Air Bubbles Introduced From Peripheral Intravenous Lines Into the Cerebral Venous System: Response

We wish to thank Dr. Horton for his interest and clinical insights regarding our report of embolism in the superior ophthalmic vein after intravenous fluid injection using a peripheral intravenous cannula (1). As Dr Horton notes, passage from the subclavian to the internal jugular vein would present the most direct pathway for an air bubble ascending from the upper limb to the head.

Letters to the Editor Air Bubbles Introduced From Peripheral Intravenous Lines Into the Cerebral Venous System I n the Journal of Neuro-Ophthalmology, RossiterThornton et al (1) illustrate air from a peripheral intravenous line lodged in the superior ophthalmic vein of an 83-year-old woman. We reported a similar case 25 years ago; our case differed in that air was trapped in the cavernous sinus (2). Numerous case reports have documented this phenomenon, with air bubbles visible on head computerized tomography imaging in 27/12,880 (0.2%) of patients after intravenous line placement (3). Rossiter-Thornton et al state that "an air bubble can ascend through the superior vena cava into the dense venous networks of the head and neck if the thorax and head are erect at the time of injection." They also suggest that atrial fibrillation might have contributed to air embolism by causing venous stasis in the atria. In fact, once an air bubble reaches the heart, it cannot enter the cerebral venous circulation. It passes through the pulmonary artery into the lungs where it is absorbed. However, if a cardiac wall defect, such as a patent foramen ovale, is present, air can pass from the right heart to the left heart, sometimes causing stroke from arterial air embolism. In our case, and that described by Rossiter-Thornton, air most likely traveled up the arm, traversed the right subclavian vein, and entered the internal jugular vein. There is no reason to postulate that the air ever entered either the right brachiocephalic vein or the superior vena cava. Once in the internal jugular vein, air ascends through the inferior petrosal sinus to reach the cavernous sinus. It remained there in our case, but in Rossiter-Thornton's case, Air Bubbles Introduced From Peripheral Intravenous Lines Into the Cerebral Venous System: Response W e wish to thank Dr. Horton for his interest and clinical insights regarding our report of embolism in the superior ophthalmic vein after intravenous fluid injection using a peripheral intravenous cannula (1). As Dr Horton notes, passage from the subclavian to the internal jugular vein would present the most direct pathway for an air bubble ascending from the upper limb to the head. Our choice of wording was intended to connote, however, that retrograde passage from more proximally in the venous system remains possible, as established by the work of Schlimp et al (2), where they demonstrated retrograde flow of an air bubble against a column of venous blood. In addition, reflux from the right atrium is commonly identified on dynamic Letters to the Editor: J Neuro-Ophthalmol 2019; 39: 437-439 it continued to rise, entering the superior ophthalmic vein. Note that it was arrested at the highest point, just where the superior ophthalmic vein must duck under the superior orbital rim to join the supraorbital vein. Many clinicians are careless about purging air from syringes and intravenous tubing. Air bubbles can also originate from the dead space in the hub of needles and catheters, as well as the Luer tip of syringes. During surgery, when I point out air bubbles traveling through the intravenous line toward a patient's arm, I am usually met with a shrug from the anesthetist. Although introduction of small amounts of air rarely causes harm, it is a potential hazard that should be avoided (4). Perhaps, a more clever design of the connections between syringes, needles, intravenous tubing, and catheters could alleviate this problem. Jonathan C. Horton, MD, PhD Departments of Ophthalmology, Neurology, and Physiology, University of California, San Francisco, San Francisco, California The author reports no conflicts of interest. REFERENCES 1. Rossiter-Thornton M, Varma A, Verma N, Hewitt AW. Orbital air embolism after intravenous injection. J Neuroophthalmol. 2018;38:486-487. 2. Horton JC, Langer PD, Turner GE. Free air in the cavernous sinus as an incidental finding. J Clin Neuroophthalmol. 1993;13:50- 53. 3. Rubinstein D, Symonds D. Gas in the cavernous sinus. AJNR Am J Neuroradiol. 1994;15:561-566. 4. Brull SJ, Prielipp RC. Vascular air embolism: a silent hazard to patient safety. J Crit Care. 2017;42:255-263. imaging and tends to be increased in atrial fibrillation (3) and apnea (4). We would thus submit that an air embolus in the superior vena cava-perhaps, even one that has not yet traversed a competent tricuspid valve (5)-may still be prone to retrograde embolization, provided the head and neck are elevated at the time of injection, and the embolus is buoyant. In any event, we share Dr. Horton's concern regarding the ease with which air emboli can be introduced during peripheral injections. This risk is vividly illustrated during echocardiographic bubble studies and intraoperative transesophageal echocardiography during cardiac surgery, where cavitations and bubbles can be visualized in the right heart after peripheral injection. The ophthalmic corollary is peripheral injection during fluorescein angiography-which is often conducted under time pressure and in conditions of poor lighting. Our case and Dr. Horton's patient illustrate how air bubbles contained in peripherally injected fluids can embolize to the head and neck, and agree that these are an avoidable risk. 437 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Letters to the Editor Michael Rossiter-Thornton, FRANZCO Department of Ophthalmology, Royal Hobart Hospital, Tasmania, Australia Aditya Varma, FRANZCR Department of Radiology, Royal Hobart Hospital, Tasmania, Australia Nitin Verma, FRANZCO, MD Alex W. Hewitt, FRANZCO, PhD Department of Ophthalmology, Royal Hobart Hospital, Hobart, Australia Menzies Research Institute, University of Tasmania, Hobart, Australia Utility of Magnetic Resonance Imaging Features for Improving the Diagnosis of Idiopathic Intracranial Hypertension Without Papilledema: Comment W e were interested in the article by Mallery et al (1) discussing the utility of MRI features to improve the diagnosis of idiopathic intracranial hypertension (IIH) in patients without papilledema. This is a challenging topic because the presence of a normal optic disc appearance in patients with IIH could suggest to perform a lumbar puncture whenever a chronic headache of unknown cause is diagnosed, even in the presence of a normal fundus examination. The authors cleverly advise to use MRI for such a purpose pointing out the possibility to detect, among the other signs, the optic nerve sheath diameter (ONSD) increase. We agree with the authors because to perform MRI in these patients is mandatory, so to detect such an increase could be a nonexpensive and easy to obtain data. On the other hand, patients with IIH need to be followed to determine the normalization of the intracranial pressure, and the ONSD regularization could be a valid alternative to the lumbar puncture. Unfortunately, to perform MRI for such a purpose could be difficult and expensive. For this reason, we suggest to execute an ONSD measurement with ultrasound that since the 70s has been used to identify the presence of intracranial hypertension, as suggested by several publications on this topic (2). We recommend not to use the B-scan for such measurements because it is well known to be subjective and not very reliable due to, among the others, the so-called blooming effect 438 The authors report no conflicts of interest. REFERENCES 1. Rossiter-Thornton M, Varma A, Verma N, Hewitt AW. Orbital air embolism after intravenous injection. J Neuroophthalmol. 2018;38:486-487. 2. Schlimp C, Loimer T, Rieger M, Lederer W, Schmidts MB. The potential of venous air embolism ascending retrograde to the brain. J Forensic Sci. 2005;50:906-909. 3. Aviram G, Cohen D, Steinvil A, Shmueli H, Keren G, Banai S, Berliner S, Rogowski O. Significance of reflux of contrast medium into the inferior vena cava on computerized tomographic pulmonary angiogram. Am J Cardiol. 2012;109:432-437. 4. Appleton C, Hatle L, Popp R. Superior vena cava and hepatic vein Doppler echocardiography in healthy adults. J Am Coll Cardiol. 1987;10:1032-1039. 5. Badano L, Muraru D, Enriquez-Sarano M. Assessment of functional tricuspid regurgitation. Eur Heart J. 2013;35:1875- 1885. (3-7), but to use the standardized A-scan technique. In fact, this ultrasound method can also safely distinguish between an optic nerve increase due to IIH from another one due to inflammation or optic nerve tumors (8-13). We are aware that this technique is not very simple to use, and that some skill is required; however the specificity and sensitivity of the A-scan, which is inexpensive and friendly to use, could be the best solution for these cases (14,15). Maddalena De Bernardo, MD, PhD Livio Vitiello, MD Nicola Rosa, MD Department of Medicine, Surgery and Dentistry, Scuola Medica Salernitana, University of Salerno, Salerno, Italy The authors report no conflicts of interest. REFERENCES 1. Mallery RM, Rehmani OF, Woo JH, Chen YJ, Reddi S, Salzman KL, Pinho MC, Ledbetter L, Tamhankar MA, Shindler KS, Digre KB, Friedman DI, Liu GT. Utility of magnetic resonance imaging features for improving the diagnosis of idiopathic intracranial hypertension without papilledema. J Neuroophthalmol. [published online ahead of print June 18, 2019] doi: 10.1097/WNO.0000000000000767. 2. Ossoinig KC. Standardized echography of the optic nerve. In: Till P, ed. Documenta Ophthalmologica Proceedings Series Vol 55, Ophthalmic Echography 13. Dordrecht, Netherlands: Springer Netherlands, 1990:3-99. 3. Rosa N, Vitiello L, De Bernardo M. Optic nerve sheath diameter measurement in hypoxic ischaemic brain injury after cardiac arrest. Resuscitation. 2019;138:310-311. Letters to the Editor: J Neuro-Ophthalmol 2019; 39: 437-439 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited.