NPPE: Anesthesia's Overlooked Complication

Anesthesia

By: Gary Kantor

Published: 10/10/2007

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How to avoid negative-pressure pulmonary edema.


Negative-pressure pulmonary edema is a potential complication of general anesthesia in any patient, in any setting. However, a particular predilection exists for young, athletic, healthy males - exactly the type of patient considered the ideal candidate for outpatient surgery.

NPPE is a form of noncardiogenic pulmonary edema in which a large, negative intrathoracic pressure generated against an obstructed upper airway results in the shift of fluid into the interstitium of the lungs. The phenomenon can occur in otherwise healthy patients who have brief periods of airway obstruction and usually manifests during emergence from general anesthesia. I believe it's often unrecognized or misdiagnosed; many cases of mild hypoxemia in PACU may actually be mild instances of NPPE. The following cases occurred over a five-year period in a large academic medical center's ambulatory surgical unit. Thanks to prompt diagnosis and effective care, no patients suffered permanent harm as a result of their brushes with NPPE.

  • Case 1. A healthy 25-year-old female had a laparoscopic tubal ligation under general anesthesia. The patient developed laryngospasm after extubation and rapidly became hypoxemic (SpO2 76%). The trachea was reintubated, facilitated with succinylcholine 20mg. Pinkish frothy secretions were suctioned from the endotracheal tube. The patient was sedated and transferred to PACU where she was treated with furosemide and positive pressure ventilation before she was eventually extubated four hours later.
  • Case 2. A healthy 33-year-old male underwent tonsillectomy and pressure equalization tube insertion under general anesthesia. Upon extubation the patient developed laryngospasm, which did not resolve with positive airway pressure. He was given succinylcholine 40mg. Pink frothy sputum was noted at the mouth and the trachea was then intubated. Bilateral rales could be heard on auscultation. Furosemide was given and a Foley catheter placed. A chest X-ray revealed pulmonary edema. The patient was sedated with propofol, transferred to PACU and eventually to the ICU.
  • Case 3. A healthy 28-year-old female had an abdominal myomectomy under general anesthesia. The patient awoke and was extubated at the end of the procedure. During transfer to the cart, the patient developed airway obstruction and became hypoxic. She was given succinylcholine and re-intubated. About 50ml of fluid was suctioned from the tube. The care team noted that 100% O2 was required to maintain SpO2 percentage in the 90s. The patient was given furosemide 5mg IV and transferred to the surgical ICU.
  • Case 4. A relatively healthy middle-aged patient had an uneventful two-hour hand operation under general anesthesia. In PACU, bilateral lung crackles were noted and a chest X-ray revealed a picture compatible with pulmonary edema. The team observed that the patient briefly "fought" the endotracheal tube during emergence.
  • Case 5. A 41-year-old with sleep apnea (treated at home with continuous positive airway pressure) and obesity successfully underwent uvulopalatopharyngoplasty. At the termination of the procedure the patient was extubated but appeared to have airway obstruction. Succinylcholine was administered, followed by the placement of a #4 laryngeal mask airway. Bloody drainage was noted in the throat. Due to lack of improvement, a 8.0mm endotracheal tube was placed. A chest X-ray taken in PACU showed pulmonary edema; the patient was extubated the following morning with no sequelae observed.

A Team Approach to Improved Care

Staff at the Center for Clinical Excellence at the University Hospitals and Health System in Cleveland, Ohio, are focused on reducing the occurrence of patient complications inside and outside the OR. "Our job involves the surveillance of case outcomes to identify trends," says Randy Harmatz, MBA, the center's vice president. "Our staff tries to understand what we're seeing in order to determine if a process in patient care needs to change."

That understanding is aided by the clinical experience of the dedicated members of the Center for Clinical Excellence. The program combines the efforts of the risk and quality review teams, comprised of eight full-time nurses with years of bedside experience and Certified Professional in Healthcare Quality credentials. Ms. Harmatz says many of the team members were advanced practice nurses looking for additional challenges. They now work on improving the quality of the system's care on a full-time basis.

Even more important than the nurses' clinical experience is their ability to facilitate large groups of strong personalities and work to turn tension-filled meetings into productive agreements. "The discussions can get a bit contentious," says Ms. Harmatz. "We need someone who understands the emotions of the situation and the realities of patient care, especially when dealing with physicians who can be forthright with their feelings."

When case surveillance reveals a complication, representatives from the Center for Clinical Excellence huddle with surgery leadership for an in-depth analysis of current protocols and future action plans. The atmosphere is one of frank communication and non-punitive discussions. The group reviews the patient's medical record, including a careful examination of the discharge summary, the surgeon's notes, relevant test results and communication occurring between providers. An interview of the care team follows, leading to the creation of a case timeline.

"We determine if there is an opportunity for improvement or if the complication was the result of normal patient care," says Ms. Harmatz. "The process creates the discipline of determining the root cause of a complication."

- Daniel Cook

Risks and origins
Rather dramtically, even a very brief period of obstruction can produce NPPE; a breath or two against the obstructed airway can apparently result in the the complication. Case reports exist that document NPPE after endotracheal tube obstruction and obstruction of an LMA. Risk factors for NPPE include obesity, obstructive sleep apnea and relatively young age. Preventive measures center on avoidance or prompt resolution of any form of airway obstruction. Standard, vigilant anesthetic care with meticulous monitoring and reversal of muscle relaxants, as well as selective insertion of oropharyngeal airways during induction or emergence, may help prevent NPPE.

The main danger period is during emergence and extubation. Problems must be rapidly recognized. Promptly secure the airway and secure and restore oxygenation - usually with an endotracheal tube. Resolution occurs over several hours with positive end-expiratory pressure and the occasional administration of diuretics.

Signs and symptoms of NPPE include tachypnea, shortness of breath, pulmonary crackles, frothy sputum production and decreased oxygen saturation, occurring very soon after an episode of upper airway obstruction. Chest radiographs may show pulmonary edema. The differential diagnosis includes aspiration of gastric contents, fluid overload and other forms of cardiogenic edema and various forms of acute lung injury.

Learning, case by case
Thanks to our internal examination process, our staff has become very familiar with NPPE, so we feel the scrutiny is essential and worthwhile. For many years we have reviewed all cases of anesthetic-related morbidity in our facility, from relatively common, minor morbidity (phlebitis and corneal abrasions, dental injuries) to medication errors and serious neurologic, cardiac or pulmonary complications.

Our department's peer review committee examines all cases involving complications (see "A Team Approach to Improved Care" on page 51). The responsible anesthesiologist submits a report to our departmental chairman as soon as possible after the event occurs. We also present most cases to departmental rounds. The purpose of this process is, simply, a way to better educate ourselves and improve patient care.

Recognize NPPE to Avoid Hospital Admission

Early diagnosis and treatment of negative-pressure pulmonary edema is imperative in the ambulatory surgery setting. As this case illustrates, expeditious treatment can result in patients meeting discharge criteria while delayed treatment can result in an unanticipated hospital admission.

' The case. An 18-year-old high school basketball player, ASA Physical Status I, was scheduled for repair of a nasal fracture under general anesthesia. Pre-operatively, the patient received oxymetazoline nasal spray, midazolam and fentanyl. The patient was induced with propofol, rocuronium and succinylcholine. He was intubated uneventfully. General anesthesia was maintained with desflurane and a N2O/O2 mixture. Dexamethasone and ondansetron (Zofran) were given as antiemetics. Morphine sulfate was used for analgesia.

The operation lasted 60 minutes and the anesthesiologist gave the patient 750ml of lactated Ringer's intravenously. At completion of surgery, blood-tinged secretions were suctioned from the oropharynx. An orogastric tube was suctioned and the muscle relaxant was reversed.

At extubation, the patient developed laryngospasm with pulse oximetry (SpO2) dropping briefly below 80 percent despite vigorous bag-valve mask positive pressure ventilation with an oral airway in place. The patient was given a small dose of succinylcholine, which quickly resolved the laryngospasm. SpO2 rose to 94% on 10L O2 facemask.

Within 10 minutes in recovery, the patient complained of dyspnea. He was anxious, but consolable. He began coughing modest amounts of blood tinged with frothy pink sputum. His blood pressure was 150/102, heart rate was 121, respiratory rate was 28 and SpO2 88% on 10L O2 facemask. Chest auscultation revealed diffuse rhonchi, crackles and mild wheezing bilaterally. Oropharyngeal exam was negative for trauma. Portable chest X-ray revealed bilateral diffuse pulmonary edema. The care team made a diagnosis of NPPE secondary to laryngospasm.

' The treatment. The patient was placed on 100% non-rebreathing facemask. He was given furosemide intravenously to promote prompt diuresis. Morphine sulfate, which also has venodilating properties, was titrated for analgesia. Intravenous fluids were set to TKO rate and a Foley catheter was placed. Albuterol unit dose nebulization was given. Blood pressure was 148/98, heart rate was 105, respiratory rate was 22 and SpO2 92% on 100% non-rebreathing facemask.

The patient's condition quickly improved with brisk diuresis and oxygen therapy. His vital signs returned to baseline and he met discharge criteria about four hours after entering the recovery room.

' The causes. NPPE is a form of non-cardiogenic pulmonary edema occurring when a patient makes a vigorous attempt to breath against a partially or completely occluded upper airway. This can occur in patients who present with laryngospasm or who bite down on their endotracheal tube or laryngeal mask airway. The complication has also been described secondary to foreign body obstruction, large tonsillar mass, epiglottitis and even hiccups.

High negative intrapleural pressures generated during inspiration against a closed glottis or an obstructed airway can cause fluid extravasation from the pulmonary capillaries into the interstitial and alveolar spaces. NPPE can develop immediately or up to six hours later. Differential diagnoses include fluid overload, myocardial infarction, pulmonary edema and adverse drug reactions.

Treatment involves early recognition of NPPE, which can be life threatening. The first treatment priority is to relieve the airway obstruction and correct the resultant hypoxemia. In the case of laryngospasm, this may require a small dose of succinylcholine if the laryngospasm cannot be overcome with positive pressure ventilation. Oral secretions can trigger laryngospasm and an antisialogogue, such as glycopyrrolate, can be useful if given early enough.

- Steve Luck, MD, MS

Dr. Luck ("[email protected]")) is a partner at Ambulatory Anesthesia Associates in Alexandria, Va.

We examine the processes of care and institute interventions, where appropriate, to change practices and protocols that have failed to produce an optimal outcome. Changes might affect medication administration systems, anesthetic equipment, communication and teamwork problems or technical and knowledge deficits. The culture we have developed is non-punitive. We take advantage of the protection offered by local and federal statutes to have frank discussions in a closed setting, but we also support the practice of full disclosure of significant events to the patient.

We experience about two incidences of NPPE each year. Set against our annual caseload of about 25,000, the occurrence is rare. While I cannot definitively determine if our review processes and subsequent education of nurse and physician groups have had an impact on incidence, I believe our recognition and care of this particular complication has improved. We have never seen long-term morbidity from NPPE. And armed with the knowledge culled from our case reviews, our staff hopes to prevent the complication or treat it early and effectively when it does occur.

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