The World Federation of Societies of Anaesthesiologists Minimum Capnometer Specifications 2021-A Guide for Health Care Decision Makers.

Capnometry, the measurement of respiratory carbon dioxide, is regarded as a highly recommended safety technology in intubated and nonintubated sedated and/or anesthetized patients. Its utility includes confirmation of initial and ongoing placement of an airway device as well as in detecting gas exchange, bronchospasm, airway obstruction, reduced cardiac output, and metabolic changes. The utility applies prehospital and throughout all phases of inhospital care. Unfortunately, capnometry devices are not readily available in many countries, especially those that are resource-limited. Constraining factors include cost, durability of devices, availability of consumables, lack of dependable power supply, difficulty with cleaning, and maintenance. There is, thus, an urgent need for all stakeholders to come together to develop, market, and distribute appropriate devices that address costs and other requirements. To foster this process, the World Federation of Societies of Anaesthesiologists (WFSA) has developed the "WFSA-Minimum Capnometer Specifications 2021." The intent of the specifications is to set the minimum that would be acceptable from industry in their attempts to reduce costs while meeting other needs in resource-constrained regions. The document also includes very desirable and preferred options. The intent is to stimulate interest and engagement among industry, clinical providers, professional associations, and ministries of health to address this important patient safety need. The WFSA-Minimum Capnometer Specifications 2021 is based on the International Organization for Standardization (ISO) capnometer specifications. While industry is familiar with such specifications and their presentation format, most clinicians are not; therefore, this article serves to more clearly explain the requirements. In addition, the specifications as described can be used as a purchasing guide by clinicians.

Transcutaneous carbon dioxide measurements in fruits, vegetables and humans: A prospective observational study.

BACKGROUND: Transcutaneous carbon dioxide measurement (TcCO2) is frequently used as a surrogate for arterial blood gas sampling in adults and children with critical illness. Data from noninvasive TcCO2 monitoring assists with clinical decisions regarding mechanical ventilation settings, estimation of metabolic consumption and determination of adequate end-organ tissue perfusion. OBJECTIVES: To report TcCO2 values obtained from various fruits, vegetables and elite critical care medicine specialists. DESIGN: Prospective, observational, nonblinded cohort study. SETTINGS: Single-centre, tertiary paediatric referral centre and organic farmers' market. PARTICIPANTS: Vegetables and fruits included 10 samples of each of the following: red delicious apple (Malus domestica), manzano banana (Musa sapientum), key lime (Citrus aurantiifolia), miniature sweet bell pepper (Capsicum annuum), sweet potato (Ipomoea batatas) and avocado (Persea americana). Ten human controls were studied including a paediatric intensivist, a paediatric inpatient hospital physician, four paediatric resident physicians and four paediatric critical care nurses. INTERVENTIONS: None. MAIN OUTCOME MEASURES: TcCO2 values for each species and device response times. RESULTS: TcCO2 readings were measurable in all study species except the sweet potato. Mean ±â€ŠSD values of TcCO2 for human controls [4.34 ±â€Š0.37 kPa (32.6 ±â€Š2.8 mmHg)] were greater than apples [3.09 ±â€Š0.19 kPa (23.2 ±â€Š1.4 mmHg), P < 0.01], bananas [2.73 ±â€Š0.28 kPa (20.5 ±â€Š2.1 mmHg), P < 0.01] and limes [2.76 ±â€Š0.52 kPa (20.7 ±â€Š3.9 mmHg), P < 0.01] but no different to those of avocados [4.29 ±â€Š0.44 kPa (32.2 ±â€Š3.3 mmHg), P = 0.77] and bell peppers [4.19 ±â€Š1.13 kPa (31.4 ±â€Š8.5 mmHg), P = 0.68]. Transcutaneous response times did not differ between research cohorts and human controls. CONCLUSION: We found nonroot, nontuberous vegetables to have TcCO2 values similar to that of healthy, human controls. Fruits yield TcCO2 readings, but substantially lower than human controls.

Variability of Transcutaneous Oxygen and Carbon Dioxide Pressure Measurements Associated with Sensor Location.

Transcutaneous measurement of oxygen and carbon dioxide pressure (PtcO2 and PtcCO2) is useful in gas exchange monitoring. However, the relationship between PtcO2, pulse oximetry (SaO2) and arterial blood gases (ABG) is unclear. The aim of the present study was to compare PtcO2 and PtcCO2 with SaO2 and ABG, to evaluate the effect of sensor location on the results and stability of PtcO2 and PtcCO2, and to assess the impact of body composition on PtcO2 and PtcCO2. PtcO2 and PtcCO2 were measured in 20 healthy volunteers at three locations: right second intercostal space, lateral surface of the abdomen, and the inner surface of the left arm. The results were recorded 10, 15, and 20 min after sensor fixation and compared with SaO2 and ABG measured 20 min after electrode placement on the chest. Body composition was evaluated by bioimpedance. The findings were that PtcO2 was stable on the chest; but on the arm and abdomen it increased and reached maximum at 20 min. Transcutaneous PCO2 stabilized at 10 min in all the three locations. No significant correlations between PtcO2 and SaO2 or PaO2 were found. Transcutaneous PCO2 correlated with PaCO2. Both PtcO2 and PtcCO2 were not influenced by body composition. We conclude that the value of PtcO2 in monitoring of blood oxygenation was not unequivocally confirmed; PtcCO2 reliably reflects PaCO2, irrespective of sensor location. Body composition does not affect PtcO2 and PtcCO2.

Can macrocirculation changes predict nonhealing diabetic foot ulcers?

PURPOSE: Transcutaneous partial oxygen tension (TcpO2) is considered the gold standard for assessment of tissue oxygenation, which is an essential factor for wound healing. The purpose of this study was to evaluate the association between macrocirculation and TcpO2 in persons with diabetes mellitus. SUBJECTS AND SETTING: Ninety-eight patients with diabetic foot ulcers participated in the study (61 men and 37 women). The subjects had a mean age of 66.6 years (range, 30-83 years) and were treated at the Diabetic Wound Center of Korea University Guro Hospital, Seoul, Republic of Korea. METHODS: Macrocirculation was evaluated using 2 techniques: computed tomographic angiography and Doppler ultrasound. Macrocirculation scores were based on the patency of the two tibial arteries in 98 patients. Computed tomographic angiography and Doppler ultrasound scores (0-4 points) were given according to intraluminal filling defects and arterial pulse waveform of each vessel, respectively. Tissue oxygenation was measured by TcpO2. Macrocirculation scores were statistically analyzed as a function of the TcpO2. RESULTS: Statistical analysis revealed no significant linear trend between the macrocirculation status and TcpO2. Biavariate analysis using the Fisher exact test, Mantel-Haenszel tests, and McNemar-Bowker tests also found no significant relationship between macrocirculation and TcpO2. CONCLUSIONS: Computed tomographic angiography and Doppler ultrasound are not sufficiently reliable substitutes for TcpO2 measurements in regard to determining the optimal treatment for diabetic patients.

The accuracy, precision and reliability of measuring ventilatory rate and detecting ventilatory pause by rainbow acoustic monitoring and capnometry.

BACKGROUND: Current methods for monitoring ventilatory rate have limitations including poor accuracy and precision and low patient tolerance. In this study, we evaluated a new acoustic ventilatory rate monitoring technology for accuracy, precision, reliability, and the ability to detect pauses in ventilation, relative to capnometry and a reference method in postsurgical patients. METHODS: Adult patients presenting to the postanesthesia care unit were connected to a Pulse CO-Oximeter with acoustic monitoring technology (Rad-87, version 7804, Masimo, Irvine, CA) through an adhesive bioacoustic sensor (RAS-125, rev C) applied to the neck. Each subject also wore a nasal cannula connected to a bedside capnometer (Capnostream20, version 4.5, Oridion, Needham, MA). The acoustic monitor and capnometer were connected to a computer for continuous acoustic and expiratory carbon dioxide waveform recordings. Recordings were retrospectively analyzed by a trained technician in a setting that allowed for the simultaneous viewing of both waveforms while listening to the breathing sounds from the acoustic signal to determine inspiration and expiration reference markers within the ventilatory cycle without using the acoustic monitor- or capnometer-calculated ventilatory rate. This allowed the automatic calculation of a reference ventilatory rate for each device through a software program (TagEditor, Masimo). Accuracy (relative to the respective reference) and precision of each device were estimated and compared with each other. Sensitivity for detection of pauses in ventilation, defined as no inspiration or expiration activity in the reference ventilatory cycle for ≥30 seconds, was also determined. The devices were also evaluated for their reliability, i.e., the percentage of the time when each displayed a value and did not drop a measurement. RESULTS: Thirty-three adults (73% female) with age of 45 ± 14 years and weight 117 ± 42 kg were enrolled. A total of 3712 minutes of monitoring time (average 112 minutes per subject) were analyzed across the 2 devices, reference ventilatory rates ranged from 1.9 to 49.1 bpm. Acoustic monitoring showed significantly greater accuracy (P = 0.0056) and precision (P- = 0.0024) for respiratory rate as compared with capnometry. On average, both devices displayed data over 97% of the monitored time. The (0.95, 0.95) lower tolerance limits for the acoustic monitor and capnometer were 94% and 84%, respectively. Acoustic monitoring was marginally more sensitive (P = 0.0461) to pauses in ventilation (81% vs 62%) in 21 apneic events. CONCLUSIONS: In this study of a population of postsurgical patients, the acoustic monitor and capnometer both reliably monitored ventilatory rate. The acoustic monitor was statistically more accurate and more precise than the capnometer, but differences in performance were modest. It is not known whether the observed differences are clinically significant. The acoustic monitor was more sensitive to detecting pauses in ventilation. Acoustic monitoring may provide an effective and convenient means of monitoring ventilatory rate in postsurgical patients.

Tissue oxygen saturation measurement in prehospital trauma patients: a pilot, feasibility study.

BACKGROUND: This study evaluated the feasibility of prehospital tissue oxygen saturation (StO2) in major trauma patients. METHODS: A prospective, pilot feasibility study carried out in a physician based prehospital trauma service. RESULTS: Prehospital StO2 was recorded on 13 patients. Continuous StO2 monitoring was achieved on all patients, despite intermittent failure of pulse oximetry and non-invasive blood pressure monitoring in six patients. No adverse outcomes of StO2 monitoring were reported. The specific equipment used was reported to be inconveniently bulky and heavy for use in the prehospital setting. CONCLUSIONS: Prehospital measurement and monitoring of StO2 is feasible in trauma patients undergoing prehospital anaesthesia and may be useful in the early identification of shock, triggering of transfusion protocols and guiding fluid resuscitation.

Performance evaluation of a noninvasive hemoglobin monitoring device.

STUDY OBJECTIVE: Hemoglobin measurement is a routine procedure, and a noninvasive point-of-care device may increase the quality of care. The aim of the present study is to compare hemoglobin concentration values obtained with a portable totally noninvasive device, the Masimo Labs Radical-7 Pulse CO-Oximeter, with the results obtained by the ADVIA 2120 in the laboratory. METHODS: This was a prospective monocentric open trial enrolling patients consulting in the emergency department of a university hospital from June 16 to December 17, 2009. The main outcome measure was the agreement between both methods and evaluation of the percentage of potential decision error for transfusion. RESULTS: Samples from 300 consecutive patients were assessed. Hemoglobin concentration could not be obtained with the new device for 24 patients. In others, the mean bias, the lower and the upper limits of agreement between the 2 methods, was 1.8 g/dL (95% estimated confidence interval [CI] 1.5 to 2.1 g/dL), -3.3 g/dL (95% CI -3.8 to -2.8 g/dL), and 6.9 g/dL (95% CI 6.4 to 7.4 g/dL), respectively. The intraclass correlation coefficient was 0.53 (estimated 95% CI 0.10 to 0.74). The number of potential errors about transfusion decision was 38 (13% of patients). The peripheral oxygen saturation and the true value of hemoglobin concentration were independently associated with the bias. CONCLUSION: Results from this widely available noninvasive point-of-care hemoglobin monitoring device were systematically biased and too unreliable to guide transfusion decisions.

Effects of the transcutaneous electrode temperature on the accuracy of transcutaneous carbon dioxide tension.

AIM: The harmful effect of hypocapnia on the neonatal brain emphasizes the importance of monitoring arterial carbon dioxide tension (PaCO2). Transcutaneous monitoring of carbon dioxide (tcPCO2) reduces the need for arterial blood sampling. Drawbacks are high electrode temperature causing risks of skin burning. The aim was to determine the accuracy and precision of tcPCO2 at reduced electrode temperature. METHODS: Forty newborns (GA 24.9-41.7) were included. Two tc-monitors were applied (TCM4, Radiometer, Copenhagen). Arterial blood gas sampling and monitoring of tcPCO2-level at different electrode temperatures was done simultaneously (39°C, 40°C, 41°C, 42°C, 44°C). Difference of PaCO2 - tcPCO2 was expressed as a percentage of the mean. RESULTS: Mean PaCO2 was 5.8kPa [3,2; 7.9]. Bias (PaCO2 - tcPCO2) increased from 5% at 44°C to 17% at 39°C, but did not differ significantly between 41°C and 40°C. The precision of the tcPCO2 at each temperature ranged from +7-10%. After correction for the temperature-dependent overreading, we found increasing PaCO2 - tcPCO2 difference with increasing PaCO2, approx. 2% pr. kPa increase of CO(2). Only mild transient erythema was observed. CONCLUSION: A lower electrode temperature in tcPCO2-monitoring increases systematic overreading of the tc-electrode. However, in very preterm babies, monitoring at 40°C or 41°C is possible provided a bias correction of 12-15% is applied.

Assessing PaCO2 in acute respiratory disease: accuracy of a transcutaneous carbon dioxide device.

BACKGROUND: Pulse oximetry non-invasively assesses the arterial oxygen saturation of patients with acute respiratory disease; however, measurement of the arterial partial pressure of carbon dioxide (PaCO(2)) requires an arterial blood gas. The transcutaneous partial pressure of carbon dioxide (PtCO(2) ) has been used in other settings with variable accuracy. We investigated the accuracy of a PtCO(2) device in the assessment of PaCO(2) in patients with asthma and suspected pneumonia attending the emergency department. METHODS: Patients with severe asthma (FEV(1) < 50% predicted) or suspected pneumonia (fever, cough and respiratory rate >18/min) were enrolled. Subjects were excluded if they had a history of chronic obstructive pulmonary disease or other conditions associated with respiratory failure. Arterial blood gases were taken at the discretion of the investigator according to clinical need, and paired with a simultaneous reading from the PtCO(2) probe. RESULTS: Twenty-five patients were studied with one set of data excluded because of poor PtCO(2) signal quality. The remaining 24 paired samples comprised 12 asthma and 12 pneumonia patients. The range of PaCO(2) was 19-64 mmHg with a median of 36.5 mmHg. Bland-Altman analysis showed a mean (SD) PaCO(2) - PtCO(2) difference of -0.13 (1.9) mmHg with limits of agreement of plus or minus 3.8 mmHg (-3.9 to +3.7). CONCLUSION: A PtCO(2) device was accurate in the assessment of PaCO(2) in patients with acute severe asthma and suspected pneumonia when compared with an arterial blood gas. These bedside monitors have the potential to improve patient care by non-invasively monitoring patients with acute respiratory disease at risk of hypercapnia.

The revised digital transcutaneous PCO2/SpO2 ear sensor is a reliable noninvasive monitoring tool in patients after cardiac surgery.

OBJECTIVE: The aim of this study was to validate the revised SenTec V-Sign 2 sensor (SenTec AG, Therwil, Switzerland) for combined noninvasive continuous assessment of pulse rate, pulse oximetry (SpO(2)), and transcutaneous carbon dioxide tension (PtcCO(2)) in adults after cardiac surgery. DESIGN: A prospective clinical study. SETTING: A single-center university hospital. PARTICIPANTS: Twenty adult patients aged 36 to 84 years after cardiac surgery. INTERVENTIONS: SpO(2) and PtcCO(2) values of three V-Sign 2 sensors (SenTec AG) attached at the earlobe, forehead, and cheek and SpO(2) values of the Nellcor Durasensor (Model DS-100A; Nellcor Puritan Bennett Inc, Pleasanton, CA) were compared with simultaneous measurements of blood gases and end-expiratory carbon dioxide. MEASUREMENTS AND MAIN RESULTS: Measurements were performed during periods of hyper-, normo-, and hypocapnia and then at 30-minute intervals up to 5 hours. Bland-Altman analysis and simple regression analysis were used. RESULTS: The detection failures for PtcCO(2) were 0.3% to 1.3%, for SpO(2) 10% to 25%, and for pulse rate 5% to 10%. The V-Sign 2 earlobe sensor provided the best results. The mean bias and limits of agreement for PtcCO(2ear) and PaCO(2) were 1.1 and -3.4/+5.5 mmHg. The drift of PtcCO(2) was negligible at all locations. The mean bias and limits of agreement of V-Sign SpO(2ear) and SaO(2), as well as V-Sign pulse rate and the electrocardiogram, were -1.7% and -6.8/+3.9% and 1.2 beats/min and -3.3/+5.8 beats/min. End-expiratory carbon dioxide showed a weak correlation with PaCO(2) (r(2) = 0.47). CONCLUSIONS: Transcutaneous capnometry using the revised V-Sign 2 sensor at the earlobe is a reliable monitoring tool during the recovery period of patients after cardiac surgery. This approach has the potential to reduce the number of arterial blood gas samples.

Clinical evaluation of the accuracy and precision of the CDI 500 in-line blood gas monitor with and without gas calibration.

During cardiopulmonary bypass blood gases can be analyzed with laboratory equipment or with an in-line monitor giving instant results. The manufacturer of the CDI 500 in-line blood gas monitor recommends gas calibration before use. In acute cases there may not be time to perform a gas calibration. We hypothesized that after calibration against laboratory results, the CDI values of pH, pO2, and pCO2 will keep the same level of accuracy, whether the CDI has been gas calibrated or not. We performed a prospective randomized observational study using a study group without gas calibration (29 patients) and a control group with gas calibration (29 patients). Blood sampling was done at the beginning of bypass, and 30 minutes later. After each blood sample the CDI was in-vivo calibrated to the values simultaneously obtained from the ABL. Before in-vivo calibration values from the CDI without gas calibration were significantly different from the ABL-values in accuracy as well as precision, whereas the results from the gas calibrated CDI were largely consistent with the ABL. Before in-vivo calibration, the CDI without gas calibration was completely unreliable. After in-vivo calibration there was no statistical difference between the values of the CDI with and without calibration. We recommend gas calibration of the CDI before use in the period before in-vivo calibration.

Transcutaneous Carbon Dioxide Measurement in Adult Patients with Neuromuscular Disorders: A quality Level Assessment.

BACKGROUND: Carbon dioxide tension (PCO2) monitoring during sleep, is crucial to identify respiratory failure in patients with neuromuscular disorders (NMD). Transcutaneous PCO2 monitoring is an available technique to measure PCO2. OBJECTIVES: To assess the quality level of transcutaneous blood gas measurements via SenTec monitor. METHODS: A 12-month analysis of SenTec measurements was conducted in a Belgian Centre for Home Mechanical Ventilation (HMV). Over two consecutive nights; SpO2 and PCO2 measurements, the presence of PCO2 drift and drift correction with SenTec, were reviewed and scores (0, 1, 2 for poor, medium and high level) were assigned to estimate the quality of measurements. RESULTS: Sixty-nine NMD patients met the inclusion criteria, of which 48/69 used HMV. PCO2 drift and drift correction were present in 15% and 68% of the 138 recordings, respectively. The quality level of measurements throughout night 1, scored 1.55 (0-2). The relevance of our clinical findings from SenTec scoring 1.94 (1-2); was considered highly satisfactory. HMV was ineffective in 24/48 patients. Among 12 patients with hypercapnia, 8 patients improved PCO2 between night 1 and 2. Among 12 patients with hypocapnia, PCO2 improved in 4/12 patients, who reached the range of normal PCO2 (35-47 mmHg). CONCLUSIONS: The quality of SenTec measurements was acceptable in the majority of recordings and clinical findings were deemed satisfactory in all cases. A single SenTec measurement was sufficient to determine the need for NIV. However, two SenTec registrations were insufficient to both improve NIV effectiveness in 50% of cases, and, to ensure follow-up of our interventions.

Nocturnal Transcutaneous Blood Gas Measurements in a Pediatric Neurologic Population: A Quality Assessment.

Objective: To assess the quality of SpO2 and PCO2 recordings via transcutaneous monitoring in children with neurological conditions.Methods: Overnight transcutaneous SpO2 and PCO2 were analyzed. The presence of drift and drift correction was noted, and the rate of disrupted recordings scored (0: absence, 1; presence). The quality of recordings was also scored (0, 1, 2 for poor, medium, and high).Results: A total of 228 recordings from 64 children aged 9.7 ± 6 years were analyzed of which 42 used positive pressure respiratory support. The mean quality of the recordings was scored as 1.27 (0-2). PCO2 drift, drift correction, and disrupted recordings were present in 25%, 58%, and 26% of recordings, respectively. Satisfactory clinical decisions were taken in 91% of cases.Conclusion: The quality of transcutaneous sensor recordings was acceptable and clinical findings were deemed as satisfactory in the large majority of cases. Correction of PCO2 drift was challenging.

Improvement in accuracy of transcutaneous measurement of oxygen with resumption of spontaneous ventilation in mechanically ventilated patients after off pump coronary artery bypass procedure: a prospective study.

INTRODUCTION: Transcutaneous measurement of gases depends on the degree of skin perfusion. Mechanical ventilation causes alteration in the peripheral perfusion. The aim of this prospective observational study was to assess change in the accuracy of interchangeability of arterial blood gases with those obtained transcutaneously at various phases of mechanical ventilation such as controlled mandatory, synchronized intermittent mandatory, continuous positive airway pressure ventilations, spontaneous breathing trail and spontaneous ventilation after extubation of endotracheal tube. METHODS: Thirty-two adult patients who underwent uncomplicated off pump coronary artery bypass surgery in a tertiary care medical center were subjected to transcutaneous measurements of gases from the sensor placed on the chest during postoperative ventilation. Arterial blood gas analysis was performed at predetermined time intervals and transcutaneous measurements were repeated each of those time. RESULTS: Fifty-four sets of data were obtained during controlled ventilation and fifty during spontaneous. Correlation coefficient for oxygen increased from 0.46 (P = 0.0004) during controlled ventilation to 0.75 (P < 0.0001) during spontaneous. Bland-Altman and mountain plots suggested better inter- changeability of values between arterial blood gas and transcutaneous gas monitoring. The bias for oxygen changed from 21 during controlled ventilation to 25 during spontaneous ventilation and the precision from 7.1 to 6.4. There was no change in the accuracy of transcutaneous carbon dioxide values during either phase of ventilation. CONCLUSION: The accuracy of transcutaneously measured values of oxygen improved significantly during spontaneous ventilation.

Transcutaneous oximetry in clinical practice: consensus statements from an expert panel based on evidence.

Transcutaneous oximetry (PtcO2) is finding increasing application as a diagnostic tool to assess the peri-wound oxygen tension of wounds, ulcers, and skin flaps. It must be remembered that PtcO2 measures the oxygen partial pressure in adjacent areas of a wound and does not represent the actual partial pressure of oxygen within the wound, which is extremely difficult to perform. To provide clinical practice guidelines, an expert panel was convened with participants drawn from the transcutaneous oximetry workshop held on June 13, 2007, in Maui, Hawaii. Important consensus statements were (a) tissue hypoxia is defined as a PtcO2 <40 mm Hg; (b) in patients without vascular disease, PtcO2 values on the extremity increase to a value >100 mm Hg when breathing 100% oxygen under normobaric pressures; (c) patients with critical limb ischemia (ankle systolic pressure of < or =50 mm Hg or toe systolic pressure of < or =30 mm Hg) breathing air will usually have a PtcO2 <30 mm Hg; (d) low PtcO2 values obtained while breathing normobaric air can be caused by a diffusion barrier; (e) a PtcO2 <40 mm Hg obtained while breathing normobaric air is associated with a reduced likelihood of amputation healing; (f) if the baseline PtcO2 increases <10 mm Hg while breathing 100% normobaric oxygen, this is at least 68% accurate in predicting failure of healing post-amputation; (g) an increase in PtcO2 to >40 mm Hg during normobaric air breathing after revascularization is usually associated with subsequent healing, although the increase in PtcO2 may be delayed; (h) PtcO2 obtained while breathing normobaric air can assist in identifying which patients will not heal spontaneously.

Determination of ideal PtcO2 measurement time in evaluation of hypoxic wound patients.

OBJECTIVE: Evaluation of ideal time for baseline PtcO2 readings in air, elevation test, and oxygen challenge during evaluation of hypoxic wound patients. DESIGN: Retrospective analysis. IRB APPROVAL: Western IRB deemed this study exempt from requiring IRB approval. PATIENTS: 202 patients with lower extremity wounds. METHOD: Patients had PtcO2 measurements using 6 electrodes positioned in 3 paired locations along the limb (above the knee: AK; below the knee: BK; and foot). Measurements were made from each electrode at 7 different time-event occasions: position of limb (supine or elevated), type of breathing gas (sea level air or oxygen), and time of measurement. A total of 8,484 measurements were analyzed by first examining each electrode's data, and then pooling the data for each location pair. MAIN RESULTS: PtcO2 readings for air (10 minutes) were less than air at 20 minutes. Maximal readings were close to the 20-minute mark for AK and BK measurements, and closer to 30 minutes for the foot. Elevation test at 3 versus 5 minutes showed a continuing decline in PtcO2 values. Oxygen challenge readings at 5 and 10 minutes were significantly different: the latter always larger than the former. CONCLUSION: Ideal times for baseline readings, leg elevation test, and oxygen challenge test are at least 20, 5, and 10 minutes, respectively.

The design, use, and results of transcutaneous carbon dioxide analysis: current and future directions.

Transcutaneous carbon dioxide (CO2) analysis was introduced in the early 1980s using locally heated electrochemical sensors that were applied to the skin surface. This methodology provides a continuous noninvasive estimation of the arterial CO2 value and can be used for assessing adequacy of ventilation. The technique is now established and used routinely in clinical practice. Transcutaneous partial pressure of CO2 (tcPco2) sensors are available as a single Pco2 sensor, as a combined Pco2/Po2 sensor, and more recently, as a combined Pco2/Spo2 sensor. CO2 is still measured potentiometrically by determining the pH of an electrolyte layer. The methodology has been continuously developed during the last 20 yr, making the tcPco2 systems easier and more reliable for use in clinical practice: smaller sensor size (diameter 15 mm, height 8 mm), less frequent sensor re-membraning (every 2 wk) and calibration (twice a day), sensor ready to use when connected to the monitor, lower sensor temperature (42 degrees C), shorter arterialization time (3 min), and increased measurement reliability through protection of the membrane. The present tcPco2 sensors still need to be regularly re-membraned and calibrated. One way to overcome these procedures is to use optical-only detection means. Two techniques have been developed using optical absorption in the near-infrared light, in the evanescent wave of a waveguide integrated in the sensor surface, or in a micro-optics sampling cell. Preliminary in vitro and in vivo CO2 measurements have been performed. The sensor is not affected by drift over several days, and its response time is <1 min.

Investigation of the efficacy of colorimetric capnometry method used to verify the correct placement of the nasogastric tube.

OBJECTIVES: This present study was designed to determine the efficacy of the colorimetric capnometry method used to verify the correct placement of the nasogastric tube. METHODS: The present study comprised forty patients who had a nasogastric tube inserted and were being monitored in the adult intensive care unit. After the insertion of the nasogastric tube, 40 colorimetric capnometry and 40 auscultation measurements were performed. Auscultation and colorimetric capnometry results were compared with tube placement results confirmed radiologically. RESULTS: In the confirmation of the placement of the nasogastric tube, the consistency was 97.5% (p<0.05) between the colorimetric capnometry method and the radiological method, and 82.5% (p>0.05) between the auscultatory method and the radiological method. The oesophageal placement of the nasogastric tube was detected with the colorimetric capnometry method, but the gastric and duodenal insertions were not determined. While the sensitivity and specificity of the colorimetric capnometry method in determining the correct placement of the nasogastric tube were 1.00 and 0.667 respectively, those of the auscultatory method were 0.89 and 0.0 respectively. CONCLUSION: As a result, for the confirmation of the NGT placement, the colorimetric capnometry method is considered more reliable than the auscultatory method and is compatible with the radiological method. However, the colorimetric capnometry method is inadequate to distinguish between the gastric or duodenal insertion.

Validation of the CAS neonatal NIRS system by monitoring vv-ECMO patients: preliminary results.

The CAS neonatal NIRS system determines absolute regional brain tissue oxygen saturation (SnO2) and brain true venous oxygen saturation (SnvO2) non-invasively. Since NIRS-interrogated tissue contains both arterial and venous blood from arterioles, venules, and capillaries, SnO2 is a mixed oxygen saturation parameter, having values between arterial oxygen saturation (SaO2) and cerebral venous oxygen saturation (SvO2). To determine a reference for SnO2, the relative contribution of SvO2 to SaO2 drawn from a brain venous site vs. systemic SaO2 is approximately 70:30 (SvO2:SaO2). If the relationship of the relative average contribution of SvO2 and SaO2 is known and does not change to a large degree, then NIRS true venous oxygen saturation, SnvO2, can be determined non-invasively using SnO2 along with SaO2 from a pulse oximeter.

Transcutaneous oxygen monitors are reliable indicators of arterial oxygen tension (if used correctly).

The following recommendations should always be kept in mind: Each new transcutaneous equipment, or modification of equipment, must be adequately tested in vivo as well as in vitro. The users must have basic understanding of the principles and the major requirements for applying the tcPO2 technique. Calibration procedures must be carefully adhered to according to the manufacturer's instruction. The temperature of the electrode must be kept at 44 degrees C for premature infants and at 44 degrees or 45 degrees C for term infants if the clinical aim is to estimate arterial PO2 levels. Resetting of the electrode must then be done every two hours. For sick infants, this may be needed more frequently. Whenever there is cause to compare tcPO2 values with arterial ones, the latter must be obtained from an appropriate vessel. Great care must be taken when drawing and analyzing blood for PO2. The infant should not be crying. Significantly lower transcutaneous PO2 values than arterial PO2 values are due to either one or several of the errors indicated above or to an insufficient circulation under the electrode. In recent years, technical or clinical errors seem to have become more and more common. Thereby the technique has unjustly fallen into disrepute. Insufficient circulation under the electrode rarely occurs in the newborn infant and then only in those who are in overt shock.