key: cord-0780336-5x41olju
authors: La Colla, Luca; Bronshteyn, Yuriy S.; Mark, Jonathan B.
title: Respiratory variation in central venous pressure (CVP) to guide ventilatory support in COVID-19-related lung injury
date: 2020-06-17
journal: J Cardiothorac Vasc Anesth
DOI: 10.1053/j.jvca.2020.06.043
sha: cea9b42b9f3e4321979c8da3796e373378311fba
doc_id: 780336
cord_uid: 5x41olju

nan

For example, current ARDS management includes treating hypoxemia by titrating up positive end-expiratory pressure (PEEP). However, increasing PEEP also decreases right ventricular preload and, in patients with low alveolar recruitability, increases both right ventricular afterload and the transpulmonary pressure gradient. The transpulmonary gradient is the pressure distending the lung parenchyma and is mathematically equal to the alveolar pressure (plateau pressure) minus the pressure in the pleural space (aka the pleural pressure). Notably, the transpulmonary gradient is a critical determinant of "lung stress" and damage in both spontaneously breathing 6 and mechanically ventilated patients. 7 Even a healthy lung is quickly damaged in the presence of a high transpulmonary gradient. 8 Conversely, knowledge of the transpulmonary gradient can be used to deliver goal-directed, lung-protective ventilation 7,9 with upper limits of 15 to 20 cm H2O for healthy patients and 10 to 12 cm H2O for ARDS patients. 9 In fact, such transpulmonary pressure-guided ventilation has been associated with decreased mortality in patients with ARDS. 10, 11 The pleural pressure component of the transpulmonary gradient is typically measured by using an esophageal manometer. But since esophageal manometry is not available in many sites treating COVID-19 patients, an alternative means of measuring the transpulmonary gradient using more ubiquitous equipment could prove valuable. In the past, multiple authors have reported that respiratory variation of central venous pressure (CVP) accurately reflects variation in transpulmonary pressure in mechanically ventilated patients (including ARDS) and with different ventilation modes 12, 13, 14 Consequently, this readily-available cardiovascular monitor may provide actionable insight into Covid-19 pulmonary physiology.

Central venous pressure monitoring with careful observation of the CVP waveform during the respiratory cycle, provides diagnostic clues that are not evident from the digital (mean) value of CVP ( Figure 1 ). 15, 16 In COVID-19 patients, these respirophasic changes in CVP could be used to guide pulmonary support. For instance, in non-intubated patients, the finding of large peakto-trough swings in CVP suggests that the patient is generating large, potentially injurious transpulmonary pressure gradients, a process that clinicians may wish to arrest with intubation and controlled ventilation. Similarly, after intubation, some COVID-19 patients are initially placed on triggered modes of ventilation (e.g., pressure support), which involve patient respiratory effort. In that context, detection of large respirophasic swings in CVP again suggests underlying, proportionally large swings in pleural pressure that are additive to the positive pressure delivered through the pressure support mode. For instance, an intubated patient receiving a standard pressure support of 15 cm H 2 O observed to have CVP peak-totrough swings of -10 mmHg (-13.6 cm H2O) is producing a net transpulmonary pressure equal to the following: 15 cm H 2 O -( -13.6 cm H 2 O) = ~29 cm H 2 O, which is significant since transpulmonary gradients greater than 10 cm H2O are known to worsen alveolar injury in already damaged lungs. 9 Thus, among intubated COVID-19 patients receiving triggered modes of ventilation, monitoring CVP changes with respiration could help determine when to escalate pulmonary support from assisted to controlled (passive) ventilation. 10, 11 A possible (although theoretical) use of ΔCVP to guide respiratory support and ventilation is provided in Table 1 .

In summary, the viral epidemic has pushed healthcare systems to their limits. Patients infected with SARS-CoV-2 will present with different pathophysiological derangements and different phenotypes that may require different therapeutic approaches. Careful observation of the respiratory variation in the CVP tracing may be a useful diagnostic tool to guide appropriate ventilatory support. 

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