Evaluation of a transportable capnometer for monitoring end‐tidal carbon dioxide

Mayo Clinic, Rochester, Minnesota. roy.tk@mayo.eduCapnography: Clinical Aspects. Edited by J. S. Gravenstein, M.D., Dr. med. h.c., Michael B. Jaffe, Ph.D., and David A. Paulus, M.D. Cambridge, United Kingdom, Cambridge University Press, 2004. Pages: 441. Price: $120.00.Practicing anesthesiologists and intensivists have come to take capnography for granted in the monitoring of surgical and critically ill patients. Although many standard anesthesiology texts contain a chapter about this important and useful technique, a comprehensive up-to-date treatment of the subject is not easy to find. Capnography: Clinical Aspects fills this void.The book is a multiauthored effort edited by two academicians and an engineer working in industry. The editors acknowledge significant overlap between chapters and characterize the book as more of a “symposium” than a textbook. There is adequate continuity of style between chapters, but as with any book written in this format, some chapters are more interesting to read than others.The book is organized into four parts. The first part is meant to be clinical and describes the interaction of respiratory, cardiovascular, and metabolic systems in determining the amount of exhaled carbon dioxide as measured by capnography. This is followed by parts on basic carbon dioxide physiology, the history of capnography, and the technology of capnography.The clinical part is divided into four sections: Ventilation, Circulation, Metabolism, and Organ Effects. The ventilation section is further divided into subsections on breathing assessment, airway management, monitoring of ventilation, weaning, and special situations. The first chapter (written by two of the editors) is a well-written introduction to time-based capnogram interpretation, the most commonly used form of capnography in the operating room setting. Of particular value is the introduction to the volume-based capnogram, a topic not commonly detailed in anesthesia texts. Subsequent chapters discuss capnography outside the operating room and in the prehospital setting for airway management, in particular to confirm tracheal intubation. The chapter on airway management in the intensive care unit includes a section on using capnography to confirm proper orogastric and nasogastric tube placement. The chapter on airway management in the operating room includes sections on confirming tracheal intubation and recognizing endobronchial tube placement.The chapter describing the use of capnography to monitor ventilation during anesthesia includes interesting comments on the Food and Drug Administration checkout relevant to capnography. This chapter also includes sections on equipment troubleshooting and how capnograms can be affected by positioning, pulmonary pathology, and several particular situations such as one-lung ventilation, laparoscopy, neurosurgery, cardiac surgery, tourniquet release, and high-frequency jet ventilation. Other chapters in this section focus on the use of capnography during transport and how it can be used in the field as a way to avoid deleterious effects of unintentional hyperventilation after intubation.A particularly comprehensive chapter describes the unique physiology and technological limitations of capnography in neonates and infants. Other chapters describe capnography in the sleep laboratory, capnography as a feedback tool for behavioral therapy in various disorders, and how the capnogram is affected by alterations in physiologic and technical limitations in high- and low-pressure environments.Chapters are also included on sedation and noninvasive ventilation. These chapters are valuable for their descriptions of how end-tidal carbon dioxide can be sampled during spontaneous ventilation in nonintubated patients and the clinical utility and limitations of end-tidal carbon dioxide as a method of estimating arterial carbon dioxide tension (PCO2) in noninvasive ventilation.Chapters relevant to critical care describe the use capnography to optimize tidal volume, alveolar minute ventilation, and positive end-expiratory pressure to wean patients from mechanical ventilation. These chapters also describe the use of volumetric capnography to assess carbon dioxide production and how the capnogram is affected by positive end-expiratory pressure, unilateral lung injury, tracheal gas insufflation, and various high-frequency ventilation modes.The circulation subsection includes chapters on how end-tidal carbon dioxide monitoring can be used to assess circulatory status during cardiopulmonary resuscitation and for prognostication during cardiac arrest in medical patients as well as the use of end-tidal and tissue carbon dioxide monitoring techniques to assess oxygen delivery in shock states. This section includes an elegant physiologic description of changes in alveolar dead space with pulmonary embolism and the use of capnography in diagnosis and treatment of pulmonary emboli and gas embolization in addition to a chapter on the utility of volumetric capnography for estimating arterial PCO2in patients with acute respiratory distress syndrome.The chapter on noninvasive pulmonary blood flow measurement describes complete and partial carbon dioxide rebreathing techniques as alternatives to invasive cardiac output monitoring. A variety of clinical scenarios illustrating the use of these techniques sets this chapter apart from other descriptions of this topic.The metabolism subsection includes a single chapter describing alterations in normal physiology induced by surgery and anesthesia that affect carbon dioxide elimination. The chapter discusses alterations in ventilation, circulation, and carbon dioxide metabolism that are influenced by temperature alterations, various anesthetic techniques, and pharmacologic agents as well as particular intraoperative situations such as laparoscopy, tourniquet release, vascular cross clamping, and cardiopulmonary bypass.The final chapter of the ventilation section describes the effects of hypercapnia and hypocapnia on tissue oxygenation and perfusion, focusing on the central nervous system, respiratory system, and cardiovascular system. This is an excellent introduction to the effect of carbon dioxide at the organ, tissue, and cellular/molecular level and could have been included in the section on physiology.The physiology section includes a chapter on carbon dioxide pathophysiology, which describes inherited and acquired mitochondrial and enzyme disorders as well as pharmacologic agents that alter carbon dioxide production. The chapter also discusses carbon dioxide embolism and the increase in PCO2during apnea testing for brain death. There is a complete if somewhat standard chapter on acid–base physiology, followed by an excellent description of how capnography can provide information on ventilation/perfusion mismatch from a physiologic standpoint, including examples of various disease states. Subsequent chapters describe clinical correlates of alterations in normal time and volume capnographic tracings and how capnograms can provide clues to the underlying pathophysiology.A particularly interesting chapter in this section summarizes a biomedical engineering approach to illustrate the underlying anatomical and physiologic processes that result in a normal volumetric capnogram. A mathematical model that accounts for bronchial airway structure, gas convection and diffusion, and the carbon dioxide release from alveolar capillary blood is shown to generate a computed washout curve that shows remarkable agreement with an experimentally measured capnogram from a healthy human subject. This illustrates the utility of physiologic modeling as a useful tool for investigating potentially complex pathophysiologies without placing patients at risk.A unique historical section describes the evolution of time and volumetric capnography with many interesting anecdotes, as well as a first-person account by Smalhout, an early proponent of capnography. A selection of capnographic tracings corresponding to clinical events that he made over a 20-yr period is one of the highlights of this book. Without reading this section of the book, few people would realize that the impetus for carbon dioxide analyzer development was to investigate the cause of death in patients who turned out to be rebreathing due to a channeling issue through carbon dioxide absorption devices, or that carbon dioxide analyzers enabled a reduction in mortality for polio patients by allowing clinicians to titrate ventilation to expired carbon dioxide instead of adjusting ventilation based on their weight.The technological section fulfills the editors’ wishes for providing clinicians with information necessary to appreciate the mechanism, design, and limitations of devices for measuring carbon dioxide. Various chapters address technical specifications and standards (e.g. , accuracy, range, drift, response time, interfering gases, alarm systems, calibration) for carbon dioxide analyzers and describe technological limitations for flow measurement, required to estimate carbon dioxide production. Another chapter describes various methods for carbon dioxide detection, including infrared, photoacoustic, colorimetric, and mass spectrometry methods. Unfortunately, Raman spectroscopy is not included simply because it is not currently commercially available. This chapter also includes a discussion of mainstream versus sidestream carbon dioxide analyzers.The book ends with a mini-atlas of capnographic waveforms typifying various physiologic states, which is useful although not exhaustive.As the editors acknowledge, there is a fair amount of redundancy; as an example, the fact that highly sensitive colorimetric carbon dioxide indicators can yield false positives with esophageal intubation is mentioned in multiple chapters along with the fact that false negatives in cardiac arrest have led to the removal of correctly placed endotracheal tubes. Other recurring themes include the predictive value of end-tidal carbon dioxide in assessing arterial PCO2and the utility of volumetric capnography. In general, I found the multiple perspectives to be helpful instead of confusing or irritating. As with any book, the onus is on the reader to formulate his or her judgment with the assistance of the most recent literature.The overall introduction to the book and the introduction chapters for each section are very short and could have been used to provide the reader with a more substantial description of the basic concepts or objectives of each section. The section and subsection titles are somewhat arbitrary, and some chapters are in fact assigned to their own sections. Although the terminology is relatively consistent, the book could also use a more comprehensive list of abbreviations and acronyms used in various chapters. I found most of the typographical and page-setting errors to be minor (with the exception of a reference to “title” volumes). In spite of these limitations, the book admirably maintains its focus on capnography; readers interested in the latest tissue oxygen tension (PO2) monitoring techniques, for example, will have to look elsewhere.In summary, Capnography: Clinical Aspects is a very readable introduction to a topic addressed by few textbooks. It is useful as a reference primarily because of its comprehensive index and contains much information useful to the practitioner of critical care as well as anesthesiology. It addresses the physiologic and technological considerations that need to be understood to make capnography a clinically useful tool and should be standard reading for those who depend on it as a basic anesthetic monitor.Mayo Clinic, Rochester, Minnesota. roy.tk@mayo.edu

Monitoring carbon dioxide in patients on mechanical ventilation is crucial for critical care nurses. Monitoring the value of arterial carbon dioxide pressure involves invasive arterial blood gas analysis. Monitoring end-tidal carbon dioxide pressure using capnography is a non-invasive method. This study aims to compare end-tidal carbon dioxide values with arterial carbon dioxide pressure in mechanically ventilated patients. The research design is a literature review. Searches were conducted through Scopus, ScienceDirect, ProQuest, and PubMed from 2018 to 2023. The Preferred Reporting Items for Systematic Review and Meta-Analyses flowchart method was used to select articles. The Critical Appraisal Skills Programme was used to assess article quality. Out of 79 articles, nine articles met the criteria. The procedures for collecting end-tidal carbon dioxide pressure and arterial carbon dioxide pressure data varied in terms of instrument types used and the subjects studied. There was no significant difference in carbon dioxide values between the end-tidal carbon dioxide and arterial carbon dioxide pressure methods. The agreement in comparing carbon dioxide values was acceptable. Measuring end-tidal carbon dioxide pressure has the potential to monitor mechanically ventilated patients, reducing the need for invasive monitoring, high costs, and repetitive arterial blood gas analysis.

IntroductionPrognosis in patients suffering out-of-hospital cardiac arrest is poor. Higher survival rates have been observed only in patients with ventricular fibrillation who were fortunate enough to have basic and advanced life support initiated soon after cardiac arrest. An ability to predict cardiac arrest outcomes would be useful for resuscitation. Changes in expired end-tidal carbon dioxide levels during cardiopulmonary resuscitation (CPR) may be a useful, noninvasive predictor of successful resuscitation and survival from cardiac arrest, and could help in determining when to cease CPR efforts.MethodsThis is a prospective, observational study of 737 cases of out-of-hospital cardiac arrest. The patients were intubated and measurements of end-tidal carbon dioxide taken. Data according to the Utstein criteria, demographic information, medical data, and partial pressure of end-tidal carbon dioxide (PetCO2) values were collected for each patient in cardiac arrest by the emergency physician. We hypothesized that an end-tidal carbon dioxide level of 1.9 kPa (14.3 mmHg) or more after 20 minutes of standard advanced cardiac life support would predict restoration of spontaneous circulation (ROSC).ResultsPetCO2 after 20 minutes of advanced life support averaged 0.92 ± 0.29 kPa (6.9 ± 2.2 mmHg) in patients who did not have ROSC and 4.36 ± 1.11 kPa (32.8 ± 9.1 mmHg) in those who did (P < 0.001). End-tidal carbon dioxide values of 1.9 kPa (14.3 mmHg) or less discriminated between the 402 patients with ROSC and 335 patients without. When a 20-minute end-tidal carbon dioxide value of 1.9 kPa (14.3 mmHg) or less was used as a screening test to predict ROSC, the sensitivity, specificity, positive predictive value, and negative predictive value were all 100%.ConclusionsEnd-tidal carbon dioxide levels of more than 1.9 kPa (14.3 mmHg) after 20 minutes may be used to predict ROSC with accuracy. End-tidal carbon dioxide levels should be monitored during CPR and considered a useful prognostic value for determining the outcome of resuscitative efforts and when to cease CPR in the field.

The Editors’ Choice

Newborns may require ventilatory support after birth; hence, confirmation of correct tracheal tube placement is vital. The most suitable method to determine intubation success and monitoring of carbon dioxide is a matter of contention, specifically regarding the use of capnography in the newborn population. In 2018, a UK survey on airway management in neonatal intensive care reported that only 18% of units always used capnography during neonatal tracheal intubations. The authors made recommendations for waveform capnography to be available and more widely implemented in order to improve safety [1]. Such recommendations, however, were extrapolated from studies in adult intensive care. The results of that survey [1] were thus met with scepticism from members of the British Association of Perinatal Medicine (BAPM), which highlighted differences in physiological characteristics of newborn infants compared with adults. Furthermore, BAPM emphasised alternative techniques in determining intubation success in neonates, such as qualitative colorimetric devices, flow sensors and clinical judgement [2]. The development of devices more suitable for use in newborns has subsequently provided clinicians with the means to continuously and non-invasively monitor carbon dioxide during resuscitation and mechanical ventilation. Novel capnographs are lightweight and have a small dead space, and are thus ideal for use in the newborn population. Indeed end-tidal carbon dioxide (ETCO2) values from small dead space sidestream capnographs have been shown to accurately reflect alveolar carbon dioxide levels in a cohort of healthy infants [3]. Capnography could also be utilised to alert clinicians to changing pulmonary pathology, with greater divergence of the end-tidal, compared with the arterial, carbon dioxide in those with more severe disease [4]. We therefore aimed to describe current clinical practice in UK neonatal units with respect to non-invasive carbon dioxide monitoring, specifically the use of capnography. All level two and level three neonatal ICUs (151 units) within the UK were identified from the BAPM Neonatal Network. The survey took place between January and May 2021 using a structured online questionnaire. Units that did not complete the survey online were followed-up with a maximum of three telephone calls by a member of the research team, with responses sought from senior clinical staff (as a minimum a registrar or band 7 nurse). A total of 126 (83.4%) units provided a complete response, 72/80 (90%) were level two and 54/71 (76.1%) were level three units. A total of 104 (82.5%) units reported monitoring carbon dioxide during all intubations. Seventy-nine (62.7%) units utilised colorimetric devices to confirm tracheal tube placement. Thirty-five (27.8%) reported use of continuous capnography monitoring, of which 10 (7.9%) also used qualitative colorimetry. Videolaryngoscopy was used to confirm successful intubation in 26 (20.6%) units. Furthermore, 23 (18.3%) confirmed tracheal tube position using clinical interpretation and chest radiography. Regarding the utility of capnography on the neonatal unit, 43 (34.1%) confirmed it formed part of routine clinical care. Specific criteria and other clinical settings for capnography use are shown in Table 1. Regarding capnography interpretation during day-to-day practice in neonatal intensive care, 14 (32.6%) units utilised only the ETCO2 value, six (13.9%) evaluated the carbon dioxide waveform trace and 21 (49%) reported evaluating both the ETCO2 value and the waveform in combination. Thirty-nine (30.9%) confirmed that capnography was part of their difficult airway trolley. We found that exhaled carbon dioxide monitoring during tracheal intubation was undertaken by over 80% of neonatal units in the UK, with the majority utilising qualitative methods. Previous concern was expressed over the lack of routine monitoring of exhaled carbon dioxide during neonatal intubation [1]; however, the 2018 survey considered only capnography to be an appropriate monitoring tool. Our results demonstrate that neonatal intensivists do now routinely monitor carbon dioxide during tracheal intubation, utilising either qualitative or quantitative methods. Indeed, one colorimetric ETCO2 device was shown to be 91% sensitive and 100% specific in confirming tracheal tube placement during neonatal resuscitation [5]. Quantitative waveform analysis during newborn resuscitation has, however, been shown to detect ETCO2 more rapidly than qualitative methods [6]. In conclusion, exhaled carbon dioxide during tracheal intubation is now monitored in the majority of neonatal units, but this is usually undertaken by qualitative methods despite increasing evidence that the new capnography devices are useable and accurate in the neonatal population. EW was supported by a grant from the Charles Wolfson Charitable Trust and a non-conditional educational grant from SLE. This research was supported by the National Institute for Health Research Biomedical Research Centre at Guy's and St Thomas' NHS Foundation Trust and King's College London. No competing interests declared.

The laryngeal mask airway (LMA) has become a popular tool for airway management in selected adult and pediatric patients undergoing routine surgical procedures. The relationship between end-tidal and arterial carbon dioxide during controlled ventilation via the LMA in infants under 10 kg has not been reported. After induction of general anesthesia, the LMA was placed in 12 healthy infants and mechanical ventilation initiated. After maintaining steady-state level of end-tidal carbon dioxide (minimum 5 min), an arterial blood sample was obtained and end-tidal carbon dioxide level noted. The laryngeal mask was then removed, the trachea intubated, and mechanical ventilation resumed with initial ventilatory variables. After reaching a steady-state level of end-tidal carbon dioxide, a second arterial sample was obtained and end-tidal carbon dioxide level noted. The mean end-tidal carbon dioxide and arterial partial pressure of carbon dioxide obtained during ventilation were 42.2 +/- 7.9 and 47.1 +/- 11.0 (LMA) and 37.4 +/- 4.6 and 42.6 +/- 6.7 (endotracheal tube), respectively. Analysis of differences between partial pressure of carbon dioxide and end-tidal carbon dioxide using the Bland and Altman method revealed bias+/-precision of 4.9 +/- 3.9 and 5.3 +/- 3.2 with ventilation via the laryngeal mask and endotracheal tube. Our data indicate that, while ventilating infants under 10 kg with LMA, end-tidal carbon dioxide is an accurate indicator of arterial partial pressure of carbon dioxide.

The laryngeal mask airway (LMA) has become a popular tool for airway management in selected adult and pediatric patients undergoing routine surgical procedures.The relationship between end-tidal and arterial carbon dioxide during controlled ventilation via the LMA in infants under 10 kg has not been reported. After induction of general anesthesia, the LMA was placed in 12 healthy infants and mechanical ventilation initiated. After maintaining steady-state level of end-tidal carbon dioxide (minimum 5 min), an arterial blood sample was obtained and end-tidal carbon dioxide level noted. The laryngeal mask was then removed, the trachea intubated, and mechanical ventilation resumed with initial ventilatory variables. After reaching a steady-state level of end-tidal carbon dioxide, a second arterial sample was obtained and end-tidal carbon dioxide level noted. The mean end-tidal carbon dioxide and arterial partial pressure of carbon dioxide obtained during ventilation were 42.2 +/- 7.9 and 47.1 +/- 11.0 (LMA) and 37.4 +/- 4.6 and 42.6 +/- 6.7 (endotracheal tube), respectively. Analysis of differences between partial pressure of carbon dioxide and end-tidal carbon dioxide using the Bland and Altman method revealed bias +/- precision of 4.9 +/- 3.9 and 5.3 +/- 3.2 with ventilation via the laryngeal mask and endotracheal tube. Our data indicate that, while ventilating infants under 10 kg with LMA, end-tidal carbon dioxide is an accurate indicator of arterial partial pressure of carbon dioxide. (Anesth Analg 1997;84:51-3)

Hyperventilation is a frequently used method for inducing hypercarbia in neurosurgical patients. This practice requires careful carbon dioxide monitoring that might be replaced by a less expensive and less invasive alternative to arterial blood gas monitoring. To determine the accuracy of end-tidal carbon dioxide monitoring in hyperventilated neurosurgical patients. Nineteen adult patients requiring hyperventilation for the reduction of intracranial pressure following head injury or neurosurgery were enrolled from the surgical intensive care unit of a level I trauma center. A correlation design was used to compare arterial carbon dioxide tensions and end-tidal carbon dioxide measurements during specific periods; secondary analysis with bias and precision estimates was performed. Also, changes in arterial carbon dioxide tensions were compared with simultaneous changes in end-tidal carbon dioxide values. End-tidal carbon dioxide values showed a moderately acceptable correlation with arterial blood gas measurements. However, changes in end-tidal carbon dioxide values failed to correlate with simultaneous changes in arterial carbon dioxide tension measures. Bias and precision measures confirmed these findings. In this patient sample, changes in end-tidal carbon dioxide values did not accurately reflect changes in arterial carbon dioxide tension levels in the intensive care setting. Further technological advances in noninvasive carbon dioxide monitoring may lead to a significant cost savings over traditional arterial blood gas analysis.

Increased respiratory drive as an inhibitor of oral feeding of preterm infants

Objective. To determine factors which influenced the relationship between blood carbon dioxide (pCO2) and end-tidal carbon dioxide (EtCO2) values in ventilated, newborn infants. Furthermore, to assess whether pCO2 levels could be predicted from continuous EtCO2 monitoring. Approach. An observational study of routinely monitored newborn infants requiring mechanical ventilation in the first 28 d after birth was undertaken. Infants received standard clinical care. Daily pCO2 and EtCO2 levels were recorded and the difference (gradient: ∆P-EtCO2) between the pairs were calculated. Ventilatory settings corresponding to the time of each blood gas assessment were noted. End-tidal capnography monitoring was performed using the Microstream sidestream Filterline H set capnograph. Main results. A total of 4697 blood gas results from one hundred and fifty infants were analysed. The infants had a median gestational age of 33.3 (range 22.3–42.0) weeks and birth weight of 1880 (395–5520) grams. Overall, there was moderate correlation between pCO2 and EtCO2 levels (r = 0.65, p < 0.001). The ∆P-EtCO2 for infants born less than 32 weeks of gestation was significantly higher (1.4 kPa) compared to infants born at greater than 32 weeks of gestation (0.8 kPa) (p < 0.001). In infants born at less than 32 completed weeks of gestation, pCO2 levels were independently associated with EtCO2, day after birth, birthweight and fraction of inspired oxygen (FiO2) (model r 2 = 0.52, p < 0.001). Significance. The results of end-tidal capnography monitoring have the potential to predict blood carbon dioxide values within the neonatal population.

Identification of patients’ fluid status in the emergency room should be made before giving fluid therapy. This study aimed to determine the effect of positive end-expiratory pressure on change in end-tidal carbon dioxide during passive leg raising maneuver to predict fluid responsiveness. Thirty subjects aged 18-65 years in the resuscitation room, all on the ventilator, were divided into three groups according to their positive end-expiratory pressure value: low (0-5 cmH2O), moderate (6-10 cmH2O), and high (&gt;10 cmH2O). Every subject underwent passive leg raising to simulate fluid administration. Values of blood pressure, heart rate, cardiac output, and end-tidal carbon dioxide were recorded before and after the maneuver. Analysis of the three groups found a significant correlation between change in end-tidal carbon dioxide with a cut-off value of 5% and 1 mmHg with fluid responsiveness of subjects in the low (p = 0.028) and moderate (p = 0.013) but not in the high positive end-expiratory pressure group (p = 0.333). In conclusion, change in end-tidal carbon dioxide in mechanically ventilated patients undergoing passive leg raising maneuvers can be used as a predictor of fluid responsiveness, but this method cannot be used on patients with high positive end-expiratory pressure (&gt; 10 cmH2O) Keywords : change in end tidal carbon dioxide, fluid responsiveness, positive end-expiratory pressure, passive leg raising, cardiac output surrogateCorrespondence : lutfithe13th@gmail.com

End-tidal carbon dioxide (ETCO2) values obtained from awake nonintubated patients may prove to be useful in estimating a patient's ventilatory status. This study examined the relationship between arterial carbon dioxide tension (PaCO2) and ETCO2 during the preoperative period in 20 premedicated patients undergoing various surgical procedures. ETCO2 was sampled from a 16-gauge intravenous catheter pierced through one of the two nasal oxygen prongs and measured at various oxygen flow rates (2, 4, and 6 L/min) by an on-line ETCO2 monitor with analog display. Both peak and time-averaged values for ETCO2 were recorded. The results showed that the peak ETCO2 values (mean = 38.8 mm Hg) correlated more closely with the PaCO2 values (mean = 38.8 mm Hg; correlation coefficient r = 0.76) than did the average ETCO2 values irrespective of the oxygen flow rates. The time-averaged PaCO2-ETCO2 difference was significantly greater than the PaCO2-peak ETCO2 difference (P less than 0.001). Values for subgroups within the patient population were also analyzed, and it was shown that patients with minute respiratory rates greater than 20 but less than 30 and patients age 65 years or older did not differ from the overall studied patient population with regard to PaCO2-ETCO2 difference. A small subset of patients with respiratory rates of 30/min or greater (n = 30) did show a significant increase in the PaCO2-ETCO2 difference (P less than 0.001). It was concluded that under the conditions of this study, peak ETCO2 values did correlate with PaCO2 values and were not significantly affected by oxygen flow rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Resuscitation highlights in 2013: Part 2

Controlling arterial carbon dioxide is paramount in mechanically ventilated patients, and an accurate and continuous noninvasive monitoring method would optimize management in dynamic situations. In this study, we validated and further refined formulas for estimating partial pressure of carbon dioxide with respiratory gas and pulse oximetry data in mechanically ventilated cardiac arrest patients. A total of 4741 data sets were collected retrospectively from 233 resuscitated patients undergoing therapeutic hypothermia. The original formula used to analyze the data is PaCO2 -est1=PETCO2 +k[(PIO2 -PETCO2 )-PaO2 ]. To achieve better accuracy, we further modified the formula to PaCO2 -est2=k1 *PETCO2 +k2 *(PIO2 -PETCO2 )+k3 *(100-SpO2 ). The coefficients were determined by identifying the minimal difference between the measured and calculated arterial carbon dioxide values in a development set. The accuracy of these two methods was compared with the estimation of the partial pressure of carbon dioxide using end-tidal carbon dioxide. With PaCO2 -est1, the mean difference between the partial pressure of carbon dioxide, and the estimated carbon dioxide was 0.08kPa (SE ±0.003); with PaCO2 -est2 the difference was 0.036kPa (SE ±0.009). The mean difference between the partial pressure of carbon dioxide and end-tidal carbon dioxide was 0.72kPa (SE ±0.01). In a mixed linear model, there was a significant difference between the estimation using end-tidal carbon dioxide and PaCO2 -est1 (P<.001) and PaCO2 -est2 (P<.001) respectively. This novel formula appears to provide an accurate, continuous, and noninvasive estimation of arterial carbon dioxide.

IntroductionClinical data considering vasopressin as an equivalent option to epinephrine in cardiopulmonary resuscitation (CPR) are limited. The aim of this prehospital study was to assess whether the use of vasopressin during CPR contributes to higher end-tidal carbon dioxide and mean arterial blood pressure (MAP) levels and thus improves the survival rate and neurological outcome.MethodsTwo treatment groups of resuscitated patients in cardiac arrest were compared: in the epinephrine group, patients received 1 mg of epinephrine intravenously every three minutes only; in the vasopressin/epinephrine group, patients received 40 units of arginine vasopressin intravenously only or followed by 1 mg of epinephrine every three minutes during CPR. Values of end-tidal carbon dioxide and MAP were recorded, and data were collected according to the Utstein style.ResultsFive hundred and ninety-eight patients were included with no significant demographic or clinical differences between compared groups. Final end-tidal carbon dioxide values and average values of MAP in patients with restoration of pulse were significantly higher in the vasopressin/epinephrine group (p < 0.01). Initial (odds ratio [OR]: 18.65), average (OR: 2.86), and final (OR: 2.26) end-tidal carbon dioxide values as well as MAP at admission to the hospital (OR: 1.79) were associated with survival at 24 hours. Initial (OR: 1.61), average (OR: 1.47), and final (OR: 2.67) end-tidal carbon dioxide values as well as MAP (OR: 1.39) were associated with improved hospital discharge. In the vasopressin group, significantly more pulse restorations and a better rate of survival at 24 hours were observed (p < 0.05). Subgroup analysis of patients with initial asystole revealed a higher hospital discharge rate when vasopressin was used (p = 0.04). Neurological outcome in discharged patients was better in the vasopressin group (p = 0.04).ConclusionEnd-tidal carbon dioxide and MAP are strong prognostic factors for the outcome of out-of-hospital cardiac arrest. Resuscitated patients treated with vasopressin alone or followed by epinephrine have higher average and final end-tidal carbon dioxide values as well as a higher MAP on admission to the hospital than patients treated with epinephrine only. This combination vasopressor therapy improves restoration of spontaneous circulation, short-term survival, and neurological outcome. In the subgroup of patients with initial asystole, it improves the hospital discharge rate.