The Journal of critical illness最新文献

Transesophageal echocardiography (TEE) is a Doppler technique that uses the esophagus as an acoustic window. In critically ill patients (particularly ventilated patients), TEE may be used to assess left ventricular function, valvular disease, endocarditis, and prosthetic valve dysfunction. It is also helpful in elucidating the cause of hypotension after cardiac surgery, and can detect chronic aortic dissection and transection, valve rupture, and myocardial contusion in trauma victims. TEE is superior to transthoracic echocardiography in evaluating a cardiac source of embolism. Contraindications to TEE include esophageal disorders and an uncorrected bleeding diathesis; a large hiatal hernia may cause suboptimal transgastric images.

Metered-dose inhaler (MDI) therapy can be an effective, cost-efficient means of managing chronic airway obstruction in many patients in medical or surgical intensive care units who have recently been extubated. Because medication is delivered directly to the airways through an MDI, a relatively low dosage may be effective, and few adverse effects may be encountered. Candidates for MDI therapy should have a vital capacity of at least 900 mL, be able to hold their breath for at least 5 seconds, and have a respiratory rate of under 25 breaths per minute. The majority of patients who meet these criteria are able to convert to MDI therapy within 24 hours of extubation.

Use of transesophageal echocardiography (TEE) is growing in ambulatory, intensive care, and intraoperative settings. Forward flexion or retroflexion of the TEE probe tip at different levels in the esophagus reveals a variety of intracardiac structures; in the basal short-axis view, for example, the aortic valve can be seen, as can the left atrial appendage lateral to the aorta and pulmonary artery. In the four-chamber view, the mitral and tricuspid valves and interatrial septum can be viewed, and the morphology of the mitral valve leaflets and mitral annulus can be assessed. Cross-sectional views of both ventricles can be obtained in the transgastric short-axis view. In addition, the entire thoracic aorta, as well as the proximal ascending and transverse arch, can be visualized with TEE.

Minitracheotomy, a new method of percutaneous tracheal cannulation, provides ready access to the trachea for removal of airway secretions in spontaneously breathing patients with sputum retention and atelectasis. The original technique calls for a vertical 1-cm stab incision over the cricothyroid membrane; a curved introducer is then passed through this incision into the trachea. A cannula is passed over the introducer, which is then removed. The external flange is secured to the patient's neck. A modified technique uses a Seldinger method for tube placement. Complications vary with the technique that is used; cough, subcutaneous emphysema, stridor, and rare instances of profuse hemorrhage have been reported.

Percutaneous transvenous mitral commissurotomy (PTMC) is the therapy of choice for patients with mitral stenosis who are candidates for commissurotomy. PTMC also offers palliative therapy for patients who are not good surgical candidates. Patients with thin, pliable valve leaflets and little subvalvular disease are the best suited. Significant thrombus in the left atrium is a strong relative contraindication. PTMC with the Inoue balloon is technically easier to perform than is conventional balloon valvotomy and is better tolerated by most patients. During this procedure, the Inoue balloon is positioned against the mitral valve; it is repeatedly inflated at increasing balloon diameters until the transmitral valve gradient is sufficiently relieved. PTMC affords marked symptomatic improvement in most patients who undergo the procedure.

Several echocardiographic techniques provide accurate, noninvasive estimates of peak or mean pulmonary artery pressure and can aid in diagnosing primary pulmonary hypertension. One such method involves converting peak tricuspid velocity to an estimated peak right ventricular minus right atrial gradient; peak pulmonary artery pressure is roughly equal to the sum of the tricuspid gradient estimate and estimated mean right atrial pressure. A second technique evaluates the contour of the transpulmonary Doppler velocity profile; a third measures the interval between pulmonary valve closure and tricuspid valve opening. An M-mode method can be used to assess wedge pressure. Echocardiographic variables can also help evaluate prognosis in primary pulmonary hypertension.

Percutaneous endoscopic gastrostomy (PEG) is an attractive method of providing enteral nutrition to patients who are candidates for operative gastrostomy or nasoenteric tube feeding; it is currently the procedure of choice for selected nutritionally compromised patients. PEG may be considered for patients who need short- or long-term enteral support; those unable to swallow or who cannot maintain adequate oral intake are ideal candidates. Several techniques are used to perform PEG; each involves the placement of a gastrostomy tube at a point where the stomach and abdominal walls are in closest contact. PEG can be done at the bedside without general anesthesia. Feeding can begin within 24 hours of PEG placement. Major complications (peritonitis and pulmonary aspiration) occur infrequently.

Therapeutic apheresis is a generic term that refers to removal of abnormal blood cells and plasma constituents. The terms "plasmapheresis," "leukapheresis," and "erythrocytapheresis" describe the specific blood element that is removed. Apheresis therapies can be performed in the ICU to manage a number of neurologic, hematologic, and autoimmune disorders, including myasthenia gravis, Guillain-Barré syndrome, sickle-cell disease, and Goodpasture's syndrome. Apheresis procedures generally require two points of contact with the circulation--one for blood withdrawal and one for return; the withdrawal site should sustain a flow rate of at least 50 mL/min. Although apheresis is generally quite safe, hemodynamic instability, hypocalcemia, and dilutional coagulopathy can occur.

Continuous arteriovenous hemofiltration (CAVH) and continuous arteriovenous hemodialysis (CAVHD) are extracorporeal ultrafiltration techniques that permit ongoing removal of plasma water and uremic toxins. Both techniques are performed in the ICU with a minimum amount of equipment and achieve overall fluid balance more readily than intermittent hemodialysis. CAVH is used to manage hypervolemia, electrolyte imbalance, and/or mild uremia. CAVHD is used in hypercatabolic patients with acute renal failure who are hypervolemic and uremic; a dialysate fluid is used for more efficient solute removal. The most serious complications of CAVH and CAVHD relate to bleeding associated with cannulation or anticoagulation. Excess fluid and electrolyte losses may also occur.