The effect of peribulbar block with ropivacaine on bi-hemispheric cerebral oxygen saturation in aged patients

Authors


V. Fodale
E-mail: vfodale@unime.it

Summary

We evaluated the effects of peribulbar block for eye surgery on bi-hemispheric regional cerebral oxygenation (rSO2) of aged patients. In 66 adult patients, peribulbar block was performed using ropivacaine 10 mg.ml−1 with hyaluronidase 100 IU.ml−1. Cerebral oxygenation was monitored using continuous non-invasive, near-infrared spectroscopy. The rSO2 data on the side where the eye block was performed were evaluated as eye block side values, whereas the data recorded on the other side were taken as control values. Mean rSO2 values on the side where regional block was performed were not significantly different from control values (p > 0.05). Nevertheless, in several patients, a slight desaturation in the cerebral hemisphere on the block side was detected. Therefore, in aged patients, peribulbar block with ropivacaine does not significantly modify bi-hemispheric rSO2, but rSO2 monitoring during peribulbar block should be a field of future research in aged patients with brain injury or disease.

Ophthalmic surgery is the most frequent surgical procedure requiring anaesthesia in developed countries [1]. Nearly 2 000 000 patients undergo cataract surgery each year in the United States and most procedures are performed under regional anaesthesia [1]. Peribulbar block for eye surgery has become increasingly popular, with advocates stating that it is a safer alternative to general anaesthesia as it offers satisfactory analgesia and akinesia [2, 3], but serious complications and accidental brainstem anaesthesia have been extensively described [4–7]. In addition, patients scheduled for intra-ocular surgery are often elderly and may have, per se, an increased risk of peri-operative neurological complications as well as cerebral ischaemia. In fact, data indicate that patient age affects regional cerebral oxygen saturation (rSO2) values [8]. Intra-operative cerebral oxygen desaturation has been associated with an increase in peri-operative stroke rate, total length of hospital stay, postoperative cognitive dysfunctions and number of adverse clinical outcomes [9]. Therefore, oxygen status dynamics during anaesthesia is one of the most important issues of anaesthetic monitoring in aged patients.

As the possibility of a life-threatening complication occurring is rare but unpredictable, the need for greater safety and for closely monitored anaesthesia care of all patients during eye block has been emphasised in the last 20 years [1]. Cerebral oximetery is a brain oxygen saturation monitoring technique introduced to evaluate brain rSO2 using continuous non-invasive, near-infrared spectroscopy. It reflects changes in cerebral oxygenation as indicated by electroencephalographic evidence of brain ischaemia [10]. During surgery, cerebral oximetry provides patient benefits including a reduction in neurological complications and in the length of hospital stay [9, 11]. Nevertheless, no data are available about the effects of regional anaesthesia for eye surgery on cerebral rSO2.

The aim of the present study was to evaluate the effects of peribulbar block on bi-hemispheric cerebral rSO2 in aged patients and thus determine the utility of cerebral oximetry for monitoring the brain effects and complications of regional anaesthesia for ophthalmic surgery. The hypothesis was that peribulbar block performed for ophthalmic surgery does not affect bi-hemispheric cerebral rSO2 values.

Methods

After informed consent and approval of the Institutional Review Board, we enrolled a series of consecutive elderly patients scheduled for elective, short-duration, ophthalmic procedures under peribulbar block in a prospective, observational study. Inclusion criteria were age over 60 years and ASA status 1–3. Patients with allergies to local anaesthetics, previous cerebral diseases, and with icterus or low haemoglobin concentrations (because of their interference with cerebral near-infrared oximetry measurement) were not included.

On arrival in the anaesthetic room, standard monitoring with continuous electrocardiography, non-invasive arterial blood pressure monitoring and peripheral pulse oximetry was started. An intravenous cannula was inserted for the administration of emergency drugs, if required. Regional cerebral oxygenation was monitored in both cerebral hemispheres using continuous bilateral non-invasive monitoring equipment (INVOS 5100B, Somanetics; Troy, MI, USA) [8]. This method uses near-infrared light at 730- and 810-nm wavelengths to measure the absorption spectra of total haemoglobin and deoxyhaemoglobin in the frontal cerebral cortex. One light-emitting diode and two detectors, spaced 3 and 4 cm from the light-emitting diode, were used. The 3-cm detector is assumed to primarily measure the light passing through shallow structures such as the skull, skin and soft tissues. The 4-cm detector is assumed to measure light passing through both the shallow structures and a deeper banana-shaped path in the frontal cerebral cortex.

Peribulbar blocks were performed by experienced doctors using a technique previously described [1]. The local anaesthetic used was a 9–10-ml mixture of ropivacaine 10 mg.ml−1 (10 ml) with hyaluronidase 100 IU.ml−1 (3 ml). As the local anaesthetic was injected, orbital compression of 20 mmHg for 10 min was maintained. A similar volume of saline solution was not administered to the contralateral eye (control) because of potential effects from mass pressure.

Haemodynamic variables (heart rate, mean arterial pressure), peripheral oxygen saturation (Spo2) and cerebral bilateral rSO2 values were measured and stored at the following times: before administration of regional anaesthesia (0 min) and 1, 3, 5, 10, 15 and 20 min after the block. During data collection, the investigator was blinded to the side (right or left eye) where the block was performed. The cerebral rSO2 data on the side where the eye block was performed were evaluated as eye block side values, whereas the data recorded on the other side were considered control values.

Statistics

Data were expressed as mean (SD). The heart rate, mean arterial pressure and Spo2 values were analysed with Student's t-test for independent groups. anova for repeated measurements was performed to analyse whether the changes in rSO2 were statistically significant. To fulfil the criteria for a significance of p < 0.05 (α) and β 0.2, leading to a statistical power of 80%, at least 63 patients were needed for the study plan to detect a 10% difference in rSO2. Thus, 68 surgery patients were included, in case of any dropouts. A p-value < 0.05 was considered statistically significant.

Results

Sixty-eight patients were initially enrolled in the study; however, case data were not fully saved for two patients, leaving 66 patients with complete data sets. Demographic variables of patients involved in the study, right/left eye anaesthetised, local anaesthetic administered and baseline rSO2 values are reported in Table 1. No sedation or supplementary oxygen was used. A wide range of variability of basal rSO2 values was detected (range: 51–90 and 53–83% in the eye block and control side, respectively).

Table 1.   Demographic variables of patients involved in the study, right/left eye anaesthetised, dosage of local anaesthetic administered and baseline rSO2 values.
  1. All variables are expressed as mean (SD).

Patients; n66
Sex; M : F21 : 45
Age; years70 (6)
Weight; kg69 (8)
Eye blocked; right : left34 : 32
Baseline rSO2; %
 Eye block side69 (7)
 Control67 (8)
Doses of anaesthetic mixture; ml 9.5 (0.3)

Mean cerebral rSO2 values on the side where regional block was performed were not significantly different from control values throughout the observation period (p > 0.05) (Fig. 1).

Figure 1.

 Mean cerebral rSO2 values on the side where regional block was performed and on opposite side (control values) throughout the observational period. Error bars are SD. There were no significant differences between the two groups.

Nevertheless, bilateral monitoring detected a slight desaturation in the cerebral hemisphere on the eye block side 3–5 min after anaesthetic injection, slowly returning to basal values within 15 min. Although the slight desaturation did not meet our criteria for statistical significance, it may be of interest to note that it was related to a decrease in rSO2 (ranging 10–22%) on the eye block side in 12 of 66 patients (18.2%), whereas two patients experienced a bilateral reduction in rSO2 ranging between 12–18%. These patients did not experience any clinical symptoms related to desaturation of the cerebral hemisphere.

No significant changes in mean arterial pressure, Spo2 or heart rate were noted after regional anaesthesia in comparison with basal values before performing the block (p > 0.05) (Fig. 2). There were no block-related complications.

Figure 2.

 Changes in heart rate (HR), mean arterial pressure (MAP), and peripheral oxygen saturation (Spo2) throughout the observational period. Error bars are SD. There were no significant differences.

Discussion

Although uncommon, central spread of local anaesthetic and brainstem anaesthesia is a potentially life-threatening complication of peribulbar block for eye surgery. Although peribulbar anaesthesia generally carries a low risk of serious complications when compared with retrobulbar block, brainstem anaesthesia, respiratory and cardiac arrest may still occur [6]. The postulated mechanism of brainstem anaesthesia, as for other regional eye blocks, is the direct injection of local anaesthetic into the dural sheath of the optic nerve and subsequent tracking along the nerve and chiasm to reach the subarachnoid space of the middle cranial fossa, the pons and midbrain [12]. Another possible cause is retrograde arterial spread from the posterior orbit into the fat outside the dural sheath [1, 13, 14]. Clearly, there is a continuum of sequelae, depending on the amount of drug reaching the central nervous system and the specific area of the brain to which the drug spreads [5].

The data from our study suggest that, in aged patients, peribulbar block for ophthalmic surgery, performed with ropivacaine by experienced staff and in the clinical conditions considered, does not significantly modify cerebral rSO2 values. Nevertheless, in one-fifth of the patients, we observed an abrupt mean decrease in rSO2 on the side where the block was performed 3–5 min after anaesthetic injection, followed by a return toward baseline values 15 min after ropivacaine administration. At the same time, two patients experienced a bilateral reduction in rSO2. However, none of the patients developed clinically detectable signs, symptoms or regional brain failure after the regional anaesthesia. If significant reductions in regional Sao2 may be tolerated without evidence of brain failure [15], monitoring and maintaining rSO2 75% above baseline values may be associated with a significant decrease in peri-operative stroke rate and overall number of adverse clinical outcomes [9]. In addition, the absence of clinical signs in our patients could be related to good compliance of the healthy brain, whereas in subjects with brain disease or injuries, with borderline rSO2 values, a relative cerebral desaturation might not be tolerated. These patients may experience a possible brain failure or cerebral ischaemia. The anaesthetist must maintain a high index of suspicion for these potential complications and must undertake appropriate monitoring. Therefore, although the decrease in rSO2 did not meet our criteria for statistical significance for the entire study group, these findings suggest that in aged patients cerebral oximetry could be an effective, non-invasive method of monitoring regional cerebral oxygenation changes during regional anaesthesia for ophthalmic surgery.

We chose ropivacaine because it provides better ocular akinesia than a bupivacaine-mepivacaine mixture, reduces the need for top-up injections, and also causes less pain on injection [16]. In addition, 1% ropivacaine as the sole agent for peribulbar anaesthesia is comparable with a mixture of 0.75% bupivacaine and 2% lidocaine [17, 18]. In our study, variables were measured and recorded up to 20 min after the block as major complications generally occur within 10–15 min of the block for eye surgery, generally before surgery has commenced [12].

This study has some limitations. First, the small number of patients may have hidden some true variations, but the number of patients included in each group of our study is very similar, or higher, to previous ones evaluating the modification of cerebral rSO2 during procedures performed with regional anaesthesia [19–21]. Other limitations in our study are imposed by the constraints of patient safety in clinical research limiting invasive monitoring. As previously shown [15], data of near-infrared spectroscopy are limited to the brain region being examined by near-infrared light, and the absence of simultaneous measurements of cerebral blood flow, arterial and jugular venous blood gases could have underestimated the brain effects of regional anaesthesia.

The clinical relevance of this study is that in aged patients, peribulbar block for eye surgery, performed with ropivacaine and in the clinical conditions considered in our study, does not significantly modify bi-hemispheric cerebral rSO2. Nevertheless, extrapolation of several data from our findings suggests that bilateral monitoring of cerebral oximetry should be a field of future research to study the effects of regional anaesthesia, especially in aged patients and in subjects with brain injury or disease.

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