Anticipation of the Difficult Airway
Anticipation of the Difficult Airway
This prospective, randomized, single-blind study was conducted from August 2008 to May 2010 at a Level 1 academic trauma center (Memorial Hermann Hospital, Texas Medical Center, Houston, TX, USA). After obtaining IRB approval (HSC-MS-07-0144), adult patients non-obstetric presenting for elective surgery requiring general anaesthesia, which did not already have their airway secured, were enrolled in the study. For patients who received more than one anaesthetic during the study period, data were collected independently for each anaesthetic encounter. Patients were provided with a written document describing the study and gave a verbal consent to participate.
All residents enrolled at the University of Texas Medical School at Houston anaesthesia residency programme for the academic year 2008–9 were recruited at the start of the study. An additional 24 incoming residents were enrolled during the second academic year (2009–2010) of the study, giving a total of 91 residents (Fig. 1). Each resident provided a verbal agreement to be enrolled on the quality improvement project. One resident joined the programme off-cycle in March 2008 and was enrolled in the study as a CA 1 (a first year anesthesia resident) (experimental group) for the remaining 2008–9 academic year and was also enrolled for the second year. No residents dropped from, or transferred in or out of the programme. Residents were randomized into two groups—an experimental group, which used the comprehensive airway assessment form in addition to the existing anaesthesia record, and a control group, which only used the existing anaesthesia record. Randomization was performed after stratification by year of training and based on 1:1 randomization. Experimental and control residents had a one-on-one tutorial (1 day, 3–4 practice assessments) on how to complete the data forms, respectively, followed by 1 month of validation at the beginning of each resident's rotation. Afterward, once a month, the residents' assessments were audited for quality control.
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Figure 1.
Resident randomization. CA 1, first-year residents during first year of study; CA 2, second-year residents during first year of study; CA 3, third-year residents during first year of study; CA 1–1, first-year residents during second year of study; CA 1–2, second-year residents during second year of study; CA 2–3, third-year residents during second year of study.
The new comprehensive airway assessment form (Appendix 1) required a detailed assessment of the patient's airway history and physical examination compared with the existing anaesthesia preoperative assessment form (Appendix 2). A common form to the experimental and control group was used to collect postoperative outcome data (Appendix 3).
(Enlarge Image)
Appendix 1
Experimental Group Airway Assessment Form This form was used by the control group to assess the expected difficulty of the patient airway before operation. The physical examination includes Mallampati score and neck mobility assessments.
(Enlarge Image)
Appendix 2
Control Group Airway Assessment Form
This form was used by the control group to assess the expected difficulty of the patient airway before operation. The physical examination includes Mallampati score and neck mobility assessments.
(Enlarge Image)
Appendix 3
Postoperative Outcome Data Form
This form was completed for all patients enrolled in the study and documented difficulties (if any) experienced with mask ventilation, supraglottic airway device, direct laryngoscopy, intubation, and surgical airway. Advanced airway techniques were documented if alternative devices were used. The number of attempts for all procedures was documented.
For the purposes of this study, difficult mask ventilation (DMV) was defined as difficulty in maintaining a mask seal and obtaining satisfactory capnography (end-tidal CO2 and tidal volume). If mask ventilation was attempted and determined to be difficult, the severity was graded either mild (requiring oral/nasal airway), moderate (can ventilate with assistance), severe (cannot ventilate with a facemask), or extreme (cannot ventilate with the supraglottic device). However, the use of neuromuscular blocking agent, type, dosage, time of administration, and use as a rescue were not included as outcome.
Difficult supraglottic airway (DSGA) was defined as either inability to physically place a supraglottic device or inadequacy of ventilation, oxygenation, or airway protection after placement that required conversion to an alternative technique. If placement of a supraglottic device was attempted, level of difficulty, number of attempts, and type of device were documented. Difficult direct laryngoscopy (DDL) was defined as the difficulty in visualizing any portion of the vocal cords after conventional laryngoscopy requiring more than one attempt. If direct laryngoscopy was attempted, the type of blade, number of attempts, Cormack–Lehane grade, and any difficulties encountered were documented. Difficult intubation (DI) was defined as proper insertion of the tracheal tube with conventional laryngoscopy requiring multiple attempts. If intubation was attempted, the number of attempts and the presence of any difficulties were documented. Difficult surgical airway (DSA) was defined as a difficult cricothyrotomy or tracheostomy, open or percutaneous, performed electively or emergently, to manage a DA due to bleeding, poor orientation and difficult instrumentation, and defined by the surgeon as technically difficult. DA was defined as the occurrence of DMV, DSGA, DDL, DI, or DSA. If a surgical airway was attempted, it was classified as either emergent or elective and either difficult or easy, with the number of attempts recorded.
Our database includes 9117 postoperative encounters; a small subset of patients received multiple anaesthetics (n=155, 1.7%). Patients who received multiple anaesthetics were excluded from statistical analysis. All statistical analyses were conducted using SAS 9.2 (SAS Institute, Cary, NC, USA). Data on the completeness of documentation were analysed using a χ test; accuracy of prediction was defined as the sum of correct assessments and significance determined using a χ test, while the changes of prediction accuracy over time among groups were analysed by a logistic regression. A P-value of <0.05 was considered significant.
Methods
This prospective, randomized, single-blind study was conducted from August 2008 to May 2010 at a Level 1 academic trauma center (Memorial Hermann Hospital, Texas Medical Center, Houston, TX, USA). After obtaining IRB approval (HSC-MS-07-0144), adult patients non-obstetric presenting for elective surgery requiring general anaesthesia, which did not already have their airway secured, were enrolled in the study. For patients who received more than one anaesthetic during the study period, data were collected independently for each anaesthetic encounter. Patients were provided with a written document describing the study and gave a verbal consent to participate.
All residents enrolled at the University of Texas Medical School at Houston anaesthesia residency programme for the academic year 2008–9 were recruited at the start of the study. An additional 24 incoming residents were enrolled during the second academic year (2009–2010) of the study, giving a total of 91 residents (Fig. 1). Each resident provided a verbal agreement to be enrolled on the quality improvement project. One resident joined the programme off-cycle in March 2008 and was enrolled in the study as a CA 1 (a first year anesthesia resident) (experimental group) for the remaining 2008–9 academic year and was also enrolled for the second year. No residents dropped from, or transferred in or out of the programme. Residents were randomized into two groups—an experimental group, which used the comprehensive airway assessment form in addition to the existing anaesthesia record, and a control group, which only used the existing anaesthesia record. Randomization was performed after stratification by year of training and based on 1:1 randomization. Experimental and control residents had a one-on-one tutorial (1 day, 3–4 practice assessments) on how to complete the data forms, respectively, followed by 1 month of validation at the beginning of each resident's rotation. Afterward, once a month, the residents' assessments were audited for quality control.
(Enlarge Image)
Figure 1.
Resident randomization. CA 1, first-year residents during first year of study; CA 2, second-year residents during first year of study; CA 3, third-year residents during first year of study; CA 1–1, first-year residents during second year of study; CA 1–2, second-year residents during second year of study; CA 2–3, third-year residents during second year of study.
The new comprehensive airway assessment form (Appendix 1) required a detailed assessment of the patient's airway history and physical examination compared with the existing anaesthesia preoperative assessment form (Appendix 2). A common form to the experimental and control group was used to collect postoperative outcome data (Appendix 3).
(Enlarge Image)
Appendix 1
Experimental Group Airway Assessment Form This form was used by the control group to assess the expected difficulty of the patient airway before operation. The physical examination includes Mallampati score and neck mobility assessments.
(Enlarge Image)
Appendix 2
Control Group Airway Assessment Form
This form was used by the control group to assess the expected difficulty of the patient airway before operation. The physical examination includes Mallampati score and neck mobility assessments.
(Enlarge Image)
Appendix 3
Postoperative Outcome Data Form
This form was completed for all patients enrolled in the study and documented difficulties (if any) experienced with mask ventilation, supraglottic airway device, direct laryngoscopy, intubation, and surgical airway. Advanced airway techniques were documented if alternative devices were used. The number of attempts for all procedures was documented.
For the purposes of this study, difficult mask ventilation (DMV) was defined as difficulty in maintaining a mask seal and obtaining satisfactory capnography (end-tidal CO2 and tidal volume). If mask ventilation was attempted and determined to be difficult, the severity was graded either mild (requiring oral/nasal airway), moderate (can ventilate with assistance), severe (cannot ventilate with a facemask), or extreme (cannot ventilate with the supraglottic device). However, the use of neuromuscular blocking agent, type, dosage, time of administration, and use as a rescue were not included as outcome.
Difficult supraglottic airway (DSGA) was defined as either inability to physically place a supraglottic device or inadequacy of ventilation, oxygenation, or airway protection after placement that required conversion to an alternative technique. If placement of a supraglottic device was attempted, level of difficulty, number of attempts, and type of device were documented. Difficult direct laryngoscopy (DDL) was defined as the difficulty in visualizing any portion of the vocal cords after conventional laryngoscopy requiring more than one attempt. If direct laryngoscopy was attempted, the type of blade, number of attempts, Cormack–Lehane grade, and any difficulties encountered were documented. Difficult intubation (DI) was defined as proper insertion of the tracheal tube with conventional laryngoscopy requiring multiple attempts. If intubation was attempted, the number of attempts and the presence of any difficulties were documented. Difficult surgical airway (DSA) was defined as a difficult cricothyrotomy or tracheostomy, open or percutaneous, performed electively or emergently, to manage a DA due to bleeding, poor orientation and difficult instrumentation, and defined by the surgeon as technically difficult. DA was defined as the occurrence of DMV, DSGA, DDL, DI, or DSA. If a surgical airway was attempted, it was classified as either emergent or elective and either difficult or easy, with the number of attempts recorded.
Statistical Analysis
Our database includes 9117 postoperative encounters; a small subset of patients received multiple anaesthetics (n=155, 1.7%). Patients who received multiple anaesthetics were excluded from statistical analysis. All statistical analyses were conducted using SAS 9.2 (SAS Institute, Cary, NC, USA). Data on the completeness of documentation were analysed using a χ test; accuracy of prediction was defined as the sum of correct assessments and significance determined using a χ test, while the changes of prediction accuracy over time among groups were analysed by a logistic regression. A P-value of <0.05 was considered significant.
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