The Anatomy of a Patient Safety Indicator

“First, do no harm.”

Although the exact origins of this phrase remain unclear, it is a powerful statement nonetheless, and one that many healthcare providers aspire to follow.

According to the Agency for Healthcare Research and Quality (AHRQ), the Institute of Medicine (IOM) (now the National Academy of Medicine [NAM]) provided an influential framework consisting of six aims for healthcare quality in its 2001 publication, Crossing the Quality Chasm: A New Health System for the 21st Century. The first domain is “safe” care, described as “avoiding harm to patients from the care that is intended to help them” (2018).

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In a discussion of safe care, one topic that stands out is Patient Safety Indicators (PSIs), one of four quality indicators developed by AHRQ, a division of the U.S. Department of Health and Human Services (HHS). PSIs provide information on evidence-based measures of health care quality that could affect the safety of the patient admitted to the hospital as an inpatient. Specifically, they focus on potential in-hospital complications and adverse events following surgeries, procedures, and childbirth.

The 2020 Version of Quality Indicators consists of the following PSIs:
- PSI 02: Death Rate in Low Mortality Diagnosis Related Groups (DRGs)
- PSI 03: Pressure Ulcer Rate
- PSI 04: Death Rate among Surgical Inpatients with Serious Treatable Complications
- PSI 05: Retained Surgical Item or Unretrieved Device Fragment Count
- PSI 06: Iatrogenic Pneumothorax Rate
- PSI 07: Central Venous Catheter-Related Blood Stream Infection Rate
- PSI 08: In Hospital Fall with Hip Fracture Rate
- PSI 09: Perioperative Hemorrhage or Hematoma Rate
- PSI 10: Postoperative Acute Kidney Injury Requiring Dialysis
- PSI 11: Postoperative Respiratory Failure Rate
- PSI 12: Perioperative Pulmonary Embolism or Deep Vein Thrombosis Rate
- PSI 13: Perioperative Sepsis Rate
- PSI 14: Postoperative Wound Dehiscence Rate
- PSI 15: Abdominopelvic Accidental Puncture or Laceration Rate
- PSI 17: Birth Trauma Rate – Injury to Neonate
- PSI 18: Obstetric Trauma Rate – Vaginal Delivery with Instrument
- PSI 19: Obstetric Trauma Rate – Vaginal Delivery without Instrument
- PSI 90 Patient Safety for Selected Indicators

PSI 90 is a composite indicator for PSIs 03, 06, 08, 09, 10, 11, 12, 13, 14, and 15

Source: AHRQ, 2020b

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Technical specifications

AHRQ publishes technical specifications for each PSI which contain the information needed for determination of each PSI. The technical specifications are divided into sections. Note that not all sections are outlined in each PSI technical specification:

Description: Outlines a summary of the PSI. In PSIs that give a rate, the rate will be per 1,000 discharges (medical, surgical [occasionally elective], or overall), or per 1,000 newborns or deliveries. One PSI is calculated by the count instead of a rate (PSI 05). The description then highlights the patient age (if applicable), and patient type (if applicable), and the numerator and denominator inclusions and exclusions.

Numerator: The number of discharged patients that meet inclusion and exclusion criteria for the denominator.

Numerator Exclusions: This section is found only in PSI 05, Retained Surgical Item or Unretrieved Device Fragment Count. This PSI is a true count, instead of a rate, and doesn’t have denominator factors.

Denominator: The pool of discharged patients outside of exclusions and inclusions. These could be the admission type (elective), DRG classification (medical, surgical), and/or age, as identified in the specific technical specification.

Denominator Exclusions: Identifies those factors that exclude the patient from being classified as having a PSI.

Code List and Appendices: Code lists are found at the bottom of the technical specification, with a link to appendices imbedded within the appropriate section of the technical specification.

Source: AHRQ, 2020b

Features of a PSI example

Using the foundation outlined above, let’s look at one of the v2020 AHRQ PSIs to get a better understanding of the application:

PSI 12 Perioperative Pulmonary Embolism or Deep Vein Thrombosis Rate

Numerator: Patient discharges with secondary diagnosis code for proximal deep vein thrombosis or a secondary diagnosis code for pulmonary embolism (code list included in the technical specification).

Denominator: Surgical discharges for patients ages 18 years and older, with any listed procedure codes for an operating room procedure (links to appendices for “operating room procedure codes” and “surgical discharge MS-DRGs” included in the technical specification).

Denominator Exclusions: Excludes cases:
- With principal diagnosis code (or secondary diagnosis present on admission) for proximal deep vein thrombosis (code list included in the technical specification).
- With a principal diagnosis code (or secondary diagnosis present on admission) for pulmonary embolism (code list included in the technical specification).
- Where a procedure for interruption of vena cava occurs before or on the same day as the first operating room procedure (code list included in the technical specification).
- Where the only operating room procedure was for interruption of vena cava (code list included in the technical specification).
- With any listed diagnosis code present on admission for acute brain or spinal injury (code list included in the technical specification).
- With any listed procedure code for extracorporeal membrane oxygenation (ECMO) (code list included in the technical specification).
- Where a procedure for pulmonary arterial thrombectomy occurs before or on the same day as the first operating room procedure (code list included in the technical specification).
- Where the only operating room procedure was for pulmonary arterial thrombectomy (code list included in the technical specification).
- MDC 14 (pregnancy, childbirth, and puerperium)
- With an ungroupable DRG

Source: AHRQ, 2020a

Possessing the knowledge of PSI inclusions and exclusions is integral to knowledge of a possible patient safety event.

Just as no one in the healthcare industry wants a PSI identified when there was no event, they also do not want a PSI to go unidentified because that is a disservice to the patient and can impact future care and management for the patient.

It is up to each of us to give PSIs the attention they deserve, for patients are counting on our integrity.

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