Chapter 76: ICU Bed Utilization

Care of critically ill patients is an integral part of hospital care,¹ but ICU beds are a limited resource in many settings.^2,3 How ICU beds are used has implications for the care of individual patients, as well as resource use and costs at the hospital and regional level. Some aspects of ICU bed utilization may be specific to individual hospitals, but others are more generalizable across hospitals and health care systems. This chapter reviews many of the factors that impact how ICU beds are used, and then discusses potential approaches to optimizing their use.

Definition of an ICU bed: The lack of an agreed on definition of an ICU bed remains a barrier to understanding bed utilization. Some countries, such as the United Kingdom, have a clear definition, describing Level 3 care (ICU-level care) as patients receiving advanced respiratory support alone, or having a minimum of two organs supported.⁴ Many countries do not seem to have any definitions. In the United States, there are no standard definitions, but a proposed system of categorization broadly defined the highest level of care as including “sophisticated equipment, specialized nurses, and physicians with critical care training”.⁵ Across developed countries, the majority of ICU beds have availability of mechanical ventilation and some form of renal support and other organ support. The meaning of an “ICU bed” in developing countries is much more questionable as it does not necessarily include resources to provide specific organ support.⁶ This chapter will discuss about the use of ICU beds in systems, with the ability to provide mechanical ventilation and other basic organ support as part of intensive care.

The question of the utilization of ICU beds is ultimately one of triage: understanding who is to be admitted to an ICU bed and why, and looking to optimize the use of this expensive resource while providing appropriate care for individual patients. The use of beds is dependent on a number of specific factors: (1) the physical number of ICU beds in a specific ICU, hospital, or system; (2) the ICU bed to hospital bed ratio; (3) other options for care of patients, such as intermediate care units; (3) the casemix of patients cared for in a specific hospital or system, including specific elective surgical patients; (4) hospital culture; and (5) regional culture and norms.

The number of ICU beds: The total number of ICU beds available will clearly have an impact on the use of those beds.⁷ This may be due to a number of factors related to the absolute number of beds. First, a hospital with only a few (3-4) ICU beds will not have a high volume of critically ill patients and is likely to have a system for transferring their critically ill patients to larger centers.⁸ Some countries or systems may have a formalized regionalization system (such as for trauma),⁹ whereas others may be more informal.⁸ However, such systems mean that small ICUs may tend to care for patients with only a low severity of illness.^10,11

Small ICUs or systems of ICUs are also at a disadvantage due to their size, leading to inefficient use of ICU beds. This is due to the concept of queuing theory, which demonstrates that the likelihood of a patient admission being delayed is a function of the occupancy and the total number of ICU beds.¹² For example, an ICU that has only 4 beds must operate at 75% occupancy in order to ensure an available bed for the next patient. In contrast, an ICU with 100 beds operating at 75% occupancy has 25 beds available for patients.

The potentially large implications of high occupancy for ICU bed utilization have now been documented in a number of studies. A study by Stelfox et al¹³ from Canada demonstrated that when beds are not immediately available, more patients have alterations in their goals of care, with no detectable difference in overall mortality, suggesting that occupancy may drive physicians and patients to choose appropriate alternative care paths. However, the knock-on effect of high occupancy may also depend on the country and the overall availability of beds. For example, data from the United Kingdom suggest that many patients are discharged prematurely due to chronic high occupancy and intense pressure regarding new admissions, with worse hospital mortality for the patients discharged prematurely.^14,15 In contrast, data from the United States suggest that premature discharges associated with “strained” ICUs do not result in increased mortality, and may consequently represent more efficient use of ICU beds.¹⁶

The ICU bed to hospital bed ratio: Little is understood about the ICU bed-to-overall hospital bed ratio and how this affects ICU bed use. We do know that most systems/countries operate on a relatively fixed ratio of ICU beds to hospital beds of approximately 2 to 5 ICU beds for every 100 hospital beds in total, while the United States operates with a very different ratio of 9 to 10 ICU beds per 100 hospital beds in total.⁷ This high ICU bed to hospital bed ratio in the United States may impact ICU bed utilization by decreasing the threshold for use, particularly if other lower acuity beds become the scarce resource. Data from the United States suggest that 40% of patients admitted to an ICU have monitoring needs only (no active treatment), and that only 35% of these patients are considered at high risk of needing active treatment during the ICU stay.¹⁷ Similarly, a study by the Veterans Affairs system in the United States found that many patients (up to 50%) admitted through the emergency room with a predicted risk of death of less than 2% were admitted to ICU beds.¹⁸ This is enabled by an overall high availability of ICU beds and a generous ICU bed to hospital bed ratio, as described above, but also may be driven by inadequate nursing or other resources in other parts of the hospital.

Other options for care of patients: The question of other care options for patients is an important one to understand ICU bed utilization. Intermediate care (also called stepdown care, or high-dependency care) has received little attention in the ICU literature. Yet in a survey of 40 hospitals as far back as 1995, 63% of hospitals reported at least one intermediate care unit.¹⁹ These types of units provide care at a higher level than available in a general ward, but usually without the ability to provide full organ support, such as mechanical ventilation. Evaluation of their use has mostly focused on elective surgical patients,^20,21,22 but, clearly, the utilization of ICU beds in a system depends on the availability of such beds. The availability of intermediate-care beds may impact both the time patients need to spend in an ICU bed prior to discharge and also the need to admit a patient to an ICU bed at all, particularly when the focus is on better monitoring and/or nursing care, rather than full organ support.

Casemix of patients: The casemix of patients admitted to an ICU can vary dramatically.²³ This may be driven by the overall availability of ICU beds, but may also be determined by the casemix of patients in a hospital or system. This point is related to the one above regarding intermediate care beds, as some individual patients are more amenable to care in alternate settings. One large driver of the routine utilization of ICU beds is specific surgical programs in a hospital. For example, a hospital that routinely performs liver transplants will use ICU beds for the care of those patients (sometimes) before and (always) after the surgical procedure. Similarly, a hospital that has a large population of oncology patients may expect a certain requirement for ICU beds for patients developing complications from chemotherapy or surgery.²⁴

Specifics of the hospital culture: Use of ICU beds is often driven by the specific culture of a hospital regarding the “perceived” need of an individual patient. For example, in a study of patients admitted to hospitals in New York State with diabetic ketoacidosis, anywhere from zero to 100% of patients received intensive care during the hospitalization.²⁵ Although much of this variation may be driven by the factors described above, such as availability of other appropriate care settings and high-level nursing on wards, at least some of this variation is likely attributable to accepted practices. There are similar findings for other diagnoses, such as patients with carotid endarterectomy.²⁶ One study examined outcomes using their standard practice of admitting almost all (98%) of the patients to the ICU for monitoring after a carotid endarterectomy versus admission based on assessment of risk (22%) and found no difference in outcomes, reinforcing the idea that practices regarding ICU bed utilization may be based on the perceived, rather than actual, need.²⁶

Regional culture and norms: Use of ICU beds may be driven not only by the culture or expectations for care within a specific hospital setting, but also by larger cultural expectations. For example, data from the ETHICUS study carried out in Europe found a large variation in the practice of withholding or withdrawing of treatment before death, depending on the region of Europe,²⁷ and comparison work of cultural expectations in the United States and United Kingdom shows stark differences in expectations and experiences.²⁸ Some of these cultural norms may be codified into laws that then underpin patterns of ICU bed utilization. In some countries, physicians may make decisions regarding escalation of care and/or end-of-life care choices, such as the placement of a do-not-resuscitate order, without much input from families, while other countries or regions mandate that patients or families must agree to the proposed care plan.³

Guidelines: Within the specific culture and laws of a region, a number of approaches may help to optimize ICU bed utilization. The first is to have clear guidelines for admission or refusal. While this approach works well in theory, the reality of such guidelines is that they provide a lot of latitude regarding the appropriateness of admission.²⁹ For example, the guidelines from the Society of Critical Care Medicine state: “ICU admission criteria should select patients who are likely to benefit from ICU care,” going on to try to define groups who may or may not benefit.³⁰ While such guidelines may help in the most extreme circumstances, the documents themselves acknowledge that they are not particularly useful for individual decision-making.³¹

All guidelines or tools for individual or even diagnosis or procedure-specific decisions are hampered by the lack of data regarding the benefit received from admission to an ICU.³¹ Whereas patients who require mechanical ventilation or are in shock requiring systemic circulatory support may be admitted to an ICU and no one doubts the benefit of intensive care for those patients,³² there are many other circumstances when it is not so straightforward. For example a patient may be too sick to be rescued by the maximal support offered in an ICU or may be too well to benefit from the additional care.³³

Gatekeepers: Another option that may improve the utilization of ICU beds is designation of appropriate caregivers to act as “gatekeepers.” Many ICUs do not have clear designees for this role; particularly for “open” ICUs, this may mean that every physician in the hospital has admitting privileges to the ICU and can decide for themselves whether a patient should be admitted if there is a bed available.³⁴ Such an approach is clearly problematic, as ICU beds are part of a system, and appropriate use of those beds involves understanding of competing interests and ability to triage based on experience with critical illness and the likely course of an individual’s illness. One study has examined the impact of a medical ICU director on resource use, finding that the presence of an active medical ICU director in US ICUs was associated with a lower average occupancy rate and lower probability of patients being “misallocated” to the ICU.³⁵

Minimizing small ICUs and specialty ICUs: Along with having appropriate decision-makers, understanding queuing theory (mentioned above)^12,36 and designing a system to minimize the number of small ICUs and maximizing the utilization of available ICU beds are paramount. Cities in England have very few ICU beds, but their utilization is optimized in places such as London by essentially creating a network of all ICU beds across London using the London Ambulance System to track available ICU beds and shift patients to the nearest available bed when needed.³⁷

The related problem of many specialty ICU beds may occur particularly in large academic medical centers, with 4 to 5 specialty ICUs (such as a “transplant” ICU). Patients may be left waiting for admission to the “appropriate” specialty ICU, rather than gaining admission to any available ICU bed. Data suggest that for most types of patients, specialty ICUs (compared with general ICUs) may not offer benefit for outcomes.³⁸ However, with the presence of specialty ICUs, patients who are “boarders” (i.e. admitted to an inappropriate ICU) may also have worse outcomes.³⁸

Alternative care options: Another way to optimize the use of ICU beds, particularly in systems such as that in the United States where many patients in ICUs are admitted solely for monitoring purposes, is to create or increase other care options, such as intermediate care areas. This type of approach may also involve such options as increasing the hours a recovery room is open to allow patients to remain in a monitored setting without full admission to an ICU.^39,40 Hand-in-hand with this option is the improvement of nursing on general wards.

High-quality and experienced nursing staff on wards: A large barrier to keeping patients in lower levels of care may often be the perceived lack of quality nursing, rather than the need for any specific interventions provided by an ICU. Many studies suggest that aspects of nursing care, such as the nurse-to-patient ratio, and the level of education of nursing staff, can have a large impact on outcomes for patients.^41,42,43 Therefore, another approach to optimizing the use of ICU beds may be to ensure quality nursing care in other areas of the hospital so that ICU beds do not become the default destination for any patient who requires good nursing care.

Removing financial misalignment: Finally, in certain systems, such as that in the United States, optimal use of ICU beds may only be achieved once competing financial incentives are removed. For example, a physician who has a salary based on the number of critical care bills generated has a strong incentive to keep patients in the ICU, or admit marginal patients. Similarly, a hospital that is paying nursing staff based on the number of ICU beds in the unit would prefer to have patients in all of those beds to offset the fixed costs of the staff.⁴⁴ Or there may be financial penalties for an institution that keeps patients waiting for beds in the Emergency Department, forcing them to use ICU beds for patients who would otherwise go to ward beds. Only once these incentives are removed can other aspects of ICU utilization be optimized.

With the goal of efficient, patient-centered care in hospitals, ICU bed utilization is an important area for further research. Many of the approaches to improve efficiency remain speculative, and warrant further investigation with rigorous study designs to determine optimal approaches.