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Biomedical subjects

D C Flemming

Publications and source records attributed to D C Flemming.

9 recordsLinked to original sources
PubMed1992

Subjective and psychomotor effects of subanesthetic doses of propofol in healthy volunteers.

Propofol is increasingly being used in medical and surgical procedures in which conscious sedation of the patient is desired. The mood-altering and psychomotor effects of subanesthetic concentrations of propofol have not been well characterized. Therefore, we examined the effects of intravenous infusions of different subanesthetic doses of propofol on mood and psychomotor/cognitive performance in healthy volunteers (n = 10). A prospective, randomized, placebo-controlled, double-blind, crossover design was used in which subjects first were administered an intravenous loading dose of propofol or placebo (Intralipid) and then were infused over a 20-min period with a given dose of propofol or placebo. Each subject received placebo (Intralipid loading dose and infusion), low-dose propofol (0.08 mg/kg loading dose and 0.5 mg.kg-1.h-1 infusion), moderate-dose propofol (0.16 mg/kg loading dose and 1.0 mg.kg-1.h-1 infusion), and high-dose propofol (0.32 mg/kg loading dose and 2.0 mg.kg-1.h-1 infusion) in four sessions spaced approximately 1 week apart. Propofol induced changes in mood in a dose-related fashion. Some of these mood-altering effects lingered for as long as 30 min after termination of the infusion, but, in general mood had returned to baseline levels 1 h after termination of the infusion. Intralipid induced no changes in mood during the infusion period. Psychomotor functioning was impaired during, and anterograde amnesia was present after, the high-dose propofol infusion. These results suggest that propofol as a sedative has a spectrum of effects that are well-suited for ambulatory surgery (e.g., sedation, amnesia, and rapid and complete recovery).

Adult↗
PubMed1979

The "D circle": closed-circuit operation of the Bain circuit.

A method of converting a Mapleson D (Bain) circuit to closed-circuit operation is presented, utilizing a laboratory air pump and a Waters carbon dioxide absorber canister to recirculate exhaled gas. The elimination of carbon dioxide from the circuit was studied and found to be adequate. The circuit would allow the use of low fresh gas flows for the maintenance of anaesthesia without the danger of carbon dioxide rebreathing. We suggest that such a circuit could provide appropriate conditions of gas humidity and temperature for endotracheal anaesthesia, while realizing the advantage of a circulator in mask anaesthesia is possible. Further design considerations for a "D circle" breathing system for clinical use are discussed.

Anesthesiology↗
PubMed1979

Use of positive airway pressure without endotracheal intubation.

Continuous positive airway pressure (CPAP) and expiratory positive airway pressure (E-PAP) may be used safely without endotracheal intubation in patients with acute respiratory failure when strict selection criteria are adhered to. The therapy should be titrated to reduce intrapulmonary shunting, improve PaO2, and reduce FIO2. Other considerations include balancing oxygen consumption against cardiac output and oxygen transport. Absolute or relative indications for abandoning the technique and using endotracheal intubation with mechanical ventilatory support include unrelenting hypoxia, patient exhaustion, rising PaCO2, development of metabolic acidosis, presence of ventricular arrhythmias, and inability to protect the airway.

Acute Disease↗
PubMed1975

Deliberate hypotension.

Deliberate hypotension can reduce major blood loss and indelicate operations can produce a drier field increasing the ease of surgery and the likelihood of a good result. The techniques used to induce hypotension can also be used to avoid dangerous hypertension during and after surgery. These benefits must be weighed against the risks of inadequate perfusion: especially cerebral, myocardial, or renal. In previously normotensive patients these risks are minimal when the arterial pressure is held above 80 torr systolic, and may be acceptably small even at mean pressure of 50 to 60 torr. Previously hypertensive patients show signs of cerebral ischemia at higher pressures; they should probably not be subjected to deliberate hypotension, but they also can be harmed by severe hypertension which can be avioded by the proper use of hypotensive agents. For most situations a balanced technique is suitable: after a stable anesthetic level has been achieved using halothane or enflurane, hypotension can be induced with sodium nitroprusside or trimethaphan camsylate. Longer-acting agents such as pentolinium are sometimes desirable, but the shorter-acting agents are easier to control. Careful monitoring with observation of intra-arterial pressure, electroencephalogram, electrocardiogram, and determination arterial blood gas tensions is likely to make for safer conduct. Close postoperative observation is essential. With careful preparation and monitoring deliberate hypotension can be a safe technique for reducing blood loss or facilitating delicate procedures.

Abdomen↗
PubMedDate not supplied

Xenon inhalation as an adjunct to computerized tomography of the brain: preliminary study.

The purpose of this study is to determine whether computerized tomography can distinguish between brain tissue and brain tissue containing dissolved xenon at physiologic concentrations. Xenon is an inert gas of high atomic number (54), and is highly soluble in tissue, particularly in fat. Its presence in the brain after inhalation is manifested by well known anesthetic effects. Phantom studies using xenon in equilibrium at atomospheric pressure with water, corn oil, and milk samples of varying known fat content, demonstrate that xenon is detectable in all cases with a steep linear increase in change of attenuation factor (EMI number) with increasing fat content. In the rhesus monkey xenon is readily detectable at 20% inhaled gas concentration, with linear detectable at 20% inhaled gas concentration, with linear increase of attenuation factor with increasing concentration. The possible application of our findings to the study of brain pathophysiology is discussed. Since xenon is a potent although safe anesthestic, caution in clinical application is advised.

Animals↗
PubMedDate not supplied

Real-time digital K-edge subtraction fluoroscopy.

We report in vitro and in vivo trials of K-edge fluoroscopy, by which iodine contrast concentration is displayed live, with tissue and bone images suppressed, free of patient-motion artifacts. Iodine and cerium, 125 and 225 mg/cm2 respectively, filter alternate TV fields of cine-pulsed 50 KVP x-rays. Weighted subtraction of successive TV fields isolates the iodine image and simultaneously minimizes artifacts. Digital techniques are used in real time. At our present x-ray tube limit, 500 mA instantaneous current, the patient exposure is 180 mR/sec and quantum mottle limits the image quality. Integrating four successive difference images provides a compromise between mottle and smoothly moving displays. Cardiovascular images of a 17-kg dog, using 1 ml/kg Renografin-60 injected into a foreleg vein, show that a 15-cm chest thickness is our present practical maximum. This method may be useful in diagnosing cardiovascular anomalies in infants without catheterization or suspension of breathing.

Animals↗