Evaluation and management of intravascular volume are a central challenge for the critical ill patients. Hypotensive patients are commonly resuscitated with intravenous crystalloid fluid as a recommendation for treatment of many shock states.

There has been a growing interest in the implementation of lung ultrasound in critical care management in the last decade as it is easy, bedside, non-expensive, non invasive and radiation free.

The object of the current study is to assess the ability of lung and inferior vena cava sonography versus pulse pressure variation to predict fluid responsiveness in patients with circulatory failure on mechanical ventilation.

The study will be conducted in intensive care units of Fayoum University Hospitals after approval of the local institutional ethics committee and local institutional review board. Hypotensive Patients on mechanical ventilation starting from August 2022 will be enrolled in this prospective study until fulfilling sample size. A detailed informed consent will be signed before recruitment. All patients who fulfilled inclusion criteria will be monitored by: 6 leads ECG, Blood pressure, Urinary catheter for urine output, Pulse oximter.Lung ultrasound (LUS), Inferior vena cava ultrasound (IVC US) and pulse pressure variation (PPV) will be done to every patient in the study. The Consolidated standards of Reporting Trials (CONSORT) recommendation will be followed. LUS and IVC measurements were performed by using a convex ultrasound probe (Philips clear vue350, Philips healthcare, Andover MAO1810, USA, Machine ID: 1385). LUS will be performed by an experienced radiologist according to standardized protocols. For each hemi-thorax 3 main areas (anterior (Ant), lateral (Lt) and posterior (Post)) marked by the para-sternal, anterior axillary and posterior axillary lines for a total of 28 sectors will be identified. Each one will be divided into upper and lower halves, making a sum of 6 different quadrants for each side: anterior superior, anterior inferior, lateral superior, lateral inferior, posterior superior, posterior inferior. Ultrasound examination of the anterolateral chest was carried out with longitudinal scan of the right and left hemi thoraces, from the second to the fourth (on the right side to the fifth) intercostal space, as previously described. For each quadrant a score will be assigned based on B lines which are defined as an echogenic artifact with a narrow origin on the pleural line, deepening to the inferior border of the screen and coherent with respiratory movements indicating subpleural interstitial edema as follows:

(0) Normal aeration: A lines with lung sliding or fewer than two isolated B lines

1. Moderate loss of lung aeration: well-defined, multiple B lines.
2. Severe loss of lung aeration: multiple coalescent B lines.
3. Complete loss of lung aeration or lung consolidation. This will be used to calculate total LUS-score (calculated as a sum of all quadrants score) and individual areas score (Ant, Lt and Post).

IVC US: The inferior vena cava was explored in the subxiphoid window in its sagittal view-just below the junction between the inferior vena cava and suprahepatic veins which lie approximately 0.5 to 3 cm from the right atrium, following the American Society of Echocardiography guidelines.; The (IVC distensibility index (dIVC) was calculated as (maximum diameter - minimum diameter)/minimum diameter.

PPV: patients will be temporarily sedated and paralyzed and on fully controlled mechanical ventilation. No spontaneous breathing effort will be detected on the mechanical ventilator waveform monitor ensuring that the respiratory changes in arterial pressure reflected only the effects of positive pressure ventilation. Modes of ventilation is selected to volume or pressure controlled ventilation, depending on the decision of the primary physicians. A tidal volume will be not less than 8 ml/ kg (predicted body weight). The preset respiratory rate will be at 14 breath/min. Positive end expiratory pressure (PEEP) will be between 8 and 10 cmH2O. The plateau pressure was kept at below 30 cmH2O. In all patients, radial artery cannulation will be done for invasive blood pressure monitoring (using a 20 G cannula), PPV is calculated directly on Nihon Kohden monitores at base line.

• Sample size: Sample size was calculated using MedCalc Statistical Software version 20 (MedCalc Software, Ostend, Belgium. Minimal sample size of patients was 118 patients with 59 responsive cases and 59 non-responsive cases. Calculation is guided by AUC of 0.915 obtained from a study in comparison to a null value of 0.8, with alpha of 0.05 and power of 90%. Sample size will be increased to 150 patients to increase precision and ensure that at least 59 responsive and 59 non-responsive cases are included.

• Statistical analysis: Data will be collected and coded using Microsoft Excel and data analysis will be performed using IBM SPSS version 28 for Windows. Descriptive statistics will be presented in the form of numbers and percentages of categorical data, while means with standard deviations or medians with interquartile ranges will be used for numerical data variables. ROC curve will be used to estimate the appropriate cut off point for the inferior vena cava distensibility index, and for the lung ultrasound score. Area under the curve (AUC) will be reported and will be used to compare the diagnostic ability of different tests. Sensitivity, specificity, positive predictive value and negative predictive value will be reported with the 95% confidence intervals. P-value < 0.05 will be considered statistically significant.

Inclusion Criteria:

• Patients on mechanical ventilation (MV).
• Aged more than 18 years.
• Mean arterial pressure (MAP) less than 65 mmHg or systolic arterial pressure less than 90mm Hg with signs of hypoperfusion (urinary flow < 0.5mL/kg/ h for > 2hr , tachycardia > 100 beats/min, or presence of skin mottling , and seurm lactate more than 2 mmol/L).

Exclusion Criteria:

• Cardiac arrhythmias.
• Previously known significant valvular disease or intracardiac shunt.
• Chest drains.
• Increasing intra abdominal pressure.
• Prephiral vascular disesaes.
• Adult respiratory distress syndrome (ARDS) patients due to low tidal volume.
• Interstitial lung disease because B-lines in these conditions are the consequence of the thickened interlobular septa characterizing fibrosis and are not modified by the state of hydration or imbibition 12
• Any contraindication for fluid administration as cardiogenic shock, acute pulmonary edema or LVEF% less than 50%.
• Renal patients with oliguria and volume overload including patients on hemodialysis or patients with acute anuric renal failure.
• Patients with lower extremity artery/vein thrombosis, significant lower extremity artery plaque, lower extremity artery occlusion, inferior vena cava filter implantation and lower extremity varicose veins.