Methods: All adult patients (>18 years) with severe head injury, maxillofacial injury with need of protection of airway, or polytrauma were intubated by an emergency physician in the field. Tube position was initially evaluated by auscultation. Then, capnometry and capnography was performed (infrared method). Emergency physicians evaluated capnogram and partial pressure of end tidal carbon dioxide (EtCO2) in millimetres of mercury. Determination of final tube placement was performed by a second direct visualisation with laryngoscope. Data are mean (SD) and percentages.
Results: There were 81 patients enrolled in this study (58 with severe head injury, 6 with maxillofacial trauma, and 17 politraumatised patients). At the first attempt eight patients were intubated into the oesophagus. Afterwards endotracheal intubation was undertaken in all without complications. The initial capnometry (sensitivity 100%, specificity 100%), capnometry after sixth breath (sensitivity 100%, specificity 100%), and capnography after sixth breath (sensitivity 100%, specificity 100%) were significantly better indicators for tracheal tube placement than auscultation (sensitivity 94%, specificity 66%, p<0.01).
Conclusion: Auscultation alone is not a reliable method to confirm endotracheal tube placement in severely traumatised patients in the prehospital setting. It is necessary to combine auscultation with other methods like capnometry or capnography.
End tidal carbon dioxide (ETCO2) monitoring is the non‐invasive measurement of exhaled CO2. The Intensive Care Society guidelines include (ETCO2) monitoring as one of the objective standards required for monitoring patients in transport, and the American Heart Association recommends that all intubations must be confirmed by some form of ETCO2 measurement. The physiological principles and technology underlying ETCO2 measurement and the clinical indication for its use in the prehospital environment are reviewed. ETCO2 monitoring has been widely established in the prehospital environment and is of particular use for verification of endotracheal tube placement. It is non‐invasive and easy to apply to breathing circuits. The units now available are compact and rugged, with extended battery operating times, which are ideally suited for prehospital use and should be considered as an essential item for advanced airway management.
End‐tidal; carbon dioxide; monitoring; prehospital; retrieval
Greater understanding of the pathophysiology of carbon dioxide kinetics during steady and nonsteady state should improve, we believe, clinical care during intensive care treatment. Capnography and the measurement of end-tidal partial pressure of carbon dioxide (PETCO2) will gradually be augmented by relatively new measurement methodology, including the volume of carbon dioxide exhaled per breath (VCO2,br) and average alveolar expired PCO2 (PA̅E̅CO2). Future directions include the study of oxygen kinetics.
airway; capnography; carbon dioxide; carbon dioxide kinetics; expirogram; nonsteady state; ventilation
Emergency physicians and intensivists are increasingly utilizing capnography and bedside echocardiography during medical resuscitations. These techniques have shown promise in predicting outcomes in cardiac arrest, and no cases of return of spontaneous circulation in the setting of sonographic cardiac standstill and low end-tidal carbon dioxide have been reported. This case report illustrates an example of such an occurrence. Our aims are to report a case of return of spontaneous circulation in a patient with sonographic cardiac standstill, electrocardiographic pulseless electrical activity, and low end-tidal carbon dioxide tensions and to place the case in the context of previous literature on this topic. Case report and brief review of the literature. In 254 cases reported, no patient has survived in the setting of sonographic cardiac standstill and low end-tidal carbon dioxide tension, making the reported case unique. This case should serve to illustrate the utility and limitations of combined cardiac sonography and end-tidal carbon dioxide measurement in determining prognosis during cardiac arrest.
Advanced cardiac life support; Echocardiography; Capnography; Case reports
Carbon dioxide has been monitored in the body using a variety of technologies with a multitude of applications. The monitoring of this common physiologic variable in medicine is an illustrative example of the different levels of evidence that are required before any new health technology should establish itself in clinical practice. End-tidal capnography and sublingual capnometry are two examples of carbon dioxide monitoring that require very different levels of evidence before being disseminated widely. The former deserves its status as a basic standard based on observational data. The latter should be considered investigational until prospective controlled data supporting its use become available. Other applications of carbon dioxide monitoring are also discussed.
biomedical technology assessment; capnography; critical care; evidence-based medicine; physiologic monitoring
In emergency settings, verification of endotracheal tube (ETT) location is important for critically ill patients. Ignorance of oesophageal intubation can be disastrous. Many methods are used for verification of the endotracheal tube location; none are ideal. Quantitative waveform capnography is considered the standard of care for this purpose but is not always available and is expensive. Therefore, this feasibility study is conducted to compare a cheaper alternative, bedside upper airway ultrasonography to waveform capnography, for verification of endotracheal tube location after intubation.
This was a prospective, single-centre, observational study, conducted at the HRPB, Ipoh. It included patients who were intubated in the emergency department from 28 March 2012 to 17 August 2012. A waiver of consent had been obtained from the Medical Research Ethics Committee. Bedside upper airway ultrasonography was performed after intubation and compared to waveform capnography. Specificity, sensitivity, positive and negative predictive value and likelihood ratio are calculated.
A sample of 107 patients were analysed, and 6 (5.6%) had oesophageal intubations. The overall accuracy of bedside upper airway ultrasonography was 98.1% (95% confidence interval (CI) 93.0% to 100.0%). The kappa value (Κ) was 0.85, indicating a very good agreement between the bedside upper airway ultrasonography and waveform capnography. Thus, bedside upper airway ultrasonography is in concordance with waveform capnography. The sensitivity, specificity, positive predictive value and negative predictive value of bedside upper airway ultrasonography were 98.0% (95% CI 93.0% to 99.8%), 100% (95% CI 54.1% to 100.0%), 100% (95% CI 96.3% to 100.0%) and 75.0% (95% CI 34.9% to 96.8%). The likelihood ratio of a positive test is infinite and the likelihood ratio of a negative test is 0.0198 (95% CI 0.005 to 0.0781). The mean confirmation time by ultrasound is 16.4 s. No adverse effects were recorded.
Our study shows that ultrasonography can replace waveform capnography in confirming ETT placement in centres without capnography. This can reduce incidence of unrecognised oesophageal intubation and prevent morbidity and mortality.
National Medical Research Register NMRR11100810230.
Bedside upper airway ultrasonography; Endotracheal intubation; Verification; Waveform capnography
Capnometry measures carbon dioxide in expired air and provides the clinician with a noninvasive measure of the systemic metabolism, circulation and ventilation. This study was carried out on patients with acute breathlessness to define the utility and role of capnometry in the emergency department.
The objectives of the study were:
To determine the correlation between end tidal CO2 and PaCO2 in non-intubated acutely breathless patients.To determine factors that influence the end tidal carbon dioxide (ETCO2).To determine the correlation between ETCO2 with PaCO2 in patients presenting with pulmonary disorders.
One hundred fifty acutely breathless patients arriving at the emergency department and fulfilling the inclusion and exclusion criteria were chosen during a 6-month study period. The patients gave written or verbal consent, and were triaged and treated according to their presenting complaints. Demographic data were collected, and the ETCO2 data were recorded. Arterial blood gas was taken in all patients. The data were compiled and analyzed using various descriptive studies from the Statistics Program for Social Studies (SPSS) version 12. Correlation between ETCO2 and PaCO2 was analyzed using the Pearson correlation coefficient. Other variables also were analyzed to determine the correlation using simple linear regression. The agreement and difference between ETCO2 and PaCO2 were analyzed using paired sample t-tests.
There is a strong correlation between ETCO2 and PaCO2 using the Pearson correlation coefficient: 0.716 and p value of 0.00 (p < 0.05). However, the paired t-test showed a mean difference between the two parameters of 4.303 with a p value < 0.05 (95% CI 2.818, 5.878). There was also a good correlation between ETCO2 and acidosis state with a Pearson correlation coefficient of 0.374 and p value 0.02 (p < 0.05). A strong correlation was also observed between ETCO2 and a hypocapnic state, with a Pearson correlation coefficient of 0.738 (p < 0.05). Weak correlation was observed between alkalosis and ETCO2, with a Pearson correlation coefficient of 0.171 (p < 0.05). A strong negative correlation was present between ETCO2 and hypercapnic patients presenting with pulmonary disorders, with a Pearson correlation coefficient of -0.738 (p < 0.05) and of -0.336 (p < 0.05), respectively.
This study shows that ETCO2 can be used to predict the PaCO2 level when the difference between the PaCO2 and ETCO2 is between 2 to 6 mmHg, especially in cases of pure acidosis and hypocapnia. Using ETCO2 to predict PaCO2 should be done with caution, especially in cases that involve pulmonary disorders and acid-base imbalance.
Capnometry; End tidal; Dyspnea; Blood gas
Spontaneous glottis closure during expiration in infants is a normal protective reflex that helps prevent alveolar and small airway collapse (due to compliant chest wall) and thereby maintains functional residual capacity. Endotracheal intubation eliminates this protective mechanism and puts the infant into the risk of hypoxaemia and hypercarbia. This report sums up the early detection of airway closure in a series of three intubated small infants undergoing surgery with general anaesthesia, by the appearance of typical pigtail shaped capnogram, associated with decreased end tidal carbon dioxide and mild hypoxaemia, which was successfully managed by early institution of positive end expiratory pressure.
Airway closure; continuous positive airway pressure end tidal carbon dioxide; glottic closure; positive end expiratory pressure; pigtail capnogram; hypercarbia; hypoxaemia
Background and Objectives:
During laparoscopy, the increase of the carbon dioxide tension may increase the synthesis of hydrochloric acid in the parietal cells of the stomach; the source of the secreted hydrogen ions is carbonic acid derived from the hydration of carbon dioxide. The present report tests this hypothesis by correlating the changes of end-tidal PCO2 (ETCO2) with the pH of the gastric juice in patients undergoing laparoscopic cholecystectomy.
40 adult patients were investigated: 20 controls, and 20 patients receiving 100 mg nizatidine intravenously, prior to surgery. In both groups, the ETCO2 was measured by capnography and the pH of the gastric juice was monitored before carbon dioxide insufflation and at the end of laparoscopy prior to carbon dioxide deflation.
In the control group, the ETCO2 increased following carbon dioxide insufflation from a mean basal value of 30.2 (standard deviation [SD] 4.6) mm Hg to 41.1 (SD 9.5) mm Hg, while the mean pH of the gastric juice decreased significantly from 1.9 (SD 0.4) to 1.27 (SD 0.43). There was a significant negative correlation between the ETCO2 and pH of the gastric juice (r=-0.4). In the Nizatidine group, the ETCO2 also increased following carbon dioxide insufflation from a mean basal value of 30.9 (SD 3.0) mm Hg to 39.4 (SD 5.3) mm Hg. However, in contrast with the control group, the mean pH of the gastric juice did not decrease, but paradoxically increased from 1.68 (SD 0.36) to 3.6 (SD 1.02).
During laparoscopy, the pH of the gastric juice is significantly decreased. This decrease is inversely related to the increase of ETCO2. The preoperative administration of the selective H2-blocker nizatidine can prevent the increase in gastric acidity and can result in a paradoxical increase of pH of the gastric juice.
Laparoscopy; Cholecystectomy; Carbon dioxide; Capnography; H2-blocker; Nizatidine; Gastric juice; HC1
For healthcare providers in the prehospital setting, bag-valve mask (BVM) ventilation could be as efficacious and safe as endotracheal intubation. To facilitate the evaluation of efficacious ventilation, capnographs have been further developed into small and convenient devices able to provide end- tidal carbon dioxide (ETCO2). The aim of this study was to investigate whether a new portable device (EMMA™) attached to a ventilation mask would provide ETCO2 values accurate enough to confirm proper BVM ventilation.
A prospective observational trial was conducted in a single level-2 centre. Twenty-two patients under general anaesthesia were manually ventilated. ETCO2 was measured every five minutes with the study device and venous PCO2 (PvCO2) was simultaneously measured for comparison. Bland- Altman plots were used to compare ETCO2, and PvCO2.
The patients were all hemodynamically and respiratory stable during anaesthesia. End-tidal carbon dioxide values were corresponding to venous gases during BVM ventilation under optimal conditions. The bias, the mean of the differences between the two methods (device versus venous blood gases), for time points 1-4 ranges from -1.37 to -1.62.
The portable device, EMMA™ is suitable for determining carbon dioxide in expired air (kPa) as compared to simultaneous samples of PvCO2. It could therefore, be a supportive tool to asses the BVM ventilation in the demanding prehospital and emergency setting.
Measurement of the end-tidal partial pressure of carbon dioxide (PETCO2) during cardiac arrest has been shown to reflect the blood flow being generated by external means and to prognosticate outcome. In the present issue of Critical Care, Grmec and colleagues compared the initial and subsequent PETCO2 in patients who had cardiac arrest precipitated by either asphyxia or ventricular arrhythmia. A much higher PETCO2 was found immediately after intubation in instances of asphyxial arrest. Yet, after 1 min of closed-chest resuscitation, both groups had essentially the same PETCO2, with higher levels in patients who eventually regained spontaneous circulation. The Grmec and colleagues' study serves to remind us that capnography can be used during cardiac resuscitation to assess the mechanism of arrest and to help optimize the forward blood flow generated by external means.
arrhythmias; asphyxia; capnography; cardiac arrest; prognosis; resuscitation
Objectives: To determine the availability of end-tidal CO2 measurement in confirmation of endotracheal tube placement in the non-arrest patient, and to assess its use in academic and non-academic emergency departments.
Methods: Emergency physicians in the USA were surveyed by mail in the beginning of the year 2000 regarding availability at their institution of both colorimetric/qualitative and quantitative end-tidal CO2 capnography, frequency of use in their own practice, and descriptor of their hospital (academic, community teaching, and community non-teaching). Additionally, data were obtained from the National Emergency Airway Registry 97 series (NEAR) about how many intubations used this method of confirmation. NEAR site coordinators were surveyed as well.
Results: Of 1000 surveys, 550 were returned (55%). Colorimetric technology existed in 77% of respondents' hospitals (n = 421); 25% of respondents (n = 138) had continuous monitoring capability. Physicians practising at academic hospitals were more likely to have continuous monitoring (36%; n = 196) than community teaching institutions (32%; n = 173) and non-teaching centres (18%; n = 100) (p<0.001). Among physicians who had this technology available, only 14% (n = 19) "always" used it in non-arrest intubations; 57% "rarely" or "never" employed it (n = 75). Among NEAR centres (institutions committed to monitoring current airway practices) only 12% of 6009 (n = 716) intubations used continuous end-tidal CO2 measurement. Of these practitioners, only 40% "always" used it (n = 6/15) (83% response rate (n = 29/35)).
Conclusions: Despite recommendations from national organisations that endorse continuous monitoring of end-tidal CO2 for confirming endotracheal tube placement, it is neither widely available nor consistently applied.
To determine whether monitoring end- tidal Carbon Dioxide (capnography) can be used to reliably identify the phrenic nerve during the supraclavicular exploration for brachial plexus injury.
Three consecutive patients with traction pan-brachial plexus injuries scheduled for neurotization were evaluated under an anesthetic protocol to allow intraoperative electrophysiology. Muscle relaxants were avoided, anaesthesia was induced with propofol and fentanyl and the airway was secured with an appropriate sized laryngeal mask airway. Routine monitoring included heart rate, noninvasive blood pressure, pulse oximetry and time capnography. The phrenic nerve was identified after blind bipolar electrical stimulation using a handheld bipolar nerve stimulator set at 2–4 mA. The capnographic wave form was observed by the neuroanesthetist and simultaneous diaphragmatic contraction was assessed by the surgical assistant. Both observers were blinded as to when the bipolar stimulating electrode was actually in use.
In all patients, the capnographic wave form revealed a notch at a stimulating amplitude of about 2–4 mA. This became progressively jagged with increasing current till diaphragmatic contraction could be palpated by the blinded surgical assistant at about 6–7 mA.
Capnography is a sensitive intraoperative test for localizing the phrenic nerve during the supraclavicular approach to the brachial plexus.
Prognosis 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.
This 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).
PetCO2 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%.
End-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.
Volatile anesthetics are generally known to exert several influences on the respiratory system, but their direct effect on oxygen saturation as measured by pulse oximetry (SpO2) in infants remains unknown. In this study, 70 infants under 2 years of age who received general anesthesia were examined to determine the effects of several volatile anesthetics and nitrous oxide on SpO2. After endotracheal intubation, the subjects were ventilated using a Jackson-Rees circuit with oxygen, nitrous oxide, and either sevoflurane, enflurane, or isoflurane adjusted to twice the adult minimum alveolar concentration (MAC) for the agents when used in combination with 67% nitrous oxide. In all cases, the end-tidal carbon dioxide tension (PetCO2) was maintained within the same range (28-35 mm Hg). Significantly lower SpO2 values (paired t test, P < .05) were observed when the subjects were ventilated with oxygen, 67% nitrous oxide, and sevoflurane or isoflurane--but not with oxygen, 67% nitrous oxide, and enflurane--than when they were administered oxygen, 50% nitrous oxide, and the original concentration of each volatile anesthetic. These results suggest that sevoflurane and isoflurane have different effects from enflurane on gas exchange systems.
Patients who present with acute myocardial infarction after a work injury (AMI-WI) often report symptoms consistent with chronic hyperventilation which date back as far as the work injury itself, rather than to the AMI. The aim of the study was to test the hypothesis that hyperventilation significantly contributes to the symptoms of AMI-WI patients. The prevalence of hyperventilation was assessed by clinical capnography in 12 AMI-WI patients, 20 normal controls, 15 AMI patients whose AMI was conventional and not subsequent to a work injury (AMI-C) and 14 patients with post-traumatic stress disorder (PTSD). End-tidal carbon dioxide partial pressure (P(et)CO2) was measured at rest, after 1 min hyperventilation (FHPT), after recall of the relevant stressor (Think) and when the breathing was felt to be normal (MBIN). P(et)CO2 levels after FHPT were: 29.0 +/- 1.5 (mean +/- SD) mmHg for AMI-WI; 26.7 +/- 1.9 mmHg for PTSD; 32.1 +/- 4.1 mmHg for AMI-C and 33.7 +/- 1.4 mmHg for the controls (P < 0.05 and P < 0.01 for AMI-WI and PTSD, respectively, versus controls). After Think, the levels were 25.8 +/- 1.6 mmHg for AMI-WI, 24.6 +/- 1.4 mmHg for PTSD, 31.2 +/- 4.1 mmHg for AMI-C and 31.2 +/- 1.5 mmHg for normals (P < 0.05 and P < 0.01 for AMI-WI and PTSD, respectively, versus controls). For MBIN, values of P(et)CO2 were 26.8 +/- 1.7 mmHg and 26.7 +/- 1.5 mmHg for AMI-WI and PTSD versus 33.8 +/- 1.2 mmHg for normals, (P < 0.01 for both versus controls).(ABSTRACT TRUNCATED AT 250 WORDS)
Monitoring cerebral saturation is increasingly seen as an aid to management of patients in the operating room and in neurocritical care. How best to manipulate cerebral saturation is not fully known. We examined cerebral saturation with graded changes in carbon dioxide tension while isoxic and with graded changes in oxygen tension while isocapnic.
The study was approved by the Research Ethics Board of the University Health Network at the University of Toronto. Thirteen studies were undertaken in healthy adults with cerebral oximetry by near infrared spectroscopy. End-tidal gas concentrations were manipulated using a model-based prospective end-tidal targeting device. End-tidal carbon dioxide was altered ±15 mmHg from baseline in 5 mmHg increments with isoxia (clamped at 110±4 mmHg). End-tidal oxygen was changed to 300, 400, 500, 80, 60 and 50 mmHg under isocapnia (37±2 mmHg). Twelve studies were completed. The end-tidal carbon dioxide versus cerebral saturation fit a linear relationship (R2 = 0.92±0.06). The end-tidal oxygen versus cerebral saturation followed log-linear behaviour and best fit a hyperbolic relationship (R2 = 0.85±0.10). Cerebral saturation was maximized in isoxia at end-tidal carbon dioxide of baseline +15 mmHg (77±3 percent). Cerebral saturation was minimal in isocapnia at an end-tidal oxygen tension of 50 mmHg (61±3 percent). The cerebral saturation during normoxic hypocapnia was equivalent to normocapnic hypoxia of 60 mmHg.
Hypocapnia reduces cerebral saturation to an extent equivalent to moderate hypoxia.
During preparation and draping of periorbital area, neck flexion causes displacement of the endotracheal tube tip toward the carina. Stimulation of the tracheal mucosa may cause bucking, increased intraocular pressure (IOP), laryngospasm, bronchospasm, change in end-tidal carbon dioxide pressure (PETCO2) or peripheral arterial haemoglobin oxygen saturation (SpaO2) during light anaesthesia.
To investigate the influence of head and neck flexion after endotracheal intubation on heart rate (HR), systolic and diastolic blood pressure (SAP and DAP), SpaO2, PETCO2 and IOP in patients undergoing cataract surgery during general anesthesia.
In this prospective observational study, 106 ASA physical status I and II patients scheduled for elective cataract surgery under general anaesthesia were studied. Anaesthesia was induced with thiopental sodium, lidocaine and fentanyl. Atracurium 0.5 mg/kg was given to facilitate tracheal intubation. HR, SAP, DAP, SpaO2, PETCO2, and IOP were measured at 1, 2, and 5 minutes after head flexion.
Mean SAP, DAP, IOP, and HR were significantly increased after head flexion compared with baseline values (P < 0.05). PETCO2 and SpaO2 were significantly decreased at 1 and 2 minutes after head flexion compared with baseline values (P < 0.001).
It is concluded that endotracheal tube movement by changes in head and neck position has significant effects on heart rate, systolic and diastolic blood pressures, laryngeal reflexes, SpaO2, PETCO2, and intraocular pressure in patients undergoing cataract surgery under general anaesthesia.
endotracheal intubation; intraocular pressure; head and neck positioning; pressor responses; respiratory responses
End-tidal carbon dioxide (ETCO2) is a surrogate, noninvasive measurement of arterial carbon dioxide (PaCO2); however, its clinical applicability in the intensive care unit setting remains unclear. Available research on the relationship between ETCO2 and PaCO2 has not taken a detailed assessment of physiologic dead space into consideration. We hypothesize that ETCO2 reliably predicts PaCO2 across all levels of physiologic dead space provided that the expected ETCO2-PaCO2 gradient is considered.
Fifty-six mechanically ventilated pediatric patients (0-17 years; 19.5 ± 24.5 kg) were monitored with volumetric capnography. For every arterial blood gas obtained during routine care, ETCO2 values were collected, and Vd/Vt values calculated. The ETCO2-PaCO2 relationship was assessed by Pearson's correlation coefficients within specified ranges of Vd/Vt.
Vd/Vt was ≤ 0.4 for 125 (25%) measurements, 0.41-0.55 for 160 (32%) measurements, 0.55-0.7 for 154 (31%) measurements, and > 0.7 for 54 (11%) measurements. The correlation coefficients between ETCO2 and PaCO2 were 0.95 (mean gradient = 0.3 ± 2.1) for Vd/Vt ≤ 0.4, 0.88 (mean gradient = 5.9 ± 4.3) for Vd/Vt 0.41-0.55, 0.86 (mean gradient = 13.6 ± 5.2) for Vd/Vt 0.55-0.7, and 0.78 (mean gradient = 17.8 ± 6.7) for Vd/Vt > 0.7.
Strong correlations between ETCO2 and PaCO2 were found for all Vd/Vt ranges. The ETCO2-PaCO2 gradient increased predictably with increasing Vd/Vt.
capnography; artificial respiration; blood gas analysis; pediatric; infant; mechanical ventilation; carbon dioxide
Objectives: Patients arriving in the emergency department (ED) need rapid and reliable evaluation of their respiratory status. Mainstream end tidal carbon dioxide (ETCO2) is one of the methods used for this purpose during general anaesthesia of intubated patients in the operating theatre. Sidestream ETCO2 (SSETCO2) might be a non-invasive, rapid, and reliable predictor of arterial PCO2 in non-intubated patients in respiratory distress. The aim of this study was to verify whether SSETCO2 can accurately predict the arterial PCO2 and to detect variables that may affect this correlation.
Methods: A prospective semi-blind study. The participants were 73 patients (47 men, 26 women) referred to the ED for respiratory distress. Arterial blood gas pressures and SSETCO2 measurements were performed and recorded for all patients. Other parameters recorded were: age; body temperature; respiratory rate; blood pressure; pulse rate; and medical diagnosis.
Results: A significant correlation was found between SSETCO2 and arterial PCO2 (r = 0.792). Compared with the correlation curve of the whole group, age under 50 years deflected the correlation curve to the left, while temperature above 37.6°C deflected it to the right. The rest of the parameters had no clear influence on the SSETCO2/PCO2 correlation curve.
Conclusions: There is a good correlation between SSETCO2 and arterial PCO2 in the ED setting. Young age may increase the arterial PCO2/SSETCO2 gradient while raised temperature may decrease this gradient. Further studies are needed to confirm these findings in the normal healthy population.
Several factors affect the end-tidal carbon dioxide pressure (PETCO2) and increase the arterial to end-tidal carbon dioxide pressure gradient (Pa-ETCO2) during general anesthesia. We evaluated the relationship between age and Pa-ETCO2 during pneumoperitoneum in the steep Trendelenburg position in patients undergoing robot-assisted laparoscopic prostatectomy (RALP).
Ninety-two consecutive patients undergoing RALP were divided by age into a middle-aged (45-65 years) and an elderly (> 65 years) group. Anesthesia was standardized. Heart rate, mean arterial pressure, peak inspiratory pressure, lung compliance, minute ventilation, PaO2, PETCO2, PaCO2, and Pa-ETCO2 were measured 10 min after intubation in the supine position without pneumoperitoneum (T0); and 10 (T1), 60 (T2), and 120 (T3) min after pneumoperitoneum in the Trendelenburg position.
Although PETCO2 did not change significantly during surgery, PaCO2 and Pa-ETCO2 increased gradually with time during pneumoperitoneum in the Trendelenburg position, and both parameters showed greater increases in the elderly than in the middle-aged group. Simple linear regression analyses revealed significant correlations between age and Pa-ETCO2 at T0 (P = 0.018), T1 (P = 0.006), T2 (P < 0.001), and T3 (P = 0.001). Linear mixed model analysis showed that Pa-ETCO2 was associated statistically significantly with age and duration of pneumoperitoneum in the Trendelenburg position, but age and duration of pneumoperitoneum in the Trendelenburg position were not associated (P = 0.090).
The magnitude of Pa-ETCO2 during pneumoperitoneum in the steep Trendelenburg position increased with age, which could be attributed to age-related respiratory physiological changes.
Age; Carbon dioxide; Pneumoperitoneum; Trendelenburg position
End-tidal carbon dioxide concentrations were measured prospectively in 12 cardiac arrest patients undergoing cardiopulmonary resuscitation (CPR) in an accident and emergency department. The end-tidal carbon dioxide (CO2) concentration decreased from a mean (+/- SD) of 4.55 +/- 0.88% 1 min after chest compression and ventilation was established, to values ranging from 2.29 +/- 0.84% at 2 min to 1.56 +/- 0.66% following 8 min of CPR. Spontaneous circulation was restored in five patients. This was accompanied by a rapid rise in end-tidal CO2 which peaked at 2 min (3.7 +/- 1.08%). Changes in end-tidal CO2 values were often the first indication of return of spontaneous cardiac output. There was a significant difference in the end-tidal CO2 in patients undergoing CPR before return of spontaneous circulation (2.63 +/- 0.32%) and patients who failed to develop spontaneous output (1.64 +/- 0.89%) (p < 0.001). We conclude that measurement of end-tidal CO2 concentration provides a simple and non-invasive method of measuring blood flow during CPR and can indicate return of spontaneous circulation.
A computer based system for measurement of respiratory variables is presented. Tidal volume, respiratory frequency, minute ventilation, alveolar ventilation, dead space, oxygen transfer, carbon dioxide transfer, respiratory exchange ratio, end-tidal oxygen, end-tidal carbon dioxide, and heart rate are determined on a breath-to-breath basis. The computer is programmed to control the duration and intensity of the work involved. This program instructs the subject when to start and stop exercising, controls switching of the ergometer from an idle speed, and selects the work load. The computer system analyzes the data, averages multiple experiments and plots averages of multiple experiments along with standard error bars. Plotting time scales can be expanded to inspect selected portions of an experiment. The system is especially adapted to careful observation of the responses within the first few seconds of a change in work load. Appropriate computer programs and mathematical equations are presented. The results of several experiments are compared with data from other sources and found to be in good agreement.
A non-invasive surrogate measurement for central venous oxygen saturation (ScVO2) would be useful in the ED for assessing therapeutic interventions in critically ill patients. We hypothesized that either linear or nonlinear mathematical manipulation of the partial pressure of oxygen in breath at end expiration (EtO2) would accurately predict ScVO2.
Prospective observational study of a convenience sample of hemodialysis patients age > 17 years with existing upper extremity central venous catheters were enrolled. Using a portable respiratory device, we collected both tidal breathing and end expiratory oxygen and carbon dioxide concentrations, volume and flow on each patient. Simultaneous ScVO2 measurements were obtained via blood samples collected from the hemodialysis catheter. Two models were used to predict ScVO2: 1) Best-fit multivariate linear regression equation incorporating all respiratory variables; 2) MathCAD to model the decay curve of EtO2 versus expiratory volume using the least squares method to estimate the pO2 that would occur at <20% of total lung capacity.
From 21 patients, the correlation between EtO2 and measured ScVO2 yielded R2 = 0.11. The best fit multivariate equation included EtCO2 and EtO2 and when solved for ScVO2, the equation yielded a mean absolute difference from the measured ScVO2 of 8 ± 6% (range -18 to +17%). The predicted ScVO2 value was within 10% of the actual value for 57% of the patients. Modeling of the EtO2 curve did not accurately predict ScVO2 at any lung volume.
We found no significant correlation between EtO2 and ScVO2. A linear equation incorporating EtCO2 and EtO2 had at best modest predictive accuracy for ScVO2.
Airway management during cardiac arrests is a controversial area. There are advantages to the provision of a patent airway with an airway adjunct, especially as this can optimize oxygenation and carbon dioxide clearance as well as facilitate continuous compressions. These advantages come at a potential cost, in particular errors in placement of the devices and interruption to compressions necessitated for insertion. The widespread availability of supraglottic airways (SGAs), their ease of insertion, and their ability to be inserted without interruptions to compressions have meant that the role of the definitive airway device - the endotracheal tube - is being challenged. In the previous issue of Critical Care, a study from Japan reported the use of advanced airways in more than 5,000 victims of cardiac arrests. The authors were not able to demonstrate a survival advantage with either SGAs or endotracheal intubation (ETI). They did, however, demonstrate improved outcomes when the emergency life-saving technicians had been trained to perform ETI and when the advanced airway device was inserted earlier.