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Biomedical subjects

N Gravenstein

Publications and source records attributed to N Gravenstein.

At least 37 records · Page 2Linked to original sources
PubMed1994

Lack of uniform definitions and reporting in laboratory models of cardiac arrest: a review of the literature and a proposal for guidelines.

BACKGROUND: Researchers are interested in improved uniformity of definitions and standards of reporting data for human CPR studies, and international guidelines (Utstein style) have been developed. However, no guidelines exist for animal CPR investigations. OBJECTIVE: To assess published animal CPR studies for adequacy of reporting and uniformity of methods and definitions regarding such important factors as the interval from the onset of ventricular fibrillation to the start of CPR (the nonintervention interval), ventilation, chest compression, coronary perfusion pressure, and return of spontaneous circulation. DESIGN: A blinded review of the methodology described in 42 articles concerned with animal CPR research published during the last ten years. An article had to report cardiac arrest and CPR as part of the protocol and return of spontaneous circulation as one of the outcome variables in order to be included in this study. We excluded abstracts, nonresuscitation models, and human CPR studies. MEASUREMENTS AND MAIN RESULTS: There was wide variation in the experimental methods reported in the studies. The nonintervention interval ranged from 0 to 15 minutes. The majority of studies initiated CPR within three minutes after the onset of ventricular fibrillation. Twenty-two percent of studies reported tidal volume, and 18% reported minute ventilation. Of the 14 studies that used blood pressure or coronary perfusion pressure as a target for titration of chest compression force, 12 used different target blood pressure values. We found 29 different definitions of return of spontaneous circulation. The duration of return of spontaneous circulation ranged from 30 seconds to 60 minutes; however, 52% of studies did not report a duration. CONCLUSION: Important differences exist in animal CPR research methodology among laboratories. Failure to define or report minute ventilation, coronary perfusion pressure, and return of spontaneous circulation made it difficult to compare studies. In order to make valid comparisons of studies, blood flow and ventilation should be measured and controlled when they are not experimental variables. Uniform definitions and guidelines for reporting should be developed for laboratory CPR research.

Animals↗
PubMed1994

Pulse oximetry monitoring can change routine oxygen supplementation practices in the postanesthesia care unit.

Routine use of supplemental oxygen (O2) in the postanesthesia care unit (PACU) traditionally has been used to minimize the incidence of hypoxemia. However, with the advent of continuous noninvasive monitoring by pulse oximetry, is routine administration of O2 necessary? We hypothesized that administering O2 as needed, based on pulse oximetry data, would effect considerable cost savings without compromising patient care. Five hundred adult (> or = 18 yr) patients breathing room air when arriving in the PACU were enrolled in the study. During PACU care, when O2 saturation (SpO2) was continuously more than 94%, no supplemental O2 was given. When SpO2 was less than 94%, supplemental O2 was given at an inspired O2 concentration (FIO2) that would increase it to above 94%. Also, when preoperative SpO2 was less than 94% and postoperative SpO2 was more than the preoperative SpO2, no supplemental O2 was given. Supplemental O2 was unnecessary in 63% of patients for the duration of their PACU stay. Cost savings to the 307 patients in one study not receiving O2 was $31,928 if it had been billed separately from the PACU global charge. The annualized figure for patients in our hospital (approximately 10,000 cases) would be an additional $623,272. Inasmuch as pulse oximetry monitoring is now standard in the PACU, perhaps it is time to apply the objective data it supplies, thereby creating cost savings while maintaining patient care standards.

Adult↗
PubMed1991

In vitro evaluation of relative perforating potential of central venous catheters: comparison of materials, selected models, number of lumens, and angles of incidence to simulated membrane.

Perforation of the vena cava or atrium is a serious complication of monitoring with a central venous catheter. We designed an in vitro model with a pulsating simulated membrane to evaluate a number of variables that could affect relative perforating potential of different types of central venous catheters. To determine the perforating potential of central venous catheters, we studied the effects of (1) the angle of incidence (n = 6) between catheter and simulated membrane; (2) catheter material (polyurethane and polyethylene); (3) make (manufacturer and model) (n = 6), with 3 catheters of each make tested; (4) design (n = 3 each: silicone rubber, open-ended, blunt-ended, and polyurethane pigtail); and (5) number of lumens (single, double, or triple). Each trial was repeated five times with each catheter that was tested. Perforation was significantly more likely when the angle of incidence between catheter and pulsating simulated membrane was greater than 40 degrees than when it was 40 degrees (P less than 0.05). Perforation was less likely with single-lumen than comparable French-sized double- and triple-lumen catheters; among single-lumen catheters, perforation required many more pulsations with a polyurethane than a polyethylene catheter (P less than 0.001). Perforation potential differed significantly among 6 makes of 7-French triple-lumen catheters (P less than 0.05). Compared with other materials or designs, silicone rubber or a pigtail tip decreased the perforation potential of catheters (P less than 0.001). These data offer additional objective information to consider when choosing and positioning central venous catheters.

Catheterization, Central Venous↗
PubMed1991

Increased pulmonary artery perforating potential of pulmonary artery catheters during hypothermia.

The rate of major complications from the use of pulmonary artery (PA) catheters has been reported to be as high as 9%, 0.2% of which may be attributed to PA perforation, a catastrophe with a fatal outcome more than 50% of the time. Although an uncommon event generally, more than one third of catheter-related PA perforations occur during cardiac surgery. Several factors act to advance the balloon-tipped PA catheter into the distal PA, where, during hypothermia, the catheter hardens and, thus, may be more likely to perforate the vessel. The relative contribution of hypothermia, itself, to the perforating potential of previously used, triple-lumen PA catheters (n = 5) was examined in vitro by mounting them in a temperature-controlled testing chamber, at a 90 degrees incident angle to a polyethylene membrane, which represented the PA wall. The membrane was made to pulsate 80 times/min against the PA catheter until it was perforated. Each catheter was tested 5 times each at 3 temperatures. At 35 degrees C, 30 degrees C, and 25 degrees C, the number of pulsations to produce perforation (perforation rate) was 488 +/- 280, 309 +/- 242, and 97 +/- 234, respectively. The perforation rates differed significantly between temperatures (P less than 0.01), but not between catheters or tests at the same temperature. This study demonstrates that perforation of a model PA by a triple-lumen PA catheter is 500% more likely during hypothermia.

Cardiac Catheterization↗
PubMed1990

Passive warming of airway gases (artificial nose) improves accuracy of esophageal temperature monitoring.

The most efficient site for monitoring heart and lung sounds by esophageal stethoscope is not the warmest segment of the esophagus. This study investigated the ability of passive warming of airway gases to increase the accuracy of temperatures measured at this site (i.e., to decrease their difference from core temperature). In 15 adult patients undergoing general anesthesia and endotracheal intubation, esophageal temperatures were measured before and after use of a heat and moisture exchanger (an artificial nose) that passively warmed inspired gases. The resulting values were compared with nasopharyngeal temperatures, which represented core temperature. Before use of the heat and moisture exchanger, esophageal and nasopharyngeal temperatures differed significantly (mean difference +/- SD, 0.9 +/- 0.4 degrees C; P less than or equal to 0.001). After passive warming of inspired gases, esophageal temperatures increased significantly (mean increase +/- SD, 0.5 +/- 0.2 degrees C; P less than or equal to 0.001) but inconsistently (range, 0.1 to 1.2 degrees C). However, the mean difference between esophageal and nasopharyngeal temperatures was still significant (0.5 +/- 0.3 degrees C; P less than 0.001). Discrepancies between esophageal and core temperatures persist when a currently available esophageal stethoscope with adjacent auscultation chamber and temperature probe is used, despite passive warming of airway gases.

Adult↗
PubMed1990

Infrared analysis of volatile anesthetics: impact of monitor agent setting, volatile mixtures, and alcohol.

Infrared analysis can determine exhaled concentrations of the three volatile anesthetics in common use because each absorbs infrared light. Many infrared analyzers use a single source of infrared light at a wavelength of 3.3 microns for measurements of all three agents but cannot identify which agent is in use. Organic gases such as ethanol also absorb infrared light. This study determined the effects on the accuracy of a single-wavelength infrared anesthetic monitor (Capnomac, Puritan-Bennett PB254) of (1) incorrect anesthetic agent setting, (2) mixtures of volatile anesthetics, and (3) ethanol vapor in the analyzed gas. Changing the agent setting on the monitor during steady-state delivery of an agent resulted in readings for the halothane setting five times higher than those for the enflurane setting, and six times higher than those for the isoflurane setting. These ratios reflect the monitor's fixed internal gain for each agent setting. Mixtures of anesthetics had a simple additive effect on the monitor's accuracy. With the monitor set for halothane, 0.2 vol% isoflurane mixed with halothane caused readings 1.2 vol% higher than the true halothane concentration. Conversely, with the monitor set for isoflurane, 1 vol% halothane mixed with isoflurane resulted in readings 0.2 vol% too high. In a model simulating alveolar gas, ethanol vapor corresponding to blood alcohol levels of 0.10, 0.30, and 0.50% had a slight but not clinically significant effect on readings for enflurane and isoflurane but increased readings with the halothane setting 3.5 times the corresponding level of blood alcohol. Clinicians can test for an interfering gas such as ethanol before induction by checking the reading in the halothane setting during preoxygenation.

Anesthesia, Inhalation↗
PubMed1990

Postoperative sore throat: effect of oropharyngeal airway in orotracheally intubated patients.

The incidence of postoperative sore throat was evaluated prospectively in 203 orotracheally intubated patients undergoing general anesthesia for surgical procedures. Patients were randomly assigned to have either a plastic oropharyngeal airway or a gauze bite-block in place during the operation and were evaluated for the occurrence of postoperative sore throat by questionnaire the day after surgery. The incidence of postoperative sore throat was 35.2% in the oropharyngeal airway group and 42.5% in the gauze bite-block group, not a statistically significant difference (P greater than 0.05). The incidence of postoperative sore throat was significantly higher when blood was noted on the airway instruments (64.5%) than when it was not (30.9%) (P less than 0.01). There was an association, although not statistically significant, between the incidence of postoperative sore throat and intubation by an anesthesia resident with less than 1 yr experience (P = 0.064). The data from this study indicate that the intraoperative use of hard plastic oropharyngeal airways, compared with the use of soft gauze bite-blocks, does not increase the incidence of postoperative sore throat. These data also suggest that pharyngeal trauma may contribute significantly to the development of postoperative sore throat. We suggest that aggressive oropharyngeal suctioning may contribute to this pharyngeal trauma.

Adult↗
PubMed1989

Endobronchial rupture from endotracheal reintubation with an endotracheal tube guide.

Endotracheal tube guides are often used to facilitate endotracheal tube exchange in patients whose airways are difficult to intubate. The absence of reported complications with this technique suggests it is a safe technique; however, we report a case of endobronchial rupture associated with such a guide. Diagnosis and management of tracheobronchial tears and alternative approaches to difficult reintubation are described.

Abdominal Injuries↗
PubMed1989

High incidence of CO2 laser beam contact with the tracheal tube during operations on the upper airway.

Polyvinyl chloride tracheal tubes from 50 consecutive CO2 laser operations of the larynx and trachea were collected after tracheal extubation. In all cases, the helium protocol for laser operations was used, which includes the following: helium in the anesthetic gas mixture at 60% or more during laser resection (FIO2 less than or equal to 0.4); tracheal intubation with plain, unmarked polyvinyl chloride tubes; laser power density less than or equal to 1,992 W/cm2; and laser bursts of less than or equal to 10-second duration. No tracheal tube fires or airway burns occurred. The polyvinyl chloride tubes were examined for marks caused by the laser, and cuffed tubes were tested for cuff viability. Of the 50 tubes examined, 18 were noncuffed and 32 were cuffed. Although most contacts did not penetrate the tubes, 58% of the tubes showed evidence of contact with the laser as a brown mark on the tube or as a cuff leak. Cuffed tubes were more likely to incur laser contact (69%) than noncuffed tubes (39%), a significant difference (p = 0.04). Most of the cuffed tubes that came in contact with the laser sustained damage at the cuff (77%). It was concluded that the risk of tracheal tube contact with a laser beam is at least 1 in 2, that cuffed tubes are more likely to be hit with a laser beam than noncuffed tubes, and that cuffed tubes that are hit usually sustain damage to the cuff. Because no fires occurred in this series despite frequent laser contact with the tube, these data indicate that the helium protocol helps to prevent polyvinyl chloride tube fires.

Carbon Dioxide↗
PubMed1989

Incidence of oxygen desaturation during oral surgery outpatient procedures.

The frequency, severity, and duration of oxygen desaturation during oral surgical procedures in outpatients was measured. Sixty patients divided into six groups received either lidocaine; lidocaine, diazepam, and meperidine; lidocaine, diazepam, meperidine, and headphone music; lidocaine, diazepam, meperidine, and nitrous oxide; lidocaine, diazepam, meperidine, methohexital, and nitrous oxide; or lidocaine and nitrous oxide. Forty-three percent of the 30 patients who did not receive supplemental oxygen experienced clinically significant oxygen desaturation (greater than 5%) with a mean duration of 4.6 minutes. Only 13% of the patients who received supplemental oxygen had significant desaturation ranging from ten seconds to 12.3 minutes with a mean duration of 1.4 minutes. An unexpected finding was hypoxia in patients receiving only lidocaine anesthesia.

Adolescent↗
PubMed1988

Extracorporeal shock-wave lithotripsy (ESWL). I. In vitro results of blast path treatment of human gallstones.

To evaluate the efficacy of extracorporeal shock-wave lithotripsy (ESWL) for human gallstone fragmentation, biliary calculi of different size and composition were evaluated to determine clinical applicability of this technique. Human biliary calculi composed primarily of cholesterol (Group I, N = 6) and calcium bilirubinate (Group II, N = 6) were shocked in vitro at varying positions along the ESWL blast path. All calculi subjected to lithotripsy were fragmented. Cumulative fragment size was less than or equal to 2, 3, 5, and 8 mm in 73, 86, 94, and 100% of all stones treated, respectively. No statistically significant differences were observed following stone fragmentation when the two groups were compared. Further, no statistically significant differences were evident when comparing the energy expended during fracture of stones in the two groups, or in comparison of fracture with old or new electrodes. However, when fragmentation for stone remnants less than or equal to 2 mm in size was compared at 6- and 10-cm positions on the blast path, a statistically significant difference was noted (P less than 0.001). Stone fragmentation was greatest at positions closest to F2. These data indicate that biliary calculi can be fragmented when subjected to lithotripsy and positioned on the ESWL blast path.

Cholelithiasis↗
PubMed1988

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.

Animals↗
PubMed1988

Simulation of ventilatory-induced stone movement and its effect on stone fracture during extracorporeal shock wave lithotripsy.

Because ventilation influences renal movement, we investigated the effect of stone motion on the efficiency of extracorporeal shock-wave lithotripsy (ESWL). Comparisons of the rates of fragmentation of an experimental model of renal calculi were made between simulated high-frequency jet ventilation at 100 breaths/min. with four-mm. stone movement as measured from the fluoroscope screen, conventional mechanical ventilation at 10 breaths/min. with 32-mm. stone movement as measured from the fluoroscope screen, and a static control. Fragmentation did not differ significantly between high-frequency jet ventilation and no ventilation (static control), but was significantly greater with high-frequency jet ventilation than with conventional ventilation.

High-Frequency Jet Ventilation↗