The “Leak test” Prior to Extubation: Another “bubbameisa” (old wives’ tale)?
Jayant K. Deshpande MD, Justin L. Lockman MD MSEd, and Myron Yaster MD
You get called STAT to the PICU for an airway emergency. You find an infant with severe stridor and worsening hypoxemia, and you assess the scene. The patient was mechanically ventilated via a microcuff endotracheal tube for five days, was on low ventilator settings, and passed an “extubation readiness test” prior to extubation. You ask about the leak test, and are told, “The leak was fine, and we gave steroids before pulling the tube to be conservative.” You recall that there was a pro/con debate in the SPA Newsletter a few years ago; you have also used microcuff tubes and done leak testing ever since then to reduce airway trauma.
But does the leak test really tell us that a child will not develop post-extubation st ridor? The leak test has been used clinically by pediatric anesthesiologists and pediatric intensivists for decades, particularly in the era of sizing uncuffed endotracheal tubes or when using high pressure, low volume cuffed tubes. Since the advent of thin, low pressure, cuffed tubes entered practice (“microcuff”) leak tests have become as common as real spare tires in new cars. There’s a lot to unpack into today’s PAAD, so I’ve asked Dr. Alan Jay Schwartz to further explore and review this topic as a “remembering the classics”, so stay tuned! Myron Yaster MD
Original article
Kanno K, Fujiwara N, Moromizato T, Fujii S, Ami Y, Tokushige A, Ueda S. Pre-Extubation Cuffed Tube Leak Test and Subsequent Post-Extubation Laryngeal Edema: Prospective, Single-Center Evaluation of PICU Patients. Pediatr Crit Care Med. 2023 May 23. PMID: 37219965
Microcuff endotracheal tubes have become standard in the PICU and ORs.1 “Air-leak testing at the time of extubation for the risk of post-extubation laryngeal edema (PLE) is considered good practice. That is, the presence of a leak may imply high likelihood of ETT extubation without complication.”2 The primary aim of today’s PAAD study by Kanno et al. was to “prospectively assess the diagnostic accuracy of the various air-leak tests used in PICU patients with microcuff pediatric tracheal tubes (MPTTs) in situ just before extubation and examine the association with subsequent post-extubation laryngeal edema (PLE).”2 The authors also carried out some exploratory analyses of optimal MPTT tube sizing since the usual formula does not account for presence of a cuff.”2
In this prospective, single-center observational study, Kanno et al.2 “investigated the diagnostic accuracy for post-extubation PLE using a pre-extubation air leak test in PICU patients with MPTTs. Eighty-five pediatric patients (<15 yr) who had been intubated for at least 12 hours using the MPTT were included. Positive rates for the standard leak, leak percentage (cutoff 10%), and cuff leak percentage (cutoff 10%) tests were 0.27, 0.20, and 0.64, respectively. The standard leak, leak percentage, and cuff leak tests showed sensitivities of 0.36, 0.27, and 0.55, respectively; and specificities of 0.74, 0.81, and 0.35, respectively. PLE occurred in 11 of 85 patients (13%), and there were no instances of needing reintubation. The results show that neither the standard leak test, leak percentage, nor cuff leak percentage are clinically useful.”2 “Ouch!” is this another “bubbameisa” (old wives’ tale) biting the dust? We think the answer is “not exactly.”
“For many years, the standard leak test has been used in the PICU. However, previous studies report limitations in identifying cases who go on to develop PLE. For example, in 2002, Mhanna et al.3 reported a low sensitivity of 65% for predicting PLE in children under 7 years old. Suominen et al.4 in 2007 reported the same in children after cardiac surgery, while Wratney et al.5 in 2008 found the test to be of no significance in the PICU. Moreover, there are problems with the question of what pressure to apply (i.e., 20–30 cm H2O) and the method of evaluation itself being qualitative and relying on the subjectivity of the evaluator.”2
So why not give it up? Because, as always, the details matter. For example, Wratney’s 2008 study5, referenced above, was not designed to show whether the leak test mattered. It was a study of whether having no leak at pressured >/= 30 cm H20 would predict extubation failure. And it didn’t – meaning that children were not more likely to be reintubated in the no leak group. But they did require more racemic epi. The authors concluded that children should not remain intubated with ETTs that are too large just because of lack of a leak.
This issue is also complicated by the various methods of performing a leak test. Is hearing an audible leak at a pressure of 20 cm H2O (obtained manually) the same as a 10% leak on the ventilator with a peak inspiratory pressure of 25 cm H2O. Is 10% different from 20% for this purpose? And are the leaks on the ventilator being observed during standard ventilation, or (as many ventilators are now capable) being obtained through a “leak test” button on the ventilator? Even in an individual PICU, three people may perform (and report) the leak test differently – so how can we know?
One thing that does seem clear from all of these studies: if there is no leak with a deflated cuff, the breathing tube that is in place is TOO LARGE and we should consider downsizing it if the clinical situation allows. Leaving oversized tubes in place for days or even hours is a recipe for subglottic injury, and many of our subglottic stenosis patients can trace their pathology to this cause.
The leak test remains recommended for gauging proper tube size as well as for providing a level of comfort that the airway will be fine after extubation, both in pediatric anesthesia and pediatric critical care practice settings. What do you think? Do you routinely use a leak test when inflating a microcuff tube in the OR? Send your responses to Myron who will post in a Friday Reader Response.
One more word about steroids: All of the patients in this study were pretreated with corticosteroids prior to extubation to prevent or limit airway edema. But do steroids work? Is this another “bubbameisa” (old wives’ tale)?
Multiple articles have suggested that steroids may be ineffective in reducing airway edema and extubation failure. A Cochrane review on the subject6 concluded that, “Using corticosteroids to prevent (or treat) stridor after extubation has not proven effective for neonates or children. However, given the consistent trends towards benefit, this intervention does merit further study, particularly for high risk children or neonates. In adults, multiple doses of corticosteroids begun 12‐24 hours prior to extubation do appear beneficial for patients with a high likelihood of post extubation stridor.”
A recent network meta-analysis of studies in pediatric patients concluded that, “Periextubation dexamethasone can prevent postextubation UAO in children, but effectiveness is highly dependent on timing and dosing regimen. Early initiation (ideally >12 h before extubation) appears to be more important than the dose of dexamethasone. Ultimately, the specific steroid strategy should be personalized, considering the potential for adverse events associated with dexamethasone and the individual risk of UAO and reintubation.”7 What are your thoughts and what do you do in your practice? Perhaps this is an opportunity for a large, prospective, multicenter trial (as suggested by the Cochrane review). If so, would you have equipoise about this and be willing to withhold steroids from children without a leak? Send your responses to Myron who will post in a Friday Reader Response.
References
1. Emeriaud G, López-Fernández YM, Iyer NP, et al. Executive Summary of the Second International Guidelines for the Diagnosis and Management of Pediatric Acute Respiratory Distress Syndrome (PALICC-2). Pediatric critical care medicine : a journal of the Society of Critical Care Medicine and the World Federation of Pediatric Intensive and Critical Care Societies. Feb 1 2023;24(2):143-168. doi:10.1097/pcc.0000000000003147
2. Kanno K, Fujiwara N, Moromizato T, et al. Pre-Extubation Cuffed Tube Leak Test and Subsequent Post-Extubation Laryngeal Edema: Prospective, Single-Center Evaluation of PICU Patients. Pediatric critical care medicine : a journal of the Society of Critical Care Medicine and the World Federation of Pediatric Intensive and Critical Care Societies. May 23 2023;doi:10.1097/pcc.0000000000003282
3. Mhanna MJ, Zamel YB, Tichy CM, Super DM. The "air leak" test around the endotracheal tube, as a predictor of postextubation stridor, is age dependent in children. Critical care medicine. Dec 2002;30(12):2639-43. doi:10.1097/00003246-200212000-00005
4. Suominen PK, Tuominen NA, Salminen JT, et al. The air-leak test is not a good predictor of postextubation adverse events in children undergoing cardiac surgery. Journal of cardiothoracic and vascular anesthesia. Apr 2007;21(2):197-202. doi:10.1053/j.jvca.2006.01.007
5. Wratney AT, Benjamin DK, Jr., Slonim AD, He J, Hamel DS, Cheifetz IM. The endotracheal tube air leak test does not predict extubation outcome in critically ill pediatric patients. Pediatric critical care medicine : a journal of the Society of Critical Care Medicine and the World Federation of Pediatric Intensive and Critical Care Societies. Sep 2008;9(5):490-6. doi:10.1097/PCC.0b013e3181849901
6. Khemani RG, Randolph A, Markovitz B. Corticosteroids for the prevention and treatment of post-extubation stridor in neonates, children and adults. The Cochrane database of systematic reviews. Jul 8 2009;2009(3):Cd001000. doi:10.1002/14651858.CD001000.pub3
7. Iyer NP, López-Fernández YM, González-Dambrauskas S, et al. A Network Meta-analysis of Dexamethasone for Preventing Postextubation Upper Airway Obstruction in Children. Ann Am Thorac Soc. Jan 2023;20(1):118-130. doi:10.1513/AnnalsATS.202203-212OC