Efficacy of ketamine as an adjuvant to local anaesthetics in ultrasound-guided popliteal nerve blocks for foot surgeries: A double-blind randomized control study

 

 

Abstract               Background and objective: Although peripheral blocks, achieved with anaesthesia, have an immediate effect when used with an adjuvant, they demonstrate prolonged action and decreases the concentration of local anaesthetics. Hence, the present study was aimed to evaluate the efficacy of ketamine, as an adjuvant to bupivacaine, for ultrasound-guided popliteal nerve blocks in foot surgeries. Methods: A total of 60 patients, scheduled for foot surgeries to receive ultrasound-guided popliteal block, were randomized into two groups: Bupivacaine group (Group B=30) received 20 ml mixture of 0.25 % Bupivacaine and normal saline and Ketamine group(Group K=30) received 20 ml of 0.25 % Bupivacaine and 0.5 mg/kg of preservative-free ketamine. Time required for the onset of sensory and motor block, duration of analgesia achieved (complete and effective), and time for first-rescue analgesia were the parameters assessed in the groups. Independent t-test was performed to compare the data between the groups. Results: Demographic data were comparable in both groups. Onset of sensory and motor block, total duration of analgesia and time for first-rescue analgesia were significantly better in group K than in group B with P < 0.001, P < 0.05, and P< 0.001, respectively. Conclusion: Ketamine as an adjunct added to bupivacaine in popliteal nerve block fastened the onset and prolonged duration of action. Time for first-rescue analgesia also has been increased in foot surgeries. Therefore, it could be considered as an option to improve the current procedure of achieving popliteal nerve blocks in foot surgeries.

Key Word: Analgesia, Bupivacaine, Hemodynamics, Pain

 

 

INTRODUCTION

Popliteal sciatic nerve blockis a commonly utilized technique to provide regional anaesthesia for foot and ankle surgeries where sciatic nerve in the popliteal fossa, providing sensory and motor innervations in lower extremities, is blocked to achieve the nerve block.^1,2 Profound analgesia during both operative and postoperative periods, avoidance of systemic complications such as nausea and vomiting, decreased opioid consumption, and earlier discharge from the anaesthesia care unit, are the potential benefits of the popliteal nerve block.¹Although blocks achieved with local anaesthesia have an immediate effect, when used with adjuvant they have a prolonged action and reduces the concentration of local anaesthetics.³ Various adjuvants such as naloxone, ketamine, opioids, steroids, dexmedetomidine, clonidine, and dexamethasone have been used with local anaesthetics in varying degrees to improve the outcome of the blocks⁴; however, ketamine has attained the maximum popularity.³ Ketamine a non-competitive antagonist, due to its unique ability to produce rapid analgesic, amnesia, and sedative properties, has been widely used as an adjuvant with local anaesthesia. It has been reported that ketamine has regional, central, local anaesthetic as well as analgesic properties.^{5, 6}Various studies have also proved that S(+) isomer of ketamine has higher local anaesthetic property and decreases the pain intensity up to 48 h.^5,6 Hence, ketamine was evaluated as an adjuvant to bupivacaine to achieve popliteal nerve block in our study. Several studies have been conducted to evaluate the efficacy of ketamine added to local anaesthetics such as lidocaine, bupivacaine, and ropivacaine for regional anaesthesia and nerve block in various surgeries.^6-9 However, the use of ketamine as an adjuvant with bupivacaine to achieve popliteal nerve blocks for foot surgeries, are scarce. Hence, the study aimed to evaluate the efficacy of ketamine when added as an adjuvant to bupivacaine for ultrasound-guided popliteal nerve blocks in foot surgeries. The primary objective was to evaluate the onset and duration of sensory and motor blockade. The secondary objective was to evaluate the time of first rescue analgesic used, postoperatively.

 

MATERIALS AND METHODS

The present1-year, prospective, double-blind, randomized control studywas conducted at the Department of Anaesthesiologyof a tertiary care hospital in Belagavi between 2017 and 2018.Approval for the study protocol was obtained from Institutional Ethical and Research Committee. Informed consent was obtained from the patients, before their enrollment. Patients aged between 18 and 65 years, belonging to The American Society of Anaesthesiologists (ASA) I ,II and III category¹⁰, and scheduled for elective foot surgeries, were included. Patient with localized sepsis, allergy to local anesthetics, and coagulation disorder, and those refused to participate were exempted from the study. A total of 60 patients scheduled to receive ultrasound-guided popliteal block were registered in this comparative study. Randomization of patients was done using a computer-generated random number table, provided to the interventional anaesthesiologist using sealed envelopes on the day of surgery, to ensure blinding. The patients were randomly allocated totwo groups Bupivacaine group (Group B) and Ketamine group (Group K), with 30 patients in each group. Group B received 20 ml mixture of 0.25 % bupivacaine and normal saline whereas group K received 20 ml of 0.25 % bupivacaine and 0.5 mg/kg of preservative-free ketamine.To preserve the double-blind design, an investigator who was not involved in the study mixed the anaesthetic solution for the anaesthetist for performing the block and observing the results.Demographic data including age, gender, weight, height, and ASA status of all the patients, were recorded.

Procedure: An ultrasound-guided, single-shot popliteal nerve block was performed in prone position via posterior approach for each patient through intravenously. The portable Sono Site ultrasound linear, 6-13 MHz probe placed in the popliteal fossa was used to identify the popliteal artery and vein, and the biceps femoris muscle. While the tibial nerve was usually located lateral and superficial to the popliteal artery. After visualization, the probe was later moved proximally to identify the bifurcation of sciatic nerve into tibial nerve and common peroneal nerve.¹¹ Hemodynamic parameters including heart rate and non-invasive blood pressure were monitored, till the end of surgery.

The following parameters were noted:

1. Sensory blockade: Sensory block was evaluated by pinprick test using a 3-point scale: 0 = sharp pin felt; 1 = dull sensation felt (analgesia); 2 = no sensation felt (anesthesia)^.11,12
2. Motor blockade: Motor block was also evaluated on a 3-point scale for motor function: 0 = normal motor function with full flexion and extension of the elbow, wrist and fingers; 1 = reduced motor strength but able to move fingers; 2 = complete motor block, with inability to move fingers.^11,13 Patients were observed in the recovery room for hemodynamic stability and side effects and were monitored for additional medications. After normalization of vital parameters, the patients were shifted to the ward where they were monitored for three hours by Anaesthesiology team members and thereafter by the nursing staffs on duty for24 h, following the end of the surgery. During recovery, parameters such as visual analogue scale, time of first rescue analgesia, total opioid (Tramadol) requirement, occurrence of side-effects and hemodynamic parameters, were recorded.
3. Visual analogue scale (VAS): VAS score was observed at 0, 3, 5, 9, 12, and 24 h, postoperatively(0: No pain, 1-2: Least pain, 3-4: Mild pain, 5-6: Moderate pain, 7-8: Severe pain, 9-10: Excruciating pain)
4. Time of first rescue analgesia: Rescue analgesia was provided by injection (Tramadol 2mg/kg b.w). This indicated the duration of analgesia from the time of administration of TAP block to VAS score > 4 or on patients requested for analgesia.

Statistical Analysis: SPSS v19 was used to analyze the data. Data are represented as Mean ± Standard deviation for continuous data and frequency or median for non-parametric data. The groups were compared with ANOVA; P< 0.05 was considered significant and P< 0.01 as highly significant.

OBSERVATIONAL AND RESULTS

In this study, both the groups were similar in terms of demographical data, ASA classification, and duration of surgery (Table 1).

Table 1: Demographic characteristics of the patients in both the groups

Group B, Bupivacaine group; Group K, Bupivacaine+Ketamine group; ASA, The American Society of Anaesthesiologists; Group B: Bupivacaine; Group K: Ketamine Sensory and motor onset of block was achieved significantly faster in group K as compared to group B (P < 0.001; Table 2).

 

Table 2: Comparison of block characteristics between both the groups

Group B, Bupivacaine group; Group K, Bupivacaine + Ketamine group; *Significant; Group B: Bupivacaine; Group K: Ketamine Duration of complete analgesia and effective analgesia were significantly higher in group K as compared to group B (P < 0.001; Table 3). Overall, the total duration of analgesia in Group K was significantly lasted longer as compared to Group B. Time for first-rescue analgesia was also significantly longer in group Kcompared to group B (P < 0.001; Table 3).

Table 3: Duration of analgesia and time of administration of the first pain medication

*Significant; Group B: Bupivacaine; Group K: Ketamine; pain was assessed using VISUAL Analog Scale

 

DISCUSSION

The findings of the study demonstrated 0.5 mg/kg ketamine added as an adjuvant to bupivacaine fastened the onset of block and improved the total duration of analgesia and the time for first rescue analgesia as compared to bupivacaine alone. As compared to ketamine with preservative, preservative-free ketamine is free of neurotoxic effects, following both single as well as repeated administration.¹⁵ Intrathecal ketamine with preservative infused in cancer patients for three weeks reported subpial vacuolar myelopathy.¹⁵ Hence, in our study, preservative-free ketamine was employed as an adjuvant. It has also reported that 0.1 mg/kg ketamine added to 0.5% lignocaine or 0.5 mg/kg to 1% lignocaine for intravenous regional anaesthesia increases the quality of anaesthesia and tourniquet tolerance, decreases analgesic administration, and enhances the duration of pain relief.¹⁶ Moreover, 0.5 mg/kg ketamine is devoid of adverse effects as well as hemodynamic changes.¹⁶ Hence in our study, 0.5 mg/kg preservative-free form of ketamine was used as an adjuvant with bupivacaine to achieve popliteal nerve block. In our study, ketamine added to bupivacaine significantly shortened the onset of both the sensory and motor block. A study conducted by Kamal et al.¹⁷ in day care surgery patient sunder spinal anaesthesia also reported that ketamine + bupivacaine group had significantly decreased the onset times of both sensory (3.1 ± 0.5 min vs. 4.6 ± 0.9 min; P < 0.001) and motor block (2.4 ± 0.8 min vs. 5.6 ± 0.1 min; P < 0.001) compared to bupivacaine group alone. Other similar studies^18,19conducted among women who underwent C-sectionunder spinal anaesthesia also reported that ketamine significantly enhances the local anaesthetic activity of bupivacaine. The inhibiting effects of ketamine on the bupivacaine metabolism might be the probable reason behind enhancement of local anaesthetic activity.⁵ Moreover, ketamine lowers the pH of bupivacaine and fastens the onset of the sensory block and further it enhances the prolongation of block.²⁰ In contrast, other study reported that co-administration of ketamine along with spinal bupivacaine increased the onset times of both sensory as well as motor blockades.²⁰ These debatable findings probably due to different methodologies, populations, type of surgeries, and doses of ketamine. Reports in the literature indicate that ketamine (10-50 mg), added to local anaesthetics, prolongs the duration of regional analgesia¹⁵ which is comparable to our study. Similar studies conducted in different regions also found that duration of analgesia was significantly increased in the ketamine + bupivacaine group, compared to bupivacaine group alone.^7,15 The pharmacological properties of ketamine are antagonizing N-methyl-D-aspartate receptors, blockade of voltage-sensitive calcium channels, suppression of sodium channels, and alteration of cholinergic neurotransmission. All these pathways implicated in pain mechanisms decrease the preoperative and postoperative pain.²⁰ Literature reports ketamine, when administered intravenously or topically in small sub-anaesthetic doses, acts as an analgesic for chronic painful conditions.¹⁶ This might be a probable reason behind an increase in time for first-rescue analgesia in group K compared to group B in our study. A study conducted by Khezri et al.²⁰,also observed elongated time to the first request for analgesics and also reduced the total analgesic consumption postoperatively in the initial 24 h as compared to bupivacaine alone (297.80 ± 31.48 min vs. 236.34 ± 22.20 min; P< 0.001) The study has few potential limitations that need to be acknowledged. Firstly, we used single-level injection block, hence multiple-level injection could have been used which might have effectively improved the quality of analgesia. Secondly, the study was limited through its sample size; hence, multicentric clinical trials with large sample size required to be conducted to validate the current findings. Thirdly, we used single concentration of ketamine, hence, future studies with different concentrations of ketamine can be investigated to optimize the effective dose for supreme improvement of analgesia. Finally, ultrasound guidance used is strenuous to perform in obese individuals and patients with distorted anatomy; hence, nerve stimulator-assisted ultrasound guidance can be used in future for more efficient nerve localization to achieve popliteal nerve block. Overall, the study is first of its kind evaluated that ketamine as an added adjuvant to bupivacaine achieved popliteal nerve blocks for foot surgeries. 

 

CONCLUSION

Ketamine 0.5 mg/kg added to bupivacaine as an adjuvant for ultrasound-guided popliteal blocksimproved the onset and duration of the sensory or motor block, decreased the postoperative pain, and increased the time for first-rescue analgesia, without any adverse effects. Therefore, it could be considered as an option to achieve popliteal nerve blocks in foot surgeries.

 

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8. Zaman B, Ashrafi SH, Siamdoust SS, Hassani V, Taheri SM, Noorizad S. The Effect of Ketamine and Dexamethasone in Combination with Lidocaine on the Onset and Duration of Axillary Block in Hand and Forearm Soft Tissue Surgery. Anesthesiology and pain medicine. 2017;7(5).
9. Rahimzadeh P, Faiz SHR, Ziyaeifard M, Niknam K. Effectiveness of adding ketamine to ropivacaine infusion via femoral nerve catheter after knee anterior cruciate ligament repair. Journal of research in medical sciences: the official journal of Isfahan University of Medical Sciences. 2013;18(8):632.
10. Doyle DJ, Garmon EH. American Society of Anesthesiologists classification (ASA class). StatPearls [Internet]: StatPearls Publishing; 2019.