Arterial to end tidal carbon dioxide tension difference during Caesarean section anaesthesia

The relationship between arterial carbon dioxide tension and end tidal carbon dioxide tension was studied in 19 patients during general anaesthesia for Caesarean section. Thirteen patients scheduled for elective abdominal hysterectomy formed a nonpregnant group. There was significant correlation between arterial and end tidal CO2 tensions in both groups. During Caesarean section, this difference was significantly less than in the nonpregnant group.     

Arterial to end-tidal carbon dioxide tension difference during anaesthesia in early pregnancy

Sixteen patients requiring general anaesthesia for termination of pregnancy by dilatation and evacuation of the uterus were studied. Arterial and end-tidal carbon dioxide tensions were determined during anaesthesia. The mean arterial to end-tidal carbon dioxide tension difference was 0.07 kPa (-0.02-0.16, 5-95 per cent confidence limits). These results were similar to those observed during Caesarean section and those during anaesthesia for post-delivery tubal ligations. The physiological changes such as increased cardiac output, haemodilution, and increased blood volume which manifest by 12 weeks of gestation probably result in a reduced (a-E')PCO2 value.     

Arterial to end-tidal carbon dioxide tensio difference during laparoscopy Magnitude and effect of anaesthetic technique

The relationship between arterial carbon dioxide tension and end-tidal carbon dioxide tension was studied in 25 patients during laparoscopy. Thirteen patients received general anaesthesia and 12 epidural anaesthesia. The overall mean difference between arterial and end-tidal carbon dioxide tensions was 0.44 kPa (95% confidence intervals 0.28-0.60 kPa) which was significantly less than that reported in studies during other procedures. The reasons for this difference are probably associated with the physiological changes induced by CO2 pneumoperitoneum and steep Trendelenburg positioning. The choice of anaesthetic technique did not affect the arterial to end-tidal carbon dioxide tension difference significantly (p greater than 0.9).     

Arterial to end-tidal carbon dioxide tension difference in children under halothane anaesthesia

Using blood gas determinations and capnography, the relationship between arterial and end-tidal PCO₂ was investigated in 20 children under halothane anaesthesia with spontaneous respiration. A median arterial to end-tidal carbon dioxide tension difference of 0.66 kPa (5 mm Hg) was found. There was a close correlation between Pa_co2 and the magnitude of the carbon dioxide difference. Our findings may largely be explained by an increase in Vd/Vt (presumably mainly due to a reduction of Vt) causing admixture of dead space air throughout expiration. It is concluded that though end-tidal carbon dioxide does not exactly reflect Pa_co2 capnography may be of value as a monitor of respiration in paediatric anaesthesia at normal or near-normal values of end-tidal carbon dioxide.     

Arterial to end-tidal carbon dioxide tension difference during laparoscopic colorectal surgery

BACKGROUND: Determination of end-tidal carbon dioxide pressure (PET(CO2)) is effective to confirm adequate ventilation, because arterial to end-tidal carbon dioxide tension difference (deltaa-ET(CO2)) does not change normally during operation. But deltaa-ET(CO2) may change during laparoscopic surgery, because peritoneal insufflation of CO2 will increase CO2 production and reduce functional residual volume. Changes in deltaa-ET(CO2) were reported in laparoscopic cholecystectomy with cardiovascular complication, but there is controversy about how deltaaET(CO2) will change in more complicated and long laparoscopic surgery. In this prospective study, we examined changes in deltaa- ET(CO2) during laparoscopic colorectal surgery. METHODS: Fifty patients received combined general and epidural anesthesia. CO2 pneumoperitoneum was initiated after obtaining arterial blood for gas analysis. Mechanical ventilation was used to maintain PET(CO2) at a stable value between 30 and 40 mmHg during the procedure. Arterial blood gas analysis was performed 10, 60, 120 minutes after CO2 insufflation, and 10 minutes after the termination of insufflation. RESULTS: The mean +/- SD for deltaa-ET(CO2) was 5.8 +/- 4.1 before pneumoperitoneum, 7.1 +/- 4.8, 8.1 +/- 5.4, 6. 4 +/- 4.9 in 10, 60, 120 minutes after pneumoperitoneum, and 6.4 +/- 4.9 in 10 minutes after the termination of pneumoperitoneum. deltaa-ET(CO2) increased significantly during pneumoperitoneum, but did not increase further even if CO2 insufflation was longer than 60 minutes. CONCLUSIONS: In laparoscopic colorectal surgery, Pa(CO2) should be checked for at least the first 60 minutes to confirm adequate ventilation.     

Arterial to end-tidal carbon dioxide difference during laparoscopy]

Arterial as well as end-tidal PCO2 (PaCO2, PetCO2), and arterial to end-tidal PCO2 difference (P(a-ET)CO2) were studied in 16 ASA-I patients anesthetized for laparoscopy under controlled ventilation. Using constant ventilation throughout the procedure, PaCO2 and PetCO2 increased significantly (P less than 0.01) to the maximum level (about 10 mmHg above the control level) within 22 min after CO2 insufflation, along with significant increase in mean arterial pressure and heart rate. There was a statistically significant correlation between PaCO2 and PetCO2 at the time of control (before surgery), at the time of maximum PetCO2 and 30 to 60 min after CO2 insufflation (P less than 0.01). Although mean P(a-ET)CO2 remained relatively constant during the procedure, a statistically significant correlation between PaCO2 and P(a-ET)CO2 was found at the time of maximum PetCO2 after CO2 insufflation (r = 0.71, P less than 0.01). These results suggest that when PvCO2 is increasing by CO2 insufflation, P(a-ET)CO2 depend on relative ventilation efficacy.     

Arterial oxygen saturation during general anaesthesia for paediatric dental extractions

Arterial oxygen saturation (SaO2) was measured in 50 healthy children undergoing dental extractions under general anaesthesia. An inhalational anaesthetic technique was employed, with an inspired oxygen concentration of 33%. There were decreases in SaO2 of greater than 5% of the baseline value in 70% of patients, and greater than 10% in 26% of patients. The majority of these decreases were associated with teeth extractions or during placement of dental prop and pack. Non-Caucasian children showed a significantly (p less than 0.05) greater maximum decrease in SaO2 from baseline value compared to Caucasian children. The maximum decreases in SaO2 from baseline value in children anaesthetised by supervised dental students, and in children whose extractions were performed by dental students, were significantly (p less than 0.05) greater than in children whose anaesthetic and surgery were performed by members of staff.     

Arterial to end-tidal carbon dioxide tension difference in children with congenital heart disease

In children with congenital cyanotic heart disease, right-to-leftintracardiac shunting causes an obligatory difference betweenarterial and end-tidal carbon dioxide tension (Pa_CO2–PE'_CO2)as venous blood, rich in carbon dioxide, is added to the arterialcirculation. This obligatory Pa_CO2–PE'_CO2 difference,which can be predicted from knowledge of oxygen saturation,haemoglobin concentration and Pa_CO2, increases as oxygen saturationdecreases, most markedly when the haemoglobin concentrationis high. A second possible cause of the Pa_CO2–PE'_CO2 differenceis the effect of pulmonary hypoperfusion caused by the shunt.We studied 60 children undergoing cardiac surgery and comparedthe predicted the Pa_CO2–PE'_CO2 difference with measuredvalues to investigate the extent to which additional factorsinfluence the clinically observed Pa_CO2–PE'_CO2. In manychildren, observed values were much greater than predicted,which is compatible with some degree of pulmonary hypoperfusion.However, this was not felt to represent the complete picturein all patients. Another cause of ventilation–perfusionmismatch was suspected in those children who showed a considerableimprovement in oxygen saturation during ventilation with anincreased FI_O2. We believe that pulmonary congestion causedby large left-to-right shunts may further increase the Pa_CO2–PE'_CO2difference. Br J Anaesth 2001; 86: 349–53     

Arterial to end-tidal carbon dioxide pressure difference during laparoscopic surgery in pregnancy

BACKGROUND: There is controversy about whether capnography is adequate to monitor pulmonary ventilation to reduce the risk of significant respiratory acidosis in pregnant patients undergoing laparoscopic surgery. In this prospective study, changes in arterial to end-tidal carbon dioxide pressure difference (PaCO2--PetCO2), induced by carbon dioxide pneumoperitoneum, were determined in pregnant patients undergoing laparoscopic cholecystectomy. METHODS: Eight pregnant women underwent general anesthesia at 17-30 weeks of gestation. Carbon dioxide pnueumoperitoneum was initiated after obtaining arterial blood for gas analysis. Pulmonary ventilation was adjusted to maintain PetCO2 around 32 mmHg during the procedure. Arterial blood gas analysis was performed during insufflation, after the termination of insufflation, after extubation, and in the postoperative period. RESULTS: The mean +/- SD for PaCO2--PetCO2 was 2.4 +/- 1.5 before carbon dioxide pneumoperitoneum, 2.6 +/- 1.2 during, and 1.9 +/- 1.4 mmHg after termination of pneumoperitoneum. PaCO2 and pH during pneumoperitoneum were 35 +/- 1.7 mmHg and 7.41 +/- 0.02, respectively. There were no significant differences in either mean PaCO2--PetCO2 or PaCO2 and pH during various phases of laparoscopy. CONCLUSIONS: Capnography is adequate to guide ventilation during laparoscopic surgery in pregnant patients. Respiratory acidosis did not occur when PetCO2 was maintained at 32 mmHg during carbon dioxide pneumoperitoneum.     

Stability of the arterial to end-tidal carbon dioxide difference during anaesthesia for prolonged neurosurgical procedures

This study was undertaken to examine the variation of the arterial to end-tidal PCO₂ (Pa-PetCO₂ difference during prolonged neurosurgical anaesthesia. Hyperventilation is often used to reduce intracranial pressure in neurosurgical patients. Continuous end-tidal CO₂ monitoring is used as a guide between arterial CO₂ measurements. We examined the stability of the Pa-PetCO₂ difference in 21 patients undergoing elective craniotomies lasting greater than four hours. A balanced neuroanaesthetic technique was used with the ventilation variables at the discretion of the attending anaesthetist. Once patients were positioned for surgery, simultaneous samples of arterial PCO₂ through an arterial catheter, and end-tidal PCO₂ via a mass spectrometer were obtained. The Pa-PETCO₂ differences of each patient were plotted against time and a slope was derived with simple linear regression. The mean slope for all patients was then computed. There were no changes in the Pa-PETCO₂ difference with time (P > 0.05) suggesting a constant relationship between the arterial and end-tidal PCO₂ measurements over time. We conclude that end-tidal PCO₂ can be used as a reliable guide to estimate arterial PCO₂ during neurosurgical procedures of greater than four hours duration once the Pa-PetCO₂ difference has been established.     

Oxygenator exhaust capnography for prediction of arterial carbon dioxide tension during hypothermic cardiopulmonary bypass

Continuous monitoring and control of arterial carbon dioxide tension (P(a)CO2) during cardiopulmonary bypass (CPB) is essential. A reliable, accurate, and inexpensive system is not currently available. This study was undertaken to assess whether the continuous monitoring of oxygenator exhaust carbon dioxide tension (PexCO2) can be used to reflect P(a)CO2 during CPB. A total of 33 patients undergoing CPB for cardiac surgery were included in the study. During normothermia (37 degrees C) and stable hypothermia (31 degrees C), the values of PexCO2 from the oxygenator exhaust outlet were monitored and compared simultaneously with the P(a)CO2 values. Regression and agreement analysis were performed between PexCO2 and temperature corrected-P(a)CO2 and temperature uncorrected-P(a)CO2. At normothermia, a significant correlation was obtained between PexCO2 and P(a)CO2 (r = 0.79; p < 0.05); there was also a strong agreement between PexCO2 and P(a)CO2 with a gradient of 3.4 +/- 1.9 mmHg. During stable hypothermia, a significant correlation was obtained between PexCO2 and the temperature corrected-P(a)CO2 (r = 0.78; p < 0.05); also, there was a strong agreement between PexCO2 and temperature corrected-P(a)CO2 with a gradient of 2.8 +/- 2.0 mmHg. During stable hypothermia, a significant correlation was obtained between PexCO2 and the temperature uncorrected-P(a)CO2 (r = 0.61; p < 0.05); however, there was a poor agreement between PexCO2 and the temperature uncorrected-P(a)CO2 with a gradient of 13.2 +/- 3.8 mmHg. Oxygenator exhaust capnography could be used as a mean for continuously monitoring P(a)CO2 during normothermic phase of cardiopulmonary bypass as well as the temperature-corrected P(a)CO2 during the stable hypothermic phase of CPB.     

Respiratory effects of spinal anaesthesia for Caesarean section

We report the changes observed in a number of pulmonary function tests performed on 36 patients undergoing Caesarean section under spinal anaesthesia. The tests comprised peak expiratory flow, forced expiratory volume in one second, forced vital capacity, forced expiratory volume in one second to forced vital capacity ratio and the maximal mid-expiratory flow. Significant changes occurred that are consistent with a restrictive ventilatory defect. These changes persisted for four hours after the induction of spinal anaesthesia. Administration of 35% oxygen by facemask failed to change significantly fetal umbilical vein pH or partial pressure of oxygen.     

Subarachnoid anaesthesia for elective Caesarean section

Forty patients who underwent elective lower segment Caesarean section under subarachnoid anaesthesia received either 2.0 ml 0.5% cinchocaine in 6% dextrose or 2.5 ml 0.5% bupivacaine in 8% dextrose via a 26-gauge needle with the patient in the left lateral position. Onset time was rapid in both groups and the distribution of maximum ascent of sensory analgesia was T1-T6. Efficacy of analgesia was greater in the bupivacaine group, although the duration of both sensory and motor blockade was shorter than following cinchocaine. There were no significant differences between the two groups either in the incidence and severity of complications or in the condition of the neonates. The high incidence (50-65%) and often profound extent of hypotension seen throughout the trial, confirm the ineffectiveness of crystalloid preload of 1500 ml as a single prophylaxis against hypotension.