Adverse event

Adverse event (AE)

An adverse event (AE) is any untoward medical occurrence in a patient or clinical investigation subject administered a pharmaceutical product and which does not necessarily have a causal relationship with this treatment. An adverse event (AE) can therefore be any unfavourable and unintended sign (including an abnormal laboratory finding), symptom, or disease temporally associated with the use of a medicinal (investigational) product, whether or not related to the medicinal (investigational) product.

see also complications.

see MAUDE.

Risk of intraop AEs, but not postop AEs, increased with increasing age. Having multiple comorbidities does not predispose to more AEs. Infections predominate among the postop AEs. Patients at increased risk of delirium or of having an increased length of hospital stay may more easily be predicted. Studies specifically designed to prospectively assess AEs have the potential to more accurately identify postop AE rates 1).

see National Cancer Institutes Common Terminology Criteria for Adverse Events


Adverse events reportedly occur in 5% to 10% of health care episodes.

A follow-up study examining 8 years of reported surgical adverse events and root causes from US Veterans Health Administration (VHA) medical centers, compared with the previous studies of 2001 to 2006 and 2006 to 2009, and to recommend actions for future prevention of such events.

This quality improvement study described patient safety adverse events and close calls reported from 86 VHA medical centers from the approximately 130 VHA facilities with a surgical program. The surgical procedures and programs vary in size and complexity from small rural centers to large, complex urban facilities. Procedures occurring between January 1, 2010, and December 31, 2017, were included. Data analysistook place in 2018.

The categories of incorrect procedure types were wrong patient, side, site (including wrong-level spine), procedure, or implant. Events included those in or out of the operating room, adverse events or close calls, surgical specialty, and harm. These results were compared with the previous studies of VHA-reported wrong-site surgery (2001-2006 and 2006-2009).

The review produced 483 reports (277 adverse events and 206 close calls). The rate of in-operating room (in-OR) reported adverse events with harm has continued to trend downward from 1.74 to 0.47 reported adverse events with harm per 100 000 procedures between 2000 and 2017 based on 6 591 986 in-OR procedures. When in-OR events were examined by discipline as a rate, dentistry had 1.54, neurosurgery had 1.53, and ophthalmology had 1.06 reported in-OR adverse events per 10 000 cases. The overall VHA in-OR rate for adverse events during 2010 to 2017 was 0.53 per 10 000 procedures based on 3 234 514 in-OR procedures. The most common root cause for adverse events was related to issues in performing a comprehensive time-out (28.4%). In these cases, the time-out either was conducted incorrectly or was incomplete in some way.

Over the period studied, the VHA identified a decrease in the rate of reported adverse events in the OR associated with harm and continued reporting of adverse event close calls. Organizational efforts continue to examine root cause analysis reports, promulgate lessons learned, and enhance policy to promote a culture and behavior that minimizes events and is transparent in reporting occurrences 2).


Not all adverse events are the result of error; they may arise from systemic faults in the delivery of health care. Catastrophic events are not only physically devastating to patients, but they also attract medical liability and increase health care costs. Root cause analysis (RCA) has become a key tool for health care services to understand those adverse events.

It is well recognized that the occurrence rate of adverse events related to surgical procedures is considerably high in neurosurgery compared with other specialties.

Adverse events during diagnostic and therapeutic procedures and medical errors associated with them are an important source of patient morbidity. In an attempt to reduce these, the WHO has proposed a series of measures applicable to medical and surgical patients. Within these last ones is the surgical safety checklist (SSC), a brief questionnaire that does not increase healthcare costs, is accessible to all surgical centres and can be adapted to each specific environment.

One hundred eighty-two events (28.3%) among 643 neurosurgical interventions over 2 years were recognized as adverse events. Among these 182 adverse events, 165 (90.7%) were closely related to procedures and 125 events (68.7%) were predictable before or during the procedures. However, even when retrospectively reviewed, only 6 (3.3%) of events were deemed avoidable. Of these 6 avoidable events, there were only 2 (1.1%) that were considered to have been caused by error.

Adverse events are not invariably rare in neurosurgery. Most of them are predictable; however, their avoidance is not necessarily easy. Avoidable adverse events caused by medical errors were observed in only 1.1% of cases 3).

Undesired harmful effect resulting from a medication or other intervention such as surgery.

An adverse effect may be termed a “side effect”, when judged to be secondary to a main or therapeutic effect. If it results from an unsuitable or incorrect dosage or procedure, this is called a medical error and not a complication. Adverse effects are sometimes referred to as “iatrogenic” because they are generated by a physician/treatment. Some adverse effects occur only when starting, increasing or discontinuing a treatment.

Using a drug or other medical intervention which is contraindicated may increase the risk of adverse effects. Adverse effects may cause complications of a disease or procedure and negatively affect its prognosis. They may also lead to non-compliance with a treatment regimen.

The harmful outcome is usually indicated by some result such as morbidity, mortality, alteration in body weight, levels of enzymes, loss of function, or as a pathological change detected at the microscopic, macroscopic or physiological level. It may also be indicated by symptoms reported by a patient. Adverse effects may cause a reversible or irreversible change, including an increase or decrease in the susceptibility of the individual to other chemicals, foods, or procedures, such as drug interactions.

see Side error.

Spine adverse events



Kelly AM, Batke JN, Dea N, Hartig DP, Fisher CG, Street JT. Prospective analysis of adverse events in surgical treatment of degenerative spondylolisthesis. Spine J. 2014 Dec 1;14(12):2905-10. doi: 10.1016/j.spinee.2014.04.016. Epub 2014 Apr 21. PubMed PMID: 24769400.

Neily J, Soncrant C, Mills PD, Paull DE, Mazzia L, Young-Xu Y, Nylander W, Lynn MM, Gunnar W. Assessment of Incorrect Surgical Procedures Within and Outside the Operating Room: A Follow-up Study From US Veterans Health Administration Medical Centers. JAMA Netw Open. 2018 Nov 2;1(7):e185147. doi: 10.1001/jamanetworkopen.2018.5147. PubMed PMID: 30646381.

Houkin K, Baba T, Minamida Y, Nonaka T, Koyanagi I, Iiboshi S. Quantitative analysis of adverse events in neurosurgery. Neurosurgery. 2009 Sep;65(3):587-94; discussion 594. doi: 10.1227/01.NEU.0000350860.59902.68. PubMed PMID: 19687705.

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