title: The effect of the prone position on venous pressure and blood loss during lumbar laminectomy.
abstract: OBJECTIVE
  To determine the effects of three different prone support systems (Andrews spinal surgery frame, Cloward surgical saddle, and longitudinal bolsters) on inferior vena cava (IVC) and superior vena cava (SVC) pressures; the validity of measuring central venous pressure (CVP) for the determination of ideal positioning of the patient; and the relationship among frame type, blood loss, and hemodynamic measurements.
  
  
  METHODS
  Prospective, randomized study of the hemodynamic effects of the prone position.
  
  
  METHODS
  Inpatient surgery at a university hospital (regional spinal cord injury treatment center).
  
  
  METHODS
  Eighteen patients free of significant coexisting disease (ASA physical status I and II) undergoing elective lumbar laminectomy.
  
  
  METHODS
  Patients were assigned to one of three support frames and measurement of SVC pressure, IVC pressure, and mean arterial pressures (MAP) were obtained supine, prone, and after repositioning. These pressures and measured blood loss were obtained every 15 minutes during the surgical laminectomy portion of the procedure.
  
  
  RESULTS
  Patients positioned on the Andrews frame had decreased mean SVC and IVC pressures from 8.7 mmHg and 8.4 mmHg in the supine position to 3.3 mmHg and 1.8 mmHg in the prone position, respectively (p less than 0.001). Prone position CVP also was significantly lower in the Andrews group compared with that in the other two groups (p less than 0.001). Repositioning efforts did not significantly decrease CVP. Blood loss was higher in the Cloward group (1,150 +/- 989 ml) than in the Andrews (245 +/- 283 ml) and bolsters (262 +/- 188 ml) groups (p less than 0.02).
  
  
  CONCLUSIONS
  Increased blood loss was not associated with increased SVC or IVC pressure, nor was there any significant correlation between any demographic or hemodynamic variable and blood loss. There was no evidence that CVP is useful in determining the ideal prone position in patients undergoing lumbar laminectomy.
authors.affiliation: Department of Anesthesiology, Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA 19107.
authors.forename: S E
authors.initials: SE
authors.lastname: McNulty
authors.forename: J
authors.initials: J
authors.lastname: Weiss
authors.forename: S S
authors.initials: SS
authors.lastname: Azad
authors.forename: D M
authors.initials: DM
authors.lastname: Schaefer
authors.forename: J L
authors.initials: JL
authors.lastname: Osterholm
authors.forename: J L
authors.initials: JL
authors.lastname: Seltzer
mesh_terms: D016063:Blood Loss, Surgical; D001794:Blood Pressure / Q000502:physiology*; D006801:Humans; D007796:Laminectomy; D008159:Lumbar Vertebrae / Q000601:surgery*; D009983:Orthopedic Equipment; D016684:Prone Position / Q000502:physiology*; D011446:Prospective Studies; D011897:Random Allocation