Extracorporeal shock-wave lithotripsy (ESWL). II. In vivo canine results of blast path treatment of human gallstones

To evaluate the role of ESWL in vivo for the treatment of human gallstones positioned on the blast path, a canine model was developed to determine the efficacy of stone fragmentation and the subsequent histopathological injury that occurs as a result of this therapeutic technique. Twenty-four 16- to 20-kg mongrel dogs were divided into five groups: I: ESWL without stone, autopsy at 48 hr (N = 6); II: ESWL with stone (mean diameter 16.8 mm, range = 14-19 mm), autopsy at 48 hr (N = 10); III: ESWL without stone, autopsy at 41-46 days (N = 6); IV: ESWL without stone, autopsy immediately after ESWL (N = 1); V: No ESWL or stone, autopsy 2 hr after anesthesia induction (N = 1). A human gallstone (96% cholesterol) was inserted by cholecystotomy (N = 10) in Group II only. All groups (N = 24) had operative placement of a 6.5 Fr accordion catheter into the gallbladder for radiographic visualization. For each blast path treatment, 2000 discharges were delivered at 18-24 kV. Histopathologically, the Group V gallbladder served as a control. Groups I, II, and IV revealed mild subacute injury; dog gallbladders in Group III showed regression of these changes. Total surface area (TSA) of Group II stones increased from a pre-ESWL mean of 6.60 +/- 0.0.84 cm2 to 53.84 +/- 26.8 cm2 post-ESWL (P less than 0.001). Cumulative post-ESWL fragment sizes for particles in less than or equal to 2-, less than or equal to 3-, less than or equal to 5-, less than 10- and greater than or equal to 10-mm categories represented 32.9, 41.6, 49.4, 74.3, and 100% of pretreatment stone weight, respectively. These data indicate that human gallstones can be fractured to a variable degree when treated on the ESWL blast path and that TSA increased significantly. Gallbladder histopathologic changes appear to be reversible by 41-46 days post-ESWL.     

Twitcher: A Device to Simulate Thumb Twitch Response to Ulnar Nerve Stimulation

Objective. To design and fabricate a device to simulate evoked thumb adduction in response to ulnar nerve stimulation. Methods. We implemented a computer-controlled, motorized thumb (TWITCHER) that responds to ulnar nerve stimulation by an unmodified peripheral nerve stimulator. Clinically realistic response patterns are generated for both depolarizing and non-depolarizing muscle relaxants and three modes of stimulation (single twitch, train-of-four, tetanus). Results. The device has been used in a full-scale patient simulator for the last six years. Discussion. TWITCHER has been well received by participants in simulation exercises including the use of neuromuscular blocking drugs.     

Sampling intervals for clinical monitoring of variables during anesthesia

Although five minutes is the sampling interval mentioned by the American Society of Anesthesiologists for monitoring blood pressure and heart rate during anesthesia, most patients are monitored more closely by continuous auscultation and with the help of automated instruments. Yet this difference between the interval recommended and that actually used indicates that sampling intervals are not defined clearly enough. Therefore, we present three methods with which to determine sampling intervals during monitoring. To explore the feasibility of these methods we examined data gathered every 7.5 seconds during three typical, noncatastrophic physiologic perturbations induced in an anesthetized dog. We chose hypercapnia secondary to rebreathing, hypotension secondary to deep anesthesia, and hypoxemia secondary to a low concentration of inspired oxygen as realistic examples of what can occur during operation and anesthesia. We studied three variables: respired carbon dioxide, femoral arterial blood pressure, and oxygen saturation of hemoglobin (pulse oximeter). The data obtained during monitoring were subjected to three methods of analysis: (1) recording of sets of data, with various starting times, at five-minute intervals only (moving grid); (2) Fourier analysis; and (3) analysis of slopes. For the data of the experiment, the Fourier analysis yielded, on average, longer sampling intervals than did the analysis of slopes.     

An accuracy evaluation of the T-Line Tensymeter (continuous noninvasive blood pressure management device) versus conventional invasive radial artery monitoring in surgical patients

Continuous beat-to-beat arterial blood pressure (BP) monitoring with a simultaneous arterial waveform display is typically achieved with an invasive arterial catheter. We evaluated a noninvasive device, the T-Line Tensymeter, that provides a calibrated arterial pressure waveform from which continuous BP measurements and heart rate may be computed by either a bedside host monitor or the tensymeter device itself. In 25 patients given general anesthesia, we measured systolic, mean, and diastolic BPs via the tensymeter and compared these measurements with those obtained from the contralateral radial artery catheter. Data were analyzed using the Bland Altman test to determine agreement between the two systems. The mean +/- sd bias and precision (mm Hg) were as follows: 1.7 +/- 7.0 and 5.7 +/- 4.4 for systolic BP; 2.3 +/- 6.9 and 5.7 +/- 4.5 for diastolic BP; and 1.7 +/- 5.3 and 4.0 +/- 4.8 for mean BP. Noninvasive pressures from the tensymeter-produced arterial waveform agreed with simultaneous contralateral BPs measured from arterial catheters within an acceptable clinical range for a limited population of surgical patients studied over a systolic arterial BP range from 41 to 189 mm Hg without significant temporal performance degradation. The tensymeter may enable physicians to circumvent arterial cannulation in certain circumstances (such as with low- or intermediate-risk procedures) on patients when beat-to-beat BP measurement is desirable.