Inhalational Anesthetics in the Intensive Care Unit

Sedation in the critically ill patient

The goal of critical care medicine is to support organ function and maintain homeostasis until healing can occur. Sedation and analgesia may blunt the physiologic and psychologic sequelae of intensive care unit stress, and support homeostasis. Although a wide variety of agents have been used empirically, the recognition of analgesia, amnesia, and hypnosis as discrete elements comprising the sedated state has facilitated an individualized approach to therapy. Because intensive care unit patients are a highly heterogeneous population with varying levels of end-organ compromise, the development of specific, easily titratable, parenteral agents has made intensive care unit sedation safer. A trend toward refining dosage regimens in order to minimize the total dose of drug administered and to reduce the occurrence of residual sedation is driven by utilization and cost concerns. The capability for simple bedside electrophysiologic monitoring of the level of sedation is expected to improve the ability to provide optimal therapy.

Inhalational anaesthetics in the ICU: theory and practice of inhalational sedation in the ICU, economics, risk-benefit

ICU sedation poses many problems. The action and side-effects of intravenous drugs in the severely ill patient population of an ICU are difficult to control. The incidence of post-traumatic stress disorder after long-term sedation is high. The recent focus on propofol infusion syndrome entails restrictions in the use of this drug. On the other hand, volatile anaesthetics very selectively suppress consciousness but leave many autonomic functions intact. In the absence of perception and disturbed information processing the number of adverse experiences should be lower, leading to a better psychological outcome. Respiration and intestinal motility are not depressed, facilitating modern therapeutic concepts such as early enteral feeding and augmentation of spontaneous breathing. Awakening after inhalational ICU sedation is quick and predictable, extubation can be planned and organized, and the time during which the patient needs very close observation will be short. Technological advances have greatly simplified the application of inhalational anaesthetics. New anaesthesia ventilators offer ventilatory modes and high flow generation comparable to ICU ventilators. However, they are not yet licensed for stand-alone use. The introduction of a volatile anaesthetic reflection filter for the first time enables the concept of inhalational sedation to be performed with very little effort by many ICUs. This 'anaesthetic conserving device' (AnaConDa) is connected between the patient and a normal ICU ventilator, and it retains 90% of the volatile anaesthetic inside the patient just like a heat and moisture exchanger. In this chapter possible advantages of the new concept and the choice of the inhalational agent are discussed. The technical prerequisites are explained, and the practice and pitfalls of inhalational ICU sedation in general and when using the AnaConDa are described in detail.

Desflurane compared with propofol for postoperative sedation in the intensive care unit

BACKGROUND

We hypothesized that emergence from sedation in postoperative patients in the intensive care unit would be faster and more predictable after sedation with desflurane than with propofol.

METHODS

Sixty patients after major operations were allocated randomly to receive either desflurane or propofol. The target level of sedation was defined by a bispectral index(TM) (BIS(TM)) of 60. All patients were receiving mechanical ventilation of the lungs for 10.6 (SD 5.5) h depending on their clinical state. The study drugs were stopped abruptly in a calm atmosphere with the fresh gas flow set to 6 litres min(-1), and the time until the BIS increased above 75 was measured (t(BIS75), the main objective measure). After extubation of the trachea, when the patients could state their birth date, they were asked to memorize five words.

RESULTS

Emergence times were shorter (P<0.001) after desflurane than after propofol (25th, 50th and 75th percentiles): t(BIS75), 3.0, 4.5 and 5.8 vs 5.2, 7.7 and 10.3 min; time to first response, 3.7, 5.0 and 5.7 vs 6.9, 8.6 and 10.7 min; time to eyes open, 4.7, 5.7 and 8.0 vs 7.3, 10.5 and 20.8 min; time to squeeze hand, 5.1, 6.5 and 10.2 vs 9.2, 11.1 and 21.1 min; time to tracheal extubation, 5.8, 7.7 and 10.0 vs 9.7, 13.5 and 18.9 min; time to saying their birth date, 7.7, 10.5 and 15.5 vs 13.0, 19.4 and 31.8 min. Patients who received desflurane recalled significantly more of the five words. We did not observe major side-effects and there were no haemodynamic or laboratory changes except for a more marked increase in systolic blood pressure after stopping desflurane. Using a low fresh gas flow (air/oxygen 1 litre min(-1)), pure drug costs were lower for desflurane than for propofol (95 vs 171 Euros day(-1)).

CONCLUSIONS

We found shorter and more predictable emergence times and quicker mental recovery after short-term postoperative sedation with desflurane compared with propofol. Desflurane allows precise timing of extubation, shortening the time during which the patient needs very close attention.

Adverse responses to analgesia, sedation, and neuromuscular blocking agents in infants and children

Analgesics, sedation, and neuromuscular blocking agents are commonly used in treating critically ill infants and children. Although these medications are beneficial and imperative to the care of the child, their use is not risk free. Adverse responses occur in these children. With improved methods for use and monitoring, adverse responses can be minimized.