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Non-invasive aortic blood flow measurement in infants during repair of craniosynostosis
British Journal of Anaesthesia 1998; 81: 696–701
Non-invasive aortic blood flow measurement in infants during repair of craniosynostosis† G. A. ORLIAGUET, P. G. MEYER, S. BLANOT, M. M. JARREAU, B. CHARRON, H. CUTTAREE, A. C. PERIE, P. A. CARLI AND D. RENIER Summary We have assessed the potential clinical benefit of a new echo-Doppler device (Dynemo 3000) which provides a continuous measure of aortic blood flow (ABF) using an aortic flowmeter and a paediatric oesophageal probe, during repair of craniosynostosis in infants under general anaesthesia. The data recorded included: ABFi (i:indexed to body surface area), stroke volume (SVi), systemic vascular resistance (TSVRi), preejection period (PEP), left ventricular ejection time (LVET), mean arterial pressure (MAP), heart rate (HR) and central venous pressure (CVP). Data were collected: before (T1) and 3 min after skin incision (T2), at the time of maximal haemorrhage (T3) and at the end of the procedure (T4). Twelve infants (aged 7.0 (range 6–12) months) were included. ABFi, MAP and CVP were significantly lower at T3 compared with T1 (2.0 (0.8) vs 3.0 (0.8) litre min91 m92, 46.1 (5.8) vs 65.2 (8.9) mm Hg and 2.8 (1.6) vs 5.2 (2.1) mm Hg; P:0.05). PEP/LVET ratio was significantly lower at T2 compared with T1 (0.25 (0.05) vs 0.30 (0.06)) and increased at T4 (0.36 (0.04); P:0.05). These preliminary results suggest that this noninvasive ABF echo-Doppler device may be useful for continuous haemodynamic monitoring during a surgical procedure associated with haemorrhage in infants. (Br. J. Anaesth. 1998; 81: 696–701). Keywords: complications, craniosynostosis; blood, flow; measurement techniques, ultrasound; anaesthesia, paediatric
Craniosynostosis is a relatively common disorder, with an estimated incidence of 1 per 2000 live births, related to premature closure of skull sutures.1 2 An early surgical correction is mandatory in the majority of cases because the compensatory deformation of the skull which occurs during rapid growth of the brain in early infancy may lead to increased intracranial pressure, especially in children older than 1 yr of age, and particularly if multiples sutures are involved.3 Surgery is aimed at restoring normal anatomy at an early age to achieve the best cosmetic result and avoid possible cerebral consequences.2 4 Therefore, surgical procedures for correction of craniosynostosis are performed in young infants with a small blood volume and represent major surgery with extensive blood loss.5 6
Accurate determination and precise restoration of blood losses represent the major concern for the anaesthetist during this surgery. However, intraoperative assessment of blood loss is difficult and requires precise haemodynamic monitoring. Although it has been argued that invasive measurement of cardiac output allows earlier interventions during critical surgical procedures, the technical difficulties of inserting balloon catheters into small children are such that haemodynamic evaluation frequently relies solely on clinical monitoring (heart rate, arterial pressure, pulse oximetry and PE′CO2 ). Unfortunately, clinical assessment of cardiac function using these measurements has been shown to be unreliable in children.7 Experience with intraoperative transoesophageal echocardiography is limited in children,8 and this monitoring is not widely available for infants. Moreover, the data provided by cardiac echocardiography only allow a diagnosis of a cardiovascular status at a given moment during the peroperative period. These factors encouraged the development of non-invasive ultrasound techniques to measure cardiac output in newborns and infants. The oesophageal route was first used in an attempt to overcome the problems noted with the suprasternal route9 and was progressively developed and improved by INSERM (U281) in France.10 11 Application of this methodology in adults during general anaesthesia and in intensive care patients revealed the clinical usefulness of aortic blood measurement.12–16 Non-invasive haemodynamic monitoring can now be performed with an echo-Doppler aortic blood flowmeter (Dynemo 3000 Sometec Inc., France). A miniaturized probe has been developed to continuously measure descending thoracic aortic diameter and blood velocity simultaneously, in infants as in adults. The aim of our preliminary study was to assess the feasibility and likely clinical benefits of continuous measurement of aortic blood flow (ABF) during repair of craniosynostosis, a surgical procedure associated with significant haemorrhage. G. A. ORLIAGUET, MD, P. G. MEYER, MD, S. BLANOT, MD, M. M. JARREAU, MD, B. CHARRON, MD, H. CUTTAREE, MD, A. C. PERIE, MD, P. A. CARLI, MD (Department of Paediatric Anaesthesiology); D. RENIER, MD (Department of Paediatric Neurosurgery); Hôpital des Enfants Malades, 149 rue de Sèvres, 75743 Paris Cedex 15, France. Accepted for publication: June 4, 1998. Correspondence to G. A. O. †Presented in part at the 4th European Congress of Paediatric Anaesthesia, May 21–24 1997, Paris.
Continuous non-invasive ABF measurement in infants
Patients and methods After obtaining approval from the Ethics Committee and informed consent from parents, we studied prospectively 12 infants (aged 6 months to 1 yr), ASA I–II, with a body weight of 6–12 kg, undergoing surgical repair of craniosynostosis. Exclusion criteria were: known or suspected oropharyngeal, oesophageal, aortic or mediastinal pathology; severe gastro-oesophageal reflux; or known or suspected latex sensitization. All procedures were performed under general anaesthesia without induced hypotension after skull skin infiltration with epinephrine (adrenaline) 1:200 000 in normal saline. After premedication with clorazepate dipotassium, general anaesthesia was induced with 2–3% halothane followed by fentanyl 5 g kg91. Neuromuscular block was achieved with atracurium 0.5 mg kg91. After orotracheal intubation, general anaesthesia was maintained using continuous i.v. infusion of fentanyl and controlled ventilation with 0.8–1.5% isoflurane and 50% nitrous oxide in oxygen. Monitoring included continuous ECG, invasive arterial and central venous pressures, core temperature, pulse oximetry, end-tidal carbon dioxide concentration and urine output. Preoperative blood samples were obtained for measurement of red blood cells, platelet count, haemoglobin concentration, packed cell volume (PCV) and coagulation screen. Serial blood samples were obtained at least every 2 h during operation and as frequently as clinically indicated, for measurement of blood-gas tensions and PCV. Intraoperative management was as described previously.5 Briefly, an isovolaemic compensation of blood loss was strictly observed, with fluid replacement based on haemodynamic variables, and including human serum albumin, colloids and packed red blood cells in order to maintain PCV in the range 0.28–0.35. Fresh frozen plasma was used only in patients requiring more than 70% of estimated blood volume transfusion. MEASUREMENT PRINCIPLE
Velocity is measured using the Doppler formula: v:((Cx⌬F)/(2Fey(x)cosI)) where C:ultrasound velocity inside the blood, ⌬F:frequency variation of emitted ultrasound, Fe:emission frequency, and I:angle of incidence and reflection of ultrasound against the red cells. Determination of ABF requires simultaneous and continuous measurement of the aortic section and blood velocity inside the aorta, at the same anatomical level where the aorta and oesophagus are nearly parallel. Using the specially designed ultrasound paediatric probe introduced into the oesophagus, we measured the diameter of the descending thoracic aorta using an M-mode echographic system and blood flow velocity with a pulsed Doppler velocimeter. PROBE AND FLOWMETER
The paediatric oesophageal probe has two ultrasound transducers (3x3 mm) located at the distal part of the probe. The first operates at 10 MHz Mecho mode scanner, perpendicular to the centre line. The second is a Doppler pulsed emission transducer operating at 5 MHz and mounted at an angle of 60⬚ to the centre line of the probe: the pulsed Doppler is
697 emitted with a 48⬚ divergent beam and the gated Doppler signal depth is adapted automatically to the aortic wall location values. This small probe, specially designed for newborns and infants, measures 5 mm (external diameter) and is 45 cm long. For infants, an 8- or 12-mm diameter cylindrical latex balloon is mounted on the sheath ready to be filled with 0.5 or 2 ml of water. This inflated balloon which surrounds the transducer maintains a constant angle of incidence of the ultrasound beams and allows the captor to rotate freely inside it without contact against the oesophageal mucosal wall. The balloon ensures transmission of ultrasound waves without air interposition and dissipates any heat produced. The oesophageal probe was inserted and positioned immediately after induction of anaesthesia. Depth of introduction of the probe into the oesophagus varied according to the height of the infant and was measured between the echo transducer placed on the third intercostal juxtasternal space and a slide rubber ring placed at the level of the mouth. This distance approximated the level where the aorta and oesophagus are parallel. The flowmeter includes three main parts: M-mode imaging system for diameter measurement, pulsed Doppler for velocity measurement, a second microprocessor system controlling flowmeter functions and peripheral monitoring devices. An invasive arterial cannula provides continuous measurement of mean arterial pressure (MAP). An electrocardioscope collects the ECG signal and calculates heart rate (HR) (Merlin, Hewlett Packard, USA). The haemodynamic profile integrates ABF, MAP and HR to calculate stroke volume (SV) in the descending aorta (obtained from the formula: SVa (ml):ABF/HR) and total systemic vascular resistance (TSVR) (calculated from the formula: TSVRa (dyn s cm95):MAP/ABFx79.9). These two variables are indexed to ABF. Moreover, systolic time intervals (STI) are measured from computerized analysis of the ECG signal (Q wave detection) and the acceleration signal which is derived from the Doppler velocity signal. Opening and closing of the aortic valve are detected by computerized analysis of the acceleration signal. The computer determines the length of the pre-ejection period (PEP) between the Q wave and the beginning of the systolic acceleration front, corresponding to aortic valve opening. Starting at the end of PEP, measurement of the left ventricular ejection time (LVET) is obtained by searching the acceleration signal for the second maximum of systolic deceleration corresponding to aortic valve closure.17 PEPi and LVETi are measured automatically and continuously and indexed to HR according to the formula of Weissler, Harris and Schoefeld.18 PEP/LVET ratio is also calculated automatically. These values are presented in table form and updated every 8 s on a screen display (fig. 1). Finally, the haemodynamic profile is recorded every 8 s (or at the operator’s request) on soft magnetic support. MEASUREMENT FOR THE STUDY
When the recorded ABF was satisfactory (stable and clear images of aortic walls and Doppler velocity signal on the screen for more than 1 min), initial data, before skull skin infiltration and skin incision, were
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British Journal of Anaesthesia
Figure 1 The Dynemo 3000 device. On the upper part of the screen, the M-mode echo of the aortic walls; on the lower part, the Doppler flow velocity. On the left part of the screen, the haemodynamic data shown in table form (updated every 8 s).
collected simultaneously and served as control values (T1). A second, third and fourth set of haemodynamic measurements were collected using the same criteria, respectively, 3 min after skin incision (T2), 60 min after skin incision (T3) and at the end of the surgical procedure during skin closure (T4). The time T3 was chosen at 60 min after skin incision because preliminary results had shown that at this time blood loss was maximal, with important haemodynamic changes. The oesophageal probe was removed at the end of surgery before discontinuation of anaesthesia. In an attempt to simplify estimation of blood loss, red cell volumes were used. Estimated body volume (EBV):80 ml kg91 and red cell volume (ERCV):EBVxPCV were calculated before operation. The following variables were then calculated for the period during operation: estimated red cell volume transfused (RCT):0.75xvolume of packed red cells; estimated red cell volume deficit (ERCD):ERCVxPCV variation; estimated red cell volume lost (ERCL):ERCD;RCT; and percent of ERCV lost:ERCL/ERCV. Results are reported as mean (SD). Data were compared between T1, T2, T3 and T4 using repeated measures analysis of variance and the Newman–Keuls test.19 All P values were two-tailed, and P:0.05 was required to reject the null hypothesis. Statistical analysis was performed using NCSS 6.0 software (BMDP Company, Los Angeles, CA, USA).
Results We studied 12 infants (eight females), treated by the same surgeon; mean age, weight, height and body surface area were 7.0 (range 6–12) months, 7.9 (SD 1.4) kg, 66.7 (3.9) cm and 0.39 (0.06) m2, respectively. The nature of the skull deformity was: plagiocephaly in four patients, trigonocephaly in four, scaphocephaly in three and brachycephaly in one. Mean duration of anaesthesia was 236 (37) min,
while mean duration of the surgical procedure was 140 (26) min. Total estimated red blood cells lost during the intraoperative period was 158 (77)% of preoperative estimated red cell volume (range 75–213%). ERCV, RCT, ERCD, ERCL and percent of ERCV lost are presented in table 1. Mean intraoperative transfusion was 360.0 (169.7) ml (range 180–480 ml) of packed red blood cells. No untoward incidents were noted using the device. Aortic diameter and ABF measurements were easily obtained in all cases and recording quality was excellent in all patients. However, it was necessary to reposition the oesophageal probe a mean of three times per patient because of loss of the Doppler signal related to displacement of the probe. These displacements were secondary to necessary movements of the head of the infant during the surgical procedure. Table 2 shows the haemodynamic variations during the surgical procedure: ABF, SVa and TSVRa were indexed to body surface area (ABFi, SVi, TSVRi). MAP, CVP and ABFi showed parallel changes in individual patients during the procedure (fig. 2). There was no significant variation in HR, SVi or TSVRi during operation. ABFi, MAP and CVP decreased significantly (P:0.0475, P:0.001, P:0.047, respectively) at the time of maximal blood loss (T3) compared with T1. While CVP and ABFi were not significantly different from control values (T1) at the end of the procedure (T4), MAP remained significantly decreased (P:0.01). PEPi and PEP/LVET ratio was significantly decreased at the time of skin incision (P:0.01, P:0.01, respectively) and increased at the end of the procedure (P:0.01, Table 1 Mean (SD) blood loss during the study Estimated red cell volume lost (ml) Packed red cell volume transfused (ml) % of patient’s estimated red cell volume lost (%) Final red cell volume deficit (ml)
281 (119) 270 (127) 158 (77) 11 (8)
Continuous non-invasive ABF measurement in infants
699
Table 2 Haemodynamic variations induced by skin incision (T2), blood loss (T3) and at the end of procedure (T4) compared with control values (T1). Data are mean (SD) (95% confidence interval). HR:Heart rate, MAP:mean arterial pressure, ABFi:aortic blood flow (indexed to body surface area), PEPi:pre-ejection period, LVETi:left ventricular ejection time, SVi:stroke volume (indexed to body surface area), TSVRi:total systemic vascular resistance (indexed to body surface area), CVP=central venous pressure. *P:0.05 vs T1 Measurement
T1
T2
T3
T4
HR (beat min91)
110 (12) (102–117) 65 (9) (60–71) 3.0 (0.8) (2.5–3.5) 131 (20) (118–144) 467 (23) (453–482) 0.30 (0.06) (0.26–0.34) 29 (8) (24–33) 2003 (822) (1481–2526) 5 (2) (4–7)
117 (16) (107–127) 69 (13) (60–77) 3.8 (1.5) (2.7–4.8) 112 (17) (99–123)* 468 (21) (454–482) 0.25 (0.05*) (0.21–0.28) 33 (13) (25–42) 1998 (1315) (1114–2882) 5 (2) (4–7)
110 (16) (101–120) 46 (6) (42–49)* 2.0 (0.8) (1.5–2.5)* 136 (8) (130–141) 462 (29) (443–480) 0.31 (0.04) (0.29–0.34) 25 (19) (13–38) 2269 (1454) (1314–3193) 3 (2*) (2–4)
109 (9) (102–115) 54 (4) (51–57)* 3.1 (1.6) (2.0–4.2) 148 (10) (142–155)* 437 (21) (423–451)* 0.36 (0.04) (0.33–0.39)* 31 (15) (21–42) 2352 (1533) (1322–3382) 6 (3) (4–7)
MAP (mm Hg) ABFi (litre min91 m92) PEPi (ms) LVETi (ms) PEP/LVET SVi (ml m92) TSVRi (dyn s cm95 m92) CVP (mm Hg)
P:0.01, respectively). LVETi was significantly decreased at the end of operation (P:0.015).
Discussion The main result of this preliminary clinical study was that non-invasive aortic blood measurement was
Figure 2 Evolution of MAP, CVP and ABFi in individual patients. MAP, CVP and ABFi showed parallel changes in individual patients. The same symbols are used for the same patients in the three figures.
feasible during repair of craniosynostosis in children, and estimated complementary haemodynamic trends. The echographic image of the aortic walls and Doppler flow were recorded easily without delay. The haemodynamic data appeared reliable in all cases and similar trends for each infant during surgical repair of craniosynostosis and haemorrhage were obtained: ABFi, MAP and CVP were decreased at the time of maximal blood loss (T3). The variations in systolic time intervals are a reflection of the inotropic variables: PEP reflects the isometric phase and LVET the isotonic phase of left ventricular contraction. A simplified expression of alterations in systolic time intervals is provided by the ratio PEP/LVET: among normal subjects this ratio averages 0.35<0.04. In adults, increase in PEP/LVET to 0.44 denotes decreased left ventricular performance.20 In contrast, decreases in PEP and PEP/LVET are observed with the use of inotropic drugs. Therefore, the decreases in PEPi and PEP/LVET ratio noted on T2, combined with a nonsignificant increase in both MAP and ABFi may be related to the positive inotropic effect of epinephrine, used for skull skin infiltration. The increase in PEP/LVET ratio, observed at the end of the surgical procedure, indicated some decrease in left ventricular contractility,21 which was not clinically relevant because ABFi was comparable with control values. This impairment in systolic time interval ratio could be related to metabolic acidosis and hypocalcaemia secondary to the massive blood transfusion. It was of interest to note that despite a significant decrease in MAP, ABFi and CVP at T3, there was no significant increase in TSVRi. This result could be related to the fact that general anaesthesia blunts the circulatory response to haemorrhage.22 Although it has been argued that invasive measurement of cardiac output allows earlier interventions in seriously ill patients or during critical surgical procedures, the practical problems of inserting a pulmonary artery catheter into small children are such that this monitoring device is not used routinely. Thus there is a need in paediatric critical care, and during critical paediatric anaesthesia, for an easy, accurate non-invasive measurement of blood flow.
700 Blood flow measurement using ultrasound techniques represents a suitable approach during general anaesthesia23 and has acceptable agreement and precision compared with the direct Fick method. In fact, this non-invasive method has been shown previously to correlate well with electromagnetic flow in animals24 25 and with thermodilution in humans.12–14 The device allows measurement of aortic diameter and velocity at the same anatomical level continuously and non-invasively. The importance of this simultaneous measurement has been outlined previously in adults26 and in children.27 Moreover, aortic diameter is probably the most important single determinant of Doppler cardiac output.28 29 Errors in measurement of aortic diameter are magnified because the square of the diameter is integrated into the calculated cardiac output.30 It is well established that aortic diameter changes during the cardiac cycle31 32 and with pressure, the relationship being almost linear.31–34 For the purpose of our study we used a device which is the only one available enabling simultaneous measurement of aortic diameter and velocity. Until recently, this monitoring technique was not available in infants, however the recent development of a miniaturized probe has remedied this. Gueugniaud and colleagues have demonstrated the feasibility of this device in infants and have shown some myocardial depression from isoflurane.35 However, contrary to our study, MAP was not measured continuously, which may have influenced the results, especially regarding the calculation of TSVRa (MAP/ABFx79.9). In summary, our results have confirmed the feasibility of this device and that it may provide non-invasive, complementary haemodynamic trends during a haemorrhagic surgical procedure in infants. Further studies are needed to evaluate how this new monitoring device may influence the perioperative management of infants and children.
British Journal of Anaesthesia
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10. 11.
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13. 14.
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18. 19. 20. 21. 22. 23.
Acknowledgements We thank Dr P.Y. Gueugniaud for revision of the article. 24.
References 1. Marchac D, Renier D. Classification of the different types of craniosynostosis. In Marchac D, Renier D, eds. Craniofacial Surgery for Craniosynostosis. Boston: Little Brown, 1982; 1–8. 2. Lajeunie E, Lemerrer M, Bonaïti-Pellie C, Marchac D, Renier D. A genetic study of non syndromic coronal craniosynostosis. American Journal of Medical Genetics 1995; 55: 500–504. 3. Renier D. Intracranial pressure in craniosynostosis: pre and postoperative recordings, correlation with functional results. In: Edgerton MT, Jane SA, eds. Scientific Foundation and Surgical Treatment of Craniosynostosis. Baltimore: Williams and Wilkins, 1989; 263–269. 4. Meyer P, Renier D, Blanot S, Orliaguet G, Arnaud E, Lajeunie E. Anesthésie-Réanimation des craniosténoses et dysmorphies craniofaciales de l’enfant. Annales Françaises d’Anesthésie et de Réanimation 1997; 16: 152–164. 5. Kearney RA, Rosales JK, Howes WJ. Craniosynostosis: an assessment of blood loss and transfusion practices. Canadian Journal of Anaesthesia 1989; 36: 473–477. 6. Meyer P, Renier D, Arnaud E, Jarreau MM, Charron B, Buy E, Buisson C, Barrier G. Blood loss during repair of craniosynostosis. British Journal of Anaesthesia 1993; 71: 854–857. 7. Wolf WJ, Neal MB, Peterson MD. The hemodynamic and cardiovascular effects of isoflurane and halothane anesthesia in children. Anesthesiology 1986; 64: 328–333. 8. Reich DL, Konstadt SN, Nejat M, Abrams HP, Bucek J. Intraoperative transesophageal echocardiography for the
25. 26.
27.
28.
29.
30.
detection of cardiac preload changes induced by transfusion and phlebotomy in pediatric patients. Anesthesiology 1993; 79: 10–15. Daigle RE, Miller CW, Histand MB, McLeod FD, Hokanson DE. Nontraumatic aortic blood flow sensing by use of an ultrasonic esophageal probe. Journal of Applied Physiology 1975; 38: 1153–1160. Cathignol D, Fourcade C. Sonde intracorporelle ultrasonore. Brevet INSERM no 78–14494. Lavandier B, Cathignol D, Muchada R, Bui Xuan B, Motin J. Noninvasive aortic blood flow measurement using an intraesopheageal probe. Ultrasound in Medicine and Biology 1985; 11: 451–460. Muchada R, Lavandier B, Cathignol D, Lamazou J, Lucchesi G, Roux MJ, Haro D, Palayer C. Non invasive haemodynamic monitoring in gynaecological laparoscopy. Annales Françaises d’Anesthésie et de Réanimation 1986; 5: 14–17. Muchada R, Cathignol D, Lavandier B, Lamazou J, Haro D. Aortic blood flow measurement. American Journal of Noninvasive Cardiology 1988; 2: 24–31. Muchada R, Cathignol D. Esophageal measurement of aortic blood flow by echo-Doppler. In: Vincent JL, ed. Update in Intensive Care and Emergency Medicine. Berlin: Springer Verlag, 1987; 356–365. Gueugniaud PY, Caritat R, Barreiro G, Muchada R, BertinMaghit M, Petit P. Noninvasive haemodynamic monitoring for burnt patients: feasibility and usefulness of aortic blood flow measurement. Réanimation Urgences 1993; 2: 533–538. Gueugniaud PY, Muchada R, Bertin-Maghit M, Griffith N, Petit P. Non invasive continuous haemodynamic and PetCO2 monitoring during peroperative cardiac arrest. Canadian Journal of Anaesthesia 1995; 42: 910–913. Muchada R, Vernier F, Fady JF, Haro D, Lavandier B, Cathignol D. A new automatic measurement method of systolic time intervals (STI). Journal of Cardiothoracic and Vascular Anesthesia 1992; 6 (Suppl.1): 22. Weissler AM, Harris WS, Schoenfeld CD. Systolic time intervals in heart failure in man. Circulation 1968; 37: 149–156. Fisher DM. Statistics in anesthesia. In: Miller RD, ed. Anesthesia 2nd Edn. New York: Churchill Livingstone, 1986; 685–712. Weissler AM. Current concepts in cardiology. Systolic time intervals. New England Journal of Medicine 1977; 296: 321–324. Boudoulas H. Systolic time intervals. European Heart Journal 1990; 11 (Suppl.1): 93–104. Vatner SF. Effects of anesthesia on cardiovascular control mechanisms. Environmental Health Perspectives 1978, 26: 193–206. Mark JB, Steinbrook RA, Gugino LD, Maddi R, Hartwell B, Shemin R, DiSese V, Rida WN. Continuous noninvasive monitoring of cardiac output with esophageal Doppler ultrasound during cardiac surgery. Anesthesia and Analgesia 1986, 65: 1013–1020. Lavandier B, Muchada R, Chignier E, Fady JF, Birer A, Cathignol D. Assessment of a potentially noninvasive method for monitoring aortic blood flow in children. Ultrasound in Medicine and Biology 1991; 17: 107–116. Muchada R, Rinaldi A, Cathignol D. Non invasive cardiovascular monitoring during general anaesthesia. Minerva Anestesiologica 1990; 56: 199–205. Muchada R, Cathignol D, Fontaine B, Lavandier B. Will morphometric data permit the determination of thoracic aorta caliber for precise measurement of blood flow in adults. Journal d’Echographie et de Médecine pars Ultrason 1990; 11: 76–80. Muchada R, Rinaldi A, Lavandier B, Cathignol D. Transesophageal Doppler ultrasound in children: importance of aortic diameter evaluation audits change for the evaluation of aortic output. Minerva Anestesiologica 1992; 58: 347–353. Lucas CL, Keagy BA, Hsia HS, Johnson TA, Henry GW, Wilcox BR. The velocity profile in the canine ascending aorta and its effects on the accuracy of pulsed Doppler determinations of mean blood velocity. Cardiovascular Research 1984; 18: 282–293. Mehta N, Iyawe VI, Cummin ARC, Bayley S, Saunders KB, Bennet D. Validation of a Doppler technique for beat-to-beat measurement of cardiac output. Clinical Science 1985; 69: 337–382. Nishimura RA, Callahan MJ, Schaff HV, Ilstrup DM, Miller FA, Tajik AJ. Noninvasive measurement of cardiac output by continuous-wave Doppler echocardiography: Initial experience and review of the literature. Mayo Clinic Proceedings 1984; 59: 484–489.
Continuous non-invasive ABF measurement in infants 31. Greenfield JC, Patel DJ. Relationship between pressure and diameter in the ascending aorta of man. Circulation Research 1962; 10: 778–781. 32. Rushmer RF. Pressure-circumference relations in the aorta. American Journal of Physiology 1955; 33: 545–549. 33. Barnett GO, Mallos AJ, Shapiro A. Relationship of aortic pressure and diameter in the dog. Journal of Applied Physiology 1961; 16: 545–548.
701 34. Patel DJ, deFreitas FM, Greenfield JC, Fry DL. Relationship of pressure along the aorta in living dogs. Journal of Applied Physiology 1963; 18: 1111–1117. 35. Gueugniaud PY, Muchada R, Moussa M, Haro D, Petit P. Continuous oesophageal aortic blood flow echo-Doppler measurement during general anaesthesia in infants. Canadian Journal of Anaesthesia 1997; 44: 745–746.
Non-invasive aortic blood flow measurement in infants during repair of craniosynostosis† G. A. ORLIAGUET, P. G. MEYER, S. BLANOT, M. M. JARREAU, B. CHARRON, H. CUTTAREE, A. C. PERIE, P. A. CARLI AND D. RENIER Summary We have assessed the potential clinical benefit of a new echo-Doppler device (Dynemo 3000) which provides a continuous measure of aortic blood flow (ABF) using an aortic flowmeter and a paediatric oesophageal probe, during repair of craniosynostosis in infants under general anaesthesia. The data recorded included: ABFi (i:indexed to body surface area), stroke volume (SVi), systemic vascular resistance (TSVRi), preejection period (PEP), left ventricular ejection time (LVET), mean arterial pressure (MAP), heart rate (HR) and central venous pressure (CVP). Data were collected: before (T1) and 3 min after skin incision (T2), at the time of maximal haemorrhage (T3) and at the end of the procedure (T4). Twelve infants (aged 7.0 (range 6–12) months) were included. ABFi, MAP and CVP were significantly lower at T3 compared with T1 (2.0 (0.8) vs 3.0 (0.8) litre min91 m92, 46.1 (5.8) vs 65.2 (8.9) mm Hg and 2.8 (1.6) vs 5.2 (2.1) mm Hg; P:0.05). PEP/LVET ratio was significantly lower at T2 compared with T1 (0.25 (0.05) vs 0.30 (0.06)) and increased at T4 (0.36 (0.04); P:0.05). These preliminary results suggest that this noninvasive ABF echo-Doppler device may be useful for continuous haemodynamic monitoring during a surgical procedure associated with haemorrhage in infants. (Br. J. Anaesth. 1998; 81: 696–701). Keywords: complications, craniosynostosis; blood, flow; measurement techniques, ultrasound; anaesthesia, paediatric
Craniosynostosis is a relatively common disorder, with an estimated incidence of 1 per 2000 live births, related to premature closure of skull sutures.1 2 An early surgical correction is mandatory in the majority of cases because the compensatory deformation of the skull which occurs during rapid growth of the brain in early infancy may lead to increased intracranial pressure, especially in children older than 1 yr of age, and particularly if multiples sutures are involved.3 Surgery is aimed at restoring normal anatomy at an early age to achieve the best cosmetic result and avoid possible cerebral consequences.2 4 Therefore, surgical procedures for correction of craniosynostosis are performed in young infants with a small blood volume and represent major surgery with extensive blood loss.5 6
Accurate determination and precise restoration of blood losses represent the major concern for the anaesthetist during this surgery. However, intraoperative assessment of blood loss is difficult and requires precise haemodynamic monitoring. Although it has been argued that invasive measurement of cardiac output allows earlier interventions during critical surgical procedures, the technical difficulties of inserting balloon catheters into small children are such that haemodynamic evaluation frequently relies solely on clinical monitoring (heart rate, arterial pressure, pulse oximetry and PE′CO2 ). Unfortunately, clinical assessment of cardiac function using these measurements has been shown to be unreliable in children.7 Experience with intraoperative transoesophageal echocardiography is limited in children,8 and this monitoring is not widely available for infants. Moreover, the data provided by cardiac echocardiography only allow a diagnosis of a cardiovascular status at a given moment during the peroperative period. These factors encouraged the development of non-invasive ultrasound techniques to measure cardiac output in newborns and infants. The oesophageal route was first used in an attempt to overcome the problems noted with the suprasternal route9 and was progressively developed and improved by INSERM (U281) in France.10 11 Application of this methodology in adults during general anaesthesia and in intensive care patients revealed the clinical usefulness of aortic blood measurement.12–16 Non-invasive haemodynamic monitoring can now be performed with an echo-Doppler aortic blood flowmeter (Dynemo 3000 Sometec Inc., France). A miniaturized probe has been developed to continuously measure descending thoracic aortic diameter and blood velocity simultaneously, in infants as in adults. The aim of our preliminary study was to assess the feasibility and likely clinical benefits of continuous measurement of aortic blood flow (ABF) during repair of craniosynostosis, a surgical procedure associated with significant haemorrhage. G. A. ORLIAGUET, MD, P. G. MEYER, MD, S. BLANOT, MD, M. M. JARREAU, MD, B. CHARRON, MD, H. CUTTAREE, MD, A. C. PERIE, MD, P. A. CARLI, MD (Department of Paediatric Anaesthesiology); D. RENIER, MD (Department of Paediatric Neurosurgery); Hôpital des Enfants Malades, 149 rue de Sèvres, 75743 Paris Cedex 15, France. Accepted for publication: June 4, 1998. Correspondence to G. A. O. †Presented in part at the 4th European Congress of Paediatric Anaesthesia, May 21–24 1997, Paris.
Continuous non-invasive ABF measurement in infants
Patients and methods After obtaining approval from the Ethics Committee and informed consent from parents, we studied prospectively 12 infants (aged 6 months to 1 yr), ASA I–II, with a body weight of 6–12 kg, undergoing surgical repair of craniosynostosis. Exclusion criteria were: known or suspected oropharyngeal, oesophageal, aortic or mediastinal pathology; severe gastro-oesophageal reflux; or known or suspected latex sensitization. All procedures were performed under general anaesthesia without induced hypotension after skull skin infiltration with epinephrine (adrenaline) 1:200 000 in normal saline. After premedication with clorazepate dipotassium, general anaesthesia was induced with 2–3% halothane followed by fentanyl 5 g kg91. Neuromuscular block was achieved with atracurium 0.5 mg kg91. After orotracheal intubation, general anaesthesia was maintained using continuous i.v. infusion of fentanyl and controlled ventilation with 0.8–1.5% isoflurane and 50% nitrous oxide in oxygen. Monitoring included continuous ECG, invasive arterial and central venous pressures, core temperature, pulse oximetry, end-tidal carbon dioxide concentration and urine output. Preoperative blood samples were obtained for measurement of red blood cells, platelet count, haemoglobin concentration, packed cell volume (PCV) and coagulation screen. Serial blood samples were obtained at least every 2 h during operation and as frequently as clinically indicated, for measurement of blood-gas tensions and PCV. Intraoperative management was as described previously.5 Briefly, an isovolaemic compensation of blood loss was strictly observed, with fluid replacement based on haemodynamic variables, and including human serum albumin, colloids and packed red blood cells in order to maintain PCV in the range 0.28–0.35. Fresh frozen plasma was used only in patients requiring more than 70% of estimated blood volume transfusion. MEASUREMENT PRINCIPLE
Velocity is measured using the Doppler formula: v:((Cx⌬F)/(2Fey(x)cosI)) where C:ultrasound velocity inside the blood, ⌬F:frequency variation of emitted ultrasound, Fe:emission frequency, and I:angle of incidence and reflection of ultrasound against the red cells. Determination of ABF requires simultaneous and continuous measurement of the aortic section and blood velocity inside the aorta, at the same anatomical level where the aorta and oesophagus are nearly parallel. Using the specially designed ultrasound paediatric probe introduced into the oesophagus, we measured the diameter of the descending thoracic aorta using an M-mode echographic system and blood flow velocity with a pulsed Doppler velocimeter. PROBE AND FLOWMETER
The paediatric oesophageal probe has two ultrasound transducers (3x3 mm) located at the distal part of the probe. The first operates at 10 MHz Mecho mode scanner, perpendicular to the centre line. The second is a Doppler pulsed emission transducer operating at 5 MHz and mounted at an angle of 60⬚ to the centre line of the probe: the pulsed Doppler is
697 emitted with a 48⬚ divergent beam and the gated Doppler signal depth is adapted automatically to the aortic wall location values. This small probe, specially designed for newborns and infants, measures 5 mm (external diameter) and is 45 cm long. For infants, an 8- or 12-mm diameter cylindrical latex balloon is mounted on the sheath ready to be filled with 0.5 or 2 ml of water. This inflated balloon which surrounds the transducer maintains a constant angle of incidence of the ultrasound beams and allows the captor to rotate freely inside it without contact against the oesophageal mucosal wall. The balloon ensures transmission of ultrasound waves without air interposition and dissipates any heat produced. The oesophageal probe was inserted and positioned immediately after induction of anaesthesia. Depth of introduction of the probe into the oesophagus varied according to the height of the infant and was measured between the echo transducer placed on the third intercostal juxtasternal space and a slide rubber ring placed at the level of the mouth. This distance approximated the level where the aorta and oesophagus are parallel. The flowmeter includes three main parts: M-mode imaging system for diameter measurement, pulsed Doppler for velocity measurement, a second microprocessor system controlling flowmeter functions and peripheral monitoring devices. An invasive arterial cannula provides continuous measurement of mean arterial pressure (MAP). An electrocardioscope collects the ECG signal and calculates heart rate (HR) (Merlin, Hewlett Packard, USA). The haemodynamic profile integrates ABF, MAP and HR to calculate stroke volume (SV) in the descending aorta (obtained from the formula: SVa (ml):ABF/HR) and total systemic vascular resistance (TSVR) (calculated from the formula: TSVRa (dyn s cm95):MAP/ABFx79.9). These two variables are indexed to ABF. Moreover, systolic time intervals (STI) are measured from computerized analysis of the ECG signal (Q wave detection) and the acceleration signal which is derived from the Doppler velocity signal. Opening and closing of the aortic valve are detected by computerized analysis of the acceleration signal. The computer determines the length of the pre-ejection period (PEP) between the Q wave and the beginning of the systolic acceleration front, corresponding to aortic valve opening. Starting at the end of PEP, measurement of the left ventricular ejection time (LVET) is obtained by searching the acceleration signal for the second maximum of systolic deceleration corresponding to aortic valve closure.17 PEPi and LVETi are measured automatically and continuously and indexed to HR according to the formula of Weissler, Harris and Schoefeld.18 PEP/LVET ratio is also calculated automatically. These values are presented in table form and updated every 8 s on a screen display (fig. 1). Finally, the haemodynamic profile is recorded every 8 s (or at the operator’s request) on soft magnetic support. MEASUREMENT FOR THE STUDY
When the recorded ABF was satisfactory (stable and clear images of aortic walls and Doppler velocity signal on the screen for more than 1 min), initial data, before skull skin infiltration and skin incision, were
698
British Journal of Anaesthesia
Figure 1 The Dynemo 3000 device. On the upper part of the screen, the M-mode echo of the aortic walls; on the lower part, the Doppler flow velocity. On the left part of the screen, the haemodynamic data shown in table form (updated every 8 s).
collected simultaneously and served as control values (T1). A second, third and fourth set of haemodynamic measurements were collected using the same criteria, respectively, 3 min after skin incision (T2), 60 min after skin incision (T3) and at the end of the surgical procedure during skin closure (T4). The time T3 was chosen at 60 min after skin incision because preliminary results had shown that at this time blood loss was maximal, with important haemodynamic changes. The oesophageal probe was removed at the end of surgery before discontinuation of anaesthesia. In an attempt to simplify estimation of blood loss, red cell volumes were used. Estimated body volume (EBV):80 ml kg91 and red cell volume (ERCV):EBVxPCV were calculated before operation. The following variables were then calculated for the period during operation: estimated red cell volume transfused (RCT):0.75xvolume of packed red cells; estimated red cell volume deficit (ERCD):ERCVxPCV variation; estimated red cell volume lost (ERCL):ERCD;RCT; and percent of ERCV lost:ERCL/ERCV. Results are reported as mean (SD). Data were compared between T1, T2, T3 and T4 using repeated measures analysis of variance and the Newman–Keuls test.19 All P values were two-tailed, and P:0.05 was required to reject the null hypothesis. Statistical analysis was performed using NCSS 6.0 software (BMDP Company, Los Angeles, CA, USA).
Results We studied 12 infants (eight females), treated by the same surgeon; mean age, weight, height and body surface area were 7.0 (range 6–12) months, 7.9 (SD 1.4) kg, 66.7 (3.9) cm and 0.39 (0.06) m2, respectively. The nature of the skull deformity was: plagiocephaly in four patients, trigonocephaly in four, scaphocephaly in three and brachycephaly in one. Mean duration of anaesthesia was 236 (37) min,
while mean duration of the surgical procedure was 140 (26) min. Total estimated red blood cells lost during the intraoperative period was 158 (77)% of preoperative estimated red cell volume (range 75–213%). ERCV, RCT, ERCD, ERCL and percent of ERCV lost are presented in table 1. Mean intraoperative transfusion was 360.0 (169.7) ml (range 180–480 ml) of packed red blood cells. No untoward incidents were noted using the device. Aortic diameter and ABF measurements were easily obtained in all cases and recording quality was excellent in all patients. However, it was necessary to reposition the oesophageal probe a mean of three times per patient because of loss of the Doppler signal related to displacement of the probe. These displacements were secondary to necessary movements of the head of the infant during the surgical procedure. Table 2 shows the haemodynamic variations during the surgical procedure: ABF, SVa and TSVRa were indexed to body surface area (ABFi, SVi, TSVRi). MAP, CVP and ABFi showed parallel changes in individual patients during the procedure (fig. 2). There was no significant variation in HR, SVi or TSVRi during operation. ABFi, MAP and CVP decreased significantly (P:0.0475, P:0.001, P:0.047, respectively) at the time of maximal blood loss (T3) compared with T1. While CVP and ABFi were not significantly different from control values (T1) at the end of the procedure (T4), MAP remained significantly decreased (P:0.01). PEPi and PEP/LVET ratio was significantly decreased at the time of skin incision (P:0.01, P:0.01, respectively) and increased at the end of the procedure (P:0.01, Table 1 Mean (SD) blood loss during the study Estimated red cell volume lost (ml) Packed red cell volume transfused (ml) % of patient’s estimated red cell volume lost (%) Final red cell volume deficit (ml)
281 (119) 270 (127) 158 (77) 11 (8)
Continuous non-invasive ABF measurement in infants
699
Table 2 Haemodynamic variations induced by skin incision (T2), blood loss (T3) and at the end of procedure (T4) compared with control values (T1). Data are mean (SD) (95% confidence interval). HR:Heart rate, MAP:mean arterial pressure, ABFi:aortic blood flow (indexed to body surface area), PEPi:pre-ejection period, LVETi:left ventricular ejection time, SVi:stroke volume (indexed to body surface area), TSVRi:total systemic vascular resistance (indexed to body surface area), CVP=central venous pressure. *P:0.05 vs T1 Measurement
T1
T2
T3
T4
HR (beat min91)
110 (12) (102–117) 65 (9) (60–71) 3.0 (0.8) (2.5–3.5) 131 (20) (118–144) 467 (23) (453–482) 0.30 (0.06) (0.26–0.34) 29 (8) (24–33) 2003 (822) (1481–2526) 5 (2) (4–7)
117 (16) (107–127) 69 (13) (60–77) 3.8 (1.5) (2.7–4.8) 112 (17) (99–123)* 468 (21) (454–482) 0.25 (0.05*) (0.21–0.28) 33 (13) (25–42) 1998 (1315) (1114–2882) 5 (2) (4–7)
110 (16) (101–120) 46 (6) (42–49)* 2.0 (0.8) (1.5–2.5)* 136 (8) (130–141) 462 (29) (443–480) 0.31 (0.04) (0.29–0.34) 25 (19) (13–38) 2269 (1454) (1314–3193) 3 (2*) (2–4)
109 (9) (102–115) 54 (4) (51–57)* 3.1 (1.6) (2.0–4.2) 148 (10) (142–155)* 437 (21) (423–451)* 0.36 (0.04) (0.33–0.39)* 31 (15) (21–42) 2352 (1533) (1322–3382) 6 (3) (4–7)
MAP (mm Hg) ABFi (litre min91 m92) PEPi (ms) LVETi (ms) PEP/LVET SVi (ml m92) TSVRi (dyn s cm95 m92) CVP (mm Hg)
P:0.01, respectively). LVETi was significantly decreased at the end of operation (P:0.015).
Discussion The main result of this preliminary clinical study was that non-invasive aortic blood measurement was
Figure 2 Evolution of MAP, CVP and ABFi in individual patients. MAP, CVP and ABFi showed parallel changes in individual patients. The same symbols are used for the same patients in the three figures.
feasible during repair of craniosynostosis in children, and estimated complementary haemodynamic trends. The echographic image of the aortic walls and Doppler flow were recorded easily without delay. The haemodynamic data appeared reliable in all cases and similar trends for each infant during surgical repair of craniosynostosis and haemorrhage were obtained: ABFi, MAP and CVP were decreased at the time of maximal blood loss (T3). The variations in systolic time intervals are a reflection of the inotropic variables: PEP reflects the isometric phase and LVET the isotonic phase of left ventricular contraction. A simplified expression of alterations in systolic time intervals is provided by the ratio PEP/LVET: among normal subjects this ratio averages 0.35<0.04. In adults, increase in PEP/LVET to 0.44 denotes decreased left ventricular performance.20 In contrast, decreases in PEP and PEP/LVET are observed with the use of inotropic drugs. Therefore, the decreases in PEPi and PEP/LVET ratio noted on T2, combined with a nonsignificant increase in both MAP and ABFi may be related to the positive inotropic effect of epinephrine, used for skull skin infiltration. The increase in PEP/LVET ratio, observed at the end of the surgical procedure, indicated some decrease in left ventricular contractility,21 which was not clinically relevant because ABFi was comparable with control values. This impairment in systolic time interval ratio could be related to metabolic acidosis and hypocalcaemia secondary to the massive blood transfusion. It was of interest to note that despite a significant decrease in MAP, ABFi and CVP at T3, there was no significant increase in TSVRi. This result could be related to the fact that general anaesthesia blunts the circulatory response to haemorrhage.22 Although it has been argued that invasive measurement of cardiac output allows earlier interventions in seriously ill patients or during critical surgical procedures, the practical problems of inserting a pulmonary artery catheter into small children are such that this monitoring device is not used routinely. Thus there is a need in paediatric critical care, and during critical paediatric anaesthesia, for an easy, accurate non-invasive measurement of blood flow.
700 Blood flow measurement using ultrasound techniques represents a suitable approach during general anaesthesia23 and has acceptable agreement and precision compared with the direct Fick method. In fact, this non-invasive method has been shown previously to correlate well with electromagnetic flow in animals24 25 and with thermodilution in humans.12–14 The device allows measurement of aortic diameter and velocity at the same anatomical level continuously and non-invasively. The importance of this simultaneous measurement has been outlined previously in adults26 and in children.27 Moreover, aortic diameter is probably the most important single determinant of Doppler cardiac output.28 29 Errors in measurement of aortic diameter are magnified because the square of the diameter is integrated into the calculated cardiac output.30 It is well established that aortic diameter changes during the cardiac cycle31 32 and with pressure, the relationship being almost linear.31–34 For the purpose of our study we used a device which is the only one available enabling simultaneous measurement of aortic diameter and velocity. Until recently, this monitoring technique was not available in infants, however the recent development of a miniaturized probe has remedied this. Gueugniaud and colleagues have demonstrated the feasibility of this device in infants and have shown some myocardial depression from isoflurane.35 However, contrary to our study, MAP was not measured continuously, which may have influenced the results, especially regarding the calculation of TSVRa (MAP/ABFx79.9). In summary, our results have confirmed the feasibility of this device and that it may provide non-invasive, complementary haemodynamic trends during a haemorrhagic surgical procedure in infants. Further studies are needed to evaluate how this new monitoring device may influence the perioperative management of infants and children.
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9.
10. 11.
12.
13. 14.
15.
16.
17.
18. 19. 20. 21. 22. 23.
Acknowledgements We thank Dr P.Y. Gueugniaud for revision of the article. 24.
References 1. Marchac D, Renier D. Classification of the different types of craniosynostosis. In Marchac D, Renier D, eds. Craniofacial Surgery for Craniosynostosis. Boston: Little Brown, 1982; 1–8. 2. Lajeunie E, Lemerrer M, Bonaïti-Pellie C, Marchac D, Renier D. A genetic study of non syndromic coronal craniosynostosis. American Journal of Medical Genetics 1995; 55: 500–504. 3. Renier D. Intracranial pressure in craniosynostosis: pre and postoperative recordings, correlation with functional results. In: Edgerton MT, Jane SA, eds. Scientific Foundation and Surgical Treatment of Craniosynostosis. Baltimore: Williams and Wilkins, 1989; 263–269. 4. Meyer P, Renier D, Blanot S, Orliaguet G, Arnaud E, Lajeunie E. Anesthésie-Réanimation des craniosténoses et dysmorphies craniofaciales de l’enfant. Annales Françaises d’Anesthésie et de Réanimation 1997; 16: 152–164. 5. Kearney RA, Rosales JK, Howes WJ. Craniosynostosis: an assessment of blood loss and transfusion practices. Canadian Journal of Anaesthesia 1989; 36: 473–477. 6. Meyer P, Renier D, Arnaud E, Jarreau MM, Charron B, Buy E, Buisson C, Barrier G. Blood loss during repair of craniosynostosis. British Journal of Anaesthesia 1993; 71: 854–857. 7. Wolf WJ, Neal MB, Peterson MD. The hemodynamic and cardiovascular effects of isoflurane and halothane anesthesia in children. Anesthesiology 1986; 64: 328–333. 8. Reich DL, Konstadt SN, Nejat M, Abrams HP, Bucek J. Intraoperative transesophageal echocardiography for the
25. 26.
27.
28.
29.
30.
detection of cardiac preload changes induced by transfusion and phlebotomy in pediatric patients. Anesthesiology 1993; 79: 10–15. Daigle RE, Miller CW, Histand MB, McLeod FD, Hokanson DE. Nontraumatic aortic blood flow sensing by use of an ultrasonic esophageal probe. Journal of Applied Physiology 1975; 38: 1153–1160. Cathignol D, Fourcade C. Sonde intracorporelle ultrasonore. Brevet INSERM no 78–14494. Lavandier B, Cathignol D, Muchada R, Bui Xuan B, Motin J. Noninvasive aortic blood flow measurement using an intraesopheageal probe. Ultrasound in Medicine and Biology 1985; 11: 451–460. Muchada R, Lavandier B, Cathignol D, Lamazou J, Lucchesi G, Roux MJ, Haro D, Palayer C. Non invasive haemodynamic monitoring in gynaecological laparoscopy. Annales Françaises d’Anesthésie et de Réanimation 1986; 5: 14–17. Muchada R, Cathignol D, Lavandier B, Lamazou J, Haro D. Aortic blood flow measurement. American Journal of Noninvasive Cardiology 1988; 2: 24–31. Muchada R, Cathignol D. Esophageal measurement of aortic blood flow by echo-Doppler. In: Vincent JL, ed. Update in Intensive Care and Emergency Medicine. Berlin: Springer Verlag, 1987; 356–365. Gueugniaud PY, Caritat R, Barreiro G, Muchada R, BertinMaghit M, Petit P. Noninvasive haemodynamic monitoring for burnt patients: feasibility and usefulness of aortic blood flow measurement. Réanimation Urgences 1993; 2: 533–538. Gueugniaud PY, Muchada R, Bertin-Maghit M, Griffith N, Petit P. Non invasive continuous haemodynamic and PetCO2 monitoring during peroperative cardiac arrest. Canadian Journal of Anaesthesia 1995; 42: 910–913. Muchada R, Vernier F, Fady JF, Haro D, Lavandier B, Cathignol D. A new automatic measurement method of systolic time intervals (STI). Journal of Cardiothoracic and Vascular Anesthesia 1992; 6 (Suppl.1): 22. Weissler AM, Harris WS, Schoenfeld CD. Systolic time intervals in heart failure in man. Circulation 1968; 37: 149–156. Fisher DM. Statistics in anesthesia. In: Miller RD, ed. Anesthesia 2nd Edn. New York: Churchill Livingstone, 1986; 685–712. Weissler AM. Current concepts in cardiology. Systolic time intervals. New England Journal of Medicine 1977; 296: 321–324. Boudoulas H. Systolic time intervals. European Heart Journal 1990; 11 (Suppl.1): 93–104. Vatner SF. Effects of anesthesia on cardiovascular control mechanisms. Environmental Health Perspectives 1978, 26: 193–206. Mark JB, Steinbrook RA, Gugino LD, Maddi R, Hartwell B, Shemin R, DiSese V, Rida WN. Continuous noninvasive monitoring of cardiac output with esophageal Doppler ultrasound during cardiac surgery. Anesthesia and Analgesia 1986, 65: 1013–1020. Lavandier B, Muchada R, Chignier E, Fady JF, Birer A, Cathignol D. Assessment of a potentially noninvasive method for monitoring aortic blood flow in children. Ultrasound in Medicine and Biology 1991; 17: 107–116. Muchada R, Rinaldi A, Cathignol D. Non invasive cardiovascular monitoring during general anaesthesia. Minerva Anestesiologica 1990; 56: 199–205. Muchada R, Cathignol D, Fontaine B, Lavandier B. Will morphometric data permit the determination of thoracic aorta caliber for precise measurement of blood flow in adults. Journal d’Echographie et de Médecine pars Ultrason 1990; 11: 76–80. Muchada R, Rinaldi A, Lavandier B, Cathignol D. Transesophageal Doppler ultrasound in children: importance of aortic diameter evaluation audits change for the evaluation of aortic output. Minerva Anestesiologica 1992; 58: 347–353. Lucas CL, Keagy BA, Hsia HS, Johnson TA, Henry GW, Wilcox BR. The velocity profile in the canine ascending aorta and its effects on the accuracy of pulsed Doppler determinations of mean blood velocity. Cardiovascular Research 1984; 18: 282–293. Mehta N, Iyawe VI, Cummin ARC, Bayley S, Saunders KB, Bennet D. Validation of a Doppler technique for beat-to-beat measurement of cardiac output. Clinical Science 1985; 69: 337–382. Nishimura RA, Callahan MJ, Schaff HV, Ilstrup DM, Miller FA, Tajik AJ. Noninvasive measurement of cardiac output by continuous-wave Doppler echocardiography: Initial experience and review of the literature. Mayo Clinic Proceedings 1984; 59: 484–489.
Continuous non-invasive ABF measurement in infants 31. Greenfield JC, Patel DJ. Relationship between pressure and diameter in the ascending aorta of man. Circulation Research 1962; 10: 778–781. 32. Rushmer RF. Pressure-circumference relations in the aorta. American Journal of Physiology 1955; 33: 545–549. 33. Barnett GO, Mallos AJ, Shapiro A. Relationship of aortic pressure and diameter in the dog. Journal of Applied Physiology 1961; 16: 545–548.
701 34. Patel DJ, deFreitas FM, Greenfield JC, Fry DL. Relationship of pressure along the aorta in living dogs. Journal of Applied Physiology 1963; 18: 1111–1117. 35. Gueugniaud PY, Muchada R, Moussa M, Haro D, Petit P. Continuous oesophageal aortic blood flow echo-Doppler measurement during general anaesthesia in infants. Canadian Journal of Anaesthesia 1997; 44: 745–746.