A method for early diagnosis and treatment of intrathoracic esophageal anastomotic leakage: prophylactic placement of a drainage tube adjacent to the anastomosis

Navigating complexities and considerations for suspected anastomotic leakage in the upper gastrointestinal tract: A state of the art review

This state-of-the-art review explores the intricacies of anastomotic leaks following oesophagectomy and gastrectomy, crucial surgeries for globally increasing esophageal and gastric cancers. Despite advancements, anastomotic leaks occur in up to 30 % and 10 % of oesophagectomy and gastrectomy cases, respectively, leading to prolonged hospital stays, substantial impact upon short- and long-term health-related quality of life and greater mortality. Recognising factors contributing to leaks, including patient characteristics and surgical techniques, are vital for preoperative risk stratification. Diagnosis is challenging, involving clinical signs, biochemical markers, and various imaging modalities. Management strategies range from non-invasive approaches, including antibiotic therapy and nutritional support, to endoscopic interventions such as stent placement and emerging vacuum-assisted closure devices, and surgical interventions, necessitating timely recognition and tailored interventions. A step-up approach, beginning non-invasively and progressing based on treatment success, is more commonly advocated. This comprehensive review highlights the absence of standardised treatment algorithms, emphasizing the importance of individualised patient-specific management.

Feasibility of utilizing mediastinal drains alone following esophageal cancer surgery: a retrospective study

BACKGROUND

It was typically necessary to place a closed thoracic drainage tube for drainage following esophageal cancer surgery. Recently, the extra use of thoracic mediastinal drainage after esophageal cancer surgery had also become more common. However, it had not yet been determined whether mediastinal drains could be used alone following esophageal cancer surgery.

METHODS

A total of 134 patients who underwent esophageal cancer surgery in our department between June 2020 and June 2023 were retrospectively analyzed. Among them, 34 patients received closed thoracic drainage (CTD), 58 patients received closed thoracic drainage combined with mediastinal drainage (CTD-MD), while 42 patients received postoperative mediastinal drainage (MD). The general condition, incidence of postoperative pulmonary complications, postoperative NRS score, and postoperative anastomotic leakage were compared. The Mann-Whitney U tests, Welch's t tests, one-way ANOVA, chi-square tests and Fisher's exact tests were applied.

RESULTS

There was no significant difference in the incidence of postoperative hyperthermia, peak leukocytes, total drainage, hospitalization days and postoperative pulmonary complications between MD group and the other two groups. Interestingly, patients in the MD group experienced significantly lower postoperative pain compared to the other two groups. Additionally, abnormal postoperative drainage fluid could be detected early in this group. Furthermore, there was no significant change in the incidence of postoperative anastomotic leakage and the mortality rate of patients after the occurrence of anastomotic leakage in the MD group compared with the other two groups.

CONCLUSIONS

Using mediastinal drain alone following esophageal cancer surgery was equally safe. Furthermore, it could substantially decrease postoperative pain, potentially replacing the closed thoracic drain in clinical practice.

Single chest drain is not inferior to double chest drain after robotic esophagectomy: a propensity score-matched analysis

Background

Chest drain management has a significant influence on postoperative recovery after robot-assisted minimally invasive esophagectomy (RAMIE). The use of chest drains increases postoperative pain by irritating intercostal nerves and hinders patients from early postoperative mobilization and recovery. To our knowledge, no study has investigated the use of two vs. one intercostal chest drains after RAMIE.

Methods

This retrospective cohort study evaluated patients undergoing elective RAMIE with gastric conduit pull-up and intrathoracic anastomosis. Patients were divided into two groups according to placement of one (11/2020-08/2022) or two (08/2018-11/2020) chest drains. Propensity score matching was performed in a 1:1 ratio, and the incidences of overall and pulmonary complications, drainage-associated re-interventions, radiological diagnostics, analgesic use, and length of hospital stay were compared between single drain and double drain groups.

Results

During the study period, 194 patients underwent RAMIE. Twenty-two patients were included after propensity score matching in the single and double chest drain group, respectively. Time until removal of the last chest drain [postoperative day (POD) 6.7 ± 4.4 vs. POD 9.4 ± 2.7, p = 0.004] and intensive care unit stay (4.2 ± 5.1 days vs. 5.3 ± 3.5 days, p = 0.01) were significantly shorter in the single drain group. Overall and pulmonary complications, drainage-associated events, re-interventions, number of diagnostic imaging, analgesic use, and length of hospital stay were comparable between both groups.

Conclusion

This study is the first to demonstrate the safety of single intercostal chest drain use and, at least, non-inferiority to double chest drains in terms of perioperative complications after RAMIE.

Case report: Drainage tube penetrating anastomosis as a rare cause for long-term nonunion of esophagogastric anastomosis in neck

Anastomotic leakage is a life-threatening complication for esophageal cancer patients who received McKeown esophagectomy. Cervical drainage tube penetrating anastomosis is a rare but noteworthy cause of long-term nonunion of esophagogastric anastomosis. Here we reported two cases of esophageal cancer patients who received McKeown esophagectomy. The first case acquired the anastomotic leakage on postoperative day (POD) 7, and lasted for 56 days. The cervical drainage tube was removed at POD 38, and the leakage healed in 25 days. The second case acquired the anastomotic leakage on POD 8 and lasted for 95 days. The cervical drainage tube was removed at POD 57, and the leakage healed in 46 days. The two cases demonstrated the duration-prolonging effect of drainage tube penetrating anastomosis, which should not be overlooked in clinical practice. We suggested paying attention to the duration of leakage, the drainage fluids amounts and characteristics, and the imaging manifestations to help diagnose. If the cervical drainage tube penetrated the anastomosis, the tube should be eliminated as soon.

Chest drainage after oesophageal resection: A systematic review

BACKGROUND

Modern enhanced recovery protocols discourage drain use due to negative impacts on patient comfort, mobility, and recovery, and lack of proven clinical benefit. After oesophagectomy, however, drains are still routinely placed. This review aimed to assess the evidence for, and how best to use chest drains after oesophageal surgery.

METHODS

A systematic literature search was performed in Medline, Embase and Cochrane collaboration databases. Studies reporting outcomes for different types or uses of thoracic drainage, or outcomes related to drains after trans-thoracic oesophagectomy were included. Studies were collated into domains based on variations in number, position, type, removal criteria, diagnostic use and complications of drains. Methodological quality was assessed with Newcastle-Ottawa and Jadad scores.

RESULTS

Among 434 potentially relevant studies, 27 studies met the inclusion criteria and these included 2564 patients. Studies that examined the number of drains showed pain reduction with a single drain compared to multiple drains (3 studies, n = 103), and transhiatal placement compared to intercostal (6 studies, n = 425). Amylase levels may aid diagnosis of anastomotic leak (9 studies, n = 888). Narrow calibre Blake drains may effectively drain both air and fluid (2 studies, n = 163). Drain removal criteria by daily drainage volumes of up to 300 mL did not impact subsequent effusion rates (2 studies, n = 130). Complications related directly to drains were reported by 3 studies (n = 59).

CONCLUSION

Available evidence on the impact of thoracic drainage after oesophagectomy is limited, but has the potential to negatively affect outcomes. Further research is required to determine optimum drainage strategies.

Application of mediastinal drainage tube in intrathoracic esophageal anastomotic leakage for early diagnosis and effective treatment: a retrospective study

Background

Intrathoracic esophageal anastomotic leakage (AL) is one of the most fatal complications after esophagectomy. In this study, we placed an additional drainage tube in the esophagus bed and evaluated its effect in early diagnosis and treatment of AL.

Methods

From January 2010 to August 2020, 312 patients with esophageal or cardia carcinoma underwent esophageal resection with intrathoracic esophagogastric anastomosis. A total of 138 patients with only one pleural drainage tube were divided into the “Control Group” and 174 patients with a pleural drainage tube and an additional mediastinal drainage tube (MDT) were divided into the “Tube Group”. For all patients, the incidence of postoperative AL, the time to diagnosis, time to recovery, and patient outcome were analyzed.

Results

No significant differences were observed in the AL rate (P = 0.837) and postoperative pain between two groups. However, in the Tube Group, almost all the patients were diagnosed prior to the appearance of hyperpyrexia, which was considered as the earliest and most common symptom after AL. In the Tube Group, a significant decrease was observed in the incidence of incurable fistula, which required re-operation or variable treatments under gastroscopy when compared to the Control Group (P = 0.032). Finally, patients in the Tube Group showed reduced post AL hospital day (P = 0.015) and a lower mortality, however, when compared to the Control Group, no significant differences were observed (P = 0.188).

Conclusions

Placement of an MDT does not prevent AL, but it is an effective approach for earlier diagnosis of AL and facilitates fistula healing and patient recovery.

The enhanced recovery after surgery (ERAS) protocol to promote recovery following esophageal cancer resection

Esophageal cancer surgery, comprising esophagectomy with radical lymphadenectomy, is a complex procedure associated with considerable morbidity and mortality. The enhanced recovery after surgery (ERAS) protocol which aims to improve perioperative care, minimize complications, and accelerate recovery is showing promise for achieving better perioperative outcomes. ERAS is a multimodal approach that has been reported to shorten the length of hospital stay, reduce surgical stress response, decrease morbidity, and expedite recovery. While ERAS components straddle preoperative, intraoperative, and postoperative periods, they need to be seen in continuum and not as isolated elements. In this review, we elaborate on the components of an ERAS protocol after esophagectomy including preoperative nutrition, prehabilitation, counselling, smoking and alcohol cessation, cardiopulmonary evaluation, surgical technique, anaesthetic management, intra- and postoperative fluid management and pain relief, mobilization and physiotherapy, enteral and oral feeding, removal of drains, and several other components. We also share our own institutional protocol for ERAS following esophageal resections.

Early detection of complications: anastomotic leakage

Anastomotic leakage (AL) is one of the most critical and detrimental complications in esophageal surgery. Early diagnosis and timely therapeutic action are necessary if patients are to avoid AL-related problems. However, there is no gold standard or consensus for early diagnosis. In this review, we focus on summarizing the definition and types of AL and modalities for early diagnosis of AL after esophagectomy.

Postoperative pulmonary complications and thoracocentesis associated with early versus late chest tube removal after thoracic esophagectomy with three-field dissection: a propensity score matching analysis

PURPOSE

To evaluate the safety of early chest tube removal after thoracic esophagectomy with three-field dissection.

METHODS

This prospective cohort study evaluated patients who underwent thoracic esophagectomy with three-field dissection during 2013-2015. Patients were divided into two groups according to whether they underwent early or late chest tube removal. Propensity score matching in a 1:1 ratio was applied. We compared the incidences of postoperative pulmonary complications and thoracocentesis in the two groups.

RESULTS

After propensity score matching, 89 patients in each group were analyzed. There was no significant difference between the groups in the incidences of pulmonary complications or thoracocentesis. Significantly more patients achieved first mobilization within 15 h postoperatively in the early removal group (89.8%) than in the late removal group (52%, p < 0.01). Multivariate analysis revealed that early chest tube removal was not a risk factor for pulmonary complications or thoracocentesis. Independent risk factors for pulmonary complications were a history of pulmonary disease (odds ratio: 0.81 [0.63-0.98]; p = 0.02) and neoadjuvant chemotherapy (odds ratio: 0.67 [0.32-0.96]; p = 0.04).

CONCLUSION

Early chest tube removal is as safe and feasible as late chest tube removal after thoracic esophagectomy with three-field dissection.

Abdominal Drainage and Amylase Measurement for Detection of Leakage After Gastrectomy for Gastric Cancer

PURPOSE

To investigate the value of daily measurement of drain amylase for detecting leakage in gastric cancer surgery.

METHODS

This was a retrospective analysis including all patients who underwent a gastrectomy for gastric cancer. From January 2013 until December 2015, an intra-abdominal drain was routinely placed. Drain amylase was measured daily. Receiver operator characteristic curves were created to assess the ability of amylase to predict leakage. Sensitivity, specificity, and negative and positive predictive value of amylase in drain fluid were determined. Leakage of the gastrojejunostomy or esophagojejunostomy, enteroenterostomy, duodenal stump, or pancreas was diagnosed by CT scan, endoscopy, or during re-operation. From January 2016 until April 2017, no drain was inserted. Surgical outcome and postoperative complications were compared between both groups.

RESULTS

Median drain amylase concentrations were higher for each postoperative day in patients with leakage. The optimal cutoff value was 1000 IU/L (sensitivity 77.8%, specificity 98.2%, negative predictive value 96.6%). Sixty-seven consecutive procedures were performed with a drain and 40 procedures without. No differences in group characteristics were observed except for gender. Fourteen patients (13.1%) had a leakage. The incidence and severity of leakage were not different between the patients with and without a drain. There was no significant difference in time to diagnosis (1 vs. 0 days; p 0.34), mortality rate (7.5 vs. 2.5%; p 0.41), and median length of hospital stay (9 days in both groups; p 0.46).

CONCLUSION

Daily amylase measurement in drain fluid does not influence the early recognition and management of leakage in gastric cancer surgery.

Experiences in the management of anastomotic leakages and analysis of the factors affecting leakage healing in patients with esophagogastric junction cancer

BACKGROUND

It was reported in the literatures that the incidence of anastomotic leakage in patients with esophagogastric junction cancer decreased due to application of staplers and closure devices as well as gastric conduit technique in recent years, however, it increased slightly at our center since widely using the above devices and gastric conduit techniques from 2009. The objective of this study was to summarize our experiences in the management of anastomotic leakages and analyze the factors affecting leakage healing in the patients with esophagogastric junction cancer after surgical resection in recent 6 years.

METHODS

All patients who received surgical resections for esophagogastric junction cancer and diagnosed anastomotic leak at our center between January 2009 and December 2014 were retrospectively analyzed, we also enrolled the patients who had a longer hospital stay (>30 days) as they may develop anastomotic leak. The binary logistic regression in SPSS 16.0 was applied to analyze the factors that may affect leakage healing.

RESULTS

Of the 1,815 surgically treated esophagogastric junction cancer patients, 91 cases were diagnosed anastomotic leakage postoperatively. The patients were divided into two groups based on the median leakage healing time (40 days) in this series: fast healing group (37 cases) and slowly healing group (54 cases). All factors that may affect the leakage healing were put into analysis by using binary logistic regression. The results of the analysis showed that leakage size (OR =1.073, P=0.004), thoracic drainage (OR =12.937, P=0.037) and smoking index ≤400 (OR =1.001, P=0.04) significantly affected the healing time, while drinking history (P=0.177), duration of fever after anastomotic leak developed (P=0.084), and hypoproteinemia after leak (P=0.169) also apparently but not significantly affect the healing time.

CONCLUSIONS

Though many factors may affect leakage healing in the esophagogastric junction carcinoma patients, leakage size, thoracic drainage and smoking index (≤400) are the most important factors affecting the leakage healing. Placement of a chest tube beside the anastomosis area during operation for early identification and control of an anastomotic leak to minimize contamination of the mediastinum is the most important way to promote leakage healing. A chest tube placing into the purulent cavities after the patients experienced leaks is also important for the cure of leakage. More attention should be paid perioperatively to the patients who had a smoking index (≥400) and the patients who suffered fever or hypoproteinemia.

Management and outcome of cervical versus intrathoracic manifestation of cervical anastomotic leakage after transthoracic esophagectomy for cancer

The aim of this study was to evaluate management strategies and related outcomes for cervical versus intrathoracic manifestation of cervical anastomotic leakage after transthoracic esophagectomy for cancer with gastric conduit reconstruction. Patients with esophageal cancer undergoing transthoracic esophagectomy with cervical anastomosis from October 2003 to December 2014 were identified from a prospectively acquired database. Management strategies and related outcomes among patients with anastomotic leakage confined to the neck were compared to patients with intrathoracic manifestation of anastomotic leakage. From a total of 286 patients, leakage of the cervical anastomosis occurred in 60 patients (21%) at a median time of 7 days after esophagectomy. Leakage was confined to the neck in 23 of 60 patients (38%), whereas 37 of 60 patients (62%) presented with intrathoracic spread. Leakages with intrathoracic manifestation were more frequently accompanied by a positive SIRS score compared to leakages confined to the neck (73% vs. 35%, respectively; P = 0.004). Drainage of the anastomotic leakage through the neck wound was effective in all of 23 patients (100%) with cervical manifestation. In patients with intrathoracic manifestation, mediastinal drainage through the neck was successful in 15 of 37 patients (41%), whereas 22 patients (59%) required an intervention through the thoracic cavity. Compared to patients with leakage confined to the neck, patients with intrathoracic manifestation showed prolonged intensive care unit (ICU) stay (median 6 vs. 2 days, respectively; P = 0.001), hospital stay (median 34 vs. 19 days, respectively; P < 0.001), and time to oral intake (32 vs. 23 days, respectively; P = 0.018). Intrathoracic manifestation of cervical anastomotic leakage occurs in more than half of patients with anastomotic leakage after transthoracic esophagectomy for cancer. A SIRS reaction should raise the suspicion of intrathoracic spread of leakage. Intrathoracic manifestation can be managed effectively by mediastinal drainage through the neck in 41% of patients, but a reintervention through the thoracic cavity is required in 59%. Intrathoracic manifestation of leakage results in prolonged ICU/hospital stay and delays time to oral intake compared with leakage confined to the neck.

Partial esophagogastrostomy with esophagogastric anastomosis below the aortic arch in cardiac carcinoma: characteristics and treatment of postoperative anastomotic leakage

BACKGROUND

Anastomotic leakage is a severe and common complication for surgeries of cardiac cancer. Here we explore the clinical features, diagnosis, and treatment strategies of anastomotic leakage in cardiac carcinoma patients after esophagogastric anastomosis.

METHODS

From January 2009 to December 2013, 1,196 patients with cardiac carcinoma underwent esophagectomy and esophagogastric anastomosis in Cancer Hospital, Peking Union Medical College & Chinese Academy of Medical Sciences. Of them, 25 patients developed symptomatic anastomotic leakage. Their clinical data were retrospectively reviewed.

RESULTS

Among these 25 patients with anastomotic leakage, three died after active treatment and fifteen healed with thoracic drainage time 18-115 days. The left seven patients who did not heal until discharge developed chronic infection sinus of anastomotic leakage. Without infection symptoms, they were discharged 30-100 days after surgery with nasoenteral tube and thoracic drainage.

CONCLUSIONS

Anastomotic leakage in cardiac carcinoma patients after esophagogastric anastomosis can be classified into five subtypes: occult type, left thoracic type, right thoracic type, mediastinal type, and mixd type. Subtyping of anastomotic leakage is useful and convenient for diagnosis and treatment.

Surgical treatments for esophageal cancers

The following, from the 12th OESO World Conference: Cancers of the Esophagus, includes commentaries on the role of the nurse in preparation of esophageal resection (ER); the management of patients who develop high-grade dysplasia after having undergone Nissen fundoplication; the trajectory of care for the patient with esophageal cancer; the influence of the site of tumor in the choice of treatment; the best location for esophagogastrostomy; management of chylous leak after esophagectomy; the optimal approach to manage thoracic esophageal leak after esophagectomy; the choice for operational approach in surgery of cardioesophageal crossing; the advantages of robot esophagectomy; the place of open esophagectomy; the advantages of esophagectomy compared to definitive chemoradiotherapy; the pathologist report in the resected specimen; the best way to manage patients with unsuspected positive microscopic margin after ER; enhanced recovery after surgery for ER: expedited care protocols; and long-term quality of life in patients following esophagectomy.

Impact of body mass index on surgical outcomes after esophagectomy for patients with esophageal squamous cell carcinoma

BACKGROUND

Patients with overweight reportedly have more comorbidities, including diabetes mellitus and cardiovascular disease, and longer operating times as well as more blood loss during surgery compared with those with normal weight. However, the impact of overweight on the short-term outcome after transthoracic esophagectomy for patients with esophageal squamous cell carcinoma (ESCC) remains unclear. We hypothesized that overweight has a negative impact on short-term surgical outcomes after esophagectomy for patients with ESCC.

METHODS

A total of 304 patients who underwent transthoracic esophagectomy for ESCC were included in this study. Body mass index (BMI) was classified into three categories, <18.49, 18.50-24.99, and >25.00 (kg/m(2)), defined as low, normal, and high BMI, respectively, according to the World Health Organization criteria. We investigated the association of BMI status with patient demographics and surgical outcomes after esophagectomy for patients with ESCC. In addition, overall survival and relapse-free survival stratified by BMI were compared.

RESULTS

Fifty-nine (19.4 %) and 41 (13.4 %) patients were classified to low BMI and high BMI, respectively. The high-BMI group had significantly higher comorbidity rates of diabetes mellitus (p < 0.01) and anastomotic leakage (p = 0.011) than the normal-BMI group. There were no significant association between high BMI and another various complications except for an anastomotic leakage, severe complications defined by Clavien-Dindo classification and in-hospital mortality. In multivariate analysis, high BMI was a significant risk factor for anastomotic leakage (p = 0.030, hazard ratio; 3.423, 95%CI; 1.128-10.38). On the other hand, no significant association was observed between low BMI and short surgical outcomes. There were no significant differences in overall and relapse-free survival among the three BMI groups in univariate and multivariate analysis (p = 0.128 and p = 0.584, respectively).

CONCLUSION

The surgical treatment should not be denied for patients with ESCC due to overweight and underweight. However, intraoperative prevention and postoperative careful monitoring for anastomotic leakage might be required after esophagectomy for overweight patients with ESCC.

Choice of therapeutic strategies in intrathoracic anastomotic leak following esophagectomy

Background

The aim of this study was to analyze our experience with management of intrathoracic anastomotic leak after esophagectomy.

Methods

Clinical data from 33 patients who developed intrathoracic anastomotic leak were evaluated retrospectively. These patients were selected from 1867 patients undergoing resection carcinoma of the esophagus and reconstruction between January 2003 and December 2012.

Results

Surgical intervention and the reformed “three-tube method” were applied in 13 and 20 patients, respectively. The overall incidence of intrathoracic anastomotic leakage was 1.8%. The median time interval from esophagectomy to diagnosis of leak was 9.7 days. Sixteen patients were confirmed as having leakage by oral contrast computed tomography (CT). Age and interval from surgery to diagnosis of leak were identified as statistically significant parameters between contained and uncontained groups. Moreover, patients with hypoalbuminemia had a longer time to leak closure than patients without hypoalbuminemia. Six patients died from intrathoracic anastomotic leak, with a mortality rate of 18.2%. There was no statistically significant difference in the time to leak closure between patients who underwent surgical exploration and those who received conservative treatment.

Conclusions

Intrathoracic anastomotic leak after esophagectomy was associated with significant mortality. Once intrathoracic anastomotic leakage following esophagectomy was diagnosed or highly suspected, individualized management strategies should be implemented according to the size of the leak, extent of the abscess, and status of the patient. In the majority of patients with anastomotic leak, we preferred the strategy of conservative treatment.

Optimal approach to the management of intrathoracic esophageal leak following esophagectomy: a systematic review

BACKGROUND

Recently, endoscopic interventions (eg, esophageal stenting) have been successfully used for the management of intrathoracic leak. The purpose of this systematic review was to assess the safety and efficacy of techniques used in the management of intrathoracic anastomotic leak.

DATA SOURCES

We performed a systematic review of MEDLINE, EMBASE, and PubMed to identify eligible studies analyzing management of intrathoracic esophageal leak following esophagectomy.

CONCLUSIONS

Intraoperative anastomotic drain placement was associated with earlier identification and resolution of anastomotic leak (mean 23.4 vs 80.7 days). In addition, reinforcement of the anastomosis with omentoplasty may reduce the incidence of anastomotic leak by nearly 50%. Endoscopic stent placement was associated with leak resolution in 72%; fatal complications were reported, however, and safety remains to be proven. Negative pressure therapy, a potentially useful tool, requires further study. If stenting and wound vacuum are used, undrained mediastinal contamination and persistent leak require surgical intervention.

Mediastinal microdialysis in the diagnosis of early anastomotic leakage after resection for cancer of the esophagus and gastroesophageal junction

BACKGROUND

Anastomotic leakage (AL) after gastroesophageal resection for cancer is a serious complication. The aim was to evaluate mediastinal microdialysis in the detection of AL before clinical symptoms.

METHODS

Sixty patients were included. Samples were collected every 4 hours in the 1st 8 postoperative days and analyzed for several metabolites.

RESULTS

Forty-four patients had an uncomplicated postoperative recovery, 7 developed anastomotic-related complications, and 5 developed major nonanastomotic-related complications. Six patients were excluded (early catheter malfunction and reoperation). Logistic regression model on several metabolites demonstrated a 100% sensitivity, specificity, and positive and negative predictive values regarding the diagnosis of anastomotic complications within postoperative day 7. However, as independent markers, none of the measured metabolites were able to predict AL.

CONCLUSION

The diagnosis of anastomotic-related complications before clinical symptoms seemed possible by mediastinal microdialysis, but the diagnosis should be based on an interpretation of several metabolic events.