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.

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.

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.

Correction and response to: Grommets in HBOT patients: GA vs. LA, unanswered questions.

We thank Gibbs and Commons for their interest in our paper. There is a key difference between the datasets for Commons et al and our study. Our data set, has grouped five years of data according to the calendar year. This is different from Commons et al's study population recruited between 01 June 2009 and 31 May 2010. We feel this may explain the difference of one case between the two papers in 2010. Our data collection used the standard clinic and operating theatre databases, and we were advised that there was no searchable clinical code for grommet procedures undertaken with local anaesthetic (LA) in the outpatient clinic. The alternative, to review many hundreds of patients, was considered beyond the study's scope. Instead, the TTH Hyperbaric Medicine Unit (HMU) database was used to recruit cases and cross checked with operating theatre data. We have since re-investigated the operating theatre database to identify any additional bilateral grommet procedures during 2008 to 2012 and cross checked these with the HMU database. This has identified one to four additional patients per year in the general anaesthesia (GA) group and one additional LA patient that meet the criteria for recruitment into the study. There was one further unconfirmed patient from each of 2008 and 2010, whose charts were unavailable for this response, and have not been included in this amendment. The corrected Figure 1 reflects these changes. Despite the additional cases, the frequency spike during 2010 remains. A published audit of the number of middle ear barotrauma (MEBT) cases between 2007-2010 also reports an increased incidence of MEBT in 2009-2010 compared with previous years at our unit. Possible reasons for this may be the introduction of new technology at the unit, in the form of the digital Macro View™ otoscope during this period, leading to a possible change in clinical practice and an increased detection of MEBT, or a lower threshold for ENT referral for grommet placement. Alternatively, a 'Hawthorne effect' from the conduct of a prospective study within the TTH HMU, during 2009-2010 may be considered. With the outliers removed using ROUT's test, the significant difference in the delay time to surgery remains (LA median 1, IQR 2, range 0-5 days; GA median 7.5, IQR 6, range 0-24 days; P < 0.0001; Figure 2). The data values of 98 days and 86 days from the GA group published in our paper are corrected to six days and 12 days respectively. On review, the first individual was found to have had two HBOT courses, and it was only in the second round of HBOT that an ENT referral for grommets was made. The second individual was found to have been offered two ENT referrals after experiencing MEBT, the first was followed by the patient declining further HBOT until representing to TTH HMU four months later and receiving prophylactic grommets before recommencing HBOT; this second ENT referral date has been used in the amended data. These corrections have not been found to change the primary outcome of statistical significance between the LA and GA groups. A delay of seven days may not be considered clinically relevant in the most common cases requiring HBOT, aside from affecting patient convenience and logistics as well as hospital efficiency and resources. In emergency cases, knowledge of factors able to reduce the delay for grommet insertion is clinically relevant. In centres where a long wait for GA is the norm, LA may convey a clinically important lesser waiting time. As a retrospective study, only data documented in the patient records could be studied, and patient discomfort was not consistently recorded in the charts. We would liken this to undertaking other surgical procedures, where clinicians often do not routinely document pain scores for the benefit of retrospective research. Several studies have examined patients' tolerance of grommets under LA, finding the technique tolerable.

Retrospective review of grommet procedures under general versus local anaesthesia among patients undergoing hyperbaric oxygen therapy.

INTRODUCTION: One significant side effect of hyperbaric oxygen treatment (HBOT) is middle ear barotrauma (MEBT) may require tympanostomy tube (grommet) insertion by the Ear, Nose and Throat service. Where timely HBOT is needed, routine insertion of grommets under local anaesthesia (LA) is becoming common. AIMS: To investigate the differences between patients receiving HBOT and concurrent grommets under LA versus general anesthesia (GA) at The Townsville Hospital (TTH). METHODS: A retrospective chart analysis of patients receiving HBOT between 2008 and 2012 and requiring grommets was undertaken. RESULTS: Thirty-one (5%) out of 685 patients treated with HBOT from 2008 to 2012 received grommets. Twelve cases received grommets under LA, and 19 under GA. Twenty out of the 31 cases had grommets following MEBT and the remainder prophylactically. Complications of grommet insertion comprised two cases with blocked grommets. There was a significant difference (P = 0.005) in the time in days from ENT referral to HBOT between the LA group (median 1 day, range 0-13 days) and the GA group (median 8 days, range 0-98 days). CONCLUSION: A greater number of hyperbaric patients received grommets under GA than LA at the TTH. Insertion of grommets under LA was safe, offering advantages to both the patient and the treating team in the setting of HBOT-associated otic barotrauma.

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.

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.

The use of deep tables in the treatment of decompression illness: the Hyperbaric Technicians and Nurses Association 2011 Workshop.

In August 2011, a one-day workshop was convened by the South Pacific Underwater Medicine Society and the Hyperbaric Technicians and Nurses Association to examine the use of deep recompression treatment tables for the treatment of decompression illness in Australia and New Zealand. The aim of the workshop was to develop a series of consensus statements to guide practice around the region. The workshop chose to focus the discussion on the use of 405 kPa (30 msw) maximum depth tables using helium-oxygen breathing periods, and covered indications, staffing and technical requirements. This report outlines the evidence basis for these discussions and summarises the series of consensus statements generated. These statements should assist hyperbaric facilities to develop and maintain appropriate policies and procedures for the use of such tables. We anticipate this work will lead to the formulation of a standard schedule for deep recompression to be developed at a future workshop.