Category Archives: Ultrasound

Sonographic bits and bobs

Is diastolic worse than systolic dysfunction in sepsis?

Septic myocardial dysfunction is a well recognised contributor to shock in sepsis but for many of us we assume this to be gross systolic impairment. Interestingly a recent study highlights that patients with severe sepsis and septic shock frequently have diastolic dysfunction1. They found that diastolic dysfunction was the strongest independent predictor of early mortality, even after adjusting for the APACHE-II score and other predictors of mortality.

In this study, 9.1% of severe sepsis/septic shock patients had isolated systolic dysfunction, 14.1% had combined systolic and diastolic dysfunction, and 38% had isolated diastolic dysfunction.

Importantly, the authors point out that although diastolic dysfunction is associated with age, hypertension, diabetes mellitus, and ischaemic heart disease, diastolic dysfunction is a stronger independent predictor of mortality than age and the other co-morbidities. However, a limitation of the study acknowledged by the authors is that it did not include follow-up echocardiography examinations, so we do not know whether sepsis was responsible for a transient diastolic dysfunction or whether the observed diastolic dysfunction was a pre-existing condition.

Both troponin and NT-ProBNP elevations also predicted mortality.

Want to know how to measure diastolic dysfunction? These authors measured mitral annular early-diastolic peak velocity, or the e’-wave (called ‘e prime’). It is a way of seeing how fast myocardial tissue relaxes in diastole, and if its peak velocity is slow (in this case < 8cm/s) there is diastolic dysfunction. We measure speed using Doppler, and in this case we’re looking at the speed of heart tissue (as opposed to the blood cells within the heart chambers) so we do ‘Tissue Doppler Imaging’, or TDI. You need an echo machine with pulsed-wave Doppler, and you need to be able to get an apical view. This is explained really nicely here2 but if you don’t have the time or the echopassion to read a whole article on TDI watch this one minute video (BY emergency physicians FOR emergency physicians!) on diastology, where TDI measurement of e’ is shown from 45 seconds into the video.

For reference, there is some more detail on diastolic function measurements at the Echobasics site.

If you think you can cope with any more of this level of awesomeness and want these geniuses to talk to you from your smartphone in the ED then get the free One Minute Ultrasound app for Android or Apple devices.


AIMS: Systolic dysfunction in septic shock is well recognized and, paradoxically, predicts better outcome. In contrast, diastolic dysfunction is often ignored and its role in determining early mortality from sepsis has not been adequately investigated.

METHODS AND RESULTS: A cohort of 262 intensive care unit patients with severe sepsis or septic shock underwent two echocardiography examinations early in the course of their disease. All clinical, laboratory, and survival data were prospectively collected. Ninety-five (36%) patients died in the hospital. Reduced mitral annular e’-wave was the strongest predictor of mortality, even after adjusting for the APACHE-II score, low urine output, low left ventricular stroke volume index, and lowest oxygen saturation, the other independent predictors of mortality (Cox’s proportional hazards: Wald = 21.5, 16.3, 9.91, 7.0 and 6.6, P< 0.0001, <0.0001, 0.002, 0.008, and 0.010, respectively). Patients with systolic dysfunction only (left ventricular ejection fraction ≤50%), diastolic dysfunction only (e’-wave <8 cm/s), or combined systolic and diastolic dysfunction (9.1, 40.4, and 14.1% of the patients, respectively) had higher mortality than those with no diastolic or systolic dysfunction (hazard ratio = 2.9, 6.0, 6.2, P= 0.035, <0.0001, <0.0001, respectively) and had significantly higher serum levels of high-sensitivity troponin-T and N-terminal pro-B-type natriuretic peptide (NT-proBNP). High-sensitivity troponin-T was only minimally elevated, whereas serum levels of NT-proBNP were markedly elevated [median (inter-quartile range): 0.07 (0.02-0.17) ng/mL and 5762 (1001-15 962) pg/mL, respectively], though both predicted mortality even after adjusting for highest creatinine levels (Wald = 5.8, 21.4 and 2.3, P= 0.015, <0.001 and 0.13).

CONCLUSION: Diastolic dysfunction is common and is a major predictor of mortality in severe sepsis and septic shock.

1. Diastolic dysfunction and mortality in severe sepsis and septic shock
Eur Heart J. 2012 Apr;33(7):895-903

2. A clinician’s guide to tissue Doppler imaging
Circulation. 2006 Mar 14;113(10):e396-8 Free Full Text

Not a pin cushion

This is the daughter of my friend. Avery is only seven months old and has survived a critical illness and is thankfully now fully recovered. Her Dad has nothing but praise for the medical and nursing staff who cared for her. But one thing could have been better. Avery endured multiple attempts at vascular access without ultrasound guidance.

If you were her parent, and you were an emergency physician with galaxy-class expertise in emergency ultrasound, how would you react? Complaints? Incident forms? Outrage?

How about education? For free. Accompanied by lavish praise for the experts who treated Avery and made her better.

Avery’s Dad is ultrasound podcaster and gentleman Dr Matt Dawson. He is offering FREE ultrasound training to anyone who wants to improve their vascular access skills.

Are there nurses, physicians, or technicians in your ED or ICU that could improve their care with this training? Please consider sending them for this training. To register for the course, and to read Avery’s full story, go to notapincushion.com.

And if you’re already comfortable with ultrasound-guided vascular access, then visit the site anyway, as there is some education here for all of us: how to turn a gut-wrenchingly distressing experience into something positive that will benefit countless others. I am thoroughly inspired.

Best wishes to an amazing family.

Cliff

Lung ultrasound for pneumothorax by paramedics

This UK study showed that paramedics could successfully acquire and identify lung ultrasound images after a two day course. The course covered the identification and management of patients who present with serious thoracic injury, with a specific focus on the use of thoracic ultrasound during early prehospital assessment. Standard 2D images for pleural sliding and comet tails and M-Mode for the ‘seashore sign’ were acquired, and colour Doppler was also used to assist in the identification of pleural sliding.


Objective This trial investigated whether advanced paramedics from a UK regional ambulance service have the ability to acquire and interpret diagnostic quality ultrasound images following a 2-day programme of education and training covering the fundamental aspects of lung ultrasound.

Method The participants were tested using a two-part examination; assessing both their theoretical understanding of image interpretation and their practical ability to acquire diagnostic quality ultrasound images. The results obtained were subsequently compared with those obtained from expert physician sonographers.

Results The advanced paramedics demonstrated an overall accuracy in identifying the presence or absence of pneumothorax in M-mode clips of 0.94 (CI 0.86 to 0.99), compared with the experts who achieved 0.93 (CI 0.67 to 1.0). In two-dimensional mode, the advanced paramedics demonstrated an overall accuracy of 0.78 (CI 0.72 to 0.83), compared with the experts who achieved 0.76 (CI 0.62 to 0.86). In total, the advanced paramedics demonstrated an overall accuracy at identifying the presence or absence of pneumothorax in prerecorded video clip images of 0.82 (CI 0.77 to 0.86), in comparison
with the expert users of 0.80 (CI 0.68 to 0.88). All of the advanced paramedics passed the objective structured clinical examination and achieved a practical standard considered by the examiners to be equivalent to that which would be expected from candidates enrolled on the thoracic module of the College of Emergency Medicine level 2 ultrasound programme.

Conclusion This trial demonstrated that ultrasound-naive practitioners can achieve an acceptable standard of competency in a simulated environment in a relatively short period of time.

Acquisition and interpretation of focused diagnostic ultrasound images by ultrasound-naive advanced paramedics: trialling a PHUS education programme
Emerg Med J, 2012 vol. 29 (4) pp. 322-326

Only when I laugh

A middle-aged martial arts enthusiast was training in Krav Maga, and participated in a high-contact punching and grappling sparring exercise in which his (younger, heavier) partner threw him to the ground and landed on him. During the throw the patient felt a ‘pop’ in his right side, and wondered whether he’d fractured a rib. During the subsequent five rounds against two additional sparring partners he noticed a clicking in the same area every time he was grappling, and pain in the right side when pushing up off the floor with his right arm. As a trained emergency physician, he assessed his own level of breathing comfort throughout the training to reassure himself he didn’t have a significant pneumothorax, and therefore elected to continue to fight in the interests of assessing his ability to defend himself while injured.

Pain on deep inspiration, coughing, and squeezing the chest suggested a fractured rib, so out of curiosity at work the next day he ultrasounded the area of maximum tenderness:

Discontinuity in cortex signifies rib fracture



Examination of the lung confirmed pleural sliding, B-lines, and ‘pearls on a string’, which excluded pneumothorax.

Sonography is more sensitive than radiography for the detection of rib fractures and may also detect costochondral junction injuries and disruption of costal cartilage1. This video from Hennepin County Medical Centre takes you through the simple procedure:



Although the management of rib fractures is no different from that of chest wall contusion, knowledge of the presence of fracture in this case is helpful to this patient in deciding when to return to the questionably sane ‘hobby’ of fighting bigger guys half his age.

The patient’s consent was obtained prior to the publication of the ultrasound image.

1. Sonography Compared with Radiography in Revealing Acute Rib Fracture
AJR Am J Roentgenol. 1999 Dec;173(6):1603-9.
Full text article




OBJECTIVE: This study was undertaken to compare the sensitivities of sonography and radiography for revealing acute rib fracture.


SUBJECTS AND METHODS: Chest radiography and rib sonography were performed on 50 patients with suspected rib fractures. Sonography was performed with a 9- or 12-MHz linear transducer. Fractures were identified by a disruption of the anterior margin of the rib, costochondral junction, or costal cartilage. The incidence, location, and degree of displacement of fractures revealed by radiography and sonography were compared. Sonography was performed again after 3 weeks in 37 subjects.


RESULTS: At presentation, radiographs revealed eight rib fractures in six (12%) of 50 patients and sonography revealed 83 rib fractures in 39 (78%) of 50 patients. Seventy-four (89%) of the 83 sonographically detected fractures were located in the rib, four (5%) were located at the costochondral junction, and five (6%) in the costal cartilage. Repeated sonography after 3 weeks showed evidence of healing in all reexamined fractures. Combining sonography at presentation and after 3 weeks, 88% of subjects had sustained a fracture.


CONCLUSION: Sonography reveals more fractures than does radiography and will reveal fractures in most patients presenting with suspected rib fracture. Further scientific studies are needed to clarify the appropriate role for sonography in rib fracture detection.


International recommendations for lung ultrasound

A multidisciplinary panel of 28 experts from eight countries reviewed the literature and came up with consensus guidelines in point-of-care lung ultrasound. There were some big names involved – all the big players in emergency/critical care ultrasound from around the World. Conspicuously absent were Matt and Mike from the Emergency Ultrasound Podcast, but maybe there was a maximum awesomeness limit or something.

Here are some snippets, taken out of context and without the grade of recommendation attached. Try to get hold of the original if you can, which might not be easy. I never understand it when ‘international recommendations’ are published as subscription-only articles. Either they want people to follow them or not. Oh well – here are some of their recommendations:

Pneumothorax

  • The sonographic signs of pneumothorax include the following: Presence of lung point(s); Absence of lung sliding; Absence of B-lines; Absence of lung pulse
  • The lung pulse refers to the subtle rhythmic movement of the visceral upon the parietal pleura with cardiac oscillations and is a rule-out sign for pneumothorax
  • In the supine patient, the sonographic technique consists of exploration of the least gravitationally dependent areas progressing more laterally.
  • Bedside lung ultrasound is a useful tool to differentiate between small and large pneumothorax, using detection of the lung point.

Interstitial syndrome

  • B-lines are defined as discrete laser-like vertical hyperechoic reverberation artifacts that arise from the pleural line (previously described as ‘‘comet tails’’), extend to the bottom of the screen without fading, and move synchronously with lung sliding.
  • The presence of multiple diffuse bilateral B-lines indicates interstitial syndrome. Causes of interstitial syndrome include the following conditions: Pulmonary edema of various causes; Interstitial pneumonia or pneumonitis; Diffuse parenchymal lung disease (pulmonary fibrosis)

Lung consolidation

  • The sonographic sign of lung consolidation is a subpleural echo-poor region or one with tissue-like echotexture.
  • Lung ultrasound is a clinically useful tool to rule in pneumonia; however, lung ultrasound does not rule out consolidations that do not reach the pleura.
  • In mechanically ventilated patients lung ultrasound should be considered as it is more accurate than portable chest radiography in the detection of consolidation.

Pleural effusion

  • Both of the following signs are present in almost all free effusions: A space (usually anechoic) between the parietal and visceral pleura; Respiratory movement of the lung within the effusion (‘‘sinusoid sign’’)
  • In opacities identified by chest radiography, lung ultrasound should be used because it is more accurate than chest radiography in distinguishing between effusion and consolidation.
  • Visualization of internal echoes, either of mobile particles or septa, is highly suggestive of exudate or hemothorax


BACKGROUND: The purpose of this study is to provide evidence-based and expert consensus recommendations for lung ultrasound with focus on emergency and critical care settings.


METHODS: A multidisciplinary panel of 28 experts from eight countries was involved. Literature was reviewed from January 1966 to June 2011. Consensus members searched multiple databases including Pubmed, Medline, OVID, Embase, and others. The process used to develop these evidence-based recommendations involved two phases: determining the level of quality of evidence and developing the recommendation. The quality of evidence is assessed by the grading of recommendation, assessment, development, and evaluation (GRADE) method. However, the GRADE system does not enforce a specific method on how the panel should reach decisions during the consensus process. Our methodology committee decided to utilize the RAND appropriateness method for panel judgment and decisions/consensus.


RESULTS: Seventy-three proposed statements were examined and discussed in three conferences held in Bologna, Pisa, and Rome. Each conference included two rounds of face-to-face modified Delphi technique. Anonymous panel voting followed each round. The panel did not reach an agreement and therefore did not adopt any recommendations for six statements. Weak/conditional recommendations were made for 2 statements, and strong recommendations were made for the remaining 65 statements. The statements were then recategorized and grouped to their current format. Internal and external peer-review processes took place before submission of the recommendations. Updates will occur at least every 4 years or whenever significant major changes in evidence appear.


CONCLUSIONS: This document reflects the overall results of the first consensus conference on “point-of-care” lung ultrasound. Statements were discussed and elaborated by experts who published the vast majority of papers on clinical use of lung ultrasound in the last 20 years. Recommendations were produced to guide implementation, development, and standardization of lung ultrasound in all relevant settings.


International evidence-based recommendations for point-of-care lung ultrasound
Intensive Care Med. 2012 Apr;38(4):577-91

Posterior pericardiocentesis

Dr Emanuele Catena and colleagues report a case of an adult male who presented 7 days post cardiac surgery with simultaneous pleural and pericardial effucions causing dyspnoea, tachycardia and hypotension.

Old skool pericardiocentesis

His pericardial effusion was posterior which usually requires surgical drainage, but the adjacent left pleural effusion was associated with pulmonary atelectasis and displacement of the lung, allowing them to insert a needle using sonographic guidance first into the pleural space then the pericardial space.

They inserted through the fourth intercostal space 4 cm medially to the left posterior axillary line (with the patient positioned in the semireclining position). They used agitated saline bubbles to confirm first the pleural then the pericardial location of the needle tip. A 30-cm-long catheter was introduced into the posterior pericardium using the Seldinger technique, and serous-haemorrhagic fluid was drained. The catheter was then retracted allowing drainage of the pleural effusion.

The procedure resulted in haemodynamic and respiratory improvement.

The authors summarise:



This case reports the technique of a “back pericardiocentesis” performed under echographic guidance as a valid alternative to surgery in the peculiar situation characterized by the simultaneous presence of a large left pleural effusion. In the presence of a large left pleural effusion, pulmonary atelectasis and displacement of air-filled pulmonary tissue allows ultrasound transmission from a patient’s back to the heart through a liquid interface and needle insertion “from back” to reach the pericardial space.


 

Pericardiocentesis From Back Under Echographic Guidance An Approach for Posterior Pericardial Effusions
Circulation. 2011 Dec 13;124(24):e835-6

Prehospital echo predicts arrest outcome

In hospital, the detection of cardiac standstill with ultrasound predicts a fatal outcome from cardiac arrest with a high degree of accuracy. A similar finding has been made in the prehospital setting. Interestingly, it was a better predictor than other commonly recognised factors associated with outcome: the presence of asystole, down time, bystander CPR, or end-tidal CO2 levels.



Introduction. The prognostic value of emergency echocardiography (EE) in the management of cardiac arrest patients has previously been studied in an in-hospital setting. These studies mainly included patients who underwent cardiopulmonary resuscitation (CPR) by emergency medicine technicians at the scene and who arrived at the emergency department (ED) still in a state of cardiac arrest. In most European countries, cardiac arrest patients are normally treated by physician-staffed emergency medical services (EMS) teams on scene. Transportation to the ED while undergoing CPR is uncommon. Objective. To evaluate the ability of EE to predict outcome in cardiac arrest patients when it is performed by ultrasound-inexperienced emergency physicians on scene.


Methods. We performed a prospective, observational study of nonconsecutive, nontrauma, adult cardiac arrest patients who were treated by physician-staffed urban EMS teams on scene. Participating emergency physicians (EPs) received a two-hour course in EE during CPR. After initial procedures were accomplished, EE was performed during a rhythm and pulse check. A single subxiphoid, four-chamber view was required for study enrollment. We defined sonographic evidence of cardiac kinetic activity as any detected motion of the myocardium, ranging from visible ventricular fibrillation to coordinated ventricular contractions. The CPR had to be continued for at least 15 minutes after the initial echocardiography. No clinical decisions were made based on the results of EE.


Results. Forty-two patients were enrolled in the study. The heart could be visualized successfully in all patients. Five (11.9%) patients survived to hospital admission. Of the 32 patients who had cardiac standstill on initial EE, only one (3.1%) survived to hospital admission, whereas four out of 10 (40%) patients with cardiac movement on initial EE survived to hospital admission (p = 0.008). Neither asystole on initial electrocardiogram nor peak capnography value, age, bystander CPR, or downtime was a significant predictor of survival. Only cardiac movement was associated with survival, and cardiac standstill at any time during CPR resulted in a positive predictive value of 97.1% for death at the scene.


Conclusion. Our results support the idea of focused echocardiography as an additional criterion in the evaluation of outcome in CPR patients and demonstrate its feasibility in the prehospital setting.


Cardiac Movement Identified on Prehospital Echocardiography Predicts Outcome
Prehosp Emerg Care. 2012 Jan 11. [Epub ahead of print]

Ultrasound for pneumonia

Lung ultrasound done by a single keen individual had better test characteristics than CXR in diagnosing pneumonia as defined by discharge diagnosis.
The lung ultrasound was considered to be positive for pneumonia if it showed consolidation (including air bronchograms) or a focal interstitial syndrome (localised increased density of ‘B’ lines)



Objective The aim of this study was to evaluate the diagnostic accuracy of bedside lung ultrasound and chest radiography (CXR) in patients with suspected pneumonia compared with CT scan and final diagnosis at discharge.


Design A prospective clinical study.


Methods Lung ultrasound and CXR were performed in sequence in adult patients admitted to the emergency department (ED) for suspected pneumonia. A chest CT scan was performed during hospital stay when clinically indicated.


Results 120 patients entered the study. A discharge diagnosis of pneumonia was confirmed in 81 (67.5%). The first CXR was positive in 54/81 patients (sensitivity 67%; 95% CI 56.4% to 76.9%) and negative in 33/39 (specificity 85%; 95% CI 73.3% to 95.9%), whereas lung ultrasound was positive in 80/81 (sensitivity 98%; 95% CI 93.3% to 99.9%) and negative in 37/39 (specificity 95%; 95% CI 82.7% to 99.4%). A CT scan was performed in 30 patients (26 of which were positive for pneumonia); in this subgroup the first CXR was diagnostic for pneumonia in 18/26 cases (sensitivity 69%), whereas ultrasound was positive in 25/26 (sensitivity 96%). The feasibility of ultrasound was 100% and the examination was always performed in less than 5 min.


Conclusions Bedside chest ultrasound is a reliable tool for the diagnosis of pneumonia in the ED, probably being superior to CXR in this setting. It is likely that its wider use will allow a faster diagnosis, conducive to a more appropriate and timely therapy.


Lung ultrasound is an accurate diagnostic tool for the diagnosis of pneumonia in the emergency department
Emerg Med J. 2012 Jan;29(1):19-23

Tension pneumo treatment and chest wall thickness

An interesting ultrasound-based study challenges the assertion that a significant proportion of adults have a chest wall that is too thick for a standard iv cannula to reach the pleural space when attempting to decompress a tension pneumothorax. Perhaps there are other factors that make this technique so frequently ineffective.

The authors postulate that ultrasound measurements of chest wall thickness might be less than those obtained by CT scan due to the downward pressure on the tissues caused when the ultrasound transducer is placed on the chest, something that may also occur when a cannula is being pushed in, but would not be maintained after insertion of a cannula, perhaps leading to subsequent misplacement as the tissues recoil.

My view is that needle decompression might buy you time as a holding measure, but the patient with a tension pneumothorax will need a thoracostomy sooner rather than later.



Objective: Computed tomography measurements of chest wall thickness (CWT) suggest that standard- length angiocatheters (4.5 cm) may fail to decompress tension pneumothoraces. We used an alternative modality, ultrasound, to measure CWT. We correlated CWT with body mass index (BMI) and used national data to estimate the percentage of patients with CWT greater than 4.5 cm.


Methods: This was an observational, cross-sectional study of a convenience sample. We recorded standing height, weight, and sex. We measured CWT with ultrasound at the second intercostal space, midclavicular line and at the fourth intercostal space, midaxillary line on supine subjects. We correlated BMI (weight [in kilograms]/height2 [in square meters]) with CWT using linear regression. 95% Confidence intervals (CIs) assessed statistical significance. National Health and Nutrition Examination Survey results for 2007-2008 were combined to estimate national BMI adult measurements.


Results: Of 51 subjects, 33 (65%) were male and 18 (35%) were female. Mean anterior CWT (male, 2.1 cm; CI, 1.9-2.3; female, 2.3 cm; CI, 1.7-2.7), lateral CWT (male, 2.4 cm; CI, 2.1-2.6; female, 2.5 cm; CI 2.0-2.9), and BMI (male, 27.7; CI, 26.1-29.3; female, 30.0; CI, 25.8-34.2) did not differ by sex. Lateral CWT was greater than anterior CWT (0.2 cm; CI, 0.1-0.4; P <.01). Only one subject with a BMI of 48.2 had a CWT that exceeded 4.5 cm. Using national BMI estimates, less than 1% of the US population would be expected to have CWT greater than 4.5 cm.


Conclusions: Ultrasound measurements suggest that most patients will have CWT less than 4.5 cm and that CWT may not be the source of the high failure rate of needle decompression in tension pneumothorax.


Ultrasound determination of chest wall thickness: implications for needle thoracostomy

Am J Emerg Med. 2011 Nov;29(9):1173-7

Ultrasound to detect difficult laryngoscopy

A pilot study suggests sonographic measurements of neck soft tissue thickness may predict difficult laryngoscopy. Laryngoscopy was difficult in patients with increased thickness of the anterior neck soft tissue at the level of the hyoid bone and thyrohyoid membrane. The authors suggest that anterior neck soft tissue thickness cutoff value of 2.8 cm at the thyrohyoid membrane level can potentially be used to detect difficult laryngoscopy, but that this would require further validation since in this pilot study there were only six subjects in the difficult laryngoscopy group.



Objectives:  Prediction of difficult laryngoscopy in emergency care settings is challenging. The preintubation clinical screening tests may not be applied in a large number of emergency intubations due to the patient’s clinical condition. The objectives of this study were 1) to determine the utility of sonographic measurements of thickness of the tongue, anterior neck soft tissue at the level of the hyoid bone, and thyrohyoid membrane in distinguishing difficult and easy laryngoscopies and 2) to examine the association between sonographic measurements (thickness of tongue and anterior neck soft tissue) and difficult airway clinical screening tests (modified Mallampati score, thyromental distance, and interincisor gap).


Methods:  This was a prospective observational study at an academic medical center. Adult patients undergoing endotracheal intubation for an elective surgical procedure were included. The investigators involved in data collection were blinded to each other’s assessments. Demographic variables were collected preoperatively. The clinical screening tests to predict a difficult airway were performed. The ultrasound (US) measurements of tongue and anterior neck soft tissue were obtained. The laryngoscopic view was graded using Cormack and Lehane classification by anesthesia providers on the day of surgery. To allow for comparisons between difficult airway and easy airway groups, a two-sided Student’s t-test and Fisher’s exact test were employed as appropriate. Spearman’s rank correlation coefficients were used to examine the association between screening tests and sonographic measurements.


Results:  The mean (±standard deviation [SD]) age of 51 eligible patients (32 female, 19 male) was 53.1 (±13.2) years. Six of the 51 patients (12%, 95% confidence interval [CI] = 3% to 20%) were classified as having difficult laryngoscopy by anesthesia providers. The distribution of laryngoscopy grades for all subjects was 63, 25, 4, and 8% for grades 1, 2, 3, and 4, respectively. In this study, 83% of subjects with difficult airways were males. No other significant differences were noted in the demographic variables and difficult airway clinical screening tests between the two groups. The sonographic measurements of anterior neck soft tissue were greater in the difficult laryngoscopy group compared to the easy laryngoscopy group at the level of the hyoid bone (1.69, 95% CI = 1.19 to 2.19 vs. 1.37, 95% CI = 1.27 to 1.46) and thyrohyoid membrane (3.47, 95% CI = 2.88 to 4.07 vs. 2.37, 95% CI = 2.29 to 2.44). No significant correlation was found between sonographic measurements and clinical screening tests.


Conclusions:  This pilot study demonstrated that sonographic measurements of anterior neck soft tissue thickness at the level of hyoid bone and thyrohyoid membrane can be used to distinguish difficult and easy laryngoscopies. Clinical screening tests did not correlate with US measurements, and US was able to detect difficult laryngoscopy, indicating the limitations of the conventional screening tests for predicting difficult laryngoscopy.


Pilot Study to Determine the Utility of Point-of-care Ultrasound in the Assessment of Difficult Laryngoscopy
Acad Emerg Med. 2011 Jul;18(7):754-8