Feasibility study of a smartphone pupillometer and evaluation of its accuracy.

Measurement of pupillary characteristics, such as pupillary unrest in ambient light, and reflex dilation have been shown to be useful in a variety of clinical situations. Dedicated pupillometers typically capture images in the near-infrared to allow imaging in both light and darkness. However, because a subset of pupillary measurements can be acquired with levels of visible light suitable for conventional cameras, it is theoretically possible to capture data using general purpose cameras and computing devices such as those found on smartphones. Here we describe the development of a smartphone-based pupillometer and compare its performance with a commercial pupillometer. Smartphone pupillometry software was developed and then compared with a commercial pupillometer by performing simultaneous scans in both eyes, using the smartphone pupillometer and a commercial pupillometer. The raw scans were compared, as well as a selected pupillary index: pupillary unrest in ambient light. In 77% of the scans the software was able to successfully identify the pupil and iris. The raw data as well as calculated values of pupillary unrest in ambient light were in clinically acceptable levels of agreement; Bland-Altman analysis of raw pupil measurements yielded a 95% confidence interval of 0.26 mm. In certain situations a smartphone pupillometer may be an appropriate alternative to a commercial pupillometer.

Preliminary study of ergonomic behavior during simulated ultrasound-guided regional anesthesia using a head-mounted display.

A head-mounted display provides continuous real-time imaging within the practitioner's visual field. We evaluated the feasibility of using head-mounted display technology to improve ergonomics in ultrasound-guided regional anesthesia in a simulated environment. Two anesthesiologists performed an equal number of ultrasound-guided popliteal-sciatic nerve blocks using the head-mounted display on a porcine hindquarter, and an independent observer assessed each practitioner's ergonomics (eg, head turning, arching, eye movements, and needle manipulation) and the overall block quality based on the injectate spread around the target nerve for each procedure. Both practitioners performed their procedures without directly viewing the ultrasound monitor, and neither practitioner showed poor ergonomic behavior. Head-mounted display technology may offer potential advantages during ultrasound-guided regional anesthesia.

Human subthalamic neuron spiking exhibits subtle responses to sedatives.

BACKGROUND: During deep brain stimulation implant surgery, microelectrode recordings are used to map the location of targeted neurons. The effects produced by propofol or remifentanil on discharge activity of subthalamic neurons were studied intraoperatively to determine whether they alter neuronal activity. METHODS: Microelectrode recordings from 11 neurons, each from individual patients, were discriminated and analyzed before and after administration of either propofol or remifentanil. Subthalamic neurons in rat brain slices were recorded in patch-clamp to investigate cellular level effects. RESULTS: Neurons discharged at 42 ± 9 spikes/s (mean ± SD) and showed a common pattern of inhibition that lasted 4.3 ms. Unique discharge profiles were evident for each neuron, seen using joint-interval analysis. Propofol (intravenous bolus 0.3 mg/kg) produced sedation, with minor effects on discharge activity (less than 2.0% change in frequency). A prolongation of recurrent inhibition was evident from joint-interval analysis, and propofol's effect peaked within 2 min, with recovery evident at 10 min. Subthalamic neurons recorded in rat brain slices exhibited inhibitory synaptic currents that were prolonged by propofol (155%) but appeared to lack tonic inhibitory currents. Propofol did not alter membrane potential, membrane resistance, current-evoked discharge, or holding current during voltage clamp. Remifentanil (0.05 mg/kg) had little effect on overall subthalamic neuron discharge activity and did not prolong recurrent inhibition. CONCLUSIONS: These results help to characterize the circuit properties and feedback inhibition of subthalamic neurons and demonstrate that both propofol and remifentanil produce only minor alterations of subthalamic neuron discharge activity that should not interfere with deep brain stimulation implant surgery.

100% Nitrous Oxide in the Oxygen Line: How Could This Happen in a Modern Anesthesia Machine?

The inadvertent crossover between O2 and N2O pipelines has become extremely rare in practice. We describe a case where it was possible to ventilate with 100% N2O instead of the intended 100% O2 on a modern anesthesia delivery system (Dräger Apollo; Drägerwerk AG & Co KgaA, Lübeck, Germany). This was the result of the incorrect assembly of diameter index safety system (DISS) components during preventative maintenance that defeated the DISS failsafe system. To make incorrect assembly easier to avoid, DISS component labeling could be more prominent and color-coded, or the internal construction of the gas manifold could incorporate DISS.

A poor correlation exists between oscillometric and radial arterial blood pressure as measured by the Philips MP90 monitor.

In anesthesia and critical care, invasive arterial blood pressure monitoring is the gold standard against which other methods of monitoring are compared. In this assessment of the Philips MP90 monitor, the objective was to determine whether or not oscillometric measurements were within the accuracy standards set by the Association for the Advancement of Medical Instrumentation (AAMI) and the British Hypertension Society (BHS). Three hundred and one invasive and noninvasive paired measurements were obtained from eleven adult patients on the neurosurgical service at Stanford University Medical Center. Bland-Altman plots were created to assess agreement between the two measurement systems. Paired correlation analysis, bias and precision calculations were performed. Oscillometric blood pressure measurements correlated with arterial measurements yielding Pearson r values of 0.68, 0.67 and 0.62 for systolic, diastolic and mean pressures, respectively (P < 0.01.) Mean differences with 95% confidence intervals were -3.8 mmHg +/- 13.6, -2.4 mmHg +/- 10.0, and 4.0 mmHg +/- 13.1 for systolic, diastolic and mean pressures, respectively. The mean difference for these measurements was

An Anesthesia Attempt to Be Green: How Do You Waste Your Carbon Dioxide Absorbers?

Operating room waste is categorized as noncontaminated solid waste (SW) and regulated medical waste (RMW). RMW is treated by autoclaving at an increased economic and environmental cost. We evaluated these costs with a focus on the disposable carbon dioxide (CO2) absorbers. At our institution, exhausted CO2 absorbers were discarded as RMW. We collaborated with product representatives, anesthesia and perioperative staff, and waste management personnel to identify opportunities and barriers for recycling and waste reduction. Ultimately, we agreed to discard CO2 absorbers as SW instead of RMW, a strategy that is practical, less expensive, and more environmentally appropriate.

Is it more difficult to cannulate the right internal jugular vein in morbidly obese patients than in nonobese patients?

BACKGROUND: The placement of an internal jugular vein (IJV) catheter is considered to be more difficult in morbidly obese patients. The objective of this study was to compare the success of simulated IJV puncture between morbidly obese patients and a nonobese control group. METHODS: Thirty-four morbidly obese patients with body mass index (BMI, kg/m(2)) >/=40 were compared with 36 patients with BMI < 30. Right IJV puncture was simulated using an ultrasound probe directed towards the sternal notch at the midpoint between the sternal notch and the mastoid process. The investigator placing the probe was blinded as to the image being created on the ultrasound machine. Success rate was assessed at three different head rotation angles from midline; 0 degrees , 30 degrees , and 60 degrees . RESULTS: There was no statistically significant difference in successful simulated IJV puncture between two groups for any of the head positions. However, there was a higher incidence of the carotid artery (CA) puncture in the morbidly obese patient group when the head rotation was advanced from neutral position to 60 degrees (p < 0.05). In addition, the ultrasound showed significantly more overlapping of the IJV over the CA in morbidly obese patients at 0 degrees (p < 0.05) and 30 degrees (p < 0.05). Our results show no statistically significant difference in success rate of IJV puncture between morbidly obese patients and nonobese patients. Keeping the head in a neutral position in morbidly obese patients minimizes the overlapping of the IJV over the CA and the risk of CA puncture. CONCLUSION: However, due to the fact that even in the neutral position there is a significant increase in overlap between IJV and CA, we recommend the use of ultrasound guidance for IJV cannulation in obese patients.

Does a delay in performing an activated clotting (ACT) test really matter? A study in nonheparinized blood and a single ACT machine.

Activating clotting time (ACT) is a point-of-care, blood clotting test used to monitor anticoagulation. Recently, institutional requirements have required that ACT testing be completed outside the operating room with trained, certified personnel other than anesthesia staff. For this reason, in this study, we looked at whether a delay in processing an ACT makes a significant difference to the ACT results. Twenty patients between 18 and 65 years of age consented to the study, each undergoing non-cardiac surgery, with no intraoperative administration of heparin. The study was approved by our Institutional Review Board. A blood sample was taken from the patient's arterial line in the operating room. Immediately afterward, 1 mL was placed into each of two ACT cartridges and the measurement was done in a Medtronic ACT2 machine. The first ACT value was 126.9 +/- 14.5 seconds. The ACT value at approximately 30 minutes was 108.3 +/- 20.3 seconds (p < .0001). The time between the first and last measurements was 29.4 +/- 3.0 minutes. The results suggest that the ACT values decrease over time between sampling all measurements. At approximately 30 minutes, the ACT values average 15% less than the control measurements. Therefore, it would seem prudent to determine ACT values immediately in the operating room without any delay, using point-of-care testing.

The effect of deliberate hypercapnia and hypocapnia on intraoperative blood loss and quality of surgical field during functional endoscopic sinus surgery.

BACKGROUND: Anesthetic management during functional endoscopic sinus surgery is aimed at minimizing bleeding and establishing a near-perfect surgical field. We investigated whether deliberate intraoperative hypercapnia and hypocapnia may affect blood loss and quality of surgical field through a proposed modulating effect of different carbon dioxide (CO2) tension levels on nasal vasculature. METHODS: One hundred and eighty patients were randomly assigned to normocapnia (end-tidal CO2 [ETco2] 37 +/- 2 mm Hg), hypercapnia (ETco2 60 +/- 2 mm Hg), and hypocapnia (ETco2 27 +/- 2 mm Hg) groups. Anesthetic management was with propofol and remifentanil infusions, nitrous oxide, and moderate controlled hypotension. Blood loss and operating conditions were assessed by the surgeon who was blinded to group assignment. Differences among the study groups, the effect of the study group and time on ETco2 levels and hemodynamic variables, and the association of blood loss with surgical covariates were analyzed. RESULTS: There were no differences in blood loss and quality of surgical field among the study groups. Patients in the hypocapnia group demonstrated the highest, and in the hypercapnia group, the lowest, requirements for remifentanil, labetalol, and administration of the antihypertensive medications in general. The computed tomography-graded severity of sinonasal disease and duration of surgery were the only independent predictors of intraoperative blood loss. CONCLUSIONS: CO2 management during functional endoscopic sinus surgery does not influence operating conditions or blood loss.

Capnoperitoneum During Peroral Endoscopic Myotomy-Recognition and Management: A Case Report.

Peroral endoscopic myotomy (POEM) is a minimally invasive procedure for treating esophageal achalasia. During POEM, carbon dioxide is insufflated under pressure into the esophagus and stomach, which can cause clinically significant capnoperitoneum, capnomediastinum, or capnothorax. We present a case in which gas accumulation in the abdomen during POEM had adverse effects on ventilation. Once the cause was recognized, needle decompression of the abdomen led to immediate improvement in ventilation.