European Heart Journal Advance Access published online on November 10, 2009
European Heart Journal, doi:10.1093/eurheartj/ehp472
Continuous positive airway pressure increases haemoglobin O2 saturation after acute but not prolonged altitude exposure
1 Centro Cardiologico Monzino, IRCCS, Istituto di Cardiologia, Università di Milano, Via Parea 4, 20138 Milan, Italy
2 Division of Critical Care and Respiratory Medicine, Department of Medicine, University of Washington, Seattle, WA, USA
3 Department of Cardiology, S.Luca Hospital, Istituto Auxologico Italiano, Milan, Italy
4 Department of Clinical Medicine and Prevention, University of Milano-Bicocca, Milan, Italy
5 Department of Internal Medicine, University of Florence, Florence, Italy
Received 22 July 2009; revised 15 September 2009; accepted 8 October 2009 * Corresponding author. Tel: +39 2 58002270, Fax: +39 2 58002283, Email: piergiuseppe.agostoni{at}ccfm.it
Aims: It is unknown whether subclinical high-altitude pulmonary oedema reduces spontaneously after prolonged altitude exposure. Continuous positive airway pressure (CPAP) removes extravascular lung fluids and improves haemoglobin oxygen saturation in acute cardiogenic oedema. We evaluated the presence of pulmonary extravascular fluid increase by assessing CPAP effects on haemoglobin oxygen saturation under acute and prolonged altitude exposure.
Methods and results: We applied 7 cm H2O CPAP for 30 min to healthy individuals after acute (Capanna Margherita, CM, 4559 m, 2 days permanence, and <36 h hike) and prolonged altitude exposure (Mount Everest South Base Camp, MEBC, 5350 m, 10 days permanence, and 9 days hike). At CM, CPAP reduced heart rate and systolic pulmonary artery pressure while haemoglobin oxygen saturation increased from 80% (median), 78–81 (first to third quartiles), to 91%, 84–97 (P < 0.001). After 10 days at MEBC, haemoglobin oxygen saturation spontaneously increased from 77% (74–82) to 86% (82–89) (P < 0.001) while heart rate (from 79, 64–92, to 70, 54–81; P < 0.001) and respiratory rate (from 15, 13–17, to 13, 13–15; P < 0.001) decreased. Under such conditions, these parameters were not influenced by CPAP.
Conclusion: After ascent excessive lung fluids accumulate affecting haemoglobin oxygen saturation and, in these circumstances, CPAP is effective. Acclimatization implies spontaneous haemoglobin oxygen saturation increase and, after prolonged altitude exposure, CPAP is not associated with HbO2-sat increase suggesting a reduction in alveolar fluids.
Key Words: Arterial blood oxygen saturation • High altitude pulmonary oedema • Hypobaric hypoxia at altitude • Positive pressure ventilation