By R. Vatras. Salisbury State University. 2019.
In the buttock and thigh of obturator internus and the gemelli discount 600mg zyvox, it it lies initially deep to gluteus maximus supplies gemellus inferior before passing lying on gemellus superior buy generic zyvox 600 mg on-line, obturator into quadratus femoris from above discount 600 mg zyvox. It passes out of the cover of gluteus from the anterior surface of the sciatic N maximus and for a short distance it is in the pelvis and leaves the pelvis through covered by only deep fascia, before it passes the greater sciatic foramen below piriformis deep to the two heads of biceps femoris. It passes runs vertically down in the midline of the medially over the ischial spine (lateral to posterior compartment of the thigh and the pudendal neurovascular bundle) and terminates by dividing into common ibular sends a branch to gemellus superior before (peroneal) and tibial Ns usually two-thirds turning forwards to pass through the lesser of the way down the thigh. In its course sciatic foramen, penetrating and supplying 6 over the gemelli, it is a close posterior obturator internus as it does so. It slopes gently medially in the lower To: Med & lat plantar Ns calf passing behind the medial malleolus of the lower tibia between the posterior tibial It arises in the lower third of the thigh artery anteromedially and the tendon of above the apex of the popliteal fossa as lexor hallucis longus posterolaterally. It the larger terminal branch of the sciatic runs under the lexor retinaculum where it N, and passes down in the midline into divides into terminal branches. Arises in the popliteal fossa, markedly lateral to the popliteal artery on passing out posteriorly over the ‘V’ behind entry to the popliteal fossa but then the the two heads of gastrocnemius and is artery crosses deep to the N to lie lateral joined by the sural communicating N from to it. The nerve leaves the fossa deep to the two It runs down laterally accompanied by the heads of gastrocnemius by passing deep to short saphenous vein to pass behind the the ibrous arch of soleus. It then runs deep lateral malleolus over the superior ibular to soleus on tibialis posterior in the midline, (peroneal) retinaculum to end in terminal crossing over the posterior tibial artery branches on the lateral side of the foot. It passes into the popliteal fossa along the upper lateral boundary just beneath It arises deep to ibularis (peroneus) the edge of biceps femoris and runs over longus and passes forwards deep to the plantaris, the lateral head of gastrocnemius muscle to wind around the ibula and to and the posterior capsule of the knee joint. It continues deep to extensor to wind around the neck of the ibula from digitorum longus to appear between it and posterior to lateral. It passes into ibularis tibialis anterior lying on the interosseous (peroneus) longus where it divides. It passes anterior to the tibia at the ankle joint between the anterior It arises deep to ibularis (peroneus) and tibial artery medially and the tendon of passes forwards and downwards to lie over extensor digitorum longus laterally, running the lateral surface of the ibula between beneath the superior and inferior extensor ibularis (peroneus) longus and brevis. It breaks up into terminal It pierces the deep fascia half way down branches on the dorsum of the foot. Its deep It arises beneath the lexor retinaculum terminal branches run medially beneath and runs forwards with the lateral plantar the long lexor tendons and across the artery around the sustentaculum tali of metatarsal shafts to end in muscular the calcaneus deep to abductor hallucis. It pierces the plantar From: Tibial N fascia in so doing and runs forwards over To: Terminal brs the tendon of lexor digitorum longus to appear more supericially again between It arises beneath the lexor retinaculum and abductor hallucis and lexor digitorum runs with the medial plantar artery around brevis in the sole of the foot. Hamstring portion: lower outer median N, its action is used as a test for quadrant of post surface of ischial this N in hand tuberosity Inserts Adductor portion: lower gluteal line & linea aspera. Short of triceps Inserts Post capsule of elbow jnt head: middle third of linea aspera, lat Action Lifts capsule away from jnt supracondylar ridge of femur Nerve Radial (C6,7,8) Inserts Styloid process of head of ibula, 8 lat collateral lig & lat tibial condyle Action Flexes & lat rotates knee. Post belly: Action Fixes perineal body & supports base of med aspect of mastoid process pelvic viscera Inserts Fibrous loop to lesser cornu of Nerve Perineal br of pudendal N (S2,3,4) hyoid bone Action Elevates hyoid bone. Ulnar head: sublime Nerve Lat plantar N (S2,3) tubercle (med border of coronoid process) & ibrous arch. Tendons of lexor Nerve Median N (C7,8,T1) (from med & digitorum longus pass through them lat cords) Action Flexes lat four toes. Lat tendon to Action Flexes distal phalanges of lat lat side of same, both via sesamoids four toes & foot at ankle. Med head: post surface of quarters into iliotibial tract (ant surface femur above med condyle of lat condyle of tibia) Inserts Tendo calcaneus to middle of three Action Extends & lat rotates hip. Maintains facets on post aspect of calcaneus knee extended via iliotibial tract Action Plantar lexes foot. Ulnar 2: cleft between rim of auditory tube tendons (bipennate) Inserts Palatine aponeurosis Inserts Extensor expansion (dorsum of Action Elevates, retracts & lat deviates prox phalanx) of ingers 2–5 radial side soft palate. Med 2: sympathetic) via pharyngeal br of vagus deep br of ulnar N (C8,T1) N (X) with its motor ibres from cranial Notes 60% have nerve supply as above. Arises Ant two-thirds of zygomatic arch & Post quarter: sup border of body of zygomatic process of maxilla hyoid bone Inserts Lat surface of angle & lower ramus Action Elevates hyoid bone, supports & of mandible raises loor of mouth. Med side of lat Arises Frontal process of maxilla pterygoid plate & fossa between med & Inserts Nasal aponeurosis lat plates. Action Clavicular head: lexes & adducts Passavant’s muscle closes nasopharyngeal arm. Arises Ant tubercles of transverse Extends hip processes of C3–6 Nerve Tibial portion of sciatic N (L5,S1,2) Inserts Scalene tubercle on sup aspect of irst rib Action Accessory to inspiration. Supericial part that make up inner layer of thoracic (downwards): lat epicondyle & lat lig of wall muscles. Others are innermost elbow & annular lig intercostals (lat) & transversus thoracis Inserts Neck & shaft of radius, between (ant) ant & post oblique lines Action Supinates forearm. Conjoint tendon Arises Post surface & muscular process of supports post wall of inguinal canal arytenoid cartilage Nerve Ant primary rami (T7–12). Joints classiied by type Articular disc can be present Fibrous joints Atypical synovial Joint cavity with Arytenocorniculate (can be synovial) synovial luid. Articular disc can be present Cuboideonavicular (can be synovial) Gomphosis (teeth) Types of synovial joint Radio-ulnar (interosseous membrane) Skull sutures Plane Sliding only Tibioibular (inferior) Hinge (ginglymus) One plane of Tibioibular (interosseous membrane) movement Modiied hinge (bicondylar) One plane of Primary cartilaginous joints movement + rotation Costochondral Condyloid (ellipsoid) Two planes of Sternochondral (irst rib) movement (circumduction) Spheno-occipital Saddle condyloid (sella) Two planes of movement + controlled rotation 9 Secondary cartilaginous joints Pivot (trochoid) Rotation only. One plane Intervertebral of movement Manubriosternal Ball and socket (spheroidal) Multi-axial. Sacrococcygeal Three planes of movement Symphysis pubis Xiphisternal Joints with interarticular Atypical synovial joints ibrocartilaginous discs Acromioclavicular Acromioclavicular (usually incomplete) Sternochondral (ribs 2–7) Femorotibial (knee) (incomplete—menisci) Sternoclavicular Radiocarpal (wrist) Temporomandibular Sternoclavicular Temporomandibular Typical synovial Acetabulofemoral (hip) Atlanto-axial (dens & facets) Atlanto-occipital Instant Anatomy, Fifth Edition. Ribs 2–10 with Type Condyloid own vertebra & one above (double Articulation Atlas with occipital bone cavity jnts separated by intra-articular lig). Talocalcaneal of inferior radio-ulnar) part (two facets) is part of subtalar jnt, 9 other being talocalcanean. Int carotid Site Between sphenoid, apex of petrous venous plexus connecting cavernous temporal & basilar occipital bones in sinus & int jugular vein middle cranial fossa Contains Int carotid art enters behind & exits above. Collectively making the spinal sphenopalatine notch of palatine bone canal (sup border of perpendicular plate & Contains Spinal cord/cauda equina, dura, orbital & sphenoidal processes). Anterior aspect of second rib Under surface of arch of aorta C1 Spinal root of accessory nerve crosses Ligamentum arteriosum transverse process of atlas Left recurrent laryngeal nerve Open mouth and dens Bifurcation of trachea Division of pulmonary trunk C2 Superior cervical ganglion Azygos vein (arch) enters superior vena cava C3 Body of hyoid bone T5 Thoracic duct crosses midline C4 Upper border of thyroid cartilage T5–8 Sternum Bifurcation of common carotid arteries T6 Upper border of liver C6 Cricoid cartilage T7 Inferior angle of scapula Larynx becomes trachea Accessory hemiazygos vein crosses Pharynx becomes oesophagus midline to azygos vein Middle cervical ganglion T8 Caval opening in diaphragm Vertebral artery enters foramen • Inferior vena cava transversarium of C6 vertebra • Right phrenic nerve Carotid tubercle of Chassaignac Left phrenic nerve pierces muscular Inferior thyroid artery crosses to diaphragm lat to central tendon thyroid gland Hemiazygos vein crosses to right to join azygos vein C7 First clearly palpable spinous process T8/9 Sternoxiphisternal joint (vertebra prominens) Stellate/inferior cervical ganglion T9 Superior epigastic vessels traverse diaphragm T2 Superior border of scapula Xiphoid T2/3 Suprasternal notch T10 Oesophageal opening in diaphragm 12 Oesophagus T3 Medial end of spine of scapula • Brs of left gastric vessels End of oblique issure of lung • Anterior and posterior vagi posteriorly at spine of T3 Instant Anatomy, Fifth Edition. Notes: (1) The thyroid gland arises from between the irst and second arch as a diverticulum (thyroglossal duct) which grows downwards leaving the foramen caecum at its origin. The head is separated from the neck with the line which begins on chin elevation – protuberantia mentalis, after that it laterally continues across the lower mandible edge, continues by the lower semicircle of outer aural meatus, goes on to the upper nuchal line, linea nuchae superior, and ends on both sides on outer elevation of occipital bone with protuberantia occipitalis externa.
Fifty to • History of sunburn sixty per cent of melanomas are ﬁrst identiﬁed as being abnormal • Family history of melanoma by patients cheap zyvox 600mg mastercard, 10–20% by spouses or relatives and the remainder by • Reducing risk from melanoma healthcare workers purchase zyvox 600mg. An American case–control study has suggested • Sun avoidance behaviour that patients who perform skin self-examination present with thin- • Avoidance of artiﬁcial ultraviolet light order 600 mg zyvox, e. Check skin regularly for: melanoma by as much as 63% compared with those who do not • Change in shape of mole perform skin self-examination. More recent data have shown that • Change in size of mole among melanoma patients who develop a further primary melano- • Change in colour of mole ma, those who perform skin self-examination present with thinner • New lesion that looks odd tumours than those who do not. Although skin self-examination has not been publicized as much as breast or testicular self-exam- that these programmes have contributed to a reduction in skin cancer ination, there appears to be sufﬁcient evidence to encourage this rates in Australians under the age of 60 years. Outside Australia, pre- in individuals at high risk of skin cancer and in patients who have liminary data show that nurse-led and media-led patient education been diagnosed with a skin cancer. More data on Referral of suspicious lesions the utility of such interventions in the generality of practice settings are needed. Access to specialist skin cancer screening clinics is ideally supported by a structured referral letter that enables general practitioners to Screening for melanoma refer patients whose skin lesions fall within the guidelines for refer- The much higher incidence of melanoma in Australia has led to ral. The relative rarity of melanoma outside Australia means that pop- New technologies may provide improved triage of patients with ulation screening is not cost-effective. For example, the use of telemedicine pro- suggest that selective screening by using practitioner- or patient- viding a live video link to clinics can improve the appropriateness administered skin cancer risk scores can identify a cohort of patients of referring patients to specialist clinics. The rationale for considering selective screening for useful where geographic access to specialist clinics is poor. Newer melanoma is the disproportionate incidence in young adults (18% technologies include image analysis, but their value and accuracy in of melanomas present in people aged 20–35years compared with early diagnosis are unclear. The role of the primary care team in the management of skin cancer 11 • Become familiar with your birthmarks, blemishes and moles so you know what they look like and can detect changes. Also look for sores that will not heal, and any growths that may be pink, red, shiny or hard. A spot lasting > 6 weeks needs diagnosing, since it is not showing signs of going away. Examine your body front and back in the mirror, then right and left sides with arms raised. Look at the backs of your legs and feet, the spaces between your toes and on the sole. Patients who perform skin self-examination present with better prognosis thinner melanoma than those who do not. All patients should be encouraged to self-examine between follow-up For patients: appointments and after discharge. The most important roles of primary and melanoma, patients should also check for recurrences in the sur- care in following up patients with skin cancer are to ensure that the rounding skin and regional lymph nodes (Box 3. This is because early patient fully understands the nature of the disease and prognosis, detection of recurrent disease may reduce the morbidity and increase how to self-examine for recurrence and for new lesions, and how to the potential for cure from subsequent treatment. This may be reinforced by directing should be demonstrated by the doctor and preferably performed every patients to appropriate internet resources (Box 3. This involves looking and feeling the skin at the site of the patients who are undergoing treatment for skin cancer is also an treated tumour, the surrounding skin and the regional lymph nodes. Impact of a multi- • Look and feel the treated area for any growths that resemble the media intervention ‘skin safe’ on patients’ knowledge and protective behav- original tumour, sores that will not heal, any thickening under the iours. And Sun Smart 1980–2000: • Report any abnormalities skin cancer control and twenty years of population-based campaigning. For patients who have had melanoma or squamous cell carcinoma: Health Educ Behav 2001; 28:290–305. Improving out- treated and the lymph glands for any growths that resemble the comes for people with skin tumours including melanoma. London: National original tumour, sores that won’t heal, any thickening under the Institute for Clinical Excellence. Effect of a public campaign about malignant melanoma on general • Feel the glands for any lumps practitioner workload in Southampton. They are caused by excessive excessive sun exposure include solar elastosis (yellowish coarse skin), exposure to ultraviolet radiation. As abnormal cells whereas ﬁeld-directed therapy is more appropriate if there are many lesions. Simi- larly, lentigo maligna is a type of in situ melanoma that is conﬁned to There are three main pre-cancerous lesions of the skin: actinic keratosis the epidermis. Dysplastic Basement membrane at the keratinocytes have breached the dermo- dermo-epidermal junction epidermal junction and invaded the dermis. Sur- rounding solar damage in the form of solar lentigines and solar elas- tosis is usually present. A wide area of solar damage is often referred to as an area of ed if lesions are symptomatic or cosmetically troublesome. Liquid nitrogen cryotherapy is the treatment of choice for le- sion-directed therapy, as it is quick and effective, with clearance rates of 70–80% (Fig. This approach has the added advantage of treating subclinical lesions which are too subtle to see with the naked eye and only become apparent because of the inﬂammatory reaction from topical agents. Sun avoidance with protective clothing and regular use of sunscreens should be encouraged in all patients, as this may promote regression of existing lesions and reduce the development of further ones. There are grey-white patches on the lower lip, loss of skin lines and blunting of the lower vermilion border. Actinic cheilitis should be referred to a specialist for treatment with cryotherapy, 5-ﬂuorouracil cream, laser ablation or vermilionectomy. Rare variants include the verrucous form, which simulates viral warts, and the pigmented form, which may be confused with melanoma. Treatment Cryotherapy or curettage and cautery are usually considered ﬁrst- line treatments for smaller lesions (Table 4. Both these approaches destroy tissue and create an area of ulceration that is left to heal by secondary intention. Destructive therapies for larger or multiple le- sions in poor healing sites such as the lower legs should be used with caution, as healing is signiﬁcantly slower. Le- in this elderly uncircumcised patient that was treated as balanitis for several sions developing on the glans penis in older uncircumcised men months despite the absence of inﬂammation. Lentigo maligna Lentigo maligna is a pre-cancerous neoplasm in which malignant melanocytes are restricted to the epidermis.
Required doses to induce cardiovascular collapse were greater for lidocaine (127 mg/kg) compared to ropivacaine (42 mg/kg) zyvox 600mg generic, levobupivacaine (27 mg/kg) trusted 600mg zyvox, and bupivacaine (22 mg/kg) generic zyvox 600 mg mastercard. Cardiac resuscitation after incremental overdosage with lidocaine, bupivacaine, levobupivacaine, and ropivacaine in anesthetized dogs. Both levobupivacaine and ropivacaine required significantly greater serum concentrations than bupivacaine. Systemic toxicity of levobupivacaine, bupivacaine, and ropivacaine during continuous intravenous infusion to nonpregnant and pregnant ewes. The central nervous system and cardiovascular effects of levobupivacaine and ropivacaine in healthy volunteers. First, bupivacaine has an inherently greater affinity for binding resting and inactivated sodium channels than lidocaine. This slow rate of dissociation prevents a complete recovery of the channels at the end of each cardiac cycle (at the physiologic heart rate of 60 to 80 beats/min), thereby leading to an accumulation and worsening of the conduction defect. In contrast, lidocaine fully dissociates from sodium channels during diastole and little accumulation of conduction delay occurs (Fig. It is widely accepted that local anesthetics bind and disrupt the normal function of the heart-specific voltage- gated sodium channel, Na 1. Local anesthetics have been shown to antagonize the currents of other cations, primarily calcium and potassium. Lastly, individuals and experimental animal models with L-carnitine deficiency exhibit an increased susceptibility to local anesthetic–associated cardiac toxicity, suggesting that local anesthetics can affect mitochondrial function and fatty acid metabolism. Sodium channels are predominantly in the resting form during diastole, open transiently during the action potential upstroke, and are in the inactive form during the 1461 action potential plateau. Block of sodium channels by bupivacaine accumulates during the action potential (systole), with recovery occurring during diastole. Recovery of sodium channels results from dissociation of bupivacaine and is time-dependent. Recovery during each diastolic interval is incomplete and results in accumulation of sodium channel block with successive heartbeats. Mechanisms for bupivacaine depression of cardiac conduction: fast block of sodium channels during the action potential with slow recovery from block during diastole. Mechanisms for bupivacaine depression of cardiac conduction: Fast block of sodium channels during the action potential with slow recovery from block during diastole. Elevated plasma levels of local anesthetics can occur by inadvertent intravascular injections or systemic absorption. The risk for intravascular injections can be reduced by using a local anesthetic test dose (about 3 mL), frequently aspirating the injectate for signs of blood return, and dividing the dose of the local anesthetics. Heart rate and rhythm, blood pressure, and oxygenation should be monitored at all times. Does local anesthetic stereoselectivity or structure predict myocardial depression in anesthetized canines? Oxygenation and ventilation should be maintained and the airway, if necessary, must be secured. This is necessary not only as a standard part of resuscitation but also to prevent further exacerbation of local anesthetic toxicity by hypoxemia, hypercapnia, and acidemia. In many cases, with91 proper airway management and reversal of acidosis, more serious complications of local anesthetic intoxication can be avoided, especially in cases involving less potent agents. Local anesthetic–induced seizure activity can vastly increase the body’s metabolism and the resultant metabolic acidosis may make resuscitation more difficult. Benzodiazepines, such as midazolam or diazepam, have been shown to raise the seizure threshold in animals and are the preferred agents for preventing and terminating seizures. Hypnotic agents, such as propofol and thiopental, may not be best suited for terminating local anesthetic–induced seizures, because at significant doses, they can potentiate the myocardial depression exerted by the causative agent. Mild myocardial depression and systemic vasodilation can be corrected with sympathomimetic agents such as ephedrine or epinephrine. Pending cardiovascular collapse from severe cardiac dysrhythmias should prompt 1463 immediate initiation of cardiopulmonary resuscitation. For ventricular fibrillation and cardiac arrest, electrocardioversion and pharmacologic means should be attempted to restore sinus rhythm. Calcium channel and β- adrenergic receptor blocking drugs can worsen myocardial function and are best avoided. Studies in animals have demonstrated efficacy of a lipid infusion in reversing bupivacaine-induced asystole. Table 22-12 Practice Advisory on Treatment of Local Anesthetic Systemic Toxicity Neural Toxicity of Local Anesthetics 1464 In addition to their systemic effects, direct application of local anesthetics can result in histopathologic changes consistent with neuronal injury. The causative mechanisms remain speculative, but studies in animals and tissue cultures show evidence of demyelination, Wallerian degeneration, dysregulation of axonal transport, disruption of the blood–nerve barrier, decreased blood flow to the vasanervorum, and loss of cell membrane integrity. Intrafascicular injections result in more histologic changes than either extrafascicular or extraneural placement, with the latter associated with the mildest damage. The use of microcatheters with a high concentration of lidocaine for continuous spinal anesthesia has been associated with an increased incidence of radiculopathy and cauda equina syndrome. These symptoms have been reported with other local anesthetics as well (Table 22-13), but have not resulted in permanent neurologic injury. However, evidence for a direct linear relation between nerve toxicity and symptoms is scant. These are regimens more effective for alleviating myofascial pain than for neuropathic pain. Myotoxicity can result from most local anesthetic agents in clinically relevant concentrations131 and manifest clinically as muscle pain and dysfunction. Histopathologic studies show hypercontracted myofibrils, followed by lytic degeneration of striated muscle sarcoplasmic reticulum, and diffuse myonecrosis (Fig. The changes are drug-specific (tetracaine and procaine produce the least injury; bupivacaine the most) and both dose- and duration-dependent,132 and seem to affect the young more than the old. A spectrum of necrobiotic changes can be encountered, ranging from slightly damaged vacuolated fibers and fibers with condensed myofibrils to entirely disintegrated and necrotic cells. Type I hypersensitivity reactions can result in anaphylaxis and potentially be life-threatening, but fortunately, the incidence is estimated to be less than 1% 1467 of all reported cases.
The initial section of this chapter discusses the biologic and pharmacologic factors that influence the absorption zyvox 600mg generic, distribution purchase 600 mg zyvox overnight delivery, and elimination of a drug from the body purchase zyvox 600mg without prescription. Where necessary, quantitative analyses of these processes are discussed to give readers insight into the intricacies of pharmacokinetics that cannot be easily described by text alone. The second section concentrates on the factors that determine the relationship between drug concentration and pharmacologic effect. Once again, mathematical models are presented as needed in order to clarify pharmacodynamic concepts. The third section applies concepts from the first two sections in order to describe the clinically important drug–drug interactions that are encountered in the perioperative period. Understanding these concepts should allow the reader to integrate the anesthetic drugs of the future into a rational anesthetic regimen. Although specific drugs are utilized to illustrate pharmacokinetic and pharmacodynamic principles throughout this chapter, the principles discussed are universal. Detailed pharmacologic information of anesthetic pharmacopeia are presented in subsequent chapters of this book. Pharmacokinetic Principles 653 Drug Absorption and Routes of Administration Transfer of Drugs across Membranes For even the simplest drug that is directly administered into the blood to exert its action, it must move across at least one cell membrane to its site of action. Because biologic membranes are lipid bilayers composed of a lipophilic core sandwiched between two hydrophilic layers, only small lipophilic drugs can passively diffuse across the membrane down their concentration gradients. In order for water-soluble drugs to passively diffuse across the membrane down its concentration gradient, transmembrane proteins that form a hydrophilic channel are required. When these transmembrane carrier proteins require energy to transport the drug across the membrane, they are able to shuttle compounds against their concentration gradients, a process called active transport. In contrast, when these carrier proteins do not require energy to shuttle drugs, they cannot overcome concentration gradients, a process called facilitated diffusion. Both active transport and facilitated diffusion of drugs are saturable processes that are primarily limited by the number of carrier proteins available to shuttle a specific drug. Conversely, lipophilic compounds can be transported6 into tissues, increasing the tissue concentration of the drug beyond what would be accomplished by passive diffusion. The degree to which transporter proteins may account for intra- and interindividual responses to anesthetic drugs has not been well studied to date. Although this can lead to rapid overshoot of the desired plasma concentration which can potentially result in immediate and severe side effects for drugs that have a low therapeutic index (the ratio of the blood concentration that produces a toxic effect in 50% of the population to the blood concentration that produces a therapeutic effect in 50% of the population). As the absorption of drug is slowed, the maximum plasma concentration achieved, and therefore the maximum drug effect achieved, is limited. However, as long as the plasma concentration is maintained at a level above the minimum effective plasma concentration, the drug will produce a drug effect. For most intravenously administered drugs, the absolute bioavailability of drug available is close to unity and the rate is nearly instantaneous. However, the pulmonary endothelium can slow the rate at which intravenously administered drugs reach the systemic circulation if distribution into the alveolar endothelium is extensive, such as occurs with the pulmonary uptake of fentanyl. The pulmonary endothelium also contains enzymes that may metabolize intravenously administered drugs (e. However, this route is not utilized significantly in anesthetic practice because of the limited and variable rate of bioavailability. The absorption rate in the gastrointestinal tract is highly variable because the main determinant of the timing of 655 absorption is gastric emptying into the small intestines, where the surface area for absorption is several orders of magnitude greater than that of the stomach or large intestines. In addition, the active metabolism of drug by the small intestine mucosal epithelium, and the obligatory path through the portal circulation before entering the systemic circulation, contribute to decreased bioavailability of orally administered drugs. In fact, the metabolic capacity13 of the liver for drugs is so high that only a small fraction of most lipophilic drugs actually reach the systemic circulation. The prolonged and variable time until peak concentrations are usually achieved from oral administration (between tens of minutes to hours), makes it impractical to utilize this mode to administer perioperative anesthetic agents. Highly lipophilic drugs that can maintain a high contact time with nasal or oral (sublingual) mucosa can be absorbed without needing to traverse the gastrointestinal tract. Sublingual administration of drug has the additional advantage over gastrointestinal absorption in that absorbed drug directly enters the systemic venous circulation and therefore is able to bypass the metabolically active intestinal mucosa and the hepatic first-pass metabolism. Therefore, small doses of drug can rapidly produce significant increases in drug plasma concentration and therapeutic effect. However, because of14 formulation limitations and the small surface area available for absorption, there are a limited number of drugs that are appropriate for sublingual administration (e. Transcutaneous Administration A few lipophilic drugs have been manufactured in formulations that are sufficient to allow penetration of intact skin. Although scopolamine, nitroglycerin, opioids, and clonidine all produce therapeutic systemic plasma concentrations when administered as “drug patches,” the extended amount of time that it takes to achieve an effective therapeutic concentration limits practical application except for maintenance therapy. Attempts to speed the passive diffusion of these drugs utilizing an electric current has been described for fentanyl, but it is still limited in its practicality. Because of the high blood flow to muscles in most physiologic states, intramuscular absorption of drugs in solution is relatively rapid and complete. Therefore, some aqueous drugs can be administered as intramuscular injection 656 with rapid and predictable effects (e. The subcutaneous route of drug absorption is more variable in its onset because of the variability of subcutaneous blood flow during varying physiologic states—this is the primary reason that subcutaneous heparin and regular insulin administered perioperatively have variable times of onset and maximum effect. Intrathecal, Epidural, and Perineural Injection Because the spinal cord is the primary site of action of many anesthetic agents, direct injection of local anesthetics and opioids into the intrathecal space bypasses the limitations of drug absorption and drug distribution of any other route of administration. This is not the case for epidural and perineural administration of local anesthetics, because not delivering the drug directly into the cerebrospinal fluid necessitates that the drug be absorbed through the dura or nerve sheath in order to reach the site of drug action. Inhalational Administration The large surface area of the pulmonary alveoli available for exchange with the large volumetric flow of blood found in the pulmonary capillaries makes inhalational administration an extremely attractive method by which to administer drugs. The relative distribution of cardiac output among organ vascular beds determines the speed at which organs are exposed to drug. The highly perfused core circulatory components—the brain, lungs, heart, and kidneys—receive the highest relative distribution of cardiac output and therefore are the initial organs to reach equilibrium with plasma drug concentrations. Drug4 concentrations then equilibrate with the less well-perfused muscles and liver and then, finally, with the relatively poorly perfused splanchnic vasculature, adipose tissue, and bone.
None of the preuse checkouts are fully automated; therefore generic zyvox 600 mg, the user must perform certain functions for the checkout to be complete zyvox 600 mg amex. It is important for the user to know what is in the automated checkout and even more important to know what is not order zyvox 600 mg overnight delivery. Figures 25-10 and 25-11 show screen shots from the Dräger Apollo workstation checkout procedures, manual and automated. A manifold-mounted vaporizer does not become a part of an anesthesia workstation’s low-pressure system until its concentration control dial is turned to the “on” position. Therefore, to detect internal vaporizer leaks in this type of a system, the “leak test” portion of the self-diagnostic must be repeated with each individual vaporizer turned to the “on” position. If this precaution is not taken, large leaks that could potentially result in patient awareness, such as those from a loose filler cap or cracked fill indicator, could go undetected. A successful automated machine checkout does not necessarily preclude machine failure. The authors concluded that a functional test of the ventilator and breathing circuit should be added to the checkout procedure. Activating the oxygen flush to inflate the bag will allow the bag 1637 to act as a model lung. Circuit pressure, tidal volume delivery, and bag inflation and deflation of the “lung” should be observed for proper function. Anesthesia Workstation Pneumatics The Anatomy of an Anesthesia Workstation A simplified diagram of a generic two-gas anesthesia machine is shown in Figure 25-6. The high-pressure circuit is confined to the cylinders and the cylinder primary pressure regulators. For oxygen, the pressure range of the high-pressure circuit extends from a high of 2,200 pounds per square inch gauge (psig) to 45 psig, which is the regulated cylinder pressure. The intermediate-pressure circuit begins at the regulated cylinder supply sources at a pressure of 45 psig, includes the pipeline sources at 50 to 55 psig and extends to the flow control valves. Depending on the manufacturer and specific machine design, second-stage pressure regulators may be used to decrease the pipeline supply pressures to the flow control valves to even lower pressures such as 14 psig or 26 psig within the intermediate-pressure circuit. Both oxygen and nitrous oxide are supplied to the workstation from two sources: a pipeline supply source and a cylinder supply source. The pipeline supply source is the primary gas source for the anesthesia workstation. The hospital pipeline supply system provides gases to the machine at 1638 approximately 50 psig, which is the normal working pressure of most machines. The cylinder supply source serves as a backup if the pipeline supply fails or acts as the primary supply if the anesthesia workstation is being used in a location without the availability of pipeline supplied gases. As previously described, the oxygen cylinder source is regulated from 2,200 psig to approximately 45 psig, and the nitrous oxide cylinder source is regulated from 745 psig to approximately 45 psig. This valve shuts off, or proportionally decreases, the supply of nitrous oxide (and other gases) if the oxygen supply pressure decreases. A high-priority alarm is actuated when a decreasing oxygen supply pressure reaches a predetermined threshold, such as 30 psig. This regulator supplies a constant pressure to the oxygen flow control valve regardless of fluctuating oxygen pipeline pressures. The flow from the oxygen flow control valve will be constant provided that its oxygen supply pressure is more than 14 psig. The oxygen and nitrous oxide flow control valves are linked mechanically or pneumatically by a proportioning system to help prevent unintended delivery of a hypoxic mixture. After leaving the flow tubes, the mixture of gases travels through a common manifold and may be directed to a concentration- calibrated vaporizer. Precise amounts of potent inhaled volatile anesthetic can be added, depending on vaporizer concentration control dial setting. Its purpose is to prevent back flow into the vaporizer during positive- pressure ventilation, therefore minimizing the effects of downstream intermittent pressure fluctuations on inhaled anesthetic concentration (see Vaporizers: Intermittent Back Pressure section). The presence or absence of this check valve profoundly influences which preoperative leak test is 1639 indicated (see Checking Your Anesthesia Workstation). The oxygen flush connection joins the mixed-gas line between the one-way check valve (when present) and the machine common gas outlet. Thus, when the oxygen flush valve is activated the pipeline oxygen flows directly to the common gas outlet at a rate of 35 to 75 L/min and potentially at a pressure of 55 psig. Pipeline Supply Source Most hospitals today have a central piping system to deliver medical gases including oxygen, nitrous oxide, air, and carbon dioxide to outlets in the operating room. The central piping system must supply the correct gases at the appropriate pressure for the anesthesia workstation to function properly. Even as recently as 2002, a large medical center with a huge cryogenic bulk oxygen storage system was not immune to component failures that contributed to a critical oxygen pipeline supply failure. In this case, a faulty joint ruptured at the41 bottom of the primary cryogenic oxygen storage tank, releasing 8,000 gallons of liquid oxygen to flood the streets in the surrounding area and compromised oxygen delivery to the medical center. In a 1976 survey of approximately 200 hospitals, 31% reported difficulties with pipeline systems. The most common problem was inadequate oxygen42 pressure, followed by excessive pipeline pressures. The most devastating reported hazard, however, was accidental crossing of oxygen and nitrous oxide pipelines, which has led to many deaths. This problem caused 23 deaths in a newly constructed wing of a general hospital in Sudbury, Ontario, during a 5-month period. These resulted from a medical gas system failure in which an altered oxygen flowmeter was connected to a wall supply source for nitrous oxide. This second step is mandatory because the machine will preferentially use the (potentially) inappropriate 50 psig pipeline supply source instead of the lower-pressure (45 psig) oxygen cylinder source if the wall supply is not disconnected. Recent publications suggest that many anesthesia providers may not appreciate the importance of or reasons for these actions. If they are “quick connect” fittings then they are gas-specific within the same manufacturer. For example, a wall oxygen outlet made by Ohmeda will not accept an oxygen connector made by Chemetron, even though the gas is the 1640 same. This can create problems if outlets and connectors by more than one manufacturer exist in the same facility. A pressure gauge measures the pipeline gas pressure when the machine is connected to a pipeline supply. It prevents reverse flow of gases from the machine to the pipeline or the atmosphere.
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Neurosurgery 2008;62:1262–1269, tive surgery and radiotherapy in the control of pituitary adenomas. Radiosurgery of growth tive in normalizing plasma insulin-like growth factor I in patients hormone-producing pituitary adenomas: factors associated with with acromegaly. Longterm followup re- for acromegaly using normalization of insulin-like growth factor I sults of postoperative radiotherapy in 36 patients with acromegaly. J Clin Endocrinol Metab 2000;85:2068–2071 J Clin Endocrinol Metab 2000;85:2476–2482 120. Int J Radiat Oncol Biol Phys 1990;32:261–270 1993;27:215–221 Cushing’s Disease 11 Charles A. Although the presence of a histologic pseudocapsule good surgical technique are the most reliable methods of around pituitary tumors was noted in the early 1900s, until achieving the optimal outcome: elimination of hypercor- recently the sequence of the stages of its development was tisolism, permanent eradication of the tumor, and preser- unexplored. In 2006 a study reported the examination of vation of pituitary function while avoiding complications. If surgery alone is unsuccessful, in almost lation to the presence of a histologic pseudocapsule were all patients hypercortisolism can be eliminated with irradi- examined. A multilayered reticulin capsule occurred in tu- ation therapy or bilateral adrenalectomy. The we frst discuss the preoperative evaluation of patients with absence of this reticulin capsule in cases of very small tu- Cushing’s syndrome, as well as the histopathologic fndings mors contributes to difculty with their identifcation dur- that form the basis of our surgical technique. When no defnite tumor is iden- I Diagnosis tifed at surgery and partial or total hypophysectomy is performed, the tissue specimen is examined using closely It is imperative to have complete and accurate diagnostic spaced sequential slices because tumors as small as 1 mm testing before surgery is considered. Salivary cortisol lev- It is important to note that pituitary adenomas compress els are also reliably used for this purpose and are well suited the immediately adjacent normal anterior lobe, producing for outpatient screening of adult and pediatric patients 109 110 Endoscopic Pituitary Surgery for hypercortisolism. For this test, The low-dose (1-mg) dexamethasone suppression test 8 mg of dexamethasone is administered orally at 11 p. The overnight test, rather than the 2-day test, obtained; suppression of morning serum cortisol of greater is the most commonly used test today. Because this is an in- Initially a wide, bloodless exposure of the sella is estab- vasive procedure with rare but serious associated risks,16 it is lished. Using a drill with a 3- to 4-mm bur, the bone cover- reserved for patients in whom the results of provocative en- ing the anterior and inferior surfaces of the sella is thinned docrine testing are conficting or equivocal and in instances to less than 0. A 2-mm Kerrison rongeur with a thin distal lip sults exist,17 these are often due to improper placement of (0. The curacy approaches 100% in patients who undergo successful bone is removed laterally until at least 2 mm of the most sampling bilaterally. Because the accuracy of the test relies medial aspect of each cavernous sinus is visible. Superiorly on successful placement of the catheter tips in the infe- bone removal extends to the tuberculum sellae. Inferiorly, rior petrosal sinuses bilaterally, venography is performed a disk dissector is used to separate gently the dura from the to confrm placement and evaluate the venous anatomy. Oozing bone margins are covered with a accuracy is only approximately 70% in patients with micro- thin layer of bone wax. Because of the very low pressure in adenomas identifed at surgery, compromising its useful- the cavernous sinus and the smaller dural veins draining ness as a localizing measure during surgery. At this I Imaging stage the operative feld should be bloodless and should ex- Magnetic resonance imaging is the imaging modality of pose the entire anterior sella dura and most of the inferior choice for detection of pituitary adenomas. Inspection of the dura reveals tecting the presence of tumors and defning their anatomy, any region of invasion of the anterior or inferior dura. In particular, the anatomy of the the pituitary gland, careful examination of the dural sur- sphenoid sinus and the parasellar anatomy, and the location face may provide clues to the site of the tumor. A curvilinear inci- defned circumferentially, the deeper adenoma margins are defned sion is made through the pituitary capsule just beyond the point at and dissected in a similar fashion (B); the posterior margin of the ad- which the most superfcial dome of the tumor reaches the surface enoma often requires dissection using a disk dissector and a small or of the gland (A, left).