What is the best way to determine oropharyngeal classification and mandibular space length to predict difficult laryngoscopy?

Hypoperfusion of the brain stem in dependence on head and body position followed by central bradycardia and apnea may be an important cause of sudden infant death syndrome (SIDS). 39 infants with a mean age of 10.6 +/- 10.2 weeks (6 days to 11 months) with apparent life threatening events (ALTE) were investigated by cranial Doppler sonography. Additionally 68 healthy infants aged 6 days to 5 months (m 3.7 +/- 4.1 weeks) were investigated. In all patients flow measurements were performed in one anterior cerebral artery (ACA), both internal carotid arteries (ICA), the basilar artery (BA), and both vertebral arteries (VA) in dependence on head (right/left/neutral) and body position (prone/supine). In healthy infants flow velocities within all intracranial arteries were independent of head and body position. In none of our infants with ALTE significant flow alterations in the ACA and both ICA in dependence on head and body position could be found. In 23 patients with ALTE no dependence of flow in the BA and both VA of head and body position could be shown. In 16 infants however pathologic flow profiles with low flow velocities could be found in the contralateral VA if the head was rotated to the other side. In 9 infants additionally pathologic flow profiles with a dramatic decrease of the flow velocities in the BA could be found. The reduction of the blood flow is caused by compression of the contralateral vertebral artery at the craniocervical junction. The reduction of blood flow in the VA and especially the BA may cause hypoperfusion of the brainstem followed by central bradycardia and apnea. Hypoperfusion of the brainstem in dependence on head and body position may be a significant cause of SIDS. By means of cerebral Dopplersonography infants at risk for SIDS may be detected. Body and head positions which should be avoided can be evaluated noninvasively.

The effects of head and body positioning on upper airway collapsibility in normal subjects who received midazolam sedation

Head-position angles in children for opening the upper airway

In supine patients with their heads in flexion, general anesthesia causes posterior displacement of upper airway structures that is associated with airway obstruction, and extension of the head helps restore patency. However, the independent effects of head position, general anesthesia, and muscle paralysis on upper airway structures are not known. Lateral radiographs of the neck were taken in supine patients with the head in flexion and extension, during consciousness, and after induction of general anesthesia and muscle paralysis. The following measurements were made distances from the horizontal plane to the epiglottis, the hyold, and the thyroid cartilage to detect anteroposterior displacements; distances from the transverse plane to the hyold and the thyroid cartilage to detect cephalocaudad displacements; and widths of the oropharynx, the laryngeal vestibule, and the laryngeal sinus. With the head in flexion, anesthesia and paralysis compared with the conscious state caused posterior displacement of the epiglottis, narrowing of the oropharynx, and widening of the laryngeal vestibule. With the head in extension, anesthesia and paralysis compared with the conscious state caused anterior displacements of the epiglottis, the hyold, and the thyroid cartilage, narrowing of the oropharynx, and widening of the laryngeal vestibule and the laryngeal sinus. Loss of tonic muscular activity due to anesthesia and paralysis results in anteroposterior displacements of the upper airway structures with flexion and extension of the head that are in the same direction as that of the mandible. Anesthesia and paralysis also widen the dimensions of the larynx. These changes might have implications for instrumentation and protection of the airway during general anesthesia or unconsciousness.

Predicting difficult intubation--worthwhile exercise or pointless ritual?

To determine the influence of altered head or tongue posture on upper airway (UA) volumes using MRI imaging based on a new objective and validated UA evaluation protocol. One supine CBCT and five sagittal MRI scans were obtained from ten subjects in different head and tongue positions: (a) supine neutral head position (NHP) with the tongue in a natural resting position with the tip of the tongue in contact with the lingual aspect of the lower incisors (TRP); (b) head extension with TRP; (c) head flexion with TRP; (d) NHP with the tip of the tongue in contact with the posterior edge of the hard palate (THP); and (e) NHP with the tip of the tongue in contact with the floor of the mouth in contact with the caruncula sublingualis. Based on a validated CBCT UA analysis, the retropalatal, oropharyngeal and the corresponding total volumes were measured from each MRI scan. Wilcoxon signed-rank test was applied to determine the statistically significant difference in mean volume between the baseline head and tongue posture (NHP with TRP) and the other postures. Five females and five males with a mean age of 46.5±13.7years volunteered for this pilot study. UA volumes, particularly the oropharyngeal volume, increased significantly with head extension and NHP with THP and decreased significantly with head flexion. Altered head and tongue posture proved to affect UA volumes, thus representing confounding variables during three-dimensional radiographic image acquisition.

Purpose: To assess the impact of various body and head positions on intraocular pressure (IOP) in cataract patients aged over 40 years with limited mobility.Methods: This cross-sectional study was conducted between August and December 2023 at Aier Eye Hospital of Wuhan University. The IOP was measured using a handheld tonometer (iCare IC200 rebound tonometer) in various head positions (forward, tilted left, and tilted right) and body positions: supine, semirecumbent, sitting, and prone.Results: In the supine position, the IOP measurements for the head positioned forward, right, and left were (13.80 ± 3.62) mmHg, (14.25 ± 3.66) mmHg, and (13.78 ± 3.40) mmHg, respectively. In the semirecumbent position, the corresponding IOPs were (12.08 ± 3.34) mmHg, (12.12 ± 3.22) mmHg, and (12.04 ± 3.38) mmHg. In the sitting position, the IOPs were recorded as (11.73 ± 3.29) mmHg, (11.73 ± 3.22) mmHg, and (11.59 ± 3.17) mmHg. Lastly, in the prone position, the IOPs were (14.19 ± 3.73) mmHg, (14.42 ± 3.93) mmHg, and (14.74 ± 3.81) mmHg, respectively. In each position group, there was no statistically significant difference in IOP among the three head positions. Regardless of the head position, the IOP is lowest in the sitting position, followed by semirecumbent and supine positions, with the prone position having the highest IOP. The analyses revealed that central corneal thickness (CCT) was correlated with an IOP value (p < 0.05) when patients were in different positions.Conclusion: IOP is influenced by body position. As the body transitions from upright to horizontal, IOP tends to increase. The position of the head, however, has no effect on IOP.

The purpose of this research was to investigate influence on the sternocleidomastoid muscle (SCM) activity in clenching depending on body and head positions. Seven male subjects without jaw-dysfunction were asked to exert maximum voluntary contraction in three body positions; sitting, supine and prone. As for the head positions, those of normal and full rotations (right and left) in each body position were required. In addition, in the sitting position, those of half rotation (right and left) were performed. EMG activity was recorded by means of bipolar surface electrodes. The results were as follows: 1. In full rotated head positions, EMG activity of the contralateral SCM varied about twice as much as in normal head positions. 2. In half rotated head positions, EMG activity of the contralateral SCM varied 1.20 times as much as in normal head positions. 3. In rotated head positions, EMG activity of the ipsilateral SCM varied from 0.81 to 1.22 times as much as in normal head positions. 4. EMG activity of SCM without clenching (background activity) had little influence on that with clenching. 5. In normal head positions, EMG activity in the supine position varied 0.86 times as much as in the sitting position. In conclusion, the head positions have much more influence on EMG activity of SCM in clenching than the body positions.

Head and jaw position influence upper airway patency and electromyographic (EMG) activity of the main upper airway dilator muscle, the genioglossus. However, it is not known whether changes in genioglossus EMG activity translate into altered muscle movement during respiration. The aim of this study was to determine the influence of head and jaw position on dilatory motion of the genioglossus in healthy adult men during quiet breathing by measuring the displacement of the posterior tongue in six positions--neutral, head extension, head rotation, head flexion, mouth opening, and mandibular advancement. Respiratory-related motion of the genioglossus was imaged with spatial modulation of magnetization (SPAMM) in 12 awake male participants. Tissue displacement was quantified with harmonic phase (HARP) analysis. The genioglossus moved anteriorly beginning immediately before or during inspiration, and there was greater movement in the oropharynx than in the velopharynx in all positions. Anterior displacements of the oropharyngeal tongue varied between neutral head position (0.81 ± 0.41 mm), head flexion (0.62 ± 0.45 mm), extension (0.39 ± 0.19 mm), axial rotation (0.39 ± 0.2 mm), mouth open (1.24 ± 0.72 mm), and mandibular advancement (1.08 ± 0.65 mm). Anteroposterior displacement increased in the mouth-open position and decreased in the rotated position relative to cross-sectional area (CSA) (P = 0.002 and 0.02, respectively), but CSA did not independently predict anteroposterior movement overall (P = 0.057). The findings of this study suggest that head position influences airway dilation during inspiration and may contribute to variation in airway patency in different head positions.

Head posture (HP) is used as part of the clinical examination of patients with neck pain to inform diagnosis, plan treatment, and monitor progress. For related information to be interpreted correctly, clinicians need to know how much of the variation in HP between measurements can be attributed to a change in the patient condition and how much is due to measurement error and/or biological variation. The aim of this study was to investigate the variability of angular measurements indicative of forward HP, head extension, and side flexion within a session, within a day, and over a 7-day period. Angles were calculated from 27 participants in three sessions over a period of 7 days through digitization of video images. Intraclass correlation coefficients (ICC) and standard error of measurement (SEM) showed that forward HP (ICC between 0.82 and 0.91; SEM between 1.42° and 1.70°) and side flexion (ICC between 0.63 and 0.85; SEM between 0.83° and 1.27°) were stable within a session, within a day, and over a 7-day period. Head extension was found to be less stable (ICC between 0.71 and 0.83; SEM between 2.69° and 3.72°). Time of day did not appear to influence forward HP, side flexion, or head extension.

Though airway ultrasonography (USG) is used to assess difficult laryngoscopy (DL), there is still ambiguity about approach followed and parameters assessed. There is need of a simple, stepwise sonographic assessment with clearly defined parameters for DL prediction. The primary objective of this study was to find diagnostic accuracy of sonographic parameters measured by a stepwise Airway-USG in DL prediction (DLP). This prospective, observational cohort study was done in 217 elective surgical adult patients administered general anaesthesia with tracheal intubation using conventional laryngoscopy from 1st May 2019 to 31st July 2020, after ethical approval. A sagittal Airway-USG was done using 2-6 Hz transducer in three steps specifying probe placement and head position. Demographic, clinical and Airway-USG measurements were noted. Correlation of the clinical/sonographic parameters was made with Cormack-Lehane score on DL. After receiver operating characteristic curve plotting, the sensitivity, specificity, positive predictive value, negative predictive value (NPV) of DL was calculated for each parameter using open-epi software. DL was observed in 19/217 patients. Airway-USG parameters of skin to epiglottis distance >2.45 cm, hyomental distance with head extension <5.13 cm, head neutral <4.5 cm, their ratio <1.18, maximum tongue thickness >3.93 cm and maximum skin to tongue distance >5.45 cm were statistically significant in predicting DL. DLP score with presence of >3 positive parameters showed 98% specificity, 98% NPV and 96% diagnostic accuracy to predict DL. DLP score derived from Airway-USG may be used as a screening and diagnostic tool for DL.

The purpose of this study was to assess the effect of changes in body and head positions on respiratory-related activity of the genioglossus muscle in normal subjects in 8 body and head positions: (1) upright body with head straight, (2) upright body with head rotated to the right, (3) upright body with head rotated to the left, (4) supine body with head straight, (5) supine body with head rotated to the right, (6) supine body with head rotated to the left, (7) lateral recumbent body to the right, and (8) lateral recumbent body to the left. Phasic activity of the genioglossus muscle decreased significantly when subjects rotated their heads and moved from the supine to the lateral recumbent position. It is therefore concluded that genioglossus muscle activity is modulated in response to head rotation and changes in body position.

Influence of head and neck position on ventilation using the air-Q® SP airway in anaesthetized paralysed patients: a prospective randomized crossover study

The aim of this study was to investigate the effects of head and neck positions on the cerebral blood flow velocity by transcranial Doppler ultrasound in patients who underwent cranial surgery. Inappropriate head elevation and body positioning in patients who undergo cranial surgery may affect cerebral blood flow and cerebral perfusion pressure. DESIGNED: Experimental clinical study. Our sample consisted of 38 patients who underwent cranial surgery between October 2009 and May 2010. The measurments of mean cerebral blood flow velocity were taken by the transcranial Doppler ultrasound through the temporal window. The mean cerebral blood flow velocity of the patients was measured in supine position with 0° and 30° head elevations, right and left lateral positions, right and left lateral positions with head flexion and extension. The measurements were taken before surgery and within 72 hours after surgery. The mean cerebral blood flow velocity of the middle cerebral arteries was increased in head elevations from 0° to 30°, in right and lateral positions with 30° head elevations, but the velocity was decreased in head flexion and extension positions in preoperative and postoperative periods. Head and body positioning, which is one of the nursing care activities, may affect intracranial pressure and cerebral perfusion pressure. Our results are similar with those of previous studies, which showed that head elevation did not affect the cerebral blood flow velocity. By the results of this study, the head elevation of the patients, who underwent cranial surgery, should be 30° during the nursing care to provide optimum cerebral blood flow. Right and left lateral positioning is safe and recommended for these patients if there is no medical contraindication.

We conducted a prospective, blind study to determine whether a difficult endotracheal intubation could be predicted preoperatively by evaluation of one or more anatomic features of the head. In 471 adults presenting for elective surgery, the size of the tongue relative to the oral cavity was assessed according to the Mallampati classification (oropharyngeal class), and the distance between the chin and thyroid cartilage (thyromental distance) and the angle at full extension of the head (head extension) were measured. At laryngoscopy, the difficulty in visualizing the larynx was determined by a different observer. Assignment to oropharyngeal Class 3, a thyromental distance < or = 7 cm, and a head extension < or = 80 degrees, considered either alone or in various combinations, had low sensitivity and positive predictive values in identifying patients with airways that were difficult to intubate, but high specificity and negative predictive values. We conclude that these three tests are of little value in predicting difficult intubation in adults, although the likelihood of an easy endotracheal intubation is high when they yield negative results.