ISSN NUMBER: 1938-7172
Issue 12.11 VOLUME 12 | NUMBER 11

Editor:
Michael A. Fiedler, PhD, CRNA

Contributing Editors:
Mary A Golinski, PhD, CRNA
Dennis Spence, PhD, CRNA

Assistant Editor
Jessica Floyd, BS

A Publication of Lifelong Learning, LLC © Copyright 2018

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


Pharmacology
Analysis of physiological respiratory variable alarm alerts among laboring women receiving remifentanil

Anesth Analg 2017;124:1211-8

DOI: 10.1213/ANE.0000000000001644

Weiniger CF, Carvalho B, Stocki D, Einav S


Abstract

 

Purpose   The purpose of this study was to report on the ability of respiratory variable alarm alerts to detect apnea in parturients receiving IV remifentanil for labor analgesia.

 

Background   Remifentanil is an ultra-short acting opioid that parturients may be offered when they cannot or do not want an epidural for labor pain. However, there have been closed claims reports of maternal morbidity associated with IV opioid administration during labor. Many nurses and providers believe that attaching a continuous respiratory monitor (i.e., end tidal carbon dioxide) to patients will warn of impending respiratory depression. There is growing evidence that these alarms may not prevent harm because of alarm fatigue, insufficient alarm sensitivity, or inaudible alarms.

 

Methodology   This was a secondary analysis on the incidence, positive predictive rate, and sensitivity of continuous EtCO2, SpO2, and respiratory rate (RR) for the detection of apnea. Apnea was defined as an EtCO2 < 5 mm Hg for at least 30 seconds. The study also looked at the lead time before an apneic episode in parturients who received remifentanil for labor analgesia (20-60 µg every 1 to 2 minutes). Patients who received remifentanil were connected to a capnography monitor, which recorded and continuously displayed RR, EtCO2, heart rate, and SpO2. Early warning alarm triggers were:

  • RR < 8 bpm
  • EtCO2 < 15 mm Hg
  • SpO2 < 92%

Sedation scores were recorded every 15 minutes for the first hour and hourly thereafter. All patients received 2 LPM of oxygen via nasal cannula. An anesthesia provider was present in the room during the remifentanil infusions, and they intervened to prevent apnea >40 seconds. The anesthesia provider documented any reasons for artifact readings. Definitions of individual physiologic variable alerts are in Table 1.

 

Table 1. Alert Definitions

Apnea

EtCO2 < 5 mm Hg for at least 30 seconds

Apnea requiring intervention

Apnea for >40 seconds

Lag time

Time from the start of the continuous physiological variable below the preset alert until the immediate early warning alert time.

Immediate alert

Continuous physiologic variable was below preset threshold for the lag time (15 consecutive seconds).

Sustained alert

Continuous physiologic variable below alert preset threshold for 25 consecutive seconds.

Early warning alert

The time point when data from a continuous physiologic variable met the definitions of a trigger.

Early warning alert time interval (lead time)

Time from immediate alert until capnography tracing met the definition of apnea.

 

Outcomes included the incidence, positive predictive rate, and sensitivity for each of the physiologic respiratory variables (EtCO2, RR, SpO2) for apnea event detection. Statistical analysis was appropriate.

 

Result   There were 19 parturients randomly assigned in the original study to receive remifentanil. There were 331 immediate early warning alarm alerts. Of these, 82% (271) were sustained alerts (Table 2). There were 62 apnea event alerts (EtCO2 < 5 mm Hg for at least 30 consecutive seconds), 72 alerts for an SpO2 <92% and 40 events for SpO2 < 90%. The 62 apneas occurred in 10 of 19 parturients (53%). Of these parturients, three had 1 event, two had 11-12 apnea events, and one obese parturient (BMI = 33) had 25 events. There was no relationship between number of apneas and sedation scores. Most (76%) apneas occurred in the first three hours of remifentanil administration. Three patients (16%) had an SpO2 <92% 30 minutes after starting remifentanil.

 

 

Table 2. Alert Events in 19 Women

 

Bradypnea, RR < 8 bpm

Hypocapnia
EtCO
2 < 15 mm Hg

Hypoxemia
SpO
2 < 92%

Total Events
EtCO
2, RR, SpO2

Immediate alert

111

118

198

331

Sustained alert

92

77

167

271

SpO2<92%

11

9

72

72

SpO2<90%

9

9

40

40

Apnea

62

48

9

62

 

Positive Predictive Value (PPV) is the percentage of the time that an alarm goes off and what it was designed to detect actually happened. Alarms with a high false positive rate will have a low positive predictive value. Here; the lower the PPV, the more often it gave a false alarm. The alarm with the best positive predictive ability for detecting apnea was bradypnea (RR < 8 bpm), but it had a PPV of only 36%. Next best was the hypocapnea alarm (EtCO2 <15 mm Hg), with a positive predictive rate of 29%. The hypoxemia alarm (SpO2 <92%) had the poorest positive predictive rate, 4.3%.

 

Sensitivity is the percentage of actual events that are correctly identified; here, the number of apneas that occur and are subsequently identified by the monitor. (The monitor was “sensitive” to them.) A monitor can be highly sensitive and detect all the real apneas while still sounding lots of false alarms. The bradypnea alarm (RR < 8 bpm) had 100% sensitivity in detecting apnea, and the early warning alert interval was 0.3 seconds. Hypocapnia (EtCO2 < 15 mm Hg) had 76% sensitivity. The hypoxemia alarm (SpO2 <92%) had the lowest sensitivity, 14.5%, and longest early warning alert time interval of 40 seconds.

 

Conclusion   A majority of women who received remifentanil for labor experienced apnea. Alert triggers with the best ability to predict apnea were the bradypnea (RR < 8 bpm) and hypopnea (EtCO2 <15 mm HG) alarms. Pulse oximetry, with an alarm set for SpO2 <92%, only detected 15% of apnea events. These results demonstrate the limitations of continuous respiratory monitoring technology in detecting apnea. Parturients receiving remifentanil should have one-on-one care, and if monitoring is available, EtCO2 is probably preferable to continuous pulse oximetry.

 

Comment

 

Remifentanil is an excellent option for parturients who cannot receive a neuraxial analgesic for labor. However, providers need to make sure there is a policy that governs its administration and that the nursing staff has the proper training, staffing, and equipment to appropriately monitor patients on remifentanil. Continuous monitoring (especially EtCO2) is great, but nothing replaces a nurse at the bedside who is able to quickly identify and treat respiratory depression.

 

The results of this study confirm what we all suspect - that hypoxemia is a late sign (as measured by pulse oximetry) of respiratory depression. In this study the sensitivity of a pulse oximeter alarm setting of <92% to predict an apneic episode of at least 30 seconds was poor at 14.5%. Results were much better when patients received continuous respiratory monitoring with EtCO2, with alarms set to a respiratory rate of <8 bpm having 100% sensitivity for detecting apnea. I believe these results support why many centers are moving to monitoring for respiratory depression with EtCO2.

 

The challenge with continuous respiratory monitoring is alarm fatigue and patient compliance with wearing the cannulas and pulse oximeter. As anesthesia providers we can help mitigate this by ensuring our nursing staff are properly trained and that we are readily available to provide support for them. Also ensure that your hospital policies ensure one-on-one nursing care when a parturient receives remifentanil!

 

Dennis Spence, PhD, CRNA


The views expressed in this article are those of the author and do not reflect official policy or position of the Department of the Navy, the Department of Defense, the Uniformed Services University of the Health Sciences, or the United States Government.

 

 

 


© Copyright 2018 Anesthesia Abstracts · Volume 12 Number 11, July 25, 2018





Effect of a high-rate versus a low-rate oxytocin infusion for maintaining uterine contractility during elective cesarean delivery: a prospective randomized clinical trial

Anesth Analg 2017;124:857–62

DOI: 10.1213/ANE.0000000000001658

Duffeld A, McKenzie C, Carvalho B, Ramachandran B, Yin V, El-Sayed YY, Riley ET, Butwick AJ


Abstract

 

Purpose   The purpose of this study was to compare differences in estimated blood loss in women undergoing elective cesarean delivery who received either a low-rate or high-rate oxytocin infusion.

 

Background   Oxytocin is the first-line agent to prevent uterine atony after delivery. It is routinely administered as an infusion to cause a strong uterine contraction thus slowing or stopping uterine blood loss. However, there is no consensus as to the optimal oxytocin maintenance infusion rate. This study compared a high-rate (15 U/h) versus a low-rate (2.5 U/h) oxytocin infusion on total estimated blood loss (EBL).

 

Methodology   This was a prospective, double-blind, randomized controlled clinical trial comparing a high-rate (15 U/h) versus a low-rate (2.5 U/h) oxytocin infusion on total estimated blood loss during elective cesarean delivery. Inclusion criteria were ASA Class II, singleton pregnancies, ≥37 weeks gestation, elective cesarean delivery with Pfannenstiel incision, and between 18 and 40 years of age. Exclusion criteria were any significant medical or obstetric disease, active labor or ruptured membranes, placenta previa or other placental disorders, multiple gestations, or known uterine abnormalities.

 

All patients received a 500 mL hetastarch bolus prior to spinal anesthesia with 1.6 mL 0.75% bupivacaine, 10 µg fentanyl, and morphine 150 to 200 µg. After delivery of the infant and clamping of the umbilical cord, all patients received a 1 U bolus of oxytocin. Then, based on their group assignment, they received an oxytocin infusion at either a high-rate - 15 U/h (60 U in 1 L lactated ringers infused at 250 mL/hr) or low-rate - 2.5 U/h (10 U in 1 L lactated ringers infused at 250 mL/hr). Infusions were discontinued after patients were discharged from the PACU.

 

If the patient had inadequate tone (per surgeon evaluation every 2 minutes), an additional 1 to 2 unit oxytocin bolus was administered. If 5 or more units of oxytocin were required and uterine tone was inadequate, then a second line agent was administered; methylergonovine maleate, carboprost, or misoprostol.

 

The primary outcome was Estimated Blood Loss. Secondary outcomes were rates of inadequate uterine tone, rate of postpartum hemorrhage >1,000 mL, postoperative hemoglobin in PACU, surgical interventions to manage postpartum hemorrhage, use of second line agents, and oxytocin-related side effects during the first 20 minutes after initiation of oxytocin infusions.

 

Statistical analysis was appropriate. The sample size of 42 women per group was based on finding a 250 mL difference in EBL.

 

Result   The study was ended after 51 patients because of slow enrollment and introduction of phenylephrine infusions for prophylaxis against spinal-induced hypotension. No significant differences were found in demographic or clinical characteristics. The difference in median EBL was 122 mL. The median total EBL for each group was 634 mL in the low-rate group and 512 mL for the high-rate group (P = NS). No differences in postoperative hemoglobin values were found. The was no difference in oxytocin infusion duration. No differences were found in “rescue” oxytocin boluses. One patient in each group required a second-line uterotonic agent in the operating room. No differences were found in oxytocin-related side effects. No differences in inadequate uterine tone were found. The rate of postpartum hemorrhage was 17% in the low-rate group and 15% in the high-rate oxytocin groups (P = NS).

 

Conclusion No differences were found in EBL in women undergoing elective cesarean delivery who received a low-rate (2.5 U/h) or high-rate (15 U/h) oxytocin infusion. Results suggest that a low-rate oxytocin infusion may be efficacious in decreasing blood loss from uterine atony.

 

Comment

 

I was taught to put 20-40 units of oxytocin in a liter of lactated ringers and to run it in fast after delivery of the baby. If the tone was adequate then I slowed down the rate. This always made me a little uncomfortable because I never knew the actual rate or how much oxytocin I was giving. So it is nice to see investigators providing evidence on this problem.

 

The authors of this study found no difference in EBL between high-rate or low-rate oxytocin infusions. The authors reported the difference was only 122 mL that was not statistically or clinically significant. However, the study was underpowered to find such a small difference in EBL. None of the other secondary outcomes were significantly different, and thus the authors concluded a low-rate oxytocin infusion (after giving a 1 unit oxytocin bolus) was as efficacious as a high-rate infusion. At best, these findings only apply to parturients undergoing elective cesarean delivery and are at lower risk for postpartum hemorrhage.

 

Having an oxytocin protocol for prevention of postpartum hemorrhage is the important take-away from this study. At my facility we revised our postpartum hemorrhage protocol and also developed an oxytocin protocol similar to this one. At my facility we run a high-rate protocol, administering a 3-unit oxytocin bolus over 3 minutes after delivery, then run an infusion at 18 U/h for 1 hour, then 3.6 U/h for 3 hours. We have found these quality improvement initiatives have decreased our rate of postpartum hemorrhage. If you do not have either of these protocols at your institution, I recommend developing a team to start putting them together.

Dennis Spence, PhD, CRNA


The views expressed in this article are those of the author and do not reflect official policy or position of the Department of the Navy, the Department of Defense, the Uniformed Services University of the Health Sciences, or the United States Government.


© Copyright 2018 Anesthesia Abstracts · Volume 12 Number 11, July 25, 2018





The effect of adding subarachnoid epinephrine to hyperbaric bupivacaine and morphine for repeat cesarean delivery: a double-blind prospective randomized trial

Anesth Analg 2018;127:171-178

DOI: 10.1213/ANE.0000000000002542

Katz D, Hamburger J, Gutman D, Wang R, Lin HM, Marotta M, Zahn J, Beilin Y


Abstract

 

Purpose   The purpose of this study was to compare the effect of adding either none, 100 µg, or 200 µg epinephrine to 1.5 mL 0.75% bupivacaine and 0.25 mg morphine. Primary effects tracked were the time until intraoperative activation of the epidural catheter and the time until postoperative regression of sensory block to the T-10 level.

 

Background   Spinal anesthesia with 0.75% bupivacaine is the most common type of anesthesia administered for cesarean delivery. However, the duration of anesthesia may not be adequate for prolonged surgery in patients undergoing repeat cesarean delivery. This has led many anesthesia professionals to place a combined spinal epidural (CSE). Spinal bupivacaine has a duration of approximately 120 minutes. The addition of epinephrine to a lidocaine spinal has been shown to prolong the duration of surgical anesthesia. However, it is not clear if the addition of epinephrine to spinal bupivacaine prolongs the duration of surgical anesthesia or need to activate a CSE for patient comfort.

 

Methodology   This was a prospective, double-blind, randomized controlled trial of 68 parturients undergoing elective repeat cesarean delivery who were randomized to receive either 100 µg, 200 µg, or no epinephrine to standard spinal admixture of 1.5 mL 0.75% bupivacaine with 0.25 mg morphine. Patients were excluded if they had allergies to any of the study medications, or had prior abdominal surgery that could impact determination of the sensory level. All patient agreed to receive a CSE. All patients received the same volume of spinal admixture (2.2 mL). Study medications were prepared by anesthesia providers not involved in the study or care of the patients. All neuraxial procedures were performed with the patient in the sitting position using a standard CSE kit. After aspiration of cerebrospinal fluid, the spinal admixture was injected, and the time was recorded until regression to a T-10 level or until the patient required a bolus of the epidural catheter for inadequate surgical anesthesia. After the epidural catheter was placed and secured patients were positioned supine.

 

Demographic and clinical data was recorded. The primary outcome was time to a T-10 sensory dermatome level or need to use the epidural catheter. The secondary outcome was time to motor recovery, as defined by a Modified Bromage Score of 3 (patient able to extend their knees). Sample size calculation and statistical analysis were appropriate.

 

Result   There were 22 in the 100 µg epi group, 21 in the 200 µg epi group, and 22 in the no epi group. There were no significant differences in any of the demographic or clinical characteristics. The median set up time to reach a T-4 level was 8 minutes in each group (P = NS). Pain scores at uterine closure were significantly greater in the no epi group (P = 0.02). Four patients in each group required supplemental analgesics (P = NS).

 

Activation of the epidural catheter occurred in 4.5% of parturients (1 of 21) in the 100 µg epi group, 9.5% (2 of 21) in the 200 µg epi group, and 23% (5 of 22) in the no epi group. The median time to T-10 regression or activation of the epidural catheter was significantly longer in the 200 µg epi group compared to the other two groups. In the 100 µg epi group it was 135 minutes, in the 200 µg epi group: 165 minutes, and in the no epi group: 120 minutes (P = 0.001; Figure 1). The addition of 200 µg epinephrine prolonged time to sensory recovery by 40 minutes (95% CI, 15-60 minutes) compared to the no epinephrine group (P = 0.007) and 30 minutes longer (95% CI, 15-45 minutes) compared to the 100 µg epi group (P = 0.007). Sensory recovery times were similar in the 100 µg epi group compared to the no epi group.

 

Time until knee extension was significantly longer in the 200 µg epi group compared to the other two groups. Time to knee extension was 172 minutes in the 200 µg epi group, 150 minutes in the 100 µg epi group, and 120 minutes in the no epi group (P < 0.001; Figure 1). The addition of 200 µg epinephrine prolonged time to knee extension by 60 minutes (95% CI 30-93 min.) compared to the no epinephrine group (P = 0.007) and 30 minutes (95% CI 0-60 min.) compared to the 100 µg epi group (P = 0.034). Motor block recovery times were also significantly longer in the 100 µg epi group compared to the no epi group (P = 0.001).

 

Figure 1. Sensory and Motor Block Recovery

Note: Time to a T-10 level or epidural catheter activation was significantly longer in the 200 µg epi group compared the other two groups (P = 0.007). Time to a Modified Bromage score = 3 was significantly longer in the 200 µg epi group compared to the other two groups (P < 0.001). No significant differences were found in sensory and motor block recovery between the 100 µg epi and no epi groups.

 

 

 

Conclusion   The addition of 200 µg epinephrine to 1.5 mL bupivacaine with 0.25 mg morphine for spinal anesthesia in parturients undergoing repeat cesarean delivery significantly prolongs sensory and motor blockade.

 

Comment

I was taught in training that the addition of epinephrine to spinal bupivacaine does not prolong surgical anesthesia. So, I rarely use it in my spinals for cesarean delivery. Some of my colleagues would use an ‘epi wash’ to prolong the spinal block with bupivacaine, but I often questioned the safety of this practice because of the imprecision in epinephrine dose. If I had a patient who I thought would have a longer procedure, I would place a CSE. However, after reading the results of this well-designed study, I might consider changing my practice and begin adding 200 µg of epinephrine to my spinal bupivacaine admixture if I think the case is going to be prolonged, or if I have a slow surgeon (or resident doing the case).

 

What can you expect if you add 200 µg of epinephrine to 1.5 mL bupivacaine with 0.25 mg morphine to the duration of surgical anesthesia? Well, your spinal could last anywhere from 150 to 180 minutes, or upwards of 3 hours. The time until patients can bend their knees, which is sufficient enough for most patients to be discharged from recovery room, will range from 30 to 90 minutes longer or 150 to 135 minutes when compared to no epinephrine. So, it might take a little longer to get the patient’s out of your recovery room.

 

Dennis Spence, PhD, CRNA


The views expressed in this article are those of the author and do not reflect official policy or position of the Department of the Navy, the Department of Defense, the Uniformed Services University of the Health Sciences, or the United States Government.


© Copyright 2018 Anesthesia Abstracts · Volume 12 Number 11, July 25, 2018