Alvin Wald

Do Standard Monitoring Sites Reflect True Brain Temperature When Profound Hypothermia Is Rapidly Induced and Reversed

Background Brain temperature is closely approximated by most body temperature measurements under normal anesthetic conditions. However, when thermal autoregulation is overridden, large temperature gradients may prevail. This study sought to determine which of the standard temperature monitoring sites best approximates brain temperature when deep hypothermia is rapidly induced and reversed during cardiopulmonary bypass. Methods Twenty-seven patients underwent cardiopulmonary bypass and deep hypothermic circulatory arrest in order for each to have a giant cerebral aneurysm surgically clipped. Brain temperatures were measured directly with a thermocouple embedded in the cerebral cortex. Eight other body temperatures were monitored simultaneously with less invasive sensors at standard sites. Results Brain temperature decreased from 32.6 + 1.4 degrees Celsius (mean plus/minus SD) to 16.7 plus/minus 1.7 degrees Celsius in 28 plus/minus 7 min, for an average cerebral cooling rate of 0.59 + 0.15 degree Celsius/min. Circulatory arrest lasted 24 plus/minus 15 min and was followed by 63 + 17 min of rewarming at 0.31 plus/minus 0.09 degree Celsius/min. None of the monitored sites tracked cerebral temperature well throughout the entire hypothermic period. During rapid temperature change, nasopharyngeal, esophageal, and pulmonary artery temperatures corresponded to brain temperature with smaller mean differences than did those of the tympanic membrane, bladder, rectum, axilla, and sole of the foot. At circulatory arrest, nasopharyngeal, esophageal, and pulmonary artery mean temperatures were within 1 degree Celsius of brain temperature, even though individual patients frequently exhibited disparate values at those sites. Conclusions When profound hypothermia is rapidly induced and reversed, temperature measurements made at standard monitoring sites may not reflect cerebral temperature. Measurements from the nasopharynx, esophagus, and pulmonary artery tend to match brain temperature best but only with an array of data can one feel comfortable disregarding discordant readings.

Nocturnal oxygenation during patient-controlled analgesia.

UNLABELLED Patient-controlled analgesia (PCA) has become a standard modality for the management of postoperative pain, although anecdotal reports of excessive sedation and respiratory depression impugn its safety. To study the prevalence and severity of nocturnal hypoxemia, we measured arterial oxygen saturation (SpO2) continuously overnight in 32 postoperative patients who were receiving morphine via PCA. To evaluate the potential benefit of providing concurrent supplemental oxygen, the patients breathed oxygen-enriched air the night of surgery and room air the next night. Patients experienced more pain and consumed twice as much morphine the first night. However, breathing supplemental oxygen that night, the nocturnal mean SpO2 was 99%+/-1%, 94%+/-4% (P<0.001), and only four patients had periods of hemoglobin desaturation <90%. In contrast, breathing room air the subsequent night, the mean SpO2 was lower (94%+/-4%; P<0.001), and hypoxemia occurred more frequently and was more severe: 18 patients experienced episodes of SpO2 <90%, 7 patients experienced episodes of SpO2 <80%, and 3 patients experienced episodes of SpO2 <70%. One patient required resuscitation for profound bradypnea and cyanosis, but none suffered permanent sequelae. We conclude that when postoperative patients use PCA at night, hypoxemia can be substantial and oxygenation can be improved by providing supplemental oxygen. IMPLICATIONS Oxygen saturation was measured postoperatively in patients using morphine patient-controlled analgesia. Substantial nocturnal hypoxemia occurred in half of the patients while they breathed room air. The severity of the hypoxemia was reduced when patients received supplemental oxygen.

Fluorescent light interferes with pulse oximetry.

Arterial oxygen saturation (SaO2) values displayed on the pulse oximeter dropped dramatically in 3 children undergoing neurosurgical procedures when a hand-held fluorescent light was used to observe the patients. Pulse rates were unchanged on both the electrocardiograph and pulse oximeter. Electromagnetic interference was excluded as the cause of desaturation. A great deal of energy was emitted by the hand-held light in the 660-nm region, which is one of the wavelengths used by the oximeter. False readings of pulse rate and SaO2 values caused by ambient light could be avoided if oximeter probes were manufactured of black opaque material that does not transmit light or enclosed in an opaque plastic housing.

Electrocardiographic Artifacts During Cardiopulmonary Bypass

An electrocardiogram (ECG) free from interference is today a necessity for safe anesthetic management. Electrocardiogram artifacts caused by surgical cautery units, power lines, and muscle twitching and fasciculation have been recognized (14). More recently, ECG interference has been observed during extracorporeal shock wave lithotripsy (5) and during crystalloid administration through a fluid warming apparatus (6). During cardiopulmonary bypass (CPB) we have been experiencing another type of ECG artifact, which has not yet been reported. The purpose of this paper is to describe the characteristics and incidence of this interference, and to suggest an etiology and possibly a solution to the problem.

Plastic Induced ECG Interference on Cardiopulmonary Bypass: An Adventure in Clinical Engineering

This paper describes ECG electrical interference present during extracorporeal perfusion for cardiac surgery, specifically under atmospheric conditions of low relative humidity. This interference was traced to an interaction between the polyvinyl-chloride polymer tubing nd the motion of roller pumps used during the cardiopulmonary bypass procedure. The possible causes of this interference are considered, static electricity or a piezoelectric effect, along with methods of its elimination or prevention.

Intraoperative data acquisition for the study of cerebral dysfunction following cardiopulmonary bypass

As a first step in our study to document postoperative cerebral dysfunction, and to determine whether global cerebral blood flow can be implicated in the etiology of this postoperative change, we have assembled a flexible data acquisition system to acquire and record data from four independent sources, three in digital form and one analog.Each of the monitors that we use has a different requirement: One has eight channels of analog output; the other three have RS-232 digital outputs, each with a data stream with different characteristics. The central element of our data collection is a personal computer running the data acquisition and analysis program, LabVIEW for Windows (National Instruments, Austin, TX). All data are processed through separate LabVIEW global variables; the data strings are concatenated and stored on the hard disk in a spreadsheet format for further analysis.We illustrate an intraoperative recording made during cardiopulmonary bypass (CPB) by showing a graph of the mean arterial pressure (MAP), mixed venous oxyhemoglobin saturation recorded from the jugular bulb (JVO2Sat), and temperature measured from the nasopharynx. A decrease in the MAP after unclamping the aorta is accompanied by a decrease in JVO2Sat.

Effective communication and supervision in the biomedical engineering department.

It is important for biomedical engineering supervisors to master the art of effective communication. Supervisors who have effective communication skills can successfully initiate creative programs and generate a harmonious Working atmosphere. Using effective communication, they can promote good working conditions, such as high morale, worker initiative and loyalty to the department, which are almost impossible to measure but imperative for a successful department. However, effective communication tends to be neglected by supervisors who are either functional specialists or managerial generalists. This paper presents several cases of what effective communication truly is and discusses some potential factors that may lead to ineffective communication.

Book Review: Further understanding of the human machine. The road to bioengineering

Book detailsMax E. Valentinuzzi (editor) Further understanding of the human machine. The road to bioengineering Series on bioengineering and biomedical engineering, volume 7.Singapore/New Jersey: World Scientific Publishing Co. Pte. Ltd.pp. xxxi+546. ISBN 9789813147256.

In Memoriam: Ivan Daskalov: 1933 – 2004

Ivan Daskalov [1933–2004] was a friend who will be missed by many. Neither the quality of a man nor the concept of a friendship can be defined with words. We may only say that both will be missed.

ELECTROPHYSIOLOGY FOR ANESTHESIOLOGISTS

Communication within the nervous system involves rapid changes in the membrane potential, which are called action potentials ( see Appendix for a glossary of terms). Any changes in the cells electrical excitability, the ability of neurons to generate action potentials, affect neuronal function. Thus, the nerve cells function may be affected by alterations in its ionic and pharmacologic environment, as well as by chemical, electrical, or mechanical stimuli. These changes may become manifest clinically as seizures or coma. This article describes the general principles by which excitable cells generate action potentials, illustrate how some pharmacologic agents and physical conditions alter excitability, and explain the principles essential for monitoring excitable organ systems, especially the brain. A complete review of the electrophysiology of nervous and muscular systems is beyond the scope of this article, and interested readers are referred to reviews significantly more detailed than this one. 1,12,18,27