Cuff bulk of tracheal tubes in adolescence

Purpose

To investigate cuff types for potential use in late childhood and early adolescence for appropriate fit.

Method

Formulae suggest the use of a tracheal tube having a 6.5 mm internal diameter at ages 8 to 10 years, so a model system was used to test the passage of cuffed and uncuffed tracheal tubes of 6.5 mm internal diameter through calibrated holes 8.1–16.6 mm diameter, in plastic plates.

Results

Uncuffed tracheal tubes passed through 9.0 mm diameter holes. “High pressure” cuffed tubes passed through 10.5 to 11.3 mm holes. “Low pressure” cuffed tubes passed through 12.3 to16.4 mm.

Conclusion

Patients aged 8 to 10 yr have a limiting internal diameter at the cricoid of 8 to 10 mm. Their unstretched tracheal diameter below the cricoid is only about 11 mm. The actual outside diameters of “low pressure” cuffs chosen by commonly used formulae considerably exceed the limiting diameters of eight to ten year old patients, even considering recommended compensation factors. Analysis of background data indicates that these problems are especially aggravated at this age by non-linear growth of the cricoid.     

Evaluation of pressure/volume loops based on intratracheal pressure measurements during dynamic conditions

BACKGROUND: The aim of this study was to evaluate and compare information about lung mechanics obtained by dynamic pressure/volume loops based on Y-piece and intratracheal airway pressure. METHODS: Airway pressure was measured simultaneously at the Y-piece and trachea. Flow/tidal volume was measured by sidestream spirometry at the Y-piece. The effect of an intraluminal catheter in the tube was evaluated in a lung model. Ten adults with acute lung injury and mechanical ventilation were studied. Measurements were performed during volume-(VC) and pressure-controlled (PC) ventilation at different ventilator settings. RESULTS: Lung model: There was a statistically significant difference (P<0.001) between trachea and Y-piece pressure/volume loop areas during both VC and PC ventilation. The ratio trachea area/Y-piece area decreased with increased endotracheal tube resistance (r=0.96). Patients: The difference between trachea and Y-piece P/V-loops was statistically significant at all 21 ventilatory settings (P<0.05-0.001). The tracheal loop revealed clearly intrinsic PEEP and lowered compliance during overinflation, which was difficult or impossible to see in the Y-piece pressure/volume loop. CONCLUSION: By measuring airway pressure at the trachea the effect of endotracheal tube resistance during inspiration is excluded while it is included during expiration, yielding correct end-points of inspiration and expiration. This makes it possible to calculate accurately total compliance of the respiratory system during dynamic conditions. By monitoring of airway pressure in the trachea, respiratory mechanics can be assessed more accurately and ventilatory settings adjusted to attenuate ventilator induced lung injury.     

Cuff failure in tracheal tubes sprayed with lidocaine]

Lidocaine jelly or spray is usually applied to tracheal tube cuffs as lubricants, and we encountered some cuff troubles in using the spray. Damages on polyvinyl chloride (PVC) tracheal tube cuffs by applying lidocaine spray have been reported. We studied cuff injury with 5 kinds of tracheal tubes (PVC and non-PVC cuffs) with three different substances (normal saline, lidocaine jelly and lidocaine spray). No tracheal tube cuffs were damaged by normal saline and lidocaine jelly, while lidocaine spray changed the shape of some tracheal tube cuffs (PVC and non-PVC). Therefore, we recommend to apply lidocaine jelly on tube cuffs rather than lidocaine spray, even on non-PVC cuffs.     

Cuff failure in polyvinyl chloride tracheal tubes sprayed with lignocaine

The incidence of tracheal tube cuff rupture was noted in 30 polyvinyl chloride tracheal tubes lubricated with three different solutions. All cuffs moistened with water were intact after 2 hours of cuff inflation whereas two of 10 lubricated with 4% lignocaine solution had burst. Both of these had leaked at the site of cuff attachment to the tube. Fifty percent of tubes lubricated with Astra lignocaine spray burst during the study. Four of the five had developed pinholes in the cuffs themselves. The remaining 50% of this group showed marked distortion and thinning of their intact cuff walls. The implications of these findings are discussed in view of the widespread use of PVC tracheal tubes.     

Evaluation of a new hydrogel coating for drainage tubes

The performance of silicone drains has been improved by coating their surfaces with a hydrogel polymer. This hydrogel is formed by reacting polyvinylpyrrolidone with an isocyanate prepolymer. By absorbing water, the hydrogel creates a drain surface with a low coefficient of friction. The results of this experimental study demonstrate that the surface coating reduces the adherence of blood clots to the drain and facilitates its removal from the wound. On the basis of these and other experiments, the Food and Drug Administration has allowed the use of hydrogel for coating surgical drains for use in patients.     

Monitoring airway pressure in pediatric anesthesia: an experimental model of intratracheal medication and pressure-volume loops

BACKGROUND: In the monitoring of anesthesia, airway pressure is measured in the ventilator or at the closest possible connection to the endotracheal tube. OBJECTIVE: To compare the airway pressures and pressure-volume loops obtained before connection to the endotracheal tube with those obtained in the trachea. MATERIAL AND METHODS: We carried out a single-blind prospective observational study on ASA 1 patients between the ages of 7 and 12 years ventilated in volume-control mode with an inspiration-to-expiration ratio of 1:2. Intratracheal and extratracheal peak and plateau pressures and pressure-volume loops were recorded. A special device was designed to monitor intratracheal pressure. Both sensors were connected to the same spirometric analysis system. The variables were measured on intubation and 5, 10, 15, 20, 30, 40, 50, and 60 minutes after intubation. The recorded pressures were compared using the t test, the Pearson product moment correlation coefficient (r), and the Spearman rank correlation coefficient (p), and regression models were fit to the data. RESULTS: Seventy-one patients were enrolled. The mean (SD) pressure difference between the 2 systems was 3.5 (0.35) cm H2O (P < .01) and no differences between the endotracheal peak pressures and the plateau pressures were observed. The intratracheal areas of the pressure-volume loops were 15% lower than the extratracheal areas. The value of r for the correlation between the intratracheal peak and plateau pressures was 0.998 (P < .01). The value of r for the correlation between the intratracheal and extratracheal peak pressures was 0.981 (P < .01). Analysis of variance confirmed the linear relationship. CONCLUSIONS: The difference between the intratracheal and extratracheal pressure measurements is due to the different locations at which the measurements are taken.     

Peak intratracheal pressure during controlled ventilation in infants and children

The mathematical relationship between peak ventilator breathing system pressure displayed on the digital meter of the Siemens SV900C ventilator, and peak intratracheal pressure measured at the distal end of the tracheal tube, was defined and incorporated into a computer program. The mean difference between peak airway pressure calculated by the computer and directly measured peak intratracheal pressure was 0.02 kPa (SD 0.10) in 18 infants and children. The mean difference between ventilator breathing system pressure and intratracheal pressure in the same group was 0.82 kPa (SD 0.91). Bench tests established that the decrease in peak pressure displayed by the ventilator (from 1.36 to 0.38 kPa) while inspiratory time was increased from 20 to 80% of the respiratory period, concealed an increase (from 0.2 to 0.38 kPa) in intratracheal pressure which occurs during this process; and that the large increase in pressure displayed by the ventilator (from 0.3 to 6 kPa) while respiratory frequency was increased from 20 to 120 breaths/minute, concealed a small increase in peak intratracheal pressure (0.2-0.3 kPa) which occurs during this process. These changes were accurately predicted by the computer program. The increase in intratracheal pressure associated with prolonged inspiratory times explains the high incidence of barotrauma which has recently been associated with this procedure in infants.     

Cuff compliance of pediatric and adult cuffed tracheal tubes: an experimental study

BACKGROUND: Tracheal mucosal damage related to tracheal intubation has been widely described in pediatric and adult patients. High volume-low pressure cuffs (HVLPC) are being advertised as safe to avoid this particularly unpleasant complication. Compliances of these supposed pediatric and adult HVLPC are not mentioned by manufacturers and still remain unknown. METHODS: The compliance of HVLPC was measured in vitro and defined as the straight portion of the pressure-volume curve. Cuff pressure was measured after incremental 0.1 ml filling volumes of air for sizes 3.0-8.0 of internal diameter of Rüsch and Mallinckrodt tracheal tubes. Compliances were assessed in air and in a rigid tube. The filling volume to achieve a 25-mmHg intracuff pressure was also measured. RESULTS: In air, each 0.1 ml step almost linearly increased cuff pressure by 1 mmHg (size 8.0) to 9 mmHg (size 3). In air, the volume needed to maintain a cuff pressure < 25 mmHg was small for sizes 3-5.5 (0.35-2 ml). The 25 mmHg inflated cuff volume and compliance were decreased within a rigid tube, especially for adult sizes. In a rigid tube simulating a trachea, the compliances of almost every Rüsch tracheal tube were statistically higher than those of the Mallinckrodt. CONCLUSION: We conclude that the tested tracheal tube cuffs have low compliance and cannot be defined as high volume-low pressure.     

Conductive hearing loss associated with pressure equalization tubes.

Pressure equalization (PE) tube placement traditionally has been used to lessen conductive hearing loss with chronic middle ear effusion. It is assumed that the small diameter of the tube should not interfere with the conduction of sound. In this article we present 5 patients in whom placement of a PE tube resulted in significantly worse conductive hearing. Occlusion of the PE tube with cigarette paper or Gelfoam improved hearing, as documented with audiometry. The average conductive hearing losses attributable to the ventilation tube for this series of patients were 22, 17, 15, 13, 4, and 10 dB at the frequencies of 250, 500, 1000, 2000, 4000, and 8000 Hz, respectively. This amount of change attributable to PE tubes in this small selection of patients is much greater than would be commonly appreciated. We conclude that the opening in the tympanic membrane provided by PE tubes can potentially result in a significant conductive hearing loss. Discussion includes those conditions in which reduced hearing may be more likely to occur.     

Evaluation of a new large animal model for controlled intracranial pressure changes induced by capnoperitoneum

Background

A standardized large animal model for controlled ICP manipulation within a relevant range and repetitive ICP measurements is missing. We sought to develop such a model on the base of controlled IPP changes induced by capnoperitoneum.

Methods

We utilized six female pigs (mean body weight 59.5?±?18.4 kg) for experiments. A ventricular catheter connected with a burr hole reservoir was implanted. ICP was measured directly as cm H₂O within a riser tube after percutaneous cannulation of the reservoir. A noninvasive intraperitoneal pressure (IPP) measurement was established (intravesical). Animals were placed in lateral position and a capnoperitoneum was induced. Measurements of ICP, IPP, MAP and respiratory parameters were performed at baseline IPP and after CO₂ insufflation to IPP levels of 20 and 30 mmHg.

Results

Baseline IPP in lateral position referenced to median line was 9.8 (±2) mm Hg, while corresponding ICP was 10 (±2.2) mm Hg. After IPP elevation to 20 mmHg, ICP increased to 18.8 (±1.9) mm Hg. At 30 mmHg IPP, ICP increased to 22.8 (±2.8) mm Hg. Except peak airway pressure, all other parameters were kept constantly. Mean ICP variation in the individual subject was 13.4 (±2.5) mm Hg, while a ICP range from minimum 9 to maximum 31 mmHg was documented.

Conclusions

We report a large animal model that allows (1) repeated measurement of the ICP and (2) manipulation of the ICP within a large pressure range by controlled IPP changes due to capnoperitoneum.     

Evaluation of a Thin-film Peripheral Nerve Cuff Electrode

Abstract

This is a study of the reaction of large nerves to implantation using a flexible, thin-film cuff electrode. Cuff electrodes were implanted on the sciatic nerve of three cats. An implantation period of six weeks allowed sufficient time for any injury responses in the nerve and connective tissue sheath around the cuff to develop. The electrode came off the nerve in one of the cats. In the remaining two cats, gross observation following explantation of the electrodes revealed encapsulation of the cuffs without swelling of nerve tissue. Histological evaluation did not demonstrate nerve injury. The nerve cuff electrodes, which are comprised of titanium and iridium coatings on a fluorocarbon polymer substrate, appeared unaffected by the implantation, and connective tissue encapsulation did not adhere to either the polymer substrate or metallization. Evaluation of the electrodes using activated iridium oxide charge injection sites in more extended studies is now being undertaken. (J Spinal Cord Med; 18:28–32)