Sedation after spinal anesthesia in elderly patients: a preliminary observational study with the PSA-4000

Effects of spinal anesthesia and sedation with dexmedetomidine or propofol on cerebral regional oxygen saturation and systemic oxygenation a period after spinal injection

PURPOSE

To evaluate changes in cerebral regional oxygen saturation (rSO₂) after spinal anesthesia and compare the changes in rSO₂ and systemic oxygenation between dexmedetomidine sedation and propofol sedation.

METHODS

Thirty-six patients scheduled to undergo transurethral surgery under spinal anesthesia were randomly assigned to the dexmedetomidine (n = 18) and propofol groups (n = 18). We used near-infrared spectroscopy sensors to measure rSO₂, and obtained data from each side were averaged. After oxygen insufflation, baseline measurements of mean arterial blood pressure (MAP), heart rate, rSO₂, pulse oximetry saturation (SpO₂), bispectral index, and body temperature were made. After spinal anesthesia, we measured these parameters every 5 min. Twenty minutes after spinal injection, dexmedetomidine or propofol administration was started. We measured each parameter at 10, 25, and 40 min after the administration of dexmedetomidine or propofol.

RESULTS

The baseline rSO₂ in the dexmedetomidine group was 71.3 ± 7.3%, and that in the propofol group was 71.8 ± 5.6%. After spinal anesthesia, rSO₂ in both groups decreased significantly (dexmedetomidine group: 65.4 ± 6.9%; propofol group: 64.3 ± 7.4%). After administering sedatives, rSO₂ was equivalent after spinal anesthesia. rSO₂ was comparable between the two groups. MAP and SpO₂ were significantly higher in the dexmedetomidine group than in the propofol group.

CONCLUSION

Spinal anesthesia decreased rSO₂; however, the decline was not severe. Dexmedetomidine and propofol did not compromise cerebral oxygenation under spinal anesthesia. Nevertheless, MAP and SpO₂ were more stable in dexmedetomidine sedation than in propofol sedation. Dexmedetomidine may be suitable for spinal anesthesia.

Relation between fentanyl dose and patient state index during spinal anesthesia for elective cesarean section

Background

In spinal anesthesia for cesarean section, the addition of fentanyl to the local anesthetic has been reported to improve perioperative analgesia. However, there is only limited knowledge on sedative effects of the added fentanyl. We examined whether the patient state index® (PSI) can detect and present the light sedated level with patients undergoing cesarean section.

Findings

We measured respiratory rate (RR), SpO2, and PSI values. Between child delivery and the completion of the operation, the proportions of time with the PSI values <90 and 80 were calculated. RR <8 breaths/min or SpO2 <95 % was defined as respiratory depression. Respiratory depression was not observed in any patient. At fentanyl doses of 10, 15, and 20 μg, the proportions of time with the PSI <90 were 14.5 ± 20.8, 49.4 ± 35.3, and 71.1 ± 22.9 %, respectively (P < 0.01). There were significant differences between 10 and 15 μg (P < 0.05), and 10 and 20 μg (P < 0.01). Similarly, the proportions of time with the PSI values <80 were 0.5 ± 1.8, 21.1 ± 24.1, and 31.8 ± 32.2 %, respectively (P < 0.05). There was a significant difference between 10 and 20 μg (P < 0.05).

Conclusions

The PSI values decreased in a dose-dependent manner with increasing dose of fentanyl, but no respiratory depression was observed. The PSI values decreased to less than 90, when fentanyl was administered more than 15 μg. Furthermore, the PSI values decreased to less than 80, when fentanyl was administered 20 μg.

Association between bispectral index and age and use of sedative drugs in high spinal anaesthesia

OBJECTIVES

A prospective, randomized, double-blind study using bispectral index values to objectively quantify the sedative effect of high spinal anaesthesia in patients stratified according to age, and to determine whether sedative drugs are associated with additional adverse respiratory and haemodynamic effects in older patients.

METHODS

Patients who were electively scheduled for lower limb or abdominal surgery were recruited and allocated into one of three groups according to their age and whether midazolam and fentanyl were used: younger (20-40 years); and older (61-80 years) with or without midazolam and fentanyl intravenous infusion.

RESULTS

The study recruited a total of 90 patients (n = 30 per group). Intraoperative bispectral index values were significantly lower than preoperative values in all groups. Patients in the older age group had significantly lower intraoperative bispectral index values than younger patients. Older patients were significantly more likely to experience respiratory depression (arterial oxyhaemoglobin saturation <90%) than younger patients.

CONCLUSIONS

The sedative effect of high spinal anaesthesia is greater in older patients than in younger patients, with an increase in respiratory instability.

Sedation in adults receiving mechanical ventilation: physiological and comfort outcomes

OBJECTIVE

To describe the relationships among sedation, stability in physiological status, and comfort during a 24-hour period in patients receiving mechanical ventilation.

METHODS

Data from 169 patients monitored continuously for 24 hours were recorded at least every 12 seconds, including sedation levels, physiological status (heart rate, respiratory rate, oxygen saturation by pulse oximetry), and comfort (movement of arms and legs as measured by actigraphy). Generalized linear mixed-effect models were used to estimate the distribution of time spent at various heart and respiratory rates and oxygen saturation and actigraphy intervals overall and as a function of level of sedation and to compare the percentage of time in these intervals between the sedation states.

RESULTS

Patients were from various intensive care units: medical respiratory (52%), surgical trauma (35%), and cardiac surgery (13%). They spent 42% of the time in deep sedation, 38% in mild/moderate sedation, and 20% awake/alert. Distributions of physiological measures did not differ during levels of sedation (deep, mild/moderate, or awake/alert: heart rate, P = .44; respirations, P = .32; oxygen saturation, P = .51). Actigraphy findings differed with level of sedation (arm, P < .001; leg, P = .01), with less movement associated with greater levels of sedation, even though patients spent the vast majority of time with no arm movement or leg movement.

CONCLUSIONS

Level of sedation most likely does not affect the stability of physiological status but does have an effect on comfort.

Limitations of anaesthesia depth monitoring

PURPOSE OF REVIEW

We critically review brain function monitors based on the processed electroencephalogram with regards to signal quality, artefacts and other limitations in clinical performance.

RECENT FINDINGS

Several studies have been showing that depth of anaesthesia monitors based on processed electroencephalogram has limitations that can lead to a wrong interpretation of the level of anaesthesia. Processed electroencephalogram indices can be altered by nonanaesthetic influences ranging from artefacts that affect signal quality and signal processing, adverse effects of some anaesthetic and nonanaesthetic drugs, neuromuscular blocking agents to conditions inherent to the patient such as cerebral tumours, brain ischemia and temperature.

SUMMARY

Clinicians should be aware of the several limitations of the commercial devices intending to monitor the depth of anaesthesia, which may not reflect the real underlying level of unconsciousness.

Sedation and regional anaesthesia in the adult patient

This review discusses sedation for regional anaesthesia in the adult population. The first section deals with general aspects of sedation and shows that the majority of patients receiving sedation for regional anaesthesia are satisfied and would choose it again. Methods of assessing the level of sedation are discussed with emphasis on clinical measures. The pharmacology of the drugs involved in sedation is discussed, with propofol and remifentanil appearing to be the combination of choice for sedation in regional anaesthesia. The techniques for administering sedation are discussed and replacement of the traditional repeated boluses or continuous infusion with pharmacokinetic and patient-controlled systems is supported. Patient satisfaction studies suggest that patient-controlled systems are preferred.

Delirium as a disorder of consciousness

Delirium is a common clinical phenomenon, often described as a disorder of consciousness. Delirium is commonly under recognised. The usual response to under recognition is to exhort practitioners to do a better job, but perhaps under recognition should instead be seen as a daily pragmatic challenge to how delirium is conceptualised. Here we retain the view that delirium is a disorder of consciousness, but propose a more multidimensional approach to this key feature. We argue that delirium can be recognised through evaluating arousal, attention and temporal orientation. We suggest that this approach can be validated by testing whether it leads to better delirium identification, accounts for the characteristic clinical disturbances, explains why delirium is common in the extreme age groups and why in later life its boundaries often blend with dementia.

The effects of the extent of spinal block on the BIS score and regional cerebral oxygen saturation in elderly patients: A prospective, randomized, and double-blinded study

BACKGROUND

Patients may become sedated with spinal anesthesia; however, the effect of the extent of spinal block on the Bispectral index (BIS), a processed electroencephalographic variable, has not been fully investigated. We evaluated the influence of the extent of spinal block on BIS values and on regional cerebral oxygen saturation (rSO(2)) in elderly patients.

METHODS

A prospective, randomized, double-blinded study was performed in 55 ASA II patients undergoing urological surgery. The patients were randomly allocated into one of two groups to receive 2.7 ml of 0.5% hyperbaric bupivacaine or 1.5 ml, and then divided into two groups according to level of spinal blockade: high spinal group (Th6 and above) or low spinal group (Th12 and below). Systolic blood pressure (SBP), heart rate (HR), cardiac output (CO), stroke volume (SV), BIS values, and rSO(2) were measured for 30 min. CO and SV were evaluated using impedance cardiograph methods.

RESULTS

The level of spinal blockade was Th4.7 +/- 1.0 in high spinal group (n = 20) and L2.5 +/- 2.2 in low spinal group (n = 20). High spinal anesthesia produced a significant decrease in SBP (p < 0.01) and SV (p < 0.01), but had no effect on CO. High spinal anesthesia significantly decreased BIS values (p < 0.01) without affecting rSO(2). There was relationship between level of spinal blockade and BIS values (r = 0.566). In contrast, no changes in above parameters were found in low spinal group.

CONCLUSIONS

This study provides evidence that the extent of spinal block may have significant influence on BIS values without affecting rSO(2) in elderly patients.

Using EEG to monitor anesthesia drug effects during surgery

The use of processed electroencephalography (EEG) using a simple frontal lead system has been made available for assessing the impact of anesthetic medications during surgery. This review discusses the basic principles behind these devices. The foundations of anesthesia monitoring rest on the observations of Guedel with ether that the depth of anesthesia relates to the cortical, brainstem and spinal effects of the anesthetic agents. Anesthesiologists strive to have a patient who is immobile, is unconscious, is hemodynamically stable and who has no intraoperative awareness or recall. These anesthetic management principles apply today, despite the absence of ether from the available anesthetic medications. The use of the EEG as a supplement to the usual monitoring techniques rests on the observation that anesthetic medications all alter the synaptic function which produces the EEG. Frontal EEG can be viewed as a surrogate for the drug effects on the entire central nervous system (CNS). Using mathematical processing techniques, commercial EEG devices create an index usually between 0 and 100 to characterize this drug effect. Critical aspects of memory formation occur in the frontal lobes making EEG monitoring in this area a possible method to assess risk of recall. Integration of processed EEG monitoring into anesthetic management is evolving and its ability to characterize all of the anesthetic effects on the CNS (in particular awareness and recall) and improve decision making is under study.

Sedation during spinal anaesthesia in infants

BACKGROUND

Neuraxial anaesthesia in adults decreases the dose of i.v. or inhalational anaesthetic needed to reach a desired level of sedation. Furthermore, spinal anaesthesia alone has a sedative effect. The mechanism behind this phenomenon is presumed to be decreased afferent stimulation of the reticular activating system after sympatholysis. We hypothesized that this mechanism is equally active in infants undergoing spinal anaesthesia.

METHODS

In total, 20 unpremedicated former preterm infants underwent surgery under spinal anaesthesia with hyperbaric bupivacaine 0.5% 1 mg kg(-1) with epinephrine 10 microg kg(-1). No additional sedatives or anaesthetics were administered. Sedation was evaluated using the bispectral index (BIS) score and the 95% spectral edge frequency (SEF(95)).

RESULTS

After spinal anaesthesia, mean (SD) BIS began to decrease significantly from baseline 97.0 (1.1) to 83.9 (14.4) after 15 min (P=0.006). BIS decreased further, reaching the lowest values after 30 min [62.2 (14.0); P<0.00001]. Mean (SD) SEF(95) declined from baseline 26.1 (1.8) Hz to 24.3 (3.1) after 5 min (P=0.02) and further to 9.9 (3.8) after 30 min (P<0.00001). Mean arterial pressure also decreased significantly from 66.5 (4.7) mm Hg within 10 min to 56.1 (5.6) after spinal anaesthesia (P=0.0002), while heart rate remained stable.

CONCLUSIONS

These results suggest that sedation after spinal anaesthesia in infants is at least as pronounced as in adults. The sedative effect of spinal anaesthesia should be kept in mind when additional sedatives are administered, especially in former preterm infants.

Sedation during regional anesthesia: inhalation versus intravenous

PURPOSE OF REVIEW

Sedation of patients either with or without regional anesthesia is discussed to ascertain sedation requirements in the two groups. The differences between 'monitored anesthesia care' and conscious sedation are defined. Several current and promising methods with which we can evaluate a patient's degree or level of sedation are assessed. Also noted are safety concerns regarding monitoring solutions for patients undergoing monitored anesthesia care. Well established techniques, including some which are decidedly 'low tech', are examined. Several routes of intravenous administration are discussed along with patient variables. Sevoflurane sedation is mentioned with regards to administration, advantages and drawbacks.

RECENT FINDINGS

Several modalities have been studied for evaluation of a patient's level of sedation, some of which have little applicability in the operating room. Processed electroencephalographic monitoring has tremendous promise but is currently not reliable enough to assess sedation level. Sevoflurane has a role in sedation, providing the limitations are understood. One drawback of sevoflurane is its greater degree of disinhibition when compared with intravenous agents, necessitating conversion to general anesthesia.

SUMMARY

Evaluating the degree of patient sedation is a need that technology has yet to meet. Several techniques have been tried in intensive care units but have little utility in the operating room. Utilization of processed electroencephalogram waveforms has the greatest potential but is of limited value at the present time. Sevoflurane is demonstrated to have a limited role in sedation but may prove useful in specific circumstances.

The changing pattern of anesthesia, 1954-2004: a review based on the content of theCanadian Journal of Anesthesia in its first half-century

PURPOSE

In order to review changes and progress in anesthesiology in the second half of the 20th century, and to recognize the first half-century of the Journal's existence.

SOURCE

The content of the Journal from its inauguration in 1954 through 2004 was reviewed.

RESULTS

Although the data base is that of the Canadian Journal, many of the contributions were from other countries, and for this reason the findings will have relevance both in Canada and elsewhere. The review suggests that anesthesiology evolved in two phases in this period: from 1954 to 1978 and from 1979 to 2004. The first was characterized by the introduction of new drugs and adaptation to new surgical techniques; the second, by a greater emphasis on clinical excellence, outcome, quality patient care both in the operating room and elsewhere in the hospital, and research.

CONCLUSIONS

Although profound advances in knowledge, techniques, and relationships, have shaped the pattern and practice of anesthesiology in this half-century, the basic concerns of anesthesiologists relating to the practice of anesthesia and to their patients remained unchanged. At the same time, the many advances that have shaped anesthesiology in this half-century have extended the understanding of the phenomenon of anesthesia and enhanced the quality of patient care, which gives rise to the hope that anesthesiologists will continue to fully achieve these twin goals in the next half-century.