The Effect of Thoracic Epidural Analgesia on the Occurrence of Late Postoperative Hypoxemia in Patients Undergoing Elective Coronary Bypass Surgery

Thoracic Epidural Anesthesia in Cardiac Surgery: A Systematic Review, Meta-Analysis, and Trial Sequential Analysis of Randomized Controlled Trials

BACKGROUND

Research on fast-track recovery protocols postulates that thoracic epidural anesthesia (TEA) in cardiac surgery contributes to improved postoperative outcomes. However, concerns about TEA's safety hinder its widespread usage. We conducted a systematic review and meta-analysis to assess the benefits and risks of TEA in cardiac surgery.

METHODS

We searched 4 databases for randomized controlled trials (RCTs) assessing the use of TEA against only general anesthesia (GA) in adults undergoing cardiac surgery, up till June 4, 2022. We conducted random-effects meta-analyses, evaluated risk of bias using the Cochrane Risk-of-Bias 2 tool, and rated certainty of evidence via the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) approach. Primary outcomes were intensive care unit (ICU), hospital length of stay, extubation time (ET), and mortality. Other outcomes included postoperative complications. Trial sequential analysis (TSA) was conducted on all outcomes to elicit statistical and clinical benefit.

RESULTS

Our meta-analysis included 51 RCTs (2112 TEA patients and 2220 GA patients). TEA significantly reduced ICU length of stay (-6.9 hours; 95% confidence interval [CI], -12.5 to -1.2; P = .018), hospital length of stay (-0.8 days; 95% CI, -1.1 to -0.4; P < .0001), and ET (-2.9 hours; 95% CI, -3.7 to -2.0; P < .0001). However, we found no significant change in mortality. TSA found that the cumulative Z-curve passed the TSA-adjusted boundary for ICU length of stay, hospital length of stay, and ET, suggesting a clinical benefit. TEA also significantly reduced pain scores, pooled pulmonary complications, transfusion requirements, delirium, and arrhythmia, without additional complications such as epidural hematomas, of which the risk was estimated to be <0.14%.

CONCLUSIONS

TEA reduces ICU and hospital length of stay, and postoperative complications in patients undergoing cardiac surgery with minimal reported complications such as epidural hematomas. These findings favor the use of TEA in cardiac surgery and warrant consideration for use in cardiac surgeries worldwide.

Nurse-guided incentive spirometry use and postoperative pulmonary complications among cardiac surgery patients: A randomized controlled trial

AIMS

To assess the effect of nurse-guided use of incentive spirometer on postoperative oxygenation and pulmonary complications after coronary artery bypass graft surgery.

BACKGROUND

Deep breathing exercises have been shown to improve postoperative lung expansion and reduce pulmonary complications. An incentive spirometer is a deep breathing exercises device that imitates continuous sigh-like maximal inspiration.

DESIGN

Randomized control trial, two groups nonblinded parallel design.

METHODS

A total of n = 89 eligible patients were randomized to either control or intervention group. Patients in the intervention group received bihourly nurse-guided incentive spirometry for 48-h postextubation. The endpoints were: the number and duration of hypoxic events during the first 24-hr postsurgery, pneumonia and pulmonary function parameters. Data were collected May to September 2019.

RESULTS

Patients in the intervention group had a significantly lower mean number of hypoxic events with shorter duration and shorter length of stay in the hospital and the ICU. Patients in the intervention group also had greater postoperative forced expiratory volume in 1 second.

CONCLUSION

Nurse-guided use of the incentive spirometer reduces the risk of pulmonary complications and hospital length of stay after cardiac surgery.

Epidural analgesia for adults undergoing cardiac surgery with or without cardiopulmonary bypass

BACKGROUND

General anaesthesia combined with epidural analgesia may have a beneficial effect on clinical outcomes. However, use of epidural analgesia for cardiac surgery is controversial due to a theoretical increased risk of epidural haematoma associated with systemic heparinization. This review was published in 2013, and it was updated in 2019.

OBJECTIVES

To determine the impact of perioperative epidural analgesia in adults undergoing cardiac surgery, with or without cardiopulmonary bypass, on perioperative mortality and cardiac, pulmonary, or neurological morbidity.

SEARCH METHODS

We searched CENTRAL, MEDLINE, and Embase in November 2018, and two trial registers up to February 2019, together with references and relevant conference abstracts.

SELECTION CRITERIA

We included all randomized controlled trials (RCTs) including adults undergoing any type of cardiac surgery under general anaesthesia and comparing epidural analgesia versus another modality of postoperative pain treatment. The primary outcome was mortality.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures as expected by Cochrane.

MAIN RESULTS

We included 69 trials with 4860 participants: 2404 given epidural analgesia and 2456 receiving comparators (systemic analgesia, peripheral nerve block, intrapleural analgesia, or wound infiltration). The mean (or median) age of participants varied between 43.5 years and 74.6 years. Surgeries performed were coronary artery bypass grafting or valvular procedures and surgeries for congenital heart disease. We judged that no trials were at low risk of bias for all domains, and that all trials were at unclear/high risk of bias for blinding of participants and personnel taking care of study participants.Epidural analgesia versus systemic analgesiaTrials show there may be no difference in mortality at 0 to 30 days (risk difference (RD) 0.00, 95% confidence interval (CI) -0.01 to 0.01; 38 trials with 3418 participants; low-quality evidence), and there may be a reduction in myocardial infarction at 0 to 30 days (RD -0.01, 95% CI -0.02 to 0.00; 26 trials with 2713 participants; low-quality evidence). Epidural analgesia may reduce the risk of 0 to 30 days respiratory depression (RD -0.03, 95% CI -0.05 to -0.01; 21 trials with 1736 participants; low-quality evidence). There is probably little or no difference in risk of pneumonia at 0 to 30 days (RD -0.03, 95% CI -0.07 to 0.01; 10 trials with 1107 participants; moderate-quality evidence), and epidural analgesia probably reduces the risk of atrial fibrillation or atrial flutter at 0 to 2 weeks (RD -0.06, 95% CI -0.10 to -0.01; 18 trials with 2431 participants; moderate-quality evidence). There may be no difference in cerebrovascular accidents at 0 to 30 days (RD -0.00, 95% CI -0.01 to 0.01; 18 trials with 2232 participants; very low-quality evidence), and none of the included trials reported any epidural haematoma events at 0 to 30 days (53 trials with 3982 participants; low-quality evidence). Epidural analgesia probably reduces the duration of tracheal intubation by the equivalent of 2.4 hours (standardized mean difference (SMD) -0.78, 95% CI -1.01 to -0.55; 40 trials with 3353 participants; moderate-quality evidence). Epidural analgesia reduces pain at rest and on movement up to 72 hours after surgery. At six to eight hours, researchers noted a reduction in pain, equivalent to a reduction of 1 point on a 0 to 10 pain scale (SMD -1.35, 95% CI -1.98 to -0.72; 10 trials with 502 participants; moderate-quality evidence). Epidural analgesia may increase risk of hypotension (RD 0.21, 95% CI 0.09 to 0.33; 17 trials with 870 participants; low-quality evidence) but may make little or no difference in the need for infusion of inotropics or vasopressors (RD 0.00, 95% CI -0.06 to 0.07; 23 trials with 1821 participants; low-quality evidence).Epidural analgesia versus other comparatorsFewer studies compared epidural analgesia versus peripheral nerve blocks (four studies), intrapleural analgesia (one study), and wound infiltration (one study). Investigators provided no data for pulmonary complications, atrial fibrillation or flutter, or for any of the comparisons. When reported, other outcomes for these comparisons (mortality, myocardial infarction, neurological complications, duration of tracheal intubation, pain, and haemodynamic support) were uncertain due to the small numbers of trials and participants.

AUTHORS' CONCLUSIONS

Compared with systemic analgesia, epidural analgesia may reduce the risk of myocardial infarction, respiratory depression, and atrial fibrillation/atrial flutter, as well as the duration of tracheal intubation and pain, in adults undergoing cardiac surgery. There may be little or no difference in mortality, pneumonia, and epidural haematoma, and effects on cerebrovascular accident are uncertain. Evidence is insufficient to show the effects of epidural analgesia compared with peripheral nerve blocks, intrapleural analgesia, or wound infiltration.

Thoracic epidural anesthesia improves outcomes in patients undergoing cardiac surgery: meta-analysis of randomized controlled trials

To assess the efficacy of thoracic epidural anesthesia (TEA) with or without general anesthesia (GA) versus GA in patients who underwent cardiac surgery, PubMed, Embase, the Cochrane online database, and Web of Science were searched with the limit of randomized controlled trials (RCTs) relevant to ‘thoracic epidural anesthesia’ and ‘cardiac surgery’. Studies were identified and data were extracted by two reviewers independently. The quality of included studies was also assessed according to the Cochrane handbook. Outcomes of mortality, cardiac and respiratory functions, and treatment-associated complications were pooled and analyzed. The comprehensive search yielded 2,230 citations, and 25 of them enrolling 3,062 participants were included according to the inclusion criteria. Compared with GA alone, patients received TEA and GA showed reduced risks of death, myocardial infarction, and stroke, though there were no significant differences (P > 0.05). With regard to treatment-related complications, the pooled results for respiratory complications (risk ratio (RR), 0.69; 95% CI: 0.51, 0.91, P < 0.05), supraventricular arrhythmias (RR, 0.61; 95% CI: 0.42, 0.87, P < 0.05), and pain (mean difference (MD), −1.27; 95% CI: −2.20, −0.35, P < 0.05) were 0.69, 0.61, and −1.27, respectively. TEA was also associated with significant reduction of stays in intensive care unit (MD, −2.36; 95% CI: −4.20, −0.52, P < 0.05) and hospital (MD, −1.51; 95% CI: −3.03, 0.02, P > 0.05) and time to tracheal extubation (MD, −2.06; 95% CI:−2.68, −1.45, P < 0.05). TEA could reduce the risk of complications such as supraventricular arrhythmias, stays in hospital or intensive care unit, and time to tracheal extubation in patients who experienced cardiac surgery.

Impact of epidural analgesia on mortality and morbidity after surgery: systematic review and meta-analysis of randomized controlled trials

OBJECTIVE

To quantify benefit and harm of epidural analgesia, compared with systemic opioid analgesia, in adults having surgery under general anesthesia.

BACKGROUND

It remains controversial whether adding epidural analgesia to general anesthesia decreases postoperative morbidity and mortality.

METHODS

We searched CENTRAL, EMBASE, PubMed, CINAHL, and BIOSIS till July 2012. We included randomized controlled trials comparing epidural analgesia (with local anesthetics, lasting for ≥ 24 hours postoperatively) with systemic analgesia in adults having surgery under general anesthesia, and reporting on mortality or any morbidity endpoint.

RESULTS

A total of 125 trials (9044 patients, 4525 received epidural analgesia) were eligible. In 10 trials (2201 patients; 87 deaths), reporting on mortality as a primary or secondary endpoint, the risk of death was decreased with epidural analgesia (3.1% vs 4.9%; odds ratio, 0.60; 95% confidence interval, 0.39-0.93). Epidural analgesia significantly decreased the risk of atrial fibrillation, supraventricular tachycardia, deep vein thrombosis, respiratory depression, atelectasis, pneumonia, ileus, and postoperative nausea and vomiting, and also improved recovery of bowel function, but significantly increased the risk of arterial hypotension, pruritus, urinary retention, and motor blockade. Technical failures occurred in 6.1% of patients.

CONCLUSIONS

In adults having surgery under general anesthesia, concomitant epidural analgesia reduces postoperative mortality and improves a multitude of cardiovascular, respiratory, and gastrointestinal morbidity endpoints compared with patients receiving systemic analgesia. Because adverse effects and technical failures cannot be ruled out, individual risk-benefit analyses and professional care are recommended.

Etiology and use of the "hanging drop" technique: a review

Background. The hanging drop (HD) technique presumably relies on the presence of subatmospheric epidural pressure. It is not clear whether this negative pressure is intrinsic or an artifact and how it is affected by body position. There are few data to indicate how often HD is currently being used. Methods. We identified studies that measured subatmospheric pressures and looked at the effect of the sitting position. We also looked at the technique used for cervical and thoracic epidural anesthesia in the last 10 years. Results. Intrinsic subatmospheric pressures were measured in the thoracic and cervical spine. Three trials studied the effect of body position, indicating a higher incidence of subatmospheric pressures when sitting. The results show lower epidural pressure (−10.7 mmHg) with the sitting position. 28.8% of trials of cervical and thoracic epidural anesthesia that documented the technique used, utilized the HD technique. When adjusting for possible bias, the rate of HD use can be as low as 11.7%. Conclusions. Intrinsic negative pressure might be present in the cervical and thoracic epidural space. This effect is more pronounced when sitting. This position might be preferable when using HD. Future studies are needed to compare it with the loss of resistance technique.

Cardiac compression of lung lower lobes after coronary artery bypass graft with cardiopulmonary bypass

Background

Atelectasis is a major cause of hypoxemia after coronary artery bypass grafting (CABG) and is commonly ascribed to general anesthesia, high inspiratory oxygen concentration and cardiopulmonary bypass (CPB). The objective of this study was to evaluate the role of heart-induced pulmonary compression after CABG with CPB.

Methods

Seventeen patients without pre-operative cardiac failure who were scheduled for coronary artery bypass graft underwent pre- and postoperative thoracic computed tomography. The cardiac mass, the pressure exerted on the lungs by the right and left heart and the fraction of collapsed lower lobe segments below and outside of the heart limits were evaluated on a computed tomography section 1 cm above the diaphragmatic cupola.

Results

In the postoperative period, cardiac mass increased by 32% (117±31 g versus 155±35 g, p<0.001), leading to an increase in the pressure that was exerted on the lungs by the right (2.2±0.6 g.cm⁻² versus 3.2±1.2 g.cm⁻², p<0.05) and left heart (2.4±0.7 g.cm⁻² versus 4.2±1.8 g.cm⁻², p<0.001). The proportion of collapsed lung segments beneath the heart markedly increased [from 6.7% to 32.9% on the right side (p<0.001) and from 6.2% to 29% on the left side (p<0.001)], whereas the proportion of collapsed lung segments outside of the heart limits slightly increased [from 0.7% to 10.8% on the right side (p<0.001) and from 1.5% to 12.6% on the left side (p<0.001)].

Conclusion

The pressure that is exerted by the heart on the lungs increased postoperatively and contributed to the collapse of subjacent pulmonary segments.

Epidural analgesia for cardiac surgery

BACKGROUND

A combination of general anaesthesia (GA) with thoracic epidural analgesia (TEA) may have a beneficial effect on clinical outcomes by reducing the risk of perioperative complications after cardiac surgery.

OBJECTIVES

The objective of this review was to determine the impact of perioperative epidural analgesia in cardiac surgery on perioperative mortality and cardiac, pulmonary or neurological morbidity. We performed a meta-analysis to compare the risk of adverse events and mortality in patients undergoing cardiac surgery under general anaesthesia with and without epidural analgesia.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (2012, Issue 12) in The Cochrane Library; MEDLINE (PubMed) (1966 to November 2012); EMBASE (1989 to November 2012); CINHAL (1982 to November 2012) and the Science Citation Index (1988 to November 2012).

SELECTION CRITERIA

We included randomized controlled trials comparing outcomes in adult patients undergoing cardiac surgery with either GA alone or GA in combination with TEA.

DATA COLLECTION AND ANALYSIS

All publications found during the search were manually and independently reviewed by the two authors. We identified 5035 titles, of which 4990 studies did not satisfy the selection criteria or were duplicate publications, that were retrieved from the five different databases. We performed a full review on 45 studies, of which 31 publications met all inclusion criteria. These 31 publications reported on a total of 3047 patients, 1578 patients with GA and 1469 patients with GA plus TEA.

MAIN RESULTS

Through our search (November 2012) we have identified 5035 titles, of which 31 publications met our inclusion criteria and reported on a total of 3047 patients. Compared with GA alone, the pooled risk ratio (RR) for patients receiving GA with TEA showed an odds ratio (OR) of 0.84 (95% CI 0.33 to 2.13, 31 studies) for mortality; 0.76 (95% CI 0.49 to 1.19, 17 studies) for myocardial infarction; and 0.50 (95% CI 0.21 to 1.18, 10 studies) for stroke. The relative risks (RR) for respiratory complications and supraventricular arrhythmias were 0.68 (95% CI 0.54 to 0.86, 14 studies) and 0.65 (95% CI 0.50 to 0.86, 15 studies) respectively.

AUTHORS' CONCLUSIONS

This meta-analysis of studies, identified to 2010, showed that the use of TEA in patients undergoing coronary artery bypass graft surgery may reduce the risk of postoperative supraventricular arrhythmias and respiratory complications. There were no effects of TEA with GA on the risk of mortality, myocardial infarction or neurological complications compared with GA alone.

Epidural analgesia improves outcome in cardiac surgery: a meta-analysis of randomized controlled trials

OBJECTIVE

The authors conducted a review of randomized studies to determine whether there were any advantages for clinically relevant outcomes by adding epidural analgesia in patients undergoing cardiac surgery under general anesthesia.

DESIGN

Meta-analysis.

SETTING

Hospitals.

PARTICIPANTS

A total of 2366 patients from 33 randomized trials.

INTERVENTIONS

None.

DATA SOURCES AND STUDY SELECTION

PubMed, BioMedCentral, CENTRAL, EMBASE, Cochrane Central Register of Controlled Trials, and conference proceedings were searched (updated January 2008) for randomized trials that compared general anesthesia with an anesthetic plan including general anesthesia and epidural analgesia in cardiac surgery. Two independent reviewers appraised study quality, with divergences resolved by consensus. Overall analysis showed that epidural analgesia reduced the risk of the composite endpoint mortality and myocardial infarction (30/1125 [2.7%] in the epidural group v 64/1241 [5.2%] in the control arm, odds ratio [OR] = 0.61 [0.40-0.95], p = 0.03 number needed to treat [NNT] = 40), the risk of acute renal failure (35/590 [5.9%] in the epidural group v 54/618 [8.7%] in the control arm, OR = 0.56 [0.34-0.93], p = 0.02, NNT = 36), and the time of mechanical ventilation (weighted mean differences = -2.48 hours [-2.64, -2.32], p < 0.001).

CONCLUSIONS

This analysis suggested that epidural analgesia on top of general anesthesia reduced the incidence of perioperative acute renal failure, the time on mechanical ventilation, and the composite endpoint of mortality and myocardial infarction in patients undergoing cardiac surgery.

For patients undergoing pancreatoduodenectomy, epidural anesthesia and analgesia improves pain but increases rates of intensive care unit admissions and alterations in analgesics

OBJECTIVES

For some procedures, epidural anesthesia and analgesia (EAA) improves clinical outcomes. It is used during pancreatoduodenectomy (PD) to mitigate morbidities and shorten hospitalizations. Although widespread, the use of this practice has not been examined extensively. The objective of this study was to do so.

METHODS

A retrospective review of 42 patients who underwent PD was performed. Patients with and without EAA were compared. End points included intraoperative blood losses, perioperative fluid requirements, intensive care unit admissions, pain, bowel function, lengths of stay, morbidities, and mortalities.

RESULTS

Eighteen patients received EAA; 24 did not. Patients with EAA who reported less pain on postoperative day 2 (P = 0.03) were more likely to require intensive care unit admissions (P = 0.02) and required more frequent alterations of analgesics (P = 0.0001001). Epidural anesthesia and analgesia was associated with a nonsignificant increase in blood losses and fluid requirements. The groups did not differ in bowel function, lengths of stay, morbidities, or mortalities.

CONCLUSIONS

For patients undergoing PD, EAA was not associated with clinical benefits except for a modest reduction in postoperative pain, which was limited to a single day. Therefore, in this study, the clinical benefits of EAA seem underwhelming.

Study on the risk factors of postoperative hypoxemia in patients undergoing coronary artery bypass grafting

BACKGROUND

To investigate 576 patients undergoing coronary artery bypass grafting (CABG) and to evaluate independent high risk factors of postoperative hypoxemia following CABG.

METHODS AND RESULTS

The pre-, intra-, and post-operative materials in patients who had CABG performed on them from March 2004 to March 2008 in our hospital were analyzed retrospectively. The relative factors of postoperative hypoxemia were tested through descriptive analysis and logistic regression, and the independent risk factors were obtained. Among the 576 patients investigated, 156 cases suffered from postoperative hypoxemia, and the incidence rate of postoperative hypoxemia was 27.08%. Through descriptive analysis and logistic regression, the independent risk factors of postoperative hypoxemia were as follows: preoperative chronic pulmonary diseases (odds ratio (OR)=8.531, 95% confidence interval (CI) 3.136-23.210), preoperative acute myocardial infarction (OR=3.351, 95% CI 1.539-7.296), and preoperative diabetes (OR=3.108, 95% CI 1.439-6.713). Preoperative acute myocardial infarction (OR=2.091, 95% CI 1.520-4.416) is the independent risk factor during assisted ventilation after surgery, and preoperative chronic pulmonary diseases (OR=7.19, 95% CI 2.807-18.413), pre-operative diabetes (OR=3.605, 95% CI 1.631-7.967), and preoperative acute myocardial infarction (OR=3.604, 95% CI 1.518-8.543) are the 3 independent risk factors after decannulation following CABG.

CONCLUSIONS

Preoperative chronic pulmonary diseases, preoperative acute myocardial infarction, and preoperative diabetes are 3 independent risk factors of postoperative hypoxemia following CABG.

Epidural analgesia in hepatic resection

BACKGROUND

Randomized trials show equivocal benefit of epidural analgesia (EA) for patients undergoing abdominal operations. Partial hepatectomy is often performed using low central venous pressure anesthesia to reduce intraoperative blood loss. We examined effects of pain management strategy on blood pressure, transfusion, and complications in patients undergoing hepatic resection with either EA or IV analgesia (IVA).

STUDY DESIGN

Data on patients undergoing hepatectomy from 2001 to 2004 at Emory University Hospital were analyzed according to route of perioperative pain management. Patient and treatment factors were analyzed for associations with transfusion and morbidity.

RESULTS

From 2001 through 2004, 367 patients underwent elective partial hepatectomy at Emory University Hospital. EA patients were more likely to be older, men, and with malignancy. There were no differences between the groups in extent of resection, operative time, blood loss, or starting hematocrit level. The EA group had lower mean arterial pressure in recovery (86.6+/-14.0 mmHg versus 94.5+/-13.2 mmHg, p < 0.001) and were more likely to be transfused with packed red cells during the hospital course (44.5% versus 27.9%, p < 0.001). On multivariate analysis, age greater than 65 years, American Society of Anesthesiologists grade>2, starting hematocrit<38%, operative time>300 minutes, blood loss>1 L, and use of EA were associated with increased numbers of patients receiving packed red blood cells. Complications and length of stay were similar for both groups.

CONCLUSIONS

Epidural analgesia was independently associated with increased risk of packed red blood cell transfusion after hepatectomy. EA did not appear to minimize complications or shorten hospital stay. Caution should be exercised when considering EA use in hepatic resection.

Influence de la stratégie analgésique sur la fonction respiratoire après chirurgie thoracique pour lobectomie

OBJECTIVE

To compare the influence of thoracic epidural analgesia (TEA) with intravenous patient-controlled analgesia with morphine (PCA) on the early postoperative respiratory function after lobectomy.

STUDY DESIGN

Prospective and comparative observational study.

PATIENTS AND METHODS

Fourty-four patients scheduled for lobectomy (n=22 per group) were studied on the evolution of the postoperative respiratory function assessed by the forced vital capacity (FVC) and the forced expired volume (FEV(1)) during the first two postoperative days and the analysis of noctural arterial desaturation during the three first postoperative nights.

RESULTS

The use of TEA resulted in fewer decrease both in FEV(1) (1.01+/-0.34 versus 1.31+/-0.51 l/s for Day 1, P=0.03; 1.13+/-0.37 versus 1.53+/-0.59 l/s for Day 2, P=0.01) and in FVC (1.23 [1.05-1.51] versus 1.57 [1.38-2.53] l for day 1, P=0.008; 1.33+/-0.43 versus 2.24+/-0.87 l for day 2, P<0.001). Moreover, the duration of arterial desaturation<90% were longer in the PCA group during the first (8.6 [0.8-28.2] versus 1.3 [0-2.6] min, P=0.02) and the second postoperative night (13.5 [3.5-54] versus 0.4 [0-2.6] min, P=0.025).

CONCLUSION

The results of this study suggest that the use of TEA is associated with a better preservation of respiratory function assessed by spirometric data and noctural arterial desaturation recording after thoracic surgery for lobectomy.

Endogenous opiates and behavior: 2005

This paper is the 28th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2005 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity, neurophysiology and transmitter release (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); immunological responses (Section 17).