Waveform Capnography Research Articles

Capnography: Principles and application in critical care medicine

Capnography has become an essential monitoring tool in perioperative and critical care setting. It helps monitor dynamic physiological processes more precisely and promptly, compared to other monitoring modalities. Methods to measure and display carbon dioxide concentrations in respired gases include infrared spectrography, mass spectrography, Raman spectrography, photoacoustic analysers or colorimetry. It is used to confirm correct endotracheal tube placement, ensure effective and consistent chest compression, detect return of spontaneous circulation and diagnose alterations in haemodynamics and ventilation of critically ill patient. It helps to optimise fluid resuscitation and monitor shock progression by providing insight into adequacy of tissue perfusion. Thus, a detailed study and interpretation of capnographic waveform is essential.

To what extent is end-tidal carbon dioxide a predictor of sepsis?

Background: Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection. It is a major cause of death worldwide; 245 000 cases are reported in the UK annually with a mortality rate of 20.3%. Rapid diagnosis and rapid treatment of sepsis can significantly reduce mortality but sepsis can be difficult to diagnose. End-tidal carbon dioxide (EtCO2) is the measurement of expired CO2 using capnometry and waveform capnography. For CO2 to be exhaled, it must be metabolised and transported before being exhaled by effective ventilation; EtCO2 can therefore provide an indication of metabolism, circulation and ventilation. EtCO2 has already been shown to be an indicator of other metabolic acidosis conditions so this review aims to identify the usefulness of EtCO2 in identifying sepsis. Methods: A systematic literature search was conducted between March and April 2021 using the CINAHL Plus and MEDLINE databases. The results were screened and evaluated. Results: Of the 44 papers identified in the original search, seven were included in this review. Conclusion: This review suggests an EtCO2 of ≤25 mmHg (3.3 kPa) in patients with a suspected infection is diagnostic of sepsis and therefore could be used to increase the speed and accuracy of diagnosis and potentially reduce sepsis mortality. It also identifies gaps in research around UK practice and in comparing EtCO2 against UK sepsis guidelines and diagnostic tools such as the UK Sepsis Trust guidelines.

Manual chest compression pause duration for ventilations during prehospital advanced life support – An observational study to explore optimal ventilation pause duration for mechanical chest compression devices

AimMechanical chest compression devices in the 30:2 mode generally provide a pause of three seconds to give two insufflations without evidence supporting this pause duration. We aimed to explore the optimal pause duration by measuring the time needed for two insufflations, during advanced life support with manual compressions. MethodsProspectively collected data in the AmsteRdam REsuscitation STudies (ARREST) registry were analysed, including thoracic impedance signal and waveform capnography from manual defibrillators of the Amsterdam ambulance service. Compression pauses were analysed for number of insufflations, time interval from start of the compression pause to the end of the second insufflation, chest compression pause duration and ventilation subintervals. ResultsDuring 132 out-of-hospital cardiac arrests, 1619 manual chest compression pauses to ventilate were identified. In 1364 (84%) pauses, two insufflations were given. In 28% of these pauses, giving two insufflations took more than three seconds. The second insufflation is completed within 3.8 seconds in 90% and within 5 seconds in 97.5% of these pauses. An increasing likelihood of achieving two insufflations is seen with increasing compression pause duration up to five seconds. ConclusionThe optimal chest compression pause duration for mechanical chest compression devices in the 30:2 mode to provide two insufflations, appears to be five seconds, warranting further studies in the context of mechanical chest compression. A 5-second pause will allow providers to give two insufflations with a very high success rate. In addition, a 5-second pause can also be used for other interventions like rhythm checks and endotracheal intubation.

Preventing unrecognised oesophageal intubation: a consensus guideline from the Project for Universal Management of Airways and international airway societies.

Across multiple disciplines undertaking airway management globally, preventable episodes of unrecognised oesophageal intubation result in profound hypoxaemia, brain injury and death. These events occur in the hands of both inexperienced and experienced practitioners. Current evidence shows that unrecognised oesophageal intubation occurs sufficiently frequently to be a major concern and to merit a co-ordinated approach to address it. Harm from unrecognised oesophageal intubation is avoidable through reducing the rate of oesophageal intubation, combined with prompt detection and immediate action when it occurs. The detection of 'sustained exhaled carbon dioxide' using waveform capnography is the mainstay for excluding oesophageal placement of an intended tracheal tube. Tube removal should be the default response when sustained exhaled carbon dioxide cannot be detected. If default tube removal is considered dangerous, urgent exclusion of oesophageal intubation using valid alternative techniques is indicated, in parallel with evaluation of other causes of inability to detect carbon dioxide. The tube should be removed if timely restoration of sustained exhaled carbon dioxide cannot be achieved. In addition to technical interventions, strategies are required to address cognitive biases and the deterioration of individual and team performance in stressful situations, to which all practitioners are vulnerable. These guidelines provide recommendations for preventing unrecognised oesophageal intubation that are relevant to all airway practitioners independent of geography, clinical location, discipline or patient type.

Investigating the Airway Opening Index during cardiopulmonary resuscitation

IntroductionChest compressions during CPR induce oscillations in capnography (ETCO2) waveforms. Studies suggest ETCO2 oscillation characteristics are associated with intrathoracic airflow dependent on airway patency. Oscillations can be quantified by the Airway Opening Index (AOI). We sought to evaluate multiple methods of computing AOI and their association with return of spontaneous circulation (ROSC). MethodsWe conducted a retrospective study of 307 out-of-hospital cardiac arrest (OHCA) cases in Seattle, WA during 2019. ETCO2 and chest impedance waveforms were annotated for the presence of intubation and CPR. We developed four methods for computing AOI based on peak ETCO2 and the oscillations in ETCO2 during chest compressions (ΔETCO2). We examined the feasibility of automating ΔETCO2 and AOI calculation and evaluated differences in AOI across the methods using nonparametric testing (α = 0.05). ResultsMedian [interquartile range] AOI across all cases using Methods 1–4 was 28.0 % [17.9–45.5 %], 20.6 % [13.0–36.6 %], 18.3 % [11.4–30.4 %], and 22.4 % [12.8–38.5 %], respectively (p < 0.001). Cases with ROSC had a higher median AOI than those without ROSC across all methods, though not statistically significant. Cases with ROSC had a significantly higher median [interquartile range] ΔETCO2 of 7.3 mmHg [4.5–13.6 mmHg] compared to those without ROSC (4.8 mmHg [2.6–9.1 mmHg], p < 0.001). ConclusionWe calculated AOI using four proposed methods resulting in significantly different AOI. Additionally, AOI and ΔETCO2 were larger in cases achieving ROSC. Further investigation is required to characterize AOI’s ability to predict OHCA outcomes, and whether this information can improve resuscitation care.

Inter-hospital transfer of a pregnant prone patient with COVID-19 as a bridge to ECMO.

Sir, Pregnant women are at a higher risk of severe coronavirus disease 2019 (COVID-19) compared to non-pregnant women and are associated with worse outcomes.[1] The management of acute respiratory distress syndrome (ARDS) in a pregnant woman is challenging because of physiological changes of pregnancy and the detrimental effects of hypoxaemia and hypercarbia on the foetus. Prone ventilation and extracorporeal membrane oxygenation (ECMO) are effective rescue strategies in severe ARDS requiring invasive mechanical ventilation. We transferred a pregnant patient with critical COVID-19 on invasive mechanical ventilation (IMV) and prone position as a bridge to ECMO. A 28-year-old primigravida at 24 weeks’ gestation, with laboratory-confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection was admitted for breathing difficulty and cough since 8 days. She was started on oxygen by face mask to target oxygen saturation (Spo2) ≥94%, dexamethasone 6 mg intravenous once daily and enoxaparin 40 mg subcutaneous 12 hourly. Laboratory parameters showed C-reactive protein 140 mg/L, haemoglobin 12.8 gm%, white cell count 4200/mm3, procalcitonin 1.1 ng/ml, lactate dehydrogenase 680 U/L, D-dimer 1011 ng/ml and normal renal and liver function tests. Her oxygenation worsened the next day, and a trial of continuous positive airway pressure (CPAP) was given in the intensive care unit (ICU). However, because of worsening oxygenation and respiratory distress, the patient was tracheal-intubated and started on IMV with lung-protective ventilation strategy. The patient remained hypoxaemic (partial pressure of oxygen to a fraction of inspired oxygen (PaO2/FiO2) ratio of 67 mm Hg) and higher plateau pressure (Pplat) of 32 cm H2O. She was proned with shoulder and thigh support and adequate padding of pressure areas. The abdomen and pelvis were kept in a suspended position. Periodical foetal assessment was performed using cardiotocography and portable Doppler ultrasound, while the suspended abdomen was checked manually for any obstruction or tension. The patient continued to be severely hypoxaemic (PaO2/FiO2 <80 mm Hg) despite two sessions of prone ventilation of 16 h each. The case was discussed with the ECMO team at Central Command Centre as a potential candidate for ECMO. Given the absence of retrieval ECMO and level III neonatal ICU, an inter-hospital transfer was planned. Due to rapid desaturation on supine positioning, a decision to transfer the patient in prone position was taken. A team of two anaesthesiologist-intensivists and three ICU trained nurses accompanied the patient. Heart rate, rhythm, arterial blood pressure, end-tidal continuous waveform capnography, SpO2 and ventilator waveforms were monitored continuously throughout the patient care [Table 1]. The tracheal tube was firmly secured with a tube holder and standard tie. An intravenous infusion of propofol and midazolam was used for sedation, and cisatracurium was used for neuromuscular blockade. The patient was transferred as a single unit with shoulder and pelvic support from the ICU bed to the ambulance stretcher. One staff was solely dedicated for foetal assessment and airway. An intensivist was responsible for IMV, and another supervised the transfer. The transfer was uneventful with continuous monitoring of the patient and foetus. The ECMO facility was approximately 9 km away and took a travel time of 28 min.Table 1: Vitals of the patient during inter-hospital transportProne ventilation is an effective rescue strategy for the management of refractory hypoxaemia in severe ARDS by improving ventilation-perfusion matching and reducing mortality.[2] Pregnancy is traditionally excluded from trials on ARDS. However, protocolised proning with due consideration to physiological changes of pregnancy and adequate monitoring is recommended as a low-cost and effective strategy in ARDS management.[3] The transfer in the prone position can be catastrophic with a risk of the misplaced airway and rapid deoxygenation or inability to perform cardiopulmonary resuscitation during an emergency.[4] The systematic planning of transfer with attention to airway, monitoring and pressure areas was found to have been successful in a smaller case series.[56] The twin issues of second-trimester pregnancy and prone position made this case challenging. However, adequate planning, team briefing and continuous patient and foetal monitoring ensured a safe transfer. In conclusion, safe transfer of a pregnant, prone patient was possible with adequate planning, risk management and an experienced team. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

Abstract No. : ABS3541: A comparative study to confirm the endotracheal tube placement using ultrasonography and standard auscultation method inchildren

Background & Aims:In paediatric patients, due to shorter trachea, suboptimal positioning of endotracheal tube (ETT) is seen in 20-50% of patients triggering grave complications. We compared standard auscultation and ultrasound-guided lung sliding to confirmposition of ETT in children.Methods:75 paediatric patients between 2-8 years of age, American Society of Anesthesiologists (ASA) I and II scheduled for surgery under general anaesthesia with endotracheal intubation were studied. Position of ETT was confirmed by chest auscultation for the breath sounds bilaterally and by ultrasound on same sites for lung-sliding sign. The data obtained were compared to findings on waveform capnography. Study outcomes included position of the ETT; tracheal or oesophageal, accuracy and time taken till confirmingthe diagnosis.Results:Compared to waveform capnography findings, ultrasound revealed sensitivity of 100% and specificity of 41.7% while that for standard auscultation were 72.86% and 100% respectively. The mean time taken for confirmation of ETT position by auscultation was 32.38±6.2s and was significantly lower (p=0.001s) than the ultrasonography time of 136.8±7s. However, ultrasonography findings were 90.7% accurate which was significantly higher than 74.7% accuracy of auscultation. VCVPCV-VG P MeanSDMeanSD% change in set parameter FiO21.654.290.098.460.607 TV2.376.671.663.780.765 RR-1.278.790.415.030.304% change in measured parameter PIP20.1010.6718.0517.160.607 PlatP28.3817.9126.6622.940.765 VTe-3.1612.04-0.287.440.304 Compl-50.7328.53-50.4946.220.982 R21.5512.1116.3124.840.339 EtCO21.199.42-3.648.160.054 SpO2-0.040.20-0.040.200.983Conclusion:Confirmation of ETT position using ultrasonography or waveform capnography is essential because of high false results using standard auscultation alone. Ultrasound-guided lung sliding method is a simple and accurate method used for detectingtube malposition.

Inadvertent severe hypercapnia during general anesthesia: drop-in oxygen saturation or electrocardiography changes; which one warns us earlier?

BackgroundDuring general anesthesia especially when the nurse or anesthesiologist forgets to change manual to controlled mode after successful endotracheal intubation, capnography shows End-tidal Co2 above 20 mmHg after checking the place of the tracheal tube and will remain on the screen permanently. In this scenario, the patient receives a high concentration of oxygen, and Spo2 (oxygen saturation) does not drop for a long time which is too late to intervene. It has been all-time questionable which one of the cardiac dysrhythmias or Spo2 dropping occurs earlier.ResultsMedical records of seven deceased patients reviewed. All of them had electrocardiogram changes including premature ventricular contraction or bradycardia as a first warning sign. Oxygen saturation remains above 95% even with cardiac dysrhythmia.ConclusionsBradycardia and premature ventricular contraction were the first warning findings for severe hypercapnia during general anesthesia and occurred earlier than dropping oxygen saturation. Furthermore, the normal capnography waveform is more reliable than the End-tidal Co2 number for monitoring.

Optimizing Physiology During Prehospital Airway Management: An NAEMSP Position Statement and Resource Document

Airway management is a critical component of resuscitation but also carries the potential to disrupt perfusion, oxygenation, and ventilation as a consequence of airway insertion efforts, the use of medications, and the conversion to positive-pressure ventilation. NAEMSP recommends: Airway management should be approached as an organized system of care, incorporating principles of teamwork and operational awareness. EMS clinicians should prevent or correct hypoxemia and hypotension prior to advanced airway insertion attempts. Continuous physiological monitoring must be used during airway management to guide the timing of, limit the duration of, and inform decision making during advanced airway insertion attempts. Initial and ongoing confirmation of advanced airway placement must be performed using waveform capnography. Airway devices must be secured using a reliable method. Perfusion, oxygenation, and ventilation should be optimized before, during, and after advanced airway insertion. To mitigate aspiration after advanced airway insertion, EMS clinicians should consider placing a patient in a semi-upright position. When appropriate, patients undergoing advanced airway placement should receive suitable pharmacologic anxiolysis, amnesia, and analgesia. In select cases, the use of neuromuscular blocking agents may be appropriate.

Prehospital Supraglottic Airways: An NAEMSP Position Statement and Resource Document

Supraglottic airway (SGA) devices provide effective conduits for oxygenation and ventilation and may offer protection from gastric aspiration. SGA devices are widely used by EMS clinicians as both rescue and primary airway management devices. While in common use for more than four decades, major developments in SGA education, science, and technology have influenced clinical strategies of SGA insertion and use in prehospital airway management for patients of all ages. NAEMSP recommends: SGAs have utility as a primary or secondary EMS airway intervention. EMS agencies should select SGA strategies that best suit available resources and local clinician skillset, as well as the nature of their clinical practice setting. EMS agencies that perform endotracheal intubation must also equip their clinicians with SGA devices and ensure adequate training and competence. In select situations, drug-assisted airway management may be used by properly credentialed EMS clinicians to facilitate SGA insertion. Confirmation of initial and continuous SGA placement using waveform capnography is strongly encouraged as a best practice. When it is functioning properly, EMS clinicians should refrain from converting an SGA to an endotracheal tube. The decision to convert an SGA to an endotracheal tube must consider the patient’s condition, the effectiveness of SGA ventilations, and the clinical context and course of initial SGA insertion SGA training, competency, and clinical use must be continuously evaluated by EMS agencies using focused quality management programs.

Prehospital Drug Assisted Airway Management: An NAEMSP Position Statement and Resource Document

Airway management is a critical intervention for patients with airway compromise, respiratory failure, and cardiac arrest. Many EMS agencies use drug-assisted airway management (DAAM) - the administration of sedatives alone or in combination with neuromuscular blockers - to facilitate advanced airway placement in patients with airway compromise or impending respiratory failure who also have altered mental status, agitation, or intact protective airway reflexes. While DAAM provides several benefits including improving laryngoscopy and making insertion of endotracheal tubes and supraglottic airways easier, DAAM also carries important risks. NAEMSP recommends: DAAM is an appropriate tool for EMS clinicians in systems with clear guidelines, sufficient training, and close EMS physician oversight. DAAM should not be used in settings without adequate resources. EMS physicians should develop clinical guidelines informed by evidence and oversee the training and credentialing for safe and effective DAAM. DAAM programs should include best practices of airway management including patient selection, assessmenct and positioning, preoxygenation strategies including apneic oxygenation, monitoring and management of physiologic abnormalities, selection of medications, post-intubation analgesia and sedation, equipment selection, airway confirmation and monitoring, and rescue airway techniques. Post-DAAM airway placement must be confirmed and continually monitored with waveform capnography. EMS clinicians must have the necessary equipment and training to manage patients with failed DAAM, including bag mask ventilation, supraglottic airway devices and surgical airway approaches. Continuous quality improvement for DAAM must include assessment of individual and aggregate performance metrics. Where available for review, continuous physiologic recordings (vital signs, pulse oximetry, and capnography), audio and video recordings, and assessment of patient outcomes should be part of DAAM continuous quality improvement.

The use of capnography for real-time monitoring of mask ventilation during induction of general anaesthesia

The use of capnography for real-time monitoring of mask ventilation during induction of general anaesthesia

Predicting Prolonged Apnea During Nurse-Administered Procedural Sedation: Machine Learning Study.

BackgroundCapnography is commonly used for nurse-administered procedural sedation. Distinguishing between capnography waveform abnormalities that signal the need for clinical intervention for an event and those that do not indicate the need for intervention is essential for the successful implementation of this technology into practice. It is possible that capnography alarm management may be improved by using machine learning to create a “smart alarm” that can alert clinicians to apneic events that are predicted to be prolonged.ObjectiveTo determine the accuracy of machine learning models for predicting at the 15-second time point if apnea will be prolonged (ie, apnea that persists for >30 seconds).MethodsA secondary analysis of an observational study was conducted. We selected several candidate models to evaluate, including a random forest model, generalized linear model (logistic regression), least absolute shrinkage and selection operator regression, ridge regression, and the XGBoost model. Out-of-sample accuracy of the models was calculated using 10-fold cross-validation. The net benefit decision analytic measure was used to assist with deciding whether using the models in practice would lead to better outcomes on average than using the current default capnography alarm management strategies. The default strategies are the aggressive approach, in which an alarm is triggered after brief periods of apnea (typically 15 seconds) and the conservative approach, in which an alarm is triggered for only prolonged periods of apnea (typically >30 seconds).ResultsA total of 384 apneic events longer than 15 seconds were observed in 61 of the 102 patients (59.8%) who participated in the observational study. Nearly half of the apneic events (180/384, 46.9%) were prolonged. The random forest model performed the best in terms of discrimination (area under the receiver operating characteristic curve 0.66) and calibration. The net benefit associated with the random forest model exceeded that associated with the aggressive strategy but was lower than that associated with the conservative strategy.ConclusionsDecision curve analysis indicated that using a random forest model would lead to a better outcome for capnography alarm management than using an aggressive strategy in which alarms are triggered after 15 seconds of apnea. The model would not be superior to the conservative strategy in which alarms are only triggered after 30 seconds.

A Review of Current Literature of Interest to the Office-Based Anesthesiologist.

A Review of Current Literature of Interest to the Office-Based Anesthesiologist.

The Assessment of End-Tidal Capnography Waveform Interpretation and Its Clinical Application for Emergency Residents in Malaysia: A Cross-Sectional Study

The Assessment of End-Tidal Capnography Waveform Interpretation and Its Clinical Application for Emergency Residents in Malaysia: A Cross-Sectional Study

Tracheal Intubation Using a Videolaryngoscope Assisted by Transtracheal Illumination with an LED Vein Finder

Introduction: Retrograde illumination of the glottis using an LED vein finder placed over the cricothyroid membrane produces a red-orange glow of light inside the airway that can be used to assist the intubator during videolaryngoscopy. The endotracheal tube can be guided through this red-orange glow illuminating the glottis and trachea. Patients and Methods: In this prospective, randomised, single-blinded study, a total of 200 patients posted for elective head and neck cancer surgeries were included. Patients were placed supine with their heads in a neutral position without a pillow. Intubation was done with The Anesthetist Scope videolaryngoscope in Group TI (transillumination) with an assistant holding the LED vein finder over the cricothyroid membrane. The glottic opening was identified by a red-orange glow within the airway and the intubation was performed. In Group C (conventional direct laryngoscopy), transillumination was not done during intubation. Exposure time was taken from the time when the patient's mouth was opened to the time when the best glottic view was obtained. Intubation time was noted from the introduction of the videolaryngoscope or conventional laryngoscope into the mouth, through successful intubation and identification of 3 complete capnographic waveforms. A total of three attempts were allowed for each patient. Results: The success rate was better in Group TI. Exposure time and intubation time were shorter in Group TI as compared to Group C. In three patients with carcinoma of the vocal cords, the glottic opening was identified only by retrograde light transmission from the vein finder. Conclusion: A combination of videolaryngoscopy and LED vein finder is an effective method to achieve a better success rate of tracheal intubation.

Awake intubation with C-MAC videolaryngoscope in a patient with difficult airway.

Sir, The role of videolaryngoscopy has increased in the management of the difficult airway in recent times. We report a case where C-MAC D-blade videolaryngoscope (VL) was used in the airway management of a patient with cervico-facial necrotising fasciitis scheduled for surgical debridement. A 28-year-old male patient was posted for surgical debridement of cervico-facial necrotising fasciitis with multi-organ dysfunction. He was a known case of type 1 diabetes mellitus (DM). On examination, the patient was irritable and disoriented due to sepsis-induced encephalopathy (GCS-E3V3M5). He had a swollen and blackened right cheek due to necrosis with extension to the neck [Figure 1]. The mouth opening of the patient was around 1.6cm with restricted neck mobility, eliminating the possibility of neck extension. Our primary airway management plan was awake intubation via C-MAC VL (Karl Storz) blade D. A fibre-optic bronchoscope with an endoscopic mask was readily available as an alternative airway management plan. A skilled ear-nose-throat (ENT) surgeon was also requested to be standby for the emergency tracheostomy.Figure 1: Cervico-facial necrotising fasciitis involving the entire right cheek and extending to the neckIn the preoperative room, the patient's airway was prepared by nebulisation with 4mL of 4% lignocaine. In the operating room, standard American Society of Anesthesiologists (ASA) monitors such as electrocardiogram, non-invasive blood pressure and pulse oximeter were attached to the patient. The patient was sedated with 50 μg fentanyl and dexmedetomidine (loading dose of 1 μg/kg, followed by the infusion of 0.5 μg/kg/h). The patient received continuous oxygen via a nasal catheter with a flow of 3 L.min−1. Topical anaesthesia was supplemented with two puffs of lidocaine 10% metered spray applied directly on the surface of the tongue and oropharynx. Videolaryngoscopy was done using an adult D-blade of C-MAC and the percentage of glottic opening (POGO) score was found to be zero. Simultaneously, the posterior pharyngeal wall was anaesthetised with two puffs of 10% lignocaine spray to blunt the reflexes during insertion of the endotracheal tube (ETT). The patient was then intubated with a 7.5 mm internal diameter (ID) ETT with the aid of Eschmann stylet (Portex; Smiths Medical). After confirmation of the capnography waveform, general anaesthesia was induced with propofol and rocuronium. The surgery lasted uneventfully for around 100 min after which the patient was shifted to the intensive care unit, and was extubated the same day. Cervico-facial necrotising fasciitis is a soft tissue infection that spreads along with the superficial musculoaponeurotic system and early aggressive surgical debridement is the mainstay in achieving a successful outcome.[1] Anaesthetic management of such patients is challenging as the pain, swelling and oedema due to inflammatory processes restrict the facial and cervical movements, making the airway potentially difficult. Awake fibre-optic intubation (AFOI) is considered the technique of choice in predicted difficult airway. AFOI has a steep learning curve and requires patient cooperation. Recently, VLs have gained immense popularity as the first-line devices in adult and paediatric difficult airways due to feasibility of orotracheal intubation in a restricted mouth opening.[23] Karmer et al. described C-MAC VL as superior to fibre-optic intubation (FOI) in terms of faster intubation time in limited mouth opening patients(>1.3cm).[4] Alhomary in a systematic review also confirmed that awake video laryngoscopy has a shorter intubation time compared to AFOI.[5] In our institute, we frequently use D-blade of C-MAC for difficult intubations and so are well versed with it. Hence, C-MAC was chosen as a primary airway management plan to quickly secure the airway. Since the D-blade has a thickness of around 1 cm, it can be easily accommodated in the limited mouth opening patient and has a better field of vision (60 degrees angle of view) with the requirement of less lifting force to visualise the glottis, especially in patients who are not fully anaesthetised.[6] To conclude, we suggest that awake videolaryngoscopy using D-blade of C-MAC VL can be considered as an alternative for tracheal intubation in difficult airway scenarios where AFOI is difficult or not possible. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest. Acknowledgement We would like to acknowledge the support and guidance of Dr Rakesh Kumar, M.D, Associate Professor, Department of Anaesthesiology and Critical Care, All India Institute of Medical Sciences, Jodhpur in helping me write this article.

Breath emulator for simulation and modelling of expired tidal breath carbon dioxide characteristics

BackgroundIn this work we describe a breath emulator system, used to simulate temporal characteristics of exhaled carbon dioxide (CO2) concentration waveform versus time simulating how much CO2 is present at each phase of the human lung respiratory process. The system provides a method for testing capnometers incorporating fast response non-dispersive infrared (NDIR) CO2 gas sensing devices - in a clinical setting, capnography devices assess ventilation which is the CO2 movement in and out of the lungs. A mathematical model describing the waveform of the expired CO2 characteristic and influence of CO2 gas sensor noise factors and speed of response is presented and compared with measured and emulated data. ObjectiveA range of emulated capnogram temporal waveforms indicative of normal and restricted respiratory function demonstrated. The system can provide controlled introduction of water vapour and/ or other gases, simulating the influence of water vapour in exhaled breath and presence of other gases in a clinical setting such as anaesthetic agents (eg N2O). This enables influence of water vapour and/ or other gases to be assessed and modelled in the performance of CO2 gas sensors incorporated into capnography systems. As such the breath emulator provides a means of controlled testing of capnometer CO2 gas sensors in a non-clinical setting, allowing device optimisation before use in a medical environment. MethodsThe breath emulator uses a unique combination of mass flow controllers, needle valves and a fast acting switchable pneumatic solenoid valve (FASV), used to controllably emulate exhaled CO2 temporal waveforms for normal and restricted respiratory function. Output data from the described emulator is compared with a mathematical model using a range of input parameters such as time constants associated with inhalation/ exhalation for different parts of the respiratory cycle and CO2 concentration levels. Sensor noise performance is modelled, taking into account input parameters such as sampling period, sensor temperature, sensing light throughput and pathlength. ResultsThe system described here produces realistic human capnographic waveforms and has the capability to emulate various waveforms associated with chronic respiratory diseases and early stage detection of exacerbations. The system has the capability of diagnosing medical conditions through analysis of CO2 waveforms.Demonstrated in this work the emulator has been used to test NDIR gas sensor technology deployed in capnometer devices prior to formal clinical trialling.

A Novel Method to Measure Transient Impairments in Cognitive Function During Acute Bouts of Hypoxia.

INTRODUCTION: Exposure to low oxygen environments (hypoxia) can impair cognitive function; however, the time-course of the transient changes in cognitive function is unknown. In this study, we assessed cognitive function with a cognitive test before, during, and after exposure to hypoxia.METHODS: Nine participants (28 4 yr, 7 women) completed Conners Continuous Performance Test (CCPT-II) during three sequential conditions: 1) baseline breathing room air (fraction of inspired oxygen, FIo₂ 0.21); 2) acute hypoxia (FIo₂ 0.118); and 3) recovery after exposure to hypoxia. End-tidal gas concentrations (waveform capnography), heart rate (electrocardiography), frontal lobe tissue oxygenation (near infrared spectroscopy), and mean arterial pressure (finger photoplethysmography) were continuously assessed.RESULTS: Relative to baseline, during the hypoxia trial end-tidal (-30%) and cerebral (-9%) oxygen saturations were reduced. Additionally, the number of commission errors during the CCPT-II was greater during hypoxia trials than baseline trials (2.6 0.4 vs. 1.9 0.4 errors per block of CCPT-II). However, the reaction time and omission errors did not differ during the hypoxia CCPT-II trials compared to baseline CCPT-II trials. During the recovery CCPT-II trials, physiological indices of tissue hypoxia all returned to baseline values and number of commission errors during the recovery CCPT-II trials was not different from baseline CCPT-II trials.DISCUSSION: Oxygen concentrations were reduced (systemically and within the frontal lobe) and commission errors were increased during hypoxia compared to baseline. These data suggest that frontal lobe hypoxia may contribute to transient impairments in cognitive function during short exposures to hypoxia.Uchida K, Baker SE, Wiggins CC, Senefeld JW, Shepherd JRA, Trenerry MR, Buchholtz ZA, Clifton HR, Holmes DR, Joyner MJ, Curry TB. A novel method to measure transient impairments in cognitive function during acute bouts of hypoxia. Aerosp Med Hum Perform. 2020; 91(11):839844.

Vital sign monitoring during out-of-hospital pediatric advanced airway management.

ObjectiveTo evaluate physiologic monitoring in pediatric patients undergoing out‐of‐hospital advanced airway management.MethodsRetrospective case series of pediatric patients (<18 years) with advanced airways placed in the out‐of‐hospital setting. Patients given cardiopulmonary resuscitation (CPR) or defibrillation before the first advanced airway attempt were excluded. Reviewers abstracted physiologic data from the patient monitor files and patient care reports. The primary outcome was the proportion of time pulse oximetry was in place during airway management. Other outcomes included the proportion of time ECG monitoring and waveform end‐tidal capnography were in place as well as the incidence of oxygen desaturation events.ResultsWe evaluated 23 pediatric patients with a mean age of 10.7 years (SD 6.5). Eleven of 18 (61%) children with medication‐facilitated intubation had pulse oximetry in place when the first medication was documented as given. Eight of 18 (44%) had ECG monitoring, 12 of 18 (66%) had waveform capnography, and 5 of 18 (28%) had a blood pressure check within the 3 minutes before receiving the first medication. In the 3‐minute preoxygenation phase, pulse oximetry was in place for an average of 1.4 minutes (47%, SD 0.37) and a visible photoplethysmogram (PPG) waveform obtained from the pulse oximeter was present for 0.6 minutes (20%, SD 0.34). During airway device placement, pulse oximetry was in place 73% (SD 0.39) of the time and 30% (SD 0.41) of the time there was a visible PPG waveform.ConclusionsPediatric patients had critical deficits in physiologic monitoring during advanced airway management.