Comparison between Natural Drainage Group and Negative Drainage Group after Cervical Laminoplasty: A retrospective STROBE-compliant cohort study

Background. A retrospective study was conducted to compare natural drainage and negative drainage Methods. 593 patients who underwent laminoplasty between January 2011 and December 2017 were engaged in this analysis. We investigated the patients’ basic characteristics, drainage characteristics and postoperative complications. Results. During the first 24 hours after laminoplasty, the drainage volume in the negative pressure drainage group was 175.69±92.02 mL, and the drainage volume in the natural drainage group was 133.33±92.40 mL. The drainage volume showed significant difference (p<0.01) between the two groups. The total drainage volume was 361.37±163.31mL and 250.16±27.44mL in the negative pressure drainage group and natural drainage group respectively. The total drainage volume between the two groups was statistically different (p=0.03). The postoperative Hb was significantly different between the natural group and negative group on the first day after the operation (108.37±23.92 mL vs. 76.33±21.25 mL, p=0.01). The number of patients required blood transfusion showed significantly different between the two groups as well (p<0.01). 3 out of which occurred symptomatic epidural hematoma (SEH) after laminoplaty. However, the occurrence of SEH among the two groups was not different significantly. 15 patients occurred surgical site infection (SSI). Of these 15 patients, 9 patients applied natural drainage and 6 patients applied negative drainage. The rate of SSI was similar between the two groups (P=0.83). Conclusion. The initial 24 hours’ drainage volume and the total drainage volume increased significantly in the negative pressure drainage group. The postoperative Hb was lower in the negative group than the natural drainage group the first postoperative day. More patients needed blood transfusion if negative drainage were performed. The application of negative drainage cannot decrease the incidence of SSI and SEH after laminoplasty. Natural drainage is recommended in the in our statistical Previous for decompression surgery no matter in the single-level surgery or multilevel decompression surgery. We can expand the conclusion that natural drainage does not increase the rate of SEH not only in the lumbar surgery but posterior cervical surgery as well. The results indicate that natural drainage does not increase the rate of SSI and SEH comparing with the negative drainage.


Background
Cervical spondylotic myelopathy (CSM) with compression of the spinal cord usually results from degenerative changes and spine instability. After the introduction of laminoplasty by Hirabayashi in 1977, laminoplasty had become an alternative treatment option for cervical spondylotic myelopathy. 1 Laminoplasty, a motion preserved surgical procedure for CSM, has became a relatively effective and safe treatment for cervical myelopathy with few complications reported and good long-term outcomes. 2 Thus, laminoplasty has been considered as a superior alternative to laminectomy or laminectomy and fusion for patients with CSM as it may decrease the incidence of progressive spinal deformity and prevent the need for subsequent spinal stabilization. 3,4 Laminoplasty can be conducted in patients with multiple-level spinal cord compression and it is suitable for elderly patients with cervical compression myelopathy. 5 The postoperative surgical site infection (SSI) represents as one of the most severe complication for any orthopedic procedure. Along with the increasing patient morbidity, a substantial medical cost is incurred through additional treatments, surgical procedures, and hospitalizations. Studies reported postoperative surgical site infection rates ranged from 1% to 6% in cervical spine procedures. 6 The rate of SSI during the summer period was higher than that during the other time of the year. 7 Placing a drainage is a method to reduce postoperative infections for posterior cervical operation. 8 Placement of drainage can also decrease the incidence of postoperative symptomatic epidural hematoma (SEH) in spinal decompression surgery. 9 To remove excess fluid, some form of closed suction drainage is usually applied. 10 In general, there are several advantages to placing a negative suction drainage after the surgery: the dead space developed after the surgery is reduced, repositioning of the flaps is facilitated and the recovery of the patient is faster. [11][12] In this study, we aimed to assess whether the negative drainage is necessarily as other surgery. An insertion of a drainage tube is also recommended since hematomas or seromas may develop after a surgery. Most cases are asymptomatic and only in rare conditions does spinal epidural hematoma become symptomatic. Once neurological deterioration due to SEH occurred, emergency evacuation is required. If operation is not performed promptly enough, neurological sequelae such as paralysis may persist. [9] In this study, we measured drainage volume and the rate of SEH and SSI after surgery in patients who conducted cervical laminoplasty in order to assess whether a negative pressure drainage tube is necessary. were excluded from the analysis. A diagnosis of CSM required radiological confirmation and at least one or two more "upper motor neuron" findings (spasticity, hyperreflexia, clonus, positive Babinski sign). "Lower motor neuron" findings (upper extremity hyporeflexia and muscle atrophy) were evaluated but not required for a diagnosis of CSM. 13 All the patients failed to or refused to at least 6 weeks of conservative treatment, such as physical therapy, epidural injections, antiinflammatory medications or opioid analgesics. The hemoglobin (Hb) level was evaluated on the first day and on the third day after the operation in all the patients. If hemoglobin level was less than 7 g per dL (70 g per L) in the first postoperative day, patients would perform blood transfusion. The Hb would be measured the third postoperative day which is also the first day after blood transfusion if conducted. If Hb level was measured as being less than 7g/dL, blood transfusion would performed again.

Methods
All patients received standard systemic antibiotic prophylaxis consisting of weight-based intravenous (IV) cefazolin within 1 hour of surgical incision, followed by IV cefazolin every 8 hours for 1 day. If the patient was allergic to penicillin, weight-based IV clindamycin was used instead. All patients were prepared with chlorhexidine. A standard midline incision and open approach was used in all cases.
Since 2015, negative drainage was used, by contrast, natural drainage was applied right before 2014 December,.
The negative drainage is the Drainobag (B. Braun Melsungen AG, Germany) which is a bottle drain with a negative pressure of 90kPa without valves. Here the vacuum with increasing filling of the container remains largely unchanged. Natural drainage was the similar drainage bag without any suction. Drainage volume was recorded every day. All drainage tubes were removed either if the fluid production was less than 30 mL on 2 consecutive days or after a maximum of 7 days regardless of the drainage volume. Each patient was followed up 1 week after discharged and weekly thereafter or more frequently if needed. The total drainage volume was recorded.
The diagnosis of SEH was made on the basis of progressing paralysis, numbness of lower extremities and MRI. Further surgery was required to evacuate the hematoma. From previous study, the outcome varies depending on the frequency of SEH evacuation for each surgical procedure. 14 A deep surgical site infection was principally suspected by clinical grounds from the clinical history, physical examination, and/or laboratory analysis and confirmed with radiological studies. The definition of deep SSI developed by the Centers for Disease Control and Prevention (CDC) was used to make this diagnosis. 15 CDC definited deep incisional infections as occurring within 30 days after surgery. Additionally, they involve purulent drainage, isolation of organism, signs or symptoms of infection (such as pain or tenderness, localized swelling, and redness or heat) combined with positive culture results, and/or diagnosis by a surgeon or an attending physician. Thus, in our study, a SSI was defined as being diagnosed during the initial hospitalization or during a hospital readmission or postoperative clinic appointment within 30 days of the surgery. All patients enrolled in this study had standard laboratory tests on admission to the hospital including erythrocyte sedimentation rate, peripheral white blood cell count, C-reactive protein, microbiology and blood cultures. The erythrocyte sedimentation rate (ESR) was counted by the Westergren method and was considered as abnormal if higher than 15 mm/h. C-reactive protein was considered abnormal if higher than 5 mg/dL. Bacterial identification and susceptibility testing was performed according to the guidelines of the CDC.
Patients' age, gender, Body Mass Index (BMI), smoking history, alcohol history and diabetic history were investigated and particular attention was paid to information about preoperative hematocrit, postoperative hematocrit, rate of SSI and rate of SEH.

Statistical Analysis
Percentages in the two study groups were compared by chi-square test without correction for continuity. For continuous variables the median and the 95 interpercentile range were calculated. The mean values of these variables in the two study groups were compared by the Mann-Whitney U Test.
The null hypothesis was rejected if P < 0.05. Analyses were performed on a personal computer by  Table 2).

Postoperative complications
Of the 593 patients, 3 patients occurred SEH. Symptoms of SEH at the cervical spinal cord level manifested in 2 patient presented as flaccid paralysis and in 1 presented as spastic paralysis. The occurrence of SEH among the two groups was not different significantly (p = 1.00). Table 3 Of the 593 patients, 15 patients occurred SSI. Of all the 15 patients, 9 patients applied natural drainage and 6 patients applied negative drainage. The causative pathogens were yield from intraoperative sampling. The most common organism isolated was Staphylococcus aureus (6 cases in natural drainage group and 3 case in negative drainage group) of the 15 cases. The second most common organism isolated was Pseudomonas aeruginosa in 4 cases (2 cases in natural drainage group and 2 case in negative drainage group). Two patients presented with mixed bacterial infection.
The rate of SSI was similar between the two groups (P = 0.83). Table 3 Discussion Laminoplasty is an effective and safe treatment for cervical spondylotic myelopathy. Closed suction tubes have generally been inserted to prevent SEH, SSI and removed serous fluid. All drainage tubes were removed either if the fluid production was less than 30 mL on two consecutive days or after a maximum of 7 days regardless of the drainage volume. Nonetheless, the kind of drainage tubes used in some kinds of surgery is still controversial. Gocyk W claimed that natural drainage could be more effective than negative drainage with regard to drainage volume, drainage duration and incidence of persistent air leakage after lung resections. 16 The literature is still sparse regarding which kind of drainage after posterior cervical surgery is more reliable and reasonable. In our study, we reached the similar conclusion that it is not necessary to place a negative drainage drain when a laminoplasty is conducted.
In this study, there were no significant differences in the age, gender, BMI, smoking history, alcohol history and diabetic history between the two groups. In order to accurately measure actual drainage volume after laminoplasty, we inserted a drainage tube and measured the volume every 24 hours after surgery. The drainage volume is an important factor that determines hospitalization period.
Decreasing the hospital stay by reducing the drainage volume not only decreases the medical cost to patients, but decreases the discomfort of patients and their guardians as well. Our results revealed that the drainage volume would increase dramatically if negative drainage are applied after laminoplasty especially on the initial day. The total drainage volume also increased in the negative drainage group. Our results revealed that the volume of drainage tube discharge was significantly lower in the natural drainage group than in the negative drainage group. As the volume of discharge is one of the criteria for tube removal, it is associated with a shorter drainage time. It is interesting that the drainage removal time showed no significant differences. We considered that the postoperative drainage volume after first 24 hours was different and the tube removal was determined by the drainage volume in the last day rather than the first day. In our study the blood loss in the two groups showed no significant differences during the operation. In our study, we found that the preoperative Hb and Hb in the third day showed no significant differences though the level of Hb in the third day is corrected by blood transfusion. In our study, postoperative Hb level in the first day showed significant differences between the two groups. The postoperative anemia was adjusted by blood transfusion. Much more patients applied blood transfusion in the negative drainage group than the natural drainage group which may contribute to the more drainage volume in the negative drainage group. If Hb level is less than 70g/L, blood transfusion would conducted in the second day.
This means that the third day Hb would be corrected by blood transfusion in some patients which may contribute to the Hb level increasing in the third day compared with the first day. Just as previous studies had indicated, our conclusions had been supported by the previous studies that negative drainage would increase the drainage volume. 17 Moreover our study draw a broad conclusion that negative drainage is a risk factor for blood transfusion.
The SSI rate was 2.99% in the natural drainage group and 2.05% in the negative drainage group respectively. The SSI rate is similar with the previous study which is 2.94%. 17 The SSI rate showed no significant differences between the two groups. This means that the natural drainage does not increase the rate of SSI. Previous study usually aimed to investigate diabetes, spine instrumentation, long duration of surgery, gender, alcohol use, and steroid usage. [18][19] Our study adds more information to the risk factors of posterior cervical SSI, although it is a negative result.
The SEH rate in our study is 0.67% in the natural drainage group and 0.34% in the negative group.
The SEH rate is much lower than the previous study (1.5%). 20 The reason might be that the two surgeons are more carefully in the hemostasis during the operation to prevent SEH because of the severe doctor-patient relationship in China. 21 The rate of SEH between the two groups showed no significantly difference in our statistical analysis. Previous study reached the similar conclusion that usage of negative drainage is not necessary for lumbar decompression surgery no matter in the single-level surgery or multilevel decompression surgery. [22][23][24] We can expand the conclusion that natural drainage does not increase the rate of SEH not only in the lumbar surgery but posterior cervical surgery as well. The results indicate that natural drainage does not increase the rate of SSI and SEH comparing with the negative drainage.
The limitations of the present study included retrospective natures of the study. However, the database for this study was constructed without our current hypothesis. Therefore all patient data were collected in an unbiased manner. Also, the patient sample with SSI and SEH is relatively small.
The small sample size may contribute to the low incidence of SSI and SEH. If possible, multi-cohort study or more patients sample is needed. More patients applied negative drainage should recruited into this study especially.

Conclusion
Based on an at least 2-year follow-up for the patients underwent laminoplasty, the first 24 hours drainage volume and the total drainage volume increased significantly in the negative pressure drainage group, compared to the natural drainage group. The postoperative Hb on the first day before the blood transfusion was lower in the negative drainage group than the natural drainage group.
Patients are more likely applied blood transfusion if negative drainage is applied. The usage of negative drainage cannot decrease the incidence of SSI and SEH after a laminoplasty. Natural drainage is recommended in the laminoplasty. Availability of data and material The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no competing interests.