Oxygen uptake and mean blood pressure as indicators of induced hyperthermia

This dog study was designed to identify which of two measurements (oxygen consumption, mean blood pressure) tracked the onset of hyperthermia as reflected by rectal temperature. The animals were anesthetized, paralyzed, and mechanically ventilated. Hyperthermia was induced with 2,4-dinitrophenol (5 mg/kg) injected intravenously in 5 dogs. It was found that the best and earliest predictor of approaching hyperthermia was the increase in oxygen consumption, which increased 10% in 1.72 min. Mean blood pressure was an insensitive indicator of approaching hyperthermia. Rectal temperature, not surprisingly, was found to be a late and undependable early indicator of developing hyperthermia, requiring about 15 minutes to exhibit a definite increase. It is concluded that among these indicators, monitoring oxygen consumption (ml/min) is the most reliable way to identify a metabolic change such as incipient hyperthermia.     

Comparative accuracies of a finger blood pressure monitor and an oscillometric blood pressure monitor

A noninvasive blood pressure monitor (Finapres) that uses the methodology of Peaz to continuously display the arterial waveform from the finger has been introduced recently. The Finapres monitor overestimated systolic pressure by 5.8±11.9 mm Hg, while the Dinamap monitor underestimated systolic pressure by –6.9±9.2 mm Hg (P=0.003). Dinamap mean and diastolic pressure biases were less than 2 mm Hg, while the Finapres biases for these variables were significantly greater (7.7±10.0 and 8.2±9.8 mm Hg, respectively). There was no difference in systolic or mean pressure precision between the two devices (approximately 10 mm Hg), but the diastolic precision of the Dinamap unit was superior to that of the Finapres. While in most patients the Finapres monitor provided continuous blood pressure data equivalent to the data from the radial artery, marked bias (>15 mm Hg) was exhibited in 2 patients for all three pressure variables. Despite this bias, blood pressure changes were tracked closely in these 2 patients. We conclude that, in its current form, the Finapres monitor cannot be relied upon independently to accurately measure blood pressure in patients undergoing general anesthesia. Since the Dinamap monitor measures mean pressure reliably and accurately, we suggest that mean blood pressure values between the Finapres and Dinamap monitors be compared to guide one in interpreting Finapres data.Supported in part by a grant from Ohmeda Company, Boulder, CO.Presented in part at the annual meeting of the American Society of Anesthesiologists, New Orleans, October 1989.     

Algorithm to identify components of arterial blood pressure signals during use of an intra-aortic balloon pump

Existing bedside cardiovascular monitors often inaccurately measure arterial blood pressure during intra-aortic balloon pump (IABP) assist. We have developed an algorithm that correctly identifies features of arterial pressure waveforms in the presence of IABP. The algorithm is adaptive, functions in real-time, and uses information from the electrocardiographic (ECG) and arterial blood pressure signals to extract features and numeric values from the arterial blood pressure waveform. In its current form, it requires reliable ECG beat detection and was not intended to operate under conditions of extremely poor balloon timing. The algorithm was evaluated by an expert (P.F-C.) on a limited data set, which consisted of 12 1-minute epochs of data recorded from 6 intensive care unit patients. A criterion for selection of patients was that the ECG beat detector could detect ECG beats correctly from the waveforms. The overall sensitivity and positive predictivity for beat detection were 94.04% and 100%, respectively. For feature identification, the overall sensitivity was greater than 89%, positive predictivity was 100%, and the false-positive rate was 0%. The performance measures may be biased by the criteria for patient selection. This approach to identifying waveform features during IABP improves the accuracy of measurements. The utility of using 2 sources of information to improve measurement accuracy has been demonstrated and should be applicable to other physiologic signal-processing applications.     

Optimal sites for forehead oscillometric blood pressure monitoring

Objective. Blood pressure is usually measured noninvasively with a cuff on the arm or the leg. Circumstances exist, however, when an alternative site for blood pressure measurement is desirable. This study is designed to identify a location on the forehead where blood pressure can be reliably measured noninvasively.Methods. We mapped the superficial temporal artery and/or the supraorbital artery in 65 volunteers and found a rectangular area where an adhesive pressure pad could be placed over each artery. Oscillometric signals were recorded from four different locations over the forehead in 19 of the 65 volunteers to compare the amplitude of the signal and mean blood pressure between locations.Results. The course of the supraorbital artery is quite consistent. It passed through a 2.5-×1-cm rectangular area on the forehead in all volunteers in which it was mapped. The medial border of the rectangle is 0.5-cm medial and 1-cm above the medial corner of the left eyebrow. The course of the superficial temporal artery differed remarkably from person to person. We could not find an area of reasonable size to cover the artery in all volunteers. Mean blood pressures were the same in all forehead locations. The signal was the weakest on the center of the forehead and strongest directly over the superficial temporal artery.Conclusions. Our results show that the supraorbital artery, an end-artery of the internal carotid artery, which emerges through the supraorbital foramen and crosses the forehead near the center, is the preferred site to monitor blood pressure noninvasively on the forehead with an adhesive pressure bladder.This study was supported, in part, by Innerspace Medical Inc., Irvine, CA, and by NASA's Rocky Mountain Space Grant Consortium. This study was presented, in part, at the 1994 Annual Meeting of the American Society of Anesthesiologists, San Francisco, October 15–19, 1994.     

Comparative effects of cuff size and tightness of fit on accuracy of blood pressure measurements

To determine the effect of snugness of cuff wrap on the accuracy of blood pressure (BP) measurements, we performed two studies on 6 healthy volunteers. In both studies, control values were obtained from the right upper arm with cuffs of appropriate size and snug fit. Study 1 had two phases. In the first, cuffs of appropriate size were wrapped snugly around the upper left arm of seated subjects. The effects of two other degrees of cuff snugness on the measurement of BP were evaluated by placing a filled 250-mL intravenous fluid bag between the cuff and arm over the triceps, measuring BP, then draining the same bag of half its contents and then all of its contents without rewrapping the cuff (loose, very loose fit), each time measuring BP. The second phase of study 1 was identical in procedure, except that the cuffs used on the left arm were one size too small. In study 2, the experimental cuffs were placed just above the right ankle. To alter the signal-to-noise ratio, BP was raised or lowered: the standing position elevated mean BP by an average of 90 mm Hg, and elevation of the legs decreased mean BP by an average of 43 mm Hg. In study 1, we found that appropriately sized cuffs, whether wrapped tightly or loosely, gave correct BP readings. Cuffs snugly wrapped, but too small for the subject, gave high BP readings, on the average by approximately 10 mm Hg. Loose wrapping of small cuffs gave variable results in individual subjects that exaggerated systolic BP from 2 to 80 mm Hg. In study 2, elevating the legs or standing decreased or increased BP consistently. Loose wrapping of appropriately sized cuffs around the ankles of the subjects had no additional significant effect on BP.     

Accuracy of four indirect methods of blood pressure measurement,with hemodynamic correlations

In 38 adults undergoing cardiac surgery, 4 indirect blood pressure techniques were compared with brachial arterial blood pressure at predetermined intervals before and after cardiopulmonary bypass. Indirect blood pressure measurement techniques included automated oscillometry, manual auscultation, visual onset of oscillation (flicker) and return-to-flow methods. Hemodynamic measurements or calculations included heart rate, cardiac index, stroke volume index, and systemic vascular resistance index. Indirect and intraarterial blood pressure values were compared by simple linear regression by patient and measurement period. Measurement errors (arterial minus indirect blood pressure) were calculated, and stepwise regression assessed the relationship between measurement error and heart rate, cardiac index, stroke volume index, and systemic vascular resistance index. Indirect to intraarterial blood pressure correlation coefficients varied over time, with the strongest correlations often occurring at the first and last measurement periods (preinduction and 60 minutes after cardiopulmonary bypass), particularly for systolic blood pressure. Within-patient correlations between indirect and arterial blood pressure varied widely—they were consistently high or low in some patients. In other patients, correlations were especially weak with a particular indirect blood pressure method for systolic, mean, or diastolic blood pressure; in some cases indirect blood pressure was inadequate for clinical diagnosis of acute blood pressure changes or trends. The mean correlations between indirect and direct blood pressure values were, for systolic blood pressure: 0.69 for oscillometry, 0.77 for auscultation, 0.73 for flicker, and 0.74 for return-to-flow; for mean blood pressure: 0.70 for oscillometry and 0.73 for auscultation; and for diastolic blood pressure: 0.73 for oscillometry and 0.69 for auscultation. The mean measurement errors (arterial minus indirect values) for the individual indirect blood pressure methods were, for systolic: 0 mm Hg for oscillometry, 9 mm Hg for auscultation, -5 mm Hg for flicker, 7 mm Hg for return-to-flow; for mean: -6 mm Hg for oscillometry, and -3 mm Hg for auscultation; and for diastolic: -9 mm Hg for oscillometry and -8 mm Hg for auscultation. Mean measurement error for systolic blood pressure was thus least with automated oscillometry and greatest with manual auscultation, while standard deviations ranging from 9 to 15 mm Hg confirmed the highly variable nature of single indirect blood pressure measurements. Except for oscillometric diastolic blood pressure, a combination of systemic hemodynamics (heart rate, stroke volume index, systemic vascular resistance index, and cardiac index) correlated with each indirect blood pressure measurement error, which suggests that particular numeric ranges of these variables minimize measurement error. This study demonstrates that striking variability occurs in the relationship between indirect and arterial blood pressure measurements, and that the systemic hemodynamic state influences accuracy of indirect blood pressure measurements. When the reproducibility of repeated indirect blood pressure measurements appears unsatisfactory or inconsistent with other clinical observations, clinicians may find that an alternative indirect blood pressure method is a better choice. Of the methods tested, no single indirect blood pressure technique showed precision superior to the others, but two methods yielded data only for systolic pressure. These findings lend support to intraarterial blood pressure measurement in conditions of hemodynamic variability, and suggest the theoretical benefits of continuous indirect blood pressure measurements. Annual meeting of the American Society of Anesthesiologists, New Orleans, LA, Oct 1984.     

Blood pressure monitoring: Automated oscillometric devices

An understanding of the principles of blood pressure measurement with automated oscillometric devices (e.g., Dinamap) allows a user to realize the purpose and level of accuracy for which the equipment is designed. Good technique calls for various actions: (1) using a cuff of proper size (too large a cuff will generally work acceptably, but too small a cuff will yield erroneously high readings); (2) squeezing all of the residual air out of the cuff before applying it to the arm or leg; (3) wrapping the cuff snugly around the arm or leg; (4) instructing the patient to refrain from talking or moving and letting nothing press against the cuff during measurement; (5) keeping the cuff and heart at the same horizontal level. (6) When instrument malfunction is suspected, first checking the status of the patient (not the status of the instrument) to be sure that a clinical emergency is not causing the suspected malfunction; (7) repeating a reading several times when it is suspicious and, if necessary, modifying the measurement conditions by using, for example, different limbs or different cuffs until the question is resolved; and (8) remembering that a leak in the cuff, hoses, or connection can cause an unexpected malfunction.     

Pulse oximetry and finger blood pressure measurement during open-heart surgery

Pulse oximeter arterial hemoglobin oxygen saturation (SpO₂) and finger arterial pressure (FINAP) were continuously monitored before, during, and after cardiopulmonary bypass in 15 male patients. SpO₂ was monitored simultaneously with two pulse oximeters, a Nellcor N-100 and an Ohmeda Biox III. The readings obtained from the two pulse oximeters were compared with arterial blood measurements obtained using a CO-oximeter. FINAP was monitored by a prototype device (Finapres) based on the Peaz volume-clamp method. FINAP was correlated with intraarterial pressure (IAP). Both pulse oximeters functioned well before cardiopulmonary bypass. The correlations with CO-oximeter values were 0.927 for the N-100 and 0.921 for the Biox III. Immediately after the onset of cardiopulmonary bypass, the N-100 pulse oximeter stopped displaying values. The Biox III pulse oximeter continued to display values during the cardiopulmonary bypass period; the correlation with CO-oximeter values was 0.813. After cardiopulmonary bypass, the N-100 began displaying values in 2 to 10 minutes. After cardiopulmonary bypass the correlation with CO-oximeter values was 0.792 for the N-100 and 0.828 for the Biox III pulse oximeter. The Finapres finger blood pressure device functioned well in 13 of 15 patients before cardiopulmonary bypass. The mean bias ± precision of FINAP-IAP for mean pressure was 8.3±10.2 mm Hg (SD) and the correlation coefficient was 0.814. During cardiopulmonary bypass, the Finapres device functioned well in 10 of 15 patients. The mean bias precision of FINAP-IAP, for mean pressure in these 10 patients was 6.6±8.7 mm Hg and the correlation coefficient was 0.902. Immediately after cardiopulmonary bypass, the Finapres functioned well in 11 of 15 patients. The mean bias ± precision of FINAP-IAP for mean pressure was 8.6±14.1 mm Hg and the correlation coefficient was 0.533. This study documented that devices for continuous noninvasive monitoring can usually function well under the extreme conditions seen during open-heart surgery. Pulse oximeters may find a place in the monitoring of patients during open-heart surgery, although they cannot totally replace the invasive techniques. Under the conditions of diminished pulsatile peripheral blood flow we observed some differences between the two pulse oximeters.     

A quantitative evaluation of the Hewlett-Packard 78354A noninvasive blood pressure meter

Oscillometrically determined brachial artery pressures were compared with simultaneous contralateral radial intraarterial pressures in 19 anesthetized adult cardiac surgical patients throughout their surgical procedures, interrupted only by nonpulsatile, low-pressure, low-flow cardiopulmonary bypass. Radial intraarterial pressure values ranged widely for systolic (55 to 207 torr), mean (43 to 141 torr), and diastolic (26 to 106 torr). Both error specification methods proposed by the Association for the Advancement of Medical Instrumentation were used and compared. As expected, error method 1 gave consistently lower mean errors, smaller error standard deviations, and higher correlation coefficients than did error method 2. The errors during time periods immediately before and after cardiopulmonary bypass were compared with those from more quiescent times. Higher mean errors, larger error standard deviations, and lower correlation and regression coefficients were found during those time periods surrounding cardiopulmonary bypass. In general, mean errors were lowest for systolic pressure, followed by mean and diastolic pressures in that order, whereas error standard deviations were smallest for mean pressure, followed by systolic and diastolic pressures. Correlation and regression coefficients were highest for systolic pressure, followed by mean and diastolic pressures. In summary, the oscillometric method provides convenient and reproducible estimates of radial intraarterial pressure during most clinical situations, typically with better accuracy than the auscultatory Korotkoff method. The accuracy and reproducibility are diminished during those periods immediately surrounding cardiopulmonary bypass, perhaps due to direct surgical manipulation of the heart with its attendant rapid changes in cardiac output and blood pressure.     

Does measurement of systolic blood pressure with a pulse oximeter correlate with conventional methods?

The pulse oximeter is commonly used in the operating room. We evaluated the use of a pulse oximeter to monitor systolic blood pressure in 20 healthy volunteers and 42 anesthetized patients. We compared the pulse oximeter method of measuring systolic blood pressure with the cuff methods using Korotkoff sounds and Doppler ultrasound as well as with direct pressure measurement through an intraarterial cannula. Systolic blood pressure values obtained by pulse oximeter correlated well with values obtained by other conventional methods. The best correlation was found with Doppler ultrasound (r = 0.996) and the worst with arterial cannulation (r = 0.880). We conclude that this method can be used intraoperatively to measure systolic blood pressure.     

Tissue hypoxia distal to a Peñaz finger blood pressure cuff

The Peñaz finger method to measure blood pressure uses a finger cuff in which the pressure level fluctuates in the vicinity of the mean arterial pressure level and thereby interferes with the circulation of blood to and from the fingertip. We measured capillary blood gases and saturation of hemoglobin in the finger during Peñaz finger blood pressure (PFBP) monitoring to assess the degree to which it impairs circulation in the fingertip. Within 2.5 minutes after initiating PFBP monitoring, capillary oxygen tension (Po₂) had decreased significantly, from about 71 mm Hg to between 49 and 58 mm Hg for up to 50 minutes. These changes were quite different from those occurring when an occlusive tourniquet was applied around the finger. Within 10 minutes of tourniquet application, acidosis (pH 7.25), hypercapnia (carbon dioxide tension, 59.0 mm Hg), and hypoxemia (Po₂, 29 mm Hg) resulted. Within 30 seconds of releasing the PFBP cuff, capillary blood gas values were back to normal. Interspersing 30-second rest periods every 5 minutes during 35 minutes of PFBP monitoring actually decreased capillary oxygen values compared with monitoring without such rest periods. A finger pulse oximeter distal to the PFBP cuff showed desaturation from an average of 97% to 93.7%, with much variability. However, desaturation was statistically significant within 1 minute of application of the PFBP cuff. Within 1 minute the finger volume increased an average of 0.05 ml. After 1 minute the volumes varied widely and, on the average, returned to normal despite continued PFBP monitoring.     

Noninvasive continuous blood pressure measurement: A clinical evaluation of the Cortronic APM 770

The Cortronic APM 770 (Cortronic, Ronkonkoma, NY) is a commercial device that claims to measure blood pressure noninvasively and continuously with the use of a standard blood pressure cuff. The aim of our study was to assess the performance of the continuous-mode blood pressure readings of the Cortronic during anesthesia and surgery. We recorded blood pressure in 5 patients bilaterally. An intraarterial pressure (IAP) curve was recorded from 1 arm and the Cortronic pressure curve (CPC) was recorded from the other. For statistical analysis the period between 2 Cortronic recalibrations was defined as the intercalibration interval. The duration of these intervals ranged from 20 to 0.5 minutes. Four paired samples were drawn from each interval. The first sample in an interval represented the recalibration blood pressure; the other samples represented the continuous blood pressure. A total of 1,232 samples were taken, of which 308 were recalibration. The median of the differences and the 2.5th and 97.5th percentile limits of agreement were determined. Their respective values for diastolic and systolic recalibration measurements were 5, –17, and 34 mm Hg, and 6, –12, and 38 mm Hg. Their values for continuous measurements were 4, –23.5, and 32 mm Hg, and 6, –30, and 70 mm Hg. Changes in CPC were evaluated against changes in the corresponding IAP by plotting them in 4-quadrant graphs. In these graphs the Spearman rank correlations were betweenr=–0.17 andr=0.01. We observed opposite CPC and IAP trends on 24 occasions during this study. We performed a simple simulation study to better understand the measurement method of the Cortronic. The study showed a positive relationship between pulsation volume and CPC amplitude, and between pulsation rate and CPC amplitude. We conclude that during anesthesia and surgery continuous-mode blood pressure readings of the Cortronic are unreliable, and suggest that the phenomenon of the two pressures' moving in opposite directions is inherent to the measurement principles of the device.     

Evaluation of a continuous noninvasive blood pressure monitor in obstetric patients undergoing spinal anesthesia

A noninvasive blood pressure monitor (Finapres) that continuously displays the arterial waveform using the Penaz methodology has recently been introduced into clinical practice. We compared this device with an automated oscillometric blood pressure monitor (Dinamap 1846SX) in 20 patients during spinal anesthesia for nonemergency cesarean section according to a procedure suggested by the Association for the Advancement of Medical Instrumentation. After administration of the spinal anesthetic, the Finapres monitor produced systolic, mean, and diastolic pressure measurements greater than those of the Dinamap monitor (6.6±12.5, 3.3±10.4, and 7.2±9.8 mm Hg, respectively). In most patients, the Finapres measurements were similar to those determined by the Dinamap; however, in 4 patients, mean systolic differences were greater than 20 mm Hg. These patients did not differ from the others in age, height, weight, or baseline blood pressure, and the pressure values recorded by the Finapres monitor were substantially higher than those measured by auscultation in the labor room. In 30% of the patients, the offset between Dinamap and Finapres blood pressure measurements changed markedly over the course of the surgical procedure. The Finapres monitor occasionally stopped working and had to be restarted. In 1 patient (not included in this analysis), the Dinamap monitor was unable to determine the blood pressure due to patient shivering; this did not appear to interfere with the Finapres. We conclude that the Finapres monitor does not consistently provide blood pressure information equivalent to that of the Dinamap in obstetric patients undergoing spinal anesthesia. When the Finapres monitor is used, pressure measurements should be verified periodically by using an auscultatory or oscillometric blood pressure methodology to rule out the presence of large differences, particularly in systolic pressure. The extreme systolic blood pressure discrepancies noted in 20% of the patients studied warrant further evaluation.     

A clinical evaluation of rapid automatic noninvasive blood pressure determination with the Ohmeda 2120 “return-to-flow” method

Most commercial noninvasive blood pressure devices use the oscillometric method for determination of blood pressure. The Ohmeda 2120 noninvasive blood pressure monitor uses the oscillometric technique, but it also includes a Sys Stat mode for rapid determination of systolic blood pressure up to ten times per minute. This Sys Stat mode uses the return-to-flow method, in which the pressure on an upper arm cuff decreases in small steps until a finger sensor detects the first pulse of blood. Data from 16 patients monitored with the Ohmeda 2120 unit and with an arterial cannula were analyzed. The line of regression was Sys Stat = 0.85 (arterial) + 9.49. The Ohmeda 2120 monitor tended to under-estimate the arterial pressure, particularly at higher pressures. Several factors could have contributed to this underestimation. Even so, the accuracy is sufficient for clinical use under most circumstances. More importantly, in an urgent situation, the Sys Stat mode can provide a reading of systolic blood pressure within seconds.Supported by a grant from Ohmeda.Presented in part as a poster presentation at the annual meeting of the American Society of Anesthesiologists, San Francisco, October 1988.     

Noninvasive blood pressure monitoring from the supraorbital artery using an artificial neural network oscillometric algorithm

Objective. Our objective was to overcome the limitations of linear models of oscillometric blood pressure determination by using a nonlinear technique to model the relationship between the oscillometric envelope and systolic and diastolic blood pressures, and then to use that technique for near-continuous arterial pressure monitoring at the supraorbital artery.Methods. An adhesive pressure pad and transducer were used to collect oscillometric data from the supraorbital artery of 85 subjects. These data were then used to train an artificial neural network (ANN) to report diastolic or systolic pressure. Arterial pressure measurements defined by brachial artery auscultation were used as a reference. ANN results were compared with those obtained using a standard oscillometric algorithm that determined pressures based on fixed percentages of the maximum oscillometric amplitude.Results. The ANN produced better estimates of reference blood pressures than the standard oscillometric algorithm. Mean difference between target and actual output for the ANN was 0.50±5.73 mm Hg for systolic pressures, compared to the mean difference of the standard algorithm of 2.78±19.38 mm Hg. For diastolic pressures, the ANN had a mean difference of 0.04±4.70 mm Hg, while the mean difference of the standard algorithm was –0.34±9.75 mm Hg.Conclusions. The ANN produced a better model of the relationship between the oscillometric envelope and reference systolic and diastolic pressures than did the standard oscillometric algorithm. Noninvasive blood pressure measured from the supraorbital artery agreed with pressure measured by auscultation in the brachial artery, and may sometimes be more clinically useful than an arm cuff device.This research was supported, in part, by a grant from Baxter Healthcare Corporation (Santa Ana, CA), and Innerspace Medical (Irvine, CA). A grant of computer time from the Utah Supercomputer Institute, which is funded by the State of Utah and the IBM Corporation, is gratefully acknowledged.     

Fuzzy-logic control of blood pressure through enflurane anesthesia

Objective. The objective of our study was to construct a closed-loop blood pressure control system using fuzzy logic during enflurane anesthesia.Methods. Direct systolic blood pressure (SBP), the input variable, was assessed by a special fuzzy-logic membership function—that is, a triangulate continuum of grades between 0 and 1. We also set up the output membership function for the inhaled enflurane concentration. Four fuzzy-rule maps, or matrices, which determined the relationship between the changes of input variables and output values, were constructed based on published anesthetic values. The first map was based on the end-tidal anesthetic concentration known to block an adrenergic response. The fourth map was derived from the anesthetic effective dose (AD₉₅). Fuzzy inference, arrived at by using fuzzy logic, followed the minimum-maximum center of gravity method. Anesthetic control started with the first map and was maintained with the succeeding maps.Results. During anesthesia, the SBP remained within ±20% of the preanesthetic SBPs in 82% of the fuzzy control cases and within 83% during manual control. The difference was not significant.Conclusion. The anesthetist’s management of the administration of the inhaled anesthetic enflurane was imitated by fuzzy-logic control of the blood pressure. This paper was presented in part at the Proceedings of the International Conference on Fuzzy Logic & Neural Networks IIZUKA ’90.     

Analysis of intracranial pressure

Methods for the acquisition and analysis of intracranial pressure (ICP) signals are reviewed from clinical and technical perspectives. The clinical importance of ICP monitoring is presented, and methods for ICP transduction are briefly discussed. These methods include intraventricular catheters, subarachnoid screws, epidural techniques, and the new fiberoptic ICP measurement systems. Approaches to the visual analysis of the ICP waveform are presented, with special emphasis on the relationship between the ICP waveform and the arterial blood pressure signal. Methods of computer-based ICP analysis are also reviewed, including histogram and systems analysis methods. Methods to predict ICP pressure rises and to estimate intracranial compliance are also discussed. Finally, ICP monitoring is reviewed from the point of view of patient outcome. It is concluded that advanced ICP waveform analysis methods warrant further clinical evaluation to demonstrate their clinical usefulness.     

Analysis of intracranial pressure

Methods for the acquisition and analysis of intracranial pressure (ICP) signals are reviewed from clinical and technical perspectives. The clinical importance of ICP monitoring is presented, and methods for ICP transduction are briefly discussed. These methods include intraventricular catheters, subarachnoid screws, epidural techniques, and the new fiberoptic ICP measurement systems. Approaches to the visual analysis of the ICP waveform are presented, with special emphasis on the relationship between the ICP waveform and the arterial blood pressure signal. Methods of computer-based ICP analysis are also reviewed, including histogram and systems analysis methods. Methods to predict ICP pressure rises and to estimate intracranial compliance are also discussed. Finally, ICP monitoring is reviewed from the point of view of patient outcome. It is concluded that advanced ICP waveform analysis methods warrant further clinical evaluation to demonstrate their clinical usefulness.     

Clinical comparison of automated auscultatory and oscillometric and catheter-transducer measurements of arterial pressure

Arterial pressure measurements recorded from a radial artery catheter-transducer (RAC) system were compared with similar data obtained from an automated sphygmomanometer that uses both oscillometric (OSC) and auscultatory measurement techniques. Data were obtained from 50 patients during and immediately after surgery. The fundamental frequency of the RAC system was 23.7 ± 6.7 Hz (mean ± SD; range, 13 to 40 Hz), and the damping coefficient was 0.26 ± 0.06 (mean ± SD; range, 0.15 to 0.34). Linear regression analysis of RAC against OSC values (n = 385) revealed the following correlations: (1) systolic pressure: OSC = 0.92(RAC) + 3.5, r = 0.91; (2) diastolic pressure: OSC = 0.92(RAC) + 1.3, r = 0.76; and (3) mean pressure: OSC = 0.96(RAC) + 0.68, r = 0.84. There were significant differences between each pair of pressure values; mean percent differences (RAC pressure minus OSC pressure) were 4.5 ±0.3%, 5.5 ± 0.7%. and - 2.7 ± 0.5% for systolic, diastolic, and mean values, respectively. Manual and automated auscultatory measurements closely agreed, and both correlated well with OSC values for systolic and diastolic pressure. However, both manual and automated auscultatory, as well as OSC measurements, underestimated RAC systolic and overestimated RAC diastolic pressure.     

Comparative analysis between epidural (Gaeltec) and suboural (Camino) intracranial pressure probes

The new fiberoptic Camino system has recently been introduced for clinical intracranial pressure (ICP) monitoring. We compared the subdural Camino system with the well-established epidural Gaeltec system in both in vitro and clinical conditions. In the in vitro experiments the intracranial vault was simulated by a tightly closed, fluid-filled box (0.9% sodium chloride) with the two probes inside. We simulated pulsating waveforms with a jet ventilator. No difference between the simulated curve patterns and values could be detected. In the clinical studies, both probes were implanted in 10 patients who had either head injuries, subarachnoid hemorrhage, or intracerebral hemorrhage. The in vivo comparison revealed no significant difference between the two systems in the recorded pressures in group 1 (ICP<20 mm=" hg).=" the=" subdurally=" placed=" camino=" probe=" showed=" insignificantly=" lower=" icp=" values=" than=" did=" the=" extradural=" gaeltec=" probe.=" although=" group=" 2=" (icp=">20 mm Hg) waveforms were nearly identical, significant differences (p<0.01) in=" pressure=" measurements=" (systolic,=" diastolic,=" and=" mean)=" occurred=" (camino,=" 18±3=" mm=" hg;=" gaeltec,=" 27±3=" mm=" hg).=" correlation=" coefficients=" for=" mean=" icp=" values=" were=" 0.82=" in=" group=" 1=" and=" 0.49=" in=" group=" 2.=" problems=" with=" the=" camino=" probe=" were=" usually=" mechanical=" and=" occurred=" in=" 2=" patients.=" the=" problems=" were=" either=" easy=" to=" recognize=" or=" manifested=" as=" an=" ostensibly=" pathologic=" curve.=" no=" infection=" occurred=" with=" either=" system=" during=" or=" following=" implantation.=" the=" dissimilar=" characteristics=" of=" the=" two=" probes=" can=" be=" ascribed=" to=" their=" different=" extradural=" and=" subdural=" implantation=" sites.=" the=" gaeltec=" probe=" was=" more=" durable=" over=" the=" period=" of=" implantation,=" which=" averaged=" 98=" hours=" and=" ranged=" from=" 44=" to=" 298=" hours.=" intracranial=" pressure=" values=" measured=" subdurally=" seemed=" to=" be=" more=" true=" to=" life=" in=" the=" high-pressure=" ranges.=" both=" probes=" can=" be=" used=" for=" routine,=" continuous=" icp=" monitoring.=" while=" subdural=" icp=" probes=" can=" give=" correct=" values=" without=" delay=" and=" in=" vivo=" show=" more=" detail=" and=" change=" with=" ventilation,=" the=" epidural=" system=" was=" more=">Presented in part at the 20th Congress of the Scandinavian Society of Anaesthesiologists, June 1989, Copenhagen, Denmark.