Topic:  Hypercapnea Under Anesthesia in a MHS Patient

An elderly, ~80 y/o, lean, (65 in, 40 kg) woman is undergoing laparoscopic hemicoloectomy for cancer.  She has experienced a full blown MH episode in the past shortly after the anesthesiolgist noted a marked rise in end tidal CO2.  During the procedure which is conducted with sevoflurane in oxygen anesthetic, following a propofol/vecuronium induction and intubation sequence.  The patient is placed in steep tredelenberg position. The surgeon experienced difficulty in visualization and dissection and after about 90 minutes, end tidal CO2 rose from the mid-30s to 80 torr range over 30 minutes.  There was no fever, tachycardia, rigidity, diaphoresis, skin mottling or arrhythmia. Urine test was negative for blood. An ABG demonstrated primary respiratory acidosis even though minute vent was greater than 2.5 predicted. 

1.      Should this patient be given dantrolene?

a.       Yes

b.      No

2.      Would you abort the operation?

a.       Yes

b.      No

3.      If the blood pressure and Oxygenation are within expected values, how should the patient be monitored?

a.             Arterial line only

b.            Central venous line only

c.             Pulmonary artery catheter and arterial line

d.             None of the above

Answers

1.)     NO - Although the patient is at increased risk for MH, by history, there is no evidence of hypermetabolism and the problem appears to be largely respiratory. Dantrolene does not help manage respiratory acidosis/hypercapnea unless it is associated with increased muscle activity and hypermetabolism.

2.)     While repeat evaluation of the patient's acid-base status, vital signs, and other suggestive signs and symptoms should continue, it is most appropriate to examine all causes of hypercapnea since this appears to be isolated respiratory academia. That should include the ventilatory circuit and tracheal tube/cuff seal. What are peak airway pressures? Is there an unexpected pneumothorax? Other sources for lost ventilation should also be examined but, when ventilator or equipment malfunction is ruled out, the clinician should also look for signs of increased CO2 production. During laparoscopic surgery and CO2 insufflation of the abdomen, gas uptake typically requires an increased minute ventilation. A marked increase in CO2 suggests that something unusual is taking place. How high are abdominal insufflation pressures? Is there evidence of gas dissection from the abdomen to other tissue compartments?

3.)     This important cancer operation can be continued so long as the patient tolerates abnormal effects of pneumoperitoneum, both ventilatory and circulatory, and there's no evidence of MH or critical problems.

4.)     Continue to monitor the patient's cardiorespiratory and metabolic status throughout the case and for at least an hours' stability afterwards. At the first suggestion of hypermetabolism, with mixed respiratory and metabolic acidosis, treat as if MH. Monitor urine for myoglobin and CKs. If an unexpected or remarkable metabolic process proves to be the culprit in causing this patients' hypercapnea, an Adverse Metabolic Reaction to Anesthesia form should be completed and information placed in the MH registry. Also, neurologic or other follow-up studies, including genetic testing, may be appropriate.

Follow Up:

In follow-up, it was discovered that, despite normal intraperitoneal insufflation pressures, subcutaneous emphysema could be appreciated over the abdomen and chest, following surgery. This type of enhanced CO2 uptake by dissection from the peritoneal or prepelvic tissues has been described during laparoscopic and pelviscopic procedures. It can take place even when no direct tissue insufflation or elevated pressures are noted. It is critical to rule out evolving tension pneumothorax or mediastinum by serial examination of the patient during such cases.

Charles B. Watson, MD, FCCM

Chairman: Department of Anesthesia

Deputy Surgeon-in-Chief

Bridgeport Hospital

Bridgeport, CT.

Yale-New Haven Health System