End-tidal partial pressure of carbon dioxide does not accurately reflect Paco2 in rabbits treated with acetazolamide during anaesthesia

Arterial carbon dioxide partial pressure measurements using the NBP-75 microstream capnometer were compared with direct PaCO2 values in patients who were (a) not intubated and spontaneously breathing, and (b) patients receiving intermittent positive pressure ventilation of the lungs and endotracheal anaesthesia. Twenty ASA physical status I-III patients, undergoing general anaesthesia for orthopaedic or vascular surgery were included in a prospective crossover study. After a 20-min equilibration period following the induction of general anaesthesia, arterial blood was drawn from an indwelling radial catheter, while the end-tidal carbon dioxide partial pressure was measured at the angle between the tracheal tube and the ventilation circuit using a microstream capnometer (NBP-75, Nellcor Puritan Bennett, Plesanton, CA, USA) with an aspiration flow rate of 30 mL min(-1). Patients were extubated at the end of surgery and transferred to the postanaesthesia care unit, where end-tidal carbon dioxide was sampled through a nasal cannula (Nasal FilterLine, Nellcor, Plesanton, CA, USA) and measured using the same microstream capnometer. In each patient six measurements were performed, three during mechanical ventilation and three during spontaneous breathing. A good correlation between arterial and end-tidal carbon dioxide partial pressure was observed both during mechanical ventilation (r = 0.59; P = 0.0005) and spontaneous breathing (r = 0.41; P = 0.001); while no differences in the arterial to end-tidal carbon dioxide tension difference were observed when patients were intubated and mechanically ventilated (7. 3 +/- 4 mmHg; CI95: 6.3-8.4) compared to values measured during spontaneous breathing in the postanesthesia care unit, after patients had been awakened and extubated (6.5 +/- 4.8 mmHg; CI95: 5. 2-7.8) (P = 0.311). The mean difference between the arterial to end-tidal carbon dioxide tension gradient measured in intubated and non-intubated spontaneously breathing patients was 1 +/- 6 mmHg (CI95: -11-+13). We conclude that measuring the end-tidal carbon dioxide partial pressure through a nasal cannula using the NBP-75 microstream capnometer provides an estimation of arterial carbon dioxide partial pressure similar to that provided when the same patients are intubated and mechanically ventilated.

:Background:Both end-tidal carbon dioxide pressure (ETCO2) is used routinely as an indicator of arterial partial pressure of carbon dioxide (PaCO2) and thus adequacy of ventilation. Accurate determination of the PaCO2 level in neuroanesthesia is quite important because of its effect on cerebral blood flow and also hyperventilation is often used to reduce intracranial pressure in neurosurgical patients. This study was aimed to evaluate the relationship between ETCO2 and arterial PaCO2 in neurosurgical patients undergoing craniotomy to assess the predictive value of ETCO2 as an indicator of PaCO2 level.Methods:Forty-five consecutive adult patients with inclusion criteria, scheduled to undergo elective craniotomy surgery were enrolled in this prospective study. Measurements of PaCO2 and ETCO2 were performed at three different intervals: Time 1: 10 min after induction of general anesthesia; time 2: after cranium opening prior to dural incision; and at time 3: start of dural closure. All patients received the same anesthetic agent (propofol, sufentanil, atracurium, oxygen). Data were initially analyzed using Pearson’s Correlation to assess the relationship between PaCO2 and ETCO2 at different stages of the operation. A p-value (P) of less than 0.05 was considered significant. The agreement between the measures of CO2 was assessed using Bland-Altman method, where mean difference and average between PaCO2 and ETCO2 were calculated. The 95% confidence intervals for the lower and upper limits of agreement were presented.Results:A total of 44 patients, aged 18 to 65 years, ASA grades 1 and 2 were participated in the study. Mean difference, standard deviation and correlation coefficient of the parameters were calculated for three time periods. The values for PaCO2, ETCO2, (PaCO2- ETCO2), and correlation coefficient for 10 min after anesthetic induction, prior to dural incision, and start of dural closure were 35.4 ± 3.2, 32.1 ± 3.2, 3.8 ± 2.1, and 0.565, 36.2 ± 3.1, 32.6 ± 3.2,4.8 ± 3.1, and 0.574, and 36.7 ± 2.4, 33 ± 3.2,3.8 ± 2.3, and 0.627, respectively (p less than 0.01 for all analyses). The greatest mean difference occurred just prior to dural incision. The lowest mean difference was observed at 10 min post-anesthetic induction. Conclusions:To the present study was aimed to correlate between End-tidal and arterial carbon dioxide partial pressure in neurosurgical patients undergoing craniotomy. Findings of this study showed that ETCO2 consistently underestimates the value of PaCO2 during craniotomy indicating that ETCO2 value can be used instead of PaCO2.Keywords:End-tidal carbon dioxide pressure, Arterial partial pressure of carbon dioxide, Craniotomy

SANDERS, A. B.; KERN, K. B.; OTTO, C. W.; MILANDER, M. M.; EWY, G. A. Author Information

The effectiveness of ongoing cardiopulmonary resuscitation efforts is difficult to evaluate. Recent studies suggest that carbon dioxide excretion may be a useful noninvasive indicator of resuscitation from cardiac arrest. A prospective clinical study was done to determine whether end-tidal carbon dioxide monitoring during cardiopulmonary resuscitation could be used as a prognostic indicator of resuscitation and survival. Thirty-five cardiac arrests in 34 patients were monitored with capnometry during cardiopulmonary resuscitation during a 1-year period. Nine patients who were successfully resuscitated had higher average end-tidal carbon dioxide partial pressures during cardiopulmonary resuscitation than 26 patients who could not be resuscitated (15 +/- 4 vs 7 +/- 5 mm Hg). The 3 patients who survived to leave the hospital had a higher average end-tidal carbon dioxide partial pressure than the 32 nonsurvivors (17 +/- 6 vs 8 +/- 5 mm Hg). All 9 patients who were successfully resuscitated had an average end-tidal carbon dioxide partial pressure of 10 mm Hg or greater. No patient with an average end-tidal carbon dioxide partial pressure of less than 10 mm Hg was resuscitated. Data from this prospective clinical trial indicate that findings from end-tidal carbon dioxide monitoring during cardiopulmonary resuscitation are correlated with resuscitation from and survival of cardiac arrest.

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)

IS THE END-TIDAL PARTIAL PRESSURE OF ISOFLURANE A GOOD PREDICTOR OF ITS ARTERIAL PARTIAL PRESSURE?

Cardiorespiratory changes induced by pneumoperitoneum and head-up tilt may generate alveolar ventilation to perfusion ratio changes and increased systemic vascular resistances. The reliability of end-tidal carbon dioxide tension and pulse oximetry in predicting arterial carbon dioxide partial pressure and arterial oxygen saturation may therefore be affected. The 35 ASA 1-2 patients in this study comprised 12 men and 23 women aged 48 (SD 17) years and weighing 71 (SD 14) kg. Twenty-nine were to undergo upper abdominal laparoscopy for cholecystectomy and six hyperselective vagotomy. Intra-abdominal pressure was 1.7 (SD 0.9) kPa and head-up tilt was 5.6 (SD 4.2) degrees. After abdominal insuflation, arterial carbon dioxide partial pressure significantly increased (p < 0.05). However, the arterial carbon dioxide partial pressure-end-tidal carbon dioxide partial pressure gradient remained constant throughout surgery. This gradient was highly correlated with arterial carbon dioxide partial pressure (p < 0.0001), but was not correlated with elapsed time, intra-abdominal pressure or head-up tilt. Arterial oxygen saturation was always greater than 95% in all patients and the arterial oxygen saturation-pulse oximetric saturation gradient was always less than or equal to +4%. In conclusion, end-tidal carbon dioxide partial pressure and pulse oximetric saturation allow reliable monitoring of arterial carbon dioxide partial pressure and arterial oxygen saturation in the absence of pre-existing cardiopulmonary disease and/or acute peroperative disturbance.

Forty-five horses were maintained on halothane or isoflurane anesthesia for at least 90 minutes and received positive pressure ventilation after the first 30 minutes of anesthesia. Parameters monitored included end-tidal partial pressure of carbon dioxide (ETPCO2), arterial blood pressure, and arterial blood gases and pH. There was a statistically significant correlation between end-tidal carbon dioxide and arterial partial pressure of carbon dioxide (PaCO2) for both halothane and isoflurane anesthesia. There was no significant correlation between end-tidal carbon dioxide and either body weight or systolic blood pressure. No statistically significant difference was found in arterial to end-tidal carbon dioxide difference nor in alveolar dead space because of time or positioning over anesthetic periods of up to 3 hours. It is concluded that end-tidal carbon dioxide monitoring is a satisfactory measure of changes in respiratory acid-base balance with inhalation anesthesia in horses when ventilation is controlled.

Carbon dioxide output in laparoscopic cholecystectomy

To evaluate the relationship between the arterial end-tidal partial pressure of carbon dioxide (PCO2) difference (deltapCO2) and the degree of desaturation in children with cyanotic heart disease (CHD) and to come to a more reliable estimation of the arterial carbon dioxide partial pressure (PaCO2) from the end-tidal carbon dioxide partial pressure (PET-CO2). In part retrospective, in part prospective observational study at a university children's hospital. We retrospectively assessed the relationship between the arterial oxygen saturation as measured by means of pulse oximetry (SpO2) and the arterial to end-tidal PCO2 differences (deltaPCO2) from the records of medical or surgical interventions in 43 patients with CHD. We derived a PaCO2-PET-CO2 correction formula that was prospectively validated in 34 patients with CHD. In the retrospective part we found a significant correlation between SpO2 and deltaPCO2 ( r (2)=0.84, p<0.001). The regression equation (corrected PET-CO2=raw PET-CO2-0.36xSpO2+39) was used in the prospective part to calculate the corrected PET-CO2. The r (2)s for the correlations between PaCO(2) and uncorrected and corrected PET-CO2 were 0.17 ( p<0.05) and 0.94 ( p<0.001), respectively. The uncorrected PET-CO2 bias was 13.0 mmHg, the bias +/- 2SDs was -0.1 and 26.2 mmHg. The corrected PET-CO2 bias was -0.6 mmHg, the bias +/- 2SD's was -4.0 and 2.9 mmHg. Correcting the PET-CO2 for the degree of hypoxia using the SpO2 in artificially ventilated infants and children with CHD results in a clinically applicable estimation of the PaCO2. As both SpO2 and PET-CO2 can be monitored continuously and non-invasively, this could facilitate artificial ventilation management in children with CHD.

We developed an acoustic capnometer to estimate the partial pressures of arterial carbon dioxide from expired air in the pulmonary rehabilitation devices for patients with respiratory failure. Because partial pressures of carbon dioxide reduce the velocity of sound propagating through expired air, we developed an acoustic capnometer. The present study proposes a unique method based on the measurement of acoustic velocity in expired air, thus eliminating the use of a specific carbon dioxide sensor. The current method can fabricate the capnometer at an appreciably low cost, enabling the device to be used for various rehabilitation purposes. The acoustic capnometer comprises a cylindrical small sample cavity, an ultrasonic transmitter-receiver system, electronic circuits for velocity determination, and a microprocessor for data processing. To validate the device, 12 patients with pulmonary disease were enrolled, and end-tidal partial pressures of carbon dioxide obtained from the current device were compared to the carbon dioxide tension measured by conventional arterial blood gas analysis. The results show a linear relationship in the region of interest (40–60 torr). Therefore, the proposed device facilitates the estimation arterial carbon dioxide partial pressures without sampling blood.

Surgical drapes used during eye surgery are impermeable to air and hence risk trapping air underneath them. We investigated the effect of a forced-air warming blanket on carbon dioxide accumulation under the drapes in patients undergoing eye surgery under local anaesthesia without sedation. Forty patients of ASA physical status 1 and 2 were randomly assigned to either the forced-air warmer (n = 20) or a control heated overblanket (n = 20). All patients were given 1 l.min(-1) oxygen. We measured transcutaneous and end-tidal carbon dioxide partial pressures, heart rate, arterial pressure, respiratory rate, temperature and oxygen saturation before and after draping, then every 5 min thereafter for 30 min. The mean (SD) transcutaneous carbon dioxide partial pressure in the forced-air warming group stayed constant after draping at 5.7 (0.2) kPa but rose to a maximum of 6.4 (0.4) kPa in the heated overblanket group (p = 0.0001 for the difference at time points 15 min and later). We conclude that forced-air warming reduces carbon dioxide accumulation under the drapes in patients undergoing eye surgery under local anaesthesia.

Objective To investigate the clinical significance of noninvasive detection of end-tidal carbon dioxide partial pressure (PetCO2) in the management of children with acute asthma, and to evaluate the association between PetCO2 and artery blood gas carbon dioxide partial pressure ( PaCO2 ). Methods This was a prospective,double blinded study of children aged 5 ～ 14 years old treated for acute asthma in a pediatric emergency department. PetCO2 and PaCO2 measurements were taken before therapy and after each nebulization treatment ( maximum of three). Various clinical parametesr were recorded. Patients with PaCO2 and PetCO2 measurements within 8 minutes of each other were eligible for inclusion. Patients with cardiac disease,chronic pulmonary disease, poor tissue perfusion, or metabolic abnormalities were excluded. Results Sixty five children were enrolled. The initial PetCO2 value was (34. 8 ±8. 6) mm Hg (95% confidence interval =34. 0 to 36. 1). The PetCO2 value of post-treatment was (33.2 ±8.2) mm Hg (95% confidence interval =32. 5 to 34. 4) ,which was decreased significantly than that before treatment(P ＜ 0. 01 ). Fifty seven PetCO2-PaCO2 paired values were available from 57 patients. The values of PetCO2 and PaCO2 were ( 34. 8 ±7. 6) mm Hg and (40. 6 ± 8. 3 ) mm Hg, respectively. PetCO2 and PaCO2 values were highly positively correlated ( r = 0. 92,P ＜ 0. 000 1 ). Conclusion Noninvasive bedside measurement of PetCO2 in children with acute asthma in emergency department is feasible. Continuous PetCO2 monitoring can provide a reliable assessment of pulmonary status. PetCO2 can serve as an important adjunct index in the clinical management of pediatric patients with acute asthma. Key words: End-tidal carbon dioxide partial pressure; Asthma; Artery blood gas carbon dioxide partial pressure; Children

The relationship between the arterial partial pressure of carbon dioxide (Paco2) and the end-tidal carbon dioxide partial pressure (PEtco2) was evaluated in 11 critically ill adult neurointensive care patients during mechanical ventilation. It was hypothesized that the Paco2 to PEtco2 gradient, or P(a-Et)co2, was maintained and that PEtco2 can be used to determine Paco2 accurately in these patients. After approval by the Clinical Investigations Committee, when clinically indicated arterial blood gases (with Paco2) were measured, the PEtco2 was determined from the capnograph (Hewlett Packard 78520A infrared capnometer). The P(a-Et)co2 was evaluated for possible effects from changes in the other monitored hemodynamic and respiratory parameters. Linear regression analysis was used to determine the significance of the relationship between Paco2 and PEtco2 and other assessed variables. Student's t tests were used where applicable. A p value </=0.05 determined significance. One hundred thirty-five comparisons, 12.3 +/- 5.8 per patient, of Paco2 and PEtco2 were made. (All values are means +/- SD.) The P(a-Et)co2 was 6.9 +/- 4.4 mm Hg (-11-21 mm Hg), with Paco2 = 34 +/- 6 mm Hg and PEtco2 = 27 +/- 6 mm Hg. There was a significant correlation between Paco2 and PEtco2 values for the total study population (r = 0.72, p = 0.001). However, when the relationship between Paco2 and PEtco2 values for individual patients was analyzed, only seven of 11 patients (64%) had significant correlations. The direction of Paco2 change was inaccurately predicted by PEtco2 changes in 31.9% of measurements. PEtco2 does not provide a stable reflection of Paco2 in all neurointensive care patients. Arterial blood gases cannot be eliminated when monitoring respiratory acid-base balance in mechanically ventilated neurointensive care patients.