Effects Of High Frequency Oscillatory Ventilation On Lung Function And Pathological Structure: A Newborn Piglets Model With Acute Lung Injury

OjectiveIn this study, repeated whole-lung lavage with normal saline was used to induce newborn piglets model for neonatal acute lung injury (ALI). The study holds two parts: 1,The effects of high frequency oscillatory ventilation on gas exchange,lung mechanics and hemodynamics in newborn piglets with acute lung injury: to investigate the effect of HFOV on lung function and hemodynamics in newborn piglets with acute lung injury, induced by pulmonary surfactant deficiency; 2,The effects of high frequency oscillatory ventilation on pathological structure and type II alveolar epithelium cells in newborn piglets with acute lung injury: to investigate the relationship between ventilation modes,time length and lung injury, what's more, to explore the mechanisms and applicable value of HFOV in neonatal ALI/ARDS, and in relieving and attenuating ventilator associated lung injury (VALI).Methods(—)Part One1,Animal Preparation15 no more than 3-day-old newborn piglets were intubated after anesthesia, ventilated with a MAQUET Servo-i ventilaor, using pressure control ventilation mode. Femoral artery was cannulated for arterial blood pressure monitoring and blood sampling. After surgical procedure and a stabilization period of 30 minutes, the arterial blood gas, arterial blood pressure, heart rate(HR), lung static compliance(Cst) were obtained, calculated for oxygenation index(OI), mean arterial blood pressure(MABP) and Cst as baseline parameters (baseline). 2,Induction of acute lung injuryAll the piglets ALI were induced using CMV mode. To induce acute lung injury, warmed normal saline (37°C) at a volume of 35 ml/kg was instilled continuously through a endotracheal tube, the lavage procedure was repeated after each 5 minutes inteval until the PaO2 remained below 100 mmHg under the fraction of inspired oxygen being 1.0 for one hour.3,Study GroupsAfter completion of lavage, piglets were randomly assigned to one of three study groups: control (n=3), conventional mechanical ventilation (CMV, n=6), or high frequency oscillatory ventilation (HFOV, n=6).Control group: piglets were killed after the completion of lavage series, no mechanical ventilation.CMV group: piglets were ventilated using a MAQUET Servo-i ventilaor with pressure control ventilation mode.Each time three piglets were killed after ventilating 24 hours and 48 hours respectively.HFOV group: piglets were ventilated using a SLE5000 ventilaor with high frequency oscillatory ventilation mode. Each time three piglets were killed after ventilating 24 hours and 48 hours respectively.4,Observing Markers and MethodsObserving markers were monitoring at preinjury,ALI 0h,1h,3h,6h,12h,24 h,48 h respectively.(1) Blood Gas Analysis: arterial blood samples were analyzed and calculated for OI.(2) Lung Static Compliance: fifth datum of respiration were recorded using low flow technique. In HFOV group, HFOV mode was changed into CMV mode before monitoring, ventilator parameters were set as those in CMV group, after monitoring completed, ventilator mode was changed back into HFOV mode immediatly.Cst was calculated.(3) Arterial Blood Pressure and Heart Rate: MABP was calculated. (二) Part Two1,Animal Preparation It is same as part one.2,Induction of acute lung injury It is same as part one.3,Study Groups It is same as part one.4,Observing Markers and Methods(1) light Microscopy (LM): right upper lung tissues were divided into gravitational dependent region and gravitational nondependent region. The numbers of polymorphonuclear leukocyte (PMN),alveolar macrophage (AM),red blood cell (RBC) were counted respectively using Hematoxylin-Eosine staining. The numbers of hyaline membrane/edema(HM/E) were counted using modified Mallory's phosphotungstic acid-hematoxylin (PTAH) staining.(2) Transmission Electron Microscope (TEM): the ultrastructure of type II alveolar epithelium cells(AEC II ) in right down-backside lung tissue was observed.Results(—) Part One1,No differences were found in OI,Cst,HR,MABP at baseline,ALI Oh between groups. At ALI 0h, P/F ratio was below 300 mmHg, apart from this, OI was significantly higher and Cst was significantly lower than those at baseline.2,As the extension of ventilation time, OI was continuously decreased in CMV group and HFOV group, however, from sixth hour to forty-eighth hour, OI in HFOV group was significantly lower than that in CMV group (P<0.05).3,In CMV group, it was observed that Cst was decreased in some piglets at the first and third hour, Cst was significantly higher than that at ALI Oh (P< 0.05). In HFOV group, Cst was continuously increased as the extension of ventilation time,it was significantly higher than that at ALI Oh from the first hour to forty-eighth hour (P<0.05), and it was significantly higher than that in CMV group from third hour to forty-eighth hour (P<0.05). 4,No differences were found in HR,MABP at each time point between groups (P>0.05).(二) Part Two1,TM(1) It presented a greater degree of histopathologic lung damage in the gravitational dependent region than that in gravitational nondependent region.(2) PMN: PMNs in gravitational dependent and nondependent region of both CMV and HFOV group were significantly more than in control group (P< 0.01). PMNs in gravitational dependent region of HFOV 48h group were significantly less than in CMV 48h group (P<0.05).(3) AM: AMs in CMV 48h group,HFOV 24h group and HFOV 48h group were significantly less than in control group (P<0.05). AMs in HFOV 24h group were significantly less than in CMV 24h group (P<0.01).(4) RBC: RBCs in gravitational dependent and nondependent region of both CMV and HFOV group were significantly more than in control group (P< 0.01). RBCs in gravitational dependent and nondependent region of all HFOV groups were significantly less than in CMV group respectively (P< 0.01).(5) HM/E: HM/Es in gravitational dependent and nondependent region of both CMV and HFOV group were significantly more than in control group (P< 0.01). HM/Es in gravitational dependent and nondependent region of all HFOV groups were significantly less than in CMV group respectively (P< 0.01).2,TEMIt was found that lamellar body (LB) with vacuole-like deformity was occurred in each group. As the extension of ventilation time, comparing with CMV group, the juxtaposition of AECII to basal membrane and AEC I in HFOV group was closer and the electron density of LB in HFOV group decreased less. In CMV 24h group, the secretion of AECII discharged into alveolar space and naive AECII were observed. In CMV 48h group, some AEC II s were dislodged from basal membrane, and the volume of some nuclei became shrank.Conclusions1,Treating neonatal ALI/ARDS with HFOV, it can more rapidly andeffectively improve gas exchange and lung mechanics, and have no adverse effect on hemodynamics.2,Treating neonatal ALI/ARDS with mechanical ventilation,histopathologic lung damage in the gravitational dependent region was more intense than that in gravitational nondependent region.3,HFOV can reduce and attenuate VALI through reducing pulmonaryinflammation,haemorrhage and alveolar edema and hyaline membrane formation, and attenuating the damage to AEC II.QIN Xiaofei (Pediatrics) Directed by professor FU Wanhai...