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The Inter-Rater Reliability of a 0 to 10 Uterine Tone Score
Abstract Number: F3H-431
Abstract Type: Original Research
Postpartum hemorrhage (PPH) complicates 3% of all deliveries in the United States and uterine atony is the etiology in the majority of cases1. Obstetricians assess uterine contractile tone immediately after each cesarean delivery (CD) before closing the hysterotomy; enhanced communication about uterine atony may improve PPH management. Several quantitative scales describing uterine tone have been utilized in research studies with a 0-10 scale most commonly reported2-5. However, no scale has been standardized or validated. We evaluated the inter-rater reliability of a 0-10 visual analog scale (VAS) used to quantify the adequacy of uterine tone as assessed by obstetricians during CD.
This was a single-center prospective observational study. After waiver of IRB consent, patients undergoing CD for any indication were enrolled in the study from August through November 2018. Using a VAS of 0-10 with "0" being no tone and "10" excellent tone, two obstetricians independently rated uterine tone at 3 and 10 minutes post-delivery. Obstetricians reported uterine tone VAS independently by silently pointing to a printed VAS held by the anesthesiologist through a clear sterile drape. To maintain blinding, the second participating obstetrician looked away during each rating. Inter-rater agreement was assessed by Bland-Altman analysis and reliability by interclass correlation coefficient (ICC) for average between two raters.
Ninety-three patients were enrolled with 8 patients excluded from analysis due to discussion of uterine tone prior to VAS scoring; 82 and 84 scores were collected from pairs of 62 unique raters at 3 and 10 minutes, respectively. Scores obtained by each rater pair were within ±1 point of each other in 74.4% of cases at 3 minutes (95% CI: 64.0%, 82.6%) and 84.5% of cases at 10 minutes (95% CI: 75.3%, 90.7%). The mean difference in scores between rater 1 and rater 2 (95% CI) was 0.4 ± 1.4 at 3 minutes and 0.1 ± 1.1 at 10 minutes. For the lower tertile subset (mean scores of 4.7 ± 1.1 and 7.1 ± 1.1 at 3 and 10 minutes respectively), the mean difference in scores between rater 1 and rater 2 was 0.5 ± 1.5 at 3 minutes and 0.3 ± 1.3 at 10 minutes. Bland-Altman analysis indicated a 95% limit of agreement between raters of -2.4 (95% CI: -3.0, -1.9) to 3.1 (95% CI: 2.6, 3.7) at 3 minutes and -2.1 (95% CI: -2.5, -1.7) to 2.4 (95% CI: 2.0, 2.8) at 10 minutes. ICCs (95% CI) at 3 and 10 minutes were 0.80 (0.71, 0.87) and 0.76 (0.63, 0.84), respectively.
Reliability of the 0-10 VAS tone score was good when averaged across two raters at 3 and 10 minutes. This suggests that the score is a valid scale and can be used in clinical practice and research for quantifying uterine tone.
1. Anesth Analg. 2010;110(5):1368-73
2. Br J Anaesth. 2010;104(3):338-43
3. Int J Obstet Anesth. 2015;24(3):217-24
4. Anaesthesia. 1988;43(1):5-7
5. Anesth Analg. 1997;84(4):753-6