Hypertension In detail
Please note that the model of the Hypertension guideline is highly simplified, as not all contraindications, relative contra-indications, relative indications and drug interactions are specified.
Guideline Segment I:
If the patient is not at the goal blood pressure, the response to the initial drug choice for hypertension is inadequate after reaching the full dose, and the patient is tolerating the first choice well, then add a second drug from another class. If a diuretic is not chosen as the first drug, it is usually indicated as a second-step agent because its addition will enhance the effects of other agents.
Assumptions for this segment:
- The history of what other drugs were previously given to the patient is irrelevant.
- The patient is on a single drug and another drug class will be added.
- The patient is already taking the maximum dose of the drug
- The response to the first drug choice for hypertension is inadequate after reaching the full dose, and the patient is tolerating the first choice well
- There is no need to check if a specific patient is allergic to a specific drug.
- It will be enough to suggest a drug class; it is not necessary to suggest a specific drug and dose.
- Never give a contra-indicated drug to a patient.
- Never choose as a second drug a drug that is in the list "Evidence-based combinations to avoid".
- Compelling indications outweigh Evidence-based combinations and relative indications.
The possible drug classes are:
- ACE I
- Beta-blockers (Distinguish between drugs that have intrinsic sympathomimetic activity (ISA) and those that do not)
- Calcium channel blockers (Distinguish between dihydropyridines and nondihydropyridines, and between long-acting (long duration) dihydropyridines and non-long-acting dihydropyridines)
- Diuretics (Distinguish between thiazide-, loop- and potassium-sparing diuretics)
Table 1: compelling indications (unless contra-indicated)
|Diabetes mellitus (type 1) with proteinuria||ACE-I|
|Heart failure||ACE-I, loop-diuretics|
|Isolated systolic hypertension in older Patients||Diuretics (preferred), dihydropyridines|
|Myocardial infarction||Non-ISA beta-blockers|
|Myocardial infarction with systolic Dysfunction||ACE-I|
|Patient does not have co-morbidities that are compelling indications of other anti-hypertensives||Diuretics, beta-blockers|
Table 2: relative indication (unless contra-indicated)
|Diabetes mellitus (type 1) with proteinuria||ACE-I (preferred), calcium channelblockers|
Table 3: relative contraindication
|Diabetes mellitus (type 1) with proteinuria||Beta blockers|
Table 4: contraindications
|Asthma or chronic airway disease||Beta blockers|
|Second- or third-degree heart block||Beta-blockers, non-dihydropyridine|
Table 5: drug interactions*
|Drug class||Evidence based combinations||Evidence based combinations to avoid|
*This representation of drug interactions is based on interpretation that the physicians from the Veterans Administration Clinic in Palo Alto gave to the drug interactions that were specified in Table 11 of the original guideline. Evidence based combinations are drugs that, when taken together, have synergetic effects. Evidence based combinations to avoid are groups of drugs that should not be taken together.
- The first task in the workflow is the Introduction action, which provides some general information about the guideline.
- Next is the Patient details enquiry, which collects data about the patient’s age group (Older/Younger) and gender.
- The Pregnancy enquiry follows the Patient details enquiry if the patient is a female; otherwise it is discarded. Pregnancy information is necessary for determining contraindicated drugs (table 4).
- The Current therapy enquiry and the Comorbidities enquiry also follow the Patient details enquiry.
- The Current therapy enquiry collects information about the current drug treatment the patient is on – so that the added drug will be selected from a different drug class
- The Comorbidities enquiry collects data about co-morbidities that can influence the selection of the added drug:
- Diabetes mellitus with proteinuria, heart failure, Isolated systolic hypertension in older Patients, myocardial infarction and Myocardial infarction with systolic dysfunction all have compelling indications (table 1)
- Diabetes mellitus with proteinuria also has relative indications and a relative contraindication (tables 2 and 3)
- Asthma, chronic airway disease (COPD) and second- or third-degree heart block all have contraindications (table 4)
- The Additional drug choice decision runs as soon as the antecedent enquiries (Current therapy, Pregnancy and Comorbidities) are all completed or discarded. The candidates in this decision are all the possible drug classes and sub-classes:
- ACE I
- ISA beta-blockers
- Non-ISA beta-blockers
- Long-acting dihydropyridine calcium channel blockers
- Non-long-acting dihydropyridine calcium channel blockers
- Nondihydropyridines calcium channel blockers
- Thiazide- diuretics
- Potassium-sparing diuretics
Information that was collected by the enquiries is used to construct the arguments for each candidate. The support type used in this decision is numeric rather than symbolic:
- Compelling indications have been given support weight of +100
- Contraindications have been given support weight of -1000
- Relative indications and contraindications have been given support weight of +1 and -1 respectively
- Evidence based combinations to avoid have been given support weight of -1000
- Beneficial evidence based combinations have been given support weight of +1
Under the decision model used in PROforma, the weight of arguments for each candidate is summed. The decision task recommends any candidate with a net positive amount of support, and will by default select whichever candidate has the most support.
Candidates from the diuretic class have been given a higher priority value than others. This means that if they get the same support level as other candidates, they are displayed higher in the recommended candidates list (if a diuretic is not chosen as the first drug, it is usually indicated as a second-step agent because its addition will enhance the effects of other agents).
Guideline Segment II:
The goal of the (new) anti-hypertensive treatment is to control blood pressure to < 140/90 mm Hg (systolic BP below 140 mm Hg and diastolic BP below 90 mm Hg). For patients with Diabetes Mellitus, the blood pressure should be controlled to below 130/85 mm Hg. Blood pressure should be controlled to 125/75 in patients with proteinuria in excess of 1 gram per 24 hours, and to 130/85 mm Hg in patients with proteinuria with at most 1 gram per 24 hours with whatever anti-hypertensive therapy is necessary.
- The Internal variables enquiry is separated from the rest of the workflow. Contrary to the other enquiries in this process, it does not collect data from the end-user, but from the process itself. It holds two data items – TargetSBP and TargetDBP – of type integer. As the status of these data items is set to optional and they have default values (140 and 90 respectively), they are not displayed to the end-user. These data items will be used to hold the goal blood-pressure values, once they are determined.
- The Target BP decision, which runs as soon as the Comorbidities enquiry completes, determines the blood-pressure goal. It has three candidates:
- Low – supported in patients with proteinuria in excess of 1 gram per 24 hours
- Medium – supported in patients with proteinuria with at most 1 gram per 24 hours, and in patients with diabetes mellitus
- Standard (140/90 mm Hg) – supported in patients with no diabetes mellitus or proteinuria
- The Setting BP values action follows the Target BP decision. As it is automatic, it runs and completes in the background without being displayed to the end-user. On its completion, it assigns blood-pressure values to the data items of the Internal variables enquiry, according to the results of the Target BP decision. These will serve as the goal blood-pressure values.
- Next is the Assess response plan. This plan has a Cycle Until condition, and so it re-runs until the condition is met; in this case, the systolic and diastolic blood pressure has to be at or below target level for the plan to stop cycling.
Within the Assess response plan are two tasks: the Continue therapy action, and the Monitor BP enquiry.
- The Continue therapy action displays the goal blood-pressure values to the end-user. To display a mixture of text and dynamic values, the concatenation function (#) is used: in the procedure field, text is enclosed in quotation marks, and separated from data items with the concatenation symbol.
- The Monitor BP enquiry collects the current blood-pressure information. When it completes, depending on the blood-pressure values, the Assess response plan either completes or runs again.
- When the goal blood pressure is reached, the Cycle Condition is met and the Assess response plan completes. The Target BP reached action, advising the end-user that the goal has been achieved, follows.
If you have installed the Tallis Toolset, you can find this sample in the World > Samples folder in the ACL Web Repository.
Click her for information about using the web enactment application.
This model is based on a model that was created as part of a study comparing six computer-interpretable guideline models (Peleg M, Tu S, Bury J, Ciccarese P, Fox J, Greenes RA, Hall R, Johnson PD, Jones N, Kumar A, Miksch S, Quaglini S, Seyfang A, Shortliffe EH, Stefanelli M. Comparing computer-interpretable guideline models: a case-study approach. J Am Med Inform Assoc. 2003 Jan-Feb;10(1):52-68.)