Opioid-induced hyperalgesia and opioid tolerance

A continuous administration of highly effective opioids in the intensive care unit might lead even after a short time to the development of an opioid-induced hyperalgesia or opioid tolerance.

Schraag et al. showed that an administration of opioids adapted to the patient’s needs is beneficial with regard to a tolerance development [87].

The additionally administered sedative/anxiolytic also plays a role in the development of an opioid tolerance. A simultaneous administration of high doses of benzodiazepine might foster a tolerance by causing a reduced stimulus of the opioid receptors [88, 89].

Hypermetabolism

Severe burn injuries cause an extreme metabolism increase that can be 100% to 150% higher than the basal metabolic rate. In theses cases it is very important to reduce the catabolism by an early and sufficient nutrition and to avoid feelings of anxiety and stress, which are factors that increase the metabolic action.

A problematic aspect is the fact that a sedoanalgesia causes gastrointestinal dysfunction in several cases. Due to the high energy demand and the benefits of enteral nutrition compared to parenteral nutrition, an intact intestinal motility and avoiding opioid-induced obstipation is very important. Furthermore, the numerous surgical interventions and dressing changes cause longer nutrition gaps.

Psychic stress factors

Severely burned patients are exposed to numerous additional stress factors during their stay in the intensive care unit. One stress factor is the intensive medical setting: loud and unfamiliar noises of the machines, bright light, care measures and numerous diagnostic and therapeutic measures disturb the day and night rhythm of the patient. Furthermore intensive care patients suffer from an enormous communication deficit. The invasive respiration limits their communication abilities and they can not participate actively in the visits of the medical personnel. All these stress factors cause anxiety and frustration in the patient and influence the sensitivity to pain and the coping with pain significantly [90].

Risk of infection

Patients receiving artificial respiration and large burns have a greater risk for ventilation associated pneumonia. Particularly in such cases the artificial respiration should be kept as short as possible.

A general aim of the analgosedation for the patient should be an optimal sedation and an adequate pain management. The pain management should ensure an individually optimized artificial respiration, a problem-free weaning and a preferably scheduled extubation [91].

Monitoring [92]

Individual and patient-specific aims and thus an adequate monitoring of the therapy effect is a precondition for the multimodal approach in an intensive treatment. Controlling the sedation depth and evaluating the pain level are very difficult in critically ill patients in the intensive care unit since very often they cannot articulate themselves verbally. An evaluation of indirect vegetative reactions as for example heart rate, blood pressure, breathing rate, lacrimation and pupil dilatation is not sufficient to securely avoid an overdose or underdose. The search for adequate means of control has lead to the development of numerous scoringsystems all of which having their benefits and shortcomings.

Sedation monitoring

Today, the following scoring systems to determine the sedation level are most commonly used:

RAMSAY-sedation-scale (RSS): very commonly used; patients are classified in 7 categories (Ramsay 0–6) [93]

Sedation-agitation scale (SAS): first score which was evaluated for reliability and validity in intensive care patients, high concordance of the different evaluators and when compared to the Ramsay scale and the Harris scale; patients can be classified in 3 categories (anxious or agitated = SAS 5 –7, calm = SAS 4, sedated = SAS 1– 3) [94].

Richmond agitation scale (RASS): score with 10 parameters to determine the level of sedation and agitation in intubated and non-intubated adult