Takafumi Azami

Dispersal of Respiratory Droplets With Open vs Closed Oxygen Delivery Masks: Implications for the Transmission of Severe Acute Respiratory Syndrome

Nosocomial transmission of droplet-borne respiratory infections such as severe acute respiratory syndrome (SARS) may be influenced by the choice of oxygen face mask. A subject inhaled saline mist and exhaled through three oxygen masks to illustrate the pattern of dispersal of pulmonary gas. In two commonly used masks, exhaled gas formed a plume emanating from the side vents, while a third mask with a valved manifold, which was modified by adding a respiratory filter, retained the droplets. Maintaining respiratory isolation during the administration of oxygen may reduce the risk of the nosocomial transmission of respiratory infections such as SARS.

A novel skin-traction method is effective for real-time ultrasound-guided internal jugular vein catheterization in infants and neonates weighing less than 5 kilograms.

BACKGROUND:Internal jugular vein (IJV) catheterization in pediatric patients is sometimes difficult because of the small sizes of veins and their collapse during catheterization. To facilitate IJV catheterization, we developed a novel skin-traction method (STM), in which the point of puncture of the skin over the IJV is stretched upward with tape during catheterization. In this study, we examined whether the STM increases the cross-sectional area of the vein and thus facilitates catheterization. METHODS:This was a prospective study conducted from December 2006 to June 2008. We enrolled 28 consecutive infants and neonates weighing <5 kg who underwent surgery for congenital heart disease. The patients were randomly assigned to a group in which STM was performed (STM group) or a group in which it was not performed (non-STM group). The cross-sectional area and diameter of the right IJV in the flat position and 10° Trendelenburg position with and without applying STM were measured. We determined time from first skin puncture to the following: (a) first blood back flow, (b) insertion of guidewire, and (c) insertion of catheter. Number of punctures, success rate, complications, and degree of IJV collapse during advancement of the needle (estimated as decrease of anteroposterior diameter during advancement of the needle compared with the diameter before advancement) were also examined. RESULTS:STM significantly increased the cross-sectional area and the anteroposterior diameter of the IJV in both positions. The time required to insert the catheter was significantly shorter in the STM group, probably mainly due to a shorter guidewire insertion time. The degree of IJV collapse during advancement of the needle was much lower in the STM group. CONCLUSIONS:STM facilitates IJV catheterization in infants and neonates weighing <5 kg by enlarging the IJV and preventing vein collapse.

Modified oxygen mask to induce target levels of hyperoxia and hypercarbia during radiotherapy: a more effective alternative to carbogen.

Purpose: Carbogen has long been under investigation as an adjuvant to radiotherapy of tumors. A major factor confounding its evaluation is its inconsistency in raising blood partial pressure of CO2 (pCO2). We investigated whether a new partial rebreathing method would provide better control of pCO2 than carbogen. Methods and materials: We compared the efficacy of each method in 10 healthy volunteers. Volunteers breathed 1.5, 3 and 5% carbogen in 5-min stages via the usual non-rebreathing circuit. All the volunteers then breathed 100% O2 through a commercial sequential gas delivery (SGD) circuit modified by attaching a reservoir to its exhalation port. Hypercarbia was induced by step reductions in oxygen flow to the SGD circuit. We monitored minute ventilation and end-tidal pCO2 (ETpCO2) as a surrogate for its arterial value. Results: Inhalation of 1.5 and 3% carbogen did not increase ETpCO2 from baseline (40 ± 1.5 mmHg); 5% carbogen increased ETpCO2 to 45 ± 1.6 mmHg (p < 0.001). With the SGD circuit, reducing O2 flow to 4.3 ± 0.7 l/min increased ETpCO2 in all subjects from 41 ± 2.0 mmHg (baseline) to 46 ± 2.1 mmHg (p < 0.001). Voluntary hyperventilation reduced ETpCO2 with 5% carbogen but not with SGD (p = 0.379). Conclusions: We confirm previous observations that carbogen inhalation does not result in a predictable rise in ETpCO2 and suggest that a precise and stable target ETpCO2 can instead be induced by simply controlling O2 flow into a modified SGD circuit. We hoped that the reliable control of pCO2 will enable studies that address first, the efficacy of raising ETpCO2 on specific tumor blood flow, and eventually, its benefit as an adjuvant to radiotherapy.

Modified N95 Mask Delivers High Inspired Oxygen Concentrations While Effectively Filtering Aerosolized Microparticles

Study objective In a pandemic, hypoxic patients will require an effective oxygen (O2) delivery mask that protects them from inhaling aerosolized particles produced by others, as well as protecting the health care provider from exposure from the patient. We modified an existing N95 mask to optimize O2 supplementation while maintaining respiratory isolation. Methods An N95 mask was modified to deliver O2 by inserting a plastic manifold consisting of a 1-way inspiratory valve, an O2 inlet and a gas reservoir. In a prospective repeated-measures study, we studied 10 healthy volunteers in each of 3 phases, investigating (1) the fractional inspiratory concentrations of O2 (FIO2) delivered by the N95 O2 mask, the Hi-Ox80 O2 mask, and the nonrebreathing mask during resting ventilation and hyperventilation, each at 3 O2 flow rates; (2) the ability of the N95 mask, the N95 O2 mask, and the nonrebreathing mask to filter microparticles from ambient air; and (3) to contain microparticles generated inside the mask. Results The FIO2s (median [range]) delivered by the Hi-Ox80 O2 mask, the N95 O2 mask, and the nonrebreathing mask during resting ventilation, at 8 L/minute O2 flow, were 0.90 (0.79 to 0.96), 0.68 (0.60 to 0.85), and 0.59 (0.52 to 0.68), respectively. During hyperventilation, the FiO2s of all 3 masks were clinically equivalent. The N95 O2 mask, but not the nonrebreathing mask, provided the same efficiency of filtration of internal and external particles as the original N95, regardless of O2 flow into the mask. Conclusion An N95 mask can be modified to administer a clinically equivalent FiO2 to a nonrebreathing mask while maintaining its filtration and isolation capabilities.

A New Enteral Diet, MHN-02, Which Contains Abundant Antioxidants and Whey Peptide, Protects Against Carbon Tetrachloride–Induced Hepatitis:

BACKGROUND Inflammatory or oxidative stress is related to various diseases, including not only inflammatory diseases, but also diabetes, cancer, and atherosclerosis. The aim of this study was to evaluate the anti-inflammatory effects of a new enteral diet, MHN-02, which contains abundant antioxidants and whey peptide. The study also investigated the ability of MHN-02 to attenuate lethality, liver injury, the production of inflammatory cytokines, and the production of oxidized products using a carbon tetrachloride-induced rat model of severe fulminant hepatitis. METHODS Male Sprague-Dawley rats were fed either a control diet or the MHN-02 diet for 14 days and injected with 2 mL/kg of carbon tetrachloride. Survival of rats was monitored from day 0 to day 3. To evaluate liver injury, inflammation, and oxidative stress, blood and liver samples were collected, and aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, interleukin 6, tumor necrosis factor-α, and superoxide dismutase activity as a free radical scavenger were measured. A portion of the liver was evaluated histologically. RESULTS The survival rates of rats receiving the MHN-02 diet and the control diet were 90% and 55%, respectively. In the MHN-02 diet group, levels of serum liver enzymes and serum cytokines were significantly lower than in the control group. Superoxide dismutase activity in the MHN-02 diet was significantly higher in the MHN-02 group. Pathological lesions were significantly larger in the control group. CONCLUSION Supplementation of enteral diets containing whey peptide and antioxidants may protect against severe hepatitis.

Skin-traction method prevents the collapse of the internal jugular vein caused by an ultrasound probe in real-time ultrasound-assisted guidance

PurposeReal-time ultrasound-assisted guidance for catheterization of the internal jugular vein (IJV) is known to be useful, especially for a small-sized vein, which is difficult to catheterize. However, one of the problems with real-time ultrasound-assisted guidance is that the ultrasound probe itself can collapse the vein. We have developed a novel “skintraction method (STM)”, in which the puncture point of the skin over the IJV is stretched upwards with several pieces of surgical tape in the cephalad and caudal directions with the aim being to facilitate catheterization of the IJV. We examined whether this method increased the compressive force required to collapse the IJV.MethodsIn ten volunteers, the compressive force required to collapse the right IJV, and the cross-sectional area and anteroposterior and transverse diameters of the IJV were measured with ultrasound imaging in the supine position (SP) with or without the STM or in the Trendelenburg position of 10° head-down (TP) without the STM.ResultsThe compressive force to required to collapse the vein was increased significantly with the STM, while the crosssectional area and anteroposterior diameter of the vein in the SP with STM were similar to those in the TP without the STM.ConclusionWith the STM, not only the cross-sectional area but also the compressive force required to collapse the IJV increased. Thus, the STM may facilitate real-time ultrasoundassisted guidance for catheterization of the IJV by maintaining the cross-sectional area of the vein during the guidance.

Severe hyponatremia occurring after surgical stress in a patient with mitochondrial disease

A 53-year-old man with mitochondrial disease underwent gastrectomy because of gastric cancer. Three days after the surgery, he developed severe hyponatremia (Na, 106 mmol·l−1) together with hypovolemic shock and lactic acidosis. Despite the hyponatremia, his urine sodium concentration was high, suggesting renal salt wasting. Although mitochondrial diseases are not common and hyponatremia in patients with these diseases is not well known, clinicians should pay close attention to serum sodium levels and maintain them properly.

Calculation Of O2 Consumption During Low-Flow Anesthesia from Tidal Gas Concentrations, Flowmeter, and Minute Ventilation

We present the principles of a new method to calculate O2 consumption (VO2) during low-flow anesthesia with a circle circuit when the source gas flows, end-tidal O2 concentrations and patient inspired minute ventilation are known. This method was tested in a model with simulated O2 uptake and CO2 production. The difference between calculated VO2 and simulated VO2 was 0.01 ± 0.02 L/min. A similar approach can be used to calculate uptake of inhaled anesthetics. At present, with this method, the limiting factor in precision of measurement of VO2 and uptake of anesthetic is the precision of measurement of gas flow and gas concentration (especially O2 concentration in end-tidal gas, FETO2) available in clinical anesthetic units.

Cardiac output increases the rate of carbon monoxide elimination in hyperpneic but not normally ventilated dogs.

PurposeThe very high solubility of carbon monoxide (CO) in blood suggests that its elimination depends predominantly on ventilation and not perfusion. Nevertheless, hyperventilation is not used for CO elimination because of the adverse effects of hypocapnia. With isocapnic hyperpnea (IH), ventilation can be increased considerably without hypocapnia. This raises the issue of whether CO elimination is limited by perfusion during IH. We studied the effect of increasing cardiac output on t1/2, the half-time of decline of blood carboxyhemoglobin concentration ([COHb]), during normal ventilation (NV) and during IH.MethodsAfter ethics approval was received, 13 pentobarbital-anesthetized ventilated dogs were exposed to CO to increase their [COHb]. They were then ventilated with NV or IH. At each level of ventilation, dogs were randomly assigned to treatment with dobutamine (to increase cardiac output) or to no dobutamine treatment. After the return of [COHb] to control levels, each dog was re-exposed to CO and treated with the same ventilatory mode, but the alternative inotropic treatment.ResultsGas exchange, [COHb], and hemodynamic measures were recorded during the study. Cardiac index values in the IH group were 4.1 ± 0.5 and 8.2 ± 1.2 l·min−1·m−2 without and with dobutamine infusion, respectively. Dobutamine infusion was associated with a reduction in t1/2 from 20.3 ± 3.6 to 16.9 ± 2.4 min (P = 0.005) in the IH group, but no change in the NV group.ConclusionThese findings suggest that CO elimination during IH treatment is limited at least partly by pulmonary blood flow and may therefore be further augmented by increasing cardiac output.

The skin-traction method increases the cross-sectional area of the internal jugular vein by increasing its anteroposterior diameter

PurposeWe developed a novel “skin-traction method” in which the puncture point of the skin over the internal jugular vein (IJV) is stretched upward with several pieces of surgical tape in the cephalad and caudad directions to facilitate cannulation of the IJV. We investigated whether this method increases the cross-sectional area of the IJV.MethodsIn 11 healthy volunteers, the cross-sectional area, anteroposterior diameter, and transverse diameter of the right IJV (RIJV) were recorded by ultrasound echo at head tilts of +10°, +5°, 0°, −5°, and −10° with and without the skin-traction method.ResultsThe skin-traction method significantly increased the cross-sectional areas of the RIJV at head tilts of +10°, +5°, and 0°. In the flat position, the skin-traction method increased the cross-sectional area of the RIJV from 1.21 ± 0.44 cm2 to 1.75 ± 0.60 cm2 (44.6% increase), which is almost the same as that in the Trendelenburg position without this method (1.60 ± 0.54 cm2 at −5° and 1.83 ± 0.56 cm2 at −10°). The anteroposterior diameter of the RIJV was significantly increased in all positions with this method, although the transverse diameter was not.ConclusionThis method significantly increased the cross-sectional area of the RIJV by increasing the anteroposterior diameter of the RIJV. Even in the flat position, this method was almost as efficacious as the Trendelenburg position. This method thus appears to facilitate IJV cannulation.