Intubation Biomechanics: Laryngoscope Force and Cervical Spine Motion during Intubation in Cadavers-Cadavers versus Patients, the Effect of Repeated Intubations, and the Effect of Type II Odontoid Fracture on C1-C2 Motion.
BACKGROUND
The aims of this study are to characterize (1) the cadaver intubation biomechanics, including the effect of repeated intubations, and (2) the relation between intubation force and the motion of an injured cervical segment.


METHODS
Fourteen cadavers were serially intubated using force-sensing Macintosh and Airtraq laryngoscopes in random order, with simultaneous cervical spine motion recorded with lateral fluoroscopy. Motion of the C1-C2 segment was measured in the intact and injured state (type II odontoid fracture). Injured C1-C2 motion was proportionately corrected for changes in intubation forces that occurred with repeated intubations.


RESULTS
Cadaver intubation biomechanics were comparable with those of patients in all parameters other than C2-C5 extension. In cadavers, intubation force (set 2/set 1 force ratio = 0.61; 95% CI, 0.46 to 0.81; P = 0.002) and Oc-C5 extension (set 2 - set 1 difference = -6.1 degrees; 95% CI, -11.4 to -0.9; P = 0.025) decreased with repeated intubations. In cadavers, C1-C2 extension did not differ (1) between intact and injured states; or (2) in the injured state, between laryngoscopes (with and without force correction). With force correction, in the injured state, C1-C2 subluxation was greater with the Airtraq (mean difference 2.8 mm; 95% CI, 0.7 to 4.9 mm; P = 0.004).


CONCLUSIONS
With limitations, cadavers may be clinically relevant models of intubation biomechanics and cervical spine motion. In the setting of a type II odontoid fracture, C1-C2 motion during intubation with either the Macintosh or the Airtraq does not appear to greatly exceed physiologic values or to have a high likelihood of hyperextension or direct cord compression.
From the Department of Anesthesia, University of Iowa Roy J. and Lucille A. Carver College of Medicine, Iowa City, Iowa (B.J.H., R.P.F., M.M.T.); Department of Neurosurgery, Rush University Medical Center, Chicago, Illinois (R.B.F., V.C.T.); Department of Biostatistics, College of Public Health, University of Iowa, Iowa City, Iowa (M.B.Z.); Department of Mechanical Engineering, School of Biomedical Engineering, Orthopaedic Bioengineering Research Laboratory, Colorado State University, Fort Collins, Colorado (C.M.P.); and Foundation for Orthopaedic Research and Education, Tampa, Florida (B.G.S.).
Bradley J
BJ
Hindman
Robert P
RP
From
Ricardo B
RB
Fontes
Vincent C
VC
Traynelis
Michael M
MM
Todd
M Bridget
MB
Zimmerman
Christian M
CM
Puttlitz
Brandon G
BG
Santoni
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D002102:Cadaver; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000502:physiology; D005260:Female; D006801:Humans; D007440:Intubation / Q000295:instrumentation / Q000379:methods*; D020704:Laryngoscopes; D007828:Laryngoscopy / Q000295:instrumentation / Q000379:methods*; D007830:Larynx / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D009038:Motion; D009809:Odontoid Process / Q000293:injuries* / Q000502:physiology; D011859:Radiography; D016103:Spinal Fractures / Q000000981:diagnostic imaging*