Human albumin is a widely used additive in cardiopulmonary bypass all around the world, but its effect on various outcomes has been debated. The goal of this observational study is to compare the effect of 100 ml 20% human albumin addition to cardiopulmonary bypass on pleural effusion development after open heart surgery.

The main question it aims to answer is:

• Does albumin, in addition to cardiopulmonary bypass, reduce pleural effusion development after open heart surgery? Patients will go under elective open heart surgery. Investigators will compare pleural effusion volume on the first day after surgery between patients who received albumin and those who didn't.

This study constituted a prospective single-center randomized controlled trial conducted at the Center of Cardiac Surgery within Pauls Stradins Clinical University Hospital, Riga, Latvia. The study received approval from the State Agency of Medicines of the Republic of Latvia on September 20, 2021 for a drug usage observation study and the medical ethics committee of Pauls Stradins Clinical University Hospital (Chairperson Prof P. Stradins) under reference number 260821-11L, dated August 26, 2021. All participants provided written informed consent before enrolment.All participants provided written informed consent before enrolment.

The study targeted 70 individuals scheduled for elective open-heart surgeries, encompassing procedures such as ascending aorta surgery, coronary artery bypass grafting, and heart valve replacement or repair, either independently or in combination, without the use of hypothermic circulatory arrest. Investigators did not include patients with a history of reduced left ventricular ejection fraction (EF < 50%), chronic kidney disease, chronic lung disease, pre-existing anemia, and pathological chest X-ray findings before surgery. Random allocation into the two groups-those receiving an additional 100 ml of 20% human albumin and those receiving standard CPB priming solution-was done in a 1:1 ratio.

Interventions The standard CPB priming volume of 1050 ml, comprising isochloremic solution Deltajonin® and 250 ml of 15% Mannitol, was used. The study group replaced 100 ml of Deltajonin® solution with 100 ml of 20% human albumin. Investigators used cold crystalloid cardioplegia in all cases. Patients were mechanically ventilated according to the local protocol using FiO2 - 0.6, 6 ml/kg tidal volume, and PEEP was set at five mmHg. After extubation, oxygen was administered via a non-rebreathing face mask at a flow rate of 10 l/min. Blood gas analysis (pO2, pCO2, FiO2/O2 ratio, A - a gradients, Lactate) was conducted following the local protocol. Serum albumin levels were measured preoperatively, 6 and 12 hours post-operation. Normal albumin was defined as ≥35 g/L, mild 30-35 g/L, moderate 25-30 g/L and severe hypoalbuminemia as <25 g/L. Colloid oncotic pressure (COP) was calculated using the formula by J C Hoefs: COP = A (1.058 G + 0.163 A + 3.11).

Thorax CT scans were performed on all patients on the first postoperative day, with subsequent image analysis conducted by a single radiologist. The radiologist measured pleural effusion size (cm), and investigators calculated effusion volume (ml) using the formula Volume = 0.365 × b^3 - 4.529 × b^2 + 159.723 × b - 88.377 by Hazlinger et al. Where b is the maximum effusion depth measured in the axial (transverse) imaging plane. If patients were hemodynamically unstable with ST-segment abnormalities, investigators refused their transportation to a CT scan.

The primary outcomes were the effect of albumin addition on serum albumin level in the early postoperative period and the development of pleural effusion.

The secondary outcome measure was the effect of albumin addition on respiratory function, measured by blood gas analysis, in the early postoperative period.

Inclusion Criteria:

• Individuals scheduled for elective open-heart surgeries, encompassing procedures such as ascending aorta surgery, coronary artery bypass grafting, and heart valve replacement or repair, either independently or in combination, without the use of hypothermic circulatory arrest.

Exclusion Criteria:

• reduced left ventricular ejection fraction (EF < 50%),
• chronic kidney disease,
• chronic lung disease,
• pre-existing anemia,
• pathological chest X-ray findings before surgery.