Contrary to our previous study, we did in the current study not find that increased haemoglobin concentration was significantly associated with low SpOdos. This might explain the lack of association in this study.
In a recent study, Smith et al. reported increased mortality rates in hospitalized patients with an SpO2 < 96%. Increased mortality has also been found in emergency care patients with a low SpO2 [8,9]. SpO2 may be a good predictor of mortality in situations where spirometry is not available and in populations with a higher frequency of low SpO2, especially when used as part of a risk-scoring system.
Strengths and weaknesses
This study was based on a single-point measurement of SpO2. We have not checked the reproducibility, but we know that the group with the lowest SpO2 (?92%) in the follow-up examinations also showed consistently low values for SaO2 in blood gas analysis. Oxygen saturation can vary during the day, especially during activity and at night in people with a pulmonary disease such as COPD . Baseline SpO2 (at rest) has been shown to predict oxygen desaturation during activity and at night . SpO2 can also be in the normal range even though FEV1% predicted is <50%.
The measurement of SpO2 could be a limitation because the accuracy of the device is ±2 digits. We tried to compensate for this possible confounding factor by using the highest of three measurements and categorizing the participants into groups.
The group with SpO2 ? 92% in this population was small and comprised only 1.0% of the entire population. One reason may be that people with the lowest values were too sick to participate. We might have found a stronger association with SpO2 in groups of patients with diseases such as COPD because such groups have a higher frequency of low SpO2 chinalovecupid desktop.
New participation price try reduced in the fresh new oldest age bracket and you may on the youngest men. This may have affected all of our overall performance by destroyed the fresh new sickest (oldest) and healthiest (youngest) organizations.
We did not measure blog post-bronchodilator spirometry. A past analysis indicates this will not be requisite when death is actually evaluated within the populace knowledge .
Recall bias and you can misclassification errors are big questions while using the surveys. A stronger organization anywhere between smoking and you can mortality may have been seen in the event that more valid data toward package-age ended up being acquired.
Measuring oxygen saturation by pulse oximetry has important limitations , especially when measuring values at the lower levels. Saturation may be overestimated in heavy smokers because high carboxyhaemoglobin levels may cause overestimation of the true SpO2. To validate the data for a particular device, future studies could include gas analysis in a subsample for comparison.
The cause of death may be uncertain or wrong in many instances because only a small percentage has an autopsy done (10–12% in Norway). Among the participants who died during this study, 36.9% had an FEV1/FVC% <70, and 9.2% reported having COPD. COPD as the main diagnosis or as one of the comorbidities was reported by only 6.5%.
We observed that lower values from pulse oximetry were associated with increased all-cause mortality in the general adult population. This was probably because of the strong association with death caused by pulmonary diseases. The association was weakened and no longer statistically significant after adjusting for FEV1% predicted but remained significant for death caused by pulmonary diseases. Pulse oximetry is easy and safe to perform, and may be particularly useful in risk assessment when spirometry is not an option and when added to spirometry for assessing the risk of death because of pulmonary disease. Low pulse oximetry values found in a patient should warrant further examination.