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Conclusion

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Conclusion

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  1. Deliberate Hypotension: A Historical PerspectiveZivCorber, MD, M. Ramez Salem, MD, George J. Crystal, PhD, Nabil R. Fahmy, MD*Department of Anesthesiology, Advocate Illinois Masonic Medical Center, Chicago, IL 60657 USA *Department of Anesthesiology and Critical Care Medicine, Massachusetts General Hospital, Boston, MA 02114 USA Abstract Timeline Intentional induction of hypotension was originally proposed by Harvey Cushing in 1917.1 Gardner reported on the use of the deliberate decrease in blood pressure by arteriotomy.2,3 The many complications, lead to quick abandonment of the technique.4 Griffiths and Gillies (1948) employed high spinal anesthesia to induce hypotension.5 A major advancement was achieved when ganglionic blockade was combined with foot-down tilt. The enthusiastic initial reception was followed by reports of unexplained morbidity and mortality. The synthesis of trimethaphan, offered a new dimension in the control of blood pressure by continuous infusion. Its short action was surpassed only by sodium nitroprusside, which was introduced in 1962.6 Halogenated anesthetics provided an easier induction of hypotension. The availability of β-adrenergic blocking drugs allowed better prevention and treatment of tachycardia.7,8 Advances in the physiology and pharmacology of induced hypotension, development of new drugs such as nitroglycerin and labetolol and the application of newer monitoring methods, have improved the safety of this technique.9,10 • Appreciation of measures that could be implemented to increase the safety of the technique. These include: • The presence of an experienced anesthesiologist trained in the use of hypotensive anesthesia • Teamwork and communication between the entire operating team • Gradual onset of hypotension, level of blood pressure and gradual recovery • Maintaining near-normal PCO2 and adequate oxygenation • Appreciation for contraindications • Prevention of cyanide toxicity 1956 – Raventos3 introduced halothane, the first modern volatile anesthetic, which allowed for easier control of blood pressure. The use of halothane greatly reduced the incidence of failed hypotension. 1917 – Cushing1 proposed the use of hypotension for optimizing operative conditions during intracranial surgery. 1946 – Gardner2,3 used arteriotomy to reduce blood pressure in neurosurgical procedures. 1948 – Griffiths & Gilles5 described the use of high spinal analgesia to induce hypotension. 1950s – Enderby3 achieved hypotension with ganglionic blockade (e.g. hexamethonium and pentolinium) combined with foot down tilt. Other novel techniques were also attempted, such as lower-body negative pressure (Figure 1). 1962 – Moraca et al. 6 introduced sodium nitroprusside as a hypotensive drug into clinical practice. Reports of failed hypotension and tachyphylaxis served to limit its immediate usage. 1966 – Hellewell & Potts7 introduced the use of propranolol to control heart rate during controlled hypotension. This new drug reduced the dose requirement for sodium nitroprusside as well as the incidence of cyanide toxicity and tachyphylaxis (Figure 2). Conclusion The concept of deliberate hypotension was introduced almost a century ago. In the years since then, many techniques have been attempted and refined. Deliberate hypotension has encountered controversies and has been in and out of favor. However, because of the tenacity of a few anesthesiologists and surgeons, the technique has survived. The discovery of new hypotensive drugs and a better understanding of its physiology were integral to the evolution of deliberate hypotension and have served to make it simpler, safer and more accessible to anesthesiologists worldwide. Figure 1: Schematic of makeshift device that exposes the lower body to subatmospheric pressure (Brown et al. J Physiology (London) 183:607-27, 1966). This technique causes venous pooling, a reduction in venous return and a decrease in arterial blood pressure. Because of its impracticality and lack of precision, this technique did not gain wide favor. 1953 – Magill et al. introduced Trimethaphan, which offered a new dimension in the control of pressure, a titratable continuous infusion. 1956 – Hampton & Little4 reported on unexplained morbidity and mortality with the use of controlled hypotension. This report, published in a book entitled “Controlled Hypotension in Anaesthesia and Surgery,“presented the results of a questionnaire that had been sent out to members of the Association of Anaesthetists of Great Britain and Ireland regarding their experience with controlled hypotension. These results indicated an alarmingly high rate (1 in every 32 cases) of complications, including oliguria, cerebral/retinal thrombosis, cardiac arrest, cardiovascular collapse, delayed awakening and blurred vision. They also indicated a mortality rate of 1 in 291 cases. This publication led to a widespread abandonment of deliberate hypotension however, it continued to be used by a small group of anesthesiologists and surgeons. Figure 2: Propranolol reduced SNP dose requirement in patients undergoing deliberate hypotension (Bedford et al., Anesth. Analg. 58:466-469, 1979). Introduction References Controlled hypotension has been widely used intraoperatively for blood conservation and to provide a blood-less surgical field. From its inception in 1946, in which arteriotomy was used to reduce blood pressure, the technique has undergone many changes and refinements based in part on the development of new drugs. This presentation traces the development of controlled hypotension with emphasis on important milestones. • 1970’s and Beyond: • New hypotensive drugs (nitroglycerin and labetalol) and new inhalational anesthetics. • More widespread use of hypotensive anesthesia. • Better understanding of the physiology and pharmacology of controlled hypotension. • New monitoring techniques such as invasive arterial blood pressure monitoring. • Combination of controlled hypotension with acute normovolemic hemodilution led to enhanced blood conservation. Cushing H. Tumors of the Nervus Acusticus. (Philadelphia) 1917. Gardner WS. JAMA 132:572, 1946. Enderby GEH. Hypotensive Anaesthesia (London) 1985. Hampton LJ, Little DM. Arch Surg 67:549, 1953. Enderby GEH. Lancet 1:1145, 1950. Moraca PP, et al.Anesthesiology 23:193, 1962. Hellewell J, Potts MW. Br J Anaesth 38:794, 1966. Salem MR, Ivankovich AD. Anesth Analg 49:427, 1970. Fahmy NR. Anesthesiology 49:17, 1978. Scott DB, et al.Anaesthesia 33:145, 1978.

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