The mixed method approach encompassed two stages: cross-cultural adaptation and psychometric validation of the PCOC phases.

Cross-cultural adaptationProcedure and participants

After obtaining consent from the PCOC, forward and backward blind translation of the Australian phase definitions [16] was performed by a native speaker and medical staff experienced in palliative care, with two expert reviews (ABJ and TG) after each translation. This translation followed the guidelines outlined by Koller et al. [17].

As the next step, interviews were conducted with all key medical staff from the 45-bed, in-patient, free-standing palliative care unit. These staff members were experienced in palliative care, and the interviews were performed by ABJ, a registered nurse with 30 years of specialized experience in the field. The interviews were based on cognitive interviewing techniques and conducted iteratively in two rounds, as outlined by Lehmann et al. [18]. This process adhered to the Consolidated Criteria for Reporting Qualitative Research (COREQ – see ‘Additional File 1’). [19]. For this part of the study, the participants were chosen to cover various professional views on palliative care (physicians, nurses, psychologists and social workers) and were recruited personally within the institution. Each participant who agreed to participate in the study was interviewed twice, for approximately 30 min. During both interviews they were initially asked to ‘think aloud’ while reading each phase definition, then received specific questions about the general understanding and precision in defining the particular phase, and suggestions for any improvement or modifications (language or graphical). An open question about the whole phase description ended each part of all the interviews. None of the interviews need to be repeated. Neither audio nor video recordings required any particular coding software; instead, the interviewer took notes during each interview to derivate the emerged themes, which were summed up at the end of the meeting. Participants were also asked to provide feedback on the findings. An item-by-item phrases analysis was performed, leaving those which were understandable and universally accepted until conviction was obtained on sufficient saturation.

The original phase model was also the subject of graphical transformations (ABJ, EW, and TG) based on coded findings within a confirmatory analysis. The table and graphical synthesis documents obtained after the first round of the interviews was checked on the same model during the second round.

Acceptability

The acceptability of the final version of the Australian phase definitions obtained after the second round of interviewing was based on the staff’s perception. For this purpose, each participant was asked to assess 25 patients who were consecutively admitted. Three questions were asked, which were to be answered on a five-point scale regarding:

1)

the accuracy of the current patient & family’s situation described by the particular phase (How appropriately does the assigned phase definition describes the current situation?; with answers from 1—‘not appropriate’ to 5—‘very appropriately’),

2)

difficulty in assigning the situation to the Palliative phase (How difficult it was to assign the current phase?; with answers from 1—‘very difficult’ to 5—‘ very easy’), and also

3)

the knowledge of the patient & family’s situation (How familiar are you with this situation?; with answers from 1—‘unfamiliar’ to—‘ very familiar’).

Psychometric validation – cross-sectional studyProcedure, setting and participants

A study of cross-sectional psychometric validation was performed in compliance with Strengthening the Reporting of Observational Studies in Epidemiology (STROBE – see Additional File 1) [20]. Patients with life-limiting diseases, predominantly cancer, consecutively admitted to the palliative care unit within a free-standing hospice and hospice home-care (within the same institution), were included in this part of the study. Patient characteristics, including gender, age, primary diagnosis and disease stages, identified by the attending physician using Gold Standard Framework needs-based coding (GSF) [21], were obtained from medical records.

The attending doctor and nurse were taught; within one 30-min session on the practical usage of PCOC phases concept and were equipped with both tabular and graphical synthesis documents. They were asked to independently (without assessment comparisons among themselves) assign the PCOC phase to the same patient & family, on the same day indicated by the researcher (MK), within the first two weeks following the patient’s admission. In parallel with assessment of the PCOC phases, = advancement of other illnesses and prognosis indicators were obtained from the medical records of all the chosen patients.

Concurrent validity measures

The palliative care phases defined as from ‘stable’ to ‘terminal’ according to PCOC [16] (the researchers did not take the ‘bereavement phase’ into account in this study) were compared with patients’ functional status, stage of the disease and their complex needs.

The patient’s current functional level and prognosis were estimated according to the Palliative Performance Scale Version 2 (PPS)—in the Polish adaptation [22]. The PPS was a modified Karnofsky Performance Scale which was developed by the Victoria Hospice Society [23] and later validated [24]. In our study, we used the Polish adaptation of the original second version of the PPS [22]. It consists of 11 levels expressed in percentages from 0 (deceased) to 100% (fully ambulatory and healthy with maximum performance state), taking five functional dimensions into account: ambulation, activity level, evidence of disease, self-care, oral intake and level of consciousness. This tool can be used to demonstrate the track of physical decline which, in consequence, may facilitate communication between staff members, timely palliative care admissions, and also end-of-life discussions in advance.

Illness advancement and spectrum of needs were assessed by using the PALCOM scale [8]. It is a five-domain multidimensional tool. It was developed to identify the specific complexness and needs of the patient & family. It has recently been validated for advanced cancer patients [25, 26]. It consists of introductory surprise questions and five domains of multidimensional assessment: symptom burden, refractory pain, performance status, socio-familial risk and existential/ethical issues. Each domain is scored dichotomously: 0 – ‘absence’ or 1 – ‘presence’, and the sum (from 0 to 5) is the total score of this scale. The final score of 0–1 point expresses ‘low complexity of palliative care needs’, 3–4 points – ‘medium level’, and 5–6 points—‘high complexity level’. In the present study, the Polish adaptation of the PALCOM scale was used [27].

Data collection took place from November 2023 to June 2024.

Statistical analysis

The minimal sample size of 300 patients was determined according to Lehman et al. [18]. The categorical variable data were presented as proportions, and the continuous variables as means (with standard deviations, SD) in normally distributed data (according to the Shapiro–Wilk test), or medians (with interquartile 25%-75% ranges). The inter-rater reliability was estimated using Cohen’s kappa statistics, with the strength of the agreement assumed according to Masso et al. [28]. The Chi square test was used to check the relationships between patients’ performance status and estimated prognosis with PCOC phases. The Dunn’s test (post-hoc for Kruskal–Wallis test) was applied to compare complex palliative care needs with PCOC phases. The P-value of < 0.05 was considered the level of statistical significance. Data were analyzed using the R program (version 4.2.2), a language and environment for statistical computing (Vienna, Austria).

All methods were performed in accordance with the 1964 Declaration of Helsinki, and participants provided informed consent for obtaining data and anonymous publication. The ethical approval was obtained by the research ethic committee of Andrzej Frycz Modrzewski Krakow University (reference number: KBKA/45/O/2023).