Sensorineural Hearing Loss in Nasopharyngeal Carcinoma Survivors in the Modern Treatment Era - The Early and Late Effects of Radiation and Cisplatin

AIMS

Hearing loss is a common debilitating complication in nasopharyngeal carcinoma (NPC) survivors. The aim of the present study was to investigate the impact of inner ear/cochlear radiation dose and cisplatin use on early and late sensorineural hearing loss (SNHL) in NPC patients treated with radiotherapy alone, concurrent chemoradiation (cCRT) and induction chemotherapy followed by cCRT (iCRT) in the intensity-modulated radiotherapy era.

MATERIALS AND METHODS

The study included 81 NPC patients treated with intensity-modulated radiotherapy between 2014 and 2016. Pure tone audiometry was carried out at baseline and follow-up. The effects of cochlear/inner ear radiation and cisplatin doses on early (<12 months) and late (≥24 months) SNHL were analysed using multivariable regression after adjusting for important predictors.

RESULTS

In total, 156 ears were examined. In early SNHL (n = 136), cisplatin use predicted the incidence of early high-frequency SHNL (HF-SNHL) (odds ratio 6.4, 95% confidence interval 1.7-23.9, P = 0.005). Ninety ears were analysed for late SNHL (median follow-up 38 months). Inner ear/cochlear radiation and cisplatin doses and better pre-treatment hearing were independent predictors of threshold change at 4 kHz. Every 10 Gy increase in inner ear/cochlear Dmean resulted in 5-dB and 6-dB threshold changes, respectively (cochlear Dmean: B = 0.005, 95% confidence interval 0.0004-0.009, P = 0.031; inner ear Dmean: B = 0.006, 95% confidence interval 0.001-0.010, P = 0.014). Cisplatin use was associated with late HF-SNHL (odds ratio 3.74, 95% confidence interval 1.1-12.3, P = 0.031). In the cCRT and iCRT subgroups, no cisplatin dose-dependent ototoxicity was observed. Severe (≥30 dB) late HF-SNHL occurred in 14% and 25% of the patients when the cochlear dose constraints were 40 Gy and 44 Gy, respectively. The radiotherapy-alone group did not develop severe late HF-SNHL.

CONCLUSION

Cochlear/inner ear radiation dose and cisplatin use showed differential and independent ototoxicity in early and late SNHL. As cochlear/inner ear dose-dependent ototoxicity was demonstrated, the cochlear dose constraint should be as low as reasonably achievable, especially when cisplatin is also administered.

Effects of pneumoperitoneum on intraoperative pulmonary mechanics and gas exchange during laparoscopic gastric bypass

BACKGROUND

Hypercarbia and elevated intraabdominal pressure resulting from carbon dioxide (CO2) pneumoperitoneum can adversely affect respiratory mechanics. This study examined the changes in mechanical ventilation, CO2 homeostasis, and pulmonary gas exchange in morbidly obese patients undergoing a laparoscopic or open gastric bypass (GBP) procedure.

METHODS

In this study, 58 patients with a body mass index (BMI) of 40 to 60 kg/m2 were randomly allocated to laparoscopic ( n = 31) or open ( n = 27) GBP. Minute ventilation was adjusted to maintain a low normal arterial partial pressure of CO2 (PaCO2), low normal end-tidal partial pressure of CO2 (ETCO2), and low airway pressure. Respiratory compliance, ETCO2, peak inspiratory pressure (PIP), total exhaled CO2 per minute (VCO2), and pulse oximetry (SO2) were measured at 30-min intervals. The acid-base balance was determined by arterial blood gas analysis at 1-h intervals. The pulmonary gas exchange was evaluated by calculation of the alveolar dead space-to-tidal volume ratio (V(Dalv)/V(T)) and alveolar-arterial oxygen gradient (PAO2-PaO2).

RESULTS

The two groups were similar in age, gender, and BMI. As compared with open GBP, laparoscopic GBP resulted in higher ETCO2, PIP, and VCO2, and a lower respiratory compliance. Arterial blood gas analysis demonstrated higher PaCO2 and lower pH during laparoscopic GBP than during open GBP ( p < 0.05). The V(Dalv)/V(T) ratio and PAO2-PaO2 gradient did not change significantly during laparoscopic GBP. Intraoperative oxygen desaturation (SO2 < 90%) did not develop in any of the patients in either group.

CONCLUSIONS

Laparoscopic GBP alters intraoperative pulmonary mechanics and acid-base balance but does not significantly affect pulmonary oxygen exchange. Changes in pulmonary mechanics are well tolerated in morbidly obese patients when proper ventilator adjustments are maintained.

Age-related differences in Na+-dependent Ca2+ accumulation in rabbit hearts exposed to hypoxia and acidification

In this study, we test the hypothesis that in newborn hearts (as in adults) hypoxia and acidification stimulate increased Na(+) uptake, in part via pH-regulatory Na(+)/H(+) exchange. Resulting increases in intracellular Na(+) (Na(i)) alter the force driving the Na(+)/Ca(2+) exchanger and lead to increased intracellular Ca(2+). NMR spectroscopy measured Na(i) and cytosolic Ca(2+) concentration ([Ca(2+)](i)) and pH (pH(i)) in isolated, Langendorff-perfused 4- to 7-day-old rabbit hearts. After Na(+)/K(+) ATPase inhibition, hypoxic hearts gained Na(+), whereas normoxic controls did not [19 +/- 3.4 to 139 +/- 14.6 vs. 22 +/- 1.9 to 22 +/- 2.5 (SE) meq/kg dry wt, respectively]. In normoxic hearts acidified using the NH(4)Cl prepulse, pH(i) fell rapidly and recovered, whereas Na(i) rose from 31 +/- 18.2 to 117.7 +/- 20.5 meq/kg dry wt. Both protocols caused increases in [Ca](i); however, [Ca](i) increased less in newborn hearts than in adults (P < 0.05). Increases in Na(i) and [Ca](i) were inhibited by the Na(+)/H(+) exchange inhibitor methylisobutylamiloride (MIA, 40 microM; P < 0.05), as well as by increasing perfusate osmolarity (+30 mosM) immediately before and during hypoxia (P < 0.05). The data support the hypothesis that in newborn hearts, like adults, increases in Na(i) and [Ca](i) during hypoxia and after normoxic acidification are in large part the result of increased uptake via Na(+)/H(+) and Na(+)/Ca(2+) exchange, respectively. However, for similar hypoxia and acidification protocols, this increase in [Ca](i) is less in newborn than adult hearts.

Cardiac function during laparoscopic vs open gastric bypass

BACKGROUND

Hypercarbia and increased intraabdominal pressure during prolonged pneumoperitoneum can adversely affect cardiac function. This study compared the intraoperative hemodynamics of morbidly obese patients during laparoscopic and open gastric bypass (GBP).

METHODS

Fifty-one patients with a body mass index (BMI) of 40-60 kg/m2 were randomly allocated to undergo laparoscopic (n = 25) or open (n = 26) GBP. Cardiac output (CO), mean pulmonary artery pressure (MPAP), pulmonary artery wedge pressure (PAWP), central venous pressure (CVP), heart rate (HR), and mean arterial pressure (MAP) were recorded at baseline, intraoperatively at 30-min intervals, and in the recovery room. Systemic vascular resistance (SVR) and stroke volume (SV) were also calculated.

RESULTS

The two groups were similar in terms of age, weight, and BMI. Operative time was longer in the laparoscopic than in the open group (p < 0.05). The HR and MAP increased significantly from baseline intraoperatively, but there was no significant difference between the two groups. In the laparoscopic group, CO was unchanged after insufflation, but it increased by 5.3% at 2.5 h compared to baseline and by 43% compared to baseline in the recovery room. In contrast, during open GBP, CO increased significantly by 25% after surgical incision and remained elevated throughout the operation. CO was higher during open GBP than during laparoscopic GBP at 0.5 h and at 1 h after surgical incision (p < 0.05). During laparoscopic GBP, CVP, MPAP, and SVR increased transiently and PAWP remained unchanged. During open GBP, CVP, MPAP, and PAWP decreased transiently and SVR remained unchanged. There was no significant difference in the amount of intraoperative fluid administered during laparoscopic (5.5 +/- 1.6 L) and open (5.6 +/- 1.7 L) GBP.

CONCLUSION

Prolonged pneumoperitoneum during laparoscopic gastric bypass does not impair cardiac function and is well tolerated by morbidly obese patients.

The Frey procedure: local resection of pancreatic head combined with lateral pancreaticojejunostomy

Management of chronic pancreatitis is mainly palliative. Most patients with chronic pancreatitis require surgical evaluation and intervention when there is suspicion of pancreatic malignancy, evidence of intractable pain, or development of pancreatitis-related local complications. The ideal operation for chronic pancreatitis, therefore, should be designed to exclude the existence of malignancy, provide long-lasting pain relief, and correct the local complications. It should be as simple and safe as possible and should preserve the remaining endocrine and exocrine functions of the pancreas.

An ergonomic evaluation of surgeons' axial skeletal and upper extremity movements during laparoscopic and open surgery

BACKGROUND

Many surgeons have complained of fatigue and musculoskeletal pain after laparoscopic surgery. We evaluated differences in surgeons' axial skeletal and upper extremity movements during laparoscopic and open operations.

METHODS

Five surgeons were videotaped performing 16 operations (8 laparoscopic and 8 open) to record their neck, trunk, shoulder, elbow, and wrist movements during the first hour of surgery. We also compared postprocedural complaints of pain, stiffness, or numbness between the two groups.

RESULTS

Compared with surgeons performing open surgery, surgeons performing laparoscopic surgery exhibited less lateral neck flexion; less trunk flexion; more internal rotation of the shoulders; more elbow flexion; more wrist supination and wrist ulnar and radial deviation. There was a trend of more shoulder stiffness after laparoscopic operations than after open operations.

CONCLUSIONS

Laparoscopic surgery involves a more static posture of the neck and trunk, but more frequent awkward movements of the upper extremities than open surgery. Ergonomic changes in the operating room environment and instrument design could ease the physical stress imposed on surgeons during laparoscopic operations.

Safety of metallic implants in magnetic resonance imaging

Magnetic resonance (MR) imaging has become a commonly accepted medical procedure. Manufacturers of medical implant devices are submitting claims that their devices are safe and effective in a MR environment. This paper concentrates on the issue of heating of patients due to the interaction of metallic implants with the strong radiofrequency (RF) magnetic field produced by the MR scanner. The commercially available program XFDTD was used to calculate the specific absorption rate (SAR) distribution in a realistic model of the human body. The body contained a metallic implant and was exposed to RF magnetic fields at 64 MHz from a model of a MR birdcage body coil. The results of the calculation showed that the magnitude of the increased heating of tissues due to the presence of the metallic implant depended on the dimensions, orientation, shape, and location of the metallic implant in the patient. This increased heating of surrounding tissues primarily concentrates in a small volume near the tip of the metallic wire. When the whole-body SAR was normalized to 1 W/kg, a calculated value of 41 W/kg was obtained at this location if the absorption was averaged over 1 g of tissue. However, a maximum value of 310 W/kg was calculated when the absorption was averaged over 1/8 g of tissue.

Factors affecting choice of surgical residency training program

BACKGROUND

A significant problem facing American surgery today is the lack of participation from women and minorities. In 1995 and 1996, 15.1 and 15.8% of United States general surgical residency graduates were women. Of our 71 graduates in the last 12 years, 38% were women. The aim of this study was to identify the factors influencing our residents' choice of training program and the reasons why our program has a high percentage of female graduates.

METHODS

Between 1989 and 2000, 27 women and 44 men completed general surgical training at our university and 44/71 (59%) responded to our survey. The age at residency completion was 34 +/- 2.2 years for men and 33.9 +/- 2.8 years for women. Fifty-five percent of men and 30% of women went on to fellowship training; and 36% of men and 20% of women are in academia.

RESULTS

Factors influencing our graduates' selection of training program are: Only 23% of men had a female faculty as their mentor, whereas 90% of women had a male faculty as their mentor during training. Only 59% of men but 80% of women (P < 0.05) agreed that female medical students need role models of successful female faculty members. Fifty-five percent of men and 45% of women would encourage a female medical student to choose surgery as a career, but 82% of men and 50% of women would encourage a male medical student to do so. Ninety-one percent of men and 85% of women would choose surgery as a career again.

CONCLUSIONS

A surgical residency training program with strong leadership, good clinical experience, and high resident morale will equally attract both genders. Women may pay more attention to the program's gender mix and geographic location.

Childbearing and child care in surgery

HYPOTHESIS

The responsibility for childbearing and child care has a major effect on general surgical residency and subsequent surgical practice.

METHODS

A survey of all graduates from a university general surgical training program between 1989 and 2000.

RESULTS

Twenty-seven women and 44 men completed general surgical training at our university during the period, and 42 (59%) responded to our survey. The age at completion of the residency was 34.0 +/- 2.2 years for men and 33.9 +/- 2.8 years for women. During residency, 64% (14/22) of the men and 15% (3/20) of the women had children. At the time of the survey, 21 (95%) of the men and 8 (40%) of the women had children. Most residents (24 [57%] of 42) relied on their spouse for child care. During surgical practice, 18 (43%) indicated that they rely on their spouse; 19 (45%) use day care, home care, or both; and (8%) of 26 are unsatisfied with their current child care arrangement. During training, 38% (5/13) of men and 67% (2/3) of women took time off for maternity leave, paternity leave, or child care. Two of 3 surgeons would like to have had more time off during residency; most men (70%, or 7 of 10) recommended a leave of 1 to 3 months, and all women preferred a 3-month maternity or child care leave of absence. During surgical practice, only 12% (2/17) of men but 64% (7/11) of women have taken time off for either childbearing or child care. Half of the respondents (21/42) have a formal leave of absence policy at work, 52% (11/21) of which are paid leave programs. Although the workweek of our practicing graduates is 69 +/- 16 hours for men and 64 +/- 12 hours for women, 62% (26/42) spend more than 20 hours per week parenting. More than 80% (27/32) would consider a part-time surgical practice for more parenting involvement; one third of the responders suggested that 30 hours a week constitutes a reasonable part-time practice, one third preferred fewer than 30 hours, and one third favored more than 30 hours per week. Data are presented as mean +/- SD.

CONCLUSIONS

Childbearing and child care may have an enormous impact on one's decision to pursue a career in surgery. To attract and retain the best candidates for future surgeons, formal policies on the availability of child care services in the residency program and the workplace should be studied and implemented. Furthermore, national studies are needed to define appropriate, acceptable workweeks for part-time or flexible practices and the duration of leaves of absence for childbearing or child care.

Computed tomography and ultrasonography do not improve and may delay the diagnosis and treatment of acute appendicitis

HYPOTHESIS

Computed tomography (CT) and ultrasonography (US) do not improve the overall diagnostic accuracy for acute appendicitis.

DESIGN

Retrospective review.

SETTING

University tertiary care center.

PATIENTS

Seven hundred sixty-six consecutive patients undergoing appendectomy for suspected appendicitis from January 1, 1995, to December 31, 1999.

MAIN OUTCOME MEASURES

Epidemiology of acute appendicitis and the roles of clinical assessment, CT, US, and laparoscopy.

RESULTS

The negative appendectomy rate was 15.7%, and the incidence of perforated appendicitis was 14.6%. A history of migratory pain had the highest positive predictive value (91%), followed by leukocytosis greater than 12 x 10(9)/L (90.1%), CT (83.8%), and US (81.3%). The false-negative rates were 60% for CT and 76.1% for US. Emergency department evaluation took a mean +/- SD of 5.2 +/- 5.4 hours and was prolonged by US or CT (6.4 +/- 7.4 h and 7.8 +/- 10.8 h, respectively). The duration of emergency department evaluation did not affect the perforation rate, but patients with postoperative complications had longer evaluations (mean +/- SD, 8.0 +/- 12.7 h) than did those without (4.8 +/- 3.3 h) (P =.04). Morbidity was 9.1%, 6.4% for nonperforated cases and 19.8% for perforated cases. Seventy-six patients had laparoscopic appendectomy, with a negative appendectomy rate of 42.1%, compared with 15.4% for open appendectomy (P<.001). Laparoscopy, however, had minimal morbidity (1.3%) and correctly identified the abnormality in 91.6% of patients who had a normal-appearing appendix.

CONCLUSIONS

Migratory pain, physical examination, and initial leukocytosis remain reliable and accurate in diagnosing acute appendicitis. Neither CT nor US improves the diagnostic accuracy or the negative appendectomy rate; in fact, they may delay surgical consultation and appendectomy. In atypical cases, one should consider the selective use of diagnostic laparoscopy instead.

A Prospective Evaluation of Intracorporeal Laparoscopic Small Bowel Anastomosis during Gastric Bypass

BACKGROUND

We evaluated the safety and feasibility of performing a laparoscopic intracorporeal end-to-side small bowel anastomosis using a stapling technique as part of a Roux-en-Y gastric bypass operation (RYGBP).

METHODS

80 consecutive patients who underwent RYGBP with laparoscopic jejunojejunostomy were evaluated. Operative time and intraoperative and postoperative complications directly related to the jejunojejunostomy anastomosis were recorded.

RESULTS

All 80 laparoscopic jejunojejunostomy procedures were successfully performed without conversion to laparotomy. Mean operative time was longer for the first 40 laparoscopic RYGBP than for the last 40 RYGBP (32+/-18 min vs 21+/-14 min, respectively, p<0.05). Intraoperative complications were staple-line bleeding (2 patients) and narrowing of the anastomosis (1 patient). Postoperative complications were four small bowel obstructions: technical narrowing at jejunojejunostomy site (2 patients), angulation of the afferent limb (1 patient), and food impaction at the jejunojejunostomy anastomosis (1 patient). These four patients underwent successful laparoscopic re-exploration and creation of another jejunojejunostomy proximal to the original anastomosis. There were no small bowel anastomotic leaks. The median time to resuming oral diet was 2 days.

CONCLUSIONS

Laparoscopic jejunojejunostomy as part of the RYGBP operation is a safe and technically feasible procedure. Postoperative small bowel obstruction is a potential complication, which can be prevented by avoiding technical narrowing of the afferent limb.

Laparoscopic suturing evaluation among surgical residents

BACKGROUND

Laparoscopic suturing is an integral part of advanced laparoscopic surgery training. The objective of this study was to evaluate the performance and preference of surgical residents performing intracorporeal and extracorporeal knot-tying techniques using conventional and Endo Stitch instruments. The residents were also evaluated on their suturing techniques using conventional instruments, the Endo Stitch, and the Suture Assistant.

METHODS

Using an inanimate laparoscopic trainer model, 39 residents were evaluated as they performed laparoscopic knot tying exercises. Endpoints of the study were execution time and subjective preference of surgical residents with respect to the type of instrument used for knot tying. Forty-three residents were evaluated as they performed laparoscopic suturing exercises with three different types of suturing instruments using the same endpoints.

RESULTS

The intracorporeal technique was the preferred (89%) method of knot tying among surgical residents. The time for completion of laparoscopic suturing was significantly (P < 0.05) shorter with the Endo Stitch (114 +/- 64 s) than with the conventional instrument (206 +/- 107 s) or the Suture Assistant (151 +/- 70 s). Residents preferred the use of the Endo Stitch in all three categories for suturing, knot tying, and handling.

CONCLUSION

The Endo Stitch enhanced laparoscopic skills and was the preferred instrument for laparoscopic knot tying and suturing among surgical residents.

A comparison study of laparoscopic versus open gastric bypass for morbid obesity

BACKGROUND

Laparoscopic Roux-en-Y gastric bypass (GBP) has been previously described, but a comparative study between laparoscopic and open GBP has not been reported. The purpose of this study was to compare surgical outcomes oflaparoscopic GBP with those of open GBP for treatment of morbid obesity.

STUDY DESIGN

From August 1998 to September 1999, we prospectively collected outcome data on 35 patients with body-mass indices between 40 kg/m2 and 60 kg/m2 who underwent laparoscopic GBP. Demographics, operative data, perioperative complications, and weight losses were collected and compared with those obtained from a retrospective chart review of 35 patients with body-mass indices between 40 kg/m2 and 60 kg/m2 who underwent open GBP before August 1998.

RESULTS

Age, gender, preoperative body-mass index, preoperative comorbidity, and earlier abdominal surgery were similar in both groups. All laparoscopic operations were completed without conversion to laparotomy. Mean operative time, operative blood loss, length of intensive care stay, and length of hospital stay were significantly less after laparoscopic GBP than after open GBP (p<0.05). There was no 30-day mortality in either group. At 1-year followup, analysis of the percentage of excess body weight loss showed no significant difference between the two groups (p<0.05).

CONCLUSIONS

Laparoscopic Roux-en-Y gastric bypass is technically feasible and safe. Laparoscopic GBP confers the clinical benefits of laparoscopy and an initial weight loss similar to that of open GBP.

Laparoscopic umbilical herniorrhaphy

BACKGROUND

Laparoscopic technique is an alternative approach to ventral hernia repair. This study evaluated the feasibility of performing umbilical hernia repair using a single 5-mm trocar technique.

PATIENTS AND METHODS

During February 1999 to November 1999, we performed laparoscopic umbilical hernia repair in 16 consecutive patients. All operations were performed under general anesthesia. One 5-mm port was used to visualize the defect. A second 5-mm port was inserted only if there was incarcerated omentum requiring reduction. The Endo Close was inserted through a 2-mm incision made directly over the hernia to perform transabdominal closure of the defect using nonabsorbable suture.

RESULTS

The mean size of the umbilical hernia defects was 1.2 cm +/- 0.4 (range 1.0-2.0 cm). All operations were completed laparoscopically with no intraoperative or postoperative complications. The mean operative time was 35 +/- 15 minutes (range 21-75 min). All cases were performed in an outpatient setting. There have been no recurrences at a mean follow-up of 5.9 months.

CONCLUSIONS

Laparoscopic umbilical herniorrhaphy is safe and technically feasible. Its potential advantages, such as a lower rate of recurrence, will need to be validated with longer follow-up.

Hypertonic perfusion inhibits intracellular Na and Ca accumulation in hypoxic myocardium

Much evidence supports the view that hypoxic/ischemic injury is largely due to increased intracellular Ca concentration ([Ca](i)) resulting from 1) decreased intracellular pH (pH(i)), 2) stimulated Na/H exchange that increases Na uptake and thus intracellular Na (Na(i)), and 3) decreased Na gradient that decreases or reverses net Ca transport via Na/Ca exchange. The Na/H exchanger (NHE) is also stimulated by hypertonic solutions; however, hypertonic media may inhibit NHE's response to changes in pH(i) (Cala PM and Maldonado HM. J Gen Physiol 103: 1035-1054, 1994). Thus we tested the hypothesis that hypertonic perfusion attenuates acid-induced increases in Na(i) in myocardium and, thereby, decreases Ca(i) accumulation during hypoxia. Rabbit hearts were Langendorff perfused with HEPES-buffered Krebs-Henseleit solution equilibrated with 100% O(2) or 100% N(2). Hypertonic perfusion began 5 min before hypoxia or normoxic acidification (NH(4)Cl washout). Na(i), [Ca](i), pH(i), and high-energy phosphates were measured by NMR. Control solutions were 295 mosM, and hypertonic solutions were adjusted to 305, 325, or 345 mosM by addition of NaCl or sucrose. During 60 min of hypoxia (295 mosM), Na(i) rose from 22+/-1 to 100+/-10 meq/kg dry wt while [Ca](i) rose from 347+/-11 to 1,306+/-89 nM. During hypertonic hypoxic perfusion (325 mosM), increases in Na(i) and [Ca](i) were reduced by 65 and 60%, respectively (P<0.05). Hypertonic perfusion also diminished Na uptake after normoxic acidification by 87% (P<0.05). The data are consistent with the hypothesis that mild hypertonic perfusion diminishes acid-induced Na accumulation and, thereby, decreases Na/Ca exchange-mediated Ca(i) accumulation during hypoxia.

Effect of intravascular volume expansion on renal function during prolonged CO2 pneumoperitoneum

OBJECTIVE

To evaluate whether intravascular volume expansion would improve renal blood flow and function during prolonged CO2 pneumoperitoneum.

SUMMARY BACKGROUND DATA

Although laparoscopic living donor nephrectomies have a considerably reduced risk of complications for the donors, significant concerns exist regarding procurement of a kidney in the altered physiologic environment of CO2 pneumoperitoneum. Recent studies have documented adverse effects of CO2 pneumoperitoneum on renal hemodynamics.

METHODS

Renal and systemic hemodynamics and renal histology were studied in a porcine CO2 pneumoperitoneum model. After placement of a pulmonary artery catheter, carotid arterial line, Foley catheter, and renal artery ultrasonic flow probe, CO2 pneumoperitoneum (15 mmHg) was maintained for 4 hours. Pigs were randomized into three intravascular fluid protocol groups: euvolemic (3 mLkg/hour isotonic crystalloid), hypervolemic (15 mL/kg/hour isotonic crystalloid), or hypertonic (3 mL/kg/hour isotonic crystalloid plus 1.2 mL/kg/hour 7.5% NaCl).

RESULTS

In the euvolemic group, prolonged CO2 pneumoperitoneum caused decreased renal blood flow, oliguria, and impaired creatinine clearance. Both isotonic and hypertonic volume expansions reversed the changes in renal blood flow and urine output, but impaired creatinine clearance persisted.

CONCLUSIONS

Intravascular volume expansion alleviates the effects of CO2 pneumoperitoneum on renal hemodynamics in a porcine model. Hypertonic saline (7.5% NaCl) solution may maximize renal blood flow in prolonged pneumoperitoneum, but it does not completely prevent renal dysfunction in this setting. This study suggests that routine intraoperative volume expansion is important during laparoscopic live donor nephrectomy.

Gastrostomy for enteral access. A comparison among placement by laparotomy, laparoscopy, and endoscopy

BACKGROUND

Access to the stomach for long-term enteral feeding can be achieved via laparotomy (open GT), laparoscopy (lap GT) or endoscopy (PEG). We compared the three methods of gastrostomy to determine whether any one has an advantage over the others.

METHODS

A retrospective analysis was done of 356 gastrostomies performed between January 1990 and June 1995.

RESULTS

Of these 356 gastrostomies, 214 were open GT, 60 were lap GT, and 82 were PEG. The completion rate was high, 98.1% to 100%. The perioperative mortality rates were low and similar among the 3 methods; 4.2% for open GT, 5.3% for lap GT, and 4.9% for PEG (p = 0.87, Chi square test). Cardiac arrest was the predominant immediate cause of all perioperative deaths (68.8%). Overall, none of the deaths was directly related to the gastrostomy procedure. Major complications occurred in 24.9% of patients receiving open GT, in 18.3% of patients with lap GT, and in 17.1% of patients with PEG. Long-term complications developed in 25.9% of open GT, 25.6% of lap GT, and 30. 4% of PEG. The revision rates were similar for all 3 methods, 6.7% for open GT, 10% for lap GT, and 6.1% for PEG.

CONCLUSIONS

Gastrostomy can be performed safely by all three techniques, with similar outcomes. PEG is our method of choice. Lap GT is preferred in patients with head and neck carcinoma, patients with obstructing esophageal carcinoma, and patients who have problems with overlying liver or colon. Open GT is reserved for cases with extensive intraabdominal adhesions or those where the procedure is done during an ongoing laparotomy.

Laparoscopic Roux-en-Y gastric bypass for super/super obesity

Laparoscopic gastric bypass has been recently introduced as an alternative method to conventional open gastric bypass. This procedure has been generally limited to patients with a BMI <60 kg/m2 due to the possible technical limitations of the laparoscopic instruments. In this article, we present a patient with super/super obesity (61 kg/m2) who underwent Rouxen-Y gastric bypass using the laparoscopic approach.

Endoscopy during laparoscopy. Reduced postprocedural bowel distention with intraluminal CO2 insufflation

BACKGROUND

Intraluminal endoscopy during laparoscopy can substitute for manual palpation in defining anatomy and pathology, but a potential problem is the persistent bowel distention associated with intraluminal air insufflation.

METHODS

To compare the rates of intraluminal absorption, a 30-cm segment of small bowel with an intact vascular supply was insufflated with either air or CO2 during CO2 pneumoperitoneum. Intraluminal pressures and bowel circumferences were monitored after the insufflation was stopped. To study the metabolic and hemodynamic effects of CO2 endoscopy during laparoscopy, the small bowel was insufflated to an intraluminal pressure of 15 mmHg during CO2 pneumoperitoneum. Nitrogen pneumoperitoneum was used to differentiate the effects from intraluminal and peritoneal CO2 insufflation.

RESULTS

The intraluminal pressures remained elevated and the bowel distended for the entire 3 h following bowel insufflation with air. Following intraluminal CO2 insufflation, both the intraluminal pressures and the bowel circumferences returned to preinsufflation values within 15 min. Intraluminal CO2 insufflation also led to systemic absorption of CO2 with significant metabolic and hemodynamic changes. These changes were effectively corrected by doubling minute ventilation.

CONCLUSIONS

Intraluminal CO2 was absorbed faster than intraluminal air. Although decreased bowel distention is certainly of practical value, endotracheal intubation needs to be done to effectively ventilate the absorbed CO2.

The use of magnesium sulphate in the intensive care management of an Asian patient with tetanus

Tetanus, a potentially fatal but largely preventable disease through immunisation, is rare in Singapore. Timely diagnosis and appropriate intensive care management is essential to ensure survival. We aim to report the management of such a patient with magnesium sulphate. This has not been reported locally. By maintaining serum magnesium at 3 to 4 mmol/l we were able to control sympathetic overactivity by day 6, stop neuromuscular blockade by day 7 and wean off ventilator by day 11. Aminoglycoside-induced hypomagnesemia was also demonstrated, necessitating an increase in magnesium sulphate infusion rate to maintain serum magnesium at therapeutic level.

Effect of open and laparoscopic surgery on cellular immunity in a swine model

Immune suppression associated with trauma has been demonstrated to be proportional to the magnitude of injury. Laparoscopic surgery has been shown to produce a diminished stress response compared to open surgery. Postoperative immune function, specifically cellular immunity, may be better preserved after laparoscopic surgery compared to open surgery. The aim of this study was to examine the effect of open versus laparoscopic surgery on cellular immunity in a swine model. Twenty domestic female pigs were randomly selected for laparoscopic cholecystectomy (LC) or open cholecystectomy (OC). Cellular immune functions were evaluated with delayed-type hypersensitivity (DTH) skin test and serial phytohemoagglutinin (PHA)-induced T-cell proliferation of the peripheral blood. There was a significant reduction in PHA-induced T-cell proliferation in both LC and OC groups on days 1 and 3 compared to preoperative values (p < 0.05). The reduction of mitogen-induced T-cell proliferation after LC was significantly less than after OC on day 1 (p = 0.03). The mean DTH reaction was 29.7 +/- 3.7 mm2 in the LC group compared to 13.9 +/- 1.2 mm2 in the OC group (p < 0.001). There was no difference in postoperative white blood count values between the two groups. Suppression of cellular immunity occurred after both LC and OC. The magnitude and duration of impaired cellular immunity after laparoscopic surgery was less than after open surgery as measured by T-cell proliferation and DTH response.

Pancreatitis-induced ascitic fluid and hepatocellular dysfunction in severe acute pancreatitis

BACKGROUND

Multiple organ failure (MOF) is the most serious complication in severe acute pancreatitis, contributing to its high mortality. It has been suggested that changes of high-energy phosphates, intracellular pH, and intracellular cation homeostasis are closely related to hepatocellular injury associated with MOF.

METHODS

Phosphorus metabolites, intracellular pH (pHi), and intracellular Na+ concentration ([Na+]i) were measured in rat livers in vivo using 31P and 23Na NMR spectroscopy after deoxycholic acid (DCA)-induced pancreatitis or intraperitoneal injection (ip) of pancreatitis-induced ascitic fluid (PAF).

RESULTS

Two hours after induction of DCA-pancreatitis, the liver experienced significant intracellular acidosis (pHi = 6.99 +/- 0.16) and sodium loading (75 +/- 9 mM) and a reduction in its energy state (beta-ATP/Pi = 0.2 +/- 0.03 and Pi = 164 +/- 12). Although ip injection of PAF into healthy rats did not induce systemic hypotension, the livers under these conditions also developed severe disturbances in hepatocellular ion homeostasis and depletion of its bioenergetics. The longer the abdomen was exposed to the PAF, the worse the changes were. At 3 h after ip injection of PAF, hepatic [Na+]i significantly increased (42 +/- 3 mM) along with a significant decrease in pHi (7.30 +/- 0. 03). At 6 h after ip injection of PAF, the hepatic beta-ATP/Pi ratio decreased to 0.34 +/- 0.05 and Pi increased to 97 +/- 27.

CONCLUSIONS

PAF induced severe hepatocellular acidosis, rapid accumulation of hepatic intracellular sodium, impaired hepatic cytosolic phosphorylation potential, and increased hepatic utilization of ATP. These effects may account for the eventual development of liver dysfunction associated with necrotizing pancreatitis.

Laparoscopic Roux-en-Y gastric bypass for morbid obesity

Surgery is currently the only effective treatment for morbid obesity. The two most commonly accepted operations are the Roux-en-Y gastric bypass and vertical banded gastroplasty. Although multiple authors have reported on a laparoscopic approach to gastric banding, the Roux-en-Y gastric bypass is a complex operation to be replicated using laparoscopic techniques. In this article, we describe our technique of the Roux-en-Y gastric bypass using a laparoscopic approach in four cases.

The impacts of experimental necrotizing pancreatitis on hepatocellular ion homeostasis and energetics: an in vivo nuclear magnetic resonance study

BACKGROUND

Liver dysfunction may be an early event or the end result of multiple organ dysfunction (MOD) in necrotizing pancreatitis. This study measured the early changes in hepatocellular ions and energetics associated with such conditions.

METHODS

Twenty-five rats, prepared with a 23Na and 31P double-tuned nuclear magnetic resonance surface coil secured over the dome of the liver, were randomized into 5 groups: control, 10 and 20 minutes of total inflow ischemia, pancreatitis induced by deoxycholic acid (DCA), and sham-DCA (saline injection). Dysprosium-TTHA3- solution was used to separate the intracellular and extracellular sodium peaks.

RESULTS

In rat liver, 20 minutes of total inflow occlusion caused irreversible depletion of high-energy phosphates. Changes at 2 hours after the onset of DCA-pancreatitis are compared with changes after 20 minutes of ischemia (mean +/- SEM). Although the DCA-pancreatitis animals did not become hypotensive until 1 hour after the induction of pancreatitis, the changes in hepatic intracellular ions and energetics began soon after such an insult. At 2 hours after the onset of pancreatitis, hepatocellular pHi and [NA+]i were 6.99 +/- 0.16 and 78.4 +/- mmol/L, respectively (P < .01, compared with sham animals). A similar pattern of changes in hepatic bioenergetics also occurred. After the onset of pancreatitis, the hepatic cytostolic phosphorylation potential decreased with time (y = 0.654 - 0.004t, where t is time in minutes and r2 = 0.967 and the rate of hepatic hydrolysis of adenosine triphosphate increased progressively (y = 0.702t + 91.363, where t is time in minutes and r2 = 0.969. These changes correlated well with the accumulated [Na]i.

CONCLUSIONS

Unresuscitated necrotizing pancreatitis caused severe hepatocellular acidosis, profound sodium accumulation, and bioenergy depletion early in its course. These effects were as severe as those induced by total liver ischemia. Liver dysfunction may be an early, not terminal, event of MOD in necrotizing pancreatitis.

Cardiopulmonary responses to experimental venous carbon dioxide embolism

BACKGROUND

Although the low-flow CO2 insufflation rate used to initiate pneumoperitoneum may reduce the severity of potential venous embolism, its safety is not established.

METHODS

Anesthetized pigs were ventilated with room air at a fixed minute ventilation. After 1 h of baseline, they were intravenously infused with CO2 at the rate of 0.3, 0.75, or 1.2 ml/kg/min for 2 h (n = 5 for each group), followed by 1 h of recovery.

RESULTS

All animals experienced pulmonary hypertension, depressed stroke volume, hypoxemia, hypercarbia, and acidemia during intravenous CO2 infusion. They had systemic hypertension at the low rate of hypotension at the highest rate of infusion. End-tidal CO2 levels briefly decreased, then increased in all cases. In the highest rate group, three of the five animals (60%) died at 50, 65, and 100 min of infusion. These three animals had severe hypotension and hypoxemia, with visible coronary gas embolism. There was no patent foramen ovale at necropsy in any animals.

CONCLUSIONS

The low-flow insufflation rate exceeds the fatal rate of continuous intravenous CO2 infusion. End-tidal CO2 levels were increased in venous CO2 embolism, not decreased as seen in venous air embolism. Severe hypoxemia and hypotension are predictors of potentially fatal cases.

Current approach to the surgical management of chronic pancreatitis

The indications for surgical intervention in chronic pancreatitis are suspicion of malignancy, local complications, and intractable pain. Chronic pancreatitis is a risk factor for development of pancreatic carcinoma, and carcinomas may present, initially with a clinical picture of chronic pancreatitis. Local complications of chronic pancreatitis such as common bile duct or duodenal obstruction and enlarging or symptomatic pseudocyst also mandate surgical intervention. Thrombosis of the splenic vein with left-sided portal hypertension is common and associated with a 10% incidence of gastric variceal hemorrhage, which requires splenectomy. The role of surgery in the management of pain associated with chronic pancreatitis is to provide relief. When the pain interferes substantially with the patient's quality of life or narcotics are required for pain relief, surgical intervention is indicated. Other factors that should be incorporated in assessing the need for surgical intervention are malnutrition due to the inability to eat or malabsorption, the need for frequent hospitalization, and the inability to work. The operation selected for chronic pancreatitis should correct or deal with all structural abnormalities, provide long-term pain relief, have a low mortality and morbidity rate, minimize subsequent exocrine and endocrine insufficiency, and have results independent of abstinence from alcohol. No single operation can provide an optimal solution to the management of pain or these diverse complications of chronic pancreatitis. The operation chosen must be individualized to treat the patient's needs.

The role of antibiotic prophylaxis in severe acute pancreatitis

OBJECTIVE

To assess the impact of intravenous (IV) antibiotic prophylaxis on the incidence of pancreatic infection and the mortality rate in severe acute pancreatitis.

DESIGN

Restropective review of a cohort of 180 patients with severe acute pancreatitis.

SETTING

A tertiary referral center in Sacramento, Calif.

INTERVENTION

The use of IV antibiotic prophylaxis evolved during 3 periods from no antibiotics in 50 patients (1982-1989), to nonprotocol use in 55 patients (1990-1992), to a 4-week course of imipenem-cilastatin sodium (1993-1996) given to 75 patients having Acute Physiology and Chronic Health Evaluation (APACHE) II scores greater than 6 and pancreatic necrosis (> 15% of the gland), peripancreatic necrosis, or peripancreatic collection.

MAIN OUTCOME MEASURES

Pancreatic infection and mortality.

RESULTS

Without antibiotic prophylaxis, the incidence of pancreatic infection was 76% (38/50). Intravenous antibiotic prophylaxis reduced the infection rate of 45% (25/55) (P = .03). The imipenem-cilastatin protocol further reduced the infection rate to 27% (20/75) (P = .04). The mortality rates showed only a decreasing trend, from 16% (1982-1989) to 7% (1990-1992) to 5% (1993-1996) (P = .11). Patients with sterile severe acute pancreatitis had a mortality rate of 2% (2/97); whereas 17% (14/83) of patients with infection succumbed to the disease. Patients developing infection within the first 4 weeks from the onset of illness had mortality rates ranging from 19% to 40%, compared with 0% to 8% for those who became infected after 4 weeks. No patient with pancreatic infection developing after 4 weeks died with the imipenem-cilastatin protocol.

CONCLUSIONS

Intravenous antibiotic prophylaxis significantly reduced the infection rate in severe acute pancreatitis, with only a trend toward improved survival. A prospective, randomized, double-blind multicenter trial comparing the efficacy of different types and/or combinations of antibiotic prophylaxis in severe acute pancreatitis is indicated.

Cardiopulmonary responses to intravenous infusion of soluble and relatively insoluble gases

BACKGROUND

Carbon dioxide is the current gas of choice for pneumoperitoneum, but hemodynamic and acid-base effects secondary to its systemic absorption have been reported. Various studies have suggested inert gases as alternatives.

METHODS

We studied the cardiopulmonary responses to intravenous infusion of carbon dioxide, nitrous oxide, argon, helium, and nitrogen in anesthetized swine. The gas was infused into the femoral vein at a rate of 0.1 ml . kg-1 . min-1 for 30 min. The changes in end-tidal CO2, mean arterial pressure, hemodynamics, and arterial blood gases were compared to baseline values.

RESULTS

No animals died during infusion of the soluble gases (CO2 and N2O). Three of the five pigs infused with nitrogen died suddenly at 20 and 30 min of infusion. The animals in the insoluble gas groups (Ar, He, N2) experienced clinical pulmonary gas embolism and severe acidemia, hypercapnea and tachycardia.

CONCLUSIONS

Venous gas embolism is poorly tolerated when the gas is relatively insoluble. Insoluble gases should not be used for pneumoperitoneum when there is any risk of venous gas embolism.

The impact of laparoscopic cholecystectomy on the treatment of symptomatic cholelithiasis

BACKGROUND

There has been a debate about the cost-effectiveness of laparoscopic cholecystectomy (LC), as well as a concern regarding its possible overutilization and changes in the indication for surgery.

METHODS

A retrospective analysis of all cholecystectomies performed at UCDMC from 1988 to 1994 was done. The annual rate of cholecystectomy increased by 50% in 1990 when LC was introduced but has since stabilized at a rate 11% higher than the rate before LC. The disease status and severity did not change.

RESULTS

The incidence of nonelective surgery remained stable at 31.2% to 37.5%. Elective cholecystectomy had lower mortality (0.16% vs 1.8%, P = 0. 029), morbidity (2.6% vs 11.2%, P = 0.0001), and conversion rate (2. 6% vs 16%, P = 0.0001) and a shorter length of stay (2.1 days vs 5.4 days), compared with nonelective procedure.

CONCLUSIONS

The indication for surgery in cholelithiasis has not changed since the introduction of LC. In patients with symptomatic gallstones, early elective surgery is recommended and may be more cost-effective.

The renal effects of 7.5% NaCl-6% dextran-70 versus lactated Ringer's resuscitation of hemorrhage in dehydrated sheep

A small volume of 7.5% NaCl/6% Dextran-70 (HSD) can rapidly expand the plasma volume, but concerns exist regarding its adverse effects on renal function in the dehydrated state. Sheep were thirsted for 4 days (13% plasma volume contraction), and subjected to a fixed-pressure shock model (mean arterial pressure of 50 mmHg for 2 h), followed by resuscitation with either HSD (4 mL/kg) or lactated Ringer's solution (LR; 37 mL/kg). Mean arterial pressure was restored to 90%, cardiac output to 125% and 120%, and plasma volume to 78% and 72% of baseline in LR and HSD groups, respectively. Glomerular filtration rate improved to 100% of baseline following HSD compared with 82% following LR. No significant urinary 70,000 molecular weight dextran was observed, suggesting an intact renal glomerular membrane. These data suggest that small volume HSD resuscitation is effective, even with pre-existing dehydration. In addition, renal function is not compromised by HSD resuscitation of hemorrhaged, dehydrated animals.

Effector of hemodynamics during laparoscopy: CO2 absorption or intra-abdominal pressure?

Controversy has been raised about the effects of systemic carbon dioxide accumulation versus the intra-abdominal pressure on hemodynamics during laparoscopy. We compared the acid-base and hemodynamic changes during pneumoperitoneum in a randomized cross-over study between CO2 and nitrogen gases to test the hypothesis that the CO2 absorbed during laparoscopy, rather than the 15 mmHg intra-abdominal pressure created, accounted for these changes. Eight adult pigs were anesthetized and ventilated with a fixed minute ventilation. Metabolic function was measured from analysis of expired flow by a metabolic measurement cart. After baseline periods, animals were randomized into two groups, for 2 hr of either CO2 or nitrogen pneumoperitoneum at 15 mmHg intra-abdominal pressure, followed by 1 hr of recovery. After at least a 48-hr recovery period, the experiment was repeated with the other gas. Metabolic data revealed that there was a significant absorption of CO2 gas across the peritoneal epithelium during CO2 pneumoperitoneum. Animals insufflated with CO2 gas experienced a 75% increase in pulmonary CO2 excretion, with significant acidemia and hypercapnia, whereas there were no acid-base disturbances in those with nitrogen insufflation. Oxygen consumption remained essentially unchanged in both groups, even during pneumoperitoneum. CO2 pneumoperitoneum was also associated with systemic and pulmonary arterial hypertension and a reduction in stroke volume of up to 15%. Pneumoperitoneum alone did not compromise hemodynamics. Pneumoperitoneum using CO2 gas during laparoscopy resulted in systemic CO2 absorption across the peritoneum. This led to acidemia, hypercapnea, and depressed hemodynamics. The intra-abdominal pressure routinely used during laparoscopic surgery did not affect metabolic function, acid-base balance, or hemodynamics in the experimental model.

Gastrointestinal and pancreatic complications associated with severe pancreatitis

OBJECTIVE

To study the outcomes of gastrointestinal fistulas and pancreatic ductal disruption in severe pancreatitis.

SETTING

University tertiary referral center.

PATIENTS

One hundred thirty-six patients from 1982 to 1994.

INTERVENTION

Diversion followed by resection and ostomy closure for gastrointestinal fistulas, pancreaticojejunostomy for pancreatic fistulas, and excision, external drainage, or internal drainage for pseudocysts.

RESULTS

The incidence of infection was 24% (8/33) for peripancreatic fluid collections and 59% (61/103) for patients with necrosis plus fluid collections or necrosis without fluid. Sixty-nine patients developed 25 gastrointestinal fistulas and 51 complications caused by pancreatic ductal disruption. Necrosis and infection but not the open packing technique were associated with increased risk of gastrointestinal fistulas. In patients with pancreatic ductal disruption, pancreatic fistulas developed following necrosectomy and external drainage, while pancreatic pseudocysts evolved from undrained peripancreatic fluid collections. Gastrointestinal fistulas required prompt operative intervention, whereas pancreatic ductal disruption was treated nonoperatively initially. The mortality rate was 13% (3/23) in patients with gastrointestinal fistulas, similar to the overall mortality rate of 10.3% (14/136). There was no mortality in patients with pancreatic fistulas or pseudocysts. Length of hospital stay was prolonged by the presence of necrosis and infection, not by gastrointestinal fistulas or ductal disruption. Thirty-eight of the 69 patients with these complications required readmission for operative management of their complications. To date, only 18 (13.2%) of 136 patients with severe pancreatitis have not required surgical intervention.

CONCLUSIONS

Gastrointestinal fistulas and pancreatic ductal disruption are common in severe pancreatitis. Although these complications are not associated with increased mortality or prolonged initial length of stay, readmission for elective surgical correction is necessary in most patients. Severe pancreatitis is a surgical disease, requiring both acute and long-term surgical care.

The effects of selected stimulus waveforms on pulse and phase characteristics at sensory and motor thresholds

BACKGROUND AND PURPOSE

The purposes of this investigation were to determine the effect of five commonly used voltage waveforms (four pulsed and one sinusoidal) on excitation of sensory and motor nerves and to characterize variables associated with reaching threshold.

SUBJECTS

Eighteen healthy subjects were stimulated during one session via surface electrodes placed over the forearm and leg.

METHODS

Stimulation amplitude was increased at a constant rate, and the threshold of sensory and motor excitation was determined. Measured variables included peak voltage, peak current, phase charge, and total pulse charge.

RESULTS

Three-factorial, repeated-measures analysis of variance and Newman-Keuls tests revealed that phase charge varied the least during excitation induced by the five waveforms. Total pulse charge markedly increased when bursts of 10 symmetrical pulses, 25 symmetrical pulses, or amplitude-modulated waveforms were used. Monophasic and symmetrical biphasic waveforms required the least amount of total pulse charge. All measurements were higher during motor threshold than during sensory threshold, and the measurements were higher in the leg than in the forearm.

CONCLUSION AND DISCUSSION

The authors concluded that all five studied waveforms were effective at threshold excitation of peripheral sensory and motor nerves. Of the five waveforms, the symmetrical biphasic waveform, having a low total pulse charge, may be the preferred waveform, and the 25 symmetrical pulses and amplitude-modulated waveforms may be considered the least preferred due to high total pulse charge.

Effects of electrode size on basic excitatory responses and on selected stimulus parameters

Recent data have implicated the size of surface electrodes as an important factor affecting peripheral nerve excitation. Therefore, we studied the effects of electrode size on the basic excitatory responses and on stimulus characteristics. Four different sizes of self-adhesive surface electrodes were applied over the medial and lateral gastrocnemius muscle of 20 healthy subjects. The excitatory levels were sensory threshold, motor threshold, pain threshold, and maximally tolerated painful stimulation. Stimulus parameters included a symmetric biphasic waveform, 200 microseconds phase duration, and a pulse repetition rate of 50 pps. Amplitude was increased until the appropriate excitatory response was achieved. At this amplitude level, the computerized recording system collected data of stimulus peak current, peak voltage, and phase charge as well as isometric plantar flexion force. Repeated measure analysis of variance and Newman-Keuls post hoc tests revealed that increasing electrode size significantly decreased voltage but increased current and phase charge magnitudes. With increasing electrode area, the ratios of voltage/current decreased nonlinearly, while the ratios of charge/voltage increased nonlinearly. The comfort of stimulation for the same amount of plantar flexion force improved significantly as electrode size became larger. We concluded that electrode size affects the stimulus parameters, comfort, and force generation associated with electrically induced excitatory responses. Electrode size should be considered an integral part of the attempt to improve subject response to transcutaneous electrical stimulation.

High level of arginine vasopressin and 7.5% NaCl/6% dextran-70 solution: cardiovascular and renal effects

A marked diuresis has been observed following resuscitation of hypotensive hemorrhaged animals with small volume hypertonic saline/dextran (HSD), 7.5% NaCl/6% dextran-70. We tested the hypothesis that high arginine vasopressin (AVP) levels associated with severe hemorrhage may exacerbate the diuretic effect of HSD infusion in euvolemic sheep. Following AVP infusion, a significant bradycardia (55% of baseline) and decreased cardiac output (62% of baseline) was observed (p < or = .05). Urine output increased during AVP infusion (25.4 +/- 2.3 ml/20 min) compared to control group (10.5 +/- 1.0 ml/20 min) (p < or = .0001). With HSD volume expansion, urine flow in the AVP group was initially 1.7 times greater than the control group (104.8 +/- 10 ml/20 min vs. 60.2 +/- 15 ml/20 min) (p < or = .05). High serum levels of AVP (600 +/- 33 pg/ml) may contribute to the diuresis seen with HSD resuscitation and possibly contribute to the bradycardia observed with severe hemorrhage.

Hemodynamic effects of argon pneumoperitoneum

The hemodynamic effects of argon pneumoperitoneum were studied to define its possible role as an alternative gas for intraperitoneal insufflation during minimally invasive surgery. Adult pigs were anesthetized and placed on mechanical ventilation. Parameters measured or determined included mean arterial (MAP), pulmonary arterial (PAP), pulmonary arterial wedge (PAWP), right atrial (CVP), and inferior vena cava venous (IVC) pressures, total excretion of CO2 (VCO2), oxygen consumption (VO2), minute ventilation, and arterial blood gases. Also determined were cardiac output, stroke volume, and systemic vascular resistance all indexed to weight (CI, SVI, SVRI). Data were recorded during a 1-h baseline, 2 h of insufflation with argon gas at a constant pressure of 15 mmHg, and 1 h recovery after desufflation. There was no significant change from baseline in VCO2, VO2, MAP, PAP, PAWP, CVP, PaCO2, or arterial pH. Argon pneumoperitoneum significantly increased systemic vascular resistance index and exerted a depressant effect on stroke volume index and cardiac index by 25% and 30% from baseline values, respectively (P < 0.05). Inferior vena cava pressure increased as a reflection of the intraabdominal pressure. Argon insufflation had no effect on respiratory function. Argon gas may not be physiologically inert, and in patients with cardiovascular disease its effects may be clinically important.

The effects of CO2 pneumoperitoneum on hemodynamics in hemorrhaged animals

BACKGROUND

Carbon dioxide (CO2), the primary gas currently used for pneumoperitoneum, has been known to cause systemic effects on acid-base balance and hemodynamic stability. We studied the hemodynamic effects of CO2 pneumoperitoneum in a hemorrhagic shock model to assess the safety of laparoscopic procedures in acute trauma patients.

METHODS

After 1 hour of baseline, 32 anesthetized adult pigs were randomized into four groups. Group 1 animals had no hemorrhage, serving as a control group. Group 2 animals had a mild hemorrhage of 10 ml/kg/hr. Group 3 animals had a moderate hemorrhage of 20 ml/kg/hr. Group 4 animals had a moderate hemorrhage but were resuscitated with 40 ml/kg of lactated Ringer's solution. All animals were then insufflated to an intraabdominal pressure of 15 mm Hg with CO2 gas for 1 hour. The abdomen was then decompressed, and the animals were observed for another hour. All animals survived hemorrhage. One death each occurred in moderate hemorrhage groups, both near the end of CO2 pneumoperitoneum. These animals were not included in statistical analysis.

RESULTS

In euvolemic animals, CO2 pneumoperitoneum induced hypercapnia (from 34 +/- 1 mm Hg to 48 +/- 1 mm Hg), acidemia (from 7.45 +/- 0.02 to 7.36 +/- 0.02), and a 20% reduction in stroke volume. Mild hemorrhage and CO2 insufflation resulted in a similar degree of acidemia (7.35 +/- 0.01), but moderate hemorrhage and CO2 insufflation led to more severe acidemia (7.26 +/- 0.02). Fluid resuscitation failed to prevent this severe fall in pH (7.30 +/- 0.03) for group 4. PaCO2 was not affected by hemorrhage, but CO2 pneumoperitoneum induced significant hypercapnia in all groups, ranging from 48 +/- 1 mm Hg for euvolemic animals to 52 +/- 1 mm Hg for moderate hemorrhage animals. Stroke volume declined as a function of blood loss, and it was further depressed by CO2 insufflation, to as low as 75% of baseline in mild hemorrhage and 55% of baseline in moderate hemorrhage. Both stroke volume and cardiac index initially responded to large-volume fluid replacement after moderate hemorrhage but quickly decreased to levels comparable to those of unresuscitated animals when CO2 pneumoperitoneum was created.

CONCLUSIONS

Intraperitoneal insufflation with CO2 for diagnostic laparoscopy may be hazardous in acute hypovolemic trauma patients.

Splenic abscess in the intensive care unit

BACKGROUND AND METHODS

From 1980 through 1990, nine patients developed de novo splenic abscess during their stay in our intensive care unit (ICU), representing the first series of such reported cases.

RESULTS

All nine patients were septic prior to the diagnosis of splenic abscess. The signs and symptoms of splenic abscess commonly described in the literature were of little help in detecting this pathology in ICU patients. Mean +/- SD platelet count, however, increased significantly, from 274 x 10(9)/L +/- 50 x 10(9)/L at admission to 647 x 10(9)/L +/- 94 x 10(9)/L at diagnosis. At diagnosis, left pleural effusion was present in all patients. Only three patients had detectable left upper quadrant tenderness. Abdominal computed tomographic scans, when used, were diagnostic in all cases. All patients were treated by splenectomy; eight had a solitary abscess. Six abscesses were caused by enteric organisms, two by Staphylococcus aureus, and one by Streptococcus epidermidis. Eight patients (89%) had had the offending organism previously isolated from their blood or from another infected site. Mortality was 45%.

CONCLUSIONS

Splenic abscess, although a rare clinical entity, does occur de novo in ICU patients and is associated with significant mortality. Unexplained thrombocytosis in a septic ICU patient with persistent left pleural effusion is suggestive of splenic abscess. Previous culture and sensitivity results are useful in guiding perioperative antibiotic choices.

Intraperitoneal carbon dioxide insufflation and cardiopulmonary functions. Laparoscopic cholecystectomy in pigs

We studied the effects of laparoscopic cholecystectomy on respiratory and hemodynamic function in eight adult pigs. Minute ventilation was adjusted to normalize baseline arterial blood gases, then fixed throughout carbon dioxide insufflation. A metabolic measurement cart recorded total CO2 excretion, oxygen consumption, and minute ventilation. Carbon dioxide pneumoperitoneum was maintained at a constant pressure of 15 mm Hg as cholecystectomy was performed. After 1 hour of insufflation, CO2 excretion increased from 115 +/- 10 mL/min to 149 +/- 9 mL/min but O2 consumption remained unchanged. The PaCO2 increased from 35 +/- 2 mm Hg to 49 +/- 3 mm Hg and arterial pH fell from 7.47 +/- 0.02 to 7.35 +/- 0.03. Systemic and pulmonary hypertension occurred and stroke volume dropped from 35.5 +/- 3.5 mL to 28.6 +/- 2.2 mL with compensatory tachycardia. Right atrial pressure remained unchanged as inferior vena cava pressure increased to reflect the intraperitoneal pressure. We conclude that CO2 pneumoperitoneum resulted in significant transperitoneal CO2 absorption, with secondary hypercapnia and acidemia. The accumulation of CO2 was also associated with an increase in systemic and pulmonary arterial pressure. Heart rate increased to compensate for the decreased stroke volume to maintain cardiac output.

Comparative study of shortwave heating patterns in phantoms with polyethylene and silk partitions

Specific absorption rate (SAR) and effective depths of heating patterns induced by a shortwave, pancake diathermy applicator in fat-muscle phantom are measured. Midplane partitions of polyethylene and silk screen with and without contact chemicals are used. Thermographically obtained SAR data show nearly the same value for silk-screen partitions with and without contact chemicals and slightly lower values with polyethylene partitions, provided that the partition midplanes are tightly pressed against each other. Thermometry data indicate that for low-power exposures the major error in thermographic measurements obtained after termination of heating is due to thermal diffusion and not evaporative cooling in the opened midplane of the phantom.

Small-volume resuscitation with hypertonic saline dextran solution

Small-volume hypertonic resuscitation has been proposed as an effective means for restoration of cardiovascular function after hemorrhage at the scene of an accident. We evaluated the cardiovascular, metabolic, and neurohumoral response of resuscitation after hemorrhage using 200 ml of 2400 mosm sodium chloride, 6% dextran 70. Unanesthetized adult sheep were bled to maintain mean arterial pressure at 50 mm Hg for 3 hours, shed blood volume = 42 +/- 7 ml/kg. The sheep were then treated with a single bolus infusion of hypertonic saline dextran (n = 7) or normal saline solution (control group, n = 7) and then observed for a 30-minute period of simulated patient transport during which no additional fluid was given. Hypertonic saline dextran caused rapid restoration of blood pressure and cardiac output within 2 minutes of infusion. Cardiac output remained at or above baseline level, while both O2 consumption and urine output increased to above baseline level during the 30 minutes of simulated patient transport. By comparison 200 ml of normal saline solution caused only a small increase in blood pressure and no improvement in cardiac output or oxygen consumption. After this 30-minute period, both groups were given lactated Ringer's solution as needed to return and maintain cardiac output at its baseline value. The volume of lactated Ringer's solution required to maintain cardiac output was less in the hypertonic group, 371 +/- 168 ml, only one sixth that of the control group, 2200 +/- 814 ml. In summary after 3 hours of hypovolemia, a small volume of hypertonic saline dextran, about 4 ml/kg, fully restored cardiovascular and metabolic function for at least 30 minutes and significantly lowered the total volume requirements of resuscitation.

Biologic effects of microwave exposure. II. Studies on the mechanisms controlling susceptibility to microwave-induced increases in complement receptor-positive spleen cells

In attempting to evaluate the mechanisms responsible for susceptibility to the inductive increase in splenic complement receptor-positive (CR+) cells following exposure to 2450-MHz microwaves, it was found that sensitivity to microwave-induced CR+ cell increases was under genetic control. In particular, evidence was accumulated suggesting that regulation was under the control of a gene or genes closely associated with but outside of the mouse major histocompatibility complex (H-2). All responsive strains of mice tested were of the H-2k haplotype, while mice of the H-2a, H-2b, H-2d and H-1i5 haplotypes were refractory to the microwave-induced increases in CR+ cells. By utilizing certain H-2k strains of mice that were genetically unable to respond to endotoxin, we were able to show that these strains of mice responded to microwaves, but not to endotoxin, by increasing CR+ cells. Microwave-induced increases in CR+ cells were not mimicked by the intraperitoneal injection of hydrocortisone. Athymic mice responded to microwave exposure, indicating that this event was not regulated by the T-cell population. Mice less than eight weeks old were found not to be susceptible to exposure to 2450-MHz microwaves. These studies indicate that microwaves do induce changes in the population of cells with specific cell-surface receptors, that susceptibility to these changes is under genetic control, and that it is unlikely that endotoxin, corticosteroids, or regulatory T cells play a significant role in the mechanisms regulating these increases.

Heat-dissipation rate of mice after microwave irradiation

The heat dissipation rate from individual CF1 male mice was determined by a bio-calorimeter before and after exposure to microwave radiation. The animals were irradiated singly in an environmentally-controlled waveguide apparatus with 2450 MHz CW microwave radiation. The incident power levels were 0 (sham), 0.4, 0.8, 1.7 and 3.3 W, which resulted in corresponding mean average absorbed dose rates of 0 (sham), 7, 12, 27 and 39 mW/g. The environmental conditions were 24 degrees C temperature, and 50% relative humidity. The results indicate an increased heat-dissipation rate of the animals (compared to sham) for average absorbed dose rates above 12 mW/g.

Dose rate distribution in triple-layered dielectric cylinder with irregular cross section irradiated by plane wave sources

Previous investigations have shown that absorptions of microwave energy in biological bodies depend, in part, on the size and shape of the biological bodies. Calculations of dose rate distributions in regularly-shaped biological tissues have been reported. In this investigation, dose distributions are calculated for a human thigh simulated by a dielectric cylinder with irregular cross section. Method of moments is used in the investigation. The results indicate possibility of using method of moments to calculate dose distribution in a two-dimensional irregularly-shaped biological body. It is concluded that additional research is needed to determine dose rate distribution in three-dimensional irregularly-shaped biological bodies.

Contrast of dose distribution in phantom heads due to aperture and plane wave sources

Current microwave biologic effects research uses both aperture and plane wave sources. In this theoretic investigation, the dose rate (time rate of energy absorption per unit mass) patterns are compared between phantom heads irradiated by both microwave sources. Two brain tissue-equivalent spheres with radii of 3.3 and 7 cm are used to simulate monkey and human heads, respectively. In addition, a five-layered tissue-equivalent sphere is employed to simulate more closely the various tissues in a monkey head. Theoretic formulations of dose rate patterns in multi-layered tissue-equivalent spheres due to separate plane wave and aperture source treatments are derived from the summation of spherical harmonics technique. Calculations are made for the dose rate patterns along two cross-sectional planes and three rectangular axes in the spheres. The results of these calculations indicate variations in dose rate patterns for different sources and phantom head sizes. For aperture irradiation, microwave energy penetration into the phantom heads appears weak compared to the "hot spots" prominent in the plane wave exposure situation. It is concluded that for different radiation sources, direct comparison of biologic results by external field measurements as the only common denominator may not be dosimetrically valid. The results also indicate that for the same measured exposure rate (power density), the microwave energy absorption pattern in a human head may vary according to the type of radiation source.