after right OLV 3 h

Group C TLV continued for 30 min after 30 min. Three groups of arterial blood were taken for blood gas analysis and oxygenation at TLV 30 min (T0) and OLV 10 min (T1), 30 min (T2), 60 min (T3), 120 min (T4), and 180 min (T5). Index (OI). Femoral artery catheterization was used to monitor blood pressure (ABP), heart rate (HR), and peak airway pressure (Ppeak). At the end of each experiment, the animals were sacrificed. The lung histopathological damage scores were taken from the bilateral lung tissues, and the contents of superoxide dismutase (SOD) and malondialdehyde (MDA) in the bilateral lung homogenates were measured. Results Compared with group H, arterial oxygen partial pressure (PaO2) in group L decreased significantly at T4 and T5, arterial oxygen saturation (SaO2) decreased significantly at T5, SOD content increased significantly at T5, MDA content decreased significantly, and lung injury The scores were decreased (P<0.05). In the H group, a large amount of red blood cells were observed in the alveolar cavity. In the L group, less inflammatory cell infiltration, alveolar exudate and alveolar interstitial destruction were observed. Conclusion Decreasing FiO2 to 60% in OLV increases the incidence of hypoxemia, but can significantly reduce lung injury in rabbits, which may be related to the reduction of oxidative stress in lung tissue.

【Key words】 Lung ventilation; Oxygen; Lung disease; Rabbit

One-lung ventilation (OLV), while facilitating surgery, can also lead to OLV-related lung injury [1-2]. The main reasons are: surgical side lung ischemia and hypoxia, ischemia-reperfusion injury, non-surgical side lung hyperperfusion and excessive expansion and hyperoxic oxygen damage [3]. Oxygen damage caused by hyperoxia is one of the main reasons, but in the clinical OLV, pure oxygen ventilation is often used to reduce the incidence of hypoxemia. The sixth edition of Miller Anesthesiology also recommends inhalation of pure oxygen at OLV, but the latest Miller anesthesiology seventh edition [4] does not explicitly recommend fraction of inspired oxygen (FiO2), but only if any The complications should first increase FiO2 to 100%. Therefore, how much FiO2 is suitable for OLV has become one of the research hotspots in the OLV field. To this end, this study intends to observe the effect of FiO2 reduced to 60% on lung injury in rabbits in the OLV model.

【Materials and Methods】

1. Animals and grouping: Choose healthy adult New Zealand white rabbits, male or female, weighing 1.9-2.4 kg, randomly divided into three groups: 60% FiO2 group (L group), 100% FiO2 group (H group) and control group (Group C, 60% FiO2). Based on the exclusion criteria, it was ensured that 10 rabbits per group were included in the analysis and the number of excluded experimental animals was recorded. In group L and group H, TLV (two-lung ventilation) was performed for 30 min after right OLV for 3 h, and group C was 60% FiO2 TLV for 30 min and then continued for TLV for 3 h. In clinical practice, because hypoxemia threatens the safety of patients, SaO2 <90% [4] will be treated accordingly. This experiment simulates clinical safety standards. If the blood gas analysis results show that SaO2 <90% at any time point, the animal is excluded from the experiment, and the results are not included in the analysis, but the number of experimental animals is removed.

2. Experimental method: All animals were banned for 8 h before the experiment. Open one side of the ear vein, anesthesia with 30% urethane 4 ml / kg intravenously, after the eyelash reflex disappeared, fix it on the animal operating table, the right femoral artery catheter to monitor blood pressure (ABP) and heart rate (HR ). Tracheal incision between the second and third tracheal rings, insert a 3.0 mm inner diameter without cuffed tracheal tube, intravenously inject cis atracurium 2 mg, connect the small animal ventilator (DW3000B, Beijing Zhongshi Di Chuang Technology Development Co., Ltd. Responsible company) TLV 30 min. The tidal volume is 10 ml/kg, the FiO2 is 60%, the respiratory rate is 40 times/min, and the respiratory ratio is 1:2. Intraoperative continuous injection of lactated Ringer's solution 10 ml·kg-1·h-1, cis-atracurium 1 mg·kg-1·h-1, urethane 1 ml·kg-1·h-1. After TLV 30 min (T0), the L and H groups were switched to the right OLV model using a self-made bronchial occlusion tube method, and then the experimental animals were changed to the right lateral position to simulate the surgical position in the right OLV. Preparation of a self-made bronchial occlusion tube: firstly cut and seal the tip of the cuff-free Endotracheal Tube with an inner diameter of 3.0 mm, and circulate along the tube wall with a 3-0 thread at a distance of 6 to 7 mm from the tip of the catheter to facilitate the occlusion of the tube. The bronchial wall was tightly sealed, and then the catheter was placed in water and connected to a small animal ventilator. The peak pressure (Ppeak) showed 4.4 cmH2O (approximately 2 times the Ppeak of the OLV in this experiment), and there was no bubble overflow in the water; An elliptical side hole of about 4 mm × 3 mm was cut at a distance of 9 to 10 mm from the tip of the catheter to open the right main bronchus (Fig. 1). A 0.5 cm incision was made in the 7-8 intercostal space on the left side of the rabbit, and the left lung collapse was directly observed with a fiberoptic bronchoscope (FI-9RBS, Japan PENTAX). After the OLV model was successfully established, the L and H groups were subjected to right OLV for 3 h, FiO2 was 60% and 100%, respectively, and group C continued to perform TLV for 3 h and FiO2 for 60%. Three groups of rabbits breathed sounds before and after turning over and during surgery, monitoring airway pressure and fiberoptic bronchoscopy to determine the correct position of the catheter.

3. Observed indicators: T0, OLV 10 min (T1), 30 min (T2), 60 min (T3), 120 min (T4) and 180 min

(T5) Collect 0.2 ml of arterial blood for blood gas analysis and calculate the oxygenation index (OI). After the blood gas analysis at T5, 2 ml of urethane was added, and then the animals were sacrificed by rapid bloodletting. Open the chest to check the position of the tracheal tube and OLV effect, and take the lung tissue (1 cm × 0.5 cm × 0.5 cm) at the same position on the same level of the left and right lower lobe, and save a part in liquid nitrogen. After the specimen is collected, according to its description Determination of superoxide dismutase (SOD) and propylene in the homogenate by enzyme-linked immunosorbent assay (ELISA)

(MDA) content; another part of HE staining histopathological examination, according to its alveolar edema, interstitial edema, neutrophil infiltration and alveolar congestion, lung injury score [5]: no damage 0 points, 1 point of injury , the damage is heavier

2 points, the damage is 3 points, and the damage is extremely serious 4 points.

4. Statistical analysis: SPSS 13.0 statistical software was used for treatment. Normally distributed measurement data were expressed as mean ± standard deviation ( x ± s ). Comparison between groups was performed by repeated measures design analysis of variance; lung tissue injury score group The rank sum test was used for comparison.

1. General: In the three groups, only 4 rabbits in group L could not maintain SaO2 more than 90% [6], and the experiment was excluded. Therefore, there were 14 rabbits in group L, and finally 10 were included in the experiment. There was no significant difference in body weight between the three groups. There was no significant difference in the amount of cis-atracurium, lactated Ringer's solution and urethane in the three groups (Table 1). Compared with group C, Ppeak in H and L groups was significantly increased after OLV (P < 0.05), but there was no significant difference between H and L groups (Table 2).

Note: compared with group C, aP<0.05; compared with group H, bP<0.05

At present, many scholars believe that inhalation of high concentrations of oxygen has adverse effects on the human body, mainly including inhaled atelectasis and oxygen poisoning [9-11]. When inhaling high concentrations of oxygen, a large amount of reactive oxygen species (ROS) is produced in the body [12]. ROS can attack the lipid bilayer and cause cell damage, which is the main cause of oxygen poisoning. In general anesthesia TLV, considering the high oxygen damage, the use of relatively low FiO2 is recommended, not recommended to exceed 60% [13]. OLV is a non-physiological ventilation method, which leads to an increase in intrapulmonary shunt and a decrease in PaO2. Due to hypoxemia concerns, pure oxygen is often inhaled during OLV, but inhalation of pure oxygen may also cause hyperoxic lung injury [14- 15]. Yang et al [16] studied 100 patients with ASA I or II lobectomy. During the OLV period, 58% of patients in the hypoxic group needed to increase the oxygen concentration to 100% to maintain adequate oxygenation, but their lungs. The incidence of complications (including lung exudation and atelectasis) was lower than in the pure oxygen group.

Hyperoxia-induced lung injury is proportional to the level of PaO2 (especially PaO2>450 mmHg or FiO2>60%) and the length of exposure [17], so this group set the FiO2 of group L to 60%. FiO2 was used as a single factor to reduce the effect of FiO2 to 60% on lung injury in rabbits when OLV was observed. The results showed that a decrease in FiO2 to 60% increased the incidence of hypoxemia. In group L, PaO2 decreased significantly at T4 and T5, and SaO2 decreased significantly at T5, but there was no significant difference in OI. Histopathological examination of the lung showed that compared with the H group, less inflammatory cell infiltration, alveolar exudate, alveolar interstitial destruction and lesion score were significantly reduced in the L group, suggesting that reducing FiO2 can alleviate acute lung injury.

MDA and SOD are clinically used antioxidant and antioxidant indicators. MDA is a product of lipid peroxidation [18]. It can also be regarded as the end product of free radical chain reaction. SOD can effectively scavenge oxygen ion free radicals [19], thus protecting cells and tissues from oxidative stress damage. Measuring MDA and SOD concentrations can indirectly reflect the level of oxidation in the body. Misthos et al [20] found that the amount of MDA in plasma was proportional to the duration of OLV. The results of this experiment showed that the content of SOD in the lung tissue homogenate of the OLV 3 h L group was significantly lower than that of the H group and the MDA content was significantly lower than that of the H group, suggesting that the oxidative stress damage in the hypoxic group was lighter than that in the pure oxygen group. This is consistent with the results of histopathological examination of the lung. In summary, reducing FiO2 to 60% at OLV can significantly reduce acute lung injury in rabbits, which may be related to the reduction of oxidative stress in lung tissue.

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