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Check for resolution of the attendant process after placement of the chest tube (e cheap 40mg propranolol with amex cardiovascular disease comorbidities. There are no strict measurements to de?ne a “normal” cardiomediastinal silhouette buy propranolol 80 mg mastercard coronary artery unroofing. Cardiomediastinal silhouette widening is relative to the patient’s body habitus purchase propranolol online now capillaries under eye circles, positioning purchase generic propranolol on line coronary artery nomenclature, and clinical picture. Look for a distinct aortic knob as an indicator that the widening may be secondary to positioning. Look for deviation of other mediastinal structures as an indicator that the aorta is enlarged and displacing adjacent tissue. Examine the mass for calci?cations, quality of the border, and air-?uid levels to narrow the di?erential diagnosis. The common etiologies of malignancy are bronchial adenoma, primary carcinoma, granuloma, hamartoma, and metastatic neoplasm. When there is a mass adjacent to a ?ssure, the ?ssure may be S shaped (E, arrows). Free air in the peritoneal cavity appears as a black stripe between the dense tissue of the diaphragm and the underlying solid organ (spleen or liver) (B, arrows). Air in the tissues around the thoracic cavity is seen as dark areas, often tracking linearly along tissue planes, interrupting the homogenously opaque appearance of normal soft tissue. Subcutaneous emphysema in the patient with penetrating thoracic trauma indicates communication of the intrathoracic cavity with the extrathoracic space and resultant pneumothorax. Air in the mediastinum (black arrows) appears as lucencies along the mediastinum that extend into the soft tissues of the neck (white arrows). The extension of the air into the neck distinguishes pneumomediastinum from pneumopericardium. Seventy percent of lung contusions are visible within 1 to 2 hours following thoracic trauma. Assess for rib fractures by following the smooth lines of the ribs and watching for interruptions. A rib series is a more sensitive view for rib fractures; however, because the di?erentiation of rib fracture from contusion is not clinically signi?cant, a rib series is rarely a necessary test. The important process to rule out when rib fractures are suspected is coincident pneumothorax and hemothorax. Acute rib fractures appear as irregularities interrupting the smooth lines of the ribs. Forty-three percent of scapular fractures are missed on the supine ?lm of a trauma patient (4). Felson B, Felson H: Localization of intrathoracic lesions by J Roentgenol 1988;151(4):747–50. These views are Indications essential in evaluating for free air and air-?uid levels within Although imaging of the abdomen is now largely performed the bowel. In many cases, the an abdominal series because the diaphragms may not be more accurate and detailed information that advanced ima- included in a large person’s upright abdominal ?lm and ging modalities provide comes at the expense of delays and because common chest pathology such as basilar pneumonia ?nancial expenditures. In addition, because physicians in or pleural e?usions can be the etiology of abdominal many locations still evaluate abdominal pain without rapid symptoms. To recognize abnormal pathol- the workup, direct supportive care, or mandate surgical inter- ogy, one must be familiar with normal radiographic ?ndings. The most common Under normal circumstances, bowel gas should invariably be indication for abdominal plain ?lm radiography is acute present in the stomach, a few non-distended loops of small abdominal pain. On an upright abdomen or circumstances, might include vomiting, nonspeci?c abdom- chest radiograph, there is almost always an air-?uid level in inal complaints, history of trauma, or unexplained fever. As the large bowel functions to remove ?uid, about only a few diseases and give indirect or nonspeci?c there should be no air-?uid levels in the colon unless the clues about a much larger number, the decision to order patient has recently taken an enema. Small bowel is distin- abdominal ?lms is subject to a variety of case- and practice- guished from large bowel by its more central location in the speci?c considerations. Case-speci?c factors include patient abdomen and by valvulae conniventes (also called plicae cir- age, altered mental status, distracting injuries, medications culares), which traverse the entire width of the small bowel (especially steroids and other immunosuppressive agents), and are closely spaced. In contrast, the plicae semilunares of and comorbid conditions (diabetes, other immunocompro- the colon are widely spaced and give rise to the characteristic mising illnesses, or those predisposing to abdominal haustral markings of that organ. The risks of complications from obstruction (ische- mia or perforation) signi?cantly increase when the small the normal plain ?lm bowel exceeds 5 cm and the cecum (the part of the colon An acute abdominal series (or “obstruction series”) of the most susceptible to perforation) exceeds 10 cm. Abnormal abdomen typically includes a supine view of the abdomen, distribution or location of bowel gas (discussed below) may be an upright view of the abdomen, and an upright view of the a clue to a pathological process. This view of the ture (the transversalis fascia), a linear lucency created by the abdomen is obtained with the patient lying supine and the properitoneal fat can be seen. It is useful in eval- following features: uniform radiodensity, well-de?ned mar- uating the overall bowel gas pattern and the presence of gins, and symmetric thickness. The upright view of the neal in?ammation causing edema in this adipose layer will abdomen is obtained with the patient standing or sitting and cause it to become relatively radiopaque, leading to loss of one the x-ray beam directed horizontally. In addition, the medial patient is unable to cooperate, a left lateral decubitus view wall of the ?ank stripe should directly abut the adjacent 55 can be obtained while the patient lies on her left side and the bowel. Dean and Ross Kessler Evaluation of solid organs and soft tissue structures in the bowel wall), the right upper quadrant sign (air outlining the abdomen is limited because of their inherent radiographic liver), the falciform ligament sign (air outlining the falciform density. The solid visceral organs (spleen, liver, and kidneys) ligament), the “inverted V sign” (air outlining the umbilical should be evaluated for their location, size, external contour, “folds” or arteries in children or the inferior epigastric vessels and abnormal densities or radiolucencies. The outline of the in adults), and the football sign (a centrally located ovoid kidneys and psoas muscles should be identi?ed and compared lucency). These structures create a silhouette similar to the For optimal horizontal beam projections, radiographic heart and diaphragm in the chest. The loss of this silhouette protocols call for the patient to be positioned (erect or decu- suggests an in?ammatory process in that location. Such collections of gas (discussed later in the chapter) or indirect conditions are seldom realized in the emergency department. Obstruction versus ileus Abnormal plain ?lm ?ndings and diagnosis Mechanical bowel obstruction can be classi?ed by location (large vs. For obstruction and ileus are dynamic processes; therefore, ?nd- that reason, it is more useful to think of the di?erential ings will vary depending on when the radiographs are diagnoses for a particular patient and consider the ways that obtained as well as the cause and location of the pathologic plain ?lm may or may not be helpful in establishing or process. Thus, the following discussion is mechanical obstruction may overlap, but obstruction can be broken into diagnoses that are expected to give rise to fairly generally distinguished based on clinical features and, radio- reliable ?ndings on plain ?lm; diagnoses for which nonspe- graphically, by a disproportionate dilatation of small bowel ci?c ?ndings are common, but speci?c ?ndings frequently compared to large bowel and by the absence of bowel gas unreliable; and diagnoses for which there are almost no indi- distal to an obstruction. Another frequent, but not invari- in situations where the pretest clinical suspicion is high. In contrast, an ileus can demon- Indications for which plain ?lms often give speci?c information strate air-?uid levels throughout the small bowel and colon Perforated viscus but typically does not demonstrate the “step laddering” the most common cause of pneumoperitoneum is the rup- appearance. This ?nding will be lost in advanced obstruction ture of an air-containing viscus.
These differences are fundamental and are among the most important characteristics to know if you use them clinically cheap propranolol 40mg mastercard arteries carry blood quizlet. Because they are so different purchase online propranolol heart disease donation, we discuss the commonly used systemic agents individually cheap 80 mg propranolol heart disease quotes. Fluconazole the introduction of fluconazole in 1990 was a breakthrough in antifungal pharmacotherapy discount generic propranolol canada cardiovascular disease heart attack. Before this, clinicians were faced with the toxicity and inconvenience of amphotericin B for serious forms of candidiasis. Though a shift toward non-albicans species of Candida has affected the use of fluconazole, it remains an important, frequently utilized agent. Mechanism of Action All azoles inhibit fungal cytochrome P450 14-alpha demethylase, inhibiting the conversion of lanosterol into ergosterol, which is a component of the fungal cell membrane. Spectrum Good: Candida albicans, Candida tropicalis, Candida parapsilosis, Candida lusitaniae, Cryptococcus neoformans, Coccidioides immitis Moderate: Candida glabrata (can be susceptible dose-dependent, or resistant) Poor: molds, many dimorphic fungi, Candida krusei Adverse Effects Though fluconazole is generally well tolerated, it can cause hepatotoxicity or rash. It has a lower propensity for serious drug interaction than many other azoles, but interactions still occur with many drugs metabolized by the cytochrome P450 system. Dosing Issues Fluconazole doses for systemic fungal infections may be escalated, particularly for the treatment of Candida glabrata infections. Be sure to adjust dosing with regard to renal function, because the drug is eliminated through the urine. Important Facts Important Facts Fluconazole is poorly active against all Candida krusei and some Candida glabrata. If you are using it for the latter infection, it is best to check susceptibilities and give 800 mg/day of fluconazole after a loading dose. If your lab does not do susceptibility testing of fungi, consider an alternative agent such as an echinocandin. Fluconazole is often given as prophylaxis against Candida infections in susceptible populations like intensive care unit patients or patients with some cancers. The high bioavailability of fluconazole makes it an excellent therapy to transition to as patients tolerate oral medications. What It’s Good For Fluconazole remains a drug of choice for many susceptible fungal infections, including invasive and noninvasive candidiasis and cryptococcal disease. Ensure that you check your patient’s isolate before committing to a definitive course of therapy with it. Itraconazole Itraconazole is a broader-spectrum azole than fluconazole that could probably have a bigger place in antifungal pharmacotherapy today if it were not for pharmacokinetic issues that have hampered its greater use. It has activity against Aspergillus and other mold species and was once commonly used as a step-down therapy in aspergillosis, but this use has declined since voriconazole became available. Mechanism of Action All azoles inhibit fungal cytochrome P450 14-alpha demethylase, inhibiting the conversion of lanosterol into ergosterol, which is a component of the fungal cell membrane. Spectrum Good: Candida albicans, Candida tropicalis, Candida parapsilosis, Candida lusitaniae, Cryptococcus neoformans, Aspergillus species, many dimorphic fungi Moderate: Candida glabrata, Candida krusei Poor: Mucorales, many other molds Adverse Effects Itraconazole’s adverse effect profile causes more concerns than that of fluconazole. In addition to causing hepatotoxicity, itraconazole is a negative ionotrope and is contraindicated in patients with heart failure. It is also a stronger inhibitor of cytochrome P450 enzymes and has a long list of drug interactions. Important Facts Itraconazole comes in two different formulations with different bioavailabilities and requirements. The capsules have lower bioavailability than the solution and are less preferred for systemic fungal infections. The oral formulations of itraconazole have different instructions with regard to taking them with meals. Capsules should always be taken with a full meal, whereas the solution should be taken on an empty stomach. Absorption can also be lowered by agents that decrease gastric acidity, such as proton-pump inhibitors; try having your patients take their itraconazole with a soda. Because itraconazole absorption is so erratic and unpredictable, concentrations are often monitored. Consider checking a trough concentration on your patient if he or she is taking it for a serious fungal infection and/or for a long time. What It’s Good For What It’s Good For Itraconazole remains a drug of choice for some dimorphic fungal infections, like histoplasmosis. It once had a larger role in the management and prophylaxis of aspergillosis and other mold infections, but it has been largely replaced by voriconazole. Watch for those drug interactions, and be sure to counsel your patients on how to take their itraconazole formulation. Voriconazole the introduction of voriconazole represented a significant improvement in the treatment of mold infections. It is also a broad-spectrum antifungal like itraconazole, with good activity against Candida species and many molds. Most importantly, voriconazole was shown to be superior to amphotericin B deoxycholate for invasive aspergillosis and has become the drug of choice for that disease. With widespread use, however, limitations in terms of highly variable pharmacokinetics and long-term adverse effects have emerged. Mechanism of Action All azoles inhibit fungal cytochrome P450 14-alpha demethylase, inhibiting the conversion of lanosterol into ergosterol, which is a component of the fungal cell membrane. Spectrum Good: Candida albicans, Candida lusitaniae, Candida parapsilosis, Candida tropicalis, Candida krusei, Cryptococcus neoformans, Aspergillus species, many other molds Moderate: Candida glabrata, Candida albicans that are fluconazole- resistant, Fusarium species Poor: Mucorales Adverse Effects Adverse Effects In addition to the hepatotoxicity, rash, and drug interactions that are common with this class, voriconazole has some agent-specific adverse effects worth watching. Renal: the cyclodextrin solubilizer that intravenous voriconazole comes in is known to accumulate in renal dysfunction. This vehicle is thought to be nephrotoxic, but it is almost certainly less nephrotoxic that amphotericin B, so the use of intravenous voriconazole with renally insufficient patients is a risk/reward equation that should be considered with each patient. Visual effects: Visual effects such as seeing wavy lines or halos around bright lights are very common and dose-related; they tend to go away with continued use. Central nervous system effects: Distinct from the common visual effects of voriconazole, patients sometimes experience visual and auditory hallucinations. These effects are not permanent and tend to occur at higher voriconazole levels (especially during peak concentration periods). Dermatologic: Voriconazole has long been known to cause sun sensitivity and patients should be advised to use sunscreen and avoid excessive sun exposure. Because voriconazole has been shown to be so useful for treating and preventing fungal infections, it has been used for durations far exceeding those studied in clinical trials. However, some studies now suggest an association between prolonged voriconazole use and certain skin cancers. Thus, it is even more essential to counsel patients on reducing sun exposure if they are taking voriconazole Dosing Issues Voriconazole has highly variable interpatient pharmacokinetics and nonlinear elimination, making it difficult to dose correctly. If you are committing your patient to an extended course of therapy for voriconazole, the standard of care has become to monitor serum drug concentrations (usually a trough level). There is no official consensus, but trough concentrations in the range of 2–5 mg/L are usually considered to be in the therapeutic window.
Because of the great variability in the position of the appendix there is not much point in trying to mark it on the surface buy 80 mg propranolol with amex coronary artery narrowing. Just remember that the average length of the appendix is 9 cm buy propranolol with a visa capillaries bruising, but it can be much shorter or longer purchase propranolol overnight arteries from aorta. The ascending colon begins at the level of the transtubercular plane (as an upward continuation of the caecum) (35 purchase 40mg propranolol fast delivery arteries feeding the heart. It ascends to a level just below the transpyloric plane, and ends at the level of the 9th right costal cartilage. It can be marked by two vertical lines, the frst drawn along the right lateral line and the second drawn 5 cm to the right of the frst line. It runs to the left, with a marked downward curve, to reach the left colic fexure. This fexure lies to the left of the left lateral line, at the level of the left 8th costal cartilage. Note that the left colic fexure is placed at a higher level than the right fexure. Between the two colic fexures, the transverse colon hangs downwards to a varying degree (as it is suspended by the transverse mesocolon) and can reach the level of the transtubercular plane or even lower. Using this information, the transverse colon can be marked using two parallel lines that are about 5 cm apart. The descending colon is somewhat narrower than the ascending or transverse colon (35. Sigm oid Colon the sigmoid colon is in the form of coils that lie predominantly in the true pelvis. It begins, as a continuation of the descending colon, just above the left inguinal ligament and descends into the true pelvis. It terminates near the middle line of the pelvis by becoming continuous with the upper end of the rectum (see below). They may not be palpable but their position is indicated by a dimple about 4 cm lateral to the second sacral spine. The parts of the lines drawn above, corresponding to the levels mentioned, enable the rectum and anal canal to be marked. The position of the liver relative to the regions of the abdomen, and to the lower ribs and costal cartilages has been described earlier. The projection of the liver can be drawn both on the anterior and posterior aspects of the trunk. This end lies just below the left nipple, in the left fifth intercostal space 9 cm from the median plane. Carry the line to the right of the middle line (with a slight upward convexity) till it reaches the place where the upper border of the right fifth costal cartilage is crossed by the right lateral line. Continue the line across the side of the thorax to the back and continue it to the inferior angle of the scapula. Finally extend the line so that it reaches the middle line at the back, at the level of the 8th thoracic spine. To mark the lower border of the liver return to the front of the trunk and go back to the left end of the superior border (i. From here draw a line running downwards and to the right so that it cuts the left costal margin over the tip of the left eighth costal cartilage. Carry the line downwards and to the right to the intersection of the transpyloric plane with the median plane. Crossing the median plane carry the line to the right costal margin which it should cut at the level of the tip of the ninth costal cartilage. Continue the line to the midaxillary line where it should lie over the tip of the tenth costal cartilage. Finally carry the line across the back of the trunk to reach the median plane (at the back) at the level of the 11th thoracic spine. Draw the lower border of the liver as described above and mark the gall bladder as a small convex area just below the border, over the place where the right linea semilunaris meets the costal margin. Take a point 5 cm above the transpyloric plane, and 2 cm to the right of the median plane. From here continue the line with an inclination to the right till it reaches the medial border of the second part of the duodenum, at about its middle. To mark the projection of the head of the pancreas, frst mark the duodenum as described above. The ‘inner’ border of the C-shaped curve of the duodenum demarcates the head of the pancreas. Continue the two lines upwards and to the left till they reach the subcostal plane. This continuation of the lines which should be about 10 cm long represents the body of the pancreas. Remember that the spleen lies on the left side of the abdomen, in contact with the posterior part of the thoracic cage. The upper border of the spleen is drawn by joining the medial and lateral ends by a line convex upwards so that its uppermost part reaches the upper border of the 9th rib. The lower border of the spleen is drawn by joining its medial and lateral ends by a line convex downwards and reaching the lower border of the 11th rib. Because of the presence of the liver on the right side, the right kidney lies slightly lower than the left kidney. The position of the kidneys relative to the anterior abdominal wall is shown in 35. The hilum of each kidney lies more or less in the transpyloric plane, a little medial to the tip of the ninth costal cartilage. Keeping in mind the points ‘a’ to ‘d’ given above the outline of the kidney can be drawn. The upper and lower boundaries of this parallelogram are formed by transverse lines drawn through the eleventh thoracic and third lumbar spines. The outline of the kidney can be drawn within the parallelogram keeping in mind points ‘a’ to ‘d’ given above. Like the marking of the kidney the abdominal part of the ureter can also be marked from the front or from the back. To mark the ureter on the front of the abdomen locate (a) the tip of the 9th costal cartilage, and (b) the pubic tubercle. A line joining these two points marks the position of the abdominal part of the ureter. Remember that the abdominal aorta lies more or less in the median plane and is about 2 cm broad. Its upper end lies in front of the lower border of vertebral body T12, and its lower end in front of L4. The lower end lies over a point about 1 cm below and to the left of the umbilicus. The aorta can be marked by drawing two vertical lines 2 cm apart between these levels. We have seen that the upper end of the abdominal aorta lies in the middle line about 2.
Intermediate acting non- depolarizing neuromuscular blocking agents and risk of postoperative respiratory complications: Prospective propensity score matched cohort study generic propranolol 80 mg amex cardiovascular disease deaths in us. Residual neuromuscular block: Lessons unlearned part 1: Defnitions propranolol 80mg low cost cardiovascular disease home remedies, incidence order cheap propranolol on-line cardiovascular journals, and adverse physiologic efects of residual neuromuscular block buy propranolol 40mg without prescription name 5 arteries. Perioperative screening for and management of patients with obstructive sleep apnoea. Preoperative assessment for obstructive sleep apnoea and the prediction of postoperative respiratory obstruction and hypoxaemia. In: Proceedings of “Essential monitoring strategies to detect clinically signifcant drug-induced respiratory depression in the postoperative period” conference. Management of sleep apnoea in adults - Functional algorithms for the perioperative period: Continuing Professional Development. Consideration for patients with obstructive sleep apnoea undergoing ambulatory surgery. Society for Ambulatory Anesthesia Consensus statement on peroperative selection of adult patients with obstructive sleep apnoea scheduled for ambulatory surgery. T e frst pacemaker implantation to electrically increase the heart rate was performed in 1958. Cardiac arrhythmia is initially treated often with drugs, but such therapy is far from perfect as there are several disadvantages of drug therapy. T is discussion will not address temporary pacing, noncardiac implantable device, and implantable cardiac mechanical assist device (e. T e letter D in the 14 Yearbook of Anesthesiology-4 third position indicates both inhibited and triggered responses (e. T e fourth and ffth positions denote programmable and anti-tachyarrhythmia functions, but these letters are infrequently used in practice, except for R (fourth position), which indicates a rate sensor (Table 2. Currently, lithium-ion batteries are being used as energy source that provide a long-durability (5–10 years) and high density energy in a small package. Electrode T is is metallic end of the lead which is in contact with the endocardium or epicardium. Unipolar Pacing In this system, there is a single electrode which is the cathode (negative pole) or active lead. Electrical impulse fows from the cathode, stimulates the heart and returns to anode (positive pole) on the casing of pulse generator via the myocardium and adjacent tissue to complete the circuit. As the current journeys through tissues other than heart, it is more likely to pick-up extracardiac signals and myopotentials. Bipolar Leads T is system consists of two separate electrodes, anode (positive pole) and cathode (negative pole); both these electrodes are located within the chamber that is being paced. T e two electrodes are very close and the signals are sharp; hence, the possibility of disturbance due to extraneous noise is signifcantly reduced. Epicardial Pacing T is type of pacing is achieved by suturing the electrode to the epicardium into the myocardium. Pacing Threshold T is is the minimum amount of energy that is required to consistently cause depolarization and therefore contraction of the heart. Pacing threshold is measured in terms of both amplitude (in volts or in milliamperes) and duration (in milliseconds) for which it is applied to the myocardium. Factors important from the anesthesia point of view, which afect the myocardial pacing threshold are listed in Table 2. R-wave Sensitivity Sensitivity is a measure of smallest voltage of intrinsic R-wave necessary to activate the sensing circuit of the pulse generator and thus inhibit or trigger the pacing circuit. Ventricular inhibited pacing is maintained with an R-wave sensitivity of about 3 mV on an external pulse generator. Very high resistance indicates fracture of the leads or impaired connection to the pacemaker. However, asynchronous pacing may compete with the patient’s intrinsic rhythm and results in induction of tachyarrhythmias. In addition, continuous asynchronous pacing depletes energy and decreases the half-life of the battery. T ere is a single pacing lead positioned in the right atrial appendage which senses the intrinsic P wave and causes inhibition or triggering of the pacemaker. In this form of pacing, the intrinsic R-wave of the ventricle is sensed the pacemaker function is inhibited. Single chamber ventricular pacing is not recommended for patients with sinus node disease, as these patients are more likely to develop the pacemaker syndrome. T e advantages of dual chamber pacemaker are that it produces efects similar to sinus rhythm and hence are benefcial in patients in whom atrial contraction is important for ventricular flling (e. T e rate responsive pacemakers are helpful as they not only sense the atrial or ventricular activity but also sense various other stimuli and thus, increase the pacemaker rate. Preoperative investigations that are carried out depend on the patient’s underlying disease(s), medication(s) and planned intervention. Interrogation of the device with a programmer reliably evaluates lead performance and obtains information of current program. A safe way to circumvent intraoperative problems is to reprogram the pacemaker appropriately especially, if monopolar electrocautery is used. If lithotripsy is planned, then consideration should be given to programming the pacing function other than an atrial paced mode, as some lithotriptors are designed to fre on the R-wave, and the atrial pacing stimulus could be misinterpreted as the contraction of the ventricle. It must be noted that electrical devices such as a nerve-stimulator may interfere with detection and display of the pacemaker spikes on the monitor. However, clinically, systolic cardiac ejections are best evaluated by pulse oximetry, plethysmography, or arterial waveform display. Arterial blood pressure monitoring either non-invasive or invasive is mandatory to assess the adequacy of tissue perfusion. Some patients might need an increased pacing rate during the preoperative period to meet an increased oxygen demand. T e choice of anesthetic technique should be decided by taking into account physical condition of the patient and surgical need. However, drugs that cause fasciculation (suxamethonium) or myoclonic movements (etomidate, ketamine) may be avoided. Transurethal resection (bladder, prostate) and uterine hysteroscopy procedures using monopolar electrocautery can be easily undertaken after device reprogramming. During nerve stimulator testing or therapy, inappropriate detection of transcutaneous electrical nerve stimulation, neuromuscular, and chiropractic electrical muscle stimulation as ventricular tachycardia or fbrillation has been reported (Table 2. If unipolar is essential, ground plate should be arranged in a path as far away as possible from pacemaker. T e pulsatile fow of blood should be monitored and the surgeon should be requested to reduce the electrocautery time; not more than 1 second bursts every 10 seconds. T e pacemaker should be programmed to asynchronous operation and if this is not possible, a magnet should be placed over the device (caution! T e cardioverter-defbrillator paddles should not be placed directly over the pulse generator and lowest possible energy shocks should be used in the event of atrial or ventricular fbrillation. Switching to an asynchronous mode may trigger ventricular arrhythmia in patients with myocardial ischemia, hypoxemia, and electrolyte imbalance.