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GENERAL ARTICLES

Flat Electroencephalogram Caused by Carbon Dioxide Pneumoperitoneum

From the Department of Anesthesiology, University of Hirosaki School of Medicine, Hirosaki, Japan.

Address correspondence and reprint requests to Hitoshi Yoshida, MD, PhD, Department of Anesthesiology, University of Hirosaki School of Medicine, Hirosaki 036-8562, Japan. Address e-mail to hyoshida{at}cc.hirosaki-u.ac.jp.

	Abstract

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Hypercapnia during laparoscopy with CO₂ is predicted in the following situations: compromised pulmonary function, retroperitoneal insufflation, and subcutaneous emphysema. We present a case of sudden electroencephalogram (EEG) depression in response to severe hypercapnia during laparoscopic ureteronephrectomy in a 77-yr-old patient with chronic pulmonary emphysema. During intraperitoneal and retroperitoneal insufflation, subcutaneous emphysema and difficult ventilation occurred. Severe hypercapnia ensued, with pH = 6.94, and Paco₂ = 137 mm Hg. Subsequent EEG activity was markedly depressed with a minimum Bispectral Index of 4, accompanied by an increase in arterial blood pressure and heart rate. Termination of the laparoscopic procedure improved ventilation, EEG, and hemodynamics. These EEG changes may result from the narcotic properties of CO₂ or hypercapnia-induced neurological abnormalities.

	Introduction

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Although laparoscopic surgery has been popularized as minimally invasive, hypercapnia during pneumoperitoneum with CO₂ gas is predicted in patients with compromised pulmonary function (1). Several factors may aggravate CO₂ insufflation-induced hypercapnia, including the need for retroperitoneal or pelvic insufflation (2,3). Inadvertent extraperitoneal insufflation, especially subcutaneous emphysema, also increases CO₂ absorption (4).

The Bispectral Index (BIS) monitor is useful for both gauging the depth of anesthesia and detecting neurological complications. For example, systemic administration of lidocaine, which has an anesthetic-sparing effect during general anesthesia, decreases BIS (5). The depressed electroencephalogram (EEG) from cerebral hypoperfusion decreases BIS (6–8). The effect of hypercapnia on EEG activity during anesthesia, however, is not well understood. Here we report a case of sudden EEG depression induced by respiratory acidosis during urologic laparoscopic surgery with CO₂ insufflation in a patient with chronic obstructive pulmonary disease (COPD).

	CASE REPORT

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A 77-yr-old, 53 kg man with chronic pulmonary emphysema and a preoperative forced expiratory volume at 1 s of 50% was scheduled to undergo right laparoscopic ureteronephrectomy for right renal cancer. After application of a BIS monitor, the patient was anesthetized with 40 mg (0.8 mg/kg) of propofol, 60 mg (1.1 mg/kg) of ketamine, and 100 µg (1.9 µg/kg) of fentanyl, accompanied by propofol and ketamine continuous infusion (5 and 1 mg · kg^–1 · h^–1, respectively). The trachea was intubated after administration of 5 mg of vecuronium and the lungs were mechanically ventilated in pressure-controlled mode. A radial arterial line was placed to continuously measure arterial blood pressure and collect blood for arterial blood gas analysis.

For the laparoscopic procedure, a blunt-tipped trocar was inserted and the peritoneal cavity and the retroperitoneal space were insufflated with CO₂ at 8 cmH₂O (5.9 mm Hg) peak pressure. End-tidal CO₂ (ETCO₂) gradually and continuously increased during insufflation. Thirty minutes after initial insufflation, ETCO₂ and partial pressure of arterial CO₂ (PAco₂) were 37 and 71 mm Hg, respectively, with a minute ventilation (V_E) of 4.5 L, accompanied by stable hemodynamics (Table 1). His BIS had reached steady-state values between 40 and 50 with 6 mg · kg^–1 · h^–1 of propofol infusion (Fig. 1A). Eighty minutes later, his expiratory tidal volume suddenly decreased to <100 mL, V_E <1.0 L, without evidence of tracheal or bronchial obstruction as assessed by fiberoptic bronchoscopy, but concurrent with subcutaneous emphysema in the anterior chest and neck. All modes of mechanical and manual ventilation failed to eliminate excess CO₂. When his ETCO₂ reached 63 mm Hg with increases in arterial blood pressure and heart rate (140/80 mm Hg and 105 bpm, respectively), BIS rapidly decreased to 4 and the burst suppression ratio increased to 90 without any change in propofol infusion (Table 1, Fig. 1B). Arterial blood gas analysis revealed severe respiratory acidosis (pH = 6.94, PAco₂ = 137 mm Hg). Therefore, we requested the surgeon to terminate the laparoscopic procedure and open the abdomen. After termination, this severe hypercapnia was controlled with higher V_E. His EEG activity and hemodynamics also returned to "pre-event " values with the same propofol infusion rate (Table 1, Fig. 1C). The patient’s oxygenation was not impaired throughout the procedure. He emerged from anesthesia without neurological sequelae.

View larger version (18K): [in this window] [in a new window]   Figure 1. (A) CO2 insufflation induced a marked reduction in Bispectral Index (BIS) with an increase of suppression ratio (SR) and hemodynamics. (B, C) Raw electroencephalogram showing almost fully depressed (Fig. 1B measured at point B in Fig. 1A) and restored (Fig. 1C measured at point C in Fig. 1A) activity. Fio2 = fractional inspired concentration of oxygen; Prop = propofol (mg · kg–1 · h–1); Keta = ketamine (mg · kg–1 · h–1); BP = arterial blood pressure; HR = heart rate; SR = suppression ratio; X = start and finish of anesthesia; T = intubation and extubation; OP = start and finish of surgery; = systolic arterial blood pressure; = diastolic arterial blood pressure; = heart rates.

	DISCUSSION

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One possibility for the flat EEG we observed in this patient relates to the narcotic properties of CO₂. Several reports (9,10) suggest that CO₂ has anesthetic properties, with a minimal alveolar anesthetic concentration (MAC) estimated at 245 mm Hg in dogs. McArdle (11) reported that the majority of the eight patients he studied required 35 to 45 respirations of 30% CO₂ to produce narcosis. Therefore, human MAC for CO₂ may be similar to that in dogs. In this present case, peak Paco₂ of 137 mm Hg would be equivalent to approximately 0.5 MAC. Thus, the increase in depth of anesthesia produced by hypercapnia could account for the acute reduction in BIS.

It has been reported that severe hypercapnia reduces EEG activity (12). An in vivo study using hippocampal slices revealed that synaptic activity was depressed by acidosis, pH approximately 6.5 (13). In our case, a similar event might occur in the cerebral cortex because synaptic activity in cortical pyramidal cells is the principle source of EEG activity.

The BIS monitor is useful not only in the assessment of the depth of anesthesia (14) but also for detecting cerebral ischemia (6–8). Cardiovascular changes during pneumoperitoneum mainly result from increases in intraabdominal pressure (15). Insufflation pressures between 12 and 20 mm Hg initially increase cardiac output, which later decreases. This reduction in cardiac output may decrease cerebral perfusion, although insufflation pressure was maintained at the relatively lower pressure of 5.9 mm Hg in the present case. In addition, animal experiments (12,16) show that CO₂ concentration dependently increases cerebral blood flow (CBF) and intracranial pressure. When Paco₂ increases to 80–120 mm Hg, CBF and intracranial pressure reach a plateau at about 2.5-fold their normocapnic values. In the present case, severe respiratory acidosis may have induced an increase in CBF leading to intracranial hypertension (17), and the subsequent reduction in BIS might reflect a reduction in cerebral perfusion caused by intracranial hypertension.

It remains controversial whether laparoscopic procedures offer benefits especially to patients with compromised pulmonary function (1,18–20). Wittgen et al. (1) indicated preoperative predictive factors of hypercapnia during conventional intraperitoneal insufflation of CO₂ gas, including the forced expiratory flow at 25% of maximal expiratory flow (FEF_25%) in pulmonary function testing; control and hypercapnia group, 79.5% ± 23.3% and 54.9% ± 28.0%, respectively. In the present case, hypercapnia might have been predicted because preoperative pulmonary function testing in this COPD patient showed low FEF_25% of 27.4%. Moreover, retroperitoneal insufflation and subcutaneous emphysema would exacerbate severe hypercapnia. A previous study revealed that the increase in CO₂ elimination above pre-insufflation values during intraperitoneal insufflation increased by 15% while the percentage increase in CO₂ elimination during retroperitoneal insufflation was significantly larger, and showed the time-dependent increase of 38%, 46%, and 63% every 30 min (2). In addition, subcutaneous emphysema also significantly increased CO₂ elimination by 113% compared with 26% in control (4). Furthermore, Sumpf et al. (21) also indicated a risk of uncontrollable hypercapnia for patients with chronic pulmonary disease; elimination of excess CO₂ during extraperitoneal insufflation required more than 14 L of V_E.

In our case, subcutaneous emphysema and difficulty in ventilation occurred simultaneously. Imai et al. (22) reported a case of subcutaneous emphysema-induced difficult ventilation that continued until the termination of CO₂ insufflation. They speculated that subcutaneous emphysema led to decreased compliance and tracheal tube compression, although the latter was excluded by fiberoptic bronchoscopy in the present case. McArdle (11) also reported that 30% CO₂ inhalation induced progressive and marked hypertension with an increase in heart rate. In some cases, potentially hazardous hypertension or paroxysmal atrial tachycardia was observed. In the present case, arterial blood pressure and heart rate also increased with elevation of ETCO₂, although the increase was small. Nevertheless, in this case, the severe respiratory acidosis might have been fatal unless the CO₂ pneumoperitoneum had been terminated.

In summary, we report a case of a patient with severe COPD who developed severe respiratory acidosis during urologic laparoscopic surgery with CO₂ insufflation sufficient to depress EEG activity as recorded on a BIS monitor.

	ACKNOWLEDGMENTS

 
The authors thank Prof. D.G. Lambert (University Department of Cardiovascular Sciences, Division of Anesthesia, Critical Care and Pain Management, Leicester Royal Infirmary, Leicester, UK) for his valuable comments.

	Footnotes

 
Accepted for publication August 10, 2007.

	REFERENCES

Top Abstract Introduction CASE REPORT DISCUSSION REFERENCES

 

1. Wittgen CM, Naunheim KS, Andrus CH, Kaminski DL. Preoperative pulmonary function evaluation for laparoscopic cholecystectomy. Arch Surg 1993;128:880–5, discussion 5–6[Free Full Text]
2. Streich B, Decailliot F, Perney C, Duvaldestin P. Increased carbon dioxide absorption during retroperitoneal laparoscopy. Br J Anaesth 2003;91:793–6[Abstract/Free Full Text]
3. Mullett CE, Viale JP, Sagnard PE, Miellet CC, Ruynat LG, Counioux HC, Motin JP, Boulez JP, Dargent DM, Annat GJ. Pulmonary CO₂ elimination during surgical procedures using intra- or extraperitoneal CO₂ insufflation. Anesth Analg 1993;76:622–6[Abstract/Free Full Text]
4. Wolf JS Jr, Monk TG, McDougall EM, McClennan BL, Clayman RV. The extraperitoneal approach and subcutaneous emphysema are associated with greater absorption of carbon dioxide during laparoscopic renal surgery. J Urol 1995;154:959–63[Web of Science][Medline]
5. Gaughen CM, Durieux M. The effect of too much intravenous lidocaine on bispectral index. Anesth Analg 2006;103:1464–5[Abstract/Free Full Text]
6. Umegaki N, Hirota K, Kitayama M, Yatsu Y, Ishihara H, Mtasuki A. A marked decrease in bispectral index with elevation of suppression ratio by cervical haematoma reducing cerebral perfusion pressure. J Clin Neurosci 2003;10:694–6[Web of Science][Medline]
7. Hemmerling TM, Olivier JF, Basile F, Le N, Prieto I. Bispectral index as an indicator of cerebral hypoperfusion during off-pump coronary artery bypass grafting. Anesth Analg 2005;100:354–6[Abstract/Free Full Text]
8. Morimoto Y, Monden Y, Ohtake K, Sakabe T, Hagihira S. The detection of cerebral hypoperfusion with bispectral index monitoring during general anesthesia. Anesth Analg 2005;100:158–61[Abstract/Free Full Text]
9. Eisele JH, Eger EI II, Muallem M. Narcotic properties of carbon dioxide in the dog. Anesthesiology 1967;28:856–65[Web of Science][Medline]
10. Martoft L, Lomholt L, Kolthoff C, Rodriguez BE, Jensen EW, Jorgensen PF, Pedersen HD, Forslid A. Effects of CO₂ anaesthesia on central nervous system activity in swine. Lab Anim 2002;36:115–26[Abstract/Free Full Text]
11. McArdle L. Electrocardiographic studies during the inhalation of 30 percent carbon dioxide in man. Br J Anaesth 1959;31:142–51[Free Full Text]
12. Kondo T, Kumagai M, Takei F, Ohta Y. A pharmacologic study on CO₂ responsiveness of intracranial pressure in rats with chronic hypercapnia. Chest 1999;115:1402–6[Web of Science][Medline]
13. Xiang Z, Bergold PJ. Synaptic depression and neuronal loss in transiently acidic hippocampal slice cultures. Brain Res 2000;881:77–87[Web of Science][Medline]
14. Myles PS, Leslie K, McNeil J, Forbes A, Chan MT. Bispectral index monitoring to prevent awareness during anaesthesia: the B-Aware randomised controlled trial. Lancet 2004;363:1757–63[Web of Science][Medline]
15. Ost MC, Tan BJ, Lee BR. Urological laparoscopy: basic physiological considerations and immunological consequences. J Urol 2005;174:1183–8[Web of Science][Medline]
16. Smith AL, Wollman H. Cerebral blood flow and metabolism: effects of anesthetic drugs and techniques. Anesthesiology 1972;36:378–400[Web of Science][Medline]
17. Nita DA, Vanhatalo S, Lafortune FD, Voipio J, Kaila K, Amzica F. Nonneuronal origin of CO2-related DC EEG shifts: an in vivo study in the cat. J Neurophysiol 2004;92:1011–22[Abstract/Free Full Text]
18. Johnson A. Laparoscopic surgery. Lancet 1997;349:631–5[Web of Science][Medline]
19. Lawrence VA, Cornell JE, Smetana GW. Strategies to reduce postoperative pulmonary complications after noncardiothoracic surgery: systematic review for the American College of Physicians. Ann Intern Med 2006;144:596–608[Abstract/Free Full Text]
20. Sharma KC, Brandstetter RD, Brensilver JM, Jung LD. Cardiopulmonary physiology and pathophysiology as a consequence of laparoscopic surgery. Chest 1996;110:810–15[Web of Science][Medline]
21. Sumpf E, Crozier TA, Ahrens D, Brauer A, Neufang T, Braun U. Carbon dioxide absorption during extraperitoneal and transperitoneal endoscopic hernioplasty. Anesth Analg 2000;91:589–95[Abstract/Free Full Text]
22. Imai H, Nakatani N, Matsuda S, Murakawa K, Tashiro C. Sudden difficulty in ventilation due to massive subcutaneous emphysema during laparoscopic cholecystectomy. Masui 2005;54:658–61[Medline]

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Yoshida, H. Articles by Hirota, K. Search for Related Content PubMed Articles by Yoshida, H. Articles by Hirota, K. Related Collections Complications Ventilation General Technology