Monitoring arterial, central venous and pulmonary capillary wedge pressure

Arterial blood pressure can be monitored non-invasively by mercury manometer, automated oscillotonometer or continuously by a Finapres based on the Penaz technique. Insertion of a cannula into an artery allows continuous beat-to-beat blood pressure monitoring with pressure transmitted along a column of saline to a piezo-resistive strain gauge transducer. Continuously monitoring blood pressure aids optimization of adequate organ perfusion and further information gained from the waveform can be used to guide treatments. Central venous pressure is the pressure within the right atrium and great veins of the thorax. In a healthy adult, it is between 0 and 8 cm H2O, varying with respiration. It is measured via a cannula inserted into the superior vena cava (usually via internal jugular or subclavian veins) and uses a pressurized transducer set to produce a reading of central venous pressure and venous waveform. Venous bloods and central venous gases can also be taken and drugs and infusions (particularly if irritant) can be administered. Serial readings are useful for assessing progress and response to treatment. Pulmonary capillary wedge pressure represents left atrial filling pressure and therefore left ventricular end-diastolic pressure and allows more accurate assessment of left-sided heart function. It is measured by floating a pulmonary artery catheter and wedging a balloon into a pulmonary artery branch. It has a complication rate of 10% and, as studies have shown it to have no clear evidence of benefit, alternative less invasive methods such as oesophageal Doppler or arterial pulse contour analysis are now common alternatives.