Blood Gas Analyses in Hyperbaric and Underwater Environments: A Systematic Review

Background: Pulmonary gas exchange during diving or in a dry hyperbaric environment is affected by increased breathing gas density and possibly water immersion. During free diving there is also the effect of apnea. Few studies have published blood gas data in underwater or hyperbaric environments: this review summarizes the available literature and was used to test the hypothesis that arterial PO2 under hyperbaric conditions can be predicted from blood gas measurement at 1 atmosphere assuming a constant arterial/alveolar PO2 ratio (a:A). Methods: A systematic search was performed on traditional sources including arterial blood gases obtained on humans in hyperbaric or underwater environments. The a:A was calculated at 1 atmosphere absolute (ATA). For each condition, predicted PaO2 at pressure was calculated using the 1 ATA a:A, and the measured PaO2 was plotted against the predicted value with Spearman correlation coefficients. Results: Of 3640 records reviewed, 30 studies were included: 25 were reports describing values obtained in hyperbaric chambers, and the remaining were collected while underwater. Increased inspired O2 at pressure resulted in increased PaO2, although underlying lung disease in patients treated with hyperbaric oxygen attenuated the rise. PaCO2 generally increased only slightly. In breath-hold divers, hyperoxemia generally occurred at maximum depth, with hypoxemia after surfacing. The a:A adequately predicted the PaO2 under various conditions: dry (r=0.993, p< 0.0001); rest vs. exercise (r=0.999, p< 0.0001); and breathing mixtures (r=0.995, p< 0.0001). Conclusion: Pulmonary oxygenation under hyperbaric conditions can be reliably and accurately predicted from 1 ATA a:A measurements.

Point-of-care ultrasound in a multiplace hyperbaric chamber

Historically, electronic devices have been generally prohibited during hyperbaric oxygen (HBO2) therapy due to risk of fire in a pressurized, oxygen-rich environment. Point-of-care ultrasound (POCUS), however, has emerged as a useful imaging modality in diverse clinical settings. Hyperbaric chambers treating critically ill patients would benefit from the application of POCUS at pressure to make real-time patient assessments. Thus far, POCUS during HBO2 therapy has been limited due to required equipment modifications to meet safety standards. Here we demonstrate proof of concept, safety, and successful performance of an off-the-shelf handheld POCUS system (SonoSite iViz) in a clinical hyperbaric environment without need for modification.

Performance characteristics of high-frequency percussive ventilation under hyperbaric conditions

Introduction: Safe administration of critical care hyperbaric medicine requires specialized equipment and advanced training. Equipment must be tested in order to evaluate function in the hyperbaric environment. High-frequency percussive ventilation (HFPV) has been used in intensive care settings effectively, but it has never been tested in a hyperbaric chamber. Methods: Following a modified U.S. Navy testing protocol used to evaluate hyperbaric ventilators, we evaluated an HFPV transport ventilator in a multiplace hyperbaric chamber at 1.0, 1.9, and 2.8 atmospheres absolute (ATA). We used a test lung with analytical software for data collection. The ventilator uses simultaneous cyclic pressure-controlled ventilation at a pulsatile flow rate (PFR)/oscillatory continuous positive airway pressure (oCPAP) ratio of 30/10 with a high-frequency oscillation percussive rate of 500 beats per minute. Inspiratory and expiratory times were maintained at two seconds throughout each breathing cycle. Results: During manned studies, the PFR/oCPAP ratios were 26/6, 22/7, and 22.5/8 at an airway resistance of 20cm H2O/L/second and 18/9, 15.2/8.5, and 13.6/7 at an airway resistance of 50 cm/H2O/L/second at 1, 1.9, and 2.8 ATA. The resulting release volumes were 800, 547, and 513 mL at airway resistance of 20 cm H2O/L/sec and 400, 253, and 180 mL at airway resistance of 50 cm/H2O/L/sec at 1, 1.9, and 2.8 ATA. Unmanned testing showed similar changes. The mean airway pressure (MAP) remained stable throughout all test conditions; theoretically, supporting adequate lung recruitment and gas exchange. A case where HFPV was used to treat a patient for CO poisoning was presented to illustrate that HFPV worked well under HBO2 conditions and no complications occurred during HBO2 treatment. Conclusion: The HFPV transport ventilator performed adequately under hyperbaric conditions and should be considered a viable option for hyperbaric critical care. This ventilator has atypical terminology and produces unique pulmonary physiology, thus requiring specialized training prior to use.

Determination of Residual Volume as Indicator of the Respiratory Function of Divers

University “Ovidius” of Constanța, Faculty of Medicine, in collaboration with the Diving Center, has conducted several research studies regarding the evolution of the vital functions of divers in the hyperbaric environment. Their breathing is constantly adapting to withstand the physiological changes. Reducing the residual volume of the lungs is an essential parameter for improving respiratory function in the event of increased physical effort. The residual volume cannot be determined by spirometry. The medical researchers and engineers developed an original test plan and verified the residual volume of the subjects, by experimental determinations on groups of divers, during simulated diving, with air, at 18 m, in the Hyperbaric Complex of the Diving Center. The study is useful in the prevention of occupational diseases specific to divers and in knowing their limits of adaptation to the hyperbaric environment.