Controlled Mechanical Ventilation in Critically Ill Patients and the Potential Role of Venous Bagging in Acute Kidney Injury

Abstract

A very low incidence of acute kidney injury (AKI) has been observed in COVID-19 patients purposefully treated with early pressure support ventilation (PSV) compared to those receiving mainly controlled ventilation. The prevention of subdiaphragmatic venous congestion through limited fluid intake and the lowering of intrathoracic pressure is a possible and attractive explanation for this observed phenomenon. Both venous congestion, or "venous bagging", and a positive fluid balance correlate with the occurrence of AKI. The impact of PSV on venous return, in addition to the effects of limiting intravenous fluids, may, at least in part, explain this even more clearly when there is no primary kidney disease or the presence of nephrotoxins. Optimizing the patient-ventilator interaction in PSV is challenging, in part because of the need for the ongoing titration of sedatives and opioids. The known benefits include improved ventilation/perfusion matching and reduced ventilator time. Furthermore, conservative fluid management positively influences cognitive and psychiatric morbidities in ICU patients and survivors. Here, it is hypothesized that cranial lymphatic congestion in relation to a more positive intrathoracic pressure, i.e., in patients predominantly treated with controlled mechanical ventilation (CMV), is a contributing risk factor for ICU delirium. No studies have addressed the question of how PSV can limit AKI, nor are there studies providing high-level evidence relating controlled mechanical ventilation to AKI. For this perspective article, we discuss studies in the literature demonstrating the effects of venous congestion leading to AKI. We aim to shed light on early PSV as a preventive measure, especially for the development of AKI and ICU delirium and emphasize the need for further research in this domain.

Keywords: ICU delirium; acute kidney injury (AKI); cerebral lymph congestion; mean systemic filling pressure (MSVP); pressure support ventilation (PSV); systemic vascular resistance (SVR); venous bagging; venous congestion.

Figure 1

Symbolic depiction of venous bagging, i.e., venous congestion with increased venous blood volume in this compartment, showing its inherent harmful effects on the kidney, liver, and possibly brain, resulting in part from a lack of diaphragmatic pump activity under controlled mechanical ventilation (CMV; on the right) compared with tailored pressure support ventilation (PSV; on the left). Contributing factors such as the level of sedation and IV fluid tailoring are left out for clarity. Water pump in relation to diaphragm activity depicts the potential increase in venous return. With PSV, urine production is maintained compared to the occurrence of decreased kidney function when venous flow is limited with CMV.