Home Dialysis in North America

Abstract

There is widespread interest in expanding the uptake of home dialysis in North America. Although kidney transplantation should be the preferred option in eligible patients, home hemodialysis (HD) and peritoneal dialysis (PD) offer cost-effective options for KRT. In this review, the motivation for promoting home dialysis is presented, and the literature supporting it is critically reviewed. Randomized comparisons of home HD and PD with in-center HD have been challenging to conduct and provide only limited information. Nonrandomized studies are heterogeneous in their design and have often yielded conflicting results. They are prone to bias, and this must be carefully considered when evaluating this literature. Home modalities seem to have equivalent clinical outcomes and quality of life when compared with in-center HD. However, the cost of providing home therapies, particularly PD, is lower than conventional, in-center HD. Measures of home dialysis utilization, the philosophy behind their measurement, and important factors to consider when interpreting them are discussed. The importance of understanding measures of home dialysis utilization in the context of rates of kidney failure, the proportion of individuals who opt for conservative care, and rates of kidney transplantation is highlighted, and a framework for proposing targets is presented, using PD as an example.

Home dialysis is being promoted in many jurisdictions worldwide and refers to dialysis treatment that is provided in a patient's home. It can be done independently or with the assistance of a care partner and includes peritoneal dialysis (PD) (continuous ambulatory PD and automated PD) and home hemodialysis (HD) (conventional home HD, nocturnal HD, and short-daily HD). Currently, the proportion of dialysis patients treated with home dialysis is 25.5% in Canada (20.6% PD; 4.9% home HD) compared with 13.7% in the United States (11.5% PD; 2.2% home HD).^1,2 Data from Mexico report that 61% of patients in Jalisco, the seventh largest state, are treated with PD.³ However, access to dialysis and transplantation is limited to the insured population in Mexico, and nearly half the population is uninsured.⁴

In this review, the case for promoting home dialysis will be presented and critically reviewed, followed by a discussion of how home dialysis utilization is measured, appropriate targets, and strategies that have been attempted to increase its uptake. Canada and the United States will be the focus of this article because they have universal coverage for KRT.

The Case for Promoting Home Dialysis

Although there are many purported benefits of home dialysis, a critical look at the evidence to support those claims reveals literature that is often contradictory and difficult to interpret. There is a lack of high-quality evidence and, particularly, adequately powered clinical trials to inform shared decision making. The various home therapies are different in how they are conducted, as well as the dose, duration, and frequency of dialysis that they deliver.

Randomized Comparisons of Home Modalities to In-Center HD

A randomized trial comparing survival on PD and in-center HD was attempted in The Netherlands at 38 sites.⁵ Of 773 eligible patients, only 38 consented to participate, and the study was stopped because of poor enrollment. Perhaps the most important finding of this study was that when patients were educated about their treatment options, most formed strong preferences for PD or HD and were unwilling to leave their modality choice to chance. A subsequent trial in China recruited 416 patients and completed enrollment in 2013 (ClinicalTrials.gov NCT01413074), but the results have not yet been published.

In 2007, a small randomized trial of 52 patients from Alberta, Canada, compared frequent nocturnal HD with conventional HD. The group treated with nocturnal HD showed improvement in left ventricular mass and required fewer BP medications and phosphate binders but did not demonstrate any change in overall quality of life.⁶ The Frequent Hemodialysis Network (FHN) trials explored whether increased frequency or duration of dialysis would lead to improvement in the coprimary, composite outcomes of death or change in left ventricular mass and death or decrease in RAND Physical Health Composite.^7,8 Although frequent in-center HD was shown to be of benefit relative to conventional HD, nocturnal HD was not found to be superior to thrice weekly home dialysis.^7,8 Ultimately, only 87 patients were randomized in the nocturnal HD trial, and it was difficult to know if the negative result was due to a lack of benefit, the fact that the trial was underpowered, or other factors, such as center practices and experience.⁹ Long-term follow-up data from the FHN trial showed a higher risk of mortality in the nocturnal HD group, and although the total number of events was low, there were frequent transfers to in-center HD, and the mortality rate in the conventional group was lower than expected.¹⁰ Data from the FHN trials also suggested that nocturnal HD led to a more rapid decline in residual kidney function.¹¹ There was no direct comparison of facility-based dialysis with home dialysis, and even nocturnal HD was provided in-center and at home.

The lack of compelling data regarding the comparative effectiveness of home therapies and in-center HD from randomized comparisons means that much of expert opinion is based on the results of observational studies.

Nonrandomized Comparisons of Home Modalities with In-Center HD

The observational literature suggests that there are likely not important differences in clinical outcomes between patients treated with PD and in-center HD. There is, however, substantial heterogeneity in the findings of nonrandomized comparisons, and key methodological considerations in the study design may explain some of the variability in findings but are often overlooked. Given the difficulty in conducting clinical trials in this area, it is important to ensure that nonrandomized studies are well designed to avoid misleading results and conclusions.^12,13 It is sometimes suggested that patients on PD have superior quality of life to patients on HD. Well-conducted observational studies, using validated tools, have not reliably shown that, and the single randomized comparison from China reported that PD was noninferior to in-center HD.^14–16 Although there are likely subdomains of quality of life that are better on in-center HD and those that are better on PD, individual patient preferences and lifestyle considerations likely have the biggest impact on the expected quality of life on dialysis. Finally, it has been suggested that PD may be associated with a lower risk of death in the first 2 years of therapy.^17–23 However, it is much more likely that the inclusion of urgent starts was responsible. Excluding them from the analysis eliminated the initial lower risk for death, regardless of the type of access they used.²⁴

There is general agreement that compared with in-center HD, home nocturnal HD delivers higher solute clearance, allows for a less-restrictive diet, provides better BP control, reduces need for BP medications, and may improve left ventricular hypertrophy.^6,7,25–28 However, the impact of nocturnal HD on survival and quality of life is less clear. Studies that compared survival on home HD with in-center HD have yielded conflicting results.^10,29–31 Similarly, studies of quality of life on home nocturnal HD or short-daily HD are relatively sparse, and it is difficult to conclude that there is a definitive benefit of home HD on the basis of the available evidence.³²

Similar to nonrandomized comparisons of PD with in-center HD, the potential for indication bias is large. Even in countries like New Zealand, which has the highest penetration of home HD, <20% of prevalent dialysis patients are treated with it.³ As a consequence, individuals on home HD are typically a select group of healthy, high-functioning patients, whereas individuals treated with in-center HD are generally older with more comorbidities.

Cost Comparisons

North American studies have shown that the annual total health care cost of treating a patient with PD was lower than in-center HD.^33,34 The relative cost differences were consistent, even when considering only dialysis-related costs. In situations where PD patients transferred to in-center HD, the cost of caring for them approached that of patients initiated on in-center HD if the switch occurred early in the course of therapy.^35,36 Of note, patients who had a PD catheter placed but never successfully started therapy were not captured and may be important to consider.^37,38

The total annual health care cost of treating a patient with home nocturnal HD was approximately Canadian dollars (CAD) $71,000–$90,000.³³ Supply costs are generally higher than in-center HD, but personnel costs are lower, and on balance, there is a cost advantage with nocturnal HD over the long term. Although home nocturnal HD is slightly less expensive than in-center HD, the first year of therapy is actually more expensive, driven by the cost of patient training. As a result, the time on therapy is a critical variable. In patients with a poor prognosis and in programs where early transfers to in-center HD are common, nocturnal HD is not likely to be cost effective. Short-daily HD seems to be less expensive to provide than nocturnal HD. A prior report from the London Daily/Nocturnal HD Study suggested that short-daily HD cost CAD $67,281 in 2003 compared with CAD $74,731 and CAD $72,688 for nocturnal HD and conventional HD, respectively.³⁹

It is also important to point out that in the Canadian context, cost savings associated with promotion of home therapies are realized by the health system. However, in the United States, reimbursement for in-center HD and home modalities are the same under the prospective payment system (although there is allowance for additional HD runs above and beyond three times per week). As a result, the cost savings are realized by the dialysis providers, rather than the payer.⁴⁰

Other Considerations

Home dialysis may have advantages for individuals who live in rural locations and would have to travel long distances to receive in-center HD.⁴¹ PD is a good modality choice for those who like to travel, and home dialysis provides the opportunity for flexibility in patients' schedules, rather than having to adhere to the schedule provided by an in-center HD unit. This makes work and social activities easier to incorporate into their days.^41,42 However, there is also evidence to suggest that Indigenous, socially disadvantaged, and low-income individuals have less access to home HD.⁴¹ In addition, there are dialysis-related expenses that are paid out-of-pocket for travel and accommodation related to training and visits, increased electrical and water requirements, and the potential need for changes to the home. Home dialysis is more complicated for those who do not own their home or have an unstable housing situation. It may be intimidating to some because it appears too complex or they fear isolation from their peers, the health care team, and services. Home dialysis modalities often require the help of a care partner. It can be stressful for family members or friends to assume responsibility for dialysis care, and there are few breaks, unless another person or home care assistance is available to provide respite.⁴¹ Care partner burnout is an important concern with home modalities. The environmental impact of dialysis therapy has received more attention in recent years.⁴³ Further research is needed to better quantify the environmental impact of home dialysis and to identify opportunities for innovation and improvement.⁴³

In summary, many arguments have been put forward to support the promotion of home dialysis therapies, but there are two that are defensible on the basis of the available data. First, having home dialysis as an option allows providers to engage patients in shared decision making in an attempt to match them to a dialysis therapy that best fits their individual preferences. For many, this will be home HD or PD. Second, given that there are no clear differences in clinical outcomes between home therapies and in-center HD, the cost savings associated with home dialysis therapies, particularly PD, are a compelling reason to promote them from a health system perspective.

Home Dialysis Utilization: Targets and How to Measure Success

This section will review how home dialysis utilization is measured, why it is measured, and how the approach that is taken to grow home dialysis might influence the appropriate metrics and targets.

Incident or prevalent home dialysis utilization is typically expressed as a percentage, calculated as

$$\text{\% Patients Treated with Home Dialysis }=\frac{\text{Home Dialysis Patients}}{\text{All Dialysis Patients }}\times 100\%$$

Nearly every discussion of this topic focuses on how to increase the numerator (i.e., number of home dialysis patients) as a means of increasing the percentage of patients treated with home dialysis. However, the denominator (i.e., total number of dialysis patients) also plays an important role, particularly in a North American context, as discussed below.⁴⁴

The Natural History of CKD

The typical progression of a patient with advanced CKD who survives to kidney failure is shown in Figure 1. Once kidney failure develops, patients have a choice between conservative, symptom-based care and KRT. If they opt for KRT, they have a choice between kidney transplantation (if they are eligible) or dialysis therapy. If patients choose dialysis, they are faced with a decision between in-center HD and home dialysis (i.e., home HD or PD, if they are eligible). Focusing on the percentage of dialysis patients treated with home HD or PD ignores the upstream decisions that are made by people with kidney failure and does not consider the proportion that are transplanted or choose conservative care, which may influence the characteristics and numbers of patients who are ultimately faced with a choice between dialysis modalities.⁴⁴ The availability and quality of CKD care may also influence patient characteristics at the time of kidney failure, as well as the circumstances under which it occurs.

Figure 1.

Decision making in individuals with kidney failure. Individuals with progressive CKD and/or AKI develop kidney failure. They are faced with a choice between conservative, symptom-based care or KRT in the form of dialysis or kidney transplantation (in eligible patients). This decision making may occur in advance of the development of kidney failure for some patients. If they opt for dialysis and are eligible for home therapies, they are faced with a choice between in-center HD, PD, or home HD. The information available and the decisions that are made upstream of this final decision point influence the number of dialysis patients as well as the characteristics of the population faced with a choice between in-center HD and home therapies. This in turn influences the observed number and proportion of patients treated with home therapies. HD, hemodialysis; PD, peritoneal dialysis.

The United States has the third highest rate of patients treated with dialysis or transplantation in the world at 2196 per million population.³ This rate is 85% higher than in Canada and is especially high among older patients. This could be due to a higher burden of CKD, more rapid progression of the disease, or the widespread availability of dialysis, but low rates of conservative care in the United States also likely contribute.⁴⁵ Regardless of the cause, many more older patients are treated with in-center HD, and this increases the denominator (total number of dialysis patients) and in doing so, decreases the percentage of patients treated with home dialysis. The United States ranked seventh in the number of people treated with home dialysis per million population but 20th when it was expressed as the percentage of dialysis patients treated with home therapies.³ High rates of KRT, particularly among older patients, tend to negatively affect measures of home dialysis utilization.

Kidney transplantation rates would also be expected to influence home dialysis utilization. In places where kidney transplantation is promoted and rates are high, many younger, healthier individuals will be taken out of the dialysis pool when they are transplanted. This means that fewer potential home dialysis candidates are available and would tend to reduce the numerator, leading to a lower percentage of home dialysis. Although this is a desirable outcome, its effect should be considered when comparing these measures across jurisdictions.

These examples illustrate why the percentage of people treated with home dialysis cannot be interpreted in isolation. Information about the total number of individuals treated with KRT, the percentage of people treated with kidney transplantation, and the proportion who opt for conservative care is required to interpret home dialysis utilization, particularly when comparing results across countries. Unfortunately, much of the required information is often not available, particularly the total numbers of individuals who develop kidney failure and the percentage of patients who opt for conservative care.

Incident versus Prevalent Patients

The focus of many discussions of home dialysis utilization is on prevalent numbers (i.e., the percentage of people who are currently being treated with home dialysis). Figure 2 illustrates the difficulty in interpreting prevalent metrics. The total number or percentage of patients treated with home dialysis at any given time is the number of new, incident patients added to the population and the ongoing loss of patients because of transfer to in-center HD, transplantation, death, or other causes. Some of the causes of loss are negative (e.g., death, transfer to in-center HD) and should be avoided, while others would be viewed as positive (e.g., transplantation) and should be encouraged. This could create a difficult situation whereby promoting transplantation, the preferred treatment modality, actually leads to poorer performance on measures of home dialysis utilization. It is also the argument for measuring the combined percentage of individuals treated with home dialysis or transplantation, which partially addresses the issue.

Figure 2.

Factors that influence the prevalent population of patients on home dialysis. The number of patients treated with home dialysis is influenced by the addition of new patients (incident rate), the time that individuals spend on home dialysis, and the loss of patients from therapy due to death, kidney transplantation, transfer to in-center HD, and other reasons (e.g., transfer out of the program). Interpreting changes in the number of individuals treated with home dialysis requires knowledge of the complex interplay of all of these factors.

However, individuals with newly diagnosed kidney failure, or incident patients, likely provide more useful information. Characterizing the incident population is more helpful to inform quality improvement initiatives and facilitates the measurement of outcomes. One can follow individuals over the course of their disease trajectory through key decision points, and then for outcomes of interest that may be more or less common at different stages of their journey. The most immediate and impactful strategy for increasing home dialysis utilization is to increase the incident rate. As a consequence, monitoring incidence provides a metric that is responsive to interventions aimed at increasing the proportion of patients treated with home dialysis. By contrast, prevalent measures take time to respond to changes in incidence and are affected by loss of patients from therapy, making them more difficult to interpret.

The Motivation for Measuring Home Dialysis Utilization

A common motivation for measuring home dialysis utilization is to compare performance across countries, regions, or programs. This is difficult at best for the reasons outlined above. Much of the information required to interpret results from different countries, such as rates of incident kidney failure and conservative care, are not available to adequately frame the comparison. As a consequence, comparative analyses should be viewed critically and interpreted cautiously.

Another reason to measure home dialysis utilization is to track performance of a jurisdiction over time or to measure the impact of interventions designed to increase home dialysis utilization. This is much more likely to be an accurate reflection of performance in places where the rate of incident kidney failure and the percentage of patients who choose conservative care are felt to be relatively constant over time.

How Philosophy Influences Targets for Home Dialysis Utilization

Understanding the appropriate target for home dialysis utilization is dependent on the approach taken to increase it. In situations where dialysis is widely available, the focus is on patient autonomy and shared decision making, and the target should be based on the assumption that eligible patients will make an informed decision about modality choice, driven by individual preferences. Alternatively, in jurisdictions where a home-first policy is adopted, the focus has traditionally been on ensuring that as many individuals with kidney failure as possible receive treatment. This is done by providing the most cost-effective option but also means that access to in-center HD is restricted and the expected utilization of home dialysis would be much higher.

A Practical Approach to Measurement and Targets

For health systems that encourage shared decision making and can offer conservative care and all forms of KRT, targets for incident home dialysis utilization are relatively straightforward to construct. PD utilization will be used for illustrative purposes, but the principles apply to any modality.

In previous publications, the six-step approach to understanding PD utilization has been presented as a way of highlighting the steps required to get a patient with kidney failure on PD.^46,47 It is helpful because it allows for the calculation of incident PD utilization, but it also allows programs to understand the local barriers to maximizing PD and how changes might influence the observed rate. An example of how this is done is shown in Figure 3.

Figure 3.

A six-step framework for understanding drivers of incident PD utilization and targets for high-performing programs. In high-performing programs, all patients with kidney failure are identified, approximately 90% will be assessed for PD, 80% will be considered eligible, and nearly 100% of eligible patients will be offered PD. In an environment where patients are educated about their treatment options and encouraged to make an informed choice, up to 60% will choose PD. Approximately, 90% of those patients will start on therapy within 6 months of starting dialysis. When the percentage of individuals making it through each step are multiplied together, the result is the incident PD rate (percentage of all patients identified who ultimately are treated with PD) in a setting where shared decision making is practiced. Adapted from ref. 47, with permission.

Patients with kidney failure must first be identified, and ideally, that number would be very close to 100%. There will be individuals who die before being assessed or refuse to participate in the assessment, so approximately 90%–95% will ultimately undergo an assessment for PD eligibility. In high-performing centers, 70%–80% of patients will be determined to be eligible for PD and approximately 50%–60% of those offered it will choose it. At that point, approximately 90% of patients will be initiated on treatment by 6 months after starting dialysis—attrition here relates to patients who change their minds and elect to stay on in-center HD, failed PD catheter attempts, death before transitioning to PD, or transfer out of the dialysis program. If the proportions of patients making it through each of these steps are multiplied together, the percentage of incident patients receiving PD within 180 days of starting dialysis is the result. A reasonable high-water mark for incident PD utilization in an environment that promotes shared decision making and allows individuals with kidney failure to make an informed decision is somewhere between 34% and 41%. This will typically translate into a PD prevalence that is 5%–10% lower than the incident rate because of the continual loss of patients and a median time on therapy of approximately 2 years.⁴⁸ In a recent international comparison from the United States Renal Data System (USRDS), home dialysis prevalence topped out between 25% and 30% of the dialysis population, except in countries that have a home-first policy or regions where access to in-center HD is restricted.³ It is important to note that there may be numerous barriers at the patient, provider, and policy levels that will affect the ability of a program to hit this target.

Strategies for Increasing Home Dialysis Utilization

A number of different strategies have been trialed to increase home dialysis utilization. A prior scoping review identified PD-first policies, modality education programs, and audit and feedback, providing assisted PD, transitional care units, and bedside catheter placement as interventions that have been associated with increased PD utilization.^49,50 It is important to note that most of these studies looking at patient-level and provider-level interventions came from single centers, lacked control groups, were implemented in centers with low PD penetration at baseline, or involved restricting patient choice. At the policy level, PD-first policies in Hong Kong and Thailand have been associated with an increase in the numbers of patients treated with PD.^51–53 The relevance of these findings to a North American context is questionable because the main motivation behind them was to provide a low-cost therapy to individuals who would not otherwise have been able to access dialysis and expand the provision of services in a cost-effective manner. In North America, dialysis services are widely available currently, and restricting access to treatments would be a paradigm shift.

Using a multidisciplinary, multipronged, system-level approach, a large, integrated health care delivery system in Northern California observed an increase in the percentage of patients receiving PD in the first 90 days of therapy from 15.2% to 31.5%. The intervention combined patient and family education, education of providers and organizations, system-level operational improvements, and monitoring and continuous quality improvement strategies.⁵⁴ The use of transitional care units where a 4-week educational intervention was delivered was associated with an increase in home dialysis utilization in Fresenius Medical Care units in the United States.⁵⁰ In Canada, the Ontario Renal Network introduced a modality-based funding formula, mandatory informatics system, and targets for prevalent home dialysis rates, and then conducted frequent meetings with nephrology programs to review progress. They funded home dialysis coordinators, encouraged and funded assisted PD, and provided support for catheter insertion and urgent start PD. Home dialysis use rose from 21.9% to 26.5%, and PD prevalence rose from 16.6% to 20.9%. One of the challenges in interpreting these findings is the lack of a clear intervention.

There have been several recent large-scale initiatives that have attempted to increase home dialysis utilization in Canada and the United States. In Canada, a cluster randomized trial at 55 CKD clinics was conducted to test a combined intervention that included audit and feedback, patient-directed and provider-directed educational tools, and an in-person medical detailing visit. In this trial, the intervention was the same at all sites and focused on reporting performance relative to peers, reinforcing home dialysis as the preferred option, and promoting knowledge of home therapies among patients and providers. They used routinely collected data from the Canadian Organ Replacement Register to evaluate programs and did not have a formal process for identifying or addressing local barriers to home dialysis use. The intervention did not increase the percentage of patients receiving home dialysis at 180 days.⁵⁵

In the United States, the first-year results of the implementation of the End-Stage Renal Disease Treatment Choice (ETC) model were recently published.⁵⁶ In this multiyear, mandatory participation randomized clinical trial designed and implemented by the US Center for Medicare and Medicaid Innovation, 91 hospital regions were assigned to the treatment arm and 211 to the control arm. The intervention involved financial incentives to providers and facilities. The primary outcome, the mean percentage of patients who received home dialysis in the first 90 days, was no different between the treatment and control groups.⁵⁶ Although previous observational studies suggested an effect of financial incentives, this trial did not show a benefit.^57–59 It may be that the financial incentives were not of sufficient magnitude to stimulate change or that they simply did not work. A more recent analysis of 18 months of data using interrupted time series methodology showed no difference in ETC sites versus non-ETC sites with respect to home dialysis utilization but a small benefit on the rate of increase in home dialysis use in ETC sites.

The Starting dialysis on Time, At Home, on the Right Therapy (START) project took a different approach to maximizing the use of PD.^47,48 Rather than implementing a generic intervention or measuring high-level performance, the START project provided dialysis programs with high-quality data about the individual steps in the process of care that drove incident PD utilization. The aim was to facilitate the identification of local barriers and allow programs to design and implement interventions to address them. The process was supported by an Innovation Learning Collaborative that consisted of three sessions where frontline staff from all sites were brought together to review results and share strategies and learnings. The final results have not been published yet, but a publicly available report showed that incident PD utilization increased from 25% to 32% over the 18 months that the project was active but also highlighted significant center-to-center differences.⁴⁸ Programs were provided with the information required to understand local barriers to maximizing PD utilization and a framework for improvement, but the work of designing and implementing interventions to address local issues was up to the individual programs, and there were no significant consequences if they did not hit targets. Finally, the duration of the START project was relatively short, and the increases in PD use that were observed likely reflected better organization of care because of regular multidisciplinary meetings and changes in behavior required for data collection. Whether or not continuing the program would have led to further increases by allowing programs to address more complicated or time-consuming issues is not known.

In total, the limited evidence supporting interventions to increase home dialysis utilization suggests that there is no magic bullet that will work in all programs and in all jurisdictions. Given the complexity of increasing home dialysis utilization, high-quality information about local barriers to growth is an important first step. Programs likely also need to be held to account for performance in a meaningful way so that they are motivated to improve and must be empowered and supported to make the required changes.

In conclusion, there is widespread interest in increasing home dialysis uptake in North America. While kidney transplantation should be the preferred option in eligible patients, home HD and PD offer cost-effective options for KRT and appear to have equivalent clinical outcomes and quality of life compared with in-center HD, notwithstanding the limitations of the existing literature. Measures of home dialysis utilization should be interpreted with caution and consideration given to the potential impact of rates of kidney failure, the proportion of patients who choose conservative care, and the proportion of patients who receive a kidney transplant when comparing performance between different geographic regions or countries. Performance targets will differ in places that take a home-first approach, as compared with one in which all modalities are made freely available, and modality choice is based on shared decision making that aligns with patient preferences.

Disclosures

R.R. Quinn is coinventor and coowner of intellectual property associate with the Dialysis Measurement Analysis and Reporting (DMAR) System and reports consultancy for Baxter Corporation, research funding from ISPD PD Catheter Registry (Baxter partially funding project), honoraria from Baxter (PD University) and Baxter Advisory Board, speaker fees from Baxter Corporation, and Canadian patent for Dialysis Measurement, Analysis, and Reporting (DMAR) System. The remaining author has nothing to disclose.

Funding

None.

Author Contributions

Conceptualization: Ngan N. Lam, Robert R. Quinn.

Data curation: Robert R. Quinn.

Methodology: Ngan N. Lam, Robert R. Quinn.

Writing – original draft: Robert R. Quinn.

Writing – review & editing: Ngan N. Lam, Robert R. Quinn.