Surgery News - February 2008 - (Page 23)

F E B R U A RY 2 0 0 8 • SURGERY NEWS OPHTHALMOLOGY In Hyphema, Be Wary of Dangerous Red Cell Sickling B Y C A R O L I N E H E LW I C K Else vier Global Medical Ne ws N E W O R L E A N S — In patients with hyphema, sickling of red blood cells should be suspected, especially in African Americans and persons of Mediterranean descent, and prompt action taken to prevent vision loss. Even a small percentage of sickled cells can produce ocular hypertension, leading to secondary optic nerve atrophy and retinal artery occlusion, said Dr. Morton F. Goldberg. This condition is seen with “garden variety hyphema” caused by trauma or occurring postoperatively, Dr. Goldberg said in the inaugural Helen Keller Lecture, sponsored by the American Society of Ocular Trauma, at the annual meeting of the American Academy of Ophthalmology. The normal anterior chamber environment has lower oxygen content than that in circulating blood or in viscera, and a higher concentration of ascorbic acid. Both conditions induce and maintain sickling of red blood cells. “It is fair to conclude that aqueous humor is the most noxious fluid in the body, as far as sickling is concerned,” he noted. “And there is something very deleterious about a hyphema associated with this,” added Dr. Goldberg, an ACS Fellow and former director of the Wilmer Eye Institute, Johns Hopkins University, Baltimore, where he is the Joseph E. Green Professor of Ophthalmology. Sickled red blood cells are dangerous in the anterior chamber because they obstruct outflow of aqueous humor and lead to ocular hypertension that is disproportionately prolonged and severe, relative to nonsickling cells. In the presence of sickled cells, even mild elevations of intraocular pressure (less than 30 mm Hg, for example) can lead to irreversible optic atrophy and permanent loss of vision because vascular perfusion is already low and is easily made worse, he explained. This has been shown in vitro and in vivo and is an invariable phenomenon. In a rabbit model of hyphema, animals injected with sickled cells, compared with those who weren’t injected, had a longer duration of hyphema (10 vs. 8.6 days) and intraocular pressure elevation (3.6 vs. 1.4 days), and a higher likelihood of spontaneous rupture (P less than .05 for all three). The potential for this disaster is not limited to persons with actual sickle cell disease, but is also seen in individuals with sickle trait. “In this situation, sickle trait is just as dangerous as the systemically severe hemoglobinopathies,” Dr. Goldberg said. The sickle gene is carried by up to 10% of blacks in the United States. “In these patients, one does not usually suspect secondary optic atrophy because the optic nerve is not visible when there is a blood clot in the anterior chamber. But once the blood clot clears and one sees through the anterior chamber to the optic nerve, there comes the nasty surprise,” Dr. Goldberg explained. “This can be avoided if you always suspect sickling in the presence of hyphema.” Red blood cells preferentially sickle in the aqueous humor, while they may not be observed at all in the venous blood. This occurs because the rigid, elongated sickled cells cannot easily escape from the anterior chamber through the trabecular meshwork to enter the conventional up flow channels, he explained. Sickling is not identified via slit lamp examination, but by a routine sickle-cell solubility test, for which same-day results are available in most hospitals. Once diagnosed, patients should be hyperoxygenated with a face mask as well as with a transcorneal delivery system. They should be promptly started on standard antiglau- coma medications, including β-blockers, α-agonists, prostaglandins, osmotics (once a day only), and carbonic anhydrase inhibitors such as methazolamide (Neptazane) rather than acetazolamide (Diamox). The therapeutic goals are to avoid optic nerve ischemia, infarction, and atrophy; macular ischemia, infarction, and atrophy; and central or branch retinal artery occlusion. If these antihypertensive measures are ineffective, clinicians should follow the “24 for 24 rule”: If the average intraocular pressure is greater than 24 mm Hg for any consecutive 24 hours, intervene immediately and aggressively with paracentesis, which is usually curative, Dr. Goldberg said. “Although there are no controlled studies, validation of this therapeutic recommendation is derived from numerous reports in the literature and my personal observation. This is a routine procedure. The only caveat is to do it slowly so as not to decompress the eye,” he added. ■ TYGACIL® (tigecycline) Brief Summary See package insert for full Prescribing Information. For further product information and current package insert, please visit www.wyeth.com or call our medical communications department toll-free at 1-800-934-5556. CONTRAINDICATIONS TYGACIL is contraindicated for use in patients who have known hypersensitivity to tigecycline. WARNINGS Anaphylaxis/anaphylactoid reactions have been reported with nearly all antibacterial agents, including tigecycline, and may be life-threatening. Glycylcycline class antibiotics are structurally similar to tetracycline class antibiotics and may have similar adverse effects. TYGACIL should be administered with caution in patients with known hypersensitivity to tetracycline class antibiotics. TYGACIL may cause fetal harm when administered to a pregnant woman. If the patient becomes pregnant while taking tigecycline, the patient should be apprised of the potential hazard to the fetus. Results of animal studies indicate that tigecycline crosses the placenta and is found in fetal tissues. Decreased fetal weights in rats and rabbits (with associated delays in ossification) and fetal loss in rabbits have been observed with tigecycline. (See PRECAUTIONS, Pregnancy.) The use of TYGACIL during tooth development (last half of pregnancy, infancy, and childhood to the age of 8 years) may cause permanent discoloration of the teeth (yellow-gray-brown). Results of studies in rats with TYGACIL have shown bone discoloration. TYGACIL should not be used during tooth development unless other drugs are not likely to be effective or are contraindicated. Clostridium difficile associated diarrhea (CDAD) has been reported with use of nearly all antibacterial agents, including TYGACIL, and may range in severity from mild diarrhea to fatal colitis. Treatment with antibacterial agents alters the normal flora of the colon leading to overgrowth of C. difficile. C. difficile produces toxins A and B which contribute to the development of CDAD. Hypertoxin producing strains of C. difficile cause increased morbidity and mortality, as these infections can be refractory to antimicrobial therapy and may require colectomy. CDAD must be considered in all patients who present with diarrhea following antibiotic use. Careful medical history is necessary since CDAD has been reported to occur over two months after the administration of antibacterial agents. If CDAD is suspected or confirmed, ongoing antibiotic use not directed against C. difficile may need to be discontinued. Appropriate fluid and electrolyte management, protein supplementation, antibiotic treatment of C. difficile, and surgical evaluation should be instituted as clinically indicated. PRECAUTIONS General Caution should be exercised when considering TYGACIL monotherapy in patients with complicated intra-abdominal infections (cIAI) secondary to clinically apparent intestinal perforation. (See ADVERSE REACTIONS.) In Phase 3 cIAI studies (n=1642), 6 patients treated with TYGACIL and 2 patients treated with imipenem/cilastatin presented with intestinal perforations and developed sepsis/septic shock. The 6 patients treated with TYGACIL had higher APACHE II scores (median = 13) vs the 2 patients treated with imipenem/cilastatin (APACHE II scores = 4 and 6). Due to differences in baseline APACHE II scores between treatment groups and small overall numbers, the relationship of this outcome to treatment cannot be established. Glycylcycline class antibiotics are structurally similar to tetracycline class antibiotics and may have similar adverse effects. Such effects may include: photosensitivity, pseudotumor cerebri, and anti-anabolic action (which has led to increased BUN, azotemia, acidosis, and hyperphosphatemia). As with tetracyclines, pancreatitis has been reported with the use of TYGACIL. The safety and efficacy of TYGACIL in patients with hospital acquired pneumonia have not been established. In a study of patients with hospital acquired pneumonia, patients were randomized to receive TYGACIL (100 mg initially, then 50 mg every 12 hours) or a comparator. In addition, patients were allowed to receive specified adjunctive therapies. The sub-group of patients with ventilator-associated pneumonia who received TYGACIL had lower cure rates (47.9% versus 70.1% for the clinically evaluable population) and greater mortality (25/131 [19.1%] versus 15/122 [12.3%]) than the comparator. As with other antibacterial drugs, use of TYGACIL may result in overgrowth of non-susceptible organisms, including fungi. Patients should be carefully monitored during therapy. If superinfection occurs, appropriate measures should be taken. Prescribing TYGACIL in the absence of a proven or strongly suspected bacterial infection is unlikely to provide benefit to the patient and increases the risk of the development of drug-resistant bacteria. Information for Patients Patients should be counseled that antibacterial drugs including TYGACIL should only be used to treat bacterial infections. They do not treat viral infections (e.g., the common cold). When TYGACIL is prescribed to treat a bacterial infection, patients should be told that although it is common to feel better early in the course of therapy, the medication should be taken exactly as directed. Skipping doses or not completing the full course of therapy may (1) decrease the effectivene http://www.wyeth.com http://www.wyeth.com

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Surgery News - February 2008

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