title: Hemodynamic changes during spinal surgery in the prone position.
abstract: BACKGROUND
  Hypertension and fluctuations in blood pressure (BP) during lumbar spinal surgery in the prone position under anesthesia are not unusual. The purpose of this study was to investigate the causes of the decrease in BP during lumbar spinal surgery in the prone position using a noninvasive monitor of cardiac output.
  
  
  METHODS
  Twenty ASA Class I or II patients, scheduled for elective lumbar spinal surgery in the prone position, had their hemodynamic status monitored by a BioZ.com system Impedance Cardiograph during anesthesia. Hemodynamic data (heart rate [HR], mean BP, cardiac index [CI], stroke volume [SV] and systemic vascular resistance [SVR]) were registered at baseline, post-induction of general anesthesia, 10 minutes after the patient was turned from the supine to the prone position and 1 hour after the start of surgery. Friedman's test and the paired t test were used to compare the collected data on hemodynamic parameters.
  
  
  RESULTS
  The mean BP, SV, CI and HR were found to have significant differences (p < 0.05) at the designated time points as analyzed by Friedman's test, while the SVR and central venous pressure showed no significant changes. CI and SV were found to be markedly decreased from 2.4 +/- 0.3 to 2.0 +/- 0.3 L/minute/m2 and from 45.8 +/- 9.7 to 36.7 +/- 9.2 mL, respectively, after patients assumed the prone position. Mean BP also decreased significantly. After 1 hour of surgery, the mean BP decreased further with a fall in HR but the SV remained unchanged.
  
  
  CONCLUSIONS
  Decreases in SV and CI are the main causes of a decrease in BP in the prone position during lumbar spinal surgery.
authors.affiliation: Department of Anesthesia, Pain Service and Critical Care Medicine, China Medical University Hospital, Taichung, Taiwan, R.O.C.
authors.forename: Kin-Shing
authors.initials: KS
authors.lastname: Poon
authors.forename: King-Chuen
authors.initials: KC
authors.lastname: Wu
authors.forename: Chia-Chen
authors.initials: CC
authors.lastname: Chen
authors.forename: Si-Tun
authors.initials: ST
authors.lastname: Fung
authors.forename: Albert Wai-Cheung
authors.initials: AW
authors.lastname: Lau
authors.forename: Chiu-Chen
authors.initials: CC
authors.lastname: Huang
authors.forename: Rick Sai-Chuen
authors.initials: RS
authors.lastname: Wu
mesh_terms: D001794:Blood Pressure; D002302:Cardiac Output; D005260:Female; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D016684:Prone Position; D013131:Spine / Q000601:surgery*; D013318:Stroke Volume