Radial Mean Arterial Pressure Reliably Reflects Femoral Mean Arterial Pressure in Uncomplicated Pediatric Cardiac Surgery

Radial Mean Arterial Pressure Reliably Reflects Femoral Mean Arterial Pressure in Uncomplicated Pediatric Cardiac Surgery Secil Cetin, MD,* Arash Pirat, MD,* Aycan Kundakci, MD,* Aynur Camkiran, MD,* Pinar Zeyneloglu, MD,* Murat Ozkan, MD,† and Gulnaz Arslan, MD* Objective: To see if radial mean arterial pressure reliably reflects femoral mean arterial pressure in uncomplicated pediatric cardiac surgery. Design: An ethics committee-approved prospective interventional study. Setting: Operating room of a tertiary care hospital. Participants: Forty-five children aged 3 months to 4 years who underwent pediatric cardiac surgery with hypothermic cardiopulmonary bypass. Measurements and Main Results: Simultaneous femoral and radial arterial pressures were recorded at 10-minute intervals intraoperatively. A pressure gradient 45 mmHg was considered to be clinically significant. The patients’ mean age was 14 ⫾ 11 months and and mean weight was 8.0 ⫾ 3.0 kg. A total of 1,816 simultaneous measurements of arterial pressure from the radial and femoral arteries were recorded during the pre-cardiopulmonary bypass, cardiopulmonary bypass, and post-cardiopulmonary bypass periods, including 520 (29%) systolic arterial pressures, 520 (29%) diastolic arterial pressures, and 776 (43%) mean arterial pressures. The paired mean arterial pressure measurements across the 3 periods were significantly and strongly correlated, and this was true for systolic arterial pressures and diastolic arterial pressures as well (r 4 0.93 and p o 0.001 for all). Bland-Altman plots demonstrated

good agreement between femoral and radial mean arterial pressures during the pre-cardiopulmonary bypass, cardiopulmonary bypass, and post-cardiopulmonary bypass periods. A significant radial-to-femoral pressure gradient was observed in 150 (8%) of the total 1,816 measurements. These gradients occurred most frequently between pairs of systolic arterial pressure measurements (n ¼ 113, 22% of all systolic arterial pressures), followed by mean arterial pressure measurements (n ¼ 28, 4% of all mean arterial pressures) and diastolic arterial pressures measurements (n ¼ 9, 2% of all diastolic arterial pressures). These significant gradients were not sustained (ie, were not recorded at 2 or more successive time points). Conclusions: The results suggested that radial mean arterial pressure provided an accurate estimate of central mean arterial pressure in uncomplicated pediatric cardiac surgery. There was a significant gradient between radial and femoral mean arterial pressure measurements in only 4% of the mean arterial pressure measurements, and these significant gradients were not sustained. & 2014 Elsevier Inc. All rights reserved.

I

gradient. Second, hypothermic CPB may significantly alter the consistency of MAP throughout the arterial tree. These changes mean that measurement of arterial blood pressure from a peripheral site, such as the radial artery, may significantly underestimate the central arterial pressure. Mismeasurement of MAP could have significant clinical implications with respect to hemodynamic mismanagement of patients. Although several investigators have examined the impacts of hypothermic CPB on the radial-to-femoral arterial pressure gradient in adults, there is very little known about this in pediatric patients. The aim of this study was to investigate alterations of the radial-to-femoral arterial pressure gradient in pediatric cardiac surgery with hypothermic CPB.

NVASIVE ARTERIAL PRESSURE MEASUREMENT via an arterial catheter is an essential component of hemodynamic monitoring during cardiac surgery and cardiopulmonary bypass (CPB). Accurate measurement of arterial pressure is a prerequisite for optimal hemodynamic management during this type of surgery. Normally, mean arterial pressure (MAP) is relatively constant throughout the arterial tree;1 however, systolic arterial pressure (SAP) rises slightly as the measurement site moves from central to peripheral arteries. This SAP gradient is negligible under normal conditions. Generally, the radial artery is the preferred site for arterial catheterization because its anatomic location is relatively consistent, catheter placement in this vessel is a relatively easy procedure, and the rate of complications is acceptable.2,3 However, several studies have demonstrated that hypothermic CPB may have significant effects on the central-to-peripheral arterial pressure gradient phenomenon.4–13 First, hypothermic CPB may reverse the normal peripheral-to-central SAP

From the *Departments of Anesthesiology and yCardiovascular Surgery, Baskent University Faculty of Medicine, Ankara, Turkey. Address reprint requests to Secil Cetin, MD, Department of Anaesthesiology, Baskent University Faculty of Medicine, 10. Sok. No: 45, Bahcelievler, 06490 Ankara, Turkey. E-mail: [email protected] & 2014 Elsevier Inc. All rights reserved. 1053-0770/26051-0031$36.00/0 http://dx.doi.org/10.1053/j.jvca.2013.02.029 76

KEY WORDS: cardiac surgical procedure, cardiopulmonary bypass, femoral artery, radial artery, congenital heart defects, blood pressure

METHODS The study was approved by the institution’s Ethics Committee and was supported by the Baskent University Research Fund. Written informed consent was obtained from the parents of all participants. The authors studied 45 American Society of Anesthesiologists class 3 or 4 children aged 3 months to 4 years who were scheduled for surgical repair of congenital heart defects with hypothermic CPB. The exclusion criteria were age o3 months, coarctation of the aorta, aortic interruption, need for vasoactive drugs preoperatively, CPB duration o30 minutes, need for deep hypothermic circulatory arrest, need for vasopressors other than dopamine o10 mg/kg/min, and signs of ischemia in the extremities. Each child completed a predetermined age-adjusted fasting period (4– 6 hours) and was premedicated with oral midazolam, 0.5 mg/kg, and

Journal of Cardiothoracic and Vascular Anesthesia, Vol 28, No 1 (February), 2014: pp 76–83

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RADIAL-TO-FEMORAL PRESSURE GRADIENT DURING CARDIOPULMONARY BYPASS IN CHILDREN

hydroxyzine, 1 mg/kg. Initial routine hemodynamic monitoring, including electrocardiography, sphygmomanometric blood pressure measurements, respiratory rate, and pulse oximetry, was applied. After mask induction with sevoflurane, 8% in oxygen, a peripheral venous catheter was inserted and midazolam, 0.1 mg/kg IV, vecuronium, 0.15 mg/kg IV, and fentanyl, 25 mg/kg IV, were administered and sevoflurane was discontinued. Incremental doses of fentanyl, 5 mg/kg IV, were administered to a total dose of 50 mg/kg IV prior to sternotomy. For anesthesia maintenance, a constant infusion of fentanyl, 20 mg/kg/h, was started after intubation, and this was continued throughout the procedure. Isoflurane 0.2% to 1.5%, also was administered to assure depth of anesthesia. Vecuronium, 0.05 mg/kg IV, was repeated during the initiation and rewarming periods of CPB. Central venous and urinary catheters, esophageal and rectal temperature probes, and a nasogastric tube were inserted. For invasive arterial pressure measurements, the femoral and radial arteries were cannulated after anesthetic induction using the catheter-overthe-needle technique. The radial artery was cannulated with a 22-G 2.5-cm catheter (Becton-Dickinson Venflons, Helsingborg, Sweden). In patients with a Blalock-Taussig shunt, the site contralateral to the shunt was cannulated. The femoral artery was cannulated with a 20-G 3.2-cm catheter (Becton-Dickinson Venflons, Helsingborg, Sweden). In patients who recently had undergone cardiac catheterization via this vessel, the site contralateral to the recent catheterization was used. The arterial catheters were connected to 2 pressure transducers (Biometrix B.V. Breda, Netherlands) using standard pressure tubing, and these transducers were zeroed at the level of the mid-axillary line. To eliminate errors from damping and frequency change, the natural frequency and damping coefficient for each system was determined by the flush method.12,14 The femoral and radial arterial pressures were displayed simultaneously throughout the operation (Siemens SC 7000, Danvers, USA). During CPB, systemic anticoagulation was achieved with heparin, 3 mg/kg. The CPB perfusate was composed of lactated Ringer’s solution, fresh frozen plasma, or whole blood to achieve a calculated hematocrit of 28% to 30%. Methylprednisolone, 10 mg/kg, furosemide, 1 mg/kg, heparin, potassium, and sodium bicarbonate were added to the prime solution as part of standard protocol. Once the target core temperature (281C) was achieved, 10 mg/kg of sodium thiopental was added to the CPB circuit. This same dose was repeated during the rewarming period. A membrane oxygenator was used for CPB, and systemic hypothermia, cold hyperkalemic cardioplegia solution, and topical cooling with ice were used to maximize myocardial preservation. Simultaneous femoral and radial MAP, SAP, and diastolic arterial pressure (DAP) were recorded at 10-minute intervals intraoperatively. The other recorded variables were heart rate, core temperature, and the durations of aortic cross-clamping, CPB, and the entire operation. Statistical analyses were performed with MedCalc 12.2.1 statistics software (9030 Mariakerke, Belgium). For each arterial pressure category (MAP, SAP, and DAP), 3 types of analyses were carried out: (1) paired-sample t tests were performed using the radial and femoral pressure measurements at each 10-minute interval, (2) Pearson correlation analysis was done to assess the relationship between measured radial and femoral pressure measurements, and (3) BlandAltman plots were constructed to assess the agreement between the arterial pressure measurements at the 2 sites. The latter was done with correction for multiple observations per individual, as described by Bland and Altman.15 Occurrence of significant pressure gradients also was analyzed. Based on our clinical experience, a radial-to-femoral arterial pressure gradient Z5 mmHg was considered significant. Numbers of these events were totaled and compared across the operative periods (preCPB, CPB, and post-CPB) and pressure categories. Results are presented as mean ⫾ SD or percentage with 95% confidence intervals (CI), as appropriate. A p value o0.05 was considered statistically significant.

RESULTS

The patients were 22 girls (44%) and 23 boys (46%). Their mean age, weight, and body surface area were 14.1 ⫾ 11.6 months (CI, 10.7–17.5 mo), 8.0 ⫾ 3.0 kg (CI, 7.1–8.9 kg), and 0.37 ⫾ 0.11 m2 (CI, 0.34–0.40 m2), respectively. The most common congenital heart defect was ventricular septal defect (n ¼ 21), followed by tetralogy of Fallot (n ¼ 10), transposition of the great arteries (n ¼ 5), complete atrioventricular septal defect (n ¼ 3), partial atrioventricular septal defect (n ¼ 3), and pulmonary stenosis (n ¼ 3). The respective durations of aortic cross-clamping, CPB, and the surgery overall were 54 ⫾ 22 minutes (CI, 48–60 min), 76 ⫾ 25 minutes (95% CI, 69–83 min), and 171 ⫾ 40 minutes (95% CI, 159–183 min). Patients’ mean heart rate and core body temperature values are shown in Fig 1. The mean baseline, minimum, and end-of-surgery hematocrits were 33.0% (95% CI, 31.1%-34.9%), 28.7% (95% CI, 28.0%29.4%), and 34.1% (95% CI, 32.9%–35.2%), respectively. A total of 1,816 simultaneous measurements of arterial pressure from the radial and femoral arteries were recorded intraoperatively, including 776 (43%) MAPs, 520 (29%) SAPs, and 520 (29%) DAPs. The numbers of measurements during pre-CPB, CPB, and post-CPB were 708 (39%), 526 (29%), and 582 (32%), respectively. During the pre-CPB period, none of the differences between mean radial MAP and mean femoral MAP at any of the 10minute intervals was significantly different from zero (p 4 0.05 for all, Fig 1 and Table 1). Regarding SAP, the only significant difference was at 40 minutes pre-CPB, with mean radial SAP higher than mean femoral SAP (p ¼ 0.042, Fig 1 and Table 1). Regarding DAP, the only significant difference was at 20 minutes pre-CPB, with mean radial DAP lower than mean femoral DAP (p ¼ 0.039, Fig 1 and Table 1). Throughout the CPB period (ie, at all 10-minute intervals), the mean values for radial MAP, SAP, and DAP were all significantly lower than their corresponding femoral values (p o 0.01 for all time points, Fig 1 and Table 1). During the post-CPB period, mean radial MAP was significantly lower than mean femoral MAP only at 0 and 10 minutes (p o 0.001 for both) (Fig 1 and Table 1). Mean radial SAP was significantly lower than mean femoral SAP at postCPB 0 and 10 minutes (p o 0.001 for both), and was significantly higher than mean femoral SAP at 30 and 40 minutes (p o 0.001 and p ¼ 0.026, respectively) (Fig 1 and Table 1). Mean radial DAP was significantly lower than mean femoral DAP at post-CPB 0, 10, 20, and 30 minutes (p o 0.05 for all, Fig 1 and Table 1). For MAP, the paired radial and femoral measurements across all 3 periods of the surgery (pre-CPB, CPB, postCPB) were significantly and strongly correlated, and this was true for SAP and DAP as well (r Z 0.937 and p o 0.001 for all, Table 2). Bland-Altman plots for each pressure category (MAP, SAP, and DAP) demonstrated good overall agreement between the femoral and radial measurements throughout the operation (Fig 2A-C). Bland-Altman plots for each individual period (pre-CPB, CPB, and post-CPB) revealed good agreement between femoral and radial measurements for MAP (Fig 3AC). Bland-Altman plots for the pre-CPB and post-CPB periods

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Fig 1. Mean body temperature and heart rate values, and mean systolic, diastolic, and paired mean arterial pressure measurements recorded simultaneously from the radial and femoral arteries intraoperatively. *p o 0.05, yp o 0.01. Abbreviation: CPB, cardiopulmonary bypass.

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55 ⫾ 10 54 ⫾ 8 57 ⫾ 10y 55 ⫾ 9

56 ⫾ 9 56 ⫾ 9

55 ⫾ 6 55 ⫾ 7

showed good agreement between femoral and radial SAP (Fig 4A and B) and between femoral and radial DAP (Fig 5A and B). Overall, 150 (8%) of the total 1,816 paired measurements exhibited significant radial-to-femoral pressure gradients (Table 3). The numbers of significant gradients during preCPB, CPB, and post-CPB were 43 (29%), 42 (28%), and 65 (43%), respectively. Significant gradients were most frequent with SAPs (n ¼ 113, 75%), followed by MAPs (n ¼ 28, 19%) and DAPs (n ¼ 9, 6%). None of the 150 significant radial-tofemoral pressure gradients was sustained; significant gradients were not recorded at 2 or more successive 10-minute time points.

46 ⫾ 7 50 ⫾ 7y

DISCUSSION

In this study of 45 children who underwent cardiac surgery with hypothermic CPB, it was found that radial MAPs reflected femoral MAPs within acceptable limits of agreement during the pre-CPB, CPB, and post-CPB periods. Bland-Altman plots commonly are used to statistically analyze agreement between results from 2 methods designed to measure the same parameter. The femoral MAPs were significantly higher than the corresponding radial MAPs at each 10-minute interval during CPB; however, Bland-Altman analysis revealed good agreement between the femoral and radial MAPs. Further, only 4% of these paired measurements revealed a 45 mmHg gradient, and in every case this difference persisted for less than 10 minutes (ie, was not observed across 2 serial measurement time points). The simultaneously measured radial and femoral DAPs also exhibited good agreement throughout the surgery, and in this case, clinically significant pressure gradients between the 2 measurement sites were even less frequent (2%). The findings for femoral and radial SAPs revealed that radial SAPs were higher than corresponding femoral SAPs during the pre-CPB period, lower than corresponding femoral SAPs immediately after initiation of CPB, and returned to preCPB status 10 minutes after termination of CPB. Despite good Table 2. Correlation Results for Systolic, Diastolic, and Mean Arterial Pressure Measurements by Intraoperative Period

49 ⫾ 11 50 ⫾ 7 49 ⫾ 10 50 ⫾ 6

47 ⫾ 10 47 ⫾ 10 47 ⫾ 8 50 ⫾ 6 47 ⫾ 7 46 ⫾ 9 49 ⫾ 11y 49 ⫾ 10y 50 ⫾ 8y 53 ⫾ 7y 50 ⫾ 8y 49 ⫾ 9y

47 ⫾ 9 42 ⫾ 6 48 ⫾ 8 53 ⫾ 9 49 ⫾ 10y 45 ⫾ 6y 52 ⫾ 9y 55 ⫾ 9y 53 ⫾ 11 49 ⫾ 10 52 ⫾ 11 50 ⫾ 10

Pre-CPB

* p o 0.05. y p o 0.01.

44 ⫾ 8 43 ⫾ 5 45 ⫾ 8y 45 ⫾ 5 43 ⫾ 7 44 ⫾ 7y 43 ⫾ 9 45 ⫾ 8y 39 ⫾ 5 45 ⫾ 9 43 ⫾ 7 42 ⫾ 5y 48 ⫾ 9y 45 ⫾ 8y 43 ⫾ 8 46 ⫾ 9y 43 ⫾ 6 46 ⫾ 6y 45 ⫾ 8 48 ⫾ 6 45 ⫾ 9 43 ⫾ 9 47 ⫾ 8y 51 ⫾ 7y 47 ⫾ 7y 45 ⫾ 9y 41 ⫾ 10 44 ⫾ 10 43 ⫾ 10y 46 ⫾ 9y 38 ⫾ 10 40 ⫾ 7 38 ⫾ 8 40 ⫾ 6 41 ⫾ 10 39 ⫾ 9 42 ⫾ 10 40 ⫾ 9

51 ⫾ 11 50 ⫾ 8 53 ⫾ 7 51 ⫾ 9 50 ⫾ 12 51 ⫾ 11 52 ⫾ 13 46 ⫾ 8 56 ⫾ 9 72 ⫾ 13 76 ⫾ 16 75 ⫾ 11 79 ⫾ 12 78 ⫾ 11* 53 ⫾ 11y 54 ⫾ 8y 56 ⫾ 7y 54 ⫾ 9y 54 ⫾ 13y 56 ⫾ 11y 56 ⫾ 13y 51 ⫾ 7y 61 ⫾ 10 75 ⫾ 13y 80 ⫾ 15y 75 ⫾ 12y 76 ⫾ 13 75 ⫾ 13 71 ⫾ 14 70 ⫾ 13* 70 ⫾ 13 70 ⫾ 10 58 ⫾ 12 71 ⫾ 14 68 ⫾ 15 68 ⫾ 13 69 ⫾ 11 58 ⫾ 13

Systolic arterial pressure (mmHg) Radial 75 ⫾ 11 77 ⫾ 13 76 ⫾ 13 Femoral 76 ⫾ 12 76 ⫾ 14 75 ⫾ 14 Diastolic arterial pressure (mmHg) Radial 42 ⫾ 8 46 ⫾ 10 43 ⫾ 10 Femoral 43 ⫾ 7 47 ⫾ 10 44 ⫾ 9* Mean arterial pressure (mmHg) Radial 54 ⫾ 9 58 ⫾ 12 55 ⫾ 11 Femoral 55 ⫾ 9 57 ⫾ 12 54 ⫾ 10

40 30 20 10

Post-cardiopulmonary bypass (minutes)

0 90 80 70 60 50 40 30

Cardiopulmonary bypass (minutes)

20 10 0 60 50 40 30 20

Pre-cardiopulmonary bypass (minutes)

10 0

Table 1. Mean Values for Systolic, Diastolic, and Mean Arterial Pressures During the Pre-Cardiopulmonary Bypass, Cardiopulmonary Bypass, and Post-Cardiopulmonary Bypass Periods (Mean ⫾ Standard Deviation)

RADIAL-TO-FEMORAL PRESSURE GRADIENT DURING CARDIOPULMONARY BYPASS IN CHILDREN

CPB

Systolic arterial pressure n 236 90 r 0.937 0.946 CI 0.917–0.952 0.916–0.965 p o0.001 o0.001 Diastolic arterial pressure n 236 90 r 0.955 0.966 CI 0.941–0.966 0.946–0.979 p o0.001 o0.001 Mean arterial pressure n 236 346 r 0.967 0.937 CI 0.958–0.976 0.917–0.952 p o0.001 o0.001

Post-CPB

Overall

194 0.937 0.917–0.952 o0.001

520 0.950 0.939–0.958 o0.001

194 0.955 0.941–0.966 o0.001

520 0.958 0.949–0.965 o0.001

194 0.969 0.958–0.976 o0.001

776 0.965 0.959–0.969 o0.001

Abbreviations: CI, 95% confidence interval; CPB, cardiopulmonary bypass; n, number of measurements; r, Pearson’s correlation coefficient.

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40

Femoral MAP - Radial MAP (mmHg)

Femoral MAP - Radial MAP (mmHg)

80

30 20 10 0 -10 -20 -30 46

48

50

52

54

56

30 20 10 0 -10 -20 -30

58

40 45 50 55 60 65 70 75 Mean of pre-CPB femoral and radial MAPs (mmHg)

40

Femoral MAP - Radial MAP (mmHg)

Femoral SAP - Radial SAP (mmHg)

Mean of all femoral and radial MAPs (mmHg)

30 20 10 0 -10 -20 -30 -40 60

65 70 75 80 85 90 Mean of all femoral and radial SAPs (mmHg)

10 0 -10 -20 -30 35

Femoral MAP - Radial MAP (mmHg)

Femoral DAP - Radial DAP (mmHg)

20 10 0 -10 -20 -30 40 45 50 Mean of all femoral and radial DAPs (mmHg)

20

95

30

35

30

55

Fig 2. Bland-Altman plots for femoral and radial mean arterial pressures (MAPs): (A) systolic arterial pressures (SAPs) and (B) diastolic arterial pressures (DAPs) over the entire course (C) of the operation.

agreement, 22% of all the paired SAPs exhibited clinically significant radial-to-femoral pressure gradients. Of the 3 arterial pressure categories examined in this study, MAP is the measurement typically used for hemodynamic management during pediatric cardiac surgery. The authors observed

40 45 50 55 60 Mean of CPB femoral and radial MAPs (mmHg)

30 20 10 0 -10 -20 -30 45 50 55 60 65 70 Mean of post-CPB femoral and radial MAPs (mmHg)

Fig 3. Bland-Altman plots for femoral and radial mean arterial pressures (MAPs) during each segment of the operation: (A) preCPB, (B) CPB, and (C) post-CPB. Abbreviation: CPB, cardiopulmonary bypass.

a relatively high rate of clinically significant radial-to-femoral SAP gradients; however, the rare use of SAP for hemodynamic management suggested that there would be minimal adverse issues related to peripheral SAP monitoring in this patient group.

81

40 30 20 10 0 -10 -20 -30 -40

Femoral SAP - Radial SAP (mmHg)

50

60 70 80 90 100 Mean of pre-CPB femoral and radial SAPs (mmHg)

40 30 20

components of the elastic properties of the arterial system, change significantly after birth, and an age-associated decrease in arterial distensibility in children has been documented.21,22 Kanazawa and colleagues19 used pulse-wave velocity as an indicator of arterial elasticity in 12 adults who underwent cardiac surgery with CPB. They concluded that their observation of lower radial arterial pressure compared with aortic pressure in these patients was likely due to reduced arterial elasticity in the radial artery. In addition to inherent age-related differences, atherosclerosis and peripheral arterial disease are very common in adults who require cardiac surgery, whereas these conditions are not issues in children. On the other hand, chronic hypoxemia, which is the hallmark feature in the clinical presentation of children who undergo cardiac surgery for cyanotic congenital heart disease, may induce structural changes in arterial walls and affect the elastic properties of these vessels.22 All physiological and pathophysiological differences between adults and children aside, patients of any age who undergo cardiac surgery require accurate measurement of arterial pressure to ensure optimal hemodynamic management.

10 0 -10 -20 -30 -40 60 65 70 75 80 85 90 95 100 Mean of post-CPB femoral and radial SAPs (mmHg)

Fig 4. Bland-Altman plots for femoral and radial systolic arterial pressures (SAPs) during each segment of the operation: (A) precardiopulmonary bypass and (B) post-CPB.

Femoral DAP - Radial DAP (mmHg)

Femoral SAP - Radial SAP (mmHg)

RADIAL-TO-FEMORAL PRESSURE GRADIENT DURING CARDIOPULMONARY BYPASS IN CHILDREN

30 20 10 0 -10 -20 -30 30

35

40

45

50

55

60

Mean of pre-CPB femoral and radial DAPs (mmHg)

Difference in DAP (femoral - radial) (mmHg)

Stern et al4 were the first to document the occurrence of CPB-associated discrepancies between peripheral and central arterial pressures during cardiac surgery in adults. Since that study, several investigators have demonstrated consistently the occurrence of peripheral-to-central arterial pressure gradients during adult cardiac surgery with hypothermic CPB.5–13,16–20 To the best of our knowledge, only one such study to date has included children in the analyses. Chauhan et al12 investigated 60 cardiac surgery patients who ranged in age from 3 to 65 years. They reported that monitoring arterial pressure via the radial artery might significantly underestimate femoral arterial pressure and lead to unnecessary use of vasoconstrictors, particularly at initiation of CPB. This is contrary to the present study’s findings in pediatric patients; however, this discrepancy may be explained by differing study groups, as the patient group investigated by Chauhan et al encompassed a wide range of ages and cardiac surgeries. Conflicting results between this pediatric study and adult studies may reflect physiologic and pathophysiological differences between these age classes. One potentially important issue is that adults and children have different arterial elasticity. Both arterial compliance and stiffness, which are important

25 20 15 10 5 0 -5 -10 -15 -20 -25 35 40 45 50 55 Mean of post-CPB femoral and radial DAPs (mmHg)

Fig 5. Bland-Altman plots for femoral and radial diastolic arterial pressures (DAPs) during each segment of the operation: (A) precardiopulmonary bypass and (B) post-CPB.

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Table 3. Numbers and Proportions of Significant Radial-to-Femoral Gradients and Numbers and Proportions of Pressure Measurement Pairs, with Listings by Intraoperative Period and for the Operation Overall Pre-CPB

Systolic arterial pressure Total significant gradients 33 Total pairs in period 236 % SAP pairs in period 14% % total SAP gradients 29% Diastolic arterial pressure Total significant gradients 4 Total pairs in period 236 % DAP pairs in period 2% % total DAP gradients 44% Mean arterial pressure Total significant gradients 6 Total pairs in period 236 % MAP pairs in period 3% % total MAP gradients 21% All pressure categories combined Total significant gradients 43 Total pairs in period 708 % all pairs in period 6% % total gradients overall 29%

CPB

Post-CPB

Overall

21 90 23% 19%

59 194 30% 52%

113 520 22% 75%

2 90 2% 22%

3 194 2% 33%

9 520 2% 6%

19 346 6% 68%

3 194 2% 11%

28 776 4% 19%

42 526 8% 28%

65 582 11% 43%

150 1816 8% 100%

Abbreviation: CPB, cardiopulmonary bypass.

Another possible reason for the discrepancy between our study and others is that it excluded patients who required substantial vasopressor support. In one investigation of 14 septic patients who received high doses of vasopressors, Dorman and colleagues23 found that radial arterial pressure significantly underestimated femoral arterial pressure. After these authors measured femoral arterial pressure, they were able to reduce the norepinephrine dose in 11 of their 14 patients. In the authors’ view, patients who require high doses of vasopressor support at termination of CPB represent a different subgroup of pediatric cardiac surgery patients, as these children usually need prolonged mechanical ventilation and a stay in the intensive care unit. Therefore, in contrast to previous studies that either have not mentioned vasopressor doses or have presented results for a subgroup of individuals who required vasopressor support, the authors decided to exclude such patients from this study.

Finally, another important difference between this study and previous ones is the statistical methods used. Bland-Altman plots were appropriate for this investigation, as it sought to assess agreement between 2 different methods of measuring the same physiological parameter. Previous studies on arterial pressures linked with CPB have either not used this type of plot or have used a classic Bland-Altman plot,24 which assumes independent measurements for a series of subjects. However, Bland and Altman15 also described methods for analyzing agreement in studies that involve multiple measures per subject, as was the case in this study. Accordingly, the authors used this latter method. This study had limitations. The first was the assumption that femoral arterial pressure is equal to central aortic pressure. Data related to this are limited; however, results from one study of adults and children suggested that femoral arterial pressure accurately reflects central aortic pressure.12 On the basis of these findings and the technical difficulties of directly measuring central aortic pressure, it was decided to use femoral arterial pressure in this study. The second limitation was that it only included relatively stable pediatric cardiac surgery patients; thus, the results cannot be generalized to children who undergo more extensive surgeries with deep hypothermic circulatory arrest or those who require high doses of vasopressors at the end of CPB. As mentioned previously, it was believed that these latter 2 groups represent a separate category of patients that should be investigated in a different study. Third, newborns and very small babies were excluded from this study because these patients also comprise a group of pediatric cardiac surgery patients who are physiologically and anatomically different from others. Finally, 2 different sized cannulae were used for radial artery (22 G) and femoral artery (20 G) catheterizations in this study, which may have led to inconsistency between the measurements from these sites. The authors concluded that, during pediatric cardiac surgery in relatively stable patients, radial MAP accurately reflects femoral MAP, and these 2 pressure-monitoring sites are clinically equivalent. However, specific studies in newborns and severely debilitated pediatric cardiac patients who frequently require deep hypothermic circulatory arrest and high doses of vasopressors are needed to assess whether the same MAP findings hold for these groups.

REFERENCES 1. Remington JW: Contour changes of the aortic pulse during propagation. Am J Physiol 199:331-334, 1960 2. Scheer B, Perel A, Pfeiffer UJ: Clinical review: complications and risk factors of peripheral arterial catheters used for haemodynamic monitoring in anaesthesia and intensive care medicine. Crit Care 6: 199-204, 2002 3. Brzezinski M, Luisetti T, London MJ: Radial artery cannulation: A comprehensive review of recent anatomic and physiologic investigations. Anesth Analg 109:1763-1781, 2009 4. Stern DH, Gerson JI, Allen FB, et al: Can we trust the direct radial artery pressure immediately following cardiopulmonary bypass? Anesthesiology 62:557-561, 1985

5. Mohr R, Lavee J, Goor DA: Inaccuracy of radial artery pressure measurement after cardiac operations. J Thorac Cardiovasc Surg 94: 286-290, 1987 6. Pauca AL, Hudspeth AS, Wallenhaupt SL, et al: Radial artery-toaorta pressure difference after discontinuation of cardiopulmonary bypass. Anesthesiology 70:935-941, 1989 7. Bazaral MG, Welch M, Golding LA, et al: Comparison of brachial and radial arterial pressure monitoring in patients undergoing coronary artery bypass surgery. Anesthesiology 73:38-45, 1990 8. Rulf EN, Mitchell MM, Prakash O, et al: Measurement of arterial pressure after cardiopulmonary bypass with long radial artery catheters. J Cardiothorac Anesth 4:19-24, 1990

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9. Rich GF, Lubanski RE Jr., McLoughlin TM: Differences between aortic and radial artery pressure associated with cardiopulmonary bypass. Anesthesiology 77:63-66, 1992 10. VanBeck JO, White RD, Abenstein JP, et al: Comparison of axillary artery or brachial artery pressure with aortic pressure after cardiopulmonary bypass using a long radial artery catheter. J Cardiothorac Vasc Anesth 7:312-315, 1993 11. Baba T, Goto T, Yoshitake A, et al: Radial artery diameter decreases with increased femoral to radial arterial pressure gradient during cardiopulmonary bypass. Anesth Analg 85:252-258, 1997 12. Chauhan S, Saxena N, Mehrotra S, et al: Femoral artery pressures are more reliable than radial artery pressures on initiation of cardiopulmonary bypass. J Cardiothorac Vasc Anesth 14:274-276, 2000 13. Manecke GR Jr., Parimucha M, Stratmann G, et al: Deep hypothermic circulatory arrest and the femoral-to-radial arterial pressure gradient. J Cardiothorac Vasc Anesth 18:175-179, 2004 14. Gardner RM: Direct blood pressure measurement–dynamic response requirements. Anesthesiology 54:227-236, 1981 15. Bland JM, Altman DG: Agreement between methods of measurement with multiple observations per individual. J Biopharm Stat 17: 571-582, 2007 16. Badner NH, Doyle JA: Comparison of pulsatile versus nonpulsatile perfusion on the postcardiopulmonary bypass aortic-radial artery pressure gradient. J Cardiothorac Vasc Anesth 11:428-431, 1997

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17. Bazaral MG, Nacht A, Petre J, et al: Radial artery pressures compared with subclavian artery pressure during coronary artery surgery. Cleve Clin J Med 55:448-457, 1988 18. Gravlee GP, Wong AB, Adkins TG, et al: A comparison of radial, brachial, and aortic pressures after cardiopulmonary bypass. J Cardiothorac Anesth 3:20-26, 1989 19. Kanazawa M, Fukuyama H, Kinefuchi Y, et al: Relationship between aortic-to-radial arterial pressure gradient after cardiopulmonary bypass and changes in arterial elasticity. Anesthesiology 99: 48-53, 2003 20. Pauca AL, Wallenhaupt SL, Kon ND, et al: Does radial artery pressure accurately reflect aortic pressure? Chest 102:1193-1198, 1992 21. Avolio AP, Chen SG, Wang RP, et al: Effects of aging on changing arterial compliance and left ventricular load in a northern Chinese urban community. Circulation 68:50-58, 1983 22. Senzaki H, Akagi M, Hishi T, et al: Age-associated changes in arterial elastic properties in children. Eur J Pediatr 161:547-551, 2002 23. Dorman T, Breslow MJ, Lipsett PA, et al: Radial artery pressure monitoring underestimates central arterial pressure during vasopressor therapy in critically ill surgical patients. Crit Care Med 26: 1646-1649, 1998 24. Bland JM, Altman DG: Statistical methods for assessing agreement between 2 methods of clinical measurement. Lancet 1: 307-310, 1986