Background: Severely obese parturients have increased 'cannot intubate, cannot oxygenate' risk during Caesarean section under general anaesthesia. Front-of-neck access (FONA) at the cricothyroid membrane (CTM) is definitive management; however, attempted FONA can fail. Point-of-care ultrasonography may provide useful information about CTM depth to aid FONA in obesity. This study determined the difference in CTM depth between severely obese and non-obese parturients, utilising ultrasonography.

Methods: In this prospective observational study, two anaesthetists performed airway ultrasonography on 15 severely obese (BMI >45 kg m^-2) and 15 normal-weight (BMI ≤25 kg m^-2) parturients in the third trimester, using the transverse and longitudinal planes, sniffing and extended head positions, and nil and firm transducer pressures. The primary outcome was CTM depth (millimetres) measured in the transverse plane with the head extended and nil transducer pressure. Secondary outcomes included CTM depth measurements using other factor configurations. Intra-class correlation coefficients assessed the inter-observer reliability.

Results: CTM depth measured in the transverse plane with head extended and nil transducer pressure was significantly greater in severely obese parturients, mean 18.0 mm (95% confidence interval 16.3-19.8), vs 10.6 mm (8.81-12.4) in non-obese (P<0.001); mean difference 7.4 mm (4.9-9.9; P<0.001). CTM depths were increased in the severely obese group regardless of scanning plane, head and neck position, or transducer pressure (all P<0.001). There was excellent inter-observer reliability.

Conclusions: Cricothyroid membrane depth is significantly increased in severely obese vs normal-weight parturients independently of scanning plane, head and neck position, or transducer pressure.

Item Type:	Refereed Article
Keywords:	airway management, intubation, oxygen inhalation therapy, pregnancy, ultrasonography
Research Division:	Biomedical and Clinical Sciences
Research Group:	Reproductive medicine
Research Field:	Obstetrics and gynaecology
Objective Division:	Health
Objective Group:	Specific population health (excl. Indigenous health)
Objective Field:	Women's and maternal health
UTAS Author:	Gadd, K (Dr Karl Gadd)
UTAS Author:	Wills, K (Dr Karen Wills)
UTAS Author:	Terblanche, N (Dr Nico Terblanche)
ID Code:	126606
Year Published:	2018
Web of Science® Times Cited:	8
Deposited By:	Menzies Institute for Medical Research
Deposited On:	2018-06-19
Last Modified:	2019-03-18
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