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Hydrocolloids, such as karaya compounds, offer the primary advantage of increased absorptive ability
Correct.
Although the simplest dressing of gauze and tape combined with the use of antibacterial ointment can achieve moist wound healing for most patients, a multitude of other products are available. These products can be classified into films, foams, hydrocolloids, hydrogels, and absorptive powders. Films are semipermeable to water, generally made of polyurethane, and nonabsorptive. They are useful to achieve a moist wound-healing environment over a minimally exudative wound such as split-thickness skin graft donor sites. The hydrocolloids deserve special mention because they have achieved widespread use. These agents contain hydrophilic materials such as karaya or carboxymethyl cellulose with an adhesive material and are covered by a semipermeable polyurethane film. The material adheres to the skin surrounding the wound, is highly absorptive, and achieves a moist healing environment. Impregnates are generally fine-mesh gauze impregnated with moisturizing, antibacterial, or bactericidal compounds. They are generally not adherent and require a secondary dressing. They promote reepithelialization and have an anti-infective effect when combined with antibacterial or bactericidal agents. The variety of absorptive powders and pastes consist of starch copolymers or colloidal hydrophilic particles. These agents have high absorbency for tissue wound fluid and débride necrotic and fibrous material from a wound.
Lung reduction operations in patients with diffuse emphysema involve resection of the most severely affected regions of diseased lung tissue. The procedure was introduced in the 1950s but abandoned because of prohibitively high mortality rates. Improvements in intensive care unit techniques and postoperative care have recently resulted in renewed interest. This operation improves lung volume by increasing airway conductance and the ratio of conductance to lung volume by increasing elastic recoil of the lung, which increases after large bullae are removed. Compromised elastic recoil of the lung plays a fundamental part in the pathophysiology of emphysema. Low expiratory flow rates result from airway obstruction, which is caused by a reduction of alveolar driving pressure and an increase in expiratory resistance along with an associated loss in elastic airway support. Functional residual capacity subsequently increases, as does end-expiratory volume. Cardiac function may be compromised as the increased intrathoracic pressure impedes cardiac contractions. All of these parameters improve after lung reduction operation. Functional residual capacity and end-expiratory esophageal pressures (reflective of expiratory volume) drop. There is an increased fractional change in right ventricular area during contraction. The essential improvement is the resulting increase in elastic recoil of the lung. When giant bullae are resected as part of the procedure, the effect on proximity parenchyma is variable. These bullae act as space-occupying lesions, with intrinsically poor elastic recoil properties. Improvement in overall lung recoil after operation results primarily from the removal of this compromised tissue, although improvement in the recoil of abutting parenchyma may play a small role. If the underlying remaining lung tissue is emphysematous, the effect on overall lung mechanics is small.