Carbon Dioxide Waveform Research Articles

Comparison of Intubating Conditions with Succinylcholine Versus Rocuronium in the Prehospital Setting

Objective Rapid sequence intubation (RSI) is frequently performed by emergency medical services (EMS). We investigated the relationship between succinylcholine and rocuronium use and time until first laryngoscopy attempt, first-pass success, and Cormack-Lehane (CL) grades. Methods We included adult patients for whom prehospital RSI was attempted from July 2015 through June 2022 in a retrospective, observational study with pre-post analysis. Timing was verified using recorded defibrillator audio in addition to review of continuous ECG, pulse oximetry, and end-tidal carbon dioxide waveforms. Our primary exposure was neuromuscular blocking agent (NMBA) used, either rocuronium or succinylcholine. Our prespecified primary outcome was the first attempt Cormack-Lehane view. Key secondary outcomes were first laryngoscopy attempt success rate, timing from NMBA administration to first attempt, number of attempts, and hypoxemic events. Results Of 5,179 patients in the EMS airway registry, 1,475 adults received an NMBA while not in cardiac arrest. Cormack-Lehane grades for succinylcholine and rocuronium were similar: grade I (64%, 59% [95% CI 0.64–1.09]), grade II (16%, 21%), grade III (18%, 16%), grade IV (3%, 3%). The median interval from NMBA administration to start of the first attempt was 57 s for succinylcholine and 83 s for rocuronium (mean difference 28 [95% CI 20–36] seconds). First attempt success was 84% for succinylcholine and 83% for rocuronium. Hypoxemic events were present in 25% of succinylcholine cases and 23% of rocuronium cases. Conclusions Prehospital use of either rocuronium or succinylcholine is associated with similar Cormack-Lehane grades, first-pass success rates, and rates of peri-intubation hypoxemia.

Machine diagnosis of chronic obstructive pulmonary disease using a novel fast-response capnometer

BackgroundAlthough currently most widely used in mechanical ventilation and cardiopulmonary resuscitation, features of the carbon dioxide (CO2) waveform produced through capnometry have been shown to correlate with V/Q mismatch, dead space volume, type of breathing pattern, and small airway obstruction. This study applied feature engineering and machine learning techniques to capnography data collected by the N-Tidal™ device across four clinical studies to build a classifier that could distinguish CO2 recordings (capnograms) of patients with COPD from those without COPD.MethodsCapnography data from four longitudinal observational studies (CBRS, GBRS, CBRS2 and ABRS) was analysed from 295 patients, generating a total of 88,186 capnograms. CO2 sensor data was processed using TidalSense’s regulated cloud platform, performing real-time geometric analysis on CO2 waveforms to generate 82 physiologic features per capnogram. These features were used to train machine learning classifiers to discriminate COPD from ‘non-COPD’ (a group that included healthy participants and those with other cardiorespiratory conditions); model performance was validated on independent test sets.ResultsThe best machine learning model (XGBoost) performance provided a class-balanced AUROC of 0.985 ± 0.013, positive predictive value (PPV) of 0.914 ± 0.039 and sensitivity of 0.915 ± 0.066 for a diagnosis of COPD. The waveform features that are most important for driving classification are related to the alpha angle and expiratory plateau regions. These features correlated with spirometry readings, supporting their proposed properties as markers of COPD.ConclusionThe N-Tidal™ device can be used to accurately diagnose COPD in near-real-time, lending support to future use in a clinical setting.Trial registration: Please see NCT03615365, NCT02814253, NCT04504838 and NCT03356288.

Usefulness of supplemental parasternal block for sternal keloid excision under general anesthesia in a child status post multiple cardiac surgeries

Sir A 12-year-old boy weighing 60 kg, with history of tricuspid atresia, had undergone right modified Blalock–Thomas–Taussig shunt, and patent ductus arteriosus ligation on day 1 of life. One year later he underwent bidirectional Glenn shunt, and extra cardiac Fontan surgery was done at 6 years. He presented now with a thick keloid in the midline sternotomy scar for keloid excision. Current screening echo showed tricuspid atresia, normally related great arteries with normal ventricular flow and unobstructed Glenn and Fontan flow profiles. Intravenous midazolam 1 mg, fentanyl 100 mcg and ketamin 60 mg were given and incremental bolus of propofol 10 mg (total 20 mg) was given till loss of response to verbal commands and relaxation of jaw. Airway was then secured with size 3 proseal laryngeal mask airway (PLMA) and correct placement was ensured with regular endtidal carbon dioxide (ETCO2) waveforms. Parasternal block was then given under ultrasound guidance at third and fifth intercostal spaces 2 cm lateral to midline bilaterally. Spread of injected solution causing separation of pectoralis major muscle from the rib and external intercostal muscle confirmed deposition of drug in the correct plane (Fig. 1). Ten milliliter of 0.25% bupivacaine was injected at each site.Figure 1: Superficial parasternal-intercostal plane block.Anesthesia was maintained with sevoflurane (1.5–2%) in air oxygen mixture under spontaneous ventilation. Intraoperatively patient remained stable with heart rate 86-98/min, systolic blood pressure 90–100 mmHg, oxygen saturation 96–98% and ETCO2 32-40 mmHg and had received 500 ml of Ringer lactate. At the end of surgery, which lasted for 2 h, PLMA was removed when patient was awake. He had good postoperative analgesia. Anesthetic goals in a child post-Fontan surgery include adequate hydration, avoidance of hypoxia, hypercabia, and acidosis and preservation of spontaneous ventilation whenever possible. If general anesthesia is mandated, low inspiratory pressures and minimal positive end expiratory pressures are to be used [1,2]. Sternotomy produces considerable pain which increases with chest wall movement and reduces pulmonary function with higher risk of development of postoperative hypoxia, atelectasis, and pneumonia [3]. Parasternal block is commonly advocated to provide supplemental anaesthesia intraoperatively and for postoperative analgesia following median sternotomy, breast surgery and cardioverter-defibrillator implantation [4,5]. The nerve targeted is the anterior branches of intercostal nerves which enters intercostal and pectoralis major muscles and innervates the antero-medial region of chest wall. Local anesthetic is injected deep to pectoralis major muscle and superficial to intercostal muscles or between internal thoracic muscle and transverses thoracis muscle. Therefore, these blocks are essentially described as superficial or deep parasternal-intercostal plane blocks, depending on where the target nerves are blocked. The anatomical injection site differentiates these techniques though both techniques provide analgesia to the antero-medial chest wall [5]. Supplemental regional block helps to reduce dose requirement of anesthetic agents intraoperatively. Use of supplemental parasternal block enabled us to keep the child spontaneously breathing under general anaesthesia using PLMA with use of lesser doses of anesthetic agents, thereby minimising drug adverse effects which could be deleterious in the presence of cardiac diseases. It is concluded that supplemental parasternal block provides good intraoperative and postoperative analgesia following anterior midline chest wall surgeries.

Awake video laryngoscopy aided intubation as an alternative to awake fiberoptic intubation in a patient with difficult airway.

Dear Editor, We are reporting the airway management of a 75-year-old male patient diagnosed with recurrent basal cell carcinoma (BCC) nose who had undergone multiple resections and facial reconstructive surgeries. He was posted for excision of recurrent BCC. On examination, his mouth had a fish-mouth appearance with restricted opening of approximately 4 cm. He had no nose, was edentulous with restricted tongue protrusion, and had a Mallampati score of 4. The patient had no other comorbidities and the investigations were within normal limits. After 6 h of fasting, the patient was taken up for surgery. The anesthetic plan was awake intubation followed by induction of general anesthesia (GA) and controlled ventilation. Fiberoptic bronchoscope (FOB) was unavailable and mask ventilation was seemingly impossible due to deformed facial contours. So, we planned to perform an initial awake check laryngoscopy under topical anesthesia. Following intravenous glycopyrrolate 0.2 mg, topicalization of oral cavity was done with 10% lignocaine spray. Then awake check laryngoscopy was performed with C MAC videolaryngoscope using D blade and we were able to visualize the glottic opening. Transtracheal block was given with 4 mL of 4% lignocaine, and then, under videolaryngoscopic visualization, a soft gum elastic bougie was introduced into the trachea. A 7.0mm internal diameter flexometallic endotracheal tube (ETT) was then railroaded over the bougie [Figure 1]. After observing regular end-tidal carbon dioxide waveforms, the patient was induced with propofol, paralyzed with vecuronium, and ETT was fixed at 21 cm at the left angle of the mouth. Fentanyl was used as an analgesic and anesthesia was maintained with isoflurane in an air–oxygen mixture. The intraoperative period was uneventful and the patient was extubated when fully awake after reversing neuromuscular blockade.Figure 1: Patient after intubationThough awake fiberoptic intubation (AFOI) is considered the gold standard for securing the airway in difficult airway patients, it may not be available always. Awake check laryngoscopy is helpful to plan mode of induction and intubation in difficult airway patients. Induction of GA in such patients is considered safe only if glottis could be visualized during check laryngoscopy. If FOB was available, oral AFOI would have been the ideal technique for our patient. Securing airway in patients with anticipated difficult airway in the absence of FOB could be accomplished by use of intubating laryngeal mask airway[1]or I gel,[2,3]a few among the many techniques described. We preferred intubation over supraglottic airway devices as they are bulkier than ETT and in the presence of reduced mouth opening, it would have further limited the surgical access for excision of the tumor at the mouth. Recent research has shown that videolaryngoscopes provide similar success rates and faster intubation times when compared with FOB-aided intubations in awake patients having difficult airways.[4,5]Optimal topicalization of the oral cavity, oropharynx, and the structures near the glottis as well as proper counseling of the patient are important for a successful outcome of this technique. We conclude that awake videolaryngoscopy followed by the introduction of soft gum elastic bougie into the trachea and railroading ETT over it is a safe alternative to AFOI during unavailability of FOB, provided the patient has adequate mouth opening. 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.

Improving Ventilation Rates During Pediatric Cardiopulmonary Resuscitation

Excessive ventilation at rates of 30 breaths per minute (bpm) or more during cardiopulmonary resuscitation (CPR) decreases venous return and coronary perfusion pressure, leading to lower survival rates in animal models. A review of our institution's pediatric CPR data revealed that patients frequently received excessive ventilation. We designed a multifaceted quality improvement program to decrease the incidence of clinically significant hyperventilation (≥30 bpm) during pediatric CPR. The program consisted of provider education, CPR ventilation tools (ventilation reminder cards, ventilation metronome), and individual CPR team member feedback. CPR events were reviewed pre- and postintervention. The first 10 minutes of each CPR event were divided into 20 second epochs, and the ventilation rate in each epoch was measured via end-tidal carbon dioxide waveform. Individual epochs were classified as within the target ventilation range (<30 bpm) or clinically significant hyperventilation (≥30 bpm). The proportion of epochs with clinically significant hyperventilation, as well as median ventilation rates, were analyzed in the pre- and postintervention periods. In the preintervention period (37 events, 699 epochs), 51% of CPR epochs had ventilation rates ≥30 bpm. In the postintervention period (24 events, 426 epochs), the proportion of CPR epochs with clinically significant hyperventilation decreased to 29% (P < .001). Median respiratory rates decreased from 30 bpm (interquartile range 21-36) preintervention to 21 bpm (interquartile range 12-30) postintervention (P < .001). A quality improvement initiative grounded in improved provider education, CPR team member feedback, and tools focused on CPR ventilation rates was effective at reducing rates of clinically significant hyperventilation during pediatric CPR.

Discrimination ability of the endotracheal tube location using real-time palpation during intubation using an endotracheal tube with a preloaded stylet.

PurposePalpation during intubation could be used as an ancillary method of providing real-time information of the endotracheal tube (ETT) placement before manual ventilation. This study aimed to evaluate the ability to discriminate the ETT location using a modified real-time palpation method with a preloaded stylet during intubation.Patients and methodsThe examiner performing the real-time palpation method placed three fingers on the lateral sides of the trachea between the sternal notch and the thyroid cartilage to determine if endotracheal intubation was successful. Endotracheal intubation was confirmed by auscultation and quantitative carbon dioxide waveform using capnography.ResultsEighty-eight patients were enrolled in this study. The discrimination accuracy of the real-time palpation method was 98.9% (95% CI: 93.8–99.8) for identifying the location of ETT between the trachea and esophagus. There was one false negative, reported as esophageal intubation rather than tracheal intubation.ConclusionThe real-time palpation method during intubation using an ETT with a preloaded stylet is an instantly applicable technique with good discrimination ability. The addition of real-time information through this palpation method to the conventional intubation process, especially in patients with poor vocal cord visualization, would be useful to facilitate the process of safe and careful endotracheal intubation.

Exploring the Waveform Characteristics of Tidal Breathing Carbon Dioxide, Measured Using the N-Tidal C Device in Different Breathing Conditions (The General Breathing Record Study): Protocol for an Observational, Longitudinal Study.

BackgroundIn an increasingly comorbid population, there are significant challenges to diagnosing the cause of breathlessness, and once diagnosed, considerable difficulty in detecting deterioration early enough to provide effective intervention. The burden of the breathless patient on the health care economy is substantial, with asthma, chronic heart failure, and pneumonia affecting over 6 million people in the United Kingdom alone. Furthermore, these patients often have more than one contributory factor to their breathlessness symptoms, with conditions such as dysfunctional breathing pattern disorders—an under-recognized component. Current methods of diagnosing and monitoring breathless conditions can be extensive and difficult to perform. As a consequence, home monitoring is poorly complied with. In contrast, capnography (the measurement of tidal breath carbon dioxide) is performed during normal breathing. There is a need for a simple, easy-to-use, personal device that can aid in the diagnosis and monitoring of respiratory and cardiac causes of breathlessness.ObjectiveThe aim of this study was to explore the use of a new, handheld capnometer (called the N-Tidal C) in different conditions that cause breathlessness. We will study whether the tidal breath carbon dioxide (TBCO2) waveform, as measured by the N-Tidal C, has different characteristics in a range of respiratory and cardiac conditions.MethodsWe will perform a longitudinal, observational study of the TBCO2 waveform (capnogram) as measured by the N-Tidal C capnometer. Participants with a confirmed diagnosis of asthma, breathing pattern disorders, chronic heart failure, motor neurone disease, pneumonia, as well as volunteers with no history of lung disease will be asked to provide twice daily, 75-second TBCO2 collection via the N-Tidal C device for 6 months duration. The collated capnograms will be correlated with the underlying diagnosis and disease state (stable or exacerbation) to determine if there are different TBCO2 characteristics that can distinguish different respiratory and cardiac causes of breathlessness.ResultsThis study’s recruitment is ongoing. It is anticipated that the results will be available in late 2018.ConclusionsThe General Breathing Record Study will provide an evaluation of the use of capnography as a diagnostic and home-monitoring tool for various diseases.Registered Report IdentifierRR1-10.2196/9767

Automatic Quantitative Analysis of Human Respired Carbon Dioxide Waveform for Asthma and Non-Asthma Classification Using Support Vector Machine

Currently, carbon dioxide (CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> waveforms measured by capnography are used to estimate respiratory rate and end-tidal CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (EtCO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) in the clinic. However, the shape of the CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> signal carries significant diagnostic information about the asthmatic condition. Previous studies have shown a strong correlation between various features that quantitatively characterize the shape of CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> signal and are used to discriminate asthma from non-asthma using pulmonary function tests, but no reliable progress was made, and no translation into clinical practice has been achieved. Therefore, this paper reports a relatively simple signal processing algorithm for automatic differentiation of asthma and non-asthma. CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> signals were recorded from 30 non-asthmatic and 43 asthmatic patients. Each breath cycle was decomposed into subcycles, and features were computationally extracted. Thereafter, feature selection was performed using the area ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$A_{z}$ </tex-math></inline-formula> ) under the receiver operating characteristics curve analysis. A classification was performed via a leave-one-out cross-validation procedure by employing a support vector machine. Our results show maximum screening capabilities for upward expiration ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$AR_{1}$ </tex-math></inline-formula> ), downward inspiration ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$AR_{2}$ </tex-math></inline-formula> ), and the sum of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$AR_{1}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$AR_{2}$ </tex-math></inline-formula> , with an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$A_{z}$ </tex-math></inline-formula> of 0.892, 0.803, and 0.793, respectively. The proposed method obtained an average accuracy of 94.52%, sensitivity of 97.67%, and specificity of 90% for discrimination of asthma and non-asthma. The proposed method allows for automatic classification of asthma and non-asthma condition by analyzing the shape of the CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> waveform. The developed method may possibly be incorporated in real-time for assessment and management of the asthmatic conditions.

Linshom thermodynamic sensor is a reliable alternative to capnography for monitoring respiratory rate.

Monitoring ventilation accurately is a technically challenging, yet indispensable aspect of patient care in the intra- and post-procedural settings. A new prototypical device known as the Linshom Respiratory Monitoring Device (LRMD) has been recently designed to non-invasively, inexpensively, and portably measure respiratory rate. The purpose of this study was to measure the accuracy and variability of LRMD measurements of respiratory rate relative to the measurement of capnography. In this prospective study, participants were enrolled and individually fitted with a face mask monitored by the LRMD and capnography. With a baseline oxygen flow rate and digital metronome to pace their respiratory rate, the participants were instructed to breathe at 10 breaths per minute (bpm) for 3min, 20bpm for 3min, 30bpm for 3min, 0bpm for 30s, and resume regular breathing for 30s. Both sensors were connected to a computer for continuous temperature and carbon dioxide waveform recordings. The data were then retrospectively analyzed. Twenty-six healthy volunteers, mean (range) age 27.8 (23-37) and mean (range) BMI 23.1 (18.8-29.2) kg/m2 were recruited. There were 15 males (57.7%) and 11 females (42.3%). After excluding 3 subjects for technical reasons, 13,800s of breathing and 4,140 expiratory breaths were recorded. Throughout the protocol, the average standard deviation (SD) for the LRMD and capnography was 1.11 and 1.81bpm, respectively. The overall mean bias (±2SD) between LRMD and capnography was -0.33 (±0.1.56) bpm. At the lowest and intermediate breathing rates reflective of hypoventilation and normal ventilation, the LRMD variance was 0.55 and 1.23 respectively, compared to capnography with 5.54 and 7.47, respectively. At higher breathing rates indicative of hyperventilation, the variance of the test device was 4.52, still less than that of capnography at 5.73. This study demonstrated a promising correlation between the LRMD and capnography for use as a respiratory rate monitor. The LRMD technology may be a significant addition to monitoring vital signs because it offers a minimally intrusive opportunity to detect respiratory rate and apnea, without expensive or complex anesthetic equipment, before the need for life-saving resuscitation arises.

Rapidity and efficacy of ultrasonographic sliding lung sign and auscultation in confirming endotracheal intubation in overweight and obese patients.

Background and Aims:Obese individuals are predisposed to difficult airway and intubation. They usually yield confusing or misleading auscultatory findings. We aimed to assess the rapidity and efficacy of ultrasonographic (USG) sliding lung sign for confirming endotracheal intubation in normal as well as overweight and obese surgical patients.Methods:This prospective, observational study was performed in forty surgical patients. Twenty patients with body mass index (BMI) <25 were recruited to Group A, whereas twenty patients with BMI ≥25 constituted Group B. Following induction and intubation, appearance of end-tidal carbon dioxide waveform was used to confirm endotracheal intubation. Presence of breath sounds bilaterally was sought by auscultation, and time taken for auscultatory confirmation was noted. The USG confirmation of air entry to the lung field as indicated by lung sliding was sought, and the time taken was noted. Chi-square test, independent t-test and paired t-test were used as applicable.Results:Auscultatory confirmation was more rapid in Group A as compared to Group B (9.34 ± 2.43 s vs. 14.35 ± 5.53 s, P = 0.001). However, there was no significant difference in USG confirmation time in both the groups (8.57 ± 2.05 s vs. 8.61 ± 1.66 s). Four patients in Group B had doubtful breath sounds against none in Group A. There was no doubtful lung slide with USG in both groups. One case of endobronchial intubation in Group B was diagnosed with USG which was doubtful by auscultation.Conclusion:Ultrasound directed confirmation of endotracheal tube placement in overweight and obese patients is superior in speed and accuracy in comparison to the standard auscultatory method.

A modified technique to improve the outcome of intubation with a left-sided double-lumen endobronchial tube

BackgroundThe use of a video-assisted laryngoscope (VL) has been shown to reduce the time to achieve intubation with a double-lumen endobronchial tube (DLT). As the blade of the VL is curved differently to a standard laryngoscope, the DLT must be angled into a hockey stick shape to fit properly. We conducted a study to establish which direction of angulation was best to facilitate correct positioning of the DLT when using a VL.MethodsWe enrolled patients scheduled for thoracic surgery who required intubation with a DLT. They were prospectively randomized into one of two groups: those intubated with a DLT angled to conceal the tracheal orifice (the tracheal orifice-covered, TOC) group or the tracheal orifice-exposed (TOE) group. The composite primary outcome measures were time taken to intubate and the frequency of first-time success. The time taken to intubate was divided into: T1, the time from mouth opening to visualization of the vocal cords with the VL; and T2, the time taken to advance the DLT through the cords until its tip lay within the trachea and three carbon dioxide waveforms had been detected by capnography. The hemodynamic responses to intubation and intubation-related adverse events were also recorded.ResultsSixty-six patients completed the study, with 33 in each group. Total intubation time was significantly shorter in the TOC group (mean 30.6 ± standard deviation 2.7 seconds versus 38.7 ± 3.3 seconds, p <0.0001). T2 was also significantly shorter in the TOC group than the TOE group (27.2 ± 2.5 seconds versus 34.9 ± 3.0 seconds, p <0.0001). The severity of hoarseness on the first postoperative day and sore throat on the fourth postoperative day were significantly lower in the TOC group than the TOE group (p = 0.02 and <0.0001, respectively). The hemodynamic responses to intubation were broadly similar between the groups.ConclusionWhen placing a left-sided DLT using a VL, angling the bronchial lumen to a hockey stick shape that conceals the tracheal lumen saves time and ameliorates the severity of post-intubation complications.Trial registrationClinicalTrials.gov Identifier: NCT01605591.

The Accuracy, Precision and Reliability of Measuring Ventilatory Rate and Detecting Ventilatory Pause by Rainbow Acoustic Monitoring and Capnometry

Current methods for monitoring ventilatory rate have limitations including poor accuracy and precision and low patient tolerance. In this study, we evaluated a new acoustic ventilatory rate monitoring technology for accuracy, precision, reliability, and the ability to detect pauses in ventilation, relative to capnometry and a reference method in postsurgical patients. Adult patients presenting to the postanesthesia care unit were connected to a Pulse CO-Oximeter with acoustic monitoring technology (Rad-87, version 7804, Masimo, Irvine, CA) through an adhesive bioacoustic sensor (RAS-125, rev C) applied to the neck. Each subject also wore a nasal cannula connected to a bedside capnometer (Capnostream20, version 4.5, Oridion, Needham, MA). The acoustic monitor and capnometer were connected to a computer for continuous acoustic and expiratory carbon dioxide waveform recordings. Recordings were retrospectively analyzed by a trained technician in a setting that allowed for the simultaneous viewing of both waveforms while listening to the breathing sounds from the acoustic signal to determine inspiration and expiration reference markers within the ventilatory cycle without using the acoustic monitor- or capnometer-calculated ventilatory rate. This allowed the automatic calculation of a reference ventilatory rate for each device through a software program (TagEditor, Masimo). Accuracy (relative to the respective reference) and precision of each device were estimated and compared with each other. Sensitivity for detection of pauses in ventilation, defined as no inspiration or expiration activity in the reference ventilatory cycle for ≥30 seconds, was also determined. The devices were also evaluated for their reliability, i.e., the percentage of the time when each displayed a value and did not drop a measurement. Thirty-three adults (73% female) with age of 45 ± 14 years and weight 117 ± 42 kg were enrolled. A total of 3712 minutes of monitoring time (average 112 minutes per subject) were analyzed across the 2 devices, reference ventilatory rates ranged from 1.9 to 49.1 bpm. Acoustic monitoring showed significantly greater accuracy (P = 0.0056) and precision (P- = 0.0024) for respiratory rate as compared with capnometry. On average, both devices displayed data over 97% of the monitored time. The (0.95, 0.95) lower tolerance limits for the acoustic monitor and capnometer were 94% and 84%, respectively. Acoustic monitoring was marginally more sensitive (P = 0.0461) to pauses in ventilation (81% vs 62%) in 21 apneic events. In this study of a population of postsurgical patients, the acoustic monitor and capnometer both reliably monitored ventilatory rate. The acoustic monitor was statistically more accurate and more precise than the capnometer, but differences in performance were modest. It is not known whether the observed differences are clinically significant. The acoustic monitor was more sensitive to detecting pauses in ventilation. Acoustic monitoring may provide an effective and convenient means of monitoring ventilatory rate in postsurgical patients.

Atrial Fibrillation Complicating Left Pneumothorax After Malpositioning of a Double-Lumen Tube

A 66-year-old woman (weight 133.3 lbs, height 158 cm) was scheduled for atrial septal defect (ASD) repair through a thoracotomy. Preoperative chest radiography was normal, and an electrocardiogram showed an incomplete right bundle-branch block. Transesophageal echocardiography revealed moderate right atrium and ventricle dilation, a pulmonary arterial pressure of 52 mmHg, and an ASD-associated left-to-right shunt. In the operating room, her blood pressure was 125/75 mmHg, her heart rate was 94 beats/min, and the SpO2 was 97% on room air. The patient was intubated with a 35F left-sided double-lumen tube (DLT) under direct laryngoscopy to a depth of 31 cm at the incisors. The DLT placement was checked by auscultation. During manual ventilation, increased airway resistance was noted, and no breath sounds were heard over either lung fields. The tube was pulled back 2 cm, and bilateral breath sounds were again documented. The end-tidal carbon dioxide waveform was present on the monitor. At that time, rapid-rate atrial fibrillation of 130 beats/min occurred with a blood pressure of 63/40 mmHg. Phenylephrine boluses were given to maintain hemodynamic stability. Correct positioning of the DLT was confirmed by fiberoptic bronchoscopy. Meanwhile, SpO2 remained within the normal range. Soon thereafter, a median sternotomy was performed instead of a thoracotomy, and a left pneumothorax was diagnosed and released by pleural opening. This was followed by rapid conversion of the atrial fibrillation into sinus rhythm and restoration of normal blood pressure. During one-lung ventilation, barotrauma from excessive tidal volume and high airway pressure may occur if a left-sided DLT is positioned distally such that the entire tidal volume is directed to only one lobe.1Silvalingam P. Tio R. Tension pneumothorax, pneumomediastinum, pneumoperitoneum, and subcutaneous emphysema in a 15-year-old Chinese girl after a double-lumen tube intubation and one-lung ventilation.J Cardiothorac Vasc Anesth. 1999; 13: 312-315Abstract Full Text PDF PubMed Scopus (34) Google Scholar, 2Malik S. Shapiro W.A. Jablons D. et al.Contralateral tension pneumothorax during one-lung ventilation for lobectomy: Diagnosis aided by fiberoptic bronchoscopy.Anesth Analg. 2002; 95: 570-572PubMed Google Scholar In our patient, high peak airway pressure may have been generated during manual ventilation to check the DLT position, which was placed too distal. The average depth of insertion for patients 170 cm tall was 29 cm, and for each 10-cm increase or decrease in height, the average placement depth was increased or decreased 1 cm.3Brodsky J.B. Benumof J.L. Ehrenwerth J. et al.Depth of placement of left double-lumen endobronchial tubes.Anesth Analg. 1991; 73: 570-572Crossref PubMed Scopus (95) Google Scholar A pneumothorax presents as increased airway pressure, decreased tidal volume, decreased SpO, and hypotension. Sudden-onset atrial fibrillation may occur for a variety of reasons during anesthesia. Our patient developed rapid-rate atrial fibrillation with hypotension, probably as a complication of the pneumothorax, which was diagnosed only after sternotomy. Had we initiated one-lung ventilation, cardiovascular collapse would have developed. Previous reports showed that a pneumothorax may be associated with numerous electrocardiographic changes.4Price J.W. Novel electrocardiographic changes associated with iatrogenic pneumothorax.Am J Crit Care. 2006; 15: 415-419PubMed Google Scholar, 5Strizik B. Forman R. New ECG changes associated with a tension pneumothorax.Chest. 1999; 115: 1742-1744Crossref PubMed Scopus (37) Google Scholar The sudden rise in intrathoracic pressure and rotation around the longitudinal axis of the heart has been suggested as a cause of these changes. A proposed mechanism for PR-segment changes is atrial ischemia caused by compression of air on the collapsed lung and subsequently on the heart. In our patient, a shift in heart position secondary to the pneumothorax in addition to the atrial enlargement may have predisposed to this mechanical irritation and subsequent atrial fibrillation. In conclusion, we report a case of atrial fibrillation complicating a left pneumothorax that was caused by barotrauma after malpositioning of a DLT in the presence of an ASD. Atrial fibrillation was reverted by releasing the pneumothorax. The diagnosis of a pneumothorax should be considered during DLT insertion whenever a patient develops cardiovascular instability.

A comparison of the Glidescope® to the McGrath® videolaryngoscope in patients

BackgroundThe Glidescope® videolaryngoscope is a new device for tracheal intubation that provides an improved view of the larynx. This study was performed to compare the Glidescope with the McGrath videolaryngoscope in terms of time to intubation (TTI) and number of attempts.MethodsPatients were randomly allocated to one of two groups, Glidescope or McGrath group, by using computer-generated numbers. Tracheal intubation was attempted by an anesthesiologist with extensive experience using these two devices. The operator recorded ease of visualization of glottic structures based on the classification described by Cormack and Lehane. Number of failures, number of attempts and their duration, total intubation time, and events during the whole procedure were recorded. The duration of one attempt was defined as the time elapsed between picking up the endotracheal tube and verification of tracheal intubation with visualization of three expiratory carbon dioxide waveforms. TTI was defined as the sum of the duration of all intubation attempts (as many as three), excluding preoxygenation procedures.ResultsTTI was significantly shorter for the Glidescope® compared to the McGrath® laryngoscope (40.5 vs. 53.3 s, respectively, P < 0.05). However, glottic views obtained at intubation were similar between the two groups. Number of intubation attempts was not significantly different between the two groups (1.03 ± 0.19 vs 1.10 ± 0.32, respectively) (mean ± SD).ConclusionsStudy results demonstrated that the Glidescope reduced total intubation time in comparison with the McGrath, in terms of TTI in patients with normal airways.

Comparison of ETT and LMA on Respiratory Mechanics during the Induction of General Anesthesia in Children

Background: Laryngeal mask airway (LMA) has recently been introduced as an alternative for the endotracheal tube. The respiratory mechanics and respiratory parameters during positive pressure ventilation (PPV) via the laryngeal mask airway (LMA) are not well known in children. So, we compared the effects of the endotracheal tube and the laryngeal mask airway on respiratory mechanics during the induction of general anesthesia in children. Methods: We studied sixty ASA physical status I and II healthy children undergoing general anesthesia. Anesthesia was induced with sleep dose ketamine 1.0 mg/kg i.v., supplemented with propofol 2 mg/kg, Rocuronium 1.0 mg/kg i.v and maintained with 50% nitrous oxide and 2.0 Vol% sevoflurane. After inserting the laryngeal mask airway, its cuff was inflated using a balloon cuff gauge until the intracuff pressure reached approximately 60 cmH2O. Adequacy of ventilation was assessed by observing the end tidal carbon dioxide wave form, chest wall movement, and by stethoscope auscultation. Data were collected with lung mechanics recorders (Ventcheck, Novametrix Medical System, U.S.) at 5 and 10 minutes after intubation or LMA insertion. The data included Peak Inspiratory Pressure (PIP), Mean Airway Pressure (MAP), Peak End Expiratory Pressure (PEEP), Inspired Tidal Volume (VTins), Expired Tidal Volume (VTexp), Airway resistance (Raw), and Compliance (Cdyn). Results: No significant difference was observed between the airway pressures, tidal volumes and gas leak fractions of the ETT and LMA groups. In terms of airway resistance and compliance, significant differences were observed between the two groups at 5 and 10 minutes. Conclusions: We conclude that the laryngeal mask airway is superior to endotracheal intubation in terms of airway resistance and compliance. The laryngeal mask airway offer an alternative for the children needing to avoid intubation under general anesthesia.

Efficacy of the Laryngeal Tube in General Anesthesia

Background: A prototype airway management device, a laryngeal tube, has been recently introduced in Korea. This study was designed to assess the efficacy of the laryngeal tube for airway management under general anesthesia. Methods: We studied thirty-six ASA physical status I and II patients undergoing general anesthesia. Anesthesia was induced with sleep dose propofol 2.0 mg/kg i.v., supplemented with fentanyl 1/kg, and maintained with 50% nitrous oxide and propofol. After inserting the laryngeal tube, its cuff was inflated using a balloon cuff gauge until the intracuff pressure reached approximately 65 cm. Adequacy of ventilation was assessed by observing the end tidal carbon dioxide wave form, chest wall movement and by stethoscope auscultation. Oropharyngeal leak pressure was also measured. Changes in heart rate, blood pressure, end-tidal carbon dioxide, airway pressure and oxygen saturation before induction, before insertion, 2, 5 and 10 minutes after insertion and 5 minutes after incision were recorded. Results: The first time success rate at achieving an effective airway was 30 in 36 (83%). The mean leak pressure was 22.9 4.6 mmHg. Heart rate, blood pressure, oxygen saturation, end-tidal carbon dioxide and airway pressure values remained stable during laryngeal tube insertion and during the surgical procedure. Conclusions: We conclude that the laryngeal tube is easy to place, allows adequate ventilation and has a lower incidence of complications. It may offer an alternative device for the oxygenation of non-intubated patients undergoing general anesthesia.

Cost-Benefit Analysis of Nasal Cannulae in Non-Tracheally Intubated Subjects

We evaluated four nasal cannulae used to deliver oxygen and measure PETC02 in a non-tracheally intubated, healthy population. The effect of various oxygen flow rates on PETC02 and respiratory rate (RR), as well as the cost and relative patient comfort of the cannulae, was compared. In this controlled study, 20 healthy volunteers tested the cannulae using oxygen flow rates of 0 (breathing room air), 2, 4, and 6 L/min. The volunteers rated the comfort of each cannula on a scale from 1 (uncomfortable) to 10 (comfortable). Hospital costs of the cannulae were also compared. All of the cannulae, except the Hospitak nasal cannula (HOS), demonstrated an oxygen flow dependency with respect to PETC02 and RR. The HOS cannula was judged by the study population to be the most comfortable and was the second least expensive cannula tested. From a qualitative standpoint, the carbon dioxide waveform recorded with the HOS cannula was the one least affected by oxygen flow. Of the nasal cannula systems evaluated in this study, the HOS system demonstrated the best cost-benefit ratio, performing well clinically while being comfortable to wear and relatively inexpensive. These conclusions are specific to a healthy population and not to patients with lung disease,those who smoke, or those having a higher ASA classification status. Our evaluation suggests that comfort and clinical performance of nasal cannulae may well depend on device design.

HOW THE RISE TIME OF CARBON DIOXIDE ANALYSERS INFLUENCES THE ACCURACY OF CARBON DIOXIDE MEASUREMENTS

Carbon dioxide measurements are not accurate, especially in children, if the response time of the carbon dioxide analyser is too slow and its output fails to reach the actual carbon dioxide concentration at the end of the breath. The distortion of the carbon dioxide waveform is a function of the "rise time" of the analyser. We have simulated an expired carbon dioxide curve and calculated the rise time required to measure accurately end-tidal carbon dioxide and VCO2 in adults and children. A rise time of 80 ms (10-70%) is sufficient to measure end-tidal carbon dioxide concentration with 5% accuracy in patients with rates of ventilation less than 100 b.p.m. and I:E ratios less than 2:1. We have measured the rise time of 11 commercially available carbon dioxide analysers and found that only six of the 11 responded quickly enough to be accurate for rates up to 100 b.p.m. All 11 responded rapidly enough to measure end-tidal carbon dioxide concentration with 5% accuracy when ventilatory rates were less than 30 b.p.m. To measure VCO2 with 5% accuracy, an analyser should have a rise time of 20 ms. Only one analyser met this specification. An analyser's rise time can be estimated clinically to within 10 (SD 8) ms by a simple breath hold and forced exhalation, thus providing an estimate of the accuracy of carbon dioxide measurements in adults or children.

A carbon dioxide monitor that does not show the waveform is worthless.

The author suggests that the carbon dioxide waveform should be displayed, as are the electrocardiogram and arterial pressure waveforms. He argues that a carbon dioxide analyzer that does not provide a waveform is not of value, as subtle changes in the carbon dioxide waveform can reflect impending problems. Only when a plateau is present in the capnogram can one be certain that end-tidal gas is being measured, and the author asserts that the presence or absence of this plateau can be detected only by visually inspecting the waveform.

Computer-assisted capnogram analysis.

Characteristic abnormal carbon dioxide waveforms from patients with mechanically ventilated lungs are observed when, for example, valves are incompetent, the airway is obstructed, the breathing circuit becomes disconnected, or a patient overrides mechanical ventilation with spontaneous breaths. Automated observation of the carbon dioxide waveform provides a uniform, concise, and consistent interpretation of the capnogram. This article describes a computer algorithm for analyzing and classifying capnograms as normal or as belonging to one of the categories above. The algorithm also generates a diagnostic message when the capnogram deviates from a learned norm for at least three consecutive waveforms (and thus reduces the influence of artifacts). Clinical experience shows reliable waveform recognition by the algorithm.