Efficacy of dead-space washout in mechanically ventilated premature newborns

The prosthetic dead space makes a significant contribution to the total dead space in low-birth-weight premature newborns receiving artificial ventilation in response to respiratory distress. Use of an endotracheal tube with capillaries molded into the tube wall enables washout of the dead space without insertion of a tracheal catheter. In 10 premature newborns (mean gestational age, 27.5 +/- 2.2 wk; mean weight, 890 +/- 260 g) receiving continuous positive-pressure ventilation (Paw = 12.7 +/- 1.8 cm H2O; FIO2 = 39 +/- 17%), tracheal gas insufflation (TGI) for CO2 washout was conducted using this technique. The flow of tracheal insufflation (0.5 L/min) was derived from the inspiratory line of the ventilator circuit and blown into the trachea. Intratracheal pressures showed little or no TGI-related modification ( < 1 cm H2O). A control system enabled TGI discontinuation in the event of a pressure rise. At constant ventilation pressure, PaCO2 decreased by 12.1 +/- 5.9 mm Hg (delta PaCO2 = -26 +/- 12%) under TGI, whereas PaO2 remained unchanged. While maintaining PaCO2 constant, peak inspiratory pressure (PIP) was decreased by 5.4 +/- 1.7 cm H2O (delta PIP = -22.0 +/- 8.3%). TGI showed immediate efficacy (PCO2 reduction of at least 5 mm Hg) in nine of the 10 newborns who then received chronic TGI (14 to 138 h). TGI appears to be an effective method, suitable for long-term clinical application, enabling a reduction in the aggressive nature of conventional ventilation.     

Prevalence of malaria in Dakar, Senegal. Comparative study of the plasmodial indices in pregnant and non-pregnant women

One hundred ASA I orthopaedic surgical patients (four randomized groups) were anaesthetized using continuous propofol and intermittent fentanyl (TIVA), with controlled ventilation via a tracheal tube in groups 1 and 2, and a laryngeal mask airway (LMA) in groups 3 and 4. Neuromuscular blockers were used in groups 1 and 3 only. There were no significant differences between groups in total anaesthetic requirements, as assessed by cardiovascular variables and movement. Coughing interfered with surgery and made controlled ventilation difficult to manage. In contrast, movement not associated with coughing did not impair surgery or ventilation. Patients in group 2 (tracheal tube, no neuromuscular blocker) required more interventions for coughing than the other groups, while patients in group 4 (LMA, no neuromuscular blocker) needed more boluses for movement than groups 1 and 3. Groups 1 and 2 (tracheal tube) had significantly higher heart rates and mean arterial pressures than groups 3 and 4 for varying periods up to 5 min after insertion of the airway management device. There was no correlation between mean arterial pressure and plasma concentrations of catecholamines related to insertion of either the tracheal tube or LMA. The LMA was found to be a highly effective device for controlled ventilation in TIVA and easier to manage than the tracheal tube in the absence of neuromuscular blockers.     

The glottic aperture seal airway: a new ventilatory device

BACKGROUND: None of the presently used airway devices are ideal regarding ease of insertion, alignment with the laryngeal inlet, and provision of a high-pressure seal from the environment. The purpose of this study was to determine, in awake volunteers, the performance of a new ventilatory device, the glottic aperture seal airway, regarding ease of insertion, alignment with the laryngeal inlet, and forced exhalation seal pressure (PFES). METHODS: The glottic aperture seal airway consists of a curved tubular component that ends in the middle of an elliptical foam cushion glottic component. The posterior surface of the foam has a curved flexible plastic backing, which imparts a 60 degree angle between the proximal half and the distal half of the foam cushion. When the glottic aperture seal airway is properly in situ in a supine patient, the proximal half of the foam cushion is opposite the laryngeal inlet. The posterior surface of the plastic backing has a balloon attached to it. Inflation of the balloon presses the ventilation hole and foam cushion up against the laryngeal inlet, thereby creating a seal from the environment. Using the laryngeal mask airway as a control device, the glottic aperture seal airway was tested for time and ease of insertion, fiberoptic alignment with the laryngeal inlet, and PFES in 18 lightly sedated and locally anesthetized volunteers. RESULTS: The glottic aperture seal and laryngeal mask airways were inserted with equal ease and speed. The fiberoptic alignment with the larynx was excellent for both the glottic aperture seal and laryngeal mask airways. In all volunteers, the mean +/- SD PFES values at 0-, 10-, 20-, 30-, and 40-ml balloon inflation volumes of the glottic aperture seal airway were 23.4 +/- 11.8, 29.6 +/- 12.4, 42.7 +/- 12.5, 56.9 +/- 5.6, and 60 +/- 0 cm H2O, respectively; the PFES at > or = 20 ml balloon inflation volume of the glottic aperture seal airway was significantly greater than with the laryngeal mask airway (19.4 +/- 6.7 cm H2O, P < 0.01). A PFES of > or =60 cm H2O was achieved with the glottic aperture seal airway in all volunteers (n = 2 at 10 ml, n = 3 at 20 ml, n = 9 at 30 ml, and n = 4 at 40 ml). The glottic aperture seal airway did not cause any trauma. CONCLUSION: In awake volunteers, the glottic aperture seal and laryngeal mask airways were equally easy to insert and position. The glottic aperture seal airway was capable of achieving a higher PFES than the laryngeal mask airway.     

Gamma knife radiosurgery and albendazole for cerebral alveolar hydatid disease

We measured pharyngeal mucosal pressures at six different locations on the laryngeal mask airway (LMA) and tested the hypothesis that the efficacy of the seal is not related to pharyngeal mucosal pressure. Twenty anesthetized, paralyzed adult patients were studied. Microchip sensors were attached to the size 5 LMA at locations corresponding to the lateral and posterior pharynx, the hypopharynx, the pyriform fossa, the base of tongue, and the oropharynx. Mucosal pressures and airway sealing pressures were recorded during inflation of the cuff from 0 to 40 mL in 10-mL increments. The highest mean mucosal pressure was in the oropharynx (26 cm H2O), and the lowest was in the posterior pharynx (2 cm H2O). Mucosal pressures increased with increasing intracuff pressure and cuff volume, but the rate of increase varied among locations. Airway sealing pressure increased with increasing intracuff volume from 0 to 10 mL (P < 0.0001) and 10 to 20 mL (P = 0.0001), was unchanged from 20 to 30 mL, and decreased from 30 to 40 mL (P = 0.005). The airway sealing pressure was higher than pharyngeal mucosal pressure until the intracuff volume was > or =30 mL. There was no correlation between mucosal pressures and airway sealing pressure at any location. We conclude that the efficacy of the seal is not related to pharyngeal mucosal pressure. Pharyngeal mucosal pressures are generally lower than those considered safe for the tracheal mucosa during prolonged intubation. IMPLICATIONS: We measured pharyngeal mucosal pressures at six different locations on the laryngeal mask airway and showed that the efficacy of the seal is not related to pharyngeal mucosal pressure. Pharyngeal mucosal pressures are generally lower than those considered safe for the tracheal mucosa during prolonged intubation.     

Lyme disease--on the basis of our observations

We biologically assessed functions of several reconstituted surfactants with the same minimum surface tension (2-3 mN/m) as "complete" porcine pulmonary surfactant (natural surfactant) but with longer surface adsorption times. Administration of natural surfactant (adsorption time 0.29 s) into the lungs of surfactant-deficient immature rabbits brought a tidal volume of 16.1 +/- 4.4 (SD) ml/kg during mechanical ventilation with 40 breaths/min and 20 cmH2O insufflation pressure. In static pressure-volume recordings, these animals showed a lung volume of 62.4 +/- 9.7 ml/kg at 30 cmH2O airway pressure and maintained 55% of this volume when the pressure decreased to 5 cmH2O. With two reconstituted surfactants consisting of synthetic lipids or isolated lipids from porcine lungs plus surfactant-associated hydrophobic proteins (adsorption times 0.57 and 0.78 s, respectively), tidal volumes were < 38% of that with natural surfactant (P < 0.05), but static pressure-volume recordings were not different. Care is therefore needed in estimating the in vivo function of surfactant preparations from minimum surface tension or static pressure-volume measurements.     

Respiratory mechanics in normal hamsters

Lung volumes and quasi-static deflation volume-pressure relationships were measured in male golden hamsters anesthetized with pentobarbital. Volume was measured with a pressure plethysmograph, and pleural pressure was estimated by the use of a water-filled esophageal catheter. Mean body weight +/- SE was 122.3 +/-3.0 g, mean lung weight was 0.74 +/- 0.2 g or about 0.6% of body weight. Mean lung volume at 25 cmH2O transpulmonary pressure (TLC25) was 7.2 +/- 0.14 ml, 9.78 +/- 0.17 ml/g lung weight or 5.92 +/- 0.06 ml/100 g body weight. Mean functional residual capacity was 2.4 +/- 0.06 ml or 33.3% of TLC25. Mean vital capacity was 5.2 +/- 0.13 ml. Mean quasi-static compliance of lung was 0.63 +/- 0.03 ml/cmH2O. Chord compliance of chest wall between lung volumes of 1 and 4 ml above RV was 3.39 +/- 0.53 ml/cmH2O. At FRC, the chest wall recoiled inward, so that pleural pressure was positive (1.4 +/- 0.13 cmH2O) and the lung was resisting further collapse. The slope of the lung's deflation volume-pressure curve changed at FRC, ERV was small (0.36 +/- 0.03 ml), and RV was determined by complete airway closure. Thus the mechanisms determining FRC are unusual and include an influence of airway closure.     

Extralobar pulmonary sequestration with an associated cyst of mixed bronchogenic and esophageal type--a case report

The aim of the study was to evaluate leakage of liquid past the low-pressure cuffs of tracheal tubes. Ten samples of each of nine different types of tubes were tested in a PVC mock trachea, using intracuff pressures of 20, 30, 40 and 50 cmH2O. In five types of tubes, 6-10 cuffs allowed profuse leakage (> 20 ml water in 5 min) even at the highest intracuff pressure, i.e. 50 cmH2O. In the most efficient tube, all the cuffs were leak-proof (leakage < 5 ml in 5 min) at 40 cmH2O and in the second best type the cuffs were leak-proof at 50 cmH2O. The leakage of fluid past the tracheal tube remains an unresolved problem with low-pressure cuffs.     

Nasal fibreoptic tracheal intubation in anaesthetised patients breathing via a modified laryngeal mask airway

A modified laryngeal mask airway was used to facilitate nasotracheal intubation with a fibreoptic laryngoscope. A size 4 laryngeal mask airway was modified by creating a defect at the base of the stem and removing the bars to allow passage of the fibreoptic laryngoscope from the nasopharynx to the larynx. The laryngeal mask airway cuff was split and the cut edges were sealed with silicone. This design allowed the cuff to function normally and allowed removal of the split laryngeal mask airway after the tracheal tube had been 'railroaded' into place. Thirty-four patients were studied. The split laryngeal mask airway was easily inserted with satisfactory airway maintenance in 32 patients. Nasal airway endoscopy and laryngoscopy were successfully achieved with the split laryngeal mask airway in place in 31 of 32 patients. Railroading the tracheal tube over the fibreoptic laryngoscope with the split laryngeal mask airway in place was successful in all 31 of these patients. This prototype split laryngeal mask airway allows good airway maintenance while fibreoptic nasotracheal intubation is performed.     

Comparison of alveolar ventilation, oxygenation, pressure support, and respiratory system resistance in response to noninvasive versus conventional mechanical ventilation in foals

OBJECTIVE: To compare the efficacy of positive pressure ventilation applied through a mask versus an endotracheal tube, using anesthetized/paralyzed foals as a model for foals with hypoventilation. ANIMALS: Six 1-month-old foals. PROCEDURE: A crossover design was used to compare the physiologic response of foals to 2 ventilatory techniques, noninvasive mask mechanical ventilation (NIMV) versus endotracheal mechanical ventilation (ETMV), during a single period of anesthesia and paralysis. Arterial pH, PaO2, PaCO2, oxygen saturation, end-tidal CO2 tension, airway pressures, total respiratory system resistance, resistance across the upper airways (proximal to the midtracheal region), and positive end-expiratory pressures (PEEP) were measured. Only tidal volume (VT; 10, 12.5, and 15 ml/kg of body weight) or PEEP (7 cm of H2O) varied. RESULTS: Compared with ETMV, use of NIMV at equivalent VT resulted in PaCO2 and pH values that were significantly higher, but PaO2 was only slightly lower. Between the 2 methods, peak airway pressure was similar, but peak expiratory flow was significantly lower and total respiratory resistance higher at each VT for NIMV. Delivery of PEEP (7 cm of H2O) was slightly better for ETMV (7.1 +/- 1.3 cm of H2O) than for NIMV (5.6 +/- 0.6 cm of H2O). CONCLUSION: These data suggest that use of NIMV induces similar physiologic effects as ETMV, but the nasal cavities and mask contribute greater dead space, manifesting in hypercapnia. Increasing the VT used on a per kilogram of body weight basis, or the use of pressure-cycled ventilation might reduce hypercapnia during NIMV. CLINICAL RELEVANCE: Use of NIMV might be applicable in selected foals, such as those with hypoventilation and minimal changes in lung compliance, during weaning from endotracheal mechanical ventilation, or for short-term ventilation in weak foals.     

Continuous tracheal gas insufflation enables a volume reduction strategy in hyaline membrane disease: technical aspects and clinical results

OBJECTIVE: Instrumental dead space wash-out can be used to improve carbon dioxide clearance. The aim of this study was to define, using a bench test, an optimal protocol for long-term use, and to assess the efficacy of this technique in neonates. DESIGN: A bench test with an artificial lung model, and an observational prospective study. Dead space wash-out was performed by continuous tracheal gas insufflation (CTGI), via six capillaries molded in the wall of a specially designed endotracheal tube, in 30 preterm neonates with hyaline membrane disease. SETTING: Neonatal intensive care unit of a regional hospital. RESULTS: The bench test study showed that a CTGI flow of 0.5 l/ min had the optimal efficacy-to-side-effect ratio, resulting in a maximal or submaximal efficacy (93 to 100%) without a marked increase in tracheal and CTGI circuit pressures. In the 30 newborns, 15 min of CTGI induced a significant fall in arterial carbon dioxide tension (PaCO2), from 45 +/- 7 to 35 +/- 5 mmHg (p = 0.0001), and in 14 patients allowed a reduction in the gradient between Peack inspirating pressure and positive end-expiratory pressure from 20.8 +/- 4.6 to 14.4 +/- 3.7 cmH2O (p < 0.0001) while keeping the transcutaneous partial pressure of carbon dioxide constant. As predicted by the bench test, the decrease in PaCO2 induced by CTGI correlated well with PaCO2 values before CTGI (r = 0.58, p < 0.002) and with instrumental dead space-to-tidal volume ratio (r = 0.54, p < 0.005). CONCLUSION: CTGI may be a useful adjunct to conventional ventilation in preterm neonates with respiratory disease, enabling an increase in CO2 clearance or a reduction in ventilatory pressure.     

Donor liver selection. The South-Eastern Organ Procurement Foundation Liver Committee

OBJECTIVE: To investigate the effectiveness of noninvasive (face mask) versus invasive (endotracheal tube) equal pressure values on blood gases and respiratory pattern and to evaluate the feasibility of using mask ventilation after the short term physiologic study. DESIGN: Open, prospective, physiologic study and uncontrolled clinical study. SETTING: Intensive care unit of a trauma center. PATIENTS: 22 intubated trauma patients were studied. INTERVENTIONS: Patients were intubated and ventilated in a pressure support mode (IPSV) of 13.5 +/- 1.5 cmH2O and a post end-expiratory pressure (PEEP) of 5.8 +/- 2.57 cmH2O. After a T-piece trial to assess patient's ability to breath spontaneously, patients were switched over to noninvasive pressure support (NIPSV). The pressure levels were set as during IPSV. Blood gases and respiratory parameters were measured during IPSV, during the T-piece trial, and after 1 h of NIPSV. After the physiologic study, all patients were asked if they wished to continue on NIPSV. The patient's subjective compliance with IPSV and NIPSV was measured by means of an arbitrary score. A successful outcome was defined as no need for reintubation. MEASUREMENTS AND RESULTS: IPSVand NIPSV showed no statistical differences for blood gas and respiratory parameters by using the same values of PSV (13 +/- 5 vs 12.8 +/- 1.7 cmH2O, NS) and PEEP (5.8 +/- 2.5 and 5.2 +/- 2.2 cmH2O NS). The median length of time on NIPSV was 47 h (range 6 to 144). All patients wished to continue on NIPSV, but 9 patients (40.9%) were reintubated after 54 +/- 54 h. Six of them died after 36 +/- 13 days while still on mechanical ventilation. There was no statistically significant difference in compliance score between IPSVand NIPSV. CONCLUSIONS: NIPSV is comparable to IPSV in terms of blood gases and respiratory pattern. The clinical uncontrolled study indicates that NIPSV could be used in selected trauma patients.     

Airway pressure release ventilation

BACKGROUND: Elevated airway pressures during mechanical ventilation are associated with hemodynamic compromise and pulmonary barotrauma. We studied the cardiopulmonary effects of a pressure-limited mode of ventilation (airway pressure release ventilation) in patients with the adult respiratory distress syndrome. METHODS: Fifteen patients requiring intermittent mandatory ventilation (IMV) and positive end-expiratory pressure (PEEP) were studied. Following measurement of hemodynamic and ventilatory data, all patients were placed on airway pressure release ventilation (APRV). Cardiorespiratory measurements were repeated after a 2-hour stabilization period. RESULTS: During ventilatory support with APRV, peak inspiratory pressure (62 +/- 10 vs 30 +/- 4 cm H2O) and PEEP (11 +/- 4 vs 7 +/- 2 cm H2O) were reduced compared with IMV. Mean airway pressure was higher with APRV (18 +/- 5 vs 24 +/- 4 cm H2O). There were no statistically significant differences in gas exchange or hemodynamic variables. Both cardiac output (8.7 +/- 1.8 vs 8.4 +/- 2.0 L/min) and partial pressure of oxygen in arterial blood (79 +/- 9 vs 86 +/- 11 mm Hg) were essentially unchanged. CONCLUSIONS: Our results suggest that while airway pressure release ventilation can provide similar oxygenation and ventilation at lower peak and end-expiratory pressures, this offers no hemodynamic advantages.     

Fetal unilateral cleft lip and palate: detection of enzymic anomalies in the amniotic fluid

BACKGROUND: Tracheal intubation frequently results in an increase in respiratory system resistance that can be reversed by inhaled bronchodilators. The authors hypothesized that insertion of a laryngeal mask airway would be less likely to result in reversible bronchoconstriction than would insertion of an endotracheal tube. METHODS: Fifty-two (45 men, 7 women) patients were randomized to receive a 7.5-mm (women) or 8-mm (men) endotracheal tube or a No. 4 (women) or No. 5 (men) laryngeal mask airway. Anesthesia was induced with 2 microg/kg fentanyl and 5 mg/kg thiopental, and airway placement was facilitated with 1 mg/kg succinylcholine. When a seal to more than 20 cm water was verified, respiratory system resistance was measured immediately after airway placement. Inhalation anesthesia was begun with isoflurane to achieve an end-tidal concentration of 1% for 10 min. Respiratory system resistance was measured again during identical conditions. RESULTS: Among patients receiving laryngeal mask airways, the initial respiratory system resistance was significantly less than among patients with endotracheal tubes (9.2+/-3.3 cm water x 1(-1) x s(-1) [mean +/- SD] compared with 13.4+/-9.6 cm water x 1(-1) x s(-1); P < 0.05). After 10 min of isoflurane, the resistance decreased to 8.6+/-3.6 cm water x 1(-1) x s(-1) in the endotracheal tube group but remained unchanged at 9.1+/-3.3 cm water x 1(-1) x s(-1) in the laryngeal mask airway group. The decrease in respiratory system resistance in the endotracheal tube group of 4.7+/-7 cm water x 1(-1) x s(-1) was highly significant compared with the lack of change in the laryngeal mask airway group (P < 0.01). CONCLUSIONS: Resistance decreased rapidly only in patients with endotracheal tubes after they received isoflurane, a potent bronchodilator, suggesting that reversible bronchoconstriction was present in patients with endotracheal tubes but not in those with laryngeal mask airways. A laryngeal mask airway is a better choice of airway to minimize airway reaction.     

Permissive hypercapnia with and without expiratory washout in patients with severe acute respiratory distress syndrome

BACKGROUND: Permissive hypercapnia is a ventilatory strategy aimed at avoiding lung volutrauma in patients with severe acute respiratory distress syndrome (ARDS). Expiratory washout (EWO) is a modality of tracheal gas insufflation that enhances carbon dioxide removal during mechanical ventilation by reducing dead space. The goal of this prospective study was to determine the efficacy of EWO in reducing the partial pressure of carbon dioxide (PaCO2) in patients with severe ARDS treated using permissive hypercapnia. METHODS: Seven critically ill patients with severe ARDS (lung injury severity score, 3.1 +/- 0.3) and no contraindications for permissive hypercapnia were studied. On the first day, hemodynamic and respiratory parameters were measured and the extent of lung hyperdensities was assessed using computed tomography. A positive end-expiratory pressure equal to the opening pressure identified on the pressure-volume curve was applied. Tidal volume was reduced until a plateau airway pressure of 25 cm H2O was reached. On the second day, after implementation of permissive hypercapnia, EWO was instituted at a flow of 15 l/min administered during the entire expiratory phase into the trachea through the proximal channel of an endotracheal tube using a ventilator equipped with a special flow generator. Cardiorespiratory parameters were studied under three conditions: permissive hypercapnia, permissive hypercapnia with EWO, and permissive hypercapnia. RESULTS: During permissive hypercapnia, EWO decreased PaCO2 from 76 +/- 4 mmHg to 53 +/- 3 mmHg (-30%; P < 0.0001), increased pH from 7.20 +/- 0.03 to 7.34 +/- 0.04 (P < 0.0001), and increased PaO2 from 205 +/- 28 to 296 +/- 38 mmHg (P < 0.05). The reduction in PaCO2 was accompanied by an increase in end-inspiratory plateau pressure from 26 +/- 1 to 32 +/- 2 cm H2O (P = 0.001). Expiratory washout also decreased cardiac index from 4.6 +/- 0.4 to 3.7 +/- 0.3 l.min-1.m-2 (P < 0.01), mean pulmonary arterial pressure from 28 +/- 2 to 25 +/- 2 mmHg (P < 0.01), and true pulmonary shunt from 47 +/- 2 to 36 +/- 3% (P < 0.01). CONCLUSIONS: Expiratory washout is an effective and easy-to-use ventilatory modality to reduce PaCO2 and increase pH during permissive hypercapnia. However, it significantly increases airway pressures and lung volume through expiratory flow limitation, reexposing some patients to a risk of lung volutrauma if the extrinsic positive end-expiratory pressure is not substantially reduced.     

Laryngeal mask airway position and the risk of gastric insufflation

A potential risk of the laryngeal mask airway (LMA) is an incomplete mask seal causing gastric insufflation or oropharyngeal air leakage. The objective of the present study was to assess the incidence of LMA malpositions by fiberoptic laryngoscopy, and to determine their influence on gastric insufflation and oropharyngeal air leakage. One hundred eight patients were studied after the induction of anesthesia, before any surgical manipulations. After clinically satisfactory LMA placement, tidal volumes were increased stepwise until air entered the stomach, airway pressure exceeded 40 cm H2O, or air leakage from the mask seal prevented further increases in tidal volume. LMA position in relation to the laryngeal entrance was verified using a flexible bronchoscope. The overall incidence of LMA malpositions was 40% (43 of 108). Gastric air insufflation occurred in 19% (21 of 108), and in 90% (19 of 21) of these patients, the LMA was malpositioned. Oropharyngeal air leakage occurred in 42%, and was independent of LMA position. We conclude that clinically unrecognized LMA malposition is a significant risk factor for gastric air insufflation. Implications: Routine placement of laryngeal mask airways does not require laryngoscopy. In our study, fiberoptic verification of mask position revealed suboptimal placement in 40% of cases. Such malpositioning considerably increased the risk of gastric air insufflation.     

High prevalence of ciprofloxacin resistance amongst strains of Neisseria gonorrhoeae isolated from commercial sex workers in Bangladesh

We have evaluated if breathing spontaneously via a laryngeal mask airway is associated with a higher risk of gastro-oesophageal reflux compared with positive pressure ventilation via a laryngeal mask airway in 40 patients undergoing day-case gynaecological laparoscopy. Patients were allocated randomly to receive either positive pressure ventilation or breathe spontaneously via a laryngeal mask airway. Using continuous oesophageal pH monitoring, three patients in the ventilated group and one in the spontaneous breathing group had gastrooesophageal reflux (P = 0.29). We found no evidence to suggest that breathing spontaneously via a laryngeal mask airway increased the risk of gastro-oesophageal reflux compared with positive pressure ventilation in this group of patients.     

Pulmonary airway resistance with the endotracheal tube versus laryngeal mask airway in paralyzed anesthetized adult patients

BACKGROUND: The hypothesis that airway resistance is less with the laryngeal mask airway than with the endotracheal tube was tested. METHODS: Thirty-six paralyzed, anesthetized adult patients with no respiratory disease (American Society of Anesthesiologists physical status 1-3; age, 18-80 yr) were randomly allocated (9 men, 9 women in each group) to receive either a size-4 laryngeal mask airway or an endotracheal tube (men, 9-mm ID; women, 8-mm ID). A pulmonary monitor with flow transducer and esophageal balloon was used to measure peak airway pressure and mean airway resistance (device resistance plus pulmonary airway resistance) at three different tidal volumes (5, 10, and 15 ml/kg). Device resistance was measured in vitro with the distal end of the endotracheal tube or laryngeal mask airway open to the atmosphere and using the same ventilator settings. Pulmonary airway resistance was derived by subtracting the mean device resistance from the mean airway resistance. RESULTS: Peak airway pressure, mean airway resistance, device resistance, and pulmonary airway resistance were greater for the endotracheal tube (all P < 0.0001). CONCLUSIONS: The laryngeal mask airway triggers less bronchoconstriction than does the endotracheal tube in paralyzed anesthetized adult patients. This may have implications for maintaining intraoperative pulmonary function and reducing the risk for atelectasis and pulmonary infection.     

Continuous low-flow tracheal gas insufflation during partial liquid ventilation in rabbits

BACKGROUND: Both partial liquid ventilation (PLV) and tracheal gas insufflation are novel techniques for mechanical ventilation. In this study we examined whether PLV superimposed by continuous low-flow tracheal gas insufflation (TGI) offers any advantage to the blood gases and lung mechanics in normal-lung rabbits compared to the use of PLV only. METHODS: Eighteen anesthetized, paralyzed and mechanically ventilated rabbits were used. After obtaining a baseline PaCO2 value between 29 and 39 mmHg (3.9 and 5.2 kPa), the animals were assigned to three equal groups according to the ventilation they received--A group: PLV superimposed by TGI; B group: PLV only; and C group: continuous mandatory ventilation (CMV) superimposed by TGI. Serial arterial blood gases, pH and lung mechanics were measured. RESULTS: The animals in each group were hemodynamically stable. In the case of the A group, PaO2 continuously increased, and PaCO2 stabilized around 40.8 +/- 5.5 mmHg (5.4 +/- 0.7 kPa, mean +/- SD, NS). In the B group, the tendency for PaO2 to increase was not as definite; PaCO2 continuously increased from 35.2 +/- 2.3 mmHg (4.7 +/- 0.3 kPa) to 56.3 +/- 12.7 mmHg (7.5 +/- 1.7 kPa, P < 0.05) at the end of the experiment. In the C group, PaO2 and PaCO2 were stable during the observation period. The superimposition of TGI on PLV did not decrease the airway pressures compared to PLV alone. CONCLUSION: In summary, continuous low-flow TGI superimposed on PLV can decrease and stabilize the PaCO2 elevation caused by the initiation of PLV.     

Clinical assessment of the single use laryngeal mask airway--the LMA-unique

We conducted a clinical comparison of the laryngeal mask airway (LMA) and the new single use PVC LMA (LMA-Unique) in 100 fasted adult patients undergoing elective surgery. Patients were allocated to one of two groups: group 1 (n = 50) was managed by two consultants and group 2 by two trainee anaesthetists. Airway management was randomized prospectively within each group, and cuff pressure in both devices was maintained at a maximum of 50 mm Hg with upward size substitution if leaks persisted during intermittent positive pressure ventilation (IPPV). Insertion with the recommended technique was successful in all patients (85 first attempt). One patient (group 1) required four attempts for insertion of the LMA-Unique and in one patient (group 2) the LMA-Unique was replaced by a tracheal tube because of persistent leaks during IPPV. In 99 patients IPPV was uneventful. The adjusted mean volume of air for cuff inflation in the LMA-Unique was significantly less in group 1 (P = 0.0013). At fibreoptic laryngoscopic examination, the vocal cords or arytenoids, or both, could be seen in 92% of patients in group 1 and in 90% of patients in group 2. Immediate throat soreness was reported in four patients in group 1 and in seven in group 2. The results suggest that the LMA-Unique was similar in clinical performance to the LMA.     

Airway control during percutaneous dilatational tracheostomy: pilot study with the intubating laryngeal mask airway

Percutaneous dilatation tracheostomy has become a common procedure for bedside insertion of tracheostomy tubes in the intensive care unit. Management of the airway during the procedure using the laryngeal mask airway (LMA) and other methods has been described. The intubating laryngeal mask airway has several potential benefits for airway management during percutaneous dilatation tracheostomy compared with the LMA. These include the use of both the fibreoptic bronchoscope and tracheal tube if necessary. We report the results of a pilot study of 10 patients that illustrates these advantages.