This study was designed to determine if microencapsulated tetracaine would provide a longer duration of local anesthesia than nonmicroencapsulated (neat) tetracaine. Local anesthesia was determined by monitoring the response of the rat to tail clamping after the installation of a subcutaneous ring block. Ten percent microencapsulated tetracaine was found to provide local anesthesia of the tail for a 43-hour duration. Ten percent tetracaine solution was toxic. One percent tetracaine solution provided a tail block lasting 8 hours. Lecithin membranes without drug provided no block. This study demonstrates that lecithin-coated tetracaine microcrystals produce a local anesthetic effect that is ultra-long in duration, reversible, and not systemically toxic.
Right atrial collapse (RAC) and right ventricular diastolic collapse (RVDC) have been shown to be
useful two-dimensional échocardiographie signs in well-established cardiac tamponade. To assess the value of these
signs in cardiac tamponade of varying severity, we studied 8 closed-chest spontaneously breathing dogs with twodimensional
echocardiography during varying grades of tamponade induced by intrapericardial saline infusion via a
preplaced catheter. Early tamponade was defined as the state when pericardial effusion caused a 20% decline in
cardiac output but with normal systolic arterial pressure and a pulsus paradoxus less than 10 mm Hg. Moderate and
severe tamponade were stages with progressively decreasing cardiac output and systolic arterial pressure and increasing
pulsus paradoxus over 10 mm Hg. Neither RAC nor RVDC was present in any animal in the control state.
Sensitivity of RAC was 50% during early tamponade and 100% during moderate and severe tamponade; the specificity
was 100% during all grades of tamponade. The sensitivity of RVDC was 38, 63 and 75% during early,
moderate and severe tamponade; the specificity was 88% during all stages. Thus, presence of RAC and RVDC in
pericardial effusion indicates that hemodynamic deterioration has begun even though conventional signs such as
pulsus paradoxus may be absent. As tamponade progresses, the sensitivity of both signs increases. At all grades of
tamponade, RAC tends to be more sensitive than RVDC.
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