An evidence-based approach to emergency ultrasound.

Paramedics bring into the ED an elderly man who is complaining of right-sided chest and abdominal pain. Earlier this morning, a friend had arrived at the patient's home and found him on the floor at the bottom of the stairs. The patient is in pain, somewhat altered, and unable to provide further details about what happened. After numerous attempts, the paramedics were only able to place a 22-gauge peripheral line. On examination, his blood pressure is 98/55 mm Hg, heart rate is 118 beats per minute, respiratory rate is 32 breaths per minute, oxygen saturation is 94% on a nonrebreather, and temperature is 36.0 degrees C (96.8 degrees F). His Glasgow Coma Scale score is 12 (eyes 3, verbal 4, motor 5). Given the unclear events surrounding his presentation and the concern for trauma, the patient is boarded and collared. His chest is stable but tender, and because of noise in the resuscitation room, you have difficulty auscultating breath sounds. The abdominal examination is notable for marked tenderness over the right upper quadrant and right flank, with some guarding. There is also mild asymmetric swelling of his right lower extremity. The patient is critically ill, his history is limited, and at this point the differential is quite broad. You consider the possibility of a syncopal episode followed by a fall, with a closed head injury, blunt thoracic trauma, and blunt abdominal trauma. His hypotension could be secondary to hypovolemia (dehydration or blood loss due to a ruptured aortic aneurysm), heart failure (left- or right-sided dysfunction), cardiac tamponade, tension pneumothorax, or sepsis. Your ED recently purchased an ultrasound machine, you wonder whether bedside ultrasound can help narrow the differential and guide your resuscitation. You call over one of your new faculty members who just finished resident training; a fortunate decision for both you and the patient.

Focused maternal ultrasound by midwives in rural Zambia.

Point-of-care ultrasound is being increasingly implemented in resource-poor settings in an ad hoc fashion. We developed a focused maternal ultrasound-training program for midwives in a rural health district in Zambia. Four hundred forty-one scans were recorded by 21 midwives during the 6-month study period. In 74 scans (17%), the ultrasound findings prompted a change in clinical decision-making. Eight of the midwives were evaluated with a 14-question observed structured clinical examination (OSCE) and demonstrated a slight overall improvement with mean scores at 2 and 6 months of 10.0/14 (71%) and 11.6/14 (83%), respectively. Our pilot project demonstrates that midwives in rural Zambia can be trained to perform basic obstetric ultrasound and that it impacts clinical decision-making. Ultrasound skills were retained over the study period. More data is necessary to determine whether the introduction of ultrasound ultimately improves outcomes of pregnant women in rural Zambia.

Using MRI of the optic nerve sheath to detect elevated intracranial pressure.

The current gold standard for the diagnosis of elevated intracranial pressure (ICP) remains invasive monitoring. Given that invasive monitoring is not always available or clinically feasible, there is growing interest in non-invasive methods of assessing ICP using diagnostic modalities such as ultrasound or magnetic resonance imaging (MRI). Increased ICP is transmitted through the cerebrospinal fluid surrounding the optic nerve, causing distention of the optic nerve sheath diameter (ONSD). In this issue of Critical Care, Geeraerts and colleagues describe a non-invasive method of diagnosing elevated ICP using MRI to measure the ONSD. They report a positive correlation between measurements of the ONSD on MRI and invasive ICP measurements. If the findings of this study can be replicated in larger populations, this technique may be a useful non-invasive screening test for elevated ICP in select populations.

Correlation of optic nerve sheath diameter with direct measurement of intracranial pressure.

BACKGROUND: Measurements of the optic nerve sheath diameter (ONSD) using bedside ultrasound (US) have been shown to correlate with clinical and radiologic signs and symptoms of increased intracranial pressure (ICP). OBJECTIVES: Previous literature has identified 5 mm as the ONSD measurement above which patients exhibit either clinical or radiologic signs of elevated ICP. The goals of this study were to evaluate the association between ONSD and ICP and to validate the commonly used ONSD threshold of 5 mm using direct measurements of ICP as measured by ventriculostomy. METHODS: A prospective blinded observational study was performed using a convenience sample of adult patients in both the emergency department (ED) and the neurologic intensive care unit (ICU) who had invasive intracranial monitors placed as part of their clinical care. Ocular USs were performed with a 10(-5) MHz linear probe. Emergency physicians (EPs) with previous ocular US experience performed ONSD measurements while blinded to the contemporaneous ICP reading obtained directly from invasive monitoring. The association between ONSD and ICP was assessed with the Spearman rank correlation coefficient, and a receiver operator characteristic (ROC) curve was created to determine the optimal ONSD cutoff to detect ICP > 20 cm H2O. RESULTS: Thirty-eight ocular USs were performed on 15 individual patients. Spearman rank correlation coefficient of ONSD and ICP was 0.59 (p < 0.0005) demonstrating a significant positive correlation. An ROC curve was created to assess the ability of ONSD to distinguish an abnormal ICP greater than 20 cm H2O. The area under the ROC curve was 0.93 (95% confidence interval [CI] = 0.84 to 0.99). Based on inspection of the ROC curve, ONSD > 5 mm performed well to detect ICP > 20 cm H(2)O with a sensitivity of 88% (95% CI = 47% to 99%) and specificity of 93% (95% CI = 78% to 99%). CONCLUSIONS: Using an ROC curve the authors systematically confirmed the commonly used threshold of ONSD > 5 mm to detect ICP > 20 cm H2O. This study directly correlates ventriculostomy measurements of ICP with US ONSD measurements and provides further support for the use of ONSD measurements as a noninvasive test for elevated ICP.