Cardiac output responses in a flow-driven protocol of resuscitation following cardiac surgery

Right Ventricular Limitation: A Tale of Two Elastances

Right ventricular (RV) dysfunction is a commonly considered cause of low cardiac output in critically ill patients. Its management can be difficult and requires an understanding of how the RV limits cardiac output. We explain that RV stroke output is caught between the passive elastance of the RV walls during diastolic filling and the active elastance produced by the RV in systole. These two elastances limit RV filling and stroke volume and consequently limit left ventricular stroke volume. We emphasize the use of the term "RV limitation" and argue that limitation of RV filling is the primary pathophysiological process by which the RV causes hemodynamic instability. Importantly, RV limitation can be present even when RV function is normal. We use the term "RV dysfunction" to indicate that RV end-systolic elastance is depressed or diastolic elastance is increased. When RV dysfunction is present, RV limitation occurs at lowerpulmonary valve opening pressures and lower stroke volume, but stroke volume and cardiac output still can be maintained until RV filling is limited. We use the term "RV failure" to indicate the condition in which RV output is insufficient for tissue needs. We discuss the physiological underpinnings of these terms and implications for clinical management.

Acute right ventricular myocardial infarction

INTRODUCTION

Acute right ventricular myocardial infarction (RVMI) is observed in 30-50% of patients presenting with inferior wall myocardial infarction (MI) and, occasionally, with anterior wall MI. The clinical consequences vary from no hemodynamic compromise to severe hypotension and cardiogenic shock depending on the extent of RV ischemia. Areas covered: The pathophysiological mechanisms, diagnostic steps, and novel therapeutic approaches of acute RVMI are described. Expert commentary: Diagnosis of acute RVMI is based on physical examination, cardiac biomarkers, electrocardiography, and coronary angiography, whereas noninvasive imaging modalities (echocardiography, cardiac magnetic resonance imaging) play a complementary role. Early revascularization, percutaneous or pharmacological, represents key step in the management of RMVI. Maintenance of reasonable heart rate and atrioventricular synchrony is essential to sustain adequate cardiac output in these patients. When conventional treatment is not successful, mechanical circulatory support, including right ventricle assist devices, percutaneous cardiopulmonary support, and intra-aortic balloon pump, might be considered. The prognosis associated with RVMI is worse in the short term, compared to non-RVMI, but those patients who survive hospitalization have a relatively good long-term prognosis.

Flow-directed vs. goal-directed strategy for management of hemodynamics

PURPOSE OF REVIEW

For the past 15 years, there has been a strong push to use goal-directed protocols for resuscitating critically ill patients and to manage perioperative patients. However, recent large clinical trials have failed to find evidence of improved outcome with this approach.

RECENT FINDINGS

A striking feature in the recent three large prospective randomized trials of septic patients and the one in high-risk perioperative patients is that outcomes in the control groups have markedly improved. This implies improvement in care and clinical acumen. Perhaps the clinical approach should be more toward further helping clinicians with their clinical choices. A good example is cardiac output. The objective of most hemodynamic interventions is to increase cardiac output. It would thus make sense to assess what happened to cardiac output after the intervention to determine if the intervention actually increased cardiac output. If it did not, another therapy should be chosen. I call this a flow-directed responsive protocol.

SUMMARY

A clinical approach that uses monitored values such as cardiac output as a feedback tool to evaluate the response to therapeutic interventions in individual patients may be better than protocols that set fixed targets for all study participants.

Right Atrial Pressure in the Critically Ill: How to Measure, What Is the Value, What Are the Limitations?

Right atrial pressure (P_ra) is determined by the interaction of the function of the heart as a pump, which is called cardiac function, and the factors that determine the return of blood to the heart, which is called return function. Thus, monitoring P_ra or its surrogate, central venous pressure (CVP), can give important insights into mechanisms behind changes in hemodynamic status, responses to interventions, and the likelihood of diagnoses. Examination of the components of the P_ra tracing, especially during the ventilator cycle, can also give information about right-sided cardiac diastolic function, the status of the tricuspid valve, volume responsiveness, and the cardiac rhythm. Importantly, the pressure difference from the large venous reservoir to the heart is small, and thus great care must be taken with technical factors that affect the measurement.

Postoperative Critical Care of the Adult Cardiac Surgical Patient. Part I: Routine Postoperative Care

OBJECTIVES

Cardiac surgery, including coronary artery bypass, cardiac valve, and aortic procedures, is among the most common surgical procedures performed in the United States. Successful outcomes after cardiac surgery depend on optimum postoperative critical care. The cardiac intensivist must have a comprehensive understanding of cardiopulmonary physiology and the sequelae of cardiopulmonary bypass. In this concise review, targeted at intensivists and surgeons, we discuss the routine management of the postoperative cardiac surgical patient.

DATA SOURCE AND SYNTHESIS

Narrative review of relevant English-language peer-reviewed medical literature.

CONCLUSIONS

Critical care of the cardiac surgical patient is a complex and dynamic endeavor. Adequate fluid resuscitation, appropriate inotropic support, attention to rewarming, and ventilator management are key components. Patient safety is enhanced by experienced personnel, a structured handover between the operating room and ICU teams, and appropriate transfusion strategies.

Invasive hemodynamic monitoring

Although invasive hemodynamic monitoring requires considerable skill, studies have shown a striking lack of knowledge of the measurements obtained with the pulmonary artery catheter (PAC). This article reviews monitoring using a PAC. Issues addressed include basic physiology that determines cardiac output and blood pressure; methodology in the measurement of data obtained from a PAC; use of the PAC in making a diagnosis and for patient management, with emphasis on a responsive approach to management; and uses of the PAC that are not indications by themselves for placing the catheter, but can provide useful information when a PAC is in place.

Current tools for assessing heart function and perfusion adequacy

PURPOSE OF REVIEW

Many devices are currently available for measuring cardiac output and function. Understanding the utility of these devices requires an understanding of the determinants of cardiac output and cardiac function, and the use of these parameters in the management of critically ill patients. This review stresses the meaning of the physiological measures that are obtained with these devices and how these values can be used.

RECENT FINDINGS

Evaluation of devices for haemodynamic monitoring can include just measurement of cardiac output, the potential to track spontaneous changes in cardiac output or changes produced by volume infusions or vasoactive drugs, or the ability to assess cardiac function. Each of these puts different demands on the need for accuracy, precision, and reliability of the devices, and thus devices must be evaluated based on the clinical need.

SUMMARY

Evaluation of cardiac function is useful when first dealing with an unstable patient, but for ongoing management measurement of cardiac output itself is key and even more so the trend in relationship to the patient's overall condition. This evaluation would be greatly benefited by the addition of objective measures of tissue perfusion.