Studies 2

Studies - Continued

            Unlike the external aspects of the patients’ pressure points, damage to the trachea from the ETT and inappropriate cuff pressure cannot be seen. It is important for anesthesia providers to be aware of the physiologic changes that can take place with tracheal intubation and high cuff pressures. Nordin (1977) studied rabbit tracheas due to their similarity in lateral wall anatomy and found progressive damage to the tracheal wall in relation to time and cuff pressure. The introduction of the endotracheal tube itself created superficial damage and inflation of the cuff resulted in progressive extension of the mucosal damage. A cuff-tracheal (C-T) pressure of 50 mmHg for 2 hours of intubation destroyed most of the epithelial cells on top of the cartilages, and 4 hours of intubation with C-T pressure of 100 could destroy the mucosa down to the cartilage and basement membrane. Bacteria were also found to be invading the damaged mucosa.¹²

An old belief is that ischemic tracheal injury can occur only with prolonged intubation. Dedo,³  Somri,¹³  Raynham¹⁴  and Rokamp⁴ all report damage within 15 to 30 minutes of cuff pressure exceeding the tracheal perfusion pressure. According to Dedo³, over-inflation of the ETT cuff for even a brief operation can lead to tracheal stenosis within 1 to 3 months. Additionally, hypovolemia, acidosis, hypoxia and anemia could cause even greater compromise.³

           Tracheal stenosis can occur anywhere the endotracheal tube is in contact with the tracheal wall, but most common site is where the ETT cuff has been in contact. In a retrospective review of 31 patients with post intubation (PI) and post tracheostomy (PT) stenosis, Zias¹⁵ found the most common profile to be female (73%) obese (66%), history of diabetes (35%), hypertension (52%), cardiovascular disease (45%) and a current smoker (39%). Eleven patients in the PI group had only oro-tracheal intubation (5.2 days mean intubation time) and developed web-like stenosis at the cuff site. All of the comorbidities in the profile would diminish tracheal perfusion even more extensively in the presence of high cuff pressure.

        Studies that examine the size of tracheas and endotracheal tube complications support using smaller ETTs. Randestad,¹⁶ in an effort to aide transplantation, stenting, intubation, cricothyroidectomy and endoscopic procedures, measured the dimensions of the cricoid cartilage and trachea. A total of 1861 measurements were taken from 34 male and 27 female patients. The longitudinal axes of the cricoaryenoid joint facets ranged from 42 to 74 degrees in women and 37 to 75 degrees in men. The authors concluded that “in some women, the inner diameter of the female cricoid ring does not permit passage of a standard size (7 mm) tracheal tube in some women, and the small distance between the cricoarytenoid joints and standard size tubes cause pressure necrosis at the medial sites of the arytenoid cartilages.”¹⁶ Randestad also points out there is a need for better-fitting tubes to avoid unnecessary hoarseness and laryngeal pain.

The tracheal diameter measurements of men and women and the inner diameter (ID) and outer diameter (OD) measurements of ETTs are provided in the table below. It is readily apparent that a size 7.0 diameter ETT with an OD of 9.6 is clearly too large to fit some women.

Measurements of trachea from Randestad: Women 6.6 to 17 mm and men 11-21.5 mm.

Diameter	Size	ID	OD
F 6.6 (smallest)	6.0	6.0	8.2
	6.5	6.5	8.9
	7.0	7.0	9.6
	7.5	7.5	10.2
M 11 (smallest)	8.0	8.0	10.9

            Many studies conclude that women are more prone to POST/PH than men.^17-20 Jaennsson²¹ (2012) however, in a prospective cross-sectional study examined risk factors for airway symptoms post-operatively and gender differences and found no significant differences. A total of 495 patients were included with a total of 31 variables. Women were intubated with a size 6.0-7.0 ETT and men with 7.0-8.0 ETT. The main risk factor found for women was ETT size 7.0 and multiple laryngoscopies. For men, the main risk factors were intubation by personnel with < 3 months experience. The main risk factor for hoarseness for both men and women was cuff pressure.

In a study to examine ETT size and sore throat following surgery, Jaensson ²² (2009) looked at 100 healthy women and allocated either a size 6.0 or 7.0 ETT. Post-operatively sore throat and discomfort were assessed at 1-2 hours and 24 hours after extubation. Cuff pressure of the ETTs was measured and maintained at 20-30 cm H₂O pressure. The severity of sore throat in the PACU was significantly greater in the ETT 7.0 (38.8%) compared with the ETT 6.0 (18.8%). The grading for throat discomfort was mild to severe for size 7.0 and mild to moderate in the 6.0 ETT group. There were no statistically significant differences between the two groups after PACU. The authors concluded that use of ETT size 6.0 reduces sore throat and discomfort in the early post-operative period.²¹

Al-Qahtani² also studied ETT size and incidence of sore throat. A total of 1,618 patients, (883 males and 735 females) were included between February 2000 and May 2003. Size 7.0-7.5 mm cuffed tracheal tubes were used for men and size 6.0-6.5 mm in females. The age group was between 16-62 yrs. and all presented for nasal surgery and/or functional endoscopic sinus surgery. Patients who had signs of common cold were excluded. The authors found that the use of small tube in intubating the trachea, together with other measures (lubricating, careful instrumentation, intubating only when fully relaxed and extubating when the cuff was fully deflated), have dramatic effects on minimizing the incidence of postoperative sore throats.

As pointed out for cuff pressure damage, anesthesia providers are unable to see the physiologic changes associated with large endotracheal tubes. It is described by Dedo in his book Surgery of the Larynx and Trachea  “… the mucosa and the perichondrium of the arytenoid cartilages can be necrosed by an endotracheal tube that is too large….If the endotracheal tube pressure causes the necrosis to extend into the cricoarytenoid joints, they will become frozen, so that even if posterior commissure stenosis is repaired, the vocal cords will not be able to adduct (open) to provide an adequate airway.”³

Vocal cord injury and hoarseness are clinically relevant complications related to short-term general anesthesia and an endotracheal tube.²³  Vocal cord paralysis is secondary to damage to the recurrent laryngeal nerve (RLN) and may occur because the endotracheal tube cuff presses the recurrent laryngeal nerve between the thyroid lamina and the arytenoid cartilage.^24,25

Cros²⁴ described two cases, one permanent, of unilateral RLN palsy following brief periods of intubation. The author concluded that the cause of paralysis was a compression of the nerve between the endotracheal tube cuff and cricoid or from compression between the thyroid ala and a dislocated artenoid cartilage from an unnecessarily large tube.

Otani²⁶ documented nerve palsy in four patients after surgery with an endotracheal tube. The explanation offered was excessive pressure for the inflated ETT on the intralaryngeal course of the anterior branch of the RLN. The authors also concluded monitoring cuff pressure is most important in preventing these nerve injuries. Brandwein²⁵ describes a bilateral vocal cord paralysis following endotracheal intubation and stated the anterior ramus of the RLN is particularly vulnerable to compression injury.

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