Corrected End-Tidal PCO2 Accurately Estimates PaCO2 at Rest and During Exercise in Morbidly Obese Adults

Abstract

Measurements of arterial blood gases are important in studies of ventilatory control during exercise and can give valuable information about the effi ciency of ventilation and gas exchange. To avoid the invasive procedure of placing arterial catheters for sampling arterial blood, partial pressure of end-tidal CO 2 (P etco 2 ) has been used as a noninvasive method to estimate Pa co 2 in young, healthy adults at rest and during exercise. [1][2][3][4] These studies have concluded that, although P etco 2 may slightly underestimate Pa co 2 at rest, P etco 2 is a good index of Pa co 2 during resting conditions. During exercise, the instantaneous P aco 2 fl uctuates cyclically with breathing, 5 and the P etco 2 is higher than the average P aco 2 over the complete breathing cycle. 6 Therefore, P etco 2 may overestimate Pa co 2 during exercise, when CO 2 production, ventilation, and tidal volume (V t ) are all increased. 7 To circumvent this problem, Jones et al 3 developed a regression equation to predict Pa co 2 from P etco 2 (P jco 2 ) and V t that corrects for the overestimation of Pa co 2 by P etco 2 :J 2 E T 2 T P CO 5.5 0.9 P CO 2.1 V (Equation 1) where V t is in liters.Background: Obesity affects lung function and gas exchange and imposes mechanical ventilatory limitations during exercise that could disrupt the predictability of Pa CO 2 from end-tidal P CO 2 (P ETCO 2 ), an important clinical tool for assessing gas exchange effi ciency during exercise testing. Pa CO 2 has been estimated during exercise with good accuracy in normal-weight individuals by using a correction equation developed by Jones and colleagues (P JCO 2 5 5.5 1 0.9 3 P ETCO 2 -2.1 3 tidal volume). The purpose of this project was to determine the accuracy of Pa CO 2 estimations from P ETCO 2 and P JCO 2 values at rest and at submaximal and peak exercise in morbidly obese adults. Methods: Pa CO 2 and P ETCO 2 values from 37 obese adults (22 women, 15 men; age, 39 Ϯ 9 y; BMI, 49 Ϯ 7; [mean Ϯ SD]) were evaluated. Subjects underwent ramped cardiopulmonary exercise testing to volitional exhaustion. P ETCO 2 was determined from expired gases simultaneously with temperature-corrected arterial blood gases (radial arterial catheter) at rest, every minute during exercise, and at peak exercise. Data were analyzed using paired t tests. Results: P ETCO 2 was not signifi cantly different from Pa CO 2 at rest (P ETCO 2 5 37 Ϯ 3 mm Hg vs Pa CO 2 5 38 Ϯ 3 mm Hg, P 5 .14). However, during exercise, P ETCO 2 was signifi cantly higher than Pa CO 2 (submaximal: 42 Ϯ 4 vs 40 Ϯ 3, P , .001; peak: 40 Ϯ 4 vs 37 Ϯ 4, P , .001, respectively). Jones' equation successfully corrected P ETCO 2 , such that P JCO 2 was not signifi cantly different from Pa CO 2 (submax: P JCO 2 5 40 Ϯ 3, P 5 .650; peak: 37 Ϯ 4, P 5 .065). Conclusion: P JCO 2 provides a better estimate of Pa CO 2 than P ETCO 2 during submaximal exercise and at peak exercise, whereas at rest both yield reasonable estimates in morbidly obese individuals. Clinicians and physiologists can obtain accurate estimations ...

Aspects of Exercise before or after Bariatric Surgery: A Systematic Review

“…16 studies were identified as possibly relevant and underwent a full text critical appraisal, resulting in 8 exclusions. One study investigated exercise programs for Prader-Willi patients [ 14 ], 3 studies investigated pulmonary physiotherapy in the bariatric population [ 15 , 16 , 17 ], 1 publication appeared to be a case report [ 18 ], 1 was a research protocol [ 19 ], 1 article was only available in Swedish [ 20 ], and 1 article was only available in Spanish [ 21 ].…”

Ventilatory efficiency in athletes, asthma and obesity

“…Often, the end-tidal partial pressure of CO 2 (P ETCO 2 ) is used as a surrogate for P aCO 2 , as it can be easily acquired noninvasively using a breath-by-breath metabolic measurement system. However, multiple studies have shown inaccuracies between arterial blood-gas derived P aCO 2 and expired gas derived P ETCO 2 in patients with pulmonary gas-exchange abnormalities and increased alveolar dead space [21][22][23][24]. Therefore, care should be taken when using end-tidal values to infer P aCO 2 and calculate dead space ventilation.…”

“…Further, individuals with obesity generally adopt a rapid and shallow breathing pattern to minimise the work of breathing, especially at higher ventilatory rates[108]. Despite the rapid and shallow breathing pattern, both arterial P CO 2 (or P ETCO 2 ) and V D /V T are generally within normal ranges during submaximal exercise[23, 108, 113,119,124]. Further, multiple studies have reported a normal V′ E -V′ CO 2 slope, even in morbid obesity, when compared to either non-obese control groups or normative values (table 1 and figure1)[6, 108,[125][126][127].…”

Exertional dyspnoea in obesity

“…In this regard, we recently showed that moderate weight loss of 8% (∼7 kg) reduced the percentage of respiratory muscle contribution to total body oxygen uptake (V′O 2 ) by 26%, which accounted for almost half of the reduction in V′O 2 [39]. Although ventilation is increased in obesity, when taking into account the increased oxygen uptake and carbon dioxide output, ventilation and the ventilatory response to exercise appear to be normal in otherwise healthy obese, morbidly obese, as well as obese patients with sleep apnoea [30,46,50,53] and arterial carbon dioxide tension is maintained within normal limits [54,55].…”