Respiratory acidosis
Hypoventilation accumulates CO2 in blood and tissues, causing “respiratory acidosis” that is benign and beneficial in the absence of hypoxia. CO2 enhances the release of oxygen into tissues via the Bohr effect, stimulates respiratory chemoreceptors, reduces blood viscosity, improves cardiac efficiency, and reversibly interacts with water in blood to form harmless carbonic acid that reduces blood pH and stimulates the respiratory drive of consciousness via pH receptors in brain ventricles. Harmless hypoventilation occurs during both normal sleep and anesthesia when respiratory drive becomes dependent on respiratory chemoreceptors, causing mild respiratory acidosis that enhances tissue perfusion, tissue oxygenation, and organ function.
Yandell Henderson, PhD (1873-1944) was the director of the Yale laboratory of applied physiology and the most prominent gas physiologist in his era. Like Crile, he was an idealist who believed that science should serve the public interest[62]. He opposed American involvement in WWI
T. He testified before congress about the dangers of automobile exhaust pollution, though his views were not accepted until long after his death[63].
In 1911 Henderson famously led a team of international experts that studied respiratory physiology at the top of Pike’s Peak[64]. His research demonstrated that spontaneous hyperventilation during anesthesia (due to inadequately controlled surgical stimulation) can cause cardiopulmonary collapse or unexpected postoperative respiratory arrest. He showed how CO2 supplementation stabilizes hemodynamic function, stimulates respiratory drive, enhances cardiac efficiency, improves tissue oxygenation, and prevents postoperative atelectasis, pneumonia, nausea, vomiting, and unexpected respiratory arrest[30,65,66]. Henderson also demonstrated that CO2 supplementation effectively treats myocardial infarction, angina, strokes, pneumonia, asthma, influenza, breathing problems in newborn babies, carbon monoxide poisoning, drowning, and smoke inhalation[30,67,68]. His work inspired the installation of Carbogen
U, which was a mixture of oxygen and carbon dioxide, on fire trucks in New York City, Chicago, and other major cities. Carbogen was widely embraced by physicians as an effective treatment, and it was credited with saving many lives, but unfounded fears of CO2 toxicity caused it to disappear from use.
In 1912 Dr. Henderson chaired a five-member Committee on Anesthesia that reported to the American Medical Association’s House of Delegates. It forcefully stated :“Anesthesia should cease to be regarded as merely an adjunct of surgery. It should be in charge of those whose principal aim is, not to see as much of the operation as possible, but to administer anesthesia in such a manner as to bring the patient through with the least possible loss of vitality.” Coming just two years after the Flexner Report, this recommendation had little effect on anesthesia practice, but it did put the AMA on record as supporting improvement in anesthesia practiceV.
Lewis Coleman, MD