Improved ventilation-perfusion matching by abdominal insufflation (pneumoperitoneum) with CO2 but not with air.

BACKGROUND: Pneumoperitoneum (PP) by CO2-insufflation causes atelectasis however with maintained or even improved oxygenation. We studied the effect of abdominal insufflation by carbon dioxide (CO2) and air on gas exchange during PP. METHODS: Twenty-seven anesthetized pigs were studied during PP with insufflations to 12 mmHg by either 1/CO2, 2/ air or 3/CO2 during intravenous nitroprusside infusion (SNP) (N.=9 in each group). In 3 pigs in each group, gamma camera technique (SPECT) was used to study ventilation and perfusion distributions, in another 6 pigs an inert-gas technique (MIGET) was used for assessing ventilation-perfusion matching (VA/Q). Measurements were made during anesthesia before and after 60 minutes of PP. RESULTS: CO2-PP caused a shift of blood flow away from dependent, non-ventilated (atelectatic) to ventilated regions. Air-PP caused smaller, and SNP-PP even less shift of lung blood flow. Shunt decreased during CO2-PP (6 ± 1% compared to baseline 9 ± 2%, P<0.05), did not change during Air-PP (10 ± 2%) and increased during SNP-PP (16 ± 2%, P<0.05). PaO2 increased from baseline 35 ± 2 to 41 ± 3 kPa during CO2-PP and decreased to 32 ± 3 kPa during Air-PP and to 27 ± 3 kPa during SNP-PP (P<0.05 for all three comparisons). PaCO2 increased during CO2- and SNP-PP. CONCLUSION: CO2-PP enhanced the shift of blood flow towards better ventilated areas of the lung compared to Air-PP and SNP blunted the effects seen with CO2-PP. SNP may thus have blunted and CO2 potentiated vasoconstriction, by hypoxic pulmonary vasoconstriction or another mechanism.

No additive effects of inhaled iloprost and prone positioning on pulmonary hypertension and oxygenation in acute respiratory distress syndrome.

BACKGROUND: In acute respiratory distress syndrome (ARDS), pulmonary hypertension is associated with a poor prognosis. Prone position is effective to improve oxygenation whereas inhaled iloprost can treat pulmonary hypertension. However, combination of these interventions has not been examined before. The hypothesis was that this combination had additive effects on oxygenation and pulmonary hemodynamics as compared with each intervention alone. METHODS: In a prospective, randomized cross-over study, ten pigs were anesthetized, intubated and ventilated with volume controlled ventilation. Carotid, jugular venous and pulmonary artery catheters were inserted. ARDS was induced with oleic acid (0.20 mL/kg). Measurements were repeated in randomized different sequences of prone or supine positions with or without iloprost inhalation (220 ng/kg/min) (four combinations). Systemic and pulmonary arterial pressures; arterial and mixed venous blood gases; and Qs/Qt and the resistances were recorded. RESULTS: Iloprost decreased pulmonary artery pressures (for MPAP: P=0.034) in both supine (37±10 vs. 31±8 mmHg; P<0.05) and prone positions (38±9 vs. 29±8 mmHg; P<0.05); but did not obtain a significant improvement in oxygenation in both positions. Prone position improved the oxygenation (p<0.0001) compared to supine position in both with (361±140 vs. 183±158 mmHg, P<0.05) or without iloprost application (331±112 vs. 167±117 mmHg, P<0.05); but did not achieve a significant decrease in MPAP. CONCLUSION: Although iloprost reduced pulmonary arterial pressures, and prone positioning improved oxygenation; there are no additive effects of the combination of both interventions on both parameters. To treat both pulmonary hypertension and hypoxemia, application of iloprost in prone position is suggested.

Improved ventilation-perfusion matching with increasing abdominal pressure during CO(2) -pneumoperitoneum in pigs.

BACKGROUND: CO(2) -pneumoperitoneum (PP) is performed at varying abdominal pressures. We studied in an animal preparation the effect of increasing abdominal pressures on gas exchange during PP. METHODS: Eighteen anaesthetized pigs were studied. Three abdominal pressures (8, 12 and 16 mmHg) were randomly selected in each animal. In six pigs, single-photon emission computed tomography (SPECT) was used for the analysis of V/Q distributions; in another six pigs, multiple inert gas elimination technique (MIGET) was used for assessing V/Q matching. In further six pigs, computed tomography (CT) was performed for the analysis of regional aeration. MIGET, CT and central haemodynamics and pulmonary gas exchange were recorded during anaesthesia and after 60 min on each of the three abdominal pressures. SPECT was performed three times, corresponding to each PP level. RESULTS: Atelectasis, as assessed by CT, increased during PP and in proportion to abdominal pressure [from 9 ± 2% (mean ± standard deviation) at 8 mmHg to 15 ± 2% at 16 mmHg, P<0.05]. SPECT during increasing abdominal CO(2) pressures showed a shift of blood flow towards better ventilated areas. V/Q analysis by MIGET showed no change in shunt during 8 mmHg PP (9 ± 1.9% compared with baseline 9 ± 1.2%) but a decrease during 12 mmHg PP (7 ± 0.9%, P<0.05) and 16 mmHg PP (5 ± 1%, P<0.01). PaO(2) increased from 39 ± 10 to 52 ± 9 kPa (baseline to 16 mmHg PP, P<0.01). Arterial carbon dioxide (PCO(2) ) increased during PP and increased further with increasing abdominal pressures. CONCLUSION: With increasing abdominal pressure during PP perfusion was redistributed more than ventilation away from dorsal, collapsed lung regions. This resulted in a better V/Q match. A possible mechanism is enhanced hypoxic pulmonary vasoconstriction mediated by increasing PCO(2) .

Ventilation-perfusion distributions and gas exchange during carbon dioxide-pneumoperitoneum in a porcine model.

BACKGROUND: Carbon dioxide (CO2)-pneumoperitoneum (PP) of 12 mm Hg increases arterial oxygenation, but it also promotes collapse of dependent lung regions. This seeming paradox prompted the present animal study on the effects of PP on ventilation-perfusion distribution (V/Q) and gas exchange. METHODS: Fourteen anaesthetized pigs were studied. In seven pigs, single photon emission computed tomography (SPECT) was used for spatial analysis of ventilation and perfusion distributions, and in another seven pigs, multiple inert gas elimination technique (MIGET) was used for detailed analysis of V/Q matching. SPECT/MIGET and central haemodynamics and pulmonary gas exchange were recorded during anaesthesia before and 60 min after induction of PP. RESULTS: SPECT during PP showed no or only poorly ventilated regions in the dependent lung compared with the ventilation distribution during anaesthesia before PP. PP was accompanied by redistribution of blood flow away from the non- or poorly ventilated regions. V/Q analysis by MIGET showed decreased shunt from 9 (sd 2) to 7 (2)% after induction of PP (P<0.05). No regions of low V/Q were seen either before or during PP. Almost no regions of high V/Q developed during PP (1% of total ventilation). Pa(o2) increased from 33 (1.2) to 35.7 (3.2) kPa (P<0.01) and arterial to end-tidal Pco2 gradient (Pae'(co2) increased from 0.3 (0.1) to 0.6 (0.2) kPa (P<0.05). CONCLUSIONS: Perfusion was redistributed away from dorsal, collapsed lung regions when PP was established. This resulted in a better V/Q match. A possible mechanism is enhanced hypoxic pulmonary vasoconstriction.

Development of atelectasis and arterial to end-tidal PCO2-difference in a porcine model of pneumoperitoneum.

BACKGROUND: Intraperitoneal insufflation of carbon dioxide (CO2) may promote collapse of dependent lung regions. The present study was undertaken to study the effects of CO2-pneumoperitoneum (CO2-PP) on atelectasis formation, arterial oxygenation, and arterial to end-tidal PCO2-gradient (Pa-E'(CO2)). METHODS: Fifteen anaesthetized pigs [mean body weight 28 (SD 2) kg] were studied. Spiral computed tomography (CT) scans were obtained for analysis of lung tissue density. In Group 1 (n=5) mechanical ventilation (V(T)=10 ml kg (-1), FI(O2)=0.5) was applied, in Group 2 (n=5) FI(O2) was increased for 30 min to 1.0 and in Group 3 (n=5) negative airway pressure was applied for 20 s in order to enhance development of atelectasis. Cardiopulmonary and CT data were obtained before, 10, and 90 min after induction of CO2-PP at an abdominal pressure of 12 mmHg. RESULTS: Before CO2-PP, in Group 1 non-aerated tissue on CT scans was 1 (1)%, in Group 2 3 (2)% (P<0.05, compared with Group 1), and in Group 3 7 (3)% (P<0.05, compared with Group 1 and Group 2). CO2-PP significantly increased atelectasis in all groups. PaO2/FI(O2) fell and venous admixture ('shunt') increased in proportion to atelectasis during anaesthesia but CO2-PP had a varying effect on PaO2/FI(O2) and shunt. Thus, no correlation was seen between atelectasis and PaO2/FI(O2) or shunt when all data before and during CO2-PP were pooled. Pa-E'(CO2), on the other hand correlated strongly with the amount of atelectasis (r2=0.92). CONCLUSIONS: Development of atelectasis during anaesthesia and PP may be estimated by an increased Pa-E'(CO2).

[Is the pneumoperitoneum minimally invasive during laparoscopic colonic surgery?]. / Ist das Pneumoperitoneum bei Kolonresektion wirklich minimalinvasiv? Standpunkt aus anästhesiologischer Sicht.

The importance of laparoscopic colonic surgery has increased considerably in the past decade. However, a minimally invasive operation with induction of pneumoperitoneum does not imply a minimally invasive anaesthesia. The haemodynamic effects of intraperitoneal carbon dioxide insufflation depend an the extent of intraabdominal pressure elevation, severity of preexisting cardiopulmonary diseases, alterations of arterial PCO (2) and pH, volume state of the patient and co-medications. In addition, positioning of the patient for laparoscopic colonic surgery and endocrinological reactions during and after induction of pneumoperitoneum may significantly affect systemic and pulmonary haemodynamics. Intraabdominal operations may impair respiratory function independent from anaesthesia. Preoperative evaluation of the high risk patient is of utmost importance. Assessment of expiratory PCO (2), extended cardiopulmonary monitoring and maintenance of intraabdominal pressure in the range of 5 - 7 mmHg are recommended during laparoscopic colonic surgery.

Endocrine effects of dopexamine vs. dopamine in high-risk surgical patients.

OBJECTIVES: To compare the endocrine effects of dopexamine and dopamine on prolactin (PRL), dihydroepiandrosterone sulfate (DHEAS), cortisol, thyrotropin (TSH), and peripheral thyroid hormone serum concentrations in surgical patients at risk of developing postoperative complications because of hypoperfusion of various organ systems. DESIGN AND SETTING: A prospective, randomized, placebo-controlled, blinded clinical trial in an adult surgical intensive care unit in a university hospital. PATIENTS: Thirty-two male surgical risk patients undergoing elective major abdominal surgery. INTERVENTIONS: Patients were randomized to receive placebo ( n=8), dopexamine (0.5 microg kg(-1) min(-1), n=8), dopexamine (1 microg kg(-1) min(-1), n=8) or dopamine (5 microg kg(-1) min(-1), n=8) on the first postoperative day. MEASUREMENTS AND RESULTS: All patients received either a placebo or catecholamine infusion for 24 h. Blood samples were obtained every 2 h for the next 2 days. PRL, DHEAS, cortisol, TSH, triiodothyronine, thyroxin, free triiodothyronine, and free thyroxin serum concentrations were determined by radioimmunoassay or luminescence immunoassay. Dopexamine (0.5 microg kg(-1) min(-1)) had no effects on serum concentrations of PRL or TSH. Higher doses of dopexamine (1 microg kg(-1) min(-1)) suppressed PRL secretion significantly, but not TSH. In contrast, infusion of dopamine (5 microg kg(-1) min(-1)) completely inhibited PRL and TSH secretion. DHEAS, cortisol, and thyroid hormone serum concentrations were not affected by either dopexamine or dopamine infusion. Measurements of hemodynamic parameters, peripheral oxygen saturation, diuresis, blood gases, and standard laboratory parameters were repeated hourly. Significant differences were not found between placebo, dopexamine (0.5 microg kg(-1) min(-1)) and dopamine (5 microg kg(-1) min(-1)) group. Dopexamine at 1 microg kg(-1) min(-1) increased the heart rate significantly. CONCLUSIONS: Routine postoperative optimizing of men undergoing abdominal surgical procedures with dopexamine at higher doses or dopamine induces at least partial hypopituitarism, which may possibly affect postoperative morbidity.

[The effects of the carbon dioxide pneumoperitoneum in laparoscopic cholecystectomy on postoperative spontaneous respiration]. / Die Auswirkungen des Kohlendioxid-Pneumoperitoneums zur laparoskopischen Cholezystektomie auf die postoperative Spontanatmung.

Laparoscopic cholecystectomy (LSC) is being performed increasingly often. The carbon dioxide cavity increases end-expiratory carbon dioxide (exCO2), which can be regulated by mechanical ventilation. Because about 20-40% carbon dioxide remains in the patient at the end of surgery, we were interested in its influence on spontaneous respiration. PATIENTS AND METHODS. Fifteen patients classed as ASA 1-2 and undergoing LSC were compared with 15 patients (also ASA 1-2) undergoing laparotomy for cholecystectomy (LAP). All patients had balanced anaesthesia with fentanyl, enflurane, nitrous oxide and vecuronium. After surgery they were extubated when spontaneous respiration and vigilance were adequate. In the next 3 h we continuously determined exCO2 in the expired air through an intranasal catheter, and oxygen saturation (SAT), respiratory rate (RR) and heart rate (HR) using Oscar (Datex) and Ohmeda (Braun) apparatus while the patients were breathing room air. The blood pressure (BP) was determined intermittently. Postoperative pain treatment was standardized. RESULTS. The groups were reduced comparable with respect of the anthropometric data, because the weight was significantly higher in the LAP group. Fentanyl consumption was also significantly higher in the LAP group, reflecting the more pronounced trauma than with LSC. Mean exCO2 was 46 mmHg after LSC and 36 mmHg after LAP (P less than or equal to 0.05), continuously decreasing in the LSC group and increasing in the LAP group to 40 mmHg after 3 h. Mean RR was 18-20.min-1 after LSC and 12-15.min-1 after LAP during this period (P less than or equal to 0.05). There were no differences in SAT (94-96%), HR (75.min-1) and BP (130/80 mmHg). DISCUSSION AND CONCLUSIONS. The remaining carbon dioxide after LSC has important implications for postoperative spontaneous respiration. Probably due to an activation of carbon dioxide receptors, RR is increased to eliminate residual carbon dioxide. This is confirmed by a significantly increased exCO2 compared with that in the LAP group. This effect lasts at least 3 h, exCO2 being comparable in both groups, but RR is still increased after LSC. This different respiratory pattern does not affect SAT, being normal without hypoxic episodes. Cardiovascular parameters were also normal without group differences. We conclude that the carbon dioxide peritoneal cavity has important consequences for postoperative ventilation. Using our anaesthetic technique and postoperative treatment exCO2 reaches normal values after about 3 h due to an increased RR. If other methods, e.g., stronger opioids, which decrease carbon dioxide response are used, this effect may even be prolonged and more pronounced. We are now performing an investigation to evaluate this effect.