Background: Direct monitoring of arterial pressure using a transducer system is not affordable in most operating rooms and ICU wards in Iran. It is, however, possible to use an aneroid manometer instead, but it is not standardized yet, nor studied enough; and its measurements may not be interpretable.

Methods: To study the correlation of the arterial pressure readings between a manometer and a transducer system, systolic and diastolic arterial pressure was measured 105 times using both systems via arterial cannulation in seven patients during surgery. Mean arterial pressure was directly recorded in the transducer system, while it was calculated in the manometer system. In the manometer system, the extension tube was filled with saline halfway from the patient and the other empty end was connected to a manometer. The transducer and the air-fluid interface in the extension tube were positioned at same level. Correlation of the arterial pressures between the systems was tested using linear regression and Pearson correlation.

Results: Mean arterial pressure differed by 2 (1-3) mmHg [mean (CI 95%)] between the systems, however, pulse pressure was lower in the manometer system by 37 (33-41) mmHg. The mean arterial pressure in the transducer system (MAP_T) correlated well and linearly with the systolic arterial pressure in the manometer system (SAP_M) by R=0.966. Therefore, MAP_T can be regarded as a function of SAP_M through the following formula: MAP_T = (1.03 ´ SAP_M) - 7.34.

Conclusion: The mean arterial pressure in the transducer system can be reliably estimated by monitoring the systolic arterial pressure in the manometer system.