Gizella Bardoczky

Ventilatory effects of pneumoperitoneum monitored with continuous spirometry

Inspiratory and expiratory tidal volume, peak and plateau airway pressure, compliance of the respiratory system, pressure‐volume and flow‐volume loops were monitored continuously and recorded in seven women undergoing laparoscopy with carbon dioxide insufflation to an intra‐abdominal pressure of 1.6 kPa. All patients were anaesthetised using a total intravenous technique and a constant minute ventilation was maintained. Peak airway and plateau airway pressures increased by 50% and 81% respectively, whilst the compliance of the respiratory system decreased by 47% during the period of increased intra‐abdominal pressure. Following release of the pneumoperitoneum, peak and plateau pressures remained elevated by 37% and 27% respectively, and the compliance was 86% of the pre‐insufflation value. On‐line monitoring of respiratory volumes, pressures and compliance may be helpful during general anaesthesia for laparoscopic procedures to avoid the potential harmful effects of increased airway pressures occurring with increased intra‐abdominal pressure.

Large Tidal Volume Ventilation Does Not Improve Oxygenation in Morbidly Obese Patients During Anesthesia

Eight morbidly obese patients (body mass index [BMI] = 46) were studied during general anesthesia and controlled mechanical ventilation.To evaluate the effect of large tidal volume ventilation on oxygenation and ventilation, the baseline 13 mL/kg tidal volume (VT) (calculated by the ideal body weight) was increased in 3 mL/kg volume increments to 22 mL/kg, while ventilatory rate (RR) and inspiratory time (TI) were kept constant. Each volume increment was maintained for 15 min. Gas exchange was assessed by measuring the arterial blood oxygen tensions, and calculating the indices of alveolar-arterial oxygen tension difference [P(A-a)O2] and arterial/alveolar oxygen tension ratio (a/A). Peak inspiratory airway pressure (Ppeak), end-inspiratory airway pressure (Pplateau), and compliance of the respiratory system (CRS) were recorded using the Capnomac Ultima Trademark (Datex, Helsinki, Finland) on-line respiratory monitor. Increasing tidal volumes to 22 mL/kg increased the recorded Ppeak (26.3 +/- 4.1 vs 37.9 +/- 3.2 cm H2 O, P < 0.008), Pplateau (21.5 +/- 3.6 vs 27.7 +/- 4.3 cm H2 O, P < 0.01), and CRS (39.8 +/- 7.7 vs 48.5 +/- 8.3 mL/cm H2 O significantly without improving arterial oxygen tension and resulted in severe hypocapnia. Since changes in arterial oxygenation were small and not statistically significant, mechanical ventilation of morbidly obese patients with large VTS seems to offer no advantage to smaller (13 mL/kg ideal body weight) VTS. (Anesth Analg 1995;81:385-8)

Two-lung and One-lung Ventilation in Patients with Chronic Obstructive Pulmonary Disease: The Effects of Position and Fio2

We compared the effects of position and fraction of inspired oxygen (FIO2) on oxygenation during thoracic surgery in 24 consenting patients randomly assigned to receive an FIO2 of 0.4 (eight patients, Group 0.4), 0.6 (eight patients, Group 0.6), or 1.0 (eight patients, Group 1.0) during the periods of two-lung (TLV) and one-lung ventilation (OLV) in the supine and lateral positions. TLV and OLV were maintained while the patients were first in the supine and then in the lateral position for 15 min each. Thereafter, respiratory mechanical data were obtained, and arterial blood gas samples were drawn. PaO2 decreased during OLV compared with TLV in both the supine and lateral positions. In all three groups, PaO2 was significantly higher during OLV in the lateral than in the supine position: 101 (72–201) vs 63 (57–144) mm Hg in Group 0.4; 268 (162–311) vs 155 (114–235) mm Hg in Group 0.6; and 486 (288–563) vs 301 (216–422) mm Hg in Group 1.0, respectively (P < 0.02, Wilcoxon’s signed rank test). We conclude that, compared with the supine position, gravity augments the redistribution of perfusion as a result of hypoxic pulmonary vasoconstriction, when patients are in the lateral position, which explains the higher PaO2 during OLV. Implications This study compares oxygenation during thoracic surgery during periods of two-lung and one-lung ventilation with patients in the supine and lateral positions when using three different fraction of inspired oxygen values. Arterial oxygen tension was decreased in all three groups during one-lung ventilation in comparison with the two-lung ventilation values, but the decrease was significantly less in the lateral, compared with the supine position.

Airway pressure changes during one-lung ventilation

This investigation analyzed the changes in inspiratory airway pressures during transition from two-lung to one-lung ventilation in patients tracheally intubated with a double-lumen endotracheal tube (DLT) using a classical method of intubation without fiberoptic bronchoscopy. All patients were anesthetized in a standardized fashion. Ventilation was accomplished with the Siemens 900 constant-flow mechanical ventilator (Solna, Sweden). Peak (Ppeak) and plateau (Pplateau) inspiratory airway pressures were recorded with an on-line respiratory monitor before and after clamping the tracheal limb of the DLT. The position of the DLTs was evaluated by fiberoptic bronchoscopy with the patient in supine position. Of the 51 intubations, the DLT was malpositioned in 15 cases (29.5%). Ppeak and Pplateau increased significantly when switched from two-lung ventilation to one-lung ventilation in both correctly and incorrectly positioned DLTs. When the DLT was in a correct position, Ppeak increased by a mean of 55.1% and Pplateau increased by a mean of 41.9%. When the DLT was malpositioned, this increase was significantly larger (74.9% and 68.8%, respectively). Three tests commonly used as markers of malpositioned DLTs were evaluated based on the data of this study, and it was established that, although the pressure differences related to position are statistically significant, as a single value, they cannot be used for clinical decision making. (Anesth Analg 1997;84:1034-7)

Intrinsic Positive End-Expiratory Pressure During One-Lung Ventilation for Thoracic Surgery: The Influence of Preoperative Pulmonary Function

OBJECTIVE To detect and to quantify intrinsic positive end-expiratory pressure (PEEPi) during thoracic surgery in the dependent lung of patients intubated with a double-lumen endotracheal tube (DLT) in the lateral position. METHODS Twenty consecutive patients undergoing elective pulmonary resection were anesthetized, paralyzed, and intubated with a DLT. Their lungs were ventilated (Siemens Servo 900 C ventilator; Siemens Elevna; Solna, Sweden) with constant inspiratory flow. Fraction of inspired oxygen, tidal volume (10 mL/kg), frequency (10/min), and inspiratory time/total time (0.33) were kept constant during the study. PEEPi and ventilatory data were measured in the dependent lung in the supine then in the lateral position with a closed hemithorax. The obtained data were analyzed according to the presence (group PH) or absence (group N) of pulmonary hyperinflation determined from the preoperative pulmonary function data as higher than 120% of predicted value of functional residual capacity (FRC) and residual volume (RV). DATA ANALYSIS In the dependent lung of patients in group PH (n = 11), PEEPi was present in the supine (n = 8) and in the lateral (n = 11) positions in the range of 1 to 10 cm H2O. In group N (n = 9), PEEPi was detected in one patient and only in the supine position. In the whole group of 20 patients, the preoperative value of FRC (% predicted) and RV (% predicted) was statistically significantly correlated to the presence of PEEPi, whereas the preoperative FEV1 (% predicted) was poorly related to PEEPi in both positions. There was no significant correlation between the value of PaCO2 and PEEPi during one-lung ventilation (OLV) but patients in group PH had a significantly higher PaCO2 during OLV than group N (p = 0.012). CONCLUSIONS In patients with chronic obstructive lung disease and pulmonary hyperinflation, PEEPi occurs commonly during the period of OLV and only occasionally in patients with normal lungs. As the ventilatory pattern, the size of DLT, and the side of surgery were similar in the two groups of patients, we conclude that the occurrence of PEEPi in our patients was influenced mainly by the preexisting pulmonary hyperinflation and airflow obstruction.

Clinical Investigations in Critical CareIntrinsic Positive End-Expiratory Pressure During One-Lung Ventilation for Thoracic Surgery: The Influence of Preoperative Pulmonary Function

OBJECTIVE To detect and to quantify intrinsic positive end-expiratory pressure (PEEPi) during thoracic surgery in the dependent lung of patients intubated with a double-lumen endotracheal tube (DLT) in the lateral position. METHODS Twenty consecutive patients undergoing elective pulmonary resection were anesthetized, paralyzed, and intubated with a DLT. Their lungs were ventilated (Siemens Servo 900 C ventilator; Siemens Elevna; Solna, Sweden) with constant inspiratory flow. Fraction of inspired oxygen, tidal volume (10 mL/kg), frequency (10/min), and inspiratory time/total time (0.33) were kept constant during the study. PEEPi and ventilatory data were measured in the dependent lung in the supine then in the lateral position with a closed hemithorax. The obtained data were analyzed according to the presence (group PH) or absence (group N) of pulmonary hyperinflation determined from the preoperative pulmonary function data as higher than 120% of predicted value of functional residual capacity (FRC) and residual volume (RV). DATA ANALYSIS In the dependent lung of patients in group PH (n = 11), PEEPi was present in the supine (n = 8) and in the lateral (n = 11) positions in the range of 1 to 10 cm H2O. In group N (n = 9), PEEPi was detected in one patient and only in the supine position. In the whole group of 20 patients, the preoperative value of FRC (% predicted) and RV (% predicted) was statistically significantly correlated to the presence of PEEPi, whereas the preoperative FEV1 (% predicted) was poorly related to PEEPi in both positions. There was no significant correlation between the value of PaCO2 and PEEPi during one-lung ventilation (OLV) but patients in group PH had a significantly higher PaCO2 during OLV than group N (p = 0.012). CONCLUSIONS In patients with chronic obstructive lung disease and pulmonary hyperinflation, PEEPi occurs commonly during the period of OLV and only occasionally in patients with normal lungs. As the ventilatory pattern, the size of DLT, and the side of surgery were similar in the two groups of patients, we conclude that the occurrence of PEEPi in our patients was influenced mainly by the preexisting pulmonary hyperinflation and airflow obstruction.

Respiratory Mechanics and Gas Exchange During One-Lung Ventilation for Thoracic Surgery: The Effects of End-Inspiratory Pause in Stable COPD Patients

OBJECTIVE To examine the effects of end-inspiratory pause (EIP) of different durations on pulmonary mechanics and gas exchange during one-lung ventilation (OLV) for thoracic surgery. DESIGN A prospective clinical study. SETTING A university hospital. PARTICIPANTS Eleven patients undergoing elective pulmonary resection with pulmonary hyperinflation on their preoperative pulmonary function studies. INTERVENTIONS Patients were anesthetized, paralyzed, and intubated with a double-lumen endotracheal tube. Their lungs were ventilated with a Siemens 900C ventilator (Siemens; Solna, Sweden), with constant inspiratory flow. Tidal volume, respiratory rate, and inspiratory time were kept constant during the study. MEASUREMENTS AND RESULTS During one-lung ventilation in the lateral decubitus position, three levels of EIP (0%, 10%, and 30%) were applied to the dependent lung in random order. After 15 minutes on the given ventilatory pattern, end-inspiratory and end-expiratory occlusions of at least 5 seconds were performed to obtain respiratory mechanics data. Arterial blood gas samples were drawn to assess gas exchange. Altering the duration of end-inspiratory pause from 0% to 30% resulted in a significant increase in intrinsic positive end-expiratory pressure (PEEPi) from 4.1 cm H2O to 7.0 cm H2O. Arterial oxygenation was significantly decreased from 109.7 to 80.5 mmHg and there was a significant negative correlation between the value of partial pressure of arterial oxygen (PaO2) and PEEPi by altering the duration of end-inspiratory pause. From the preoperative pulmonary function studies, the value of functional residual capacity (FRC) (% predicted) showed a significant negative correlation with the PaO2 changes. Partial pressure of arterial carbon dioxide (PaCO2) was not altered significantly by increasing the duration of end-inspiratory pause. CONCLUSION During the period of OLV in the lateral position of patients with preexisting pulmonary hyperinflation, the magnitude of PEEPi increased and oxygenation decreased significantly, whereas the efficacy of ventilation was not changed by the addition of an end-inspiratory pause to the ventilatory pattern. Because arterial oxygenation is affected by the presence of pulmonary hyperinflation, the method of ventilation should take into account the magnitude of preoperative pulmonary hyperinflation.

Continuous Monitoring of Pulmonary Mechanics With the Sidestream Spirometer During Lung Transplantation

P ERIOPERATIVE care of the patient undergoing single-lung transplantation is challenging for the anesthesiologist because of the major hemodynamic and respiratory changes that occur during this procedure. These patients are extensively monitored hemodynamically (invasive direct arterial pressure, multiple-lumen central venous access, pulmonary artery catheter), but their respiratory monitoring is far less complex, restricted to periodic arterial blood gas determinations, end-tidal CO* monitoring, and pulse oximetry. Despite the fact that several commercially available ventilators (Siemens 9OOC, Elmsford, NY; PuritanBennett 7200, Puritan Bennett, Carlsbad, CA), have built-in devices for continuously measuring flow, pressure, and derived respiratory variables, interest in detailed respiratory mechanics during anesthesia has only recently increased.’ Potential problems associated with this technique are attributable to the sampling site (inside the ventilator), and the influence by gas compression, tubing compliance, and leaks. If the flow and volume measuring device is at the level of the endotracheal tube, these errors can be avoided.* With the sidestream spirometer (Datex Instrumentarium, Helsinki, Finland), continuous monitoring of pressure, volume, and flow characteristics of the respiratory system is possible at the endotracheal tube, with a continuous display of the flow-volume and/or pressure-volume curves, and digital display of ventilatory parameters (Fig 1). The D-lite flow sensor and gas sampling tube is the crucial part of the monitor (Fig 2). This two-sided Pitot tube is essentially a pressure-based flowmeter with two fixed resistances interposed into the airstream. Pressure difference caused by the gas flow is measured between the two pressure ports of the D-lite probe. From the measured flows (flow rate, peak flow) and pressure (end-expiratory, plateau, minimum, and maximum pressures), the inspiratory and expiratory tidal and minute volumes, compliance, and resistance are calculated. Two loops are drawn from these values: flow-volume (resistance) and pressure-volume (compliance) loops3 (Fig 1). A case of single-lung transplantation using continuous flow-volume and pressure-volume loop monitoring is reported.

Prilocaine‐induced methemoglobinemia evidenced by pulse oximetry

Methemoglobinemia was suspected in a healthy 19‐year‐old woman, when the pulse oximeter reading (Spo2) was 88% after a plexus brachialis block with 550 mg (35 ml, 1.5%) prilocaine. The patient was receiving 50% oxygen, and the Pao2 was 48.6 kPa (365 mmHg). After start of methylene blue treatment, with a total dose of 1 mg/kg, the Spo2 showed a gradual increase. This case report emphasises the potential advantage of arterial oxygen saturation monitoring with a pulse oximeter, but also the importance of the correct interpretation of the Spo2 reading.

Continuous noninvasive blood pressure monitoring during thoracic surgery

To evaluate the usefulness of noninvasive blood pressure monitoring during thoracic surgery, blood pressure measurements obtained with the Finapres 2300 (Ohmeda, Boulder, CO) were compared with an intraarterial catheter system in 10 patients undergoing thoracotomy for lobectomy or pneumonectomy. The Finapres measurements were compared with pressure data obtained ipsilaterally from a radial artery catheter-transducer system. The waveforms were recorded using a strip chart recorder; the systolic (SBP) and diastolic blood pressures (DBP) were measured every 20 seconds on the paper trace. Precision and bias were calculated for SBP and DBP for each patient and for the pooled data, with the invasive blood pressure being considered the gold standard. A total of 1,861 measurement pairs were recorded, 938 pairs during one-lung ventilation. The Finapres underestimated SBP during two-lung ventilation, and overestimated SBP during one-lung ventilation. The precision was good and the biases were small, but there were wide individual variations. It is concluded that the Finapres can be useful in estimating the variability and following the trends of radial arterial blood pressure during thoracic surgery, and is an acceptable alternative to invasive blood pressure monitoring.