Does Unprecedented ICU Capacity Strain, as Experienced During the COVID-19 Pandemic, Impact Patient Outcome?

M. Elizabeth Wilcox, MD, PhD; Kathryn M. Rowan, PhD; David A. Harrison, PhD; James C. Doidge, PhD


Crit Care Med. 2022;50(6):e548-e556. 

In This Article

Abstract and Introduction


Objectives: To determine whether patients admitted to an ICU during times of unprecedented ICU capacity strain, during the COVID-19 pandemic in the United Kingdom, experienced a higher risk of death.

Design: Multicenter, observational cohort study using routine clinical audit data.

Setting: Adult general ICUs participating the Intensive Care National Audit & Research Centre Case Mix Programme in England, Wales, and Northern Ireland.

Patients: One-hundred thirty-thousand six-hundred eighty-nine patients admitted to 210 adult general ICUs in 207 hospitals.

Interventions: Multilevel, mixed effects, logistic regression models were used to examine the relationship between levels of ICU capacity strain on the day of admission (typical low, typical, typical high, pandemic high, and pandemic extreme) and risk-adjusted hospital mortality.

Measurements and Main Results: In adjusted analyses, compared with patients admitted during periods of typical ICU capacity strain, we found that COVID-19 patients admitted during periods of pandemic high or pandemic extreme ICU capacity strain during the first wave had no difference in hospital mortality, whereas those admitted during the pandemic high or pandemic extreme ICU capacity strain in the second wave had a 17% (odds ratio [OR], 1.17; 95% CI, 1.05–1.30) and 15% (OR, 1.15; 95% CI, 1.00–1.31) higher odds of hospital mortality, respectively. For non-COVID-19 patients, there was little difference in trend between waves, with those admitted during periods of pandemic high and pandemic extreme ICU capacity strain having 16% (OR, 1.16; 95% CI, 1.08–1.25) and 30% (OR, 1.30; 95% CI, 1.14–1.48) higher overall odds of acute hospital mortality, respectively.

Conclusions: For patients admitted to ICU during the pandemic, unprecedented levels of ICU capacity strain were significantly associated with higher acute hospital mortality, after accounting for differences in baseline characteristics. Further study into possible differences in the provision of care and outcome for COVID-19 and non-COVID-19 patients is needed.


Outcomes for critically ill patients admitted to ICUs are influenced by a variety of factors, in addition to the therapies received. These factors include: the organization of care (e.g., "closed" compared with "open" ICUs),[1] the experience gained from previously treating similar patients (e.g., volume-outcome relationships),[2,3] and the numbers/skill mix of available staff (e.g., patient to intensivist ratios).[4] We recently reported that how busy an ICU is on any given day (termed ICU capacity strain) is associated with acute hospital mortality.[5] ICU capacity strain can be seen as a mismatch between supply and demand, with availability of beds, staff, and/or other resources (as supply) and the need to admit and provide care for critically ill patients (as demand). ICU capacity strain not only has adverse consequences for patient outcomes but may also adversely affect the well-being of members of the healthcare delivery team.[6,7]

The severe acute respiratory syndrome coronavirus 2 (COVID-19) pandemic created a huge demand in the number of patients requiring critical care worldwide. Meeting this demand placed an unprecedented capacity strain on healthcare systems, and particularly on ICUs[8–10] with hospitals having to rapidly expand their critical care capacity. This translated into hospitals increasing the number of, and staffing for, beds within ICUs and creating new "surge" critical care beds in areas outside of recognized ICUs. Meeting the staffing and resources challenges for these additional beds resulted in reduced critical care staffing ratios within ICUs and redeployment of healthcare personnel with little to no experience in providing critical care. On top of this, resources such as equipment (e.g., mechanical ventilators) and medications (e.g., sedatives) may have been, at times, in short supply.[11,12]

The COVID-19 pandemic offered the opportunity to explore the relationship between patient outcome and unprecedented ICU capacity strain. Using the national clinical audit of the Intensive Care National Audit & Research Centre (ICNARC) Case Mix Programme, this study compared acute hospital mortality in patients admitted during periods of typical ICU capacity strain with patients admitted during periods with pandemic levels of ICU capacity strain outside of the typical range. We then compared trends between the first two "waves" of the COVID-19 pandemic in the United Kingdom.[13]