Patient Safety: Types and Causes of Error

There is a global consensus that quality health care should be safe, effective, and patient-centered, yet adverse events during hospital care cause death and disability worldwide. Almost half of these adverse events are preventable in high-income countries, and that proportion is even higher in low- and middle-income countries. The growing complexity of health care systems has been linked to an increase in medical errors resulting in health care–related adverse events. The term “error” has negative connotations, and the goal of patient safety measures is to prevent adverse events by following accepted practice at a system or individual level. Sentinel events that result in unexpected mortality or major harm to a patient signal the need for investigation and response. Types of medical errors include adverse drug events, incorrect or delayed diagnosis, and errors during procedures and surgeries. The science and culture of patient safety are based on the premise that human error will occur and that we can build systems that prevent and reduce these occurrences. This culture provides a framework for balanced accountability of the individual and the organization in designing workplace systems that are safe and reliable. Many strategies have been implemented to prevent and address medical errors that affect patient safety.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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By definition, errors are unintentional and involve either poor planning or poor execution of a process involved in the medical care of individuals.

The WHO defines patient safety as “a framework of organized activities that creates cultures, processes, procedures, behaviors, technologies, and environments in health care that consistently and sustainably lower risks, reduce the occurrence of avoidable harm, make error less likely and reduce its impact when it does occur.”


  • Worldwide, particularly in low- and middle-income countries, the rising number of adverse events occurring while individuals receive care has led to patient safety initiatives.  
  • With their growing complexity, health care systems have been linked to an increase in health care–related adverse events.
  • 1 in 10 patients in high-income countries receiving hospital care experience adverse events, and about half of these are preventable.  
  • Globally, 4 in 10 patients receiving care in the outpatient setting experience an adverse event, of which an estimated almost 80% are considered to be preventable. 
  • Most detrimental errors involve:
    • Diagnosis
    • Prescribing/medication use
    • Procedures/surgeries

WHO response

  • Recognized the considerable burden of patient harm in health care
  • Adopted a resolution to identify patient safety as a global health priority
  • Proposed formulating a global patient safety action plan in conjunction with members
  • Launched the WHO Flagship Initiative, “A Decade of Patient Safety 2020–2030”

Types and Causes of Medical Errors

Medical errors with serious consequences are most likely to occur when there is increased urgency and severity of the medical condition being treated, as in the ED or ICU. Medical errors are also associated with extremes of age and new procedures.

Types of medical errors

  • Error of omission: a result of an action not taken
  • Error of commission: a consequence of taking the wrong action

Categories of medical errors

  • Diagnostic:
    • Error or delay in diagnosis
    • Failure to order indicated tests
    • Not using current evidence for tests or therapy
    • Failure to act on results of monitoring or tests
  • Treatment:
    • Error in the performance of an operation, procedure, or test
    • Error in treatment administration
    • Error in the dose or method of using a drug
    • Avoidable delay in treatment or responding to an abnormal test
    • Inappropriate care (not indicated)
  • Preventive:
    • Failure to provide prophylactic treatment
    • Failure to prevent infection by accepted measures
    • Inadequate monitoring or follow-up of treatment
  • Other:
    • Failure of communication
    • Equipment failure
    • Other system failures

Contributing factors

  • Communication problems:
    • Written or verbal
    • Between members of the team or with patient
    • Not using qualified interpreters when needed
    • Increasing fragmentation of health care → more care transitions
  • Inadequate information flow:
    • Lack of essential information for prescribing
    • Lack of appropriate communication about test results
    • Poor coordination of medication orders for transfer of care
  • Human problems:
    • Not following standards of care, policies, or procedures
    • Inadequate or incorrect knowledge to provide the care needed
  • Patient-related issues:
    • Inadequate patient identification, assessment, or education
    • Failure to obtain consent
  • Organizational transfer of knowledge: insufficient training
  • Inadequate staffing
  • Technical failures: medical device or equipment failure
  • Inadequate or lack of policies and procedures

Most common patient safety issues (included in medical “errors”) in the United States

  • Adverse drug events
  • Catheter-associated urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract infection
  • Central line–associated bloodstream infection
  • Injury from falls and immobility
  • Obstetrical adverse events
  • Pressure ulcers
  • Surgical site infections Surgical site infections Surgical site infection (SSI) is a type of surgical infection that occurs at or near a surgical incision within 30 days of the procedure or within 90 days if prosthetic material is implanted. Surgical site infections are classified according to the depth of involvement as superficial, deep, or organ/space. Surgical Site Infections
  • Venous thrombosis
  • Ventilator-associated pneumonia Pneumonia Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy. Pneumonia
  • Wrong site/wrong procedure surgery

Most common misdiagnosed conditions

  • In the ED:
    • Acute stroke ( cerebrovascular accident Cerebrovascular accident An ischemic stroke (also known as cerebrovascular accident) is an acute neurologic injury that occurs as a result of brain ischemia; this condition may be due to cerebral blood vessel occlusion by thrombosis or embolism, or rarely due to systemic hypoperfusion. Ischemic Stroke)
    • MI MI MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Myocardial Infarction
    • Spinal epidural abscess
    • Pulmonary embolism Pulmonary Embolism Pulmonary embolism (PE) is a potentially fatal condition that occurs as a result of intraluminal obstruction of the main pulmonary artery or its branches. The causative factors include thrombi, air, amniotic fluid, and fat. In PE, gas exchange is impaired due to the decreased return of deoxygenated blood to the lungs. Pulmonary Embolism
    • Necrotizing fasciitis Necrotizing fasciitis Necrotizing fasciitis is a life-threatening infection that causes rapid destruction and necrosis of the fascia and subcutaneous tissues. Patients may present with significant pain out of proportion to the presenting symptoms and rapidly progressive erythema of the affected area. Necrotizing Fasciitis
    • Meningitis Meningitis Meningitis is inflammation of the meninges, the protective membranes of the brain, and spinal cord. The causes of meningitis are varied, with the most common being bacterial or viral infection. The classic presentation of meningitis is a triad of fever, altered mental status, and nuchal rigidity. Meningitis
    • Testicular torsion Testicular torsion Testicular torsion is the sudden rotation of the testicle, specifically the spermatic cord, around its axis in the inguinal canal or below. The acute rotation results in compromised blood flow to and from the testicle, which puts the testicle at risk for necrosis. Testicular Torsion
    • Subarachnoid hemorrhage Subarachnoid Hemorrhage Subarachnoid hemorrhage (SAH) is a type of cerebrovascular accident (stroke) resulting from intracranial hemorrhage into the subarachnoid space between the arachnoid and the pia mater layers of the meninges surrounding the brain. Most SAHs originate from a saccular aneurysm in the circle of Willis but may also occur as a result of trauma, uncontrolled hypertension, vasculitis, anticoagulant use, or stimulant use. Subarachnoid Hemorrhage (SAH)
    • Sepsis Sepsis Organ dysfunction resulting from a dysregulated systemic host response to infection separates sepsis from uncomplicated infection. The etiology is mainly bacterial and pneumonia is the most common known source. Patients commonly present with fever, tachycardia, tachypnea, hypotension, and/or altered mentation. Sepsis and Septic Shock
    • Fractures
    • Appendicitis Appendicitis Appendicitis is the acute inflammation of the vermiform appendix and the most common abdominal surgical emergency globally. The condition has a lifetime risk of 8%. Characteristic features include periumbilical abdominal pain that migrates to the right lower quadrant, fever, anorexia, nausea, and vomiting. Appendicitis
  • Recurring themes in unexpected deaths:
    • Atypical presentations of unusual problems
    • Chronic diseases with decompensation
    • Abnormal vital signs (most often tachycardia) at discharge
    • New medical conditions in patients with a mental disability or psychiatric problems

Medical Error Prevention

Strategies for improving the prevention of errors that affect patient safety have been implemented in a wide variety of patient care areas. Many of these involve reducing health care–associated infections or complications, which are not by definition “errors” but are included as such in the patient safety literature when they are thought to be preventable.

Patient safety tips for hospitals

The Agency for Healthcare Research and Quality (AHRQ) has published 10 evidence-based patient safety tips to prevent adverse events in hospitals:

  • Prevent central line–associated bloodstream infections by:
    • Handwashing
    • Using full-barrier precautions
    • Cleaning the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin with chlorhexidine
    • Avoiding femoral lines
    • Removing unnecessary lines
  • Redesign hospital discharge:
    • Assign a dedicated staff member to work closely with patients and with other staff for medication reconciliation and scheduling follow-up appointments.
    • Create an easy-to-understand discharge plan with a medication schedule, follow-up appointments, and phone numbers to call if problems should arise.
  • Prevent hospital-acquired venous thromboembolism (VTE):
    • Considered a preventable cause of hospital deaths
    • Create a VTE protocol using an evidence-based guide to identify best practices.
  • Educate patients on safe anticoagulant use:
    • Anticoagulants Anticoagulants Anticoagulants are drugs that retard or interrupt the coagulation cascade. The primary classes of available anticoagulants include heparins, vitamin K-dependent antagonists (e.g., warfarin), direct thrombin inhibitors, and factor Xa inhibitors. Anticoagulants are among the top causes of adverse drug events.
    • If used incorrectly, they can cause uncontrollable bleeding.
  • Limit shift durations for medical residents and other hospital staff, if possible:
    • Adhere to a maximum 80-hour workweek.
    • Limit residents who work 30-hour shifts to a maximum of 16 consecutive hours of patient care plus a 5-hour protected sleep Sleep Sleep is a reversible phase of diminished responsiveness, motor activity, and metabolism. This process is a complex and dynamic phenomenon, occurring in 4-5 cycles a night, and generally divided into non-rapid eye movement (NREM) sleep and REM sleep stages. Physiology of Sleep period during the night hours.
  • Collaborate with a patient safety organization (PSO), which:
    • Helps others avoid preventable errors
    • Creates a secure and confidential environment where data can be collected, aggregated, and analyzed to improve quality and reduce risks
  • Use sound hospital design principles:
    • To prevent falls: well-designed patient rooms and bathrooms 
    • To allow easy access to patient rooms: decentralized nursing stations
    • To reduce medication errors: well-lit, quiet, private space for pharmacists to fill prescriptions without distractions 
    • To reduce infections: single-bed rooms, multiple convenient locations for handwashing, and improved air filtration systems
  • Measure the hospital’s patient safety culture:
    • Survey hospital staff to assess patient safety culture.
    • Evaluate the impact of interventions and track changes over time.
  • Build teams and rapid response systems:
    • Train hospital staff in effective team communication.
    • Use tools that provide evidence-based techniques for improving team communication for rapid response teams.
  • Provide safe chest tube insertion based on the mnemonic UWET:
    • Universal precautions (sterile cap, mask, gown, gloves)
    • Wider skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin prep
    • Extensive draping
    • Tray positioning

Specific types of errors and strategies for prevention

  • Action or skill-based errors:
    • Require immediate and associative thinking
    • Examples:
      • Skipping a step in medication dilution
      • “Pattern matching,” such as assuming chest pain Chest Pain Chest pain is one of the most common and challenging complaints that may present in an inpatient and outpatient setting. The differential diagnosis of chest pain is large and includes cardiac, gastrointestinal, pulmonary, musculoskeletal, and psychiatric etiologies. Chest Pain is due to an MI MI MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Myocardial Infarction instead of considering a comprehensive differential diagnosis
    • Prevention of fast-thinking errors:
      • Use checklists for steps of a procedure.
      • Avoid distractions during critical tasks.
      • Implement evidence-based clinical practice guidelines.
      • Build checks into systems, such as 2-person verification.
  • Decision-based errors:
    • Involve logical thinking that requires a conscious effort
    • Often occur during a crisis 
    • May be compounded by persisting in following an incorrect path
    • Examples:
      • Faulty knowledge or judgment, such as incorrect treatment choice
      • Critical thinking failure, such as incorrect diagnosis
    • Prevention of decision-based errors:
      • Simulation training for specific clinical scenarios
      • Cognitive aids such as algorithms and computerized decision support
  • Technical errors:
    • Occur when the task exceeds the clinician’s proficiency or when the patient’s anatomy is abnormal and complex
    • Example: intubating the esophagus Esophagus The esophagus is a muscular tube-shaped organ of around 25 centimeters in length that connects the pharynx to the stomach. The organ extends from approximately the 6th cervical vertebra to the 11th thoracic vertebra and can be divided grossly into 3 parts: the cervical part, the thoracic part, and the abdominal part. Esophagus instead of the trachea Trachea The trachea is a tubular structure that forms part of the lower respiratory tract. The trachea is continuous superiorly with the larynx and inferiorly becomes the bronchial tree within the lungs. The trachea consists of a support frame of semicircular, or C-shaped, rings made out of hyaline cartilage and reinforced by collagenous connective tissue. Trachea
    • Prevention of technical errors:
      • Implement known safety precautions for skill-based tasks (e.g., ultrasound guidance for central line placement)
      • Conscious evaluation of the task and one’s proficiency; having backup expertise available
  • Communication-based errors:
    • Result in an unintended act that leads to adverse events that cause patient harm
    • Examples:
      • Surgeon’s communication misheard by the anesthesiologist
      • Hospitalist communication regarding acting on a critical pending test result missed by the physician who is assuming responsibility for patient care on the next shift
    • Prevention of errors based on poor communication:
      • Use structured communication, such as requiring the receiver to repeat the message as heard and having the sender verify accuracy.
      • Numerous accrediting agencies for hospitals in the United States now require education regarding handoffs of patient care between providers.

A Culture of Safety in Health Care

It is essential that health care organizations establish a culture of safety that focuses on system improvement and views preventable medical errors as opportunities to improve patient care processes.

  • Establish a culture of safety:
    • Every individual must assume responsibility to monitor and report medical errors or near misses.
    • Organizations must collect, analyze, and learn from the data collected.
  • Human errors will occur: 
    • Avoid blame, shame, or punitive approach toward the individual.
    • Provide confidential support for clinicians to work through feelings of anger, guilt, inadequacy, depression, and potential suicidal thoughts after a serious medical error.
    • Identify ways to mitigate preventable errors and improve patient safety.
  • Develop a learning culture oriented toward patient safety and continual improvement.
  • Provide a framework for balanced accountability of the individual and the organization in designing workplace systems that are safe and reliable.
  • When medical errors occur:
    • Provide full disclosure and an apology to the patient to decrease anger and blame, increase trust, and improve relationships.
    • An apology includes acknowledging the error and its consequences and communicating regret.


  1. WHO. (n.d.). Patient safety. Retrieved November 2, 2021, from
  2. Global Patient Safety Action Plan 2021–2030. (2021). Towards eliminating avoidable harm in health care.  Retrieved December 14, 2021, from
  3. Rodziewicz TL, Houseman B, Hipskind, JE (2021). Medical error reduction and prevention. StatPearls. Retrieved December 14, 2021, from
  4. Agency for Healthcare Research and Quality. Medical errors. Retrieved November 2, 2021, from
  5. Zhu J, Weingart SN. (2020). Prevention of adverse drug events in hospitals. UpToDate. Retrieved December 17, 2021, from
  6. Wahr JA. (2021). Safety in the operating room. UpToDate. Retrieved December 17, 2021, from

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