Preoperative Ultrasound-based Protocol for Optimization of Fluid Therapy to Prevent Early Intraoperative Hypotension

Background: Intraoperative hypotension increases 30-day mortality and the risks of myocardial injury and acute renal failure. Patients with inadequate volume reserve before the induction of anesthesia are highly exposed. The identification of latent hypovolemia is therefore crucial. Ultrasonographic measurement of the inferior vena cava collapsibility index (IVCCI) is able to detect volume responsiveness in circulatory shock and growing evidence support the theory that higher IVCCI can predict intraoperative hypotension.

The aim of the present study is to evaluate the potential benefit of an ultrasound-based protocol for preoperative fluid optimization. The investigators will perform a randomized-controlled study involving elective surgical patients. An ultrasound-based protocol (USP) arm and a conventional fluid therapy group (CFT) are to be formed. Ultrasound examinations will be performed twice in both groups: 2 hours and 30 minutes preoperatively. The inferior vena cava and the anterior lung fields will be scanned. In the USP group the participants will receive fluid therapy according to the ultrasonographic findings: high level of IVCCI and absence of signs of pulmonary edema will indicate fluid therapy. In the CFT group the attending anesthesiologist (blinded to the results of ultrasonography) will order fluid therapy on the basis of daily routine and clinical judgement.

The investigators will evaluate the incidence of intraoperative hypotension (primary outcome), postoperative metabolic status and organ functions and the amount of the administered intravenous fluids in both groups.

A randomized-controlled study with 80 participants.

The investigators will use computer-generated unpaired random allocation method to an ultrasound-based protocol (USP) group or to the conventional fluid therapy (CFT) group.

Preoperative ultrasound examinations will be performed twice in both groups: 2 hours and 30 minutes preoperatively. The inferior vena cava and the lung fields (so called BLUE - Bedside Lung Ultrasound in Emergency - points: 2nd or 3rd intercostal space anterior, 5th-6th interspace anterior and posterior axillary line position) will be scanned. The collapsibility index (IVCCI) of the IVC is calculated, \>40 percent is considered 'high IVCCI'. Lung ultrasound (LUS) is evaluated as indicative for 'lung congestion' if symmetric anterior B-profiles (at least 3 B-lines in anterior lung fields) are detected.

Baseline demographic (age, sex, height, weight) and comorbidity data (history of hypertension, chronic heart failure, coronary or cerebrovascular disease, respiratory illness e.g. COPD, past COVID, diabetes on insulin treatment) together with laboratory data (haemoglobin, creatinine, blood urea) are to be recorded.

A standardized practice of monitoring and induction of general anesthesia will allow for the detection of immediate and early (first 10 minutes of anesthesia) hypotensive events. A follow up for 24 hours is necessary for evaluating the fulfillment of secondary endpoints. A semi-quantitative lung ultrasound after 24 hours will estimate lung aeration.

Eligibility Criteria:
Inclusion Criteria:

Elective surgery

* General surgical procedures
* Estimated duration of anesthesia \> 60 minutes
* ASA class 2 or 3

Exclusion Criteria:

* Emergency procedure
* Reoperation, redo procedure
* Patient who is incapable of acting
* Uncontrolled hypotension (\<90 mmHg)
* Uncontrolled hypertension (\>180 mmHg)
* High risk valvular disease (Aortic Stenosis)
* Endocrine hypertension (Conn's syndrome, phaeochromocytoma)
* Sepsis (infection and SOFA≥2 pt)
* Conditions blocking lung ultrasound (pneumothorax without drainage, former pulmonary resection, pleural effusion affecting more than 2 interspaces)
* Pregnancy