Pulse Pressure: The Breath-to-Blood Connection

Aim: To provide a concise overview of pulse pressure variation as an indicator of fluid responsiveness during anaesthesia and critical care. (2 minute read).

By: J. de la Cruz

Background

Every breath, whether spontaneous of delivered with mechanical ventilation (under anaesthesia), changes the pressure inside the chest. The contrasting pressure changes affect the heart and lungs. Pulse pressure variation (PPV) is most commonly and most accurately measured using an invasive arterial line, because the monitor analyses beat-to-beat changes in the arterial waveform throughout the respiratory cycle.

However, there are also non-invasive technologies that attempt to estimate similar haemodynamic variation using:

• finger cuff systems,

• pulse contour analysis devices,

• waveform variation from pulse oximetry

What is PPV

During spontaneous breathing, pressure drops as the chest expands during inspiration. Inhalation creates negative pressure to draw air in the lungs and helps blood return to the heart. And because this is normal physiological function, the heart-lung interaction does not lead to significant haemodynamic issues.

In contrast, during mechanical ventilation, chest pressure increases (becomes positive) during inspiration, which makes it a bit harder for the blood to return to the right side of the heart. After a short delay, there will be less blood pumped from the left side of the heart. On exhalation, chest pressure falls, and more blood returns to the heart. The left side of the heart eventually pumps more blood, and the pulse pressure increases.

As the pressures influence the blood flow, the pulse pressure (reflected by the arterial waveform) gets smaller or larger depending on where you are in the breathing cycle. Most anaesthetic monitors automatically calculate the PPV once a good arterial waveform is detected. In many cases, a clinician can simply select the haemodynamic menu and enable the PPV display.

The monitor continuously analyses changes in the arterial waveform during the breathing cycle and displays PPV as a percentage (%). High PPV means that the heart is sensitive to volume changes. Typically a PPV of more than 13% may suggest that the patient may benefit from fluid administration.

Relevance

 PPV is particularly useful during major surgery or prolonged surgery. PPV helps clinicians decide whether fluid administration is likely to improve circulation and cardiac output, rather than relying on guesswork alone.

For nurses, understanding PPV also helps explain why anaesthetic teams may choose vasopressors, or other interventions instead of automatically administering more intravenous fluid.

PPV is useful but it has limitations. The accuracy is influenced by cardiac arrythmias, patients with significant dysfunction of the heart, or patients with spontaneous breathing efforts.

References:

Myatra, S. N., & Monnet, X. (2017). Use of a tidal volume challenge to improve the reliability of pulse pressure variation. Critical Care, 21(1), 60. https://doi.org/10.1186/s13054-017-1637-x

Teboul, J. L., Monnet, X., Chemla, D., & Michard, F. (2019). Arterial pulse pressure variation with mechanical ventilation. American Journal of Respiratory and Critical Care Medicine, 199(1), 22–31. https://doi.org/10.1164/rccm.201801-0088CI

Yang, X., Du, B., & Long, Y. (2014). Does pulse pressure variation predict fluid responsiveness in critically ill patients? A systematic review and meta-analysis. Critical Care, 18(6), 650. https://doi.org/10.1186/s13054-014-0650-6