Evaluation of a single transcutaneous PO2-PCO2 sensor in adult patients

We evaluated a new transcutaneous gas monitor designed to measure simultaneously transcutaneous oxygen (PtcO2) and carbon dioxide (PtcCO2) tensions. A total of 514 simultaneous transcutaneous and arterial gases were obtained in 47 adult ICU patients. Mean PtcCO2 was close (SEE less than 4 torr) to mean PaCO2, but mean PtcO2 was considerably less than mean PaO2. However, PtcO2 changes larger than 15 torr virtually always indicated respective increases or decreases in PaO2. Similarly, PtcCO2 changes larger than 5 torr almost invariably indicated a parallel change in PaCO2. From this study we conclude that monitoring of transcutaneous gases yields reliable trend information on arterial gases and that it is a valuable noninvasive adjunct in the monitoring of gas exchange in adult patients.     

Transcutaneous carbon dioxide monitoring during neonatal transport

We studied the value of transcutaneous carbon dioxide (PtcCO2) monitoring during neonatal transport. Thirty-two neonates with respiratory distress were alternately enrolled in an experimental group (results of PtcO2 and PtcCO2 available for clinical management) and a control group (results of only PtcO2 available). Although differences were not significant, infants in the experimental group had more changes in the intermittent mandatory ventilation (IMV) settings during transport, and more such infants arrived at the receiving hospital with acceptable pH and PCO2 values. On arrival at the receiving hospital, two patients in the control group had acidosis and hypercarbia and were placed on IMV immediately on arrival. No such patients were encountered in the experimental group. For patients needing IMV during transport, the percentage of study time spent with PtcCO2 measurements in the normal range (35 to 45 torr) was greater for the experimental group (p less than .02). Continuous PtcCO2 monitoring during transport offers the opportunity to further decrease the risks of transporting a critically ill neonate.     

Monitoring and analysis of oxygenation and ventilation during rigid bronchoscopic neodymium-YAG laser resection of airway tumors

Neodymium-YAG (yttrium-aluminum-garnet) laser resection of obstructing and inoperable tumors of the large airways is used as palliative therapy to improve the quality of survival in patients by alleviating airway obstruction. Rapid changes in oxygenation and ventilation can occur during these procedures. In a study of 14 patients, transcutaneous oxygen (PtcO2) and carbon dioxide (PtcCO2) monitors responded slowly to these changes and frequently provided misleading values. Pulse oximetry (SNO2) accurately reflected arterial oxygen saturation but did not indicate severe desaturation until arterial oxygen tension approached dangerously low values. Thus, we did not find PtcO2 or PtcCO2 monitoring to be clinically useful during neodymium-YAG laser resection of airway tumors through a rigid bronchoscope. SNO2 was clinically useful and accurate; however, a large decrement in oxygenation may occur before changes in oxygen saturation ensue and are detected.     

Cardiopulmonary and intracranial pressure changes related to endotracheal suctioning in preterm infants

Although endotracheal (ET) suctioning is performed frequently in sick newborn infants, its effects on cardiorespiratory variables and intracranial pressure (ICP) have not been thoroughly documented in neonates greater than 24 h who were not paralyzed while receiving mechanical ventilation. This study evaluates these changes in preterm infants who required ventilatory assistance. We measured transcutaneous PO2 and PCO2 (PtcO2 and PtcCO2, respectively), intra-arterial BP, heart rate, ICP, and cerebral perfusion pressure (CPP) before, during, and for at least 5 min after ET suctioning in 15 low birth weight infants less than 1500 g and less than or equal to 30 days of age. One infant was studied twice. A suction adaptor was used to avoid disconnecting the patient from the ventilator and to attempt to minimize hypoxemia and hypercapnia during suctioning. The patients were studied in the supine position and muscle relaxants were not used. PtcO2 decreased 12.1% while PtcCO2 increased 4.7% 1 min after suctioning; however, greater increases in mean BP (33%) and ICP (117%) were observed during suctioning. CPP also increased during the procedure. ICP returned to baseline almost immediately, whereas BP remained slightly elevated 1 min after suctioning. Our findings demonstrate that ET suctioning significantly increases BP, ICP, and CPP in preterm infants on assisted ventilation in the first month of life. These changes appear to be independent of changes observed in oxygenation and ventilation.     

Transcutaneous O2 and CO2 monitoring of high risk surgical patients during the perioperative period

The usefulness of noninvasive transcutaneous oxygen (PtcO2) and carbon dioxide (PtcCO2) sensors as well as invasive monitoring of flow and oxygen transport were evaluated in the perioperative period of a small series of high risk surgical patients. We used the pattern of physiological events preceding intraoperative death as the criteria for evaluation of the relative usefulness of these variables. Cardiac output (CO), oxygen delivery (DO2), and O2 consumption (VO2) provided the earliest warning of impending circulatory deterioration and were most useful during critical nonlethal circulatory episodes; these were closely paralleled by the PtcO2 index (PtcO2/PaO2); the PtcCO2 was less sensitive. Heart rate (HR) and mean arterial pressure (MAP) were highly variable with frequent changes unrelated to change in flow and O2 transport.     

Factors influencing transcutaneous oxygen and carbon dioxide measurements in adult intensive care patients

Transcutaneous PO2 (PtcO2) is suggested to reflect tissue oxygenation in intensive care patients, whereas transcutaneous PCO2 (PtcCO2) is advocated as a noninvasive method for assessing PaCO2. In 24 critically ill adult patients (mean Apache II score 14.2, SD 4.7) we investigated the impact of variables that are commonly thought to determine PtcO2 and PtcCO2 measurements. A linear correlation was found between PtcO2 and PaO2 (r = 0.6; p less than or equal to 0.0001) and between PtcO2 and mean arterial blood pressure (MAP; r = 0.42; p less than or equal to 0.003). Cardiac index (CI) correlated with tc-index (PtcO2/PaO2; r = 0.31; p less than or equal to 0.03). There was no relationship between PtcO2 and hemoglobin concentration (Hb) and the position of the oxygen dissociation curve (ODC). Stepwise multiple regression analysis demonstrated a significant influence of PaO2 and MAP on PtcO2. The contribution of CI, Hb and the ODC was not significant. Only 40% of the variability of a single PtcO2 measurement could be explained by PaO2 and MAP. A significant linear correlation was demonstrated between PtcCO2 and PaCO2 (r = 0.76; p less than or equal to 0.0001) but not between PtcCO2 and CI, MAP and arterial base excess (BEa). Stepwise multiple regression analysis revealed an influence of PaCO2 and of CI on PtcCO2; 66% of the variability of a single PtcCO2-value could be explained by PaCO2 and CI. Our data demonstrate that transcutaneous derived gas tensions result from complex interaction between hemodynamic, respiratory and local factors, which can hardly be defined in ICU-patients.     

Factors affecting heated transcutaneous PO2 and unheated transcutaneous PO2 in preterm infants

The authors evaluated transcutaneous PCO2 (PtcCO2) and PO2 (PtcO2) electrodes in 25 infants. Their diagnosis were severe hyaline membrane disease (HMD) (18), aspiration syndrome (3), severe hydrops, (3) persistent fetal circulation (6), and the others, congenital pneumonia, congenital plural effusion, pulmonary hemorrhage. In most all, the cardiovascular system was compromised, i.e., PDA with congestive heart failure and shock. PtcO2 electrode was heated to 43.5 degrees C while PtcCO2 electrode was not heated. Simultaneous arterial blood pressure (ABP), pH, arterial blood gases were obtained with the transcutaneous gas measurements. The data were analyzed first dividing all the paired arterial and transcutaneous gas tensions into those with and without cardiovascular drugs (dopamine, isoproterenol), and second, the paired values were divided into those taken (a) during severe acidosis (pH less than 7.25), (b) hypotension (less than 2 SD) of normal, and (c) hypotension and acidosis. These data show: (1) the unheated PtcCO2 and heated PtcO2 accurately correlated with the simultaneous arterial measurements: (2) PtcCO2 reflects tissue PCO2; (3) drugs affect both the PtcCO2 and PtcO2; (4) elevated PtcCO2 dissociating from the simultaneous PaCO2 in neonates with cardiovascular compromise results from decreased tissue perfusion. These data suggest that transcutaneous gas sensors perform dual functions; first, as gas monitors in patients without cardiovascular alterations, and second, in patients with cardiovascular compromise, PtcCO2 reflected tissue perfusion and PtcCO2 monitored oxygen delivery to the tissues.     

Use of transcutaneous O2 monitoring in the intraoperative management of severe peripheral vascular disease

Transcutaneous O2 (PtcO2) and CO2 (PtcCO2) monitoring has been used in infants, in critically ill adults, and more recently, in peripheral vascular disease. The present report compares values of centrally placed chest (PtcO2 and PtcCO2) sensors with values of peripherally placed calf (Ptc'O2 and Ptc'CO2) sensors in a patient with severe peripheral vascular disease during performance of an axillofemoral bypass graft. The calf Ptc'O2 values may be expressed as a ratio of their corresponding PaO2 values or as a percentage of the chest PtcO2, i.e., calf Ptc'O2/chest PtcO2 X 100. The ratio reflects local tissue perfusion in the face of fluctuating PaO2 and central PtcO2 values. The data demonstrate that PtcO2 sensors reflect tissue blood flow and oxygenation and, therefore, are useful measures of tissue perfusion, especially during limb revascularization.     

Setting positive end-expiratory pressure during jet ventilation to replicate the mean airway pressure of oscillatory ventilation

BACKGROUND: High-frequency ventilation can be delivered with either oscillatory ventilation (HFOV) or jet ventilation (HFJV). Traditional clinician biases may limit the range of function of these important ventilation modes. We hypothesized that (1) the jet ventilator can be an accurate monitor of mean airway pressure (P (aw)) during HFOV, and (2) a mathematical relationship can be used to determine the positive end-expiratory pressure (PEEP) setting required for HFJV to reproduce the P (aw) of HFOV. METHODS: In phase 1 of our experiment, we used a differential pressure pneumotachometer and a jet adapter in-line between an oscillator circuit and a pediatric lung model to measure P (aw), PEEP, and peak inspiratory pressure (PIP). Thirty-six HFOV setting combinations were studied, in random order. We analyzed the correlation between the pneumotachometer and HFJV measurements. In phase 2 we used the jet as the monitoring device during each of the same 36 combinations of HFOV settings, and recorded P (aw), PIP, and DeltaP. Then, for each combination of settings, the jet ventilator was placed in-line with a conventional ventilator and was set at the same rate and PIP as was monitored during HFOV. To determine the appropriate PEEP setting, we calculated the P (aw) contributed by the PIP, respiratory rate, and inspiratory time set for HFJV, and subtracted this from the goal P (aw). This value was the PEEP predicted for HFJV to match the HFOV P (aw). RESULTS: The correlation coefficient between the pneumotachometer and HFJV measurements was r = 0.99 (mean difference 0.62 +/- 0.30 cm H(2)O, p < 0.001). The predicted and actual PEEP required were highly correlated (r = 0.99, p < 0.001). The mean difference in these values is not statistically significantly different from zero (mean difference 0.25 +/- 1.02 cm H(2)O, p > 0.15). CONCLUSIONS: HFJV is an accurate monitor during HFOV. These measurements can be used to calculate the predicted PEEP necessary to match P (aw) on the 2 ventilators. Replicating the P (aw) with adequate PEEP on HFJV may help simplify transitioning between ventilators when clinically indicated.     

Simultaneous monitoring of transcutaneous blood gases and heart-rate variability in neonates

Instantaneous heart rate, indices of long-term and short-term heart-rate variability (HRV), and transcutaneous O2 (PtcO2) and CO2 (PtcCO2) tensions were recorded simultaneously on 164 occasions in 16 neonates. There was significant inverse correlation between PtcCO2 and both HRV indices, while no linear correlation was detected between HRV and PtcO2. The heart rate was positively related to PtcCO2 and inversely correlated with PO2. It is suggested that increasing PCO2 decreases medullary pH, thus increasing heart rate and decreasing HRV. We conclude that each of these monitoring variables is unique: the transcutaneous measurements display the efficiency of respiration, whereas the heart-rate patterns reflect the dynamic condition of the autonomic nervous system.     

Setting and monitoring of high-frequency jet ventilation in severe respiratory distress syndrome

High-frequency jet ventilation (HFJV) is used in respiratory distress syndrome (RDS) to avoid high airway pressures and barotrauma. This study was designed to find rational strategies to regulate oxygenation and alveolar ventilation at HFJV and to determine appropriate monitoring methods. Seven dogs were subjected to total lung lavage with saline to induce RDS. PEEP was increased at conventional intermittent positive-pressure ventilation until re-expansion was indicated by a PaO2 of 300 torr at an FIO2 of 1.0 HFJV at 4 and 15 Hz was each tried at 0 and 10 cm H2O PEEP. Intermittent low-frequency inflations were also added to HFJV at 0 PEEP. Lung expansion was maintained without circulatory depression by adjustment of minute ventilation (VE) delivered by the HFJ ventilator; external PEEP was a useful complement. PaCO2 was controlled by frequency adjustment. HFJV at 4 Hz resulted in hypocapnia; intermittent low-frequency inflations had no effect. VE monitoring, CO2 elimination monitoring, and PEEP adjustment was done with a standard ventilator during HFJV. This study illustrates that HFJV is efficient in RDS; VE and external PEEP strongly influence oxygenation and may be used to regulate this factor, and frequency affects CO2 elimination, thus suggesting a method of PaCO2 control.     

Driving pressure and arterial carbon dioxide tension during high-frequency jet ventilation in postoperative patients

To achieve normocarbia during conventional mechanical ventilation, ventilator settings are determined initially on the basis of body weight. The best ventilator settings for CO2 elimination during high-frequency jet ventilation (HFJV) have not been so clearly defined. A recent study has suggested that eucarbia will be obtained with HFJV when tidal volume (VT) per kg of body weight is kept within a narrow, well-defined range. In the same study, a "bench test" demonstrated that VT was directly proportional to the jet ventilator driving pressure (DP). The goal of our study was to confirm this recommended VT/kg to obtain eucarbia and to determine whether the relation observed between VT and DP in the laboratory was true clinically. We studied 14 patients admitted to the ICU for postoperative support. We determined a good correlation between DP and VT/kg (r = .811, p less than .001) for the group as a whole and a good inverse correlation between DP or VT/kg and PaCO2 for most individual patients; however, there was a poor inverse correlation between DP or VT/kg and PaCO2 for the group as a whole, due to wide patient-to-patient variation in the efficiency of jet ventilation. We conclude that there is no universal formula for setting jet ventilator DP or VT/kg to affect normocarbia in humans.     

Invasive and noninvasive haemodynamic monitoring of acutely ill sepsis and septic shock patients in the emergency department.

The objective of this study was to describe early circulatory events of patients presenting to the emergency department (ED) with severe sepsis or septic shock. Invasive and noninvasive monitoring were used to evaluate sequential patterns of both central haemodynamics and peripheral tissue perfusion/oxygenation and to test the hypothesis that increased cardiac output is an early compensation to increased body metabolism. This is a prospective observational study of 45 patients who entered the ED with severe sepsis or septic shock in an urban academic ED. Invasive clinical monitoring was performed using a radial artery catheter and a thermodilution pulmonary artery catheter. Noninvasive monitoring consisted of an improved thoracic electrical bioimpedance device to estimate cardiac output; pulse oximetry for arterial saturation to reflect changes in pulmonary function, and transcutaneous oxygen (PtcO2) and carbon dioxide tensions (PtcCO2) as a reflection of tissue perfusion. Survivors had higher cardiac index, mean arterial pressure (MAP), and better tissue perfusion as measured by PtcO2, oxygen delivery, and oxygen consumption. Oxygen extraction ratio was higher in the nonsurvivors (p < 0.05) and there were episodes of high PtcCO2 values in the nonsurvivors. No significant differences were found in the heart rate, PAOP (wedge pressure) and SaO2 by pulse oximetry between the two groups. It is concluded that ED monitoring septic patients provides a unique opportunity to document early physiologic interactions between cardiac, pulmonary, and tissue perfusion functions in surviving and nonsurviving patients with septic shock. The data is consistent with the concept that increased cardiac output is an early compensatory response to increased body metabolism. Real time haemodynamic monitoring of patients in the ED provides early warning of outcome and may be used to guide therapy.     

High-frequency jet ventilation in the postoperative period: a review of 100 patients

One hundred patients were ventilated with high-frequency jet ventilation (HFJV) during the initial 24-h postoperative period in the surgical and neurosurgical ICUs. Eighty-three were successfully weaned, 2 could not be ventilated adequately with HFJV, and 15 with criteria of acute respiratory failure received HFJV for up to 21 days. A HFJV delivery system consisted of jetting and entrainment systems, both with their own humidification designs. An initial mode of HFJV using 35 psi, jet rate 100 cycle/min and inspiratory time 30% provided a mean PaCO2 of 34 torr in 38 patients studied. A comparison of HFJV without and with a positive end-expiratory pressure (PEEP) of 10 cm H2O indicated a decrease in mean Qsp/Qt from 17% to 13% with decrease in cardiac index (CI) from 3.39 to 2.81 L/min X m2; this effect is similar to PEEP applied to a conventional ventilator. Weaning proved to be simple and comfortable for the patient. In the light of our experience, we believe that HFJV is both feasible and practical for the postoperative patient and should be introduced into routine clinical use.     

Simple and accurate monitoring of end-tidal carbon dioxide tensions during high-frequency jet ventilation

To determine whether end-tidal carbon dioxide tension (PETCO2) accurately reflects PaCO2 during high-frequency jet ventilation (HFJV), 43 studies were performed on eight mongrel dogs with normal lungs. During HFJV, minute volume was modified to obtain a range of PaCO2 values from 15.5 to 74.5 torr. When PETCO2 was measured with an infrared gas analyzer, there was a poor correlation between PaCO2 and PETCO2 values. However, when the high-frequency ventilator was adjusted to deliver large tidal-volume (sigh) breaths, PETCO2 values were significantly (r = 0.94, p less than .001) correlated with PaCO2. Our data suggest that the PETCO2 of alveolar gas is an accurate indicator of the PaCO2 during HFJV in nondiseased lungs.     

The significance of hypoxemia with low inspired O2 fraction before extubation

Arterial and transcutaneous O2 (PtcO2) and CO2 (PtcCO2) tensions, arterial O2 saturations (SaO2) and P50 values were measured in 47 patients before extubation. In order to unmask ventilation to perfusion (VA/Q) inequality, all variables were obtained without CPAP and with FIO2 of 0.40 as well as with CPAP of 5 cm H2O and FIO2 of 0.40, 0.35, 0.30, 0.25, and 0.21. Eighty to 90% of the patients had PaO2/FIO2 lower than 300 torr and no significant difference in PaO2 or SaO2 was found between those who were successfully extubated (group S, n = 38) and those who required reintubation (group R, n = 9). On the other hand, the patients in group R had significantly lower P50 values, and their PtcO2 values decreased at a greater incline with the lowering of FIO2 than those in group S. Pulmonary dysfunction does not solely explain the need for reintubation in group R. It is obvious that arterial hypoxemia may become more dangerous when the patient has a low P50, anemia, or hypermetabolism. Because PtcO2 seems to uncover these factors, it is a valuable method for predicting the patient's condition before extubation.     

Comparison of noninvasive measurements of carbon dioxide tension during withdrawal from mechanical ventilation

End tidal CO2 tension (PetCO2) and transcutaneous CO2 tension (PtcCO2) were compared with arterial CO2 (PaCO2) before and after withdrawal of mechanical ventilation in 20 patients predisposed to hypercarbia. With stable PaCO2 during mechanical ventilation, the correlation coefficient (r) between PaCO2 and PetCO2 was .9, and between PaCO2 and PtcCO2, .87. PtcCO2 considerably overestimated PaCO2 in three patients who were receiving dopamine. After withdrawal of mechanical ventilation, changes in PaCO2 were closely paralleled by changes in PetCO2 and PtcCO2 (r = .82 and .86, respectively). Nine of 20 patients had an increased PaCO2 of 10 torr or greater. In eight of these, PetCO2 and PtcCO2 rose by at least 5 torr, and in seven, the rise in PetCO2 and PtcCO2 was within 5 torr of the rise in PaCO2. During mechanical ventilation, PetCO2 and PtcCO2 estimated stable PaCO2 with sufficient accuracy for clinical use, except in patients with cutaneous vasoconstriction. After withdrawal of mechanical ventilation, changes in PetCO2 and PtcCO2 were predictive of important PaCO2 increases, warranting continued exploration and evaluation as to their use in monitoring patients predisposed to hypercarbia.     

A cart to provide high frequency jet ventilation during transport of neonates

We report the evaluation of a cart we created to provide high frequency jet ventilation (HFJV) to neonates during intrahospital or interhospital transport. DESCRIPTION: The cart carries a conventional ventilator, jet ventilator (JV), incubator, gas blender, 3 E cylinders of oxygen and 2 of air, uninterruptible electric power supply (UPS), 2 syringe infusion pumps, cardiac monitor, and oximeter. EVALUATION METHODS: To determine the available operating time of the ventilators, we ran tests with 60% and 100% oxygen, high and low ventilator settings, 2.5-mm and 3.5-mm endotracheal tubes, and lung simulator set for low and high time constants. With five different combinations of these variables, the system was run to exhaustion of its gas supply. To determine the operating time limit of the UPS, we used it to operate the JV until the low-battery alarm sounded. RESULTS: The UPS always provided electrical power for at least 2 hours. In no case did a single cylinder of oxygen fail to power the system for less than 20 min. Because the cart carries 3 cylinders of oxygen and 2 of air, under the conditions tested a minimum of 60 min of continuous operation, using 100% oxygen, should be available during those portions of transports when the system is away from hospital and ambulance bulk power sources and is dependent on its own UPS and E cylinders of gas. EXPERIENCE: We have used the cart on two occasions to transport a 30-week gestational age, 1-kg, HFJV-dependent infant, first from ICU to surgery, then to another hospital for cardiac catheterization. Total transport time was 3 hours; there were no problems. The cart has also been used to transport three patients between hospitals during ECMO, without HFJV. CONCLUSIONS: Our HFJV transport system is adequate to transport an HFJV-dependent infant during the 30 to 60 minutes that may elapse when the cart is away from ambulance or hospital sources of electricity and gas. Available operating time with an HFJV transport system should be estimated conservatively; when an infant is dependent on HFJV, it would be well to have aircraft backup in case of ambulance breakdown or other contingencies.     

Transcutaneous oxygen monitoring beyond the neonatal period

Transcutaneous O2 (PtcO2) tensions were compared with PaO2 measurements in 57 infants and children (age range 2 wk to 15.5 yr) using electrode temperatures of 43 degrees and 44 degrees C. At both temperatures, the relationships between PtcO2 and PaO2 were linear over the whole range of data (PaO2 39.75 to 120 torr) although mean PtcO2/PaO2 fell from 44 degrees to 43 degrees C. Skin stripping by repeated applications of adhesive tape immediately before electrode placement did not improve these relationships. In an additional 20 children with a mean age of 2.4 yr (range 0.08 to 15.85) who were being investigated for sleep-disordered breathing, the mean PaO2/PtcO2 ratio of 1.22 at 44 degrees C was used as a correction factor during air calibration for PtcO2. This resulted in a mean PtcO2/PaO2 of 0.99 (range 0.83 to 1.15) provided blood flow is not impaired. Extending the monitoring period from 4 to 8 h between site changes did not result in any burns or persisting erythema. In hemodynamically stable infants and children, and at electrode temperatures of 44 degrees C and 43 degrees C, PtcO2 is linearly related to PaO2 over a wide range of PaO2 values. At an electrode temperature of 44 degrees C, PtcO2 can be arterialized effectively by allowing for transepidermal O2 loss during air calibration; at this electrode temperature, intervals between site changes can be extended safely up to 8 h.