I'm sorry that your question wasn't answered in a timely manner. Try as I might I can't find any studies in people much less dogs or cats concerning lasting effects from prolonged exposure to natural gas. There are anecdotal reports from people attributing their headaches, cancers, and whatever else ails them to such exposure but no proof that that was, indeed, the case. Acute hydrocarbon toxicity is well-known to cause nausea and vomiting as you noted. Toxicity from hydrocarbon exposure can be thought of as different syndromes, depending on which organ system is predominately involved. Organ systems that can be affected by hydrocarbons include the pulmonary, neurologic, cardiac, gastrointestinal, hepatic, renal, dermatologic, and hematologic systems. The pulmonary system is the most commonly involved system and your pets may have experienced irritation and possibly long-lasting damage to their lungs. Here's a review of possible adverse effects in people and I would expect, animals:
Pulmonary complications, especially aspiration, are the most frequently reported adverse effect of hydrocarbon exposure. While most aliphatic hydrocarbons have little GI absorption, aspiration frequently occurs, either initially or in a semidelayed fashion as the patient coughs or vomits, thereby resulting in pulmonary effects. Once aspirated, the hydrocarbons can create a severe pneumonitis.
Hydrocarbon pneumonitis results from a direct toxic affect by the hydrocarbon on the lung parenchyma. The type II pneumocytes are most affected, resulting in decreased surfactant production. This decrease in surfactant, results in alveolar collapse, ventilation-perfusion mismatch, and hypoxemia. Hemorrhagic alveolitis can subsequently occur, which peaks 3 days after ingestion. The end result of hydrocarbon aspiration is interstitial inflammation, intra-alveolar hemorrhage and edema, hyperemia, bronchial necrosis, and vascular necrosis. Rare pulmonary complications include the development a pneumothorax, pneumatocele, or bronchopleural fistula.
CNS toxicity can result from several mechanisms, including direct injury to the brain or indirectly as a result of severe hypoxia or simple asphyxiation.
Many of the hydrocarbons that affect the CNS directly can make their way across the blood-brain barrier because certain hydrocarbons are highly lipophilic. In addition, for individuals who are huffing or bagging, the act of rebreathing can result in hypercarbia, which can contribute to decreased level of arousal.
Prolonged abuse of hydrocarbons can result in white matter degeneration (leukoencephalopathy) and atrophy. In addition, prolonged exposure to certain hydrocarbons (eg, n -hexane or methyl-n -butyl ketone [MnBK]) can result in peripheral neuropathy, blurred vision, sensory impairment, muscle atrophy, and parkinsonism.
Exposure to hydrocarbons can result in cardiotoxicity.
Most importantly, the myocardium becomes sensitized to the effects of catecholamines, which can predispose the patient to tachydysrhythmias, which can result in syncope or sudden death.
Many of the hydrocarbons create a burning sensation because they are irritating to the GI mucosa. Vomiting has been reported in up to one third of all hydrocarbon exposures.
The chlorinated hydrocarbons, in particular carbon tetrachloride, are hepatotoxic. Usually, the hepatotoxicity results after the hydrocarbon undergoes phase I metabolism, thereby inducing free radical formation. These free radicals subsequently bond with hepatic macromolecules and ultimately cause lipid peroxidation. This metabolite creates a covalent bond with the hepatic macromolecules, thereby initiating lipid peroxidation.
The common histopathologic pattern is centrilobular (zone III) necrosis.
Liver function test results can be abnormal within 24 hours after ingestion, and clinically apparent jaundice can occur within 48-96 hours.
Methylene chloride, a hydrocarbon commonly found in paint remover, is metabolized via the P450 mixed function oxidase system in the liver to carbon monoxide (CO). Unlike other cases of CO exposure, with methylene chloride, CO formation can continue for a prolonged period of time.
Chronic exposure to toluene an aromatic hydrocarbon, can result in a distal renal tubular acidosis and present with an anion gap acidosis. A patient may have chronic exposure either via an occupational environment or by repeated recreational inhalation.
Prolonged exposure to certain aromatic hydrocarbons (especially benzene) can lead to an increased risk of aplastic anemia, multiple myeloma, and acute myelogenous leukemia. In addition, hemolysis has been reported following the acute ingestion of various types of hydrocarbons.
Please respond with further questions or concerns if you wish.