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The Anaesthesia Science Viva Book - part 9

Radial động mạch cẳng tay xa động mạch xuyên tâm nằm giữa flexor carpi radialis và brachioradialis. Các dây chằng của các cơ bắp bao gồm các điểm mốc giữa động mạch palpated ở cổ tay. - Ngoài những xung xuyên tâm, động mạch cung cấp một chi nhánh góp phần lòng bàn tay trên bề mặt kiến trúc. | CHAPTER 5 Electrical safety Commentary Patients are in general well protected from electrical danger and so for most anaesthetists this topic will remain only theoretical. Electricity does appear as a subject but its main application apart from biological potentials relates to safety. This by itself barely constitutes a full question unless it is extended by a discussion of the grades of equipment protection which can happen and so the viva may start with an outline of basic concepts which seem a bit disparate and haphazard. Basic knowledge and an understanding of how potential dangers can arise will be sufficient to allow you to pass. The viva You will be asked about the electrical risks to patients and how they are minimised but as a prelude to this discussion you may be asked to define some basic electrical terms. Electricity This is the flow of electrons which is driven by potential difference the voltage through a conductor past a given point per unit time. This current is measured in amperes. Resistance This is the resistance along a conductor to the flow of current. It is not frequency dependent. Resistance is measured in ohms. Ohm s law This states that the electrical potential V current I X resistance R . Impedance The impedance is the sum of all the forces impeding electron flow in an AC circuit. Unlike resistance it is dependent upon frequency and includes resistors capacitors and inductors. Insulators are high-impedance devices conductors are low-impedance devices. Impedance through capacitors and inductors is related to the frequency at which AC reverses direction. Impedance is also measured in ohms volt ampere . Direction the viva may take You will be asked how this relates to patient safety. Effects of electricity These can be summarised as follows at 1 mA a subject will feel tingling and at 5 mA definite pain. At 15 mA there will be tonic contraction of muscles which at 50 mA will involve all the muscles of respiration. At 100 mA VF will supervene.