Effect of Pre-operative Intravenous Crystalloids on Post-Induction Blood Pressure

Theoretical framework Hypotension during surgery directly impacts patients` postoperative outcomes and complications. Decrease in blood pressure measurements secondary to anesthetic drugs is an expected scenario in most surgical cases. Moreover, hypovolemia secondary to fast pre-operative period may facilitate post- induction hypotension which can be compensated by fluid bolus pre- operatively. Our purpose is to conduct a randomized intervention cohort study using pre- operative fluid therapy to assess its effect in blood pressure during the post- induction period. Methods We will conduct a randomized intervention cohort study using pre-operative fluid therapy to assess its effect on blood pressure during the post-induction period. The intervention group will receive a balanced crystalloid solution bolus within 60 (+/-15) minutes before induction of anesthesia. The control group will be treated according to the current clinical standard of care. We will compare the time-weighted average (TWA) mean arterial pressure (MAP) under 65 mmHg during the first 20 minutes after anesthetic induction or until surgical incision (whichever comes first). Discussion According to the literature, hypotension after induction of general anaesthesia mainly depends on age, pre-existing arterial hypertension, and diabetes mellitus. Consequently, it occurs frequently and contributes to adverse perioperative outcomes. One potential intervention mitigating this effect is the administration of pre-operative fluid, which is often prescribed. This simple intervention can easily be done by various healthcare providers, and neither is cost-intensive, nor combined with additional effort. However, there is no consensus for using pre-operative fluids to prevent post- induction hypotension because of a lack of evidence and adequately conducted studies. This appropriately powered study will deliver this answer and can improve perioperative outcomes through a simple intervention.

Low blood pressure shortly after the start of general anaesthesia is a common problem during major surgery. This drop in blood pressure can reduce blood flow to vital organs such as the heart, brain, and kidneys, and is linked to complications after surgery. Because of this, doctors often try to prevent low blood pressure by giving patients intravenous fluids before anaesthesia begins. However, it has remained unclear whether this approach is truly effective, especially in patients who already have an increased risk due to heart or vascular disease. In this study, we investigated whether giving a standard fluid infusion shortly before surgery can reduce the occurrence or severity of low blood pressure after anaesthesia is started. We focused on adult patients aged 45 years and older who had cardiovascular risk factors and were scheduled for major surgery, excluding the heart. The study was carried out as a carefully designed clinical trial at two Austrian university hospitals. Patients were randomly assigned to one of two groups. One group received a fluid infusion in the vein within about one hour before anaesthesia, while the other group received standard care without planned extra fluids. We closely monitored blood pressure during the first minutes after anaesthesia, a period when dangerous drops in blood pressure are most likely to occur. We then compared how long and how severely blood pressure fell below a commonly accepted safety threshold. More than 500 patients were included in the final analysis. The results were clear: patients who received extra fluids before surgery did not have better blood pressure control after anaesthesia than those who received standard care. In other words, giving fluids in advance did not reduce low blood pressure during this critical early phase. These findings are important for everyday clinical practice. They suggest that routinely giving intravenous fluids before surgery is unlikely to prevent low blood pressure in high-risk patients. This means that doctors may need to focus more on other strategies, such as careful choice of anaesthetic drugs, closer monitoring, or timely use of medications that support blood pressure.