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 Ultrasound is used in medicine for imaging, therapy and for measurement of blood velocity. The use of this low energy, non-ionising waveform means that ultrasound exposures are thought to be less hazardous than other imaging modalities, though mild local tissue heating occurs with absorption of ultrasound energy. Ultrasonic vibration is defined as being in the bandwidth of 20 kHz to the MHz range, above human hearing ability. An ultrasound probe or transducer consists of a piezoelectric crystal, which me­chanically generates and transmits a vibrating pressure wave in a tissue in response to an alternating electrical input (Fig 1A). Conversely, it also transduces an alternating electrical output in response to a vibrating pressure wave input from the tissue. Hence, the piezoelectric crystal can be used both to transmit a pressure wave and to detect a reflected wave (Fig 1B). The reflection of the ultrasound wave at the interface between two tissues of different densities, or at tissue-flui

 Pre-operative Management Pre-operative Assessment "People don't die of their diseases: they die of the pathophysiological effects of disease." Sir William Osler 1897. Pre-operative assessment should aim to identify risk factors which could be optimised to minimize complications, improve outcome and ensure patient safety and comfort. AIMS . Establish rapport the patient and family, and allay anxiety. Assess functional status, optimise and balance risk and benefit. Plan peri-operative management according to the risk factors. Explain all procedures, establish communication and obtain informed consent. HISTORY Vital and most informative and cannot be substituted for by investigations Age : biological age is more important than chronological age Profession, lifestyle, effort tolerance and metabolic equivalents (see page 10.1) Presenting complaint, its complications and surgery planned Current and past medical diseases, drug therapy, sepsis, allergies Coagulopathy: gum bleedi

 LOCAL ANAESTHETIC AGENTS (see page 19.23 for toxicity) Lignocaine : Low lipid solubility and potency (use 0.5-2%); low pKa 7.9 onset 5-10 min.); low protein binding 70% (duration short 30-60 min); maximum safe dose (MSD) 3 mg/kg. Vasodilates, so use with adrenaline to increase duration to 2-3h, and MSD to 7 mg/kg. Bupivacaine : High lipid solubility (use 0.1-0.5%); high pKa 8.1 (onset 10-15min): high protein binding 95% (duration 2-4h). No vasodilatation. MSD 2mg/kg. Ropivacaine : Pure 'S' enantiomer of bupivacaine, with less lipophylicity, toxicity, and motor block, and therefore most useful for nerve blocks, labour and post operative pain relief. Use 0.2%. Onset 10 min. Duration 2-6h. MSD 3-4mg/kg. PRE-OPERATIVE ASSESSMENT Similar to that of general anaesthesia but should specifically include: 1. An examination of the spine (kyphoscoliosis, skin lesions, local sepsis and fat deposition which renders landmark identification difficult) 2. Evaluation of coagulopathy and anticoa