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Re: Preloading: lots for POTS?
- Ashraf S Habib (3 November 2006)
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Preloading: lots for POTS?
- Sukanya Mitra, Kanti K. Gombar (4 October 2006)
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Ashraf S Habib, Assistant Professor of Anaesthesiology Duke University Medical Center
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We thank Dr. Mitra and colleagues for their interest in our article. Our patient did have characteristics consistent with the “hyperadrenergic” subtype of POTS, as evidenced by her previous autonomic studies. 1 We noted that Dr. Mitra describes this mechanism as having central nervous system underpinnings. Whereas several mechanisms have been described to account for this physiological phenotype, none appear to have a primary central etiology.2 Suggested mechanisms include peripheral denervation supersensitivity, exaggerated vasodilatory response to beta-receptor stimulation, and/or reduced norepinephrine clearance in the post- ganglionic synaptic cleft.2 In these patients the excessive sympathetic activation set off by the baroreceptor response to a decrease in venous return is not appropriately attenuated by baroreflex mechanisms.3 Therefore, we felt that adequate preloading was appropriate in this patient to avoid triggering a tachycardic response with the induction of neuraxial anaesthesia with subsequent vasodilatation. Furthermore, there are no well-designed studies that show a specific pharmacological response corresponding to POTS subtype, except that beta-adrenergic blockade can make patients having the partial dysautonomia form feel worse. Volume expansion and alpha agonists form the foundation of drug therapy in this condition. We agree with Dr. Mitra that a number of studies reported that colloids are more effective than crystalloids for the prevention of hypotension following the induction of neuraxial blockade for caesarean section. This is probably due to their longer intravascular half life. The important fact however, is that it is mainly the volume of fluids that makes the difference. As illustrated by Ueyama, an adequate preload volume is that which increases a patient’s blood volume sufficiently to result in a significant increase in cardiac output, countering the relative hypovolaemia induced by neuraxial anaesthesia.4 We provided our preload using a mixture of crystalloids and colloids. One could argue however, that we could have provided a similar and more sustained increase in intravascular blood volume using a smaller volume of colloids. It has been shown by Datta and colleagues that pregnant women have increased plasma levels of atrial natriuretic peptide (ANP) compared with non pregnant controls. 5 Additional volume loading, whether with crystalloids or a combination of crystalloids and colloids, will further increase ANP.6 While this increase in ANP may theoretically lead to further vasodilation and natriuresis; the clinical relevance of this in the setting of a caesarean section is not clear. In fact, it seems that the preload used in the study demonstrating an increase in ANP was effective, since the authors did not report hypotension associated with the ANP increase. 6 Finally, we feel that the increase in blood pressure to 150/100 after delivery was likely a normal response to pain and not due to excessive volume preloading, since this immediately normalized following the induction of general anaesthesia and was not sudden or resistant as indicated by Dr. Mitra. William L Corbett1 Ronald J Kanter2 Ashraf S Habib1* 1Department of Anaesthesiology, and 2Department of Paediatric Cardiology, Duke University Medical Center, Durham, North Carolina 27710, USA Conflict of Interest:None declared |
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Sukanya Mitra, Reader in Anaesthesia Department of Anaesthesia & Intensive Care, Government Medical College, Chandigarh, India, Kanti K. Gombar
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To The Editor, We read with interest the case report by Corbett et al.1 Central hyperadrenergic subtype of the postural orthostatic tachycardia syndrome (POTS) is much less common than the partial dysautonomic subtype, with its unique pathophysiology of centrally increased adrenergic tone rather than anything being wrong with the peripheral or reflex baroreceptor pathways.2 Thus, the central issue here is postural tachycardia rather than hypotension. As such, we are unclear regarding the rationale of a heavy preloading of this patient (she received a total of 2.5 L of crystalloid and 0.5 L of colloid solution). Further, there is evidence that preloading may not be effective or even necessary to prevent hypotension in Caesarean section.3- 6 Even if used, recent evidence suggests somewhat greater usefulness of colloids rather than crystalloids in this regard.7, 8 Finally, it has been shown that rapid volume expansion can release atrial natriuretic peptide (ANP) from the cardiocytes and can thus modify the purported effects of the volume expansion itself.9, 10 Indeed, there was a significant correlation between the volume of maternal Ringer's lactate infusion received prior to Caesarean section and maternal ANP concentration.10 Thus, we wonder if the preloading in this case was necessary, or if so, if only 500 ml of colloids could have been sufficient. In this connection, it is interesting to note that after delivery the patient developed a high blood pressure of 150/100 mm Hg despite receiving further lidocaine, fentanyl and midazolam. This would be atypical of POTS, where tachycardia is the hallmark feature, (not any drastic blood pressure changes), and it makes us wonder if the rather high volume of preloaded fluids, coupled with the central hyderadrenergic tone, might have contributed to this sudden and resistant hypertension. E-mail: drsmitra12@yahoo.com 1. Corbett WL, Reiter CM, Schultz JR, Kanter RJ, Habib AS. Anesthetic management of a parturient with the postural orthostatic tachycardia syndrome: a case report. Br J Anaesth 2006; 97: 196-9. 2. Raj SR. The Postural Tachycardia Syndrome (POTS): Pathophysiology, Diagnosis & Management. Indian Pacing Electrophysiol J 2006; 6: 84-99. 3. Karinen J, Rasanen J, Alahuhta S, Jouppila R, Jouppila P. Effect of crystalloid and colloid preloading on uteroplacental and mternal haemodynamic state during spinal anaesthesia for Caesarean section. Br J Anaesth 1995; 75: 531-5. 4. Rout CC, Rocke DA, Levin J, Gouws E, Reddy D. A reevaluation of the role of crystalloid preload in the prevention of hypotension associated with spinal anesthesia for elective cesarean section. Anesthesiology 1993; 79; 262-9. 5. Rout CC, Akoujee SS, Rocke DA, Gouws E. Rapid administration of crystalloid preload does not decrease the incidence of hypotension after spinal anaesthesia for elective Caesarean section. Br J Anaesth 1992; 68: 394-7. 6. Jackson R, Reid JA, Thorburn J. Volume preloading is not essential to prevent spinal-induced hypotension at Caesarean section. Br J Anaesth 1995; 75: 262-5. 7. Siddik SM, Aouad MT, Kai GE, Sfeir MM, Baraka AS. Hydroxyethylstarch 10% is superior to Ringer’s solution for preloading before spinal anesthesia for Cesarean section. Can J Anaesth 2000; 47: 616 -21. 8. Dahlgren G, Granath F, Pregner K, Rosblad PG, Wessel H, Irestedt L. Colloid vs. crystalloid preloading to prevent maternal hypotension during spinal anaesthesia for elective Caesarean section. Acta Anaesthesiol Scand 2005; 49: 1200-6. 9. Pouta AM, Karinen J, Vuolteenaho OJ, Laatikainen TJ. Effect of intravenous fluid preload on vasoactive peptide secretion during Caesarean section under spinal anaesthesia. Anaesthesia 1996; 51: 128-32. 10. Datta S, Murphy MT, Carr DB, Bader AM, Johnson MD. Maternal and foetal plasma atrial natriuretic peptide concentrations during elective Caesarean section. Acta Anaesthesiol Scand 1991; 35: 93-6. Conflict of Interest:None declared |
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