Supplementary oxygen administration for elective Caesarean section under spinal anaesthesia

We investigated the necessity for administration of supplementary oxygen to mothers undergoing elective Caesarean section under spinal anaesthesia. Sixty-nine women undergoing elective Caesarean section were randomly allocated to one of three groups to be given either oxygen (40%) by facemask, air by facemask or oxygen at 2 l x min(-1) by nasal cannulae. Umbilical arterial and venous blood samples were taken and analysed immediately after delivery. The results showed that there were no significant differences in the umbilical arterial or venous pH, partial pressure of oxygen and partial pressure of carbon dioxide between any of the three groups. We also assessed the patient acceptability of oxygen administered by facemask vs. nasal cannulae should the need for supplementary oxygen arise. It was found that use of the facemask impeded communication.     

Oxygen and Carbon Dioxide Concentrations in Anaesthetic Circuits Ventilated with an AGA UV 705 in an Oxygen Consuming Model Lung

An oxygen consuming and carbon dioxide producing model lung was used for evaluation of anaesthetic circle systems. Two different circles, the AGA metal circle and the AGA Monosorbcircle ventilated hy an AGA UV-705 were tested with reference to inspired oxygen concentrations and end-tidal CO₂ levels. Cartmn dioxide is dependent on alveolar ventilation and CO₂ production and thus was stable throughout the experiments. The oxygen concentration of inspired gas decreased progressively with decreasing fresh gas flow. When using the fresh gas inlet on the ventilator outlet block, the inspired oxygen concentration fell 8% as compared to using the fresh gas inlet in the circle. Fresh gas flows under 3 1/min should only be used with oxygen monitoring in the circle. The fresh gas inlet must be directly into the circle, and not in the ventilator outlet block, to avoid hypoxia.     

A non-rebreathing coaxial anaesthesia system: dependence of end-tidal gas concentrations on fresh gas flow and tidal volume

A non-rebreathing adaptation of the Bain coaxial anaesthesia circuit was developed in Nepal as a simple and economical anaesthetic system for underdeveloped countries. It was made by inserting a coaxial (Bain) tubing between an Ambu-E valve and an Ambu self-inflating bag. The present study examined the dependence of end-tidal gas concentrations on fresh gas flow and tidal volume during halothane/oxygen/air inhalation anaesthesia. Four levels of fresh gas flow with normocapnia (0.2–3 l.min⁻¹) and three levels of tidal volume at a constant respiratory rate of 15 breath.min⁻¹ (to achieve end-tidal carbon dioxide values of 4 ± 0.5%, 5 ± 0.5% and 6 ± 0.5%) were introduced in random order. Twelve ASA class 1 and 2 adult patients having intra-abdominal or pelvic surgery were studied. With increasing fresh gas flow rates, there were proportionate increases in the end-tidal concentrations of oxygen and halothane; with decreasing tidal volume and therefore less air dilution, there were proportionate increases in the end-tidal concentrations of carbon dioxide, oxygen and halothane. Both effects were statistically and clinically significant. Thus, when this system is used as described, the end-tidal concentrations of oxygen and halothane are highly dependent upon both the fresh gas flow and the tidal volume.     

Anesthetic apparatus: failure of fresh gas delivery to the auxiliary circuit]

A case of sudden loss of fresh gas delivery to a manual auxiliary anaesthetic circuit is reported. The corresponding fresh gas outlet was disunited from the anaesthesia machine and had been inadvertently rotated in its housing, allowing the rubber tubing linking the fresh gas delivery unit to the gas outlet to be twisted.     

Preparation of anesthesia machines for patients susceptible to malignant hyperthermia

Malignant hyperthermia is a potentially lethal syndrome that can be triggered by inhaled anesthetics. Thus, it may be appropriate to utilize equipment that minimizes exposure of susceptible patients to inhaled anesthetics. The rate of release of anesthetic stored in anesthesia delivery systems is unknown. To determine residual anesthetic concentrations, the washout rates of halothane and isoflurane were compared, and the effects of a 1-l/min and a 10-l/min fresh gas flow were evaluated. Halothane concentrations were also measured in samples taken from the fresh gas outlet and the Y-piece of the circle system during four separate studies in which various components of the anesthesia system were replaced. In each study an Ohio Modulus anesthesia machine equipped with an Air-Shields ventilator was exposed to 2% halothane for 18 h. Anesthetic concentrations were determined by a gas chromatograph having a sensitivity of 0.1 ppm. Isoflurane washed out 3-4 times faster than halothane. Residual halothane concentration was approximately equal to tenfold greater when the fresh gas flow was 1 l/min rather than 10 l/min: 194 versus 19 ppm after 1 h of washout. Using a 10-l/min fresh gas flow, halothane concentrations in samples obtained from the Y-piece were similar with original or fresh soda lime but were more than tenfold lower after the fresh gas outlet hose and circle system were replaced (approximately equal to 50 ppm vs. approximately equal to 5 ppm after 5 min of washout).(ABSTRACT TRUNCATED AT 250 WORDS)     

Pre-oxygenation using high-flow nasal oxygen vs. tight facemask during rapid sequence induction

Pre-oxygenation using high-flow nasal oxygen can decrease the risk of desaturation during rapid sequence induction in patients undergoing emergency surgery. Previous studies were single-centre and often in limited settings. This randomised, international, multicentre trial compared high-flow nasal oxygen with standard facemask pre-oxygenation for rapid sequence induction in emergency surgery at all hours of the day and night. A total of 350 adult patients from six centres in Sweden and one in Switzerland undergoing emergency surgery where rapid sequence induction was required were included and randomly allocated to pre-oxygenation with 100% oxygen using high-flow nasal oxygen or a standard tight-fitting facemask. The primary outcome was the number of patients developing oxygen saturations <93% from the start of pre-oxygenation until 1 min after tracheal intubation. Data from 349 of 350 patients who entered the study were analysed (174 in the high-flow nasal oxygen group and 175 in the facemask group). No difference was detected in the number of patients desaturating <93%, five (2.9%) vs. six (3.4%) patients in the high-flow nasal oxygen and facemask group, respectively (p = 0.77). The risk of desaturation was not increased during on-call hours. No difference was seen in end-tidal carbon dioxide levels in the first breath after tracheal intubation or in the number of patients with signs of regurgitation between groups. These results confirm that high-flow nasal oxygen maintains adequate oxygen levels during pre-oxygenation for rapid sequence induction.     

High Carboxyhemoglobin Concentrations Occur in Swine during Desflurane Anesthesia in the Presence of Partially Dried Carbon Dioxide Absorbents

Background: Increased carboxyhemoglobin concentrations in patients receiving inhalation anesthetics (desflurane, enflurane, and isoflurane) have been reported. Recent in vitro studies suggest that dry carbon dioxide absorbents may allow the production of carbon monoxide.

Methods: The authors used high fresh oxygen flow (5 or 10 l/min) through a conventional circle breathing system of an anesthesia machine for 24 or 48 h to produce absorbent drying. Initial studies used 10 l/min oxygen flow with the reservoir bag removed or with the reservoir bag left in place during absorbent drying (this increases resistance to gas flow through the canister). A third investigation evaluated a lower flow rate (5 l/min) for absorbent drying. Water content of the absorbent and temperature were measured. Pigs received a 1.0 (human) minimum alveolar concentration desflurane anesthetic (7.5%) for 240 min using a 1 l/min oxygen flow rate with dried absorbent. Carbon monoxide concentrations in the circuit and carboxyhemoglobin concentrations in the pigs were measured.

Results: Pigs anesthetized with desflurane using Baralyme exposed to 48 h of 10 l/min oxygen flow (reservoir bag removed) had extremely high carboxyhemoglobin concentrations (more than 80%). Circuit carbon monoxide concentrations during desflurane anesthesia using absorbents exposed to 10 l/min oxygen flow (reservoir bag, 24 h) reached peak values of 8,800 to 13,600 ppm, depending on the absorbent used. Carboxyhemoglobin concentrations reached peak values of 73% (Baralyme) and 53% (soda lime). The water content of Baralyme decreased from 12.1 +/- 0.3% (mean +/- SEM) to as low as 1.9 +/- 0.4% at the bottom of the lower canister (oxygen flow direction during drying was from bottom to top). Absorbent temperatures in the bottom canister increased to temperatures as high as 50 [degree sign] Celsius. With the reservoir bag in place during drying (10 l/min oxygen flow), water removal from Baralyme was insufficient to produce carbon monoxide (lowest water content = 5.5%). Use of 5 l/min oxygen flow (reservoir bag removed) for 24 h did not reduce water content sufficiently to produce carbon dioxide with desflurane.     

Performance of an oxygen delivery device for weaning potentially infectious critically ill patients

Oxygen delivery via a heat and moisture exchange filter with an attached T-shaped reservoir satisfies infection control requirements of high efficiency bacterial and viral filtration and low gas flows. In order to assess the performance of such a device in critically ill patients being weaned from mechanical ventilation, we simulated 16 patients using a human patient simulator, measuring fractional inspired oxygen and carbon dioxide concentrations and work of breathing at three oxygen flow rates. Oxygen concentration was dependent on peak inspiratory flow rate, tidal volume and oxygen flow rate. Rebreathing, as indicated by inspired carbon dioxide concentration, was greatest at high respiratory rates and low tidal volumes. Imposed inspiratory work of breathing was relatively high (mean 0.88 J.l(-1)[SD 0.30]). We conclude that this method of oxygen delivery is only suitable for patients in whom rapid extubation is anticipated.     

Physical factors affecting the production of carbon monoxide from anesthetic breakdown

BACKGROUND: Parameters determining carbon monoxide (CO) concentrations produced by anesthetic breakdown have not been adequately studied in clinical situations. The authors hypothesized that these data will identify modifiable risk factors. METHODS: Carbon monoxide concentrations were measured when partially desiccated barium hydroxide lime was reacted with isoflurane (1.5%) and desflurane (7.5%) in a Draeger Narkomed 2 anesthesia machine with a latex breathing bag substituting for a patient. Additional experiments determined the effects of carbon dioxide (0 or 350 ml/min), fresh gas flow rates (1 or 4 l/min), minute ventilation (6 or 18 l/min), or absorbent quantity (1 or 2 canisters). End-tidal anesthetic concentrations were adjusted according to a monochromatic infrared monitor. RESULTS: Desflurane produced approximately 20 times more CO than isoflurane when completely dried absorbents were used. Peak CO concentrations approached 100,000 ppm with desflurane. Traces of water remaining after a 66-h drying time (one weekend) markedly reduced the generation of CO compared with 2 weeks of drying. Reducing the quantity of desiccated absorbent by 50% reduced the total CO production by 40% in the first hour. Increasing the fresh gas flow rate from 1 to 4 l/min increased CO production by 67% in the first hour but simultaneously decreased average inspiratory concentrations by 53%. Carbon dioxide decreased CO production by 12% in completely desiccated absorbents. CONCLUSION: Anesthetic identity, fresh gas flow rates, absorbent quantity, and water content are the most important factors determining patient exposures. Minute ventilation and carbon dioxide production by the patient are relatively unimportant.     

Preparation of the Siemens KION anesthetic machine for patients susceptible to malignant hyperthermia

BACKGROUND: Preparation of anesthetic machines for use with malignant hyperthermia-susceptible (MHS) patients requires that the machines be flushed with clean fresh gas. We investigated the washout of inhalational anesthetics from the KION anesthetic machine. METHODS: In part 1, halothane was circulated through KION anesthetic machines for either 2 or 12 h using a test lung. The times to washout halothane (to 10 parts per million [ppm]) first, from the internal circuitry and second, from the ventilator-patient cassette (without the carbon dioxide absorber) were determined at 5 and 10 l/min fresh gas flow (FGF). In part 2, the rates of washout of halothane or isoflurane from either the KION or Ohmeda Excel 210 machines were compared. The effluent gases were analyzed using calibrated Datex Capnomac Ultima (Helsinki, Finland) and a Miran LB2 Portable Ambient Air Analyzer (Foxboro, Norwalk, CT). RESULTS: Halothane was washed out of the internal circuitry of the KION within 5 min at 10 l/min FGF. Halothane was eliminated from the ventilator-patient cassette in 22 min at the same FGF. The times to reach 10 ppm concentration of halothane and isoflurane in the KION at 10 l/min FGF, 23 to 25 min, was four-fold greater than those in the Ohmeda Excel 210, 6 min. CONCLUSIONS: To prepare the KION anesthetic machine for MHS patients, the machine without the carbon dioxide absorber must be flushed with 10 l/min FGF for at least 25 min to achieve 10 ppm anesthetic concentration. This FGF should be maintained throughout the anesthetic to avoid increases in anesthetic concentration in the FGF.     

Progressive hypoxemia, hypercarbia and hyperthermia associated with prolonged anesthesia--a case report

The authors report a case of 66-year-old female patient, 55 kg, ASA I who, under general anesthesia in supine position, developed gradual hypoxemia (from a baseline PaO2 of 250 to 91 mmHg), carbon dioxide build up (from a baseline PaCO2 31 to 41 mmHg) associated with gradual hyperthermia up to 38.3 degrees C over seven hours, intraoperatively. These observations were noted while using a semi-closed carbon dioxide absorption circuit in conjunction with the Hygroster filter at a fresh gas flow of 4 1/min of 50% nitrous oxide in oxygen. While the ventilation pattern was unchanged throughout the procedure, there was a change in exhaled tidal and minute ventilation volume with a net decrease of 28 ml and 0.4 l/min respectively. Findings are probably the result of pulmonary atelecatasis under general anesthesia due to the use of a relatively high-inspired oxygen concentration (50%). In addition, the use of a high humidity and temperature heat moisture exchanger (HME) filter (Hygroster) in conjunction with the circle absorber system may have resulted in over humidification and aggravated the pulmonary atelecatasis over the long operative time.     

Preparing a new generation anaesthetic machine for patients susceptible to malignant hyperthermia

Anaesthetic machines are prepared for use with patients who are susceptible to malignant hyperpyrexia (MH) by flushing with oxygen at 10 l/min for ten minutes to reduce the anaesthetic concentration to 1 part per million (ppm) or less. Anaesthetic workstations are now often used in place of traditional machines. Workstations have greater internal complexity, and it is not known if they can be made safe for susceptible patients by flushing with oxygen. We used a high sensitivity infrared gas analyser to measure the washout of isoflurane from five Datex-Ohmeda workstations. Measurements were then repeated with a patient breathing circuit. Isoflurane washout occurred in an exponential manner. The time to reach a concentration of 1 ppm at the fresh gas outlet was 17 +/- 7 minutes, and all machines had reached less than 2 ppm by ten minutes. The washout of isoflurane from the machine and patient breathing circuit was much slower than from the machine alone, with a concentration less than 2 ppm reached only after 30 minutes. We conclude that the Datex-Ohmeda workstation can be prepared for use in MH susceptible patients by flushing with oxygen at 10 l/min for ten minutes. Flushing of the patient breathing system is not straightforward, and we recommend using a clean T-piece circuit. If the circle system and ventilator are required for anaesthesia, we suggest using new breathing hoses, rebreathing bag and soda lime cartridge, and ventilating an artificial lung for 30 minutes with a fresh gas flow rate of 10 l/min and tidal volume of 1 litre.     

The effects of fresh gas flow on the amount of sevoflurane vaporized during 1 minimum alveolar concentration anaesthesia for day surgery: a clinical study

BACKGROUND: Even small costs per case can become economically significant in high volume day surgical units. While general anaesthesia with higher fresh gas flow rates has technical advantages, they result in higher costs. The aim of the present study was to evaluate drug consumption and direct costs related to variations in the fresh gas flow and use of nitrous oxide at a 1 minimum alveolar concentration (MAC) sevoflurane end-tidal anaesthesia for day surgery. METHODS: Thirty-two ASA I-II patients undergoing elective day surgery under general anaesthesia [14 (10-21) min] were studied. Induction was with propofol and fentanyl 100 microg. After laryngeal mask airway placement, patients were randomized to one of four different fresh gas flows: 1 or 2 l/min oxygen in air (50% oxygen), 3 l/min (33% oxygen), or 3 l/min oxygen in nitrous oxide (33% oxygen). Anaesthesia was maintained at 1 MAC. The vaporizer was weighed before and after each procedure. The primary study variable was the sevoflurane utilization per minute. RESULTS: Sevoflurane utilization increased with increasing fresh gas flow for oxygen in air (r2 = 0.89). The nitrous oxide in oxygen group had the lowest sevoflurane utilization, even compared with the lowest oxygen in air group (0.36 vs. 0.48 g/min). CONCLUSION: Sevoflurane utilization during 1 MAC anaesthesia increases linearly with fresh gas flow and is still higher than when nitrous oxide is used even with very low fresh gas flow rates. Direct inhaled anaesthesia-related costs are consequently 20% higher than when nitrous oxide is used, even for the lowest oxygen in air fresh gas flows.     

Effect of N2O on Sevoflurane Vaporizer Settings during Minimal- and Low-flow Anesthesia

Background: Uptake of a second gas of a delivered gas mixture decreases the amount of carrier gas and potent inhaled anesthetic leaving the circle system through the pop-off valve. The authors hypothesized that the vaporizer settings required to maintain constant end-expired sevoflurane concentration (Etsevo) during minimal-flow anesthesia (MFA, fresh gas flow of 0.5 l/min) or low-flow anesthesia (LFA, fresh gas flow of 1 l/min) would be lower when sevoflurane is used in oxygen-nitrous oxide than in oxygen.

Methods: Fifty-six patients receiving general anesthesia were randomly assigned to one of four groups (n = 14 each), depending on the carrier gas and fresh gas flow used: group Ox.5 l (oxygen, MFA), group NOx.5 l (oxygen-nitrous oxide, MFA after 10 min high fresh gas flow), group Ox1 l (oxygen, LFA), and group NOx1 l (oxygen-nitrous oxide, LFA after 10 min high fresh gas flow). The vaporizer dial settings required to maintain Etsevo at 1.3% were compared between groups.

Results: Vaporizer settings were higher in group Ox.5 l than in groups NOx.5 l, Ox1 l, and NOx1 l; vaporizer settings were higher in group NOx.5 l than in group NOx1 l between 23 and 47 min, and vaporizer settings did not differ between groups Ox1 l and NOx1 l.     

A comparison of carbon dioxide monitoring and oxygenation between facemask and divided nasal cannula

The divided nasal cannula is a device recently released in Australia that couples oxygen delivery and end-tidal carbon dioxide (PETCO2) monitoring. This study compares the accuracy of PETCO2 measurements by the divided nasal cannula and those measured by a modified facemask (as currently used in this institution), with arterial partial pressure of carbon dioxide (PaCO2). In this crossover study, 30 patients who had arterial lines as part of their routine monitoring were given oxygen via nasal cannula and facemask preoperatively. The PETCO2 was measured with each device and a simultaneous PaCO2 and PaO2 measured after equilibration. The results demonstrate a significant difference between the PETCO2 as measured by each technique. The divided nasal cannula more accurately reflects PaCO2 (mean arterial to end expired gradient of 5 mmHg) and provides a more representative trace when compared to a traditional facemask system. Both methods provided adequate oxygenation.     

Effect of N2O on sevoflurane vaporizer settings during minimal- and low-flow anesthesia

BACKGROUND: Uptake of a second gas of a delivered gas mixture decreases the amount of carrier gas and potent inhaled anesthetic leaving the circle system through the pop-off valve. The authors hypothesized that the vaporizer settings required to maintain constant end-expired sevoflurane concentration (Etsevo) during minimal-flow anesthesia (MFA, fresh gas flow of 0.5 l/min) or low-flow anesthesia (LFA, fresh gas flow of 1 l/min) would be lower when sevoflurane is used in oxygen-nitrous oxide than in oxygen. METHODS: Fifty-six patients receiving general anesthesia were randomly assigned to one of four groups (n = 14 each), depending on the carrier gas and fresh gas flow used: group Ox.5 l (oxygen, MFA), group NOx.5 l (oxygen-nitrous oxide, MFA after 10 min high fresh gas flow), group Ox1 l (oxygen, LFA), and group NOx1 l (oxygen-nitrous oxide, LFA after 10 min high fresh gas flow). The vaporizer dial settings required to maintain Etsevo at 1.3% were compared between groups. RESULTS: Vaporizer settings were higher in group Ox.5 l than in groups NOx.5 l, Ox1 l, and NOx1 l; vaporizer settings were higher in group NOx.5 l than in group NOx1 l between 23 and 47 min, and vaporizer settings did not differ between groups Ox1 l and NOx1 l. CONCLUSIONS: When using oxygen-nitrous oxide as the carrier gas, less gas and vapor are wasted through the pop-off valve than when 100% oxygen is used. During MFA with an oxygen-nitrous oxide mixture, when almost all of the delivered oxygen and nitrous oxide is taken up by the patient, the vaporizer dial setting required to maintain a constant Etsevo is lower than when 100% oxygen is used. With higher fresh gas flows (LFA), this effect of nitrous oxide becomes insignificant, presumably because the proportion of excess gas leaving the pop-off valve relative to the amount taken up by the patient increases. However, other unexplored factors affecting gas kinetics in a circle system may contribute to our observations.     

Physical Factors Affecting the Production of Carbon Monoxide from Anesthetic Breakdown

Background: Parameters determining carbon monoxide (CO) concentrations produced by anesthetic breakdown have not been adequately studied in clinical situations. The authors hypothesized that these data will identify modifiable risk factors.

Methods: Carbon monoxide concentrations were measured when partially desiccated barium hydroxide lime was reacted with isoflurane (1.5%) and desflurane (7.5%) in a Draeger Narkomed 2 anesthesia machine with a latex breathing bag substituting for a patient. Additional experiments determined the effects of carbon dioxide (0 or 350 ml/min), fresh gas flow rates (1 or 4 l/min), minute ventilation (6 or 18 l/min), or absorbent quantity (1 or 2 canisters). End-tidal anesthetic concentrations were adjusted according to a monochromatic infrared monitor.

Results: Desflurane produced approximately 20 times more CO than isoflurane when completely dried absorbents were used. Peak CO concentrations approached 100,000 ppm with desflurane. Traces of water remaining after a 66-h drying time (one weekend) markedly reduced the generation of CO compared with 2 weeks of drying. Reducing the quantity of desiccated absorbent by 50% reduced the total CO production by 40% in the first hour. Increasing the fresh gas flow rate from 1 to 4 l/min increased CO production by 67% in the first hour but simultaneously decreased average inspiratory concentrations by 53%. Carbon dioxide decreased CO production by 12% in completely desiccated absorbents.     

SOURCES OF ERROR AND THEIR CORRECTION IN THE MEASUREMENT OF CARBON DIOXIDE ELIMINATION USING THE SIEMENS-ELEMA CO2 ANALYZER

The Siemens-Elema CO₂ Analyzer 930 allows calculation of carbondioxide elimination from the instantaneous measurement of expiredgas flow (E) and carbon dioxide fraction (Fe_CO2). E is measured in the ventilator and FE _CO2 at the Y-piece. The most importantsource of error in the measurement of carbon dioxide eliminationis rebreathing, which corresponds to about 24 ml of end-expiratorygas per breath with the standard Y-piece and tubing. This problemmay be decreased by the use of non-return valves in the Y-piece.Allowance must be made for the effects of intermolecular interactionbetween carbon dioxide and the carrier gas, as the reading isabout 20% greater with nitrous oxide than with oxygen. Thisproblem can be largely circumvented by calibration with appropriategas mixtures. Errors resulting from analyser delay are small,and are eliminated completely by the inclution of fast electroniccomponents. Carbon dioxide analysis is linear with air as carriergas, but slightly alinear with nitrous oxide in oxygen mixtures.This error can be minimized by using calibration gases witha carbon dioxide content dene to that of expired gas. The expiratoryflow meter is linear if kept in good condition. Variations intemperature and water content of expired gas cause oveiesliinationof mean expired carbon dioxide fraction (FE_CO2) by a factorof 1.01–1.02. Compressed gas in the tubing causes a smallerror which may be neglected at normal airway pressures withtubing of low compliance. Carbon dioxide measurement is slightlyaffected by barometric pressure. During mechanical ventilationof the lungs in 10 patients with air, FE_CO2 obtained after correctionsfor known errors agreed well with Scholander analysis of mixedexpired gas     

Gas embolus and cardiac arrest during laparoscopic pyloromyotomy in an infant

Purpose

High volume tubing is used to deliver carbon dioxide during laparoscopic procedures. Failure to prime the tubing with carbon dioxide prior to abdominal insufflation may result in the delivery of nitrogen-containing air to the abdominal cavity. We report a case in which initial insufflation of laparoscopic gas resulted in immediate cardiovascular collapse requiring prolonged resuscitation. Persistent intracranial emboli following the arrest may have resulted from nitrogen contamination of the delivered gas.

Clinical features

A 12-day-old female underwent laparoscopy for pyloric stenosis. During initial insufflation of the abdomen, the patient had an abrupt decrease in end-tidal carbon dioxide (CO_2ET) associated with bradycardia and pulseless electrical activity. Three hours after successful resuscitation and open pyloromyotomy, computerized tomography documented intra-arterial gas within the cerebral and hepatic circulations that resolved following hyperbaric oxygen therapy. Magnetic resonance imaging five days later revealed watershed infarcts in the right frontal and parietal regions. Nitrogen, an insoluble gas not easily eliminated from the body, was likely the gas present within the patient’s circulation several hours after the event. It was unlikely carbon dioxide, which is a highly soluble gas that binds to hemoglobin and is rapidly buffered by the carbonic anhydrase system and excreted by the lung. Room air contamination of high volume insufflation tubing allows nitrogen to enter body cavities during endoscopic procedures.

Conclusion

Persistence of emboli following endoscopic procedures suggests that the entrained gas is insoluble. Room air contamination increases the potential for catastrophic events during laparoscopy and other endoscopic procedures.     

A method for producing normocarbia during general anasthesia for Caesarean section

Twenty-six patients were anaesthetised for Caesarean section using the Bain anaesthetic system for intermittent positive pressure ventilation. There was an inverse relationship between maximum end tidal carbon dioxide tension and the fresh gas flow (FGF) to the system. A significant difference existed between the patients receiving 80 ml/kg/min FGF and those receiving 120 ml/kg/min. Estimated carbon dioxide levels in the pregnant term patient were higher at each FGF rate than the levels reported in non-pregnant patients by other workers. In order to maintain maternal arterial carbon dioxide tension at or close to the normally quoted term value of 4.1-4.4 kPa, when using positive pressure ventilation with a Bain system, a fresh gas flow rate of at least 120 ml/kg body weight/minute is required.