August 2009 - Clinical Business Strategies

INSIDE THE CURRENT ISSUE

August 2009

Infection Protection

The strengths and weaknesses of endotracheal tube cuffs

by Wava Truscott, PhD, director scientific affairs and clinical education, Kimberly-Clark Health Care

As part of Kimberly-Clark’s Scientific Affairs and Clinical Education team, I’m often asked about healthcare associated infections. Lately, the lion’s share of those questions have focused on airway management and, in many cases, ventilator-associated pneumonia (VAP). While much awareness has been generated about the importance of implementing VAP practice bundles, there is growing interest in understanding whether the very devices used during intubation can make the difference between a good clinical outcome and a bad one. Below are a few of the inquiries that I find myself routinely addressing.

Q Why don’t they call it endotracheal tube cuff pneumonia instead of VAP?

A By far, the majority of VAPs are caused by bacteria that make their way around the balloon (aka cuff) that holds the endotracheal (ET) tube in place and forms a seal against the walls (mucosa) of the "wind pipe" (trachea). Once bacteria make their way past the cuff, it’s clear sailing into the lungs. The weakest link in VAP prevention is a "leaky cuff". So, it really is more appropriately termed ETTCP—but VAP is just easier to say.

Q How do bacteria get past the cuff if it’s supposed to form a seal?

A Most cuffs are made of polyvinyl chloride (PVC); the same translucent material from which vinyl gloves are made. The ET tube cuff is deflated for insertion below the vocal cords, being careful not to injure the cords or tracheal wall.

Once the tube is in position, the cuff is inflated. Because the trachea has an uneven surface with irregular widths, the cuff is often oversized to compensate for the "ins-and-outs". Inflation within the tracheal enclosure causes the extra material to fold on itself, forming tiny channels – virtual highways for microbial transport! In efforts to reduce leakage, cuffs are sometimes over-inflated, causing enough pressure against the tracheal wall that capillaries bringing oxygen to that area can collapse. Deprived of oxygen, it doesn’t take long for the tissue to sustain injury. Nerves may be lost impairing throat function. Dying tissue may slough off opening the way for throat infections and creating a reservoir of bacteria available for causing pneumonia in the future. The fine "hairs" that move mucus up from the throat and lungs may be denuded, creating a "conveyor belt dead zone" rendering the patient more vulnerable to pneumonia long after the endotracheal tube is removed.

Q If cuffs leak partly due to the channel forming characteristics inherent in PVC; the PVC cuff does not form a perfect seal; and the PVC cuff possesses several insertion and inflation pressure risks, why hasn’t PVC been replaced with some better material?

A It has! A pediatric anesthesiologist, intent on correcting these problems recently collaborated with a physician engineer to develop an ultra thin, transparent, polyurethane cuff that anneals to itself (sticks to itself like plastic wrap) without creating gap-channels. The polyurethane is so thin that it molds to the irregular walls of the trachea with ease at much lower pressure than what is necessary for PVC cuff inflation. Although the risk cannot be completely eliminated, when less pressure is exerted by the cuff- there is less risk for pressure induced injuries. The successful tracheal seal of this very-low pressure cuff is also attributed to its cylindrical design. The inflated "sausage" shape enables a snug fit over a longer length of the trachea equally distributing pressure.

Despite the thinness of the polyurethane membrane, it is several times stronger than conventional PVC cuffs. The polyurethane version is more difficult to puncture and has a higher burst strength.

Q Guidelines have previously recommended that patients under the age of 8 not be intubated with inflated ET tubes. Have things changed?

A Yes, clinical care recommendations have changed. Knowledge of the risks of not using a cuff has accumulated while cuffs themselves have improved. Studies have measured significant levels of anesthesia released into the ambient environment of ORs when anesthesia is being delivered through un-cuffed ET tubes, putting safety of repeatedly exposed surgical teams at risk. Oxygen also slips out along the sides of the un-cuffed ET tubes during surgery and when patients are on mechanical ventilation support increasing the risk of fire. With less oxygen reaching the patient, there is increased risk of low blood oxygen saturation. The pressure maintained in the alveoli (positive end expiratory pressure –PEEP) necessary to ensure alveolar patency is reduced due to the escaping air, increasing the risk of alveolar de-recruitment (close down so they cannot take in air) and even lung collapse. Without a cuff, patient aspiration of microorganisms and fluid secretions is a constant problem as is the potential spreading of infectious aerosols from the patient.

Cuffed ET tubes have now been shown to be safe and effective for children and infants in numerous clinical studies. The American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care of Pediatric and Neonatal Patients states that cuffed endotracheal tubes may be used in children and infants (except newborns) provided the cuff inflation pressure is kept <20 cm H2O. The transparency and low profile inherent in polyurethane cuffed ET tubes make insertion and placement safer and easier than traditional cuffs. The low inflation cylinder shape also permits wider tubes to be used addressing the concern that traditional cuffed tubes are too narrow to deliver sufficient oxygen and anesthetic gasses to infants and children. The reduced pressure necessary for a good seal minimizes potential concerns for damaging delicate tracheal tissues. Now, adults, children and infants can receive full benefits of this new technology in cuffed ET tubes.

VAP prevention requires adherence to best practices across a wide range of activities in addition to the selection of the right cuff, inserted and inflated correctly. Components include maintaining patients in a semi-recumbent position (30° – 40° elevation of head of bed) unless there are contraindications, the use of closed endotracheal suction systems, subglottic secretion suctioning/drainage, orotracheal rather than nasogastric intubation, avoidance of gastric overdistintion during feeding, performance of regular and appropriate oral care, and extubation as soon as clinically feasible.

With VAP responsible for 60% of the deaths due to healthcare-associated infections in the United States; approximately 8-28% of critical care patients developing VAP; and the costs of an extended average ICU stay of 4 to 6 days, VAP requires prevention vigilance and implementation of the most up-to-date evidence-based improvement strategies.

Resources:

1. 2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care of Pediatric and Neonatal Patients: Pediatric Advanced Life Support. American Heart Association. Pediatrics. 2006;117:e1005-1028

2. Collin SE, et. al. Strategies to prevent ventilator-associated pneumonia in acute care hospitals. Infect Control Hosp Epidemiol 2008;29(Sup 1): S31-S40

3. Dullenkopf A, et.al. Air leakage around endotracheal tube cuffs. European Journal of Anaesthesiology 2004; 21(6):448-453

4. Dullenkopf A, et.al. Fluid leakage past tracheal tube cuffs: evaluation of the new Microcuff endotracheal tube. Intensive care medicine 2003;29(10):1849-1853

5. Poelaert J, et.al. Polyurethane cuffed endotracheal tubes to prevent early postoperative pneumonia after cardiac surgery J Thorac Cardiovasc Surg 2008;135:771-776