Variability of toe pressures during haemodialysis: comparison of people with and without diabetes; a pilot study

Participants were included if they had ESRD, were on haemodialysis at either the Carrington or Kererū dialysis centres, were between 18 and 80 years of age, tolerated toe pressure assessment, and were able to consent. Participants were excluded if TSBP could not be determined at baseline, revascularisation of both limbs had occurred within the past 3 months, they had undergone hallux amputation, or they had ulceration that would limit the ability to take a toe pressure measurement. Non-English speakers with no family/friends available for interpretation at the time of the dialysis session were also excluded. Participants were asked to refrain from having caffeine, smoking, or strenuous physical activity two hours prior to data collection, as per the technique paper by Tehan et al. [12].

Within the two centres, 108 patients were available for recruitment. After a four-week recruitment process, 30 people with ESRD agreed to participate in the pilot study. Recruitment occurred through a non-probability voluntary response sampling method, in which renal case managers identified potential participants based upon the inclusion criteria and then approached patients to determine their interest in participation. The names of potential participants were then passed onto the researcher. The researcher approached the patients during a dialysis session, discussed the protocol, consent processes, and participation date. The prospective participant could opt-out at this time or on the day of data collection. This sampling was deemed the most appropriate as the renal case managers have an in-depth knowledge of their clients and would be in the best position to approach those who may be interested; this recruitment method acknowledging that this can be a vulnerable population.

TSBP was measured bilaterally according to the protocol described by Tehan [12]. The protocol was modified with regard to the resting time before the initial TSBP measurement. Participants were rested in a 30 degree or lower supine position for 5 min prior to assessment, as opposed to the recommended 10 min. This protocol was adjusted to cause minimal disruption when participants were preparing for dialysis. Brachial systolic blood pressure was measured on one side only, which was determined by the presence of fistular, or by the participants' preference, using the dialysis machine. This procedure was performed before dialysis (T1), one hour after the start of dialysis (T2), and in the last 15 min of the dialysis session (T3). All TSBP readings were taken by R.C., a podiatrist with 18 years of clinical experience.

Demographic and medical history were collected by interviewing participants and reviewing medical records to obtain information on a history of ESRD, hypertension, dyslipidemia, previous stroke, previous heart attack, history of diabetes and history of diabetes-related foot complications, and smoking history. Dialysis notes were reviewed to determine type of dialysis used, duration of dialysis, interdialytic blood pressure variance, weight change, target weight, completion of a full dialysis session, and history of urination. Intermittent claudication was assessed using the Edinburgh Claudication Questionnaire [22]. Foot deformity was assessed using the 6-point scale, with one point assigned for small muscle wasting, hammer/claw toes, bony prominences, Charcot deformity and limited joint mobility [23]. A score of 3 and above indicates the presence of foot deformity [24]. Current callus was determined by the researcher and defined as minor, moderate or heavy. LOPS was defined by a 10 g monofilament assessment over the plantar hallux, first, and fifth metatarsal. If any of these points were absent, the participant was noted as having LOPS [7]. Frailty was self-assessed using two questions derived from the Clinical Frailty Scale [25]. Participants were asked “Do you go outdoors independently?” and “Do you exercise outside at all?”. If they were unable to go outdoors independently, they were scored 5 or above and were considered frail. If they do go outdoors independently, the self-assessed score was 1 to 4 depending on how often they exercise outdoors (1 = not frail, very fit and exercise often, 2 = not frail, fit, 3 = not frail and managing well, 4 = living with very mild frailty, but not dependent on others for daily help). The participant’s residential address was extracted from hospital notes and entered into the New Zealand Index of Deprivation [26], which is an area-based measure of socioeconomic deprivation in New Zealand and was derived from the 2018 census. This is an important indicator because of the relationship between socioeconomic status and mortality in New Zealand [27].

Demographic and medical data were described separately for each group (diabetes, no diabetes), with n (%) used for categorical data and mean (SD) for continuous data. A linear mixed effects model was used to determine the variability in TSBP and TBPI across the three time points (T1, T2, T3) (primary aim) and whether this variability differed between people with and without diabetes (secondary aim). Time point (T1, T2, T3) was included as a within-subject fixed effect and participant group (people with diabetes, people without diabetes) was included as a between-subject fixed effect. The interaction effect (time point*participant group) was also examined. Repeated measures between right and left limbs were accounted for by the inclusion of a participant-specific random effect [28]. Mean estimates (adjusted for dependence between right and left limbs) were presented along with their 95% confidences intervals (CI).

Thirty participants were recruited, including 17 (57%) participants with diabetes and 13 (43%) participants with no diabetes. The median age for participants with diabetes was 56, (range 42–78) and 59 (range 24–79) for the no diabetes participants. Of the participants with diabetes, 10 (59%) were female, and of the no diabetes participants, seven (54%) were female (Table 1). Socioeconomic deprivation as determined from the participant’s address revealed more participants with diabetes resided in areas of higher deprivation with 94% being in decile 5 or above, compared to 69% of the no diabetes participants within this study. Decile 1 represents the least deprived areas, decile 10 represents areas with the most deprivation.

Foot deformity, minor callus formation, and peripheral neuropathy were more common in participants with diabetes than no diabetes. All participants reported low scores on the frailty grade (Table 2).

General haemodialysis characteristics are presented in Table 3. Persons with diabetes were on haemodialysis for a mean of 3.8 years and persons with no diabetes for a mean of 6.2 years. The aetiology of ESRD in participants with diabetes was attributed to diabetes in 88% of cases, and lupus and glomerulosclerosis to 6% of cases. In the no diabetes participants, the aetiology of ESRD was attributed to lupus (15% of cases), glomerulosclerosis (15%), hypertension (8%), glomerulonephritis (23%), uretic obstruction (8%), and was unknown in 30% of cases.

Data showed a significant overall reduction in TSBP (P < 0.001) with all participants. There was a significant reduction in TSBP between T1 and T2 (mean difference [95% CI]: -8.34 [-14.22, -2.54], P = 0.006) and between T1 and T3 (mean difference [95% CI]: -11.95 [-17.83, -6.06], P < 0.001). No significant difference was found between T2 and T3 (mean difference [95% CI]: -3.61 [-9.49, 2.27], P = 0.17) (Table 4). There was no significant overall change in TBPI over time (P = 0.62).

There was no significant overall difference in TSBP between persons with diabetes and persons with no diabetes (mean difference [95% CI]: -9.28 [-40.20, 21.64], P = 0.54). There was no significant difference in TSBP across the three time points between people with and without diabetes (time point*participant group interaction) (P = 0.39) (Table 4). The change in mean TSBP is displayed in Fig. 1. There was also no significant overall difference in TBPI between people with diabetes and people without diabetes (mean difference [95% CI]: -0.01 [-0.17, 03.16], P = 0.91). There was no significant difference in TBPI across the three time points between persons with and without diabetes (P = 0.53) (Table 4). The change in mean TBPI is displayed in Fig. 2.

The sub-analysis included 15 participants with LOPS and 15 participants without LOPS. There was no overall difference in TSBP or TBPI between people with and without LOPS (P = 0.97, and P = 0.62, respectively) (Table 5). There was no significant difference in TSBP variability across the three time points between people with and without LOPS (time point*neuropathy interaction) (P = 0.67), however, there was a significant difference in TBPI variability across these time points between people with and without LOPS (P = 0.003). There was no significant difference in TSBP or TBPI variability based on participant group (diabetes, no diabetes) between people with and LOPS (participant group*neuropathy interaction) (P = 0.32, and P = 0.84, respectively).