Incidence of Sedation-Related Complications With Propofol Use During Advanced Endoscopic Procedures

Article Outline

• Abstract
• Methods
  • Outcomes
  • Airway Modifications
  • Data Collection
  • Patient Monitoring
  • Statistical Analysis
• Results
• Discussion
• References
• Copyright

Background & Aims

Propofol is an effective sedative in advanced endoscopy. However, the incidence of sedation-related complications is unclear. We sought to define the frequency of sedation-related adverse events, particularly the rate of airway modifications (AMs), with propofol use during advanced endoscopy. We also evaluated independent predictors of AMs.

Methods

Patients undergoing sedation with propofol for advanced endoscopic procedures, including endoscopic retrograde cholangiopancreatography, endoscopic ultrasound, and small-bowel enteroscopy, were studied prospectively. Sedative dosing was determined by a certified registered nurse anesthetist with the goal of achieving deep sedation. Sedation-related complications included AMs, hypoxemia (pulse oximetry [SpO2] < 90%), hypotension requiring vasopressors, and early procedure termination. AMs were defined as chin lift, modified face mask ventilation, and nasal airway. We performed a regression analysis to compare characteristics of patients requiring AMs (AM+) with those who did not (AM−).

Results

A total of 799 patients were enrolled over 7 months. Procedures included endoscopic ultrasound (423), endoscopic retrograde cholangiopancreatography (336), and small-bowel enteroscopy (40). A total of 87.2% of patients showed no response to endoscopic intubation. Hypoxemia occurred in 12.8%, hypotension in 0.5%, and premature termination in 0.6% of the patients. No patients required bag-mask ventilation or endotracheal intubation. There were 154 AMs performed in 115 (14.4%) patients, including chin lift (12.1%), modified face mask ventilation (3.6%), and nasal airway (3.5%). Body mass index, male sex, and American Society of Anesthesiologists class of 3 or higher were independent predictors of AMs.

Conclusions

Propofol can be used safely for advanced endoscopic procedures when administered by a trained professional. Independent predictors of AMs included male sex, American Society of Anesthesiologists class of 3 or higher, and increased body mass index.

Abbreviations used in this paper: AM, airway modification, ASA, American Society of Anesthesiologists, BMI, body mass index, CRNA, certified registered nurse anesthetist, ERCP, endoscopic retrograde cholangiopancreatography, EUS, endoscopic ultrasound

The administration of sedatives and analgesics during endoscopic procedures is common in the United States.¹ Traditionally, sedation consisted of a combination of low-dose benzodiazepine with an opiate to achieve a moderate level of sedation (also known as conscious sedation).², ³ Initially approved for the induction and maintenance of anesthesia, propofol (2,6-di-isopropofol) has become an increasingly popular sedative for endoscopic procedures because of its rapid onset of action (30–45 s) and short duration of effect (4–8 min).⁴, ⁵ When administered by a gastroenterologist, the safety and efficacy of propofol for standard endoscopic procedures has been reported in multiple trials.⁶, ⁷, ⁸ There also are data to support the safe use of gastroenterologist-administered propofol for advanced endoscopic procedures such as endoscopic retrograde cholangiopancreatography (ERCP) and endoscopic ultrasound (EUS).⁹, ¹⁰, ¹¹, ¹², ¹³, ¹⁴ However, most of these studies were limited by controlled patient populations at low risk of developing cardiopulmonary complications. Furthermore, there is limited information on the clinical predictors of developing sedation-related cardiopulmonary complications during advanced endoscopy.⁹, ¹⁴

The American College of Gastroenterology and the American Society for Gastrointestinal Endoscopy have published a joint statement supporting the use of gastroenterologist-supervised, nurse-administered propofol for endoscopy.¹⁵ However, this report acknowledges that “Patients receiving propofol should receive care consistent with deep sedation. Personnel should be capable of rescuing the patient from general anesthesia and/or severe respiratory depression.”¹⁵ To elaborate on the implications of this statement, we sought to define the specific airway interventions required during advanced endoscopic procedures while using propofol in the setting of monitored anesthesia care.

The primary goal of this study was to report the incidence of sedation-related complications associated with propofol used by nurse anesthetists for advanced endoscopic procedures, with a particular focus on the frequency of airway modifications (AMs). We also evaluated for independent clinical predictors of requiring AMs during advanced endoscopy. Finally, we compared the use of propofol alone with combination propofol regimens in terms of propofol dosing and postprocedure recovery.

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Methods 

We performed a prospective analysis of patients undergoing advanced endoscopic procedures (ERCP, EUS, single-balloon or spiral overtube-assisted small-bowel enteroscopy and enteral stenting) at Washington University in St. Louis, a tertiary care medical center. In our endoscopy unit, standard practice is to sedate patients undergoing advanced procedures using propofol alone or in combination with low-dose opiate and/or benzodiazepine. Propofol dosing and patient monitoring is directed by a certified registered nurse anesthetist (CRNA) under the supervision of an anesthesiologist. For induction, the use of propofol alone or in combination with low-dose benzodiazepine and/or opiate is left to the discretion of the CRNA/anesthesiologist team. Sedative dosing is adjusted to maintain at least deep sedation throughout the procedure (Table 1). We performed a convenience sampling of patients undergoing advanced endoscopic procedures with CRNA-directed sedation from May 2008 through November 2008. One anesthesiologist (L.W.) and 3 CRNAs participated, all of whom have extensive experience sedating patients for advanced endoscopic procedures. The anesthesiologist obtained informed consent and enrolled patients in the endoscopy unit. Patient, procedural, and pharmacologic data were collected on all participants. Other than the inability to give informed consent, there were no exclusion criteria. Specifically, we did not exclude patients based on clinical characteristics that could predict sedation-related complications, such as morbid obesity and American Society of Anesthesiologists (ASA) class of 3 or higher.¹⁶ The protocol was approved by our local Human Research Protection Office.

Table 1. Levels of Sedation and Analgesia³

Outcomes 

Our primary outcome was to define the frequency of sedation-related adverse events and the need for one or more AMs during the endoscopy. In addition to AMs, sedation-related adverse events were defined as hypoxemia (pulse oximetry [SpO2], <90% of any duration), hypotension (systolic blood pressure, <90 mm Hg requiring use of vasopressors), and the need to terminate the endoscopy prematurely for issues related to sedation. We also sought to evaluate for independent predictors of AMs by comparing clinical, procedural, and pharmacologic data of patients requiring AMs (AM+) with those who did not (AM−). Finally, we evaluated the procedural and pharmacologic data of patients who received combination propofol versus propofol alone for induction.

Airway Modifications 

AMs were defined as a chin lift maneuver, nasopharyngeal airway, modified mask airway, bag-mask ventilation, or endotracheal intubation. We classified a chin lift maneuver as any chin or jaw manipulation performed to improve the patency of the upper airway for optimal airflow. A modified mask airway was defined as the use of a customized air entrapment mask to deliver higher flows of oxygen compared with a nasal cannula without interfering with the endoscope. A nasopharyngeal airway involved the insertion of a tube through a nostril and into the nasopharynx to prevent the tongue from blocking air flow. These maneuvers were performed at the discretion of the CRNA for laryngospasm, upper-airway obstruction, and hypopnea/apnea (defined as <6 breaths/min), which may have occurred with or without hypoxemia. We did not distinguish laryngospasm, upper-airway obstruction, and hypopnea/apnea but classified each of these as an AM. An AM also would be performed for hypoxemia in the absence of these airway complications (eg, patients with underlying parenchymal lung disease). Of note, all patients with hypoxemia required one or more AMs, but not all patients who required an AM necessarily developed hypoxemia. Bag-mask ventilation and endotracheal intubation were reserved for patients who did not respond to these maneuvers in conjunction with alterations in the sedation regimen.

Data Collection 

Clinical characteristics including age, sex, body mass index (BMI) (kg/m²), Mallampati score,¹⁷ and ASA class were recorded before the endoscopy. The anesthesiologist (L.W.) recorded these data elements and assigned the Mallampati score and ASA class for all patients enrolled in the study. In addition to AMs, induction dose (mg/kg) and total propofol dose (mg/kg/min) were recorded, along with doses of concomitant sedatives used for induction and during the endoscopy. We present the total propofol dose on a per-minute basis to account for variable infusion times and length of endoscopy. The patient's level of responsiveness at the time of endoscopic intubation was documented: some response (ie, grimace, withdrawal, coughing) versus no response. Patient positioning (prone or other) and Aldrete score¹⁸ at arrival to the recovery unit also were recorded. The sedating CRNA recorded all intraprocedural data on a data collection form.

Patient Monitoring 

All patients were monitored using continuous electrocardiography and heart rate, pulse oximetry, nasal capnography, and intermittent blood pressure. If nasal capnography suggested hypopnea/apnea, the CRNA evaluated for oral respiratory activity (air flow) and chest expansion before intervening. As a part of this evaluation, the CRNA also moved the nasal cannula in front of the oropharynx to assess end-tidal CO2. The CRNA used all of these variables in assessing for the presence of hypopnea/apnea. Supplemental oxygen by nasal cannula (2 L/min) was provided to all patients at the onset of sedation. Administration of propofol and other sedatives was determined solely by the CRNA, who had no other involvement in the procedure except to monitor the patient. Patients undergoing ERCP typically were placed in the prone position and those undergoing EUS or small-bowel enteroscopy were maintained in the left lateral decubitus position.

Statistical Analysis 

Descriptive statistics were used to define the frequency of sedation-related adverse events. Patients were classified by the incidence of one or more AMs (AM+) during the endoscopy. We performed a univariate analysis of potential clinical predictors of AMs, including age, sex, BMI, ASA score, Mallampati score, patient position (prone vs other), endoscopy time, propofol infusion time, induction propofol dose (mg/kg), total propofol dose (mg/kg/min), and the use of combination propofol for induction. Categoric outcomes were analyzed using the chi-squared test or the Fisher exact test where appropriate. Continuous outcomes were analyzed using the Student 2-sample t test for normally distributed data and the Wilcoxon–Mann–Whitney test for nonparametric variables. Reported P values are 2-tailed with values of .05 or less considered statistically significant. Based on the results of univariate analysis, we performed a logistic regression of potential independent predictors of AMs. Without available pilot data, we were unable to perform sample size estimates before patient enrollment. However, we aimed to have at least 120 patients in each group (AM+ and AM−) to include 12 variables in our multivariate analysis. Statistical calculations were performing using Stata v. 10.0 (StataCorp LP, College Station, TX).

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Results 

A total of 799 patients were enrolled over the 7-month study period, including 423 EUS patients (52.9%), 336 ERCP patients (42.1%), and 40 small-bowel enteroscopy or other patients (5.0%). Additional patient characteristics along with procedural and pharmacologic data are summarized in Table 2. Of note, 60.5% of patients met criteria for ASA class 3 or higher and 0.5% had a Mallampati score equal to 4. In addition, no response to endoscopic intubation was observed in 87.2% of cases, which would at least meet standard criteria for deep sedation at the onset of endoscopy.³

Table 2. Patient Characteristics and Procedural Data

Variable	Result
Patient characteristics
Age, y, mean ± SD	57.8±16.5
Male sex, %	46.6
ASA class ≥3, %	60.5
Mallampati score = 4, %	0.5
BMI, mean ± SD	27.1±6.5
Procedural data
Endoscopy time, min, mean ± SD	29.5±18.8
Prone position, %	37.3
No response to endoscopic intubation, %	87.2
Aldrete score in recovery, median (25%–75% interquartile range)	9 (8–9)
Pharmacologic data
Combination propofol for induction, %	61.1
Induction propofol dose, mg/kg, mean ± SD	1.79±1.06
Total propofol dose, mg/kg/min, mean ± SD	0.19±0.11
Propofol infusion time, min, mean ± SD	34.4±18.8

NOTE. A total of 799 patients were included in the study.

Sedation-related adverse events and AMs are summarized in Table 3. Hypoxemia was the most commonly reported adverse event, occurring in 12.8% of procedures. A total of 154 AMs were performed in 115 (14.4%) patients, including 97 chin lift maneuvers, 29 modified mask airways, and 28 nasal airways. One AM was performed in 88 patients (76.5%), 2 AMs in 15 patients (13.1%), and 3 AMs in 12 patients (10.4%). No patients required bag-mask ventilation or endotracheal intubation. The endoscopy had to be terminated early for sedation-related issues in 5 (0.6%) patients; 4 of these cases were aborted because of hypotension that required a single dose of a vasopressor. This maneuver led to stabilization of the blood pressure when performed in conjunction with terminating sedation and the procedure.

Table 3. Sedation-Related Adverse Events and AMs

Complication/intervention	Number of patients (%)
Airway modifications (n=154)	115(14.4)
Chin lift maneuver	97(12.1)
Modified mask airway	29(3.6)
Nasal airway	28(3.5)
Bag-mask ventilation	0(0.0)
Endotracheal intubation	0(0.0)
Hypoxemia (SpO2 < 90%)	102(12.8)
Hypotension requiring vasopressors	4(0.5)
Procedure termination	5(0.6)

NOTE. A total of 799 patients were included in the study. A total of 154 AMs were performed on 115 patients. AMs were not counted more than once if the same maneuver was repeated on a patient. AMs were performed for laryngospasm, upper-airway obstruction, or hypopnea/apnea with or without hypoxemia. Of note, all patients with hypoxemia required one or more AMs, but not all patients who required an AM necessarily developed hypoxemia.

Clinical, procedural, and pharmacologic data of AM+ were compared with AM− patients (Table 4). AM+ patients were more likely to be male (P = .006) and have a higher BMI (P < .0001) compared with AM− patients. The frequency of ASA class 3 or higher and Mallampati score of 4 were higher in AM+ patients, although these did not reach statistical significance in univariate analysis. All procedural and pharmacologic variables were similar between groups. To evaluate for independent predictors of AMs, we incorporated these variables into a logistic regression model with the exception of propofol infusion time. This was excluded because the total propofol dose was expressed on a per-minute basis (mg/kg/min). Male sex and BMI remained independent predictors of AMs. When controlling for other clinical and procedural characteristics, ASA class of 3 or higher was also an independent predictor of AMs.

Table 4. Univariate and Multivariate Analysis of Clinical Predictors of AMs

Variable	AM+ (n = 115)	AM− (n = 684)	Univariate P value	Multivariate P value	Adjusted OR (95% CI)
Patient characteristics
Age, y, mean ± SD	59.3±16.4	57.6±16.6	.33	.52
Male sex, %	58.3	44.6	.006	.02	1.75(1.08–2.85)
ASA class ≥3, %	67.8	59.2	.08	.02	1.90(1.11–3.25)
Mallampati et al17 score of 4, %	1.7	0.3	.10	.19
BMI, mg/kg2, mean ± SD	29.3±7.2	26.7±6.3	.0001	.009	1.05(1.01–1.09)
Procedural data
Endoscopy time, min	29.9±19.5	29.5±18.7	.85	.34
Prone position, %	33.0	38.0	.31	.49
No response to endoscopic intubation, %	86.1	88.9	.39	.76
Pharmacologic data
Combination propofol, %	67.8	60.0	.11	.82
Propofol infusion time, min, mean ± SD	34.9±19.5	34.3±18.7	.74	Not includeda
Total propofol dose, mg/kg/min, mean ± SD	0.18±0.14	0.19±0.11	.39	.95
Induction propofol dose, mg/kg, mean ± SD	1.70±0.96	1.81±1.07	.35	.82

NOTE. A total of 799 patients were included in the study.

CI, confidence interval; OR, odds ratio.

Combination propofol was used for induction in 488 of 799 (61.1%) patients. We compared procedural and pharmacologic data of patients who received combination propofol with those who received propofol alone for induction (Table 5). Although propofol infusion time and endoscopy time were similar in both groups, induction doses and total doses of propofol were significantly lower using propofol in combination with low-dose opiate and/or benzodiazepene. Aldrete scores at arrival to the recovery unit also were significantly higher in the combination group (8.9 ± 0.9) compared with the propofol-alone group (8.5 ± 0.7) (Mann–Whitney, P < .0001). The frequency of airway modifications and other sedation-related complications were similar in both groups (data not shown).

Table 5. Propofol Alone Versus Combination Propofol for Induction

Variable	Propofol alone (n = 311)	Combination propofol (n = 488)	P value
Propofol infusion time, min, mean ± SD	34.0±18.0	34.6±19.3	.67
Endoscopy time, min, mean ± SD	29.5±18.5	29.6±19.1	.99
No response to endoscopic intubation, %	86.6	89.6	.20
Induction propofol dose, mg/kg, mean ± SD	2.41±1.13	1.37±0.75	<.0001
Total propofol dose, mg/kg/min, mean ± SD	0.23±0.10	0.17±0.11	<.0001
Aldrete score in recovery, median (25%–75% interquartile range)	9 (8–9)	9 (8–10)	<.0001

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Discussion 

Propofol can be administered safely to patients undergoing advanced endoscopic procedures. In our series of 799 patients managed by CRNAs, we observed no major sedation-related complications, and our reported rates of hypoxemia (12.8%) and significant hypotension (0.5%) are comparable with published data.⁹, ¹⁰, ¹¹, ¹², ¹³, ¹⁴, ¹⁹, ²⁰ Our study population is uniquely complex, with 61% of patients having an ASA class of 3 or higher and endoscopy times of 30 ± 19 minutes.

We report the frequency of AMs associated with propofol use in endoscopy. Although this is a unique outcome variable, we believe the need to perform AMs highlights the importance of a trained professional who is solely responsible for maintenance of sedation and patient monitoring while using propofol. AMs were required in 14.4% of patients, higher than our rate of hypoxemia (12.8%). In some cases, AMs were performed to pre-empt the onset of hypoxemia when upper-airway obstruction, laryngospasm, or hypopnea/apnea were noted by the CRNA. Importantly, no patients in our series required bag-mask ventilation or endotracheal intubation.

With the major gastroenterology societies supporting gastroenterologist-supervised, nurse-administered propofol for sedation, it is paramount to identify which patients are at highest risk of developing sedation-related complications. Perhaps the highest-risk groups should be managed by professionals trained in advanced airway interventions whereas lower-risk populations can be managed safely by professionals with less-intensive airway training. In a regression model that included clinical, procedural, and pharmacologic variables, we identified male sex, increased BMI, and an ASA class of 3 or higher as independent predictors of needing one or more AMs. In a series of more than 9000 advanced endoscopic procedures, Wehrmann and Riphaus⁹ also identified ASA class of 3 or higher as an independent risk factor for complications, defined in their study as need for bag-mask ventilation, endotracheal intubation, or premature termination of the procedure. The investigators also found total propofol dose, history of alcohol use, and having an emergency endoscopy as independent factors. However, because propofol was reported as total milligram dose, longer endoscopy times and higher BMI are likely to be responsible for their observation. We controlled for these confounders by reporting propofol on a per-minute basis. However, BMI remained an independent predictor in our regression model.

Although deep sedation or greater may not be necessary for standard endoscopy, advanced procedures typically require greater patient cooperation for a longer duration.²¹ Despite numerous publications describing propofol use in endoscopy, there are limited data studying the targeted depth of sedation.²¹, ²² In our series, 87.2% of patients had no response to endoscopic intubation. Although this is a crude surrogate for monitoring sedation depth, these patients would meet criteria for deep sedation or greater at the onset of endoscopy. Although it is reasonable to consider endoscopic intubation as a painful stimulus, reaction to endoscopic intubation has not been classified within the ASA continuum. Quantitative measures of sedation depth during endoscopy are problematic, and there are conflicting data on the utility of bispectral index monitoring.²³, ²⁴, ²⁵ Based on intermittent clinical assessments, the Modified Observer's Assessment of Alertness/Sedation scale appears to be the best indicator of sedation depth.²⁶ Based on the Modified Observer's Assessment of Alertness/Sedation scale, many patients receiving meperidine/midazolam to achieve conscious sedation actually meet the criteria for deep sedation during standard and advanced procedures.²⁶, ²⁷ Similarly, patients receiving propofol who are targeted for deep sedation likely meet ASA criteria for deep sedation and potentially general anesthesia. Alteration in sedation depth during advanced endoscopic procedures is particularly important because they tend to be of longer duration with varying degrees of stimulation. Future studies should correlate sedation-related complications with the varying depth of sedation achieved using propofol. A quantitative measure such as the Modified Observer's Assessment of Alertness/Sedation instrument is preferred to the ASA classification because many patients sedated with propofol maintain normal ventilation and perfusion despite becoming unresponsive to noxious stimuli.

Our study had limitations. In our endoscopy unit, propofol is administered exclusively by CRNAs who have extensive experience in sedation for advanced endoscopic procedures. It is unclear if our safety data can be extrapolated to a comparable patient population that is managed using a nurse-administered propofol sedation protocol.² Although there are no randomized trials addressing this, Clarke et al⁸ reported comparable rates of sedation-related complications during standard endoscopic procedures when propofol was administered by a general practitioner or an anesthesiologist. In addition, our observation that males are at greater risk of airway complications may be as a result of unmeasured confounding variables such as tobacco and alcohol use, along with underlying medical comorbidities. Furthermore, although we did not identify a Mallampati et al¹⁷ score of 4 to be an independent predictor, this may be a type II statistical error because of the relatively low number of patients (n = 4) meeting this criteria in our study population.

Although propofol is undoubtedly an attractive sedative for endoscopic procedures, there continues to be debate regarding its safe use by nonanesthesiologists. It is clear that when propofol is administered by an experienced professional, the rate of sedation-related adverse events is low. Newer technologies such as computer-assisted personalized sedation are likely to standardize the use of propofol by nonanesthesiologists in endoscopy.²⁸, ²⁹, ³⁰ With increasing use of gastroenterologist-administered propofol for endoscopy, it is important to identify patients and procedures at highest risk of airway interventions and sedation-related complications. We have shown that increased BMI, an ASA score of 3 or higher, and males are at highest risk of needing AMs during advanced endoscopy. Future studies are likely to identify additional clinical predictors that may impact the choice of sedatives and level of airway training required to safely administer propofol.

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