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An Audit of Hypoxaemia, Hyperoxaemia, Hypercapnia and Acidosis in Blood Gas Specimens

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An Audit of Hypoxaemia, Hyperoxaemia, Hypercapnia and Acidosis in Blood Gas Specimens 1 *Section of Pulmonary Medicine, Dept of Pathology, Ioannina 4 Constantopoulos SG, Malamou-Mitsi V, Goudevenos JA, et al. University Hospital, #Pulmonary Dept ‘‘G. Hatzikosta’’ General High incidence of malignant pleural mesothelioma in neighbour- " + ing villages of Northwest Greece. Respiration 1987; 51: 266–271. Hospital, Depts of Hygiene and Epidemiology, and Anatomy, 5 Constantopoulos SH, Goudevenos JA, Saratzis NA, et al. Metsovo University of Ioannina, Ioannina, Greece. lung: pleural calcifications and restrictive lung function in North- Western Greece; environmental exposure to mineral fiber as Correspondence: S.H. Constantopoulos, Dept of Medicine, etiology. Environ Res 1985; 38: 319–331. Section of Pulmonary Medicine, Medical School, University of 6 Langer AM, Nolan RP, Constantopoulos SH, et al. Association of Ioannina, Ioannina 45500, Greece. E-mail: [email protected] Metsovo lung and pleural mesothelioma with exposure to tremolite-containing whitewash. Lancet 1987; 1: 965–967. 7 Constantopoulos SH, Saratzis NA, Goudevenos JA, et al. Tremolite Statement of Interest: None declared. white-washing and pleural calcifications. Chest 1987; 92: 709–712. 8 Sakellariou K, Malamou-Mitsi V, Haritou A, et al. Malignant pleural mesothelioma from non-occupational asbestos exposure in REFERENCES Metsovo (North West Greece); slow end of an epidemic? Eur Respir 1 Hillerdal G. Mesothelioma: cases associated with non-occupational J 1996; 9: 1206–1210. and low dose exposures. Occup Environ Med 1999; 56: 505–513. 9 Senyig˘it A, Babayig˘it C,Go¨kirmak M, et al. Incidence of malignant 2 Constantopoulos SH. Environmental mesothelioma associated with pleural mesothelioma due to environmental asbestos fiber ex- tremolite asbestos: lessons from the experiences of Turkey, Greece, posure in the southeast of Turkey. Respiration 2000; 67: 610–614. Corsica, New Caledonia and Cyprus. Regul Toxicol Pharmacol 2008; 10 Darcey DJ, Alleman T. Occupational and environmental exposure 52: 110–115. to asbestos. In: Roggli VL, Oury TD, Sporn ThA, eds. Pathology of 3 Baris YI, Simonato M, Artvinli M, et al. Epidemiological and Asbestos-Associated Diseases. 2nd Edn. Springer, New York, 2004; environmental evidence of the health effects of exposure to erionite pp. 17–33. fibres: a four year study in the Cappadocian region of Turkey. Int J Cancer 1987; 39: 10–17. DOI: 10.1183/09031936.00017011 An audit of hypoxaemia, hyperoxaemia, hypercapnia and acidosis in blood gas specimens To the Editors: We studied an anonymised database consisting of blood gas analysis results from 3,524 specimens sent to the Biochemistry The emergency management of hypoxaemic patients requires Laboratory of the Salford Royal University Hospital (Salford, clinicians to avoid the hazard of dangerous hypoxaemia due to UK) between June and November 2007. More than 95% of under-treatment with oxygen, whilst also avoiding the hazards of samples were from adult patients (neonatal and paediatric hypercapnic respiratory failure (iatrogenic hypercapnia) and samples were analysed separately). About 5% of samples were oxygen toxicity, which may be caused by over-treatment with arterialised earlobe capillary samples. Most emergency depart- oxygen. In the past, many clinicians acted cautiously by giving ment and ICU samples were analysed on separate blood gas high concentrations of oxygen to all potentially hypoxaemic analysers and were not included in this analysis. The results are patients and a culture evolved that ‘‘more is better’’. However, summarised in table 1. The saturation bands were chosen to since the 1960s, it has been known that some patient groups, correspond with the recommended target saturation ranges in particularly those with chronic obstructive pulmonary disease the BTS guidelines, in addition to saturation bands above, below (COPD), are especially vulnerable to uncontrolled oxygen therapy and between these ranges. The majority of patients were and a recent randomised study showed that mortality in this receiving oxygen therapy at the time of sampling. 2,693 samples patient group was doubled when high-concentration oxygen was had information about the inspired oxygen concentration, of used compared with controlled oxygen therapy [1–4]. It has which 19% were said to be breathing air at the time of sampling also been demonstrated that hyperoxaemia is associated with and 81% were on oxygen therapy ranging 24–100%. increased mortality in patients with stroke, and in survivors of cardiac resuscitation and critically ill patients in the intensive care More than a quarter of samples (26.9%) demonstrated hyper- unit (ICU) [5–7]. The British Thoracic Society (BTS) guidelines for capnia with carbon dioxide tension (PCO2) .6.0 kPa or 45 mmHg emergency oxygen use recommend a target oxygen saturation consistent with type 2 respiratory failure, but only 198 (5.6%) range of 94–98% for most emergency medical patients and a lower samples had evidence of type 1 respiratory failure (oxygen target range of 88–92% for those at risk of hypercapnic respiratory tension (PO2) ,8.0 kPa or 60 mmHg with normal PCO2). Detailed failure [8]. The proportion of emergency medical patients for results are summarised in table 1. whom each target range is appropriate is not known but a recent study of 1,022 emergency ambulance patients in the UK reported 1,458 (41.3%) samples had oxygen saturation .98% and 1,074 that 4% of ambulance patients had exacerbated COPD as the main samples (30% of all samples) were hyperoxaemic with PO2 diagnosis and 5.5% of non-COPD patients had saturation ,90% at .15.0 kPa (112 mmHg), which is the upper limit of normal in c some time during the ambulance journey [9]. our laboratory at the Salford Royal University Hospital. EUROPEAN RESPIRATORY JOURNAL VOLUME 39 NUMBER 1 219 TABLE 1 Summary of blood gas results grouped according to oxygen saturation levels Oxygen saturation range Samples Hypercapnia# Uncompensated Compensated Uncompensated respiratory acidosis" respiratory acidosis+ metabolic acidosis1 .98% 1458 (41.3) 305 (21) 83 (6) 161 (11) 111 (8) 94–98% 1291 (36.6) 294 (23) 65 (5) 167 (13) 90 (7) 92.1–93.9% 237 (6.7) 85 (36) 14 (6) 58 (24) 15 (6) 88–92% 288 (8.2) 119 (41) 35 (12) 61 (21) 17 (6) 80–87.9% 154 (4.3) 76 (49) 18 (12) 41 (27) 6 (4) 70–79.9% 53 (1.5) 40 (75) 12 (23) 21 (40) 1 (2) 60–69.9% 22 (0.6) 14 (64) 6 (27) 4 (18) 4 (18) ,60% 21 (0.6) 15 (71) 6 (29) 5 (24) 2 (10) Total 3524 (100) 948 (26.9) 239 (6.8) 518 (14.7) 246 (7.0) Data are presented as n (%). 94–98% is the suggested target range for the majority of acutely unwell patients and 88–92% is the suggested target range for those at risk of # " hypercapnic respiratory failure [6]. : carbon dioxide tension (PCO2) .6.0 kPa or 45 mmHg. :pH,7.35, PCO2 .6.0 kPa or 45 mmHg, and normal or elevated base excess. Includes 140 samples with uncompensated respiratory acidosis (base excess -2.0 to +2.0 mmol?L-1) and 99 samples with incompletely compensated respiratory -1 + acidosis (pH remains ,7.35 despite base excess .2.0 mmol?L ). : compensated respiratory acidosis (pH 7.35–7.45, PCO2 .6.0 kPa or 45 mmHg, and base excess -1 1 -1 .2.0 mmol?L ). : uncompensated metabolic acidosis (pH ,7.35, PCO2 f6.0 kPa or 45 mmHg, and base excess ,-2.0 mmol?L ). 65 (1.8%) samples demonstrated -1 mixed metabolic and respiratory acidosis (pH ,7.35, PCO2 .6.0 kPa or 45 mmHg, and base excess ,-2.0 mmol?L ). 362 (10%) samples were grossly hyperoxaemic with PO2 acidosis, which might be an expected consequence of severe o20 kPa (o150 mmHg). 362 (10.2%) samples had oxygen hypoxaemia. Although severe hypoxaemia was uncommon, saturation ,90% but only 2.7% were severely hypoxaemic with hyperoxaemia (30% of samples), hypercapnia (27% of samples) oxygen saturation ,80%, and the majority of these samples and respiratory acidosis (21% of samples) were relatively exhibited hypercapnia with respiratory acidosis, indicating a common findings and we found that hypercapnic (type 2) need for either cautious oxygen therapy or ventilatory support. respiratory failure was five times more common than pure hypoxaemia (type 1 respiratory failure). These findings suggest The oxygen saturation was above the recommended target that oxygen needs to be used with more caution in hospitals, . range for hypercapnic patients (saturation 92%) in 72% of particularly as it has recently been reported that hyperoxaemia in our hypercapnic samples. 21.5% of all samples had findings ICUs (arterial oxygen tension Pa,O2 .16 kPa or 120 mmHg) was consistent with respiratory acidosis (6.8% uncompensated and associated with higher mortality than hypoxaemia (Pa,O2 ,9kPa 14.7% compensated; table 1). Of the 239 patients with uncom- or 67 mmHg) [7]. Our findings do not support the view of some pensated respiratory acidosis, 59% had a normal base excess clinicians that more patients are at risk of harm from lack of measurement consistent with acute respiratory acidosis and oxygen than from too much oxygen [10]. We now plan to seek . ? -1 41% had an elevated base excess ( 2.0 mmol L ) consistent permission to conduct a prospective study, which will involve with chronic respiratory acidosis, although a proportion of these review of diagnosis and outcome for each patient. patients would have had acute decompensation of chronic respiratory acidosis. B.R. O’Driscoll*, A. Rudenski*, P.M. Turkington* and Although it can be assumed that blood gas samples are usually L.S. Howard# taken from hospital patients at the highest risk of hypoxaemia, these results demonstrate that severe uncorrected hypoxaemia *Manchester Academic Health Science Centre, University of was relatively uncommon in this large database compared with Manchester, Salford Royal University Hospital, Salford, and # the high prevalence of iatrogenic hyperoxaemia and hypercapnia, Dept of Respiratory Medicine, Hammersmith Hospital, both of which may be associated with increased mortality [1–8].
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