ISSN NUMBER: 1938-7172
Issue 3.4 VOLUME 3 | NUMBER 4

Editor:
Michael A. Fiedler, PhD, CRNA

Contributing Editors:
Mary A. Golinski, PhD, CRNA
Alfred E. Lupien, PhD, CRNA
Dennis Spence, PhD, CRNA
Steven R. Wooden, MS, CRNA

Guest Editors:



Assistant Editor
Jessica Floyd, BS

A Publication of Lifelong Learning, LLC © Copyright 2009

New health information becomes available constantly. While we strive to provide accurate information, factual and typographical errors may occur. The authors, editors, publisher, and Lifelong Learning, LLC is/are not responsible for any errors or omissions in the information presented. We endeavor to provide accurate information helpful in your clinical practice. Remember, though, that there is a lot of information out there and we are only presenting some of it here. Also, the comments of contributors represent their personal views, colored by their knowledge, understanding, experience, and judgment which may differ from yours. Their comments are written without knowing details of the clinical situation in which you may apply the information. In the end, your clinical decisions should be based upon your best judgment for each specific patient situation. We do not accept responsibility for clinical decisions or outcomes.

Table of Contents

GENERAL
LEVELS OF CONSCIOUSNESS DURING REGIONAL ANESTHESIA AND MONITORED ANESTHESIA CARE: PATIENT EXPECTATIONS AND EXPERIENCES
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THE EFFECTS OF PLATELET TRANSFUSIONS EVALUATED USING ROTATIONAL THROMBOELASTOMETRY
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PREOPERATIVE FLUID BOLUS AND REDUCTION OF POSTOPERATIVE NAUSEA AND VOMITING IN PATIENTS UNDERGOING LAPAROSCOPIC GYNECOLOGIC SURGERY
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OBSTETRIC ANESTHESIA
  EFFECT OF TIMING OF FLUID BOLUS ON REDUCTION OF SPINAL-INDUCED HYPOTENSION IN PATIENTS UNDERGOING ELECTIVE CESAREAN DELIVERY
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  EFFECT OF TIMING OF FLUID BOLUS ON REDUCTION OF SPINAL INDUCED HYPOTENSION IN PATIENTS UNDERGOING ELECTIVE CESAREAN DELIVERY
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COLLOID PRELOAD VERSUS COLOAD FOR SPINAL ANESTHESIA FOR CESAREAN DELIVERY: THE EFFECTS ON MATERNAL CARDIAC OUTPUT
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PAIN
PRACTICE GUIDELINES FOR THE PREVENTION, DETECTION, AND MANAGEMENT OF RESPIRATORY DEPRESSION ASSOCIATED WITH NEURAXIAL OPIOID ADMINISTRATION
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REGIONAL ANESTHESIA
EVOLUTION OF ULTRASOUND GUIDED AXILLARY BRACHIAL PLEXUS BLOCKADE: RETROSPECTIVE ANALYSIS OF 662 BLOCKS
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General

Esaki RK, Mashour GA


 

 

Levels of consciousness during regional anesthesia and monitored anesthesia care: patient expectations and experiences

Anesth Analg 2009;108:1560-1563

Esaki RK, Mashour GA

 

Abstract

Purpose            The purpose of this report was to describe the results of a survey of patient expectations and subjective experiences during regional or MAC anesthesia.

Background            Anesthesia providers and the public have shown greater interest in consciousness of late. While mostly focused on consciousness during general anesthesia, some patients have complained of “intraoperative awareness” following regional anesthesia or monitored anesthesia care (MAC). The incidence of awareness during general anesthesia has been suggested to be about 0.023%. Complaints of awareness following regional or MAC have been reported to be slightly higher at 0.03%. Patients undergoing regional or MAC anesthesia may believe they have experienced a general anesthetic due to amnesia for perioperative events or may have unmet expectations during regional or MAC anesthesia.

Methodology            For this survey, patients at least 18 years old who underwent surgical procedures during regional anesthesia or MAC at two different institutions were interviewed. Interviews were conducted after patients had met PACU discharge criteria. Two forms of the interview, containing the same questions, were used to minimize the likelihood of response order bias in the overall findings. Patients were asked to report their expected, highest, and lowest levels of consciousness during their procedure on a scale from 1 to 10. Complete unconsciousness was 1 and complete consciousness was 10. Patients were also asked about the source of their expectation for the level of consciousness they would experience during the procedure and overall satisfaction.

Result            Interviews were completed with 117 patients. The anesthesia provider was identified as the source of the patient’s expectation regarding level of consciousness during the procedure by 58% of patients. Other sources of patients’ expected level of consciousness included the patients themselves (25%), nurses, surgeons, and other sources.

The most commonly reported expected level of consciousness was “complete unconsciousness” (32% of patients). The highest level of consciousness reported by most patients was complete unconsciousness (46% of patients). Likewise, the lowest level of consciousness reported by most patients was complete unconsciousness (68% of patients). At some point during their procedure, 8% of patients were more awake then expected while 15% of patients were less awake than expected. Almost all patients reported their overall experience as either “good” or “better than expected.”

Conclusion            Patients who undergo regional or MAC anesthesia often expect, and most often subjectively experience, complete unconsciousness. The distinction between general anesthesia and sedation may be unclear to many patients. Anesthesia providers should discuss expectations regarding the level of consciousness experienced during regional or MAC anesthesia with patients preoperatively.

 

Comment

This survey left me with one of those, “why didn’t I think of that” moments. It succeeds in raising some important questions and it rightly points out that patients may see things much differently than most anesthesia providers. I’ll have to admit, I have not been in the habit of explicitly discussing the expected level of consciousness a patient will experience during a non-general anesthetic. I often talk about the likelihood, but not promise, of amnesia. I often talk about making them sleepy or helping them not to be nervous. But, now, in hindsight, I wonder if I’ve ever done enough to accurately communicate to patients the difference between sedation and general anesthesia. In this survey a significant number of patients believed they were unconscious during their procedure. Clearly, what I see during the case and what they experience are two different things.

We should be providing the information that sets a patient’s expectation for level of consciousness during a procedure for which we are providing the anesthesia care. If we don’t, they will still have an expectation and it will probably be different than ours. I don’t know what the surgeon, a nurse in the admitting area, or a next door neighbor who had surgery last week told them that influenced their expectation. I fear it may well have been, “oh, don’t worry, you won’t remember a thing.” While that may sometimes be true, it will not, and should not, always be true. Both the patient and the anesthesia provider stand to have a bad experience if patients expect to be unconscious throughout their procedure.

As the delivery of anesthesia services is more and more influenced by production pressure it becomes harder to have the discussions needed to set reasonable expectations about a patient’s level of consciousness during a non-general anesthetic. But as expectations of healthcare quality increase, these discussions become more and more important. I agree with the authors that the distinction between general anesthesia and sedation may be lost on a significant portion of our patients. We should think about how to clearly communicate the difference in terms even the least sophisticated patient will understand. I also agree that we should discuss expectations about level of consciousness during non-general anesthetics with patients preoperatively. Doing so can only improve patients experience despite the high overall satisfaction level reported here.

 

Michael Fiedler, PhD, CRNA

© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 4, April 30, 2009





Flisberg P, Rundgren M, Engstr?m M


 

 

The effects of platelet transfusions evaluated using rotational thromboelastometry

Anesth Analg 2009;108:1430-1432

Flisberg P, Rundgren M, Engström M

 

Abstract

Purpose            The purpose of this study was to assess the effects of platelet transfusion on clot formation and clot strength in thrombocytopenic patients scheduled to receive a platelet transfusion prior to an invasive procedure.

Background            Appropriate platelet transfusion triggers, and subsequent efficacy of platelet transfusion, continues to be debated. Most studies of platelet transfusion have focused on platelet viability and absolute increase in platelet numbers following transfusion, but the improvement in hemostasis post-transfusion is also important. Platelet aggregometry and thromboelastography have been used to study the effects of platelet count in vitro. Thromboelastography appears to be a more robust test than those now routinely used. Rotational thromboelastometry (ROTEM) is a more refined technique of thromboelastography.

Methodology            Patients with a platelet count below 50,000 /mm3 were scheduled to receive a unit of platelets prior to an invasive procedure. No patient had received an anticoagulant for at least seven days prior to platelet transfusion. Each unit of platelets contained 200 – 300 x 109 platelets in sodium chloride, sodium acetate, sodium citrate solution and 100 mL of plasma. Immediately before, and within one hour after platelet transfusion, patient samples were drawn for PT, aPTT, platelet count, and ROTEM.

ROTEM produces values for three parameters. Clotting Time is affected primarily by humoral coagulation factors. Clot Formation Time (CFT) measures the rate of clot formation. It is affected by the rate of conversion of fibrinogen to fibrin and by platelet activity. Maximum Clot Firmness (MCF) is an indicator of clot strength. It is determined by platelet activity. A derivative value of the MCF, elastic modulus, reports clot strength in dynes/cm2.

Result            Data were collected from 10 patients, six male and four female, between the ages of 22 and 75 years. PT and aPTT were unchanged after platelet transfusion. Post transfusion, median platelet count increased from 31,500 / mm3 (range 20k to 44k / mm3) to 43,500 / mm3 (range 38k to 71k / mm3) (P=0.005). Clot Formation Time decreased from 181.5 (range 108 – 347) sec to 123 (range 89 – 233) sec (P= 0.005). Clot strength increased by 47% (P=0.005).

Conclusion            In thrombocytopenic patients, platelet infusion increased the speed with which clots formed and increased the strength of clots within one hour after platelet transfusion.

 

Comment

We have long known that simply having a lot of platelets in circulation didn’t mean they were actually going to do anything. So, we did our best to make sure there were enough of them and assessed their “activity,” rather crudely; qualitatively assessing bleeding or “oozing” compared to what we were used to seeing in patient with normal coagulation. I remember first using thromboesastography in the early 1990’s. It was useful, though a bit laborious, and we could keep it in the OR. It represented many aspects of coagulation graphically but it didn’t quantify clot strength. In this study, an improved version, ROTEM®, adds a quantification of clot strength. This information is quite useful.

I learned two things from this study. First, infusing a clinically feasible number of platelets can make an enormous improvement in the strength of the clots formed even when the absolute platelet concentration remains rather low. And second, we now have a clinical method to assess clot strength, which I see as quite helpful. Time will tell whether or not this test of clot strength becomes commonly available in hospital laboratories.

 

Michael Fiedler, PhD, CRNA

© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 4, April 30, 2009





Lambert KG, Wakim JH, Lambert NE


 

 

Preoperative fluid bolus and reduction of postoperative nausea and vomiting in patients undergoing laparoscopic gynecologic surgery

AANA J 2009;77:110-114

Lambert KG, Wakim JH, Lambert NE

 

Abstract

Purpose            The purpose of this study was to determine if preoperative IV fluid replacement reduced the incidence of PostOperative Nausea and Vomiting (PONV) in women undergoing elective laparoscopic gynecologic surgery.

Background            PONV is associated with prolonged recovery, delayed discharge, patient dissatisfaction and discomfort, increased costs, and even mortality. The overall incidence of PONV following general anesthesia has been reported to be between 30% and 70%. Laparoscopic gynecologic surgery has been associated with a greater than average risk of PONV. Dehydration and hypovolemia have been identified as risk factors for PONV, as has hypotension at induction of general anesthesia that may result, in part, due to hypovolemia. Other studies have demonstrated some decrease in the incidence of PONV as a result of the infusion of up to 30 mL/kg IV fluid. No mechanism by which hydration is protective against PONV has been proposed.

Methodology            This prospective, single blinded study included female patients undergoing an elective laparoscopic gynecologic procedure. Exclusion criteria included hypertension, congestive heart failure, valvular heart disease, diabetes mellitus, and those who had received an antiemetic drug within the previous 24 hours. PONV risk factors not recorded for this study included smoking and motion sickness history. All patients received a 2 mg midazolam preoperatively. General anesthesia was induced with up to 5 µg/kg fentanyl, 1 mg/kg lidocaine, 2 mg/kg propofol, and 0.1 mg/kg vecuronium. Anesthesia was maintained with 50% nitrous oxide and isoflurane. Each patient had a gastric tube placed and aspirated. At the end of surgery all patients received a full reversal dose of neostigmine and glycopyrrolate.

Prior to induction of anesthesia, women in the Fluid group received up to 1 L lactated ringers solution over a one hour period. Fluid volume was calculated to replace the NPO deficit. If the NPO deficit was greater than 1 L, the excess fluid was administered after the induction of anesthesia. Women in the control group received fluid according to the “anesthesia provider’s standard fluid replacement” technique. The volume of fluid administered to the control group was not standardized by the study.

Result            The study included 23 women in each group, ranging in age from 18 years to 72 years old. The duration of the surgical procedure ranged from 29 minutes to 238 minutes (3 hours 58 minutes). Average preoperative IV fluid administered was 996 mL (range 900 mL to 1000 mL) in the Fluid group and 474 mL (range 100 mL to 1000 mL) in the Control group. PONV was experienced by a total of 16 patients, 35% of all patients in the study. In the Fluid group, 5 patients (22%) experienced PONV. In the Control group, 12 patients (52%) experienced PONV (P<0.05).

Conclusion            Preoperative IV fluid administration to replace the NPO deficit was a simple, cost-effective means to reduce the incidence of PONV in women undergoing gynecologic laparoscopy.

 

Comment

This study did a fair job of demonstrating that crystalloid IV fluid administration significantly decreases the incidence of PONV in women undergoing laparoscopic gynecologic surgery. I say “fair” because there are a few curious limitations in the study methodology. For one, the investigators didn’t statistically compare the demographic variables to demonstrate whether or not the Fluid and Control groups were similar. For another, while a prospective design; history of cigarette smoking, motion sickness, previous PONV, and other known risk factors was not addressed in the study. We are left not knowing for sure that one of those factors didn’t account for the difference in PONV between the groups. That said, the results are consistent with other studies with the added benefit of being specific to laparoscopic gynecologic surgery.

Unlike other studies I’ve read, this one administered all, or almost all, the IV fluid before induction of anesthesia. The investigators properly identified induction hypotension as a risk factor for PONV and wondered if preloading before induction would reduce the incidence of hypotension and, thus, reduce the incidence of PONV. Well, it didn’t. In fact, the Fluid group experienced a slightly greater incidence of hypotension (probably not statistically significant). That finding suggests to me that it may not be so important when IV fluid is administered as long as you get it in sometime between preop holding and emergence from anesthesia.

I wish more anesthetists were aware that adequate hydration significantly reduces PONV. In this study PONV was more than cut in half (22% vs. 52%) in the Fluid group. In young, healthy patients it is an easy, cheap way to significantly reduce PONV. I use it regularly.

 

Michael Fiedler, PhD, CRNA

© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 4, April 30, 2009




Obstetric Anesthesia

Williamson W, Burks D, Pipkin J, Burkard, JF, Osborne LA, Pellegrini JE


 

Effect of timing of fluid bolus on reduction of spinal-induced hypotension in patients undergoing elective cesarean delivery

AANA J 2009;77:130-136

Williamson W, Burks D, Pipkin J, Burkard, JF, Osborne LA, Pellegrini JE

 

Abstract

Purpose            The purpose of this study was to determine the effect of a 10 mL/kg crystalloid fluid bolus given before and immediately after placement of a subarachnoid block (SAB) on spinal-induced hypotension (SIH) in patients undergoing elective cesarean section.

Background            Spinal-induced hypotension is a frequent problem after placement of an SAB for cesarean delivery. Typically a 10-20 mL/kg fluid bolus is administered within 30 minutes of the SAB to minimize SIH. However, only 28% of a crystalloid solution remains in the vascular space when the fluid preload is given 20-30 minutes before the SAB. Nonetheless, research suggests that fluid preloading does minimize SIH in the first five minutes after placement of the SAB, which is the time when SIH is most severe. More recent research suggests a fluid bolus given with a rapid infusion device at the time of the spinal injection (coload) results in less maternal hypotension. However, there is a potential for complications (i.e., pulmonary edema) with the administration of a coload with a rapid infusion device.  Therefore, this study sought to determine if combining 10 mL/kg preload and 10 mL/kg coload techniques would be more effective in reducing SIH, total fluid volume infused and vasopressor requirements than a 20 mL/kg preload of lactated ringers (LR) given 20 minutes prior to SAB in patients undergoing elective cesarean delivery.

Methodology            This prospective, randomized investigation included 89 healthy parturients undergoing elective cesarean delivery for singleton pregnancy (at least 37 weeks gestation and less than 120 kg) with SAB. Subjects were excluded in they had preexisting comorbidities or complications of pregnancy. All subjects were randomized into a control (preload) group or an experimental (preload/coload) group. The control groups received a 20 mL/kg fluid bolus of LR over 20 minutes then were transported to the operating room. The experimental group received a 10 mL/kg LR preload beginning 10 minutes before transport to the operating room, followed by a 10 mL/kg bolus (coload) of LR over 10 minutes immediately following injection of the SAB. The SAB was performed in the sitting position and 8-15 mg of hyperbaric marcaine, 0-50 µg fentanyl, and 0-300 µg of preservative-free morphine were used. Choice of vasopressor was at the anesthesia providers’ discretion. Additional 250-500 mL fluid boluses could be administered as needed to treat hypotension. The primary outcome was hypotension, which was defined as a systolic blood pressure of less than 100 mm Hg or a decrease in mean arterial pressure of 20% from baseline. Secondary outcome variables included time to additional bolus requirements, total fluid requirements, frequency of vasopressor use and neonatal Apgar scores.

Result            There were 43 subjects in the control group and 44 in the experimental group. There were no significant differences between groups in demographic data, time to place SAB, SAB to delivery time, SAB dermatome level, blood loss, neonatal Apgar scores, neonatal weights, urinary output, satisfaction scores, and duration of anesthesia, surgery or PACU time.

The experimental group received significantly less total volume of LR (P = 0.02), and required less supplemental fluid boluses (experimental group 39% vs. 72% in control group) (P = 0.004). Some subjects in the control group required as many as 7 additional fluid boluses, whereas a maximum of 3 fluid boluses were required in the experimental group. The timing for the first 3 additional fluid boluses was significantly shorter in the control group compared to the experimental group (P < .05). There was no difference in requirements for vasopressors or maternal vital signs between the two groups.

Conclusion            A combination preload and coload of fluid helps minimize SIH. More studies are needed with tighter controls on fluid administration and treatment of hypotension. The amount of perioperative fluid required during cesarean delivery can be safely reduced with a preload and coload fluid bolus combination. Additional studies are needed in parturients with coexisting diseases to determine if similar effects can be found.

 

Comment

I thought this study was very relevant and important to clinical practice because it provides evidence of an effective alternative fluid bolus method for minimizing SIH. Spinal-induced hypotension is probably the most common problem many of us face when performing a SAB for cesarean delivery. How many times have you been told by the nurses that the fluid bolus was given, then for whatever reason there was a delay in getting the case started. Then prior to performing the SAB, or after placement, you end up treating SIH with multiple fluid boluses and vasopressors. I know I have experienced this on multiple occasions, and as a result now administer my fluid bolus similar to what these investigators described. Though, I must admit I find it is difficult to give a 10 mL/kg bolus over 10 minutes without having to use a pressure bag. I would imagine the investigators found it challenging to administer this amount of fluid without a pressure bag (e.g., 800 mL in an 80 kg patient).

Several issues came to me as I thought about the importance of this study. First, it demonstrates how important it is to communicate with our nursing and surgical colleagues about when the case is going to start. This is important so the fluid bolus can be timed accordingly. Along those same lines, as anesthetists it is important for us to educate the nurses and support staff about how fluid boluses work. Take the time to explain to them: (1) what effect SAB has on the vasculature and why preload (and coloading) is important and (2) that less than 30% of the crystalloid solution is left in the intravascular space after 20-30 minutes.  Giving them this information will help them understand why both the timing and amount of fluid bolus administered is so important. The nurses will appreciate the teaching and it may help you minimize the need to treat SIH.

 

Dennis Spence, PhD, CRNA

© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 4, April 30, 2009





Williamson W, Burks D, Pipkin J, Burkard J, Osborne L, Pellegrini J


 

Effect of timing of fluid bolus on reduction of spinal induced hypotension in patients undergoing elective cesarean delivery

AANA J 2009;77:130-136

Williamson W, Burks D, Pipkin J, Burkard J, Osborne L, Pellegrini J

 

Abstract

Purpose            This study evaluated the effectiveness of two different methods of fluid administration in preventing spinal induced hypotension in cesarean section patients.

Background            Spinal induced hypotension continues to be a serious problem in 25-75% of patients undergoing cesarean section. Hypotension in pregnant patients can lead to serious complications including nausea and vomiting, dysrhythmia, aspiration, and fetal acidosis secondary to decreased intrauterine blood flow. Methods used to prevent hypotension in obstetric patients include left hip displacement, intravenous fluid bolus, and prophylactic administration of vasopressors. Hip displacement has had limited success, fluid bolus has shown promise but the scientific evidence is contradictory, and prophylactic vasopressor administration has inherent risks and should be reserved for the treatment of hypotension. Fluid bolus appears to have some promise, but timing of fluid bolus could play a major role in the success of this technique.

Methodology            The study included 87 parturients scheduled for cesarean section using a spinal anesthetic. Subjects with essential hypertension, pulmonary complications, preeclampsia, decreased uterine perfusion, or coagulopathy were excluded. The patients were placed in one of two groups. The control group received a commonly used method of pre-loading fluid. Each patient selected for this group received 20 mg/kg of lactated ringer’s solution just before being taken to the operating room. The experimental group was given 10 mg/kg of the same solution prior to being moved to the operating room and then an additional 10 mg/kg after the administration of the spinal block. Hyperbaric bupivacaine 8 mg to 15 mg in additional to fentanyl 0 µg to 50 µg and morphine 0 µg to 300 µg was used for the spinal in all patients. Hypotension was defined as a systolic pressure of less than 100 mm Hg or a decrease in mean arterial pressure of 20 % from baseline. Patients who became hypotensive were treated at the discretion of the provider with ephedrine, phenylephrine, or an additional fluid bolus.

Result            There were no significant differences between the two groups when comparing demographic data, timing issues with the fluid, block, or delivery, or duration of anesthetic. When comparing total fluid volume, the control group required about 10% more total fluid. This difference was statistically significant but the clinical significance is questionable. Additionally, 72 % of the control group patient’s required additional fluid boluses to keep their blood pressure up compared to 39 % of the experimental group. Vasopressors were required in 72 % of the control group compared to 55 % of the experimental group but the total vasopressor dose administered was not statistically significantly different.

Conclusion            This study demonstrated that the combination of fluid boluses prior to (pre-load) and after (co-load) the administration of a spinal anesthetic in obstetric patients undergoing cesarean section was more effective in preventing spinal induced hypotension than the use of pre-load only.

 

Comment

This was an excellent study. It was simple in its approach and dramatic in its findings. I have used the pre-load method for years and have had mixed success, but I plan on using the combination of pre-load and co-load and I will pay close attention to its effectiveness. I think subconsciously I have sometimes used this method by continuing my fluid bolus during and after the administration of the spinal anesthetic. This study has convinced me that continuing this method of fluid administration is beneficial.

 

Steven Wooden MS, CRNA

© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 4, April 30, 2009





Teoh WHL, Sia ATH


 

Colloid preload versus coload for spinal anesthesia for cesarean delivery: the effects on maternal cardiac output

Anesth Analg 2009;108:1592-1598

Teoh WHL, Sia ATH

 

Abstract

Purpose            The purpose of this study was to compare the effects of a colloid “Preload” or “Coload” on maternal Cardiac Output (CO) and systolic blood pressure (BP) during a subarachnoid block for cesarean section.

Background            Hypotension is a common complication during subarachnoid block for cesarean section. Hypotension increases risk for both mother and fetus or neonate. Historically, wrapping the legs, patient positioning, IV fluid administration, and vasopressors have been used to prevent or treat hypotension. Crystalloid IV fluids have been administered before the administration of a subarachnoid block as an IV “Preload,” but this practice has been shown to do little to prevent subsequent hypotension. Crystalloid IV fluids rapidly leave the intravascular space after administration. Furthermore, aggressive IV fluid administration may stimulate the release of Atrial Natriuretic Peptide (ANP) resulting in vasodilation and diuresis. Some have suggested administering IV fluid as a “Coload,” at the same time that the block is performed, rather than before the block. Some studies have shown a Coload to be more effective than a crystalloid preload. To prevent hypotension, an IV fluid load should cause an increase in Cardiac Output (CO). Maternal blood pressure has been used as a proxy for CO but changes in peripheral resistance may prevent changes in CO from being reflected in maternal BP.

Methodology            This randomized, double-blinded study included ASA physical status I and II women carrying term, singleton pregnancies scheduled for elective cesarean section with subarachnoid block anesthesia. Women with preexisting or pregnancy-induced hypertension, diabetes being treated with medication, cardiovascular or cerebrovascular disease, or fetal abnormalities were excluded. All women received ranitidine and sodium citrate preoperatively and were NPO. Baseline vital signs were recorded with women in the supine position with left uterine displacement. Cardiac output and stroke volume was measured noninvasively with an Ultrasonic Cardiac Output Monitor (USCOM™, USCOM Pty, Coffs Harbor, NSW, Australia).

Patients received either a Preload or a Coload of hydroxyethyl starch (HES) (Voluven ® 6%, Fresenius Kabi, Bad Homberg, Germany) through an 16 g IV. In Preload patients, 15 mL/kg HES was administered and the subarachnoid block performed immediately after. Coload patients received the same volume of HES beginning when cerebrospinal fluid was seen during the subarachnoid block procedure. Phenylepherine 50 µg IV was administered whenever maternal BP decreased by 10% compared to baseline.

Result            There were no demographic differences between the Preload and the Coload groups. The volume of colloid administered and the duration of the infusion was the same between groups. Baseline Stroke Volume (SV) was lower in the Coload group for reasons unrelated to patient selection or study interventions.

During the first five minutes after induction of the block, CO was higher in Preload patients (P=0.01) but by 10 minutes there was no difference between groups. There were no significant differences in BP between groups at baseline or any time within the first 10 minutes after the block (P=0.99). Hypotension (≥10% decrease in BP) occurred in 90% of Preload patients and 75% of Coload patients (P=0.41). The minimum BP and the median dose of phenylephrine administered. was not different between groups. Neonatal outcomes were similar. All neonates had an APGAR score of 9 at both one minute and five minutes post delivery.

Conclusion            While there was no difference in systolic BP between women in the Preload and Coload groups, a colloid Preload resulted in a significantly greater Cardiac Output during the first 10 minutes after subarachnoid block for cesarean section. Despite the greater Cardiac Output in the Preload group, uteroplacental perfusion, APGAR scores, and rates of maternal hypotension were not statistically significantly different compared to the Coload group.

 

Comment

The inspiration for this study seems to be previous studies looking at the hemodynamic differences between crystalloid preloads and coloads for spinal and epidural anesthesia. Previous work had shown that only 28% of a 1.5 L crystalloid preload remained in the circulation at the end of a 30 minute infusion.1 The idea, then, was to give the fluid load right when the block was setting up to insure that more of the volume would be intravascular and contribute to maintaining BP. I’m confused about why the investigators would repeat such a study with a colloid since colloids stay in the circulation until they are metabolized. Basically, this study showed that with colloids the problem is reversed. When you wait to start the colloid fluid load until the block is setting up, the benefit of the fluid load is delayed because little of the volume has been infused when the sympathectomy begins.

It is instructive to note that, while the definition of hypotension in this study (≥10 torr decrease in systolic BP) was a relatively small decrease in BP, most patients in both groups experienced hypotension despite a 15 mL/kg colloid infusion (Preload group 90%, Coload group 75%). The cause of hypotension in pregnant women receiving spinals and epidurals has long been thought to be venous dilation thus reduced venous return to the heart thus reduced cardiac output thus a fall in blood pressure. As best as I can determine, this belief is based upon studies in men, mostly healthy volunteers not undergoing a surgical procedure.2 Since these studies, we have learned much about cardiovascular changes in pregnancy. Term pregnant women experience an average 100% increase in baseline sympathetic outflow3, decreased sensitivity to the vasoconstricting effects of Angiotensin II4-6, and a 3-4 fold increase in the clearance of vasopressin7 (the most potent endogenous vasoconstrictor), among other physiologic changes. Despite a lack of evidence, anesthesia seems to be clinging to the idea that hypotension during regional anesthesia in pregnancy is due to reduced venous return and can be fixed with sufficient IV fluid. There are scores of studies attempting to find the “right” volume of crystalloid or colloid IV fluid to prevent hypotension in pregnant women. While some have shown progress, no study has solved the hypotension problem by administering IV fluids.

Everything I have learned leads me to believe that maternal hypotension during regional anesthesia is due primarily to a reduction is Systemic Vascular Resistance (SVR). We know that BP is determined by a combination of SV, HR, and SVR. If SVR falls enough from the sympathectomy caused by a spinal or epidural it would take a huge increase in Cardiac Output (SV x HR) to maintain BP. In this study, baseline CO in the Preload group was normal for pregnancy, a bit over 6.5 L/min. Between 2 and 5 minutes after induction of the subarachnoid block, the average CO increased to 8.5 L/min, a 31% increase. During this same time average systolic BP fell by 14%, from 119 torr to 102 torr. The only possible cause for a fall in BP while CO increased is a fall in SVR. (BP = SV•HR•SVR.) Clearly, in this study a fall in SVR was the cause of the falling BP despite an increase in CO and despite administration of 15 mL/kg colloid solution. While I have little doubt that we are wise to replace a woman’s NPO deficit prior to regional anesthesia, it is very likely that we have misidentified the cause of maternal hypotension. To effectively treat it we must clearly identify what the cause of her hypotension really is.

 

Michael Fiedler, PhD, CRNA

 

1) Ueyama H, He YL, Tanigami H, Mashimo T, Yoshiya I. Effects of crystalloid and colloid preload on blood volume in the parturient undergoing spinal anesthesia for elective Cesarean section. Anesthesiology. 1999;91:1571-1576.

2) Greene NM, Brull SJ. Physiology of spinal anesthesia. 4th ed. Baltimore, Md.: Williams & Wilkins; 1993.

3) Greenwood JP, Scott EM, Stoker JB, Walker JJ, Mary DA. Sympathetic neural mechanisms in normal and hypertensive pregnancy in humans. Circulation. 2001;104:2200-2204.

4) Magness RR, Cox K, Rosenfeld CR, Gant NF. Angiotensin II metabolic clearance rate and pressor responses in nonpregnant and pregnant women. Am J Obstet Gynecol. 1994;171:668-679.

5) Lumbers ER. Peripheral vascular reactivity to angiotensin and noradrenaline in pregnant and non-pregnant women. Aust J Exp Biol Med Sci. 1970;48:493-500.

6) Chesley LC, Talledo e, Bohler CS, Zuspan FP. Vascular reactivity to angiotensin II and norepinephrine in pregnant and nonpregnant women. Am J Obstet Gynecol. 1965;91:837-842.

7) Davison JM, Sheills EA, Barron WM, Robinson AG, Lindheimer MD. Changes in the metabolic clearance of vasopressin and in plasma vasopressinase throughout human pregnancy. J Clin Invest. 1989;83:1313-1318.

© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 4, April 30, 2009




Pain

Horlocker T, Burton A, Connis R, Hughes S, Nickinvich D, Palmer C, Pollock J, Rathmell J, Rosenquist R, Swisher J, Wu C


 

 

Practice guidelines for the prevention, detection, and management of respiratory depression associated with neuraxial opioid administration

Anesthesiology 2009;110:21-30

Horlocker T, Burton A, Connis R, Hughes S, Nickinvich D, Palmer C, Pollock J, Rathmell J, Rosenquist R, Swisher J, Wu C

 

Abstract

Purpose            The purpose of these guidelines were to improve patient safety by addressing potential adverse outcomes associated with the neuraxial administration of opioids.

Background            The American Society of Anesthesiologists (ASA) originally adopted neuraxial opioid administration guidelines in 2007. These guidelines were an update focusing on patients receiving epidural and intrathecal opioids, including morphine, expended release morphine, fentanyl, and sufentanil.

Methodology            Respiratory depression was defined as a respiratory rate below 12 breaths per minute, oxygen saturation below 92%, or an arterial carbon dioxide tension above 50 mm Hg. Those monitoring parameters may also be associated with clinical signs of drowsiness, sedation, periodic apnea or cyanosis. The task force evaluated peer reviewed journals for relevant studies on the topic, collected opinions from experts using a random survey, and solicited comments from ASA members on the findings.

Result            The updated guidelines included the following:

I.               Identification of Patients at Increased Risk of Respiratory Depression. It was recommended that anesthesia providers evaluate each patient’s risk of respiratory depression prior to administration of neuraxial opioids. Increased risks would include a history of sleep apnea, coexisting diseases such as diabetes and obesity, and medications that might contribute to respiratory depression.

II.             Prevention of Respiratory Depression after Neuraxial Opioid Administration. This guideline included the effects of positive pressure breathing devices, drug selection, and drug dose. Patients who use a positive pressure breathing device at home should bring it to the hospital and use it as necessary. A continuous epidural opioid infusion reduced the risk of respiratory depression compared to single dose epidural opioids or IV, IM, or sub-q administration routes. However, single dose epidural administration of morphine, extended release morphine, fentanyl, or sufentanil appears to be just as safe IV, IM, or sub-q opioids. The lowest effective dose of opioid be used.

III.           Detection of Respiratory Depression. All patients receiving neuraxial opioids should be monitored for clinical signs of respiratory depression and pulse oxymetry used when appropriate. With single dose opioid administration, continuous monitoring should be used for a minimum of 20 minutes and then once an hour for at least two hours. When a continuous infusion is used or when extended release morphine is used, monitoring should be performed continually for the first 20 minutes, hourly for the first two hours, every two hours for the next 12 hours, and then once every 4 hours for a minimum of 48 hours or as appropriate for the patient’s clinical condition and concurrent medications.

IV.           Management and Treatment of Respiratory Depression. Patients receiving neuraxial opioids should have supplemental oxygen available and administered to those with altered levels of consciousness, respiratory depression, or hypoxemia. Routine use of supplemental oxygen should be avoided because it could hinder the detection of respiratory problems. Intravenous access should be maintained in case resuscitative measures are needed, and noninvasive positive pressure ventilation should be considered when appropriate.

Conclusion            The appendix section of the guidelines included a detailed list of recommendations and methods of analyses.

 

Comment

I am very much in favor of our professional organizations providing evidenced based practice guidelines to help guide the practitioner through an ever increasing body of clinical knowledge. I was happy to see that the document included a preamble that indicated the guidelines were not intended to be the standard of care or absolute requirements. I support the methodology of combining scientific evidence with expert opinion and practitioner comments, but it appears to me that they gave just as much weight to opinion as they did to scientific evidence when formulating their recommendations. I felt the document was weak, the recommendations were too broadly defined, and scientific evidence was lacking. For example, they offer the recommendation that lower doses are better than higher doses of drugs when preventing respiratory depression, but they do not specify a range or maximum effective dose. They did not provide any helpful information about use of reversal agents or any specifics about the relationship of drug doses to complication rate. I would have found more specific information in those areas to be clinically helpful.

Overall, it is hard to argue with these recommendations, but it is very hard to find these guidelines very useful in the real world. I also find the comment about supplemental oxygen a bit odd. I personally think that the risks of providing low dose supplemental oxygen are minimal compared to the benefits. Perhaps that is a topic worth reviewing in future abstracts.

 

Steven Wooden, MS CRNA

© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 4, April 30, 2009




Regional Anesthesia

Lo N, Brull R, Perlas A, Chan V, McCartney CJL, Sacco R, El-Beheiry H


 

 

Evolution of ultrasound guided axillary brachial plexus blockade: retrospective analysis of 662 blocks

Can J Anesth 2008;55:408-413

Lo N, Brull R, Perlas A, Chan V, McCartney CJL, Sacco R, El-Beheiry H

 

Abstract

Purpose            A retrospective study to determine if ultrasonographic guidance (US) increased the success rate, decreased block onset time, or reduced local anesthetic volume for axillary brachial plexus blockade (AXB) when compared to traditional approaches, peripheral nerve stimulation (PNS) and transarterial (TA) techniques.

Background            Axillary brachial plexus blockade provides excellent pain relief, and is associated with reduced nausea and vomiting, and reduced hospital stay compared to general anesthesia for hand surgery. AXB has traditionally been performed using a PNS or TA approach; however, these traditional approaches have variable success rates resulting in an unplanned general anesthetic. Additionally, there is concern that these blind techniques may increase the potential for complications such as vascular puncture or nerve injury.

In recent years, there has been a tremendous increase in interest in regional anesthesia using real-time US techniques to perform peripheral nerve blocks, especially the AXB. Randomized controlled trials suggest US may hasten AXB performance and improve block quality and duration. Some research suggests that US approaches may improve block success, though studies differ in the definition of “success.” Large scale studies comparing outcomes after US or traditional approaches to the AXB are currently lacking. This study sought to retrospectively examine and compare success rates of US guidance with traditional approaches to the AXB. The investigators hypothesized that US guidance would improve success compared to traditional techniques.

Methodology            This was a retrospective review of 662 AXB anesthetics for hand, wrist, or elbow surgery performed at Toronto Western Hospital between October 2003 and November 2006. The AXBs were performed either by US-guidance or using traditional techniques, either multiple injection PNS or TA. The PNS blocks used a nerve stimulator to elicit distal motor response in the hand in the distribution of each of the median, ulnar, and radial nerves with a current of 0.5 mA or less. The transarterial AXB was performed using a 23 g hypodermic needle with 1.5% lidocaine 10 mg kg-1, with 1:200,000 epinephrine. Starting in mid 2004 US guidance became the preferred method for AXB using a 22 g insulated needle and nerve stimulator to confirm nerve identity. For ultrasound AXB local anesthetic was injected to produce a circumferential spread around the median, ulnar and radial nerves. For PNS and US-guided AXB a 40 mL 50:50 mixture of 2% lidocaine and 0.5% bupivacaine with 1:200,000 epinephrine was most commonly used. Records from a regional anesthesia electronic database were reviewed for pertinent demographic, surgical, and procedural data. The primary outcome was AXB “success.” Success of AXB was graded as complete (no supplemental local anesthetic or “rescue block” required for surgical anesthesia), incomplete (local anesthetic supplementation or “rescue block” required) or failed (general anesthesia required). Secondary outcomes included duration in the block room and in the Phase I and II recovery areas, respectively. Blocks were performed by one of 11 staff regional anesthesiologists or one of 43 regional anesthesia trainees (fellows or residents) under the direct supervision of a staff anesthesiologist.

Result            A total of 662 patient records were reviewed, with 535 undergoing US-guided AXB (US group) and 127 using traditional techniques (PNS: n = 56; TA: n = 71). Demographic data, surgical duration, and time spent in Phase I or II recovery were similar between groups. When compared to traditional techniques, US resulted in more complete blocks (91.6% vs. 81.9%, P = 0.003), with shorter duration of time in the block room (30.6 ± 14.2 min vs. 40.1 ± 27.3 min, P <0.0001), and less local anesthetic volume (39.8 ± 6.4 mL vs. 46.7± 17.1 mL, P <0.0001).

Subgroup analysis of the traditional techniques indicated TA subgroup had significantly larger volume of local anesthetic (56.9 mL TA vs. 44.2 ± 16.8 mL PNS, P < .0001). US provided more complete blocks (91.6% vs. 78.6%, P < .003) with shorter duration (30.6 ± 14.2 min vs. 46.4 ± 31.7 min, P < .0001) when compared to the PNS group only. A majority of blocks were performed by trainees (n = 374 vs. staff n = 84) in the US group and in the traditional group (n = 88 vs. staff n =13). No difference in percentage of complete, incomplete, or failed blocks in US or traditional groups was noted between staff or trainee. However, complete block rates were similar for US and traditional blocks when performed by staff (92.9% vs. 92.3%).

There were six major complications, with five events involving local anesthetic intravascular injection (US group frequency 2/535 or 0.37%; TA group frequency 2/71 or 2.8%; PNS group frequency 1/56 or 1.8%). One patient in PNS group suffered a postoperative AXB-neuropathy which resolved after approximately two months. Overall complication rates were significantly lower in the US group compared to the traditional group (0.37% vs 3.15%, P = 0.014).

Conclusion            These results suggest US guidance may shorten time spent in block room, reduce local anesthetic volume needed to produce a block, and improve success of AXB when compared to traditional approaches.

 

Comment

This is one of the largest studies published to date comparing US and traditional approaches to the AXB. It is important to point out that it was a retrospective study, and thus it has a lower level of evidence. Large randomized controlled trials are thus needed to confirm the finding of reduced complication with US. Having said that, I thought the findings were interesting, and the study highlights the resurgence of interest in peripheral nerve blocks.

This resurgence of interest is driven by multiple factors, such as the ability to see in real-time where the needle and local anesthetic is going in relation to the nerve(s). The theory is that this helps reduce complications. Additionally there is increased emphasis placed on management of acute postoperative pain and the development of regional anesthesia or acute pain services within anesthesia departments. Having a dedicated team to place peripheral nerve blocks, in my opinion, helps improve overall block success, efficiency, and probably helps decrease complications.

One issue I have with this study is their definition of success. Success in many studies in Canada and Europe is defined as the ability to perform the case under block with MAC. At my facility, when we tried to use this as an outcome measure in block studies we found very high rates of block “failure.” Not because the block wasn’t adequate, but because the staff or patient did not want to have the surgery under block with sedation. Furthermore some studies include blocking only 3 of 4 nerves (radial, median, & ulnar),1,2 whereas others include all four (radial, median, ulnar, & musculocutaneous). Additionally, emphasis on rapid turn over between cases sometimes limits block “soak time.” Therefore, more important outcomes for “success” should focus on postoperative pain and complications (i.e., nerve injury).

Probably the most important finding from this study was that success rates were quite high (complete blocks > 92%) when both US and traditional blocks were performed by a staff anesthesiologist as opposed to a trainee (traditional complete blocks 83%). In experienced hands outcomes from PNB using either technique will be very similar.1,2 Looking at the data, the majority of the blocks were US and I suspect the staff’s emphasis was on teaching their trainees to perform US guided blocks. This is similar to what my trainees experience and I believe it is one factor that contributes to lower success with traditional, especially peripheral nerve stimulator (PNS) blocks. Needle control techniques are very different between US and PNS, and one of the trends I have noticed is that some trainees who learn to do US guided blocks first have difficulty when they have to place an AXB with a PNS. This is probably a combination of inexperience (by staff and trainees) or being “rusty” (i.e., staff having not done a PNS block in a long time).

The important take home message I got from this study is that we ensure our trainees who will be performing peripheral nerve blocks when they graduate (i.e., military anesthetists) are competent with PNS and US. This is essential because they may be in locations where ultrasound equipment is unavailable.

 

Dennis Spence, PhD, CRNA

 

1. Borgeat A, Capdevila X. Neurostimulation/Ultrasonography. The Trojan war will not take place. Anesthesiology 2007;106:896-898.

2. Casati A, Danelli G, Baciarello M, Corradi M, Leone S, Di Cianni S, Fanelli G. A prospective, randomized comparison between ultrasound and nerve stimulation guidance for multiple injection axillary brachial plexus block. Anesthesiology 2007;106:992–996.

© Copyright 2009 Anesthesia Abstracts · Volume 3 Number 4, April 30, 2009