Search PubMed⌕ Search

Biomedical subjects

S J Barker

Publications and source records attributed to S J Barker.

64 records · Page 4Linked to original sources
PubMed1987

Cardiovascular effects of anesthesia and operation.

Anesthesia and surgery have a wide range of effects on the cardiovascular system. Even in healthy patients having minor operations, anesthetic agents can cause significant cardiac depression and hemodynamic instability. Virtually all anesthetic agents have intrinsic myocardial depressant properties, although some may mask this with sympathetic stimulation. The vasodilatory effects of the volatile agents can result in serious hypotension when combined with this negative inotropy. In the patient with pre-existing cardiac disease, these cardiovascular anesthetic effects become much more serious. These patients will not tolerate wide swings of hemodynamic variables, and the cardiodepressant effects of anesthetics are more pronounced in them. The stress of anesthesia and surgery frequently unmasks previously undiagnosed heart disease. Surgery itself provides many insults to the cardiovascular system, and these may be additive with the effects of anesthesia. These include loss of blood and other volume shifts, release of various substances into the circulation, hypothermia, sudden changes in cardiac preload and afterload, myocardial ischemia, and effects of drugs or blood products given for surgical reasons. The signs and symptoms of these surgical stresses to the cardiovascular system are often masked by anesthesia.

Anesthesia, Inhalation↗
PubMed1986

Effects of anesthetic agents on the drift of a transcutaneous oxygen tension sensor.

Both halothane and nitrous oxide can be reduced at the cathode of a polarographic oxygen electrode, causing the electrode current to drift upward and report falsely high oxygen tension. Because transcutaneous oxygen tension is measured by a heated oxygen electrode, there is a potential for significant upward drift of these values. To examine the clinical significance of this drift, the following study was performed. Transcutaneous oxygen tension sensors were calibrated at oxygen tensions of 0 mm Hg and 157 mm Hg (room air) just before clinical use during anesthesia. This calibration was rechecked immediately upon removal of the sensor from the patient at the end of the anesthesia. The predominant anesthetic agent used and the duration of monitoring were noted from the record. Data were collected from 208 patients representing a total of 463.6 hours of anesthesia. The patients were divided into five groups based on anesthetic administered: halothane, enflurane, isoflurane, nitrous oxide-narcotic, and local/regional. The mean zero point recalibration value was 0.4 mm Hg or less for all agents except halothane, for which it was 1.8 +/- 3.2 mm Hg. This halothane drift was significantly greater than that for the other agents (P less than 0.01). Room air recalibration was not significantly different in any of the five groups, varying from 160 +/- 4.9 mm Hg for halothane to 157 +/- 4.9 mm Hg for enflurane. All these drift values are within the manufacturer's specifications. We conclude that the drift of the transcutaneous oxygen tension sensor due to anesthetic agents is not clinically significant. However, caution should be exercised when halothane is used during an extremely long period of anesthesia.

Anesthetics↗
PubMed1986

Continuous noninvasive estimation of cardiac output by electrical bioimpedance: an experimental study in dogs.

A new device has been developed to estimate continuously and noninvasively cardiac output from the thoracic electrical bioimpedance (CObi). CObi was compared to cardiac output by thermodilution (COtd) in five anesthetized dogs. Blood pressure, blood volume, and blood flow were manipulated by hemorrhage and infusions of sodium nitroprusside and phenylephrine. These data were used to determine the correlation between CObi and COtd under conditions of hypotensive normal flow and normotensive low flow, as well as during hemorrhagic shock and resuscitation. The CObi device was calibrated in vivo to COtd for each dog at the beginning of each experiment. CObi had a significant positive correlation with COtd throughout the experiments (r = 0.84, slope = 0.91, intercept = 0.55, p less than 0.01), and CObi predicted COtd with a standard error of the estimate of 0.81 L/min. Neither heart rate nor mean arterial pressure was significantly correlated with COtd or CObi. During severe hemorrhagic shock, CObi could not determine cardiac output in two of the dogs when COtd averaged 1.7 L/min. These data indicate that CObi is a blood-flow related variable that can be monitored continuously.

Animals↗