The search yielded 3054 articles. Duplicates were removed leaving 2210 articles. Due to the large number of remaining studies, both reviewers agreed to exclude articles published before 2010 (n=440). This decision was based on the knowledge that the term “post intensive care syndrome” was not common until after the 2010 [15]. Titles and abstracts of 1770 articles were screened by a single reviewer (ZH) with 55 full text articles identified for further screening. A quality audit was then conducted by a second reviewer (SB), with agreement to include twenty-five articles in the final analysis (see Figure 1.).
Characteristics of included studies:
Of the 25 articles included for analysis, there were six systematic literature reviews, two randomised controlled trials, and seventeen cohort studies. At the time of this review, publications relating to PICS or ICU survivorship have been dominated by research from the UK (24%) and Germany (24%) (see Table 1.), with articles published across 11 countries.
Table 1
Overview of the countries of publication for included articles.
Country of Publication | Number of Publications |
UK | 6 |
Germany | 6 |
Japan | 3 |
USA | 2 |
Greece | 2 |
Korea | 1 |
Netherlands | 1 |
Australia | 1 |
Taiwan | 1 |
Switzerland | 1 |
Canada | 1 |
When looking at date of publication, an increasing number of publications is evident (see Figure 2.)
Patient factors and characteristics of the patient’s condition were commonly considered selection criteria of included studies (see Table 2.). Age (>18-years) and ICU discharge status remained consistent between studies. There was, however, considerable variability between studies regarding the patients’ length of stay (LOS) in hospital and the ICU, and the duration of mechanical ventilation. Gender, the presence of comorbidities, education level, body mass index (BMI), and additional demographic factors were variables commonly considered. The impact of delirium and the acquisition of ICU-aw on recovery during the post-intensive care period were also considered [33].
Table 2
Variables identified within included studies.
Characteristics of the Condition | Patient Factors |
ICU-aw Illness Severity Delirium Duration of Mechanical Ventilation* | Age Gender Comorbidities Demographic Factors Education Level BMI |
*Also considered in Social/Contextual Factors |
Taking a biopsychosocial approach, the characteristics of PICS have been characterised into biological, psychological, and social/contextual characteristics. We identified that overarching the three categories, were ten key outcomes that have been used to describe the recovery trajectory of individuals (see Figure 3.).
Biological Characteristics
We defined biological characteristics as those closely resembling the physical characteristics described in previous PICS models [12]. Eleven studies considered biological factors among ICU survivors. These factors were used to report on biopsychosocial outcomes, such as functional status, exercise capacity, physical functioning, participation, and HRQOL.
Muscle strength was commonly measured, either via the Medical Research Council (MRC) scale for muscle strength [34, 35] or dynamometry [34, 35, 36]. Two studies used muscle strength as a determinant of functional status during the post-intensive care period, concluding that improved muscle strength positively correlates with functional status [34, 35]. These two studies also highlighted the impact of ICU-aw on the recovery trajectory, ascertaining that poorer functional outcomes are likely among patients diagnosed with ICU-aw.
Cardiopulmonary exercise testing (CPET) was used to measure peak oxygen consumption (VO2) and anaerobic threshold (AT) in two studies [37, 38]. CPET is considered the gold standard for assessing an individual’s exercise capacity [39]. McWilliams et al. [38] concluded that exercise capacity is likely to improve within 12-weeks following discharge from the ICU, regardless of whether rehabilitation is received following discharge from the hospital. However, for patients experiencing more severe illness or requiring mechanical ventilation for more than 14-days, the risk of persistent deficits in exercise capacity is heightened [37].
Considerable variation was evident between methods of data reporting among our included studies. Eggman et al. [40] considered patients’ exercise capacity and functional status. However, data were reported via the 6-minute walk test (6MWT) and Functional Independence Measure (FIM). Despite a variation in reporting methodology compared to Benington et al. [37] and McWilliams et al. [38], results remain the same. Patients who experienced moderate-severe muscle weakness also experienced significantly poorer outcomes in the 6MWT (p=0.013), FIM (p=0.001), and hospital LOS (p=0.008). This emphasises the need to consider the characteristics of a patient’s condition and social and contextual factors as risk factors for poorer outcomes during the post-intensive care period.
Pain and fatigue are considered primarily biological factors. However, their impact on psychosocial factors should be noted. One included study reported that around two-thirds of ICU survivors report “new” chronic pain during the first 6-months following discharge from the ICU [40]. The interference of pain on everyday life significantly decreased (p=0.04) during the first year following hospital discharge. However, pain remained the most common reason participants reported a reduced “enjoyment of life”.
Similarly, fatigue is reported to impact nearly half of ICU survivors during the first 6-months of their recovery [41]. Fatigue has been shown to significantly positively correlate with PTSD (p<0.001) and significantly negatively correlate with HRQOL (p<0.001). Additionally, patient factors, including comorbidities and gender (male), were associated with higher perceived fatigue. In contrast, a patient’s level of social support provides a salutogenic factor.
Psychological Characteristics
Anxiety, depression, and PTSD are commonly considered psychological characteristics of PICS [12]. For this review, cognition is also considered a psychological factor due to the impact cognitive deficits can have on an individual’s level of understanding and ability to participate in their recovery journey [28].
This review found the current literature inconclusive regarding the prevalence of impaired cognitive function following discharge from the ICU. Chung, Yoo, Park & Ryu [42] measured cognitive impairment using the Mini-Cog Test at ICU discharge, reporting that 43% of patients experienced cognitive deficits. However, 12-months following discharge from the ICU, 88% of ICU survivors demonstrate cognitive functioning within a normal range [43].
As with biological factors, characteristics of the condition and patient factors can impact an individual’s cognitive recovery trajectory. Sumida et al. [44] conducted an observational cohort study to evaluate cognitive function in patients following discharge from a cardiac intensive care unit. Multiple logistic regression analysis identified that older age (p=0.042), nutritional status (p=0.017), and physical function (p=0.012) are significant and independent factors associated with impaired cognition in ICU survivors [44]. Also emphasising the interwoven nature of characteristics, Thomas & Mehrholz [43] concluded that regaining walking function is the best predictor of normal cognitive function one year following hospital discharge.
Self-report questionnaires, including the EuroQol-5D (EQ-5D) and the Short Form 36 (SF-36) questionnaire, have been used to identify psychological characteristics such as anxiety, depression, and PTSD [43, 45]. These are commonly reflected in an individual’s perceived HRQOL. Research suggests that when symptoms of anxiety, depression, or PTSD are experienced, there is a marked reduction in HRQOL [46]. Chung et al. [42] found that 60% of patients exhibited depressive symptoms upon discharge from the ICU, with more than 75% recalling one or more stressful experience from their time within the ICU.
Patient characteristics also appear to contribute to the presence of psychological symptoms. Our review identified that at discharge from the ICU, female patients (88.9%) were significantly more likely to experience depressive symptoms than males (47.6%, p=0.03) [42]. Additionally, it is reported that fatigue is likely to be exacerbated by current or previous anxiety or depression, impacting not only HRQOL but also participation [41].
The recovery of psychological symptoms during the post-intensive care period has also been described by an improvement in HRQOL. However, support for rehabilitation services remains inconclusive. Taito et al. [47] found moderate-quality evidence suggesting that at 6- and 12-months post-ICU discharge, physical rehabilitation provided during the post-intensive care period did not significantly improve HRQOL compared to usual care [physical component scores: (p=0.51); mental component scores: (p=0.61)]. All remaining systematic reviews remained inconclusive as to whether rehabilitation delivered during the post-intensive care period was beneficial in improving HRQOL. In contrast, McWilliams et al. [38] reported a significant improvement in HRQOL following a 7-week outpatient rehabilitation program that included physical rehabilitation and patient education.
Social & Contextual Characteristics
Our strict inclusion criteria did not identify studies that described the characteristics of PICS as “social and contextual”. We defined social and contextual characteristics as the factors surrounding an individual externally – for example, the patient’s social supports, life stressors, situational characteristics, and their rehabilitation or recovery environment. For occupational therapists, these characteristics align with the “environmental factors” depicted by the Person-Environment-Occupation (PEO) Model [48].
Our review found that contextual factors, such as the duration of mechanical ventilation and the patient’s hospital or ICU LOS, were commonly considered. Frequently, these variables were considered in the study’s selection criteria, although several studies report considerable impacts of these factors on patient outcomes. A cohort study conducted by Benington et al. [37] identified a positive correlation between more than 14-days on mechanical ventilation and a reduced exercise capacity [peak VO2: (p=0.022); AT: (p=0.009)]. Similarly, a longer duration on mechanical ventilation appears to negatively impact the recovery of sit-to-stand function [49].
The impact of contextual factors on post-intensive care recovery was also highlighted by Chao et al. [50]. Their cohort study considered long-term mortality rates (up to 10-years) and identified that patients at “high risk” of mortality had experienced more severe illness, required a longer stay in hospital or the ICU or had spent more time on mechanical ventilation. Their study identified that rehabilitation provided during the post-intensive care period is most beneficial for this “high risk” group. They recommend this group of patients should be routinely considered a target population for post-intensive care rehabilitation.
Being surrounded by social supports, such as rehabilitation providers, family, and friends, has been suggested to considerably improve outcome indicators [41]. Occupational therapists have the potential to provide such social support to facilitate holistic recovery during the post-intensive care period. The results of our review suggest that allied health input is currently being underutilised to support PICS recovery during the post-intensive care period. A cohort study conducted by Thomas & Mehrholz [43] reported that during the first 12-months following discharge, 71% of patients received no follow-up from a physiotherapist, and 86% received no follow-up from an occupational therapist.
While the benefits of allied health have been noted, no articles were identified that directly report on the role of occupational therapists working within the post-intensive care period. A single-centre cohort study reported that the time spent engaging in walking practice with a physiotherapist significantly increased the chance of regaining walking ability (p<0.0001) [51].