Blood Gas Analysis and Critical Care Medicine

Blood Gas Analysis and Critical Care Medicine
JOHN W. SEVERINGHAUS, POUL ASTRUP, and JOHN F. MURRAY

Departments of Anesthesiology and Medicine, and the Cardiovascular Research Institute, University of California San Francisco, and the San Francisco General Hospital Medical Center, San Francisco, California; and Department of Clinical Chemistry, Rigshospitalet, Copenhagen, Denmark

Critical care medicine is one of the newest and most rapidly growing medical specialties. Surprisingly new, in fact, because critical care medicine is, basically, applying physiologic principles to the care of seriously ill patients, something physicians have been trying to do for centuries. Modern critical care medicine is distinguished from its predecessors by incredible products of technology, advances in biochemistry, and astonishing know-how. We now have at our disposal sophisticated monitoring devices that provide moment to moment information about key circulatory and respiratory physiologic variables, how they are deranged by disease, and how they respond to intervention. We also have available an astonishing variety of high-tech instruments and powerful medications that we use to remedy ailing physiology, ventilators for breathing, machines to rid the body of excess fluid and impurities, vasopressor drugs to shore up flagging blood pressure, and even instruments to supplement a failing heart. Another distinguishing feature of critical care medicine is that it is practiced in specialized facilities, intensive care units, within acute care hospitals; these focal points for costly instrumentation are also headquarters for the expertly trained and knowledgeable physicians, nurses, and other professionals who care for desperately ill patients.

This paper retraces the history of the development of knowledge about blood gas transport, including the discovery of oxygen and carbon dioxide, the evolution of techniques to measure respiratory gases in the blood, and finally, how all this came together in Blegdamshospital, Copenhagen, on August 25, 1952, when an ingenious anesthetist, Bjorn Ibsen, came out of the operating room and started the modern critical care movement. We conclude with some comments about the remarkable changes that have occurred during the 45 years between then and now, and we make a few speculations about what the future might have in store.

BLOOD GAS TRANSPORT

According to Hippocrates (460-377 BC), good health resided in a proper balance among the four humors: blood, phlegm, black bile, and yellow bile, a balance that depended on the generation of life-giving heat within the left ventricle. Aristotle (384-323 BC) concluded that arteries carried air, but Erasistratus of Cos (about 330-250 BC) taught that "pneuma," created within the left ventricle from lung air, was the substance pumped through arteries to the tissues. Galen (130-199 AD) believed that the heart sucked blood-cooling air from the lungs into the left ventricle where the vital heat was generated, that pneuma was transported in arteries to the tissues, hence to veins via anastomoses, and that after arriving back in the heart, blood passed through minute pores in the septum from the right into the left ventricle for replenishment. These ideas went unchallenged by physicians until the 16th century.

Michael Servetus (1511-53) studied and practiced medicine, but his principal interest became theology (1). In Christianismi Restitutio (1553), Servetus contradicted Galen, concluding that the communication between the right and left sides of the heart was "not through the middle wall of the heart . . . but by a very ingenious arrangement the subtle blood is urged forward by a long course through the lungs," the first postulate of the existence of pulmonary capillaries. Severtus sent his book to John Calvin, who considered it heresy, had him arrested, jailed, and burned at the stake within the year of publication.

It remained for William Harvey (1578-1657), a brilliant anatomist and physician, to describe the circuit of blood flow around the body, including its circulation through the lungs. In his monumental De Motu Cordis (1628), Harvey flatly stated that blood was pumped from the right ventricle through the pulmonary circulation to the left ventricle, passing through "the invisible porosities of the lungs and the minute connections of the lung vessels." These theoretic pulmonary porosities became anatomic reality when first seen by the celebrated Italian microscopist Marcello Malpigi (1628-94) (2). Thus, the anatomy of the circulation was concisely described, but the nature of the vital ingredient by which breathing fed the inner life-giving flame remained elusive. It took over 100 years to find it.

Discovery of Carbon Dioxide

Joseph Black (1728-99), who became Professor of Chemistry in Edinburgh, showed while he was a medical student that large quantities of a gas, which he called "fixed air" (carbon dioxide), were generated by heating or acidifying chalk. He was the first to prove that the same gas was present in exhaled air (3).

Discovery of Oxygen

Robert Boyle (1627-91) established the fact that the long-sought, life-sustaining substance was contained within air itself (4). His assistant, Robert Hooke (1635-1703), demonstrated in 1667 that a dog whose exposed lungs had multiple pleural punctures could be kept alive by providing a constant flow of air through the trachea without any movement of the lungs. Hooke showed, as had Richard Lower (1631-91), that arterialization of blood in the lungs occurred through the introduction of fresh air. No one noted that something was taken out of the air and something else was added.

The English Unitarian "dissenting" minister and amateur chemist, Joseph Priestley (1733-1804), who lived next door to a brewery, got interested in the waste gas product of fermentation and started investigating gases. He discovered that the gas given off by heating mercuric oxide caused a much brighter flame than plain air. In 1774, he showed that this gas was essential not only to combustion, but also to respiration and to the greening of plants. Priestley was the first to demonstrate that ordinary air, in which a candle would no longer burn and a mouse no longer live, might regain its former vital properties if green plants were kept within the sealed chamber. He eventually managed to isolate 10 new gases, including nitrous oxide and carbon monoxide, invented carbonated beverages, gum rubber erasers, and refrigeration. In 1791 his Birmingham home was burned and his laboratory trashed by a royalist-sectarian mob incensed by his support of the French revolution. He emigrated with his family to Pennsylvania in 1794. Priestley was one of the great social and political minds of the Enlightenment. He had a significant influence on his good friend Thomas Jefferson, and had his portrait painted (Figure 1) by the most famous American painter of the time, Gilbert Stuart.