CHESTCHEST NewsAccurately representing delirium

Accurately representing the complications and impact of delirium

In a formal letter to Centers for Medicare & Medicaid Services (CMS), the American College of Chest Physicians (CHEST) endorsed the need to make a key change to the designation of delirium that recognizes it as a major complication or comorbidity. CHEST is grateful to the American Delirium Society for leading this charge.

The proposed change would more accurately represent the clinical importance of delirium and the tremendous costs associated with it. The suggested change will make the complexity designation consistent with toxic (G92) and metabolic (G93.41) encephalopathy (TME) which is implied in cases of delirium as an underlying factor.

CHEST, which represents a large portion of the community of critical care clinicians, recognizes that this change is essential to our ability to improve the clinical care and outcomes of patients who are cognitively vulnerable.

The full letter can be found below.

Update: An article, "Requesting That Delirium Achieve Parity With Acute Encephalopathy in the MS-DRG System," was published in February 2024 in the Journal of the Academy of Consultation-Liaison Psychiatry and recognized CHEST's support of this request.

Dear Center for Medicare & Medicaid Services,

We write to request that causally specified delirium be designated as major complication or comorbidity (MCC), which would make its complexity designation consistent with toxic (G92) and metabolic (G93.41) encephalopathy (TME).

This change is essential to recognizing the clinical importance of delirium and, crucially, the tremendous costs associated with it.1,2 Placing delirium and encephalopathy on par with TME in terms of reimbursement is intended to facilitate systematic efforts to detect delirium as recommended across specialties and settings,3-6 thereby enhancing awareness of delirium and its dire impact on patients, their families, care delivery, and healthcare systems.7 The ultimate goal of this change is to improve the clinical care and outcomes of cognitively vulnerable patients.

Executive summary

We request that all causally specified delirium diagnoses be designated as MCC, consistent with TME. This is justified because a delirium diagnosis in the DSM-5-TR8 and ICD-109 requires both a defined clinical syndrome plus attribution to a direct physiological cause. In other words, a diagnosis of causally specified delirium implies an underlying TME. Our requests are tabulated below (Table 1), with requested changes are in red.

Table 1: Current rule compared with Requested Changes


Endorsed by 10 medical societies (Table 2), a 2020 position statement on preferred nomenclature of delirium and acute encephalopathy, clarified definitions of “acute encephalopathy” and “delirium,” as well the relationship between them.1 The statement provides the following definitions:

Acute encephalopathy: “a rapidly developing (in less than 4 weeks) pathobiological brain process which is expressed clinically as either subsyndromal delirium, delirium or coma.” The diagnostic codes for acute encephalopathy include toxic, metabolic, other, and unspecified encephalopathy.

Subsyndromal delirium: “acute cognitive changes that are compatible with delirium, but do not fulfil all DSM-5 delirium criteria”

Delirium: “a clinical state defined according to the criteria of the DSM-5” (n.b., the current edition is DSM-5-TR8)

Coma: “a state of severely depressed responsiveness defined using diagnostic systems such as the Glasgow Coma Score (GCS) or the Full Outline of UnResponsiveness (FOUR) score”

Table 2: Professional societies endorsing preferred nomenclature

The clinical syndromes of subsyndromal delirium, delirium, and coma alert the clinician to an underlying acute encephalopathy, as they are the cognitive evidence of a pathobiological brain process disrupting global consciousness. Conversely, acute encephalopathy would not be suspected, let alone diagnosed, in the absence of such clinical syndromes. That is, the presence of a delirium-spectrum syndrome entails the presence of an underlying acute encephalopathy,10 as all editions of the DSM have included a diagnostic criterion for delirium, variably worded, requiring that the cognitive disturbances be attributable to the “direct physiological consequence of another medical condition, substance intoxication or withdrawal, or exposure to a toxin, or is due to multiple etiologies.”

Delirium in relation to acute encephalopathy

Reliability is necessary for high-quality care; however, the diagnosis of acute encephalopathy risks being unreliable on its own because it lacks operationalized diagnostic criteria. Further, to our knowledge, no clinical severity thresholds have ever been validated to define acute encephalopathy caseness. Several EEG patterns may support a diagnosis of acute encephalopathy,11,12 but without reliable criteria this diagnosis will be diagnosed based on nonspecific changes in mental status. At the same time, these same EEG findings for acute encephalopathy are correlated with delirium severity,13 which is important because delirium is a well validated clinical construct with reliable operationalized criteria.14 The severity of the delirium-spectrum illness from subsyndromal delirium to delirium to coma is the bedside clinical analog of an EEG that indexes the severity of the underlying acute encephalopathy. Clinical complexity increases and outcomes worsen incrementally with the severity of mental status change: subsyndromal delirium with moderate impact,15,16 delirium with major impact,7,17,18 and coma with severe impact.19

A robust literature details the impact of delirium on care complexity and costs,20,21 readmissions,22 rates of functional decline,23,24 institutionalization,25 cognitive decline,26-28 dementia,29 and mortality,30,31 yet curiously there is no parallel in the “toxic/metabolic encephalopathy” literature (Table 3). Delirium continues to attract increasing32 and increasingly serious international attention33,34 for its tremendous public health impact. Further, the relationship between delirium and Alzheimer’s disease and related dementias is prioritized in research.35

Table 3: Impact of delirium on healthcare and outcomes

The models of delirium and acute encephalopathy each have a rich tradition,2 yet a variety of historical, institutional, and even clinician-level factors have conspired against their integration.10 This is despite the fact that they represent interdependent aspects of a shared set of acute neurocognitive syndromes. Among the most pressing reasons for their division, though, is economic.55 Currently, at each level of specification, each acute encephalopathy code (G-series) is designated as a higher complexity of illness than the corresponding delirium (F-series) code even though causally specified delirium codes provide even greater specificity (Table 4).

Table 4: MS-DRG complexity of delirium and acute encephalopathy vs neurocognitive and causal specification

* ICD-10-CM requires that one “Code first the underlying physiological condition” for F05, whereas the relevant substance is denoted by the ones digit in the diagnostic code for intoxication denoted x in the table and withdrawal deliria. The tenths digit denoted by y in the table refers to the substance use pattern. ICD-10-CM requires that one “Code first, if applicable, drug induced (T36-T50) or use (T51-T65) to identify toxic agent” for G92 but does not have similar coding requirements for G93.41.56

The coding landscape in the U.S. bears this out: in 2011 encephalopathy diagnoses outnumbered delirium nearly 4:1 but in 2018 the ratio was more than 13:1,57 which one suspects is due in large part due to the higher reimbursement.55 [Note, in a supplementary document, we provide an updated analysis based on the National Inpatient Sample for 2019—the last full year before the COVID pandemic—that considers the impact of our proposal.] The effects of the current system, by prioritizing reimbursement of G-series codes over F-series codes, may inadvertently reward institutions that are savvier with such billing incentives, either institutions whose practitioners have been taught to code the corresponding G-series code preferentially or those with separate coding departments. The issue of upcoding delirium to TME was among the key allegations in a whistleblower lawsuit brought by Integra Med Analytics LLC against Providence Health and Services.58 Although the case was ultimately dismissed,59 it clearly highlights this disparity. In the initial filing, the Integra complaint noted that “[e]ncephalopathy is a term for brain disease or damage to the brain where the brain is regarded as ‘altered in its structure or function.’ The telltale symptom is an altered mental state, but altered mental state alone is insufficient for diagnosing encephalopathy” (as quoted in the minutes from the case60). However, one considers it telling that no clinical definition for encephalopathy appears to be offered by the plaintiff in this case.

On the origins of the disparity

Why, when the MS-DRG was being developed, might acute encephalopathy—and, in particular, TME—have performed like an MCC whereas delirium performed like a CC?55 Whereas these diagnoses had been on par in terms of reimbursement prior to the MS-DRG system, they were clearly not being used interchangeably in hospitals. How might coding practices at the time have introduced an artifact of severity?

The first observation applies to both delirium and TME diagnoses. That is, only a fraction of patients with TME/delirium ever receive either diagnosis. A review of coding in 2018 revealed that the combined prevalence of both was roughly 3%,57 yet prospective studies find substantially higher values. For instance, it is rare to find studies that report a lower than 10% prevalence of delirium after major surgery, and more than half of patients in critical care develop delirium.61 Delirium rates across acute medical settings vary by population and, typically, age, pre-existing cognitive impairment, and overall morbidity.62 Therefore, in view of this likely type II error in national coding, the question becomes, “What clinical factors would lead to an artifact of differential complexity?”

Consider TME. First, neurologists have historically favored the term TME whereas most other specialties have favored delirium2 (notably, coding in internal medicine has increasingly favored TME for reasons that are addressed in this proposal1). Returning to the mid-2000’s when the MS-DRG system was developed, we should consider the role of neurology in clinical care. For a neurologist to be involved in a patient’s care either as the primary or consulting service, the mental status change is typically to such a degree that it warrants independent clinical attention for neurological evaluation, often being accompanied by focal neurological findings. Diagnostic consideration would naturally include encephalitis, seizure disorders, space-occupying lesions, cerebrovascular accidents, and the like. Such an evaluation often involves head imaging, EEG evaluation, or even lumbar puncture. As such, TME diagnoses at the time were all but certainly enriched with more severe clinical scenarios.

Next, consider delirium. The vast majority of delirium is never diagnosed, which means that it would be more informative to ask, “When is delirium diagnosed?” rather than “When is it undiagnosed?”63-66 In general, a diagnosis of delirium tends to be made when there is hyperactivity and, in particular, behavioral disturbances. The far more common hypoactive presentations go either undiagnosed or preferentially diagnosed as TME . Additionally, the tradition of the neurologists Victor and Adams was to reserve the diagnosis of delirium for hyperactive states and encephalopathy for hypoactive ones.2 However, of the motoric subtypes of delirium, hypoactive delirium is consistently associated with worse clinical outcomes, including greater risk of mortality.67-71 That is, the data used to create the MS-DRG likely would have included a small group of largely hyperactive delirium as the complication or comorbidity in question, leaving the majority of patients with the more severe hypoactive delirium in the non-delirium reference group, thereby creating a false impression that delirium is of lower complexity.

Delirium and the nine guiding principles for reconsideration of its MS-DRG complexity designation

Delirium is a textbook example that maps onto the nine guiding principles to evaluate when considering a potential change to CMS coding and reimbursement.72 However, an epistemic principle, even more foundational than the nine, is added as a preceding item as number zero below because the ability to detect a condition reliably is necessary for consistent detection and clinical intervention.

0. Delirium can be diagnosed reliably whereas TME cannot be diagnosed reliably without a defined threshold.

  • An independent TME diagnosis currently lacks demonstrated reliability whereas delirium has reliable, operationalized diagnostic criteria.8
  • Delirium instruments are available to detect delirium reliably across settings. In particular, the suite of Confusion Assessment Method delirium assessment instruments has been validated extensively both categorically and as severity instruments,73-78 leading the CAM to be the most widely used set of instruments to detect delirium worldwide. Further, the Ultra-Brief CAM79 can equip a large range of healthcare clinicians to detect delirium reliably in less than a minute and a half, with most patients screening negative in less than a minute on an initial 2-item screener.80
  • Recognizing the link between delirium and acute encephalopathy encourages diagnostic reliability by standardizing clinical definitions and allowing for systematic detection efforts.81

1. “Involves a chronic illness with susceptibility to exacerbations or abrupt decline.”

  • Acute and chronic forms of cognitive impairment share a bidirectional relationship such that preexisting cognitive impairment increases the risk of delirium and delirium increases the risk of subsequent cognitive decline and dementia.82 The relationship between delirium and Alzheimer’s disease and related dementias remains of critical importance to older adults, especially within the Age-Friendly Health Systems and Geriatric Surgery Verification Program initiatives.
  • Delirium superimposed on dementia may be a particularly virulent condition and appears to involve the acceleration of decline and increased risk of mortality.83
  • Further, these proposed changes, by requiring clinical specificity, bear similarity to the recent changes in dementia diagnostic codes that provide greater specification of neuropsychiatric disturbances beyond simply “with/without behavioral disturbances.”84

2. “Serves as a marker for advanced disease states across multiple different comorbid conditions.”

  • Delirium is common across hospital settings and comorbidities, in particular occurring in roughly a third of hospitalized older adults.81
  • Prioritizing delirium detection facilitates the recognition of mental status changes heralding clinical deterioration for prompt recognition and redress of contributing clinical factors.
  • Regarding its broad applicability to clinical care, mental status changes may be regarded as a vital sign.85,86

3. “Reflects systemic impact.”

  • Delirium is an essential element of the Age-Friendly Health System, with deep interconnections with each of the 4M’s,87 and Geriatric Verification Program88 initiatives.
  • Delirium in post-acute care settings is associated with more than twice the risk of 30-day mortality, 40% increased risk of 30-day hospital readmission, and 40% lower rate of discharge home within 30 days.89
  • Table 3 (see above) details many aspects of delirium’s systemic impact.

4. “Post-operative/post-procedure condition/complication impacting recovery.”

  • “Postoperative delirium” is the uniformly recommended term to describe acute neurocognitive disturbances after surgery.90
  • Apart from the nearly universal experience of postoperative pain, delirium is arguably the most common complication after major surgery and has an outsized impact on postoperative recovery.91 As described in the clinically focused review in NEJM by Dr. Marcantonio,91 delirium is associated with: a 2- to 5-fold increased risk of postoperative complications, including risk of death, an additional 2–5 days length of stay, a 3-fold increased risk of institutional placement at discharge, poor functional recovery, and new dementia diagnosis.
  • The healthcare costs and sequelae attributable to delirium consider not only incremental costs during the index episode of care but also care utilization over the following year.21

5. “Typically requires higher level of care (that is, intensive monitoring, greater number of caregivers, additional testing, intensive care unit care, extended length of stay).”

  • We refer, again, to Table 3 above.

6. “Impedes patient cooperation or management of care or both.”

  • Patient experience must be considered when discussing the distinctions between delirium and TME. TME draws attention to underlying pathobiology, but it does not specify the clinical manifestation of that disturbance and the diverse ways that its neuropsychiatric disturbances routinely impede care delivery and recovery.10 A diagnosis of delirium, on the other hand, centralizes the patient’s experience, drawing attention to the importance of the patient’s mental status and care engagement.50,92,93
  • A diagnosis of delirium requires a clinician to characterize a patient’s mental status. This information is essential so that clinicians understand a patient’s ability to engage meaningfully in care decisions, have discussions about their care with clinicians and loved ones, and participate productively in various aspects of care.
  • Additionally, identifying delirium as “delirium” encourages evaluation and monitoring for neuropsychiatric disturbances that increase the risk of danger, including impulsivity, risk of falls, inadvertent self-extubation or line removals, and other elements of compromised care.94

7. “Recent (last 10 years) change in best practice, or in practice guidelines and review of the extent to which these changes have led to concomitant changes in expected resource use.”

  • To our knowledge, there is no defined treatment pathway for the TME diagnoses; however, several guidelines published in the past 10 years exist for delirium, both in the United States (e.g., by the American Geriatrics Society,the Society for Critical Care Medicine,Cochrane Database of Systematic Reviews,95 and American Psychiatric Association [update currently in process]) and internationally (e.g., the National Institute for Health and Clinical Excellence,96 the Scottish Intercollegiate Guidelines Network,97 Australian Delirium Care Standard,98 European Society of Anaesthesiology,99 Association of Scientific Medical Societies of Germany,100 and Japanese Psycho-Oncology Society and Japanese Association of Supportive Care in Cancer101).

8. “Denotes organ system instability or failure.”

  • Although the term “acute brain failure” is discouraged by the recent multi-society statement on nomenclature (for its redundancy rather than for its inaccurate connotations),this term was the subtitle of Lipowski’s first of two delirium monographs.102 Nomenclature aside, there is no question that delirium represents a global disturbance in cognition as a form of “failure of neurocognition”103 and global dysfunction.
  • Delirium is associated with markers of brain damage including on postmortem neuropathology,104 elevated neurofilament light chain (marker of axonal damage),105,106 elevated serum tau,107 and several inflammatory markers known to index neural injury.108

9. “Represents end of life/near death or has reached an advanced stage associated with systemic physiologic decompensation and debility.”

  • Delirium is a state of systemic physiological decompensation associated with advanced illness. Delirium at the end of life (“terminal delirium”) is a common expression of advanced disease that can cause patients and their families distress, and dangerous behavioral disturbances.109

Rectifying reimbursement actively facilitates prevention efforts

Finally, we consider that these changes would facilitate delirium prevention efforts as well. Delirium is costly, and its complexity designation should be commensurate with its economic impact. However, delirium prevention efforts work, preventing roughly 40% of delirium.110,111 The costs associated with delirium not only justify its designation as MCC but also encourage widespread delirium prevention efforts. Care bundles such as the AGS CoCare® HELP 112,113 and the Society of Critical Care Medicine’s ICU Liberation A-to-F bundle114,115 have been shown to be both effective at preventing delirium and cost effective. How might a change in delirium’s complexity designation incentivize adoption of such delirium care bundles?

Despite the effectiveness of delirium prevention bundles, encouraging delirium prevention efforts alone, without changing the complexity designation of delirium, would not be enough. This is because most delirium is not preventable; this includes both delirium prevalent on admission (inherently not preventable116) and the 60% of incident delirium that is not currently preventable with modern delirium bundles.111 Designating delirium as MCC would signal to hospitals the costs associated with delirium, thereby leading to a greater awareness of its scope and healthcare impact. It would also be apparent that additional reimbursement for delirium as MCC is modest relative to the cost savings realized by delirium prevention.113 This is because the incremental increase in reimbursement for delirium as MCC is relevant only for the portion of patients without a separate qualifying MCC . Insurance companies would also have reason to incentivize hospitals to implement delirium preventive care. Further still, parallel efforts by the Age-Friendly Health Systems initiative117 along with the increasingly integrated AGS CoCare® HELP,118 the Society of Critical Care Medicine’s ICU Liberation A-F Bundle,119 and the American College of Surgery’s Geriatric Surgery Verification Program,120 and the integrative work of the American Delirium Society121 provide a collective counterbalance in leading and advocating for delirium prevention.

In fact, one imagines a potentially stronger argument for how addressing the current reimbursement disparity between delirium and acute encephalopathy could advance not only best practices but also facilitate delirium prevention and improve patient care. We are currently witnessing an epidemic of burnout among clinicians in acute medical settings,122 fueled in part by the behavioral complexity of hospitalized patients with cognitive disorders. Currently, however, the burden of delirium bundles and other non-pharmacological interventions to prevent delirium is being placed on nurses, practitioners, and other clinicians providing direct patient care. Based on the change in reimbursement outlined in our request, improved revenue for delirium is expected to more than offset the costs of investing in dedicated staff to ensure the consistent, successful implementation of delirium bundles, thereby offloading already-overstretched clinicians. Again, the cost equation of these bundles strongly suggests that, given sufficient ‘energy of activation’ to see them implemented, they would be financially self-sustaining.113

Clinical impact statement

Our proposal represents the logical conclusion of understanding the integrated nature of delirium and acute encephalopathy. We expect that this proposal, which aligns reimbursement with a robust scientific literature and clinical practice guidelines, will facilitate improved patient care and outcomes by way of encouraging enhanced delirium detection and actionable delirium clinical pathways.

Many clinicians and healthcare systems are simply unaware of the scope and impact of delirium. Those who know the scope and have attempted to implement delirium detection efforts and delirium pathways know how hard it is to get buy-in for these efforts, or to develop sustainable quality improvement projects that do not depend on a single person or a small group of dedicated champions to keep it alive. Our proposal, if accepted, would provide healthcare institutions with appropriate and justified incentives to provide appropriate support to patients with the greatest cognitive and functional vulnerability—specifically, those at risk for complications and poor outcomes. In view of such a change, one envisions education efforts to clinical staff about what delirium is, what it looks like, and why it matters, as well as practical tools including optimized electronic health records for delirium functionality and the availability of non-pharmacological interventions.


We are requesting that causally specified delirium codes be designated as MCC. This proposal is aligned with the principles of value-based care and the aim of the MS-DRG system to accurately account for the variance in healthcare costs.

Respectfully submitted,

Mark Oldham, MD
President-Elect, American Delirium Society

The following organizations are in support of this proposal (in alphabetical order) :

  • Academy of Consultation-Liaison Psychiatry
  • American Association for Geriatric Psychiatry
  • American Delirium Society
  • American Geriatrics Society
  • American Thoracic Society
  • Association of Medicine and Psychiatry
  • Society of Critical Care Medicine
  • Society of Hospital Medicine (preliminarily)

Additionally, the American Academy of Neurology and American Psychiatric Association

Additional Supplements

  • “An Analysis of Annual Nationwide Coding of CC Specified Delirium and MCC Encephalopathy.” This analysis estimates the number of hospital encounters this proposal would affect annually.
  • Slooter AJC, Otte WM, Devlin JW, et al. Updated nomenclature of delirium and acute encephalopathy: statement of ten Societies. Intensive care medicine 2020;46(5):1020-1022.
  • Oldham MA, Holloway RG. Delirium disorder: Integrating delirium and acute encephalopathy. Neurology 2020;95(4):173-178.


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