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 INVASIVE TECHNIQUES If an artery is cannulated a direct measurement of blood pressure can be obtained with the help of an infusion system, transducer and recorder. Ideally, for arterial cannulation, a peripheral artery should be chosen so that the whole limb is not threatened if a clot or haematoma forms. Although some physicians use the brachial artery, the radial artery is usually the first choice but, before cannulation, a modified Allen test is carried out. The patient's hand is clenched into a fist and the doctor occludes both the radial and ulnar arteries with his fingers. Then the patient relaxes his clenched fist and the doctor releases the pressure on the ulnar artery. The patient's hand should then flush within 5 seconds. If flushing does not occur or is delayed, then this indicates that there are poor blood vessel collaterals between the radial and ulnar arteries and, therefore, another artery should be used. If the ulnar artery is to be cannulated the test is perfo

 Protein Binding Most drugs are bound to some extent to plasma proteins, primarily albumin, a1-acid glycoprotein, and lipoproteins.6 Most acidic drugs bind to albumin, whereas basic drugs bind to a1-acid glycoprotein. Protein binding effects both the distribution of drugs (because only the free or unbound fraction can readily cross cell membranes) and the apparent potency of drugs, again because it is the free fraction that determines the concentration of bound drug on the receptor. The extent of protein binding parallels the lipid solubility of the drug. This is because drugs that are hydrophobic are more likely to bind to proteins in the plasma and to lipids in the fat. For intravenous anesthetic drugs, which tend to be quite potent, the number of available protein binding sites in the plasma vastly exceeds the number of sites actually bound. As a result, the fraction bound is not dependent on the concentration of the anesthetic and only dependent on the protein concentration. Bindin

 Opioid Antagonists Minor changes in the structure of an opioid agonist can convert the drug into an opioid antagonist at one or more of the opioid receptor sites (Fig. 7-22).189 Th most common change is substitution of an alkyl group for a methyl group on an opioid agonist. For example, naloxone is the N-alkyl derivative of oxymorphone (see Fig. 7-21). Naloxone, naltrexone, and nalmefene are pure m opioid receptor antagonists with no agonist activity. The high affinity for opioid receptors characteristic of pure opioid antagonists results in displacement of the opioid agonist from m receptors. After this displacement, the binding of the pure antagonist does not activate m receptors and antagonism occurs.  Naloxone Naloxone is a nonselective antagonist at all three opioid receptors. Naloxone is selective when used to (a) treat opioid-induced depression of ventilation as may be present in the postoperative period, (b) treat opioid-induced depression of ventilation in the neonate due to

Diuretics, drugs commonly used in the treatment of hypertension and heart failure, consist of a group of drugs with diff ring pharmacokinetic and pharmacodynamic properties. Their primary effect is to increase urine flow and to promote diuresis. Most diuretics produce their clinical effect by blocking sodium (Na1) reabsorption in different locations of the nephron,1 resulting in increased sodium ion delivery to the distal tubules. The normal driving force for potassium (K1) excretion by distal renal tubules is the transtubular electrical potential difference created by sodium reabsorption. The presence of Na1 in the distal tubules promotes its reabsorption in exchange for secretion of K1 and results in hypokalemia. The sites of action of the different diuretics are illustrated in Figure 22-1. In general, diuretics with a site of action upstream of the collecting duct result in hyponatremia, hypokalemia, and metabolic alkalosis. In contrast, collecting duct diuretics result in hyperkale