Neuro Resus

A podcast by two intensivists from Westmead PICU on post resuscitation care.

Blood Pressure (BP) is one of the vital hemodynamic parameters that we often aim to optimize for critically ill patients. Our decisions regarding BP targets, and ensuing use (or avoidance) of vasopressor agents, may directly impact on outcomes for these patients. Despite being a fundamental tenet of critical care, there is a lack of quality evidence to suggest optimal BP targets or to guide the use of vasopressors for individual patients with shock. A mean arterial BP (MAP) of 65-70 mmHg is an often-cited initial BP target for patients during vasopressor therapy. Use of vasopressors to maintain MAP of 65 mmHg or greater remains one of the core clinical criteria in the new definition of septic shock. However, such standard targets are unlikely to be applicable to all patients, many of whom would have a basal MAP higher than 65-70 mmHg, often to a varying degree, during their usual pre-illness state. Therefore, a vasopressor therapy guided by standard BP thresholds may result in a variable degree of untreated relative hypotension, which is associated with new-onset acute kidney injury (AKI). From a physiological standpoint, any relative reduction in net perfusion pressure across an organ’s vasculature can overwhelm its autoregulatory mechanisms, which are already under stress during a shock state. In a recent major RCT, among patients with chronic hypertension, targeting a higher MAP of 80-85 mmHg, versus 65-70 mmHg, showed a lower incidence of subsequent AKI, but with no difference in mortality. However, this RCT did not take patients’ pre-illness basal BP into account, making it difficult to extrapolate these results to those patients with chronic hypertension, who usually have a well-controlled basal BP, or to those patients, who although have a higher-than-normal basal BP but are not formally diagnosed with hypertension. Accounting for a patient’s pre-illness basal BP can minimize variation in the degree of untreated relative hypotension that is often inadvertently accepted in conventional care. It is a simple, but untested, strategy. Further, new tools that can monitor cerebral autoregulation in real-time are on the horizon and have shown some promise in suggesting an optimal BP for individual patients with shock. This technology can further help adjust the initial BP target as a patient deteriorates or recovers from the shock state.

There has been a potpourri of papers released in the last 12 months of interest to Intensivists. Some have solved the great mysteries of the universe, some have sparked the interest for more high-quality research and others have left us scratching our heads. This talk will give a snapshot of the Top 10 Critical Care papers of the last year.

Introduction: Recent times have witnessed almost half, or sometimes more cardiac surgical procedures are performed in patients above 75 years of age. Traditionally, the EuroSCORE II and STS risk scoring systems have been widely used across the globe. Extensive reviews have shown that EuroSCORE II probably overestimates the perioperative risk at lower score levels while the STS score tends to underestimate the risk.

Frailty is a broad term that encircles aspects of nutrition, lack of agility, inactivity, lack of strength and wasting; and is seen in 25-50% of elderly patients. It has been defined as a geriatric syndrome reflecting a state of reduced physiological reserve and increased vulnerability to poor resolution of homeostasis after a stressor event. Conversely, pre-frailty, which is potentially reversible, is associated with higher risk of older adults developing cardiovascular disease.

Frailty assessment includes a variety of physical and cognitive tests, functional assessments and evaluating nutritional status. Literature has highlighted what is referred to as the ‘obesity paradox’, meaning obese patients with heart failure fair better than leaner patients, possibly because they have more metabolic reserve and also because weight loss in itself is a risk factor for frailty.

Patient Selection: To comprehensively assess a patient, factors that describe the biological status of the patient should be incorporated. There are various methods of assessment and modified Fried criteria or comprehensive assessment of frailty are a couple of systems commonly used.

Conclusion: Systematic reviews have shown that frail patients have higher chance of mortality, major adverse cardiac and cerebrovascular events and functional decline after cardiac surgery. A holistic assessment not only categorises patients into the apt risk category and hence match goals and treatments; but also, will pick up patients with pre-frailty who will benefit from multidisciplinary intervention and be better prepared for the intervention.

"The real benefit to the patient [of echocardiography] is not the technical skill, but rather the application of intellectual input... information, communication and teamwork are essential" Jos Roelandt, 1993

Of all the imaging techniques used in intensive care, echocardiography has come to the fore, in particular due to its accessibility, immediate availability and applicability as a point-of-care technique, thereby removing the risks of transportation of the critically ill. Over the preceding 20 years evidence has continued to emerge for its extended use in the acute/emergency setting, to the extent that it is now included in national and international guidelines relating to the universal definition of myocardial infarction, as well as in shock pathways, and as an adjunctive technique in advanced life support. Its potential scope is huge, with applications relating to monitoring, cardiac pathophysiology and coronary perfusion as well as its more evident use to define cardiac anatomy.

The three main uses of ultrasound to interrogate the heart relate to the way in which the technique is used: first, as an extension to the clinical examination using binary questions and 2D imaging only (focused cardiac ultrasound, FoCUS) which forms the basis of 'basic' techniques. Second, incorporating the full range of echocardiographic techniques for diagnostic capability (echocardiography), and third, selective application of the full range of techniques in order to answer specific questions raised in the critical care/emergency arena (targeted echocardiography). This includes speckle strain/strain-rate to determine abnormalities of myocardial function suggestive of myocarditis, calculation of myocardial electromechanical efficiency in order to maximise cardiac output, recognition of parameters that suggest restrictive right ventricular physiology, with the requirement for modification of ventilatory techniques and parameters, detection of myocardial ischaemia, estimation of LVEDP and LAP, and its application in the institution, monitoring and weaning of mechanical circulatory support.

Key questions for the clinician undertaking echocardiography in the critical/acute/emergency setting can be summarised in a checklist format, which includes:

Background questions:

1. What is the clinical context?
2. What does the treating clinician want to know (ie why won't the patient wean from mechanical ventilation? or is this pulmonary oedema, and if so, why?).
3. Can echocardiography answer the required question, and what is the accuracy in this setting?
4. What is the underlying diagnosis (cardiac and non-cardiac)?
5. How is the patient being sedated/ventilated/supported

Specific echocardiographic data:

1. What is limiting the cardiac output/elevating the venous pressure?
2. Is the left atrial pressure elevated?
3. Is the heart rate/AV delay/VV delay appropriate?
4. Is there any other relevant information that the treating clinician needs to know that may inform planned interventions?

To reach its full potential in the critical arena demands therefore not only understanding of the whole range of echocardiographic techniques, but also the confounding factors that will be found in this setting, including filling status, ventilatory parameters, mechanical support and the use of vasoactive agents. Although frequently 'simplified' for application in FoCUS, expert echocardiography in this setting can be extremely challenging, and the potential to cause harm to the patient through misinterpretation should not be underestimated.