Accurateness and precision of transcutaneous carbon dioxide monitoring: a systematic review and meta-analysis

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  1. http://orcid.org/0000-0002-9583-8636Aaron Conway1,2,three,
  2. Elizabeth Tipton4,
  3. Wei-Hong Liu1,
  4. Zachary Conway5,
  5. Kathleen Soalheira1,
  6. Joanna Sutherlandsix,
  7. http://orcid.org/0000-0001-9148-196XJames Fingleton7
  1. ane Institution of Health and Biomedical Innovation, Queensland University of Applied science, Kelvin Grove, Queensland, Australia
  2. two Bloomberg Faculty of Nursing, Academy of Toronto, Toronto, Ontario, Canada
  3. three Peter Munk Cardiac Centre, Academy Health Network, Toronto, Ontario, Canada
  4. 4 Teachers College, Columbia Academy, New York, United states
  5. five School of Do Sciences, AustralianCatholic University, Brisbane, Queensland, Commonwealth of australia
  6. 6 Coffs Harbour Health Campus and Rural Clinical School, University of New Due south Wales, Coffs Harbour, New South Wales, Australia
  7. 7 Medical Enquiry Institute of New Zealand, Wellington, New Zealand
  1. Correspondence to Dr Aaron Conway, Bloomberg Faculty of Nursing, Academy of Toronto, Toronto, Ontario, Canada ; aaron.conway{at}utoronto.ca

Abstract

Groundwork Transcutaneous carbon dioxide (TcCO2) monitoring is a non-invasive alternative to arterial claret sampling. The aim of this review was to determine the accuracy and precision of TcCOii measurements.

Methods Medline and EMBASE (2000–2016) were searched for studies that reported on a measurement of PaCO2 that coincided with a measurement of TcCO2. Study pick and quality assessment (using the revised Quality Assessment of Diagnostic Accurateness Studies tool (QUADAS-2)) were performed independently. The Grading Quality of Evidence and Force of Recommendation approach was used to summarise the force of the trunk of evidence. Pooled estimates of the mean bias between TcCO2 and PaCOtwo and limits of understanding with outer 95% CIs (termed population limits of understanding) were calculated.

Results The mean bias was −0.i mm Hg and the population limits of agreement were −15 to 15 mm Hg for 7021 paired measurements taken from 2817 participants in 73 studies, which was outside of the clinically acceptable range (7.5 mm Hg). The lowest PaCO2 reported in the studies was eighteen mm Hg and the highest was 103 mm Hg. The major sources of inconsistency were sensor location and temperature. The population limits of understanding were within the clinically acceptable range beyond 3974 paired measurements from 1786 participants in 44 studies that applied the sensor to the earlobe using the TOSCA and Sentec devices (−vi to 6 mm Hg).

Determination At that place are substantial differences between TcCO2 and PaCO2 depending on the context in which this engineering science is used. TcCOii sensors should preferentially be applied to the earlobe and users should consider setting the temperature of the sensor higher than 42°C when monitoring at other sites.

Systematic review registration number PROSPERO; CRD42017057450.

  • respiratory measurement
  • clinical epidemiology

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  • respiratory measurement
  • clinical epidemiology

Key messages

What is the key question?

  • Transcutaneous carbon dioxide (TcCO2) monitoring devices are commercially bachelor and are being used in clinical practice, so it is vital that clinicians have a clear agreement of the accuracy of these devices to ensure they are applied in appropriate circumstances.

What is the bottom line?

  • A TcCO2 measurement at any single bespeak in time could be as much as 15 mm Hg college or lower than PaCO2, meaning that an arterial blood gas sample would be required to confirm diagnosis prior to initiation (or cessation) of handling.

Why read on?

  • As clinicians would exist interested in the accurateness of the type of transcutaneous monitoring device they use and for the population in which they use it, we provide population limits of understanding according to the indication for monitoring (eg, respiratory failure, surgery, intensive care unit, sedation and postoperative recovery), type of device (Sentec and TOSCA), as well as location of sensor placement and sensor temperature.

Introduction

Measurement of PaCO2 in arterial claret is the reference standard for ventilation assessment.1 Arterial puncture is painful and time-consuming, and at that place is risk of infection as well every bit tissue and nerve impairment.2 Measurement of carbon dioxide (COii) levels from the skin, which is known as transcutaneous carbon dioxide (TcCOtwo) monitoring, is a non-invasive alternative to arterial blood sampling. TcCOii monitors measure PaCOii that diffuses through the skin by the awarding of a sensor, which is heated in a higher place body temperature (typically to between 40°C and 44°C) to achieve local arterialisation. Local arterialisation, combined with awarding of an algorithm that corrects the COii value detected by the sensor to 37°C, is thought to provide an accurate approximate of PaCO2. False-positive and false-negative indications of worsening ventilation condition are both important issues to consider regarding the application of these monitors to the clinical practise context. A false-positive or imitation-negative indication almost ventilation status from TcCOtwo monitoring may lead to inappropriate initiation, delay or avoidance of treatment, which could be detrimental for the patient.

The agreement between TcCO2 and PaCO2 has been investigated in a big number of studies. Synthesis of the information through meta-analysis would aid clinical decision-making regarding the advisable circumstances in which TcCO2 monitoring can exist used. We aimed to make up one's mind if TcCO2 has clinically adequate accuracy and precision compared with PaCO2. Accuracy is defined in this context equally the average divergence between TcCO2 and PaCOii measurements and precision as the variance (typically reported as SD) in the differences.

Methods

A systematic review was conducted co-ordinate to a prespecified protocol (PROSPERO trial registration number: CRD42017057450).

Data sources and searches

Published studies were located by searching Medline and EMBASE from January 2000 to December 2016, also as the reference lists of articles identified to be relevant to the review. This search strategy is an efficient approach for systematic reviews of diagnostic test accuracy studies.3 Unpublished and ongoing studies were located by searching the International Clinical Trials Platform. Published conference abstracts were planned to exist included if in that location was sufficient item reported to assess study quality. Language restrictions were not imposed for the search. The Cochrane-recommended search strategy combining terms for the 'target status' and 'alphabetize test' was used.4 The specific search strategy for each database is in online supplementary file 1. Study selection was performed by ii independent reviewers.

Supplementary file ane

Studies that reported a measurement of PaCOii that coincided with a measurement of TcCOii were included. Studies conducted before the yr 2000 were excluded as earlier studies evaluated outdated technology. Only studies that reported on PaCO2 measured either by a point-of-intendance blood gas analyser or central laboratory that coincided with a measurement of the index examination were included.

Data extraction and quality assessment

Information near the study characteristics (author, yr of publication, country, design, sample size, clinical setting, number studied and number analysed for each outcome, number of dropouts with reason, and funding source), population characteristics (inclusion/exclusion criteria, mean/median and range of PaCO2) and TcCO2 characteristics (timing and methods of sampling/measurements, method of sampling/calibration) was extracted. Outcomes extracted were the mean bias (ie, accuracy) and variance or SD (ie, precision) in CO2 between transcutaneous and arterial claret gas analyses. Data was extracted nearly how repeated measurements were handled: (1) analysed each pair of data separately; (2) treated each pair of information equally independent; or (3) used either analysis of variance or a random-effects model as a way to control for the dependent nature of the repeated measures data.5

Risk of bias assessment of the included studies was undertaken independently in duplicate using the revised Quality Cess of Diagnositc Accurateness Studies (QUADAS-2) tool.6 Guiding questions were used to rate the take a chance of bias for patient selection, conduct of the TcCO2 measurement, behave of the PaCOii measurement and flow and timing (eg, timing of TcCO2 or PcCOtwo measurements and dropouts) as 'high', 'depression' or 'unclear'. The hazard of publication bias was minimised by comprehensively searching multiple databases and an international clinical trial registry.vii Language restrictions were non imposed for the search. Notwithstanding, we were unable to allocate 4 potentially eligible studies considering the full text was not in English language. Statistical analyses to find reporting bias were non conducted due to lack of validated methods.viii Although some meta-analyses of method comparison studies take used tests for detecting funnel plot asymmetry,9 simulations have revealed that such tests will result in publication bias being incorrectly identified too often.x

We applied the Grading Quality of Evidence and Strength of Recommendations methodology to rate the quality of prove.11 Reasons used to downgrade the evidence were study limitations, inconsistency and imprecision. We did not downgrade for indirectness because this systematic review excluded studies that were not relevant. Publication bias was not formally assessed and then the possibility of this bias was non excluded but not considered sufficient to require downgrading the quality of evidence.

Data synthesis and analysis

Our goal for the meta-analysis was to guess the population limits of agreement betwixt TcCO2 and PaCO2. The framework for meta-analysis of Bland-Altman method comparing studies based on a limits of agreement (LoA) approach was used.12 We selected this method since it mirrors the approach in primary Bland-Altman studies, providing an gauge of the pooled LoAs in the population (not only the samples studied). The 'population LoA' is wider than those typically reported in meta-analyses of Bland-Altman studies.12 Here the pooled LoAs are calculated using δ±2√(σtwo+τtwo), where δ is the average bias across studies, σ2 is the average within-study variation in differences and τ2 is the variation in bias across studies. We estimated δ and σtwo using a weighted least-squares model (similar to a random-furnishings arroyo) and estimated their SEs using robust variance estimation (RVE). We used RVE instead of model-based SEs considering many studies included in our review used repeated-measures designs without accounting for the correlation between measurements.thirteen–xv The method-of-moments calculator from ref 16 was used for the τ2 parameter. Following ref 12 we too (1) included measures of uncertainty when interpreting the LoA estimates by calculating the outer 95% CIs for pooled LoA; and (2) adjusted repeated measurements which were not properly adjusted in individual studies (by using weights proportional to the number of samples non the total number of measurements). Formulas for these calculations from ref 12 are provided in online supplementary file ane. All analyses were conducted in the R statistical program.17 The R code (provided in ref 12) and all data used in the meta-analyses are available at https://doi.org/10.6084/m9.figshare.6244058.v2.

The results from the individual studies were converted into a standard format to deport meta-analyses, with bias meaning PaCO2-TcCO2 measured in mm Hg. In two of the studies, the results were reported for two split groups of participants, so these were treated in the meta-analyses as divide 'studies'. Other studies reported carve up results for analyses conducted using different TcCO2 device types or sensor locations performed on the same patients. Only the result with the largest number of paired measurements betwixt PaCO2 and TcCO2 was selected for inclusion in the main analysis, with others included in subgroup meta-analyses where appropriate. For the studies that reported results for patients while receiving both two-lung and i-lung ventilation during thoracic surgery, we used the result for two-lung ventilation in the main analysis.

The conventionally cited clinically acceptable understanding between TcCOii and PaCO2 is seven.5 mm Hg (or one kPa).18 We accounted that outer confidence bounds for 95% LoA between transcutaneous and arterial CO2 measurements (termed as 'population limits of agreement') exterior of these bounds would not exist clinically adequate.

We performed sensitivity assay for the primary meta-assay based on risk of bias (eg, treating 'unclear risk of bias' as 'high take chances' and removing 'high risk of bias' studies from the analyses). As clinicians would be interested in the accuracy of the type of transcutaneous monitoring device they use and for the population in which they utilise it, we conducted subgroup analyses according to the indication for monitoring (eg, volunteer study, respiratory failure, surgery, intensive care unit (ICU), sedation and postoperative recovery), type of device (Sentec and TOSCA), also as location of sensor placement and sensor temperature.

Results

Report choice and description

There were 73 studies eligible for inclusion (figure 1). The characteristics of each study are in online supplementary file 1. The 73 studies enrolled 2817 participants predominantly from Europe, Usa and United kingdom. Sixteen (22%) studies included adult participants in ICUs, half-dozen (seven%) studies included paediatric participants in ICUs or having surgery, 7 (10%) studies included neonates, thirteen (18%) studies were conducted with adults undergoing surgery with general anaesthesia, 13 (18%) studies were focused on acute respiratory failure, ix (12%) studies included participants with chronic respiratory failure, v (7%) studies included patients who were sedated merely spontaneously animate either during or later surgery, and 4 (5%) studies were conducted with patients undergoing lung office testing. Two studies intentionally manipulated the range of PaCOtwo by inducing hypoventilation and hyperventilation. The everyman PaCOii reported in the studies was 18 mm Hg and the highest was 103 mm Hg.

Several different TcCO2 monitors were evaluated beyond the studies included in this review, including the TCM3 (n=12), TCM4 (n=xi), TOSCA 500 with Sensor 92 (n=seven), TOSCA not otherwise classified (n=13), Sentec with V-Sign sensor (n=27), Sentec with V-Sign 2 sensor (n=2), Fastrac (northward=1), Microgas (due north=two) and PeriFlux (n=i). All studies reported that device manufacturer instructions were followed regarding scale and stabilisation of the sensor prior to undertaking assessments. Most studies reported that the temperature of the TcCO2 sensor was less than 43°C (north=49; 67%). The earlobe was the most common sensor location site evaluated (n=45). Other sensor location sites included the chest, upper arm, abdomen, forehead, cheek and palmar surface of the forearm.

There was a high risk of bias associated with patient selection for 14 (xix%) studies, deport of TcCOii and PaCO2 measurements in vii (x%) and ix (12%) studies, respectively (mostly due to PaCO2 measurements being taken with cognition of the TcCO2 measurement and vice versa), and participant menstruum for 7 (ten%) studies. The authors declared that they either had a disharmonize of interest or had received equipment or funding from the manufacturers of the device beingness evaluated in 19 (26%) studies.

Agreement between transcutaneous and arterial CO2 measurements

Table 1 presents the results of the primary meta-analysis, sensitivity analysis and subgroup analyses. Data from all 73 studies were included in the primary meta-analysis. Although the pooled estimate of the mean bias betwixt PaCO2 and TcCO2 was small (0.1 mm Hg), the variation in these differences was large (effigy two), resulting in the two methods differing from −xv mm Hg to 15 mm Hg beyond all patients studied. These population limits of agreement were not in the clinically adequate range. A summary of findings is presented in table 2. We downgraded the quality of evidence for the primary effect to low quality due to concerns about study limitations and inconsistency. Population limits of agreement for the sensitivity analysis restricted to studies rated equally having low take a chance of bias were also outside of the clinically adequate range (−9 mm Hg to 10 mm Hg; 1600 paired measurements from 842 participants in 23 studies).

Figure 2

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Effigy 2

Comparisons within and across studies. Dotted curves are distributions of the differences betwixt arterial and transcutaneous carbon dioxide (CO2) in individual studies. Solid curve filled with blue is the distribution of the pooled estimate of the difference between arterial and transcutaneous CO2. Dotted vertical lines indicate bounds for the pooled estimates for limits of agreement between arterial and transcutaneous CO2. Solid vertical lines indicate bounds for the outer 95% CIs for the pooled estimates of limits of understanding betwixt arterial and transcutaneous CO2 (ie, population limits of understanding).

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Table i

Results of meta-analysis of understanding between transcutaneous and arterial carbon dioxide

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Tabular array two

Summary of findings for accuracy and precision of transcutaneous carbon dioxide monitoring

The population limits of understanding for the TOSCA device were inside the clinically adequate range (−seven to 6 mm Hg; 3313 paired measurements from 1561 participants in 45 studies) but not for the Sentec device (−9 to 9 mm Hg; 3585 paired measurements from 1256 participants in 30 studies). However, population limits of agreement differed co-ordinate to the location that the sensor was applied and the temperature of the sensor. TcCO2 monitoring was accurate to a clinically acceptable degree in a meta-assay of 44 studies (3974 paired measurements from 1786 participants) where the sensor was applied to the earlobe with either the TOSCA (20 studies) or Sentec (24 studies) device. The population limits of agreement were −6 to 6 mm Hg. In contrast, population limits of agreement were outside the clinically acceptable range where TcCO2 monitoring was conducted with the sensor on the chest (−eleven to 12.7 mm Hg; 1041 paired measurements from 471 participants in xiii studies) and the arm (−8 mm Hg to v.three mm Hg; 247 paired measurements from 157 participants in 7 studies). There was a large corporeality of variation in bias between the 16 studies where TcCO2 sensors were located at other sites (τ2=30.ane), resulting in extremely broad estimates for population limits of agreement (−134 to 133 mm Hg). Of note, studies that practical the sensor to the earlobe ready the temperature of the device to 42°C, whereas studies that applied sensors to the chest or other sites used a multifariousness of different temperature settings. Population limits of agreement were wider in meta-analysis of studies which ready the temperature of the sensor to 42°C (−25 to 26 mm Hg) compared with studies where the sensor temperature was college (−seven to 7 mm Hg). There was large variation in bias between these studies (τ2=12.0), which was likely due to the location of sensor placement (earlobe in 35 studies, chest in 4 studies and arm/forearm in 3 studies).

TcCOtwo monitoring was accurate to a clinically acceptable degree for only a minority of the subgroup meta-analyses conducted co-ordinate to clinical indication. Population limits of understanding were within the clinically adequate range for studies that enrolled adults in ICU (sixteen studies), children undergoing surgery or in ICU (6 studies) and adults undergoing lung function testing (4 studies).

Discussion

It is vital that clinicians have a clear agreement of the accuracy of TcCO2 monitoring devices to ensure they are applied in appropriate circumstances. Both the primary meta-analysis and sensitivity assay, including simply studies at low gamble of bias, revealed population limits of agreement outside of the clinically acceptable range. Clinicians using transcutaneous monitoring to assess ventilation condition in patients across the broad range of populations included in our systematic review should therefore determine baseline PaCO2 and the TcCO2-PaCO2 gradient and to confirm the diagnosis of hypercapnoea prior to initiation (or cessation) of treatment.

The results from our subgroup analyses have of import implications for how TcCO2 monitoring should exist practical. No specific recommendations for a preferred site or sites are provided by manufacturers. Similarly, guidelines on transcutaneous monitoring from the American Association for Respiratory Care do not provide a recommendation for the optimal site to place a TcCOii sensor.eighteen Our analysis indicates that TOSCA and Sentec TcCO2 device sensors should preferentially be placed on the earlobe because the population limits of understanding were within the bounds of the clinically acceptable range (<vii.5 mm Hg). Monitoring on the earlobe had like LoAs to those reported in a meta-analysis of capillary blood gas LoAs, where the mean bias was −0.1 mm Hg and the SD of bias was 2.9 mm Hg.19 If TcCOtwo monitoring is viable from the earlobe, information technology should be considered the preferable solution to employ for ventilation assessment over capillary blood gas because of its not-invasiveness and ability to provide a continuous assessment of ventilation. Likewise, the results of our meta-analyses suggest that TcCOtwo measurements would be more accurate than estimations of PaCOtwo derived from venous blood gas samples. The hateful bias between PaCO2 and venous claret CO2 measurements was estimated to range from −10.7 mm Hg and 2.4 mm Hg in a meta-analysis of xvi studies.xx Pooled estimates of the LoAs betwixt venous and arterial measurements of COii were not reported.20 It should be noted though that not all patients who may benefit from continuous ventilation assessment will be suitable for application of a TcCOtwo monitoring sensor to their earlobes. For example, the earlobes of a neonate requiring ventilation assessment may not be big enough to accommodate a TcCO2 sensor. Adult patients with multiple piercings, undergoing surgery to or with trauma around the head and neck would also prevent the application of a TcCO2 sensor to the earlobe.

We found big differences in population limits of agreement in subgroup analyses focusing on sensor temperature. Meta-analysis restricted to studies that used a sensor temperature of 42°C exhibited worse understanding with PaCOtwo in comparing with meta-analysis of studies that used higher temperatures. The divergence in these results can exist explained by the big between-study variation in bias in the subgroup assay of studies that used a sensor temperature of 42°C but practical the sensor to either the earlobe, chest or arm. Of annotation, the majority of studies where the sensor was practical to participants' earlobes prepare the temperature of the sensor to 42°C but still yielded clinically adequate population limits of agreement. Together, the findings from both subgroup analyses indicate that if monitoring on the earlobe is not possible, the sensor temperature should be fix college than 42°C.

A strength of this assay is the incorporation of the variation in bias between studies, the bias associated with repeated measures not accounted for in the assay of individual studies, as well as measures of uncertainty (CIs) into our estimates of the understanding between transcutaneous and arterial CO2 measurements. Standard meta-analysis approaches focused on providing the average bias and the average precision separately may have erroneously led clinicians to believe that the agreement betwixt TcCO2 and PaCO2 measurements is adequate. The chance here is clearly evident for the primary meta-analysis where the guess of the population limits of agreement were within clinically acceptable bounds but the outer 95% CIs were far wider. In that location was a larger difference betwixt the population limits of agreement and the CIs because the sampling variation in each component of the LoA is taken into account when calculating the CIs (the mean bias, SD and variation in bias betwixt studies). By incorporating the betwixt-study heterogeneity in bias and sampling variation, it is clear that the LoAs in the population are much broader and not clinically adequate for interchangeable use across the range of situations in which TcCOii monitoring was tested in the main analysis.

The trending power of TcCO2 monitors is an important information for clinicians to consider when using TcCOii in practice. This is because PaCOtwo continuously changes in response to a diverseness of factors. In addition, evaluating trends in TcCO2 may be useful in clinical practice for evaluating the effectiveness of interventions employed to improve ventilation status. Conclusions near trending ability can be drawn from the accurateness and precision of absolute measurements (ie, LoAs) by making a qualitative judgement about whether or not the alphabetize test is sufficiently precise. We did not identify strong evidence to back up the trending ability of TcCO2 for ventilation assessment in this systematic review because the population limits of agreement for the primary meta-assay were wide. If part of the imprecision relates to patient-specific characteristics, such as vascularity, it is possible that there will be a systematic measurement error for within-patient readings, and therefore the within-patient trend may have tighter LoAs than individual measurements. Therefore, methods other than the Banal-Altman approach may exist more suited to quantitatively assess trending ability. For example, the 4Q, polar assay and clinical concordance methods have recently been recommended for consideration in method comparison studies evaluating the validity of cardiac output monitors.21 Similar to TcCOii monitoring, cardiac output monitors provide a continuous judge of a dynamic physiological parameter, which changes rapidly from various influences. Every bit such, farther inquiry aiming to examine the trending power of TcCOtwo monitoring should consider incorporating such assessments.

The results of subgroup analyses according to the indication for monitoring identified specific clinical areas where further research into the accuracy of TcCOtwo monitoring would be beneficial because population limits of understanding were outside of the clinically acceptable range. These include acute respiratory failure, thoracic surgery with unmarried lung ventilation and for assessment of ventilation in patients who are sedated during or after surgery. Nevertheless, it should be noted that studies within these subgroups applied TcCOii monitoring using different devices (Sentec and TOSCA), sensor locations and temperatures, which may explain the large variation in bias between studies and resulting imprecise estimates of LoAs. Clinicians who use TcCO2 monitoring in these areas should be confident that TcCO2 measurements would be within clinically adequate agreements if applied to the earlobe or some other monitoring site at a temperature higher up 42°C using either the Sentec or TOSCA device.

Transcutaneous CO2 monitoring is normally used to reduce the frequency of arterial blood gas analysis in neonates due to the limitations of other methods to estimate PaCOii in this population, such as terminate-tidal COtwo and capillary blood gas analysis.22 Yet we identified weak evidence for accuracy and precision with population limits of understanding that were far exterior the clinically acceptable range. It should be noted though that we only included studies that compared TcCO2 with PaCOtwo. Several articles were excluded due to TcCOtwo being compared instead with capillary blood gas assay.23

Limitations

Data were non extracted on adverse events related to transcutaneous monitoring. We cannot dominion out the possibility of publication bias. Yet, this may not exist as serious a problem for diagnostic test accurateness studies every bit it is for randomised trials.8 We did not use meta-regression or tests for interaction between subgroups to investigate for sources of heterogeneity because of our focus on the population limits of agreement, which incorporated the variation in bias between studies into the estimates. This systematic review did not assess the clinical utility of these monitors. Therefore, the bear witness to be derived from this systematic review should only be considered within the context of other data virtually the clinical utility, reliability and ease of use of these devices during normal clinical practice. Of notation, the level we prepare as the limit for clinically acceptable understanding betwixt PaCO2 and TcCOii (7.five mm Hg) was chosen based on recommendations for ventilation monitoring made by the American Association for Respiratory Care therapists. If a difference in repeated measurements of PaCO2 less than this magnitude would be of import for a given situation in clinical practice, then an arterial blood sample should exist fatigued to confirm diagnosis when a modify in TcCO2 is observed during monitoring.

Conclusion

This meta-analysis has identified that in that location may be substantial differences between TcCO2 and PaCOii depending on the context in which this applied science is used in clinical practise. Measuring TcCOtwo from the earlobe with either the TOSCA or Sentec device would yield clinically acceptable accuracy. As such, this monitoring site is recommended for use in clinical practice. For optimal accuracy and precision, users should set the temperature of the sensor higher than 42°C when monitoring at sites other than the earlobe.

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