Predictable Paco2, with two different flow settings using the Mapleson D system

Two different settings of fresh gas flow (VFG) and minute ventilation (VE) used with the coaxial Mapleson D system (Bain), were evaluated in 59 adults (ASA I-III) during controlled ventilation and different types of surgical procedures. The two flow settings (alternatives A and B) were VFG of 75 and 110 ml.min-1.kg-1 and VE of 150 and 175 ml.min-1.kg-1, aiming to generate normocapnea and mild hypocapnea, respectively. The PaCO2 obtained with alternative A was 5.5 +/- 0.5 kPa (mean +/- s.d.), with 92% of the patients within the range 4.7-6.1 kPa. With alternative B, the PaCO2 was 4.4 +/- 0.5 kPa, with 82% of the patients within the range 3.5-4.9 kPa. It is concluded that these two flow regimes are suitable for clinical use when either normocapnea or mild hypocapnea is desired.     

Effects of rectal thiopentone and methohexitone on carbon dioxide tension in infant anaesthesia with spontaneous ventilation

The influence of rectal administration of barbiturates on PCO2 during mask anaesthesia with spontaneous ventilation was studied in 72 infants. The age of the patients ranged between 6 and 24 months and they were all subjected to minor paediatric surgery. The patients were divided into four equally large groups: a control group receiving no premedication, a group receiving rectal thiopentone 30 mg X kg-1 and two groups receiving methohexitone either 20 or 30 mg X kg-1. In all patients PCO2 was measured in an arterialized capillary blood sample obtained during stable anaesthesia with oxygen, nitrous oxide and halothane before and after surgery. After rectal induction with barbiturates, the mean PCO2 was significantly higher in the different barbiturate groups than in the control group (P less than 0.05). The mean PCO2 value +/- s.d. in kPa for the control group was 5.6 +/- 0.7, for the group receiving thiopentone 30 mg X kg-1 6.5 +/- 1.6, for the groups receiving methohexitone 20 or 30 mg X kg-1 6.1 +/- 1.2 and 6.3 +/- 1.1, respectively. It is concluded that the combination of rectal induction with barbiturates and mask anaesthesia with oxygen, nitrous oxide and halothane carries an increased risk of hypoventilation in infants under 2 years of age.     

A new concept in controlled ventilation of children with the Bain anesthetic circuit

The Bain anesthesia circuit was studied as a semi-open or partial rebreathing system during controlled ventilation in 16 children weighing from 7.5 to 48 kg. During anesthesia the lungs were ventilated with a volume ventilator set at three times the calculated alveolar ventilation to provide optimum mixing in the exhalation tube of the Bain circuit. Fresh gas inflow rates initially were set equal to the calculated alveolar ventilation, and after 30 to 45 min, PCO2, PO2 and pH values were measured. At the same time, the fractional concentration of mixed expired carbon dioxide (FECO2) was recorded from a capnograph inserted between the ventilator and the Bain circuit. After initial readings, the fresh gas inflow was varied over a range of 1,400-3,000 ml/m2/min at 20-min intervals, with the arterial blood-gas values and FECO2 recorded at each setting. The results indicate that a lower fresh gas inflow than previously recommended can be used safely in children. When the minute ventilation is three times the fresh gas inflow, values for FECO2 correlate closely with PaCO2 values; with a fresh gas inflow of 2,500 ml/m2/min,PaCO2 values can be maintained near 40 torr.     

Carbon dioxide tensions in infants during mask anaesthesia with spontaneous ventilation

Carbon dioxide tensions (PCO2) in arterialized capillary blood samples were measured in 39 infants anaesthetized for minor paediatric surgery. Anaesthesia was induced and maintained with oxygen, nitrous oxide and halothane, using a Mapleson-D system with spontaneous ventilation and a Rendell-Baker face mask. The duration of anaesthesia was between 15 and 95 min. Two capillary blood samples were obtained during stable anaesthesia before and after surgery. The PCO2 values varied between 3.7 and 8.0 kPa. The highest values were found in infants aged 15-30 days, 6.6 +/- 0.7 kPa (mean +/- s.d.), compared to 5.9 +/- 0.7 in infants aged 31-60 days, 5.6 +/- 0.8 in infants aged 61-180 days and 5.5 +/- 0.7 in infants aged 181-300 days. Comparison between measurements before and after surgery did not in any group indicate a progressive hypoventilation or a correlation between the length of the anaesthesia and the PCO2. It is concluded that anaesthesia with oxygen, nitrous oxide and halothane with spontaneous mask ventilation is a satisfactory method for minor procedures in infants over 1 month of age, while in younger infants controlled ventilation with intubation may be a safer choice of method.     

Single breath end-tidal CO2 estimates of arterial PCO2 in infants and children

To determine whether single breath end-tidal carbon dioxide (PE'CO2) measurements accurately estimate arterial PCO2 (PaCO2) in infants and children, 68 healthy infants and children, ASA physical status I or II scheduled for peripheral and lower abdominal surgery requiring endotracheal intubation were studied. A 3 ml single breath sample was obtained with a 23-gauge needle which was inserted through the wall of the endotracheal tube below the connector. The mean +/- SD PE'CO2 33.6 +/- 6.9 mmHg did not differ significantly from the corresponding mean +/- SD PaCO2 33.6 +/- 5.6 mmHg. The coefficient of determination, r2, was 0.97. The authors conclude that single breath PE'CO2 measurements from the proximal end of the endotracheal tube accurately estimate the PaCO2 in infants and children.     

Fresh gas flow changes during controlled mechanical ventilation with the circle breathing system have significantly greater effects on the ventilatory parameters of toddlers compared with children*

Fresh gas flow into a circle system can affect the delivered minute ventilation because fresh gas flow augments the flow delivered by the ventilator bellows during inspiration. After establishing a stable ventilatory pattern with 3.0 l·min^-1 fresh gas flow into a circle system, changes in peak inflation pressure, minute ventilation and end-tidal carbon dioxide were measured at 1.5 l·min^-1 and 6.0 l·min^-1 in 10 toddlers (10–20 kg) and 10 children (30–60 kg). Changes in all variables were observed but these changes were greater in toddlers compared with children (P < 0.001). Some toddlers were noted to have as much as a 37% change in ventilatory parameters when fresh gas flow was altered between 1.5 and 6.0 l·min^-1. Whenever changes are made in fresh gas flow, compensatory changes in minute ventilation should be considered to avoid unintended hyperventilation or hypoventilation. This is especially important during anaesthesia for toddlers.     

Tight control of prehospital ventilation by capnography in major trauma victims

Background. Tracheal intubation combined with controlled ventilationof the lungs is an important part of the prehospital managementof major trauma victims, but gauging the adequacy of ventilationremains a major problem. Methods. Ninety-seven major trauma victims who underwent trachealintubation in the field and controlled ventilation of the lungsduring prehospital treatment by a Helicopter Emergency MedicalService were assigned randomly to one of two groups: (1) monitorgroup (n=57) and (2) monitor-blind group (n=40), according towhether the anaesthetist could or could not see an attachedcapnograph screen. In the monitor-blind group ventilation wasset by using a tidal-volume of 10 ml kg^–1 estimated bodyweight and an age-appropriate ventilatory frequency. In themonitor group, ventilation was adjusted to achieve target end-tidalcarbon dioxide values determined by the ‘physiologicalstate’ of the trauma victim. Arterial blood gases weremeasured upon hospital admission while maintaining the ventilationinitiated in the field and the Pa_CO2 value obtained was usedas the determinant of the adequacy of prehospital ventilation. Results. The incidence of ‘normoventilation’ wassignificantly higher (63.2 vs 20%; P<0.0001) and the incidenceof ‘hypoventilation’ upon hospital admission wassignificantly lower (5.3 vs 37.5%; P<0.0001) in the monitorgroup; patients with severe head and chest trauma and haemodynamicallyunstable patients and those with a high injury severity scorewere significantly more likely to be ‘normoventilated’upon hospital admission in the monitor group than in the monitor-blindgroup. Conclusions. The data support the routine use of prehospitalcapnographic monitoring using target end-tidal carbon dioxidevalues adapted to the physiological state of the patient inmajor trauma victims requiring tracheal intubation in the field. Br J Anaesth 2003; 90: 327–32     

Mivacurium chloride in infants and children

Mivacurium has been little studied in infants and children without a volatile anaesthetic agent. We analysed onset time and maximal neuromuscular response after mivacurium 0.1 mg/kg, and the infusion requirement of mivacurium to maintain a 50, 90, or 95% neuromuscular block in 76 infants and children under N₂O-O₂ alfentanil anaesthesia. Furthermore, we assessed the time course of potentiation of 1 MAC end-tidal halothane or isoflurane on the infusion requirement of mivacurium. Neuromuscular response was recorded by adductor pollicis electromyogram. The onset time of mivacurium was shorter in infants than in children (2.1 ± 0.6 and 3.2 ± 0.9 min (mean±SD); P =0.0001). The dose potency of mivacurium did not depend on the age of a paediatric patient. The estimated ED₉₅ of mivacurium was 136±46 μg/kg. The mivacurium requirement to maintain a 50, 90, or 95% neuromuscular block averaged 340, 730, and 900 μg/kg/h, respectively. Halothane and isoflurane decreased this hourly requirement by 35 and 70%, respectively. The decrease in the mivacurium infusion requirement was fastest in the youngest children. In conclusion, mivacurium is easy to administer as bolus doses or continuous infusion in paediatric patients because its potency is similar in all patients from 1 month to 15 years of age. Halothane and isoflurane produce their maximal potentiation of neuromuscular block only after 30–60 min of administration. This potentiation is similar in magnitude in all patients, but takes place fastest in the youngest children.     

Spontaneous versus controlled ventilation in anaesthetized children with congenital cardiac malformations

The effects of intermittent positive pressure ventilation on gas exchange were studied in 12 children with congenital cardiac malformation. Six children (b.w. 3.7-16 kg) had a left-to-right shunt (Group LR) resulting in overperfused lungs, while six others (b.w. 3.4-12 kg) had a right-to-left shunt (Group RL) with oligaemic lungs. Measurements, prior to surgery, were done during spontaneous breathing (SB) and controlled mechanical ventilation (CMV) with a short (25%) and a long (55%) duration of inspiration. In children with oligaemic lungs P(a-E')CO2 differences and VD/VT ratios were greater and PaO2 was lower than in those with overperfused lungs, indicating a less efficient ventilation. In Group RL, ventilation and gas exchange during SB were similar at the two settings of CMV. In Group LR, however, VD/VT was reduced during CMV, with the lowest VD/VT ratio at the longer inspiration time. It is concluded that in children with an oligaemic lung perfusion, either of the two ventilator settings could be used. When controlled ventilation is to be used in children with overperfused lungs, the longer duration of inspiration seems to be preferable.     

Combined spinal-propofol anesthesia with noninvasive positive-pressure ventilation

Twenty-three adult patients undergoing repair of inguinal hernia under spinal anesthesia received propofol infusion for sedation with the assist of noninvasive positive-pressure ventilation (NPPV). Circulatory and respiratory parameters, such as percutaneous oxygen saturation, transcutaneous carbon dioxide tension, respiratory rate, tidal volume, blood pressure, and heart rate, were maintained within physiological ranges during the anesthesia. There were no adverse effects. These findings suggest that the application of NPPV in patients receiving propofol infusion for sedation is clinically practicable during anesthesia.     

Single-lung ventilation in infants and children

During the past decade, the use of video-assisted thoracoscopic surgery (VATS) has dramatically increased in children as well as adults. Although VATS can be performed while both lungs are being ventilated, single-lung ventilation (SLV) is desirable during VATS. In addition, anaesthesiologists are performing (and paediatric surgeons are requesting) SLV more frequently for open thoracotomies in infants and children.     

Fresh gas flow in the Bain circuit during laparoscopy

Twenty-two women were studied during laparoscopy with abdominal insufflation of carbon dioxide. A bain anaesthetic breathing circuit was used with a fresh gas flow (VFG) of 110 ml.min-1.kg-1, and controlled ventilation was applied with a minute ventilation (VE) of 175 ml.min-1.kg-1. Arterial blood gases were analysed at the end of the operation. Nineteen of the women (86 per cent) were found to have a PaCO2 within the range for normocapnia (i.e., 4.7-5.9 kPa (35-45 mmHg), two were hypocapnic with a PaCO2 of 4.4 and 4.5 kPa (33 and 34 mmHg) respectively and one was found to have a PaCO2 of 6.2 kPa (46.5 mmHg). It was concluded that the carbon dioxide absorbed from the abdomen during laparoscopy demands fresh gas flows that are higher than normally used in the Bain circuit if a PaCO2 within the normal range is to be obtained. A simultaneous increase in VFG and VE of about 45 per cent is sufficient to achieve normocapnia.     

Arterial to end‐tidal carbon dioxide difference in children undergoing mechanical ventilation of the lungs during general anaesthesia

Capnography (ETCO₂) is routinely used as a non‐invasive estimate of arterial carbon dioxide (PaCO₂) levels in order to modify ventilatory settings, whereby it is assumed that there is a positive gap between PaCO₂ and ETCO₂ of approximately 0.5 kPa. However, negative values (ETCO₂ > PaCO₂) can be observed. We retrospectively analysed arterial to end‐tidal carbon dioxide differences in 799 children undergoing general anaesthesia with mechanical ventilation of the lungs in order to elucidate predictors for a negative gap. A total of 2452 blood gas analysis readings with complete vital sign monitoring, anaesthesia gas analysis and spirometry data were analysed. Mean arterial to end‐tidal carbon dioxide difference was ?0.18 kPa (limits of 95% agreement ?1.10 to 0.74) and 71.2% of samples demonstrated negative values. The intercept model revealed PaCO₂ to be the strongest predictor for a negative PaCO₂‐ETCO₂ difference. A decrease in PaCO₂ by 1 kPa resulted in a decrease in the PaCO₂‐ETCO₂ difference by 0.23 kPa. This study demonstrates that ETCO₂ monitoring in children whose lungs are mechanically ventilated may paradoxically lead to overestimation of ETCO₂ (ETCO₂ > PaCO₂) with a subsequent risk of unrecognised hypocarbia.     

Respiratory and haemodynamic effects of conventional volume controlled PEEP ventilation, pressure regulated volume controlled ventilation and low frequency positive pressure ventilation with extracorporeal carbon dioxide removal in pigs with acute ARDS

The purpose of this study was to evaluate whether any benefit of low frequency positive pressure ventilation with extracorporeal carbon dioxide removal (LFPPV–ECCO₂R) existed over either volume controlled ventilation (VCV) with measured best–PEEP or pressure regulated volume controlled ventilation (PRVCV) with an inspiration/expiration (I/E) ratio of 4:1, with respect to arterial oxygenation, lung mechanics and haemodynamics, in acute respiratory failure.
Fifteen adult pigs were used for the study. Respiratory failure was induced by surfactant depletion by repeated lung lavage. The different therapeutic approaches were applied randomly to each pig for 1 h. Measurements of gas exchange, airway pressures and haemodynamics were performed during ventilatory and haemodynamic steady state. Paco₂ was kept constant in all modes.
At almost similar total–PEEP, Pao₂ values were significantly higher with LFPPV–ECCO₂R comared to VCV with best–PEEP. Peak inspiratory pressure (PIP) and intrapulmonary pressure amplitude defined as the difference between PIP and total–PEEP were significantly lower with PRVCV and LFPPV–ECCO₂R compared to VCV with best–PEEP. There was no significant difference between the modes concerning cardiocircu–latory parameters.
PRVCV with I/E ratio of 4:1 and LFPPV–ECCO₂R proved to be better modes to achieve better gas exchange and lower PIP at lower intrapulmonary pressure amplitudes. It is concluded that PRVCV is an adequate form of treatment under these experimental conditions imitating acute respiratory failure, without necessitating other invasive measures.     

Effects of carbon dioxide absorbent cooling and temperature gradient reduction on water condensation in the anaesthesia circuit

BACKGROUND: Large quantities of water condensation occur in the anaesthesia circuit during low-flow anaesthesia. We hypothesized that cooling of the CO2 absorbent would prevent water condensation. METHODS: To cool CO2 absorbent efficiently, we constructed a novel temperature gradient reduction (TGR) canister, which was cooled by a blower. Experiments were divided into three groups: the conventional canister group (control group, n=6), the TGR canister without cooling group (TGR group, n=6), and the TGR canister with cooling group (TGR cooling group, n=6). One kilogramme of CO2 absorbent was placed into the canister. The anaesthetic ventilator was connected to a 3 litre bag and 300 ml min(-1) of CO2 was introduced. About 500 ml min(-1) of oxygen was used as fresh gas. The anaesthetic ventilator was set at a ventilatory frequency of 12 bpm, and tidal volume was adjusted to 700 ml. RESULTS: The longevity of the CO2 absorbent was 437 (sd 7.8) min in the control group, 564 (13.8) min in the TGR group (P<0.001 vs control), and 501 (5.8) min in the TGR cooling group (P<0.001 vs control, TGR). Total water condensation in the anaesthesia circuit was 215 (9.4) mg min(-1) in the control group, 223 (9.7) mg min(-1) in the TGR group, and 47.7 (5.7) mg min(-1) in the TGR cooling group (P<0.001 vs control, TGR). CONCLUSIONS: TGR of CO2 absorbent with cooling is a useful and simple method to reduce water condensation in the anaesthesia circuit in low-flow anaesthesia, with a little increase in the longevity of the CO2 absorbent.     

Metabolic gas exchange during aortocoronary bypass surgery using a double pump systemand mechanical ventilation

Oxygen uptake and carbon dioxide excretion during aorto-coronary bypass surgery were studied in seven patients by indirect calorimetry and compared to blood-gas based measurements. Medium-high dose fentanyl, droperidol and midazolam were used for maintaining anaesthesia. During the period of extracorporeal circulation no external oxygenator was used. Circulation was maintained by two pumps by-passing the left and right heart respectively and the patient's lungs were ventilated with O2/N2 using a Servo 900C ventilator. For indirect calorimetric measurements gas concentrations were analysed by Beckman instruments and gas volumes were measured by the Servo 900C ventilator. Oxygen uptake and carbon dioxide excretion decreased by 31% and 39%, respectively. For invasive measurements during extracorporeal circulation, arterial and venous blood gases and pump flow were used. Using pump flow instead of cardiac output when calculating oxygen uptake circumvented errors in thermodilution measurements. There was a good correlation (r = 0.88) between the invasive and the indirect calorimetric measurements. Further, there was a good correlation between naso-pharyngeal temperature and indirect calorimetric measurements of oxygen uptake (r = 0.87).     

Automatic jet ventilation in children anaesthetized by the T-piece circuit

Investigation was carried out in ten children aged between one month and six years, who were anaesthetized by the T-piece circuit. The volume of the reservoir tubing of the T-piece was 250 ml. Ventilation was controlled automatically by oxygen jets which were delivered via an injector attached to the reservoir tubing. The oxygen jets were regulated by an electronically-controlled solenoid valve. The children were ventilated by a tidal volume about 12 ml±kg^?1 at a rate of 12-20 per min depending on their age, while the FGF varied between 3 and 6 l min^?1 depending on their body weight. The resulting FIO₂ ranged between 0.32 and 0.34 which was expected from the oxygen:nitrous oxide mixture (1:2), denoting no mixing of the oxygen jets with the anaesthetic mixture. The PA_co2 was ventilation-dependent, and ranged between 4±6-5±3 kPa (35-41 mmHg). The results suggest that automatic jet ventilation facilitates controlled ventilation in children anaesthetized by the T-piece circuit, while maintaining the original simplicity of the T-piece.;     

Intracuff pressure during one-lung ventilation in infants and children

ObjectiveWe prospectively evaluated intracuff pressure (IP) during one-lung ventilation (OLV) to characterize potential risk associated with overinflation of the cuff used for OLV.DesignProspective observational study over a 2-year period, in infants and children undergoing thoracic surgery. The IPs of the tracheal and bronchial balloon were measured using a manometer and compared to a previously recommended threshold of 30 cmH2O. Data were compared by the device type used to achieve OLV.SettingFreestanding tertiary-care pediatric hospital.ParticipantsPatients ≤ 18 years of age undergoing thoracic procedures requiring OLV.InterventionsMeasurement of IP.Measurements and main resultsThirty patients were enrolled (age 5 months–18 years) with a median weight of 28 kg. Median tracheal and bronchial IPs were 32 cmH2O (range: 11, 90) and 44 cmH2O (range: 10, 100), respectively. The tracheal and bronchial IPs exceeded 30 cmH2O in 13 of 20 patients (65%) and 21 of 30 patients (70%), respectively.ConclusionsIP was high and in excess of recommended levels in most children undergoing OLV. Continuous monitoring of IP may be indicated during OLV to address the risks involved and ensure the prevention of complications related to high IP.Type of studyProspective comparative study.Level of evidenceLevel II.