Interactions between extracorporeal support and the cardiopulmonary system.

This review describes the intricate physiological interactions involved in the application of extracorporeal therapy, with specific focus on cardiopulmonary relationships. Extracorporeal therapy significantly influences cardiovascular and pulmonary physiology, highlighting the necessity for clinicians to understand these interactions for improved patient care. Veno-arterial extracorporeal membrane oxygenation (veno-arterial ECMO) unloads the right ventricle and increases left ventricular (LV) afterload, potentially exacerbating LV failure and pulmonary edema. Veno-venous (VV) ECMO presents different challenges, where optimal device and ventilator settings remain unknown. Influences on right heart function and native gas exchange as well as end-expiratory lung volumes are important concepts that should be incorporated into daily practice. Future studies should not be limited to large clinical trials focused on mortality but rather address physiological questions to advance the understanding of extracorporeal therapies. This includes exploring optimal device and ventilator settings in VV ECMO, standardizing cardiopulmonary function monitoring strategies, and developing better strategies for device management throughout their use. In this regard, small human or animal studies and computational physiological modeling may contribute valuable insights into optimizing the management of extracorporeal therapies

Behaviour and stability of thermodilution signals in a closed extracorporeal circuit: a bench study.

Thermodilution is the gold standard for cardiac output measurement in critically ill patients. Its application in extracorporeal therapy is limited, as a portion of the thermal indicator is drawn into the extracorporeal circuit. The behaviour of thermodilution signals in extracorporeal circuits is unknown. We investigated thermodilution curves within a closed-circuit and assessed the impact of injection volume, flow and distance on the behaviour of the thermodilution signals and catheter constants. We injected 3, 5, 7 and 10 ml of thermal indicator into a heated closed circuit. Thermistors at distances of 40, 60, 80, and 100 cm from the injection port recorded the thermodilution signals (at flow settings of 0.5, 1, 1.5, and 2 L/min). Area under the curve (AUC), rise time, exponential decay and catheter constants were analysed. Linear mixed-effects models were used to evaluate the impact of circuit flow, distance and injection volume. Catheter positioning did not influence AUC (78 injections). Catheter constants were independent of flow, injection volume or distance to the injection port. The distance to the injection port increased peak temperature and rise time and decreased exponential time constant significantly. The distance to the injection port did not influence catheter constants, but the properties of the thermodilution signal itself. This may influence measurements that depend on the exponential decay of the thermodilution signal such as right ventricular ejection fraction

Bilateral phrenic nerve block to reduce hazardous respiratory drive in a mechanically ventilated patient with COVID-19—A case report

Key Clinical Message Forced inspiration during mechanical ventilation risks self‐inflicted lung injury. However, controlling it with sedation or paralysis may cause polyneuropathy and myopathy. We tested bilateral phrenic nerve paralysis with local anesthetic in a patient, showing reduced inspiratory force. This offers an alternative to drug‐induced muscle paralysis.Mechanical ventilation, although a life‐saving measure, can also pose a risk of causing lung injury known as “ventilator‐induced lung injury” or VILI. Patients undergoing mechanical ventilation sometimes exhibit heightened inspiratory efforts, wherein the negative pressure generated by the respiratory muscles adds to the positive pressure generated by the ventilator. This combination of high pressures can lead to a syndrome similar to VILI, referred to as “patient self‐inflicted lung injury” or P‐SILI. Prevention of P‐SILI requires the administration of deep sedation and muscle paralysis to the patients, but both these measures can have undesired effects on their health. In this case report, we demonstrate the effect of a bilateral phrenic nerve block aiming to reduce excessive inspiratory respiratory efforts in a patient suffering from COVID‐19 pneumonitis

Mechanisms maintaining right ventricular contractility-to-pulmonary arterial elastance ratio in VA ECMO: a retrospective animal data analysis of RV-PA coupling.

BACKGROUND To optimize right ventricular-pulmonary coupling during veno-arterial (VA) ECMO weaning, inotropes, vasopressors and/or vasodilators are used to change right ventricular (RV) function (contractility) and pulmonary artery (PA) elastance (afterload). RV-PA coupling is the ratio between right ventricular contractility and pulmonary vascular elastance and as such, is a measure of optimized crosstalk between ventricle and vasculature. Little is known about the physiology of RV-PA coupling during VA ECMO. This study describes adaptive mechanisms for maintaining RV-PA coupling resulting from changing pre- and afterload conditions in VA ECMO. METHODS In 13 pigs, extracorporeal flow was reduced from 4 to 1 L/min at baseline and increased afterload (pulmonary embolism and hypoxic vasoconstriction). Pressure and flow signals estimated right ventricular end-systolic elastance and pulmonary arterial elastance. Linear mixed-effect models estimated the association between conditions and elastance. RESULTS At no extracorporeal flow, end-systolic elastance increased from 0.83 [0.66 to 1.00] mmHg/mL at baseline by 0.44 [0.29 to 0.59] mmHg/mL with pulmonary embolism and by 1.36 [1.21 to 1.51] mmHg/mL with hypoxic pulmonary vasoconstriction (p  0.05). Extracorporeal flow did not change coupling (0.0 [- 0.0 to 0.1] per change of 1 L/min, p > 0.05). End-diastolic volume increased with decreasing extracorporeal flow (7.2 [6.6 to 7.8] ml change per 1 L/min, p < 0.001). CONCLUSIONS The right ventricle dilates with increased preload and increases its contractility in response to afterload changes to maintain ventricular-arterial coupling during VA extracorporeal membrane oxygenation

The Role of Intraoperative and Early Postoperative Blood Pressure Variations, Fluid Balance and Inotropics in Fibula Free Flap Head and Neck Reconstruction: A Retrospective Analysis.

BACKGROUND In head and neck reconstructive surgery, postoperative complications are a well-known concern. METHODS We examined 46 patients who underwent ablative surgery and received fibula free flap reconstruction. The main focus was to assess the influence of intraoperative blood pressure fluctuations and the administration of inotropic drugs on complications, either related to the flap or systemic, serving as the primary endpoint. RESULTS Utilizing logistic regression models, we identified that intraoperative mean arterial blood pressure (MAP) drops did not correlate with the occurrence of either flap-related complications (MAP < 70, p = 0.79; MAP < 65, p = 0.865; MAP < 60, p = 0.803; MAP < 55, p = 0.937) or systemic medical complications (MAP < 70, p = 0.559; MAP < 65, p = 0.396; MAP < 60, p = 0.211; MAP < 55, p = 0.936). The occurrence of flap-related complications significantly increased if a higher dosage of dobutamine was administered (median 27.5 (IQR 0-47.5) vs. 62 (38-109) mg, p = 0.019) but not if norepinephrine was administered (p = 0.493). This correlation was especially noticeable given the uptick in complications associated with fluid overload (3692 (3101-4388) vs. 4859 (3555-6216) mL, p = 0.026). CONCLUSION Intraoperative and immediate postoperative blood pressure fluctuations are common but are not directly associated with flap-related complications; however, dobutamine application as well as fluid overload may impact flap-specific complications