08 March 2023: Human Study
Study of 60 Adult Patients to Compare Standard Postoperative Clinical Assessment with Train-of-Four Ratio ≥0.9 on Patient Outcomes Using Postoperative Spirometry and Neuromuscular Function Measurements Following ExtubationChunlong Chen1AEF, Qingzhen Liu1CD, Hong Fan1BD, Zhiyang Yu1CF, Xueyan Leng1B, Lidong Zhang1ADF, Zhiqiang Zhou1ADE*
Med Sci Monit Basic Res 2023; 29:e938849
BACKGROUND: Postoperative tracheal extubation requires optimal timing to ensure patient safety and normal muscle function. The train-of-four ratio (TOFR) of the fourth muscle response compared with the first indicates a non-depolarizing neuromuscular block, and a ratio ≥0.9 can be used as an objective measurement of neuromuscular reversal. This study of 60 adult patients who underwent elective surgery with general anesthesia that included the neuromuscular blocking agent cisatracurium aimed to compare standard postoperative clinical assessment with the TOFR ≥0.9 on patient outcomes using postoperative neuromuscular function assessed by grip strength and ability to sit up unaided and spirometry measurements following extubation.
MATERIAL AND METHODS: The 30 patients extubated postoperatively in the TOF group were required to have a TOFR ≥0.9, while the 30 patients in the clinical assessment group were awake and following simple commands and had a 5-second head lift and spontaneous breathing with acceptable oxygenation. The main outcomes were the incentive spirometry and grip strength and ability to sit up unaided measured at 10, 30, 50 min and 24 h after extubation.
RESULTS: The groups had no difference in recovery path of incentive spirometry volume (P=0.072) and no difference in postoperative incentive spirometry decrease from baseline except at 10 min after extubation (P=0.005). There was no difference in handgrip strength and independent sitting between groups.
CONCLUSIONS: The findings showed that using the TOF ratio ≥0.9 before extubation did not improve early postoperative strength quantified by spirometry volume, handgrip strength, and proportion of unaided sitting.
Keywords: Airway Extubation, Hypoxia, Paresis, Humans, Adult, Hand Strength, Spirometry
An effective balanced anesthetic requires muscle relaxation for effective endotracheal intubation and optimized surgical conditions . Residual neuromuscular block (rNMB) results in delayed or partial return of muscle function in the postoperative period, which can cause respiratory and other complications, such as hypercapnia, hypoxia, upper airway obstruction, and functional impairment following surgery [2–4]. Additionally, if it does not fully reverse after surgery, rNMB can increase the risk of postoperative pneumonia . Therefore, the timing of weaning and extubation is particularly important. A meta-analysis comparing automated weaning systems with clinician-directed weaning strategies showed that automated weaning systems can reduce the weaning and ventilation time of non-surgical intensive care unit (ICU) patients but not surgical patients . A patient’s being adequately awake and communicative, hemodynamically stable, and adequately oxygenated were required for the timing of physician-guided extubation, but these factors cannot guarantee the success of weaning and extubation . Clinical judgment sometimes tends to overestimate or underestimate a patient’s extubation readiness . Thus, using some objective indicators to guide the extubation, such as vital capacity, ratio of arterial oxygen to the fraction of inspired oxygen ratio, and respiratory muscle strength were suggested . The reason there are so many indicators is that none of them are perfect yet .
Postoperative neuromuscular monitoring can be classified into 3 categories: clinical testing, qualitative evaluation, and quantitative measurement . Clinical testing includes measurements of respiratory parameters, such as vital capacity, and measurements of muscle strength, such as grip strength . By stimulating a peripheral nerve, qualitative neuromuscular devices evaluate the muscle’s response subjectively, either visually or tactilely . During quantitative neuromuscular monitoring, rNMB is objectively measured and displayed numerically in real time . A train-of-four (TOF) measured by a neuromuscular stimulator is composed of 4 equal stimuli delivered at intervals of 0.5 s. The TOF ratio (TOFR), which is calculated by comparing the magnitude of the fourth twitch to the first, is one of the quantitative monitoring methods of neuromuscular block, while clinical assessment is the most commonly used method in daily clinical practice [10,11]. To assess the recovery of muscle power, anesthesiologists can use criteria including the ability to grip the hand with the utmost strength or keep the head elevated for 5 s on recovery from neuromuscular blockade . These clinical methods, however, can be affected by other factors, such as whether the patients are sedated or able to follow instructions, and are unreliable . Early data suggested a TOFR <0.7 before extubation as an indicator of rNMB, while to guarantee optimal safety, a recent consensus and studies support a TOFR not less than 0.9 [4,11].
There have been contradictory investigations in the scientific documentation about the evaluation of rNMB using TOF. Some suggested that a TOFR ≥0.9 before extubation would decrease the incidence of residual paralysis, pneumonia, and postoperative atelectasis after surgery and reflect an acceptable neuromuscular palinesthesia, while others reported that even though there was a TOFR ≥0.9 before extubation, it did not exactly represent the recovery of neuromuscular status from anesthesia for patients [13–16]. In these studies, however, the TOFR has been emphasized more than clinical outcomes, such as capacity to breathe, aspiration, and the ability to sit up without assistance [13–16]. In both developed and developing countries, there are neuromuscular monitors, yet neuromuscular monitoring is not routinely done [10,13]. In addition to financial limitations, the status quo may also result from a lack of knowledge regarding alternate methods of monitoring neuromuscular blockade among medical staff .
Inconsistent results have been found when comparing the relationship between quantitative neuromuscular monitoring with TOFR before extubation and postoperative pulmonary complications. Using TOFR ≥0.9 before extubation did not affect the incidence of severe hypoxia when compared with clinical assessment according to a study conducted by Adembesa et al , while a prospective observational study by Azizoğlu and Özdemir showed that TOFR ≥0.9 before extubation reduced the incidence of hypoxia . Therefore, the present study of 60 adult patients who underwent elective surgery with general anesthesia that included the neuromuscular blocking agent cisatracurium aimed to compare standard postoperative clinical assessment with the TOFR ≥0.9 on patient outcomes using postoperative neuromuscular function assessed by grip strength and ability to sit up unaided and spirometry measurements following extubation.
Material and Methods
ETHICS COMMITTEE APPROVAL AND WRITTEN INFORMED CONSENT:
This was a clinical research study performed at Jinling hospital between November 24, 2021, and March 15, 2022. The Clinical Trial Ethics Committee of Jinling Hospital approved this study (November 11, 2021; no. 2021NZKY-050-01; Nanjing, China). All patients were informed about the purpose and content of the study, and written consent was obtained from the patients participating in the study or patients’ carers during the preoperative assessment. The study was registered at
SELECTION OF PATIENTS:
Inclusion criteria included all adult patients aged between 18 and 65 years undergoing general anesthesia for elective surgery with American Society of Anesthesiologists (ASA) class I and II; neuromuscular blocking drugs were used; orotracheal intubation was performed; and planned extubation was conducted in the postoperative anesthesia care unit (PACU). Exclusion criteria included allergy to muscle relaxants, neuromuscular diseases, a history of renal, hepatic, or respiratory diseases, preoperative hypothyroidism, surgery on the upper extremity, and undergoing brain or thoracic surgery. A total of 60 adult patients were included in the study, with 30 patients in each group.
After entering the operating room, intravenous access was established, crystalloid colloid fluid was injected intravenously, and regular monitoring of electrocardiography (ECG), invasive arterial blood pressure, pulse oxygen saturation (SpO2), and bispectral index was conducted. It was recommended that midazolam 2 mg, sufentanil 0.4 ug/kg, cisatracurium 0.2 mg/kg, and propofol 2 to 2.5 mg/kg at induction were the standardized doses. After orotracheal intubation was performed and mechanical ventilation was set at a tidal volume of 6 to 8 mL/kg, respiratory rate was adjusted to keep end-tidal carbon dioxide between 35 and 45 mmHg. Additional sufentanil or remifentanyl could be given if the anesthesiologist deemed it appropriate and interrupted at the suturing of the last layer of skin. Propofol or sevoflurane was continuously administered to maintained the depth of the bispectral index between 45 and 60, at the discretion of anesthesiologist during surgery. A bolus of 20 to 40 ug phenylephrine was administered to maintain blood pressure within 20% of baseline. A TOF-Watch acceleromyograph was calibrated before the relaxant was administrated during the induction of anesthesia. Cisatracurium 0.05 mg/kg was given every 30 min to 60 min if the anesthesiologist deemed it appropriate during surgery, without referring to TOFR.
Once the surgery was completed, the anesthesiologist transferred the patient to the PACU for endotracheal extubation using a simple respirator. Upon entering the PACU, the tracheal tube was connected to a ventilator for assisted breathing, and parameters such as tidal volume and respiratory rate were set the same as the intraoperative period, with 40% oxygen concentration. We had a full-time anesthesiologist who was responsible for the extubation of all patients in the PACU. The extubation criteria were as follows: patient awake and following simple commands, 5-second head lift, spontaneous breathing with acceptable oxygenation (regular respiratory rate ≥8 breaths/min, and tidal volume 4–6 mL/kg). TOFR values were available to the clinical staff but were not used as extubation criteria in the clinical assessment group. Immediately after extubation, oxygen 3 L/min was administered through a nasal catheter. Neostigmine 1 mg with atropine 0.5 mg would be given if SpO2 <90% lasted for more than 5 s and required airway manipulation to recover . A TOFR ≥0.9 was required for extubation in the TOF group. Patients were extubated as per the above criteria in the clinical assessment group.
STRENGTH MEASUREMENTS AND DATA COLLECTION:
Baseline data measurements of spirometry volume were performed in the preoperative holding area using an AP 1000 (AOPI, Guangzhou, Guangdong, China); hand grip was measured using an electronic dynamometer AP 1005 (AOPI, Guangzhou, Guangdong, China); and the ability to sit up was assessed. Our primary objective was to determine the spirometry volume recovery trajectory at 10, 30, and 50 min and 24 h after extubation. For all spirometry measurements, patients were seated at a 30 to 45 degree angle in bed, inhaled slowly, held breath for a few seconds, and then exhaled quickly toward the spirometer mouthpiece. Recording of the spirometry volumes was done until the display on the device no longer fluctuated. Spirometry volumes were conducted 3 times with a 30-s interval for each measurement, and the highest value was recorded. TOFR was measured immediately prior to extubation using the TOF-Watch (Organon, Dublin, Ireland).
Handgrip strength assessments were performed 3 times with a 30-s interval at each time point using the electronic dynamometer at 10, 30, and 50 min and 24 h after extubation. The highest strength value was recorded. At each time point after extubation, patients were assessed for the ability to sit unaided with their upper body elevated 30 degrees from a recumbent position. We adopted the Richmond Agitation Sedation Scale (RASS)  scores to measure the level of sedation at each time point. Before surgery (baseline) and before leaving the PACU at 24 h after surgery, patients were asked to complete a Quality of Recovery-40 survey (QoR-40) . SpO2 <90% for at least 5 s was considered hypoxia. The presence of any airway obstruction features, such as bronchospasm, stridor, and aspiration were recorded.
All data were analyzed using SPSS 25.0 (IBM, Armonk, NY, USA). Normality of each variable was assessed using the Kolmogorov-Smirnov test. Categorical variables were expressed as percentages and frequencies, while continuous variables were expressed as means and standard deviations. Relative and absolute spirometry values and handgrip force in the groups were compared at every time point using 2-way repeated measures ANOVA or generalized linear models. The ability to sit independently, QoR-40 survey, and TOFR before extubation and airway variables were compared using the Wilcoxon rank-sum, chi-square,
Sixty patients participated in the study from November 24, 2021, to March 15, 2022. Figure 1 shows the design of the study. The 60 patients were randomized equally to the clinical assessment group or TOF group. A summary of the demographic and baseline measurement data for the patients is shown in Table 1. The groups had no differences in age, weight, height, ASA classification, respiratory rate, heart rate, mean arterial pressure, body temperature, surgical division, or medical comorbidities. There was no difference in measurements of the baseline spirometry volumes or handgrip strength. All patients were able to sit up on their own before surgery.
INTRAOPERATIVE ANESTHETIC AND RELAXANT APPLICATION:
As shown in Table 2, the groups had no difference in dosage of intraoperative anesthetic and muscle relaxant. The RASS scores did not differ between the 2 groups at each time point in the PACU.
RECOVERY OF POSTOPERATIVE SPIROMETRY VOLUMES:
As shown in Figure 2, there was no significant difference in the recovery trajectory between the 2 groups (P=0.072). In addition, the absolute incentive spirometry volumes at 10 min (1800±913 mL vs1529±718 mL, P=0.214), 30 min (1883±860 mL vs 1788±686 mL, P=0.644), 50 min (2011±826 mL vs 1925±676 mL, P=0.664), and 24 h (2699±796 mL vs 2823±882 mL, P=0.575) revealed no differences between the 2 groups. However, there was a significant decrease (−1012 [−1201 to −183] mL vs −1447 [−1682 to −1210] mL, P=0.005) in the TOF group in incentive spirometry from baseline at 10 min after extubation. For the 3 remaining postoperative time points 30 min (−933 [−1118 to −748] mL vs −1187 [−1415 to −959] mL, P=0.09), 50 min (−801 [−973 to −631] mL vs −1069 [−1273 to −865] mL, P=0.059), and 24 h (−118 [−183 to −54] mL vs −191 [−309 to −72] mL, P=0.282) after extubation, the TOF group did not outperform the clinical assessment group in terms of reduced incentive spirometry volumes (Figure 2, Table 3).
RECOVERY OF POSTOPERATIVE HANDGRIP STRENGTH AND ABILITY TO SIT UP:
Although handgrip strength and the ability to sit up were both decreased immediately after surgery, the TOF group did not exhibit any beneficial trends. Also, other secondary outcomes did not show significant differences between the groups. Incidence of rNMB (TOFR <0.9) in the clinical assessment group was 50% (50% vs 0, P<0.001). Incidence of hypoxia (SpO2 <90%) in the clinical assessment group was 30% vs 3.3% in the TOF group (P=0.012; Table 3). There was no significant difference between the 2 groups in QoR-40 results except at 24 h after extubation on physical independence (25 [25– vs 25 [22.75–25], P=0.026; Table 4).
In this study, we found that using a TOF ratio ≥0.9 at the time of extubation did not improve the early postoperative strength quantified by spirometry volume, handgrip strength, and the proportion of unaided sitting when compared with the clinical assessment methods.
A significant decrease in incentive spirometry volumes was expected immediately following surgery from baseline, as demonstrated in previous studies . From 10 min to 24 h after extubation, in both study groups, patients exhibited similar trends in recovery with regard to spirometry volumes, independence in sitting, and handgrip strength. The reasons we did not observe a difference between study groups are not clear. The most likely explanation is that the anesthesiologist responsible for extubation has extensive tracheal extubation experience. There was a significant reduction in spirometry volume compared with baseline in the TOF group (−1447 mL) compared with that of the clinical assessment group (−1012 mL) at 10 min after extubation. One possible reason is that the mean preoperative baseline volume of the TOF group (2975 mL) was higher than that of the clinical assessment group (2812 mL). Interestingly, such a short time (10 min) to extubation has not been assessed in previous studies. Volume change in spirometry between the 2 groups from baseline at 30 min was greater than that of a previous study; this could be attributed to the method of neuromuscular reversal. In our study, the only available reversal agent, neostigmine, was not routinely used clinically, whereas previous studies used neostigmine or sugammadex .
Interestingly, we found that spirometry volumes in both groups had not returned to preoperative levels at 24 h after extubation. The decrease in incentive spirometry volume from preoperative baseline to 24 h after surgery was smaller in the clinical assessment group. The results were not significantly different from what was expected in the TOF group, but they were contrary to what we anticipated. This suggests that patients’ vital signs should be closely monitored even 24 h after surgery.
In the clinical assessment group, conducted according to routine clinical procedures in our hospital, 50% patients had rNMB after tracheal extubation. This was similar to the results of a prospective observational study in which the incidence of rNMB was 48.8% at extubation, with a lower incidence of postoperative respiratory complications, possibly due to the routine use of the reversal agent neostigmine and additional low-dose neostigmine or sugammadex . Using a TOFR threshold of 0.9, studies conducted over the past 15 years have found that rNMB occurred in 0% to 90.5% of patients at extubation [13,21,22]. In the present study, rNMB was slightly lower than that of Yu et al, who reported that 57.8% of patients had a TOFR <0.9 at extubation . The reason might be that we did not target a specific high-risk population but rather used broad inclusion criteria. Probably due to proactive interventions taken by PACU staff, hypoxia incidence decreased. However, it was still higher than that reported by Murphy et al, who did not observe any cases of severe hypoxia in the PACU . This may be because of the higher patient to nurse ratio in our PACU. In addition, the incidence of hypoxia was also higher than that of another randomized controlled study, possibly because the patients we observed were older and the duration of surgery and anesthesia were longer . Another reason may be related to the calibration of the TOF monitor before endotracheal intubation in our study.
Clinical interest lies in the measurement of QoR-40, as poor quality recovery in the early postoperative period is closely linked to postoperative complications . The outcome of our study is similar to that of a previous study on the QoR-40 questionnaire used to evaluate early postoperative recovery quality , in which dimension of physical independence was temporarily affected postoperatively, but soon recovered on early postoperative days. This could probably be related to the type of surgery, as there were few orthopedic and no thoracic surgeries in our clinical trial.
The strength of this study is that we adopted multiple time points (10, 30, and 50 min and 24 h) and a variety of measurements (incentive spirometry, hand grip strength, and sitting up unaided) to overall assess the postoperative condition so that we would not be limited to just one factor.
There are also limitations to this study. First, because our study was carried out at a single center, our results may not be generalizable. Second, the sample size was not very large, and a higher number of patients might be able to provide more specific rNMB data. The TOF-Watch may overestimate the degree of recovery at the end of a surgery based on acceleromyography, as it lacks the accuracy of conventional mechanomyelography or electromyelography . In most cases, acceleromyography yields baseline TOF ratios that are greater than 100% (typically 105–115%). Furthermore, the accuracy of acceleromyography in awake postoperative patients has been questioned .
On the basis of the results of this study and in this patient population, the findings showed that using the TOFR ≥0.9 before extubation did not improve postoperative strength quantified by spirometry volume, handgrip strength, and proportion of unaided sitting.
FiguresFigure 1. The design of the study. TOF – train-of-four, measured by neuromuscular stimulator is composed of 4 equal stimuli delivered at intervals of 0.5 s. TOFR – train-of-four ratio, which is calculated by comparing the magnitude of the fourth twitch to the first one and indicates a non-depolarizing neuromuscular block, and a ratio ≥0.90 can be used as an objective measurement of neuromuscular reversal. PACU – Postanesthesia Care Unit. Strength measurements include spirometry and handgrip strength and ability to sit up unaided. Figure 2. Strength measurements of different time points. (A) Change from baseline spirometry volume varies with time; (B) absolute incentive spirometry volume varies with time; (C) handgrip strength varies with time; (D) ability to sit up varies with time. (A) Data are shown with (median, IQR); IQR – interquartile range; * P<0.05 when compared with clinical assessment group at the same time point; (B) Data are shown with (Mean, Std), Std – standard deviation; there was no significant difference between the two groups at the same time point; (C) Data are shown with (Median, IQR), there was no significant difference between the two groups at the same time point; (D) Data are shown with (Proportion of Total), there was no significant difference between the 2 groups at the same time point. @10 min – time point of 10 min after extubation; @30 min – time point of 30 min after extubation; @50 min – time point of 50 min after extubation; @24 h – time point of 24 h after extubation.
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