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Posted on March 16th, 2013, by

There is no need to argue that gestation is absolutely exclusive state of a woman. Preparing accommodating to a give birth to a new life, the organism of a woman is to undergo through numerous changes, and naturally these changes essentially affect all her organs, systems and even way of thinking. Woman’s body has to experience a lot of modifications, and most of all bring at least much discomfort to her. What is more, not only discomfort, but often some additional health problems may arise. Thus, it is quite reasonable to hold absolutely different approach in treating obstetrical population. In particular, obstetrical women often have problems with breathing, and there are a number of reasons for that. The pregnant woman finds herself at greater risk for airway management problems more than a non-pregnant woman because of a list of anatomical and physiological changes. This list includes cardiovascular and gastrointestinal modifications, respiratory changes and correlating capillary engorgement affecting all airways. In turn, capillary engorgement causes distortion and increased friability of the upper airway structures leading to decreased visualization during laryngoscopy. Further on, progesterone induced tracheal and bronchial dilation, upward displacement of diaphragm, enlarged breasts and weight gain contribute too (Chestnut et al. 2009). Since the maternal airway is more difficult to manage, it is very important for nurse practice to understand the difference between an obstetrical and a non-obstetrical airway in order to provide adequate care for pregnant women. Hereby, this work is intended to explore the current situation both in the scholar research and empirical practice concerning the issues of obstetrical airways and their management.

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According to the American Society of Anesthesiologists (ASA) Task Force’s definition, a difficult airway is “the clinical situation in which a conventionally trained anesthesiologist experiences difficulty with mask ventilation, difficulty with tracheal intubation, or both”¯ (Shinga 2005). First of all, the studies of Samsoon & Young (1982-1985), Glassenberg (1990), Yeo & Chang (1991), Dhallwall (1991-1994), Rocke (1992), Hawthome et al. (1996), Wong & Hung (1998) were reviewed in order to trace back the roots of the relevant research. The main research has been conducted through the literature of the last six years (2005-2011) and the extra attention has been paid to respectful sources in scholar journals and other printed media as well as online data bases on current medical issues. To make sound conclusions, the data from CINHAL, MEDLINE and EMBASE were gathered. It has been revealed that with the ever increasing prevalence of cesarean sections and high risk deliveries related to advanced maternal age, multiple gestations and maternal co-existing diseases among other factors, the focus on maternal airway has increased substantially.

According to the majority of the sources, the best way to determine if there is a difference between airways in parturients and non-pregnant patients is first of all to identify the list of identifiable risk factors for complicated intubation. Then the same anesthesiologic techniques are reported to be applied to both categories of patients.

Trying to find the mean position of medical personnel, Eric Goldszmidt has written the article Is there a difference between the obstetrical and non-obstetrical airway? (2005). to a list of conventional difficulties resulting in more problematic airway Goldszmidt adds that “thoracic lift from a poorly placed hip wedge and overly aggressive cricoid pressure may exacerbate a difficult situation”¯ (Goldszmidt, p. 225 in Halpern & Douglas 2005). Further he states that for pregnant patients general anesthesia can be rather dangerous, especially under emergency conditions. For anesthesiologist it can become an anxiety-provoking situation which can lead to an incomplete assessment of the patient. The fetal is put under greater risk when risk for aspiration pneumonitis and metabolic rate are rising. Apnea may result in oxygen desaturation too. At the same time, Goldszmidt underlines, being restrained in using general anesthesia, the trainees lack experience, while more experienced anesthesiologists lack opportunity for better expertise.

Making up a statistics for complicated intubation, Goldszmidt proposes to register the incidence of “difficulty”¯ and “failure to intubate”¯. However, he explains that to demonstrate a difference, a large study is needed: “if one considers that the rate of difficult intubation is approximately 2% in parturients, the study would need to include approximately 9000 patients per group to find a difference of 75% (to 0.5% in non-parturients)”¯ (Goldszmidt, 2005, p. 225 in Halpern & Douglas). Therefore, instead of clinical tests the author relies on the investigation on endotracheal intubation and information on which parturients are found to be at greater risk for difficult airway management.

At the same time, Shinga et al. conducted a meta-analysis to determine the diagnostic accuracy of bedside tests in predicting difficult intubations. The selected data from electronic database were used to review 50,760 patients. Screening tests included the Mallampati classification, thyromental distance, sternomental distance, and mouth opening. The most reliable predictor in the general population was found to be the Mallampati classification and the thyromental distance combined as demonstrated by a positive likelihood ratio, 9.9 (Shinga, 2005). However, later research has shown that it is not reasonable to rely on the Mallampati test alone. The tests are considered to lack statistical power.

What is more, Thomas & Hagberg (2009) have found that inability to secure an airway is the leading cause of anesthesia related maternal fatality. Then, Kodali et al. (2008) focused on airway alterations during pregnancy. With an aim to collect the necessary data, the group of researchers organized a kind of study on 70 randomly selected women undergoing labor and delivery. The quantitative analysis of airway changes was conducted be means of the Mallampati classification system as an evaluation tool. Their airways were scanned with the subject’s head in the neutral position, prior to delivery as well as 20 minutes and 36-48 hours post partum. To increase reliability and accuracy, the camera was situated precisely ten inches away from the participant’s airway in each picture. To decrease the inter-rater variability the photographs were coded and an experienced anesthesiologist with no vested interest in the study was blinded to the source of the photographs and asked to provide a mallampati classification for each subject. A comparison between samples was formulated through the Wilcoxon signed rank test. This clinical test has demonstrated a substantial change in airway class between pre-labor and post labor airway data. The authors of the study made the suggestion that obstetrical patients should receive frequent airway evaluations because airway changes may continue to progress up to the post-partum period. The airway assessment value on admission most likely has changed during the patients stay.
Apart from that, particular studies are devoted to the problems of general anesthesia during a cesarean delivery. Although the need for general anesthesia has decreased due to the increased use of neuraxial techniques in the obstetric population, there are still many concerns with complications, contraindications and refusal of neuraxial techniques. For example, Palanisamy and Mitani (2010) studied the elements responsible for the administration of general anesthesia in cesarean delivery patients and analyzed variations in practice between two time eras where data were available. When they received the approval from the Institutional Review Board, Palanisamy and Mitani collected information from January 1, 2000 through December 31, 2005 from a database at an obstetric hospital. They reviewed and obtained medical records from all parturient who received general anesthesia (98 cases were registered). The date was gathered separately for the first part of the day (from 7 a. m. to 3 p. m. and from 3 p. m. to 7 a. m.), with discrimination on suggestions for general anesthesia with cesarean deliveries, approach of airway management and anesthetic complications. The researchers compared the received data with the data of 2004 and found out that “the average rate of administration of GA declined dramatically to a low 0.6% from 4.5% (previous study; p< 0.001) with the majority being associated with emergency cesarean delivery (85.7%)”¯ (Palanisamy, 2010, p. 14). The majority of cases with the application of general anesthesia were associated with severe preeclampsia, eclampsia and HELLP syndrome (including hemolytic anemia, elevated liver enzymes and low platelet count).

Another risk factor is obesity. This issue was also studied by Palanisamy (2010). Body mass index was reported to be collected in 79 out of the 98 cases, in which key points were discovered. The mean BMI was 30.5 kg/m associated with an increased prevalence of obesity in parturient. This factor is significant to study because obesity in the obstetric population is a spread source of many challenges including the complexity in placement of neuraxial techniques. With neuraxial techniques are unable to obtain, general anesthesia is essential, but when the incidence of obesity is increase, “intubation as well as extubation must be carried out diligently and safely ”¦.maternal obesity per se was considered an important risk factor for anesthesia- related maternal mortality”¯ Palanisamy reports (2010, p. 15).

Out of 98 one women participating in the study experienced a difficult intubation requiring a cricothyroidotomy to be performed after three unsuccessful attempts to intubate and ventilate with a size 4 laryngeal mask airway. While prior to labor this woman had a Mallampati class III airway, in five days she was assessed to have a Mallampati class I. The conclusion was made that “pregnancy is associated with dynamic airway changes even in the absence of labor, particularly in the setting of preeclampsia”¯ and “the early communication to surgical colleagues of an anticipated difficult airway is critical in preventing management delays and subsequent adverse outcomes”¯ (Palanisamy, 2010, p. 16).

Finally, in the recent research conducted by Osborn (2011), the importance of assessing the airways is observed too. In standard general patients, bedside evaluation will only pick up less than 50% who have true clinically difficult intubations and on the other hand, will also categorize normal patients as being difficult (Osborn, 2011). Osborn restricted his research to the women not older than 18, with monofetal pregnancy at 37 weeks gestation, and epidural analgesia for childbirth. All in all there were 87 women recruited. The Mallampati class showed a declining trend after delivery, but the study lacks accuracy. Unfortunately, no predictive factor is identified. What is more, Mallampati class alone has restricted discriminative power for difficult intubations when used alone.

Conclusion
The overall research has shown that it is rather difficult to gain a proper and exact material on obstetrical vs. non-obstetrical airway, because the incidence of difficulties is rather small and large study, with much time spent and consequently other resources are required. That is why the necessary clinical trials fail to be conducted. Hence, predicting difficult intubation remains limited as well. Nonetheless, the existing literature proves that the difference is dramatic and there are many details to be taken to account by anesthesiologists and nurses while treating the pregnant women. It is obvious now that when preparing to manage the obstetrical patient, there is a strong need for backup airway measures. No patient should undergo general anesthesia without an airway assessment because unanticipated difficult intubation can be very challenging. The principal changes contributing to anatomical difficulties among obstetric patients require planning for and preventing airway problems and this is an area for potential future research. The lack of training and experience available to the anesthesia providers in the obstetric specialty is partly responsible for unwanted outcomes, however, LMAs and video laryngoscopes make difficult intubations easier to manage. In obstetrics there is not one but two lives in the balance with every anesthetic delivery, therefore a greater focus should be placed on procuring solid evidence based practice guidelines that can be applied to the clinical setting for ensuring the safety of both mother and child intra-operatively because airway undoubtedly always comes first.

References
Goldszmidt, E. (2005). Is there a difference between the obstetrical and non-obstetrical airway? In Halpern, Stephen H. & Douglas, M. Joanne (Ed.). Evidence-based obstetric anesthesia (pp. 225-230). West Sussex: Wiley-Blackwell.
Kodali, B., Chandrasekhar, S., Bulich, L. N., Topulos, G. P., & Datta, S. (2008). Airway changes during labor and delivery. .Anesthesiology, 108(3), 357-362.
Osborn, I. (2011). Management of the difficult airway. Clinical Foundations, 1. Retrieved June 28, 2011, from http://www.clinicalfoundations.org
Palanisamy, A. M. (2010). General anesthesia for cesarean delivery at a tertiary care hospital from 2000-2005: a retrospective analysis and 10-year update. International Journal of Obstetric Anesthesia, 20(1), 10-16.
Shinga, T., Wajima, Z., Inoue, T., & Sakamoto, A. (2005). Predicting difficult intubation in apparently normal patients. Anesthesiology, 103(2).
Thomas, J. A., & Hagberg, C. A. (2009). The Difficult Airway: Risks, Prophylaxis, and Management. In Chestnut, D. H. (Ed.) Obstetric Anesthesia: Principles and Practice (4th ed., pp. 651-672). Philadelphia, PA: Elsevier.

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