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Accuracy of non-invasive body temperature measurement methods in adult patients admitted to the intensive care unit: a systematic review and meta-analysis
Salvatore L Cutuli, Emily J See, Eduardo A Osawa, Paolo Ancona, David Marshall, Glenn M Eastwood, Neil J Glassford, Rinaldo Bellomo
Crit Care Resusc 2021; 23 (1): 6-13
- Salvatore L Cutuli 1, 2
- Emily J See 1, 3
- Eduardo A Osawa 1
- Paolo Ancona 1
- David Marshall 1
- Glenn M Eastwood 1
- Neil J Glassford 1
- Rinaldo Bellomo 1, 4
OBJECTIVE: Non-invasive thermometers are widely used in both clinical practice and trials to estimate core temperature. We aimed to investigate their accuracy and precision in patients admitted to the intensive care unit (ICU).
STUDY DESIGN: Systematic review and meta-analysis.
DATA SOURCES: We searched MEDLINE, EMBASE and the Cochrane Central Register of Controlled Trials to identify all relevant studies from 1966 to 2017. We selected published trials that reported the accuracy and precision of non-invasive peripheral thermometers (index test) in ICU patients compared with intravascular temperature measurement (reference test). The extracted data included the study design and setting, authors, study population, devices, and body temperature measurements.
METHODS: Two reviewers performed the initial search, selected studies, and extracted data. Study quality was assessed using the QUADAS-2 tool. Pooled estimates of the mean bias between index and reference tests and the standard deviation of mean bias were synthesised using DerSimonian and Laird random effects meta-analyses.
RESULTS: We included 13 cohort studies (632 patients, 105 375 measurements). Axillary, tympanic infrared and zero heat flux thermometers all underestimated intravascular temperature. Only oesophageal measurements showed clinically acceptable accuracy. We found an insufficient number of studies to assess precision for any technique. Study heterogeneity was high (99–100%). Risk of bias for the index test was unclear, mostly because of no device calibration or control for confounders.
CONCLUSIONS: Compared with the gold standard of intravascular temperature measurement, non-invasive peripheral thermometers have low accuracy. This makes their clinical and trial-related use in ICU patients unreliable and potentially misleading.
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Study inclusion and exclusion criteria
Assessment of accuracy and precision
Study selection and data extraction
Statistical analysisContinuous variables were pooled and reported as median (interquartile range [IQR]) or mean (standard deviation [SD]), as appropriate. Categorical variables were reported as frequencies and percentages. Pooled estimates of the mean bias between index and reference tests and the standard deviation of mean bias were synthesised using DerSimonian and Laird random effects meta-analyses. 34
Between-study heterogeneity was evaluated by the Cochran Q test and quantified by the I2 statistic. 37
Characteristics of included studiesWe identified 601 unique citations (Figure 1), among which, 13 studies from 1991 to 2017 33, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50
The median number of patients was 42 (IQR, 21–60) per study and the median number of index-reference comparisons per study was 529 (IQR, 66–2000). The mean patient age was 64 years (SD, 7) and the percentage of male patients ranged from 47% to 86%. The percentage of mechanically ventilated patients ranged from 64% to 100% (n = 4), while the percentage of patients requiring vasopressor support ranged from 35% to 71% (n = 5). Three studies reported mean APACHE II scores that ranged from 15 to 25, while one study reported a mean SAPS 2 score of 43.4.
Intravascular measurements were performed by PAC (n = 12) or temperature-sensing catheters placed in the iliac artery (n = 1). The mean PAC-derived temperature ranged from 34.7°C to 37.7°C.
Accuracy and precision of non-invasive peripheral thermometers compared with PACThirteen studies (632 patients) compared PAC with non-invasive peripheral thermometers (Figure 2). The results of the random effect meta-analysis are shown in Table1 and in the Online Appendix, figures S1 and S2. We did not find enough data to conduct a meta-analysis on the accuracy of cutaneous, oral thermometers and temporal scanner. None of the peripheral thermometers showed clinically acceptable mean bias and LoA.
A post hoc sensitivity analysis for studies comparing PAC with tympanic infrared set in core mode found a clinically acceptable mean bias (-0.02°C), but the LoA was still wide (-0.88 to 0.84°C).
We found an insufficient number of studies on precision of peripheral body temperature measurement methods to perform a meta-analysis.
Study heterogeneity was very high (99–100%). Study variability was partly explained by year of publication (coefficient 0.05; 95% CI, 0.01–0.09; P = 0.03) and mean variation in number of patients (coefficient 0.01; 95% CI, 0.00–0.02; P = 0.04).
Accuracy and precision of invasive extravascular thermometers compared with PACSeven studies (331 patients) compared PAC with invasive extravascular thermometers (Figure 3). The results of the random effect meta-analysis are shown in Table1 and in the Online Appendix, figures S3 and S4. All invasive extravascular thermometers showed clinically acceptable mean bias, although only oesophageal probes had LoA within the a priori set range. We did not find enough data to conduct a meta-analysis on endotracheal tube and nasopharyngeal body temperature sensing-probes.
Study heterogeneity was very high (99–100%). Study variability was not explained by any year of publication or number of patients.
We found an insufficient number of studies on precision of invasive body temperature measurement methods to perform a meta-analysis.
Sensitivity analysesWhen excluding studies that did not fully account for repeated measures within individual subjects, 33, 41, 44, 48, 50
Quality assessmentThe results of the QUADAS-2 evaluations are provided in the Online Appendix, table S3 and figure S5. The risk of bias for the index test was unclear, mostly because device calibration was not undertaken, 33, 43, 44, 45, 46, 47, 48, 50
Publication biasThere was no funnel plot asymmetry in any of the analyses to support the presence of small study effects (Online Appendix, figures S6a and S6b).
Main findingsThis systematic review and meta-analysis investigated the accuracy of non-invasive peripheral body temperature measurement methods in ICU patients, most of whom were mechanically ventilated and/or haemodynamically unstable. Core temperature ranged from moderate hypothermia to just above normothermia. We found that none of the non-invasive peripheral thermometers had clinically acceptable mean bias and LoA. Moreover, all provided a variable underestimation of core temperature. When tympanic infrared thermometers were set in “core mode”, the mean bias decreased ten-fold and became clinically acceptable, but the LoA remained wide. We found an insufficient number of studies on oral, skin surface, and temporal scanner to perform a meta-analysis on the accuracy of such methods.
Among invasive extravascular methods, only temperature-sensing oesophageal probes were clinically acceptable. Study heterogeneity was high and the risk of bias was unclear. We did not find enough studies to assess accuracy of endotracheal tube and nasopharyngeal body temperature-sensing probes. Finally, we found an insufficient number of studies on precision to perform a meta-analysis.
Relationship with previous studiesTo date, no study has conducted a systematic review and meta-analysis of the accuracy of body temperature measurement methods in ICU patients. In 2006, Hooper and Andrews 51
In 2011, Jefferies and colleagues 29
ImplicationsThe lack of accuracy of peripheral thermometers in estimating core temperature implies the need to limit the use of such methods in severe ICU patients due to the risk of obtaining misleading clinical information. Moreover, our study implies that, among invasive body temperature measurement methods, only oesophageal probes have acceptable accuracy and should, therefore, be preferred in clinical practice. Finally, the lack of evidence on precision among all measurement techniques as well as the low accuracy of several peripheral and even invasive extravascular body temperature methods are of great concern. This is particularly relevant to trials focusing on temperature control in patients after cardiac arrest 8, 9, 10, 12
Strengths and limitationsTo our knowledge, we are the first to perform a comprehensive systematic review and meta-analysis of daily used body temperature monitoring tools in ICU patients. In addition, we shed light on the major shortcomings of peripheral thermometers in clinical practice. Finally, we provide strong evidence to inform the research agenda in this field, specifically when temperature management is intended to be an intervention that modifies patient-centred outcomes in specific clinical conditions, such as cardiac arrest, traumatic brain injury, and sepsis.
However, we acknowledge some limitations. We restricted our research to articles that evaluated the accuracy of peripheral thermometers using the Bland–Altman approach. Although many statistical methods have been used in this kind of research 33
ConclusionIn our systematic review and meta-analysis, peripheral thermometers showed a clinically unacceptably low degree of accuracy compared with PAC. In contrast, oesophageal measurements showed clinically acceptable accuracy in ICU patients, suggesting that their use may be justified. However, in most of the trials of temperature management in clinical conditions in which its accurate measurement matters, the technology of body temperature measurement was flawed. Finally, the lack of data for most thermometer types and the low quality of the evidence available remain a major problem.
Acknowledgements: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.