Mercury and its compounds are highly toxic to humans, ecosystems and wildlife. Mercury can exist in several chemical forms (Hgo, Hg1+, Hg2+), each with its own toxicological profile. In general terms, the toxicity of these chemical forms is highest for the organic mercury compounds, followed by elemental mercury and inorganic mercury compounds. In measuring devices like sphygmomanometers and previously thermometers, elemental liquid mercury is used. A Community Strategy Concerning Mercury was adopted in January 2005 with the key aim of reducing mercury levels in the environment and reducing human exposure. This Opinion addresses the issue of whether the replacement of mercury-containing blood-pressure measuring devices (sphygmomanometers) would
(i) endanger proper health care including specific groups of patients, and/or
(ii) compromise long term translational epidemiological studies for public health. In addition, the availability and quality of alternative devices for blood pressure measurements have been considered.
Blood pressure measurement is vital for the prevention and treatment of blood pressure related diseases, and for monitoring cardiovascular homeostasis. The indirect measurement of blood pressure with mercury sphygmomanometers (applying the auscultatory technique) has identified arterial hypertension as a major risk factor for cardiovascular diseases. The auscultation method is based on the observation of the recurrence of the blood flow in the occluded artery (using a cuff) of the upper arm by listening to the sounds generated by the recurrent blood flow and disappearance of the sounds when the occlusion is completely removed (by dilation of the cuff), and normal blood flow is restored. In addition to use in clinical settings the mercury sphygmomanometer is also used in long-term epidemiological/observational studies on cardiovascular disease development. A change in population blood pressure has a direct effect on the morbidity and mortality of cardiovascular diseases. Based on long-term experience, blood pressure measurement using the mercury sphygmomanometer is regarded as the gold standard method for indirect measurement of blood pressure. Several factors, however, affect the measurement of blood pressure including the technical skills of the observer, the inherent variability of blood pressure, the accuracy of the device, and the difficulty in measuring blood pressure in some special groups (e.g. the elderly, patients with arrhythmias, patients with a large arm, children, and pregnant women). The use of the mercury sphygmomanometer has practical and technical limitations, and requires specific training. In addition, there should be a special emphasis on regular maintenance of the mercury sphygmomanometer in order to maintain its accuracy. When blood pressure is measured by a trained observer using the auscultatory technique, the mercury sphygmomanometer currently remains the most accurate device for indirect blood pressure measurement.
The mercury column functions as a pressure sensing and displaying component, so it seems likely that this can be replaced by a mercury-free manometer. Indeed, mercury- free alternatives for pressure measurement are commercially available such as the aneroid manometer and the electronic pressure transducer. These alternative sphygmomanometers use auscultation for determination of the blood pressure, and therefore, have the advantages and limitations (such as the observer performance) which also apply to the mercury sphygmomanometer, and are characteristic of the auscultatory technique. In addition, there are non-auscultatory, non-mercury devices available which use the oscillometric technique to measure blood pressure based on changes in arterial pulsation during cuff inflation/deflation. Oscillometric instruments operate under a completely different principle and are thus not considered as true "alternatives" to Hg sphygmomanometers. The various alternatives have widely varying levels of accuracy, emphasising the importance of clinical validation. Regular maintenance is of the utmost importance for proper functioning of all measurement instruments. Even validated oscillometric devices may have accuracy limitations in special patient groups, including patients with arrhythmias, diabetes, the elderly and pre-eclampsia. This is related to the arterial/vascular changes in these patients affecting the oscillometric signal. These limitations do not apply to devices using the auscultatory technique. Therefore, validated non-mercury auscultatory alternatives are appropriate for these patients.
For alternative blood pressure measurement devices a metrological verification is needed to ensure the accuracy of the measurements. In addition, an independent device accuracy assessment is recommended to evaluate the clinical performance. Various clinical validation protocols are available to assess the accuracy of automated alternative devices against mercury sphygmomanometers.
In conclusion, the mercury sphygmomanometer is gradually disappearing from clinical use and there are several appropriate alternatives available. When blood pressure is measured by a trained observer using the auscultatory technique, the mercury sphygmomanometer or a validated auscultatory alternative currently remains the most accurate instrument for indirect blood pressure measurement, especially for certain patient groups. The alternative devices using auscultation have similar limitations as the mercury sphygmomanometers regarding the observer technique and bias associated with auscultation itself. These may be avoided by using automated oscillometric devices, which, when properly validated, allow accurate blood pressure measurements. For all blood-pressure measuring devices, regular maintenance is of primary importance.
In order to maintain a high-level quality of blood pressure measurements it is recommended that mercury sphygmomanometers remain available as reference standards for clinical validation studies of existing and future non-mercury-containing blood-pressure measurement devices. It is emphasised that mercury devices should remain available as standards until an alternative standard is developed and recognised.
8.2 Specific answers to questions raised in the Terms of Reference
Is there sufficient evidence to demonstrate that mercury-free blood pressure measuring devices such as aneroid or electronic instruments are generally reliable substitutes for mercury-containing sphygmomanometers?
Yes. There is sufficient scientific evidence that mercury-free blood pressure measuring devices (when clinically validated) are generally reliable substitutes for mercury- containing sphygmomanometers in routine clinical practice. These alternative devices include both auscultatory devices requiring a trained observer, and also automated oscillometric devices for which some instruction is needed.
Have mercury-free sphygmomanometers been adequately validated over a wide range of blood pressures, ages, and clinical conditions to allow for routine use in hospitals and outpatient settings? Yes. Clinically validated, auscultatory mercury-free devices are equivalent to mercury sphygmomanometers. For the oscillometric devices the situation is different as these devices have mainly been clinically validated in adult populations including a wide range of blood pressures but not in a wide range of ages and clinical conditions.
Have mercury-free sphygmomanometers been adequately validated for the diagnosis of hypertension in specific clinical conditions such as arrhythmia, pre-eclampsia in obstetrics and certain vascular diseases?
Yes. Clinically validated, auscultatory mercury-free devices are equivalent to mercury sphygmomanometers, and are thus suitable for these specific groups of patients. In addition, some oscillometric devices have achieved accuracy in certain conditions although in others, like arrhythmias, the auscultation technique is necessary. Moreover,there is a need for more clinical validations of oscillometric devices to make them usable in specific groups of patients, including elderly patients, children, and pre-eclamptic women.
Yes. Mercury-containing sphygmomanometers are considered essential as reference devices for the clinical validation of the alternatives. For on-going, long-term epidemiological studies currently using mercury sphygmomanometers it is advisable not to change the method of measurement. Therefore, it will be necessary to keep mercury sphygmomanometers available in order to compare them with the alternatives in these studies.
No, they are not essential as reference devices for the metrological verification (calibration) needed to ensure the accuracy of the measurement of the blood pressure devices. In general, more accurate manometers are available for metrological verification.
Is SCENIHR aware of any adverse effects for patients' health due to the replacement of mercury-containing sphygmomanometers by mercury-free alternatives?
No evidence was found for adverse effects for patients' health in clinical settings due to the replacement of mercury-containing sphygmomanometers by validated mercury-free alternatives. There are adequate alternatives in most clinical condition/setting. In special conditions, such as pre-eclampsia, non-mercury auscultatory devices should be preferred until further validation of oscillometric devices.
8.3 MINORITY OPINION