Original ArticleAccuracy of cricothyroid membrane identification using ultrasound and palpation techniques in obese obstetric patients: an observational study
Introduction
Emergency front of neck access (e-FONA) is the final step in the management algorithms for the ‘can’t intubate, can’t oxygenate’ (CICO) scenario in adult and obstetric populations.1, 2 This is a potentially life-saving and morbidity-reducing intervention. However, its accurate performance depends on the ability to palpate anatomical landmarks. Research shows that accuracy in identifying the cricothyroid membrane (CTM) using palpation techniques is low, even for skilled providers,4, 5, 6, 7, 8 and CTM identification failure occurs most frequently in obese females.4, 5, 6 The Fourth National Audit Project (NAP4), a UK study on airway management complications, showed that obese patients were twice as likely as non-obese patients to suffer serious airway problems during general anaesthesia.9 Severe obesity (body mass index (BMI) ≥40 kg/m2) is becoming more prevalent in obstetric populations.10 Obesity significantly increases the risk of emergency and elective caesarean section.11 This patient cohort has a higher risk of difficult or failed intubation, and effective, evidence-based rescue strategies are of vital importance.12
The increasing availability of bedside ultrasound (US) has driven a rapid increase in its use and has led to its evolution from a research tool to a clinical tool.13 Several studies have looked at the use of US compared with palpation to identify the CTM in obese pregnant patients.4, 6 However, these studies had a variable skill-mix in terms of clinician participants which might potentially lead to inter-rater variability. The aim of the study was to compare CTM identification accuracy by an expert when using US compared with palpation in a group at high risk of CTM identification failure. We hypothesised that using US in this population would result in a shorter distance between the actual and estimated CTM midpoints when compared with palpation.
Section snippets
Methods
This single centre, prospective observational investigation was carried out in the University Maternity Hospital in Limerick, Ireland. Ethical approval was granted by the institutional review board. We recruited patients from the obstetric anaesthesia clinic and obtained written informed consent prior to their participation. Inclusion criteria were: late second or third trimester of pregnancy, age ≥18 years, and a booking BMI ≥35 kg/m2. Exclusion criteria were: age <18 years, known neck
Results
The mean distance between the clinician estimate to the actual CTM midpoint was shorter in group U than group L (2.5 mm [95% CI 1.8 to 3.3] vs 5.5 mm [95% CI 3.7 to 7.2], using Wilkinson matched pairs signed rank test P=0.002 (Fig. 2, Table 2). The proportion of correctly identified CTMs was greater in group U than group L (20/28 (71.4%) vs 11/28 (39.3%); P=0.015 using McNemar’s test). The median time to identify the CTM was shorter in group L than group U (16.9 s [95% CI 13.6 to 19.4] vs
Discussion
Our results show that US identification of the CTM in a skilled clinician's hands is more accurate in terms of distance from the CTM midpoint and proportion of correct estimates than palpation. However, it takes longer to perform, which may be a drawback in time-critical events. We note that US assessment did not result in universally accurate identification of the CTM and observed a progressive improvement in US accuracy with repetition that did not occur with palpation. Correlation analysis
Declaration of interests
None.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors.
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