Investigación Científica y Tecnológica

Regional Spinal Anesthesia for C-section and Postpartum Pomeroy. Administering a Local Anesthetic at a <60 or >60 Seconds Injection Rate

Diana Carolina Hoyos Cerón*, José Ricardo Navarro Vargas**, Javier Eslava-Schmalbach***.

* Médica, Universidad Nacional de Colombia. Correo electrónico: danashc@gmail.com

** Profesor Asociado, Departamento de Cirugía Universidad Nacional de Colombia. Correspondencia: Carrera 30 No. 45-03, Facultad de Medicina. Of. 205. Bogotá, Colombia. Correo electrónico: jrnavarrov@unal.edu.co

*** Profesor Asociado, Departamento de Cirugía Universidad Nacional de Colombia. Correo electrónico: jheslavas@unal.edu.co

Recibido: agosto 26 de 2010. Enviado para modificaciones: octubre 22 de 2010. Aceptado: mayo 11 de 2011.

SUMMARY

Objective. To identify any potential relationship between the rate of administration of the anesthetic agent in the subarachnoid space and the development of hypotension and side effects in patients scheduled for C-section and postpartum Pomeroy.

Methods. Observational case series study at the Instituto Materno Infantil-Hospital La Victoria. 60 patients who underwent a C-section procedure or a postpartum Pomeroy were included and two variables were measured: the rate of administration of the anesthetic agent in the subarachnoid space (<60 or >60 seconds) and the effects of two anesthetics combined (0.5 % hyperbaric bupivacaine 7.5 mg, plus morphine 100 mcg, and 0.5 % hyperbaric bupivacaine 12 mg, plus fentanyl 20 mcg). The mean blood pressure values were recorded, together with any side effects following the administration of the anesthetic agent at 1, 5, 10 and 15 minutes and at the end of surgery.

Results. The evidence obtained suggests that there are no differences in the hemodynamic effects of the combination or the anesthetic technique used, nor with regards to the occurrence of side effects.

Key Words: Anesthesia, cesarean section, tubal ligation, local anesthetic agents. (Source: MeSH, NLM).

INTRODUCTION

Spinal anesthesia is the main anesthetic technique used in obstetric patients undergoing elective or emergency C-section (1) and in postpartum tubal ligation procedures (2). An incidence of over 80 % of hypotension has been described in this group of patients (3,4).

The blood flow into the placenta depends on the maternal arterial pressure. Hypotension exposes the fetus to a perfusion deficiency and secondary acidemia (5). The hemodynamic effect of certain procedures has been described, such as left uterine displacement, water preload (10-20 mL/Kg of crystalloids in 15 minutes) (6), body position (Trendelenburg) (7), prophylactic vasoconstrictors (8), change of dose (9) and the rate of administration of the anesthetic agent (10,11).

The relationship between the rate of injection of the anesthetic agent in the subarchnoid technique and the incidence of intraoperative hypotension is an issue yet to be solved in anesthesiology (12).

The purpose of this study is to observe the effect of the rate of injection in a group of women undergoing cesarean section or postpartum Pomeroy on the incidence of hypotension and other perioperative adverse events.

METHODOLOGY

Observational study (case series) of patients undergoing C-section or minilaparotomy tubal ligation under spinal anesthesia. Three anesthesiologists administered the anesthetic agent and were unaware of the fact that they were being observed until the completion of the study.

The rate of administration of the spinal anesthesia was measured under 60 seconds, with an average of 30 seconds and over 60 seconds with an average of 70 seconds (<60 s and >60 s technique, respectively), in addition to the effects of the combination of two anesthetic agents: 0.5 % hyperbaric bupivacaine 7.5 mg, plus morphine 100 mcg, and 0.5 % hyperbaric bupivacaine 12 mg, plus fentanyl 20 mcg (BUPI/MORFI and BUPI/FENTA, respectively). The difference in the administration of two different anesthetic masses is explained by the selection of different anesthetic combinations by two of the anesthetists in the study. The volume of the combination with morphine was 2.5 ml while the fentanyl volume was 2.6 ml.

A previously trained medical student in her last year recorded the information using a Case Report Format. The Committee of Institutional Research approved the study.

DEFINITION OF VARIABLES

• Systolic blood pressure (SBP) and diastolic blood pressure (DBP): measured in millimeters of mercury (Datascope unit).

• Mean blood pressure (MBP): ((SBP - DBP)/ 3) + DBP.

• Arterial hypotension: reduced SBP, DBP and mean below 20 % of baseline values.

• Rate of administration of regional anesthesia: time in seconds since the beginning of the administration in the subarachnoid space until the end of the administration. Two groups were identified: <60 seconds and 60 seconds or more.

• Vasoconstrictor use (ephedrine): yes/no.

ANALYSIS OF THE DATA

The data had a percentage frequency distribution. Non-parametric statistics was used, because the data did not meet the normal distribution criterion in the Shapiro Wilks test. Excel® and STATA version 10.1 were used.

RESULTS

The patients were monitored for blood pressure, heart rate, pulse oxymetry, cardioviewer); these measurements were recorded every five minutes. According to the protocol, every patient received an infusion of 500 mL ringer lactate in 15 minutes, in addition to 50 mg of ranitidine as a direct intravenous bolus and a 10 mg infusion of metoclopramide, 15 minutes prior to the administration of the anesthetic agent.

The patients were placed in a left lateral decubitus position. The tap was made in the L3-L4 or L4-L5 space. The Spinocan® needle, number 27Gx31/2" (size 0.42 x 88 mm), sharp edge (Quincke type) was used in every patient. Also in every patient the supine decubitus position was used, with a 20º lateral angulation and gravity maneuvers to achieve a T4 sensitive level in 5 to 10 minutes time.

This study included 60 cases; 4 of the patients (6.7 %) had a failed regional anesthesia: 3 due to insufficient dose (2 patients from the <60 s group) and due to technical difficulties and hence general anesthesia had to be administered.

The average weight of the patients was 71 Kg, and the size as 1.57 m; there were no intergroup differences. There were no differences in terms of the age of the mothers, the gestational age of the patients undergoing C-section or the diagnosis of the C-section for the technique chosen (table 1). There were clinical differences in the postpartum times of the Pomeroy patients and the choice of C-section of Pomeroy, according to the technique selected (table 1). The diagnosis of iterative C-section was clinically more frequent in the group of patients of the >60 s technique.

The average blood pressure was 112/64, with a MBP of 80 mm Hg in the 60 patients and only 4 patients experienced pregnancy-associated hypertension with an average blood pressure of 170/100 and MBP of 120 mm Hg.

As expected, the rate of injection was associated to the type of combination (table 2).

Of the 56 patients followed, 17 (30.4 %) had no hypotension and 39 (69.6 %) experienced hypotension at some point during the recorded times.

Of the patients with BUPI/FENTA, 32/47 (68.1 %) experienced hypotension, while 7/9 of the patients with BUPI/MORFI (77.8 %) also exhibited hypotension.

A significant difference was observed however in the occurrence of hypotension after 15 minutes; it was less frequent in the <60 s technique (table 3).

Table 4 shows the mean MBP and the changes in the MBP according to the anesthetic technique.

Of the 3 patients with severe preeclampsia, 2 experienced changes of up to 50 % in the MBP throughout surgery (both received the >60 s technique with BUPI/FENTA). The incidence of hypotension was greater at 15 minutes; i.e., in 20/37 patients (55.1 %), in the >60 s technique, and in 5/19 patients (26.3 %) in the < 60 s technique (χ2, p = 0.048).

40/56 (71 %) of the patients had no side effects. There were no side effects in 14/19 (73 %) with the <60 s techniques and no side effects in 26/37 (70 %) with the >60 s technique. The side effects included nausea (both groups) and vomiting, bradycardia and diaphoresis in the >60 s technique. There was one case of nausea and bradycardia in each group.

8 patients (14.3 %) received ephedrine (5.35 % of the group in the <60 s technique, and 8.92 % in the >60 s technique); when the <60 s technique was used at minute 5, 2 patients required ephedrine; at minute 10, one patient; at minute 15, none. Of the patients with the >60 s technique, at 5 minutes none of them required ephedrine and only 2 of them at 10 minutes while other at 15 minutes. The average dose was 18 mg in infusion for 20 minutes.

The post hoc analysis suggested a stronger effect with regards to the technique, rather than with regards to the combination of local anesthetic agent, both at 10 and at 15 minutes (table 5).

DISCUSSION

A protocol for preparing patients for regional anesthesia is used at the institution. This protocol provides a standard management for every patient and hence facilitates the observation.

Differences were found with regards to the number of hours postpartum of the patients with Pomeroy and the technique used. This could be related to the preferences of the anesthesiologists working during the morning shift versus the afternoon shift.

It should be stressed that the slow technique was preferably used in the patients undergoing iterative C-section, possibly because the surgical conditions and the “elective” procedure made the decision easier.

The slow technique was more often used when the combinations had a larger amount of local anesthetic agent as expected for a predictable management of the level of anesthesia. The injection rate was related to the combination used and thus the resulting hypotension may have been due to the higher dose of anesthetic agent (in the >60 s group), as reported (10). The difference in hypotension in both groups was more evident at 15 minutes.

Regional subarachnoid anesthesia does not necessarily cause hypotension, as reported in the literature (13). One third of these patients did not experience any hypotension at all. A small percentage of patients required ephedrine.

Opiates enhance the anesthetic effect of the local anesthetic agent and extend the duration of analgesia during the postoperative period. The duration of analgesia is longer with morphine than with fentanyl (14,15).

Considering that the goal was to identify any side effects or adverse events related to the use of both techniques, it was inappropriate to follow an experimental study to assess this association.

Case series studies are not intended to use inferential statistics but rather to suggest potential proof of hypothesis in studies with stronger causal strength. This is basically a exploratory study of the association between hypotension and the injection technique used, with the addition of a post hoc analysis of the confounder effect of the type of combination used; the analysis suggests a major role of the technique over the combination.

Many factors affecting the extension of the sympathetic block despite the rate of injection of the local anesthetic agent have been identified in the literature; i.e., the dose, the density, the temperature of the solution, the patient's position and even the variability across patients (16,17). This is the first time that the effects of the use of both techniques are explored in Colombia and the results suggest that the occurrence of hypotension maybe more related to the anesthetic technique used, rather than with the combination.

The recommendation is to undertake observational analytical studies to assess the effect of the rate of injection, either controlling or standardizing the combination used in this type of obstetric patients in which occasionally the waiting times demand the use of faster spinal injection techniques.

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