Intraoperative bronchospasm caused by adenosine

Controlled hypotension: a guide to drug choice

For half a century, controlled hypotension has been used to reduce bleeding and the need for blood transfusions, and provide a satisfactory bloodless surgical field. It has been indicated in oromaxillofacial surgery (mandibular osteotomy, facial repair), endoscopic sinus or middle ear microsurgery, spinal surgery and other neurosurgery (aneurysm), major orthopaedic surgery (hip or knee replacement, spinal), prostatectomy, cardiovascular surgery and liver transplant surgery. Controlled hypotension is defined as a reduction of the systolic blood pressure to 80-90 mm Hg, a reduction of mean arterial pressure (MAP) to 50-65 mm Hg or a 30% reduction of baseline MAP. Pharmacological agents used for controlled hypotension include those agents that can be used successfully alone and those that are used adjunctively to limit dosage requirements and, therefore, the adverse effects of the other agents. Agents used successfully alone include inhalation anaesthetics, sodium nitroprusside, nitroglycerin, trimethaphan camsilate, alprostadil (prostaglandin E1), adenosine, remifentanil, and agents used in spinal anaesthesia. Agents that can be used alone or in combination include calcium channel antagonists (e.g. nicardipine), beta-adrenoceptor antagonists (beta-blockers) [e.g. propranolol, esmolol] and fenoldopam. Agents that are mainly used adjunctively include ACE inhibitors and clonidine. New agents and techniques have been recently evaluated for their ability to induce effective hypotension without impairing the perfusion of vital organs. This development has been aided by new knowledge on the physiology of peripheral microcirculatory regulation. Apart from the adverse effects of major hypotension on the perfusion of vital organs, potent hypotensive agents have their own adverse effects depending on their concentration, which can be reduced by adjuvant treatment. Care with use limits the major risks of these agents in controlled hypotension; risks that are generally less important than those of transfusion or alternatives to transfusion. New hypotensive drugs, such as fenoldopam, adenosine and alprostadil, are currently being evaluated; however, they have disadvantages and a high treatment cost that limits their development in this indication. New techniques of controlled hypotension subscribe to the use of the natural hypotensive effect of the anaesthetic drug with regard to the definition of the ideal hypotensive agent. It must be easy to administer, have a short onset time, an effect that disappears quickly when administration is discontinued, a rapid elimination without toxic metabolites, negligible effects on vital organs, and a predictable and dose-dependent effect. Inhalation agents (isoflurane, sevoflurane) provide the benefit of being hypnotic and hypotensive agents at clinical concentrations, and are used alone or in combination with adjuvant agents to limit tachycardia and rebound hypertension, for example, inhibitors of the autonomic nervous system (clonidine, beta-blockers) or ACE inhibitors. When they are used alone, inhalation anaesthetics require high concentrations for a significant reduction in bleeding that can lead to hepatic or renal injury. The greatest efficacy and ease-of-use to toxicity ratio is for techniques of anaesthesia that associate analgesia and hypotension at clinical concentrations without the need for potent hypotensive agents. The first and oldest technique is epidural anaesthesia, but depending on the surgery, it is not always appropriate. The most recent satisfactory technique is a combination treatment of remifentanil with either propofol or an inhalation agent (isoflurane, desflurane or sevoflurane) at clinical concentrations. In light of the current literature, and because of their safety and ease of use, these two techniques are preferred.

Effects of propofol and ketamine on ATP-induced contraction of the rat trachea

PURPOSE

ATP causes airway smooth-muscle contraction in patients with asthma and chronic obstructive pulmonary disease. Propofol and ketamine attenuate the airway smooth-muscle contraction induced by histamine and acetylcholine. However, it is not clear whether propofol and ketamine affect the ATP-induced airway smooth-muscle contraction.

METHODS

We examined the effects of propofol and ketamine on the ATP-induced contraction and ATP-P(2)-purinoceptor binding.

RESULTS

Propofol attenuated the ATP-induced contraction in a dose-dependent manner, with a 50% inhibitory concentration of 54 +/- 22 microM. Ketamine at 300 microM attenuated the ATP-induced contraction. In the binding study, propofol attenuated the binding of the P(2)-purinoceptor with [(3)H]-ATP in a dose-dependent manner, while ketamine did not attenuate this binding.

CONCLUSION

Propofol attenuates ATP-induced contraction through the inhibition of ATP-P(2)-purinoceptor binding.

Controlled hypotension in children: a critical review of available agents

Due to the potential for the transmission of infectious diseases with the homologous transfusion of blood products, there has been an increased interest in measures to limit intraoperative blood loss and avoid the need for homologous transfusion during high-risk surgical procedures including spinal surgery. Controlled hypotension (also referred to as deliberate or induced hypotension), defined as a reduction of systolic blood pressure to 80 to 90 mm Hg, a reduction of mean arterial pressure (MAP) to 50 to 65 mm Hg or a 30% reduction of baseline MAP, is one technique that has been used to limit intraoperative blood loss. In the adult population, several agents have been used alone or in combination for controlled hypotension including the inhalational anesthetic agents, direct-acting vasodilators such as nitroglycerin (glyceryl trinitrate) and nitroprusside, beta-adrenoceptor antagonists, and calcium channel antagonists. Despite clinical studies that have clearly demonstrated a reduction in blood loss with controlled hypotension when compared with the normotensive state and despite potential theoretical issues with each agent, there are no definitive studies demonstrating the preferred pharmacologic agent. When considering the pediatric-aged patient, studies have reported the use of the inhalational agent sevoflurane, the alpha(2)-adrenoceptor agonist dexmedetomidine as well as various vasodilators including sodium nitroprusside, nitroglycerin, fenoldopam, and alprostadil for controlled hypotension. Sevoflurane offers the advantages of easy dosage titration, no need for an additional intravenous infusion as well as providing anesthesia in addition to controlled hypotension. Disadvantages include a slightly higher cost than some of the intravenous agents and the inability to monitor evoked potentials with high sevoflurane concentrations. Whereas sodium nitroprusside, nicardipine and fenoldopam all provide the desired level of hypotension in pediatric-aged patients, nitroglycerin was not effective in this age group of patients in one study. When comparing nicardipine and sodium nitroprusside, nicardipine offers the potential advantages of fewer episodes of excessive hypotension, less rebound tachycardia and, in one study, less blood loss. Although fenoldopam has been shown to be effective, cost issues may limit is widespread application for this technique. The pharmacologic profile of dexmedetomidine indicates that this drug has potential in controlled hypotension and clinical data are needed to define its role.

Pharmacotherapeutic considerations in anesthesia

This article focuses on new findings leading to improved understanding of the pathophysiology and mechanisms of potential drug interactions between anesthetic drugs or techniques and cardiovascular medications in patients scheduled for surgery. Only the most frequently used drugs are reviewed. Elective surgery provides the luxury to consider these risks and alter therapy accordingly. Under urgent circumstances, however, the increased risks associated with these agents should be anticipated with the goal to minimize adverse effects while maintaining optimal cardiovascular function in the perioperative period.

Pharmacologic drugs for controlled hypotension

Due to the risks of transfusion reactions and the transmission of infectious diseases, there has been increased interest in measures to limit intraoperative blood loss and avoid the need for homologous transfusion. Controlled hypotension is one technique that has been used to limit intraoperative blood loss. Several drugs have been used alone or in combination for controlled hypotension, including the inhalational anesthetics, direct acting vasodilators such as nitroglycerin and nitroprusside, beta adrenergic antagonists, and calcium channel blockers. Various drugs available to the clinician for controlled hypotension are reviewed.