The WuScope is a fiberoptic intubating device, combining rigid laryngoscope blades with a flexible fiberscope. Since the WuScope system can allow visualization of the larynx and intubation of the trachea without head or neck movement, it has proven to be an effective method for tracheal intubation of patients with cervical spine injury(1). However, the WuScope�s capabilities under other conditions has yet to be determined.
The application of cricoid pressure is a commonly utilized practice during rapid sequence intubation to minimize the risk of pulmonary aspiration(2). The purpose of this study was to assess the effect of cricoid pressure on the ease and time for successful intubation using the WuScope fiberoptic laryngoscope system.

Methods

Thirty-three patients undergoing elective surgery requiring general anesthesia and neuromuscular blockade (NMB) were studied prospectively. Each patient had their trachea intubated under two conditions. The order of conditions was determined by a table of random numbers: 1. application of cricoid pressure as the first technique (n=17) or 2. no application of cricoid pressure as the first technique (n=16). Patients were excluded if they were under eighteen years of age, had a risk of regurgitation due to full stomach precautions, or had a difficult airway.
Standard monitoring of ECG, BP, pulse oximetry, and capnography was done. Following induction of general anesthesia and NMB, patients were manually ventilated until onset of NMB proven by loss of all four orbicularis oculi twitches in response to train-of-four supramaximal stimulation of the facial nerve(3). Tracheas were then intubated according to their assigned group. Following the first intubation, the endotracheal tube (ETT) was removed and the trachea was intubated a second time, under the complementary condition. Application of cricoid pressure was done according to Sellick�s maneuver(4).
For all intubations, time to visualize the vocal cords, time to successfully intubate, and the intubation difficulty scale (IDS) score were recorded. Non-parametric statistical analyses were done with the Kruskal-Wallis test to compare time to visualize vocal cords and time to intubate between the two conditions. IDS scores between conditions were compared with a Chi-Square test. A P value of < 0.05 was considered significant.

Results

There were no significant demographic differences between groups. Time to visualize vocal cords and intubate the trachea was longer (P<0.05) with cricoid pressure (Table 1). Twenty-seven patients (82%) receiving cricoid pressure had an IDS score of 0 indicating an ideal intubation as compared with thirty patients (91%) not receiving cricoid pressure (Fig. 1, P=NS). Additionally, cricoid pressure was noted to markedly compress the vocal cords in nine patients (27%) and impede the placement of the ETT in five patients (15%). For three patients (9%), the pressure had to be released in order to successfully intubate. The included table lists time data between groups for visualization of vocal cords and completion of successful intubation.

Discussion

The study demonstrated that there is no significant difference in ease of intubation between groups receiving cricoid pressure as compared to groups not receiving cricoid pressure when using the WuScope system but vocal cord visualization and tracheal intubation took slightly longer with cricoid pressure. While the application of cricoid pressure was found to compress the vocal cords in 27% of patients and impede advancement of the ETT in 15% of patients, it is still a valuable method for the prevention of regurgitation and possible pulmonary aspiration.

References

1. Smith CE, et al. Evaluation of tracheal intubation difficulty in patients with cervical spine immobilization: fiberoptic (WuScope) versus conventional laryngoscopy. Anesthesiology. 1999; in press.
2. Brimacombe J, Berry A. Cricoid pressure. Can J Anaesth. 1997; 44/4: 414-25.
3. Patel N, et al. Tracheal intubating conditions and orbicularis oculi neuromuscular block during modified rapid sequence intubation. Am J Anesthesiol. Jan/Feb 1998: 15-20.
4. Sellick BA. Cricoid pressure to control regurgitation of stomach contents during induction of anaesthesia. The Lancet. Aug. 19, 1961: 404-6.