Safety Questions and Answers
Questions and answers to pressing safety topics that you can discuss with your colleagues.
“Can a PAC be inserted safely in patients with pre-existing left bundle branch block (LBBB)?”
Yes, but additional measures to insure a stable cardiac rhythm are necessary. During passage of the PAC, a temporary right bundle branch block is often induced as the catheter impacts the interventricular septum. Thus, in a patient with a pre-existing LBBB, cardiac asystole may occur. The risk of asystole in this setting is probably in the range of 1 – 2%. Therefore, during insertion of the PAC in these patients, an alternative mechanism to pace the heart must be immediately available. This could include an internal temporary endocardial pacing wire, epicardial pacing wires, or placement of transcutaneous pacing patches (Zoll? transcutaneous pacemakers).
“What dangers are associated with outpatient liposuction procedures?”
Liposuction is now the most frequently performed cosmetic surgical procedure in the United States, utilizing both general anesthesia and MAC. The most common operative technique today is called tumescent liposuction, where large volumes of saline, epinephrine, and lidocaine are infused into the subcutaneous fat, augmenting subsequent aspiration via operative cannulas. While the content of the infusate varies, it typically contains 500 – 1,000 mg of lidocaine, and 0.25 – 1.0 mg epinephrine, per liter of saline. Several case reports have noted patient deaths as a result of unheralded, and precipitous intraoperative hypotension and bradycardia. Two patient who arrested intraoperatively had received total lidocaine doses of 10 and 14.3 mg/kg, with blood lidocaine concentrations of 5.2 and 2.0 mg/liter (determined at autopsy). Other problems associated with this procedure may include: peripheral nerve injury; local infection and sepsis; overhydration, leading to pulmonary edema and respiratory distress; congestive heart failure; pulmonary embolism; fat embolization; and marked hemorrhage leading to severe anemia.
“What risks are associated with mild hypothermia of patients in the perioperative period?”
There are three major perioperative adverse outcomes associated with a core temperature of < 35.0 to 35.5 degrees C. These include increased risk of wound infection, increased bleeding, and cardiac complications, especially in elderly or other vulnerable patients. One study found a three-fold increase in the incidence of postoperative wound infections in patients who develop hypothermia during colon resection, despite antibiotics in all cases. It is theorized these wound infections are due to decreased tissue oxygenation secondary to thermoregulatory vasoconstriction. Hypothermic patients having hip surgery had a 20% increase in intraoperative and postoperative bleeding. Lastly, this degree of hypothermia increases the duration of the PACU stay, and the thermal discomfort experienced by patients. Thus, this issue also has economic and quality of care ramifications as well.
“What factors should you consider in deciding whether to attempt oral intubation or request a immediate surgical airway when presented with a patient with massive facial trauma from a motor vehicle crash?”
Factors to consider include hemodynamic stability of the patient, immediate airway patency, mental status, rate of blood loss, severity of facial injury, expertise of anesthesia and surgical/ER personnel, the most likely next step in the management of the patient, etc.
“How would you transfer a patient from the ICU to the OR for a emergent procedure when that patient has ARDS and is on pressure control ventilation with a pressure limit of 36, with an FIO2 of 0.6, and 15 cm of PEEP?”
This is dependent on transfer ventilator equipment available in individual hospitals. The need to maintain the complex regimen and not just “go quickly” is key to the response.
“What circumstances would cause discrepant readings between the pulse oximeter hemoglobin saturation value and those measured by a laboratory cooximeter?”
This would most likely happen in situations where there are greater than the usual (insignificant) amounts of carboxyhemoglobin (CO-Hb) or methemoglobin (MetHb). The pulse oximeter reading (called the functional saturation) will be falsely elevated compared to a laboratory cooximeter measurement of Hb saturation (called functional saturation). Why? The oximeter measures the percentage of 02Hb and reduced Hb using the relative absorption of only two wavelengths of light. Other hemoglobin types, such as carboxyhemoglobin and methemoglobin are not measured by this method. Conversely, laboratory cooximeters measure 02Hb, reduced Hb, CO-Hb, and MetHb by using at least four wavelengths of light. As a theoretical example, if a patient has 15 gm Hgb, of which 11gm are 02Hb, 3 gm are CO-Hb, 1 gm is reduced Hb, the pulse oximeter reading(fractional saturation) will be the following: 02Hb/02Hb+ reduced Hb, 11/11 + 1 or 11/12, 92% but the Cooximeter (functional saturation) reading will be: 02Hb/02 Hb + reduced Hb + CO-Hb or 11/ 11 + 3 + 1 or 11/15, 73%.
“How is temperature monitoring different in the neonate compared to the adult?”
Temperature regulation in the newborn is difficult for a variety of reasons. Neonates have a large surfacearea to body weight ratio, less subcutaneous fat and minimal ability to shiver. Rectal temperature probes provide a reasonable measure of core temperature, but placement of the well lubricated probe should be done carefully since rectal perforation is a risk of using this site. Leak of inspired gases around endotracheal tubes may cool probes placed into the nasopharynx, resulting in inaccurate readings from nasopharyngeal probes. Tympanic measurement has been advocated as a measure of central temperature but it is uncertain whether or not tympanic temperature reflects central temperature and there have been reports of tympanic membrane perforation. Esophageal probes will accurately reflect aortic root temperature if placed into the distal third of the esophagus.
“Is it safe to place a lumber epidural catheter in a 6 year old child after the induction of general anesthesia?”
Placement of lumbar epidural catheters in children is regularly done after anesthesia, because placement in an anxious, uncooperative child is not only painful and frightening but also exposes the child to excessive risk. However, correct placement of the catheter can be ascertained only through indirect means. Test doses are still done in the usual fashion, while recognizing the limitations. Numerous investigator have shown that IV administration of the doses of epinephrine used in epidural test doses lead to inconsistent increases in heart rate in the anesthetized child. In studies which followed blood pressure increase and T wave changes following IV injection of an epinephrine dose equal to that used in epidural test doses, the results have also been inconsistent. Certainly if the vital signs do change intravascular placement should be assumed and the catheter replaced or the technique abandoned. In cases where inadvertent intrathecal placement has occurred, in young children administration of a test dose with a local anesthetic will not lead to a significant lowering of blood pressure. Slight lowering of blood pressure after intrathecal administration of local anesthetics is seen in children older then 7 years of age. Teenagers exhibit the degree of hypotension similar to that seen in adults. Obtaining an Xray (epidurogram) after injection of a small amount of contrast into the catheter may be used to confirm correct placement. In cases where the epidural is crucial for intra and post operative care, fluoroscopy may be used during placement to confirm correct position of the catheter.
“How do the types of anesthesia errors differs between children and adults?”
According to the American Society of Anesthesiologists Closed Claims Data Base, a comparison of adult and pediatric closed claims indicates a large prevalence of airwayrelated damaging events, most frequently related to inadequate ventilation, occurring in children. In particular, respiratory events were more common among pediatric patients (43% in children versus 30% in adult claims). In the opinion of the reviewers, 89% of the pediatric claims related to inadequate ventilation could have been prevented with pulse oximetry and/or end tidal CO2 measurement. However, pulse oximetry appeared to prevent poor outcome in only one of seven claims in which pulse oximetry was used and could possibly have done so. Moreover, in pediatric (compared with adult inadequate ventilation claims), poor medical condition and/or obesity (6% versus 41%; P < or = 0.01) were uncommon factors.
“What types of nerve injuries occur most commonly and what factors are associated with them?”
Again, according to the American Society of Anesthesiologists Closed Claims Data Base, 16% of claims are for anesthesiarelated nerve injury. The most frequent sites of injury are the ulnar nerve (28%), brachial plexus (20%), lumbosacral nerve root (16%), and spinal cord (13%). Ulnar nerve (85%) injuries are more likely to have occurred in association with general anesthesia, whereas spinal cord (58%) and lumbosacral nerve root (92%) injuries were more likely to occur with regional techniques. Ulnar nerve injury occur predominately in men (75%) and are also more apt to have a delayed onset of symptoms (62%) than other nerve injuries. Spinal cord injuries are the leading cause of claims for nerve injury that occurred in the 1990s. Advanced age, thinness, obesity and the presence of diabetes increase the incidence of perioperative neuropathy. The length of anesthesia or the intraoperative positioning do not correlate with the incidence of this neuropathy but the length of the hospital stay does. Bilateral neuropathy has been reported in 9% of patients. Interestingly, asymptomatic ulnar neuropathy as indicated by nerve conduction studies has been found to be present in the contralateral extremity in almost all patients who suffered from postoperative ulnar neuropathy.
Neuropathy can develop in patients who received local anesthesia or light sedation and can occur during hospitalization without surgery. This suggests mechanisms of nerve compression and stretching may occur outside the operating room. Remember that the findings of the Closed Claims analysis may differ from those experienced in everyday clinical practice since this database includes only closed (“settled”) law suits.
“Can succinylcholine be safely used in children?”
Yes, however children with myopathic conditions may be susceptible to both malignant hyperthermia and catastrophic hyperkalemia when given succinylcholine. Young children, particularly males under the age of 8, may present with undiagnosed myopathies, such as Duchenne Muscular Dystrophy. Dangerous hyperkalemia can occur and present with sudden onset of life threatening arrhythmias. If this happens after the administration of succinylcholine, hyperkalemia should be strongly suspected. The immediate treatment of life threatening hyperkalemia is the administration of intravenous calcium chloride or calcium gluconate. Calcium is an electrophysiologic antagonist of hyperkalemia and should be the first line treatment. Subsequent administration of glucose, insulin and sodium bicarbonate should also be strongly considered, to facilitate the movement of potassium to the intracellular space. Life threatening hyperkalemia can also occur when in patients who have sustained upper motor neuron lesions, burns, trauma, crush injuries, sustained period of bedrest or immobility, sepsis, stroke, spinal cord injury and progressive degenerative neurological states such as amyotrophic lateral sclerosis.
“What is the appropriate endpoint for reversal of neuromuscular blockade?”
A train-of-four (TOF) ratio of 0.60 correlates with a vital capacity of 55 ml/kg, a negative inspiratory force of 70 cm H2O, and a peak expiratory flow of 95% control values. This degree of recovery allows most patients to cough adequately and maintain a patent airway. Double burst stimulation (DBS) of the ulnar nerve detects 40% fade between the first and the second response, thereby improving the clinician’s ability to detect more subtle degrees of residual neuromuscular block.
The clinical implications of residual neuromuscular block are important. Precurarization decreases the TOF ratio to as low as 0.63, may cause difficulty breathing and swallowing, and decreases inspiratory force and peak expiratory flow rate. Even a decrease in the TOF ratio to 0.85 is associated with general discomfort, malaise, ptosis and blurred vision.Other more recent studies with volunteers have shown that TOF ratios of 0.6 to 0.7 are associated with decreased upper esophageal tone and a decrease in the coordination of the esophageal musculature during swallowing. Fluoroscopic study of these individuals while swallowing demonstrated significant pharyngeal dysfunction resulting in misdirected swallowing, leading to a four to five-fold increase in the risk of aspiration. A TOF recovery = 0.90 is required to return esophageal tone and pharyngeal coordination to baseline. NMB drugs also interfere with hypoxic ventilatory control. In vitro, while application of acetylcholine to the carotid body results in hyperventilation, application of anticholinergics eliminated the increase in neuronal activity of the carotid body sinus nerve that otherwise occurs with hypoxia. In awake volunteers who have received atracurium, vecuronium or pancuronium, with a train-of-four ratio of 0.70, the hypoxic ventilatory drive is reduced by 30%.
“Does residual neuromuscular weakness affect clinical outcomes?”
A recent prospective, randomized, blinded study indicates that residual neuromuscular block after administration of pancuronium is associated with an increased incidence of postoperative pulmonary complications. Thus, an optimal level of neuromuscular recovery may be TOF ratio of > 0.90. Only with this degree of recovery do patients manifest normal swallowing, fully protect their airways, and resume normal respiratory function. It may require this more robust level of neuromuscular recovery to minimize the postoperative risk of aspiration and pneumonia.