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PubMed1993

Extracorporeal life support for status asthmaticus.

Status asthmaticus is a life-threatening form of reactive airway disease, refractory to initial control with ordinary medical measures, sometimes requiring mechanical ventilatory assistance. In this report, we describe a patient whose bronchospasm could not be controlled with conventional measures, with severe respiratory acidosis (PaCO2 consistently > 100 mm Hg), who was successfully supported with extracorporeal life support (ECLS). During ECLS, arterial blood gas values rapidly returned to normal, and bronchospasm resolved during the subsequent 24 h. The patient was extubated hours later, and discharged to home 4 days later, neurologically normal. We believe that this represents the first application of this technology to this disease in an adult patient.

Adult↗
PubMed1991

A case of glutaric acidemia type II (severe multiple acyl-CoA dehydrogenation disorder) with subsequent prenatal exclusion in a sibling.

A case of severe multiple acyl-CoA dehydrogenation disorder is described. This is the second such case reported to have had an elevated maternal serum alpha-fetoprotein and normal amniotic alpha-fetoprotein. The child's 3-day extrauterine life was characterized by intractable acidosis, respiratory distress, and ventricular fibrillation. The characteristic biochemical, morphologic, and microscopic findings of this condition are reviewed. A subsequent pregnancy was evaluated using chorionic villus sampling and analysis of cultured trophoblasts. The trophoblasts were biochemically normal, and a normal child was subsequently delivered. Since the manifestations of this disorder developed in utero, prenatal diagnosis and therapy offer the only hope for a more prolonged survival.

Acidosis↗
PubMed1997

Midazolam and ketamine induction before halothane anaesthesia in ponies: cardiorespiratory, endocrine and metabolic changes.

Six Welsh gelding ponies were premedicated with 0.03 mg/kg of acepromazine intravenously (i.v.) prior to induction of anaesthesia with midazolam at 0.2 mg/kg and ketamine at 2 mg/kg i.v.. Anaesthesia was maintained for 2 h using 1.2% halothane concentration in oxygen. Heart rate, electrocardiograph (ECG), arterial blood pressure, respiratory rate, blood gases, temperature, haematocrit, plasma arginine vasopressin (AVP), dynorphin, beta-endorphin, adrenocorticotropic hormone (ACTH), cortisol, dopamine, noradrenaline, adrenaline, glucose and lactate concentrations were measured before and after premedication, immediately after induction, every 20 min during anaesthesia, and at 20 and 120 min after disconnection. Induction was rapid, excitement-free and good muscle relaxation was observed. There were no changes in heart and respiratory rates. Decrease in temperature, hyperoxia and respiratory acidosis developed during anaesthesia and slight hypotension was observed (minimum value 76 +/- 10 mm Hg at 40 mins). No changes were observed in dynorphin, beta-endorphin, ACTH, catecholamines and glucose. Plasma cortisol concentration increased from 220 +/- 17 basal to 354 +/- 22 nmol/L at 120 min during anaesthesia; plasma AVP concentration increased from 3 +/- 1 basal to 346 +/- 64 pmol/L at 100 min during anaesthesia and plasma lactate concentration increased from 1.22 +/- 0.08 basal to 1.76 +/- 0.13 mmol/L at 80 min during anaesthesia. Recovery was rapid and uneventful with ponies taking 46 +/- 6 min to stand. When midazolam/ketamine was compared with thiopentone or detomidine/ketamine for induction before halothane anaesthesia using an otherwise similar protocol in the same ponies, it caused slightly more respiratory depression, but less hypotension. Additionally, midazolam reduced the hormonal stress response commonly observed during halothane anaesthesia and appears to have a good potential for use in horses.

Adjuvants, Anesthesia↗
PubMed1976

The effect of hypercapnia on a blood-brain barrier mechanism in foetal and new-born sheep.

1. The effect of marked hypercapnia (arterial PCO2 100 mmHg), nonrespiratory acidosis (pH 6-95-7-15) or hypoxia (arterial PO2 10-15 mmHg) upon penetration of labelled sucrose from blood into brain and c.s.f. has been investigated in exteriorized foetal sheep and new-born lambs. 2. In hypercapnia there was a consistent increase in c.s.f./plasma sucrose ratio after 90 min I.V. sucrose to four to five times control. Brain/plasma sucrose ratios were more variable. Usually there was an increase (up to three-and-a-half-times control); sometimes there was no change or even a decrease. The effect of hypercapnia on sucrose penetration was reversible. 3. Hypercapnia reduced c.s.f. secretion rate to approximately half the control value. Hypercapnia also caused a decrease in brain extracellular space. 4. Non-respiratory acidosis did not affect sucrose penetration. Hypoxia caused a decrease in brain/plasma sucrose ratio. 5. It is concluded that hypercapnia can cuase an increase in cerebral vascular permeability to sucrose in foetal and new-born sheep. Some possible mechanisms are discussed.

Acid-Base Equilibrium↗
PubMedDate not supplied

Cardiorespiratory effects of forced activity and digestion in toads.

Digestion and physical activity are associated with large and sometimes opposite changes in several physiological parameters. Gastric acid secretion during digestion causes increased levels of plasma bicarbonate ([HCO-3](pl)), whereas activity leads to a metabolic acidosis with increased lactate and decrease in plasma bicarbonate. Here we describe the combined effects of feeding and activity in the toad Bufo marinus to investigate whether the increased bicarbonate buffering capacity during digestion (the so-called alkaline tide) protects the acid-base disturbance during activity and enhances the subsequent recovery. In addition, we describe the changes in arterial oxygen levels and plasma ion composition, as well as rates of gas exchange, heart rates, and blood pressures. Toads were equipped with catheters in the femoral artery and divided into four experimental regimes: control, digestion, forced activity, and forced activity during the postprandial period (N=6 in each). Digestion induced a significant metabolic alkalosis with increased [HCO-3](pl) that was completely balanced by a respiratory acidosis; that is, increased arterial Pco(2) (P(a)co(2)), so that arterial pH (pH(a)) did not change. Forced activity led to a substantial reduction in pH(a) by 0.43 units, an increase in plasma lactate concentration by 12.5 mmol L(-1), and a reduction in [HCO-3](pl) of similar magnitude. While digesting animals had higher P(a)co(2) and [HCO-3](pl) at rest, the magnitude and duration of the changes in arterial acid-base parameters were similar to those of fasting animals, although the reduction in pH(a) was somewhat lower (0.32 units). In conclusion, while recovery from the acidosis following exercise did not seem to be affected by digestion, the alkaline tide did slightly dampen the reduction in pH(a) during activity.

Acid-Base Equilibrium↗
PubMed1999

Exercise and forced submergence in the pond slider (Trachemys scripta) and softshell turtle (Apalone ferox): influence on bimodal gas exchange, diving behaviour and blood acid-base status

The dynamics of bimodal respiration, diving behaviour and blood acid-base status in the softshell turtle Trachemys scripta and the pond slider Apalone ferox were investigated at rest and under conditions of stress induced by exercise and forced submergence. During periods of forced submergence, only A. ferox doubled its aquatic gas exchange rate. Both A. ferox and T. scripta increased their aerial gas exchange profoundly following exercise and forced submergence, a pattern indicative of increased anaerobic respiration. Emersion duration increased significantly in A. ferox following forced submergence, and mean apnoeic time decreased significantly in A. ferox following exercise, indicating that a larger proportion of time at the surface was spent ventilating. Also, A. ferox maintained a one-breath breathing bout regardless of treatment. Submergence produced a respiratory acidosis in the plasma of approximately 0.2 pH units in magnitude in T. scripta and a mixed respiratory/metabolic acidosis of 0.4 pH units in A. ferox. Exercise induced an acidosis of 0.2 pH units of primarily metabolic origin in both species. Intra-erythrocyte pH was also reduced in both species in response to submergence and exercise. Both intracellular and extracellular acidoses were more severe and longer lasting in A. ferox after each treatment. Plasma [HCO3-] decreased by 25 % in both species following exercise, but only in A. ferox following submergence. Plasma lactate concentrations increased by equal amounts in each species following exercise; however, they returned to resting concentrations sooner in T. scripta than in A. ferox. A. ferox had significantly higher lactate levels than T. scripta following forced submergence as well as a slower recovery time. A. ferox, which is normally a good bimodal gas exchanger at rest, utilizes aerial respiration to a greater extent when under respiratory and/or metabolic stress. T. scripta, although almost entirely dependent on aerial respiration, is physiologically better able to deal with the respiratory and metabolic stresses associated with both forced submergence and exercise.

Journal Article↗
PubMed1989

Routine use of dexamethasone for the prevention of postextubation respiratory distress.

We evaluated the routine use of dexamethasone for the prevention of postextubation respiratory distress by entering 60 ventilated infants into a prospective, randomized, blinded study. Thirty minutes before extubation, 30 infants were given a single dose of intravenous dexamethasone (0.25 mg/kg), and 30 infants received saline placebo. Infants were intubated orotracheally for at least 48 hours following a single intubation and were maintained on low ventilator settings (F10(2) less than 0.35, intermittent mandatory ventilation [IMV] less than 6, positive end-expiratory pressure [PEEP] less than 4) at least 12 hours before extubation. Following extubation, all infants weighing less than 1500 g were routinely placed on nasal continuous positive airway pressure (NCPAP). There was no difference between the two groups in postextubation Downes' score, serum pH, PCO2, or oxygen requirement at 30 minutes, 6 hours, and 24 hours. Respiratory acidosis occurred in one steroid-treated patient and in two placebo-treated infants. Stridor occurred in four infants in each group. No infant developed postextubation lobar atelectasis or required reintubation. We conclude that prophylactic administration of dexamethasone does not improve the immediate postextubation course of infants following a single intubation and that its routine use at the time of extubation is not indicated.

Dexamethasone↗
PubMed1986

Comparison of isoflurane and halothane as inhalation anaesthetics in the dog.

A number of clinically important features of isoflurane anaesthesia were studied in comparison to those of halothane. Two groups of dogs were used. After light premedication, anaesthesia was induced by mask, and both groups of dogs were maintained for 30 minutes at 1.5 X MAC value of either halothane or isoflurane in a combination of oxygen and nitrous oxide (50:50). All animals were ventilating spontaneously. There was no difference in the speed of induction of the halothane and isoflurane groups. Blood pressure in both groups dropped to approximately 7.5 kPa (56 mm Hg) during maintenance anesthesia (1.5 MAC), while the heart rate was significantly higher in the isoflurane group. Individual respiratory variables were not significantly different between the two groups, however the differences between the trends of the mean values were significant (Sign-test). In general, with isoflurane, respiration rates were lower, with the tidal volume and end tidal CO2 being greater. The trends in pH and arterial pCO2 showed a slightly more severe respiratory acidosis in the isoflurane group. However, neither group showed values corresponding to any expected clinical problems. Speed of recovery (determined by times to head-lift and righting-reflex) was greater in the isoflurane group. Previously known important features of isoflurane are low biodegradability, low blood: gas partition coefficient, and decreased myocardial sensitivity to catecholamines. It is concluded from this study that isoflurane deserves a place in canine anesthesia whenever these specific pharmacologic properties are desired.

Anesthesia, Inhalation↗
PubMed2004

Maternal insufflation during the second trimester equivalent produces hypercapnia, acidosis, and prolonged hypoxia in fetal sheep.

BACKGROUND: Anecdotal reports suggest that the second trimester is the safest time to conduct a laparoscopic procedure on a pregnant patient, but this supposition has not been tested empirically. METHODS: Previously instrumented preterm sheep (total n = 8) at gestational day 90 (term, 145 days) were anesthetized and then insufflated with carbon dioxide for 60 min at a pressure of 15 mmHg. Cardiovascular parameters were continuously recorded while blood gas status was determined before and at 15-min intervals during and up to 2 h after insufflation. RESULTS: Insufflation produced minimal maternal blood gas or cardiovascular changes except for a significant reduction in uterine blood flow. The decrease in perfusion increased fetal arterial blood partial pressure of carbon dioxide and decreased fetal pH, oxygen saturation, and oxygen content; there was also progressive fetal hypotension and bradycardia. After manually deflating the ewe, uterine blood flow returned to normal, and the fetal partial pressure of carbon dioxide and pH changes resolved within 1 h. However, fetal oxygen saturation and content remained depressed, and fetal cardiovascular status continued to decline during the 2-h postinsufflation monitoring period. CONCLUSION: Previous studies with near-term sheep determined that carbon dioxide pneumoperitoneum produces respiratory acidosis but does not decrease fetal oxygenation. In contrast, the current findings indicate that in the preterm fetus, insufflation-induced hypercapnia and acidosis are accompanied by prolonged fetal hypoxia and cardiovascular depression. This result suggests that additional work should be conducted to confirm the presumed safety of conducting minimally invasive procedures during the second trimester.

Acidosis↗
PubMed1989

[Respiratory insufficiency in acute bronchiolitis in infancy].

Forty-one infants with acute viral bronchiolitis were hospitalized in our paediatric intensive care unit during the seven year period from 1980 to 1987. In 14 out of 27 evaluated patients, Respiratory Syncitial Virus (RSV) was detected in the nasal secretions. Twenty-three children required only supportive care and monitoring. Eighteen infants had to be ventilated because of respiratory failure. The major indication for mechanical ventilation was an arterial or capillary pCO2 of more than 64 mmHg; other criteria were repeated apnoea, respiratory acidosis, and clinical deterioration. In all cases the type of the mechanical ventilation was an intermittent mandatory ventilation (IMV) with flow and time cycled respirators; muscle relaxation was not required in any case. The average duration of mechanical ventilation was 40 hours. All the children recovered uneventfully. These data suggest that even the most severe cases of acute bronchiolotis can be treated successfully, and that the mortality rate of this disease entity can be reduced to zero.

Bronchiolitis, Viral↗
PubMed1994

Carbon dioxide absorption is not linearly related to intraperitoneal carbon dioxide insufflation pressure in pigs.

BACKGROUND: Carbon dioxide absorption into the blood during laparoscopic surgery using intraperitoneal carbon dioxide insufflation may lead to respiratory acidosis, increased ventilation requirements, and possible serious cardiovascular compromise. The relationship between increased carbon dioxide excretion (VCO2) and intraperitoneal carbon dioxide insufflation pressure has not been well defined. METHODS: In 12 anesthesized pigs instrumented for laparoscopic surgery, intraperitoneal carbon dioxide (n = 6) or helium (n = 6) insufflation pressure was increased in steps, and VCO2 (metabolic cart), dead space, and hemodynamics were measured during constant minute ventilation. RESULTS: VCO2 increases rapidly as intraperitoneal insufflation pressure increases from 0 to 10 mmHg; but from 10 to 25 mmHg, VCO2 does not increase much further. PaCO2 increases continuously as intraperitoneal insufflation pressure increases from 0 to 25 mmHg. Hemodynamic parameters remained stable. CONCLUSIONS: By considering Fick's law of diffusion, the initial increase in VCO2 is likely accounted for by increasing peritoneal surface area exposed during insufflation. The continued increase in PaCO2 without a corresponding increase in VCO2 is accounted for by increasing respiratory dead space.

Absorption↗
PubMed1989

[Evolutionary biological aspects of the physiology of extracorporeal CO2 removal].

Extracorporeal CO2 elimination (ECCO2-R) is a new approach to the treatment of severe respiratory failure. Gas exchange is separated into oxygen uptake by apneic oxygenation through the natural lungs while CO2 is removed extracorporeally with an artificial organ. The physiological conditions of both processes can thus be optimized. In the course of evolution, a similar bimodal gas exchange has developed during the respiratory transition from aquatic gas exchange to pulmonary gas exchange: In air-breathing fish or amphibia oxygenation is accomplished predominantly via the lungs while CO2 is eliminated via gill or skin. Today's air-breathing vertebrates maintain a considerable respiratory acidosis which has to be compensated for by an appropriate bicarbonate level. This is dependent upon gill reduction and skin armor to prevent evaporation leading to a rise in pCO2 from 3-4 to 40 mmHg and a tenfold increase of serum bicarbonate levels. We believe that the developmental history of respiration justifies the use of a bimodal gas exchange system. It is clinically applied as extracorporeal CO2 removal with membrane lungs (ECCO2-R) or, still under investigation, in a hemodialysis-related procedure (extracorporeal bicarbonate/CO2 removal: ECBicCO2).

Animals↗
PubMedDate not supplied

[The acute effect of nifedipine in chronic obstructive lung disease].

Acute effects of calcium channel blocker nifedipine were investigated in patients with chronic obstructive pulmonary disease (COPD. In the present study 10 patients were included in the early phase of COPD and 20 patients in the late phase with chronic respiratory insufficiency characterized with resting hypoxemia, hypercapnia and respiratory acidosis. The patients were examined before and after sublingual application of nifedipine (10 mg) or placebo in single-blind study design. Nifedipine did not alter spirometric parameters (FVC, FEV1, FEV1/FVC), except in the late phase of COPD (FEV1). However, acute nifedipine treatment significantly improved resting arterial blood gases: PaO2 increased in both groups while PaCO2 decreased only in the patients in advanced phase of COPD. Additionally, nifedipine increased DLCOSB in the early phase of COPD. Acute nifedipine was found to have a beneficial effect in COPD patients.

Humans↗
PubMed1977

[Indications for and results of extracorporeal membrane oxygenation (author's transl)].

Extracorporeal membrane oxygenation (ECMO) is a new and, in the hands of an experienced team, safe method for treating severe acute respiratory insufficiency. It protects the patient against the risk of hypoxia and respiratory acidosis and, provided there is a chance of survival, allows the repair of the damaged lung tissue. The chances of success depend on whether the lung damage is reversible since, so far as is known, ECMO has not, or only very rarely, any effect on the actual lesion. Reliable prognostic criteria are therefore needed in the choice of suitable cases. Persons with acute non-infectious lung disease who receive this treatment within a few hours or days after the onset of the disease have the best chances of survival.

Hemodynamics↗
PubMed1997

Temporal hemodynamic effects of permissive hypercapnia associated with ideal PEEP in ARDS.

The associated use of permissive hypercapnia (PHY) and high PEEP levels (PEEP(IDEAL)) has been recently indicated as part of a lung-protective-approach (LPA) in acute respiratory distress syndrome (ARDS). However, the net hemodynamic effect produced by this association is not known. We analyzed the temporal hemodynamic effects of this combined strategy in 48 patients (mean age 34 +/- 13 yr) with ARDS, focusing on its immediate (after 1 h), early (first 36 h), and late (2nd-7th d) consequences. Twenty-five patients were submitted to LPA--with the combined use of permissive hypercapnia (PHY), VT < 6 ml/kg, distending pressures above PEEP < 20 cm H2O, and PEEP 2 cm H2O above the lower inflection point on the static inspiratory P-V curve (P(FLEX))- and 23 control patients were submitted to conventional mechanical ventilation. LPA was initiated at once, resulting in an immediate increase in heart rate (p = 0.0002), cardiac output (p = 0.0002), oxygen delivery (DO2l, p = 0.0003), and mixed venous Po2 (p = 0.0006), with a maintained systemic oxygen consumption (p = 0.52). The mean pulmonary arterial pressure markedly increased (mean increment 8.8 mm Hg; p < 0.0001), but the pulmonary vascular resistance did not change (p = 0.32). Cardiac filling pressures increased (p < 0.001) and the systemic vascular resistance fell (p = 0.003). All these alterations were progressively attenuated in the course of the first 36 h, despite persisting hypercapnia. Plasma lactate suffered a progressive decrement along the early period in LPA but not in control patients (p < 0.0001). No hemodynamic consequences of LPA were noticed in the late period and renal function was preserved. A multivariate analysis suggested that these acute hyperdynamic effects were related to respiratory acidosis, with no depressant effects ascribed to high PEEP levels. In contrast, high plateau pressures were associated with cardiovascular depression. Thus, as long as sufficiently low distending pressures are concomitantly applied, the sudden installation of PHY plus PEEP(IDEAL) induces a transitory hyperdynamic state and pulmonary hypertension without harmful consequences to this young ARDS population.

Adult↗
PubMed1993

Pressure support ventilation via face mask in acute respiratory failure in hypercapnic COPD patients.

OBJECTIVE: To test whether non-invasive ventilation via facial mask could reduce the need for tracheal intubation when mechanical ventilation must be initiated in COPD patients. DESIGN: Open prospective interventional study. SETTING: General Intensive Care Service of a County Hospital. PATIENTS: We have studied 12 COPD patients during 14 episodes of acute exacerbation of chronic respiratory failure who failed to improve with intensive medical therapy and showed impairments in severe respiratory acidosis and/or hypercapnic encephalopathy leading their attending physicians to order mechanical ventilation. INTERVENTIONS: In these circumstances, a trial of pressure-support (PS) ventilation (Servo Ventilator 900C) via facial mask Vital Signs Inc.) was performed. The level of pressure support was adjusted to obtain a tidal volume > 400 ml. If the patient deteriorated, tracheal intubation and standard mechanical ventilation were performed. MEASUREMENTS AND RESULTS: Measurements are presented as means +/- SEM. A pressure-support level of 14 +/- 3 cmH2O was used during a period of 8 +/- 4 h. Low levels of external PEEP were used in 4 patients, while it generated excessive leaks in the others. Significant differences (p < 0.05 ANOVA for repeated measures) in data obtained on admission, when patients deteriorated and after pressure support was administered were only observed in PaCO2 (68 +/- 3 versus 92 +/- 3 versus 67 +/- 3 mmHg), arterial pH (7.27 +/- 0.03 versus 7.19 +/- 0.02 versus 7.31 +/- 0.01). SaO2 (60 +/- 4 versus 86 +/- 3 versus 92 +/- 1%) and respiratory rate (35 +/- 2 versus 32 +/- 2 versus 23 +/- 1 breaths.min-1). Three patients needed intubation and one of them died in the ICU. CONCLUSION: Non-invasive ventilation (pressure-support) via face mask may reduce the need for tracheal intubation in the severe hypercapnic failure of COPD patients.

Acute Disease↗
PubMed1992

Nasal mask ventilation in acute respiratory failure. Experience in elderly patients.

Nasal mask ventilation (NMV) has been used successfully in chronic restrictive respiratory failure and more recently in acute exacerbations of chronic obstructive pulmonary disease (COPD). This study aimed to evaluate the possible role of NMV in acute respiratory failure (ARF) episodes when mechanical ventilation with endotracheal intubation is questionable. Thirty patients (age, 76 +/- 8.1 years) were treated by NMV during ARF episodes (COPD, 20; other chronic respiratory failure [CRF], 5; chronic heart failure [CHF], 4). All patients were hypoxemic (PaO2, 5.85 +/- 1.62 kPa) and hypercapnic (PaCO2, 8.63 +/- 1.89 kPa) with respiratory acidosis (pH, 7.29 +/- 0.08). In all cases, clinical or physiologic parameters indicated the need for mechanical ventilation, but endotracheal intubation was either not applied because of the age and the physiologic condition of the patients (17 cases) or was postponed (13 cases). NMV was performed using a volume-cycled ventilator and a customized nasal mask. Ventilation was continuous during the first 12 hours and the following nights and was then intermittent during the day. Twenty-one patients improved clinically, within a few hours. Progressive correction of arterial blood gases was observed: PaO2 increased during the first hour, but PaCO2 decreased more slowly. Eighteen patients were able to be successfully weaned from NMV. Twelve patients failed to improve despite NMV: eight of them died and four required endotracheal intubation. There was no difference in the success rate between patients in whom endotracheal ventilation was contraindicated or postponed. Clinical tolerance was satisfactory in 23 patients and poor in seven patients. A return to the respiratory condition was observed in the surviving patients with subsequent discharge from hospital. NMV therefore successfully treated respiratory distress initially in 60 percent of the 30 patients. These results suggest that NMV could be a possible alternative in the treatment of ARF, even in very ill patients, when endotracheal ventilation is controversial or not immediately required.

Acute Disease↗
PubMed2000

Effects of feeding on arterial blood gases in the American alligator Alligator mississippiensis.

Reptiles habitually ingest large meals at infrequent intervals, leading to changes in acid-base status as the net secretion of acid to the stomach causes a metabolic alkalosis (the alkaline tide). In chronically cannulated and undisturbed amphibians and reptiles, the pH changes in arterial blood are, nevertheless, reduced by a concomitant respiratory acidosis (increased P(CO2) caused by a relative hypoventilation). Alligators (Alligator mississippiensis) have been reported to exhibit exceptionally large increases in plasma [HCO3(-)] following feeding, but these studies were based on blood samples obtained by cardiac puncture, so stress and disturbance may have affected the blood gas levels. Furthermore, crocodilian haemoglobin is characterised by a unique binding of HCO3(-) that act to reduce blood oxygen-affinity, and it has been proposed that this feature safeguards oxygen offloading by counteracting pH effects on blood oxygen-affinity. Therefore, to study acid-base regulation and the interaction between the alkaline tide and oxygen transport in more detail, we describe the arterial blood gas composition of chronically cannulated and undisturbed alligators before and after voluntary feeding (meal size 7.5+/-1% of body mass). Digestion was associated with an approximately fourfold increase in metabolic rate (from 0.63+/-0.04 to 2.32+/-0.24 ml O(2) min(-1)kg(-1)) and was accompanied by a small increase in the respiratory gas exchange ratio. The arterial P(O2) of fasting alligators was 60.3+/-6.8 mmHg (1 mmHg = 0.133 kPa) and reached a maximum of 81.3+/-2.7 mmHg at 96 h following feeding; there was only a small increase in lactate levels, so the increased metabolic rate seems to be entirely aerobic. Plasma [HCO3(-)] increased from 24.4+/-1.1 to 36.9+/-1.7 mmol l(-1) (at 24 h), but since arterial P(CO2) increased from 29.0+/-1.1 to 36.8+/-1.3 mmHg, arterial pH remained virtually unaffected (changing from 7.51+/-0.01 to 7.58+/-0.01 at 24 h). The changes in plasma [HCO3(-)] were mirrored by equimolar reductions in plasma [Cl(-)]. The in vitro blood oxygen-affinity was reduced during the post-prandial period, whereas the estimated in vivo blood oxygen-affinity remained virtually constant. This supports the view that the specific HCO3(-) effect prevents an increased blood oxygen-affinity during digestion in alligators.

Alligators and Crocodiles↗