Effect of isobaric breathing gas shifts from air to heliox mixtures on resolution of air bubbles in lipid and aqueous tissues of recompressed rats

Comparison of treatment recompression tables for neurologic decompression illness in swine model

BACKGROUND

Significant reductions in ambient pressure subject an individual to risk of decompression illness (DCI); with incidence up to 35 per 10,000 dives. In severe cases, the central nervous system is often compromised (>80%), making DCI among the most morbid of diving related injuries. While hyperbaric specialists suggest initiating recompression therapy with either a Treatment Table 6 (TT6) or 6A (TT6A), the optimal initial recompression treatment for severe DCI is unknown.

METHODS

Swine were exposed to an insult dive breathing air at 7.06 ATA (715.35 kPa) for 24 min followed by rapid decompression at a rate of 1.82 ATA/min (184.41 kPa/min). Swine that developed neurologic DCI within 1 hour of surfacing were block randomized to one of four United States Navy Treatment Tables (USN TT): TT6, TT6A-air (21% oxygen, 79% nitrogen), TT6A-nitrox (50% oxygen, 50% nitrogen), and TT6A-heliox (50% oxygen, 50% helium). The primary outcome was the mean number of spinal cord lesions, which was analyzed following cord harvest 24 hours after successful recompression treatment. Secondary outcomes included spinal cord lesion incidence and gross neurologic outcomes based on a pre- and post- modified Tarlov assessment. We compared outcomes among these four groups and between the two treatment profiles (i.e. TT6 and TT6A).

RESULTS

One-hundred and forty-one swine underwent the insult dive, with 61 swine meeting inclusion criteria (43%). We found no differences in baseline characteristics among the groups. We found no significant differences in functional neurologic outcomes (p = 0.77 and 0.33), spinal cord lesion incidence (p = 0.09 and 0.07), or spinal cord lesion area (p = 0.51 and 0.17) among the four treatment groups or between the two treatment profiles, respectively. While the trends were not statistically significant, animals treated with TT6 had the lowest rates of functional deficits and the fewest spinal cord lesions. Moreover, across all animals, functional neurologic deficit had strong correlation with lesion area pathology (Logistic Regression, p < 0.01, Somers' D = 0.74).

CONCLUSIONS

TT6 performed as well as the other treatment tables and is the least resource intensive. TT6 is the most appropriate initial treatment for neurologic DCI in swine, among the tables that we compared.

Helium preconditioning protects against neonatal hypoxia-ischemia via nitric oxide mediated up-regulation of antioxidases in a rat model

This study aimed to investigate the role of nitric oxide (NO) in the neuroprotective effects of helium preconditioning (He-PC) in a neonatal hypoxia/ischemia (HI) rat model. Seven-day old rat pups were divided into normal control group, He-PC group, HI group, He-PC+HI group, L-NAME+HI group and L-NAME+He-PC+HI group. HI was induced by exposure to 80% oxygen for 90 min. He-PC was conducted with 70% helium-30% oxygen for three 5-min periods. Three hours after He-PC, animals in control group and He-PC group were sacrificed, and the brain was collected for the detection of NO content. At 24h after HI, animals in control group, HI group, He-PC+HI group, and L-NAME+He-PC+HI group were sacrificed, and the brain was collected for detection of infarct ratio, antioxidases (SOD, HO-1 and Nrf2), DNA binding activity of Nrf2 and TUNEL staining. Three weeks later, the neurological function and brain atrophy were determined. Results showed pretreatment with L-NAME alone failed to exert protective effect on HI. He-PC significantly increased NO content, reduced the brain infarct area, increased anti-oxidases expression and DNA binding activity of Nrf2, decreased the apoptotic cells, and improved the neurological function and brain atrophy. In addition, this protection was markedly inhibited by L-NAME (a non-selective NOS inhibitor). These findings suggest that the He-PC may induce NO production to activate Nrf2, exerting neuroprotective effect on neonatal HI.

Mechanical ventilation and resuscitation under water: Exploring one of the last undiscovered environments--A pilot study

INTRODUCTION

Airway management, mechanical ventilation and resuscitation can be performed almost everywhere--even in space--but not under water. The present study assessed the technical feasibility of resuscitation under water in a manikin model.

METHODS

Tracheal intubation was assessed in a hyperbaric chamber filled with water at 20 m of depth using the Pentax AWS S100 video laryngoscope, the Fastrach™ intubating laryngeal mask and the Clarus optical stylet with guidance by a laryngeal mask airway (LMA) and without guidance. A closed suction system was used to remove water from the airways. A test lung was ventilated to a maximum depth of 50 m with a modified Oxylator(®) EMX resuscitator with its expiratory port connected either to a demand valve or a diving regulator. Automated chest compressions were performed to a maximum depth of 50 m using the air-driven LUCAS™ 1.

RESULTS

The mean cumulative time span for airway management until the activation of the ventilator was 36 s for the Fastrach™, 57 s for the Pentax AWS S100, 53s for the LMA-guided stylet and 43 s for the stylet without LMA guidance. Complete suctioning of the water from the airways was not possible with the suction system used. The Oxylator(®) connected to the demand valve ventilated at 50 m depth with a mean ventilation rate of 6.5 min(-1) vs. 14.7 min(-1) and minute volume of 4.5 l min(-1) vs. 7.6 l min(-1) compared to the surface. The rate of chest compression at 50 m was 228 min(-1) vs. 106 min(-1) compared to surface. The depth of compressions decreased with increasing depth.

CONCLUSION

Airway management under water appears to be feasible in this manikin model. The suction system requires further modification. Mechanical ventilation at depth is possible but modifications of the Oxylator(®) are required to stabilize ventilation rate and administered minute volumes. The LUCAS™ 1 cannot be recommended at major depth.