Babette Horn

The effect of circuit compliance on delivered ventilation with use of an adult circle system for time cycled volume controlled ventilation using an infant lung model

This in vitro study examined the effect of circuit compliance on delivered ventilation (VE) using a time‐cycled, volume controlled circle system in an infant lung model. A Bio‐Tek ventilator tester set to simulate normal and abnormal lung compliance measured VE delivered by the Narkomed 2B system. Circle circuits of varied compliance (2.75, 1.22 and 0.73 μl·cm H2O−1) were tested. Tidal volume was adjusted to peak inflation pressures (PIP) of 20, 30, 40, and 50 cm H2O with three circuits, two lung compliances, and four different size tracheal tubes (TT) (2.5, 3.5, 4, 4.5 mm ID). Data were analysed using the multiple regression technique. Delivered VE was directly related to PIP and lung compliance. Delivered VE was not affected by the choice of circuit. TT size had minimal effects on VE when lung compliance was low; TT size was a more important factor when test lung compliance was normal. Extrapolating this data to the clinical setting, adequate ventilation of infants can be achieved with an adult circle system if an appropriate PIP is chosen, regardless of the compliance of the circuit used. Infants with poor lung compliance may require very high PIP for adequate ventilation.

Retrograde fibreoptic intubation in a child with Nager's syndrome.

PurposeThe authors describe a retrograde fibreoptic technique for tracheal intubation in a micrognathic child with a tracheo-cutaneous fistula.Clinical featuresA four-year-old child with Nager’s syndrome presented for surgical closure of a tracheocutaneous fistula. A tracheostomy tube had been placed in the neonatal period for management of upper airway obstruction due to severe micrognathia. At 2 1/2 yr of age, after a successful mandibular advancement procedure, the tracheostomy was removed and the child allowed to breathe through the natural airway. Preoperative physical examination revealed an uncooperative child, unable to open her mouth due to limited temporo-mandibular motion. The child was first anaesthetized with ketamine, 70 mg im, then halothane by mask. The authors were unable to open the child’s mouth sufficiently to allow rigid laryngoscopy. Attempts at oral and nasal fibreoptic intubation were unsuccessful. Ultimately, the authors were able to intubate nasally by passing an ultrathin Olympus LF-P laryngoscope under direct vision through the tracheocutaneous fistula in a cephalad direction, through the larynx and nasopharynx, then out the nares. An endotracheal tube was then advanced over the fibreoptic scope and positioned distal to the tracheocutaneous fistula. The surgical procedure was successfully accomplished and the trachea was extubated postoperatively without difficulty.ConclusionRetrograde fibreoptic intubation may be an option for airway management of a select group of children who cannot be intubated by traditional techniques.RésuméObjectifDécrire la technique d’intubation endotrachéale fibroscopique utilisée par voie rétrograde chez un enfant micrognathe et porteur d’une fistule trachéocutanée.Caractéristiques cliniquesUn enfant de quatre ans porteur du syndrome de Nager était programmé pour la fermeture chirurgicale d’une fistule trachéocutanée. Préalablement, à la période néonatale, une canule de trachéostomie avait été insérée pour traiter l’obstruction des voies aétiennes causée par une importante micrognathie. À deux ans et demi, après unerintervention réussie pour avancer la mandibule, la trachéostomie avait été délaissée pour permettre à l’enfant de respirer par les voies naturelles. L’examen préopératoire montrait un enfant non coopératif et incapable d’ouvrir la bouche suffisamment pour permettre la laryngoscopie rigide. L’enfant a d’abord été anesthésié à la kétamine 70 mg im et ensuite au masque avec halothane: Les tentatives d’intubation par laryngofibroscopie orale et nasale se sont avérées infructueuses. Finalement, les auteurs ont réussi à intuber pr voie nasale en passant un laryngoscope Olympus LF-P ultrafin sous vision directe à travers la fistule trachéocutanée en direction céphalique, à travers la larynx et le nasopharynx et ensuite à travers une narine. Le tube endotrachéal a été ensuite poussé sur le fibroscope et positionné distalement à la fistule trachéocutanée. L’intervention chirurgicale a pu être effectuée et la trachée extubée en postopératoire sans difficultés.ConclusionL’intubation fibroscopîque rétrograde peut représenter une solution applicable à la gestion des voies aériennes chez un groupe choisi d’enfants qui nepeuvent être intubés par les techniques conventionnelles.

A comparison of three modes of ventilation with the use of an adult circle system in an infant lung model

We examined the efficiency of an adult circle system with adult bellows to deliver minute ventilation (VE) to an infant test lung model.A Narkomed 2B system (North American Drager, Telford, PA) using three modes of ventilator setup were used: A = time-cycled, volume-controlled using bellows excursion to control delivered volume; B = time-cycled, pressure-controlled using inspiratory pressure limit adjustment to control delivered volume; C = time-cycled, pressure-controlled using the inspiratory flow adjustment to control delivered volume. VE was measured with two compliances (normal and low) and four endotracheal tube (ETT) sizes (2.5-, 3.0-, 3.5-, and 4.0-mm inner diameter). VE was measured at peak inspiratory pressures (PIP) of 20, 30, 40 or 50 cm H2 O while respiratory rate (RR) was held constant at 20 breaths/min. VE was measured as RR was set at 20, 30, 40, or 50 breaths/min while target PIP was held constant at 20 cm H2 O. Data were analyzed using the multiple regression technique. With the low compliance model, VE was nearly identical regardless of the ventilator setup. With the normal compliance model, minor differences in VE were observed, especially at the highest RR and PIP. VE was dependent on RR, PIP, and lung compliance. Overall, the ventilator setup resulted in minor changes in VE. Very high PIPs were required to deliver VE to the low compliance model. ETT size did not affect VE when lung compliance was low; however, smaller ETT size was a factor when test lung compliance was normal, decreasing delivered VE at higher PIP and RR. We conclude that with a Narkomed 2B adult circle system VE is dependent on PIP, RR, and lung compliance, but not on mode of ventilator setup. Implications: The results of this laboratory investigation indicate that when an adult circle system is used during infant anesthesia, the ventilation delivered depends primarily on the respiratory rate, peak inspiratory pressure, and the compliance of the lung being ventilated, rather than on the specific mode of ventilator setup. (Anesth Analg 1998;87:766-71)

Pressure-limited ventilation of infants with low-compliance lungs: the efficacy of an adult circle system versus two free-standing intensive care unit ventilator systems using an in vitro model.

UNLABELLED We compared the efficacy of a Drager Narkomed GS (North American Drager, Telford, PA) equipped with an adult circle system with two free-standing infant ventilator systems (Servo 300; Siemens Medical Systems, Danvers, MA and Babylog 8000; North American Drager) to deliver minute ventilation (VE) using pressure-limited ventilation to a test lung set to low compliance. To simulate a wide variety of potential patterns of ventilation, VE was measured at peak inspiratory pressures (PIP) of 20, 30, 40, and 50 cm H2O and at respiratory rates (RR) of 20, 30, 40, and 50 breaths/min. Each measurement was made three times; the average was used for data analysis using the multiple regression technique. Delivered V(E) was positively correlated with both PIP (P = 0.001) and RR (P = 0.001). Only minimal differences in VE were observed between the circle and the two free-standing systems. At lower RR and PIP, the Babylog 8000 system delivered slightly higher VE than the circle system, whereas at higher RR and PIP, the Babylog 8000 delivered slightly lower VE than the circle system; these differences in VE were not statistically significant (P = 0.45). The Servo 300 delivered slightly higher VE than the circle system in all test conditions, but these differences were not statistically significant (P = 0.09). None of the differences in delivered VE between the Servo 300 and the circle system are of clinical importance. IMPLICATIONS Our laboratory investigation suggests that pressure-limited ventilation delivered by a standard adult circle system compares favorably with that of freestanding infant ventilators used in pressure-limited mode. Changing from an adult circle system to a free-standing pressure-limited ventilator may not substantially improve ventilation of a low-compliance infant lung; the efficacy of such a practice should be investigated.

An adult system versus a Bain system: Comparative ability to deliver minute ventilation to an infant lung model with pressure-limited ventilation

UNLABELLED We compared the efficacy of an adult circle system versus a Bain system to deliver minute ventilation (V(E)) to an infant test lung model using pressure-limited ventilation. To simulate a wide variety of potential infant clinical states, V(E) was measured with two compliances: at peak inspiratory pressures (PIP) of 20, 30, 40, and 50 cm H2O and at respiratory rates (RR) of 20, 30, 40, and 50 breaths/min. Each measurement was made three times, and their average was used for analysis. Data were analyzed using the multiple regression technique. In both normal and low-compliance lung models, V(E) was nearly identical between adult circle and Bain systems (P = 0.67 for normal compliance model, P = 0.89 for low-compliance model). V(E) positively correlated with RR (P < 0.001), PIP (P < 0.001), and lung compliance (P < 0.001). Very high PIP or RR were required to deliver V(E) to the low-compliance lung model. The adult circle system is equivalent to the Bain system in its ability to ventilate an infant test lung over a wide range of RR, PIP, and two compliances during pressure-limited ventilation. V(E) is dependent of PIP, RR, and lung compliance. With low-compliance lungs, both systems require a high PIP. We conclude that both anesthetic systems deliver ventilation over a wide range of respiratory variables during pressure-limited ventilation in infants. IMPLICATIONS We obtained results from this infant test lung study that indicate that either an adult circle breathing system or the Bain system can reliably deliver ventilation over a wide range of respiratory variables during pressure-limited ventilation in infants.

A Comparison of Two Ventilator Systems Using an Infant Lung Model

STANDARD adult circle systems (with adult ventilator bellows and carbon dioxide absorber) equipped with pediatric circuit hoses, rather than semiclosed partial rebreathing systems or specially designed pediatric circle systems (with small ventilator bellows and carbon dioxide canister), often are used to ventilate infants and children during administration of anesthesia. If adult circle ventilator systems are used, it is important to understand the possible limitations and to make necessary modifications of adult techniques for use with infants. One limitation of this equipment for infant ventilation is the difficulty in determining how to set the tidal volume (‘IT) if using a time-cycled, volume-limited mode of ventilation to ensure that the patient receives the desired TV. The large compression volume of the circle