title: Prospective randomised comparison of Marsh and Schnider pharmacokinetic models for propofol during induction of anaesthesia in elective cardiac surgery.
abstract: BACKGROUND
  Haemodynamic stability during induction is a cornerstone of cardiac anaesthesia. The evaluation of pharmacokinetic models for propofol during induction is lacking.
  
  
  OBJECTIVE
  To compare haemodynamics during cardiac anaesthesia induction with two pharmacokinetic models.
  
  
  METHODS
  Randomised controlled trial.
  
  
  METHODS
  Department of Cardiothoracic Surgery, São João Hospital; July to December 2010.
  
  
  METHODS
  Ninety consecutive elective adult cardiac surgical patients.
  
  
  METHODS
  Random assignment to effect-site target-controlled infusion by Marsh (n = 45) or Schnider (n = 45) pharmacokinetic models with an equilibration constant of 1.2 min(-1) adapted to Marsh's model. Invasive blood pressure measurements, propofol dose, and bispectral index (BIS) were recorded. After an initial target concentration of 1.5 μg ml(-1), concentrations were upward-titrated in 0.5 μg ml(-1) increments until the BIS was <50.
  
  
  RESULTS
  No differences were observed between Marsh and Schnider models in required propofol dose (0.99 ± 0.26 vs. 0.93 ± 0.31 mg kg(-1), P = 0.322), decrease in mean blood pressure (25 ± 13 vs. 22 ± 14%, P = 0.192) or the need for vasopressors (20 vs. 24%, P = 0.800), but the use of the Marsh model resulted in a lower predicted effect-site concentration (2.3 ± 0.4 vs. 2.7 ± 0.6 μg ml(-1), P = 0.006) and shorter time to induction (296 ± 59 vs. 338 ± 87 s, P = 0.024). There was a greater decrease in mean blood pressure in older patients (>60 years; 29 ± 10 vs. 22 ± 11%, P = 0.004) irrespective of model, but obese (BMI ≥30 kg m(-2)) and nonobese patients did not differ.
  
  
  METHODS
  Decrease in mean blood pressure.
  
  
  CONCLUSIONS
  In effect-site targeting with a 1.2 min(-1) equilibration constant, Marsh's model is comparable to Schnider's during induction of anaesthesia.
authors.affiliation: Department of Anesthesiology, Hospital São João, EPE, Porto, Portugal. joao.viterbo@sapo.pt
authors.forename: João F
authors.initials: JF
authors.lastname: Viterbo
authors.forename: André P
authors.initials: AP
authors.lastname: Lourenço
authors.forename: Adelino F
authors.initials: AF
authors.lastname: Leite-Moreira
authors.forename: Paulo
authors.initials: P
authors.lastname: Pinho
authors.forename: Fernanda
authors.initials: F
authors.lastname: Barros
mesh_terms: D000368:Aged; D000758:Anesthesia / Q000379:methods*; D001794:Blood Pressure; D015992:Body Mass Index; D006348:Cardiac Surgical Procedures / Q000295:instrumentation / Q000379:methods*; D001026:Coronary Artery Bypass / Q000379:methods; D004305:Dose-Response Relationship, Drug; D005260:Female; D006351:Heart Valves / Q000601:surgery; D006439:Hemodynamics; D006801:Humans; D008297:Male; D008875:Middle Aged; D015742:Propofol / Q000493:pharmacokinetics*; D011446:Prospective Studies; D016896:Treatment Outcome
chemical_list: D015742:Propofol