The principles of presenting statistical results using figures / 대한마취과학회지

Tables and figures are commonly adopted methods for presenting specific data or statistical analysis results. Figures can be used to display characteristics and distributions of data, allowing for intuitive understanding through visualization and thus making it easier to interpret the statistical results. To maximize the positive aspects of figure presentation and increase the accuracy of the content, in this article, the authors will describe how to choose an appropriate figure type and the necessary components to include. Additionally, this article includes examples of figures that are commonly used in research and their essential components using virtual data.

The principles of presenting statistical results: Table / 대한마취과학회지

General medical journals such as the Korean Journal of Anesthesiology (KJA) receive numerous manuscripts every year. However, reviewers have noticed that the tables presented in various manuscripts have great diversity in their appearance, resulting in difficulties in the review and publication process. It might be due to the lack of clear written instructions regarding reporting of statistical results for authors. Therefore, the present article aims to briefly outline reporting methods for several table types, which are commonly used to present statistical results. We hope this article will serve as a guideline for reviewers as well as for authors, who wish to submit a manuscript to the KJA.

The principles of presenting statistical results: Table / 대한마취과학회지

General medical journals such as the Korean Journal of Anesthesiology (KJA) receive numerous manuscripts every year. However, reviewers have noticed that the tables presented in various manuscripts have great diversity in their appearance, resulting in difficulties in the review and publication process. It might be due to the lack of clear written instructions regarding reporting of statistical results for authors. Therefore, the present article aims to briefly outline reporting methods for several table types, which are commonly used to present statistical results. We hope this article will serve as a guideline for reviewers as well as for authors, who wish to submit a manuscript to the KJA.

Tips for troublesome sample-size calculation / 대한마취과학회지

Properly set sample size is one of the important factors for scientific and persuasive research. The sample size that can guarantee both clinically significant differences and adequate power in the phenomena of interest to the investigator, without causing excessive financial or medical considerations, will always be the object of concern. In this paper, we reviewed the essential factors for sample size calculation. We described the primary endpoints that are the main concern of the study and the basis for calculating sample size, the statistics used to analyze the primary endpoints, type I error and power, the effect size and the rationale. It also included a method of calculating the adjusted sample size considering the dropout rate inevitably occurring during the research. Finally, examples regarding sample size calculation that are appropriately and incorrectly described in the published papers are presented with explanations.

Assessment of P values for demographic data in randomized controlled trials / 대한마취과학회지

In a large number of randomized controlled trials, researchers provide P values for demographic data, which are commonly reported in table 1 of the article for the purpose of emphasizing the lack of differences between or among groups. As such, the authors intend to demonstrate that statistically insignificant P values in the demographic data confirm that group randomization was adequately performed. However, statistically insignificant P values do not necessarily reflect successful randomization. It is more important to rigorously establish a plan for statistical analysis during the design and planning stage of the study, and to consider whether any of the variables included in the demographic data could potentially affect the research results. If a researcher rigorously designed and planned a study, and performed it accordingly, the conclusions drawn from the results would not be influenced by P values, regardless of whether they were significant. In contrasts, imbalanced variables could affect the results after variance controlling, even though whole study process are well planned and executed. In this situation, the researcher can provide results with both the initial method and a second stage of analysis including such variables. Otherwise, for brief conclusions, it would be pointless to report P values in a table simply listing baseline data of the participants.

Multicollinearity and misleading statistical results / 대한마취과학회지

Multicollinearity represents a high degree of linear intercorrelation between explanatory variables in a multiple regression model and leads to incorrect results of regression analyses. Diagnostic tools of multicollinearity include the variance inflation factor (VIF), condition index and condition number, and variance decomposition proportion (VDP). The multicollinearity can be expressed by the coefficient of determination (R(h)²) of a multiple regression model with one explanatory variable (X(h)) as the model’s response variable and the others (X(i) [i≠h] as its explanatory variables. The variance (σ(h)²) of the regression coefficients constituting the final regression model are proportional to the VIF(1/1−R(h)²). Hence, an increase in R(h)² (strong multicollinearity) increases σ(h)². The larger σ(h)² produces unreliable probability values and confidence intervals of the regression coefficients. The square root of the ratio of the maximum eigenvalue to each eigenvalue from the correlation matrix of standardized explanatory variables is referred to as the condition index. The condition number is the maximum condition index. Multicollinearity is present when the VIF is higher than 5 to 10 or the condition indices are higher than 10 to 30. However, they cannot indicate multicollinear explanatory variables. VDPs obtained from the eigenvectors can identify the multicollinear variables by showing the extent of the inflation of σ(h)² according to each condition index. When two or more VDPs, which correspond to a common condition index higher than 10 to 30, are higher than 0.8 to 0.9, their associated explanatory variables are multicollinear. Excluding multicollinear explanatory variables leads to statistically stable multiple regression models.

Multicollinearity and misleading statistical results / 대한마취과학회지

Multicollinearity represents a high degree of linear intercorrelation between explanatory variables in a multiple regression model and leads to incorrect results of regression analyses. Diagnostic tools of multicollinearity include the variance inflation factor (VIF), condition index and condition number, and variance decomposition proportion (VDP). The multicollinearity can be expressed by the coefficient of determination (R(h)²) of a multiple regression model with one explanatory variable (X(h)) as the model’s response variable and the others (X(i) [i≠h] as its explanatory variables. The variance (σ(h)²) of the regression coefficients constituting the final regression model are proportional to the VIF(1/1−R(h)²). Hence, an increase in R(h)² (strong multicollinearity) increases σ(h)². The larger σ(h)² produces unreliable probability values and confidence intervals of the regression coefficients. The square root of the ratio of the maximum eigenvalue to each eigenvalue from the correlation matrix of standardized explanatory variables is referred to as the condition index. The condition number is the maximum condition index. Multicollinearity is present when the VIF is higher than 5 to 10 or the condition indices are higher than 10 to 30. However, they cannot indicate multicollinear explanatory variables. VDPs obtained from the eigenvectors can identify the multicollinear variables by showing the extent of the inflation of σ(h)² according to each condition index. When two or more VDPs, which correspond to a common condition index higher than 10 to 30, are higher than 0.8 to 0.9, their associated explanatory variables are multicollinear. Excluding multicollinear explanatory variables leads to statistically stable multiple regression models.

Assessment of P values for demographic data in randomized controlled trials / 대한마취과학회지

In a large number of randomized controlled trials, researchers provide P values for demographic data, which are commonly reported in table 1 of the article for the purpose of emphasizing the lack of differences between or among groups. As such, the authors intend to demonstrate that statistically insignificant P values in the demographic data confirm that group randomization was adequately performed. However, statistically insignificant P values do not necessarily reflect successful randomization. It is more important to rigorously establish a plan for statistical analysis during the design and planning stage of the study, and to consider whether any of the variables included in the demographic data could potentially affect the research results. If a researcher rigorously designed and planned a study, and performed it accordingly, the conclusions drawn from the results would not be influenced by P values, regardless of whether they were significant. In contrasts, imbalanced variables could affect the results after variance controlling, even though whole study process are well planned and executed. In this situation, the researcher can provide results with both the initial method and a second stage of analysis including such variables. Otherwise, for brief conclusions, it would be pointless to report P values in a table simply listing baseline data of the participants.

Statistical data preparation: management of missing values and outliers / 대한마취과학회지

Missing values and outliers are frequently encountered while collecting data. The presence of missing values reduces the data available to be analyzed, compromising the statistical power of the study, and eventually the reliability of its results. In addition, it causes a significant bias in the results and degrades the efficiency of the data. Outliers significantly affect the process of estimating statistics (e.g., the average and standard deviation of a sample), resulting in overestimated or underestimated values. Therefore, the results of data analysis are considerably dependent on the ways in which the missing values and outliers are processed. In this regard, this review discusses the types of missing values, ways of identifying outliers, and dealing with the two.

Assessment of risk of bias in quasi-randomized controlled trials and randomized controlled trials reported in the Korean Journal of Anesthesiology between 2010 and 2016 / 대한마취과학회지

Bias affects the true intervention effect in randomized controlled trials (RCTs), making the results unreliable. We evaluated the risk of bias (ROB) of quasi-RCTs or RCTs reported in the Korean Journal of Anesthesiology (KJA) between 2010 and 2016. Six kinds of bias (selection, performance, detection, attrition, reporting, and other biases) were evaluated by determining low, unclear, or high ROB for eight domains (random sequence generation, allocation concealment, blinding of participants, blinding of personnel, blinding of outcome assessment, incomplete outcome data, selective reporting, and other bias) according to publication year. We identified 296 quasi-RCTs or RCTs. Random sequence generation was performed better than allocation concealment (51.7% vs. 20.9% for the proportion of low ROB, P < 0.001 and P = 0.943 for trend, respectively). Blinding of outcome assessment was superior to blinding of participants and personnel (42.9% vs. 15.5% and 23.0% for the proportion of low ROB, P = 0.026 vs. P = 0.003 and 0.896 for trend, respectively). Handling of incomplete outcome data was performed best with the highest proportion of low ROB (84.8%). Selective reporting had the lowest proportion of low ROB (4.7%). However, the ROB improved year by year (P < 0.001 for trend). Authors and reviewers should consider allocation concealment after random sequence generation, blinding of participants and personnel, and full reporting of results to improve the quality of RCTs submitted hereafter for publication in the KJA.

Central limit theorem: the cornerstone of modern statistics / 대한마취과학회지

According to the central limit theorem, the means of a random sample of size, n, from a population with mean, µ, and variance, σ², distribute normally with mean, µ, and variance, σ²/n. Using the central limit theorem, a variety of parametric tests have been developed under assumptions about the parameters that determine the population probability distribution. Compared to non-parametric tests, which do not require any assumptions about the population probability distribution, parametric tests produce more accurate and precise estimates with higher statistical powers. However, many medical researchers use parametric tests to present their data without knowledge of the contribution of the central limit theorem to the development of such tests. Thus, this review presents the basic concepts of the central limit theorem and its role in binomial distributions and the Student's t-test, and provides an example of the sampling distributions of small populations. A proof of the central limit theorem is also described with the mathematical concepts required for its near-complete understanding.

Knot Formation at Removal of an Epidural Catheter Placed Against Insertion Resistance Encountered at the Entrance of the Epidural Space / 고신대학교의과대학학술지

Knotting of an epidural catheter occurs very rarely with an estimated incidence of 0.0015%. We present a case of an epidural catheter knot formed at removal of an epidural catheter following a forceful insertion of the catheter against resistance met at the entrance of the epidural space during threading of the catheter through Tuohy needle placed uneventfully in a 65 year-old male patient undergoing epidural anesthesia. During removal of the epidural catheter, significant resistance was encountered on traction and it was found that approximately 1.5 cm portion of the catheter had been retained within the patient's subcutaneous tissue. Firm traction was employed to withdraw the catheter against the resistance. The catheter was pulled out uneventfully from the patient. A knot estimated to be formed during removal of the catheter was observed at 0.6 cm proximal to the catheter tip. No complications and side effects were noted until the patient's discharge.

Effects of portal hyperperfusion on partial liver grafts in the presence of hyperdynamic splanchnic circulation: hepatic regeneration versus portal hyperperfusion injury

In cirrhotic patients undergoing liver transplantation, reperfusion of a liver graft typically increases portal venous blood flow (PVF) because of a decrease in resistance in the liver graft to the PVF and underlying hyperdynamic splanchnic circulation, which develops due to liver cirrhosis complicated by portal hypertension and persists even after successful liver transplantation. If the liver graft has enough capacity to accommodate the increased PVF, the shear stress inflicted on the sinusoidal endothelial cells of the graft promotes hepatic regeneration; otherwise, small-for-size syndrome (SFSS) develops, leading to poor graft function and graft failure. In particular, a partial graft transplanted to patients undergoing living donor liver transplantation has less capacity to accommodate the enhanced PVF than a whole liver graft. Thus, the clinical conditions that the partial graft encounters determine either hepatic regeneration or development of SFSS. Consistent with this, this review will discuss the two conflicting effects of portal hyperperfusion (hepatic regeneration vs. portal hyperperfusion injury) on the partial grafts in cirrhotic patients suffering from hyperdynamic splanchnic circulation, in addition to normal physiology and pathophysiology of hepatic hemodynamics.

Femoral subtrochanteric insufficiency fracture after long-term bisphosphonate therapy masked from foraminal stenosis of lumbar spine: A case report

We present a case of an insufficiency fracture of the subtrochanteric region of the femur in a 78-year-old woman masked by lumbar spinal foraminal stenosis. She complained of pain and a tingling sensation in the anterior and lateral side of the right thigh, leg, and ankle. Selective transforaminal epidural (L4-5, Rt.) and caudal block were done under the diagnosis of lumbar foraminal stenosis. The tingling sensation was completely relieved, but the pain was not completely relieved. The patient had been receiving bisphosphonate therapy for 6 years under the diagnosis of osteoporosis. We performed magnetic resonance imaging, which showed a unicortical break line and marrow edema around the hypertrophied area. Surgery was done. In cases with incomplete relief of the pain in the thigh following epidural block, physicians should keep in mind the possibility of femoral insufficiency fracture in patients who have received long-term bisphosphonate therapy.

Analysis of ultrastructural changes in the rat sciatic nerve after exposure to pulsed radiofrequency using small angle X-ray scattering (SAXS)

BACKGROUND: Pulsed radiofrequency (PRF) may be used in the treatment of patients with some pain syndromes that cannot be controlled by alternative techniques. The objective of the present study is to examine the ultrastructural changes in rat sciatic nerve after PRF, using synchrotron small angle X-ray scattering (SAXS). METHODS: Twenty rats (Male Sprague-Dawley, about 250 grams) were used this study. The PRF is applied to the afferent axons of the sciatic nerves of the rats in ex vivo state, and the ultrastructure of axons were studied after 1 (N = 5), 4 (N = 5), and 6 (N = 5) weeks by SAXS. The control (N = 5) consisted of non-treated sciatic nerve to provide a statistical differential comparison. RESULTS: In the PRF group, the periodic peaks of myelin sheath and collagen fibrils were not changed compared to the control group, in the time progression of 1, 4, and 6 weeks. But the periodic peaks of interfibrillar distance of collagen were greater at 1 and 4 weeks after PRF, comparing to the control group, but it had tendency to return to normal in 6 weeks. CONCLUSIONS: It is suggested that PRF did not induce ultrastructural change of myelin sheath and collagen fiber, but it induced the change of distance between collagen fibrils of the nerve tissue. This change was not caused by thermal injury but by electromagnetic fields and it is reversible.

Volume-controlled versus pressure-controlled ventilation-volume guaranteed mode during one-lung ventilation / 대한마취과학회지

BACKGROUND: The purpose of this study was to investigate the changes in airway pressure and arterial oxygenation between ventilation modes during one-lung ventilation (OLV) in patients undergoing thoracic surgery. METHODS: We enrolled 27 patients for thoracic surgery with OLV in the lateral decubitus position. The subjects received various modes of ventilation in random sequences during surgery, including volume-controlled ventilation (VCV) and pressure-controlled ventilation-volume guaranteed (PCV-VG) with a tidal volume (TV) of 8 ml/kg of actual body weight. Target-controlled infusion (TCI) with propofol and remifentanil was used for anesthesia induction and maintenance. After double-lumen endobronchial tube (DLT) insertion, the proper positioning of the DLT was assessed using a fiberoptic bronchoscope. Peak inspiratory pressure (Ppeak), exhaled TV, and arterial blood gas were measured 30 min after each ventilation mode. RESULTS: P(peak) was significantly reduced with the PCV-VG mode (19.6 +/- 2.5 cmH2O) compared with the VCV mode (23.2 +/- 3.1 cmH2O) (P < 0.000). However, no difference in arterial oxygen tension was noted between the groups (PCV-VG, 375.8 +/- 145.1 mmHg; VCV, 328.1 +/- 123.7 mmHg) (P = 0.063). The exhaled TV was also significantly increased in PCV-VG compared with VCV (451.4 +/- 85.4 vs. 443.9 +/- 85.9 ml; P = 0.035). CONCLUSIONS: During OLV in patients with normal lung function, although PCV-VG did not provide significantly improved arterial oxygen tension compared with VCV, PCV-VG provided significantly attenuated airway pressure despite significantly increased exhaled TV compared with VCV.

Volume-controlled versus pressure-controlled ventilation-volume guaranteed mode during one-lung ventilation / 대한마취과학회지

BACKGROUND: The purpose of this study was to investigate the changes in airway pressure and arterial oxygenation between ventilation modes during one-lung ventilation (OLV) in patients undergoing thoracic surgery. METHODS: We enrolled 27 patients for thoracic surgery with OLV in the lateral decubitus position. The subjects received various modes of ventilation in random sequences during surgery, including volume-controlled ventilation (VCV) and pressure-controlled ventilation-volume guaranteed (PCV-VG) with a tidal volume (TV) of 8 ml/kg of actual body weight. Target-controlled infusion (TCI) with propofol and remifentanil was used for anesthesia induction and maintenance. After double-lumen endobronchial tube (DLT) insertion, the proper positioning of the DLT was assessed using a fiberoptic bronchoscope. Peak inspiratory pressure (Ppeak), exhaled TV, and arterial blood gas were measured 30 min after each ventilation mode. RESULTS: P(peak) was significantly reduced with the PCV-VG mode (19.6 +/- 2.5 cmH2O) compared with the VCV mode (23.2 +/- 3.1 cmH2O) (P < 0.000). However, no difference in arterial oxygen tension was noted between the groups (PCV-VG, 375.8 +/- 145.1 mmHg; VCV, 328.1 +/- 123.7 mmHg) (P = 0.063). The exhaled TV was also significantly increased in PCV-VG compared with VCV (451.4 +/- 85.4 vs. 443.9 +/- 85.9 ml; P = 0.035). CONCLUSIONS: During OLV in patients with normal lung function, although PCV-VG did not provide significantly improved arterial oxygen tension compared with VCV, PCV-VG provided significantly attenuated airway pressure despite significantly increased exhaled TV compared with VCV.

Epidural catheterization with a subcutaneous injection port for the long-term administration of opioids and local anesthetics to treat zoster-associated pain: a report of two cases / 대한마취과학회지

Continuous epidural analgesia has been used for decades to treat acute herpes zoster pain and to prevent postherpetic neuralgia. However, many technical problems can arise during chronic treatment with epidural medications. These complications include catheter dislodgement, infection, injection pain, leakage, and occlusion. Epidural catheter placement utilizing subcutaneous injection port implantation has gained widespread acceptance as a method to overcome such complications. The technique reduces the risk of infection, the most feared complication, compared to the use of a percutaneous epidural catheter. Herein, we present 2 cases in which the continuous thoracic epidural administration of opioids and local anesthetics through an implantable subcutaneous injection port for over 2 months successfully treated zoster-associated pain without any technique- or medication-related complications in patients with risk factors for epidural abscess.

Intraoperative Fluid Management in Combined Liver-Kidney Transplantation / 대한구급학회지

A review of the literature regarding combined liver-kidney transplantation (CLKT) does not provide adequate central venous pressure (CVP) values that would allow for unimpaired hepatic venous outflow and early renal allograft diuresis during the procedure. We report a case of fluid management of CLKT based on the limited literature available in a 59-year-old male with liver cirrhosis and end-stage renal disease. During the preanhepatic phase, CVP was maintained at 5 mmHg. Following portal vein clamping, CVP was reduced to below 5 mmHg until venovenous bypass was initiated. From the neohepatic phase to 1 hour before renal allograft reperfusion, CVP was slowly increased to 10 mmHg. Within an hour before renal allograft reperfusion, maximal crystalloid hydration was used to increase CVP to 15 mmHg. The urine output was replaced to maintain CVP at 8 to 10 mmHg until the end of the surgery. The postoperative course was uneventful. In conclusion, fluid management tailored to each phase yielded beneficial results in a patient with CLKT.

Continuous Intrathecal Morphine Administration for Cancer Pain Management Using an Intrathecal Catheter Connected to a Subcutaneous Injection Port: A Retrospective Analysis of 22 Terminal Cancer Patients in Korean Population

BACKGROUND: Intrathecal opioid administration has been used widely in patients suffering from severe cancer pain that is not managed with conventional modalities. However, the potential serious neurological complications from the procedure and the side effects of intrathecal opioids have made many clinicians reluctant to employ continuous intrathecal analgesia as a first-line therapeutic option despite its dramatic effect on intractable pain. We retrospectively investigated the efficacy, side effects, and complications of intrathecal morphine administration through intrathecal catheters connected to a subcutaneous injection port (ICSP) in 22 Korean terminal cancer patients with successful intrathecal morphine trials. METHODS: Patient demographic data, the duration of intrathecal opioid administration, preoperative numerical pain rating scales (NRS) and doses of systemic opioids, side effects and complications related to intrathecal opioids and the procedure, and the numerical pain rating scales and doses of intrathecal and systemic opioids on the 1st, 3rd, 7th and 30th postoperative days were determined from medical records. RESULTS: Intrathecal morphine administration for 46.0 +/- 61.3 days significantly reduced NRS from baseline on all the postoperative days. A significant increase in intrathecal opioids with a nonsignificant decrease in systemic opioids was observed on the 7th and 30th postoperative days compared to the 1st postoperative day. The most common side effects of intrathecal opioids were nausea/vomiting (31.8%) and urinary retention (38.9%), which were managed with conservative therapies. CONCLUSIONS: Intrathecal morphine administration using ICSP provided immediate and beneficial effects on pain scores with tolerable side effects in terminal cancer patients.