الفهرس 
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Abstract
The American-European Consensus Conference Committee defines ARDS as: (2)
1- The ratio of arterial partial oxygen tension PaO2 / FiO2 below 200, if ratio less than 300 with bilateral infiltrates this indicates (ALI), although formally considered different from ARDS, ALI is usually just a precursor to ARDS.
2- The presence of bilateral lung infiltration on the chest x-ray. These infiltrates may appear similar to those of left ventricular failure, but the cardiac silhouette appears normal in ARDS.
3- The pulmonary capillary wedge pressure is normal (less than 18 mmHg) in ARDS, but raised in left ventricular failure (more than 18 mmHg).
There are several causes of ARDS; the most common causes are sepsis, trauma and aspiration of gastric contents. ARDS is classified to pulmonary as (aspiration pneumonia, pneumonia, inhalation injury, pulmonary contusions, fat emboli, near drowning, reperfusion injury) and extra-pulmonary causes as (sepsis,severe trauma, shock, Acute pancreatitis, cardiopulmonary bypass, transfusion-related TRALI, disseminated intravascular coagulation, Burns, head injury, Drug overdose).(5)
The main line of treatment of ARDS patients is mechanical ventilation. It has been clearly established that mechanical ventilation can induce acute lung injury (ALI) by causing hyperinflation of healthy lung regions and repetitive opening and closing of unstable lung units. As a consequence, the therapeutic target of mechanical ventilation in patients with ARDS has shifted from the maintenance of normal gas exchange to the protection of the lung from ventilator induced lung injury. Reduction of tidal volume (VT) to limit plateau pressure (Pplat) is recommended for the ventilator management of ARDS. However, a reduction in VT promotes a decrease in lung aeration. Several studies recommend the adjunction of recruitment maneuvers (RMs) to mechanical ventilation to limit alveolar derecruitment induced by low tidal volume. (9, 10, 11)
The aim of the present work was to compare three different ventilator strategies of mechanically ventilated ARDS patients as regards:
1. Oxygenation and lung mechanics.
2. Hemodynamic parameters.
3. Duration of mechanical ventilation.
4. Mortality and morbidity during hospital stay.
This prospective randomized study was conducted on 36 mechanically ventilated ARDS patients admitted to the units of Critical Care Medicine Department in Alexandria University Hospital. All patients included in this study were selected randomly (sealed envelope randomization). All patients were classified randomly and consecutively into three equal groups each group included 12 patients:
- Group I: lung protective strategy group, ventilator setting adjusted to all patients in this group as follow: The predicted body weight (PBW) was calculated by the following formula: - Males 50 + 2.3 [height (inches) - 60], Females 45.5 + 2.3 [height (inches) -60]. Then:
The ventilators were adjusted to provide assist control mode to the patients with initial tidal volume of 8 ml/kg PBW then tidal volume was reduced by 1 ml /kg at intervals every 2 hours until tidal volume reached 6ml/kg PBW, initial respiratory rate to approximate baseline patient minute ventilation (VE) (not> 35 breaths per minute). Target oxygen tension goal (PaO2) was 55-80 mmHg and the target goal SpO2% was 88-95% by using incremental FiO2/PEEP combinations, plateau pressure (Pplat) goal of 30 cmH2O to keep pH in the range of 7.30-7.45.
- Group II: lung protective strategy + recruitment with BiPAP (RecruitBiPAP) group, the patients in this group were switched to pressure-controlled ventilation starting with plateau pressure/PEEP = 45/30, RR= 20, I: E ratio of 1/1.5 at FiO2 of 1.0 for 2 minutes, then 50/35 for another 2 minutes then 55/40 for another 2 minutes then maximum pressure control/ PEEP was 60/45. The RM was performed with stepwise increases of 5 CmH2O of PEEP every 2 minutes. After these 8 minutes of recruitment maneuver, all patients returned to lung protective strategy again with the same ventilation parameters that was just before each recruitment maneuver in each patient.
-Group III: lung protective strategy + recruitment with CPAP (RecruitCPAP) group,12 patients with ARDS ventilated with lung-protective strategy as mentioned above and after stabilization of the cases for 6 hours recruitment maneuver was done as follow:FiO2 was increased to 1.0 for 15 minutes then recruitment was done with 40 cmH2O CPAP for 40 seconds.
The results of the present study showed that the mean age in the three groups ranged between 20-59 years with no statistical significant differences between the studied mechanically ventilated ARDS groups.The three studied groups showed mean arterial blood pressure (MABP)at ZERO time within normal values without any statistically significant differences between them. Then at thirty minutes after recruitment there was a significant decrease in MABP in group II and group III compared to group I patients (group I=734.2 mmHg, in group II=66.24.2 mmHg and in group III=64.26.8 mmHg). One hour after recruitment MABP in group II and III became close to each other but still there was a significant decrease in MABP in group II and group III compared with group I at 6 hour and thereafter till 72 hour the MABP was close to each other in the three groups without any significant differences.
Heart rate increased significantly in group II and group III compared to group I after thirty minutes from zero time (after recruitment in group II andgroup III) and persisted significantly high in group II and group III till 12 hours and there after the mean pulse rate values showed no significant differences.
The mean cardiac index values showed no statistically significant differences between the three studied groups at different times, except at 12 hours (CI=2.860.3, 2.90.34 and 3.10.3L/min/m2 for group I, II and III respectively) Group III had statistically significant higher cardiac index than group I with P= 0.03.
As regard respiratory parameters there were no statistical significant differences between the three studied groups as regard respiratory rate, tidal volume, lung compliance, PH and oxygen tension (PaO2).
Oxygen saturation (SpO2%) values showed that, there were no statistical significant differences between the three studied groups at different times, except at 1, 6 and 12 hr. This mean that recruitment maneuvers improves oxygen saturation and this improvement started to be significant at 1 hour after recruitment and persist up to 12 hours after recruitment as group I have values statistically lower than group II and III (90.42.3%, 92.21.9% and 93.12% at 1 hr and 90.52%, 91.001.6% and 93.22.3% at 6 hr. and 902.3%, 91.922.1% and 92.51.7 at 12 hour for group I, II and III respectively).
The mean FiO2 required at 12 hours, group I required the highest mean FiO2 (mean value=0.580.1) after recruitment and this was statistically significant compared to group III (mean value=0.50.1) with P=0.01, and also between group II (mean value=0.54 0.1) and group III (mean value=0.50.1) with P3=0.008. Group III had the lowest FiO2 requirement.
Plateau pressure values showed that there were no statistically significant differences between the mean values of plateau pressure in the three studied groups at different times, except at 12 hours as group I had values greater than group III (mean=27.1.53 CmH2O in group I, mean=26.581.08 CmH2O in group III). (p=0.015)
The PEEP level showed that, at 1 hour there were statistically significant differences between group I (mean=19.50.6 CmH2O) and group II (mean=180.7 CmH2O) as group I had higher mean PEEP level than group II with P=0.003, in contrast group I had significantly lower mean PEEP level than group III (mean=20.50.87 CmH2O) with P=0.004. Also at 12 hour group I (mean=21.52.9) had PEEP significantly higher than group III (mean=19.5 2.8 CmH2O) and group II (mean=16.52.9 CmH2O) had PEEP significantly lower than group III (mean=19.5 2.8 CmH2O) with P=0.013 and P=0.017.
Measurements of the thoracic fluid content (TFC) between the three studied groups showed a statistically significant differences between the three studied groups at different times, starting at ZREO point group III had mean of TFC lower than groups I and II (mean=1043.46, 100.501.96 and84.923.15 1/KΩ in group I, II and III respectively). This starting lower TFC in group III continued till 12 hours with statistically significant values at 30 minute, 1, 6 and 12 hour respectively was due to that Group III patients had a lower starting TFC than the other groups.
Duration of mechanical ventilation ranged between 13.0-34.0, 12.0-34.0 and 12.0-31.0 with the means of 24.426.57 days, 20.337.34 days and 21.675.65 days for group I, II and III respectively. There were no statistical significant differences between the studied groups. Mortality was reported in 5(20.0%), 4 (16%) and 4 (16%) patients for group I, II and III respectively. There were no statistical significant differences between the studied groups regarding mortality.
from this study we concluded that:
1. Recruitment maneuver is used only if there is resistant hypoxemia in spite of using conventional lung protective strategy in hemodynamically stable patient and no barotraumas.
2. Recruitment with BiPAP (Recruit BiPAP) and recruitment with CPAP (Recruit CPAP) leads to more significant decrease in FiO2, more decrease in thoracic fluid content and more increase of oxygen saturation compared to conventional lung protective strategy alone.
3. Recruit BiPAP is better than Recruit CPAP because it has less hemodynamic changes; more ever it facilitates to lower the maintenance PEEP level more significantly than Recruit CPAP.