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Biomedical subjects

R V Johnston

Publications and source records attributed to R V Johnston.

At least 19 recordsLinked to original sources
PubMed2000

Video-capture teleradiology for the after-hours reading of computerized tomography scans.

We evaluated the after-hours support that radiologists could provide from their homes to an urban hospital for reading emergency computerized tomography (CT) scans. During a six-month study period, 36 CT scans were acquired using a video-capture card in a PC and transmitted via an ordinary telephone line. The teleradiology interpretation and the formal report (from the hard copy) were compared with a reference or gold standard interpretation made by a radiologist and an emergency physician for 31 of the 36 cases. In comparison with the gold standard, there were 26 correct diagnoses by teleradiology (84%) and five incorrect (16%). Head CT scans accounted for 74% of the transmitted scans and all five of the cases with discrepant diagnoses. The cause of the single clinically relevant discrepancy was found to be unrelated to the use of teleradiology. In comparison with the formal report, the accuracy of the teleradiologist was not significantly different for all categories combined or for head CT scans alone. Video-capture technology provided a reliable means of transmitting CT scans for after-hours interpretation in emergency cases.

Emergency Medical Services↗
PubMed1999

Repetitive hypoxia rapidly depresses cardio-respiratory responses during active sleep but not quiet sleep in the newborn lamb.

1. Arousal from sleep is an important protective response to hypoxia that becomes rapidly depressed in active sleep (AS) when hypoxia is repeated. This study questioned whether there might also be selective depression of cardio-respiratory responses to hypoxia during AS. 2. Nine newborn lambs (7-22 days of age) were studied over three successive nights. The first and third nights were baseline studies (inspired oxygen fraction, Fi,O2 = 0.21). During the second night, during every epoch of sleep, lambs were exposed to 60 s episodes of isocapnic hypoxia (Fi,O2 = 0.10). 3. During quiet sleep (QS), the probability of arousal in hypoxia exceeded the probability of spontaneous arousal (P < 0.001) throughout repeated exposures to hypoxia. Similarly, there were persisting increases in ventilation (135 +/- 25 %), blood pressure (3 +/- 1 %) and heart rate (3 +/- 1 %). 4. By contrast, rapid depression of all responses occurred during repetitive hypoxia in AS. Thus, the probability of arousal in hypoxia exceeded the probability of spontaneous arousal during the first 10 hypoxia exposures (P < 0.001) but not thereafter. Similarly, during the first 10 exposures to hypoxia, the changes in ventilation (88 +/- 15 %) and blood pressure (5 +/- 1 %) were greater than subsequent responses (P < 0.05). 5. We conclude that, when repeated, hypoxia rapidly becomes ineffective in stimulating protective arousal, ventilatory and blood pressure responses in AS, but not in QS. Selective depression of responses during AS may render the newborn particularly vulnerable to hypoxia in this state.

Animals↗
PubMed1999

Dye rashes.

Physicians may administer intravenous dyes to patients, most commonly to delineate vascular or urinary anatomy, without an appreciation of the potential hazards associated with these compounds. We report two cases in which skin eruptions followed the intravenous administration of the dyes fluorescein and methylene blue; these eruptions were the same colors as the dyes. In our first patient, urticaria, which was yellowish in color and fluorescent under a Wood's lamp, occurred after the administration of fluorescein. In the second patient, painful blue macules appeared randomly on the forearm within 15 seconds after methylene blue was injected into a free-flowing intravenous cannula on the dorsal aspect of the hand.

Adult↗
PubMed1998

Repetitive hypoxia rapidly depresses arousal from active sleep in newborn lambs.

1. Arousal from sleep is an important protective mechanism that is depressed by repeated episodes of hypoxia. We aimed to determine how rapidly arousal depression occurs during repeated hypoxia and to determine if the depression is sleep state specific. 2. Three successive 12 h overnight sleep recordings were performed in six newborn lambs instrumented to record sleep state, blood pressure, heart rate and blood gases. The first (control) and third (recovery) nights were baseline studies (inspired oxygen fraction, FI,O2 = 0.21) to determine the spontaneous arousal probability. During the second (test) study night, lambs were exposed to a 60 s episode of isocapnic hypoxia (FI,O2 = 0.10; inspired carbon dioxide fraction, FI,CO2 = 0.03) during every epoch of sleep. 3. During quiet sleep (QS), the probability of arousing to hypoxia (56%) remained significantly higher than the probability of arousing spontaneously (18%) throughout the repeated hypoxic exposures (chi(2) = 81.5, P < 0.001). By contrast, during active sleep (AS) arousal rapidly became depressed with repetition of the hypoxic stimulus; the probability of arousal in hypoxia (52%) was significantly higher than the probability of spontaneous arousal (12%) during the first ten hypoxic exposures (chi(2) = 18.2, P < 0.001), but there was no difference thereafter. 4. We conclude that, when repeated, moderate hypoxia very rapidly becomes ineffective as an arousing stimulus in AS, but not in QS. These results suggest that the arousal mechanism is particularly vulnerable to failure during AS.

Animals↗
PubMed1994

Cryotherapy for postoperative pain relief following knee arthroplasty.

Ninety consecutive patients undergoing primary knee arthroplasty received local cryotherapy 72 hours after surgery for pain relief. Thermal-pad circulating temperatures were randomly assigned to 50 degrees, 60 degrees, or 70 degrees F (room temperature). Pain relief was monitored using patient-controlled analgesia machines. The amount of morphine received and number of attempts per hour were statistically analyzed with relation to temperature group, age, sex, weight, side, and diagnosis. The amount of morphine injected was positively correlated to the number of attempts per hour and moderately correlated to body weight. There was no correlation between thermal-pad temperature or any other parameter and the amount of morphine injected after surgery.

Aged↗
PubMed1994

The effects of carrier gas composition on the performance of the Tec 6 desflurane vaporizer.

The new Tec 6 desflurane vaporizer is an electrically heated, pressurized, electromechanically coupled dual-circuit blender. We hypothesized that carrier gas viscosity should affect the electromechanical coupling of the fresh gas and vapor circuits, and that desflurane output should vary with different carrier gases. In the first portion of the study, the performance of eight vaporizers was evaluated using a constant dial setting of 10% desflurane with four different carrier gases and three different fresh gas flow rates. In the second portion of the study, the carrier gas flow rate was maintained at 1, 5, or 10 L/min, and vaporizer output was analyzed at all integer dial settings from 1% to 18%. Vaporizer output was highest when oxygen was the carrier gas and lowest when nitrous oxide was the carrier gas. This effect was accentuated at low fresh gas flow rates and correlated with carrier gas viscosity. At a flow rate of 1.0 L/min with a constant dial setting of 10%, the averaged output from vaporizers was 10.3 +/- 0.66, 9.4 +/- 0.58, 8.7 +/- 0.52, and 8.1 +/- 0.44 vol% for 100% oxygen, air, 30% oxygen plus 70% nitrous oxide, and 100% nitrous oxide, respectively. With 100% nitrous oxide as the carrier gas at a flow rate of 1.0 L/min, the vaporizer delivered 2 vol% less than the dial setting at dial settings in excess of 12%. Differences between the analyzed concentration and the dial setting were most pronounced with high concentrations of nitrous oxide at low fresh gas flow rates.

Anesthetics↗
PubMed1993

Consequences of misfilling contemporary vaporizers with desflurane.

Desflurane is a volatile anaesthetic that combines low blood gas solubility (blood/gas partition coefficient = 0.42 at 37 degrees C), moderate potency (MAC = 6-7%), and high volatility (vapour pressure = 681 mmHg at 20 degrees C, boiling point = 23.5 degrees C). The volatility and potency of desflurane prevent its safe use in vaporizers of traditional design. We present a mathematical model which demonstrates the potential for desflurane overdose if contemporary vaporizers are misfilled with desflurane. The most hazardous filling error occurs if an enflurane vaporizer is misfilled with desflurane. The calculated desflurane output of a misfilled enflurane vaporizer at a dial setting of 1% and a temperature of 22 degrees C is 57.8%, or 9.6 MAC. For misfilled enflurane, isoflurane, and halothane vaporizers at dial settings equivalent to one MAC at 22 degrees C, the calculated desflurane output is 14.0, 10.2, and 7.8 MAC, respectively. We conclude that the safe delivery of desflurane will require engineering safeguards, additional monitoring, and education of the anesthesia community.

Accident Prevention↗
PubMed1993

The new Tec6 desflurane vaporizer.

The Tec 6 vaporizer is an electrically heated, thermostatically controlled, constant temperature, pressurized, electromechanically coupled dual circuit, gas/vapor blender. The pressure in the vapor circuit is electronically regulated to equal the pressure in the fresh gas circuit. At a constant fresh gas flowrate, the operator regulates vapor flow with a conventional concentration control dial. When the fresh gas flowrate increases, the working pressure increases proportionally. At a specific dial setting at different fresh gas flowrates, vaporizer output is constant because the amount of flow through each circuit is proportional. Independent confirmation of vaporizer performance and design characteristics awaits vaporizer availability.

Anesthesia, Inhalation↗
PubMed1992

Serum bupivacaine concentrations after intraarticular injection for pain relief after knee arthroscopy.

Intraarticular injection of local anesthetic drugs after arthroscopic knee surgery is used to provide postoperative analgesia. Toxic serum levels of bupivacaine have been reported after its use both in regional anesthesia and for intraarticular injection. The toxicity of the former is related to needle misplacement and the latter is presumed to be absorptive. This study evaluates the effect of tourniquet inflation and the addition of epinephrine on serum concentrations of bupivacaine after intraarticular injection. The results shows that the peak serum bupivacaine concentrations can be reduced by adding epinephrine and injecting it after tourniquet inflation.

Adult↗
PubMed1991

Reflex sympathetic dystrophy after clavicle fracture: case report.

Reflex sympathetic dystrophy (RSD) of the anterior chest wall is a rare entity. A MEDLINE search in all languages of the world's literature from 1966 to the present yielded no report of the association of clavicle fracture with this pain syndrome. Two cases are presented and the anatomic variations of the supraclavicular nerves in relation to the clavicle are discussed.

Accidents, Traffic↗
PubMed1990

Photodeactivation of ethyl violet: a potential hazard of Sodasorb.

Breathing circuit cannisters containing functional CO2 absorbent are critical to prevent rebreathing CO2 during general anesthesia using closed or semiclosed breathing systems. Ethyl violet is the indicator dye added to Sodasorb to indicate impending exhaustion of the absorbent. A case of CO2 rebreathing due to failure of ethyl violet indicator in exhausted Sodasorb was encountered. Laboratory investigation demonstrated that dye failure could result from photodeactivation caused by fluorescent lights. Using a fixed intensity fluorescent light source and quantitative spectrophotometric analysis, a highly significant dose-response relationship was demonstrated between duration of light exposure and the decrease in ethyl violet concentration. After 24 h of fluorescent light exposure with a received flux density of 46 nwatts/cm2 at 254 nm, the concentration of functional ethyl violet remaining in pulverized Sodasorb was 16% of the baseline value. Furthermore, using multiple light sources of various intensities, the greater the intensity of light, the more rapid the rate of decline of the ethyl violet concentration. It is recommended to minimize the problem by using ultraviolet filters and incorporating additional ethyl violet in Sodasorb. Finally, ethyl violet undergoes temporal deactivation after a Sodasorb container is opened, even if it is stored in the dark.

Absorption↗