Prognostic Value of Lung Ultrasound in Predicting Intensive Care Unit Length of Stay in Adult Cardiac Surgery

Being easy, bedside, non-expensive, noninvasive and radiation free, there has been a growing interest in the implementation of lung ultrasound in critical care management in the last decade, cardiac surgery was not an exception in both adult and pediatric surgeries Many predictors for open heart surgery outcomes have been studied in past years including The Society of Thoracic Surgeons (STS) risk score and the EuroSCORE (ES), preoperative clinical condition, associated chronic diseases, type of surgery, age, duration of cardiopulmonary bypass and brain natriuretic peptide (BNP), cystatin-C A recent study described the use of a novel postoperative lung ultrasound score scanning for B lines which denote subpleural interstitial edema in various lung regions for predicting critical care length of stay in pediatric cardiac surgeries.

The objective of the current study is to evaluate the role of the new lung ultrasound score in predicting the length of postoperative intensive care stay after adult open heart surgeries.

After approval of the local institutional ethics committee and local institutional review board. All patients scheduled for open heart surgery in Fayoum university hospital starting from August 2020 will be enrolled in this prospective observational study until fulfilling sample size. A detailed informed consent will be signed by the eligible participants before recruitment ANESTHETIC TECHNIQUE All patients will be preoperatively assessed and investigated by complete blood count, coagulation profile, Liver and kidney functions and serum electrolytes. Chest X-ray, Electrocardiography (ECG) and echocardiography will be routinely done. Coronary angiography and carotid arterial duplex will be requested if needed.

Patient will be premedicated by 10 mg morphine intramuscularly at morning of the operation. Prior to induction of anesthesia, standard monitoring will be applied including a five-lead electrocardiography system, a pulse oximeter probe. A peripheral intravenous (IV) cannula will be placed. An arterial will be inserted using a 20 G cannula either right or left radial artery under local anesthesia. After pre-oxygenation, general anesthesia will be induced using midazolam 2-5 mg, fentanyl (3-10 μg/kg), propofol (1-1.5 mg/Kg), followed by atracurium (0.5 mg/kg).

After trachea intubation, patients will be mechanically ventilated with oxygen in air so as to achieve normocarbia. A main stream capnogram, an esophageal temperature probe and a Foley catheter will also be placed. A triple-lumen central venous catheter will be placed usually through the right internal jugular vein.

Maintenance of anesthesia will be achieved by inhaled Isoflurane 0.4 to 1% and atracurium infusion at a rate of 0.5 mg/kg/h. After initiating extracorporeal circulation, Propofol infusion at a rate of 50-100 µg/kg/min will be added to replace isoflurane inhalation.

Patients will receive intravenous heparin (300-500 IU/kg body weight) before the initiation of cardiopulmonary bypass (CPB) to achieve an activated clotting time (ACT) of more than 480 seconds. Cardiopulmonary bypass was instituted with the use of a non-pulsatile blood flow at 2.4 L/min/m2, a non-heparin-coated circuit, and a membrane oxygenator. Mean arterial pressure will be adjusted to exceed 60mmHg before, during and after cardiopulmonary bypass (CBP) . Cardiac arrest will be induced using St Thomas crystalloid solution (Hamburg). Lactated Ringer's solution will be added to the CPB circuit to maintain reservoir volume if needed, and packed red blood cells will be infused when hemoglobin level drops to less than 7g/dl. After rewarming the patient to 37°C and weaning from CPB; Protamine sulfate will be used to reverse the effect of heparin.

After skin closure and wound dressing, patients will be transferred to the intensive care unit intubated with manual ventilation and full monitoring during transfer.

Intensive care Tracheal extubation will be performed when the patient meets the following criteria: awake or arousable, hemodynamically stable, no ongoing active bleeding, warm extremities, no electrolyte abnormalities, no or minimal inotropic support and a satisfactory arterial blood gas with a fraction of inspired oxygen (FiO2) \< 0.5, Ventilator pressure support reduced to 10 CmH2O with Positive End Expiratory Pressure (PEEP) 5-7 CmH2O.

ICU management and decisions will be left to the intensivist who is responsible of the postoperative cardiac critical care.

Patient will be discharged from ICU when the following criteria are met: Awake patient with oxygen saturation (SpO2) \< 90% at FIO2 \> 0.5 by facemask, adequate cardiac stability, no intravenous inotropic or vasopressor supportive therapy, no hemodynamically significant arrhythmia, not dependent on epicardial external pacing no major bleeding i.e. chest tube drainage less than 50 ml/h, urine output of more than 0.5 ml/kg/h and no vital threats to other organ systems such as kidneys and liver.

Lung Ultrasound scan (LUS) All patients will be examined at 12 hours postoperatively as per our institution routine using a convex ultrasound probe, any other LUS will be done upon demand.

LUS will be performed by an experienced radiologist according to standardized protocols.

This will be used to calculate total LUS-score (calculated as a sum of all quadrants score) and individual areas score.

Sample size was calculated using (G power). Minimal sample size of patients was 191 needed to get power level 0.80, alpha level 0.05 (two tailed) and 0.20 as expected β (slope of regression line) for predicting intensive care Length of stay .

Data management will be performed using the Statistical Package for Social Sciences (version 22.0; SPSS Inc., Chicago, IL, USA). Descriptive statistics (mean, standard deviation for quantitative data, and number and percentages for qualitative data) will be used to summarize the data. Nominal data will be analyzed using simple chi squared test, while independent sample t-test or one-way ANOVA procedure will be used to compare means for two or three groups of cases, respectively. Regression analysis will be performed to determine the predictors for LOS. A probability value (P value) ≤ 0.05 is considered significant.

Eligibility Criteria:
Inclusion Criteria:

* all patients Scheduled for elective cardiac surgery for valve replacement, CABG or adult congenital (VSD or ASD) via median sternotomy

Exclusion Criteria:

* subjects with inadequate acoustic windows or incomplete examinations (as defined below),
* Patients with emergency surgeries.
* Patients with thoracic deformities or preexisting pulmonary pathology