Ventilation and ventilatory CO2 response in children during halothane anaesthesia after nonopioid (midazolam) and opioid (papaveretum) premedication

The influence of non-opioid (NO) and opioid (O) premedication on ventilation and ventilatory CO2 response was studied in 18 spontaneously breathing children during halothane anaesthesia. Eight patients in Group NO and 10 in Group O were comparable in age, body weight and type of surgery performed. The sedative effect was evaluated and measurements by pneumotachography and in-line capnography were made immediately after induction of sleep, just before the start of surgery, during surgery and after surgery both before and after 3 min of about 2% CO2 inhalation. Immediately after induction the mean value (+/- s.e. mean) of end-tidal CO2 concentration (ETCO2) was 4.86 +/- 0.21% in Group NO and 5.28 +/- 0.22% in Group O. Before and during surgery, minute ventilation (VE) was higher in Group NO (P less than 0.05) mainly due to higher respiratory rates. ETCO2 was similar in the two groups before, during and after surgery. The ratio of VE to CO2 elimination (VCO2) and of dead space (VD) to tidal volume (VT) was higher in Group NO, but ventilatory response to CO2 inhalation immediately before the postoperative period was similar in both groups. It was concluded that opioid premedication resulted in more efficient ventilation during anaesthesia and surgery, and that CO2 response at the end of surgery was maintained in both groups.     

Pulmonary ventilation, CO2 response and inspiratory drive in spontaneously breathing young infants during halothane anaesthesia

Pulmonary ventilation, CO2 response and inspiratory drive were studied during halothane anaesthesia prior to surgery in 13 spontaneously breathing infants less than 6 months of age. Pneumotachography and capnography were used. Airway and oesophageal pressures were measured and occlusion tests were performed at functional residual capacity. Measurements were made before and during 8 min of 4% CO2 stimulation. Inspiratory drive increased significantly (P less than 0.001) at CO2 stimulation. This resulted in increased minute ventilation (P less than 0.001) and tidal volume (P less than 0.001) while respiratory rate was unchanged. As VBohrD/VT ratios were the same, the net effect was increased alveolar ventilation (P less than 0.001). CO2 elimination was unpredictable in these young infants and decreased during CO2 stimulation (P less than 0.05), while mean end-tidal CO2 concentration only increased from 5.2 to 6.3% (P less than 0.001). The ventilatory response to 4% CO2 could therefore be deemed to be adequate during the short period (8 min) of CO2 breathing. However, this was achieved at the cost of increased work as witnessed by the increased ratio between minute ventilation and CO2 elimination (P less than 0.01). Stabilisation of end-tidal CO2 concentrations during CO2 inhalation took only 10 s while the maximal increase in ventilation volumes was not achieved until after 150 s. It is concluded that young spontaneously breathing infants anaesthetized with halothane (MAC 1.3) have an increased respiratory drive with greater tidal volumes during CO2 stimulations. Respiratory timing, dynamic compliance and total pulmonary resistance were, however, uninfluenced by 4% CO2 stimulation. Increased monitoring of CO2 output in anaesthetized infants is suggested.     

CO2 production after suxamethonium and diazepam

The CO2-production and degree of relaxation after increasing doses of suxamethonium were measured in seven patients undergoing alloplastic surgery of the hip. The study indicates that the CO2-production rises following the injection of increasing doses of suxamethonium. Another group of patients received diazepam 0.1 mg kg-1 before the injection of suxamethonium 1 mg kg-1. CO2-production was significantly reduced compared to CO2 production when suxamethonium was not preceded by diazepam. It is suggested that diazepam in doses larger than 0.1 mg kg-1 might be effective in preventing fasciculations and postoperative muscle pains before the injection of suxamethonium in a dose of 0.5 mg kg-1.     

Airway Deadspace, End-Tidal CO2, and Christian Bohr

In order to calculate alveolar deadspace, an important measure of ventilation/perfusion mismatching, it is necessary to measure airway or anatomical deadspace (VDaw) and physiological deadspace. VDaw is usually measured graphically or by similar means, but sometimes it is estimated from a formula, based on Christian Bohr's work, in which end-tidal PCO2 is used as a measure of alveolar PCO2. In 58 patients undergoing anaesthesia and positive pressure ventilation, there were large errors in this estimate of VDaw compared to a graphical method. At tidal volumes of 400-500 ml, the median error was 34 ml; at larger tidal volumes, the median error increased to 74 ml (P less than 0.001). The size of the error was correlated to the slope of phase III, the part of the CO2 tracing representing alveolar CO2, at both ventilator settings (P less than 0.01). It is concluded that estimates of VDaw based on end-tidal PCO2 are unreliable, and their use will lead to a large part of the alveolar deadspace being wrongly accredited to VDaw.     

CO2 production and breathing pattern during invasive and non-invasive respiratory monitoring

A computerized non-invasive strain gauge system for respiratory monitoring is described and compared with pneumotachography. With the use of simultaneous capnography, changes in breathing pattern, end-tidal PCO2 and CO2 production were evaluated during non-invasive (NIM) and invasive breathing monitoring (IM) in 14 healthy subjects. An overall absolute difference between measured and calculated tidal volumes of 4.6 +/- 3.47% (r = 0.97) was found. When switching from NIM to IM, tidal volume increased by 19% and breathing frequency decreased by 11% with a 10% increase in minute ventilation. These changes were mainly accomplished by an increased respiratory drive with the timing component unaltered. During IM both end-tidal PCO2 and CO2 production increased significantly as compared with those during NIM.     

Postoperative analgesia by nicomorphine intramuscularly versus high thoracic epidural administration: Effects on ventilatory and airway occlusion pressure responses to CO2

In this study the effects of nicomorphine, administered either intramuscularly or by high thoracic epidural route, on the ventilatory and airway occlusion pressure response to CO₂ were investigated and compared. Twenty-four patients scheduled for thoracic surgery were allocated randomly to postoperative pain relief by i.m. nicomorphine or by high thoracic epidural nicomorphine. The ventilatory response to 5% carbon dioxide was measured in all patients: first 1 day before operation, secondly on the first day after surgery immediately before nicomorphine administration and finally after the administration, at the moment when no further rise in end-tidal Pco₂ (P_etco₂) was measured. Respiratory response was assessed in two ways, by measuring minute ventilation (Ve) and mouth occlusion pressure (p_0.1). There was a significant depression in ventilatory response to CO₂ in the intramuscular group ( P = 0.03) due to nicomorphine as assessed by the slope of V_e vs P_etCO₂ No significant depression was found in the epidural group, irrespective of measurement of V_E, or P_0.1. No significant shift of apnoeie threshold-P_ETco₂ was observed in either group.     

Single breath end-tidal Pco2, measurement during high frequency jet ventilation in critical care patients

The relationship between arterial and end-tidal carbon dioxide tensions following a single large breath was investigated in seven critically ill patients receiving high frequency jet ventilation. There was a close correlation (r = 0.989) between arterial and end-tidal carbon dioxide tensions over a wide range (3.29-8.95 kPa). Measurement of the end-tidal carbon dioxide tension following a single large breath may be useful in monitoring the efficiency of high frequency jet ventilation in the elimination of carbon dioxide.     

End-tidal CO2 monitoring

Two cases of malignant hyperthermia are described where the earliest sign was a rise in the end-tidal CO2 concentration. This led to nearly immediate detection and adequate treatment with sodium dantrolene. These cases demonstrate the efficacy of monitoring end-expired CO2 concentrations in patients at risk from malignant hyperthermia, as well as a means for following the adequacy of treatment.     

Early detection of CO2 pneumothorax with continuous spirometry during laparoscopic fundoplication

In two patients, operated on because of gastroesophageal reflux, carbon dioxide pneumothorax developed during laparoscopic Nissen fundoplication. In both instances, decrease of lung compliance and a change of pressure-volume loop configuration, computed and illustrated with on-line spirometry, led quickly to diagnosis of this complication. We conclude that continuous spirometry is valuable as an early indicator of intraoperative pneumothorax.     

A New Perfusion Circuit for the Newborn with Lung Immaturity: Extracorporeal CO2 Removal via an Umbilical Arteriovenous Shunt During Apneic O2 Diffusion

In spite of improved prophylaxis and therapy, the respiratory distress syndrome is still a major cause of morbidity and mortality in premature babies. Owing to the fact that a number of patients are unresponsive to other methods of neonatal care, an increasing number of perinatal centers have started to treat this group of patients with extracorporeal membrane oxygenation successfully. To make the extracorporeal gas exchange more practicable for the neonate directly after birth, a modification of this method using an umbilical arteriovenous shunt for CO2 removal in apneic premature lambs as an animal model was evaluated. A miniaturized low-resistance extracorporeal circuit that is totally incorporated in a regular intensive care baby incubator was developed. The benefit of using extracorporeal CO2 removal in very low birth weight newborns could be a conditioning of the premature lung during a short period of bypass, after which ventilation at nontraumatic pressures and nontoxic O2 concentrations would become possible.     

Gas exchange during thoracotomy in children. A study using the single-breath test for CO2

Gas exchange during thoracotomy was studied in 13 children aged 6 months to 14 years (median age 5 years), anaesthetized for repair of coarctation of the aorta or closure of a patent ductus arteriosus. All received halothane in equal parts of N2O/O2 supplemented with fentanyl. CO2 single-breath tests were obtained with a computerised on-line system based on the Servo ventilator. From signals for airway flow pressure, CO2 concentration and timing, the computer calculated the airway deadspace (VDaw) and the static compliance and resistance of the respiratory system. Given a value for PaCO2, the computer also calculated the physiological and alveolar deadspaces. Measurements were taken at six stages during the procedure, starting with the supine position before surgery. After turning to the lateral position, airway deadspace increased by 19%, thus increasing the physiological deadspace fraction. When the pleura was opened, both VDaw and PaO2 were reduced. When the upper lung was retracted, compliance was reduced and also PaO2 - the minimum value noted was 17.3 kPa. Hypoxic PaO2 values were possibly avoided because both ventilation and perfusion were reduced in the retracted lung. The alveolar deadspace fraction increased during these intra-operative stages. Although the net effect of the changes in airway and alveolar deadspace during surgery was a significant increase in physiological deadspace fraction (from 0.23 to 0.28), gas exchange could be maintained at the cost of only moderate increases in peak airway pressure: the mean increase was from 2.4 to 2.8 kPa (24 to 29 cmH2O).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of esmolol on haemodynamic response to CO2 pneumoperitoneum for laparoscopic surgery

Background : Carbon dioxide (CO₂) pneumoperitoneum for laparoscopic surgery increases arterial pressures, systemic vascular resistance and heart rate and decreases urine output.
Methods : In this double-blind randomized study esmolol, an ultrashort-acting β1-adrenoceptor antagonist was compared with physiological saline (control) in 28 patients undergoing laparoscopic surgery in standardized 1 MAC isoflurane anaesthesia. Alfentanil infusion was used to prevent the increase of mean arterial pressure more than 25% from baseline.
Results : Esmolol effectively prevented the pressor response to induction and maintenance of CO₂ pneumoperitoneum. Significantly ( P <0.001) less alfentanil was needed in the esmolol group than in the control group. Urine output was higher ( P <0.05) and plasma renin activity ( P <0.01) and urine N-acetyl-β-D-glucosaminidase levels lower in the esmolol group when compared with the control group.
Conclusions : Esmolol blunts the pressor response to induction and maintenance of pneumoperitoneum and may protect against renal ischaemia during pneumoperitoneum.     

Attenuation of the Cardiovascular Intubation Response with N2O, Halothane or Enflurane

The circulatory intubation response was studied in 75 normotensive, otolaryngological patients after a thiopentone-suxamethonium induction followed by 2 min artificial ventilation with 100% oxygen (control), 70% nitrous oxide in oxygen (N₂O), halothane 2% with N₂O, enflurane 3% with N₂O or enflurane 5% in oxygen. The above study groups (n = 15) were chosen after preliminary experiments performed in 25 different patients with halothane 2% (n = 8) or enflurane 3% (n = 6) in oxygen, which did not prevent the increase of arterial pressure after intubation, or with halothane 3% (n = 11) which attenuated the pressor response but caused cardiac arrhythmias in 55% of patients. Enflurane 5% in oxygen attenuated the increase of systolic arterial pressure by 53%, enflurane 3% with N₂O by 34% and halothane 2% with N₂O by 31 %. The increase in heart rate after intubation was lowest in the halothane 2% with N₂O group, but there were no statistically significant differences between the groups. Cardiac arrhythmias were commonest in the enflurane 3% with N₂O group (20%) and they did not occur in the halothane 2% with N₂O group. Considering the total effect on arterial pressure, heart rate and rate-pressure product, we recommend the combination of halothane 2% with N₂O.     

Effects of changes in frequency and inspiratory time on arterial oxygenation and CO2 elimination during high-frequency jet ventilation in a child with laryngotracheal papillomata

An 11-yr-old female without any pulmonary disorders underwent laser resections of laryngotracheal tumors using high-frequency jet ventilation (HFJV) 6 times over a period of 17 months at our institute. In this series of surgeries, we studied the effects on PaO2 and PaCO2 during HFJV of changes of either frequency or inspiratory time. Increasing the frequency from 100 to 400/min decreased the PaO2 and increased the PaCO2. Decreasing the inspiratory time from 30% to 20% increased the PaCO2, although it did not affect the PaO2. All the procedures were uneventfully carried out without critically impairing gas exchange during HFJV. In this patient with normal lung function, CO2 elimination during HFJV appeared to be facilitated by either decreasing the frequency or increasing the inspiratory time. Arterial oxygen tension during HFJV was higher at lower frequencies.     

Reduced CO2-elimination during combined high-frequency ventilation compared to conventional pressure-controlled ventilation in surfactant-deficient piglets

Background: Combined high-frequency ventilation (CHFV) combines a conventional low-frequency component with superimposed high-frequency jet pulses. The intention is to overcome the limited CO₂-elimination of high-frequency ventilation, and to decrease airway pressures and enhance hemodynamic performance by reducing the conventional component. The present study was performed to compare the effects of conventional continuous positive-pressure ventilation (CPPV) on gas exchange, airway pressures and cardiac output to those of CHFV at matched minute volume (MV) and mean airway pressure (MPAW). Methods: Sixteen anaesthetised piglets with lavage-induced surfactant deficiency were ventilated with CPPV, with positive end-expiratory pressure (PEEP) set to obliterate the lower inflection point of the inspiratory pressure-volume loop. This setting was compared to CHFV during which 50% of the total MV was applied as superimposed jet pulses of 20 Hz at otherwise unchanged settings, and to CPPV at a PEEP level which was reduced (CPPV_red) until MPAW matched MPAW during CHFV. Gas exchange, airway pressures and hemodynamics were measured after the ventilatory setting had been applied for 20 min. Results: MPAW decreased from (median) 2.7 kPa with CPPV to 2.4 kPa with CHFV (P≤0.05). Peak inspiratory pressure was 3.6 kPa with CPPV, 3.2 kPa with CHFV, and 3.2 kPa with CPPV_red (P≤0.05 for differences to CPPV), respectively. PaCO₂ was comparable during CPPV (5.9 kPa), CPPV_red and CHFV_CO2, while it increased during CHFV (6.8 kPa, (P≤0.05)). Cardiac output did not differ significantly between the settings. Conclusions: In the porcine lavage model, CO₂-elimination is reduced during CHFV compared to CPPV at matched minute volume. At matched mean airway pressure, CHFV fails to reduce peak inspiratory airway pressure and to improve hemodynamic performance compared to CPPV.