Frank E. Block

Normal fluctuation of physiologic cardiovascular variables during anesthesia and the phenomenon of “smoothing”

With the advent of automated anesthesia record keeping devices, concern has arisen that “abnormal” values will appear in the record and possibly lead to medicolegal compromise. A retrospective review of automated records from a series of anesthesia cases was undertaken to determine if abnormal values do occur, how frequent they are, and whether they cause problems. A total of 14,826 (4,942 each) noninvasive heart rate, systolic, and diastolic blood pressure readings from 118 case printouts generated by a Diatek Arkive Patient Information Management System (63 cases) or a Data-scope Datatrac record keeper (55 cases) were recorded. The study sample covered a broad range of surgical operations, anesthetic procedures, and patient ages and medical histories. During these 118 anesthetics, the majority of readings of all three variables fell within normal ranges (defined for this study as 80 to 180 and 50 to 110 mm Hg for systolic and diastolic blood pressures, respectively, and 60 to 140 beats/min for heart rate). During the anesthetics, 3.6% of the systolic pressure readings, 13.25% of the diastolic readings, and 4.25% of the heart rate readings were recorded outside these ranges. No serious intraoperative or postoperative anesthesia complications were associated with these out-of-range readings, nor would they be expected in a sample of this size, since serious anesthetic complications are rare. This preliminary observation of one persons experience may help address the concern associated with allowing high and low blood pressure and heart rate readings to be automatically recorded “unsmoothed.” In medicolegal situations, it should also begin to demonstrate that such fluctuations are neither uncommon nor abnormal, and that a true record of these readings should be neither a cause for concern nor an opportunity for medicolegal exploitation.With the advent of automated anesthesia record keeping devices, concern has arisen that “abnormal” values will appear in the record and possibly lead to medicolegal compromise. A retrospective review of automated records from a series of anesthesia cases was undertaken to determine if abnormal values do occur, how frequent they are, and whether they cause problems. A total of 14,826 (4,942 each) noninvasive heart rate, systolic, and diastolic blood pressure readings from 118 case printouts generated by a Diatek Arkive Patient Information Management System (63 cases) or a Data-scope Datatrac record keeper (55 cases) were recorded. The study sample covered a broad range of surgical operations, anesthetic procedures, and patient ages and medical histories. During these 118 anesthetics, the majority of readings of all three variables fell within normal ranges (defined for this study as 80 to 180 and 50 to 110 mm Hg for systolic and diastolic blood pressures, respectively, and 60 to 140 beats/min for heart rate). During the anesthetics, 3.6% of the systolic pressure readings, 13.25% of the diastolic readings, and 4.25% of the heart rate readings were recorded outside these ranges. No serious intraoperative or postoperative anesthesia complications were associated with these out-of-range readings, nor would they be expected in a sample of this size, since serious anesthetic complications are rare. This preliminary observation of one persons experience may help address the concern associated with allowing high and low blood pressure and heart rate readings to be automatically recorded “unsmoothed.” In medicolegal situations, it should also begin to demonstrate that such fluctuations are neither uncommon nor abnormal, and that a true record of these readings should be neither a cause for concern nor an opportunity for medicolegal exploitation.

Ankle blood pressure measurement, an acceptable alternative to arm measurements

The use of automatic noninvasive blood pressure (NIBP) devices has become a common technique to monitor blood pressure intraoperatively. The usual cuff placement for these devices on the upper arm sometimes poses problems. As an alternative, many clinicians place the cuff on the ankle. This practice has not been previously investigated to determine its efficacy. The purpose of our study was to determine whether a noninvasive blood pressure cuff on the arm could be replaced by one on the ankle.We monitored 24 patients intraoperatively with two non-invasive blood pressure cuffs, one on the upper arm and one on the ankle. Systolic, diastolic, and mean pressures were obtained from each cuff placement at intervals of no shorter than 3 minutes. The time necessary to obtain the measurements and the presence of any artifact were also recorded.A total of 404 pairs of data were obtained and the systolic blood pressure ranged from 82 to 196 mm Hg. The mean and diastolic pressure readings were equivalent between the arm and ankle blood pressure readings. The systolic pressures were not equivalent, reflecting the fact that the ankle systolic blood pressure is physiologically higher than the arm systolic blood pressure. The difference between the times necessary to obtain the readings from arm or ankle was not statistically significant. Eight of the paired readings 2.0%) represented artifact, arbitrarily defined as a difference in mean blood pressure readings of 15 mm Hg between the arm and the ankle. Since the mean blood pressure readings obtained at the arm and at the ankle were statistically equivalent, we concluded that the ankle cuff placement provided a reliable alternative to the placement of the cuff on the arm.

Evaluation of users' abilities to recognize musical alarm tones

The problem of accurate identification of alarm sounds in the operating room, recovery room, and intensive care environment has persisted for many years. Monitors made by different companies may have different alarm sounds for the same monitored variable, and similar alarm sounds for different variables. In an effort to illustrate universal alarms sounds, a system of six musical alarm tones was designed with musical themes from popular songs used for oxygenation, ventilation, cardiovascular monitoring, temperature monitoring, artificial perfusion, and drug administration systems. These melodies were played for a group of anesthesiologists and others, who were initially asked to guess the organ system for each melody. The answers were then given to the participants, and after a short delay the melodies were played again in a different order. Seventy-nine response sheets were collected. The expected random score was 1.0±1.0 SEM correct. The observed score on the first hearing was 1.5±1.6 SEM,p=0.01 compared with the random score. The observed score on the second testing was 4.3±2.2 SEM,p=0.001 compared with the first hearing. Indeed, 42 of 79 (53%) respondents got all six answers correct on the second testing, versus three respondents for the first testing. The implications of these findings are discussed in the context of integrated alarm systems used in complex medical environments such as the operating room.The problem of accurate identification of alarm sounds in the operating room, recovery room, and intensive care environment has persisted for many years. Monitors made by different companies may have different alarm sounds for the same monitored variable, and similar alarm sounds for different variables. In an effort to illustrate universal alarms sounds, a system of six musical alarm tones was designed with musical themes from popular songs used for oxygenation, ventilation, cardiovascular monitoring, temperature monitoring, artificial perfusion, and drug administration systems. These melodies were played for a group of anesthesiologists and others, who were initially asked to guess the organ system for each melody. The answers were then given to the participants, and after a short delay the melodies were played again in a different order. Seventy-nine response sheets were collected. The expected random score was 1.0±1.0 SEM correct. The observed score on the first hearing was 1.5±1.6 SEM,p=0.01 compared with the random score. The observed score on the second testing was 4.3±2.2 SEM,p=0.001 compared with the first hearing. Indeed, 42 of 79 (53%) respondents got all six answers correct on the second testing, versus three respondents for the first testing. The implications of these findings are discussed in the context of integrated alarm systems used in complex medical environments such as the operating room.

Technology evaluation report: Obtaining pulse oximeter signals when the usual probe cannot be used

We studied the function of four different monitoring probes used with the Satlite™ pulse oximeter (Datex, Helsinki). The aim was to evaluate ease of use and compare the function of the probes and their attachment methods in different locations (finger, toe, ear, thumb web, instep, wrist, and ankle).Two similar pulse wave oximeters were used in the study. To select the best signal we determined the absolute height of the Plethysmographic waveform for each probe. Probes were compared on awake normal adult volunteers (N=13), in anesthetized adult patients (N=12), and in neonates weighting 500–1000 g (N=8). In all the adult trials, the clip-on finger probe was used as a reference, and probes taped or clipped onto the finger provided adequate signals in comparison. Taped-on probes gave also satisfactory results on the toe. It was difficult to get a quality signal from the ear or from the thumb web, however. In the neonates, taped-on probes were most satisfactory.

Clinical evaluation of the 'head-up' display of anesthesia data - Preliminary communication

To solve the problem of monitoring the patient during administration of anesthesia, a commercially available headup display (HUD) was evaluated during one day of surgery at the Ohio State University Hospitals. This monitor is mounted on a headband worn by the anesthesiologist. It projects a monochrome image of monitor data directly into one eye. Eleven anesthesiologists tested the device. Most users were able to adjust to the monitor in about fifteen minutes. Nine of the testers expressed a desire to evaluate the monitor further. Their major complaints were that the connecting cable between the HUD and its computer was too short, the resolution of the monitor was inadequate, and the data on the screen were not organized in a familiar way. If these problems could be corrected, most users believed that this HUD could be a valuable tool to aid the anesthesiologist in the operating room.

Can people hear the pitch change on a variable-pitch pulse oximeter ?

The introduction of the variable-pitch feature on pulse oximeters in 1983 by the Nellcor Corporation (Hayward, CA) allowed users to rapidly detect changes in oxygen saturation by listening for changes in the pitch of the tones emitted by the pulse oximeter. A few individuals have reported that they have been unable to detect a change in pitch when oxygen saturation changes. To these individuals, the variable-pitch feature of these pulse oximeters has not been beneficial. Using the pitches from one manufacturer of oximeters, we created a computer program to simulate the pitches that accompanied various oxygen saturations. The pitches were recorded onto a tape player and played for 75 volunteer subjects unfamiliar with the pitches of a variable-pitch pulse oximeter. Of our sample, 67% were able to detect a single change in pitch corresponding to a 1% fall in oxygen saturation, and 11% of the population could not detect a change in pitch until there was a change in pitch with every beat. We suggested four alternative designs that may prove beneficial to this group of individuals.

Auditory alarms during anesthesia monitoring with an integrated monitoring system

Alarms in the operating room remain a major source of annoyance and confusion. A previous study by Kestin et al. utilized a specific combination of distinct, separate monitors in 50 pediatric patients. He reported a mean of 10 alarms per case with a mean frequency of one alarm every 4.5 minutes. The alarms were classified as spurious (75%), change outside the alarm limits (22%), or patient risk (3%). We performed a similar study with 50 adult patients under general anesthesia with default alarm settings on an integrated monitor, (Cardiocap™, Datex, Helsinki). In our study, the number of alarms averaged 3 per case with a mean frequency of one every 34 minutes. Spurious alarms (those caused by electrocautery, accidental patient movement, or other non-physiological reasons) represented only 24% of all alarms. Those alarms sounding that were outside the limits occurred at a rate of 53%, and those that were considered patient risks occurred at a rate of 23%. Of the alarms, 67% occurred during the beginning and end of anesthesia. The end-tidal carbon dioxide accounted for 42% of the alarms, mostly during intubation and extubation. Suggestions are made for further improvement in alarm systems.

An expert system to teach troubleshooting of common problems associated with the automated anesthesia recordkeeper

Automated anesthesia recordkeepers have been used to monitor patients during surgery in up to 90% of cases at The Ohio State University. The record-keeping devices are complex and can be difficult to troubleshoot. The 1st-CLASS Fusion Program, an expert system “shell-program,” has been programmed to allow the resident or nurse anesthetist to solve the two most common types of problems associated with the recordkeeper: printer problems and patient monitor problems. Use of this program allows the resident or nurse anesthetist to troubleshoot the recordkeeper quickly and accurately and promotes in the user a sense of competence and control over the technology.

Anesthetic management of labor in a patient with dextrocardia, congenitally corrected transposition, Wolff-Parkinson-White syndrome, and congestive heart failure

Labor and delivery greatly stress the cardiovascular system. In this patient with underlying congenital heart disease and congestive heart failure, hemodynamic stability was maintained with a combination of lumbar epidural and caudal epidural anesthesia.

A carbon dioxide monitor that does not show the waveform is worthless

The author suggests that the carbon dioxide waveform should be displayed, as are the electrocardiogram and arterial pressure waveforms. He argues that a carbon dioxide analyzer that does not provide a waveform is not of value, as subtle changes in the carbon dioxide waveform can reflect impending problems. Only when a plateau is present in the capnogram can one be certain that end-tidal gas is being measured, and the author asserts that the presence or absence of this plateau can be detected only by visually inspecting the waveform.The author suggests that the carbon dioxide waveform should be displayed, as are the electrocardiogram and arterial pressure waveforms. He argues that a carbon dioxide analyzer that does not provide a waveform is not of value, as subtle changes in the carbon dioxide waveform can reflect impending problems. Only when a plateau is present in the capnogram can one be certain that end-tidal gas is being measured, and the author asserts that the presence or absence of this plateau can be detected only by visually inspecting the waveform.