Does a Preop Fluid Bolus Prevent Post-Induction Hypotension?
A lot of us were trained to "tank up" patients before induction. The idea is simple. Patients come in after fasting, induction drugs drop vascular tone, so a liter of crystalloid in preop should soften the blood pressure drop. A randomized trial published online in Anesthesiology on September 25, 2026 tested that idea directly, and it did not hold up.
What the study did
Investigators at the Medical University of Graz and the Medical University of Vienna enrolled adults 45 and older with cardiovascular risk factors who were having major noncardiac surgery under general anesthesia. Patients were randomized to a crystalloid bolus given within about an hour before induction or to standard care. The primary outcome was the time-weighted average of mean arterial pressure below 65 mmHg in the first 20 minutes after induction, or until incision.
They analyzed 504 patients, 247 in the bolus group and 257 in the standard care group. There was no significant difference. The median time-weighted average below 65 mmHg was 0.0 mmHg in both groups, with interquartile ranges of 0.0 to 0.56 and 0.0 to 0.84 (p = 0.368). The authors concluded that giving crystalloid before surgery does not prevent post-induction hypotension.
How I read it
First, notice how low the numbers were in both arms. The median was zero in both groups, so at least half the patients in each arm never dropped below a MAP of 65 in that early window. That tells me the induction and early management in this trial were already pretty careful. A preop bolus has a hard time adding much on top of good technique, titrated induction doses, and a vasopressor that is ready to go.
Second, the result fits what we know about crystalloid. A good share of a bolus leaves the vascular space fairly quickly, and fasting alone does not leave most elective patients as dry as we used to assume, especially now that clear liquids are allowed closer to surgery. Post-induction hypotension is mostly about vasodilation and reduced sympathetic tone, not an empty tank.
Third, the fluid is not free. Extra volume adds up over a long case, and in patients with heart failure or kidney disease it can work against us. If the bolus does not buy better pressures, I would rather spend that volume where it actually helps.
What I take into the OR
For patients like the ones in this trial, I do not think a routine preop bolus is the answer to induction hypotension. What helps more is thinking about it ahead of time: reviewing home medications like ACE inhibitors and ARBs, dosing induction agents for the patient in front of me rather than by weight alone, having phenylephrine or norepinephrine drawn up, and treating low pressures early instead of waiting them out. Patients who are truly volume depleted from bowel prep, vomiting, or bleeding are a different situation and still need fluid.
One limit to keep in mind is that this was a single study at two centers in Austria, and it was single blinded. It also looked at the first 20 minutes, not at longer term outcomes. Still, it is a well sized randomized trial on a habit many of us have, and it gives a clear answer for this group of patients.
Source
- Eichinger M, Reiterer C, Eichlseder M, et al. Effect of Pre-operative Intravenous Crystalloid Bolus on Post-Induction Blood Pressure: a randomized blinded intervention trial. Anesthesiology. Published online September 25, 2026. DOI: 10.1097/ALN.0000000000006308 · Abstract (Medical University of Graz)
This post is clinician commentary for educational discussion. It is not medical advice for any reader's personal care. Anesthesia and perioperative decisions should be made with the treating clinician based on the individual patient's circumstances.