MH Hotline
800MH-HYPER or 800-644-9737
available 24/7
_________________________________________________
Topic: Laparoscopy: hypercarbia, subcultaneous emphysema
A 72-year-old female with a history of hypertension, well controlled on atenolol, is scheduled for elective laparoscopically-assisted GYN surgery. She is 5’3” and weighs 68 kg. She has had general anesthesia without complication in the past, and has no family history of serious complications of anesthesia. Anesthesia is induced with fentanyl, etomidate, and succinylcholine for endotracheal intubation. Anesthesia is maintained with desflurane and supplemental fentanyl. After 1 hour of carbon dioxide insufflation, it is noted that the end-tidal CO2 level is rising. Despite a measured minute ventilation of 10 liters/minute (20 breaths/minute X 500 cc), the end-tidal CO2 reaches 60 mm. The patient is in a head-down lithotomy position and peak inflation pressure (PIP) is 30 cm. The patient did not have masseter muscle rigidity, was not difficult to intubate, and no rigidity is detected in the arms or legs. Heart rate is 78/minute and BP is 130/75.
1) Potential causes for the hypercarbia include which of the following? (More than one answer may be correct)
a) carbon dioxide venous embolization
b) endobronchial intubation
c) malignant hyperthermia
d) incompetent unidirectional valves
e) exhausted CO2 absorbent
f) complication of CO2 insufflation (e.g. subcutaneous emphysema)
There is no significant inspired CO2 noted with capnography.
2) This finding excludes which of the answers to question 1)?
3) Absence of tachycardia excludes the diagnosis of MH in this patient.
a) True
b) False
The circulating nurse stops further insufflation of CO2. An end-tidal CO2 of 60 mm persists after 5 minutes despite return to supine position, continuing minute ventilation of 10 liters/minute and noting a decrease in PIP to 25 cm.
4) Which of the following diagnoses are consistent with the data?
a) endobronchial intubation
b) malignant hyperthermia
c) exhausted CO2 absorbent
d) subcutaneous emphysema
e) tension pneumothorax
The chest wall is palpated and no subcutaneous emphysema is detected. An ABG shows PaO2 400 PaCO2 60 and pH 7.17; K+ is 4.6. The urine is grossly clear to inspection. Desflurane is discontinued and the surgery is aborted. Dantrolene 2.5 mg/kg intravenously is given to the patient and the end-tidal CO2 gradually declines to 50 mm, but increased ventilation is still required to prevent the CO2 from increasing. The patient’s temperature is 35.8° C (esophageal).
Within 20 minutes, overt subcutaneous emphysema is evident over the chest and abdominal wall. The subcutaneous emphysema and hypercarbia resolve. Serum CK (creatine kinase) levels remain within the normal range 8 and 16 hours post-anesthesia.
Answers:
1. C, D, E, F
2. D and E
3. FALSE
4. B and D
Narrative:
This case illustrates the challenge in evaluating hypercarbia during laparoscopic procedures. These procedures typically take place in an OR with dim lighting and limited ability to examine the patient’s abdomen and lower extremities. An indwelling bladder catheter is not routine; myoglobinuria may go undetected. Classic signs of MH – generalized muscle rigidity, and tachycardia (in the beta-blocked patient) -- are not always present. We do not routinely measure oxygen consumption. Also, if surgery is underway and one decides to discontinue potent inhalational anesthesia, signs of emergence – hypertension, tachycardia, posturing with increased muscle tone – may understandably be confused as signs of acute MH.
Regarding potential causes of hypercarbia during CO2 insufflation:
1) Endobronchial intubation will not result in hypercarbia unless it results in hypoventilation.
2) Significant embolization of CO2 will not result in high-levels of end-tidal CO2; end-tidal CO2 may transiently increase slightly, followed by a decrease as pulmonary blood flow drops.
3) Both incompetent unidirectional valves and exhausted CO2 absorbent will result in significant levels of inspired CO2.
4) Subcutaneous emphysema may occur during any procedure using CO2 insufflation, and may occur in slender or obese patients. It may result in an inexorable rise in end-tidal CO2 despite attempted hyperventilation. The hypercarbia may result in hypertension and tachycardia. While one might think the diagnosis should be obvious, this is not always the case. As this case illustrates, there may be a delay in the appearance of subcutaneous emphysema as the gas dissects through tissue planes.
5) Other complications of CO2 insufflation may cause hypercarbia. Capnothorax (i.e. a CO2-containing pneumothorax) or capnomediastinum may occur with or without accompanying subcutaneous emphysema.
While the ultimate cause of hypercarbia proved to be a technical complication of CO2 insufflation, the hotline consultant absolutely agreed with the treating anesthesiologist’s decision to stop the procedure and urgently start treatment for a suspected MH crisis. At the time of the decision, acute MH was a serious possibility. The appearance of subcutaneous emphysema was delayed. In the presence of hypercarbia that persists despite increasing ventilation (and without a clear alternative explanation), one must consider and institute urgent treatment of MH. Delayed treatment of acute MH may result in death or permanent injury (e.g. neurologic deficit) to the patient.
________________________________________
MH Hotline Consultant
Professor of Anesthesiology
UCLA School of Medicine
Los Angeles CA 90095-1778
