Capnography monitoring during neurosurgery: reliability in relation to various intraoperative positions

Difference between arterial and end-tidal carbon dioxide and adverse events after non-cardiac surgery: a historical cohort study

Purpose

The difference between arterial and end-tidal partial pressure of carbon dioxide (ΔCO₂) is a measure of alveolar dead space, commonly evaluated intraoperatively. Given its relationship to ventilation and perfusion, ΔCO₂ may provide prognostic information and guide clinical decisions. We hypothesized that higher ΔCO₂ values are associated with occurrence of a composite outcome of re-intubation, postoperative mechanical ventilation, or 30-day mortality in patients undergoing non-cardiac surgery.

Methods

We conducted a historical cohort study of adult patients undergoing non-cardiac surgery with an arterial line at a single tertiary care medical centre. The composite outcome, identified from electronic health records, was re-intubation, postoperative mechanical ventilation, or 30-day mortality. Student’s t test and Chi-squared test were used for univariable analysis. Logistic regression was used for multivariable analysis of the relationship of ΔCO₂ with the composite outcome.

Results

A total of 19,425 patients were included in the final study population. Univariable analysis showed an association between higher mean (standard deviation [SD]) intraoperative ΔCO₂ values and the composite outcome (6.1 [5.3] vs 5.7 [4.5] mm Hg; P = 0.002). After adjusting for baseline subject characteristics, every 5-mm Hg increase in the ΔCO₂ was associated with a nearly 20% increased odds of the composite outcome (odds ratio, 1.20; 95% confidence interval, 1.12 to 1.28; P < 0.001).

Conclusions

In this patient population, increased intraoperative ΔCO₂ was associated with an increased odds of the composite outcome of postoperative mechanical ventilation, re-intubation, or 30-day mortality that was independent of its relationship with pre-existing pulmonary disease. Future studies are needed to determine if ΔCO₂ can be used to guide patient management and improve patient outcomes.

Usefulness of Measurement of End-tidal CO2 Using a Portable Capnometer in Patients with Chronic Respiratory Failure Receiving Long-term Oxygen Therapy

Objective Patients with chronic respiratory failure requiring long-term oxygen therapy (LTOT) are at a risk of CO₂ retention because of excessive oxygen administration. The CapnoEye™ is a novel portable capnometer that can measure end-tidal CO₂ (EtCO₂) noninvasively. This retrospective study evaluated the usefulness of this device. Methods EtCO₂ was measured using the CapnoEye™. The EtCO₂ and partial pressure of venous carbon dioxide (PvCO₂) were analyzed, and other clinical data were assessed. Patients Sixty-one consecutive patients with chronic respiratory failure receiving LTOT in the outpatient department at the Japanese Red Cross Medical Center between July 2017 and March 2018 were retrospectively reviewed. Results There was a significant correlation between EtCO₂ and PvCO₂ (r=0.63) in the total study population as well as in the COPD group (r=0.65) and ILD group (r=0.67). The PvCO₂ and EtCO₂ gradient was correlated with only the body mass index in a multivariate analysis (p=0.0235). The EtCO₂ levels on the day of admission were significantly higher than those in the same patients when they were in a stable condition (p=0.0049). There was a significant correlation between ΔEtCO₂ and ΔPvCO₂ (r=0.4). A receiver-operating characteristic curve analysis revealed the optimal cut-off EtCO₂ value for identifying hypercapnia to be 34 mmHg (p=0.0005). Conclusion The evaluation of EtCO₂ by the CapnoEye™ was useful for predicting PvCO₂. The body mass index was identified as a possible predictor of the PvCO₂ and EtCO₂ gradient. An increase in EtCO₂ may indicate deterioration of the respiratory status in patients with chronic respiratory failure receiving LTOT.

Non-invasive carbon dioxide monitoring in patients with cystic fibrosis during general anesthesia: end-tidal versus transcutaneous techniques

INTRODUCTION

The gold standard for measuring the partial pressure of carbon dioxide remains arterial blood gas (ABG) analysis. For patients with cystic fibrosis undergoing general anesthesia or polysomnography studies, continuous non-invasive carbon dioxide monitoring may be required. The current study compares end-tidal (ETCO₂), transcutaneous (TCCO₂), and capillary blood gas carbon dioxide (Cap-CO₂) monitoring with the partial pressure of carbon dioxide (PaCO₂) from an ABG in patients with cystic fibrosis.

METHODS

Intraoperatively, a single CO₂ value was simultaneously obtained using ABG (PaCO₂), capillary (Cap-CO₂), TCCO₂, and ETCO₂ techniques. Tests for correlation (Pearson's coefficient) and agreement (Bland-Altman analysis) were performed. Data were further stratified into two subgroups based on body mass index (BMI) and percent predicted forced expiratory volume in 1 s (FEV₁%). Additionally, the absolute difference in the TCCO₂, ETCO₂, and Cap-CO₂ values versus PaCO₂ was calculated. The mean ± SD differences were compared using a paired t test while the number of times the values were ≤ 3 mmHg and ≤ 5 mmHg from the PaCO₂ were compared using a Fishers' exact test.

RESULTS

The study cohort included 47 patients (22 males, 47%) with a mean age of 13.4 ± 7.8 years, median (IQR) BMI of 18.7 kg/m² (16.7, 21.4), and mean FEV₁% of 87.3 ± 18.3%. Bias (SD) was 4.8 (5.7) mmHg with Cap-CO₂ monitoring, 7.3 (9.7) mmHg with TCCO₂ monitoring, and 9.7 (7.7) mmHg with ETCO₂ monitoring. Although there was no difference between the degree of bias in the population as a whole, when divided based on FEV₁% and BMI, there was greater bias with ETCO₂ in patients with a lower FEV₁% and a higher BMI. The Cap-CO₂ vs. PaCO₂ difference was 5.2 ± 5.3 mmHg (SD), with 16 (48%) ≤ 3 mmHg and 20 (61%) ≤ 5 mmHg from the ABG value. The TCCO₂-PaCO₂ difference was 9.1 ± 7.2 mmHg (SD), with 11 (27%) ≤ 3 mmHg and 15 (37%) ≤ 5 mmHg from the ABG value. The ETCO₂-PaCO₂ mean difference was 11.2 ± 7.9 mmHg (SD), with 5 (12%) ≤ 3 mmHg and 11 (26%) ≤ 5 mmHg from the ABG value.

CONCLUSIONS

While Cap-CO₂ most accurately reflects PaCO₂ as measured on ABG, of the non-invasive continuous monitors, TCCO₂ was a more accurate and reliable measure of PaCO₂ than ETCO₂, especially in patients with worsening pulmonary function (FEV₁% ≤ 81%) and/or a higher BMI (≥ 18.7 kg/m²).

Evaluation of Arterial to End-tidal Carbon Dioxide Pressure Differences during Laparoscopic Renal Surgery in the Lateral Decubitus Position

Background:

End-tidal carbon dioxide (PEtCO₂) is a noninvasive reliable technique to measure arterial partial pressure of carbon dioxide (PaCO2) in the body under general anesthesia. However, gradient between PaCO₂ and PEtCO₂ (P[a-Et] CO₂) is influenced by many factors.

Aims:

In the present study, we evaluated the changes in P (a-Et) CO₂ for laparoscopic donor nephrectomy in lateral decubitus position (LDP).

Settings and Design:

This was an observational, double-blinded, tertiary care center-based study.

Methods:

Thirty-one American Society of Anesthesiologists Class I and Class II patients of either sex undergoing laparoscopic donor nephrectomy in LDP under general anesthesia were included. An arterial cannula was inserted, PaCO₂ was measured at eight predesignated time intervals, and PEtCO₂ was also noted at the corresponding time period.

Statistical Analysis:

Data were analyzed using a two-way analysis of variance for repeated measurements using one dependent variable and one within-subject factor (time). Quantitative data were presented as mean ± standard deviation or median and interquartile range, as appropriate.

Results:

The mean P (a-Et) CO₂ gradient was 5.67 ± 1.36 mmHg 10 min after induction of anesthesia in the supine position (T1a). Ten minutes after LDP, P (a-Et) CO₂ gradient was 7.38 ± 1.45 mmHg (T1b) and was higher than T1a. The P (a-Et) CO₂ values 10 min after release of pneumoperitoneum and 10 min after making the patient supine were significantly higher than the T1a value. The highest value of P (a-Et) CO₂ gradient was at 30 min after creation of pneumoperitoneum (T30), i.e., 9.99 ± 1.70 mmHg. Pearson's correlation coefficient showed that the degree of correlation varied considerably during surgery due to interindividual variability (R² T1a vs. T60 was 0.61 vs. 0.17).

Conclusions:

PEtCO₂ does not reliably predict PaCO₂ in healthy patients scheduled for laparoscopic renal surgery in LDP.

Carbon dioxide monitoring during laparoscopic-assisted bariatric surgery in severely obese patients: transcutaneous versus end-tidal techniques

Various factors including severe obesity or increases in intra-abdominal pressure during laparoscopy can lead to inaccuracies in end-tidal carbon dioxide (PETCO2) monitoring. The current study prospectively compares ET and transcutaneous (TC) CO2 monitoring in severely obese adolescents and young adults during laparoscopic-assisted bariatric surgery. Carbon dioxide was measured with both ET and TC devices during insufflation and laparoscopic bariatric surgery. The differences between each measure (PETCO2 and TC-CO2) and the PaCO2 were compared using a non-paired t test, Fisher's exact test, and a Bland-Altman analysis. The study cohort included 25 adolescents with a mean body mass index of 50.2 kg/m2 undergoing laparoscopic bariatric surgery. There was no difference in the absolute difference between the TC-CO2 and PaCO2 (3.2±3.0 mmHg) and the absolute difference between the PETCO2 and PaCO2 (3.7±2.5 mmHg). The bias and precision were 0.3 and 4.3 mmHg for TC monitoring versus PaCO2 and 3.2 and 3.2 mmHg for ET monitoring versus PaCO2. In the young severely obese population both TC and PETCO2 monitoring can be used to effectively estimate PaCO2. The correlation of PaCO2 to TC-CO2 is good, and similar to the correlation of PaCO2 to PETCO2. In this population, both of these non-invasive measures of PaCO2 can be used to monitor ventilation and minimize arterial blood gas sampling.

Measuring cerebrovascular reactivity: what stimulus to use?

Cerebrovascular reactivity is the change in cerebral blood flow in response to a vasodilatory or vasoconstrictive stimulus. Measuring variations of cerebrovascular reactivity between different regions of the brain has the potential to not only advance understanding of how the cerebral vasculature controls the distribution of blood flow but also to detect cerebrovascular pathophysiology. While there are standardized and repeatable methods for estimating the changes in cerebral blood flow in response to a vasoactive stimulus, the same cannot be said for the stimulus itself. Indeed, the wide variety of vasoactive challenges currently employed in these studies impedes comparisons between them. This review therefore critically examines the vasoactive stimuli in current use for their ability to provide a standard repeatable challenge and for the practicality of their implementation. Such challenges include induced reductions in systemic blood pressure, and the administration of vasoactive substances such as acetazolamide and carbon dioxide. We conclude that many of the stimuli in current use do not provide a standard stimulus comparable between individuals and in the same individual over time. We suggest that carbon dioxide is the most suitable vasoactive stimulus. We describe recently developed computer-controlled MRI compatible gas delivery systems which are capable of administering reliable and repeatable vasoactive CO2 stimuli.

Noninvasive monitoring of PaCO(2) during one-lung ventilation and minimal access surgery in adults: End-tidal versus transcutaneous techniques

Background:

Previous studies have suggested that end-tidal CO₂ (ET-CO₂) may be inaccurate during one-lung ventilation (OLV). This study was performed to compare the accuracy of the noninvasive monitoring of PCO₂ using transcutaneous CO₂ (TC-CO₂) with ET-CO₂ in patients undergoing video-assisted thoracoscopic surgery (VATS) during OLV.

Materials and Methods:

In adult patients undergoing thoracoscopic surgical procedures, PCO₂ was simultaneously measured with TC-CO₂ and ET-CO₂ devices and compared with PaCO₂.

Results:

The cohort for the study included 15 patients ranging in age from 19 to 71 years and in weight from 76 to 126 kg. During TLV, the difference between the TC-CO₂ and the PaCO₂ was 3.0 ± 1.8 mmHg and the difference between the ET-CO₂ and PaCO₂ was 6.2 ± 4.7 mmHg (P=0.02). Linear regression analysis of TC-CO2 vs. PaCO₂ resulted in an r² = 0.6280 and a slope = 0.7650 ± 0.1428, while linear regression analysis of ET-CO₂vs. PaCO₂ resulted in an r² = 0.05528 and a slope = 0.1986 ± 0.1883. During OLV, the difference between the TC-CO₂ and PaCO₂ was 3.5 ± 1.7 mmHg and the ET-CO₂ to PaCO₂ difference was 9.6 ± 3.6 mmHg (P=0.03 vs. ET-CO₂ to PaCO₂ difference during TLV; and P<0.0001 vs. TC-CO₂ to PaCO₂ difference during OLV). In 13 of the 15 patients, the TC-CO₂ value was closer to the actual PaCO₂ than the ET-CO₂ value (P =0.0001). Linear regression analysis of TC-CO₂vs. PaCO₂ resulted in an r² = 0.7827 and a slope = 0.8142 ± 0.0.07965, while linear regression analysis of ET-CO₂vs. PaCO₂ resulted in an r² = 0.2989 and a slope = 0.3026 ± 0.08605.

Conclusions:

During OLV, TC-CO₂ monitoring provides a better estimate of PaCO₂ than ET-CO2 in patients undergoing VATS.

End-inspiratory rebreathing reduces the end-tidal to arterial PCO2 gradient in mechanically ventilated pigs

PURPOSE

Noninvasive monitoring of the arterial partial pressures of CO(2) (PaCO(2)) of critically ill patients by measuring their end-tidal partial pressures of CO(2) (PETCO(2)) would be of great clinical value. However, the gradient between PETCO(2) and PaCO(2) (PET-aCO(2)) in such patients typically varies over a wide range. A reduction of the PET-aCO(2) gradient can be achieved in spontaneously breathing healthy humans using an end-inspiratory rebreathing technique. We investigated whether this method would be effective in reducing the PET-aCO(2) gradient in a ventilated animal model.

METHODS

Six anesthetized pigs were ventilated mechanically. End-tidal gases were systematically adjusted over a wide range of PETCO(2) (30-55 mmHg) and PETO(2) (35-500 mmHg) while employing the end-inspiratory rebreathing technique and measuring the PET-aCO(2) gradient. Duplicate arterial blood samples were taken for blood gas analysis at each set of gas tensions.

RESULTS

PETCO(2) and PaCO(2) remained equal within the error of measurement at all gas tension combinations. The mean ± SD PET-aCO(2) gradient (0.13 ± 0.12 mmHg, 95% CI -0.36, 0.10) was the same (p = 0.66) as that between duplicate PaCO(2) measurements at all PETCO(2) and PETO(2) combinations (0.19 ± 0.06, 95% CI -0.32, -0.06).

CONCLUSIONS

The end-inspiratory rebreathing technique is capable of reducing the PET-aCO(2) gradient sufficiently to make the noninvasive measurement of PETCO(2) a useful clinical surrogate for PaCO(2) over a wide range of PETCO(2) and PETO(2) combinations in mechanically ventilated pigs. Further studies in the presence of severe ventilation-perfusion (V/Q) mismatching will be required to identify the limitations of the method.