Comparison between the cuffed oropharyngeal airway and the laryngeal mask with respect to breathing pattern and capnography

This study evaluates spontaneous breathing and CO2-monitoring under sevoflurane anesthesia with a cuffed oropharyngeal (COPA) or laryngeal mask (LMA) as airway. Forty patients (ASA I-II) scheduled for varicose vein surgery were given 2 mg.kg-1 propofol for insertion of a COPA or a LMA. Anesthesia was maintained with sevoflurane at 2.5 vol% in 40/60% O2/N2O, while the patients breathed spontaneously. Arterial and end-tidal CO2 partial pressures (PaCO2, PE'CO2), respiratory rate (RR), tidal volume (VT) and expired minute volume (EMV) were recorded at different times before and during the procedure. The dead space (VD) was calculated from the modified Bohr equation. The PaCO2 and the PE'CO2 were generally lower in the LMA group as compared to the COPA group during most of the procedure. EMV was also higher in the LMA group as compared to the COPA group. This difference becomes statistically significant 5 min. before the end of surgery (6.22 +/- 0.34 vs. 5.23 +/- 0.39 L.min-1). RR was consistently higher in the LMA group, while VT and VD were similar. Correlation of PE'CO2 and PaCO2 was 0.87 when measured in the COPA group and 0.88 in the LMA group. The prediction of PaCO2 by PE'CO2 was more sensitive in the LMA group as compared to the COPA group. We conclude that spontaneous breathing is better with the LMA.     

Comparative evaluation of the prolonged use of the cuffed oropharyngeal airway and the laryngeal mask airway in spontaneously breathing anaesthetized patients.

The cuffed oropharyngeal airway (COPA) was compared with the laryngeal mask airway (LMA) with respect to airway quality and respiratory adverse events in 140 spontaneously breathing patients undergoing procedures of duration more than 1 h. Patients were allocated randomly to receive either a COPA (n = 72) or a LMA (n = 68) for airway management during anaesthesia induced with propofol and maintained with sevoflurane, nitrous oxide and oxygen. Groups were similar when comparing the first-time successful insertion rates (COPA: 94.5%, LMA: 95.6%), but airway manipulations (head tilt, chin lift, jaw thrust) were reported more frequently in the COPA group, 27.8% vs. LMA, 4.4%; P = 0.0005. During the post-induction apnoeic period, all patients were ventilated manually and although, mean (SD) leak pressure was lower in the COPA group (18 (4) cm H2O vs. LMA, 22 (3) cm H2O; P < 0.0001), the tidal volumes achieved did not differ in both groups: COPA, 9.5 (4) mL kg-1 vs. LMA, 10.5 (4.5) mL kg-1. The incidences of intra-operative coughing, gagging, laryngospasm, oxygen desaturation and hypercarbia were similar in both groups. Although both devices are equivalent with respect to the overall respiratory problems during spontaneous breathing anaesthesia of intermediate or prolonged duration, the LMA was associated with fewer airway quality problems, suggesting that it is more efficacious in securing the airway.     

Spontaneous breathing with the use of a laryngeal mask airway in children: comparison of sevoflurane and isoflurane

We compared respiratory parameters during anaesthesia with sevoflurane and isoflurane through a laryngeal mask airway (LMA). Children were anaesthetized with O₂ and air with 2.3% (1MAC) sevoflurane ( n =20) or 1.5% (1MAC) isoflurane ( n =20). After insertion of LMA, patients were allowed to breathe spontaneously and respiratory rate (RR) and P ECO2 were measured (presurgery state). After the measurement, anaesthetic concentration was increased to 1.3 MAC (3.0% sevoflurane or 2.0% isoflurane) and surgical stimulation was added. Fifteen min after incision, the measurements were again performed (during surgery). In the sevoflurane group, mean RR and P ECO2 were 32 breaths.min⁻¹, and 6.0 kPa (45 mmHg) respectively, before surgery, and 35 breaths.min⁻¹ and 7.0 kPa (52 mmHg) during surgery. In the isoflurane group, mean RR and P ECO2 were 32 breaths.min⁻¹ and 6.1 kPa (46 mmHg) respectively, before surgery, and 37 breaths.min⁻¹ and 6.7 kPa (52 mmHg) during surgery. There were no statistical differences between the two anaesthetic groups. Clinical respiratory and cardiovascular parameters during spontaneous breathing with LMA in children are similar during sevoflurane and isoflurane anaesthesia.     

Double lung transplantation without cardiopulmonary bypass: arterial to end-tidal carbon dioxide partial pressure differences

Bilateral lung transplantation without cardiopulmonary bypass consists of two sequential single lung transplantations. Variations in ventilatory status during the procedure led us to study the (PaCO2- PE'CO2) gradient to see if PE'CO2 might reflect PaCO2. The gradient was studied in 14 patients at six times during operation. (PaCO2-PE'CO2) (kPa) was mean 1.97 (SD 0.7) after induction, 3.2 (1.4) during single lung ventilation, 1.9 (1.1) after clamping of the contralateral pulmonary artery, 2.96 (1.6) after ventilation and vascularization of the first transplant and the remaining native lung, 0.99 (0.8) during single lung ventilation with the first transplant and 1.3 (0.8) during ventilation of both transplants. With ventilation by the allograft lung(s) alone, the small (PaCO2-PE'CO2) value demonstrated improvement in ventilatory status, enabled PaCO2 to be assessed by PE'CO2 and demonstrated efficiency of the grafts.      

Italian experience with the cuffed oropharyngeal airway (COPA). A prospective, observational study

BACKGROUND: The cuffed oropharyngeal airway (COPA) has been recently introduced into the market, but few is known about its clinical use in Italy. We therefore conducted a prospective, observational investigation to evaluate the use of this new extra-tracheal airway in clinical practice. METHODS: Anesthesiologists participating in the study received a simple questionnaire where data concerning anthropometric variables, surgical procedure, type and doses of drugs used to induce and maintain general anesthesia, type of ventilation during the procedure, and occurrence of untoward events during either COPA placement, general anesthesia maintenance, or postoperative period were prospectively recorded. The number of previously placed COPA, and the adequacy of airway control (subjective four point scale: excellent, good, fair, and poor) were also assessed. RESULTS: A total of 210 patients (139 female and 71 male) were prospectively studied. General anesthesia was induced with propofol in 204 patients (98%), sodium thiopental in 3 patients (1.5%), and midazolam in 1 patient (0.5%); while only one patient received muscle relaxants (0.5%); 126 patients (64%) were spontaneously breathing while 71 patients (36%) received positive pressure mechanical ventilation. No differences in the incidence of untoward events was reported between spontaneously breathing and mechanically ventilated patients. No differences in the incidence of untoward events were reported according to the number of previously placed COPA. Difficulties in COPA placement were reported in 7 patients with normal dentiture (5%) and 9 patients (39%) with dental prosthesis (p = 0.003), (Odds Ratio: 5.1; Cl95%: 3.0-8.7). Furthermore, airway obstruction was more frequently reported in patients with dental prosthesis (8% vs 0%; p = 0.002). The seal pressure was higher in mechanically ventilated (17 +/- 10 cm H2O) than spontaneously breathing patients (10 +/- 8 cm H2O), (p = 0.0005), while a sealing pressure higher than 12 cm H2O was associated with an increased risk for postoperative sore throat (Odds ratio: 4.3; Cl95%: 2.6-7.1; p = 0.002). Airway control was graded as excellent in 61.4% of cases by physician previously placing more than 50 COPA, compared with only 26.5% when less than 50 COPA had been previously placed (p = 0.0005). CONCLUSIONS: COPA provided as safe and effective airway management in mechanically ventilated patients as that observed during spontaneous breathing. Experience with COPA placement had no effects on the placement success rate or incidence of untoward events, but improved the quality of airway control.     

Nasal versus oral fiberoptic intubation via a cuffed oropharyngeal airway (COPA) during spontaneous ventilation

STUDY OBJECTIVE: To compare the success rate of nasal versus oral fiberoptic intubation in anesthetized patients breathing spontaneously via the cuffed oropharyngeal airway (COPAtrade mark). DESIGN: Prospective, randomized, controlled study. SETTING: Two university-affiliated hospitals. PATIENTS: Patients scheduled for general or plastic surgery of the torso or extremities. INTERVENTIONS: Nasal (n=20) and oral (n=20) fiberoptic intubation were performed in patients while breathing spontaneously via the COPA during standardized anesthesia. MEASUREMENTS: Demographic data, mean arterial pressure, heart rate, end-tidal carbon dioxide (ETCO2), oxygen saturation (SpO2), COPA size, difficult airway predictors, rate of failed ventilation via COPA, and frequency of hypoxemia (SpO2 < 90%) during the procedure, and perioperative untoward events were recorded. MAIN RESULTS: The background, airway difficulty, vital signs and untoward effects were similar in the two groups. Nasal fiberoptic laryngeal view (scale 1-4) was better than the oral grading (3 [median] vs. 2, respectively; p <0.05). Eighty percent of the nasal intubations were successful compared with 40% of the oral intubations (p <0.05). Nasal intubations were accomplished within 153 +/- 15 SD seconds compared with 236 +/- 22 seconds (p <0.05) for the oral intubations, and less propofol was needed in the nasal intubations during the procedures (240 +/- 27 mg [nasal] vs. 277+/- 39 mg [oral]; p <0.05). CONCLUSIONS: Nasal fiberoptic laryngoscopy is more successful and easy than the oral approach in anesthetized patients who are breathing spontaneously through the COPA.     

The use of the cuffed oropharyngeal airway in paediatric patients

BACKGROUND: The cuffed oropharyngeal airway (COPA) is a device which has already been demonstrated to be suitable for anaesthetized adult patients undergoing either spontaneous or mechanical ventilation. There are few reports on the use of the COPA in children. In this study, the authors assessed the COPA in paediatric patients undergoing minor surgery. METHODS: The same anaesthesiologist inserted the COPA in 40 consecutive paediatric patients, ASA I and II, aged 1.8-15.3 years. (7.4 +/- 3.9), after induction of anaesthesia with N2O/O2/sevoflurane. COPA size was chosen by measuring the distal tip of the device at the angle of the jaw with the COPA perpendicular to the patient's bed. The proper positioning of the COPA was assessed by observing thoracoabdominal movements, regular capnograph trace, the reservoir bag movements and SpO2 > 94% with a fraction of inspired oxygen of 0.5. Anaesthesia was maintained with 1 MAC halothane, sevoflurane, or isoflurane in N2O/O2 (50%) and the patients were spontaneously breathing. The stability of the COPA following changes in head, neck and body position was tested. We recorded the duration time for COPA insertion, the side-effects of placement of the COPA and during the intraoperative period, the number of attempts, the type of manipulation in order to provide an effective airway and postoperative symptoms, such as the presence of blood on the device, sore throat, neckache, jaw pain and PONV. RESULTS: Successful COPA insertion at the first attempt was 90% and at the second attempt in the remaining 10%. The most frequent airway manipulations were head tilt in 27.5% (obtained by a pillow under shoulders) and chin lift in 5%. No complications both at COPA placement nor during the intraoperative period were observed. On the basis of weight and age, the COPA size was no. 8 in 50%, no. 9 in 30%, no. 10 in 12.5%, and no. 11 in 7.5%. The COPA demonstrated stability after changes in head, neck and body position. Postoperative complications were the presence of blood stains in one case and PONV in six cases (15%). CONCLUSIONS: The COPA is an extratracheal airway device suitable in paediatric patients undergoing general anaesthesia with spontaneous ventilation for minor surgery and other painful procedures. This study shows that for paediatric patients: (i) complications seem to be rare; (ii) the COPA allows hands free anaesthesia; (iii) specific indication for the COPA could be obese patients with a small mouth; and (iv) COPA sizing can be easily established by the weight or age of the patients.     

Postganglionic sympathetic nerve activity in halothane–anaesthetized rats during controlled and spontaneous ventilation

The aim of the study was to compare the effect of halothane anaesthesia on sympathetic nerve discharge in mechanically normoventilated and spontaneously breathing rats. Renal sympathetic nerve activity (rSNA), mean arterial pressure (MAP) and heart rate (HR) were measured in the conscious state and at the inspiratory halothane concentrations of 0.6%, 1.2% and 2.4% in one mechanically normoventilated and one spontaneously breathing group, while a third group was subjected to controlled hypoventilation at 1.2% halothane concentration. Halothane in blood was determined in two separate groups at 1.2%. In an additional group of spontaneously breathing rats, PaCO2 was analysed during consciousness and the halothane concentrations of 1.2% and 2.4%. There was a pronounced decrease in rSNA, MAP and HR at all levels of anaesthesia in the mechanically ventilated rats. However, rSNA, HR and MAP were significantly higher in the spontaneously breathing rats at increasing levels of halothane anaesthesia. Controlled hypoventilation at 1.2% halothane increased the variables significantly. In spontaneously breathing animals, PaCO2 increased significantly during the halothane exposure. The concentration of halothane in blood was significantly higher in the spontaneously breathing rats. Thus, the halothane-induced respiratory depression in the spontaneously breathing rats preserved rSNA during halothane anaesthesia, possibly via CO2-mediated chemoreceptor stimulation.     

Airway management in spontaneously breathing anaesthetized children: comparison of the Laryngeal Mask Airway with the cuffed oropharyngeal airway

BACKGROUND: The efficacy and safety of the smallest size of the cuffed oropharyngeal airway (COPA) for school age, spontaneously breathing children was investigated and compared with the Laryngeal Mask Airway (LMA). METHODS: Seventy children of school age (7-16 years) were divided into two groups: the COPA (n=35) and the LMA (n=35). Induction was with propofol i.v. or halothane, nitrous oxide, oxygen and fentanyl. After depression of laryngopharyngeal reflexes, a COPA size 8 cm or an LMA was inserted. Ventilation was manually assisted until spontaneous breathing was established. For maintenance, propofol i.v. and fentanyl or halothane with nitrous oxide were used. Local anaesthesia or peripheral blocks were also used. RESULTS: Both extratracheal airways had a highly successful insertion rate, but more positional manoeuvres to achieve a satisfactory airway were required with the COPA, 28.6% versus LMA 2.9%. The need to change the method of airway management was higher (8.6%) in the COPA group. After induction, the need for assisted ventilation was higher in the LMA group 54.3% versus 20% in the COPA group. Airway reaction to cuff inflation was higher in the LMA group 14.3% versus COPA 5.7%. Problems during surgery were similar, except continuous chin support to establish an effective airway was more frequent (11.4%) in the COPA group. In the postoperative period, blood on the device and incidence of sore throat were detected less in the COPA group. CONCLUSIONS: The COPA is a good extratracheal airway that provides new possibilities for airway management in school age children with an adequate and well sealed airway, during spontaneous breathing or during short-term assisted manual ventilation.     

Similar haemodynamic, respiratory and metabolic changes with the use of sevoflurane or halothane in children breathing spontaneously via a laryngeal mask airway

BACKGROUND: In preschool children, short-lasting surgical procedures are often performed under combined inhalational and regional anaesthesia with the child breathing spontaneously via a laryngeal mask airway (LMA). Despite widespread use, only limited data are available on haemodynamic, respiratory and metabolic effects of sevoflurane and halothane during LMA anaesthesia. METHODS: In an open-label, randomised, controlled study, 49 children (aged 3-8 years) were allocated to receive either sevoflurane or halothane in 60% nitrous oxide. After insertion of the LMA, end-tidal concentrations of sevoflurane or halothane were maintained at 1 MAC with the child ventilating spontaneously throughout the entire procedure. Analgesia was provided by caudal block. Haemodynamic and respiratory parameters were recorded, and capillary blood-gas samples were obtained repeatedly. RESULTS: Changes in heart rate (HR) and systolic blood pressure were similar in both groups during all observed periods, apart from a significantly higher increase in HR during inhalational induction with sevoflurane (P<0.05). Regression slope analysis during anaesthesia revealed a decrease of the respiratory rate of 5 breaths h-1 (P<0.001) and an increase of end-tidal PCO2 and capillary PCO2 of about 0.25 kPa h-1 (P<0.001), with no significant difference between the two groups. Base excess, calculated in capillary blood gas samples, did not change over time (P>0.5) in either group. CONCLUSIONS: The use of approximately 1 MAC sevoflurane or halothane in 60% N2O in children breathing spontaneously via LMA resulted in comparable haemodynamic, respiratory and metabolic changes, and clinically relevant deteriorations did not occur during the 65-min study period.     

Cuffed oropharyngeal airway and capnometry: comparison of end-tidal and arterial carbon dioxide pressures

Purpose. The aim of this study was to investigate the reliability of end-tidal CO₂ tension (PetCO₂) as a predictor of PaCO₂ during anesthesia in patients breathing spontaneously via a cuffed oropharyngeal airway (COPA). Methods. Twenty adult patients scheduled for minor sur-gery were included in this study. After propofol injection, an appropriate size of COPA was inserted. Anesthesia was maintained with 60% nitrous oxide in oxygen (total flow rate of 5 l·min⁻¹) supplemented with propofol infusion. The patients were allowed to breathe spontaneously throughout the procedure. PaCO₂ and PetCO₂ were simultaneously measured when a steady state of anesthesia was reached. Results. PaCO₂ (48.8 ± 5.4 mmHg, range 36.2–58.0 mmHg) was higher than PetCO₂ (43.1 ± 4.2 mmHg, range 32–51 mmHg) in all patients. The difference between end-tidal and arterial CO₂ tension was 5.7 ± 3.2 mmHg (range 0.5–13.0 mmHg), and was significantly correlated with PaCO₂ (P < 0.01). Conclusion. The results of this study suggest that PetCO₂ in anesthetized patients breathing spontaneously through a COPA is sometimes unreliable as an indicator of PaCO₂ level, and there is some possibility of unexpected hypercapnia. Received for publication on August 31, 1998; accepted on February 9, 1999     

Flow requirements for the Bain breathing circuit during anaesthesia for caesarean section

We studied the relationship between arterial carbon dioxide tension (PaCO2) and fresh gas flow (FGF) during use of the Bain breathing circuit for Caesarean section anaesthesia. Thirty-one patients undergoing Caesarean section were anaesthetised using the Bain circuit with intermittent positive pressure ventilation. The PaCO2 were measured at FGF of 70 ml X kg-1 X min-1, 80 ml X kg-1 X min-1, and 100 ml X kg-1 X min-1. The FGF requirement to maintain a given PaCO2 during Caesarean section anaesthesia is the same as the requirements for nonpregnant subjects, despite the increase in carbon dioxide production associated with pregnancy. This is probably because the total FGF determined by body weight and given during Caesarean section anaesthesia is 15-20 per cent higher than nonpregnant levels, due to the weight gain associated with pregnancy. A FGF of 100 ml X kg-1 of pregnant weight/min maintains PaCO2 of 4.44 kPa predelivery, which is in the desirable range of PaCO2 during Caesarean section.     

Modified nasal cannula for simultaneous oxygen delivery and end-tidal CO2 monitoring during spontaneous breathing

BACKGROUND AND OBJECTIVES: Supplemental oxygen is commonly given via nasal cannulae in spontaneously breathing patients. Our modified nasal cannula with a clamp between the nasal prongs can provide O2 via one nostril and CO2 can be sampled through the other one. We have studied whether this cannula can provide oxygenation similar to a standard cannula without affecting end-tidal CO2 monitoring. METHODS: Eighty-six patients were studied during spinal anaesthesia and sedation. In 15 patients, arterial blood was sampled while O2 was delivered at flow rates of 0, 2 and 4 L min(-1), with or without clamping between the prongs of our modified nasal cannula. In the remaining 71 patients, arterial O2 was measured while using our modified nasal cannula with the clamp applied. End-tidal CO2 was recorded on a capnograph and the correlation between end-tidal and arterial values with our modified nasal cannula was investigated. RESULTS: No end-tidal CO2 waveforms were found with oxygen flow greater than 2L min(-1) without clamping between the prongs. With clamping there was a significant correlation (r = 0.83) between arterial and end-tidal CO2. A Bland-Altman analysis revealed a bias of 0.49 kPa with precision of +/-0.76 kPa. Arterial oxygenation was not affected by our modified nasal prongs with clamp as compared to the standard cannula. CONCLUSION: Our modified nasal cannula can provide continuous monitoring of end-tidal CO2 without affecting oxygen delivery in sedated, spontaneously breathing patients.     

Arterial to end-tidal carbon dioxide tension difference in anaesthetized adults mechanically ventilated via a laryngeal mask or a cuffed oropharyngeal airway.

To evaluate arterial (PaCO2), end-tidal (PETCO2) and carbon dioxide tension difference during mechanical ventilation with extratracheal airways, 60 patients ASA physical status I-II, receiving general anaesthesia for minor extra-abdominal procedures were randomly allocated to receive either a cuffed oropharyngeal airway (group COPA, n = 30) or a laryngeal mask (group LMA, n = 30). The lungs were mechanically ventilated by IPPV using a 60% nitrous oxide and 1-1.5% isoflurane in oxygen mixture (VT = 8 mL kg-1; RR = 12 b min-1; l/E = 1/2). After PETCO2 had been stable for at least 10 min after airway placement, haemodynamic variables and PETCO2 were recorded and an arterial blood sample was obtained for measurement of PaCO2. No differences in anthropometric parameters, smoking habit, haemodynamic variables and incidence of untoward events were observed between the two groups. Airway manipulation, to maintain adequate ventilation, was required in only nine patients in the cuffed oropharyngeal airway group (30%) (P < 0.0005); however, in no case was it necessary to remove the designated extratracheal airway due to unsuccessful mechanical ventilation. The mean difference between arterial and end-tidal carbon dioxide partial pressure was 0.4 +/- 0.3 KPa in the laryngeal mask group (95% confidence intervals: 0.3-0.5 KPa) and 0.3 +/- 0.26 KPa in the cuffed oropharyngeal airway group (95% confidence intervals: 0.24-0.4 KPa) (P = NS). We conclude that in healthy adults who are mechanically ventilated via the cuffed oropharyngeal airway, the end-tidal carbon dioxide determination is as accurate an indicator of PaCO2 as that measured via the laryngeal mask, allowing capnometry to be reliably used to evaluate the adequacy of ventilation.     

Ventilatory changes during nitrous oxide isoflurane anaesthesia in children

The changes in ventilatory variables under nitrous oxide isoflurane anaesthesia were studied in 10 children (mean age 46 +/- 13.4 months, mean weight 16.2 +/- 2.1 kg). Measurements of flow and volume were performed by pneumotachography. PE'CO2 was measured by capnography. The following variables (VE, VT, TI/TTOT, VI, PE'CO2) were measured or calculated under three increasing inspired isoflurane concentrations (0.75%, 1.5%, 2.25%). At each level of anaesthesia, ventilatory changes during exposure to an inspired CO2 fraction of 2% were studied. The increase in the inspired concentration of isoflurane was associated with a decrease in alveolar ventilation. PE'CO2 increased significantly with increasing depth of anaesthesia. The respiratory rate was slightly increased under light nitrous oxide isoflurane anaesthesia, but no further changes were observed with increasing depth of anaesthesia, although the children were breathing a mixture of nitrous oxide and oxygen. The ventilatory response to a raised inspired CO2 is markedly decreased under light nitrous oxide isoflurane anaesthesia, and decreases significantly with increasing depth of anaesthesia. In response to a raised CO2, VE, VT and VI increase, but respiratory rate decreases or remains constant and TI/TTOT is unchanged.     

Efficacy of the cuffed oropharyngeal airway in spontaneously breathing patients]

A cuffed oropharyngeal airway (COPA) was used in 20 adult patients for airway management under epidural and brachial plexus block supplemented with light general anesthesia. Insertion of a COPA was successful at first attempt in 17 of 20 patients (85%). Sore throat developed in one patient (5%). Aspiration regurgitation, or laryngospasm was not observed. We conclude that a COPA can be an efficient airway device is spontaneously breathing patients under anesthesia.     

Alveolar partial pressures of carbon dioxide and oxygen measured by a helium washout technique.

A non-invasive technique was developed for measuring alveolar carbon dioxide and oxygen tension during tidal breathing. This was achieved by solving the Bohr equations for mean alveolar carbon dioxide and oxygen tensions (PACO2, PAO2) from known values of the dead-space:tidal volume ratio measured by helium washout, and from the mixed expired partial pressure of carbon dioxide and oxygen. The derived values of wPACO2 and wPAO2 were compared with PaCO2 obtained from arterial gas analysis and PAO2 calculated from the ideal air equation. Four normal subjects and 58 patients were studied. Calculated and measured PCO2 values agreed closely with a difference in mean values (wPACO2 - PaCO2) of 0.01 kPa; the SD of the differences was 0.7 kPa. The difference in mean values between wPAO2 and PAO2 was 0.02 kPa; the SD of the differences was 0.93 kPa. The method is simple and not time consuming, and requires no special cooperation from the patients. It can be applied in the laboratory or at the bedside to any subject breathing tidally. Physiological deadspace:tidal volume ratio, PAO2 and PACO2, static lung volumes, respiratory exchange ratio, carbon dioxide production, oxygen uptake, tidal volume, and total ventilation can be measured with acceptable accuracy and reproducibility in one test. An arterial blood sample is needed initially to provide an independent measure of PaCO2 and for measurement of the alveolar-arterial PO2 difference. Subsequently, PaCO2 can be estimated from wPACO2 sufficiently well for clinical purposes and PaO2 or SaO2 can be monitored by non-invasive methods.     

Accuracy of end-tidal carbon dioxide monitoring using the NBP-75 microstream capnometer. A study in intubated ventilated and spontaneously breathing nonintubated patients

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.     

The influence of breathing system filters on paediatric capnography

Breathing system filters are in common use during paediatric anaesthesia. Expired gas sampling from the patient side of these filters may contaminate and saturate the sampling line, while sampling from the machine side may cause underestimation of end-tidal carbon dioxide (PECO 2). The aim of this investigation was to elucidate the degree of underestimation of PECO 2 induced by sampling from the machine side of a breathing system filter. Ten spontaneously breathing children and ten children receiving mechanical ventilation under general anaesthesia were studied. PECO 2 was higher at the patient side of the filter in both ventilated and spontaneously breathing groups (P<0.002 for each). The bias in measuring at the machine side of the filter was significantly greater in the spontaneously breathing children as compared with the mechanically ventilated children (-1.8 vs -0.7 kPa; P<0.004).     

The reliability of endtidal CO2 in spontaneously breathing children during anaesthesia with laryngeal mask airway,low flow,sevoflurane and caudal epidural

BACKGROUND: Noninvasive devices for monitoring endtidal CO2 (PECO2) are in common use in paediatric anaesthesia. Questions have been raised concerning the reliability of these devices in spontaneous breathing children during surgery. Our anaesthetic technique for elective infraumbilical surgery consists of spontaneous breathing through a Laryngeal Mask Airway (LMA), low fresh gas flow, sevoflurane and a caudal epidural. We wanted to compare PECO2 and arterial CO2 (PaCO2) during surgery. METHODS: Twenty children, aged 1-6 years, scheduled for infraumbilical surgery, were studied and one arterial sample was taken 45 min after induction of anaesthesia. PECO2, inspiratory PCO2, oxygen saturation, heart rate, respiratory rate, mean arterial blood pressure and expiratory sevoflurane concentration were measured every 5 min. The respiratory and circulatory parameters were stable during surgery. RESULTS: The mean PaCO2 - PECO2 difference was 0.15 (0.16) kPa [1.1 (1.2 mmHg)]. CONCLUSIONS: PECO2 is a good indicator of PaCO2 in our anaesthetic setting.