Journal of clinical monitoring and computing
-
J Clin Monit Comput · Jan 2000
Bispectral index (BIS) and burst suppression: revealing a part of the BIS algorithm.
The bispectral index (BIS) is a complex EEG parameter which integrates several disparate descriptors of the EEG into a single variable. One of the subparameters incorporated in the BIS is the suppression ratio, quantifying the percentage of suppression during burst suppression pattern. The exact algorithm used to synthetize the information to the BIS value is unpublished and still unknown. This study provides insight into the integration of the suppression ratio into the BIS algorithm. ⋯ Suppression ratio values > 40% are linearly correlated with BIS values from 30 to 0. An increasing anesthetic drug effect resulting in an increase of the duration of suppression to a suppression ratio up to 40% is not adequately reflected by the BIS value.
-
J Clin Monit Comput · Jan 2000
Systolic blood pressure at end-expiration measured by the automated systolic pressure variation monitor is equivalent to systolic blood pressure during apnea.
It is necessary to define a reference systolic arterial blood pressure (RP) to calculate delta-Up (dUp) and delta-Down (dDown) for systolic pressure variation. Most studies define the reference pressure as the average systolic blood pressure during a short period of apnea. We describe an automated systolic pressure variation monitor that measures airway pressure and defines the reference pressure as the systolic blood pressure at end-expiration. The present study compares the reference systolic blood pressure measured at end-expiration by the automated systolic pressure variation monitor and the reference systolic blood pressure measured during apnea to test whether the end-expiration value is an adequate substitute for the value during apnea. ⋯ dUp and dDown are calculated using the reference pressure. RPmonitor is an average of 0.2 mm Hg less than RPapnea, thus dUp calculated by the automated SPV monitor is an avenge of 0.2 mm Hg greater than dUp measured by the reference pressure during apnea and dDown is 0.2 mm Hg less. Since the bias of -0.2 mmHg is clinically insignificant, there is acceptable agreement between the reference pressure obtained during apnea and that obtained by the automated SPV monitor at end-expiration. The mean difference between RPmonitor and RPapnea is explained by the continued rise in systolic pressure during the period of apnea as demonstrated by the difference between SBP6 and RPapnea.
-
J Clin Monit Comput · Jan 2000
Effects of one-lung ventilation on cardiac autonomic nervous activity as evaluated by power spectral analysis of heart rate variability.
The purpose of this prospective study was to evaluate the effects of one-lung ventilation on the activity of the cardiac autonomic nervous system. Ten adult patients who underwent thoracotomy were endotracheally intubated with a double-lumen tube under general anesthesia using isoflurane. After induction of anesthesia, a continuous, 256-sec electrocardiogram (ECG) was obtained during bilateral lung ventilation (control) followed by recordings during one-lung ventilation of each side. ⋯ Log(LF), which represents sympathetic and parasympathetic activity, increased similarly to log(HF) on both sides. Log(HF/LF), the balance of the sympathetic and parasympathetic activity, did not change during one-lung ventilation. We suggest that one-lung ventilation alone does not substantially affect the cardiac autonomic nervous system.
-
J Clin Monit Comput · Jan 2000
Comparative StudyComparison of a prototype esophageal oximetry probe with two conventional digital pulse oximetry monitors in aortocoronary bypass patients.
Pulse oximetry (SpO2) is the non-invasive standard for monitoring arterial oxygen saturation in patients undergoing anesthesia, but is subject to external interference by motion artifact, peripheral vasoconstriction, and low cardiac output. We hypothesized that oximetry signals could be acquired from the esophagus when peripheral pulse oximetry is unobtainable. Therefore, we tested an esophageal stethoscope which incorporates transverse oximetry photodetectors and emitters in patients undergoing coronary bypass surgery. ⋯ Digital pulse oximetry failure is common in CABG patients, probably because of marginal cardiac output and peripheral vasoconstriction associated with hypothermia. Our study could not confirm that esophageal technology, which utilizes the esophagus as a site of transflectance oximetry, was superior to conventional digital pulse oximetry.