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This is typically present in Freeman-Sheldon syndrome discount generic alavert uk allergy medicine for kids age 3, arthrogryposis multiplex congenita purchase alavert with mastercard allergy symptoms plants, and the congenital ulnar drift deformity “wind- blown” hand cheap alavert 10mg visa allergy symptoms 6 months. Note the wrist has been fused to correct severe fexion defor- a patient with cerebral palsy with a common thumb presentation of ad- mity order discount alavert online allergy medicine green pill. The thumb extensors are intrinsic muscles, most often the frst dorsal interosseous and adductor not absent as in clasp thumb but rather attenuated and weak References Associated Syndromes 1. Congenital clasped thumb (congenital Stuve-Wiedemann syndrome fexion-adduction deformity of the thumb): a syndrome, not a spe- cifc entity. Characteristics of patients with congenital clasped thumb: a prospective study of 40 pa- Waardenburg syndrome tients with the results of treatment. Complete annular and partial oblique pulley re- lease for pediatric locked trigger thumb. Treatment of spastic thumb-in-palm deformity: A modifed extensor pollicis longus tendon rerouting. X-linked mental retardation associated with Etiology The condition is caused by mutation in the gene bilateral clasp thumb anomaly. General musculoskeletal Generalized muscle spasticity but affecting more severely those of the lower extremity. However, index fnger contracture was reported [4] along with rounded shoulders and internally ro- tated arms [6]. In addition, camptodactyly involving one or more of the ulnar three digits on either or both hands may be seen (. Stüve-Wiedemann syndrome and re- Hallmarks Hyperthermia, respiratory abnormalities, short lated bent bone dysplasias. Clinical ho- a frst-cousin male with congenital bowing of the long bones mogeneity of the Stuve-Wiedemann syndrome and overlap with the and digital contractures. Stuve-Wiedemann syn- drome: a skeletal dysplasia characterized by bowed long bones. Ul- Etiology The condition results from autosomal recessive mu- trasound Obstet Gynecol. General musculoskeletal Postnatal short stature is common [6,7] along with long bone dysplasia, which leads to curvature or bowing of bones [3]. Multiple muscle and joint contrac- tures, [3] muscle hypotonia, and osteoporosis may be present. Upper extremity Camptodactyly seems to be the most com- mon hand anomaly followed by multiple digital fexion defor- mity of all the small joints in the hand including the thumb. Frontal bossing, midface hypoplasia, short nose, low-set ears, and micrognathia are also seen. Systemic Cardiac anomalies mostly in the form of premature closure of the ductus arteriosus. Bell was initially described by Fort, [1] as digital deviation in any [6] also described an entity consisting of brachyphalangy of direction. The condition may affect any digit including the all fngers and proximal phalanx of the thumb, which is clas- thumb, and may be encountered in the index or middle fnger sifed as Bell’s A-1 brachydactyly. The middle it is defned as an angular deformity of the small fnger in phalanx is the most commonly involved because it is the last the coronal plane i. When the thumb is affected the tip shifts radial epiphysis spanning the short side of a phalanx [8]. When the deviation of the thumb C-shaped epiphysis that spans the short side of the diaphysis, is ulnar, there is usually associated radial polydactyly and/ which is responsible for the abnormal growth of this bone, or triphalangeal thumb. All variations of clinodactyly ex- and they used the term longitudinally bracketed diaphysis. The distal phalanx is usually not affected ulnar plane is related to the underlying skeletal or soft tissue in clinodactyly but there is secondary angular deformity at cause (. Progressive angulation of the Clinodactyly occurs in 1 % of normal newborns and 10 % distal phalanx at the distal interphalangeal joint is expected es- of abnormal newborns. Ten degrees of deviation does history with an autosomal dominant pattern of inheritance not cause any functional problems for these patients whereas and variable penetrance, [2,4] but it can be sporadic in na- deviation in excess of 20 degrees in the fnger or thumb may ture. There can be a correlation with mental differences when present a functional problem. On physical examination both clinodactyly is part of a syndrome; up to 79% of children rotation and deviation deformities of the digits are magnifed with the Down syndrome have clinodactyly of the ffth digit. Bilateral involvement is common and males slightly outnum- Because of its ubiquitous nature in congenital hand anom- ber females. The anomalous middle phalanx leads to digital devia- polydactyly and the typical cleft hand all have these anoma- tion because of its abnormal shape, which is also known as lous bones. From left to tyly are encountered among congenital hand patients and the anatomic right are (1) a two-fngered hand with radial deviation of the thumb and confguration of the skeletal parts and growth plates seen on radio- ulnar deviation of the ulnar ray, (2) a ffth digit containing a continu- graphs presents almost limitless variation. Multiple family c The same straight digits 26 years later (With kind permission from members had the same deformity with no other associated anomalies. Note the poorly developed distal fexion crease vere cant of the distal articular surface. With severe clinodactyly there is invariably a rotational is an important indicator of other underlying malformations component to the deformed digit or thumb, which is usually and has been described by Poznanski [5] to be associated with exaggerated in fexion (. We found clinodactyly to be associated Clinodactyly is frequently associated with other muscu- with more than 65 syndromes hence it has one of the greatest loskeletal anomalies including syndactyly, polydactyly, cleft numbers of associated syndromes compared to other congeni- hand, triphalangeal thumb, and symphalangism. The latter has no motion as diographs show clinodactyly of index and ffth digits of both hands. The deformity are seen in triphalangeal thumb deformities and from Kirner may be encountered with syndromes including Turner, Down, deformity. The nail has a parrot’s beak deformity due to its lack of dorsal cor- tical support. Kirner deformity is more common among females and there may be 27 Clinodactyly 357 References 1. Longitudinally bracketed diaphysis in young children: radiologic-histopathologic correlations. Doppelseitige Verkrümmung des Kleinfngergrundgliedes als selbständiges Krankheitsbild. The dorsal nail plate has a spoon shaped appearance and palmar pulp is markedly defcient. Radiographs show hypoplasia of the middle Hallmarks Peculiar facies, intrauterine growth retardation, phalanx of the ffth ray, but may also reveal undergrowth of low birth weight, growth retardation, and ffth digit clinod- other phalanges, delayed carpal ossifcation, or negative ul- actyly. They described within several years of life and their clinodactyly rarely re- small-for-gestational-age children whose pregnancies had quires surgical correction (. Parental consanguinity and affected siblings of both genders Craniofacial A triangular-shaped face is a very common de- were strongly suggested to have an autosomal recessive in- formity.

Sommer Rathbun Battles syndrome

Apart from these three main categories generic alavert 10 mg with mastercard allergy eye drops for dogs, various other schemes are also used effective alavert 10 mg allergy treatment delhi, since individualization is a basic rule in insulin therapy cheap alavert 10mg overnight delivery allergy symptoms 3 days. Moreover best purchase alavert allergy shots birth control, particularly in very obese patients with high insulin needs, schemes with three injections of insulin mixtures (usually 30/70 or 40/60) have also been tried before each meal. As already mentioned, the initial regimen of insulin therapy in these individuals is determined after many factors have been appreciated, the most important of which are the age and intellectual situation of the individual (ability to respond to the requirements of complicated schemes), possible coexisting diseases and preceding glucose control. A general rule is that the bigger the disturbance of insulin secretory ability, the more complicated are the schemes required to achieve the objectives. A lot of studies have shown that these schemes are superior compared to insulin therapy alone, both for the achieved HbA1c, as well as for the appearance of hypoglycaemias, the increase of weight and also – particularly important – the acceptance of the treatment by the patients. A very recent study showed that the initiation of insulin therapy with two injections of insulin mixtures of very-rapid/ intermediate acting insulin 30/70 (in combination with metformin) led to better control compared to an injection of insulin at bedtime (again in combination with metformin). Ultimately, the most important thing is glycaemic control and achieve- ment of the targets set by the doctor and the patient; the question of which means (which particular scheme) is selected to achieve this, is of course less important. Any one of the intermediate- or slow-acting insulins can be administered, in one dose, before bedtime. Studies conducted in the past few years showed that the insulin Glargine causes fewer night-time hypoglycae- mias, improves fasting plasma glucose and causes a slightly smaller weight gain compared to isophane insulin. Moreover, Glargine can be adminis- tered in the morning, after rising, with the same results. If the desirable metabolic control with the combination of an evening insulin injection and metformin is not achieved, a sulfonylurea can be added. Some authors recommend maintenance with the sulfonylurea (toge- ther with metformin) from the beginning, when evening insulin is added. The combination of insulin with a sulfonylurea decreases the insulin needs and limits (to a smaller degree than metformin) the increase of body weight. The combination of insulin with meglitinides has not been tried in clinical studies. The coadministration of insulin with glitazones is expected to be approved soon in the European Union. The choice of the most suitable mixture, but also the dosage of insulin, depends on many factors, including the age of the patient, his or her nutritional programme, his or her physical activity, renal and hepatic function, etc. The most ‘popular’ mixtures are those that contain 30 percent rapid or very rapid-acting insulin and 70 percent intermediate- acting insulin (Figure 28. Usually, 2/3 of the total dose are given in the morning and 1/3 in the evening, pre-prandially (30–45 minutes before the meal) if the mixture contains regular insulin or immediately before the meal if it contains a very rapid-acting insulin analogue. However, the proportion of morning/evening dose varies considerably among patients. In certain cases the administration of a different mixture in the morning and in the evening may be required. The onset of the treatment is done with the lowest dose in order to achieve metabolic control progressively and to avoid possible Treatment of diabetes with insulin 391 Figure 28. Schematic representation of a therapeutic scheme with administration of a) mixture of insulin (30% regular insulin, 70% intermediate acting insulin) in the morning and evening pre-prandially and b) mixture insulin of (30% very-rapid-acting insulin analogue, 70% intermediate acting insulin analogue) in the morning and evening pre-prandially. Notice the smaller overlaps among the insulins in scheme b) where there is usually no need for intake of additional snacks in between. The schemes with two injections of premixed insulin compounds are widely used because they are relatively simple and practical. However, 392 Diabetes in Clinical Practice in order for the blood sugar to get under control, the daily programme of the patients should be relatively stable, with only small divergences from day to day as regards the timing and content of meals and the level of physical activity. Patients who receive an insulin mixture that contains regular insulin in the morning, should usually eat a snack 2–3 hours after the injection to avoid hypoglycaemias (see Figure 28. At the same time, lunch should be temporally placed when the peak of the morning intermediate-acting insulin begins (i. The administration of an insulin mixture in the evening before dinner, leads sometimes to night-time hypoglycaemia, especially if the dinner is consumed early, whereby the peak of the intermediate-acting insulin coincides with the early morning hours (1–3 a. This is avoided either by instructing the patients to receive a small quantity of carbohydrates (for example, a glass of milk with a rusk) before bedtime (if at that time the blood glucose level is < 140 mg/dl [7. This is due to the shorter duration of action of the analogue which leads to only a small degree of overlap with the intermediate-acting insulin. On the other hand, the administration of these mixtures presupposes the reception of a large breakfast, and sometimes they do not sufficiently cover the lunch needs, resulting in post-prandial hyperglycaemia. The latter is corrected by administering one dose of very rapid-acting insulin pre-prandially. Even if some of them could ultimately familiarize themselves, very few would accept injecting insulin 4–5 times daily. He has now come to the Diabetes Clinic to receive advice from specialists in the care of diabetes. The patient had had the typical symptoms of hyperglycaemia for roughly 3–4 months before the diagnosis. The concept of an intensive insulin regimen of basal-bolus insulin was explicitly explained to them. They had extensive discussions with a dietitian so that the elements of a right diet could be analyzed but also so patient could be informed about the carbohydrate equivalents. The need of self-monitoring of blood glucose at home with a portable glucose meter was stressed to the patient and the technique of measurement was explained to him. It is explicit that in the first visit it is impossible for the patient to consolidate all this overwhelming new information, especially since he is under intense psychological stress because of the recent diagnosis of his disease. If feasible, discussion with a psychologist specialized in the subject is often very beneficial. As already mentioned, from the very first visit the patient was informed about the advantages, but also the requirements, of an intensified insulin regimen. Moreover, a very-rapid-acting insulin analogue was 394 Diabetes in Clinical Practice prescribed, with instructions to inject a few units (2–5, depending on the blood sugar levels) before lunch. The fact that significant insulin resis- tance coexisted (because of the recent ketoacidosis) as well as gluco- toxicity (because of the prolonged and intense hyperglycaemia that preceded the diagnosis) was taken into consideration. At the follow-up, the patient brought the blood sugar measurements shown in the following table (the last four days are shown [in mg/dl (mmol/L)]): Breakfast Lunch Dinner Date Pre 2 hrs Pre 2 hrs Pre 2 hrs Bedtime 24/1 278 314 294 221 298 301 265 (15. As the patient moves away from the episode of ketoacidosis and the glucotoxicity is removed, he will very probably enter the honeymoon period, during which insulin needs decrease significantly. At the second visit, new extensive discussion took place, focused on the resolution of various queries of the patient. It was decided to start him on Glargine (basal insulin) before bedtime and a very-rapid acting insulin analogue (Lispro or Aspart) before each main meal. The dose of Glargine was calculated by dividing the total number of insulin units administered up to now by two: 20 ðin the morningÞþ14 ðin the eveningÞ þ 4 ðon average middayÞ¼38=2 ¼ 19 units: Treatment of diabetes with insulin 395 Another method of calculation is to subtract from the total intermediate/ slowly acting dose of insulin what the patient was receiving (in this case): 34 Â 70% ¼ 23:8 units À 20% ðthat is : 23:8 À 4:76 ¼ 19 unitsÞ: The patient’s diet usually included 4–5 carbohydrate equivalents (bread) in the morning, 6–8 at lunch and 4–6 in the evening. He also receives a snack between breakfast and lunch time, which contains three carbohy- drate equivalents. Thus, the remainding 17 units of insulin (that are intended for the 18–21 carbohydrate equivalents) were dis- tributed first as one unit per equivalent.

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A 24- hour urine for sulfonylurea levels is obtained to rule out the use of oral hypoglycemic drugs cheap alavert 10 mg line allergy testing san francisco. At the Diagnosis and Recommendation start of the fast buy alavert visa zofran allergy symptoms, a venous catheter is placed to al- The findings are diagnostic of insulinoma purchase 10 mg alavert overnight delivery allergy testing johns hopkins. Manage- low administration of dextrose-50 if hypoglycemic ment of the hypoglycemia and localization of the symptoms occur purchase genuine alavert allergy symptoms everyday. As the test continues, serum levels of glucose and insulin are measured every 6 hours. If ■ Approach the patient develops confusion, slurred speech, al- tered mental status, or inability to answer simple The next step is to maintain normal blood glucose questions, then serum levels of glucose, insulin, C- levels by asking the patient to set the alarm clock at peptide, and proinsulin are measured and an am- night to awaken from sleep and eat a snack. It is best poule of D-50 is administered to see if the neuro- to mix cornstarch with some of the food so that glycopenic symptoms resolve. Patients with slower absorption of carbohydrates will allow less 350 Case 77 351 frequent feeding. Insulinomas vascular insulinoma within the head of the pancreas are generally small (<2 cm), benign, and located (T). Endoscopic ul- trasound is performed by gastroenterology, and the tumor is imaged by a high-resolution transducer that is placed in the stomach for the body and tail and in the duodenum for the head of the pancreas. This study is supposed to have a high sensitivity and specificity, but it is very observer dependent, and false-positive and false-negative results may occur. A standard angiogram is performed to determine the arteries that perfuse the various sections of the pancreas (head, body, and tail). During the angiogram, 60% of the time the insulinoma will be imaged as a blush in the pan- creas. Calcium is injected sequentially into the dif- ferent pancreatic arteries and insulin levels are measured in the hepatic vein. When the area of the pancreas with the insulinoma is injected with calcium, the insulin levels in the hepatic vein in- crease within seconds following the injection. If no tumor is clearly iden- tified at surgery, the region with the step-up can be removed. Insulinoma is diag- nosed by a 72-hour fast with the development of neuroglycopenic symptoms. Close supervi- sion is necessary to exclude factitious hypo- glycemia, which is the use of medications to falsely decrease blood glucose levels. After the diagnosis of insulinoma is made based on the results of the fast, localization studies are used to try to image and identify the tumor. It can image all large tumors (>2 cm) and it images approximately 50% of tumors as small as 1 Figure 77. Somatostatin receptor scintigra- phy is the imaging study of choice for all pancreatic neuroendocrine tumors except insulinomas. Endo- scopic ultrasound is able to identify most insulino- Intraoperative Ultrasonography Report mas, and identifies more of them preoperatively On intraoperative ultrasound of the insulinoma, than all other studies. It is sonolucent on have false-positive results that lead to misguidance ultrasound compared with the more echo-dense of the surgery. Speci- ficity of endoscopic ultrasound can be improved by needle biopsy that is used for pancreatic tumors and lymph nodes. In a study of 18 consecutive patients, creas are identical to that described for gastrinoma, this combination identified an insulinoma in each except insulinomas are always within the pancreas patient. The major breakthrough during surgery is the shown to localize most (>90%) insulinomas. Similar use of intraoperative ultrasound that identifies the studies have been done with secretin injection for tumor and guides the enucleation. However, recently calcium angiogram tumors are generally small and benign, the tumor has been shown to effectively localize most gastri- should be enucleated, preserving as much pancreas nomas as well. Sometimes the tail Because insulinomas are generally benign and of the pancreas and spleen must be removed if the located within the pancreas, the goal of surgery is to tumor is near the pancreatic duct. Blind subtotal precisely identify the tumor and remove it while pancreatectomy should be avoided. Intraopera- tive identification with ultrasound will facilitate tive ultrasound has been useful for precise operative excision and allow the safest route to avoid injury localization. Well-localized tionship to vital structures like the common bile tumors like the one imaged here may be able to be duct and the pancreatic duct. It allows the surgeon removed by laparoscopic techniques using laparo- to decide the best way to remove the tumor and scopic ultrasound to guide the procedure. Further, modern methods have allowed laparoscopic enucleation of insulino- mas based on laparoscopic ultrasound done during Discussion the surgery. If it can be done, this procedure results Insulinomas occur in the pancreas and are evenly in less pain and a more rapid recovery. Insuli- similar complications, like pancreatic fistula and ab- nomas are most often benign, but 5% to 10% of scess, may occur with laparoscopic pancreatic opera- Case 77 353 tions and must be considered. Because of this fact, and a combined protocol for preoperative evaluation of pan- creatic insulinomas. Intraoperative ultra- sulinoma has not been dramatically different than sound and preoperative localization detects all occult insuli- open operations. Localization of gastrinomas scopic pancreatic surgery: endocrine and nonendocrine tu- by selective intra-arterial calcium injection. The diagnosis of medul- Presentation: Case 78A lary carcinoma of the thyroid should be rare, but A 25-year-old woman who is a medical student pres- needs to be considered, and obtaining a careful fam- ents with a history of routine physical examination ily history is crucial. Metastatic tumors to physical examination reveals a well-defined mass the thyroid at this age are extremely rare and need involving the right lobe of the thyroid. However, in a young woman examination of the neck does not reveal any suspi- with a solitary thyroid nodule that is firm, the most cious lymphadenopathy. Examination of the oral important diagnosis is to exclude papillary carcino- cavity, larynx, and pharynx is within normal limits. There is no A variety of diagnostic tests are available in this past history of thyroid disease or history of radiation patient including blood studies, imaging studies, and as a child. The question is not what is available, thyroid-related problem or thyroid cancer in the but what is necessary. The patient does not give any history of radi- tic study in this patient is fine-needle aspiration ation to the neck as a child. In a patient who presents with a well-defined solitary thyroid nodule, a fine-needle aspiration biopsy would be the first diagnostic study. The accu- racy of fine-needle aspiration biopsy is over 95% and Differential Diagnosis it can be reliably used in the evaluation and man- agement of this patient. This young female patient presents with a mass in the thyroid, which measures approximately 2.

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Pulmonary perfusion E ff ects on the Respiratory Pattern Pulmonary emboli ↑ Hypotension ↑ Regardless of the agent used discount alavert 10 mg amex allergy shots refrigeration, light anesthesia ofen results in irregular breathing patterns; breath hold- Pulmonary vascular disease ing is common buy alavert with paypal allergy shots large local reaction. Inhalation agents generally pro- duce rapid buy alavert australia allergy medicine pregnancy category, shallow breaths generic 10 mg alavert with mastercard allergy testing gold coast, whereas nitrous–opioid techniques result in slow, deep breaths. Dead space Ventilation is usually measured as the sum of all can be afected by a variety of factors (Table 23–3). Tis ratio can be derived by the Bohr equation: Minute ventilation = Respiratory rate × Tidal volume Vd Paco2 − Peco2 For the average adulThat rest, minute ventilation = Vt Paco2 is about 5 L/min. Terefore, even with a normal inspiratory (becomes less negative) per 3-cm decrease in lung time, abnormalities in either compliance or resistance height. Because of a higher Time Constants transpulmonary pressure, alveoli in upper lung areas Lung infation can be described mathematically by are near-maximally infated and relatively noncom- the time constant, τ. In contrast, the smaller alveoli in depen- dent areas have a lower transpulmonary pressure, Regional variations in resistance or compliance are more compliant, and undergo greater expansion not only interfere with alveolar flling but can cause during inspiration. In reality, inspira- lung can be demonstrated in normal individuals tory time is necessarily limited by the respiratory rate breathing spontaneously during abnormally high and the time necessary for expiration; consequently, respiratory rates. Hypercapnia and acidosis have a constrictor efect, whereas hypocapnia causes pulmonary vaso- 2. Pulmonary Perfusion dilation, the opposite of what occurs in the systemic circulation. Of the approximately 5 L/min of blood fowing through the lungs, only about 70–100 mL at any one time are within the pulmonary capillaries undergo- Distribution of Pulmonary ing gas exchange. At the alveolar–capillary mem- Perfusion brane, this small volume forms a 50–100 m -sheet of2 Pulmonary blood fow is also not uniform. Moreover, to Regardless of body position, lower (dependent) areas ensure optimal gas exchange, each capillary perfuses of the lung receive greater blood fow than upper more than one alveolus. Tis pattern is the result of a Although capillary volume remains relatively gravitational gradient of 1 cm H2O/cm lung height. Large increases in lation allow gravity to exert a signifcant infuence either cardiac output or blood volume are tolerated on blood fow. Also, in vivo perfusion scanning in with little change in pressure as a result of passive normal individuals has shown an “onion-like” layer- dilation of open vessels and perhaps some recruit- ing distribution of perfusion, with reduced fow at ment of collapsed pulmonary vessels. Small the periphery of the lung and increased perfusion increases in pulmonary blood volume normally toward the hilum. A shif in posture from not uniform across the lung, the alveolar distending supine to erect decreases pulmonary blood volume pressure is relatively constant. The interplay of these (up to 27%); Trendelenburg positioning has the pressures results in the dividing of the lung into four opposite efect. Changes in systemic capacitance distinct zones (ie, the West Zones) (Figure 23–15 ). In in obstruction of blood fow and creation of alveolar this way, the lung acts as a reservoir for the systemic dead space. In lower areas of the lungs, Pa 7 autonomic system in infuencing pulmonary progressively increases due to lower elevation above vascular tone (above). In zone 2 (Pa > P a > Pv), Pa is higher lus for pulmonary vasoconstriction (the opposite of than Pa, but Pv remains lower than both, resulting its systemic efect). Both pulmonary arterial (mixed in blood fow that is dependent on the diferential venous) and alveolar hypoxia induce vasoconstric- between Pa and Pa. The bulk of the lung is described tion, but the latter is a more powerful stimulus. Tis by zone 3 (Pa > Pv > Pa), where both Pa and Pv are response seems to be due to either the direct efect of higher than Pa, resulting in blood fow independent hypoxia on the pulmonary vasculature or increased of the alveolar pressure. Zone 4, the most dependent production of leukotrienes relative to vasodilatory part of the lung, is where atelectasis and/or intersti- prostaglandins. Inhibition of nitric oxide production tial pulmonary edema occur, resulting in blood fow may also play a role. Hypoxic pulmonary vasocon- that is dependent on the diferential between Pa and striction is an important physiological mechanism pulmonary interstitial pressure. V/Q for individual lung units (each alveolus and increase in alveolar ventilation. An appreciable com- its capillary) can range from 0 (no ventilation) to pensatory increase in O2 uptake cannot take place infnity (no perfusion); the former is referred to as in remaining areas where V/Q is normal, because intrapulmonary shunt, whereas the latter constitutes • pulmonary end-capillary blood is usually already alveolar dead space. Because perfusion increases at a greater rate than ventilation, nonde- • pendent (apical) areas tend to have higher V/Q ratios 3. Absolute shunt refers to ana- with the law for the conservation of mass for O • 2 tomic shunts and lung units where V/Q is zero. A across the pulmonary bed: • relative shunt is an area of the lung with a low V/Q ratio. Clinically, hypoxemia from a relative shunt Qt × Cao2= (Qs × Cvo2) + (Qc´× C c´o 2) can usually be partially corrected by increasing the where inspired O2 concentration; hypoxemia caused by an absolute shunt cannot. Qs = blood fow through the physiologic shunt compartment Venous Admixture Qt = total cardiac output Qc´& = blood fow across normally ventilated Venous admixture refers to a concept rather than an actual physiological entity. Venous admixture is pulmonary capillaries the amount of mixed venous blood that would have Qt& = Qc´& + Qs& to be mixed with pulmonary end-capillary blood to Cc´o2 = oxygen content of ideal pulmonary account for the diference in O2 tension between arte- end-capillary blood rial and pulmonary end-capillary blood. Normal • Qs/Qt is primarily due to communication between • C c´o 2 − Cao2 Qs/Qt = deep bronchial veins and pulmonary veins, the the- C c´o − Cvo 2 2 besian circulation in the heart, and areas of low V/Q in the lungs (Figure 23–18). The venous admixture The formula for calculating the O2 content of in normal individuals (physiological shunt) is typi- blood is given below. Qs/Qt can be calculated clinically by obtaining mixed venous and arterial blood gas measurements; 4. The alveolar gas equation is used to derive pulmo- on Gas Exchange nary end-capillary O2 tension. Pulmonary capillary Abnormalities in gas exchange during anesthesia are blood is usually assumed to be 100% saturated for common. General admixture and preventing hypoxemia during gen- 10 anesthesia commonly increases venous admix- eral anesthesia, as long as cardiac output is main- ture to 5% to 10%, probably as a result of atelectasis tained Prolonged administration of high inspired and airway collapse in dependent areas of the lung. O2 concentrations may be associated with atelecta- Inhalation agents, including nitrous oxide, also can sis formation and increases in absolute shunt. Elderly ratio ventilated at an O - inspired concentration • 2 patients seem to have the largest increases in Qs/Qt. Perfusion results in O being trans- 2 Inspired O2 tensions of 30% to 40% usually prevent ported out of the alveoli at a rate faster than it hypoxemia, suggesting anesthesia increases relative enters the alveoli, leading to an emptying of the shunt. Note that large barometric pressure is 760 mm Hg (sea level), the 11 increases in Paco2 ( >75 mm Hg) readily pro- partial pressure of O (P o 2 2) in air is normally 159. Pio2 = Pb × Fio2 Pulmonary End-Capillary where P b = barometric pressure and Fio2 = the frac- Oxygen Tension tion of inspired O. Enhanced O 2 2 binding to hemoglobin at saturations above 80% Alveolar Oxygen Tension also augments O difusion (see below). Capillary 2 With every breath, the inspired gas mixture is transit time can be estimated by dividing pulmonary humidifed at 37°C in the upper airway. The inspired capillary blood volume by cardiac output (pulmo- tension of O2 ( P i o 2) is therefore reduced by the nary blood fow); thus, normal capillary transit time added water vapor. Maximum Pc′ o 2 is dent only upon temperature and is 47 mm Hg at usually attained afer only 0.