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Residual Anesthesia: Tepid Burn

Matt M. Kurrek, MD, and Rebecca S. Twersky, MD, MPH | August 1, 2012
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The Case

A 42-year-old Filipino man presented to an outpatient surgery center for scheduled repair of an anal fistula. The patient received pre-procedure anesthesia with a "saddle block" and underwent a successful intervention. When his anesthesia block began to wear off, he was deemed safe for discharge and instructed to take sitz baths with tepid water.

One month later, the patient returned for a second evaluation under anesthesia, and the surgeon noted scarring on the patient's buttocks and proximal posterior thighs. There were also large areas of healed burns and associated skin changes. Additional history from the patient and his wife indicated that they misunderstood the term "tepid" and used scalding hot water for the sitz baths. It also appears the patient's slowly resolving saddle anesthesia in the first 24 hours home blunted his response to the hot water. Unfortunately, the patient did not seek additional medical attention. It was felt that challenges with both health literacy and language barriers contributed to the patient's failed understanding of discharge instructions.

The Commentary

Ambulatory-based surgical procedures have grown significantly over the past decade as many interventions traditionally performed in the hospital setting have shifted to freestanding surgical centers and offices.(1) The key factors contributing to this trend are advances in minimally invasive surgery and newer anesthesia techniques. The case presented highlights how a seemingly low-risk procedure can lead to unintended patient harm due to residual anesthesia. To understand the elements of this case, it's important to review the approach to anesthesia in the ambulatory setting, the patient recovery and discharge process, and the critical patient education and follow-up strategies to assure a safe outcome.

Approach to Anesthesia in Ambulatory Surgery

Anesthesia for ambulatory surgery focuses on (i) rapid emergence and awakening, (ii) prevention of nausea and vomiting (PONV), and (iii) control of early postoperative pain. Problems in these three areas are among the most common reasons for delayed discharge or unplanned admission.(2) The choice of anesthetic depends on the type of surgery, patient preference, and careful assessment and evaluation by the anesthesiologist. All outpatient surgery centers should be equipped to deliver general, regional, peripheral nerve blocks, intravenous (IV) sedation, or local anesthesia. This also allows necessary safeguards in case a patient requires a change in the anesthetic plan during the procedure. We'll provide a brief discussion of the most commonly used anesthesia options and their tradeoffs in the ambulatory setting.

When traditional general anesthesia is chosen, providers typically employ total IV anesthesia, using ultrashort-acting anesthetic agents by continuous infusion, and combine it with the prophylactic use of antiemetic agents to promote rapid recovery and adequate control of PONV. Postoperative pain is often controlled pre-emptively with a combination of agents administered before the end of surgery along with generous use of local anesthesia or nerve blocks. This multimodal strategy helps to limit each individual agent's undesirable adverse effects and allow early discharge in the ambulatory setting. However, the risks associated with general anesthesia are similar to those in the hospital setting.

In recent years, regional anesthesia use has grown in ambulatory surgery, a key contributing factor to the increased safety and volume of ambulatory-based procedures overall. The liberal use of local anesthetics for nerve blocks minimizes the use of other anesthetic agents, so that the patient wakes up faster and has less PONV. Additionally, regional anesthesia provides excellent control of early postoperative pain, and patients require less systemic analgesics.(3) This makes it a particularly popular approach for procedures on limbs and those involving the perineum.

In the case presented, the type of regional anesthesia used was a saddle block, which anesthetizes the sacral nerve roots supplying the inner thighs and perineum. When properly performed, a saddle block leads to minimal or no motor changes in the legs. A saddle block is also easy to perform, leaves the patient fully alert, and may decrease the turnaround times between cases, especially if a separate area is available outside the procedure area to place the block. These advantages need to be balanced against possible adverse effects, such as a spinal headache or urinary retention. Regional anesthesia can also be associated with unintentional injury involving a body part left with decreased muscular strength and/or rendered insensitive to pain, such as the patient in this case. Patients are often discharged with at least some part of the regional block still working to maximize postoperative pain control, yet they are no longer under the direct supervision of the health care provider. This is a challenging issue in ambulatory surgery, particularly in counseling patients and preparing them for discharge.

Patient Consent & Counseling

Preoperatively, anesthesia providers must obtain informed consent, which includes explicit discussion of anesthetic options and their risks and benefits.(4) The discussion should not be limited to the most severe risks, and special consideration should be given to the anesthetic technique used. Traditionally, the consent process for hospital-based interventions focuses on discussion of potential intraoperative events; however, since the patient's rapid recovery and discharge after ambulatory surgery plays such a crucial role, detailed counseling about expectations for recovery and discharge should be an equal focus. For example, in cases involving regional anesthesia techniques, the discussion should include the implications of residual neurologic deficits if the patient will be discharged before the block has completely worn off.

Patient Recovery & Discharge Process

Recovery is a continuous process that starts with the end of the surgical intervention and lasts until the patient has returned to his or her normal state. It is divided into three phases: (i) the earliest and most acute phase, in which the patient may not yet have regained all his/her protective reflexes; (ii) the intermediate phase, in which the patient continues recovery until ready for discharge; and (iii) the late and final recovery, in which the patient returns to his/her preoperative state. Following ambulatory surgery, patients are expected to leave the facility shortly after the intervention and thus need to be formally assessed for discharge readiness. The Post Anesthesia Discharge Score (PADS) is commonly used to assess "street fitness" after ambulatory surgery and includes specific assessment of nausea/vomiting, surgical bleeding, and pain control (Table 1).(5,6) Such discharge scoring tools tend to emphasize recovery elements following general anesthesia rather than local/regional anesthesia, leaving individual facilities to establish their own policies and procedures for the latter. Nevertheless, the principles are similar and focused on preventing unsafe discharges or unintended hospitalizations. For instance, with spinal anesthesia, the patient must be able to ambulate, and sufficient regression of motor, sensory, and sympathetic block must be demonstrated. After saddle blocks, patients have little or no motor weakness in the lower extremities, which means that the patient's cutaneous sensation in the perineum should be assessed and regression documented to avoid premature discharge with excessive anesthesia. An example of a "spinal add-on module" to the PADS is shown in Table 2; all criteria in the module must be met in addition to a PADS score of at least 9 points before discharging the patient home after spinal anesthesia. It is not clear whether the patient in this case had such an assessment or what communication occurred at the time of discharge that might have raised appropriate concerns.

Patient Education & Follow-up

Regardless of the anesthesia technique and the discharge criteria used, the patient must receive detailed postoperative instructions for routine and emergency follow-up. If a patient is discharged with residual effects following regional anesthesia, instructions must include a detailed briefing of the precautions to be taken. They should include that patients without full motor strength or cutaneous sensation must avoid driving and placing hot pads or applying excessive cold to areas with residual anesthesia. Once the numbness subsides, analgesic medication will need to be started. The onus to ensure that the patient has understood the instructions rests with the health care provider, especially when patients present with language barriers or limitations in health literacy, such as in this case.

Even though a personal follow-up within the first 24 hours may not be required in every case, special follow-up arrangements after local/regional anesthesia should be considered. Such follow-up would allow monitoring of compliance with postoperative instructions to prevent unintended injury, as in this case, and alert the health care provider to unexpected post-operative neurologic symptoms, ranging from minor neuropathies to more severe complications.(7) The follow-up should focus on early signs of possible infection, especially following continuous infusions via indwelling catheters.(8)

In summary, the addition of local/regional anesthesia represents an important tool for ambulatory anesthesia, facilitating early discharge with good pain control. It is, however, not without risk and may not be the right choice for every patient or setting. In this particular case, a saddle block may not have been the ideal choice, given the patient's lack of health literacy and difficulties in communication, coupled with a lack of timely follow-up. Appropriate policies and procedures should assist facilities in ensuring patient safety.

Take-Home Points

  • Consider the use of local/regional anesthesia as a valuable adjunct to other anesthetic techniques for ambulatory anesthesia, where appropriate.
  • When planning for the anesthesia, consider the impact of various factors including the patient's health literacy, ability and availability to communicate after discharge, compliance, and availability for follow-up.
  • Whenever regional anesthesia is used, inform patients about the possibility of decreased cutaneous sensation and motor strength and educate patients about the need for certain precautions to prevent unintentional injury or falls.
  • Consider a special follow-up protocol for patients receiving local/regional anesthesia who are discharged with residual neurologic deficits.

Matt M. Kurrek, MD Associate Professor Department of Anesthesia University of Toronto

Rebecca S. Twersky, MD, MPH Professor, Vice-Chair for Research Department of Anesthesiology Medical Director, Ambulatory Surgery Unit SUNY Downstate Medical Center


1. Kurrek MM, Twersky RS. Office-based anesthesia. Can J Anaesth. 2010;57:256-272. [go to PubMed]

2. Chung F, Mezei G. Adverse outcomes in ambulatory anesthesia. Can J Anaesth. 1999;46(5Pt2):R18-R34. [go to PubMed]

3. Mulroy MF, McDonald SB. Regional anesthesia for outpatient surgery. Anesthesiol Clin North America. 2003;21:289-303. [go to PubMed]

4. Paterick TJ, Carson GV, Allen MC, Paterick TE. Medical informed consent: general considerations for physicians. Mayo Clin Proc. 2008;83:313-319. [go to PubMed]

5. Aldrete JA. The post-anesthesia recovery score revisited. J Clin Anesth. 1995;7:89-91. [go to PubMed]

6. Awad IT, Chung F. Factors affecting recovery and discharge following ambulatory surgery. Can J Anaesth. 2006;53:858-872. [go to PubMed]

7. Brull R, McCartney CJ, Chan VW, El-Beheiry H. Neurological complications after regional anesthesia: contemporary estimates of risk. Anesth Analg. 2007;104:965-974. [go to PubMed]

8. Capdevila X, Bringuier S, Borgeat A. Infectious risk of continuous peripheral nerve blocks. Anesthesiology. 2009;110:182-188. [go to PubMed]


Table 1. The Post Anesthesia Discharge Score (PADS) is used to assess fitness for discharge home.(7)

Post Anesthesia Discharge Score
Vital signs
  • Within 20% of preoperative baseline
  • 20% to 40% of preoperative baseline
  • 40% of preoperative baseline
Activity level
  • Steady gait, no dizziness, consistent with preoperative level
  • Requires assistance
  • Unable to ambulate / assess
Nausea and vomiting
  • Minimal: mild, no treatment needed
  • Moderate: treatment effective
  • Severe: treatment not effective
  • VAS = 0 to 3 the patient has minimal or no pain prior to discharge
  • VAS = 4 to 6 the patient has moderate pain
  • VAS = 7 to 10 the patient has severe pain
Surgical bleeding
  • Minimal: does not require dressing change
  • Moderate: required up to two dressing changes with no further bleeding
  • Severe: required three or more dressing changes and continues bleed

VAS = visual analogue scale. Maximum score = 10; patients scoring ≥ 9 are fit for discharge.

Table 2. Post Anesthesia Discharge Score "add-on module" for patients after spinal anesthesia.

Spinal Anesthesia Add-on Module
  1. Patients should have sensory block at dermatome level of T8 or below and sensory dermatome should recede by at least one level
  1. Patients should have NO pain, PONV, and shivering
  1. Patients admitted to PACU with a sensory block at dermatome T10 or below, with some movement of the lower extremity, may be discharged from PACU if above factors are satisfactory
  1. Patient has voided
  1. Resolution of sympathetic blockade (i.e., orthostasis)

Patients scoring ≥ 9 on PADS and 5 "yes" marks on spinal anesthesia module are fit for discharge. (Adapted with permission from Sunnybrook Health Science Centre, University of Toronto, courtesy of Drs. Awad and Belo).

This project was funded under contract number 75Q80119C00004 from the Agency for Healthcare Research and Quality (AHRQ), U.S. Department of Health and Human Services. The authors are solely responsible for this report’s contents, findings, and conclusions, which do not necessarily represent the views of AHRQ. Readers should not interpret any statement in this report as an official position of AHRQ or of the U.S. Department of Health and Human Services. None of the authors has any affiliation or financial involvement that conflicts with the material presented in this report. View AHRQ Disclaimers
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