Comparison of Schnider versus Eleveld models for propofol target-controlled infusion anaesthesia in adult bariatric surgery: A randomised controlled study

Bariatric surgery has emerged as a crucial intervention in the management of morbid obesity

offering significant long-term benefits in terms of weight reduction and improvement of

obesity related comorbidities. However, the anaesthetic management of patients undergoing

bariatric procedures presents unique challenges due to altered pharmacokinetics, increased risk

of airway complications and heightened sensitivity to anaesthetic agents. Inhalational

anaesthesia and total intravenous anaesthesia (TIVA) are both widely used techniques for

inducing and maintaining general anaesthesia. Inhalational agents such as sevoflurane and

desflurane offer ease of administration and rapid titration but may be associated with

postoperative nausea and vomiting (PONV) and environmental pollution. On the other hand,

TIVA—most commonly using propofol with or without adjuncts like remifentanil—provides

a smoother recovery profile, reduced PONV, and better haemodynamic stability in these

patients.

TIVA, especially when delivered via target-controlled infusion (TCI), allows for precise

control of drug concentration at the effect site. This is particularly beneficial in obese patients,

where altered pharmacokinetics can impact drug distribution and metabolism. Propofol a

widely used intravenous anaesthetic, is commonly administered using target -controlled

infusion systems to maintain stable anaesthesia. These systems rely on pharmacokinetics

models to predict drug concentration and guide infusion rates. Amongst the various models

developed the Schnider and Eleveld effect site models are two prominent TCI frameworks

employed in clinical practice. The Schnider model, established earlier, is tailored primarily for

average weight adults, while the more recent Eleveld model is population based and designed

to accommodate a broader range of patient characteristics including age weight and lean body

mass -making it potentially more suitable for obese patients4 which may not be available in all

TCI pumps. Weight correction formula for the same model is CBW=IBW+[0.4×(TBW

IBW). Although the Schnider model uses fixed ke0 while Eleveld uses variable ke0 based on

covariates like age and weight, weight correction formula has been derived for use with the

Schnider model and is widely used in the absence of Eleveld model.

LACUNAE IN EXISTING KNOWLEDGE

The Schnider model is designed to be a universal model across a broad population, however

real-world clinical validation specifically in morbidly obese patients undergoing bariatric

surgery is still limited. Similarly, despite the theoretical advantages of the Eleveld model in the

bariatric populations, there is a lack of robust clinical evidence directly comparing its

performance with the Schnider model in this specific group. This study aims to evaluate and

compare the efficacy, safety and recovery profiles of propofol TCI guided by the Eleveld versus

the Schnider model in adult patients undergoing bariatric surgery.