VAE: NHSN Surveillance Definition, VAC/IVAC/PVAP Criteria, and Reporting

VAE (ventilator-associated event) is a National Healthcare Safety Network (NHSN) surveillance category, not a clinical diagnosis. NHSN defines it through a tiered, retrospective algorithm applied to ventilator settings recorded in the chart: a baseline period of stability or improvement on the ventilator, followed by a sustained increase in the daily minimum PEEP or FiO2, escalating — only if further criteria are met inside a defined day window — through three named tiers. The protocol itself states the point plainly: “The VAE definition algorithm is for use in surveillance. It is not a clinical definition algorithm and is not intended for use in the clinical management of patients.” This guide works through that adjudication using the criteria published in the CDC NHSN Patient Safety Component Manual, Device-associated Module, Chapter 10 (Ventilator-Associated Event), January 2024 edition, the most recent edition available for direct verification. NHSN revises this manual annually, typically each January; confirm the current-year manual before using any of this for official reporting.

Surveillance VAE Is Not a Diagnosis of Ventilator-Associated Pneumonia

This is the distinction that drives the most consequential confusion in the field, and unlike some surveillance-versus-clinical gaps it was designed in deliberately rather than emerging by accident.

Before 2013, NHSN’s ventilator surveillance was limited to ventilator-associated pneumonia (VAP) under the PNEU definitions. CDC’s own protocol is blunt about why that changed: there is no valid, reliable definition for VAP, and even the most widely used VAP criteria are neither sensitive nor specific. The PNEU definitions require radiographic findings, and the subjectivity and variability inherent in chest radiograph technique, interpretation and reporting make chest imaging ill-suited for a definition used for public reporting, inter-facility comparison, and pay-for-reporting programs. A CDC Working Group convened in 2011 — drawing on the Critical Care Societies Collaborative, the American Association for Respiratory Care, APIC, CSTE, HICPAC’s Surveillance Working Group, IDSA and SHEA — built the VAE algorithm around objective, streamlined and potentially automatable criteria instead. It was implemented in NHSN in January 2013.

The practical consequences of that design choice:

• A patient can be clinically diagnosed and treated for ventilator-associated pneumonia without ever meeting a VAE criterion — most obviously if the pneumonia never produced a sustained two-day rise in daily minimum PEEP or FiO2 following a qualifying baseline period, because that oxygenation trigger is the gate every VAE must pass through first.
• Conversely, a patient can meet the VAE definition without having pneumonia at all. CDC’s own protocol states that research suggests most VACs are due to pneumonia, ARDS, atelectasis and pulmonary edema — four different conditions. The top tier of the algorithm is deliberately named Possible VAP for exactly this reason: it identifies cases with laboratory evidence of respiratory infection, not cases where pneumonia has been confirmed.
• VAE is location-based and adult-only. The PNEU/VAP definitions have not been retired — in-plan surveillance for ventilator-associated PNEU may still be conducted for pediatric patients (“PedVAP”), and the PNEU definitions remain available for off-plan PNEU/VAP surveillance at any age and for assigning a secondary bloodstream infection.

So an infection preventionist adjudicating a VAE is not asking “did this patient have a ventilator-associated pneumonia.” They are asking whether a specific, ordered set of objective chart findings falls inside a specific set of day windows.

Step 1: Is the Patient Eligible, and Is There a Ventilator?

NHSN defines a ventilator as a device used to support, assist or control respiration (inclusive of the weaning period) through the application of positive pressure to the airway when delivered via an artificial airway — specifically an oral or nasal endotracheal tube, or a tracheostomy tube. Devices delivering positive pressure by non-invasive means (CPAP, BiPAP, Bi-level, IPPB and PEEP via nasal prongs, nasal mask, full face mask or total mask) are not ventilators for VAE purposes unless the positive pressure is delivered through an artificial airway. This is the mirror image of the device-eligibility question that opens CLABSI and CAUTI adjudication: the device gate comes first, and it is defined by mechanism rather than by clinical intent.

Eligible locations are adult inpatient locations in acute care hospitals, long term acute care hospitals and inpatient rehabilitation facilities where ventilator days and patient days can be collected — ICUs, specialty care areas, step-down units and wards. Non-acute-care mapped locations within acute care facilities (for example chronic care units) are not eligible.

• Included: all patients in eligible adult inpatient locations regardless of the patient’s age; patients on a conventional mode of mechanical ventilation; patients on Airway Pressure Release Ventilation (APRV) or related modes; and patients on a conventional mode or APRV while in the prone position or while receiving nitric oxide, helium-oxygen mixtures (heliox) or epoprostenol therapy.
• Excluded: all patients in neonatal and pediatric inpatient locations, regardless of the patient’s age; and patients on high-frequency ventilation, extracorporeal life support or paracorporeal membrane oxygenation, excluded during periods when that support is in place for the entire calendar day.
• APRV carries a mechanical exception: while a patient is on APRV or a related mode, both the period of stability or improvement and the period of worsening oxygenation are determined by changes in FiO2 only, because the PEEP changes the algorithm looks for may not be applicable to APRV.

Two more gates before the algorithm can produce anything. First, the patient must have been mechanically ventilated for at least 4 calendar days, where the day of intubation and initiation of mechanical ventilation is day 1 — and the earliest possible date of event is day 3 of mechanical ventilation. Second, an episode of mechanical ventilation is a period of days during which the patient was ventilated for some portion of each consecutive day; a break of at least one full calendar day followed by reintubation during the same hospitalization starts a new episode, and therefore a new day count.

Step 2: Establish the Baseline Period of Stability or Improvement

The whole algorithm hangs off a comparison against a baseline, so the baseline has to be defined before anything can be called a deterioration. The baseline period of stability or improvement is the 2 calendar days immediately preceding the first day of increased daily minimum PEEP or FiO2, and it must be characterised by at least 2 calendar days of stable or decreasing daily minimum FiO2 or PEEP values — specifically, the daily minimum on the second day of the baseline must be equal to or less than the daily minimum on the first day.

That means the sequence is fixed and cannot be reordered: a rise in PEEP or FiO2 with no qualifying two-day stable-or-improving period in front of it is not a VAE, however large the rise. A patient whose FiO2 went 0.50, 0.35, 0.40 across three days has not had a qualifying baseline in days two and three, because day three is higher than day two.

The values compared are daily minimums, and NHSN’s definition of a daily minimum is itself a rule rather than a lookup:

• The daily minimum PEEP is the lowest PEEP value during a calendar day that is set on the ventilator and maintained for more than 1 hour. The daily minimum FiO2 is defined the same way.
• If settings are recorded less frequently than hourly (every 2 or 4 hours, say), the daily minimum is simply the lowest value set during the calendar day.
• If settings are recorded hourly or more often, there must be enough consecutive recordings at a level to cover more than 1 hour — two consecutive hourly recordings, three consecutive half-hourly recordings, or five consecutive fifteen-minute recordings. A lower value recorded at two non-consecutive time points does not qualify, and the daily minimum becomes the next-lowest value that does.
• If no value was maintained for more than 1 hour at all — because ventilation started late in the day, was discontinued early, or the settings were changed constantly — the daily minimum defaults to the lowest value set during the calendar day, regardless of how long it was held.

One further convention matters more than its single sentence in the protocol suggests: for VAE surveillance, PEEP values between 0 and 5 cmH2O are considered equivalent. A patient sitting at a daily minimum PEEP anywhere in the 0–5 range must therefore rise to at least 8 cmH2O, sustained for at least 2 calendar days, to meet the PEEP pathway — and a climb from 0 to 3 to 5 cmH2O across a baseline period still counts as a stable baseline, because every value in it is treated as 5.

Step 3: VAC — The Sustained Increase in Daily Minimum PEEP or FiO2

Tier one is Ventilator-Associated Condition (VAC). After a qualifying baseline period, the patient must have at least one of the following indicators of worsening oxygenation:

• An increase in daily minimum FiO2 of at least 0.20 (20 points) over the daily minimum FiO2 of the first day in the baseline period, sustained for at least 2 calendar days; or
• An increase in daily minimum PEEP of at least 3 cmH2O over the daily minimum PEEP of the first day in the baseline period, sustained for at least 2 calendar days.

Two details in that wording are easy to lose and both change outcomes. The comparison is against the first day of the baseline, not the day immediately before the rise. And the increase must be sustained across two calendar days — a single day at a higher setting that falls back the next day is not a VAC.

The date of event is the date of onset of worsening oxygenation: the first calendar day on which either threshold is met, that is, day 1 of the required two-day period of worsening. It is explicitly not the date on which all VAE criteria were finally satisfied. Because so much of the rest of the algorithm is measured relative to this date, getting it wrong shifts every subsequent window.

Nothing beyond oxygenation is required at this tier. A VAC is a deterioration in ventilator support after a period of stability, and nothing more — no fever, no culture, no antibiotic. That is the design: the objective, automatable floor.

Step 4: IVAC — Adding Inflammation and a New Antimicrobial

Tier two is Infection-related Ventilator-Associated Complication (IVAC). On or after calendar day 3 of mechanical ventilation, and within 2 calendar days before or after the onset of worsening oxygenation, the patient must meet both of the following:

• Temperature greater than 38 °C or less than 36 °C, OR a white blood cell count of at least 12,000 cells/mm³ or no more than 4,000 cells/mm³; and
• A new antimicrobial agent is started and continued for at least 4 qualifying antimicrobial days (QADs).

Both halves carry definitions of their own. A new antimicrobial agent is any agent on the protocol’s eligible-agent appendix that is initiated on or after the third calendar day of mechanical ventilation AND within the VAE window period, and that was not given to the patient on either of the 2 days preceding the current start date. An agent started on day 1 and simply continued into the window is not new. Route matters too: only intravenous, intramuscular, digestive-tract and respiratory-tract administration count, and other routes — antibiotic locks, intraperitoneal, intraventricular, irrigation, topical — are excluded.

A qualifying antimicrobial day is a day on which the patient was given an agent determined to be new within the VAE window period, and four consecutive QADs are needed, starting within that window. The counting rules are specific:

• Days on which a new antimicrobial agent is administered count as QADs.
• Days between administrations of the same new agent also count, as long as the gap is no more than 1 calendar day. Levofloxacin given on VAE days 1, 3, 5 and 7 yields seven QADs, not four.
• Days between administrations of different new agents do not count. Swapping agents across a gap day breaks the consecutive run rather than bridging it.

Step 5: PVAP — Laboratory Evidence of Respiratory Infection

Tier three is Possible Ventilator-Associated Pneumonia (PVAP). Under the same day constraints — on or after calendar day 3 of mechanical ventilation and within 2 calendar days before or after the onset of worsening oxygenation — one of three criteria must be met, subject to the organism exclusions below.

• Criterion 1 — positive culture meeting a quantitative threshold, with no requirement for purulent secretions. The thresholds stated in the algorithm are: endotracheal aspirate at least 10⁵ CFU/ml; bronchoalveolar lavage at least 10⁴ CFU/ml; lung tissue at least 10⁴ CFU/g; protected specimen brush at least 10³ CFU/ml. The protocol’s Table 3 breaks the lavage and brush thresholds out further by whether the specimen was obtained bronchoscopically or non-bronchoscopically (blind), so read that table rather than the summary figure when the specimen type is ambiguous. Semi-quantitative results may be used only if they correspond to these quantitative thresholds, which the protocol tells facilities to confirm with their own laboratory rather than assume.
• Criterion 2 — purulent respiratory secretions plus an organism that did not reach the Criterion 1 threshold. NHSN defines purulent respiratory secretions numerically: secretions from the lungs, bronchi or trachea containing at least 25 neutrophils and no more than 10 squamous epithelial cells per low power field (×100). The organism may come from sputum, endotracheal aspirate, bronchoalveolar lavage, lung tissue or protected specimen brush, by qualitative culture or by quantitative/semi-quantitative culture without enough growth for Criterion 1. Laboratories that report direct-examination results in other formats should be reconciled against the protocol’s Table 2 before this criterion is applied.
• Criterion 3 — one of a defined set of other positive tests: an organism identified from pleural fluid obtained during thoracentesis or within 24 hours of chest tube placement (fluid from a repositioned chest tube, or from a tube in place more than 24 hours, is not eligible); positive lung histopathology; lower respiratory specimen cytology suggestive of infection; a positive diagnostic test for Legionella species; or a positive diagnostic test on respiratory secretions for influenza virus, respiratory syncytial virus, adenovirus, parainfluenza virus, rhinovirus, human metapneumovirus or coronavirus.

Organisms that cannot be used to meet PVAP are set out explicitly, and this is where a surveillance-versus-clinical instinct most often misleads:

• Results reported as normal or mixed respiratory or oral flora, altered oral flora, or similar commensal-flora findings. A report of “flora” excludes only the flora — an eligible organism identified from the same specimen can still be used.
• Any Candida species or yeast not otherwise specified, any coagulase-negative Staphylococcus, and any Enterococcus, when identified from sputum, endotracheal aspirate, bronchoalveolar lavage or protected specimen brushings. The same organisms can be reported as PVAP pathogens when identified from lung tissue or eligible pleural fluid.
• Blastomyces, Histoplasma, Coccidioides, Paracoccidioides, Cryptococcus and Pneumocystis — excluded from any eligible specimen type, including lung tissue and pleural fluid, because they are typically community-associated and rarely or never healthcare-associated.

The Day Windows That Govern Everything

Three separate day windows run in parallel, and confusing them is the most common source of misclassification.

• The baseline period — the 2 calendar days immediately preceding the first day of increased daily minimum PEEP or FiO2.
• The VAE window period — the period around the date of event within which all the other VAE criteria must be met. It is usually 5 days: the 2 days before, the day of, and the 2 days after the date of event. There is a hard-edged exception. Because the window can never include any day before the 3rd day of mechanical ventilation, a date of event falling on MV day 3 or day 4 produces a window of only 3 or 4 days respectively. With a date of event on MV day 3, the window is the day of onset plus the 2 days after it, and nothing before.
• The 14-day event period — a VAE occupies 14 days beginning on the date of event as day 1. A new VAE cannot be identified or reported until that period has elapsed.

A related reporting instruction follows directly from the window: do not upgrade an event using findings that occur outside the VAE window period. A culture that would have satisfied PVAP but was collected on day 4 after onset does not move a VAC to a PVAP; the case stays where the in-window findings put it.

How the Three Tiers Are Reported

The tiers are cumulative and hierarchical, not alternatives. A facility conducting in-plan VAE surveillance must assess patients for all events in the algorithm, from VAC through IVAC to PVAP — a unit cannot elect to do VAC surveillance only. The hierarchy then determines what gets reported:

• Meets VAC only → report as VAC.
• Meets VAC and IVAC → report as IVAC.
• Meets VAC, IVAC and PVAP → report as PVAP.

What travels with the report also differs by tier. Pathogens are not reported for VAC or IVAC events, and secondary bloodstream infections are not reported for VAC or IVAC events. Pathogens may be reported for PVAP, subject to the exclusion list above. A secondary BSI may be reported for a PVAP only where at least one organism from blood matches an organism from an eligible respiratory tract specimen; the respiratory specimen must have been collected on or after MV day 3 and within 2 calendar days either side of the onset of worsening oxygenation, and the blood specimen must have been collected during the 14-day event period. Where PVAP was met on the histopathology criterion alone with no culture performed, no secondary BSI is reported even if a blood specimen was positive.

One further exclusion sits outside the algorithm’s logic entirely: if the date of event falls on or after the date documented evidence of consent was obtained AND the patient is being supported for organ donation purposes, the event is not reported as a VAE.

Putting It Together: What “VAE” Means as a Count

A case becomes a reportable VAE when an eligible adult ventilated patient, on or after MV day 3, shows a sustained two-day rise in daily minimum PEEP (at least 3 cmH2O) or FiO2 (at least 0.20) following a two-day baseline of stability or improvement. It becomes an IVAC if temperature or white-cell criteria plus a new antimicrobial continued for 4 QADs also fall inside the VAE window period, and a PVAP if one of the three laboratory criteria does too.

Events are reported on the Ventilator-Associated Event form (CDC 57.112). Facilities collect ventilator days and patient days as denominators, counted daily at the same time each day; all ventilator days are counted, including days for patients ventilated fewer than 3 days. Electronic denominator counts may be substituted for manual ones only where they fall within ±5% of manually collected counts, validated for a minimum of 3 consecutive months, and validated separately for each location doing VAE surveillance.

From there NHSN produces a VAE rate per 1,000 ventilator days, a VAE rate per 100 episodes of mechanical ventilation, a ventilator Standardized Utilization Ratio, and a Standardized Infection Ratio (SIR) — the latter computed for each VAE category, for “IVAC Plus” (all events meeting at least the IVAC definition) and for Total VAE, using a negative binomial regression model. NHSN calculates the SIR only where the number of predicted events is at least 1, a deliberate minimum-precision rule that suppresses the statistically unstable ratios small units would otherwise generate; the SIR entry covers why that instability arises.

The protocol distinguishes which of these measures suits which purpose. Rates and SIRs that may be appropriate for public reporting, inter-facility comparison and pay-for-reporting or pay-for-performance programs are the overall VAE rate, whose numerator is all events meeting at least the VAC definition. The IVAC-plus rate and tier-specific rates are described as appropriate for internal use within a unit or facility. That is a statement about measure construction, not about any particular programme’s requirements — whether and how VAE is reported under a given CMS or state programme should be confirmed against that programme’s own current specifications rather than inferred from the NHSN manual.

Frequently Asked Questions

Is a ventilator-associated event the same as ventilator-associated pneumonia?

No. VAE is a surveillance construct with three tiers, only the top of which (PVAP) requires laboratory evidence of respiratory infection — and even that tier is named Possible VAP rather than confirmed pneumonia. CDC replaced VAP-only surveillance precisely because no valid, reliable VAP surveillance definition exists. A clinically diagnosed VAP need not be a reportable VAE, and a reportable VAE need not be pneumonia.

How many days must a patient be ventilated before a VAE can be identified?

At least 4 calendar days of mechanical ventilation, counting the day of intubation as day 1. The earliest possible date of event — the date of onset of worsening oxygenation — is mechanical ventilation day 3.

What increase in PEEP or FiO2 defines a VAC?

An increase in the daily minimum FiO2 of at least 0.20 (20 points), or in the daily minimum PEEP of at least 3 cmH2O, over the daily minimum of the first day of the baseline period, sustained for at least 2 calendar days. Because PEEP values from 0 to 5 cmH2O are treated as equivalent, a patient with a daily minimum PEEP in that range must reach at least 8 cmH2O to qualify.

Does a patient on CPAP or BiPAP by face mask fall under VAE surveillance?

No. NHSN’s ventilator definition requires positive pressure delivered through an artificial airway — an oral or nasal endotracheal tube, or a tracheostomy tube. Non-invasive delivery by nasal prongs or any form of mask does not make the device a ventilator for VAE purposes.

Are pediatric patients included?

No. VAE surveillance is location-based and restricted to adult inpatient locations; neonatal and pediatric inpatient locations are excluded regardless of an individual patient’s age. Pediatric ventilator surveillance runs under the separate PedVAE and PedVAP definitions.

If a patient meets VAC, IVAC and PVAP criteria, how many events are reported?

One. The tiers are hierarchical: a case meeting VAC and IVAC is reported as an IVAC, and a case meeting all three is reported as a PVAP. A new VAE cannot be reported at all until the 14-day event period beginning at the date of event has elapsed.

Who applies the VAE definition in a hospital?

In most US hospitals this adjudication is performed by an infection preventionist working from the chart and the recorded ventilator settings, not by the treating clinician’s diagnosis — though the objective, setting-driven nature of the VAC tier is exactly what makes VAE more amenable to electronic detection than the PNEU definitions it replaced.

This guide summarizes the structure of the NHSN Chapter 10 (VAE) surveillance criteria as published in the January 2024 Patient Safety Component Manual for general orientation. It is not a substitute for the current-year NHSN manual, and it is not clinical guidance for individual patient management. For official reporting, always work from the exact current-year CDC NHSN manual chapter, eligible-antimicrobial appendix, threshold tables and any programme-specific reporting instructions.

Related: see the Patient Safety & Infection Prevention hub, the CLABSI and CAUTI guides for the equivalent device-day and laboratory-criteria logic applied to central lines and urinary catheters, and the hemovigilance guide for how NHSN’s parallel transfusion-safety surveillance module works.