Patient controlled sedation during central neuraxial anesthesiaM Tripathi1, SS Nath1, A Chaudhary1, PK Singh1, CM Pandey2
1 Department of Anaesthesiology, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow - 226014, India
2 Department of Biostatistics, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow - 226014, India
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0022-3859.52841
Source of Support: None, Conflict of Interest: None
Background: Patient controlled sedation (PCS) gives liberty to patients to choose the time of sedative administration to attain a desired level of comfort. Aims: The PCS use was evaluated in patients during surgery under central neuraxial blockade. Settings and Design: Prospective, cross-sectional, clinical study on consecutive patients in a tertiary care university hospital. Materials and Methods: PCS technique, using propofol (1%) 2 ml in 2 min was used in 160 adult patients undergoing urologic procedures under central neuraxial block. We observed the time to first PCS activation by patient, duration of surgery, propofol dose, sedation score, hemodynamic stability, patient's acceptability, and the factors correlating with the PCS use. Statistical analysis used: Non-parametric two-tailed Pearson's test, univariate correlation analysis for the factors favoring PCS use followed by multivariate logistic regression analysis amongst correlating factors. Results: In our cohort, the majority (83%) of the patients activated PCS during surgery under central neuraxial blocks at median time of 30 min and (17%) did not activate PCS. Female patients activated sedation earlier (median 15 min) than male patients (median 30 min). All patients were hemodynamically stable and without significant side effects. Multivariate analysis showed that sedative use significantly ( P <0.05) correlated with female gender (odds ratio-3.54 [IR-2.64 to 4.73]) and prolonged surgery (>90 min). Majority (91%) of patients rated PCS technique excellent to good. Conclusions: PCS was very well accepted by patients during central neuraxial block. Propofol regimen (2 ml in 2 min) in PCS was safe, as it caused neither apnea nor significant hypotension.
Keywords: Central neuraxial anesthesia, epidural block, patient controlled sedation, propofol, subarachnoid block
It is widely accepted that the central neuraxial blocks (epidural and spinal) are effective and safe methods during surgery below the diaphragm. Stress factors in operation room, block level mismatch from the area of surgery, and patchy epidural effect  due to retained air pockets  may contribute to discomfort, anxiety, and restlessness in patients under spinal/epidural anesthesia. Therefore many anesthesiologists favor supplementary sedation. ,, Since over-sedation may jeopardize the safety of the patient, obligatory sedative administration by anesthesiologist is debatable. Patients are the best judge of their discomfort and the patient controlled sedation (PCS) gives liberty to patient to attain sedation by their assessment. It has been used with excellent satisfaction during dental extraction,  and plastic surgery under local anesthesia.  PCS devices are modified syringe pumps, which can deliver a predetermined bolus dose of drug in a defined time interval with or without a lockout time. Since the sedated patient cannot activate PCS button, they are protected from overdosing themselves, which forms an in-built safety. There are very few studies done on PCS use during epidural block,  and none has been done during spinal block.  We postulated that the non techno-savvy patients might have difficulty in handling it. Thus, the aim of our study was to evaluate PCS use during surgery under central neuraxial block.
Approval for the study was taken from the Institute's ethical committee and informed, written consent was taken from the patients after explaining the device and the nature of the study. Priori sample size for the study was calculated by using G*Power version 3.0.8 (University Kiel, Kiel, Germany) and assumption was that that all patients will use sedation and a +10% difference in sedative use from constant (one sample case), a error probability (0.05), and power of test (1-b) 95%. Based on these assumptions the 156 patients were required to be studied. Thus this prospective study included 160 consecutive healthy (American Society of Anesthesiologists grade I and II), adult patients of both genders, posted for elective urologic procedures under central neuraxial blocks over a period of six months. Patients with a history of neurological disorders like stroke, hemiparesis, mental retardation, or chronic backache, were excluded from the study at the time of pre-anesthetic assessment.
On the day of surgery, an intravenous catheter (20G) was inserted into a large vein on the dorsum of the non-dominant hand of all patients. This catheter was then connected via extension tubing to the propofol (1%) syringe of the patient controlled infusion pump (PCIP), Graseby-3300PCA pump (Graseby Medical Limited, UK). The PCIP activation button was tied to the dominant hand of the patient. The PCS protocol was set to deliver propofol (1%), 20 mg bolus in 2 min, on its activation without lockout time.  One day prior to the surgery, the use of the pump was thoroughly explained to each patient and they were able to experience the force needed to activate the PCS. No sedative, anxiolytic premedication or background propofol infusion were prescribed to these patients on the morning of surgery.
We monitored all patients with electrocardiography (lead II), non-invasive arterial blood pressure, and pulse oximetry (SpO 2 ). All patients were given oxygen by facemask and were encouraged to use PCS until they felt relaxed. The side stream connecting line of the capnometer was placed under the facemask to detect airway obstruction (absence of carbon dioxide during exhalation). Patients were placed in the left lateral position. Under full aseptic precaution, subarachnoid block ( n =113) was performed at the lumbar interspinous space (L 2 -L 3 or L 3 -L 4 ). Hyperbaric bupivacaine (0.5%) 1.5 to 2 ml was used for subarachnoid block. For patients undergoing epidural block, the epidural catheter ( n =47) was placed in similar spinal spaces and isobaric bupivacaine (0.5%) 12 to 15 ml was injected. Additional doses of bupivacaine (0.5%) 5 ml were given epidurally at hourly interval. The block level was assessed by pinprick on skin along the mid-axillary line. Surgery was allowed after ensuring block level up to T 6 segment.
We observed for the level of sedation was assessed on observers' assessment of alertness/sedation (OAA/S) score [Table 1] every 5 min in the first 30 min and then at 15 min intervals until the end of surgery. Since interaction (e.g. reaction to verbal command) with patient is likely to change the level of sedation, the conversation was initiated if the patient talked or moved. We also recorded time from block to first PCS activation, number of good press (activating PCS pump/hour), duration of surgery, and maximum level spinal block. Each patient was visited in the ward the following day, and asked to fill in a questionnaire for their assessment about the anesthesia technique in terms of satisfaction, ease of use, preference to use in future, and their reason for the first activation.
The data was entered in statistical package SPSS-10.0 for windows (SPSS Inc, Chicago, IL). Non-parametric two-tailed Pearson's correlations coefficient, univariate analysis was done between PCS use and the patient characteristics [educational qualifications (matriculation or non-matriculation); social background (rural or urban)], type of surgery (endoscopic or open surgery), type of block (spinal or epidural), and the patient's position, duration and types of surgery. Later multivariate logistic regression correlation was performed between the identified correlating factors for PCS use. The log rank test was used to analyze the difference in initiating PCS use by two genders during surgery and a Kaplan-Meier graph was plotted. A calculated value of P <0.05 was considered statistically significant.
The mean age of the cohort was 45 years. There were more males (115) than females (45). The onset time for spinal block was faster (mean+SD; 4+1.2 min) than epidural block (9+3.2 min). The level of spinal segmental block were similar in all two types of neuraxial techniques and the more patients in spinal block (45%) had tendency to develop more than 20% fall in systolic arterial pressure than epidural block (22%) patients [Table 2]. Although a majority of the patients (83%) used sedation at one or more points of time during surgery, a significant number of patients (17%) even without sedative use remained quiet during surgery under regional anesthesia. Thus, the median sedation score (IR-25%-75%) 3 (1-4) was attained by all patients during surgery [Table 2].
The characteristics like age, gender (female using more than male), social background (urban using more than rural), type of surgery (open procedure using more than endoscopic), duration of surgery (more use with prolonged [>90min] surgery), and type of neuraxial block (spinal using more than epidural block) showed a significant correlation with PCS use on univariate analysis. However, multivariate stepwise logistic regression analysis with these factors showed that only the prolonged surgery and female gender significantly ( P <0.05) correlated with the PCS use [Table 3].
The Kaplan-Meier graph depicted the probability of PCS use in female versus male patients [Figure 1]. The median (IR) time interval to the first PCS activation in female patients was 14.5 (10-45) min and in male patients was 30 (15-45) min. On regrouping patients on the basis of longer surgery >90 min, (94%) patient used sedation, but 3 (6%) still did not use PCS after 2 hours of surgery under epidural block [Table 4]. The main side effect noticed in 8% patients was pain at the site of propofol injection and restlessness in 4% [Table 5].
There were 34 (21%) patients who activated PCS only once and of these, 24 (71%) within one hour of the start of surgery. The majority of patients (91%) rated this anesthesia method good to excellent. Although 31% of the patients had not studied up to matriculation, only nine (6%) patients expressed difficulty in understanding its use. Regarding use of the method, 5 (3%) did not recommend its reuse and 20 (12%) patients preferred not to decide on their own but to leave this decision to the attending anesthesiologist [Table 6].
The main findings of this study are that the patient controlled sedation was well understood and satisfactorily used by Indian patients in spite of varied education (matriculation vs. non-matriculation), and social background (rural vs. urban). The state of relaxation during surgery under spinal/epidural block corresponded with OAA/S score of '3' i.e. 'lying still, eyes closed but arousable to command' either with or without sedation use. The PCS protocol of propofol (bolus of 20 mg in 2 min without lock out time) could be safely used to provide sedation without apnea.
For the proper functioning of the PCS and to reap maximum benefit from the technique, patient's cooperation and understanding about it is essential. Contrary to our belief, the majority (91%) Indian patients in study expressed satisfaction (excellent to good) with PCS use. This is consistent with the greater level of satisfaction in the PCS group than the anesthesiologists administered sedation or propofol infusion in western population.  The higher satisfaction with PCS is correlated with positive psychological control over the situation. ,, Female patients activated PCIP earlier (median first press-15 min) than male (median first press-30 min). It could probably be due to a higher level of anxiety in females related to the site of surgery being lower abdomen and perineum in our study.
Although a majority of the patients activated PCIP, still 17% did not use it. Interestingly amongst the PCS users, 24/133 (18%) patients activated PCIP only once during surgery lasting for an hour and 19 (79%) of these patients responded that they activated PCIP being inquisitive to see the response and neither had any intention of getting sedated nor had discomfort in the questionnaire. This means that nearly 41 (26%) patients may not require sedation during short surgery (<90 min) under spinal/epidural block.
Anesthesiologists often administer intermittent bolus or infusion of centrally acting drugs ,, to patients during regional anesthesia. The bolus technique may abruptly raise drug levels in blood and the effect-site, to show variability in sedation level, apnea and the hemodynamic instability.  The continuous infusion tends to increase blood concentration over time, , and may require frequent adjustments in infusion rate. Therefore, while obligatory sedatives may not be necessary in nearly 26% patients, it can unduly expose patients to deep sedation, loss of airway control and cardio-respiratory depression. Although PCS gives control of sedative delivery in hands of patient, we wish to emphasize that it cannot be a substitute for monitored anesthesia care by anesthesiologist.
Spinal  and epidural blocks  are known to reduce anesthetic requirements and induce sleep. The hypothesis to explain this is by a decrease in afferent sensory input with consecutive inhibition of the reticulo-thalamo-cortical mechanisms,  as systemic levels of bupivacaine do not seem to explain sedation.  This could easily explain observed sedation in non-PCS users and the effective small bolus of propofol (0.66 mg/kg) for sedation.
Propofol offers faster onset of pharmadodynamic effect and has been shown to have higher patient preference.  It has the distinction of less respiratory effect,  less post-operative sedation, drowsiness, confusion, clumsiness, and amnesia with rapid recovery of cognitive function, , to make our preference for it in PCS. The propofol doses, the lockout intervals and the use of continuous infusion have been variedly studied. , Propofol in bolus injection is associated with transient apnea,  hypotension and to avoid these a slow rate of infusion is recommended.  The protocol of fixed dose (20 mg) delivery in 2 min not only avoided apnea and hypotension but retained the lockout safety by keeping the PCS refractory during slow drug delivery in 2 min. Coimbra and colleagues have also reported safety of a no lockout regimen for propofol sedation,  however SpO 2 monitoring and oxygen by face mask is recommended.  Ghouri and colleagues  used propofol 2 ml bolus on demand with a background infusion of propofol but thinking that compulsory sedation by infusion might impair decision-making power in our patients, we did not use propofol infusion.
Ganapathy and colleagues  reported pain on propofol injection in 80% patients. As we added lignocaine (2%) with the propofol, only 5% of the patients reported pain during its infusion which is similar to previous reports. , Hence, routine use of lignocaine mixing shall be practiced. Two patients had brief episodes of hypotension correlating with the spinal anesthesia and responded to rapid infusion of crystalloid. Six (4%) patients during surgery shuffled excessively to attain comfortable position and disturbed the operating surgeon. These patients also repeatedly kept activating PCS in the period of surgery lasting longer than 90 min. Although they did not complain of pain at the site of surgery, probably, the prolonged supine posture induced pain in the upper unblocked area of the body was the source of discomfort and restlessness.  Hence, we feel that addition of an analgesic drug to the PCS regimen could be beneficial.  This aspect can be a future area of investigation.
Since it was a cross-sectional study, the results could be viewed with limitation for unequal distribution of patients between PCS use. Randomization of patients to get similar patient distribution in two significantly correlating factors like gender and duration of surgery can give better understanding to the multi-factorial effects on sedation need.
In conclusion, a slow bolus delivery of propofol in 2 min without lockout setting of PCS was effective, safe, and satisfactory to patients during central neuraxial block, although a significant number of patients preferred not to use sedation during short surgical time.
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]