The effect of intraoperative blood loss on serum cefazolin level in patients undergoing instrumented spinal fusion. A prospective, controlled study.

STUDY DESIGN: This study is a prospective, controlled study of the effect of intraoperative and postoperative blood loss during spinal surgery on serum cefazolin level. OBJECTIVES: To determine what effect, if any, intraoperative blood loss has on serum antibiotic levels, and to determine if adjustment of the dose or dose interval is appropriate in operative cases of significant blood loss. SUMMARY OF BACKGROUND DATA: The problem of infection at the operative site after posterior spinal fusion with internal fixation is significant. It commonly has been accepted that blood loss results in a more rapid clearance of antibiotic. METHODS: Nineteen patients scheduled for elective spinal fusion with internal fixation were enrolled in this study. Each patient served as his or her own control. Baseline cefazolin clearance was determined the week before surgery. Cefazolin clearance again was determined intraoperatively. Blood loss was recorded throughout the procedure. RESULTS: The mean blood loss was 650 mL. There was no significant difference between preoperative and intraoperative cefazolin clearance, and there was no correlation between blood loss and cefazolin level. CONCLUSIONS: It is not necessary to give cefazolin at a dosing interval of less than 4 hours with blood losses of up to 1200 mL. This will maintain the antibiotic concentrations well above the minimum inhibitory concentration.

Effect of intraoperative blood loss on the serum level of cefazolin in patients managed with total hip arthroplasty. A prospective, controlled study.

The effect of intraoperative blood loss on serum levels of cefazolin in patients being managed with total hip arthroplasty was studied. Eighteen patients, thirteen men and five women, with a mean age of sixty-five years (range, forty to eighty-five years) were enrolled in the study. Fifteen had a primary total hip arthroplasty and three, a revision. Each patient served as his or her own control. Baseline clearance of cefazolin was determined at a minimum of forty-eight hours before the operation. Each patient received one gram of cefazolin intravenously. Serial serum concentrations were determined from specimens drawn at zero, five, ten, twenty, thirty, sixty, 120, 240, and 300 minutes after administration. Fifteen minutes before the skin incision was made, each patient again received one gram of cefazolin intravenously. Serum samples were collected at the same time-intervals, and the serum levels of cefazolin were determined with use of capillary electrophoresis. Data regarding intraoperative blood loss as well as replacement of fluid and blood were recorded. The administration of the antibiotic, retrieval of the serum samples, and estimation of the blood loss were performed by the same person in the same manner for all patients. The preoperative and intraoperative creatinine clearances (mean and standard deviation), estimated with use of the formula of Cockcroft and Gault, were 62.06 +/- 21.28 and 74.02 +/- 24.75 milliliters per minute, respectively. The amount of intraoperative blood loss averaged 1137 +/- 436 milliliters (range, 675 to 2437 milliliters). The preoperative and intraoperative cefazolin clearances averaged 0.49 +/- 0.21 and 0.52 +/- 0.30 milliliter per minute per kilogram, respectively. During joint replacement, the commonly accepted interval between doses of cefazolin is four hours. In the present study, the serum level of cefazolin at four hours was forty-five micrograms per milliliter. This corresponds to an osseous concentration that well exceeds the minimum inhibitory concentration for Staphylococcus aureus, which is 0.5 microgram per milliliter. This study suggests that, with blood losses of less [corrected] than 2000 milliliters, it is not necessary to administer cefazolin at intraoperative intervals of less than four hours in order to maintain a concentration of antibiotics that is higher than the minimum inhibitory concentration for the most common infecting organisms.

A method for radiographic evaluation of pedicle screw violation of the vertebral endplate. Technique.

STUDY DESIGN: This study evaluated the utility of intraoperative radiographs for minimizing the risk of pedicle screw tip violation of the superior vertebral endplate. OBJECTIVES: An intraoperative radiographic technique is demonstrated that ensures that a screw has not penetrated the intervertebral disk. SUMMARY OF BACKGROUND DATA: Although methods to avoid penetration of the medial pedicle cortex and the anterior body cortex have been described, no study has discussed screw penetration of the superior endplate and disc. METHODS: Pedicle screws were inserted into 11 cadaveric lumbar spines, randomly, with the tip interior to the endplate, at the endplate, and through the endplate. Radiographs were evaluated to measure the penetration, if any, of the screws. Spine segments were dissected and evaluated anatomically. The anatomic and radiographic results were then compared. RESULTS: The overall error rate for radiographs was 22/312 (7%). Oblique radiographs gave a much higher error rate. CONCLUSIONS: A true lateral or anteroposterior radiographic view of the vertebra provides a high degree of certainty that the screw has not crossed the endplate when a "safe zone" of 3 mm remains superior to the screw tip. Intraoperative radiography can reduce concern about violation of the superior vertebral endplate.