Josh D. Stanton

Measurement of oxygen concentration delivered via nasal cannulae by tracheal sampling

Oxygen is used in many clinical scenarios, however the variable performance of nasal cannulae makes determining the precise fraction of inspired oxygen (FiO2) difficult. We developed a novel method for measurement of the tracheal FiO2 using a catheter placed via bronchoscopy. We investigate the effects of oxygen delivery, respiratory rate, mouth position and estimated minute ventilation (VE) on the FiO2 delivered by nasal cannulae.

Resting and exercise response to altitude in patients with chronic obstructive pulmonary disease.

INTRODUCTION Exposure to altitude invariably involves some form of physical activity. There are limited data available to help predict the response to activity at altitude in patients with chronic obstructive pulmonary disease (COPD). The aim of the present study was to investigate the response to acute altitude exposure at rest and during exercise in patients with COPD. METHODS Sea level measures of cardio-pulmonary function were compared to the resting and exercise hypoxemic response at the summit of the Mt. Hutt ski field (2086 m), New Zealand, in 18 patients with COPD. RESULTS Ascent from sea level to altitude caused significant hypoxemia at rest (PaO2: 75 +/- 9 vs. 51 +/- 6 mmHg), and during a walk test (41 +/- 7 mmHg). At altitude, the walk test distance was reduced by 52%. Sea level PaO2 and SaO2 correlated with resting PaO2 (r = 0.69) and SaO2 (r = 0.79) at altitude. Diffusion capacity corrected for alveolar volume (K(CO)) correlated with resting SaO2 (r = 0.74) and exercise PaO2 (r = 0.75) at altitude. Aerobic capacity correlated with the walk test distance at altitude (r = 0.70). Spirometry, lung volumes, and ventilatory reserve did not correlate with the hypoxemic response to altitude. DISCUSSION Baseline arterial oxygen levels and K(CO) are key measures in predicting the hypoxemic response to acute altitude exposure in patients with COPD. The impairment in gas exchange associated with COPD is a significant mechanism causing altitude-related hypoxemia in this group.

Supplemental oxygen effect on hypoxemia at moderate altitude in patients with COPD.

INTRODUCTION Altitude exposure will cause moderate to severe hypoxemia in patients with chronic obstructive pulmonary disease (COPD). Supplemental oxygen can be used to attenuate this hypoxemia; however, individual response is variable and difficult to predict. The aim of this study was to assess the efficacy of oxygen supplementation in patients with COPD at a barometric pressure similar to that of a commercial aircraft cabin. METHODS Following sea-level (40 m) arterial blood gases measurements, 18 patients with COPD were driven to altitude (2086 m), where blood gases were repeated at rest and while on 2 L x min(-1) of supplementary oxygen (altitude O2). RESULTS Ascent from sea level to altitude caused significant hypoxemia (75 +/- 9 vs. 51 +/- 6 mmHg), which was partially reversed by supplemental oxygen (64 +/- 9 mmHg). Oxygen supplementation did not significantly alter PaCO2 levels (vs. altitude PaCO2). There was a significant relationship between the sea-level CaO2 versus the altitude O2 CaO2 (r = 0.89, P < 0.001). There was a significant relationship (r = 0.81, P < 0.001) between altitude-induced desaturation and resaturation with the administration of oxygen. There was a significant negative correlation (r = -0.74, P < 0.001) between baseline K(CO) and the improvement in CaO2 with the administration of oxygen. CONCLUSION Low-flow supplemental oxygen during acute altitude exposure will partially reverse altitude-induced hypoxemia in patients with COPD. Patients with diffusion impairments are likely to experience the greatest altitude desaturation, but will gain the most benefit from supplemental oxygen. Supplemental oxygen, delivered at 2 L x min(-1), should maintain clinically acceptable oxygenation during commercial air travel in patients with COPD.

Effect of salbutamol on the measurement of single-breath diffusing capacity

The bronchodilation and cardiovascular effects of bronchodilators may alter alveolar ventilation and perfusion distribution, which could subsequently affect single‐breath diffusing capacity of the lungs for carbon monoxide (DL,CO) measurements. The aim of this study was to investigate the effect of salbutamol on DL,CO in subjects with and without airway obstruction and reversibility.

The development of a community-based spirometry service in the Canterbury region of New Zealand: observations on new service delivery

In 2008, as part of the changes to develop integrated health care services in the Canterbury region of New Zealand, the local health board in collaboration with general practitioners, respiratory specialists and scientists introduced a programme for general practices to provide laboratory-quality spirometry in the community. The service adhered to the 2005 ATS/ERS international spirometry standards. The spirometry service was provided by trained practice nurses and community respiratory nurses, and was monitored and quality assured by certified respiratory scientists in the Respiratory Physiology Laboratory, Christchurch Hospital and CISO (Canterbury Initiative Services Organisation). These two organisations were responsible for organising training seminars and refresher courses on spirometry technique and interpretation of results. A total of 10 practices have now become approved spirometry providers, with the number of tests carried out in the primary care setting increasing gradually. Consistently high-quality spirometry tests have been obtained and are now presented on a centrally available results database for all hospital and community clinicians to review. Although the service has proved to be more convenient for patients, the tests have not been delivered as quickly as those carried out by the Respiratory Physiology Laboratory. However, the time scales for testing achieved by the community service is considered suitable for investigation of chronic disease. The success of the service has been dependent on several key factors including hospital and clinical support and a centralised quality assurance programme, a comprehensive training schedule and online clinical guidance and close integration between primary and secondary care clinicians.

Comparison of p50 determination by siemens and radiometer blood gas analysers with tonometry

Introduction The partial pressure of oxygen at half saturation (p50) is useful to detect altered oxygen-affinity states in isolated polycythaemia. Commercial gas analysers calculate this parameter from a single oxygen tension (PO 2 ) and saturation (sO 2 ) measurement utilising the Hill plot. The accuracy of these calculated p50s in patients with variant haemoglobin is not well documented. We compared results from two commercial analysers (Radiometer ABLFlex 800 and Siemens Rapidlab 1265) with tonometry for five patients with variant haemoglobin or red-cell enzyme deficiency and one control subject. Methods A reference interval for p50 was determined. Venous blood was analysed sequentially on the commercial analysers and by tonometry. Hill plots were prepared from the tonometry data and the Hill coefficient ( n ) derived, least-squares regression was used to calculate the standard error. Results The reference interval was 22–27mmHg. The p50 values showed good agreement between analysers, and between analysers and tonometry, except in the case of Haemoglobin Heathrow. Discussion Measuring p50 on a commercial gas analyser is convenient, readily available and shows good agreement with tonometry, except in haemoglobin variants with altered cooperativity ( n ), as in the case of Haemoglobin Heathrow. Gas-analyser derived numerical estimates of p50 for haemoglobin variants with altered cooperativity should be interpreted with caution; in this situation formal tonometry is more accurate.