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PubMed1986

Respiratory disturbance and posterior fossa surgery. A case report.

This report, of a 16-month-old child recovering from surgery for a posterior fossa tumour, illustrates how pneumotachography, capnography and occlusion testing before and during CO2 challenge can be of clinical value in the analysis of a difficult respiratory disturbance in the early postoperative period. The application of these techniques to assist decisions regarding timing of extubation as well as for assessment of the influence of remaining tumour on respiratory competence is discussed.

Brain Neoplasms↗
PubMed1987

Respiratory depression in children at different end tidal halothane concentrations.

Respiratory motor function and timing were investigated at end tidal halothane concentrations of 1.5%, 1.0% and 0.5% before and during 4% carbon dioxide stimulation in 10 spontaneously breathing children who weighed between 10.2 and 25.2 kg, during hypospadias repair under halothane anaesthesia. Their tracheas were intubated and all received a caudal block to eliminate surgical stimulation. Pneumotachography and capnography were used and in three cases movements of ribcage and abdomen were also studied by magnetometers. Respiratory drive was evaluated by occlusion tests. Ventilation was depressed at an end tidal halothane concentration of 1.5%, with smaller tidal volumes, higher respiratory rates, higher end tidal carbon dioxide tensions and a weaker respiratory drive compared with 1.0% and 0.5% halothane. Paradoxical breathing was noted at 1.5% as well as at 1.0% but not at 0.5% halothane anaesthesia; the ribcage moved inwards during inspiration. Respiratory compensation during periods of 4% carbon dioxide stimulation was inadequate at 1.5% halothane, as indicated by higher end tidal carbon dioxide tensions, less negative occlusion pressures and movements of ribcage and abdomen that were unresponsive to 4% carbon dioxide, when compared with 1.0% and 0.5% halothane. Respiratory rates were higher and duration of inspiration longer at 1.5% than at 1.0% and 0.5% halothane. Respiratory timing was unaltered by carbon dioxide stimulation. It is concluded that the ventilatory motor response to carbon dioxide is dose dependent and improves at more superficial anaesthetic levels, while respiratory timing is unresponsive to carbon dioxide stimulation irrespective of the halothane concentration used. Paradoxical breathing existed at end tidal halothane concentrations higher than 1%.

Abdomen↗
PubMed1994

End-tidal carbon dioxide tension during laparoscopic cholecystectomy. Correlation with the baseline value prior to carbon dioxide insufflation.

An investigation of end-tidal carbon dioxide tension changes was carried out in 19 healthy adult patients undergoing laparoscopic cholecystectomy. Following induction of anaesthesia, and throughout surgery, the end-tidal carbon dioxide tension was continuously monitored by capnography. The value following carbon dioxide insufflation increased with time to reach a maximum value after 40 min. Correlation of the individual maximum end-tidal carbon dioxide tension during laparoscopy with the corresponding baseline value prior to carbon dioxide insufflation showed a positive linear relationship (correlation coefficient 0.86). The correlation showed that an end-tidal carbon dioxide tension of 5.32 kPa (40 mmHg) can be achieved during laparoscopy when the baseline value is adjusted to around 4.0 kPa (30 mmHg).

Adult↗
PubMed1995

Air embolism during awake craniotomy.

A case of venous air embolism during awake craniotomy is described. Chest pain and electrocardiographic changes were the major presenting features. Capnography detected a decrease in end-tidal carbon dioxide and demonstrates its use as an aid in the diagnosis of air embolism in the awake patient. Following this episode persistent hypoxaemia developed secondary to acute pulmonary oedema and a pleural effusion.

Adult↗
PubMed1996

The use of bromothymol blue and sodium thiopentone to confirm tracheal intubation.

The possibility of using chemical changes to confirm correct tracheal tube placement was investigated with a view to their use in developing countries where more sophisticated methods are unavailable. The effect of bubbling expired gases through a 10% solution of bromothymol blue and a 0.25% solution of thiopentone led to chemical changes producing, in the case of bromothymol blue, a colour change and in that of thiopentone, precipitation, probably due to a change in pH caused by carbon dioxide. We also discovered that the time to precipitation of the thiopentone could be greatly reduced if it was mixed with a precise quantity of lignocaine. These simple end points can reliably confirm the correct placement of a tracheal tube at least as rapidly as the correct use of capnography.

Adult↗
PubMed1996

Measuring rebreathing in spontaneous ventilation. A new lung model.

The performance of breathing systems is tested by means of physical lung models. We describe a new lung model, allowing direct measurement of the dead space/tidal volume ratios produced by any breathing system at different fresh gas flows. The model allows a range of different patterns of spontaneous respiration to be studied. Although rebreathing is measured by capnography, the design ensures that the results are unaffected by changes in carbon dioxide inflow, or even calibration drift in the capnograph.

Anesthesia, Closed-Circuit↗
PubMed1998

Airway auscultation. A new method of confirming tracheal intubation.

Unrecognised accidental oesophageal intubation remains an important cause of morbidity and mortality in anaesthetic practice. We have evaluated a new method of distinguishing tracheal from oesophageal intubation using a simple adaptation of an ordinary stethoscope which is inserted into the patient end of the breathing system. We call this technique 'airway auscultation'. Characteristic sounds are heard with the stethoscope during inflation and deflation which allow the observer to diagnose the position of the tube. When the tube is in the trachea loud breath sounds are heard. In contrast, when the tube is in the oesophagus either squeaks or a flatus-like noise is heard or else there is no sound. In 100 healthy adults two observers rapidly identified 99 intubations correctly in a randomised single-blind trial. We recommend further widespread evaluation of this device as it appears to be an effective, simple and rapid method of detecting oesophageal intubation and confirming tracheal intubation which may be of particular use in situations where capnography is not available.

Adolescent↗
PubMed2005

Survival after massive bleeding into the airway in a patient at risk from "can't intubate, can't ventilate".

A patient survived massive bleeding into the airway due to blowout of the right internal jugular vein associated with a failed free-flap graft for pharyngeal malignancy. A recently decannulated "covering tracheostomy" could not be easily re-established. Direct laryngoscopy and mask ventilation were inappropriate because the pharyngeal mucosal wound opened spontaneously and progressively and bleeding was dramatic. Positive pressure ventilation via a facemask risked widespread surgical emphysema and further wound disruption and because bleeding was from the internal jugular vein, there would also have been a risk of air embolism. The clinical situation evolved rapidly so time management and consideration of hierarchy of mortality risks was critical. It was eventually possible to re-establish the previous tracheostomy site as a result of close co-operation between the surgical and anaesthetic teams. In difficult intubation where the problems are anticipated, the notion of responsive contingency planning is suggested to be of more general relevance than the current standard of considering alternative fallback options. The limitations of conventional capnography in this situation are also noteworthy.

Contraindications↗
PubMed1976

Breathing mechanics, dead space and gas exchange in the extremely obese, breathing spontaneously and during anaesthesia with intermittent positive pressure ventilation.

Breathing mechanics and gas exchange were studied in 10 extremely obese subjects (average weight 138 kg) prior to and during anaesthesia with mechanical ventilation. Breathing mechanics were analysed from measurements of transpulmonary pressure (during anaesthesia, trans-chest wall pressure as well) inspiratory gas flow and tidal volume. Gas exchange was studied by analysing inspired and from the Bohr equation, and the division into anatomical and alveolar dead space was arrived at by capnography. The patients were anaesthetised with neuroltpt agents and ventilated with an air-oxygen mixture. Lung compliance during spontaneous breathing was below normal and decreased further during artificial ventilation. Chest wall compliance measured during anaesthesia was within normal limits. Lung resistance was above normal during spontaneous breathing and increased further during mechanical ventilation. Total dead space was normal during spontaneous breathing and increased moderately during artificial ventilation, the increment coming mainly from alveolar dead space. A moderate hypoxaemia was recorded during spontaneous breathing, and the alveolar-arterial oxygen tension difference was slightly elevated. During anaesthesia this difference was markedly greater. It is concluded that the most probable reason for the relative hypoxaemia is right-to-left shunting.

Adult↗
PubMed1976

The flow requirement in a non-polluting Mapleson C circuit.

Capnography and measurement of the respiratory minute volume were carried out on normal, conscious subjects during breathing of pure O2 via a Mapleson C modification of a Magill attachment, with and without continuous gas evacuation. The measurements were performed in two series, with intermittent discharge and with continuous evacuation. Rebreathing was calculated in relation to the test subject's basal respiratory minute volume, measured at the commencement of the test. The measurements indicated CO2 accumulation at a flow below 200% of the respiratory minute volume. There was no significant difference between the systems with and without evacuation.

Adult↗
PubMed1979

Open scavenging systems.

A mathematical model was developed to cover the dynamic characteristics of open scavenging systems. The performance of such a device depends on the expiratory tidal volume (VT), the scavenging flow (Vs) and the mode of exhalational volume build-up. A widely used open scavenging system was tested by using carbon dioxide in oxygen as a marker gas. Capnography revealed gross turbulence in the expiratory reservoir, which tends to increase the polluted gas volumes and loads extra requirements onto the scavenging equipment. Increases in the scavenging flow or the expiratory reservoir volume are the aids in obtaining satisfactory safety margins for pollution-free scavenging of surplus anaesthetic gases. The theoretical basis of a new method to determine the expiratory time constant of the respiratory system is also presented.

Air Pollutants↗
PubMed1982

Gas exchange and respiratory mechanics during hip arthroplasty.

Gas exchange and respiratory mechanics were studied during hip arthroplasty, according to Charnley (1961). Dead space measurements were made by capnography and thoracic compliance and resistance, calculated from tracheal pressure variations and respiratory gas flow. PaO2 fell by 2.5 kPa with the insertion of each prosthesis. Small increases in PaCO2 were also seen. Distal (approximately corresponding to alveolar) dead space increased by 25% when each prosthesis was anchored. Dynamic thoracic compliance fell by 30-40 ml/kPa at the insertion of either prosthesis, while inspiratory and expiratory resistance were unaffected. The findings may indicate interference with the functions of both the bronchial and the pulmonary vascular tree.

Adult↗
PubMed1982

Halothane anaesthesia with spontaneous respiration for tonsillectomy in children.

Bains's anaesthetic circuit was used in 22 children undergoing tonsillectomy under halothane anaesthesia with spontaneous respiration. End-tidal CO2 was monitored by capnography. The median maximum end-tidal CO2 was 7%, and during surgery nine patients had an end-tidal CO2 higher than 7%, corresponding to a Paco2 close to 8 kPa when the arterial to end-tidal CO2 difference is taken into consideration. Increase in fresh gas flow or change to a non-rebreathing system had virtually no effect on end-tidal CO2. However, following discontinuation of halothane or during controlled respiration, acceptable values of end-tidal CO2 were reached, leading to the conclusion that respiratory depression was responsible for the high values of end-tidal CO2 rather than properties of Bain's circuit or too low gas flow rates.

Anesthesia, General↗
PubMed1986

Ventilation and ventilatory CO2 response in children during halothane anaesthesia after non-opioid (midazolam) and opioid (papaveretum) premedication.

The influence of non-opioid (NO) and opioid (O) premedication on ventilation and ventilatory CO2 response was studied in 18 spontaneously breathing children during halothane anaesthesia. Eight patients in Group NO and 10 in Group O were comparable in age, body weight and type of surgery performed. The sedative effect was evaluated and measurements by pneumotachography and in-line capnography were made immediately after induction of sleep, just before the start of surgery, during surgery and after surgery both before and after 3 min of about 2% CO2 inhalation. Immediately after induction the mean value (+/- s.e. mean) of end-tidal CO2 concentration (ETCO2) was 4.86 +/- 0.21% in Group NO and 5.28 +/- 0.22% in Group O. Before and during surgery, minute ventilation (VE) was higher in Group NO (P less than 0.05) mainly due to higher respiratory rates. ETCO2 was similar in the two groups before, during and after surgery. The ratio of VE to CO2 elimination (VCO2) and of dead space (VD) to tidal volume (VT) was higher in Group NO, but ventilatory response to CO2 inhalation immediately before the postoperative period was similar in both groups. It was concluded that opioid premedication resulted in more efficient ventilation during anaesthesia and surgery, and that CO2 response at the end of surgery was maintained in both groups.

Analgesics↗
PubMed1986

Pulmonary ventilation, CO2 response and inspiratory drive in spontaneously breathing young infants during halothane anaesthesia.

Pulmonary ventilation, CO2 response and inspiratory drive were studied during halothane anaesthesia prior to surgery in 13 spontaneously breathing infants less than 6 months of age. Pneumotachography and capnography were used. Airway and oesophageal pressures were measured and occlusion tests were performed at functional residual capacity. Measurements were made before and during 8 min of 4% CO2 stimulation. Inspiratory drive increased significantly (P less than 0.001) at CO2 stimulation. This resulted in increased minute ventilation (P less than 0.001) and tidal volume (P less than 0.001) while respiratory rate was unchanged. As VBohrD/VT ratios were the same, the net effect was increased alveolar ventilation (P less than 0.001). CO2 elimination was unpredictable in these young infants and decreased during CO2 stimulation (P less than 0.05), while mean end-tidal CO2 concentration only increased from 5.2 to 6.3% (P less than 0.001). The ventilatory response to 4% CO2 could therefore be deemed to be adequate during the short period (8 min) of CO2 breathing. However, this was achieved at the cost of increased work as witnessed by the increased ratio between minute ventilation and CO2 elimination (P less than 0.01). Stabilisation of end-tidal CO2 concentrations during CO2 inhalation took only 10 s while the maximal increase in ventilation volumes was not achieved until after 150 s. It is concluded that young spontaneously breathing infants anaesthetized with halothane (MAC 1.3) have an increased respiratory drive with greater tidal volumes during CO2 stimulations. Respiratory timing, dynamic compliance and total pulmonary resistance were, however, uninfluenced by 4% CO2 stimulation. Increased monitoring of CO2 output in anaesthetized infants is suggested.

Anesthesia, General↗
PubMed1986

CO2 production and breathing pattern during invasive and non-invasive respiratory monitoring.

A computerized non-invasive strain gauge system for respiratory monitoring is described and compared with pneumotachography. With the use of simultaneous capnography, changes in breathing pattern, end-tidal PCO2 and CO2 production were evaluated during non-invasive (NIM) and invasive breathing monitoring (IM) in 14 healthy subjects. An overall absolute difference between measured and calculated tidal volumes of 4.6 +/- 3.47% (r = 0.97) was found. When switching from NIM to IM, tidal volume increased by 19% and breathing frequency decreased by 11% with a 10% increase in minute ventilation. These changes were mainly accomplished by an increased respiratory drive with the timing component unaltered. During IM both end-tidal PCO2 and CO2 production increased significantly as compared with those during NIM.

Adult↗
PubMed1987

Pulmonary ventilation and gas exchange in children anaesthetized with halothane, enflurane and isoflurane.

The effects of similar anaesthetic levels of halothane (1.3 MAC), enflurane (1.2 MAC) and isoflurane (1.1 MAC) on pulmonary ventilation and gas exchange were investigated in 24 children subjected to minor and intermediate paediatric surgical procedures. Eight children were anaesthetized with each agent, pneumotachography and capnography were used, and airway as well as oesophageal pressures were measured. Minute ventilation (VE) was lower with enflurane than with halothane (P less than 0.001) and isoflurane (ns). Tidal volumes were, however, similar and variations in VE were thus caused by lower respiratory rates with enflurane than with the two other agents. Alveolar ventilation (VABohr) and carbon dioxide elimination (VCO2) were smaller and end-tidal CO2 tension higher with enflurane. Ventilatory efficiency was, however, somewhat better with enflurane as indicated by lower VDBohr/VT (ns) and VE/VCO2 (P less than 0.05) ratios compared with the two other agents. The effects of all three agents on dynamic compliance were similar, while total pulmonary resistance was less with isoflurane than with halothane and enflurane. It is concluded that although minute ventilation was smaller with enflurane than with halothane and isoflurane, ventilatory efficiency was similar due to a smaller dead space ventilation as a result of the lower respiratory rates in children anaesthetized with enflurane.

Airway Resistance↗
PubMed1992

Effects of low-dose propofol administration on central respiratory drive, gas exchanges and respiratory pattern.

The effects of sedative-hypnotic doses of propofol on respiratory drive and pattern have not yet been extensively described. Repeated small boluses of propofol (0.6-0.3 mg.kg-1) were administered to ten ASA I patients undergoing carpal tunnel release using regional anaesthesia. Airway pressure, capnography and pneumotachography were continuously recorded. With respect to basal values, no significant variations of respiratory rate, minute volume, tidal volume, inspiratory and expiratory time, total expiratory cycle, Ti/Ttot, TV/Ti, P0.1, EtCO2 and blood gas analysis were observed. Low doses of propofol, to maintain conscious sedation of light sleep, have not been shown to cause respiratory depression.

Ambulatory Surgical Procedures↗