[Epidural anesthesia : Clinical application and current developments]. / Periduralanästhesie : Klinische Anwendung und aktuelle Entwicklungen.

Epidural anesthesia has been an established procedure in anesthesia for many years. Possibly due to its invasiveness, the associated fear of serious complications and the proliferation of alternative methods, an overall decline in its use can be observed. Several alternative procedures have been developed, especially the introduction of ultrasound into anesthesia, which are increasingly being used in clinical practice. The aim of this continuing medical education (CME) article is to shed light on the remaining range of indications for epidural anesthesia, to present the approaches and possible clinical benefits as well as to evaluate the effects that go beyond pure analgesia, according to the current evidence. In addition, potential complications and preventive approaches are discussed. This article is based on a literature search in PubMed and Google Scholar.

High-fidelity is not superior to low-fidelity simulation but leads to overconfidence in medical students.

BACKGROUND: Simulation has become integral to the training of both undergraduate medical students and medical professionals. Due to the increasing degree of realism and range of features, the latest mannequins are referred to as high-fidelity simulators. Whether increased realism leads to a general improvement in trainees' outcomes is currently controversial and there are few data on the effects of these simulators on participants' personal confidence and self-assessment. METHODS: One-hundred-and-thirty-five fourth-year medical students were randomly allocated to participate in either a high- or a low-fidelity simulated Advanced Life Support training session. Theoretical knowledge and self-assessment pre- and post-tests were completed. Students' performance in simulated scenarios was recorded and rated by experts. RESULTS: Participants in both groups showed a significant improvement in theoretical knowledge in the post-test as compared to the pre-test, without significant intergroup differences. Performance, as assessed by video analysis, was comparable between groups, but, unexpectedly, the low-fidelity group had significantly better results in several sub-items. Irrespective of the findings, participants of the high-fidelity group considered themselves to be advantaged, solely based on their group allocation, compared with those in the low-fidelity group, at both pre- and post-self-assessments. Self-rated confidence regarding their individual performance was also significantly overrated. CONCLUSION: The use of high-fidelity simulation led to equal or even worse performance and growth in knowledge as compared to low-fidelity simulation, while also inducing undesirable effects such as overconfidence. Hence, in this study, it was not beneficial compared to low-fidelity, but rather proved to be an adverse learning tool.

Is epidural analgesia still a viable option for enhanced recovery after abdominal surgery.

PURPOSE OF REVIEW: Although thoracic epidural analgesia (TEA) is considered often as gold standard in multimodal analgesia with regard to major abdominal surgery, there is an ongoing debate if it is still a viable option for enhanced recovery because of its potential severe complications. RECENT FINDINGS: In addition to the unsurpassed analgesic quality, a TEA offers several advantages. Studies have shown that a TEA does have a positive effect on perioperative morbidity and mortality, bowel function, the occurrence of ileus and patient mobility. Furthermore, TEA can reduce opioid-induced side effects, cardiac arrhythmias and pneumonia. When it is embedded into a multimodal fast-track program, it also shortens intensive care and hospital stay. SUMMARY: TEA provides superior pain control with a handful of important advantages if used sensibly and with caution. Because of associated risks for severe neurological complications, clear contraindications should be ruled out. Special attention needs be paid to potential hypotension in the setting of epidural analgesia. If these key points are considered, a TEA still represents a viable option for enhanced recovery after major abdominal surgery.

Availability of cookies during an academic course session affects evaluation of teaching.

OBJECTIVES: Results from end-of-course student evaluations of teaching (SETs) are taken seriously by faculties and form part of a decision base for the recruitment of academic staff, the distribution of funds and changes to curricula. However, there is some doubt as to whether these evaluation instruments accurately measure the quality of course content, teaching and knowledge transfer. We investigated whether the provision of chocolate cookies as a content-unrelated intervention influences SET results. METHODS: We performed a randomised controlled trial in the setting of a curricular emergency medicine course. Participants were 118 third-year medical students. Participants were randomly allocated into 20 groups, 10 of which had free access to 500 g of chocolate cookies during an emergency medicine course session (cookie group) and 10 of which did not (control group). All groups were taught by the same teachers. Educational content and course material were the same for both groups. After the course, all students were asked to complete a 38-question evaluation form. RESULTS: A total of 112 students completed the evaluation form. The cookie group evaluated teachers significantly better than the control group (113.4 ± 4.9 versus 109.2 ± 7.3; p = 0.001, effect size 0.68). Course material was considered better (10.1 ± 2.3 versus 8.4 ± 2.8; p = 0.001, effect size 0.66) and summation scores evaluating the course overall were significantly higher (224.5 ± 12.5 versus 217.2 ± 16.1; p = 0.008, effect size 0.51) in the cookie group. CONCLUSIONS: The provision of chocolate cookies had a significant effect on course evaluation. These findings question the validity of SETs and their use in making widespread decisions within a faculty.

Intra- versus postoperative initiation of pain control via a thoracic epidural catheter for lumbar spinal fusion surgery.

BACKGROUND: Thoracic epidural anesthesia (TEA) is one of the pillars of perioperative pain care. Particularly for spine surgery which causes significant postoperative pain TEA seems like an appealing option. However, beneficial effects of a TEA are questionable when the catheter is not used intraoperatively, a decision that is usually based on the surgeon's wish to perform immediate neurological examination postoperatively. METHODS: Forty patients undergoing transforaminal lumbar interbody fusion surgery (TLIF) were randomized into two groups. Patients received preoperative insertion of a TEA. For patients in the intraoperative group an epidural infusion was started preoperatively and maintained throughout. For patients in the postoperative group the epidural infusion was started once neurological examination had been performed. The primary outcome measure in this study was postoperative requirements of piritramide during the first two postoperative hours. Secondary outcomes involved postoperative pain numeric rating scale (NRS) scores, intraoperative opioid requirements, side effects and ability to perform direct postoperative neurological examination. RESULTS: Postoperative group patients required significantly more opioids both intra- and postoperatively (P=0.036 and P=0.039) and NRS scores were significantly higher on admission to recovery, at 30 and 60 min as compared to patients in the intraoperative group (P=0.013; P=0.004 and P=0.012). Early postoperative neurological examination was feasible in all patients in both groups. CONCLUSIONS: Epidural catheters used intraoperatively during TLIF are feasible, significantly reduce pain, intra- and postoperative use of opioids and do not influence the quality of neurological tests directly after the surgical procedure.

Feasibility of Cervical Epidural Anesthesia for Breast Cancer Surgery.

BACKGROUND: Effects of perioperative cervical level neuraxial blocks on the dissemination of cancer metastases have become a matter of substantial interest. However, experience with these catheters has been limited and data on feasibility and efficacy is sparse. METHODS: Data from 39 patients scheduled to undergo breast cancer surgery while awake with a cervical epidural alone was retrospectively analyzed. RESULTS: In 26 patients (66,7%, 95% CI 51,7-81,7) the cervical epidural catheter was sufficient for surgery. In one patient (2.6%, 95% CI 0-7.6) identification of the epidural space was not possible. Four patients (10.3%, 95% CI 0,7-19,9) had an insufficient sensory block. Seven patients (17.9%, 95% CI 5,7-30,1) had a partially insufficient sensory block. Rates of failed epidural blocks were not significantly different between different insertion levels. 21 patients (80.8%, 95% CI 65,4-96,1) developed hypotension and required an intravenous vasopressor. One patient developed nausea. In one patient the dura was accidentally punctured. No neurological damage was observed. No other major complications were observed. DISCUSSION: Epidural punctures in the cervical region are feasible but do bear potential for major complications. Anesthesiologists should familiarize themselves with high epidural block techniques.

How do authors of systematic reviews deal with research malpractice and misconduct in original studies? A cross-sectional analysis of systematic reviews and survey of their authors.

OBJECTIVES: To study whether systematic reviewers apply procedures to counter-balance some common forms of research malpractice such as not publishing completed research, duplicate publications, or selective reporting of outcomes, and to see whether they identify and report misconduct. DESIGN: Cross-sectional analysis of systematic reviews and survey of their authors. PARTICIPANTS: 118 systematic reviews published in four journals (Ann Int Med, BMJ, JAMA, Lancet), and the Cochrane Library, in 2013. MAIN OUTCOMES AND MEASURES: Number (%) of reviews that applied procedures to reduce the impact of: (1) publication bias (through searching of unpublished trials), (2) selective outcome reporting (by contacting the authors of the original studies), (3) duplicate publications, (4) sponsors' and (5) authors' conflicts of interest, on the conclusions of the review, and (6) looked for ethical approval of the studies. Number (%) of reviewers who suspected misconduct are reported. The procedures applied were compared across journals. RESULTS: 80 (68%) reviewers confirmed their data. 59 (50%) reviews applied three or more procedures; 11 (9%) applied none. Unpublished trials were searched in 79 (66%) reviews. Authors of original studies were contacted in 73 (62%). Duplicate publications were searched in 81 (69%). 27 reviews (23%) reported sponsors of the included studies; 6 (5%) analysed their impact on the conclusions of the review. Five reviews (4%) looked at conflicts of interest of study authors; none of them analysed their impact. Three reviews (2.5%) looked at ethical approval of the studies. Seven reviews (6%) suspected misconduct; only 2 (2%) reported it explicitly. Procedures applied differed across the journals. CONCLUSIONS: Only half of the systematic reviews applied three or more of the six procedures examined. Sponsors, conflicts of interest of authors and ethical approval remain overlooked. Research misconduct is sometimes identified, but rarely reported. Guidance on when, and how, to report suspected misconduct is needed.

Simulation for anesthesia in obstetrics.

Simulation has become a major player in the medical world. Still way behind other high-risk industries, simulation is being increasingly accepted and finds its ways into many clinical areas. Simulation offers the possibility to train individual skills as well as to evaluate performance, provide group crisis management training or even investigate the safety of installed systems and algorithms without risking patient's life. Obstetric units and labor suites have been identified as high-risk areas in the hospital setting and can be challenging environments for the anesthesiologist. Simulators can be used to improve communication skills and workload distribution, and specifically drill for obstetric-relevant crisis scenarios. However, it remains unclear how well these trainings do transfer into clinical performance and improved patient outcome. Being a relevant cost factor, simulation will have to provide answers to these questions; hence, more research is needed in the future.

Ability of a meta-analysis to prevent redundant research: systematic review of studies on pain from propofol injection.

OBJECTIVE: To examine whether, according to the conclusions of a 2000 systematic review with meta-analysis on interventions to prevent pain from propofol injection that provided a research agenda to guide further research on the topic, subsequently published trials were more often optimally blinded, reported on children, and used the most efficacious intervention as comparator; and to check whether the number of new trials published each year had decreased and whether the designs of trials that cited the review differed from those that did not. STUDY DESIGN: Systematic review comparing old trials (published before, and included in, the review) with new trials (published afterwards). DATA SOURCES: Medline, Cochrane, Embase, and bibliographies to January 2013. ELIGIBILITY CRITERIA FOR STUDY SELECTION: Randomised studies testing any intervention to prevent pain from propofol injection in humans. RESULTS: 136 new trials (19,778 patients) were retrieved. Compared with the 56 old trials (6264 patients), the proportion of optimally blinded trials had increased from 10.7% to 38.2% (difference 27.5%, 95% confidence interval 16.0% to 39.0%, P<0.001), and the proportion of trials that used the most efficacious intervention as comparator had increased from 12.5% to 27.9% (difference 15.4%, 4.0% to 26.9%, P=0.022). The proportion of paediatric trials had increased from 5.4% to 12.5%, although this was not significant (difference 7.1%, -1.0% to 15.2%, P=0.141). The number of new trials published each year was significantly higher (median number/year 12 (range 7-20) v 2.5 (0-9), P<0.001) with no obvious decreasing trend. 72.8% (n=99) of the new trials cited the review, with their designs similar to trials not citing the review. Only 36.0% (n=49) of the new trials were considered clinically relevant since they used the most efficacious intervention as comparator or included a paediatric population. CONCLUSIONS: The impact of the systematic review on the design of subsequent research was low. There was an improvement in the reporting of optimal blinding procedures and a tendency towards an increase in the proportion of paediatric trials. The most efficacious intervention was more often chosen as comparator but remained marginally used, and the number of trials published per year had not decreased. The use of systematic reviews should be encouraged to inform rational, and thus ethical, trial design and improve the relevance of new research.

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.

Combination of a reduced dose of an intrathecal local anesthetic with a small dose of an opioid: a meta-analysis of randomized trials.

We tested whether the combination of a reduced dose of a local anesthetic (LA) with an opioid compared with a standard dose of the same LA alone guaranteed adequate intraoperative anesthesia and postoperative analgesia and decreased LA-related adverse effects. We systematically searched (to November 2012) for randomized comparisons of combinations of a reduced dose of an LA with a concomitant opioid (experimental) with a standard dose of the LA alone (control) in adults undergoing surgery with single-injection intrathecal anesthesia without general anesthesia. We included 28 trials (1393 patients). In experimental groups, the median decrease in LA doses was 40% (range, 12%-70%). There was no difference between experimental and control groups in the need for intraoperative opioids or general anesthesia for failed block or in the duration of postoperative analgesia. With experimental interventions, there was evidence of a reduction in the duration of motor blockade postoperatively (average, -50 minutes), time to discharge from hospital or PACU (-33 minutes), time to ambulation (-28 minutes), and time to urination (-14 minutes). There was also evidence of a decrease in the risk of shivering (risk ratio [RR]: 0.26; 95% confidence interval [CI]: 0.12-0.56), nausea (RR: 0.45; 95% CI: 0.31-0.66), and arterial hypotension (RR: 0.52; 95% CI: 0.35-0.78). The risk of pruritus was increased (RR: 11.7; 95% CI: 6.2-21.9). Adding an opioid to a reduced dose of an intrathecal LA can decrease LA-related adverse effects and improve recovery from the spinal block without compromising intraoperative anesthesia or duration of postoperative analgesia.

[Neurologic complications after epidural analgesia]. / Nervenschäden bei Regionalanästhesie - Neurologische Komplikationen durch die Epiduralanalgesie.

Epidural analgesia is regarded as gold standard after major abdominal or thoracic surgery in combination with general anaesthesia. Apart from well documented positive effects of epidural analgesia on the postoperative period, evidence for the incidence of neurologic complications is less clear. Complications include direct spinal cord damage during epidural puncture, epidural hematoma, abscesses or meningitis. The review article gives an overview about current data on neurologic complications related to epidural analgesia and shows feasibility of prevention and early detection. Furthermore a therapeutic approach in case of a neurologic incident will be demonstrated.

Opioids added to local anesthetics for single-shot intrathecal anesthesia in patients undergoing minor surgery: a meta-analysis of randomized trials.

Opioids are widely used as additives to local anesthetics for intrathecal anesthesia. Benefit and risk remain unclear. We systematically searched databases and bibliographies to February 2011 for full reports of randomized comparisons of any opioid added to any intrathecal local anesthetic with the local anesthetic alone in adults undergoing surgery (except cesarean section) and receiving single-shot intrathecal anesthesia without general anesthesia. We included 65 trials (3338 patients, 1932 of whom received opioids) published between 1983 and 2010. Morphine (0.05-2mg) and fentanyl (10-50 µg) added to bupivacaine were the most frequently tested. Duration of postoperative analgesia was prolonged with morphine (weighted mean difference 503 min; 95% confidence interval [CI] 315 to 641) and fentanyl (weighted mean difference 114 min; 95% CI 60 to 168). Morphine decreased the number of patients needing opioid analgesia after surgery and decreased pain intensity to the 12th postoperative hour. Morphine increased the risk of nausea (number needed to harm [NNH] 9.9), vomiting (NNH 10), urinary retention (NNH 6.5), and pruritus (NNH 4.4). Fentanyl increased the risk of pruritus (NNH 3.3). With morphine 0.05 to 0.5mg, the NNH for respiratory depression varied between 38 and 59 depending on the definition of respiratory depression chosen. With fentanyl 10 to 40 µg, the risk of respiratory depression was not significantly increased. For none of these effects, beneficial or harmful, was there evidence of dose-responsiveness. Consequently, minimal effective doses of intrathecal morphine and fentanyl should be sought. For intrathecal buprenorphine, diamorphine, hydromorphone, meperidine, methadone, pentazocine, sufentanil, and tramadol, there were not enough data to allow for meaningful conclusions.

Feasibility and efficacy of preoperative epidural catheter placement for anterior scoliosis surgery.

BACKGROUND: Postoperative pain control via thoracic epidural catheters (TECs) is an important aspect of postoperative care, and ample evidence highlights its positive physiologic effects and superiority to intravenous analgesia. If epidural catheters for postoperative pain relief are used in scoliosis surgery, current practice is the intraoperative placement of the TEC by the surgeon because preoperative placement is considered challenging and dangerous. On the basis of magnetic resonance imaging of scoliotic spines, the authors developed a technique for preoperative placement of TEC and investigated its safety and feasibility. METHODS: Patients undergoing anterior scoliosis surgery were included, who received preoperative placement of TEC. Postoperative pain, problems associated with the TEC placement, possible side effects, radiographic data, and insertion levels of the TEC were noted. RESULTS: The apex vertebra was identified as a possible site for TEC placement due to dural sac shift leaving a wider epidural space on the convex side. Scoliosis-induced rotation of the vertebrae required realignment of the needle toward the convex side. Sixty patients were included. The success rate for TEC placement was 96.6%: one failed attempt, one catheter placed intrapleurally, and one patient with Horner syndrome. Seven percent of patients required additional rescue analgesia. All other patients had pain scores within acceptable limits (Visual Analogue Scale <5). CONCLUSIONS: The authors have demonstrated that it is possible to insert a TEC in patients with scoliotic spines with a high degree of success using a redesigned approach and thus provide adequate postoperative analgesia with a single epidural catheter. However, precautions have to be taken.

[Patient care according to the latest state of the science--implications of evidence-based medicine]. / Patientenversorgung nach dem neuesten Stand der Wissenschaft - Was bedeutet Evidence-based Medicine?

Evidence-based medicine implies that recommendations ideally exist for each clinical question based on a systematic data search in the current literature, a data extraction, a summary and critical appraisal. Over the last fifty years evidence-based medicine has been growing rapidly. Systematic reviews and randomised controlled trials are of high impact in this field. However, the question remains: in which way is daily clinical practice affected? In an era of time- and cost-pressures as well as manpower shortages, the complex process of evidence-based medicine is difficult. Examples from perioperative pain therapy are provided to demonstrate how evidence-based medicine could be feasible and incorporated into daily practice.

Clonidine as an adjuvant to local anesthetics for peripheral nerve and plexus blocks: a meta-analysis of randomized trials.

The effect of adding clonidine to local anesthetics for nerve or plexus blocks remains unclear. The authors searched for randomized placebo-controlled trials testing the impact of adding clonidine to local anesthetics for peripheral single-injection nerve or plexus blocks in adults undergoing any surgery (except eye) without general anesthesia. Twenty trials (1,054 patients, 573 received clonidine) published 1992-2006 tested plexus (14 brachial, 1 cervical) and nerve blocks (2 sciatic/femoral, 1 midhumeral, 1 ilioinguinal/iliohypogastric, 1 ankle). Clonidine doses ranged from 30 to 300 microg; most patients received 150 microg. Clonidine prolonged the duration of postoperative analgesia (weighted mean difference 122 min; 95% confidence interval [CI] 74-169), sensory block (weighted mean difference 74 min; 95% CI 37-111), and motor block (weighted mean difference 141 min; 95% CI 82-199). In a subgroup of patients receiving an axillary plexus block, these effects were independent of whether clonidine was added to an intermediate or a long-acting local anesthetic. Clonidine increased the risk of arterial hypotension (odds ratio 3.61; 95% CI 1.52-8.55; number-needed-to-harm 11), orthostatic hypotension or fainting (odds ratio 5.07; 95% CI 1.20-21.4; number-needed-to-harm 10), bradycardia (odds ratio 3.09; 95% CI 1.10-8.64; number-needed-to-harm 13), and sedation (odds ratio 2.28; 95% CI 1.15-4.51; number-needed-to-harm 5). There was a lack of evidence of dose-responsiveness for beneficial or harmful effects. Clonidine added to intermediate or long-acting local anesthetics for single-shot peripheral nerve or plexus blocks prolongs duration of analgesia and motor block by about 2 h. The increased risk of hypotension, fainting, and sedation may limit its usefulness. Dose-responsiveness remains unclear.

Simulation-based medical education is no better than problem-based discussions and induces misjudgment in self-assessment.

Simulation-based teaching (SBT) is increasingly used in medical education. As an alternative to other teaching methods there is a lack of evidence concerning its efficacy. The aim of this study was to evaluate the potency of SBT in anesthesia in comparison to problem-based discussion (PBD) with students in a randomized controlled setting. Thirty-three fourth-year medical students attending a curricular anesthesiology course were randomly allocated to either a session of SBT or a session of PBD on an emergency induction method. Ten days later all students underwent examination in a simulator. The performance of each student was evaluated by weighted tasks, established according to a modified Delphi process. Confidence and a multiple-choice questionnaire were additionally performed pre- and post-intervention. A total of 32 students completed the study. Participants in the SBT group presented with significantly higher self-assessment scores after the intervention than students in the PBD group. However, students in the SBT group achieved only slightly and statistically insignificantly higher scores in the theoretical and simulator examination (p > 0.05) with only a moderate effect size of d = 0.52. The current study demonstrates that both PBD and SBT lead to comparable short-term outcomes in theoretical knowledge and clinical skills. However, undesirably, SBT students overrated their anticipated clinical abilities and knowledge improvement.

Protective effects of epidural analgesia on pulmonary complications after abdominal and thoracic surgery: a meta-analysis.

OBJECTIVE: To review the impact of epidural vs systemic analgesia on postoperative pulmonary complications. DATA SOURCES: Search of databases (1966 to March 2006) and bibliographies. STUDY SELECTION: Inclusion criteria were randomized comparison of epidural vs systemic analgesia lasting 24 hours or longer postoperatively and reporting of pulmonary complications, lung function, or gas exchange. Fifty-eight trials (5904 patients) were included. DATA EXTRACTION: Articles were reviewed and data extracted. Data were combined using fixed-effect and random-effects models. DATA SYNTHESIS: The odds of pneumonia were decreased with epidural analgesia (odds ratio [OR], 0.54; 95% confidence interval [CI], 0.43-0.68), independent of site of surgery or catheter insertion, duration of analgesia, or regimen. The effect was weaker in trials that used patient-controlled analgesia in controls (OR, 0.64; 95% CI, 0.49-0.83) compared with trials that did not (OR, 0.30; 95% CI, 0.18-0.49) and in larger studies (OR, 0.62; 95% CI, 0.47-0.81) compared with smaller studies (OR, 0.37; 95% CI, 0.23-0.58). From 1971-2006, the incidence of pneumonia with epidural analgesia remained about 8% but decreased from 34% to 12% with systemic analgesia (P < .001); consequently, the relative benefit of epidural analgesia decreased also. Epidural analgesia reduced the need for prolonged ventilation or reintubation, improved lung function and blood oxygenation, and increased the risk of hypotension, urinary retention, and pruritus. Technical failures occurred in 7%. CONCLUSION: Epidural analgesia protects against pneumonia following abdominal or thoracic surgery, although this beneficial effect has lessened over the last 35 years because of a decrease in the baseline risk.