Whether pulse oximeter perfusion index (PI) may be applied to detect the onset of caudal block in pediatric patients under ketamine intravenous basal anesthesia is investigated. 40 ASA I, 2–8-year-old boys scheduled for elective circumcision surgery were randomized into two groups. Group I: 20 patients were anesthetized by 2 mg·kg−1 ketamine intravenous injection (IV) followed by caudal block using 1 mL·kg−1 lidocaine (1%); Group II: 20 patients were anesthetized by 2 mg·kg−1 ketamine IV only. PI on the toe in Group II decreased by 33 ± 12%, 71 ± 9% and 65 ± 8% at 1 min, 15 min, and 30 min after ketamine injection. The maximum increase in MAP and HR after ketamine IV was 11 ± 6% at 3 min and 10 ± 6% at 2 min. Compared to the PI value before caudal injection of lidocaine, PI in Group I increased by 363 ± 318% and 778 ± 578% at 5 min and 20 min after caudal block, while no significant changes in MAP and HR were found compared to the baseline before caudal block. Thus, PI provides an earlier, more objective, and more sensitive indicator to assess the early onset of caudal block under basal ketamine anesthesia.
Caudal block under basal ketamine anesthesia is widely used for pediatric lower abdominal and lower limbs surgeries in developing countries, especially for those uncooperative children. Successful caudal block can provide a safe, efficacious regional anesthesia and excellent postoperative pain control [
Recent advances in pulse oximeter technology have expanded the abilities to measure more parameters, such as perfusion index (PI). Perfusion index is an assessment of the pulsatile strength at a monitoring site; it is calculated by means of pulse oximetry by expressing the pulsatile signal as a percentage of the nonpulsatile signal, both of which are derived from the amount of infrared light absorbed. PI can provide useful information about the peripheral perfusion status of the patients. Recent study suggested that PI could be used as an early and sensitive indicator to assess the development of epidural-induced sympathectomy in conscious adults; it is more sensitive than other parameters such as changes of skin temperature gradients or mean arterial pressure (MAP) [
After the study protocol was approved by our institutional ethic committee and written informed consent from the parents was obtained, 40 ASA I, 2–8-year-old children scheduled for elective circumcision surgery were randomly allocated into two groups (20 patients, each group) using computer-generated random numbers. Group I: 20 patients were received caudal block under basal ketamine anesthesia; Group II: 20 patients under basal ketamine anesthesia only. All caudal blocks were performed by the same two anesthesiologists at left lateral decubitus position 5 min after 2 mg·kg−1 ketamine IV injection. After loss of resistance of the needle and negative aspiration, a test dose of 2–4 mL lidocaine (1%) was injected. If no lump in the subcutaneous tissues, a feeling of resistance to the injection, or any systemic effects such as arrhythmias or hypotension occurred, then the remaining lidocaine was injected (total amount: 1 mL·kg−1) slowly. The injection speed should be less than 10 mL/30 seconds, and then the patients were immediately placed at supine position. Additional 0.5 mg·kg−1 ketamine IV bolus was given to the patients as needed during performing the caudal block.
All the patients were not given any premedication. HR and MAP were monitored by an S/5 anesthesia monitor (Datex-Ohmeda, Finland), and the PI was recorded using Masimo Radical-7 SET (Masimo Corporation, Irvine, CA). The pulse oximeter probe for monitoring the PI was placed on the left second toe and was wrapped in a towel to reduce heat loss and to avoid the light contamination from operating room. The CR was elicited by stroking the upper inner part of the thigh, and was judged to be present if the scrotum and testis on the examined side were pulled up by the contract of cremasteric muscle. The patients who have neuromuscular disease, cerebral palsy with or without mental retardation, and back sepsis, or whose CR were unable to be evoked before caudal block, were eliminated from the study. Group I: PI, HR, and MAP were recorded at 0, 5, 10, 15, and 20 min (T0, T5, T10, T15, and T20) following caudal drug administration. The CR was recorded as yes (Y) or no (N) at T0, T5, T10, T15, and T20. Group II: PI, HR, and MAP were assessed at 0, 1, 2, 3, 5, 10, 15, 20, 25, and 30 min following ketamine IV administration. The endpoints were expressed as an incremental change or as a relative change as stated below. The dPI in the toe was calculated as the absolute changes in PI following ketamine IV injection or lidocaine caudal administration with respect to baseline (T0),
The effects of caudal administration of lidocaine under basal ketamine anesthesia and basal ketamine anesthesia itself on PI were assessed by repeated measures analysis of variance (RM-ANOVA). Drug effects at specific time (5, 10, 15, and 20 min and 1, 2, 3, 5, 10, 15, 20, 25, and 30 min) were determined using the simple repeated measures contrast option, which referenced the baseline values at T0; the conservative Greenhouse-Geisser modification was used if sphericity assumptions were not met.
For assessing the onset of adequate caudal block, we took the following criteria as indicators of onset of success of caudal block: absence of CR; a 100% increase of PI value from baseline; a 15% decrease of MAP from baseline; a 15% increase of HR from baseline. We recorded the number of patients who met or failed these criteria for each of these four parameters. ANOVAs test was used to compare the changes of these indices (PI, CR, MAP, and HR) over time. The ability of changes of PI value for assessing the onset of caudal block was compared separately with each of the other three parameters (CR, MAP, and HR) using McNemar’s
Forty-three children were initially recruited into the study, and three of them were excluded due to inability to identify caudal space or failure of caudal injection. Therefore, 40 children aged 2–8 years were randomized into two groups. There was no significant demographic difference between the two groups and no significant difference in baseline value of PI, MAP, HR, and CR at preinduction (Table
Demographic data and baseline value in all patients.
Group 1 ( |
Group 2 ( |
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Age (yr) |
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0.231 |
Height (cm) |
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0.182 |
Weight (kg) |
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0.534 |
Preinduction | |||
MAP (mmHg) |
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0.693 |
HR (bmp) |
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0.779 |
PI |
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0.788 |
CR (N/Y) | 0/20 | 0/20 |
MAP: mean artery pressure; HR: heart rate; PI: perfusion index; CR: cremasteric reflex; N: no; Y: yes.
Data are expressed as mean ± SD or numbers.
The changes of PI value on the toe, MAP, and HR following the caudal block under basal ketamine anesthesia were presented in Table
Bedside indices for the onset of caudal block under ketamine basal anesthesia: changes over time following caudal lidocaine administration.
Time after caudal block (min) | PI toe |
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dPI toe | MAP (mmHg) |
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dMAP (mmHg) | HR (bpm) |
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dHR (bpm) |
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0 |
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— | — | 90.00 (14.19) | — | — |
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— | — |
5 |
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10 |
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15 |
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20 |
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PI: perfusion index; MAP: mean arterial pressure; HR: heart rate. Data are expressed as mean ± SD.
Changes in HR (bpm), MAP (mmHg), and percent perfusion index (PI) following intravenous ketamine administration. Indices were expressed as a change from T0 (preinjection values). Data were analyzed using repeated measures ANOVA, and statistical significance was defined as
Following caudal administration of lidocaine, changes of PI value to meet the preset criteria for onset of successful caudal block were much earlier and more reliable than changes of other three indices in patients in Group I (Table
Bedside indices for the onset of caudal block: numbers of patients meeting predefined “clinically obvious” targets indicative of onset of caudal block over time.
Pre-defined “clinically obvious” targets for positive test of onset of caudal block | Time after caudal injection (min) | Number (%) of patients reaching targets for positive test | Comparison with rPI for the same dose and time interval | |
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rPI toe (100% change from time 0) | 5 | 17/20 (85%) | — | |
10 | 19/20 (95%) | — | ||
15 | 20/20 (100%)* | — | ||
20 | 20/20 (100%)* | — | ||
CR (absence %) | 5 | 0/20 (0%)* | rPI > CR | 0% for CR |
10 | 2/20 (10%) | rPI > CR |
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15 | 9/20 (45%) | rPI > CR | 100% for dPI* | |
20 | 20/20 (100%) | rPI = CR | 100% for dPI, CR | |
rMAP (15% change from time 0) | 5 | 0/20 (0%)* | rPI > rMAP | 0% for rMAP |
10 | 1/20 (5%) | rPI > rMAP |
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15 | 2/20 (10%) | rPI > rMAP | 100% for dPI* | |
20 | 2/20 (10%) | rPI > rMAP | 100% for dPI* | |
rHR (15% change from time 0) | 5 | 0/20 (0%)* | rPI > rHR | 0% for rHR |
10 | 3/20 (15%) | rPI > rHR |
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15 | 4/20 (20%) | rPI > rHR | 100% for dPI* | |
20 | 4/20 (20%) | rPI > rHR | 100% for dPI* |
PI: perfusion index; CR: cremasteric reflex; HR: heart rate; MAP: mean arterial pressure. Separate
Previous studies demonstrated that PI could provide an early and reliable indicator of the onset of epidural anesthesia and intravascular injection of epinephrine-containing epidural test dose in adults [
Our study has shown that (1) ketamine IV injection in pediatric patients produced a fast and long-lasting decrease in peripheral PI; (2) caudal block not only reversed the decrease of PI on the toe caused by ketamine anesthesia in pediatric patients but also went far beyond the preinduction PI; (3) PI response criterion achieved 100% sensitivity and specificity in detecting the effects of caudal anesthesia under IV ketamine anesthesia in pediatric patients. On the other hand, neither HR nor MAP criteria were 100% reliable. Furthermore, the changes of PI caused by caudal block under ketamine anesthesia were much earlier than those of HR and MAP.
PI is a noninvasive numerical value of peripheral perfusion derived from calculating the amount of infrared light absorbed by pulsating arterial flow (AC) and nonpulsating blood and tissue (DC) by a pulse oximetry. The pulsating signal indexed against nonpulsating signal and expressed as ratio (
As what we speculated, ketamine as a widely used intravenous anesthetic in pediatric patients produced a quick and long-lasting decrease in peripheral PI due to its sympathomimetic effects via both central and peripheral mechanisms [
We further compared the number of patients who meet predefined criteria for each of the bedside indices used for assessment of caudal block onset as Ginosar et al. did in their study [
The disappearance of the cremasteric reflex has long been thought as a more reliable indicator of successful caudal block, but it only applies to male pediatric patients, and it usually takes much longer to show the effects of caudal block [
Skin temperature gradients have also been used as an effective indicator of sympathectomy [
Our data clearly demonstrated that an increase in PI is an early, reliable, and objective indicator of the successful onset of caudal anesthesia under ketamine anesthesia. Conversely, failure to increase in PI might give the anesthesiologist an early warning of failure of adequate caudal block, which may help the anesthesiologist to optimize the management of anesthesia and finally to avoid the side effects of ketamine or other adjunctive medicines overdose.
PI provides an earlier, more objective, and more sensitive indicator to assess the early onset of caudal anesthesia under ketamine anesthesia. This result may encourage anesthesiologists to use PI instead of pinching, pinpricking, CR, and so forth, to assess the efficacy of pediatric caudal block under basal anesthesia, and to guide the management of pediatric caudal block.
This work was sponsored by the Science and Technology Support Program from the Science and Technology Commission of Shanghai Municipality, China (124119a3400 to Zifeng Xu), Medical Climbing Program from Songjiang Health Bureau, China (2011PD15 to Jijian Zheng), and Shanghai Pujiang Talent Program from Science and Technology Commission of Shanghai Municipality, China (11PJ1408000 to Jijian Zheng).