Hemodynamic instability and fluid responsiveness

Indirect cardiac output assessment in a swine pediatric acute respiratory distress syndrome model

PURPOSE

To investigate the correlation between volume of carbon dioxide elimination (V̇CO2) and end-tidal carbon dioxide (PETCO2) with cardiac output (CO) in a swine pediatric acute respiratory distress syndrome (ARDS) model.

METHODS

Respiratory and hemodynamic variables were collected from twenty-six mechanically ventilated juvenile pigs under general anesthesia before and after inducing ARDS, using oleic acid infusion.

RESULTS

Prior to ARDS induction, mean (SD) CO, V̇CO2, PETCO2, and dead space to tidal volume ratio (Vd/Vt) were 4.16 (1.10) L/min, 103.69 (18.06) ml/min, 40.72 (3.88) mmHg and 0.25 (0.09) respectively. Partial correlation coefficients between average CO, V̇CO2, and PETCO2 were 0.44 (95% confidence interval: 0.18-0.69) and 0.50 (0.18-0.74), respectively. After ARDS induction, mean CO, V̇CO2, PETCO2, and Vd/Vt were 3.33 (0.97) L/min, 113.71 (22.97) ml/min, 50.17 (9.73) mmHg and 0.40 (0.08). Partial correlations between CO and V̇CO2 was 0.01 (-0.31 to 0.37) and between CO and PETCO2 was 0.35 (-0.002 to 0.65).

CONCLUSION

ARDS may limit the utility of volumetric capnography to monitor CO.

Application of POCUS in patients with COVID-19 for acute respiratory distress syndrome management: a narrative review

COVID-19 has inflicted the world for over two years. The recent mutant virus strains pose greater challenges to disease prevention and treatment. COVID-19 can cause acute respiratory distress syndrome (ARDS) and extrapulmonary injury. Dynamic monitoring of each patient's condition is necessary to timely tailor treatments, improve prognosis and reduce mortality. Point-of-care ultrasound (POCUS) is broadly used in patients with ARDS. POCUS is recommended to be performed regularly in COVID-19 patients for respiratory failure management. In this review, we summarized the ultrasound characteristics of COVID-19 patients, mainly focusing on lung ultrasound and echocardiography. Furthermore, we also provided the experience of using POCUS to manage COVID-19-related ARDS.

The Role of Point-of-Care Ultrasound Monitoring in Cardiac Surgical Patients With Acute Kidney Injury

The approach to the patient with acute kidney injury (AKI) after cardiac surgery involves multiple aspects. These include the rapid recognition of reversible causes, the accurate identification of patients who will progress to severe stages of AKI, and the subsequent management of complications resulting from severe renal dysfunction. Unfortunately, the inherent limitations of physical examination and laboratory parameter results are often responsible for suboptimal clinical management. In this review article, the authors explore how point-of-care ultrasound, including renal and extrarenal ultrasound, can be used to complement all aspects of the care of cardiac surgery patients with AKI, from the initial approach of early AKI to fluid balance management during renal replacement therapy. The current evidence is reviewed, including knowledge gaps and future areas of research.

Ultrasound findings in critical care patients: the "liver sign" and other abnormal abdominal air patterns

In critical care patients, point of care abdominal ultrasound examination, although it has been practiced for over 30 years, is not as widespread as its cardiac or pulmonary counterparts. We report two cases in which detection of air during abdominal ultrasound allowed the early detection of life-threatening pathologies. In the first case, a patient with severe Clostridium difficile was found to have portal venous gas but its significance was confounded by a recent surgery. Serial ultrasonographic exams triggered a surgical intervention. In the second case, we report what we call the "liver sign" a finding in patients with pneumoperitoneum. These findings, all obtained prior to conventional abdominal imaging, had immediate clinical impact and avoided unnecessary delays and radiation. Detection of abdominal air should be part of the routine-focused ultrasonographic exam and for critically ill patients an algorithm is proposed.

The Critical Importance of Hepatic Venous Blood Flow Doppler Assessment for Patients in Shock

Hepatic venous blood flow can be easily obtained using bedside ultrasound with either transthoracic or transesophageal echocardiography. Six critically ill patients with shock associated with absent or significantly reduced hepatic venous blood flow in the presence of normal or increased pulmonary venous flow are presented. In all these patients, the etiology of shock was secondary to increased resistance to venous return from either an intraabdominal process or through extrinsic or intrinsic occlusion of the proximal inferior vena cava or right atrium. These shock situations are secondary to increased resistance to venous return. Their treatment is highly specific and typically involves a surgical intervention.

Extracardiac Signs of Fluid Overload in the Critically Ill Cardiac Patient: A Focused Evaluation Using Bedside Ultrasound

Fluid balance management is of great importance in the critically ill cardiac patient. Although intravenous fluids are a cornerstone therapy in the management of unstable patients, excessive administration coupled with cardiac dysfunction leads to elevation in central venous pressure and end-organ venous congestion. Fluid overload is known to have a detrimental effect on organ function and is responsible for significant morbidity in critically ill patients. Multisystem bedside point of care ultrasound imaging can be used to assess signs of fluid overload and venous congestion in critically ill patients. In this review we describe the ultrasonographic extracardiac signs of fluid overload and how they can be used to complement clinical evaluation to individualize patient management.

A bedside clinical and ultrasound-based approach to hemodynamic instability - Part II: bedside ultrasound in hemodynamic shock: continuing professional development

Shock is defined as a situation where oxygen transport and delivery is inadequate to meet oxygen demand. The patient in shock is evaluated through medical history, physical examination, and careful observation of the hemodynamic and respiratory monitors. The patient is initially managed with basic resuscitation measures, however bedside ultrasound should be performed if hemodynamic instability persists. We propose to use ultrasound of the inferior vena cava (IVC), and the concept of venous return, as the initial step in order to identify the mechanism of shock. Doppler examination of the hepatic venous flow can also be added. Further ultrasound examination of the patient's heart, thorax, and abdomen can then be performed in order to determine the etiology of shock. In patients with reduced mean systemic venous pressure, an examination of the patient's thoracic and abdominal cavities to detect free fluid, pneumonia, or empyema can be considered. In patients with increased right atrial pressure, transthoracic echocardiography will allow identification of left or right ventricular dysfunction. Finally, in the presence of increased resistance to venous return, thoracic examination for pneumothorax or cardiac tamponade and abdominal examination for signs of abdominal compartment syndrome or IVC occlusion can be considered. Subsequent treatment can then be tailored to the etiology of shock. Elements of bedside ultrasound examination are currently taught in many anesthesia training programs.

PURPOSE

To develop an approach to the patient in shock that incorporates bedside ultrasound examination.

Bedside clinical and ultrasound-based approaches to the management of hemodynamic instability--part I: focus on the clinical approach: continuing professional development

Shock is defined as a situation where oxygen transport is inadequate to meet the body's oxygen demand. An understanding of the mechanism(s) of reduced cardiac output, a determinant of oxygen transport, is crucial in order to initiate appropriate therapy to manage shock. Combining the concept of venous return with the ventricular pressure-volume relationship is a useful method to appreciate the complex circulatory physiology of shock. Clues from the patient's history, physical examination, and key laboratory tests, along with the careful inspection of hemodynamic, electrocardiographic and respiratory waveforms can help with the identification of the etiology and mechanism(s) of shock. Following verification of the arterial pressure, general resuscitation can begin, and more specific treatment can be undertaken to manage shock. If the patient is unresponsive to these measures, bedside ultrasound can then be performed to ascertain more detail regarding the mechanism(s) and etiology of shock.

PURPOSE

To develop an approach to the management of the hemodynamically unstable patient.

PRINCIPAL FINDING

Not applicable.

CONCLUSION

Not applicable.