Management of Post-Induction Hypotension in Emergency Abdominal Surgery

Post-induction hypotension is a frequent and clinically significant event in patients undergoing emergency abdominal surgery, where baseline hemodynamic instability and reduced physiological reserve are common. The combination of absolute or relative hypovolemia, systemic inflammation, sepsis, and the cardiovascular depressive effects of anesthetic drugs increases the likelihood of early intraoperative hypotension. Preventing and promptly correcting this hemodynamic deterioration is essential, as sustained hypotension has been associated with renal injury, myocardial ischemia, and increased postoperative morbidity.

Ephedrine has historically been used as the first-line agent for anesthesia-induced hypotension because of its mixed α- and β-adrenergic activity. However, concerns regarding tachycardia, variable efficacy, and diminished responsiveness in catecholamine-depleted states have encouraged interest in using diluted norepinephrine as an alternative. Low-dose norepinephrine boluses provide predominantly α-adrenergic vasoconstriction with minimal chronotropic effect, offering a potentially more stable hemodynamic profile. Recent evidence from obstetric and non-obstetric anesthesia suggests that norepinephrine may be effective in restoring blood pressure while reducing heart rate fluctuations.

This randomized double-blind study was designed to compare norepinephrine boluses with ephedrine boluses for the management of anesthesia-induced hypotension in the specific setting of emergency abdominal surgery. The study aims to better characterize the hemodynamic response to each drug in a high-risk population frequently presenting with metabolic disturbances, fluid deficits, and variable sympathetic tone. By evaluating the need for repeated vasopressor administration and the rapidity of blood pressure restoration, the study seeks to determine whether norepinephrine may offer superior intraoperative stability compared with the traditional use of ephedrine. The findings may contribute to optimizing vasopressor strategies in emergency surgical anesthesia and reducing short-term hemodynamic complications.

Conditions Conditions: Post-induction Hypotension Keywords: norepinephrine ephedrine post-induction hypotension general anesthesia abdominal emergency Study Design Study Type: Interventional The intraoperative protocol begins with standard patient preparation including verification of the pre-anesthesia checklist and initiation of monitoring with ECG, pulse oximetry and non-invasive blood pressure measurements at 3minute intervals. Three baseline hemodynamic measurements are recorded and averaged to establish reference values, while two 18G peripheral venous lines are secured for fluid and medication administration. Preload status is assessed using ultrasound measurement of inferior vena cava collapsibility, with crystalloid fluid administration of 10-20 mL/kg initiated if the collapsibility index exceeds 40-50%. Following preoxygenation with 100% FiO2, rapid sequence induction is performed using propofol 2-5 mg/kg and succinylcholine 1 mg/kg, followed by endotracheal intubation confirmed by capnography. Anesthesia maintenance consists of propofol infusion at 6-12 mg/kg/h, fentanyl 2-3 μg/kg for analgesia, and intermittent cisatracurium for neuromuscular blockade, with mechanical ventilation parameters set to 6-8 mL/kg tidal volume and 16-25 breaths per minute targeting end-tidal CO2 of 35-45 mmHg. Hypotension, defined as SBP <90 mmHg, MAP <65 mmHg or a 20% decrease from baseline, is managed with 2 mL boluses of the study drug (either 6 mg ephedrine or 10 μg norepinephrine) repeated after 1 minute if needed, with escalation to norepinephrine infusion at 0.25 mg/mL for refractory cases. Hemodynamic parameters are recorded every 3 minutes for the first 20 minutes post-induction and every 5 minutes thereafter, with documentation of hypotensive episodes, vasopressor requirements, and any adverse hemodynamic events including hypertension, bradycardia or tachycardia. The procedure concludes with extubation when standard criteria are met and transfer to the post-anesthesia care unit for continued monitoring.

Statistical Analysis: Data entry and analysis will be performed using SPSS software (version 25.0). Graphical representations will be prepared using Microsoft Excel 2019.

Descriptive Analysis: Normally distributed continuous quantitative variables will be summarized as mean ± standard deviation. Non-normally distributed continuous variables will be reported as median and interquartile range [IQR: 25%-75%]. Categorical variables will be presented as absolute frequencies (n) and relative frequencies (%).

Analytical Analysis: Associations between two categorical variables will be assessed using Pearson's chi-square test when conditions are met; otherwise, Fisher's exact test will be applied. For comparisons between a categorical and a normally distributed quantitative variable, Student's t-test will be used, while the Mann-Whitney U test will be employed for non-parametric data. A significance level of p < 0.05 will be considered statistically significant. In multivariate analysis, risk estimates will be expressed as odds ratios (OR) with 95% confidence intervals (95% CI).