Liquid vs. air-filled cuff during air transport

文章

作者: Simon Franz

日期: 11.06.2020

During fixed- or rotary-wing transport, my usual practice is to inject 10 ml of saline into the cuff of the patient’s endotracheal tube to prevent over-inflation. What would be the advantage of using an air-filled cuff in combination with an automatic cuff-pressure controller in these situations?

Liquid vs. air-filled cuff during air transport

Cuff pressure at altitudes up to 3,000 ft

While the ambient pressure drops with the height above sea level, a closed system such as an ETT cuff keeps its absolute pressure constant. This results in a relative pressure increase of the ETT cuff pressure compared to the environment. Many endotracheal tube (ETT) cuffs are therefore over-inflated during air transport, potentially causing pressure-related tracheal injuries. Weisberg et al. (2017) discovered that there is no linear relationship between ETT cuff pressures and maximum altitude during transports near sea level (up to an altitude of 3,000 ft). Their results support routine monitoring of ETT cuff pressures, as many cuffs were initially over-inflated. However, there appears to be no need to replace air with saline at altitudes near sea level (Weisberg SN, McCall JC Jr, Tennyson J. Altitude-Related Change in Endotracheal Tube Cuff Pressures in Helicopter EMS. West J Emerg Med. 2017;18(4):624-629. doi:10.5811/westjem.2017.3.320781).

Cuff pressure at higher altitudes

For information about this behavior at higher altitudes, such as in the pressurized cabin of a fixed-wing airplane (8,000 ft), we can refer to the work of Britton et al. (2014). They compared four different methods of managing endotracheal cuff pressure, and evaluated the pressure at sea level (baseline) and 8,000 ft (see Figure 1). They showed that filling the cuff with saline did not prevent the cuff pressure from increasing with higher altitudes (Britton T, Blakeman TC, Eggert J, Rodriquez D, Ortiz H, Branson RD. Managing endotracheal tube cuff pressure at altitude: a comparison of four methods. J Trauma Acute Care Surg. 2014;77(3 Suppl 2):S240-S244. doi:10.1097/TA.00000000000003392). This is probably due to residual air inside the cuff. In addition, they showed that a fixed volume of saline could lead to a dangerously high level of cuff pressure even at sea level.

Diagram - evaluation of pressure at sea leven and 8.000 feet using different cuff management techniques — Figure 1: Continuous pressure monitoring of all four cuff management techniques using the 8.0 mm ID ETT. The dotted red line reflects the safety threshold of 30 cmH20 cuff pressure (Britton et al., 2014).

Insufficient protection with saline

It is generally accepted that the potential harmful effects of a cuffed endotracheal tube are due to transmural pressures between the cuff and tracheal mucosa, which exceed the capillary perfusion pressure of the tissue. Using saline instead of air does not provide sufficient protection against these high pressures, and also affects the ability to measure the actual cuff pressure. From a pathophysiological view, it therefore makes much more sense to control the pressure rather than the volume in the cuff.

With the automatic cuff-pressure controller, IntelliCuff®, Hamilton Medical offers a solution for automatic measurement and maintainence of cuff pressure for all patient groups for critical care, interhospital transport, and anesthesia.

脚注

参考文献

1. Weisberg SN, McCall JC Jr, Tennyson J. Altitude-Related Change in Endotracheal Tube Cuff Pressures in Helicopter EMS. West J Emerg Med. 2017;18(4):624-629. doi:10.5811/westjem.2017.3.32078
2. Britton T, Blakeman TC, Eggert J, Rodriquez D, Ortiz H, Branson RD. Managing endotracheal tube cuff pressure at altitude: a comparison of four methods. J Trauma Acute Care Surg. 2014;77(3 Suppl 2):S240-S244. doi:10.1097/TA.0000000000000339

Altitude-Related Change in Endotracheal Tube Cuff Pressures in Helicopter EMS.

Weisberg SN, McCall JC Jr, Tennyson J. Altitude-Related Change in Endotracheal Tube Cuff Pressures in Helicopter EMS. West J Emerg Med. 2017;18(4):624-629. doi:10.5811/westjem.2017.3.32078

Link to article

INTRODUCTION

Over-inflation of endotracheal tube (ETT) cuffs has the potential to lead to scarring and stenosis of the trachea.1, 2,3, 4 The air inside an ETT cuff is subject to expansion as atmospheric pressure decreases, as happens with an increase in altitude. Emergency medical services helicopters are not pressurized, thereby providing a good environment for studying the effects of altitude changes ETT cuff pressures. This study aims to explore the relationship between altitude and ETT cuff pressures in a helicopter air-medical transport program.

METHODS

ETT cuffs were initially inflated in a nonstandardized manner and then adjusted to a pressure of 25 cmH2O. The pressure was again measured when the helicopter reached maximum altitude. A final pressure was recorded when the helicopter landed at the receiving facility.

RESULTS

We enrolled 60 subjects in the study. The mean for initial tube cuff pressures was 70 cmH2O. Maximum altitude for the program ranged from 1,000-3,000 feet above sea level, with a change in altitude from 800-2,480 feet. Mean cuff pressure at altitude was 36.52 ± 8.56 cmH2O. Despite the significant change in cuff pressure at maximum altitude, there was no relationship found between the maximum altitude and the cuff pressures measured.

CONCLUSION

Our study failed to demonstrate the expected linear relationship between ETT cuff pressures and the maximum altitude achieved during typical air-medical transportation in our system. At altitudes less than 3,000 feet above sea level, the effect of altitude change on ETT pressure is minimal and does not require a change in practice to saline-filled cuffs.

Managing endotracheal tube cuff pressure at altitude: a comparison of four methods.

Britton T, Blakeman TC, Eggert J, Rodriquez D, Ortiz H, Branson RD. Managing endotracheal tube cuff pressure at altitude: a comparison of four methods. J Trauma Acute Care Surg. 2014;77(3 Suppl 2):S240-S244. doi:10.1097/TA.0000000000000339

Link to article

BACKGROUND

Ascent to altitude results in the expansion of gases in closed spaces. The management of overinflation of the endotracheal tube (ETT) cuff at altitude is critical to prevent mucosal injury.

METHODS

We continuously measured ETT cuff pressures during a Critical Care Air Transport Team training flight to 8,000-ft cabin pressure using four methods of cuff pressure management. ETTs were placed in a tracheal model, and mechanical ventilation was performed. In the control ETT, the cuff was inflated to 20 mm Hg to 22 mm Hg and not manipulated. The manual method used a pressure manometer to adjust pressure at cruising altitude and after landing. A PressureEasy device was connected to the pilot balloon of the third tube and set to a pressure of 20 mm Hg to 22 mm Hg. The final method filled the balloon with 10 mL of saline. Both size 8.0-mm and 7.5-mm ETT were studied during three flights.

RESULTS

In the control tube, pressure exceeded 70 mm Hg at cruising altitude. Manual management corrected for pressure at altitude but resulted in low cuff pressures upon landing (<10 mm Hg). The PressureEasy reduced the pressure change to a maximum of 36 mm Hg, but on landing, cuff pressures were less than 15 mm Hg. Saline inflation ameliorated cuff pressure changes at altitude, but initial pressures were 40 mm Hg.

CONCLUSION

None of the three methods using air inflation managed to maintain cuff pressures below those associated with tracheal damage at altitude or above pressures associated with secretion aspiration during descent. Saline inflation minimizes altitude-related alteration in cuff pressure but creates excessive pressures at sea level. New techniques need to be developed.