Anesth Analg 2002;94:1165-1168
© 2002 International Anesthesia Research Society
PEDIATRIC ANESTHESIA
The Hemodynamic Effects of Pediatric Caudal Anesthesia Assessed by Esophageal Doppler
Eric Larousse, MD*,
Karim Asehnoune, MD*,
Bruno Dartayet, MD*,
Pierre Albaladejo, MD*,
Anne-Marie Dubousset, MD*,
Frédéric Gauthier, MD
, and
Dan Benhamou, MD*
*Department of Anesthesiology and Critical Care Medicine and Department of Pediatric Surgery, Centre hospitalo-universitaire du Kremlin Bicêtre, France
Address correspondence and reprint requests to Eric Larousse, MD, Department of Anesthesia and Intensive Care Medicine, Hôpital Kremlin Bicêtre, 78, rue du Général Leclerc, F-94275 Kremlin Bicêtre, France. Address e-mail to larousse.eric{at}wanadoo.fr
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Abstract
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Pediatric caudal anesthesia is an effective method with an infrequent complication rate. However, little is known about its cardiovascular consequences. Transesophageal Doppler, a noninvasive method, provides the opportunity for a reappraisal of the hemodynamic effects of this technique. After parental informed consent, we studied 10 children aged 2 mo to 5 yr who were scheduled for lower abdominal surgery. General anesthesia was induced using sevoflurane and was followed by the insertion of a transesophageal Doppler probe. Caudal anesthesia was performed using 1 mL/kg of 0.25% bupivacaine with 1/200,000 epinephrine. Hemodynamic variables were collected before and after caudal anesthesia. No complications arose during insertion of the probe. The mean time between the two sets of measurements was 15 min. Heart rate, systolic, diastolic, and mean arterial blood pressures were not modified by caudal anesthesia. Descending aortic blood flow increased significantly from 1.14 to 1.92 L/min. (P = 0.0002). Aortic ejection volume increased from 8.5 to 14.5 mL (P = 0.0002). Aortic vascular resistances decreased from 6279 to 3901 dynes · s-1 · m-5 (P = 0.005). Caudal anesthesia did not affect heart rate and mean arterial blood pressure but induced a significant increase in descending aortic blood flow.
IMPLICATIONS: Although pediatric caudal anesthesia does not alter heart rate nor arterial blood pressure, significant changes occur in regional blood flow distribution. Descending aortic blood flow increases significantly after caudal anesthesia, whereas lower body vascular resistances decrease.
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Introduction
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Caudal anesthesia has been increasingly used in pediatric surgery in recent years (1,2) and represents more than 60% of all regional anesthetics in this age group (3). Lower abdominal, urinary tract, and lower extremity surgery are the most recognized indications for caudal anesthesia (2). This technique is reliable, safe, and easy to perform in young children (1). Nevertheless, the hemodynamic alterations induced by caudal anesthesia are not wholly understood. Arterial blood pressure is maintained during pediatric caudal block (4), and this has been related to a lower basal sympathetic tone in children (5). This concept has been challenged by Payen et al. (6) who suggested that caudal anesthesia induces blood pooling in the denervated lower extremities (caudal blocked areas) and a reflex vasoconstriction in the innervated areas.
At present, there is a lack of information concerning the changes in cardiac output (CO) and in regional blood flows occurring after caudal anesthesia in children. The recent introduction in clinical practice of a reliable and noninvasive measurement of aortic blood flow (ABF) for pediatric patients (7) allowed us to examine the hemodynamic effects of caudal block in children.
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Methods
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After the protocol had been approved by our Human Studies Committee, and after parental informed consent, 10 consecutive ASA physical status I and II children undergoing lower abdominal or genitourinary surgery were studied. All infants had fasted for 4 h except for oral intake of 15 mL/kg of 15% glucose 3 h before surgery. Midazolam 0.5 mg/kg per os was administered 45 min before surgery. On arrival in the operating room, heart rate (HR) was continuously recorded, and noninvasive blood pressure was measured by an automated blood pressure cuff every 5 min. Anesthesia was induced by inhalation of 100% oxygen and 6% sevoflurane until loss of consciousness and then decreased to 4%. End-tidal CO2 and inhaled anesthetic end-expiratory fraction were monitored with an AS3® monitor (Datex-Ohmeda SAS, Champagne au Mont d’Or, France). An IV catheter was inserted into a brachial vein, and 1% dextrose in Ringer’s lactate solution was infused at a rate of 10 mL · kg-1 · h-1 during the first hour. A weight adapted orotracheal tube was inserted. Anesthesia was maintained with nitrous oxide (50%) and sevoflurane (expirated fraction of sevoflurane 1.5%). Hemodynamic measurements started after a 10-min steady-state period. The noninvasive hemodynamic measurements were performed with an echo-Doppler device (Arrow International, Inc, Reading, PA). As indicated by the manufacturer, the pediatric probe was used for children <15 kg in weight (5.1 mm in diameter and 35 cm long), whereas the adult probe was used for those >15 kg (7 mm in diameter and 61 cm long). These probes have two ultrasound transducers on their distal part. The first operates a 10-MHz A-echo scanner, perpendicular to the centerline, used to measure aortic diameter (Ao). The second is a Doppler-pulsed emission transducer operating at 5 MHz and mounted at an angle of 60° to the centerline of the probe. The pulsed Doppler is emitted with a 20° divergent beam, and the gate Doppler signal depth is automatically adapted to the Ao. Thus, Ao and ABF are simultaneously and continuously recorded at the same anatomical level. The ABF is calculated from the mean of the instantaneous velocity and the aortic cross-section area. The depth into the esophagus varies according to the height of the infant and is estimated between the echo transducer placed on the third anterior intercostal space and the mouth. This is the level where the aorta and the esophagus are parallel. The Doppler probe (HemosonicTM 100®, Arrow International, Inc) was introduced orally. The following baseline mea-surements were collected: HR, systolic, mean, and diastolic blood pressure, end-tidal CO2 pressure (ETCO2), aortic stroke volume (SVa), ABF, and Ao. Systemic vascular resistances (SVRa) were calculated from the formula SVRa (dynes · sec-1 · cm-5) = mean arterial blood pressure (MAP)/ABF x 79.9. ABF and SVa were indexed as a function of body surface area. Children were then positioned on their left side, and a 22-gauge needle was aseptically inserted into the caudal epidural space. Bupivacaine 0.25% (2.5 mg/kg) with 1/200,000 epinephrine was slowly injected. After repositioning the children on their backs, and after a 10-min steady-state period, a second set of measurements was obtained. For each variable, a mean for 10 consecutive measurements was obtained before and after caudal anesthesia and was computed.
Results are reported as means and 95% confidence interval. Data were compared using a paired Student’s t-test. Differences were considered statistically significant at the 5% level (P < 0.05).
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Results
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Patients’ characteristics are summarized in Table 1. Children ranged in age from 2 mo to 5 yr (mean age, 2.6 yr). Six patients were scheduled for lower abdominal surgery and four for genitourinary surgery. No complications arose while using the transesophageal Doppler, and the probe was easy to insert in each case. ABF and Ao measurements were easily obtained in the supine position.
There was no statistical difference in arterial blood pressure, HR, and ETCO2 after caudal anesthesia when compared with general anesthesia alone (Table 2). However, indexed ABF and SVa significantly increased, respectively, from 2.1 to 3.6 L · min-1 · m-2 (P = 0.003) and 8.5 to 14.5 mL (P = 0.0002). SVRa significantly decreased from 6280 to 3902 dynes · sec-1 · m-5 (P = 0.005) after caudal anesthesia. Also, Ao significantly increased from 9.1 to 10.5 mm (P = 0.03) (Fig. 1).
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Figure 1. Aortic blood flow (ABF), aortic stroke volume (SVa), systemic vascular resistances (SVRa), and aortic diameter (Ao). Significant differences induced by caudal anesthesia expressed as percent changes (± 95% confidence interval). *P < 0.05.
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Discussion
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In this study, caudal anesthesia altered neither HR nor MAP. However, significant increases in descending ABF and in SVa were associated with a decrease in lower body vascular resistance. These results suggest that caudal anesthesia results in arterial vasodilation in the anesthetized location. The local anesthetic-induced sympathetic block is the probable cause of this vasodilation.
The Doppler technique is widely used to measure CO, and studies have demonstrated good agreement with thermodilution (8). The esophageal approach provides excellent signals and avoids positional artifact (9), whereas external probes cannot be fixed in place for continuous monitoring, especially in the operating room. When compared with thermodilution CO, the esophageal approach is a reliable and minimally invasive tool for estimating CO and monitoring its changes (10,11). The clinical usefulness of the transesophageal Doppler monitoring has been demonstrated in numerous anesthetic situations such as vascular surgery, orthopedic surgery (12), or laparoscopic surgery (13) in adults. Monitoring hemodynamic changes during pediatric anesthesia is difficult, especially in the youngest children because appropriate devices were initially developed for adult patients. A pediatric esophageal probe has been available since 1996, providing an interesting noninvasive tool for studying hemodynamic changes during anesthesia. In four studies (7,14–16) (78 children), correct probe positioning was easily obtained, and the recording quality was excellent whatever the operative position. No adverse effect was described. However, a training period is required to ensure accurate measurements when using the transesophageal probe (17). In our study, the same trained investigator performed all measurements. The correlation between thermodilution and transesophageal Doppler CO is likely related to the fact that the HemosonicTM 100® system uses the instantaneous A-scan measurement of Ao to calculate and display the real-time ABF value (18). A scan determination of Ao by the HemosonicTM 100® device is highly related to what is obtained by the transesophageal echocardiograph bidimensional echography (18). Other esophageal Doppler devices do not provide echographic Ao measurement and estimate Ao using nomograms. Nevertheless, comparing estimated Ao by nomograms with computerized axial tomography in 100 patients, Muchada et al. (13) found an unsatisfactory reliability using age, weight, and height nomograms (95% confidence interval, -5.5 to 5.4 mm).
The main weakness of transesophageal Doppler is that this device measures blood flow velocity in the descending thoracic aorta and not CO. Extrapolation of descending aortic blood velocity to CO requires knowing the aortic surface (which is directly measured by A-scan system) but also the ascending/descending ABF ratio. Unfortunately, no system provides an online determination of the exact ascending/descending ABF ratio. A correcting factor is applied to take into account the distribution of CO between the vessels originating for the aortic arch and those constituting flow in the descending aorta (19), but the validity of this correcting factor for the estimation of CO is still debated. A 20% overestimation has been observed in low CO situations in an in vitro study (20). In our study, we monitored healthy children (ASA I or II) undergoing minor surgeries. Because we were interested in evaluating regional blood flow alterations, especially in caudal blocked areas, descending ABF was an adequate variable to monitor.
In adult patients, the influence of central blocks on the distribution of blood has already been reported (21). In supine humans, epidural anesthesia and spinal anesthesia lead to sympathetic block, which lead to blood pooling in the denervated lower extremities with a reflex vasoconstriction in the innervated arms (22). A similar phenomenon was described by Payen et al. (6) in eight children during caudal anesthesia who suggested that vasoconstriction of the innervated areas maintains CO unchanged. In the present study, the increase in descending ABF may be associated with an increase or with an unchanged CO. The stability of HR, MAP, and ETCO2 suggests that CO remains unchanged, as shown by Payen et al. (6). However, the larger intraoperative fluid loading (10 mL · kg-1 · h-1 compared with 4 mL · kg-1 · h-1 in the Payen et al. study (6)), the increase in ABF (2.1 to 3.6 L · mL-1 · m-2; P = 0.003), the important contribution to CO of superior vena cava flow in children, and the reflex vasoconstriction in these territories are in favor of an increase of CO after caudal anesthesia. Salim et al. (23) showed that the superior vena cava flow accounted for 49% of CO in newborn infants. This contribution increased to a maximum of 55% at the age of 2.5 years, the mean age of our study, allowing an increased blood volume redistribution efficacy because of innervated areas reflex vasoconstriction. Afterward, there was a slow decline in the ratio of superior vena cava-pulmonary artery blood flow; it reached the adult value of 35% by 6.6 years of age. An increase in CO is also likely because we used an epinephrine-containing solution. Morau et al. (15) indeed showed that extradural anesthesia in children increases ABF when epinephrine is used.
Our preliminary study has several limitations. First, because patients were receiving general anesthesia and also because patients were young children, the dermatomal spread of the block could not be assessed. This could prove important because epidural/caudal anesthesia-induced hemodynamic effects are related to the intensity of the sympathetic block, which is related to the spread of the block. Our results do therefore apply for children receiving the caudal administration of 1 mL/kg of 0.25% bupivacaine with epinephrine and who require validation in different clinical conditions. Moreover, drugs used for underlying general anesthesia can cause by themselves a sympathetic block, and basal hemodynamic values obtained before caudal injection should be interpreted with this in mind. A further limitation is that a small number of patients were studied. However, hemodynamic changes were consistently obtained, suggesting that our results can be generalized to the whole population of children studied in similar conditions.
In this study, we demonstrated alterations in regional blood flow after caudal anesthesia, although MAP, HR, and ETCO2 remained unchanged. The significant increase in ABF and the decrease in lower body vascular resistances after caudal anesthesia suggest that vasodilation was induced by a sympathetic block. However, further studies are required to better understand the consequences of caudal anesthesia on CO and on regional blood flow.
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Accepted for publication December 28, 2001.
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Abstract
Introduction
