From 1,615 initial records, we screened 73 papers according to eligibility, of which 32 were included in the full review (Figure 1). A summary of the characteristics of these 32 studies is presented in Table 2.
Countries and research methods
The year of publication, country, study methods, type of institution, and population of the 32 studies included in our review are summarized in Table 3. The majority of the studies were conducted in Europe (n = 19)(8, 10, 11, 20–34), followed by 7 from the USA(35–41). Studies conducted in Asia were not included. They were, however, included in the searching results, but did not meet the eligibility criteria. Two studies were published in the 1990s(20, 42), and three studies in the 2000s(21, 35, 36). Twenty-seven studies were published after 2010(8, 10, 11, 22–34, 37–41, 43–47).
Quantitative methods were used in 13 studies(24, 25, 30–35, 38, 39, 41, 46, 47), while 12 were qualitative(10, 11, 22, 23, 27–29, 42–45). All the quantitative studies were descriptive or observational (cross-sectional, retrospective, or cohort studies). Thirteen of the studies were conducted in medical settings such as palliative care units or hospices(10, 11, 23, 24, 27, 31, 32, 35, 39, 41, 42, 45, 47), ten were conducted by academic societies or professional teams(22, 25, 28, 30, 33, 34, 38, 43, 46), and two were conducted over the telephone or at health centers for people living in specific areas(29, 44). Other publications were reviews or case studies that did not specify the facility where they were conducted. Eighteen studies were conducted on patients; eleven on adult or pediatric cancer patients(21, 24, 25, 28, 31, 32, 36, 38, 39, 42, 46) and seven on cancer patients, as well as non-cancer patients suffering from dementia and neurological diseases(29, 30, 33–35, 41, 47).
Factors of complexity in palliative care
The factors of complexity in palliative care are shown in Table 4.
Patient level of complexity. All 32 studies reported the patient level of complexity. The categories of patient-level complexity were background, physical, psychological, social, and spiritual. In addition, specific factors were described for each category. The factors of background complexity were sex(30, 33), race(38, 41), language(10), age(8, 10, 25, 31, 38, 41, 44, 45), living situation(10, 11, 29, 44), family burden(8, 10, 24, 29, 44–46), resources(10, 20, 22, 23, 27, 32, 37, 42, 43), treatment(11, 21, 33, 35, 39, 40), decision-making(10, 22, 27, 33, 36, 37), communication(10, 11, 27, 32), prognosis(8, 11, 23, 25–27, 45), disease(10, 11, 29, 30, 32–34, 39, 41, 44, 45), and comorbidities/multimorbidity(8, 11, 24, 25, 27, 31, 38, 39, 41, 44, 45, 47). Patient-level complexity was a factor for both men and women of all ages(8, 10, 25, 30, 31, 33, 38, 41, 44, 45). In English-speaking countries, non-English language barriers were a factor of complexity(10). Family burden was another factor, involving family stress and anxiety(8, 10, 24, 29, 44–46). Treatment was a factor of complexity including previous surgery, polypharmacy, and side effects of drugs(11, 21, 33, 35, 39, 40). Disease included progressive diseases such as heart failure, dementia, psychological disorders such as schizophrenia, and drug addiction(10, 11, 29, 30, 32–34, 39, 41, 44, 45). Moreover, the presence of these diseases as comorbidities or multimorbidity was also a factor of complexity(8, 11, 24, 25, 27, 31, 38, 39, 41, 44, 45, 47). However, the studies reported multiple types and numbers of comorbidities and multimorbidity, ranging from two to five.
In the physical category of patient-level complexity, the factors were physical function(8, 24, 27, 31–33, 40, 43, 47), pain(10, 11, 24, 25, 28, 29, 31, 33, 36, 43, 46), pain treatment(21), symptoms(11, 24, 27, 33, 43), and symptom burden(8, 31, 32, 36, 37, 40). Physical functioning included factors such as low performance status and disability(24, 33). Pain included factors such as Numeric Rating Scale>5 pain, refractory pain, and uncontrolled pain(11, 25). Pain treatment included factors such as cytokine activity and ineffective analgesics(21). Symptoms included various factors such as nausea, dyspnea, tiredness, and appetite(11, 24, 27, 33, 43).
In the psychological category of patient-level complexity, the factors were anxiety(25, 30, 33), depression(25, 33), and mental health(8, 23–25, 30, 40, 41). Anxiety and depression included factors such as higher anxiety and feeling depressed(25, 30). Mental health included factors such as emotional distress and psychological burden(8, 24, 40).
In the social category, the factors were social risks(10, 11, 25, 29, 31, 32, 34, 36, 40) and financial problems(10, 40). Social risks included factors such as social roles and family roles(32, 36). Financial problems included factors such as financial difficulties(40).
In the spiritual category of patient-level complexity, the factors were existential problems(25, 27, 31) and spirituality(22, 40). Existential problems included factors such as ethical dilemmas and conflicts(25). Spirituality included factors such as spiritual needs(40).
Healthcare setting level of complexity. Fifteen studies reported the healthcare setting level of complexity(8, 10, 11, 20, 22, 23, 25–27, 29, 32, 34, 41, 44). In relation to the role of healthcare providers, the factors of complexity included truth-telling(20), advocacy(20), and differing or conflicting priorities of care and treatment(27). In addition, the role of the nurse included demands for emotional support, skills, and confidence(11, 20, 26).
Socio-cultural landscape level of complexity. Four studies reported the socio-cultural landscape level of complexity(10, 11, 40). Social capital, which includes the systems that support the interrelationships and connections among people in a society or local community, was a factor of complexity(11). Other factors of complexity included local and national cultures, as well as societal cultures which might affect the patients(40). The cultural factor was the value of the end of life in society; this was a factor in the structuring of health and social systems of care(10).
Interaction of the factors of complexity in palliative care. Ten studies reported interactions of the factors(8–11, 21, 31–33, 40, 42). In all studies, patient complexity arose from the interaction of physical, psychological, social, and spiritual factors. Hodiamont et al. showed the interaction and dynamics of the factors of complexity(9). Interactions of factors of complexity were reported not only at the patient level, but also at the healthcare setting level and the socio-cultural landscape level(10, 11). Park et al. reported that interactions among healthcare providers and care settings can make patients better or worse(10). Tuca et al. also reported that the interventions that healthcare providers provide to patients result in outcomes that are more than the sum of the parts(25).