An Introduction to Monitoring Therapeutic Interventions in Clinical Practice

Monitoring is repeated testing aimed at guiding and adjusting the management of a chronic or recurrent condition [1]. As the opening quote suggests,
monitoring is a central activity in the management of patients and a major part
of the ritual of routine visits for most chronic diseases. Measuring the patient’s
current state and responses to treatment is central to managing hypertension,
diabetes mellitus, thyroid disease, asthma, depression, chronic pain and a host
of other long-term conditions. Although managing acute diseases may begin
with diagnostic testing, the focus should soon shift to monitoring. For example,
much of the activity of intensive therapy or high-dependency units is monitoring, such as the repeated measurement of blood gases and electrolytes in a
patient with trauma, or the tracking of glucose and other variables in diabetic
ketoacidosis. The principles of monitoring are similar in both cases.
Although neglected as an area of research, monitoring is a substantial part
of the clinical workload. Chronic conditions account for 80% of consultations
by general practitioners (GPs, primary-care physicians), and such visits usually involve interpreting a set of monitoring tests and perhaps ordering some
more. In the UK, the use of monitoring has accelerated as many of the quality indicators for GPs have involved monitoring, for example the targets and intervals of blood pressure, HbA1c (Chapter 16), cholesterol (Chapter 18), TSH
(Chapter 19), FEV1 and drugs such as lithium, aminoglycosides and digoxin
[2]. The costs of such monitoring are substantial and not all of them are clearly
worthwhile. Despite weak evidence for the effectiveness of self-monitoring in
type 2 diabetes [3], the costs of blood glucose monitoring strips alone in 2002
in the UK was £118m—larger than the expenditure on oral hypoglycaemic
agents [4]. However, despite financial and emotional investment in monitoring, many patients are poorly controlled. For example, in a UK study before
the new GP contract was introduced in 2006, only 14% of 21,024 patients
with newly diagnosed hypertension had met the target blood pressure after
12 months [5], and among treated patients about 40% of INR measurements
are outside target ranges, compared with the ideal of 5% [6].
Intuitively, monitoring should obviously be beneficial. Nevertheless, clinicians forgo monitoring in many areas; for example, aspirin is used for preventing stroke without assessing aspirin responsiveness by measuring platelet
aggregation. Deciding whether and how to monitor is clearly of central interest to both good clinical care and to the wise use of resources. In this book, we
outline the principles needed to guide better monitoring and then illustrate
those principles with examples. In doing so, we have built on what is known,
but have also found many unexplored areas in which we have attempted to
outline the problems and suggest directions for both clinical practice and research. In this chapter, I shall review the problems involved in monitoring and provide a guide to how these are dealt with in the other chapters in this book.