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Observational Study
. 2021 Sep 27;21(1):354.
doi: 10.1186/s12893-021-01345-6.

Application of an index derived from the area under a neutrophil curve as a predictor of surgical site infection after spinal surgery

Hiroyuki Inose  1 , Yutaka Kobayashi  2 , Shingo Morishita  2 , Yu Matsukura  2 , Masato Yuasa  2 , Takashi Hirai  2 , Toshitaka Yoshii  2 , Atsushi Okawa  2
Affiliations
Observational Study

Application of an index derived from the area under a neutrophil curve as a predictor of surgical site infection after spinal surgery

Hiroyuki Inose et al. BMC Surg. .

Abstract

Background: Patients with prolonged and intense neutrophilia after spinal surgery are at high risk of developing surgical site infection (SSI). To date, there is no standard method for the objective assessment of the intensity and duration of neutrophilia. Thus, this retrospective observational study aimed to test a new index (I-index), developed by combining the duration and intensity of neutrophilia, as a predictor of SSI.

Methods: I-index was calculated based on the postoperative neutrophil percentage. A total of 17 patients with SSI were enrolled as cases, and 51 patients without SSI were selected as controls. The groups were matched at a ratio of 1:3 by age, sex, and surgery type. The differences in the I-index were compared between the groups. Moreover, we checked the cumulative I-index (c-I-index), which we defined as the area under the neutrophil curve from postoperative day 1 until the first clinical manifestation of SSI in each case. Furthermore, a cutoff for SSI was defined using the receiver operating characteristic curve.

Results: The median I-index-7, I-index-14, and c-I-index were significantly higher in the SSI group than those in the control group. For a cutoff point of 42.1 of the I-index-7, the sensitivity and specificity were 0.706 and 0.882, respectively. For a cutoff point of 45.95 of the I-index-14, the sensitivity and specificity were 0.824 and 0.804, respectively. For a cutoff point of 45.95 of the c-I-index, the sensitivity and specificity were 0.824 and 0.804, respectively.

Conclusion: We devised a new indicator of infection, i.e., the I-Index and c-I-index, and confirmed its usefulness in predicting SSI.

Keywords: I-index; Neutrophil curve; Predictor; Receiver operating characteristic curve; Spinal surgery; Surgical site infection.

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Conflict of interest statement

Hiroyuki Inose is an associate editor of BMC surgery. There are no other conflicts of interest.

Figures

Fig. 1
Fig. 1
Graph of the neutrophil percentage versus the number of postoperative days. The area under the neutrophil curve above the 70% neutrophil percentage is the I-index-7
Fig. 2
Fig. 2
Graph of the neutrophil percentage versus the number of postoperative days. The area under the neutrophil curve above the 70% neutrophil percentage is the I-index-14
Fig. 3
Fig. 3
Graph of the neutrophil percentage versus the number of postoperative days. The area under the neutrophil curve above the 70% neutrophil percentage is the c-I-index
Fig. 4
Fig. 4
Identification of the cutoff value of the I-index-7 for surgical site infection using the receiver operating characteristic analysis; area under the curve = 0.751; p = 0.0002
Fig. 5
Fig. 5
Identification of the cutoff value of the I-index-14 for surgical site infection using the receiver operating characteristic analysis; area under the curve = 0.776; p < 0.0001
Fig. 6
Fig. 6
Identification of the cutoff value of the c-I-index for surgical site infection using the receiver operating characteristic analysis; area under the curve = 0.842; p < 0.0001
See this image and copyright information in PMC

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