“Difficult” airways, including difficult intubation, are one of the biggest challenges and tasks anaesthesiologists have to face. According to the ASA Management Closed Claims Project, particularly focused on difficult airway-related critical events, the percentage of events associated with respiratory complications decreased from 42% in 1980 to 32% at the beginning of 1990. Such complications remain a relevant cause of anaesthesia-induced mortality and morbidity. Moreover, in the years 1985-1999, 156 (87%) out of 179 registered and instituted legal proceedings due to difficult airways were bound up with the perioperative period [1, 2].

The subsequent analyses of critical events in anaesthesiology revealed that the majority of fatal or severe injuries to CNS were related to difficult airways and developed during the induction of anaesthesia rather than other stages of anaesthesia, in which the number of respiratory complications was successively decreasing over the last 25 years. According to the database of 2000, their incidence was tenfold lower than in 1975 [1, 3, 4]. Furthermore, the data showed that from 503 causes of critical respiratory events responsible for death or permanent CNS damage, 115 were related to difficult intubation, 111 – to inadequate oxygenation and 66 – to undiagnosed oesophageal intubation. The number of cases of improper lung ventilation and oesophageal intubation was found to have dramatically decreased, from 25% in 1980 to 9% in 1990, which resulted from the institution of management standards and obligatory pulsoxymeters and capnometers at anaesthetic stations.

Unfortunately, in Poland these equipment requirements for anaesthetic stations became standards ten years later when the respective directive was finally signed by the authorities; professional experience shows that in many centres, the directive has not been adhered to. In Poland, “anaesthetic standards” included in legal regulations cannot be overestimated as for the reduction of morbidity and mortality; following anaesthetic standards is the expression of respect for law; yet its ethico-moral aspect is even more important. This concerns anaesthesiologists and those responsible for organization and management of the health care institutions, who call themselves managers. The respect for legal regulations created by a given community should be essential, and any violations considered as the attempts to provide medical services going beyond the rightly understood corporative rules.

In everyday anaesthetic practice, difficult airway-related complications and their occurrence as mainly technical problems in conducting the planned manoeuvres, i.e. endotracheal intubation, have nothing to do with the presence of pulsoxymeters and capnometers. The incidence of technically difficult intubations resulting in severe hypoxia or cardiac arrest and causing death or CNS damage has remained at the level of 8-9% of all critical events related to difficult airways throughout the eighties, nineties and until the XXI century [1, 3, 4, 5, 6]. The anaesthesia-related mortality is considered dramatically low; however, this regards ASA I and II patients. When physical conditions of patients are worse, the epidemiological dimension of an event increases resulting in worsened statistics, particularly in the population of elderly male patients. The incidence of complications in  this group is found to be even higher  [4, 5, 6, 7].

This phenomenon is also extremely relevant while analyzing causes and numbers of suspected medical malpractice claims. Out of 2046 lawsuits in 1986 (720 deaths, 253 permanent CNS injuries) 37% were cases related to respiratory complications, including 12% – inadequate lung ventilation and oxygenation, 6% – difficult intubation, 6% – oesophageal intubation, 3% – airway obstruction, 3% – aspiration of gastric contents, 2% – bronchospasm and 6% – others [4, 6, 7]. 

Perinatal deaths of parturients have always been spectacular; a significant proportion of them is caused directly by anaesthesia-related complications. According to the analysis involving 1453 perinatal deaths of parturients between 1987-1990, almost 30% of them were associated with haemorrhage. Another 20% of deaths were related to acute thromboembolic disease, further 17% to pregnancy-induced hypertension whereas 2.5% concerned anaesthesia, namely 36 cases of difficult endotracheal intubation (which constituted only half of infection-induced perinatal deaths). In Caesarean sections under general anaesthesia, the commonest cause of death was associated with aspiration of gastric contents to airways (33%) followed by difficult endotracheal intubation (22%) and inadequate or unfeasible oxygenation (18%). In fact, deaths of parturients are tenfold commoner in Caesarean sections performed under general anaesthesia or central blockade compared to deliveries through natural passages. In the USA, 129 anaesthesia-related deaths of parturients were noted in the years 1979-1990. Difficult airway was the direct cause of death in over 50% of such cases [8, 9].

The ASA Task Force Management Practice Guidelines for Management of the Difficult Airway [11] define difficult airways as:

• failed intubation (FI) or multiple failures to place the endotracheal tube in the trachea, which occur in 0.05% of cases, i.e. 1:2230 surgical patients and in 0.13-0.35% of cases or in 1:280 – 1:750 parturients [12];

• difficult tracheal intubation (DI)): requiring multiple attempts in the presence of upper airway pathology or otherwise. The number of such cases is higher than that of FI – 1.2-3.8% [12];

• difficult laryngoscopy (DL): failed visualization of the vocal cords after multiple attempts at conventional laryngoscopy (III and/or IV degree according to Cormack-Lehan). The incidence of DL is 1.5-13% of surgical patients. The definition presented considers the number of laryngoscopy attempts in the best position provided after changes of the patient`s placement, suitable choices of sizes and types of laryngoscopic blades and simple manoeuvres such as pressure on the innominate cartilage, backwards, upwards, rightwards pressure (BURP) or optimal external laryngeal manipulation (OELM);  

• difficult mask ventilation (DMV) occurs in 0.01-5% of cases involving inadequate mask seal, excessive gas leak and excessive resistance during inhalation of respiratory gases to the lungs or lack of effective expiration [12].  

The usefulness of some methods predicting difficult endotracheal intubation is assessed by comparing DI with the picture observed on direct laryngoscopy and does not consider ‘‘the best position”. Therefore, the bank of pictures for all degrees of the Cormack-Lehane scale should be compiled to compare a real picture with a critical event (difficult intubation). In the group of 1200 patients with the intubation conditions assessed as Cormack-Lehane grade III and IV, in 40% of cases the intubations were performed without difficulties [13].

In many cases, difficult intubation is not anticipated until laryngoscopy has been carried out [14, 15, 16, 17]. Moreover, there are serious divergences in the definition of “difficult”.

Many authors use the terms of easy, restricted and difficult intubations [2, 4, 5, 15, 17]:

• easy: the true glottis visualized, suitable conditions for insertion of the tube to the trachea in 95% of cases (<3% of cases requires additional manipulations),

• restricted: the posterior wall of  true glottis with the arytenoid cartilage visualized or the true glottis visible, which can be elevated,

• difficult: the true glottis cannot be elevated or none of the glottic structures are visible; requires additional manipulations without visual control.

In restricted intubations, as opposed to difficult ones, the “bougie” guide is enough to insert the endotracheal tube [14, 15, 16, 17, 18].

The optimal prognostic tests for difficult intubation should be adequately sensitive and specific. Their sensitivity and prognostic values are assessed as 33-37%; additionally, some prognoses are false positive. Thus, the essence of the problem is to use prognostic factors in such a way as to increase the number of true positive prognoses and reduce that of false positive and false negative ones; once available scales or their combinations are properly used, this goal should be accomplished [19, 20, 21].

The current guidelines for perioperative identification of difficult airways are slightly surprising. They recommend focusing on medical histories, physical exams and additional tests. Thus, there is no medical evidence for effectiveness of difficult intubation assessment based on prognostic factors (scales) as for the final points of management, i.e. mortality and morbidity.

Medical histories and analysis of reliable medical records provide information about congenital defects, earlier endotracheal intubations or intubation-related problems and past procedures within the larynx and neck region. On physical examination, the following should be considered: face hair, possible protrusions or micrognathias, limited mouth opening (<4 cm), Mallampati class II intubation conditions, thyro-mental (<6 cm), hyoid-mental (<4 cm) and sterno-mental (<12 cm) distances, limited range of motion of the cervical spine (<800), neck circumference (>60 cm), body weight (BMI >30 kg m-2), upper airway constriction.

For the reasons listed above, it is extremely important to adapt the Difficult Airway Society guidelines with algorithms of proper management and put them into action to eliminate the consequences of critical events associated with difficult airways. Such events cannot be avoided in anaesthetic practice; therefore anaesthesiologists should be solidly and professionally prepared to manage them, if need be. It is worth remembering that situational stress increases the risk of medical errors by 25%; therefore, if not for other reasons, algorithms of management cannot be overestimated [22, 23, 24, 25, 26, 27, 28].

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REFERENCES

1.   Peterson GN, Domino KB, Kaplan RA, Posner KL, Lee LA, Cheney FW: Management of the difficult airways; aclaims analysis. Anesthesiology 2005; 103: 33-39.

2.   Chenny FW: Changing trends in anesthesia related death and permanent brain damage. ASA closed claims project. ASA Newsletter 2002; 66: 6-8.

3.   Benumof JL: Difficult laryngoscopy: obtaining the best view. Can J Anaesth 1994; 41: 361-365.
4.   Chenny FW, Posner KL, Lee LA, Kaplan RA, Domino KB: Trends in anesthesia-related death and brain damage. Anesthsiology 2006; 105: 1081-1086.

5.   Turkan S, Ates Y, Cuhruk H, Tekdemir I: Should we reevaluate the variables for predicting the airway in anesthesiology? Anesth Analg 2002; 94: 1340-1344.

6.   Jacobsen J, Jensen E, Waldan T, Poulsen TD: Preoperative evaluation of intubation conditions in patients scheduled for elective surgery. Acta Anaesthesiol Scand 1996; 40: 421-424.

7.   Chou HC, Wu TL: Thyreomental distance-shouldn’t we redefine its role in the prediction of difficult laryngoscopy? Acta Anaesthesiol Scand 1998; 42: 136-137.

8.   Chenney FW, Posner K, Kaplan RA, Ward RJ: Standard of care and anesthesia liability. Can  Anaesth  Soc J 1986; 33: 336.

9.   Berg C, Atrash HK, Koonin LM, Tucker M: Pregnancy-related mortality in the United States, 1987-1990. Obstet Gynecol 1996; 88: 161-167.  

10.  Hawkins JL, Koonin LM, Palmer SK, Gibbs CP: Anesthesia during obstetric delivery in the United States 1979-1990. Anesthesiology 1997; 86: 277-284.

11.  Practice guidelines for management of the difficult airways: an updated report by American Society of Anesthesiologists Task Force on Management of the Difficult Airways. Anesthesiology 2003; 98: 1269-1277.

12.  Rocke DA, Murray WB, Rout CC, Gouws E: Relative risk analysis of factors associated with difficult intubation in obstetric anesthesia. Anesthesiology 1992; 77: 67-73.

13.  Arne J, Descoines P,Fusciardi J, Ingrand P, Ferrier B, Boudiques D, Aries J: Preoperative assessment of difficult intubation in general and ENT surgery: predictive value of amultivariate risk index. Br J Anaesth 1998; 80: 140-146.

14.  Samsoon GL Young JRB: Difficult tracheal intubation: astudy. Anaesthesia 1987; 42: 487-490.

15.  Cattano D, Pescini A, Paolicchi A, Giunta F: Difficult intubation: an overview on acohort 1327 consecutive patients. Minerva Anestesiol 2001; 67: 45.

16.  Langeron O, Mazzo E, Huraux C: Prediction of difficult mask ventilation. Anesthesiology 2000; 92: 1229-1236.

17.  Rose DK, Cohen MM: The airway: problems and prediction in 18,500 patients. Can J Anesth 1994; 41: 372-383.

18.  Butler PJ, Dhara SS: Prediction of difficult laryngoscopy: An assessment of thyreomental distance and Mallampati predictive tests. Anesth Intensive Care 1992; 20: 139-142.

19.  Pearce A: Evaluation of the airway and preparation for difficulty. Best Prac Res Clin Anaesthesiol 2005; 19: 559-579.

20.  Koh LD, Kong CF, Ip-Yam PC: The modified Cormack-Lehane score for grading of direct laryngoscopy: evaluation in the Asian population. Anaesth Intensive Care 2002; 30: 48-51.

21.  Cook TM: Apractical classification of laryngeal view. Anaesthesia 2000; 55: 274-279.

22.  Sustic A: Role of ultrasound in the airway management of critically ill patient. Crit Care Med 2007; 35: 5173.

23.  Khan ZH, Kashfi A, Ebrahimkhani E: Aof the upper lip bite test (asimply new technique) with modified Mallampati classification in predicting difficulty in endotracheal intubation. Ablinded study. Anesth Analg 2003; 96: 595-599.

24.  Lee A, Fan LTY, Karmakar MK, Ngan Kee WD: Areview (meta-analysis) of the accuracy of the Mallampati tests to predict difficult airway. Anesth Analg 2006; 102: 1867-1878.

25.  KrobbuabanB, Diregpoke S, Kumkeaw S, Tanomsat M: The predictive value of the height ratio and thyromental distance: four predictive tests for difficult laryngoscopy. Anesth Analg 2005; 101: 1542-1545.

26.  Khetepral S, Han R, Tremper KK,Shanks A, Tait AR, Michael OReilly, Ludwig TA: Incidence and predictors of difficult and impossible mask ventilation. Anesthesiology 2006; 105: 855-891.

27.  Shiga T, Wajima Z, Inoue T, Sakamoto A: Predicting difficult intubation in apparently normal patients. Anesthesiology 2005; 103: 429-437.

28.  Ghate S, Hagberg CA: Does the airway examination predict difficult intubation? Evidence-Based Practice of Anesthesiology (Ed.: Fleisher LA), Saunders-Elsevier 2009; 17: 101-115.

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Address:

*Krzysztof Kusza
Katedra i Klinika Anestezjologii
i Intensywnej Terapii, CM UMK w Bydgoszczy
ul. M. Skłodowskiej-Curie 9, 85-094 Bydgoszcz
tel.: (52) 585 4750
e-mail: kikanest@cm.umk.pl

Received: 22.07.2009
Accepted: 10.08.2009