Central venous O2 saturation and rate of arterial desaturation during obstructive apnea

Abstract

We examined the rate of fall of arterial O2 saturation (dSao2/dt) after apnea onset in four spontaneously breathing adult male baboons. We postulated that a lower mixed venous O2 saturation (Svo2) would steepen dSao2/dt by more rapid depletion of alveolar O2. Single isolated (NREP) and five or more sequential repetitive apneas (REP) were created by clamping an indwelling cuffed endotracheal tube at end expiration. Fiberoptic catheters were used for continuous monitoring of Sao2, Svo2, and cardiac output. The mean dSao2/dt for all duration NREP apneas was 0.60%/s. Mean dSao2/dt increased above base line for each consecutive REP apnea and was higher in 60 s than in 45 and 30 s REP apnea series. The increase in dSao2/dt corresponded closely with the fall in preapneic Svo2. Preapneic arterial O2 content fell during successive REP apneas but the maximal decrement from base line (1.3 ml/dl) was much less than the maximal decrement in preapneic mixed venous O2 content of 5.1 ml/dl. Preapneic cardiac output for NREP apneas and nadir cardiac output for REP apneas remained constant. Nadir cardiac output for NREP apneas showed higher values for longer duration apneas. We concluded that dSao2/dt is inversely related to preapneic Svo2.

Oxygen Transport and Utilization during Feeding in the Young Lamb

“…This decrease in body oxygen stores, in conjunction with the observed increase in total body oxygen consumption and increased total body oxygen extraction, may, as we argue below, be a key predisposing factor in the onset of rapidly developing cyanosis during feeding. The cyclic pattern of Sa,Oµ desaturation and resaturation, coupled with a sustained decrease in Sv,Oµ during feeding, closely resembles the pattern of Sa,Oµ and Sv,Oµ observed during repetitive apnoea (Fletcher et al 1989;Poets & Southall, 1991;Samuels, Poets, Stebbens, Alexander & Southall, 1992;Poets, Stebbens, Samuels & Southall, 1993;Wilkinson et al 1995 Total body oxygen consumption (ýOµ) increased during the nonsucking periods of feeding and remained elevated into the recovery period (P û 0·05). Systemic oxygen transport (SOT) was unchanged while total body oxygen extraction (TBOE) increased significantly (P û 0·05).…”

“…the rate of desaturation in the second and subsequent apnoeas increases as preapnoeic Sv,Oµ decreases, even though Sa,Oµ may return to normal between apnoeas (Fletcher et al 1989;Wilkinson et al 1995). Just as in apnoea, where Sv,Oµ is of key importance in determining the rate at which arterial desaturation occurs (Fletcher et al 1989;Wilkinson et al 1995), Sv,Oµ may similarly be important in determining the rate at which Sa,Oµ decreases during an epoch of feeding.…”

“…Just as in apnoea, where Sv,Oµ is of key importance in determining the rate at which arterial desaturation occurs (Fletcher et al 1989;Wilkinson et al 1995), Sv,Oµ may similarly be important in determining the rate at which Sa,Oµ decreases during an epoch of feeding. Rapid arterial desaturation would be predicted to occur during feeding if apnoea develops, while body Oµ stores (Sv,Oµ) are decreased.…”

“…When apnoea occurs in a series the rate and extent of desaturation commonly increases with each succeeding apnoeic event even though Sa,Oµ may return to normal between apnoeas. In explanation of the apnoeic desaturation pattern, Fletcher et al (Fletcher, Kass, Thornby, Rosborough & Miller, 1989) and Wilkinson et al (Wilkinson, Berger, Blanch & Brodecky, 1995) have shown that it is the body oxygen stores, and in particular the mixed venous oxyhaemoglobin saturation level (Sv,Oµ), that are pivotal in determining the rate of arterial desaturation during repeated apnoea. Other factors important in determining oxygen storage and utilization include the initial Sa,Oµ (Strohl & Altose, 1980), lung volume (Henderson-Smart, 1980;Bradley et al 1985;Findley, Ries, Tisi & Wagner, 1986), and the rate of oxygen consumption and transport.…”

Simulating hypoxia and modelling the airway

“…If we wanted more precision, we could certainly take account of air resistance, but if we try to include an exhaustive array of influencing factors, we will sacrifice simplicity of the model for enhanced precision. So often, in modelling, the balance between the beauty of parsimony and the necessity of complexity has to be carefully considered [1][2][3][4].…”