Acceptable ranges for vital signs during general anesthesia

Objective. Define the ranges for normal vital signs during general anesthesia.Methods. We studied 50 patients undergoing general anesthesia. We asked residents to state desirable ranges for each patient's systolic and diastolic blood pressure (BP), heart rate (HR), SpO₂, andPetCO₂ during induction, intubation, maintenance, and emergence from anesthesia. We called these ranges the clinical operating range (COR) and observed the frequency, duration, and magnitude of transgressions of these CORs. We also recorded whether the transgressions were treated or tolerated, or whether the COR values were changed.Results. Upper COR values in the maintenance phase for systolic BP were 38%±20% above the preoperative values and 30%±20% above the values recorded just before induction of anesthesia. Lower COR values in the maintenance phase for systolic BP were 27%±9% below preoperative, and 31%±11% below pre-induction values. For HR, upper and lower COR values in the maintenance phase were 53%±44% above and 38%±17% below preinduction values, respectively. Transgressions of COR values for BP and HR were common, treatment frequent, and redefinition of COR values rare.Conclusion. Clinicians recognize ranges for vital signs during uneventful anesthesia. These CORs may differ from one stage of anesthesia to the next. Transgressions of these ranges are common. Not all transgressions are treated.Reprints are not available.     

Absence of a capnogram after positive end-expiratory pressure

Objective. The objective of this study was to evaluate the effect of positive end-expiratory pressure (PEEP) on capnography.Design. The study design was experimental and open, and it was performed in the Anesthesiology Experimental Research Laboratory.Methods. Six dogs (9.8±0.8 kg) were anesthetized and intubated. The animals' lungs were ventilated with a tidal volume of 137±34 ml and a respiratory frequency of 34±10 breaths/min to produce a Paco ₂ of 35 to 45 mm Hg. Application of 20 cm H₂O of PEEP was initiated for 1 minute, then repeated twice after 10-minute stabilization periods. Arterial pH and gas tensions were measured, and capnogram, airway gas flow, and airway pressure were recorded continuously. Airway gas flow was electronically integrated to calculate tidal volume.Results. Mean values before application of PEEP were as follows: pHa, 7.37±0.04 mm Hg; Paco ₂, 37.1±3.2 mm Hg; PaO₂, 93.4±1.6 mm Hg; andPetco ₂, 32.0±3.5 mm Hg. Compliance of the ventilator circuit was 3.3 ml/cm H₂O. Mean deflation lung-thorax compliance was 41.5±10.3 ml/cm H₂O. After application of PEEP, no capnogram was reported for 1 to 6 breaths, an average of 2.7±1.8 breaths.Conclusions. These results demonstrated that absence of gas flow immediately after the application of PEEP may transiently abolish a capnogram when the lung volume increases.     

Simultaneous in vivo comparison of two-versus three-wavelength mixed venous (Svo 2) oximetry catheters

Objective. Venous oximetry catheters provide useful realtime information about mixed venous hemoglobin saturation (Svo ₂). Currently available systems utilize either two or three wavelengths of light to obtain these measurements. Previous animal and clinical studies have attempted to compare the accuracy of these two devices under similar circumstances. However, the relative accuracy of the two-wavelength versus three-wavelength systems has never been assessed under identical conditions. For this purpose, we designed an animal model for simultaneous measurement ofSvo ₂ over a wide range of physiologic and pathologic states.Methods. Seven anesthetized swine underwent simultaneous placement of two- and three-wavelength catheters. Paired data points consisted of values obtained from a reference oximeter and from each of the catheters. Observations were obtained every 15 min during the following manipulations: (1) eucarbic hypoxia induced by reducing Fio ₂ to 0.18, 0.15, and 0.12 for 15 min each; (2) simulated surgical manipulation; and (3) hypovolemic shock produced by hemorrhage to a mean arterial pressure of 50 torr for 1 hr. Data were analyzed by calculation of mean error (bias) and precision for each system in comparison with the oximeter.Results. The overall error of the two-wavelength system was +0.15%, with a precision of ±2.54%. The three-wavelength system had an overall error of +3.71%, with a precision of ±2.30%. Overall correlation between catheterSvo ₂ and oximeter values was the same for both devices (r=0.99).Conclusions. Both currently available in vivo spectrophotometric systems are capable of producing satisfactory results over wide ranges ofSvo ₂. In contradistinction to older reports, we found that the two-wavelengthSvo ₂ system produced results equivalent to those obtained from the three-wavelength device. In this regard, there is no detectable advantage in accuracy to measuring in vivoSvo ₂ with three rather than with two wavelengths.This work was supported by a grant from Baxter Edwards Critical Care, Irvine, California.     

Effects of intravenous anesthetic agents on middle cerebral artery blood flow velocity during induction of general anesthesia

Objective. Our objective was to quantify the effects of intravenous anesthetics on values measured by or derived from transcranial Doppler sonography (TCD) during induction of general anesthesia.Methods. We recorded blood flow velocity in the middle cerebral artery (V-MCA) before, during, and after induction of general anesthesia in six groups of young patients without intracranial pathology (n=10 each) using TCD. Patients were randomized to receive either 2 mg/kg propofol, 1.5 mg/kg methohexital, 5 mg/kg thiopental, 0.3 mg/kg etomidate, 2 µg/kg fentanyl and 0.15 mg/kg midazolam, or 1.5 mg/kg ketamine and 0.15 mg/kg midazolam intravenously. At 2 min after injection, each patient was intubated and given isoflurane 0.8% and nitrous oxide 66% in oxygen. Ventilation was set to achieve an end-tidalPco ₂ of 40 mm Hg. V-MCA, arterial blood pressure, heart rate, hematocrit, andPco ₂ (venous samples) were measured before and 1, 3, 5, 10, and 30 min after induction of anesthesia.Results. The preinduction data were not different between groups. At 1 min after injection, propofol, thiopental, methohexital, and etomidate significantly decreased V-MCA. TCD values were only slightly affected following fentanyl/midazolam. Ketamine/midazolam induced a modest rise in V-MCA. After endotracheal intubation, V-MCA increased in all groups, and slowly declined thereafter.Conclusions. Under the circumstances of our study, values derived from TCD measurements responded differently to the agents used to induce general anesthesia in nonneurosurgical patients.     

An improved nasal prong apparatus for end-tidal carbon dioxide monitoring in awake,sedated patients

We describe and evaluate a new apparatus that monitors end-tidal carbon dioxide (PetCO₂) and augments the inspired oxygen concentration in awake, sedated patients. The unit was evaluated for its effectiveness as an oxygenation device and its accuracy as a predictor of PaCO₂ through the correlation of PaCO₂ withPetCO₂. Twenty cardiac surgical patients, physical status ASA 2–4, participated in this study. ThePetCO₂ monitoring device consisted of a dual-prong nasal oxygen cannula and a 14-gauge intravenous catheter that was inserted into one limb of the oxygen supply tubing and connected to a Datex gas analyzer (Datex Instrumentation Corp, Helsinki, Finland) to measurePetCO₂. The cross-over passage between the prongs was intentionally blocked with the end of a wooden-core cotton swab. The oxygen flow rates were randomly varied (2, 4, and 6 L/min) every 5 minutes, and values forPetCO₂ as well as arterial blood samples for analysis of PaCO₂ and PaO₂ were obtained at the end of each 5-minute period. The accuracy of the system was assessed by comparing the PaCO₂-PetCO₂ differences (bias) at each oxygen flow rate. The ratios ofPetCO₂ compared with PaCO₂ were 0.98, 0.94, and 0.85, with correlation coefficients ofr=0.81, 0.85, and 0.63, respectively. The PaO₂ values were 114, 154, and 183 mm Hg for the corresponding nasal oxygen flow rates of 2, 4, and 6 L/min, respectively. This study indicates that this modified nasal cannula provides supplemental oxygen adequately and yields a satisfactory reflection of the PaCO₂ depending on the oxygen flow rate delivered.     

Use of end-tidalPco2 and transcutaneousPco2 as noninvasive measurement of arterialPco2 in extubated patients recovering from general anesthesia

This study was designed to assess the accuracy of end-tidalPco ₂ and transcutaneousPco ₂ as measurements of arterialPco ₂ in extubated, spontaneously breathing patients recovering from general anesthesia. In 30 patients, measurement of arterial transcutaneous, and end-tidalPco ₂ were taken simultaneously with body temperature approximately every 15 minutes over a 2-hour period. ArterialPco ₂ values were corrected for body temperature. Values for Paco ₂ were compared with those forPetCO₂ and Psco ₂ by linear regression analysis and by calculation of bias ± precision. Thirty-six percent of the capnogram tracings obtained did not develop a plateau phase. We found poor correlation between end-tidal and arterialPco ₂ regardless of the shape of the capnogram tracing, as well as poor correlation between transcutaneous and arterialPco ₂. Although the measurements of bias and precision of noninvasivePco ₂ monitors in this population are comparable to studies in other populations, we advise caution in relying on the routine use ofPetCO₂ or Psco ₂ for the noninvasive assessment of respiratory depression in extubated, spontaneously breathing patients recovering from general anesthesia.     

Variability of blood gases, pulse oximeter saturation, and end-tidal carbon dioxide pressure in stable, mechanically ventilated trauma patients

We evaluated the short-term variability of Pao ₂, Paco ₂, pulse oximeter saturation (Spo ₂), and end-tidalPco ₂ (Petco ₂) in mechanically ventilated trauma patients. All patients were stable and undisturbed during the evaluation periods. Blood gases were obtained from an arterial catheter 4 times at 20-minute intervals.Spo ₂ andPetco ₂ were recorded when the blood gases were obtained. Fifty evaluations were made in 26 patients; 24 patients were evaluated twice, with 24 hours between evaluation periods. Variability was expressed as coefficient of variation (%CV) for each evaluation period. The median %CVs were 3.6% for Pao ₂ (95th percentile = 9.8%), 0.5% forSpo ₂ (95th percentile = 1.4%), 2.8% for Paco ₂ (95th percentile = 7.4%), and 2.4% forPetco ₂ (95th percentile = 7.1%). The overall correlation between Paco ₂ andPetco ₂ wasr=0.80, and the mean difference between Paco ₂ andPetco ₂ was 0.9±3.6 mm Hg. The variability ofPetco ₂ was similar to the variability of Paco ₂. However, the variability of Pao ₂ was considerably greater than that ofSpo ₂, which was probably related to the shape of the oxyhemoglobin dissociation curve and the relatively high saturations of the patients in this study. Variability of blood gases,Spo ₂, andPetco ₂ should be considered when these values are clinically interpreted.A version of this paper was presented at the 56th Annual Assembly of the American College of Chest Physicians, October 24, 1990.     

End-tidal carbon dioxide as a measure of arterial carbon dioxide during intermittent mandatory ventilation

To determine if end-tidal carbon dioxide tension (PetCO₂) is a clinically reliable indicator of arterial carbon dioxide tension (PaCO₂) under conditions of heterogeneous tidal volumes and ventilation-perfusion inequality, we examined the expiratory gases of 25 postcardiotomy patients being weaned from ventilator support with intermittent mandatory ventilation. Using a computerized system that automatically sampled airway flow, pressure, and expired carbon dioxide tension, we were able to distinguish spontaneous ventilatory efforts from mechanical ventilatory efforts. ThePetCO₂ values varied widely from breath to breath, and the arterial to end-tidal carbon dioxide tension gradient was appreciably altered during the course of several hours. About two-thirds of the time, thePetCO₂ of spontaneous breaths was greater than that of ventilator breaths during the same 70-second sample period. The most accurate indicator of PaCO₂ was the maximalPetCO₂ value in each sample period, the correlation coefficient being 0.768 (P < 0.001) and the arterial to end-tidal gradient being 4.24 ± 4.42 mm Hg (P < 0.01 compared with all other measures). When all values from an 8-minute period were averaged, stability was significantly improved without sacrificing accuracy. We conclude that monitoring the maximalPetCO₂, independent of breathing pattern, provides a clinically useful indicator of PaCO₂ in postcardiotomy patients receiving intermittent mandatory ventilation.     

Mean blood pressure algorithms

Alternative methods of calculating average blood pressure are examined. It is suggested that the preferred method is calculation of the arithmetic mean if the average value itself is required. However, when blood pressure values arc used to calculate other results, only the instantaneous value is appropriate in all situations. Arithmetic mean blood pressure values may be used with arithmetic mean flow values to calculate resistance, but only if resistance is constant over the interval (laminar flow). To calculate ventricular stroke work, the root mean square averages must be used because in this instance the arithmetic average yields large errors. Most monitors do not use these methods consistently to derive average blood pressure values, thus, the displayed values differ from those obtained from the appropriate calculation. Computational convenience, truncation error in averaging, or true errors in measurement or understanding of the associated physiologic state may account for observed differences. The interpretation of maximum systolic and minimum diastolic pressures with each beat requires additional considerations. Common monitoring algorithms obscure clinically important details, particularly by distorting the relationship between respiratory variation and pulse pressure. Electrical Engineering Physiology     

Variability of blood gases,pulse oximeter saturation,and end-tidal carbon dioxide pressure in stable,mechanically ventilated trauma patients

We evaluated the short-term variability of Pao ₂, Paco ₂, pulse oximeter saturation (Spo ₂), and end-tidalPco ₂ (Petco ₂) in mechanically ventilated trauma patients. All patients were stable and undisturbed during the evaluation periods. Blood gases were obtained from an arterial catheter 4 times at 20-minute intervals.Spo ₂ andPetco ₂ were recorded when the blood gases were obtained. Fifty evaluations were made in 26 patients; 24 patients were evaluated twice, with 24 hours between evaluation periods. Variability was expressed as coefficient of variation (%CV) for each evaluation period. The median %CVs were 3.6% for Pao ₂ (95th percentile = 9.8%), 0.5% forSpo ₂ (95th percentile = 1.4%), 2.8% for Paco ₂ (95th percentile = 7.4%), and 2.4% forPetco ₂ (95th percentile = 7.1%). The overall correlation between Paco ₂ andPetco ₂ wasr=0.80, and the mean difference between Paco ₂ andPetco ₂ was 0.9±3.6 mm Hg. The variability ofPetco ₂ was similar to the variability of Paco ₂. However, the variability of Pao ₂ was considerably greater than that ofSpo ₂, which was probably related to the shape of the oxyhemoglobin dissociation curve and the relatively high saturations of the patients in this study. Variability of blood gases,Spo ₂, andPetco ₂ should be considered when these values are clinically interpreted.A version of this paper was presented at the 56th Annual Assembly of the American College of Chest Physicians, October 24, 1990.     

Sampled gas need not be returned during low-flow anesthesia

Objective. The purpose of this investigation was to study the N₂ flux between the patient and the breathing circuit, and the excess gas during N₂O anesthesia with the low, fresh gas flow technique.Methods. Forty patients were studied. After a 6-minute high, fresh gas flow denitrogenation period, the O₂ fresh gas flow was set at about 4 ml/kg/min and the N₂O fresh gas flow was set to maintain an inspired O₂ fraction of 0.30. The excess gas flow and N₂ excretion were measured by a variant of the Douglas bag method.Results. The mean inspired N₂ concentration reached a peak of 5.9% at 40 minutes. The estimated mean N₂ excretion was 39 ml/min at 10 minutes, declining to 18 ml/min at 60 minutes. A calculation of N₂ homeostasis during closed-circuit anesthesia based on the results of the patient study indicated that sampling for gas analysis actually reduces the gas costs if the sampled gas is scavenged instead of returned to the circle system, since intermittent flushing with high, fresh gas flow for denitrogenation is unnecessary in the former situation.Conclusions. Regardless of the fresh gas flow used, sampled gas need not be returned during N₂O anesthesia.Financial support was provided by AGA AB Medical Research Fund (supplier of O₂ and N₂O).     

The evaluation of a new intravascular blood gas monitoring system in the pig

Objective. Our objective was to investigate the accuracy of a new intravascular blood gas sensor, the Paratrend 7 (P7) (Biomedical Sensors Ltd, Pfizer Hospital Products Group, High Wycombe, England) in a porcine model.Methods. A total of 12 sensors were inserted into 10 animals under total intravenous anesthesia. Changes in blood gas chemistry were produced over a wide range by manipulating the inspired oxygen and carbon dioxide concentrations and by adjustments in minute ventilation. Blood gas samples (BGA) were taken and analyzed during periods of stability; the results obtained were compared with the readings from the intravascular sensor.Results. A total of 292 blood gas samples were taken and analyzed for pHa, Paco ₂, andPo ₂; the results were compared with the readings from the intravascular sensor. Correlation coefficients ofr=0.98 forPco ₂ andr=0.99 for Po ₂ were obtained. Analysis of bias and precision as mean±SD of the difference (P7 — BGA) gave the following results: pH bias=–0.03, precision=±0.04;Pco ₂ bias = 0.65 mm Hg, precision=±3.1 mm Hg; andPo ₂ bias=–6.50 mm Hg, precision=±0.6 mm Hg. No problems with clot formation on the sensor were seen, and the sensors did not appear to show the wall effect seen with other systems.Conclusions. The results obtained were well within the requirements for a clinically useful blood gas monitoring system.     

Capnographic trend curve monitoring can detect 1-ML pulmonary emboli in humans

To evaluate the potential of trend monitoring of end-tidalPco ₂ (Petco ₂) to detect pulmonary embolization, the capnograms of 24 mechanically ventilated patients were monitored during simulation of 1-ml pulmonary embolization by inflation of the balloons of their pulmonary artery catheters. Within 1 minute of balloon inflation,Petco ₂ showed an exponential decrease to a new equilibrium. This response is characteristic of a CO₂ wash-out curve produced by a step increase in dead space. Because of a steady baseline, the depression of the trend line during balloon inflation was apparent to a naive reader repeatedly in 20 of the 24 patients (sensitivity, 85%; specificity, 94%; positive predictive value, 98%; negative predictive value, 89%), despite a small mean decrease inPetco ₂ (2±1.97 mm Hg). ThePetco ₂ trend curve did not reliably allow detection of balloon inflation in 4 patients whose capnograms were poorly formed. In conclusion, during constant ventilation,Petco ₂ trend curve monitoring might provide clinically useful on line information regarding pulmonary embolization.     

Capnometry for continuous postoperative monitoring of nonintubated,spontaneously breathing patients

We continuously monitored spontaneous respiration after extubation by end-tidal CO₂ tension (PetCO₂) in 19 patients aged 20 to 72 years who had undergone major operations. The respiratory gas was sampled from the nasopharynx via a special nasal catheter and analyzed by a side-stream analyzer. In each case, optimal placement of the nasal catheter was determined by CO₂ waveform and the capnograms were recorded for waveform analysis and trend monitoring.PetCO₂ was compared with arterial CO₂ tension (PaCO₂) two to four times during the 2- to 19-hour observation periods by simultaneous measurements. For 65 simultaneous measurements, meanPetCO₂ was 38.9 ± 5.7 mm Hg (range, 26.3 to 48.3 mm Hg) and mean PaCO₂ was 38.9 ± 5.7 mm Hg (range, 26.8 to 46.0 mm Hg;r=0.82;p<0.01). While the mean values forPetCO₂ and PaCO₂ were similar, several patients had large differences for PaCO₂ toPetCO₂. The differences of the individual patients did not differ significantly between the various times of measurement. We conclude that this form of capnometry is well suited for continuous, noninvasive monitoring of respiration in nonintubated, spontaneously breathing patients.     

Determining Reliability of a Dual-Task Functional Mobility Protocol for Individuals With Lower Extremity Amputation

ObjectiveTo determine the relative and absolute reliability of a dual-task functional mobility assessment.DesignCross-sectional study.SettingAcademic rehabilitation hospital.ParticipantsIndividuals (N=60) with lower extremity amputation attending an outpatient amputee clinic (mean age, 58.21±12.59y; 18, 80% male) who were stratified into 3 groups: (1) transtibial amputation of vascular etiology (n=20); (2) transtibial amputation of nonvascular etiology (n=20); and (3) transfemoral or bilateral amputation of any etiology (n=20).InterventionsNot applicable.Main Outcome MeasuresTime to complete the L Test measured functional mobility under single- and dual-task conditions. The addition of a cognitive task (serial subtractions by 3's) created dual-task conditions. Single-task performance on the cognitive task was also reported. Intraclass correlation coefficients (ICCs) measured relative reliability; SEM and minimal detectable change with a 95% confidence interval (MDC₉₅) measured absolute reliability. Bland-Altman plots measured agreement between assessments.ResultsRelative reliability results were excellent for all 3 groups. Values for the dual-task L Test for those with transtibial amputation of vascular etiology (n=20; mean age, 60.36±7.84y; 19, 90% men) were ICC=.98 (95% confidence interval [CI], .94–.99), SEM=1.36 seconds, and MDC₉₅=3.76 seconds; for those with transtibial amputation of nonvascular etiology (n=20; mean age, 55.85±14.08y; 17, 85% men), values were ICC=.93 (95% CI, .80–.98), SEM=1.34 seconds, and MDC₉₅=3.71 seconds; and for those with transfemoral or bilateral amputation (n=20; mean age, 58.21±14.88y; 13, 65% men), values were ICC=.998 (95% CI, .996–.999), SEM=1.03 seconds, and MDC₉₅=2.85 seconds. Bland-Altman plots indicated that assessments did not vary systematically for each group.ConclusionsThis dual-task assessment protocol achieved approved levels of relative reliability values for the 3 groups tested. This protocol may be used clinically or in research settings to assess the interaction between cognition and functional mobility in the population with lower extremity amputation.     

Acute effects of mat Pilates session on heart rate and rating of perceived exertion

AimsThe aim of this study was to analyze the acute effects of Heart Rate (HR) and Rating of Perceived Exertion (RPE) for 21 of 34 original Mat Pilates (MP) exercises, to estimate maximum oxygen consumption (VO_2max), and energy expenditure (EE) of a MP session.MethodsTen participants volunteered (26.30 ± 3.98 yrs) to measure the intensity of each exercise; HR and RPE were monitored immediately after the end of each exercise. VO_2maxwas estimated using the Astrand-Ryhming step submaximal test, and EE by a linear regression equation. HR and RPE mean values and standard deviations were calculated for each exercise.ResultsThe maximum value for each participant normalized the EE and VO_2max values, which were ranked from highest to lowest. The percentage of the mean values of HR_max and RPE_max in each exercise showed significant, strong and positive correlation (p = 0.82; p = 0.001). In 10 exercises, HR was 60% higher than HR_max. The mean values of EE and VO_2max were 213.71 ± (76.41) Kcal and 34.69 ml (Kg^.min)⁻¹ (±3.5), respectively, for the entire MP session. Half of the exercises achieved moderate intensity in HR with low estimated VO_2max during the whole MP session. However, if the MP session of this study was practiced five times per week, it would meet the weekly American College of Sports Medicine (ACSM) EE recommendations.ConclusionThe 21 MP exercises monitored in this study promote considerably acute and high increments in HR and RPE.     

The influence of basic ventilation strategies on cerebral oxygenation in anesthetized patients without vascular disease

Objectives. Optimizing cerebral oxygenation is of paramount importance in certain intraoperative situations. There is, however, a paucity of published data pertaining to changes in cerebral oxygenation seen with increases in the inspired fraction of oxygen (Fio ₂) or end-tidal carbon dioxide (Petco ₂) in anesthetized patients without vascular disease. Here we tested the hypothesis that changes in Fio ₂ or Petco ₂ correlate to a significant change in regional cerebral oxygenation (rSO₂) in anesthetized patients without vascular disease. Methods. This was a prospective pilot study approved by the IRB. We measured rSO₂ using the INVOS 5100B monitor in ten anesthetized patients. Patients were excluded if they had a history of or risk factors for vascular disease, suffered from respiratory failure, or did not speak English. Following induction of anesthesia and intubation, Fio ₂ and minute ventilation were sequentially adjusted. At each set point, rSO₂ was recorded and arterial blood gas analysis was performed. Each patient acted as their own control. A paired-sample t test was used to evaluate the change in rSO₂ resultant upon each intervention. Results. The baseline rSO₂ was measured with patients awake, breathing room air and varied between 48 and 72%. While maintaining Petco ₂ in the range 30–35 mmHg, rSO₂ was 8% higher when 100% oxygen was delivered compared to Fio ₂ 30% (P = 0.021). While maintaining Petco ₂ in the range 40–45 mmHg, rSO₂ was 7% higher when 100% oxygen is delivered compared to Fio ₂ 30% (P = 0.032). While maintaining Fio ₂ at 100%, rSO₂ was 2% higher when Petco ₂ was in the range 40–45 mmHg compared to Petco ₂ 30–35 mmHg (P = 0.017). While maintaining Fio ₂ at 30%, rSO₂ was not statistically different between P_ECO₂ 40–45 mmHg and Petco ₂ 30–35 mmHg. Conclusions. Modulating oxygenation and ventilation in anesthetized patients without vascular disease leads to measurable changes in rSO₂.     

Reliability and accuracy of the thoracic impedance signal for measuring cardiopulmonary resuscitation quality metrics

AimTo determine the accuracy and reliability of the thoracic impedance (TI) signal to assess cardiopulmonary resuscitation (CPR) quality metrics.MethodsA dataset of 63 out-of-hospital cardiac arrest episodes containing the compression depth (CD), capnography and TI signals was used. We developed a chest compression (CC) and ventilation detector based on the TI signal. TI shows fluctuations due to CCs and ventilations. A decision algorithm classified the local maxima as CCs or ventilations. Seven CPR quality metrics were computed: mean CC-rate, fraction of minutes with inadequate CC-rate, chest compression fraction, mean ventilation rate, fraction of minutes with hyperventilation, instantaneous CC-rate and instantaneous ventilation rate. The CD and capnography signals were accepted as the gold standard for CC and ventilation detection respectively. The accuracy of the detector was evaluated in terms of sensitivity and positive predictive value (PPV). Distributions for each metric computed from the TI and from the gold standard were calculated and tested for normality using one sample Kolmogorov–Smirnov test. For normal and not normal distributions, two sample t-test and Mann–Whitney U test respectively were applied to test for equal means and medians respectively. Bland–Altman plots were represented for each metric to analyze the level of agreement between values obtained from the TI and gold standard.ResultsThe CC/ventilation detector had a median sensitivity/PPV of 97.2%/97.7% for CCs and 92.2%/81.0% for ventilations respectively. Distributions for all the metrics showed equal means or medians, and agreements >95% between metrics and gold standard was achieved for most of the episodes in the test set, except for the instantaneous ventilation rate.ConclusionWith our data, the TI can be reliably used to measure all the CPR quality metrics proposed in this study, except for the instantaneous ventilation rate.     

Clinician accountability in a primary care clinic time-interval blood pressure measurements study: Practice implications

BackgroundAccurate blood pressure measurements (BPM) are important, as clinicians are tasked daily with using such measurements to make clinical diagnoses and patient care judgments. Research studies and controlled trials hold such measurements to a higher standard than everyday clinical practice.ObjectiveThe aim of this study was to evaluate difference in BPM outcomes of individuals in a clinic setting when clinicians collect BPM as usual vs BPM after 5- (USPSTF recommendation) and 10- minute (study unique intervention) timed rest interval.MethodsA repeated-measures design was used to examine individual BPMs at the intervals of baseline, after a 5-minute rest interval post-baseline, and after a 10-minute rest interval post-baseline. Results Pairwise comparisons indicated that baseline SBP was the highest when compared to SBP measured at both 5- and 10-minutes post-baseline. SBP measured at 5-minutes was also significantly higher compared to SBP collected at 10-minutes post-baseline (ps < .05). For DBP, the repeated-measures ANOVA indicated that there was no significant difference across BPMs, F(2,198) = 1.25, p = .29.ConclusionsResults from this study revealed that implementing a 5-minute rest interval before BPMs are taken in a clinic setting produces a “clinically observable” reduction in the overall mean systolic BPs as seen at both 5- and 10-minute BPM intervals. It is important for all healthcare clinicians to recognize the importance of accurate BPM and the need to encourage better regulated BPM standard in everyday practice.     

18FDG-PET/MR观察宫颈鳞状细胞癌ADC值与SUV的相关性

目的 应用¹⁸FDG-PET/MR一体机观察宫颈鳞状细胞癌ADC值与FDG-PET标准化摄取值（SUV）的相关性。方法 对30例宫颈鳞状细胞癌患者行盆腔PET/MR检查。采用随机自带软件,利用轴位像对PET图像、ADC图及T2WI进行自动配准,并在同一层面勾画ROI,测量感兴趣体积（VOI）内肿瘤最大SUV（SUV_max）和平均SUV（SUV_mean）、最小ADC值（ADC_min）和平均ADC值（ADC_mean）。结果 30例宫颈鳞状细胞癌的ADC_min与SUV_max、ADC_min与SUV_mean、ADC_mean与SUV_max、ADC_mean与SUV_mean均无明显相关性;中-高分化和低分化宫颈鳞状细胞癌的上述ADC和SUV指标间亦无明显相关性。中-高分化与低分化宫颈鳞状细胞癌ADC_min差异有统计学意义（t=-2.06,P=0.049）。结论 ADC和SUV是诊断宫颈鳞状细胞癌的相互独立的指标。恶性程度分级评价中,ADC可能较SUV敏感。