The goal of this observational study is to learn about the performance of a new index for hypotension prediction during the immediate postoperative period of cardiac surgery patients in the intensive care unit. The main questions it aims to answer are:

1. Is this new index, Hypotension Prediction Index, able to predict hypotension during the immediate postoperative period in cardiac surgery patients in the intensive care unit?
2. How frequent hypotension is during the immediate postoperative period of cardiac surgery patients in the intensive care unit? Participants will not receive any treatment beyond the usual clinical practice during the study. All patients will have an invasive arterial line that is part of the usual clinical practice. This arterial line is connected to a pressure transducer for continuous measurement of arterial pressure. A transducer equipped with the necessary technology to calculate the hypotension prediction index will be used instead of the usual transducer. An echocardiogram will be performed in every patient in the study. This test is done frequently in patients after a cardiac surgery.

A non-interventional study will be performed, in which physiological signals will be acquired using usual clinical practice monitoring devices. These devices will be connected to catheters that are used as a routine management of the study patients. No management indication will be performed as part of the study.

The patients who accepted to participate in the study by previously signing the informed consent, will be received at the intensive care unit coming from the surgical room after a programmed cardiac surgery and once stability is ensured, investigators will proceed to connect an arterial pressure catheter that is routinely inserted into the radial artery to an Acumen IQ sensor (Edwards Lifesciences, Irvine California, USA). This sensor replaces the pressure transducer normally used in clinical practice, has similar characteristics and its use does not interfere with the usual routine. This sensor will be connected to the multiparametric monitor situated at the patient's bedside and to the Hemosphere monitoring platform (Edwards Lifesciences, Irvine California, USA). Besides being used as a pressure transducer, the Acumen IQ sensor allows for a more detailed arterial pressure signal analysis together with the Acumen Hypotension Prediction Index software. This software automatically calculates every 20 seconds the HPI, the main study parameter of this project, which as previously mentioned predicts hypotension episodes (defining hypotension as mean arterial blood pressure below 65 mmHg for at least 1 minute). Besides the HPI, the Acumen Hypotension Prediction Index software calculates complementary hemodynamic monitoring parameters that can help managing patients with different conditions among which there an be found the moderate and high risk postoperative conditions. These parameters are: stroke volume, stroke volume variation, mean arterial pressure, dP/dt (the maximal of the first derivative during the ascending phase of the arterial pressure - time curve, related to the left ventricular contractility), cardiac index, systemic vascular resistance and arterial dynamic elastance (the ratio between the pulse pressure variation and the stroke volume variation, which allows to evaluate the afterload).

The study time will be 12 hours (counting from the moment of the beginning of the patient monitoring in the intensive care unit), during which, besides the parameters calculated by the Acumen Hypotension Prediction Index, monitoring clinical and analytical routine parameters will be collected as furtherly detailed. Moreover, a transthoracic echocardiogram will be routinely performed during the first 6 hours of the patient's stay in the intensive care unit. This is a noninvasive procedure and will not interfere with the patient's usual care.

The HPI will not be shown on the monitoring platform to avoid any influence on the normal clinical practice and to be able to measure the real incidence of hypotension episodes. The complementary parameters calculated by the software will be available to the treating physician and can be used for decision making based on his criteria. The results of the echocardiogram will be available as well to the treating physician and will be interpreted and used based on treating physician criteria.

As described, besides the evaluation of the HPI performance, the results of this study will allow to have information regarding the behavior of arterial pressure in cardiac surgery postoperative patients and the creation of a protocol to reduce hypotension in these patients.

Variables

The following variables will be studied:

• Epidemiologic: age, sex, weight, height.
• Severity and risk assessment and classification systems: APACHE II, EUROSCORE II, Sequential Organ Failure Assessment Score (SOFA), Simplified Acute Physiology Score III (SAPS III)
• Risk factors: renal failure, hypertension, diabetes, dyslipidemia
• Surgery: type, total surgery time, circulatory bypass time, ischemia time
• Monitoring: HPI, arterial pressure (mean, systolic, diastolic), stroke volume variation, pulse pressure variation, dynamic arterial elastance, dP/dt, cardiac index, central venous pressure, at admission and 12h later, besides variability analysis of these parameters. Continuous arterial pressure register will be analyzed and mean arterial pressure below 65 mmHg will be determined, normalized by the monitoring time.
• Hypotension treatment: fluid bolus, vasoactive and inotropic types and doses. This management will be performed according to physician criteria.
• Echocardiographic variables: right ventricle (RV) diameter /left ventricle (LV) diameter, Tricuspid Annular Plane Systolic Excursion (TAPSE), S wave, RV/LV ratio, pulmonary artery systolic pressure (PASP) estimation, LV ejection fraction, Left Ventricular Outflow Tract Velocity Time Integral (LVOT VTI), Right Ventricular Outflow Tract Velocity Time Integral (RVOT VTI), Pulmonary Velocity Acceleration Time (PVAT), inferior vena cava (IVC) diameter.
• Mechanical ventilation at admission and 12h later: positive end expiratory pressure (PEEP), FiO2 - Fraction of inspired oxygen (FiO2), tidal volume (VT), respiratory rate, mean pressure, plateau pressure, peak pressure.
• Blood analysis: hemoglobin, leukocytes, lymphocytes, arterial blood gas parameters, renal function, ferritin, D-dimer, interleukin 6 (IL-6), peak creatin kinase (CK), creatin kinase myocardial band (CK-MB), troponin I, brain natriuretic peptide (BNP).
• Clinical results: ICU length of stay, hospital length of stay, mechanical ventilation time, vasoactive support, and mechanical ventilation. Acute kidney failure development, peak troponin I, perioperative acute myocardial infarction, mortality, stroke, evolutive SOFA, other complications (sepsis)

Data Analysis

The adequate analytic and statistical methods will be used to:

• Describe arterial pressure and complementary hemodynamic variables behavior
• Evaluate HPI performance predicting hypotension in the postoperative cardiac surgery period in the intensive care unit
• Create a predictive model for hypotension development in the cardiac surgery postoperative period
• Analyze the relationship between postoperative hypotension and complications development.

Inclusion Criteria:

• age ≥ 18 y.o.
• Programmed cardiac surgery
• Hemosphere platform availability
• Signed informed consent

Exclusion Criteria:

• Need for circulatory or respiratory mechanical assistance device support
• Urgent/emergent surgery

Consecutive patients in the postoperative period of programmed cardiac surgery, who are admitted to the intensive care unit after the surgery. according to inverstigator and Hemosphere monitor disponibilty

In this study exists a potential generation of intellectual property generation.