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Revista Colombiana de Anestesiología

Print version ISSN 0120-3347

Rev. colomb. anestesiol. vol.39 no.2 Bogotá Apr./July 2011

http://dx.doi.org/10.5554/rca.v39i2.98 

Artículo de Reflexión

The Blind Spot in Obstetric Anesthesia: Intra-Surgical Fetal Monitoring

Andrés Felipe Corrales*, Ricardo Augusto Sandoval**, José Ricardo Navarro***

* Médico, estudiante posgrado de Anestesiología, Universidad Nacional de Colombia, Bogotá, Colombia. Correspondencia: Carrera 32A No. 25B-75, Ap 802 T1 Bogotá, Colombia. Correo electrónico: anfecori@hotmail.com
** Interno especial de Anestesiología, Universidad Nacional de Colombia, Bogotá, Colombia. Correo electrónico: ricardo870608@hotmail.com
*** Médico, profesor asociado Departamento de Cirugía, Universidad Nacional de Colombia, Bogotá, Colombia. Correo electrónico: jrnavarrov@unal.edu.co

Recibido: septiembre 10 de 2010. Enviado para modificaciones: diciembre 12 de 2010. Aceptado: abril 1 de 2011.


SUMMARY

Introduction: There is a big gap in fetal monitoring in obstetric patients undergoing cesarean section during the transoperative period. Despite the astonishing technological developments in all medical areas, we have failed to develop a practical method for the evaluation of the fetus wellbeing during a c-section intervention.

Objective. A non-invasive and practical method is suggested that can be used in a site distant from the abdominal surgical field to record the continuous fetal heart rate as an indicator of fetal wellbeing. This task would not only involve the anesthesiologist, but the obstetrician and the pediatrician as well.

Methodology. Producing an article that should be food for thought, based on a question asked by students of anesthesiology in the OR (graduate and postgraduate students), about a practical method for intraoperative fetal, noninvasive monitoring. The search was conducted using the Medline, Ovid and Science Direct data basis.

Results. Notwithstanding the absence of an appropriate fetal monitoring method (optimal and practical) for this period of time in the OR, it is mandatory to find a technology-based solution to assess the wellbeing of the fetus during the transoperative period of the c-section, firstly because there are multiple factors that may extend the surgical time and become a determining factor for the lack of control of a hypoxic or schemic event of the fetus; secondly, because safety of obstetric and fetal anesthesia must be demanding and is critical.

Key words: Fetal monitoring, c-section, intraoperative period (Source: MeSH, NLM).


The conventional transoperative system (c-section) currently used includes the basic hemodynamic parameters (non-invasive arterial pressure), pulse oximetry and electrocardiographic tracing, to control de patient’s response to surgical stress. These monitoring approaches however, do not allow for evaluating the fetal status during surgery. Currently, institutions with more advanced technologies have invasive methods available which are not practical or easy to use and entail some risks because a catheter must be inserted into the uterus to measure the pressure and the uterine activity, in addition to a deep intra-cervical probe to monitor the fetal cardiac activity (1-3). The latter has been performed by placing an electrode inside the mother’s vagina and over the scalp of the fetus, fixing it with a plate to the mother’s thigh; the signal detected is then amplified in a monitor including a cardiotachometer that measures the fetal heart rate (FHR) (1). All anesthetic agents finally affect the fetus in a similar way to the pharmacodynamic process that takes place in the mother, causing hypnosis, sedation and analgesia, in addition to a disruption of the fetal heart output (4), which is variable and non-measurable during the transoperatorive period. Hence, it is not susceptible to optimization and control. The utero-placental circuit is low resistance, high flow and does not self-regulate; it is exclusively dependant on the maternal flow to preserve approximately 700 ml/min. required by the fetus at the end of gestation (5). It has been established by “extrapolation” that this flow maintains the O2, CO2 and pH conditions required by the fetus. These parameters may change however, depending on the anesthetic technique or the underlying pathology, resulting in a reduction of placental perfusion or compromising oxygenation and fetal wellbeing secondary to a maternal acid-base disorder (6,7).

Anesthesia, hysterectomy, fetal manipulation and surgical stress may all have a dramatic impact on the fetal-placental or uterine-placental circulation due to several mechanisms: fetal hypotension, increased uterine activity, maternal hyperventilation, fetal cardiac output disruption, umbilical blood flow alteration, compression of the umbilical chord, of the inferior vena cava or the mediastinum, etc. (8).

The intraoperative fetal monitoring methods are invasive and rather impractical, including: electronic FHR monitoring, fetal pulse oximetry, echocardiography and blood gasses measurements of the scalp or fetal skin. Continuous electronic intraoperative fetal monitoring (9) is done routinely to oversee the fetal status during labor and is a resource that has proven to be useful to detect changes in fetal wellbeing (10); however, it is unable to detect intrapartum fetal asphyxia and hence the opportunity for early intervention to ensure the wellbeing of the fetus is missed (11).

The following are some of the limitations of electronic FHR monitoring: the interpretations are observer-dependant; a professional must constantly be available to assess the FHR tracings; there are inherent risks to the procedure and contraindications; since its implementation, the FHR records are a legal document. Furthermore, it is considered to be a poor positive predictive value resource due to the lack of consistency between an abnormal FHR and abnormal results; consequently, the American College of Obstetricians and Gynecologists (ACOG) recommends that an abnormal FHR tracing be interpreted as an “nonreassuring fetal status” (NRFS) instead of using the expression “acute fetal distress” or “birth asphyxia” (12,13).

The following are some of the relative contraindications to perform FHR intraoperative monitoring: the presence of intact membranes and a fetal presentation other than cephalic; infection such as chorioamnionitis, HIV, herpes simplex; additionally, there has to be a dilatation of the cervix allowing for the passage of the probe down to the fetal scalp (14).

In the developed countries this monitoring has been practiced for approximately 40 years and with very rare reported complications (neonatal seizures or fetal intrauterine deaths); however, the most important finding is that it has definitely increased the rate of c-sections (15,16).

Despite the efforts to measure the physiological changes of the fetus, whether using invasive or non-invasive methods during the transoperative period, currently there are no simple, easy-touse and safe method applicable to every case. It is as if there was a blind spot in intra-surgical fetal monitoring. Currently the trend in the development of monitoring equipment focuses on optimizing the automated and non-invasive methods due to a multiplicity of reasons: speed, reliability, preservation of the anatomic and functional integrity and lower costs.

The difficulties are varied, including the absence of a static landmark to direct the monitor to, since the fetus floats freely inside the uterine cavity and access is restricted by the c-section procedure itself. Nevertheless, there is a need for such technological development, particularly using devices that capture vibration- acoustic signals or powerful transducers able to record the continuous fetal heart rate from a site distant from the surgical field, such as the esophagus or the mother’s lumbar region that enables heart rate and uterine activity monitoring.

The authors suggest that the initiative to develope such invention must come from the anesthesiologist, since the obstetrician’s concern is to operate on the patient and the pediatrician, though aware of the mother’s clinical record and the pre-surgical evolution of the fetus, in only willing to take action after the neonate is delivered.

Studies from Queen’s University have compared the effectiveness of using FHR monitoring, blood gasses and acid-base evaluation to detect early hypoxia in vaginal deliveries, with acceptable results (17). However, these methods cannot be extrapolated to surgical practice because of the downsides already listed (position of the catheters and monitor probes); furthermore, sampling of blood gasses in the fetus is an invasive procedure that requires, among other things, rupture of the membranes and adequate dilatation of the cervix, absence of fetal clotting disorders, absence of latent or active infection in the mother or the amniotic fluid, in addition to the feasibility of taking several blood samples from the scalp which may cause fetal trauma (18).

Approximately 40 % of fetal cardiac output is devoted to perfuse the placental exchange area. The perfusion, oxygenation, ventilation, acid-base status and metabolic analysis of an individual can all be interpreted through arteriovenous gas measurements, as long as the samples are appropriately taken from the radial artery and the cerebral venous and body mix (19,20). Likewise, the placenta may be another target for an accurate monitoring of the fetal status by taking blood samples for gas analysis of the uterine and venous vessels of the newborn (NB) (Table 1) (21). However, the clinical approach for doing these tests is impractical and entails risks (22).

Obstetric patients may undergo abdominal surgery for reasons other than their pregnancy, including intrauterine fetal surgery – laparoscoscopic, optical or with open access to the uterus. These techniques are complex and it is difficult to make periodic umbilical chord Doppler evaluations (23-25).

In conclusion, there is a huge gap in fetal monitoring during the trans-operative period which directly concerns the medical specialties involved. In view of the above considerations, there is a need to develop preferably non-invasive fetal monitoring methods, with a view to physiologically maintain the hemodynamic and metabolic variables in these little patients that require a direct trans-operative control of their clinical status.

References

1. Reiss RE, Gabbe SG, Petrie RH. Intrapartum fetal evaluation. En: Gabbe SG, Niebyl JR, Simpson JL, editors. Obstetrics: normal and problem pregnancies. 3rd ed. New York: Churchill Livingstone. 1996;401-2.

2. American College of Obstetricians and Gynecologists. Intrapartum fetal heart rate monitoring. ACOG Practice Bulletin No. 70. Obstet Gynecol. 2005;106: 1453-60.

3. Gourounti K, Sandall J. Admission cardiotocography versus intermittent auscultation of fetal heart rate: effects on neonatal Apgar score, on the rate of caesarean sections and the rate of instrumental delivery. A systematic review. Int J Nurs Stud. 2007;44:1029-35.

4. Braveman F. Obstetrical Anesthesia. En: Barash PG, Cullen BF, Stoelting RK, editores. Clinical Anesthesia. 6th ed. Philadelphia: Lippincot Williams and Wilkins; 2009. p. 1138-70.

5. Birnbach D, Browne I. Anesthesia for obstetrics. En: Miller RD, Eriksson LI, Fleisher LA, et al, editors. Miller’s Anesthesia. 7th ed. Philadelphia: Elsevier; 2009. Chapter 69.

6. Ngan Kee WD, Khaw KS, Ma KC, et al. Maternal and neonatal effects of remifentanil at induction of general anesthesia for cesarean delivery: a randomized, double-blind, controlled trial. Anesthesiology. 2006;104:14-20.

7. Penning DH. Fetal and neonatal neurologic injury. En: Chesnut DH, Polley LS, Tsen LC, et al, editors. Obstetric anesthesia: principles and practice. 4th ed. Philadelphia: Mosby Elsevier; 2009. Chapter 10.

8. Rosen MA. Anesthesia for fetal surgery and other intrauterine procedures. En: Chesnut DH, Polley LS, Tsen LC, et al, editors. Obstetric Anesthesia: principles and practice. 4th ed. Philadelphia: Mosby Elsevier; 2009. Chapter 7.

9. National Institute of child health and human development research planning workshop. Electronic fetal heart rate monitoring: research guidelines for interpretation. Am J Obstet Gynecol. 1997;177:1385-90.

10. Martin JA, Hamilton BE, Sutton PD, et al. Births: final data for 2002. Natl Vital Stat Rep. 2003;52: 1-113.

11. Low JA, Simpson LL, Tonni G, et al. Limitations in the clinical prediction of intrapartum fetal asphyxia. Am J Obstet Gynecol. 1995;172:801-4.

12. Figueras F, Albela S, Bonino S, et al. Visual analysis of antepartum fetal heart rate tracings: inter and intra observer agreement and impact of knowledge of neonatal outcome. J Perinat Med. 2005;33:241-5.

13. American College of Obstetricians and Gynecologists. Inappropiate use of the terms fetal distress and birth asphyxia. Int J Gynaecol Obstet. 1998;61:309-10.

14. Livingston EG. Intrapartum fetal assessment and terapy. En: Chesnut DH, Polley LS, Tsen LC, et al, editors. Obstetric anesthesia: principles and practice. 4th ed. Philadelphia: Mosby Elsevier; 2009. Chapter 8.

15. Tracker SB, Stroup DF, Peterson HB. Efficacy and safety of intrapartum electronic fetal monitoring: an update. Obstet Gynecol. 1995;86:613-620.

16. Vintzileos AM, Nochimson DJ, Guzmán ER, et al. Intrapartum electronic fetal heart rate monitoring versus intermittent auscultation: a meta- analysis. Obstet Gynecol. 1995;85:149-55.

17. Low JA, Pickersgill H, Killen H, et al. The prediction and prevention of intrapartum fetal asphyxia in term pregnancies. Am J Obstet Gynecol. 2001;184: 724-30.

18. Parer JT. Handbook of fetal heart rate monitoring. 2nd ed. Philadelphia: WB Saunders; 1997.

19. Ordóñez CA, Martínez JE, Buitrago R. Valoración integral del estado hemodinámico en el paciente crítico. En: Ordóñez CA, Ferrada R, Buitrago R,. editores. Cuidado Intensivo y trauma. 2ª ed. Bogotá: Distribuna Editorial; 2009. p. 289-305.

20. Clarck LC Jr. Measurement of oxygen tension: a historical perspective. Crit Care Med. 1981;9:690-2.

21. Cunningham FG, Leveno KJ, Blomm SL, Hauth J, Rouse D, Spong C (Ed). Williams Obstetrics. 23ra ed. Bethesda, Maryland: McGraw-Hill Companies; 2010. Chapter 28.

22. Weiner CP, Wenstrom KD, Sipes SL, et al. Risk factors for cordocentesis and fetal intravascular transfusion. Am J Obstet Gynecol. 1991;165:1020-5.

23. Quintero RA, Shukla AR, Homsy YL, et al. Successful in utero endoscopi ablation of posterior urethal valves: a new dimensión in fetal urology. Urology. 2000;55:774.

24. Agarwal SK, Fisk NM. In utero therapy for lower urinary tract obstruction. Prenat Diagn. 2001;21: 970-6.

25. Lissauer D, Morris RK, Kilby MD. Fetal lower urinary tract obstruction. Semin Fetal Neonatal Med. 2007;12:464-70.

1. Reiss RE, Gabbe SG, Petrie RH. Intrapartum fetal evaluation. En: Gabbe SG, Niebyl JR, Simpson JL, editors. Obstetrics: normal and problem pregnancies. 3rd ed. New York: Churchill Livingstone. 1996;401-2.         [ Links ]

2. American College of Obstetricians and Gynecologists. Intrapartum fetal heart rate monitoring. ACOG Practice Bulletin No. 70. Obstet Gynecol. 2005;106: 1453-60.         [ Links ]

3. Gourounti K, Sandall J. Admission cardiotocography versus intermittent auscultation of fetal heart rate: effects on neonatal Apgar score, on the rate of caesarean sections and the rate of instrumental delivery. A systematic review. Int J Nurs Stud. 2007;44:1029-35.         [ Links ]

4. Braveman F. Obstetrical Anesthesia. En: Barash PG, Cullen BF, Stoelting RK, editores. Clinical Anesthesia. 6th ed. Philadelphia: Lippincot Williams and Wilkins; 2009. p. 1138-70.         [ Links ]

5. Birnbach D, Browne I. Anesthesia for obstetrics. En: Miller RD, Eriksson LI, Fleisher LA, et al, editors. Miller's Anesthesia. 7th ed. Philadelphia: Elsevier; 2009. Chapter 69.         [ Links ]

6. Ngan Kee WD, Khaw KS, Ma KC, et al. Maternal and neonatal effects of remifentanil at induction of general anesthesia for cesarean delivery: a randomized, double-blind, controlled trial. Anesthesiology. 2006;104:14-20.         [ Links ]

7. Penning DH. Fetal and neonatal neurologic injury. En: Chesnut DH, Polley LS, Tsen LC, et al, editors. Obstetric anesthesia: principles and practice. 4th ed. Philadelphia: Mosby Elsevier; 2009. Chapter 10.         [ Links ]

8. Rosen MA. Anesthesia for fetal surgery and other intrauterine procedures. En: Chesnut DH, Polley LS, Tsen LC, et al, editors. Obstetric Anesthesia: principles and practice. 4th ed. Philadelphia: Mosby Elsevier; 2009. Chapter 7.         [ Links ]

9. National Institute of child health and human development research planning workshop. Electronic fetal heart rate monitoring: research guidelines for interpretation. Am J Obstet Gynecol. 1997;177:1385-90.         [ Links ]

10. Martin JA, Hamilton BE, Sutton PD, et al. Births: final data for 2002. Natl Vital Stat Rep. 2003;52: 1-113.         [ Links ]

11. Low JA, Simpson LL, Tonni G, et al. Limitations in the clinical prediction of intrapartum fetal asphyxia. Am J Obstet Gynecol. 1995;172:801-4.         [ Links ]

12. Figueras F, Albela S, Bonino S, et al. Visual analysis of antepartum fetal heart rate tracings: inter and intra observer agreement and impact of knowledge of neonatal outcome. J Perinat Med. 2005;33:241-5.         [ Links ]

13. American College of Obstetricians and Gynecologists. Inappropiate use of the terms fetal distress and birth asphyxia. Int J Gynaecol Obstet. 1998;61:309-10.         [ Links ]

14. Livingston EG. Intrapartum fetal assessment and terapy. En: Chesnut DH, Polley LS, Tsen LC, et al, editors. Obstetric anesthesia: principles and practice. 4th ed. Philadelphia: Mosby Elsevier; 2009. Chapter 8.         [ Links ]

15. Tracker SB, Stroup DF, Peterson HB. Efficacy and safety of intrapartum electronic fetal monitoring: an update. Obstet Gynecol. 1995;86:613-620.         [ Links ]

16. Vintzileos AM, Nochimson DJ, Guzmán ER, et al. Intrapartum electronic fetal heart rate monitoring versus intermittent auscultation: a meta- analysis. Obstet Gynecol. 1995;85:149-55.         [ Links ]

17. Low JA, Pickersgill H, Killen H, et al. The prediction and prevention of intrapartum fetal asphyxia in term pregnancies. Am J Obstet Gynecol. 2001;184: 724-30.         [ Links ]

18. Parer JT. Handbook of fetal heart rate monitoring. 2nd ed. Philadelphia: WB Saunders; 1997.         [ Links ]

19. Ordóñez CA, Martínez JE, Buitrago R. Valoración integral del estado hemodinámico en el paciente crítico. En: Ordóñez CA, Ferrada R, Buitrago R,. editores. Cuidado Intensivo y trauma. 2ª ed. Bogotá: Distribuna Editorial; 2009. p. 289-305.         [ Links ]

20. Clarck LC Jr. Measurement of oxygen tension: a historical perspective. Crit Care Med. 1981;9:690-2.         [ Links ]

21. Cunningham FG, Leveno KJ, Blomm SL, Hauth J, Rouse D, Spong C (Ed). Williams Obstetrics. 23ra ed. Bethesda, Maryland: McGraw-Hill Companies; 2010. Chapter 28.         [ Links ]

22. Weiner CP, Wenstrom KD, Sipes SL, et al. Risk factors for cordocentesis and fetal intravascular transfusion. Am J Obstet Gynecol. 1991;165:1020-5.         [ Links ]

23. Quintero RA, Shukla AR, Homsy YL, et al. Successful in utero endoscopi ablation of posterior urethal valves: a new dimensión in fetal urology. Urology. 2000;55:774.         [ Links ]

24. Agarwal SK, Fisk NM. In utero therapy for lower urinary tract obstruction. Prenat Diagn. 2001;21: 970-6.         [ Links ]

25. Lissauer D, Morris RK, Kilby MD. Fetal lower urinary tract obstruction. Semin Fetal Neonatal Med. 2007;12:464-70.         [ Links ]