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From the Department of Anesthesiology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea.
Address correspondence to: Dr. Jeong Jin Lee, Department of Anesthesiology, Samsung Medical Center, 50 Ilwon-dong, Kangnam-gu, Seoul 135-710, South Korea. Phone: 82-2-3410-2465; Fax: 82-2-3410-0361; E-mail: jjlee{at}smc.samsung.co.kr
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Abstract |
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Methods: A retrospective case-control study was undertaken following approval from the Institutional Review Board on human studies. The data from 90 patients with a polysomnograph-confirmed diagnosis of OSAS, who had undergone UPPP surgery under general anesthesia, were used to evaluate the apnea-hypopnea index (AHI), the preoperative lowest arterial saturation, the occurrence of difficult intubation as assessed by the operator intubation difficulty scale score, extubation time, lowest arterial saturation in postanesthesia care unit, and length of stay in postanesthesia care unit. We compared OSAS patients with 90 age and sex-matched control patients with respect to the prevalence of difficult intubation.
Results: The prevalence of difficult intubation was higher in the OSAS group than in the control group (16.7% vs 3.3%, P = 0.003). When evaluating the OSAS group according to the occurrence of difficult intubation, AHI was significantly higher in the difficult intubation subgroup (67.4 ± 22.5 vs 49.9 ± 28.0, P = 0.026), and patients with an AHI 
40 showed a significantly higher prevalence of difficult intubation.
Conclusion: This study shows that the occurrence of difficult intubation can be predicted using AHI in patients who undergo UPPP surgery for OSAS.
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Introduction |
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Upper airway control is one of the most important aspects of anesthesia management in patients with OSAS. An association between the severity of OSAS and the occurrence of difficult intubation has been speculated, and a prospective case-control study elicited the conclusion that patients with difficult intubation and OSAS are related significantly and share anatomical features.4 Other authors speculated that clinical factors that predict difficult intubation could also predict OSAS.5 Another retrospective study showed that difficult intubation occurred more often in OSAS patients than in controls, but failed to confirm the relationship between the severity of OSAS and the occurrence of difficult intubation in OSAS patients.6
Here, we undertook a retrospective case-control study to determine the occurrence of difficult intubation in OSAS patients compared to patients without OSAS, to assess the relationship between the severity of OSAS and the occurrence of difficult intubation in OSAS patients, and to search for any factor capable of predicting difficult intubation in patients with OSAS.
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Methods |
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Polysomnographic data, anesthesia/recovery room records and progress notes were reviewed. Polysomnography was checked routinely in the OSAS patients who had undergone UPPP surgery. The sleep stage (electroencephalogram (C4/A1), the right and left electro-oculogram and submental electromyogram), oronasal airflow (thermistor), ribcage and abdominal wall motion (inductance plethysmography), arterial oxyhemoglobin saturation (pulse oximetry), electrocardiogram and sound were recorded and analyzed automatically (EmblaN7000, Medcare, Reykjavik, Iceland). Obstructive sleep apnea syndrome severity was measured using the apnea hypopnea index (AHI), and using the lowest oxygen saturation associated with an abnormal respiratory event during sleep (LSAT-PREOP). Apnea was defined as cessation of breathing more than ten seconds. Hypopnea was a decreased effort to breathe at least 50% less than the baseline and with at least a 4% decrease in SaO2. Apnea hypopnea index was calculated as the sum of total events (apneas and hypopneas) per hour.7
For each OSAS patient, the next control patient from the same month’s list of endoscopic sinus surgery was included in the study if he (she) had the same sex, and a similar age (± 2 yr). Factors previously described as being importantly related with OSAS during the perioperative period were defined. These factors included a history of smoking, excessive alcohol intake, arterial hypertension, and a history of diabetes mellitus. Preoperative hemoglobin values were also recorded.
Operator’s subjective judgment as to the ease of intubation performance was defined with the subjective operator intubation difficulty scale score,8 as assessed by one of two board-certified anesthesiologists with more than five years experience. Operator intubation difficulty scale score was checked and recorded routinely in those patients who had undergone general anesthesia in our hospital. Endotracheal intubation was rated as easy when immediate visualization of the glottis (Cormack and Lehane grade I or II)9 was obtained and tube progression into the trachea was achieved without the use of any intubation aid within three attempts. Endotracheal intubation was rated as difficult in the presence of poor visualization of the glottis (Cormack and Lehane grade III or IV),9 when an intubation aid (stylet, intubating laryngeal mask airway, fibreoptic bronchoscope) was needed, or when three or more intubation attempts were required. Data pertaining to stay in the postanesthesia care unit (PACU) were recorded, i.e., extubation time, lowest oxygen saturation and length of stay.
Statistical analysis
Data were analyzed using SPSS 11.0 for windows (SPSS Inc., Chicago, IL, USA). Data are presented as means ± standard deviation or percentages as appropriate. Assuming the overall occurrence of difficult intubation in control patients of 5%, we decided that a 15% difference in overall occurrence of difficult intubation between groups would be clinically important. Seventy-five patients in each group would thus be necessary with 
= 0.05 and ß = 0.2. To take into consideration possible protocol variances we enrolled 90 patients per group. Chi-square analysis was used to compare proportion of subjects in the two study groups with difficult intubation, and the Student’s t test and the Mann-Whitney U test were used to compare other variables between the two groups. The OSAS patients were divided into three subgroups according to AHI (patients with AHI of < 40: mild to moderate OSAS,10 from 40 to 70: severe OSAS, > than 70: extremely severe OSAS) and the incidence of difficult intubation was compared using Chi-square analysis. We divided the OSAS patients into two subgroups according to intubation difficulty and compared them with the Student’s t test and the Mann-Whitney U test. Values of P < 0.05 were defined as statistically significant.
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Results |
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. Weight and body mass index (BMI) were significantly higher in OSAS than in the control patients. Arterial hypertension was more frequently encountered in OSAS patients, difficult intubation occurred more often in OSAS patients (16.6% vs 3.3%). When we divided the OSAS patients into two subgroups according to intubation difficultly, a significant difference in AHI was observed. In OSAS patients with difficult intubation, age, height, weight, LSAT-PREOP, BMI, and hemoglobin were not significantly different from those of OSAS patients with easy intubation. In the PACU, extubation time, LSAT, and length of stay were similar in these two subgroups (Table II).
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). Moreover, the incidence of difficult intubation was the same for OSAS patients with an AHI of < 40 as in the control group.
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Discussion |
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The relationship between difficult intubation and the severity of OSAS has been speculated upon for a long time,1–3,11 but few reports have shown an association between difficult intubation and OSAS.4–6 Esclamado et al.11 showed that OSAS patients with perioperative complications, including failed intubation, have LSATs and higher apnea indexes in a pre-operative sleep study. However, they did not compare patients with failed intubation to patients with successful intubation with respect to AHI. Friedman et al.5 found that the modified Mallampati index, BMI, and tonsil size were not only predictive of OSAS but also correlated well with AHI. Recently, Siyam et al.6 reported that intubation was more difficult in 36 OSAS patients than in controls. However, they found no significant relationship between AHI and difficult intubation in OSAS patients. Our data regarding the relationship between OSAS severity and difficult intubation were different from that of Siyam et al.6 Several possible explanations for this difference exist. Our study was performed on a larger population. Accordingly, this difference may be due to the higher statistical power of the present study. Another possible explanation may be that our patients had a higher AHI than their patients (53.3 ± 27.8 vs 41.7 ± 22.1).6 When we divided patients according to AHI, those with an AHI of < 40 were found to have the same difficult intubation incidence as the control group. Only patients with an AHI of > 40 showed a higher incidence of difficult intubation.
The most plausible explanation for the observed relationship between difficult intubation and OSAS is that they may share the same anatomical characteristics. Hiremath et al.4 affirmed strong relationships between increased Mallampati scores and difficult intubation and OSAS after performing a radiographic evaluation of both patient types. According to their study, difficult intubation and OSAS are both associated with a greater Mallampati score and anterior mandibular depth, and smaller mandibular and cervical angles; these share anatomical features that act to reduce the skeletal confines of the tongue.
Though BMI was related significantly with AHI in the present study, we did not find any correlation between BMI and the occurrence of difficult intubation. A large prospective study of 1,833 patients identified obesity is a factor predisposing difficult intubation.12 The mean BMI of our OSAS patients was 27.9 ± 2.9, which would place our patients in their non-obese category.
In the postoperative period, patients with difficult intubation tended to have slightly longer extubation times and lengths of stay in PACU than patients without, but there were no statistical significances. This may be due to our hospital patient management guidelines for OSAS, namely, that the endotracheal tube be removed after full awakening, and time to full awakening might be related to the anesthetic agent.
In conclusion, the present study indicates that the occurrence of difficult intubation can be predicted from AHI values in the patients who undergo UPPP surgery for OSAS.
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Footnotes |
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Competing interests: None declared.
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References |
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2 Chung F, Crago RR. Sleep apnoea syndrome and anaesthesia. Can Anaesth Soc J 1982; 29: 439–45.[Medline]
3 Hillman DR, Loadsman JA, Platt PR, Eastwood PR. Obstructive sleep apnoea and anaesthesia. Sleep Med Rev 2004; 8: 459–71.[Medline]
4 Hiremath AS, Hillman DR, James AL, Noffsinger WJ, Platt PR, Singer SL. Relationship between difficult tracheal intubation and obstructive sleep apnoea. Br J Anaesth 1998; 80: 606–11.
5 Friedman M, Tanyeri H, La Rosa M, et al. Clinical predictors of obstructive sleep apnea. Laryngoscope 1999; 109: 1901–7.[Medline]
6 Siyam MA, Benhamou D. Difficult endotracheal intubation in patients with sleep apnea syndrome. Anesth Analg 2002; 95: 1098–102.
7 Anonymous. Sleep-related breathing disorders in adults: recommendations for syndrome definition and measurement techniques in clinical research. The Report of an American Academy of Sleep Medicine Task Force. Sleep 1999; 22: 667–89.[Medline]
8 Cattano D, Panicucci E, Paolicchi A, Forfori F, Giunta F, Hagberg C. Risk factors assessment of the difficult airway: an Italian survey of 1956 patients. Anesth Analg 2004; 99: 1774–9.
9 Cormack RS, Lehane J. Difficult tracheal intubation in obstetrics. Anaesthesia 1984; 39: 1105–11.[Medline]
10 Steward DL. Effectiveness of multilevel (tongue and palate) radiofrequency tissue ablation for patients with obstructive sleep apnea syndrome. Laryngoscope 2004; 114: 2073–84.[Medline]
11 Esclamado RM, Glenn MG, McCulloch TM, Cummings CW. Perioperative complications and risk factors in the surgical treatment of obstructive sleep apnea syndrome. Laryngoscope 1989; 99: 1125–9.[Medline]
12 Voyagis GS, Kyriakis KP, Dimitriou V, Vrettou I. Value of oropharyngeal Mallampati classification in predicting difficult laryngoscopy among obese patients. Eur J Anaesthesiol 1998; 15: 330–4.[Medline]
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