Edmond I Eger

Clinical and Economic Factors Important to Anaesthetic Choice for Day-Case Surgery

AbstractClinical and economic factors that are important to consider when selecting anaesthesia for day-case surgery can differ from those for inpatient anaesthesia. Patients undergoing day-case surgery tend to be healthier and have shorter durations of surgery. They expect less anxiety before surgery, amnesia for the surgical experience, a rapid return to normal (normal mentation with minimal pain and nausea) after surgery, and lower expenses. However, the latter 2 expectations can conflict; older generic drugs have lower acquisition costs but often impose longer recovery times. Longer recovery periods can increase costs by prolonging the time to discharge from labour-intensive areas such as the operating suite or the postanaesthesia recovery unit.The challenge for today’s anaesthetist is to use newer drugs judiciously to minimise their expense without compromising the rate or quality of recovery. Several approaches can secure these aims. Most apply the least anaesthetic needed. ‘Least anaesthetic’may mean the particular form of anaesthetic (e.g. local infiltration with monitored anaesthesia care versus a general anaesthetic), or may mean the delivery of the smallest effective dose, perhaps guided by anaesthetic monitors such as end-tidal analysers or the bispectral index.For patients requiring general anaesthesia, a combination of several drugs usually secures the closest approach to the ideal. Drug combinations used usually include a short-acting preoperative anxiolytic (e.g. midazolam), intravenous propofol (a short-acting potent anxiolytic and amnestic agent) for induction of anaesthesia (and sometimes for maintenance) and primary maintenance of anaesthesia with inhaled nitrous oxide combined with a poorly soluble (low solubility produces rapid recovery; the least soluble is desflurane) potent inhaled anaesthetic delivered at a low inflow rate (to minimise cost). Although old, nitrous oxide is inexpensive and has favourable pharmacokinetic and cardiovascular advantages; however, it is limited in its anaesthetic/amnestic potency, and has the capacity to increase nausea.In children, induction of anaesthesia is often accomplished with sevoflurane rather than desflurane; although sevoflurane is modestly more soluble than desflurane, it is nonpungent whereas desflurane is pungent. Moderate- or shortacting opioids (fentanyl is popular) or nonsteroidal anti-inflammatory agents (especially ketorolac), or local anaesthetics are added to secure analgesia during and after surgery. Similarly, when needed,moderate- or short-acting muscle relaxants are selected. Before the end of anaesthesia, an intravenous antiemetic may be given. With this drug combination, patients usually awaken within minutes after anaesthesia and can often move themselves to the vehicle for transport to the recovery unit. These combinations of anaesthetics and techniques minimise use of expensive drugs while expediting recovery (again minimising cost) with minimal or no compromise in the quality of recovery.n

The neuromuscular effects of sevoflurane and isoflurane alone and in combination with vecuronium or atracurium in the rat

Sevoflurane was compared to isoflurane anesthesia alone and in combination with atracurium or vecuronium in 84 rats using the sciatic nerve — anterior tibialis muscle preparation. Both bolus injection and infusion rate techniques were used to evaluate these drug interactions. The ED50 (dose which produced a 50% depression of twitch tension) of atracurium was 311±31 and 360±32 μg·kg−1 during 1.25 MAC sevoflurane and isoflurane anesthesia respectively. The ED50 of vecuronium was 190±27 and 149±14 μg·kg−1 during 1.25 MAC sevoflurane and isoflurane anesthesia respectively. The mean infusion rates of atracurium and vecuronium required to maintain a 50% depression of twitch tension were 5.04±0.7 and 2.02±0.3 mg·kg−1·hr−1. These infusion rates were 5.04±0.7 and 2.02±0.3 mg·kg−1·hr−1 during 1.25 MAC sevoflurane and 3.73±0.3 and 1.81±0.4 mg·kg−1·hr−1 during 1.25 MAC isoflurane anesthesia respectively. With both atracurium and vecuronium, the infusion rate required to maintain a 50% depression twitch of tension was inversely related to the concentrations of isoflurane and sevoflurane. The authors conclude that sevoflurane is similar in potency to that of isoflurane in augmenting a vecuronium or atracurium induced neuromuscular blockade in a dose-dependent manner.

1910–1950: Anesthesia Before, During, and After Two World Wars

A renaissance in anesthesia, particularly in the US and GB, occurred between 1910 and 1950. World War I drew physicians into anesthesia and forced some technical improvements such as the Boyles anesthetic machine and a use of blood transfusions. Guedel developed his technique for defining depth of anesthesia. As the numbers of anesthetists grew in the US, two societies arose: the American Society of Anesthesiologists and the International Anesthesia Research Society, and in Great Britain the Association of Anaesthetists of Great Britain and Ireland. Academic departments developed at the University of Wisconsin (Waters chair); Harvard (Beecher) and Oxford (Macintosh). In combination, the societies and academic departments increased recognition of the role of the anesthetist and improved quality through education and examination for certification/credentialing. Similar developments occurred in the rest of the world in subsequent years.

1860–1910: The Specialty of Anesthesia Develops Slowly

The discovery of anesthesia ultimately enabled remarkable advances in surgical care, but did not immediately change operations. At first, surgeons still pulled teeth, managed injuries, amputated limbs, and performed brief operations requiring momentary but deep levels of anesthesia. So the anesthetist drove the level of anesthesia down and then allowed it to “bounce” up, the surgeon operating at deeper levels of anesthesia. Further advances required improvements.

Significant Developments in the 1990s

The 1990s advanced safety, control and understanding of clinical anesthesia. Two new, poorly soluble inhaled anesthetics, sevoflurane and desflurane allowed a more precise control over the anesthetic state. Sevoflurane did so without cardiorespiratory stimulation. Both protected the heart from hypoxia. An older anesthetic, isoflurane, could reverse mental depression. We learned that all these anesthetics acted on central pattern generators in the ventral spinal cord to make patients immobile despite ongoing surgery. We also learned that the Meyer-Overton theory correlating lipophilicity and anesthetic potency didn’t always work, indirectly suggesting that inhaled anesthetics operated on proteins. Two new muscle relaxants, recuronium and cis-atracurium added to safety by acting more rapidly and for shorter times.

History to 1798

Surgeons in ancient times undertook diverse operations, usually at great speed to diminish the duration of suffering. Skulls from 5,000 BCE show trephination, the removal of a piece of bone from the head. Egyptians in 3,600 BCE performed circumcisions and tracheotomies. In 1700 BCE, Babylonians excised tumors. Egyptians cauterized breast tumors and excised peripheral aneurysms. The Roman surgeon, Galen, in the second Century CE, treated cataracts to restore sight, and he cut out the uvula to cure chronic coughing. Surgeons in Europe might be physicians, monks or barbers who in the thirteenth and fourteenth centuries wrote books on surgery. They gained recognition by their study of the anatomy of cadavers. Thus, in 1543 Vesalius published “On the Fabric of the Human Body”, demolishing centuries of errors, and opening the door to the performance of accurate surgery.

A History of Research in Anesthesia

Research in anesthesia has taken several forms. Other essays in this book supply detailed histories of those specific researches, including the discovery of new anesthetics and anesthetic adjuvant drugs, advances in anesthetic delivery and monitoring, measurement and codification of anesthetic pharmacodynamics and kinetics, and the development of vehicles for the exchange of information on research (societies, books and journals). We refer the reader to these chapters for details of the histories of specific researches. The present chapter supplies an overview, a summary of the progress in anesthesia research.

1844–1846: The Discovery and Demonstration of Anesthesia

Gardner Colton, a Columbia University medical student, began the discovery of anesthesia by offering (for pay) a public entertainment, a demonstration of the intoxicating effect of nitrous oxide. The dentist Horace Wells attended a demonstration in Hartford, observing that while inebriated, Samuel Cooley injured himself, apparently not feeling the injury as it occurred. Seeking a means to practice painless dentistry, Wells asked Colton to attend his office the next day, and to administer nitrous oxide to Wells while an associate, John Riggs, pulled one of Wells’ teeth. Wells felt no pain, and then gave nitrous oxide to several of his patients, practicing painless dentistry on most of them. His success prompted him to approach the great surgeon Warren at the Massachusetts General Hospital (MGH), requesting that he allow Wells to attempt a public demonstration at the Harvard Medical School. The demonstration failed, the audience denouncing Wells for his “humbug.”

1846–1860: Following the Discovery of Anesthesia

Four things soon followed the discovery of ether anesthesia. First, within weeks to months, ether was used in distant and disparate parts of the world’Europe, Australia, Mexico and Latin America. Second, for the moment, nitrous oxide was abandoned. Third, in 1847 Simpson discovered the anesthetic properties of chloroform that, for a time, replaced the pungent, flammable ether, especially in the UK. Fourth, the discovery of anesthesia was one thing, but how to deliver it safely was another. We needed a guidebook, a description of the clinical characteristics of anesthesia that might allow control of the anesthetic state. In 1847, Snow supplied just that for ether. In 1858, he similarly described the degrees of chloroform anesthesia, in the process analyzing the dangers of this more dangerous anesthetic and teaching how to avoid disaster. He, more than anyone, laid the groundwork for the specialty we call anesthesiology.

History Reflected in the Evolving Approaches to Anesthesia for a Patient Undergoing Cholecystectomy

The evolving nature of modern anesthesia shows the progression of drugs used (inhaled anesthetics, induction agents, anxiolytics, opioids, neuromuscular blocking drugs), the means of their delivery (for both injected and inhaled agents), approaches to anesthetic and surgical practice (in patient vs. out patient; long stay vs. short stay), control over the anesthetic state and postoperative pain, and means to manage the airway and postoperative nausea and vomiting. They hint at the evolution of patient, surgeon, and anesthetist and the interactions among the three. But beyond surface appearances, they do not show the profound changes wrought in the quality and education of the anesthetist and surgeon, the improvement in outcomes, the amazing decreases in mortality and morbidity. They do not consider the implications of those changes to the future of the specialty.