Abstract
Background
Conscious sedation during spinal anaesthesia can be achieved by administering propofol using manual controlled infusions (MPI) or target-controlled infusions (TCI). We compared the characteristics of sedation with propofol administered by MPI and TCI in patients undergoing lower limb surgery under spinal anaesthesia.
Methods
A total of 60 patients aged 18–60 years with American Society of Anaesthesiologists physical status 1 and 2 who were scheduled for elective lower limb surgery of an anticipated duration of 1–2 h under spinal anaesthesia were enrolled. Participants were randomly allocated in 1:1 to either Group TCI or Group MPI to receive propofol sedation to maintain OAA/S 3. The primary outcome measure was the recovery time. Secondary outcomes were time to reach the desired level of sedation (OAA/S 3) and the total dose of propofol consumed.
Main results
The mean recovery time was 6.23 ± 1.63 min in the TCI group and 7.30 ± 1.44 min in the MPI group ( p = 0.010). The total dose of propofol used in the TCI group (230.07 ± 83.77) was significantly higher than in the MPI group (162.33 ± 62.29) with a p = 0.001. A very strong positive correlation was observed between OAA/S and BIS in the TCI group ( r = 0.969) as well as in the MPI group ( r = 0.955) with a p < 0.001.
Conclusion
With the study design employed, TCI was associated with a faster recovery and MPI with less propofol consumption. There was a high correlation between OAA/S and BIS values.
1
Introduction
Spinal anaesthesia is a widely used technique for lower limb surgeries due to its ability to provide excellent operating conditions while avoiding the risks associated with general anaesthesia. However, being awake during a surgical procedure may lead to patient anxiety, recall of the procedure and non-cooperation, thereby reducing surgeon and patient satisfaction. Hence, sedation and some anxiolysis and amnesia should be offered to all patients undergoing surgery under regional anaesthesia to increase patient comfort and satisfaction and their acceptance of the regional anaesthesia technique. Sedation has a spectrum ranging from anxiolysis to deep sedation. Achieving minimal to moderate sedation allows verbal communication with the patient without respiratory depression or obtundation of airway reflexes. It aims for a comfortable and pain-free patient who is sedated but remains arousable, able to obey commands and maintain the airway independently while avoiding potential risks like respiratory depression, haemodynamic instability and involuntary movements. Thus, it is important to titrate the level of sedation carefully as oversedation may negate many of the advantages of regional anaesthesia. Many previous studies have proven that subarachnoid bupivacaine enhances the hypnotic effects of midazolam, thiopentone and propofol. , This interaction can be explained by the systemic effects of the absorbed local anaesthetics, rostral spread of local anaesthetic with direct action on the brain and deafferentation. , Due to a decrease in dose requirements during subarachnoid block, it becomes even more essential to precisely titrate intraoperative sedation and also ensure the patient is awake and alert at the end of surgery.
Propofol is a commonly used agent for conscious sedation due to its rapid onset, titration capabilities, amnesic and antiemetic effects and prompt and clear-headed recovery, even after prolonged infusion. Propofol sedation can be achieved by administering repeated boluses, manual controlled infusions or target-controlled infusions (TCI) . , Sedation with single or repeated doses of propofol results in unstable blood and target organ concentrations, variable sedation levels, and hemodynamic side effects. In a manual controlled infusion, a loading dose is administered followed by a continuous infusion. This results in increased blood concentrations over time and the infusion rate needs to be changed manually intermittently to maintain a desired level of sedation. This problem can be eliminated by using a target -controlled infusion (TCI) in which a target plasma or effect site concentration is set and the microprocessor -controlled infusion pump adjusts the rate of infusion based on pre- programmed pharmacokinetic models of that drug. TCI offers distinct advantages in terms of precise dosing and maintaining of desired sedation levels but requires use of specialized equipment. , The purported advantages of TCI are that the concentration of the drug at the effect site reaches equilibrium more rapidly, maintenance of equilibrium is easier, and if the level of sedation needs to be changed, a new equilibrium can be reached faster and more easily. This method offers real-time feedback allowing clinicians to have precise control over drug delivery. While TCI offers advantages in terms of precision and control, its widespread adoption may be hindered by the requirement of dedicated equipment and the associated learning curve.
While TCI offers advantages in precision and control, a manually controlled infusion remains a viable option, especially where TCI equipment is not readily available. The aim of this study was to compare the characteristics of sedation with propofol administered by a manually controlled propofol infusion (MPI) and TCI in patients undergoing lower limb surgery under spinal anaesthesia with regards to recovery and onset times of sedation and total propofol consumption. We hypothesized that use of propofol by TCI is associated with a quicker recovery and faster onset of a desired level of sedation when compared with MPI.
2
Methods
2.1
Ethics approval
This prospective, randomized, double-blind controlled trial was conducted in the Department of Anaesthesiology at Maulana Azad Medical College and associated Hospitals, New Delhi, India between December 2022 and December 2023. The study protocol was approved by the Institutional Ethics Committee on 28 August 2022 and the trial was prospectively registered under the Clinical Trials Registry of India (CTRI/2022/11/047789) on 30 November 2022. The trial adheres to the principles of the Declaration of Helsinki. Written and informed consent was obtained from all participating patients. This manuscript adheres to the Consolidated Standards of Reporting Trials (CONSORT) guidelines for randomized controlled trials. The full trial protocol and statistical analysis plan are available on request.
2.2
Inclusion and exclusion criteria
We studied adults of American Society of Anaesthesiologists (ASA) physical status I/ II of ages 18–60 years of either sex scheduled to undergo elective lower limb surgery of an anticipated duration of 1–2 h under spinal anaesthesia. Patients with contraindications to spinal anaesthesia or previous failed spinal anaesthesia, long-standing diabetes mellitus, cardiac or neurological disease, neuropsychiatric disorders, renal or hepatic disease, hypersensitivity to soybean/egg, chronic treatment with opioids/sedatives, obesity (BMI>30kg.m −2 ), anticipated difficult airway and pregnant women were excluded.
2.3
Randomization and group allocation
Prospective patients were screened for eligibility and included in the study on the morning of surgery. Randomization was done by computer-generated numbers and allocation into groups by opening a sealed opaque envelope before surgery by an anaesthesiologist not involved in the study protocol. Patients were randomly allocated in 1:1 to either Group TCI to receive propofol sedation using a target -controlled infusion pump or Group MPI to receive propofol sedation using a manually controlled infusion pump.
2.4
Blinding
Patients were blinded to their group allocation. Preparation of all the study material and conduct of anaesthesia was done by an independent anaesthesiologist who was not involved in the subsequent conduct of the study. Intraoperative observations were made by an anaesthesiologist who was unaware of the patient’s group allocation. The infusion pump being used (manual or TCI) was concealed under the drapes and required adjustments were made by another investigating anaesthesiologist.
2.5
Anaesthesia technique
A detailed pre-anaesthetic check-up including history, physical examination, and investigations as indicated was carried out in all patients. The anaesthetic procedure was explained and written informed consent was obtained in a language that was understood by the patient. All patients were fasted as per ASA guidelines. On arrival in the operation theatre, standard monitoring was instituted consisting of ECG, non-invasive blood pressure (NIBP), pulse oximetry and Bi-spectral index (BIS). Intravenous access was secured and lactated Ringer’s solution 5–7 mL/kg was infused before the spinal block.
Spinal anaesthesia was administered in the sitting or lateral position using a full aseptic technique. After subcutaneous infiltration with 1 ml of 2 % lignocaine at L3-L4 or L4-L5 interspace, using a 25 G spinal needle by a midline approach, 12.5 mg 0.5 % hyperbaric bupivacaine was injected intrathecally. The patient was then made supine and the propofol infusion was started using a MPI or TCI pump as per group allocation.
The level of sedation was assessed using the observer’s assessment of alertness/sedation (OAA/S) scale in which an observer graded the level of sedation from 1 to 5 where 5 is fully awake, 4 is drowsy, 3 is a patient whose eyes are closed, but is immediately responsive to verbal stimulation, 2 is a patient with eyes closed but who is only responsive to physical stimulation and 1 is a deeply sedated patient who does not respond to physical stimuli. The desired target sedation level was a score of 3 on the OAA/S scale (OAA/S3).
2.5.1
Group TCI
The patients received propofol infusion with a TCI pump using the Schnider model with an initial target plasma concentration set at 1.5mcg/ml. The propofol dose administered was adjusted by increasing or decreasing the plasma concentration of propofol in 0.2 mcg/ml increments to maintain OAA/S3.
2.5.2
Group MPI
The patients received propofol using a manual infusion pump in a bolus of 0.5 mg/kg followed by a maintenance infusion of 1.5 mg/kg/h. If the OAA/S score was >3, a bolus of 10 mg propofol was administered and the infusion rate was increased by 0.25 mg/kg/h. If the patient had an OAAS score <3, the propofol infusion was paused till an OAS/S 3 was achieved and the subsequent infusion rate was decreased by 0.25 mg/kg/h.
During surgery, all patients in both groups received oxygen by nasal cannula @ 2 l/min. If SpO2 fell to < 94 %, 100 % oxygen was to be given using an anaesthesia circuit. In both groups, administration of propofol was stopped at the end of the surgery (once dressing was commenced).
2.6
Measurements and data handling
The OAA/S score was recorded before spinal anaesthesia, after giving spinal anaesthesia, every one min after starting sedation until OAA/S 3 was reached, and then every 10 min till the end of surgery. Values of BIS were also recorded at the same time as the OAA/S. The time taken to reach an OAA/S 3 was noted. Intraoperative haemodynamic parameters, mean arterial pressure (MAP), systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate (HR) was recorded before spinal anaesthesia, after giving spinal anaesthesia, 5 min after starting sedation and then every 10 min till the end of surgery. Propofol infusion was stopped at the end of the surgery and the OAA/S was noted every 1 min after stopping the propofol infusion until adequate response to verbal commands was regained or OAA/S was equal to 5. Recovery time was noted as time from the discontinuation of propofol infusion until OAA/S score was 5. The total dose of propofol used was recorded. Patient satisfaction and surgeon satisfaction were assessed after surgery in the PACU using a 5-point Likert scale as excellent, very good, good, fair or poor. Any complications like pain on injection, nausea and vomiting, oxygen desaturation (SpO2<94 %), breath holding, apnea, bradycardia (HR < 50 beats/min), and agitation were noted.
2.7
Primary and secondary outcomes
The primary outcome measure was the recovery time. Secondary outcomes were time to reach the desired level of sedation (OAA/S 3) and the total dose of propofol consumed.
2.8
Sample size calculation
In an earlier study, the mean recovery time in the TCI group was 3.6 ± 1.09 min and 5.1 ± 1.7 min in the MPI group. Taking these values as reference and at 95 % confidence interval and 80 % power, the sample size was calculated as 28 per group. We recruited 30 patients to either group to account for any attrition.
2.9
Statistical analysis
Data was collected and analyzed using Statistical Package for Social sciences version 25.0 software. The normality of the distribution of data was assessed using the Kolmogorov-Smirnov and Shapiro-Wilk tests. Quantitative data was expressed as Mean ± standard deviation or median with inter-quartile range and depended on normality of distribution. The difference between the two means was tested by the student t -test or Mann Whitney U test while for pre-post comparison, paired t -test or Wilcoxon signed rank was used. Qualitative data was expressed in frequencies/percentages and the difference between the proportions was tested by the chi-square test or Fisher’s exact test. A p value < 0.05 was considered statistically significant.
3
Results
Sixty- six patients were screened for participation in the trial. Three patients had limited mouth opening, one had BMI> 30 kg. m −2 and two patients refused to give consent. Sixty patients were randomized to Group TCI and Group MPI and their data was analyzed ( Fig. 1 ).
3.1
Patient characteristics
No differences in baseline patient characteristics were observed between the study groups ( Table 1 ).
| Parameter | TCI group ( n = 30) | MPI group ( n = 30) | p value |
|---|---|---|---|
| Age (years) | 33 [48.5-25.5] | 29[45-22] | 0.233 |
| Sex (Male/Female) | 24/6 | 23/7 | 0.754 |
| Height (cm) | 169 [176-162] | 168 [170-162] | 0.236 |
| Weight (kg) | 69 [77-60] | 68[74–60] | 0.261 |
| BMI (kg. m −2 ) | 24.37 ± 3.14 | 24.19 ± 2.84 | 0.820 |
| ASA class (I/II) | 21/9 | 17/13 | 0.284 |
3.2
Primary outcome
The mean recovery time was 6.23 ± 1.63 min in the TCI group and 7.30 ± 1.44 min in the MPI group ( p = 0.010) ( Table 2 ).
| Parameter | TCI group ( n = 30) | MPI group ( n = 30) | p value |
|---|---|---|---|
| Duration of sedation (min) | 86.53 ± 14.61 | 88.47 ± 12.95 | 0.590 |
| Duration of surgery (min) | 81.03 ± 14.74 | 83.00 ± 12.70 | 0.582 |
| Recovery time (min) | 6.23 ± 1.63 | 7.30 ± 1.44 | 0.010 |
| Onset time (min) | 4.70 ± 1.56 | 5.37 ± 1.65 | 0.113 |
| Total dose of propofol (mg) | 230.07 ± 83.77 | 162.33 ± 62.29 | 0.001 |
| Pain on injection | 22/8 | 16/14 | 0.108 |
| Bradycardia | 3/27 | 2/28 | 0.640 |
| Oxygen Desaturation | 0/30 | 0/30 | – |
| Nausea and vomiting | 0/30 | 0/30 | – |
| Agitation | 3/27 | 5/25 | 0.448 |
| Surgeon Satisfaction Score | 5[5-5] | 5[5-5] | 0.496 |
| Patient Satisfaction Score | 4[5-4] | 4[5-4] | 0.405 |
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