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Dead space is an important component of ventilation–perfusion abnormalities. Measurement of dead space has diagnostic, prognostic and therapeutic applications. In the intensive care unit (ICU) dead space measurement can be used to guide therapy for patients with acute respiratory distress syndrome (ARDS); in the emergency department it can guide thrombolytic therapy for pulmonary embolism; in peri-operative patients it can indicate the success of recruitment maneuvers. A newly available technique called volumetric capnography (Vcap) allows measurement of physiological and alveolar dead space on a regular basis at the bedside. We discuss the components of dead space, explain important differences between the Bohr and Enghoff approaches, discuss the clinical significance of arterial to end-tidal CO 2 gradient and finally summarize potential clinical indications for Vcap measurements in the emergency room, operating room and ICU.

Background Hypoxia is a very common adverse event that occurs during gastrointestinal endoscopy under sedation, especially in older patients, owing to limited reservation of heart, brain, lung, and other organs. Prolonged or severe hypoxia can cause ischemia of the coronary artery and permanent nervous system damage, and even result in death. Hence, it is imperative to reduce or prevent hypoxia during gastrointestinal endoscopy under sedation in older patients. Although several oxygen delivery methods would reduce hypoxia during this procedure, early detection of respiratory depression and early administration of intervention would be the best method to reduce or even confirm the hypoxia. Capnographic monitoring is reportedly more sensitive for detecting respiratory depression before the onset of hypoxia than the current clinical routine monitoring of pulse oxygen saturation; however, its effect is controversial. Therefore, in this study, we aimed to improve the safety of gastrointestinal endoscopy under sedation in older patients. Methods A multicenter, randomized, single-blind, two-arm parallel-group, controlled with an active comparator, interventional superiority clinical trial will be conducted to evaluate the impact of an additional capnographic monitoring-based intervention on the incidence of hypoxia in older patients. Patients ( n = 1800) scheduled for gastrointestinal endoscopy with propofol sedation will be randomly assigned to either a control or interventional arm, wherein standard or capnographic monitoring is implemented, respectively. Discussion This study primarily aims to examine whether an additional capnographic monitoring-based intervention can reduce the incidence of hypoxia in older patients during gastrointestinal endoscopy under propofol and sufentanil sedation. The results of this study may extensively impact gastrointestinal endoscopy under sedation and the development of associated guidelines. Trial registration ClinicalTrials.gov NCT05030870. Registered on September 1, 2021.

Appropriate monitoring during sedation has been recognized as vital to patient safety in procedures outside of the operating room. Capnography can identify hypoventilation prior to hypoxemia; however, it is not clear whether the addition of capnography improves safety or is cost effective during routine colonoscopy, a high volume, low-risk procedure. Our aim was to evaluate the value of EtCO2 monitoring during colonoscopy with moderate sedation. We conducted a prospective study of sedation safety and patient satisfaction before and after the introduction of EtCO2 monitoring during outpatient colonoscopy with midazolam and fentanyl using the validated PROcedural Sedation Assessment Survey (PROSAS). Complications of sedation and PROSAS scores were compared among colonoscopies with and without capnography. A total of 966 patients participated in our study, 465 in the pre-EtCO2 group and 501 in the EtCO2 group. On multivariate analysis, patients and nurses reported higher levels of procedural discomfort after adoption of capnography (1.71 vs. 1.00, P<0.001). No serious adverse events were seen, and minor sedation-related adverse events occurred with similar frequency in both groups (8.2% pre-EtCO2 vs. 11.2% EtCO2, P=0.115). The cost of implementing EtCO2 in our unit was $40,169.95 and added $11.68 per case. Colonoscopy with moderate sedation is a low-risk procedure, and the addition of EtCO2 did not improve safety or patient satisfaction but did increase cost. These data suggest that routine capnography in this setting may not be cost effective and that EtCO2 might be reserved for patients at higher risk of adverse events.

Background Mixed exhaled air has been widely used to determine exhaled propofol concentrations with online analyzers, but changes in dead space proportions may lead to inaccurate assessments of critical drug concentration data. This study proposes a method to correct propofol concentration in mixed air by estimating pulmonary dead space through reconstructing volumetric capnography (Vcap) from time-CO 2 and time-volume curves, validated with vacuum ultraviolet time-of-flight mass spectrometry (VUV-TOF MS). Methods Existing monitoring parameters, including time-volume and time-CO 2 curves, were used to determine Vcap. The ratio of physiological dead space to tidal volume (V D /V T ) was calculated using Bohr’s formula. Additionally, an animal experiment on beagles was conducted with continuous propofol administration until a pseudo-steady state in exhaled propofol concentration was achieved. The propofol concentration in mixed air (CONC mix ), and in alveolar air combined with N 2 (CONC AN ) were measured using VUV-TOF MS to calculate V D /V T . The agreements between V D /V T values from the two methods, along with the predicted CONC AN values based on Vcap and the actual measured CONC AN values were evaluated using the intraclass correlation coefficient (ICC) and Pearson correlation analysis. Results After 30 min of continuous propofol administration, a stable respiratory cycle was selected for analysis in each beagle. The calculated V D /V T-Bohr values were 0.535 for beagle A, 0.544 for beagle B, and 0.552 for beagle C. Additionally, based on CONC mix and CONC AN , the calculated V D /V T-VUV-TOF MS values were 0.494, 0.504, and 0.513, respectively. Strong agreement between the two methods was demonstrated by an ICC of 0.994 ( P  = 0.003) and Pearson’s r of 0.995 ( P  = 0.045). Additionally, the predicted CONC AN values from mixed exhaled air (5.11 parts per billion by volume (ppbv) for beagle A, 5.93 ppbv for beagle B, and 2.56 ppbv for beagle C) showed strong agreement with the actual CONC AN values, with an ICC of 0.996 ( P  = 0.002) and Pearson’s r of 0.994 ( P  = 0.046). Conclusion The physiological dead space to tidal volume ratio from mixed air in beagles can be accurately measured using the existing time-volume and time-CO 2 curves from the anesthesia machine, enabling corrections of exhaled propofol concentrations in mixed air samples.

Endotracheal intubation is an important emergency procedure, especially in critical care settings. Capnography-guided intubation (CGI) is a technology that may enhance procedural efficiency. This study aimed to compare the effectiveness of CGI with conventional intubation (CI) using a manikin simulation. A case-crossover manikin simulation study was conducted with three clinical scenarios: normal airway, cervical immobilization, and cardiopulmonary resuscitation. A CO2-exhalation simulation manikin was developed for this purpose. Participants were randomly assigned to perform CGI or CI first, followed by the alternative method. The primary outcome was the first-attempt success rate, and the secondary outcome was the procedure time of intubation. A linear mixed-effects model with a random effect for each subject was applied. A total of 40 participants were enrolled, and 20 in each study group. The first-attempt success rate was higher with CGI than CI across all clinical situations, with statistically significant differences in the normal airway and cervical immobilization settings. Specifically, for the normal airway, the success rate was 40 (100.0 %) for CGI vs. 33 (82.5 %) for CI [abs diff: 17.5 %, 95 % CI: 5.7 %–29.3 %]; for cervical immobilization, 39 (97.5 %) vs. 32 (80.0 %) [abs diff: 17.5 %, 95 % CI: 4.2 %–30.8 %]; and for cardiopulmonary resuscitation, 40 (100.0 %) vs. 38 (95.0 %) [abs diff: 5.0 %, 95 % CI: −1.8 %-11.8 %]. The intubation time was shorter with CGI in the normal airway and cervical immobilization scenarios. The median [interquartile range (IQR)] time for normal airway was 23.5 (19.2–28.4) sec for CGI vs. 31.6 (22.2–59.7) sec for CI, and for cervical immobilization, 24.4 (20.4–30.8) sec for CGI vs. 28.6 (22.6–56.9) sec for CI. In cardiopulmonary resuscitation, the median [IQR] was 23.1 (19.6–31.4) sec for CGI vs. 25.1 (18.6–32.4) sec for CI. In the manikin-based randomized crossover simulation, CGI achieved a higher first-attempt success rate and shorter intubation time than CI in the normal airway and cervical immobilization scenarios.

Prehospital identification of shock in trauma patients lacks accurate markers. Low end tidal carbon dioxide (ETCO2) correlates with mortality in intubated patients. The predictive value of ETCO2 obtained by nasal capnography cannula (NCC) is unknown. We hypothesized that prehospital ETCO2 values obtained by NCC and in-line ventilator circuit (ILVC) would be predictive of mortality. This was a prospective, observational, multicenter study. ETCO2 values were collected by a NCC or through ILVC. AUROCs were compared with prehospital systolic blood pressure (SBP) and shock index (SI). The Youden index defined optimal cutoffs. Of 550 enrolled patients, 487 (88.5%) had ETCO2 measured through an NCC. Median age was 37 (27–52) years; 76.5% were male; median ISS was 13 (5–22). Mortality was 10.4%. Minimum prehospital ETCO2 significantly predicted mortality with an AUROC of 0.76 (CI 0.69–0.84; Youden index ​= ​22 ​mmHg), outperforming SBP with an AUROC of 0.68; (CI 0.62–0.74, p ​= ​0.04) and shock index with an AUROC of 0.67 (CI 0.59–0.74, p ​= ​0.03). Prehospital ETCO2 measured by non-invasive NCC or ILVC may be predictive of mortality in injured patients. •Lowest prehospital ETCO2 value predicts mortality in trauma patients.•Lowest prehospital ETCO2 value predicts massive transfusion in trauma patients.•Values were obtained via nasal capnography cannula and in-line ventilator circuit.

Remimazolam, a novel ultra-short-acting benzodiazepine, has gained attention for its favourable safety profile, particularly its reduced risk of respiratory depression compared to propofol during procedural sedation. However, previous studies have primarily relied on visual assessment or pulse oximetry, which may underestimate the incidence of respiratory compromise. In this prospective randomized controlled trial, we compared the respiratory effects of remimazolam and propofol using continuous capnography monitoring, a more sensitive method for detecting hypoventilation and apnoea. Seventy adult patients undergoing procedural sedation were randomly assigned to receive either remimazolam with remifentanil or propofol with remifentanil. The primary outcome was the frequency of respiratory depression events during sedation. The median [IQR] number of respiratory depression episodes was comparable between the remimazolam and propofol groups (2 [1–3] vs. 2 [1–5], p  = 0.44). Respiratory polygraphy showed no significant difference in sleep apnoea severity between groups. However, the propofol group experienced more frequent hypotensive episodes and greater blood pressure reductions. These results suggest that remimazolam does not significantly reduce the incidence of respiratory depression compared to propofol under continuous capnographic monitoring, but it may offer advantages in haemodynamic stability. Our findings support the consideration of remimazolam as a safer alternative in patients at risk of hypotension during procedural sedation. Trial registration : Clinical Trial Registry of Korea on December 2, 2021 (KCT0006797, https//cris.nih.go.kr principal investigator Suk Young Lee).

PurposeIntraoperative hypotension is associated with adverse outcomes. Predicting and proactively managing hypotension can reduce its incidence. Previously, hypotension prediction algorithms using artificial intelligence were developed for invasive arterial blood pressure monitors. This study tested whether routine non-invasive monitors could also predict intraoperative hypotension using deep learning algorithms.MethodsAn open-source database of non-cardiac surgery patients (https://vitadb.net/dataset) was used to develop the deep learning algorithm. The algorithm was validated using external data obtained from a tertiary Korean hospital. Intraoperative hypotension was defined as a systolic blood pressure less than 90 mmHg. The input data included five monitors: non-invasive blood pressure, electrocardiography, photoplethysmography, capnography, and bispectral index. The primary outcome was the performance of the deep learning model as assessed by the area under the receiver operating characteristic curve (AUROC).ResultsData from 4754 and 421 patients were used for algorithm development and external validation, respectively. The fully connected model of Multi-head Attention architecture and the Globally Attentive Locally Recurrent model with Focal Loss function were able to predict intraoperative hypotension 5 min before its occurrence. The AUROC of the algorithm was 0.917 (95% confidence interval [CI], 0.915–0.918) for the original data and 0.833 (95% CI, 0.830–0.836) for the external validation data. Attention map, which quantified the contributions of each monitor, showed that our algorithm utilized data from each monitor with weights ranging from 8 to 22% for determining hypotension.ConclusionsA deep learning model utilizing multi-channel non-invasive monitors could predict intraoperative hypotension with high accuracy. Future prospective studies are needed to determine whether this model can assist clinicians in preventing hypotension in patients undergoing surgery with non-invasive monitoring.

Although capnography is a standard tool in mechanically ventilated adult and pediatric patients, it has physiological and technical limitations in neonates. Gas exchange differs between small and adult lungs due to the greater impact of small airways on gas exchange, the higher impact of the apparatus dead space on measurements due to lower tidal volume and the occurrence of air leaks in intubated patients. The high respiratory rate and low tidal volume in newborns, especially those with stiff lungs, require main-stream sensors with fast response times and minimal dead-space or low suction flow when using side-stream measurements. If these technical requirements are not fulfilled, the measured end-tidal CO 2 ( P et CO 2 ), which should reflect the alveolar CO 2 and the calculated airway dead spaces, can be misleading. The aim of this survey is to highlight the current limitations of capnography in very young patients to avoid pitfalls associated with the interpretation of capnographic parameters, and to describe further developments.