Comparative Study Between Airway Pressure Release Ventilation and Pressure Regulated Volume Control (PRVC) in Protective Lung Strategy as a Recruitment Maneuver for Severe ARDS Mechanically Ventilated Patients Using Lung Ultrasound Score

Acute Respiratory distress syndrome (ARDS) is the most severe form of acute lung injury (ALI) which still has high rates of morbidity and mortality. Mechanical ventilation is still the backbone of patient management. One of the newly developed and successfully used strategies in patients with ARDS is lung protective strategies (LPS). However, use of low tidal volumes during LPS may be associated with atelectasis due to decreased alveolar inflation.

In acute respiratory distress syndrome (ARDS) patients, a recruitment strategy combines recruitment maneuvers (RMs) and positive end-expiratory pressure (PEEP) to prevent atelectrauma. Recruitment maneuvers are a voluntary strategy for effecting a temporary increase in trans-pulmonary pressure (PL), which in turn should reopen those alveolar units that are either poorly aerated or not aerated at all. PEEP may decrease ventilator-induced lung injury (VILI) by keeping those lung regions open that may otherwise collapse The Open lung approach is another ventilatory strategy complementary with the concept of protective ventilation. Lachmann was the first who introduced the open lung concept combining a lung recruitment maneuver (RM) with a sufficient level of PEEP. Recruitment maneuvers minimize the impact of the two known VILI mediators: tidal over distension (i.e., alveoli that receive volume and pressure that exceed their elastic limit) and tidal recruitment (i.e., the repetitive opening and closing of atelectasis during mechanical breathing), Airway pressure release ventilation (APRV) is one of the newly introduced modes in ARDS management. It is a pressure-controlled mode that uses two levels of pressures with inverted ratio ventilation. Release of airway pressure during APRV simulates expiration while elevated baseline pressure improves oxygenation. One of the advantages of this mode is that it allows spontaneous breathing It is considered an alternative, life-saving modality in patients with acute respiratory distress syndrome (ARDS) who struggle for oxygenation. Compared to the classical ventilation, APRV has been shown to provide lower peak pressure, better oxygenation, less circulatory loss, and better gas exchange without deteriorating the hemodynamic condition of the ARDS patient. This mode is believed to help to achieve the target of opening consolidated lung areas (recruitment) and to prevent repeated opening-closing of alveoli (recruitment). However, there still needs to be more and more proof to support this hypothesis. Recently, it has been proposed that the early use of protective mechanical ventilation with APRV could be used preemptively to prevent the development of ARDS in high-risk patients Lung Ultrasound has favorable features to assess RM due to its high specificity and sensitivity to detect lung collapse together with its non-invasiveness, availability, and simple use at the bedside. Ultrasound also has the capability of providing a differential diagnosis between atelectasis and lung consolidation of other origin such as pneumonia. The bilateral distribution of consolidations, presence of static air bronchograms, images of tidal recruitment within consolidation and absence of a companion pleural effusion strongly support the diagnosis of atelectasis. Furthermore, retrospectively the disappearance of the lung consolidation pattern after a RM confirms the diagnosis Acute respiratory distress syndrome (ARDS) is a severe life-threatening lung reaction to various forms of injuries that cause hypoxia. it has been demonstrated that mechanical ventilation by lung protection strategy can be provided in patients with ARDS, resulting in better pulmonary function and higher rates of weaning from the ventilator. lung-protective strategy was associated with improved survival in 28 days and a lower rate of barotrauma in patients with acute respiratory distress syndrome. Protective ventilation was not associated with a higher rate of survival to hospital discharge.

Inclusion criteria

• Age between 18-60 years old.
• Sex: both males and females
• Accepts health volunteers: No
• all Patients who were mechanically ventilated and diagnosed to have ARDS due to sepsis according to Berlin definition.

During the course of the study, a new global definition for ARDS was introduced. To ensure our findings align with the most updated classification, we modified our inclusion criteria to incorporate the new global definition. Patients meeting the Berlin Definition or the new definition were included.

Berlin Definition of the acute respiratory distress syndrome (ARDS) Acute Respiratory Distress Syndrome Timing Within 1 week of a known clinical insult or new or worsening respiratory Symptoms Chest imaging Bilateral opacities - not fully explained by effusion, lobar/lung collapse, or nodules. Origin of edema Respiratory failure not fully explained by cardiac failure or fluid overload need objective assessment (eg, echocardiography) to exclude hydrostatic edema if no risk factor present.

Oxygenation Mild 200 mmHg <Pao2/Fio2 < 300 mmHg with PEEP or CPAP > 5 cmH2O. Moderate 100 mmHg <Pao2/Fio2 < 200 mmHg with PEEP > 5 cmH2O. Severe Pao2/Fio2 < 100 mmHg with PEEP > 5 cmH2O. (Gordon D, et al; 2012). Diagnostic Criteria for the New Global Definition of ARDS Acute Respiratory Distress Syndrome Risk factors and origin of edema Precipitated by an acute predisposing risk factor, such as pneumonia, non-pulmonary infection, trauma, transfusion, aspiration, or shock.

Pulmonary edema is not exclusively or primarily attributable to cardiogenic pulmonary edema/fluid overload, and hypoxemia/gas exchange abnormalities are not primarily attributable to atelectasis. However, ARDS can be diagnosed in the presence of these conditions if a predisposing risk factor for ARDS is also present.

Timing Acute onset or worsening of hypoxemic respiratory failure within 1 week of the estimated onset of the predisposing risk factor or new or worsening respiratory symptoms.

Chest imaging Bilateral opacities on chest radiography and computed tomography or bilateral B lines and/or consolidations on ultrasound* not fully explained by effusions, atelectasis, or nodules / masses.

Oxygenation Non-intubated ARDS Intubated ARDS Modified Definition for Resource-Limited Settings

• PaO2:FIO2<300mmHg or
• SpO2:FIO2<315 (if SpO2<97%) on HFNO with flow of >30 L/min or NIV/CPAP with at least 5 cm H2O end-expiratory pressure Mild:
• 200<PaO2:FIO2<300 mm Hg Or
• 235<SpO2:FIO2<315 (if SpO2<97%)

Moderate:

• 100, PaO2:FIO2<200 mm Hg or
• 148<SpO2:FIO2<235 (if SpO2<97%)

Severe:

• PaO2:FIO2<100 mm Hg or
• SpO2:FIO2<148 (if SpO2<97%) • SpO2:FIO2<315 (if SpO2<97%).
• Neither positive end-expiratory pressure nor a minimum flow rate of oxygen is required for diagnosis in resource-limited settings.

(Matthay MA, et al; 2024).

Exclusion criteria

• Patient refusal
• Patient with advanced cardiac disorders (rheumatic or ischemic).
• Patients with COPD, pneumothorax, surgical emphysema.
• Patients with advanced liver or renal disorders
• Patients with advanced malignancy.
• Female patients during pregnancy.