Clinical review: interpretation of arterial pressure wave in shock states

Abstract

In critically ill patients monitored with an arterial catheter, the arterial pressure signal provides two types of information that may help the clinician to interpret haemodynamic status better: the mean values of systolic, diastolic, mean and pulse pressures; and the magnitude of the respiratory variation in arterial pressure in patients undergoing mechanical ventilation. In this review we briefly discuss the physiological mechanisms responsible for arterial pressure generation, with special focus on resistance, compliance and pulse wave amplification phenomena. We also emphasize the utility of taking into consideration the overall arterial pressure set (systolic, diastolic, mean and pulse pressures) in order to define haemodynamic status better. Finally, we review recent studies showing that quantification of respiratory variation in pulse and systolic arterial pressures can allow one to identify the mechanically ventilated patients who may benefit from volume resuscitation.

Figure 1

Respiratory changes in arterial pressure in a mechanically ventilated patient. The pulse pressure (PP; systolic minus diastolic pressure) is minimal (PPmin) three heart beats after its maximal value (PPmax). The respiratory changes in pulse pressure (ΔPP) can be calculated as the difference between PPmax and PPmin, divided by the mean of the two values, and expressed as a percentage: ΔPP (%) = 100 × (PPmax - PPmin)/([PPmax + PPmin]/2). In this case, the high value of ΔPP (30%) suggests that the patient would be potentially responsive to volume resuscitation.