title: Effects of phenylephrine on cardiac output and venous return depend on the position of the heart on the Frank-Starling relationship.
abstract: BACKGROUND
  phenylephrine is used daily during anesthesia for treating hypotension. However, the effects of phenylephrine on cardiac output (CO) are not clear. We hypothesized that the impact of phenylephrine on cardiac output is related to preload dependency.
  
  
  METHODS
  eight pigs were studied at a preload independent stage (after CO augmentation) and at a preload dependent stage (after a 21 ml/kg hemorrhage). At each stage, phenylephrine boluses (0.5, 1.0, 2.0, and 4.0 μg/kg) were given randomly while mean arterial pressure (MAP), CO, inferior vena cava flow (IVCf) (both measured using ultrasonic flow probes), and pulse pressure variation were measured.
  
  
  RESULTS
  at the preload independent stage, phenylephrine boluses induced significant increases in MAP (from 72 ± 6 to 100 ± 6 mmHg; P < 0.05) and decreases in CO and IVCf (from 7.0 ± 0.8 to 6.0 ± 1.1 l/min and from 4.6 ± 0.5 to 3.8 ± 0.6 l/min, respectively). At the preload-dependent stage, phenylephrine boluses induced significant increases in MAP (from 40 ± 7 to 65 ± 9 mmHg), CO (from 4.1 ± 0.6 to 4.9 ± 0.7 l/min), and IVCf (from 3.0 ± 0.4 to 3.5 ± 0.6 l/min; all data presented are for 4 μg/kg). Incremental doses of phenylephrine induced incremental changes in cardiac output. A pulse pressure variation >16.4% before phenylephrine predicted an increase in stroke volume with a 93% sensitivity and a 100% specificity.
  
  
  CONCLUSIONS
  impact of phenylephrine on cardiac output is related to preload dependency. When the heart is preload independent, phenylephrine boluses induce on average a decrease in cardiac output. When the heart is preload dependent, phenylephrine boluses induce on average an increase in cardiac output.
authors.affiliation: Department of Anesthesiology and Perioperative Care, School of Medicine, University of California-Irvine, 333 City Boulevard West Side, Orange, CA 92868-3301, USA. maxime_cannesson@hotmail.com
authors.forename: Maxime
authors.initials: M
authors.lastname: Cannesson
authors.forename: Zhongping
authors.initials: Z
authors.lastname: Jian
authors.forename: Guo
authors.initials: G
authors.lastname: Chen
authors.forename: Trung Q
authors.initials: TQ
authors.lastname: Vu
authors.forename: Feras
authors.initials: F
authors.lastname: Hatib
mesh_terms: D000818:Animals; D002302:Cardiac Output / Q000187:drug effects* / Q000502:physiology*; D002316:Cardiotonic Agents; D004305:Dose-Response Relationship, Drug; D010656:Phenylephrine / Q000008:administration & dosage*; D011187:Posture / Q000502:physiology*; D013318:Stroke Volume / Q000187:drug effects* / Q000502:physiology*; D013552:Swine; D014680:Veins / Q000187:drug effects / Q000502:physiology*
chemical_list: D002316:Cardiotonic Agents; D010656:Phenylephrine