Technical communication: design and in vitro testing of a pressure-sensing syringe for endotracheal tube cuffs

The Relationship between Cuff Pressure and Air Injection Volume of Endotracheal Tube: A Study with Sheep Trachea Ex Vivo

Background

Endotracheal intubation is a widely used treatment. Excessive pressure of the endotracheal tube cuff leads to a series of complications. Here, we used tracheae of sheep to analyze the relationship between the air injection volume and endotracheal tube cuff pressure so as to guide the doctors and nurses in controlling the pressure of the endotracheal tube cuff during clinical work and minimise the risk of complications.

Materials and Methods

Forty sheep tracheae were utilised and were divided into five groups according to their diameters. Different sizes of endotracheal tubes were inserted into each trachea, and the cuff pressure with the increase of air injection volume was recorded. The formulas that reflect the relationship between air injection volume and cuff pressure were obtained. Then, sheep tracheae were randomly selected; different types of tubes were inserted, and the stipulated volume of air was injected. The actual pressure was measured and compared with the pressure predicted from the formulas. Statistical analysis was conducted to verify whether the formulas obtained from the first part of the experiment were in accordance with the expert evaluation table, which consists of opinions of several experts.

Results

After obtaining 15 formulas, we collected the differences between the theoretical cuff pressure and the actual cuff pressure that satisfied the expert evaluation. Relying on the formulas, the medical turntable was obtained, which is a tool that consists of two round cards with data on them. The top card has a notch. The two cards are stacked together, and as the top card rotates, the data on the bottom card can be easily seen in a one-to-one relationship.

Conclusion

The formulas are capable of showing the relationship between the cuff air injection volume and pressure of endotracheal tube cuff. The medical turntable can estimate the air injection volume to ensure that the pressure stays in an acceptable range.

Measuring endotracheal tube intracuff pressure: no room for complacency

Tracheal intubation constitutes a routine part in the care of critically ill and anaesthetised patients. Prolonged use of endotracheal with inflated cuff is one of the major multifactorial causes of complications. Both under-inflation and over-inflation of cuff are associated with complications. Despite known problems, regular measurement of cuff pressure is not routine, and it is performed on an ad hoc basis.

Evidence Based Use of Cuffed Endotracheal Tubes in Children

Historically, the use of cuffed endotracheal tubes (ETTs) was reserved for children aged 8 years or older to minimize the risks of postextubation laryngeal edema. However, since publication of a 1997 study, researchers have consistently presented evidence that appropriately used cuffed ETTs are as safe as uncuffed ETTs. Because of the advantages of cuffed ETTs in the perianesthesia setting, the transition to cuffed ETTs in children is now complete. However, risks related to using cuffed ETTs in young children increase when guidelines for safe and appropriate use are not followed. Perianesthesia practitioners caring for children must understand the implications related to ETT type, correct ETT sizing, and the monitoring and control of ETT cuff pressure. The purpose of this educational module is to present evidence-based guidelines for the appropriate use of cuffed ETTs in children less than 8 years of age in the perianesthesia setting.

In vitro evaluation of the method effectiveness to limit inflation pressure cuffs of endotracheal tubes

BACKGROUND AND OBJECTIVE

Cuffs of tracheal tubes protect the lower airway from aspiration of gastric contents and facilitate ventilation, but may cause many complications, especially when the cuff pressure exceeds 30cm H2O. This occurs in over 30% of conventional insufflations, so it is recommended to limit this pressure. In this study we evaluated the in vitro effectiveness of a method of limiting the cuff pressure to a range between 20 and 30cm H2O.

METHOD

Using an adapter to connect the tested tube to the anesthesia machine, the relief valve was regulated to 30cm H2O, inflating the cuff by operating the rapid flow of oxygen button. There were 33 trials for each tube of three manufacturers, of five sizes (6.5-8.5), using three times inflation (10, 15 and 20s), totaling 1485 tests. After inflation, the pressure obtained was measured with a manometer. Pressure >30cm H2O or <20cm H2O were considered failures.

RESULTS

There were eight failures (0.5%, 95% CI: 0.1-0.9%), with all by pressures <20cm H2O and after 10s inflation (1.6%, 95% CI: 0 5-2.7%). One failure occurred with a 6.5 tube (0.3%, 95% CI: -0.3 to 0.9%), six with 7.0 tubes (2%, 95% CI: 0.4-3.6%), and one with a 7.5 tube (0.3%, 95% CI: -0.3 to 0.9%).

CONCLUSION

This method was effective for inflating tracheal tube cuffs of different sizes and manufacturers, limiting its pressure to a range between 20 and 30cm H2O, with a success rate of 99.5% (95% CI: 99.1-99.9%).

[In vitro evaluation of the method effectiveness to limit inflation pressure cuffs of endotracheal tubes]

BACKGROUND AND OBJECTIVE

Cuffs of tracheal tubes protect the lower airway from aspiration of gastric contents and facilitate ventilation, but may cause many complications, especially when the cuff pressure exceeds 30cm H2O. This occurs in over 30% of conventional insufflations, so it is recommended to limit this pressure. In this study we evaluated the in vitro effectiveness of a method of limiting the cuff pressure to a range between 20 and 30cm H2O.

METHOD

Using an adapter to connect the tested tube to the anesthesia machine, the relief valve was regulated to 30cm H2O, inflating the cuff by operating the rapid flow of oxygen button. There were 33 trials for each tube of three manufacturers, of five sizes (6.5 to 8.5), using three times inflation (10, 15 and 20seconds), totaling 1485 tests. After inflation, the pressure obtained was measured with a manometer. Pressure >30cm H2O or <20cm H2O were considered failures.

RESULTS

There were eight failures (0.5%, 95% CI: 0.1-0.9%), with all by pressures <20cm H2O and after 10seconds inflation (1.6%, 95% CI: 0 5-2.7%). One failure occurred with a 6.5 tube (0.3%, 95% CI: -0.3-0.9%), six with 7.0 tubes (2%, 95% CI: 0.4 to 3.6%), and one with a 7.5 tube (0.3%, 95% CI: -0.3-0.9%).

CONCLUSION

This method was effective for inflating tracheal tube cuffs of different sizes and manufacturers, limiting its pressure to a range between 20 and 30cm H2O, with a success rate of 99.5% (95% CI: 99.1-99.9%).

Prospective observational study on tracheal tube cuff pressures in emergency patients--is neglecting the problem the problem?

Background

Inappropriately cuffed tracheal tubes can lead to inadequate ventilation or silent aspiration, or to serious tracheal damage. Cuff pressures are of particular importance during aeromedical transport as they increase due to decreased atmospheric pressure at flight level. We hypothesised, that cuff pressures are frequently too high in emergency and critically ill patients but are dependent on providers’ professional background.

Methods

Tracheal cuff pressures in patients intubated before arrival of a helicopter-based rescue team were prospectively recorded during a 12-month period. Information about the method used for initial cuff pressure assessment, profession of provider and time since intubation was collected by interview during patient handover. Indications for helicopter missions were either Intensive Care Unit (ICU) transports or emergency transfers. ICU transports were between ICUs of two hospitals. Emergency transfers were either evacuation from the scene or transfer from an emergency department to a higher facility.

Results

This study included 101 patients scheduled for aeromedical transport. Median cuff pressure measured at handover was 45 (25.0/80.0) cmH₂O; range, 8-120 cmH₂O. There was no difference between patient characteristics and tracheal tube-size or whether anaesthesia personnel or non-anaesthesia personnel inflated the cuff (30 (24.8/70.0) cmH₂O vs. 50 (28.0/90.0) cmH₂O); p = 0.113.

With regard to mission type (63 patients underwent an emergency transfer, 38 patients an ICU transport), median cuff pressure was different: 58 (30.0/100.0) cmH₂O in emergency transfers vs. 30 (20.0/45.8) cmH₂O in inter-ICU transports; p < 0.001. For cuff pressure assessment by the intubating team, a manometer had been applied in 2 of 59 emergency transfers and in 20 of 34 inter-ICU transports (method was unknown for 4 cases each). If a manometer was used, median cuff pressure was 27 (20.0/30.0) cmH₂O, if not 70 (47.3/102.8) cmH₂O; p < 0.001.

Conclusions

Cuff pressures in the pre-hospital setting and in intensive care units are often too high. Interestingly, there is no significant difference between non-anaesthesia and anaesthesia personnel. Acceptable cuff pressures are best achieved when a cuff pressure manometer has been used. This method seems to be the only feasible one and is recommended for general use.

Endotracheal tube cuff leaks: causes, consequences, and management

The consequences of endotracheal tube (ETT) cuff leak may range from a bubbling noise to a life-threatening ventilatory failure. Although the definitive solution is ETT replacement, this is often neither needed nor safe to perform. Frequently, the leak is not caused by a structural defect in the ETT. Cuff underinflation, cephalad migration of the ETT (partial tracheal extubation), misplaced orogastric or nasogastric tubes, wide discrepancy between ETT and tracheal diameters, or increased peak airway pressure can cause leaks around intact cuffs. Correction of these problems will stop the leak without ETT replacement. Alternatively, ETT cuff, pilot balloon, and inflation system damage due to inadvertent trauma or manufacturing defects may be responsible. Conservative management ideas (management without ETT replacement) were previously published to solve the problem. However, when a large structural defect is identified or conservative measures fail, ETT replacement becomes necessary. This can be performed with direct laryngoscopy if laryngeal visualization is adequate. A difficult exchange with possible airway loss should be anticipated, and prepared for, when there are signs and/or history of difficult intubation. A risk/benefit analysis of each individual situation is warranted before decisions are made on how best to proceed. Alternative back-up ventilation plans should be preformulated and the necessary equipment ready before the exchange. In this review, various management concerns and plans are discussed, and a simple algorithm to manage leaky ETT cuff situations is presented.

Can the Intracuff Pressure Be Estimated by Palpation of the Pilot Balloon?

Background. Over the past 5 years, there has been a change in the clinical practice of pediatric anesthesiology with a transition to the use of cuffed instead of uncuffed endotracheal tubes in infants and children. However, there has been limited attention to techniques to ensure a safe intracuff pressure. We sought to determine the accuracy of estimating endotracheal tube intracuff pressure by palpation of the pilot balloon by anesthesiologists, anesthesia residents, pediatric anesthesia fellows, certified nurse anesthetists, and student nurse anesthetists. Methods. A tracheal simulation model was constructed with 3 different diameters of polyvinylchloride tubing. Three different-sized endotracheal tubes (4.0, 5.0, and 6.0 mm) were then placed into the tubes and the cuffs inflated to various pressures. Each participant was given 3 different scenarios of cuff pressure for each endotracheal tube size for a total of 9 scenarios per practitioner. By feeling the pilot balloon, the anesthesia provider was asked to estimate whether the cuff pressure was greater than 30 cm H2O, 20 to 30 cm H2O, or less than 20 cm H2O. The cuff pressure was then measured using a manometer to determine whether they had correctly estimated the intracuff pressure. Results. A total of 106 anesthesia providers participated in the study. Participants were able to estimate the correct intracuff pressure with palpation of the pilot balloon 45% of the time. In the remaining cases, the intracuff pressure was overestimated 29.4% of the time and underestimated 25.7% of the time. The intracuff pressure was correctly identified 44.4% of the time by attending physicians, 55.67% of the time by anesthesia residents or fellows, 50.6% of the time by certified nurse anesthetists, and 38.4% of the time by student nurse anesthetists. Conclusion. Participants from all the groups were unable to reliably estimate endotracheal intracuff pressure from palpation of the pilot balloon. Given the potential injury from excessive intracuff pressures, other techniques are necessary to ensure that excessive pressures are not present.

Design, Manufacture, and Testing of the Easycuff™ Pressure Measuring Syringe

A pressure measuring syringe, known as the EasyCuff™, has been designed and manufactured to provide physicians with a tool to accurately measure the pressure inside the distal cuff of endotracheal tube tubes (ETTs). The syringe, identical in size to a standard 10 cc syringe, has four components: a seal, a plunger, a barrel, and a silicone-rubber bellows (the pressure measuring component). A finite-element model of the bellows was created using ADINA™; silicone rubber bellows were then produced and shown to correlate linearly with the model to within ±5% up to a load equivalent to an internal pressure of 200 cm H2O. 20 of these bellows were then assembled into EasyCuff™ syringes and tested to assess their accuracy and repeatability. The experimental setup used a currently-available manometer, which the EasyCuff™ is designed to replace, as a reference tool. The data show that the relationship between measured pressure and bellows deflection is linear, with a correlation factor of R2 = 0.99; additionally, environmental testing showed that the EasyCuff™ is unaffected by temperature cycling between −15 °F and +170 °F.