Transcutaneous PTCCO2 measurement in combination with arterial blood gas analysis provides superior accuracy and reliability in ICU patients

Increased risk of respiratory events during endobronchial ultrasound examination in patients with reduced forced expiratory volume: a prospective observational study

Background

The incidence of adverse events during endobronchial ultrasound is low. Nevertheless, it is unclear, whether patients with impaired pulmonary function have an increased risk of respiratory events during the intervention.

Methods

A monocentric prospective observational study was performed at the Department of Respiratory Medicine, University Hospital Frankfurt/Main, Germany. Adult patients undergoing an endobronchial ultrasound examination with propofol-sedation were included. Pre-interventional screening included pulmonary function testing, laboratory tests and electrocardiogram. The occurrence of hypercapnia >55 mmHg or reduced oxygen saturation <85% was defined as a respiratory event was recorded and compared between patients with normal and impaired pulmonary function tests.

Results

In total, 126 patients were included. Pulmonary function testing revealed a median FEV1 of 2.2 l (range 0.4-6.04l) and a predicted FEV1 of 79.5% (range 20-127.8%) respectively. The median FVC was 3.0 l (range 0.87-7.28l), the median predicted FVC was 82% (range 31.4-128.4%). In 72 examinations (60%) pCO2 levels >55 mmHg were measured. Transient oxygen desaturation <85% occurred in 31 cases (25.8%). The Mann Whitney U-test showed a significantly lower FEV1 (% predicted value) in patients with respiratory events (p = 0.007). ROC analysis identified a predicted FEV1 of 78.5% as the optimal cut-off with a sensitivity of 58% and a specificity of 71%. Using Z-score instead of predicted values, there was no significant association between a lower Z- score of FEV or FVC and hypercapnic or hypoxic events. However, both a lower absolute value of FEV1/FVC and a lower Z-score of the FEV1/FVC index were associated with the occurrence of respiratory events. In binary logistic regression analysis, we could not demonstrate any association with other relevant parameters (age, BMI, sedation dosage, sedation duration, or ASA-score).

Conclusions

An impaired forced expiratory volume is associated with the frequency of respiratory events during endobronchial ultrasound examination under propofol-sedation.

Analysis of arterial blood gas values when discarding different volumes of blood samples in an arterial heparin blood collector during thoracoscopic surgery

BACKGROUND

Arterial blood gas analysis (ABGA) plays a vital role in emergency and intensive care, which is affected by many factors, such as different instrumentation, temperature, and testing time. However, there are still no relevant reports on the difference in discarding different blood volumes on ABGA values.

METHODS

We enrolled 54 patients who underwent thoracoscopic surgery and analysed differences in blood gas analysis results when different blood volumes were discarded from the front line of the arterial heparin blood collector. A paired t test was used to compare the results of the same patient with different volumes of blood discarded from the samples. The difference was corrected by Bonferroni correction.

RESULTS

Our results demonstrated that the PaO2, PaCO2, and THbc were more stable in the 4th ml (PaO2 = 231.3600 ± 68.4878 mmHg, PaCO2 = 41.9232 ± 7.4490 mmHg) and 5th ml (PaO2 = 223.7600 ± 12.9895 mmHg, PaCO2 = 42.5679 ± 7.6410 mmHg) blood sample than in the 3rd ml (PaO2 = 234.1000 ± 99.7570 mmHg, PaCO2 = 40.6179 ± 7.2040 mmHg).

CONCLUSION

It may be more appropriate to discard the first 3 ml of blood sample in the analysis of blood gas results without wasting blood samples.

Trending Ability of End-Tidal Capnography Monitoring During Mechanical Ventilation to Track Changes in Arterial Partial Pressure of Carbon Dioxide in Critically Ill Patients With Acute Brain Injury: A Monocenter Retrospective Study

BACKGROUND

Changes in arterial partial pressure of carbon dioxide (Pa co2 ) may alter cerebral perfusion in critically ill patients with acute brain injury. Consequently, international guidelines recommend normocapnia in mechanically ventilated patients with acute brain injury. The measurement of end-tidal capnography (Et co2 ) allows its approximation. Our objective was to report the agreement between trends in Et co2 and Pa co2 during mechanical ventilation in patients with acute brain injury.

METHODS

Retrospective monocenter study was conducted for 2 years. Critically ill patients with acute brain injury who required mechanical ventilation with continuous Et co2 monitoring and with 2 or more arterial gas were included. The agreement was evaluated according to the Bland and Altman analysis for repeated measurements with calculation of bias, and upper and lower limits of agreement. The directional concordance rate of changes between Et co2 and Pa co2 was evaluated with a 4-quadrant plot. A polar plot analysis was performed using the Critchley methods.

RESULTS

We analyzed the data of 255 patients with a total of 3923 paired ΔEt co2 and ΔPa co2 (9 values per patient in median). Mean bias by Bland and Altman analysis was -8.1 (95 CI, -7.9 to -8.3) mm Hg. The directional concordance rate between Et co2 and Pa co2 was 55.8%. The mean radial bias by polar plot analysis was -4.4° (95% CI, -5.5 to -3.3) with radial limit of agreement (LOA) of ±62.8° with radial LOA 95% CI of ±1.9°.

CONCLUSIONS

Our results question the performance of trending ability of Et co2 to track changes in Pa co2 in a population of critically ill patients with acute brain injury. Changes in Et co2 largely failed to follow changes in Pa co2 in both direction (ie, low concordance rate) and magnitude (ie, large radial LOA). These results need to be confirmed in prospective studies to minimize the risk of bias.

Associations between clinical interventions and transcutaneous blood gas values in postoperative patients

PURPOSE

Postoperative monitoring of circulation and respiration is pivotal to guide intervention strategies and ensure patient outcomes. Transcutaneous blood gas monitoring (TCM) may allow for noninvasive assessment of changes in cardiopulmonary function after surgery, including a more direct assessment of local micro-perfusion and metabolism. To form the basis for studies assessing the clinical impact of TCM complication detection and goal-directed-therapy, we examined the association between clinical interventions in the postoperative period and changes in transcutaneous blood gasses.

METHODS

Two-hundred adult patients who have had major surgery were enrolled prospectively and monitored with transcutaneous blood gas measurements (oxygen (TcPO2) and carbon dioxide (TcPCO2)) for 2 h in the post anaesthesia care unit, with recording of all clinical interventions. The primary outcome was changes in TcPO2, secondarily TcPCO2, from 5 min before a clinical intervention versus 5 min after, analysed with paired t-test.

RESULTS

Data from 190 patients with 686 interventions were analysed. During clinical interventions, a mean change in TcPO2 of 0.99 mmHg (95% CI-1.79-0.2, p = 0.015) and TcPCO2 of-0.67 mmHg (95% CI 0.36-0.98, p < 0.001) was detected.

CONCLUSION

Clinical interventions resulted in significant changes in transcutaneous oxygen and carbon dioxide. These findings suggest future studies to assess the clinical value of changes in transcutaneous PO2 and PCO2 in a postoperative setting.

TRIAL REGISTRY

Clinical trial number: NCT04735380.

CLINICAL TRIAL REGISTRY

https://clinicaltrials.gov/ct2/show/NCT04735380.

Limitations of transcutaneous carbon dioxide monitoring in apneic oxygenation

BACKGROUND

High-flow nasal oxygenation is increasingly used during sedation procedures and general anesthesia in apneic patients. Transcutaneous CO2 (ptcCO2)-monitoring is used to monitor hypercapnia. This study investigated ptcCO2-monitoring during apneic oxygenation.

METHODS

We included 100 patients scheduled for elective surgery under general anesthesia in this secondary analysis of a randomized controlled trial. Before surgery, we collected ptcCO2 measured by TCM4 and TCM5 monitors and arterial blood gas (ABG) measurements every two minutes during 15 minutes of apnea. Bland-Altman plots analyzed agreement between measurement slopes; linear mixed models estimated the different measuring method effect, and outlined differences in slope and offset between transcutaneous and arterial CO2 partial pressures.

RESULTS

Bland-Altman plots showed a bias in slope (95% confidence intervals) between ABG and TCM4-measurements of 0.05mmHg/min (-0.05 to 0.15), and limits of agreement were -0.88mmHg/min (-1.06 to -0.70) and 0.98mmHg/min (0.81 to 1.16). Bias between ABG and TCM5 was -0.14mmHg/min (-0.23 to -0.04), and limits of agreement were -0.98mmHg/min (-1.14 to -0.83) and 0.71mmHg/min (0.55 to 0.87). A linear mixed model (predicting the CO2-values) showed an offset between arterial and transcutaneous measurements of TCM4 (-15.2mmHg, 95%CI: -16.3 to -14.2) and TCM5 (-19.1mmHg, -20.1 to -18.0). Differences between the two transcutaneous measurements were statistically significant.

CONCLUSIONS

Substantial differences were found between the two transcutaneous measurement systems, and between them and ABG. Transcutaneous CO2 monitoring cannot replace arterial CO2-monitoring during apneic oxygenation. In clinical settings with rapidly changing CO2-values, arterial blood gas measurements are needed to reliably assess the CO2-partial pressure in blood.

TRIAL REGISTRATION

ClinicalTrials.gov (NCT03478774).

Daytime Hypercapnia Impairs Working Memory in Young and Middle-Aged Patients with Obstructive Sleep Apnea Hypopnea Syndrome

Purpose

Obstructive sleep apnea hypopnea syndrome (OSAHS) can lead to cognitive impairment, though few studies have so far examined hypercapnia as its causal mechanism, due to the invasive nature of conventional arterial CO2 measurement. The study aims to investigate the effects of daytime hypercapnia on working memory in young and middle-aged patients with OSAHS.

Patients and Methods

This prospective study screened 218 patients and eventually recruited 131 patients (aged 25-60 years) with polysomnography (PSG)-diagnosed OSAHS. Using a cut-off of 45mmHg daytime transcutaneous partial pressure of carbon dioxide (PtcCO2), 86 patients were assigned into the normocapnic group and 45 patients into the hypercapnic group. Working memory was evaluated using the Digit Span Backward Test (DSB) and the Cambridge Neuropsychological Test Automated Battery.

Results

Compared with the normocapnic group, the hypercapnic group performed worse in verbal, visual, and spatial working memory tasks. PtcCO2≥45mmHg was an independent predictor for lower DSB scores (OR=4.057), lower accuracy in the immediate Pattern Recognition Memory (OR=2.600), delayed Pattern Recognition Memory (OR=2.766) and Spatial Recognition Memory (OR=2.722) tasks, lower Spatial Span scores (OR=4.795), and more between errors in the Spatial Working Memory task (OR=2.734 and 2.558, respectively). Notably, PSG indicators of hypoxia and sleep fragmentation did not predict task performance.

Conclusion

Hypercapnia may be plays an important role in working memory impairment in patients with OSAHS, perhaps more so than hypoxia and sleep fragmentation. Routine CO2 monitoring in these patients could prove of utility in clinical practices.

Transcutaneous carbon dioxide monitoring during prolonged apnoea with high-flow nasal oxygen

BACKGROUND

The duration of apnoeic oxygenation with high-flow nasal oxygen is limited by hypercapnia and acidosis and monitoring of arterial carbon dioxide level is therefore essential. We have performed a study in patients undergoing prolonged apnoeic oxygenation where we monitored the progressive hypercapnia with transcutaneous carbon dioxide. In this paper, we compared the transcutaneous carbon dioxide level with arterial carbon dioxide tension.

METHODS

This is a secondary publication based on data from a study exploring the limits of apnoeic oxygenation. We compared transcutaneous carbon dioxide monitoring with arterial carbon dioxide tension using Bland-Altman analyses in anaesthetised and paralysed patients undergoing prolonged apnoeic oxygenation until a predefined limit of pH 7.15 or PCO₂ of 12 kPa was reached.

RESULTS

We included 35 patients with a median apnoea duration of 25 min. Mean pH was 7.14 and mean arterial carbon dioxide tension was 11.2 kPa at the termination of apnoeic oxygenation. Transcutaneous carbon dioxide monitoring initially slightly underestimated the arterial tension but at carbon dioxide levels above 10 kPa it overestimated the value. Bias ranged from -0.55 to 0.81 kPa with limits of agreement between -1.25 and 2.11 kPa.

CONCLUSION

Transcutaneous carbon dioxide monitoring provided a clinically acceptable substitute for arterial blood gases but as hypercapnia developed to considerable levels, we observed overestimation at high carbon dioxide tensions in patients undergoing apnoeic oxygenation with high-flow nasal oxygen.

Microfluidics-assisted optimization of highly adhesive haemostatic hydrogel coating for arterial puncture

Although common in clinical practice, bleeding after tissue puncture may cause serious outcomes, especially in arterial puncture. Herein, gelatin-tannic acid composite hydrogels with varying compositions are prepared, and their adhesive properties are further optimized in microfluidic channel-based simulated vessels for haemostasis in arterial puncture. It is revealed that the composite hydrogels on the syringe needles used for arterial puncture should possess underwater adhesion higher than 4.9 kPa and mechanical strength higher than 86.0 kPa. The needles coated with the gelatin-tannic acid composite hydrogel completely prevent blood loss after both vein and arterial puncture in different animal models. This study holds great significance for the preparation of haemostatic needles for vessel puncture, and gelatin-tannic acid hydrogel coated needles may help to prevent complications associated with arterial puncture.

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Haemostatic needles were prepared with coating of gelatin-tannic acid hydrogel.

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Microfluidic system was employed to optimize the underwater adhesion of gelatin-tannic acid hydrogel coating.

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Needles coated with the gelatin-tannic acid hydrogel exhibited complete haemostasis after arterial puncture.

Continuous transcutaneous carbon-dioxide monitoring to avoid hypercapnia in complex catheter ablations under conscious sedation

BACKGROUND

Ablation of complex cardiac arrhythmias requires an immobilized patient. For a successful and safe intervention and for patient comfort, this can be achieved by conscious sedation. Administered sedatives and analgesics have respiratory depressant side effects and require close monitoring. We investigated the feasibility and accuracy of additional, continuous transcutaneous carbon-dioxide partial pressure (tpCO₂) measurement during conscious sedation in complex electrophysiological catheter ablation procedures.

METHOD

We evaluated the accuracy and additional value of continuous tpCO₂ detection by application of a Severinghaus electrode in comparison to arterial and venous blood gas analyses.

RESULTS

We included 110 patients in this prospective observational study. Arterial pCO₂ (paCO₂) and tpCO₂ showed good correlation throughout the procedures (r = 0.60-0.87, p < 0.005). Venous pCO₂ (pvCO₂) were also well correlated to transcutaneous values (r = 0.65-0.85, p < 0.0001). Analyses of the difference of pvCO₂ and tpCO₂ measurements showed a tolerance within <10 mmHg in up to 96-98% of patients. Hypercapnia (pCO₂ < 70 mmHg) was detected more likely and earlier by continuous tpCO₂ monitoring compared to half-hourly pvCO₂ measurements.

CONCLUSION

Continuous tpCO₂ monitoring is feasible and precise with good correlation to arterial and venous blood gas carbon-dioxide analysis during complex catheter ablations under conscious sedation and may contribute to additional safety.

Arterial and transcutaneous variability and agreement between multiple successive measurements of carbon dioxide in patients with chronic obstructive lung disease

PURPOSE

This study evaluates agreement between carbon dioxide measured arterial (PaCO₂) and transcutaneous (PtcCO₂) over time, by repeated successive measures, taking into consideration the inherent variability of arterial measurements.

METHODS AND RESULTS

11 patients receiving LTOT, with severe to very severe COPD in a stable phase were studied. Repeated arterial blood samples were drawn and PtcCO₂ measured simultaneously at the ear lobe. Bland-Altman analysis was used to evaluate 95 % limits of agreement (LoA). 194 paired samples were analysed. Following correction for bias, the difference between PaCO₂ and PtCO₂ during dynamic conditions was 0.02 kPa and LoA 0.94 to -0.90 kPa while 29 % of PtCO₂ measurements were outside the range of variability for arterial measurements.

CONCLUSION

PtcCO₂ corrected for intra-patient bias provide reasonable description of PaCO₂ values within but not outside steady state conditions. Our results suggest that PtcCO₂ is a valuable method for monitoring in chronic rather than acute conditions when bias can be removed.

Volume Capnography in the Intensive Care Unit: Potential Clinical Applications

Volume capnography provides a noninvasive, continuous display of the fractional concentration or partial pressure of carbon dioxide (Pco₂) versus exhaled volume. Derived measurements and calculations are influenced by changes in both ventilation and perfusion and are therefore useful for assessing both respiratory and cardiovascular function. This article provides an evidence-based review of several potential uses of volume capnography in the intensive care unit: 1) monitoring the effectiveness of ventilation by using end-tidal Pco₂ as a surrogate for arterial Pco₂, 2) assessing volume responsiveness, 3) measuring cardiac output, 4) determining prognosis in patients with the acute respiratory distress syndrome, 5) optimizing alveolar recruitment, and 6) excluding pulmonary embolism. Studies performed during the past few decades have clearly shown that volume capnography can provide important prognostic information in patients with acute respiratory distress syndrome and that end-tidal Pco₂ should not be used to estimate or even to monitor the direction of change in the arterial Pco₂ in mechanically ventilated intensive care unit patients. Unfortunately, few conclusions can be made from studies evaluating other potential applications. Of these, the most promising are the noninvasive measurement of cardiac output and optimization of alveolar recruitment in patients with acute respiratory distress syndrome and in mechanically ventilated, morbidly obese patients.

Respiratory acidosis during bronchoscopy-guided percutaneous dilatational tracheostomy: impact of ventilator settings and endotracheal tube size

Background

The current study investigates the effect of bronchoscopy-guided percutaneous dilatational tracheostomy (PDT) on the evolution of respiratory acidosis depending on endotracheal tube (ET) sizes. In addition, the impact of increasing tidal volumes during the intervention was investigated.

Methods

Two groups of ICU-patients undergoing bronchoscopy-guided PDT with varying tidal volumes and tube sizes were consecutively investigated: 6 ml/kg (N = 29, mean age 57.4 ± 14.5 years) and 12 ml/kg predicted body weight (N = 34, mean age 59.5 ± 12.8 years).

Results

The mean intervention time during all procedures was 10 ± 3 min. The combination of low tidal volumes and ETs of 7.5 mm internal diameter resulted in the most profound increase in PaCO₂ (32.2 ± 11.6 mmHg) and decrease in pH-value (− 0.18 ± 0.05). In contrast, the combination of high tidal volumes and ETs of 8.5 mm internal diameter resulted in the least profound increase in PaCO₂ (8.8 ± 9.0 mmHg) and decrease of pH (− 0.05 ± 0.04). The intervention-related increase in PaCO₂ was significantly lower when using higher tidal volumes for larger ET: internal diameter 7.5, 8.0 and 8.5: P > 0.05, =0.006 and = 0.002, respectively. Transcutaneous PCO₂ monitoring revealed steadily worsening hypercapnia during the intervention with a high correlation of 0.87 and a low bias of 0.7 ± 9.4 mmHg according to the Bland-Altman analysis when compared to PaCO₂ measurements.

Conclusions

Profound respiratory acidosis following bronchoscopy-guided PDT evolves in a rapid and dynamic process. Increasing the tidal volume from 6 to 12 ml/kg PBW was capable of attenuating the evolution of respiratory acidosis, but this effect was only evident when using larger ETs.

Trial registration

DRKS00011004. Registered 20th September 2016.

Electronic supplementary material

The online version of this article (10.1186/s12871-019-0824-5) contains supplementary material, which is available to authorized users.

Response time of indirectly accessed gas exchange depends on measurement method

Noninvasive techniques are routinely used for assessment of tissue effects of lung ventilation. However, comprehensive studies of the response time of the methods are scarce. The aim of this study was to compare the response time of noninvasive methods for monitoring of gas exchange to sudden changes in the composition of the inspired gas. A prospective experimental study with 16 healthy volunteers was conducted. A ventilation circuit was designed that enabled a fast change in the composition of the inspiratory gas mixture while allowing spontaneous breathing. The volunteers inhaled a hypoxic mixture, then a hypercapnic mixture, a hyperoxic mixture and finally a 0.3% CO mixture. The parameters with the fastest response to the sudden change of O2 in inhaled gas were peripheral capillary oxygen saturation (SpO2) and regional tissue oxygenation (rSO2). Transcutaneous oxygen partial pressure (tcpO2) had almost the same time of reaction, but its time of relaxation was 2-3 times longer. End-tidal carbon dioxide (EtCO2) response time to change of CO2 concentration in inhaled gas was less than half in comparison with transcutaneous carbon dioxide partial pressure (tcpCO2). All the examined parameters and devices reacted adequately to changes in gas concentration in the inspiratory gas mixture.

Estimation of Arterial Carbon Dioxide Based on End-Tidal Gas Pressure and Oxygen Saturation

Arterial blood gas (ABG) analysis is the traditional method for measuring the partial pressure of carbon dioxide. In mechanically ventilated patients a continuous noninvasive monitoring of carbon dioxide would obviously be attractive. In the current study, we present a novel formula for noninvasive estimation of arterial carbon dioxide. Eighty-one datasets were collected from 19 anesthetized and mechanically ventilated pigs. Eleven animals were mechanically ventilated without interventions. In the remaining eight pigs the partial pressure of carbon dioxide was manipulated. The new formula (Formula 1) is PaCO₂ = PETCO₂ + k(PETO₂ − PaO₂) where PaO₂ was calculated from the oxygen saturation. We tested the agreements of this novel formula and compared it to a traditional method using the baseline PaCO₂ − ETCO₂ gap added to subsequently measured, end-tidal carbon dioxide levels (Formula 2). The mean difference between PaCO₂ and calculated carbon dioxide (Formula 1) was 0.16 kPa (±SE 1.17). The mean difference between PaCO₂ and carbon dioxide with Formula 2 was 0.66 kPa (±SE 0.18). With a mixed linear model excluding cases with cardiorespiratory collapse, there was a significant difference between formulae (p < 0.001), as well as significant interaction between formulae and time (p < 0.001). In this preliminary animal study, this novel formula appears to have a reasonable agreement with PaCO₂ values measured with ABG analysis, but needs further validation in human patients.

Estimating Arterial Partial Pressure of Carbon Dioxide in Ventilated Patients: How Valid Are Surrogate Measures?

The arterial partial pressure of carbon dioxide (Pa_CO2) is an important parameter in critically ill, mechanically ventilated patients. To limit invasive procedures or for more continuous monitoring of Pa_CO2, clinicians often rely on venous blood gases, capnography, or transcutaneous monitoring. Each of these has advantages and limitations. Central venous Pco₂ allows accurate estimation of Pa_CO2, differing from it by an amount described by the Fick principle. As long as cardiac output is relatively normal, central venous Pco₂ exceeds the arterial value by approximately 4 mm Hg. In contrast, peripheral venous Pco₂ is a poor predictor of Pa_CO2, and we do not recommend using peripheral venous Pco₂ in this manner. Capnography offers measurement of the end-tidal Pco₂ (Pet_CO2), a value that is close to Pa_CO2 when the lung is healthy. It has the advantage of being noninvasive and continuously available. In mechanically ventilated patients with lung disease, however, Pet_CO2 often differs from Pa_CO2, sometimes by a large degree, often seriously underestimating the arterial value. Dependence of Pet_CO2 on alveolar dead space and ventilator expiratory time limits its value to predict Pa_CO2. When lung function or ventilator settings change, Pet_CO2 and Pa_CO2 can vary in different directions, producing further uncertainty. Transcutaneous Pco₂ measurement has become practical and reliable. It is promising for judging steady state values for Pa_CO2 unless there is overt vasoconstriction of the skin. Moreover, it can be useful in conditions where capnography fails (high-frequency ventilation) or where arterial blood gas analysis is burdensome (clinic or home management of mechanical ventilation).