Robert G. Stout

Different responses of ear and finger pulse oximeter wave form to cold pressor test.

The cold pressor test is often used to assess vasoconstrictive responses because it simulates the vasoconstrictive challenges commonly encountered in the clinical setting. With IRB approval, 12 healthy volunteers, aged 25–50 yr, underwent baseline plethysmographic monitoring on the finger and ear. The contralateral hand was immersed in ice water for 30 s to elicit a systemic vasoconstrictive response while the recordings were continued. The changes in plethysmographic amplitude for the first 30 s of ice water immersion (period of maximum response) of the finger and ear were compared. The data indicate a significant disparity between the finger and the ear signals in response to the cold stimulus. The average finger plethysmographic amplitude measurement decreased by 48% ± 19%. In contrast, no significant change was seen in the ear plethysmographic amplitude measurement, which decreased by 2% ± 10%. We conclude that the ear is relatively immune to the vasoconstrictive effects. These findings suggest that the comparison of the ear and finger pulse oximeter wave forms might be used as a real-time monitor of sympathetic tone and that the ear plethysmography may be a suitable monitor of the systemic circulation.

What is the best site for measuring the effect of ventilation on the pulse oximeter waveform

The cardiac pulse is the predominant feature of the pulse oximeter (plethysmographic) waveform. Less obvious is the effect of ventilation on the waveform. There have been efforts to measure the effect of ventilation on the waveform to determine respiratory rate, tidal volume, and blood volume. We measured the relative strength of the effect of ventilation on the reflective plethysmographic waveform at three different sites: the finger, ear, and forehead. The plethysmographic waveforms from 18 patients undergoing positive pressure ventilation during surgery and 10 patients spontaneously breathing during renal dialysis were collected. The respiratory signal was isolated from the waveform using spectral analysis. It was found that the respiratory signal in the pulse oximeter waveform was more than 10 times stronger in the region of the head when compared with the finger. This was true with both controlled positive pressure ventilation and spontaneous breathing. A significant correlation was demonstrated between the estimated blood loss from surgical procedures and the impact of ventilation on ear plethysmographic data (rs = 0.624, P = 0.006).

The Use of Joint Time Frequency Analysis to Quantify the Effect of Ventilation on the Pulse Oximeter Waveform

Objective. In the process of determining oxygen saturation, the pulse oximeter functions as a photoelectric plethysmograph. By analyzing how the frequency spectrum of the pulse oximeter waveform changes over time, new clinically relevant features can be extracted. Methods. Thirty patients undergoing general anesthesia for abdominal surgery had their pulse oximeter, airway pressure and CO2 waveforms collected (50 Hz). The pulse oximeter waveform was analyzed with a short-time Fourier transform using a moving 4096 point Hann window of 82 seconds duration. The frequency signal created by positive pressure ventilation was extracted using a peak detection algorithm in the frequency range of ventilation (0.08–0.4 Hz = 5–24 breaths/minute). The respiratory rate derived in this manner was compared to the respiratory rate as determined by CO2 detection. Results. In total, 52 hours of telemetry data were analyzed. The respiratory rate measured from the pulse oximeter waveform was found to have a 0.89 linear correlation when compared to CO2 detection and airway pressure change. the bias was 0.03 breath/min, SD was 0.557 breath/min and the upper and lower limits of agreement were 1.145 and −1.083 breath/min respectively. The presence of motion artifact proved to be the primary cause of failure of this technique. Conclusion. Joint time frequency analysis of the pulse oximeter waveform can be used to determine the respiratory rate of ventilated patients and to quantify the impact of ventilation on the waveform. In addition, when applied to the pulse oximeter waveform new clinically relevant features were observed.

The effect of venous pulsation on the forehead pulse oximeter wave form as a possible source of error in Spo2 calculation.

Reflective forehead pulse oximeter sensors have recently been introduced into clinical practice. They reportedly have the advantage of faster response times and immunity to the effects of vasoconstriction. Of concern are reports of signal instability and erroneously low Spo2 values with some of these new sensors. During a study of the plethysmographic wave forms from various sites (finger, ear, and forehead) it was noted that in some cases the forehead wave form became unexpectedly complex in configuration. The plethysmographic signals from 25 general anesthetic cases were obtained, which revealed the complex forehead wave form during 5 cases. We hypothesized that the complex wave form was attributable to an underlying venous signal. It was determined that the use of a pressure dressing over the sensor resulted in a return of a normal plethysmographic wave form. Further examination of the complex forehead wave form reveal a morphology consistent with a central venous trace with atrial, cuspidal, and venous waves. It is speculated that the presence of the venous signal is the source of the problems reported with the forehead sensors. It is believed that the venous wave form is a result of the method of attachment rather than the use of reflective plethysmographic sensors.

How Does the Plethysmogram Derived from the Pulse Oximeter Relate to Arterial Blood Pressure in Coronary Artery Bypass Graft Patients

Twenty patients scheduled for coronary artery bypass grafting had their ear and finger oximeter and radial artery blood pressure (Bpmeas) waveforms collected. The ear and finger pulse oximeter waveforms were analyzed to extract beat-to-beat amplitude and area and width measurements. The Bpmeas waveforms were analyzed to measured systolic blood pressure (BP), mean BP, and pulse pressure. The correlation coefficient was determined between the derived waveforms from the pulse oximeter and Bpmeas for the first 10 patients. The ear pulse oximeter width (WidthEar) had the best correlation (r = 0.8). Linear regression was done between WidthEar and Bpmeas based on slope (b) and intercept (a) values, BP was calculated (Bpcalc) in the next 10 patients as:MATHwhere i = systolic BP, mean BP, and pulse pressure. The initial bias was too large to be clinically useful. To improve clinical applicability a period of calibration was introduced in which the first 50 readings of WidthEar and Bpmeas for each patient were used to calculate the intercept. After calibration the systolic BP, mean BP and pulse pressure bias values were −2.6, −1.88 and −1.28 mm Hg, and the precision values were 15.9 10.09, and 9.94 mm Hg, respectively. The present attempt to develop a clinically useful method of noninvasive BP measuring was partly successful with the requirement of a calibration period.

Analysis of the ear pulse oximeter waveform

Objective: For years researchers have been attempting to understand the relationship between central hemodynamics and the resulting peripheral waveforms. This study is designed to further understanding of the relationship between ear pulse oximeter waveforms, finger pulse oximeter waveforms and cardiac output (CO). It is hoped that with appropriate analysis of the peripheral waveforms, clues can be gained to help to optimize cardiac performance. Methods.Part 1: Studying the effect of cold immersion test on plethysmographic waveforms. Part 2: Studying the correlation between ear and finger plethysmographic waveforms and (CO) during CABG surgery. The ear and finger plethysmographic waveforms were analyzed to determine amplitude, width, area, upstroke and downslope. The CO was measured using continuous PA catheter. Using multi-linear regression, ear plethysmographic waveforms, together with heart rate (HR), were used to determine the CO Agreement between the two methods of CO determination was assessed. Results.Part 1: On contralateral hand immersion, all finger plethysmographic waveforms were reduced, there was no significant change seen in ear plethysmographic waveforms, except an increase in ear plethysmographic width. Part 2: Phase1: Significant correlation detected between the ear plethysmographic width and other ear and finger plethysmographic waveforms. Phase 2: The ear plethysmographic width had a significant correlation with the HR and CO. The correlation of the other ear plethysmographic waveforms with CO and HR are summarized (Table 5). Multi-linear regression analysis was done and the best fit equation was found to be: CO = 8.084 − 14.248 × Ear width + 0.03 ×HR+ 92.322 × Ear down slope+0.027 × Ear Area Using Bland & Altman, the bias was (0.05 L) but the precision (2.46) is large to be clinically accepted. Conclusion. The ear is relatively immune to vasoconstrictive challenges which make ear plethysmographic waveforms a suitable monitor for central hemodynamic changes. The ear plethysmographic width has a good correlation with CO.

Efficacy and safety of divided dose administration of mivacurium for a 90-second tracheal intubation

STUDY OBJECTIVE To compare the safety and effectiveness of 0.25 mg divided doses of mivacurium chloride to succinylcholine for a 90-second tracheal intubation. DESIGN Randomized, double-blind, multicenter study in two groups. SETTING Operating rooms at four university medical centers. PATIENTS 200 healthy ASA status I and II adult patients scheduled for elective surgery with general anesthesia and endotracheal intubation. INTERVENTIONS Patients were premedicated with 1 to 2 mg midazolam and 2 micrograms/kg fentanyl. Anesthesia was induced with 2 mg/kg propofol. Group A received 0.25 mg/kg mivacurium given as a divided dose (0.15 mg/kg followed in 30 seconds with 0.1 mg/kg). Group B (control) received 1.5 mg/kg succinylcholine (SCh) preceded two minutes earlier by 50 micrograms/kg d-tubocurarine (dtc). MEASUREMENTS AND MAIN RESULTS Tracheal intubation grading, train-of-four response of the adductor pollicis, heart rate (HR), and mean arterial blood pressure (MAP) were measured and evaluated. Chi-square analysis was performed for comparison between Group A and Group B with respect to the frequency distribution of intubation using the scores excellent, good, and poor and not possible (combined). Group B had a significantly higher excellent score of intubation than Group A, 84% versus 56% (p < 0.0001). No significant difference was found between the two groups when the scores excellent and good were combined (Fishers Exact test, p = 0.28). The changes in MAP and HR were similar for the two groups. CONCLUSIONS When Sch is not desirable, mivacurium 0.25 mg/kg given as a divided dose provides good to excellent intubation conditions 90 seconds after the initial dose without significant changes in MAP or HR. It can be an appropriate alternative for short surgical procedures. It must be emphasized that this conclusion does not apply to rapid-sequence induction-intubation.

Synchronous Rhythmical Vasomotion in the Human Cutaneous Microvasculature during Nonpulsatile Cardiopulmonary Bypass

Background The origin, control mechanisms, and functional significance of oscillations in microvascular flow are incompletely understood. Although the traditional belief has been that only low-frequency oscillations (0.04–0.10 Hz) can originate at the microvascular level, recent evidence in healthy volunteers has suggested that high-frequency oscillations (> 0.10 Hz) also may have a microvascular origin (as opposed to being mechanically transmitted respiratory-induced variations in stroke volume). The current study determined if such oscillations would emerge in the absence of cardiac and respiratory activity during nonpulsatile cardiopulmonary bypass (NP-CPB). Methods Forehead and finger laser Doppler flow, arterial pressure, and core temperature were simultaneously recorded in eight patients during NP-CPB. Analyses included time- domain indices, frequency-domain indices (auto power spectral density), and a measure of regularity (approximate entropy) for standardized time segments. Results Nonpulsatile cardiopulmonary bypass was associated with the emergence of rhythmical oscillations in laser Doppler flow, with characteristic frequencies for the forehead (0.13 ± 0.03 Hz) and finger (0.07 ± 0.02 Hz). Forehead vasomotion became progressively synchronized, with a gain in high-frequency spectral power from 17.5 (minute 1) to 89.1 (minute 40) normalized units, and a decrease in approximate entropy from 1.2 (before NP-CPB) to less than 0.5 (minute 40). Conclusions The emergence of forehead microvascular oscillations at greater than 0.10 Hz (characteristic of parasympathetic frequency response), in the absence of cardiac and respiratory variability, demonstrates their peripheral origin and provides insights into parasympathetic vasoregulatory mechanisms. The progressive synchronization of forehead vasomotion during NP-CPB, suggestive of increased coupling among microvascular biologic oscillators, may represent a microcirculatory homeostatic response to systemic depulsation, with potential implications for end-organ perfusion.

Comparing the effect of arginine vasopressin on ear and finger photoplethysmography.

STUDY OBJECTIVE To test whether the relative insensitivity of craniofacial vessels to catecholamines differs in response to arginine vasopressin. DESIGN Prospective, observational human study. SETTING University hospital. PATIENTS 8 ASA physical status I and II women scheduled for elective myomectomy. INTERVENTIONS Patients underwent elective myomectomy surgery with intrauterine injection of arginine vasopressin. MEASUREMENTS Finger, ear, and forehead photoplethysmographs were monitored. Changes in the plethysmographic amplitudes were recorded before and after arginine vasopressin injection. MAIN RESULTS In all subjects, ear photoplethysmographic amplitude (but not oxygen saturation) decreased precipitously (62% +/- 10%; P < 0.001) after arginine vasopressin injection. In contrast, there was no significant decline in the finger signal (4.5% +/- 27%; P = 0.19). The forehead plethysmograph decreased in amplitude, but this finding did not achieve significance (33% +/- 18%; P = 0.18). CONCLUSION In contrast to prior observations during adrenergic activation, arginine vasopressin induced relatively greater vasoconstriction at the ear and forehead than at the finger. This finding has potential implications with respect to arginine vasopressins effect on blood flow and indicates that monitoring the ear plethysmographic signal may provide useful information during arginine vasopressin administration.

Early neuromuscular recovery characteristics following administration of mivacurium plus vecuronium

PurposeThis study was designed to describe the early recovery characteristics, as well as the speed of onset of neuromuscular block, after a combination of mivacurium and vecuronium.MethodsIn this controlled, randomized study, 30 consenting ASA I–III patients were assigned to three treatment groups. The “2M2V” group received twice the dose necessary to cause 95% depression of the evoked twitch response (2 × ED95) of mivacurium (0.15 mg · kg−1) plus 2 × ED95 of vecuronium (0.1 mg · kg−1); the “2V” group received 2 × ED95 of vecuronium; and the “4V” group received 4 × ED95 of vecuronium. Evoked neuromuscular responses of the adductor pollicis were assessed with an adductor pollicis force transducer. The time until maximum block and times to 10% and 25% recovery (T10 and T25) in each group were expressed as mean ± standard deviation and compared using ANOVA.ResultsOnset of block in the 2M2V group was 27% faster than in the 2V group (2.0 ± 0.6 vs. 2.7 ± 0.8 min respectively, P < 0.05) and was similar to the 4V group (1.95 ± 0.3 min, P = NS). The times until 10% recovery were similar in the 2M2V and 4V groups (59.9 ± 12 vs 68.2 ± 25 min, P = NS) and were slower than in the 2V group (37.2 ± 9 min, P < 0.05). Between T10 and T25, recovery after 2M2V resembled that after 2V (6.7 ± 3 vs 5.7 ± 1 min, P = NS) and was faster than after 4V (10.9 ± 7 min, P<0.05).ConclusionsWhen 2 × ED95 of mivacurium is added to 2 × ED95 of an intermediate or long-acting relaxant, recovery after T10 will proceed as if one had administered the longeracting agent alone.RésuméObjectifDécrire les caractéristiques de la curarisation initiale et de la décurarisation après l’administration du mivacurium associé au vécuronium.MéthodesAu cours de cette étude contrôlée aléatoire, 30 adultes consentants ASA I–III ont été répartis en trois groupes. Le groupe 2M2V a reçu deux fois la dose (2 × ED95) de mivacurium (0,15 mg · kg−1) nécessaire pour causer une dépression de 95% de la réponse au twitch plus 2 × ED95 de vécuronium (0,1 mg · kg−1), le groupe 2V a reçu 2 × ED95 de vécuronium, et le groupe 4V, 4 × ED95 de vécuronium. Les réponses évoquées au niveau de l’adducteur du pouce ont été évaluées à l’aide d’un transducteur. Les temps nécessaires à une curarisation maximale et à 10% et 25% de décurarisation (T10 et T25) dans chaque groupe ont été exprimés en moyenne ± écart-type et comparés avec ANOVA.RésultatsLe début de la curarisation dans le groupe 2M2V a été de 27% plus rapide que dans le groupe 2V (respectivement 2,0 ± 0,6 vs 2,7 ± 0,8 min, P < 0,05) et identique au groupe 4V (1,95 ± 0,3 min, P = NS). Le temps nécessaire à 10% de décurarisation a été identique dans les groupes 2M2V et 4V (59 ± 0,3 vs 68 ± 25 min, P = NS) et était plus prolongé que dans le groupe 2V (37,2 ± 0 min, P < 0,05). La décurarisation entre T10 et T25 était identique après 2M2V et 2V (6,7 vs 5,7 ± 1 min, P = NS) et était plus rapide après 4V (10,9 ± 7 min, P < 0,05).ConclusionQuand le mivacurium 2 × ED95 est ajouté à ≥ 2 × ED95 d’un relaxant intermédiaire ou de longue durée, la décurarisation après T10 a les mêmes caractéristiques qu’un agent de longue durée administré seul.