Comparison of tissue oxygenation achieved breathing oxygen using different delivery devices and flow rates.

INTRODUCTION: Divers with suspected decompression illness require high concentration oxygen (O2). There are many different O2 delivery devices, with few data comparing their performance. This study evaluated O2 delivery, using tissue O2 partial pressure (PtcO2), in healthy divers breathing O2 via three different delivery devices. METHODS: Twelve divers had PtcO2 measured at six limb sites. Participants breathed O2 from: a demand valve using an intraoral mask with a nose clip (NC); a medical O2 rebreathing system (MORS) with an oronasal mask and with an intraoral mask; and a non-rebreather mask (NRB) at 15 or 10 L·min⁻¹ O2 flow. In-line inspired O2 FIO2) and nasopharyngeal FIO2 were measured. Participants provided subjective ratings of device comfort, ease of breathing, and overall ease of use. RESULTS: PtcO2 values and nasopharyngeal FIO2 were similar with the demand valve with intraoral mask, MORS with both masks and the NRB at 15 L·min⁻¹. PtcO2 and nasopharyngeal FIO2 values were significantly lower with the NRB at 10 L·min⁻¹. The NRB was rated as the most comfortable to wear, easiest to breathe with, and overall the easiest to use. CONCLUSION: Of the commonly available devices promoted for O2 delivery to injured divers, similar PtcO2 and nasopharyngeal FIO2 values were obtained with the three devices tested: MORS with an oronasal or intraoral mask, demand valve with an intraoral mask and NRB at a flow rate of 15 L·min⁻¹. PtcO2 and nasopharyngeal FIO2 values were significantly lower when the flow rate using the NRB was decreased to 10 L·min⁻¹.

Transcutaneous oximetry: variability in normal values for the upper and lower limb.

INTRODUCTION: Published normal transcutaneous oxygen partial pressures (PtcO2) for the chest and lower limb have defined tissue hypoxia as a value of < 40 mmHg (< 30 mmHg in some patients, < 50 mmHg in others). AIM: To determine 'normal' PtcO2 for the upper and lower limb in healthy, non-smoking adults using the Radiometer® TCM400 with tc Sensor E5250. METHOD: Thirty-two volunteers had transcutaneous oxygen measurements (TCOM) performed on the chest, upper and lower limbs breathing air, with leg then arm elevated and whilst breathing 100% oxygen. RESULTS: Room-air PtcO2 (mmHg, mean (95% confidence interval)) were: chest: 53.6 (48.7-58.5); upper arm: 60.0 (56.1-64.0); forearm: 52.3 (44.8-55.8); dorsum of hand: 50.2 (46.1-54.3); thenar eminence: 70.8 (67.7-73.8); hypothenar eminence: 77.9 (75.1-80.7); lateral leg: 50.2 (46.2-54.2); lateral malleolus: 50.5 (46.6-54.3); medial malleolus: 48.9 (45.6-52.1); dorsum, between first and second toe: 53.1 (49.2-57.0); dorsum, proximal to fifth toe: 58.5 (55.0 - -62.0); plantar, 1st MTP: 73.7 (70.3-77.1). Nineteen subjects had at least one room-air PtcO2 below 40 mmHg (nine upper limb, 13 lower limb, four chest). Approximately 10% lower limb PtcO2 were < 100 mmHg on normobaric oxygen. Only one subject at one site had an upper limb PtcO2 < 100 mmHg breathing oxygen. CONCLUSION: The broad dispersion in PtcO2 in our healthy cohort reflects the inherent biologic variability in dermal perfusion and oxygen delivery, making it difficult to define narrow, rigid 'normal' values. Thus, we cannot recommend a single PtcO2 value as 'normal' for the upper or lower limb. A thorough patient assessment is essential to establish appropriateness for hyperbaric oxygen therapy, with TCOM used as an aid to guide this decision and not as an absolute.

Vibration and bubbles: a systematic review of the effects of helicopter retrieval on injured divers.

INTRODUCTION: Vibration from a helicopter during aeromedical retrieval of divers may increase venous gas emboli (VGE) production, evolution or distribution, potentially worsening the patient's condition. AIM: To review the literature surrounding the helicopter transport of injured divers and establish if vibration contributes to increased VGE. METHOD: A systematic literature search of key databases was conducted to identify articles investigating vibration and bubbles during helicopter retrieval of divers. Level of evidence was graded using the Oxford Centre for Evidence-Based Medicine guidelines. A modified quality assessment tool for studies with diverse designs (QATSDD) was used to assess the overall quality of evidence. RESULTS: Seven studies were included in the review. An in vitro research paper provided some evidence of bubble formation with gas supersaturation and vibration. Only one prospective intervention study was identified which examined the effect of vibration on VGE formation. Bubble duration was used to quantify VGE load with no difference found between the vibration and non-vibration time periods. This study was published in 1980 and technological advances since that time suggest cautious interpretation of the results. The remaining studies were retrospective chart reviews of helicopter retrieval of divers. Mode of transport, altitude exposure, oxygen and intravenous fluids use were examined. CONCLUSION: There is some physical evidence that vibration leads to bubble formation although there is a paucity of research on the specific effects of helicopter vibration and VGE in divers. Technological advances have led to improved assessment of VGE in divers and will aid in further research.

Comparison of tissue oxygenation achieved breathing oxygen from a demand valve with four different mask configurations.

INTRODUCTION: High concentration normobaric oxygen (O2) is a priority in treating divers with suspected decompression illness. The effect of different O2 mask configurations on tissue oxygenation when breathing with a demand valve was evaluated. METHODS: Sixteen divers had tissue oxygen partial pressure (PtcO2) measured at six limb sites. Participants breathed O2 from a demand valve using: an intraoral mask (IOM®) with and without a nose clip (NC), a pocket face mask and an oronasal mask. In-line inspired O2 (FIO2) and nasopharyngeal FIO2 were measured. Participants provided subjective ratings of mask comfort, ease of breathing and holding in position. RESULTS: PtcO2 values and nasopharyngeal FIO2 (median and range) were greatest using the IOM with NC and similar with the IOM without NC. O2 measurements were lowest with the oronasal mask which also was rated as the most difficult to breathe from and to hold in position. The pocket face mask was reported as the most comfortable to wear. The NC was widely described as uncomfortable. The IOM and pocket face mask were rated best for ease of breathing. The IOM was rated as the easiest to hold in position. CONCLUSION: Of the commonly available O2 masks for use with a demand valve, the IOM with NC achieved the highest PtcO2 values. PtcO2 and nasopharyngeal FIO2 values were similar between the IOM with and without NC. Given the reported discomfort of the NC, the IOM without NC may be the best option.

Transcutaneous oximetry measurements of the leg: comparing different measuring equipment and establishing values in healthy young adults.

INTRODUCTION: Transcutaneous oximetry measurement (TCOM) is a non-invasive method of determining oxygen tension at the skin level using heated electrodes. AIM: To compare TCOM values generated by different machines and to establish lower limb TCOM values in a cohort of healthy individuals younger than 40 years of age. METHOD: Sixteen healthy, non-smoking volunteers aged 18 to 39 years were recruited. TCOM was obtained at six locations on the lower leg and foot using three different Radiometer machines. Measurements were taken with subjects lying supine, breathing air. RESULTS: Except for one sensor site, there were no statistical differences in measurements obtained by the different TCOM machines. There was no statistical difference in measurements comparing left and right legs. Room air TCOM values for the different lower leg sites were (mean (SD) in mmHg): lateral leg 61.5 (9.2); lateral ankle 61.1 (9.7); medial ankle 59.1 (10.8); foot, first and second toe 63.4 (10.6); foot, fifth toe 59.9 (13.2) and plantar foot 74.1 (8.8). The overall mean TCOM value for the lower limb was 61 (10.8; 95% confidence intervals 60.05-62.0) mmHg. CONCLUSION: Lower-leg TCOM measurements using different Radiometer TCOM machines were comparable. Hypoxia has been defined as lower-leg TCOM values of less than 40 mmHg in non-diabetic patients and this is supported by our measurements. The majority (96.9%) of the lower leg TCOM values in healthy young adults are above the hypoxic threshold.

An assessment of the performance of the Baxter elastomeric (LV10) Infusor™ pump under hyperbaric conditions.

INTRODUCTION: There are limited data on the use of elastomeric infusion pumps during hyperbaric oxygen treatment. AIM: This study evaluated the flow rate of the Baxter elastomeric LV10 Infusor™ pump under normobaric (101.3 kPa) and three hyperbaric conditions of 203 kPa, 243 kPa and 284 kPa. METHODS: Elastomeric pumps were secured to participants in the same manner as for a typical patient, except that a container collected the delivered antibiotic solution. Pumps and tubing were weighed before and after the test period to determine volume delivered and to calculate flow rates at sea level and the three commonly used hyperbaric treatment pressures at two different time periods, 0-2 hours (h) and 19-21 h into the infusion. RESULTS: The mean flow rates in ml·h⁻¹ (SD) were: 9.5 (0.4), 10.3 (0.6), 10.4 (0.6), 10.4 (0.5) at 0-2 h and 10.5 (1.0), 12.2 (0.6), 9.4 (0.5), 10.3 (0.9) at 19-21 h for the normobaric, 203 kPa, 243 kPa and 284 kPa conditions respectively. There was no significant association between flow rate and time period (P = 0.166) but the 203 kPa flow rates were significantly faster than the other flow rates (P = 0.008). In retrospect, the 203 kPa experiments had all been conducted with the same antibiotic solution (ceftazidime 6 g). Repeating that experimental arm using flucloxacillin 8 g produced flow rates of 10.4 (0.8) ml·h⁻¹, with no significant associations between flow rate and time period (P = 0.652) or pressure (P = 0.705). CONCLUSION: In this study, the flow rate of the Baxter LV10 Infusor™ device was not significantly affected by increases in ambient pressure across the pressure range of 101.3 kPa to 284 kPa, and flow rates were generally within a clinically acceptable range of 9-12 ml·h⁻¹. However, there was evidence that the specific antibiotic solution might affect flow rates and this requires further study.

Middle ear barotrauma in a tourist-oriented, condensed open-water diver certification course: incidence and effect of language of instruction.

INTRODUCTION: In Professional Association of Diving Instructors (PADI) Open Water Diver certification courses that cater to tourists, instruction is often condensed and potentially delivered in a language that is not the candidate's native language. OBJECTIVE: To assess the incidence of middle ear barotrauma (MEBt) in open-water diver candidates during a condensed four-day certification course, and to determine if language of instruction affects the incidence of MEBt in these divers. METHOD: The ears of participating diving candidates were assessed prior to commencing any in-water compression. Tympanic membranes (TM) were assessed and graded for MEBt after the confined and open-water training sessions. Tympanometry was performed if the candidate had no movement of their TM during Valsalva. Photographs were taken with a digital otoscope. RESULTS: Sixty-seven candidates participated in the study. Forty-eight had MEBt at some time during their course. MEBt was not associated with instruction in non-native language (adjusted odds ratio = 0.82; 95% confidence intervals 0.21-3.91). There was also no significant association between the severity of MEBt and language of instruction. CONCLUSION: Open-water diver candidates have a high incidence of MEBt. Education in non-native language does not affect the overall incidence of MEBt.

A comparison of the tissue oxygenation achieved using different oxygen delivery devices and flow rates.

INTRODUCTION: High-concentration normobaric oxygen (O2) administration is the first-aid priority in treating divers with suspected decompression illness. The best O2 delivery device and flow rate are yet to be determined. AIM: To determine whether administering O2 with a non-rebreather mask (NRB) at a flow rate of 10 or 15 L·min ⁻¹ or with a demand valve with oronasal mask significantly affects the tissue partial pressure of O2 (PtcO2) in healthy volunteer scuba divers. METHODS: Fifteen certified scuba divers had PtcO2 measured at six positions on the arm and leg. Measurements were taken with subjects lying supine whilst breathing O2 from a NRB at 10 or 15·L·min⁻¹, a demand valve with an adult Tru-Fit oronasal mask and, as a reference standard, an oxygen 'head hood'. End-tidal carbon dioxide was also measured. RESULTS: While none of the emergency delivery devices performed as well as the head hood, limb tissue oxygenation was greatest when O2 was delivered via the NRB at 15 L·min⁻¹. There were no clinically significant differences in end-tidal carbon dioxide regardless of the delivery device or flow rate. CONCLUSION: Based on transcutaneous oximetry values, of the commonly available emergency O2 delivery devices, the NRB at 15 L·min ⁻¹ is the device and flow rate that deliver the most O2 to body tissues and, therefore, should be considered as a first-line pre-hospital treatment in divers with suspected decompression illness.

Association of microparticles and neutrophil activation with decompression sickness.

Decompression sickness (DCS) is a systemic disorder, assumed due to gas bubbles, but additional factors are likely to play a role. Circulating microparticles (MPs)--vesicular structures with diameters of 0.1-1.0 µm--have been implicated, but data in human divers have been lacking. We hypothesized that the number of blood-borne, Annexin V-positive MPs and neutrophil activation, assessed as surface MPO staining, would differ between self-contained underwater breathing-apparatus divers suffering from DCS vs. asymptomatic divers. Blood was analyzed from 280 divers who had been exposed to maximum depths from 7 to 105 meters; 185 were control/asymptomatic divers, and 90 were diagnosed with DCS. Elevations of MPs and neutrophil activation occurred in all divers but normalized within 24 h in those who were asymptomatic. MPs, bearing the following proteins: CD66b, CD41, CD31, CD142, CD235, and von Willebrand factor, were between 2.4- and 11.7-fold higher in blood from divers with DCS vs. asymptomatic divers, matched for time of sample acquisition, maximum diving depth, and breathing gas. Multiple logistic regression analysis documented significant associations (P < 0.001) between DCS and MPs and for neutrophil MPO staining. Effect estimates were not altered by gender, body mass index, use of nonsteroidal anti-inflammatory agents, or emergency oxygen treatment and were modestly influenced by divers' age, choice of breathing gas during diving, maximum diving depth, and whether repetitive diving had been performed. There were no significant associations between DCS and number of MPs without surface proteins listed above. We conclude that MP production and neutrophil activation exhibit strong associations with DCS.

Transcutaneous oximetry: normal values for the lower limb.

INTRODUCTION: Current guidelines for transcutaneous oximetry measurement (TCOM) for the lower limb define tissue hypoxia as a transcutaneous oxygen partial pressure < 40 mmHg. Values obtained with some newer machines and current research bring these reference values into question. AIM: To determine 'normal' TCOM values for the lower limb in healthy, non-smoking adults using the TCM400 oximeter with tc Sensor E5250. METHOD: Thirty-two healthy, non-smoking volunteers had TCOM performed at six positions on the lower leg and foot. Measurements were taken with subjects lying supine breathing air, then with leg elevated and whilst breathing 100 % oxygen. RESULTS: Room-air TCOM values (mean mmHg, 95 % confidence interval (CI) ) were: lateral leg 41.3, CI 37.8 to 44.7; lateral malleolus 38.6, CI 34.1 to 43.1; medial malleolus 43.9, CI 40.2 to 47.6; dorsum, between first and second toe 39.3, CI 35.9 to 42.7; dorsum, proximal to fifth metatarsal-phalangeal joint 46.4, CI 43.4 to 49.3; plantar 52.3, CI 49.6 to 55.1. Using the currently accepted value of less than 40 mmHg for tissue hypoxia, 24 of our 32 'healthy' subjects had at least one air sensor reading that would have been classified as hypoxic. Seventeen subjects had TCOM values less than 100 mmHg when breathing 100 % normobaric oxygen. CONCLUSION: Normal lower limb TCOM readings using the TCOM400 with tc Sensor E5250 may be lower than 40 mmHg, used to define tissue hypoxia, but consistent with the wide range of values found in the literature. Because of the wide variability in TCOM at the different sensor sites we cannot recommend one TCOM value as indicative of tissue hypoxia. A thorough clinical assessment of the patient is essential to establish appropriateness for hyperbaric oxygen treatment, with TCOM used as an aid to help guide this decision, but not as an absolute diagnostic tool.

The efficacy of oxygen wafting using different delivery devices, flow rates and device positioning.

BACKGROUND: Oxygen "wafting" provides a non-contact oxygen alternative for uncooperative paediatric patients in the emergency department (ED). The aim of this study was to identify the combination of oxygen delivery device, flow rate and device positioning that delivers the highest concentration of wafted oxygen. METHODS: ED nursing staff were surveyed to determine current oxygen wafting practice. A simulated patient and oxygen sensor were used to compare wafted oxygen concentrations for six delivery devices in various positions and oxygen flow rates. RESULTS: Only oxygen tubing and the paediatric non-rebreather mask consistently delivered wafted oxygen concentrations above 30%. The paediatric non-rebreather held below the face produced concentrations ranging from 26.1% (10 cm) to 39.8% (5 cm). At 15 L/min, tubing held in front of the face produced concentrations ranging from 31.2% (15 cm) to 56.7% (5 cm); reducing the flow rate to 6-8 L/min had no meaningful effect on the delivered oxygen concentration. When tubing was used below the face, flow rates between 6 and 8 L/min produced somewhat higher concentrations than 15 L/min (5 cm: 36.3% vs. 30.9%). CONCLUSIONS: When delivering oxygen by wafting, the highest oxygen concentrations are achieved when positioning tubing 5-15 cm in front of the face or positioning tubing or a paediatric non-rebreather mask 5-10 cm below the face at 10-15 L/min flow. This should be considered when using oxygen wafting in the ED.

'Did not waits': a regional Australian emergency department experience.

OBJECTIVE: Describe the characteristics, reasons for leaving and outcomes of patients who did not wait (DNW) to be seen by a health practitioner in a regional Australian ED. METHODS: Prospective observational study of a convenience sample of ED DNW patients presenting to The Townsville Hospital between June 2011 and July 2012. Seven days from each month were selected, and DNW patients presenting on those days were enrolled. An investigator attempted to contact every DNW patient by telephone in the following week to elicit reasons for leaving, subsequent health contacts, outcomes and suggestions for system improvements. Additional outcome information was obtained from hospital electronic medical records. RESULTS: Nearly 15 000 patients presented on the study days, with 648 (4.3%) DNWs: 415 (64.0%) adults, 193 (29.8%) children (1-16 years old) and 40 (6.2%) infants. Thirty-eight (5.9%) patients who DNW were Australasian Triage Scale (ATS) category 3, 546 (84.3%) were ATS category 4 and 64 (9.9%) were ATS category 5. Most DNW patients presented on Sundays and between 1600 and 2359. Just over half of the patients who DNW (52.9%) sought additional medical treatment, with 4.9% requiring subsequent hospital admission. Three psychiatric patients who DNW required urgent mental health interventions organised by the investigators. Frustration with perceived waiting times was the most common reason for leaving without being seen. CONCLUSIONS: Regional Australia ED patients who DNW often still require medical care, with approximately 1 in 20 requiring subsequent hospital admission. Patients with psychiatric conditions who DNW might be at particular risk.

A prospective analysis of independent patient risk factors for middle ear barotrauma in a multiplace hyperbaric chamber.

INTRODUCTION: Middle ear barotrauma (MEBT) is the most common complication of hyperbaric oxygen therapy (HBOT). We wished to determine whether independent risk factors could predict which patients will require tympanostomy tubes in order to continue HBOT. METHODS: Data regarding demographics, medical history and physical examination were collected prospectively over one year. Multivariate logistic regression was used to analyse the data. RESULTS: One hundred and six patients were included. The cumulative risk of MEBT over the first five treatments was 35.8% and that for needing tympanostomy tubes was 10.3%, while that for needing tubes at any time was 13.2%. Risk factors for MEBT on bivariate analysis were older age, history of ENT radiation and anticoagulant use. Risk factors for requiring tympanostomy tubes included a history of cardiovascular disease and patients being treated for an infective condition. The adjusted multivariate logistic model identified history of difficulty equalising as the only characteristic significantly associated with MEBT during the first five treatments, adjusted odds ratio (AOR) (95%CI): 11.0 (1.1 - 111.7). Being female, AOR (95%CI): 24.7 (1.8 - 339.7), and having a history of cardiovascular disease, AOR (95%CI): 20.7 (2.0 - 215.3), were significantly associated with the need for tympanostomy tubes during the first five HBOT, but there was no significant association between any other characteristics and the need for tubes at any point. CONCLUSION: Despite some significant risk factors for MEBT being identified, we were unable to predict accurately enough which patients needed tympanostomy tubes during their HBOT to recommend these being placed prophylactically in selected patients.

Transcutaneous oximetry measurement: normal values for the upper limb.

INTRODUCTION: Several studies define normal transcutaneous oximetry measurements (TCOM) for the chest and lower limb, but not the upper limb. Standardised healthy-subject reference values for upper limb TCOM would make interpretation of these measurements in disease or injury more meaningful. AIM: To determine 'normal' TCOM values for the upper limb in healthy non-smoking adults. METHOD: Thirty-two healthy volunteers (16 male, 16 female) had TCOM performed on the chest and at five upper limb positions: lateral aspect of the upper arm midway between the shoulder and elbow; lateral aspect of the forearm, dorsum of the hand, thenar and hypothenar eminences. Measurements were taken using the TCM400 Monitoring System (Radiometer) with subjects breathing room air and whilst breathing 100% oxygen. RESULTS: Room-air TCOM values (mean (SD), 95% confidence interval (CI)) were: chest: 50 (11.4) mmHg, 95% CI 46.0 to 54.2; upper arm: 53 (9.3) mmHg, 95% CI 49.7 to 56.4; forearm: 45 (11.3) mmHg, 95% CI 40.4 to 48.6; dorsum of hand: 39 (8.5) mmHg, 95% CI 35.5 to 41.7; thenar eminence: 54 (7.7) mmHg, 95% CI 51.7 to 57.2; and hypothenar eminence: 57 (7.5) mmHg, 95% CI 54.1 to 59.6. All readings showed a substantial increase when subjects breathed 100% oxygen. Using the currently accepted threshold for tissue hypoxia of < 40 mmHg, six forearm and 14 dorsum of the hand TCOM readings would have been classified as hypoxic. CONCLUSION: Normal upper limb TCOM readings are less than those established for the lower limb. Using lower-limb reference standards could result in false-positive determinations of tissue hypoxia. We recommend TCOM ≤ 30 mmHg as indicative of tissue hypoxia in the upper arm, thenar and hypothenar eminences, and < 20 mmHg in the forearm and dorsum of the hand.

'Sea legs': sharpened Romberg test after three days on a live-aboard dive boat.

INTRODUCTION: The sharpened Romberg test (SRT) is commonly used by diving and hyperbaric physicians as an indicator of neurological decompression illness (DCI). People who spend a prolonged time on a boat at sea experience impairment in their balance on returning to shore, a condition known as mal de debarquement ('sea legs'). This conditioning of the vestibular system to the rocking motion of a boat at sea may impact on the utility of the SRT in assessing a diver with potential DCI after a live-aboard dive trip. AIM: To assess the impact 'sea legs' has on the SRT after three days on a live-aboard dive trip. METHODS: Thirty-nine staff and passengers of a three-day, live-aboard dive trip performed a SRT before and after their journey, with assessment of potential variables, including middle ear barotrauma, alcohol consumption, sea-sickness and occult DCI. RESULTS: There was no statistically significant impact on SRT performance, with 100% completion pre-trip and 35 out of 36 divers (97.2%) post-trip. There were trends towards more attempts being required and time needed for successful SRT post-trip, but these were not statistically significant. There was a small, but noteworthy incidence of middle-ear barotrauma, with seven people affected pre-trip, and 13 post-trip. There was a higher incidence in student divers. Middle-ear barotrauma did not appear to have a direct impact on SRT performance. CONCLUSION: There was no significant impact on SRT performance resulting from 'sea legs' after three days at sea. Recreational divers, especially dive students, have a substantial incidence of mild middle ear barotrauma.