The New Zealand priority criteria project. Part 2: Coronary
artery bypass graft surgery
David C Hadorn, Andrew C Holmes
Abstract
Priority criteria developed during a national project were used
to conduct an audit of all 662 patients on waiting lists for coronary
artery bypass surgery in New Zealand during spring 1996. Based on the
observed distribution of priority scores, the cost of providing surgery
to all patients down to various levels of priority was estimated.
Descriptions incorporating life expectancy and quality of life
implications of surgery were developed of the kinds of patients who
would or would not receive surgery at each of several possible funding
levels. Cardiologists and cardiac surgeons agreed that a threshold of
25 points was a reasonable clinical goal but to work with a threshold
of 35, which can be sustained with current levels of funding. All agree
that the gap between these clinically preferred and currently afforded
thresholds is a subject for wider societal dialogue and decision. The
ability to measure the size of the gap between clinical desirability
and financial sustainability provides a new transparency to the problem
of healthcare resource allocation.
Introduction
This paper discusses several issues arising from the
priority criteria project in the context of the criteria developed for
coronary artery bypass surgery. We describe the process of developing
criteria, including the results of a pilot test, and discuss how the
results of a clinical audit of all patients on New Zealand's waiting
lists for coronary artery bypass grafting were used to estimate the
cost of providing surgery to patients down to each of several possible
clinical thresholds. A new government initiative to clear waiting lists
is described which requires use of explicit criteria such as those
developed in this project. We discuss how cardiologists and cardiac
surgeons agreed to accept a specific numerical threshold as indicative
of reasonable levels of service provision. Finally, we describe how the
criteria were used to identify and describe the kinds of patients
who would or would not receive coronary artery bypass surgery at
defined levels of public funding.
Background
Development of the criteria for coronary artery bypass grafting as
part of the priority criteria project followed similar work reported by
clinicians at Greenlane Hospital in Auckland,(1) which
itself had been motivated by earlier work on waiting lists sponsored by
the National Health Committee on Health and
Disability.(2)(3) The results of the Greenlane study, which
used a method based on the rating system developed by Naylor and
coworkers,(4) had called into question the extent to which
quantitative measures could capture clinicians' overall judgments of
priority and likely benefit. Nevertheless, the Greenlane investigators,
all of whom were also members of our professional advisory group on
coronary artery bypass grafting, agreed it was important to continue
the effort to develop such criteria.
Clinicians' reactions to the project
In general clinicians in New Zealand were very interested in the
project and willing to participate despite tight timetables and nominal
reimbursement. Almost all clinicians who were nominated by regional
health authorities agreed to serve as professional advisory group
members, and 20-30 additional clinicians from around the country took
time to provide often extensive responses to requests for comments on
each procedure. As described in part 1, all relevant specialists and
surgeons were invited to provide comments as part of a modified Delphi
process.
As might be expected, clinicians had mixed views on the project. The
most commonly expressed concern was that the government or the regional
health authorities would use the criteria to specify arbitrary
numerical cut off points below which surgery would not be funded. In
the minds of many clinicians the real problem was that the level of
funding for surgical services was inadequate. Developing a priority
system in the context of such scarcity would be like "rearranging the
deck chairs on the Titanic," as one commentator put it. Similarly, a
member of the professional advisory group for coronary artery bypass
grafting wrote, "If the available surgical resource is inadequate, it
is not possible to produce a workable numerical system of
prioritisation for patients in need of coronary artery surgery."
Despite these concerns physicians and surgeons from around New Zealand
cooperated with this project to a very substantial extent. Two
principal reasons for this cooperation were identified. Firstly,
clinicians almost universally acknowledged that decisions about urgency
and priority were made inconsistently. Often, the "squeaky wheel
would get the grease," and more deserving but uncomplaining patients
would be disadvantaged. One cardiologist put it like this:
Manipulation by referring doctors, friends
in high places, MP letters, or just persistent nagging, and just slight
exaggeration of symptoms, is rampant, and the poor benign patient
simply sits on the list and is leap frogged. I support any system which
will provide fair, humane, and prognostic order of surgery.
The second major reason for clinicians' cooperation in
this project was their wish to develop an objective measure of symptoms
and functional status that policymakers could understand. Participating
clinicians viewed the development of standardised assessment criteria
as having the potential to provide additional, more comprehensible, and
possibly dramatic information concerning the extent of "unmet
need."
Development of criteria for coronary artery bypass grafting
The priority criteria for coronary artery bypass grafting were
developed by a professional advisory group consisting of seven
cardiologists, four cardiac surgeons, one physician, and two general
practitioners. These individuals were nominated by the four regional
health authorities and by the Royal New Zealand College of General
Practitioners. Selection of the criteria followed an iterative modified
Delphi consensus process, including consideration of written comments
received from an additional 25 cardiologists and surgeons from around
New Zealand (see part 1).
As described in part 1, the priority criteria represent the clinical
factors - for example, the extent of coronary artery obstruction - that
have been shown, or are considered, to be associated with the degree of
benefit obtained from the procedure. Numerical scores (or weights) are
assigned to each of multiple levels of severity on each criterion;
relevant scores on each criterion are then added together to form a
total score. This score is considered indicative of the overall degree
of benefit expected from surgery (see table
1).
| Table 1 - Priority criteria for coronary artery bypass
surgery (maximum score 100)
|
| Clinical features | Score
|
| Degree of coronary artery obstruction (% diameter
occluded) |
| No coronary artery disease (50% and over) | 0 |
| 1 Vessel
disease (50-74%) | 8 |
| less than 1 Vessel disease (50-74%) | 9 |
| 1
Vessel disease (75%) | 9 |
| 1 Vessel disease (90% and over) | 14 |
| 2
Vessel disease (50-89%) | 15 |
| 2 Vessel disease (both 90% and over) | 15
|
| 1 Vessel disease (90% and over) proximal left anterior descending
artery | 19 |
| 2 Vessel disease (90% and over) left anterior descending
artery | 19 |
| 2 Vessel disease (90% and over) proximal left anterior
descending artery | 19 |
| 3 Vessel disease | 19 |
| 3 Vessel disease
(90% and over) in at least one | 19 |
| 3 Vessel disease (75%) proximal
left anterior descending artery | 19 |
| 3 Vessel disease ( 90% and over)
proximal left anterior descending artery | 27 |
| Left main
(50%) | 27 |
| Left main (75%) | 32 |
| Left main (90% and over) | 36
|
| Angina (Canadian Cardiovascular Society
criteria: class of angina after appropriate treatment) |
| Class I:
angina on strenuous exertion | 1 |
| Class II: angina on walking or
climbing stairs rapidly | 2 |
| Class III: angina on walking one or
two level blocks | 8 |
| Class IV A: unstable angina, rest pain | 18
|
| Class IV B: unstable angina on oral treatment, in hospital.
Symptoms improved on treatment but angina with minimal
provocation | 22 |
| Class IV C: in hospital on intravenous heparin or
glyceryl trinitrate | 26 |
| Exercise stress test
(Bruce protocol*) |
| Negative | 0 |
| Mildly positive | 8
|
| Positive | 12 |
| Very positive | 22
|
| Ability to work, care for dependants, or live
independently |
| Not threatened but more difficult | 1
|
| Threatened but not immediately | 5 |
| Immediately
threatened | 16 |
| *Very positive: 2 mm and over ST depression +/- angina in stage I, fall
in blood pressure over 15 mm Hg in stages I-II, ventricular tachycardia or
fibrillation in stages I-II, or unsafe to perform test; Positive: any
of the above criteria but patient not on optimal treatment or inability
to progress beyond stage II for other reasons; Mildly positive: test
stopped at stage III; Negative: none of the above or test stopped at
stage IV. |
In selecting priority criteria for coronary artery bypass grafting the
professional advisory group was able to rely to a much greater extent
on published outcome studies than were the advisory groups for the
other procedures (cataract surgery, hip and knee replacement,
cholecystectomy, and grommets for glue ear). For example, a table
listing the various possible degrees of coronary artery obstruction was
adopted without significant change from a then newly published analysis
of 10 years' experience with coronary artery bypass grafting by Duke
University investigators.(5) The initial weights assigned to
these degrees of obstruction were taken directly from this published
report, although recalibrated to accommodate the 100 point maximum
adopted for each set of criteria.
Weights were assigned to the remaining factors based on
additional information in this report and from a meta-analysis of
outcomes of coronary artery bypass grafting published during this
process.(6) It was agreed that these initial weights would
be revised as appropriate based on the results of a pilot study. As
described in part 1, both a "social factor" and an age adjustment
factor were incorporated into the clinical criteria to reflect both
common clinical practice and the balance of social values, as gleaned
by the national health committee via public meetings and consultation.
Pilot study
A formal pilot study was conducted of each set of criteria.
Details of the methods and results of these studies are available on
the BMJ's worldwide web site (www.bmj.com).
We briefly describe the coronary artery bypass grafting criteria pilot
study here.
A total of 260 patients were assessed during the study. Of these, 133
patients were evaluated at Greenlane Hospital (Auckland), 119 at
Dunedin Hospital, and eight at Waikato Hospital (Hamilton). Although
patients were enrolled more or less consecutively during the study
period, the sample should be considered a convenience sample.
Total priority scores were calculated for each patient by adding the
weights assigned to various factors at the appropriate levels. In
addition, physicians were asked to estimate what a "reasonable
waiting time" (in days) would be for each patient, considering an
"adequately, not infinitely funded service" and "keeping in mind
competing claims for resources both within and outside the health
sector." Reasonable waiting time, which was considered indicative of
likely benefit, was used as the outcome (dependent) variable in our
analyses. Alternative dependent variables could have been used, such as
clinicians' global assessment of expected benefit on a scale of 0-100.
It is unclear whether the results of our analysis would have differed
substantially had an alternative dependent variable been used.
Regression analysis was used to determine the set of criteria weights
resulting in the highest degree of correlation between priority scores
and clinicians' judgments of reasonable waiting times. Slight
modifications were then made in a few weights based on clinical
judgment. The final criteria and weights (table 1) correlated
quite closely with estimates of reasonable waiting time, with a
statistical test of correspondence (coefficient of variation, or
r 2) of 0.62 (perfect correlation would score 1.0, no
correlation would score 0).
Based on the results of the pilot test we calculated the approximate
cost of providing surgery to patients who present for coronary artery
bypass grafting in New Zealand on a steady state basis - that is,
assuming that a separate (and separately funded) initiative were used
to clear the waiting lists (as discussed below). Table 2 shows the
estimated cost of providing surgery to patients at or above each of
various possible clinical thresholds. On current funding levels we
estimate that coronary artery bypass grafting can be provided to
patients scoring 35 points or higher.
| Table 2 - The estimated cost of providing surgery on a
steady state basis to patients at or above each of various possible
clinical thresholds, highlighting the level of current funding
(threshold 35 points)
|
| No of operations per week | No of operations per year
| Priority threshold | Estimated cost
(NZ$)*
|
| 17 | 884 | 44 | 14,500,000
|
| 18 | 936 | 42 | 15,400,000
|
| 19 | 988 | 40 | 16,300,000
|
| 20 | 1040 | 39 | 17,200,000
|
| 21 | 1092 | 37 | 18,100,000
|
| 22 | 1144 | 35 | 19,000,000
|
| 23 | 1196 | 34 | 19,900,000
|
| 24 | 1248 | 32 | 20,700,000
|
| 25 | 1300 | 31 | 21,600,000
|
| 26 | 1352 | 29 | 22,500,000
|
| 27 | 1404 | 27 | 23,400,000
|
| 28 | 1456 | 25 | 24,300,000
|
| 29 | 1508 | 21 | 25,200,000
|
| 30 | 1560 | 7 | 26,000,000 |
| *Based on unit costs of NZ$17,000 per elective operation,
NZ$22,000 per acute operation (10 per week). 1NZ$=£0.44, $0.70. |
Audit of waiting lists for coronary artery bypass grafting
Following development, testing, and revision of the criteria for
coronary artery bypass grafting a clinical audit was conducted of all
patients on New Zealand's waiting lists for coronary artery bypass
grafting using the revised criteria. A single, experienced, independent
nurse reviewer examined the clinical records of all 662 patients on the
four regional waiting lists and abstracted from those records the data
required for calculating priority scores. Standardised abstraction
forms and coding protocols were developed to provide additional
assurance of comparability across centres.
The observed distribution of priority scores for patients on waiting
lists for coronary artery bypass grafting in New Zealand was roughly
normal (fig 1).
Fig 1 - Distribution of priority scores for coronary
artery bypass grafting among 662 patients waiting for the operation in
New Zealand. Numbers of patients are given above each bar
Based on this distribution, we calculated the cost of providing
coronary artery bypass grafting surgery to all patients on current
public waiting lists at or above specified thresholds of clinical
priority (table 3). These estimates were derived using various
assumptions concerning the unit cost of coronary artery bypass grafting
and the proportion of patients on lists who would no longer benefit
from surgery.
| Table 3 - Summary of costs for performing coronary
artery bypass grafting on 662 patients on New Zealand's waiting lists
|
| Priority score threshold | Proportion operated
on | No of patients operated on | Cost (NZ$)*
|
| 65 | 0.02 | 12 | 200,000
|
| 60 | 0.04 | 25 | 430,000
|
| 55 | 0.08 | 56 | 950,000
|
| 50 | 0.14 | 94 | 1,600,000
|
| 45 | 0.24 | 157 | 2,700,000
|
| 40 | 0.36 | 237 | 4,000,000
|
| 35 | 0.51 | 337 | 5,700,000
|
| 30 | 0.69 | 454 | 7,700,000
|
| 25 | 0.87 | 574 | 9,800,000
|
| 20 | 0.95 | 626 | 10,600,000
|
| 15 | 0.99 | 655 | 11,100,000
|
| 10 | 1.00 | 660 | 11,200,000
|
| 5 | 1.00 | 661 | 11,200,000
|
| 0 | 1.00 | 662 | 11,300,000 |
| *Based on a unit cost of NZ$17,000 per operation. 1 NZ$=£0.44,
$0.70. |
Describing kinds of patients
The priority criteria used in this project lend themselves to the
purpose of providing a "common insight into the life of the
patient."(7) In the case of coronary artery bypass
grafting, patients were described by reference to five point bands on
the scale of clinical priority. Within each band, patients were ordered
on each variable and the median values of each variable identified. The
collection of median values on all four variables was used to describe
the "average patient" within each five point band. Table 4 depicts
the results of this process.
| Table 4 - Median levels of each clinical variable within
each 5 point priority score band for coronary artery bypass grafting
April 1996
|
| Priority score | No | Coronary artery
disease | Angina | Exercise stress
test | Ability | Age
|
| 10-14 | 6 | 1 Vessel disease
(75%) | Class
II | Negative | Not
threatened | 67.5 |
| 15-19 | 29 | 2 Vessel disease
(50-94%) | Class II | Negative | Not threatened | 66.9
|
| 20-24 | 54 | 3 Vessel disease | Class II | Mildly
positive | Not threatened | 64.6 |
| 25-29 | 126 | 3 Vessel
disease | Class II | Mildly positive | Not threatened | 63.2
|
| 30-34 | 123 | 3 Vessel disease (95% and over) in at least 1 | Class
II | Positive | Not threatened | 62.8 |
| 35-39 | 112 | 3 Vessel
disease (95% and over) in at least 1 | Class III | Positive | Threatened
but not immediately | 62.0 |
| 40-44 | 89 | 3 Vessel disease (75%)
proximal left anterior descending artery | Class
II | Positive | Threatened but not immediately | 59.9
|
| 45-49 | 68 | 3 Vessel disease (75%) proximal left anterior
descending artery | Class III | Positive | Immediately
threatened | 63.2 |
| 50-54 | 42 | 3 Vessel disease (75%) proximal
left anterior descending artery | Class III | Very
positive | Immediately threatened | 59.6 |
| 55-59 | 35 | 3 Vessel
disease (95% and over) proximal left anterior descending artery | Class
III | Very positive | Immediately threatened | 60.4
|
| 60-64 | 15 | 3 Vessel disease (95% and over) proximal left
anterior descending artery | Class III | Very
positive | Immediately threatened | 64.8 |
| 65-69 | 8 | 3 Vessel
disease (75%) proximal left anterior descending artery | Class
IV A | Very positive | Immediately threatened | 59.6 |
For purposes of communicating more directly to politicians,
policymakers, and the public a greater degree of descriptive richness
was considered necessary. For this reason, the range of priority scores
was divided into three levels and the median values of patients within
each level identified. Descriptions based on these values were
constructed using the operational definitions of angina (table 1)
together with estimates of the likely implications of coronary artery
bypass grafting surgery on life expectancy. These estimates were based
on an examination of a recent meta-analysis.(6) The
resulting descriptions are presented in the box. These descriptions
were deemed by most observers to be valid and effective descriptions of
patient severity with which to communicate to the public and
policymakers.
Specification of clinically desirable threshold
As described in part 1, on 8 May 1996 the minister of health
announced the creation of a NZ$130m fund to be used for clearing
surgical waiting lists and replacing them with booking systems. On that
same day the minister also launched a meeting attended by
cardiologists, cardiac surgeons, and representatives of the Ministry of
Health, national health committee, and regional health authorities.
| Descriptions of average patient at each of three
levels of priority score |
| Patients with a score of 55 or more have considerably reduced
quality of life due to chest pain and breathlessness on almost any
physical activity and a reduction in life expectancy of perhaps 1-2
years in the absence of surgery.
Patients with scores of 35-54 experience much reduced quality of life,
mainly through pain on exertion, such as walking one or two blocks, as
well as moderately (8-12 months) reduced life expectancy in the absence
of surgery.
Patients with scores of 25-34 points experience intermittent pain or
breathlessness when undertaking such activities as walking or climbing
stairs rapidly and experience a modest reduction in life expectancy
(4-8 months) in the absence of surgery. |
The results of the audit just described were presented at that meeting.
The clinicians accepted the results of the audit and, after discussion,
agreed that a clinical threshold of 25 points before considering
coronary artery bypass grafting was reasonable given the degree of
benefit expected and competing claims on resources. Whether public
funding would be sufficient to operate on all patients above this
threshold was recognised by all participants to be a separate, societal
question. Indeed, at the meeting the minister agreed to be held
accountable for any gap between what is clinically desirable and what
is financially sustainable, reasoning that appropriate funding levels
must take into account competing claims on resources - adjudication of
which is ultimately up to society to resolve through democratic
processes.
As noted earlier, preliminary estimates indicate that current funding
levels will permit surgery to be offered to patients scoring at or
above 35 points. As such, there is an apparent 10 point gap between
what is clinically preferred and what can be afforded. We believe that
the ability to quantify this gap, even if imperfectly, represents a
major advantage of the general approach described in this article.
The acceptance by clinicians of a quantitative threshold for surgery,
based on priority criteria, represents a key development in the
transition within New Zealand from waiting lists to booking systems.
Such explicit acceptance by clinicians of the inevitability of limits
is vital to the success of any attempt to distribute healthcare dollars
more equitably. On balance, we believe the experiences described in
this article are an important step towards the goal of a fair,
transparent, and evidence based allocation policy.
We thank our professional advisory group for their support and
help, especially Dr Trevor Agnew and Mr Richard Bunton; Annmarie Banchy
for her excellent work in conducting the national audit of coronary
artery bypass graft waiting lists; and Paul O'Connor for performing
the statistical analysis.
Funding: National Advisory Committee on Health and Disability
and the four regional health authorities.
Conflict of interest: None.
References
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(Accepted 16 October 1996)
National Advisory Committee on Health and Disability,
Ministry of Health,
Wellington,
New Zealand
David C
Hadorn, manager, special projects
Andrew C
Holmes, senior medical
adviser
Correspondence to: Dr Hadorn.
