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ORIGINAL RESEARCH |
From the Departments of Anesthesiology and Obstetrics and Gynecology, University of Pennsylvania Health System, Philadelphia, Pennsylvania.
Address reprint requests to: Robert R. Gaiser, MD Department of Anesthesiology Hospital of the University of Pennsylvania 3400 Spruce Street Philadelphia, PA 19104 E-mail: gaiserr{at}mail.med.upenn.edu
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Abstract |
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Methods: The airways of 160 parturients were examined by four physicians: one attending and one resident obstetrician, and one attending and one resident anesthesiologist. After each airway examination, the physicians completed questionnaires about possible difficult intubation, use of antepartum consultation, and choice of analgesia early in labor.
Results: Instruction in airway examination did not affect obstetricians’ ability to assess airways. Compared with the attending anesthesiologist’s opinion, the sensitivity and specificity of the attending obstetrician before instruction were 0.59 and 0.82, respectively, and for the obstetric resident, 0.41 and 0.89, respectively. After instruction, the sensitivity and specificity for the obstetric attending physician were 0.60 and 0.83, respectively and for the obstetric resident, 0.50 and 0.87, respectively. In airways judged possible difficult intubations by the obstetricians, instruction did not affect the use of antepartum consultation or early epidural analgesia by the residents. In the obstetric attending physicians there was a significant increase in use of early epidural analgesia.
Conclusion: Although instruction in airway examination did not affect obstetricians’ ability to predict difficult airways, it did affect treatment of labor analgesia.
Death from anesthesia is the sixth leading cause of pregnancy-related deaths in the United States.1 A recent investigation of the causes of those deaths found that most occurred during general anesthesia for cesarean delivery.2 The number of deaths involving general anesthesia remained stable over 12 years, 1979–1990; in contrast, those involving regional anesthesia have decreased. The concern about general anesthesia regards airway management. In the Closed Claims Study, difficult tracheal intubation, inadequate ventilation, aspiration, and esophageal intubation were the most common events cited for maternal death.3 One way to avoid these complications would be to place a functioning epidural catheter early in women judged to be potentially difficult to intubate. Regional anesthesia can be used if emergency delivery is needed4; however, the decision to place an epidural catheter is the obstetrician’s. Section III of the Guidelines for Regional Anesthesia in Obstetrics by the American Society of Anesthesiologists states, "Major conduction anesthesia should not be administered until the patient has been examined, and the fetal status and progress of labor evaluated by a qualified physician who is readily available to supervise the labor and to deal with any obstetric complications that may arise."5
ACOG also has recognized the importance of identifying women at risk for possible difficult intubation in their Committee Opinion Number 104, "The obstetric care team should be alert to the presence of risk factors that place the parturient at increased risk for complications from general anesthesia. . . . When such risk factors are identified, a physician who is credentialed to provide general and regional anesthesia should be consulted in the antepartum period. For those patients at risk, consideration should be given to the planned placement in early labor of an epidural catheter, with confirmation that the catheter is functional."6 No study has examined obstetricians’ ability to assess the airway. We compared obstetricians’ airway examinations with those of an attending anesthesiologist and hypothesized that a conference regarding airway examination would improve obstetricians’ ability to assess the airway and predict possible difficult intubation.
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Materials and Methods |
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The study was completed in two parts. For the first 80 subjects, the obstetricians received no guidance or education. For the second 80, the obstetricians received a 30-minute instruction describing airway examination, specifically relating to the degree of mouth opening and the Malampati classification.7 They also observed an airway examination by an anesthesiologist. Part of the instruction included a discussion about difficult intubation and the risk to the woman. Each obstetrician received a copy of ACOG Committee Opinion Number 104.
The results of the questionnaires completed by the residents and attending obstetricians were compared with those of the attending anesthesiologist. Using the opinion of the attending anesthesiologist as the standard, the sensitivity, specificity, positive predictive value, and negative predictive value were calculated for the resident anesthesiologist, resident obstetrician, and attending obstetrician. The sensitivity was defined as the number of women classified as having possible difficult intubations by the group being studied and the attending anesthesiologist divided by the total number of women classified as possible difficult intubations by the attending anesthesiologist. Specificity was defined as the number of women classified as not possible difficult intubations by the group being studied and the attending anesthesiologist divided by the total number of women classified as not possible difficult intubations by the attending anesthesiologist. Positive predictive value was defined as the number of women classified as possible difficult intubations by the group being studied and the attending anesthesiologist divided by the total number of women classified as possible difficult intubations by the group being studied. Negative predictive value was defined as the number of women classified as not possible difficult intubations by the group being studied and the attending anesthesiologist divided by the total number of women classified as not possible difficult intubations by the group being studied. If the resident or attending obstetrician rated a woman as having a possible difficult intubation, the decision was made for antepartum consultation or early epidural analgesia. The results before instruction were compared with those after instruction. Statistical analysis included Student t test and the 
2 test. The statistical analysis was paired according to the woman in each phase of the study. Results were expressed as mean ± standard deviation (SD) unless otherwise specified.
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Results |
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). Of the obstetric residents, five in their second or third year of training participated in the first part and five different residents in their second or third year of training participated in the second part.
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). There were no differences in incidence of preeclampsia, diabetes, or multiple gestation between groups.
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. For the attending and resident obstetricians, there were no significant differences in those values before and after instruction. For the resident anesthesiologist, the sensitivity decreased statistically in the second part.
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).
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Discussion |
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On the basis of sensitivity and specificity, attending and resident obstetricians tended to underpredict difficult airways compared with attending anesthesiologists, which might also mean that attending anesthesiologists tended to overpredict possible difficult intubations. Given the severity of the complications associated with difficult intubation, it is better to overestimate because a difficult intubation contains significant implications, so it is better to have lower specificity. In that scenario, the obstetrician would notify the anesthesiologist of women who were possible difficult intubations more frequently than the anesthesiologist would consider necessary. Most anesthesiologists would not mind more frequent notifications because it would identify possible difficult intubations and help them formulate a plan for the management of labor.
One methodologic weakness of the study is that different obstetrics and anesthesiology residents were used for the two parts. We were prevented from making conclusions about the obstetrics or anesthesiology residents. For the obstetrics residents, there were two possible conclusions: there was no change in the ability to predict the possible difficult intubation with instruction or the original group was already skilled in prediction, resulting in no significant difference. The latter stance seems unlikely because both groups of obstetrics residents had results similar to attending obstetricians before instruction. That change in resident composition probably explains the change in sensitivity for the anesthesiology residents. The method was chosen as the study was conducted over several months, with residents rotating into the labor and delivery suite for two months.
During the instruction on airway examination, the Mallampati classification was highlighted. In that system, there are three classes based on the structures visible in the oropharynx when the woman opens her mouth. In a class I airway, the faucial pillars, soft palate, and uvula are visible. In a class II airway, the faucial pillars are visible, but the uvula is not. In a class III airway, only the soft palate is visible. According to that classification in the general surgical population, in women with class III airways, laryngoscopy and intubation were more difficult.7 Rocke et al8 investigated whether the Mallampati score applied in obstetrics. According to those authors, class III airways had significantly increased risk of difficulty with intubation over class I airways. The Mallampati system was useful in obstetrics in predicting possible difficult intubation and was easy to teach. There was no change in the percentage of women with class III airways and classified as possible difficult intubations after instruction for obstetrics residents and attending physicians, suggesting that obstetricians already had some knowledge of airway examination before instruction.
The percentage of women classified as possible difficult intubations was high, which results from the high percentage of women with class III airways. The number of class III airways seems greater in the obstetric population than the general population. Pilkington et al9 showed in 242 pregnant women that the incidence of class III airways increased by 34% as pregnancy progressed. They postulated that fluid retention with pharyngeal edema accounted for that increase; therefore, it is not surprising that such a high number of women in our study were judged as possible difficult intubations.
After identifying women with possible difficult intubations, certain clinical decisions, such as antepartum consultation or early epidural analgesia, must be made. The definition of early epidural analgesia varies among institutions depending on obstetricians’ practice. Recent studies suggested that epidural analgesia initiated at 3 cm cervical dilatation does not affect the course of labor.10,11 Epidural analgesia initiated at 2 cm cervical dilatation is controversial. Although a discussion about possible complications accompanying a difficult intubation did not affect obstetricians’ decisions about antepartum consultation, it did affect the attending obstetricians’ decisions concerning early epidural analgesia in our subjects. Anesthesiologists need to discuss the airway and its management frequently with obstetrics colleagues. It appears that such discussion can have a significant clinical effect. The same discussion did not alter the use of early epidural analgesia in obstetrics residents. That difference is explained by level of experience. Attending obstetricians are more likely to have experienced cases involving difficult intubations or have direct knowledge from a colleague who experienced complications. That knowledge affects decision making, so it is important to present cases, even old ones, to obstetrics residents to reinforce concerns regarding cases with possible difficult intubation.
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Footnotes |
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Received August 28, 1998. Received in revised form October 26, 1998. Accepted November 5, 1998.
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References |
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2. Hawkins JL, Koonin LM, Palmer SK, Gibbs CP. Anesthesia-related deaths during obstetric delivery in the United States, 1979–1990. Anesthesiology 1987;86:277–84.
3. Chadwick HS, Posner K, Caplan RA, Ward RJ, Cheney FW. A comparison of obstetric and nonobstetric anesthesia malpractice claims. Anesthesiology 1991;74:242–9.[Medline]
4. Morgan BM, Magni V, Goroszenuik T. Anaesthesia for emergency caesarean section. Br J Obstet Gynaecol 1990;97:420–4.[Medline]
5. American Society of Anesthesiologists. Guidelines for regional anesthesia in obstetrics. Washington, DC: American Society of Anesthesiologists, 1991.
6. The American College of Obstetricians and Gynecologists. Anesthesia for emergency deliveries. ACOG committee opinion no. 104. Washington DC: American College of Obstetricians and Gynecologists, 1992.
7. Mallampati SR, Gatt SP, Gugino LD, Desai SP, Waraksa B, Freiberger D, et al. A clinical sign to predict difficult tracheal intubation: A prospective study. Can Anaesth Soc J 1985;32:429–34.[Medline]
8. 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.[Medline]
9. Pilkington S, Carli F, Dakin MJ, Romney M, De Witt KA, Dore CJ, et al. Increase in Mallampati score during pregnancy. Br J Anaesth 1995;74:638–42.
10. Chestnut DH, McGrath JM, Vincent RD, Penning DH, Choi WW, Bates TN, et al. Does early administration of epidural analgesia affect obstetric outcome in nulliparous women who are in spontaneous labor? Anesthesiology 1994;80:1201–8.[Medline]
11. Chestnut DH, Vincent RD Jr, McGrath JM, Choi WW, Bates JN. Does early administration of epidural analgesia affect obstetric outcome in nulliparous women who are receiving intravenous oxytocin? Anesthesiology 1994;80:1193–1200.[Medline]
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