Oxygen consumption after hypothermic cardiopulmonary bypass: the effect of continuing a propofol infusion postoperatively

The Implementation of Targeted Temperature Management: An Evidence-Based Guideline from the Neurocritical Care Society

BACKGROUND

Targeted temperature management (TTM) is often used in neurocritical care to minimize secondary neurologic injury and improve outcomes. TTM encompasses therapeutic hypothermia, controlled normothermia, and treatment of fever. TTM is best supported by evidence from neonatal hypoxic-ischemic encephalopathy and out-of-hospital cardiac arrest, although it has also been explored in ischemic stroke, traumatic brain injury, and intracranial hemorrhage patients. Critical care clinicians using TTM must select appropriate cooling techniques, provide a reasonable rate of cooling, manage shivering, and ensure adequate patient monitoring among other challenges.

METHODS

The Neurocritical Care Society recruited experts in neurocritical care, nursing, and pharmacotherapy to form a writing Committee in 2015. The group generated a set of 16 clinical questions relevant to TTM using the PICO format. With the assistance of a research librarian, the Committee undertook a comprehensive literature search with no back date through November 2016 with additional references up to March 2017.

RESULTS

The Committee utilized GRADE methodology to adjudicate the quality of evidence as high, moderate, low, or very low based on their confidence that the estimate of effect approximated the true effect. They generated recommendations regarding the implementation of TTM based on this systematic review only after considering the quality of evidence, relative risks and benefits, patient values and preferences, and resource allocation.

CONCLUSION

This guideline is intended for neurocritical care clinicians who have chosen to use TTM in patient care; it is not meant to provide guidance regarding the clinical indications for TTM itself. While there are areas of TTM practice where clear evidence guides strong recommendations, many of the recommendations are conditional, and must be contextualized to individual patient and system needs.

[Effects of sedative agents on metabolic demand]

Literature about the effects of sedative drugs on the metabolic demand of critically ill patients is relatively old and of relatively poor quality. Most are experimental or observational studies. Level of evidence is therefore relatively low corresponding to "expert opinion". The effects of analgesics and hypnotics on tissue metabolic demand associated remain difficult to be adequately quantified. They are essentially related to a decreased neuro-humoral response to stress. This response involves principally the sympathetic system, which could be effectively blocked by most of the anesthetic agents. Other factors could participate to the observed reduction in tissue metabolic demand, as a decrease in spontaneous muscular activity, a reduction in work of breathing and/or a decrease in body temperature. The relative contribution of these different factors will depend on the clinical situation of the patient. Proper effects of anesthetic agents on cellular metabolism are limited as they can only decrease the functional component of this metabolism especially at the level of the heart and to some extent, at the level of the brain. Although the control of the sympathetic activity may be beneficial in critically ill patient, complete sympathetic blockade could be detrimental. Indeed, when oxygen transport to the tissues is acutely reduced, the sympathetic system plays an important role in the redistribution of blood flow according of local metabolic demand. The complete blunting of the neuro-humoral response to stress and therefore of the sympathetic system alters this physiological mechanism and results in a decrease in tissue oxygen extraction capabilities. An imbalance between tissue oxygen demand and delivery could appear with the development of cellular hypoxia. The institution of sedation in a critically ill patient requires careful evaluation of the sedation level using an appropriate scale. In patients in whom a reduction in metabolic demand is specifically requested, but also in patients with limited oxygen transport, the effects of sedative agents on the oxygen consumption-oxygen delivery relationship must also be monitored. The choice of the different agents to be administered will depend on the predefined objectives. As far as intravenous agents are concerned, there is no evidence than one association is more efficient in reducing patient's metabolic demand.

Propofol: a review of its use in intensive care sedation of adults

Propofol (Diprivan) is a phenolic derivative with sedative and hypnotic properties but is unrelated to other sedative/hypnotic agents. Formulated as an oil-in-water emulsion for intravenous use, it is highly lipophilic and rapidly crosses the blood-brain barrier resulting in a rapid onset of action. Emergence from sedation is also rapid because of a fast redistribution into peripheral tissues and metabolic clearance. The depth of sedation increases in a dose-dependent manner. In well designed clinical trials in patients receiving sedation in the intensive care unit (ICU) for a variety of indications, propofol provided adequate sedation for a similar proportion of time to midazolam, but the rate of recovery was faster with propofol. Even after periods of prolonged sedation (>72 hours), propofol was generally associated with a faster time to recovery than midazolam. Propofol facilitated better predictability of recovery and an improved control of the depth of sedation in response to titration than midazolam. In patients sedated following head trauma, propofol reduced or maintained intracranial pressure. Propofol is associated with generally good haemodynamic stability but induces a dose-dependent decrease in blood pressure and heart rate. Bolus administration may cause transient hypotension, and slow initial infusions are recommended in most patients. Serum triglyceride concentrations should be monitored during prolonged infusions (>3 days) because of the risk of hypertriglyceridaemia. The administration of 2% propofol can reduce this risk. Strict aseptic technique must be used during the handling of the product to prevent accidental extrinsic microbial contamination. Despite a higher acquisition cost with propofol, most studies of short-term sedation (approximately <3 days) showed that overall costs were lower with propofol than with midazolam, because a faster time to extubation reduced total ICU costs. However, as the period of sedation increased, the cost difference decreased.

CONCLUSION

The efficacy of propofol in the sedation of adults in the ICU is well established, and clinical trials have demonstrated a similar quality of sedation to midazolam. Because of a rapid distribution and clearance, the duration of action of propofol is short and recovery is rapid. Emergence from sedation is more rapid with propofol than with midazolam, even after long-term administration (>72 hours), which enables better control of the depth of sedation in response to titration and more predictable recovery times. Thus, for the ICU sedation of adults in a variety of clinical settings, propofol provides effective sedation with a more rapid and predictable emergence time than midazolam.