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Assessing the demands placed on the national information infrastructure by health care services requires considering the needs of the health care providers and their intermediaries. This analysis is thus based on customer pull rather than on technology push. This approach is likely to lead to lower estimates than would a model focusing on technological capabilities. However, we will assume a progressive environment, where much paper has been displaced by the technologies that are on our horizon.

In our model, information requests are initially generated for the delivery of health care by the providers and their intermediaries. Pharmacies and laboratories are important nodes in the health care delivery system. Education for providers and patients is crucial as well and will be affected by the new technologies. Managers of health care facilities have their needs as well, paralleled at a broader level by the needs of public health agencies. Functions such as the publication of medical literature and the production of therapeutics are not covered here, since we expect that topics such as digital libraries and manufacturing in this report will do justice to those areas.

Services for the Health Care Provider

The initial point in our model is the interaction of the provider with the patient. Such an interaction may be the initial encounter, where tradition demands a thorough workup and recording of physical findings; it may be a visit motivated by a problem, where diagnostic expertise is at a premium; it may be an emergency, perhaps due to trauma, where the problem may be obvious but the treatment less so; or it may be a more routine follow-up visit. In practice, the majority of visits fall into this routine category.

Adequate follow-up is crucial to health care effectiveness and is an area where information technology has much to offer. Having the right data at hand permits the charting of progress, as well as the therapeutic adjustments needed to improve or maintain the patient's health care status. Follow-up care is mainly provided locally. The majority of the consumers of such care are the older, less mobile population. It is this population that has the more complex, longer-term illnesses that require more information

The needs for information differ for each of the interactions described above. Initial workups mainly produce data. The diagnostic encounter has the greatest access demands. Emergency trauma care may require some crucial information, but it is rarely available, so that reliance is placed on tests and asking the patient or relatives for information. Note that many visits to emergency facilities, especially in urban settings, are made to obtain routine care, because of the absence of accessible clinical services. For our analysis these are recategorized. A goal for health care modernization should be better allocation of resources to points of need, but here we discuss only the information needs. Information for follow-up visits should summarize the patient's history; unexpected findings will trigger a diagnostic routine.

To assess the need for data transmission we need to look at both the distance and the media likely to carry the needed information. Media differ greatly, and all must be supported. Many physical findings can be described compactly with text. Laboratory findings are compactly represented in numeric form. Sensor-based tests, such as EKGs and EEGs, are time series, requiring some, but still modest, data volumes. Sonograms can be voluminous. The results of ultrasound scans are often presented as images. Other diagnostic procedures often produce images directly, such as x-ray or CT and similar scans that are digitally represented. High-quality x-rays require much storage and transmission capacity, whereas most digital images have larger pixels or voxels and require more modest storage volumes. The practitioner typically relies on intermediate specialists to interpret the data obtained from sensors and images, although for validation access to the source material is also wanted.

The distance that this information has to travel depends both on setting and data source. Table 1 indicates estimated sources of patient care information for the types of clinical encounters listed.

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