«June 2010 Supervisor: Curt Löfgren ‘The only thing worse than being blind is having sight but no vision.’ -Helen Keller, American author ...»
Cheap doesn’t always mean better
Anaesthesia in cataract extractions in the
normal eye in the Netherlands; a deterministic
cost utility analysis using a Markov Model.
Janna Maria Brouwer
Supervisor: Curt Löfgren
‘The only thing worse than being blind is having sight but no vision.’
-Helen Keller, American author (1880-1968)-
Introduction: Cataract surgery is one of the most performed surgeries in the Netherlands
and with that a substantial part of the health care budget is accounted for. Considering the ageing population it can be expected to increase in the future. One of the parts of the surgery where there is a possibility for saving is the anaesthesia, currently there is no guideline or economical evidence about which method is preferred, sub-Tenon, retrobulbar or topical anaesthesia.
Methods: A deterministic Markov model is used to estimate and compare the cost per QALY gained for the three anaesthetic methods. The annual transition probabilities and linked costs are based on several studies. This study is done from a third payer perspective.
Comparisons are made for different age groups and both sexes. The influence of changing the costs, transition probabilities or the utility score is tested in the sensitivity analysis.
Results: Retrobulbar anaesthesia showed to be the most cost effective method when compared to sub-Tenon’s or topical anaesthesia. A cohort of 70 year old men gave an ACER estimate of € 0,93 per QALY gained for retrobulbar anaesthesia, € 1,79 for topical anaesthesia and € 2,01 for sub-Tenon’s anaesthesia. Thus retrobulbar anaesthesia dominates both topical and sub-Tenon’s anaesthesia. These results were similar for all age groups and both sexes. The model showed to be robust during the sensitivity analysis.
Conclusion: Considering cost effectiveness it is recommended to use retrobulbar anaesthetics in case of cataract surgery for the normal eye.
Key words: Markov model, cataract surgery, cost effectiveness analysis, local anaesthesia, the Netherlands.
LIST OF FIGURES
LIST OF TABLES
2. OBJECTIVES AND STRUCTURE
3.1.1 Cataract extraction
3.1.2 Anaesthesia methods used
3.1.3 The ‘normal’ and ‘abnormal’ eye
3.1.4 Possible complications
3.2 HEALTH ECONOMICS AND MODELLING
4.1 MARKOV MODELLING
4.2 MODEL UNDER STUDY
4.2.2 Transition probabilities
4.2.3 Cost data
4.3 UTILITY SCORES
4.4 TIME HORIZON
4.7 SENSITIVITY ANALYSIS
5.1 SENSITIVITY ANALYSIS
6. DISCUSSION AND LIMITATIONS
6.1 INFLUENCE OF AGE AND SEX
6.3 MODEL UNDER STUDY
6.4 TRANSITION PROBABILITIES
6.5 COST DATA
6.6 COMPARISON TO EXISTING LITERATURE
iv List of figures Figure 1 The anterior chamber
Figure 2 Retrobulbar injection
Figure 3 Schematic Markov model: Anaesthesia in cataract surgery
v List of tables Table 1 Transition matrix
Table 2 Transition probabilities per anaesthetic method
Table 3 cCat with topical anaesthesia
Table 4 cCat with sub-Tenon's anaesthesia
Table 5 cCat with retrobulbar anaesthesia
Table 6 Average costs and effects for men by age
Table 7 Average costs and effects for women by age
Table 8 ACER after sensitivity analysis for a cohort of 70 year olds
Table 9 ICERs for a 70 year old cohort with changed transition probabilities
1. Introduction The past decades have been characterised by extensive changes in the medical field.
Particularly in ophthalmology, different and new techniques have changed the treatment options fundamentally. One of the diseases where the treatment has changed over the last decades is cataract surgery (Allen & Vasavada, 2006). Whereas a patient would be admitted to the hospital for at least two weeks 50 years ago, nowadays a patient can leave the hospital the same day with relatively good vision. In line with the changes of the surgical techniques have the anaesthetic methods changed over time.
Together with the changes in techniques, the costs have been increasing over the years. In 2005 eye diseases accounted for 2,7% (1,9 billion euro) of the total medical costs of 68,5 billion Euro in the Netherlands. A total amount of 290 million Euro was spent on cataract;
this comprises all possible care given when a patient is diagnosed with cataract, both curative and supportive care (Poos, Smit, Groen, Kommer & Slobbe, 2008). When considering the trends of the last decades of increasing cataract incidence combined with an ageing population with a higher life expectancy, it can be expected that this amount will rise in the future. Given the scarcity of resources and the necessary cuts in the health care budget at present, there is an objective to provide the most cost effective care possible.
The current Dutch guideline for cataract provides no information on the cost effectiveness of the different methods of anaesthesia. Aside from this, the guideline gives no advice on which anaesthetic method to use, apart from which characteristics and preferences need to be taken in mind when making the decision. In practice this means that the majority of the cataract extractions are performed under topical, retrobulbar or sub-Tenon’s anaesthesia and this decision is mainly made out of preference of the surgeon.
With this thesis the author wants to provide evidence from an economical perspective for those who need to make the decision as to which anaesthetic method to use for a cataract extraction.
2. Objectives and structure The primary objective of this thesis is to provide economic based evidence for the decision of which anaesthetic method, sub-Tenon, topical or retrobulbar, to use in cataract extractions.
This thesis is mainly aimed at ophthalmologists, and decision makers in the ophthalmic field in the Netherlands. Since these target groups are quite different from each other in expected background knowledge the author provides background information from both fields, ophthalmology and health economics.
A second objective of this thesis is to explore the different views on the use of utility scores in health economic evaluations concerning ophthalmic interventions.
2.1 Structure The background section of this thesis will be used to explain some basics about ophthalmology, cataract and the surgery. While the methods section will be used to explain Markov modelling and its uses in health economics. This part will also be used to go deeper into the discussion about the utility scores in ophthalmology. The results section will show the results of the initial cohort simulations for different age groups and both sexes as well as the results of the sensitivity analysis. In the discussion section the limitations of current analysis, implications for the future and a comparison with existing literature will be discussed. At last a conclusion of the analysis as a whole will be given in the conclusion section.
This section will mainly provide background information considering the medical part of the analysis as well as a brief background on health economics.
3.1 Cataract Cataract is defined as the opacification of the eye lens; this opaficifation causes a gradual decrease in vision and will lead to blindness if left untreated. The eye lens is one of the few structures that continue growing after puberty. During life the structure of the lens fibres change, together with a build up of yellow-brown pigments, which causes a decrease in clarity of the lens and thus a decrease in vision (Allen & Vasavada, 2006). The lens is built from different layers from the middle to the outside. The layers are the nucleus, epinucleus, cortex and the capsule as illustrated in the figure below.
Figure 1 The anterior chamber (Source: Asbell et al., 2005)
Besides primary cataract, as described above, there are 3 other categories of cataract.
Congenital cataract, classifies the cataracts that are caused by genetic variations or other hereditary diseases. Secondary cataract, are those forms of cataract that are caused by systemic diseases or medication use, most often steroids. Traumatic cataract is classified as those forms of cataract that are caused by a blunt or perforating trauma, or in case the eye is exposed to radiation (Access Economics, 2009).
Apart from avoiding the known risk factors, i.e. smoking and an unhealthy diet, there is no treatment possible to slow down the development of cataract. The only therapeutic option in case the cataract is hindering someone’s functioning is surgery. Until now, there are no known alternative treatments, such as medication, available for the treatment of cataract.
3.1.1 Cataract extraction Cataract extraction (surgical removal of the opacified lens) is decided in case the vision of the patient is notably affected and a sufficient improvement of vision after surgery can be expected. There are no strict rules about at what level of vision an extraction is necessary, this 3 is dependent on the patient’s pre-existent vision, the patient’s vision needed for normal functioning and the ophthalmologist’s prerequisites. In short, the decision for extraction will be made if the expected benefit is bigger than the risk of complications (NOG, 2006).
In the last three centuries a lot has changed in the field of ophthalmic surgery and maybe even more specifically in cataract surgery. Since 1949, artificial lenses have been implanted after the removal of the original lens, and this was the major increase in vision outcome in the history of cataract extraction (Apple & Sims, 1996). The first surgical procedure with only two small incisions needed was performed in 1967 (Linebarger, Hardten, Shah & Lindstrom, 1999). Since then this technique has been improved to a method where the use of stitches is, in most cases, not necessary anymore. When eye surgery can be done without stitches this means that there will be no more stitch induced distortion of the cornea and thus a better vision directly after surgery. Additionally, the risk of other complications such as protrusion of the iris through the wound and leakage of the anterior chamber are reduced as well, since the incisions made are much smaller than before.
In this thesis only the modern technique of phaco-emulsification will be explained since this is the most used technique in the Netherlands and the developed world (NOG, 2006). The aim of a cataract extraction is to remove the clouded lens and to insert an artificial lens at the same time. The lens is fitted in a small bag, the so-called capsule. As the artificial lens will be placed in this capsule during the extraction, this capsule needs to be kept in one piece.
During the extraction, two small incisions are made at the sides of the eye. Through these incisions the instruments as well as the artificial lens are brought into the eye. To be able to remove the lens, an ultrasonic probe is used to break the lens into small pieces that are possible to be aspirated (Asbell et al. 2005).
The process in steps:
1. Dilation of the pupil by giving mydriatic agents, the pupil will widen to provide an optimal access to the lens.
2. Anaesthetising the eye depending on the surgeon’s choice of method.
3. Making an incision at the corneal base for the main instruments.
4. Injecting a viscous fluid in the anterior chamber to keep the shape of the eye during the operation and to protect the endothelium of the cornea.
5. Making the incision for the sideport, for the assistant instruments.
6. Removing a small part of the front part of the capsule to get access to the lens.
7. Administering basic saline solution to separate the lens from the capsule and the nucleus from the cortex (outer) layer.
8. Using the ultrasonic probe to make a cross in the nucleus to be able to crack it into quadrants. Breaking the quadrants into small pieces and aspirate them.
11. Place the artificial lens, rotate and put it in the right position.
12. Remove the instruments and seal the corneal incisions.
After this procedure, antibiotic drops will be administered and the eye will be patched. In a normal procedure, instructions will be given to the patient how to handle the coming days and when to contact the hospital in case of complaints of the eye that has been subject to surgery (Lundqvist, 2010).
3.1.2 Anaesthesia methods used In the Netherlands, the most methods for anaesthesia used are topical anaesthesia, subTenon’s injection and retrobulbar injection (NOG, 2006). All of those methods are local anaesthesia methods.
188.8.131.52 Topical Topical anaesthesia is the simplest form of anaesthesia with cataract extraction. A combination of drops is administered with set intervals. Most often it is a combination of both tetracaine 0.5% and lidocaine 2% that is used, depending on the existing protocols. A nurse or a surgery assistant administers the anaesthetic drops in the lower fornix of the eye.
Twenty minutes after the last administration, the eye should be optimally anaesthetised. In some cases an additional anaesthetic will be injected in the eye after the corneal incisions are made. With this method one will only reach analgesia and not akinesia, in other words the patient is still able to move his or her eye. The advantages of this technique are that it’s a fast method, not invasive and comfortable during administration. The disadvantages are that the patient is still able to move the eye, which increases the risk of complicated surgery. Some patients are threatened by the idea of being operated under this kind of anaesthetics (Davison, Padroni, Bunce & Rüschen 2007).