The Dewey monitor: Pulse oximetry can independently detect hypoxia in a rebreather diver

Abstract

_____________________________________________________________________________________________________________________________________________________________________Rebreather diving has one of the highest fatality rates per man hour of any diving activity in the world. The leading cause of death is hypoxia, typically from equipment or procedural failures. Hypoxia causes very few symptoms prior to causing loss of consciousness. Additionally, since the electronics responsible for controlling oxygen levels in rebreathers often control their alarm systems, frequently divers do not receive any external warnings.This study investigated the use of a forehead pulse oximeter as an independent warning device in the event of rebreather failure. Ten test subjects (seven male, three female, median age 29, range 26-35) exercised at a targeted rate of 2 L/minute oxygen consumption while on a non-functional rebreather breathing loop (mean consumption achieved 2.09 ± 0.36 L/minute).Each subject was tested both at the surface and at pressurized depth of 77 fsw (starting pO 2 =0.7 atm). The data show that a pulse oximeter could be used to provide an Mk 16 rebreather diver with a minimum mean of 49 seconds (± 17 seconds SD) of warning time after a noticeable change in blood oxygen saturation (SpO 2 ≤ 95%) but before any risk of loss of consciousness (calculated SpO 2 ≤ 80%), so that the diver may take mitigating actions. No statistical difference in warning time was found between the tests at surface and at 77 fsw (P=0.46).

The Dewey Monitor: Pulse Oximetry can Warn of Hypoxia in an Immersed Rebreather Diver in Multiple Scenarios

“…The value of 95% was selected for consistency with Ref. 6 , which determined 95% to be a desirable level to avoid false positives for a SpO2-based hypoxia alarm.…”

“… 9 , 10 A previously reported pilot study investigated the utility of a forehead-worn pulse oximeter to detect falling oxygen levels in the rebreather’s breathing loop by measuring the blood oxygen saturation (SpO 2 ) of the diver rather than the partial pressure of oxygen (piO 2 ) inspired from the breathing loop. 6 The pilot study indicated that a forehead-worn oximeter may provide a minimum of 49 s (± 17 s SD) of warning time to the diver independently of the rebreather’s electronics package. However, this pilot study was performed with test subjects in the air rather than immersed in water, and thermal changes in water have been shown to cause delays of up to four minutes for pulse oximeters placed at certain measuring locations.…”

Comparison between Arterial Blood Gases and Oxygen Reserve Index™ in a SCUBA Diver: A Case Report

“…Another valid parameter is arterial oxygen saturation (SaO 2 ) or the amount of O 2 carried by the hemoglobin in arterial blood, expressed in terms of percentage, which is still measured in arterial blood. The most non-invasive method used is pulse oximetry, especially to detect and monitor for hypoxia by tracking peripheral oxygen saturation (SpO 2 ) [ 10 , 11 , 12 ]. In healthy people resting and breathing at sea level, a value above 95% is considered normal [ 13 ].…”

Gut Microbiome Alterations and Hepatic Metabolic Flexibility in the Gansu Zokor, Eospalax cansus: Adaptation to Hypoxic Niches

“…Gut microbiota, being emerged as a pivotal transducer of environmental factors, influences to exert effects on the heath and the metabolism of host animals ( 18 – 20 ), and its composition can be influenced by several environmental extremes, such as hypoxia, heat, and cold ( 21 , 22 ). Hypoxia is a life-threatening environmental factor to most mammals, which leads to loss of consciousness or even death within minutes ( 23 , 24 ). Indeed, even though hypoxia adaptation has been studied for several decades, the relationship between the gut microbiota and hypoxia has been receiving some attention only during the last few years.…”