Hyperleukocytosis as a risk factor for death of pertussis patients has been confirmed in many previous studies[1–3]。Early effective leukocyte-reducing treatment can reduce patient mortality and improve patient prognosis.From now, many studies have focused on the application of exchange transfusion therapy in hyperleukocytosis. But there is no unified understanding of the effect and standard use of ET in patients with pertussis. Some scholars believe that it should be considered based on pulse, respiratory rate, total number of WBC and ascent speed, and the early incidence of pneumonia.In our study, exchange transfusion criteria for infants with pertussis:1. Who are ≤ 1 year of age 2. Total WBC count ≥ 50,000/mm3 with ≥ 15,000/mm3 lymphocytes;2. Persistent tachycardia;3. Early symptoms of dyspnea, respiratory failure, continuous mechanical ventilation. When considering transfusion therapy, we refer to respiration, heart rate, early pneumonia and WBC count.And we also refer to the age of onset, continuous mechanical ventilation, lymphocytes count. Tian et al. summarized the 56 patients with hyperleukocytosis from 2004 to 2017, with a survival rate of 68% (38/56) .In our study, 7 cases survived, and the survival rate was 53.8% (7/13).TOur study is slightly lower than previous studies.
The incidence of pulmonary hypertension, heart failure, pertussis encephalopathy, Increased C-reactive protein, and increased PCT in the survival group were lower than those in the death group,The incidence of received Gamma globulin and received steroids were higher than those in the death group.We know that pulmonary hypertension, heart failure, and pertussis encephalopathy are risk factors for severe pertussis and death. However, it is not clear whether the use of hormones and gamma globulin has a clear meaning. Some scholars found that after 3 days of intravenous injection of pertussis immunoglobulin in children with pertussis, the white blood cell count was significantly reduced, the spastic cough was reduced, and the tachycardia improved.But currently there is no pertussis immunoglobulin in our hospital༌After using gamma globulin, we found that the use rate of gamma globulin in the survival group was 71.42%, which was significantly higher than 16.67% in the death group, suggesting that gamma globulin use may also improve the prognosis of children. Hormones are used more in pertussis༌Kathleen Winter et al found that steroid hormones were used in fatal cases more than non-fatal cases, suggesting that steroid hormones may be a risk factor for death from pertussis༌James D. Cherry et al  also believe that steroid hormones should not be used in patients with pertussis. However, the use rate of hormones in the survival group was higher than that in the death group in this study, suggesting that hormones may be meaningful for disease improvement. However, this study has a small sample size compared with previous studies, and the death of patients is related to many factors. Hormones play a role in the final prognosis of patients. It may be inaccurate and needs further discussion
The change in the level of WBC is an intuitive indicator that reflects the effect of exchange transfusion. Analyzing the level of WBC counts and the rate of WBC decline in the two groups of patient, The WBC counts of the two groups decreased significantly after exchange transfusion, but there was no significant difference in two groups(P = 0.636). It suggesting that exchange transfusion can effectively reduce the level of WBC.
Decrease rate of WBC after the first ET in the survival group was significantly higher than that of the death group (P༜0.05). In the survival group, there were 5 patients (71.42%) which decrease rate of WBC after the first ET more than 50%, and the remaining 2 patients (28.58%) all exceeded 45%.In contrast, there was 1 patient which decrease rate of WBC exceeded 45% ,no patient exceed 50%. All patients with Decrease rate of WBC after the first ET exceed 50% survived. It shows that Decrease rate of WBC after the first ET may have a certain effect on the prognosis of death.
The patient's blood exchange volume was 87.99 ± 17.36ml/kg, there was no significant difference between the two groups (P = 0.918). However, in the death group, only 3 (50%) patients had a blood exchange volume of more than 80ml/kg for the first time of ET; In the survival group, 6 patients( 85.71%), it indicating that blood exchange volume may also have an impact on the prognosis of the disease At the same time, we also recommend that the first exchange blood volume should exceed 80ml/kg.
N/L ratio is an easily available biomarker that may help predict the severity of the disease in children with pertussis. Clinical studies have shown that the proportion of lymphocytes in ordinary children with whooping cough is mainly increased, but in children with severe pertussis, the ratio of neutrophils to lymphocytes may be inverted. In patients with benign pertussis with leukocytosis, within 48 hours of admission, The median N/L were 0.33 and 0.39. In contrast, the median N/L of children with malignant pertussis within 48 hours of admission were 1.1 and 1.6, respectively. In the death group, there were 4 patients (66.67%) which N/L exceeded 1, 3patients (50%)which N/L exceeded 2. In the survival group, only 3 patients (42.85%) which N/L exceeded 1, but there was no patient which N/L exceed 2. It indicate patients with hyperleukocytoemia which N/L exceeding 2 predict death.
Complications during or after transfusion are important factors affecting patient prognosis. In our study, complications occurred in 4 patients with exchange transfusion. There was 1 patient in the survival group which showed convulsions; there were 3 patients in the death group which showed convulsions(1patient) and Cardiac arrest (2 patients). It is suggested that the occurrence of complications may be a poor prognosis, especially the occurrence of cardiac arrest. At the same time, we found that patients with complications are mainly those with more than 100*10^9/L white blood cells. There were 3 patients with the highest white blood cell exceeding 100*10^9/L, all of which had complications during or after exchange transfusion, while only 1 case had complications in patients with white blood cell lower than 100*10^9/L. It suggests that white blood cells are significantly increased, especially patients with higher than 100*10^9/L are very prone to complications.